Extracellular matrix protein in calcified endoskeleton: a potential additive for crystal growth and design

NASA Astrophysics Data System (ADS)

Azizur Rahman, M.; Fujimura, Hiroyuki; Shinjo, Ryuichi; Oomori, Tamotsu

2011-06-01

In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on seed crystals, which are isolated from calcified endoskeletons of soft coral and contain only CaCO 3 without any living cells. This is the first report that an ECMP protein extracted from a marine organism could potentially influence in modifying the surface of a substrate for designing materials via crystallization. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any seed crystals in the process , which showed different results. Thus, crystallization on the seed in the presence of ECMPs of present species is an important first step toward linking function to individual proteins from soft coral. For understanding this interesting phenomenon, in vitro crystallization was initiated in a supersaturated solution on seed particles of calcite (1 0 4) with and without ECMPs. No change in the crystal growth shape occurred without ECMPs present during the crystallization process. However, with ECMPs, the morphology and phase of the crystals in the crystallization process changed dramatically. Upon completion of crystallization with ECMPs, an attractive crystal morphology was found. Scanning electron microscopy (SEM) was utilized to observe the crystal morphologies on the seeds surface. The mineral phases of crystals nucleated by ECMPs on the seeds surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the crystallization process, the ECMPs significantly made calcite crystals even when 50 mM Mg 2+ was present in the process. Crystallization with the ECMP additive seems to be a technically attractive strategy to generate assembled micro crystals that could be used in crystals growth and design in the Pharmaceutical and biotechnology industries.

Seed-Mediated Growth of Gold Nanocrystals: Changes to the Crystallinity or Morphology as Induced by the Treatment of Seeds with a Sulfur Species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Yiqun; Luo, Ming; Tao, Jing

We report our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S₂O₃²⁻ ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S₂O₃²⁻ ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S₂O₃²⁻ ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to themore » spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S₂O₃²⁻ ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth.« less

Seed-Mediated Growth of Gold Nanocrystals: Changes to the Crystallinity or Morphology as Induced by the Treatment of Seeds with a Sulfur Species

DOE PAGES

Zheng, Yiqun; Luo, Ming; Tao, Jing; ...

2014-12-11

We report our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S₂O₃²⁻ ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S₂O₃²⁻ ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S₂O₃²⁻ ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to themore » spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S₂O₃²⁻ ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth.« less

Smectic C liquid crystal growth through surface orientation by ZnxCd1-xSe thin films

NASA Astrophysics Data System (ADS)

Katranchev, B.; Petrov, M.; Bineva, I.; Levi, Z.; Mineva, M.

2012-12-01

A smectic C liquid crystal (LC) texture, consisting of distinct local single crystals (DLSCs) was grown using predefined orientation of ternary nanocrystalline thin films of ZnxCd1-xSe. The surface morphology and orientation features of the ZnxCd1-xSe films were investigated by AFM measurements and micro-texture polarization analysis. The ZnxCd1-xSe surface causes a substantial enlargement of the smectic C DLSCs and induction of a surface bistable state. The specific character of the morphology of this coating leads to the decrease of the corresponding anchoring energy. Two new chiral states, not typical for this LC were indicated. The physical mechanism providing these new effects is presented.

Site-discrimination by molecular imposters at dissymmetric molecular crystal surfaces

NASA Astrophysics Data System (ADS)

Poloni, Laura N.

The organization of atoms and molecules into crystalline forms is ubiquitous in nature and has been critical to the development of many technologies on which modern society relies. Classical crystal growth theory can describe atomic crystal growth, however, a description of molecular crystal growth is lacking. Molecular crystals are often characterized by anisotropic intermolecular interactions and dissymmetric crystal surfaces with anisotropic growth rates along different crystallographic directions. This thesis describes combination of experimental and computational techniques to relate crystal structure to surface structure and observed growth rates. Molecular imposters, also known as tailor-made impurities, can be used to control crystal growth for practical applications such as inhibition of pathological crystals, but can also be used to understand site specificity at crystal growth surfaces. The first part of this thesis builds on previous real-time in situ atomic force microscopy (AFM) observations of dislocation-actuated growth on the morphologically significant face of hexagonal L-cystine crystals, which aggregate in vivo to form kidney stones in patients suffering from cystinuria. The inhibitory effect of various L-cystine structural mimics (a.k.a. molecular imposters) was investigated through experimental and computational methods to identify the key structural factors responsible for molecular recognition between molecular imposters and L-cystine crystal surface sites. The investigation of L-cystine crystal growth in the presence of molecular imposters through a combination of kinetic analysis using in situ AFM, morphology analysis and birefringence measurements of bulk crystals, and molecular modeling of imposter binding to energetically inequivalent surface sites revealed that different molecular imposters inhibited crystal growth by a Cabrera-Vermilyea pinning mechanism and that imposters bind to a single binding site on the dissymmetric {1000} L-cystine surfaces. Collectively, these findings identify the key structural factors responsible for molecular recognition between molecular imposters and L-cystine crystal step sites, thereby articulating a strategy for stone prevention based on molecular design. The second part of this thesis describes the crystal growth and inhibition of a P2X3 receptor antagonist, denoted as DAPSA, recently reported as a non-opioid treatment of chronic pain. The low solubility of this compound results in the formation of drug-induced renal calculi (a.k.a. xenostones). in situ AFM of the morphologically significant (011) DAPSA surface revealed dislocation-actuated growth spirals with an anisotropic morphology, behavior that can be attributed to the non-uniform rate of solute attachment to eight crystallographically unique steps of the spiral, a direct consequence of the dissymmetry of this crystal surface. Eighteen molecular imposters were selected from the screening library to systematically investigate the roles of imposter substitute position, size, and functionality on the step velocities along the eight unique crystallographic directions. A non-uniform reduction in step velocities was observed, signaling site discrimination of imposter binding that can be attributed to stereochemical recognition of the imposters at specific crystal sites. The anisotropy of growth inhibition observed in the presence of the various imposters is consistent with binding energies calculated for the thirty-two crystallographically unique kink sites on steps advancing along predominant growth directions. These results provide insight to the design of growth inhibitors for molecular crystalline solids with complex and dissymmetric surfaces, while also suggesting a strategy for formulations containing congeners that can prevent harmful crystal growth in human renal structures. The last two crystalline systems discussed in this thesis are two isomorphous crystal systems that are ideal for the study of impurity incorporation at dissymmetric surfaces because their morphology is dominated by dissymmetric {101} growth faces. Growth processes on the dissymmetric (101) surfaces of these crystalline systems were investigated using metadynamics simulations to determine the free energy of adsorption for solute and impurity attachment to different flat, stepped, and kinked (101) surface terminations. Results suggest that growth occurs via a non-Kossel crystal growth mechanism, and highlights the need for dissymmetric surface structures (i.e. steps and kinks) for a higher fidelity in the orientation of adsorbed molecules. Overall, the results presented in this thesis suggest that growth of molecular crystals, particularly at dissymmetric surfaces, is complex and requires the combination of several experimental and computational techniques to decipher the mechanisms responsible for growth phenomena. The use of molecular imposters to inhibit growth can be useful for the development of therapeutics for pathological crystals, but can also inform processes by which crystal growth occurs at complex surfaces as a result of their site selectivity.

Plateau-Rayleigh Crystal Growth of Nanowire Heterostructures: Strain-Modified Surface Chemistry and Morphological Control in One, Two, and Three Dimensions.

PubMed

Day, Robert W; Mankin, Max N; Lieber, Charles M

2016-04-13

One-dimensional (1D) structures offer unique opportunities for materials synthesis since crystal phases and morphologies that are difficult or impossible to achieve in macroscopic crystals can be synthesized as 1D nanowires (NWs). Recently, we demonstrated one such phenomenon unique to growth on a 1D substrate, termed Plateau-Rayleigh (P-R) crystal growth, where periodic shells develop along a NW core to form diameter-modulated NW homostructures with tunable morphologies. Here we report a novel extension of the P-R crystal growth concept with the synthesis of heterostructures in which Ge (Si) is deposited on Si (Ge) 1D cores to generate complex NW morphologies in 1, 2, or 3D. Depositing Ge on 50 nm Si cores with a constant GeH4 pressure yields a single set of periodic shells, while sequential variation of GeH4 pressure can yield multimodulated 1D NWs with two distinct sets of shell periodicities. P-R crystal growth on 30 nm cores also produces 2D loop structures, where Ge (Si) shells lie primarily on the outside (inside) of a highly curved Si (Ge) core. Systematic investigation of shell morphology as a function of growth time indicates that Ge shells grow in length along positive curvature Si cores faster than along straight Si cores by an order of magnitude. Short Ge deposition times reveal that shells develop on opposite sides of 50 and 100 nm Si cores to form straight 1D morphologies but that shells develop on the same side of 20 nm cores to produce 2D loop and 3D spring structures. These results suggest that strain mediates the formation of 2 and 3D morphologies by altering the NW's surface chemistry and that surface diffusion of heteroatoms on flexible freestanding 1D substrates can facilitate this strain-mediated mechanism.

Morphology of growth of Bi2Sr2CaCu2O8 single crystals

NASA Astrophysics Data System (ADS)

Indenbom, M. V.; van der Beek, C. J.; Berseth, V.; Wolf, Th.; Berger, H.; Benoit, W.

1996-12-01

A good correlation of twins on the basal surface of flux-grown Bi2Sr2CaCu2Ox (BSCCO) single crystals with surface. growth steps is observed, the b-axis being perpendicular to the steps and, thus, parallel to the growth direction. It is found that mono-twin BSCCO single crystals produced by the travelling solvent floating zone method also grow preferentially along b, i.e. nearly perpendicularly to the boule axis, contrary to the common belief. This new understanding of the morphology of growth explains the nature of major defects in these crystals, which considerably change their measured superconducting properties, in a different way.

Banded Spherulitic Morphology in Blends of Poly(propylene fumarate) and Poly( -caprolactone) and Interaction with MC3T3-E1 Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Kan; Jesse, Stephen; Wang, Shanfeng

2012-01-01

The thermal properties, morphological development, crystallization behavior, and miscibility of semicrystalline PCL and its 25, 50, and 75 wt% blends with amorphous PPF in spin-coated thin films crystallized at various crystallization temperatures (T{sub c}) from 25 to 52 C are investigated. The surface roughness of PPF/PCL ({phi}{sub PCL} = 75%) films increases with increasing T{sub c} and consequently the adsorption of serum proteins is also increased. No significant variance is found in surface hydrophilicity or in mouse MC3T3-E1 cell attachment, spreading, and proliferation on PPF/PCL ({phi}{sub PCL} = 75%) films crystallized isothermally at 25, 37, and 45 C, because ofmore » low ridge height, nonuniformity in structures, and PPF surface segregation« less

Molecular-Scale Structural Controls on Nanoscale Growth Processes: Step-Specific Regulation of Biomineral Morphology

NASA Astrophysics Data System (ADS)

Dove, P. M.; Davis, K. J.; De Yoreo, J. J.; Orme, C. A.

2001-12-01

Deciphering the complex strategies by which organisms produce nanocrystalline materials with exquisite morphologies is central to understanding biomineralizing systems. One control on the morphology of biogenic nanoparticles is the specific interactions of their surfaces with the organic functional groups provided by the organism and the various inorganic species present in the ambient environment. It is now possible to directly probe the microscopic structural controls on crystal morphology by making quantitative measurements of the dynamic processes occurring at the mineral-water interface. These observations can provide crucial information concerning the actual mechanisms of growth that is otherwise unobtainable through macroscopic techniques. Here we use in situ molecular-scale observations of step dynamics and growth hillock morphology to directly resolve roles of principal impurities in regulating calcite surface morphologies. We show that the interactions of certain inorganic as well as organic impurities with the calcite surface are dependent upon the molecular-scale structures of step-edges. These interactions can assume a primary role in directing crystal morphology. In calcite growth experiments containing magnesium, we show that growth hillock structures become modified owing to the preferential inhibition of step motion along directions approximately parallel to the [010]. Compositional analyses have shown that Mg incorporates at different levels into the two types of nonequivalent steps, which meet at the hillock corner parallel to [010]. A simple calculation of the strain caused by this difference indicates that we should expect a significant retardation at this corner, in agreement with the observed development of [010] steps. If the low-energy step-risers produced by these [010] steps is perpendicular to the c-axis as seems likely from crystallographic considerations, this effect provides a plausible mechanism for the elongated calcite crystal habits found in natural environments that contain magnesium. In a separate study, step-specific interactions are also found between chiral aspartate molecules and the calcite surface. The L and D- aspartate enantiomers exhibit structure preferences for the different types of step-risers on the calcite surface. These site-specific interactions result in the transfer of asymmetry from the organic molecule to the crystal surface through the formation of chiral growth hillocks and surface morphologies. These studies yield direct experimental insight into the molecular-scale structural controls on nanocrystal morphology in biomineralizing systems.

A scanning electron microscope study of olivine crystal surfaces

NASA Technical Reports Server (NTRS)

Olsen, E. J.; Grossman, L.

1974-01-01

SEM photographs were taken of euhedral olivine grains from the Murchison C2 chondrite and several terrestrial and lunar occurrences. In general, the crystal faces of the meteorite grains are rough and uneven, with irregular growth patterns. They are very similar to crystal faces on terrestrial olivine grains that formed by sublimation from a vapor phase. They are very different from the relatively smooth and featureless surfaces of magmatic olivine crystals that precipitated from igneous melts. Qualitatively, the surface morphology of the crystal supports the contention that many euhedral crystals of olivine in C2 meteorites condensed from a gas phase.

Formation of different micro-morphologies from VO2 and ZnO crystallization using macro-porous silicon substrates

NASA Astrophysics Data System (ADS)

Salazar-Kuri, U.; Antúnez, E. E.; Estevez, J. O.; Olive-Méndez, Sion F.; Silva-González, N. R.; Agarwal, V.

2017-05-01

Square-shaped macropores produced by electrochemical anodization of n- and p-type Si wafers have been used as centers of nucleation to crystallize VO2 and ZnO. Substrate roughness dependent formation of different morphologies is revealed in the form of squared particles, spheres, bars and ribbons in the case of VO2 and hexagonal piles and spheres in the case of ZnO, have been observed.The presence of nano-/micro-metric crystals was studied through field emission scanning electron microscopy and energy dispersive X-ray spectroscopy mapping. Crystal structure of metal oxides was confirmed by micro-Raman spectroscopy. The growth of the different morphologies has been explained in terms of the surface free energy of a bare Si/SiO2 substrate and its modification originated from the roughness of the surface and of the walls of the porous substrates. This energy plays a crucial role on the minimization of the required energy to induce heterogeneous nucleation and crystal growth. Present work strengthens and provides an experimental evidence of roughness dependent metal oxide crystal growth with well-defined habits from pore corners and rough sides of the pore walls, similar to already reported protein crystals.

Amelogenin-assisted ex vivo remineralization of human enamel: effects of supersaturation degree and fluoride concentration

PubMed Central

Fan, Yuwei; Nelson, James R.; Alvarez, Jason R.; Hagan, Joseph; Berrier, Allison; Xu, Xiaoming

2011-01-01

The formation of organized nanocrystals that resemble enamel is crucial for successful enamel remineralization. Calcium, phosphate and fluoride ions and amelogenin are important ingredients for the formation of organized hydroxyapatite (HAP) crystals in vitro. However, the effects of these remineralization agents on the enamel crystal morphology have not been thoroughly studied. The objective of this study was to investigate the effects of fluoride ions, supersaturation degree and amelogenin on the crystal morphology and organization of ex vivo remineralized human enamel. Extracted third molars were sliced thin and acid-etched to provide the enamel surface for immersion in different remineralization solutions. The crystal morphology and mineral phase of the remineralized enamel surface were analyzed by FE-SEM, ATR-FTIR and XRD. The concentration of fluoride and supersaturation degree of hydroxyapatite had significant effects on the crystal morphology and crystal organization, which varied from plate-like loose crystals to rod-like densely packed nanocrystal arrays. Densely packed arrays of fluoridated hydroxyapatite nanorods were observed under the following conditions: σ(HAP) = 10.2±2.0 with fluoride 1.5±0.5 mg/L and amelogenin 40±10 µg/mL, pH 6.8±0.4. A phase diagram summarized the conditions that form dense or loose hydroxyapatite nanocrystal structures. This study provides the basis for the development of novel dental materials for caries management. PMID:21256987

Morphology of poly-p-xylylene crystallized during polymerization.

NASA Technical Reports Server (NTRS)

Kubo, S.; Wunderlich, B.

1971-01-01

The morphology of as-polymerized poly-p-xylylene grown between -17 and 30 C is found to consist of lame llar alpha crystals oriented with the (010) plane parallel to the support surface. The crystallinity decreases with decreasing polymerization temperature. Spherulitic and nonspherulitic portions of the polymer film consist of folded chain lamellas with the chain axis parallel to the support surface. The results were obtained by small- and wide-angle X-ray measurements, electron and optical microscopy, and differential thermal analysis.

On the morphological and chemical stability of vitamin C crystals

NASA Astrophysics Data System (ADS)

Halász, Susan; Bodor, Beáta

1993-03-01

Mass cooling crystallization of aqueous vitamin C solution was studied by applying different cooling rates, initial supersaturations and mixing intensity. The morphology of the products (size, habit and colour) well followed the changes of process parameters. Comparing a high purity (99.9%) standard with a yellow coloured heterodisperse product and a slowly grown single crystal, HPLC chromatography detected decreasing purity of the bigger single crystals, while X-ray and NMR analysis did not show any perceptible difference. It has been concluded that not the surface oxidation (chemical degredation), but rather the inclusions are the main sources of impurities within the crystals.

Parallel computational and experimental studies of the morphological modification of calcium carbonate by cobalt

NASA Astrophysics Data System (ADS)

Braybrook, A. L.; Heywood, B. R.; Jackson, R. A.; Pitt, K.

2002-08-01

Crystal growth can be controlled by the incorporation of dopant ions into the lattice and yet the question of how such substituents affect the morphology has not been addressed. This paper describes the forms of calcite (CaCO 3) which arise when the growth assay is doped with cobalt. Distinct and specific morphological changes are observed; the calcite crystals adopt a morphology which is dominated by the {01.1} family of faces. These experimental studies paralleled the development of computational methods for the analysis of crystal habit as a function of dopant concentration. In this case, the predicted defect morphology also argued for the dominance of the (01.1) face in the growth form. The appearance of this face was related to the preferential segregation of the dopant ions to the crystal surface. This study confirms the evolution of a robust computational model for the analysis of calcite growth forms under a range of environmental conditions and presages the use of such tools for the predictive development of crystal morphologies in those applications where chemico-physical functionality is linked closely to a specific crystallographic form.

Comparative analysis of surface wax in mature fruits between Satsuma mandarin (Citrus unshiu) and 'Newhall' navel orange (Citrus sinensis) from the perspective of crystal morphology, chemical composition and key gene expression.

PubMed

Wang, Jinqiu; Hao, Haohao; Liu, Runsheng; Ma, Qiaoli; Xu, Juan; Chen, Feng; Cheng, Yunjiang; Deng, Xiuxin

2014-06-15

Surface wax of mature Satsuma mandarin (Citrus unshiu) and 'Newhall' navel orange (Citrus sinensis) was analysed by crystal morphology, chemical composition, and gene expression levels. The epicuticular and total waxes of both citrus cultivars were mostly composed of aldehydes, alkanes, fatty acids and primary alcohols. The epicuticular wax accounted for 80% of the total wax in the Newhall fruits and was higher than that in the Satsuma fruits. Scanning electron microscopy showed that larger and more wax platelets were deposited on the surface of Newhall fruits than on the Satsuma fruits. Moreover, the expression levels of genes involved in the wax formation were consistent with the biochemical and crystal morphological analyses. These diversities of fruit wax between the two cultivars may contribute to the differences of fruit postharvest storage properties, which can provide important information for the production of synthetic wax for citrus fruits. Copyright © 2013 Elsevier Ltd. All rights reserved.

Construction of hydrophobic wood surfaces by room temperature deposition of rutile (TiO2) nanostructures

Treesearch

Rongbo Zheng; Mandla A. Tshabalala; Qingyu Li; Hongyan Wang

2015-01-01

A convenient room temperature approach was developed for growing rutile TiO2 hierarchical structures on the wood surface by direct hydrolysis and crystallization of TiCl3 in saturated NaCl aqueous solution.The morphology and the crystal structure of TiO2 coated on the wood surface were characterized...

Control of Orientation and Morphology of Crystals Grown Under Organic Templates

NASA Astrophysics Data System (ADS)

Stripe, Benjamin

Living creatures demonstrate an extraordinary ability to both grow and control the growth of inorganic crystals. These biominerals are found almost everywhere in nature from simple plants and plankton to our own teeth and bones. A great deal of research has been focused on how living creatures are able to achieve such control over the shape, size, orientation, and arrangement of these biominerals. Many studies have been done demonstrating the effects the presence of organic molecules can have on the morphology of nucleating inorganic crystals. These studies have led to the use of ordered arrays of biological molecules as templates to select the orientation of the crystals. Such experiments have had amazing success cataloging monolayers, orientations and morphologies of crystals grown beneath them. However, despite several decades of work, the exact mechanisms by which the orientation and morphology of crystals is selected by organic templates are still not known. The present study attempts to explain the complex interactions that take place at the template surface and decide the orientations and morphologies of the crystals that nucleate there. To do this, scanning electron microscopy (SEM), grazing incidence x-ray diffraction (GID), and x-ray reflectivity have been used to probe the templates and nucleating crystals in situ. The experiments described here seek to move beyond the well-studied two-component systems. In many of these two-component systems a single template and a single type of crystal are grown, and often many claims and comparisons are made about monolayer charge, crystal surface energies, stereochemical recognition, and lattice matches. However, almost all of the claims and comparisons are between systems that are different enough that assumptions about relative charge, strain, recognition, and lattice dynamics are either unfounded or poorly supported. To bridge this gap in the comparison of these different two-component systems the studies presented here are tunable three-component systems. These experiments allow for either continuously adjusting the template by means of two miscible monolayers or adjusting the growing crystals by incorporation of secondary ions. In either case, the idea is the same: we can more accurately compare two-component systems and isolate the controlling factor in the selection of orientation and morphology of the nucleating crystals. The results of these studies have shown that there is a complex interplay of charge, lattice parameters and kinetics. Despite this, we have been able to show that well-oriented growth of single non-dendritic crystals is limited to a fairly small range of surface charges and relative growth kinetics. Within this range, variations in the growing crystals can be seen based on changes in the average lattice parameters despite there being no evidence of direct epitaxy. Theories have evolved around the idea of stereochemical matching between the template and nucleating surface. These theories correlate the template molecular tilt to the orientation relative to the nucleation plane. However, these theories are not supported by the results presented in this manuscript. The data presented in this manuscript are suggestive of far more complex interfacial interactions involving an intermediary amorphous precursor, or possible networks of hydrated or hydrogen bonded ions than has been suggested in previous studies. Excitingly, it appears to be possible to control the selection of orientation using these multicomponent systems despite the complex interactions at the surface.

Effect of Interaction of the Temperature Field and Supersaturation on the Morphology of the Solid-Vapor Interface in Crystal Growth by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Grasza, K.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

An in-situ study of the morphology of the solid-vapor interface during iodine crystal growth was done. The conditions for terrace growth, flat faces formation and retraction, competition between sources of steps, formation of protrusions, surface roughening, and defect overgrowth are demonstrated and discussed.

Periodic surface instabilities in stressed polymer solids

NASA Astrophysics Data System (ADS)

Tsukruk, Vladimir V.; Reneker, Darrell H.

1995-03-01

The surface morphology of isothermally grown polymer single crystals of polypropylene is observed by atomic force microscopy. The distinguishing features of the polymer single crystals studied are periodic undulations and transverse fractures (cracks) across the single crystal laths. Up to 20 wrinkles are observed near the edges of the cracks. The periodicity of these surface perturbations is 400+/-100 nm and the amplitude is 6+/-3 nm. The formation of the periodic modulations and transverse fractures is attributed to surface stress relief caused by the uniaxial thermal contraction of polymer solids.

Calcium oxalate crystal growth modification; investigations with confocal Raman microscopy

NASA Astrophysics Data System (ADS)

McMulkin, Calum J.; Massi, Massimiliano; Jones, Franca

2017-06-01

Confocal Raman Microscopy (CRM) in combination with a photophysical investigation has been employed to give insight into the interaction between calcium oxalate monohydrate (COM) and a series of tetrazole containing crystal growth modifier's (CGM's), in conjunction with characterisation of morphological changes using scanning electron and optical microscopy. The tetrazole CGM's were found to interact by surface adsorption with minimal morphological changes to the COM crystals however, significant interactions via chemisorption were observed; it was discovered that the chemisorption is sufficiently strong for aggregation of the tetrazole species to occur within the crystal during crystallisation.

Structural changes of anodic layer on titanium in sulfate solution as a function of anodization duration in constant current mode

NASA Astrophysics Data System (ADS)

Komiya, Shinji; Sakamoto, Kouta; Ohtsu, Naofumi

2014-03-01

The present study investigated the effect of anodization time, in constant current mode, on the anodic oxide layer formed on titanium (Ti). Anodization of the Ti substrate was　carried out in a 0.1 M (NH4)2SO4 aqueous solution with reaction times of various durations, after which the characteristics and photocatalytic activity were investigated in detail. The TiO2 layer fabricated in a short duration exhibited comparatively flat surface morphology and an anatase-type crystal structure. This layer acted as a photocatalyst only under ultraviolet light (UV) illumination. Upon prolonging the anodization, the layer structure changed drastically. The surface morphology became rough, and the crystal structure changed to rutile-type TiO2. Furthermore, the layer showed photocatalytic activity both under UV and visible light illumination. Further anodization increased the amount of methylene blue (MB) adsorbed on the surface, but did not cause additional change to the structure of the anodic layer. The surface morphology and crystal structure of the anodic layer were predominantly controlled by the anodization time; thus, the anodization time is an important parameter for controlling the characteristics of the anodic layer.

Crystallization of Skeletal Diamonds from Graphite and Natural Coal in Presence of Hydrous Fluids at P=8 GPa and T=1400-1500° C

NASA Astrophysics Data System (ADS)

Dobrzhinetskaya, L. F.; Renfro, A. P.; Green, H. W.

2001-12-01

Most metamorphic microdiamonds from crustal UHP rocks of the Kokchetav massive, Kazakhstan are characterized by skeletal-hopper crystals, cuboid-like crystals with cavities "healed over" by graphite, rose-like crystals, and other imperfect morphologies. According to the classical theory of crystal growth at thermodynamic equilibrium, only shapes with a minimum surface energy are stable. Thus imperfect crystallographic forms of most metamorphic diamonds formally may be interpreted as metastable while the presence of other high pressure phases associated with diamond indicates that the rocks have been subjected to UHP metamorphism within the diamond stability field. The classical theory also says that a skeletal-hopper crystal is one that develops under conditions of rapid growth, a high degree of supersaturation and in the presence of impurities. In contrast to these observations, most experiments on diamond synthesis at high P (5-7.7 GPa) and T (1250 - 1900° C) from graphite (Wang et al., 1999; Hong et al., 1999; Yamaoka et al., 2000) and carbonate material (Pal'anov et al., 1999; Sokol et al.,2000) in presence of fluid phase produced perfect octahedral and cube-octahedral diamond crystals. Advanced analytical research on metamorphic diamonds and their inclusions has demonstrated that they were crystallized from a multicomponent COH-rich supercritical fluid phase, the composition of which suggests intermixture of crustal and mantle components (de Corte et al., 1999; Dobrzhinetskaya et al., 2001, Stockhert et al., 2001). We have recently synthesized imperfect diamond crystals (skeletal-hopper morphologies with effect of etching of the diamond surfaces) from graphite and natural coal + 2% Mg(OH)2 as a source for fluid phase. Conditions of experiments are: P=8-8.5 GPa, T=1400-1500° C, t=14 to 136 hours. Our experimental data are in a good agreement with similar experiments conducted by Kanda et al. (1984) who showed that with increasing water content of the system, the morphology of diamond crystals changes progressively from octahedra to crystals with elements of dodecahedra to hollow/hopper and skeletal morphologies. We hypothesize that imperfect morphologies of metamorphic diamonds are due to the presence of OH in the system.

Tailoring Graphene Morphology and Orientation on Cu(100), Cu(110), and Cu(111)

NASA Astrophysics Data System (ADS)

Jacobberger, Robert; Arnold, Michael

2013-03-01

Graphene CVD on Cu is phenomenologically complex, yielding diverse crystal morphologies, such as lobes, dendrites, stars, and hexagons, of various orientations. We present a comprehensive study of the evolution of these morphologies as a function of Cu surface orientation, pressure, H2:CH4, and nucleation density. Growth was studied on ultra-smooth, epitaxial Cu films inside Cu enclosures to minimize factors that normally complicate growth. With low H2:CH4, Mullins-Sekerka instabilities propagate to form dendrites, indicating transport limited growth. In LPCVD, the dendrites extend hundreds of microns in the 100, 111, and 110 directions on Cu(100), (110), and (111) and are perturbed by twin boundaries. In APCVD, multiple preferred dendrite orientations exist. With increasing H2:CH4, the dendritic nature of growth is suppressed. In LPCVD, square, rectangle, and hexagon crystals form on Cu(100), (110) and (111), reflecting the Cu crystallography. In APCVD, the morphology becomes hexagonal on each surface. If given ample time, every growth regime yields high-quality monolayers with D:G Raman ratio <0.1. The understanding gained here provides a framework to rationally tailor the graphene crystal morphology and orientation.

Effects of humidity and surfaces on the melt crystallization of ibuprofen.

PubMed

Lee, Dong-Joo; Lee, Suyang; Kim, Il Won

2012-01-01

Melt crystallization of ibuprofen was studied to understand the effects of humidity and surfaces. The molecular self-assembly during the amorphous-to-crystal transformation was examined in terms of the nucleation and growth of the crystals. The crystallization was on Al, Au, and self-assembled monolayers with -CH(3), -OH, and -COOH functional groups. Effects of the humidity were studied at room temperature (18-20 °C) with relative humidity 33%, 75%, and 100%. Effects of the surfaces were observed at -20 °C (relative humidity 36%) to enable close monitoring with slower crystal growth. The nucleation time of ibuprofen was faster at high humidity conditions probably due to the local formation of the unfavorable ibuprofen melt/water interface. The crystal morphologies of ibuprofen were governed by the nature of the surfaces, and they could be associated with the growth kinetics by the Avrami equation. The current study demonstrated the effective control of the melt crystallization of ibuprofen through the melt/atmosphere and melt/surface interfaces.

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Brebrick, R. F.; Burger, A.; Dudley, M.; Matyi, R.; Ramachandran, N.; Sha, Yi-Gao; Volz, M.; Shih, Hung-Dah

1999-01-01

Complete and systematic ground-based experimental and theoretical analyses on the Physical Vapor Transport (PVT) of ZnSe and related ternary compound semiconductors have been performed. The analyses included thermodynamics, mass flux, heat treatment of starting material, crystal growth, partial pressure measurements, optical interferometry, chemical analyses, photoluminescence, microscopy, x-ray diffraction and topography as well as theoretical, analytical and numerical analyses. The experimental results showed the influence of gravity orientation on the characteristics of: (1) the morphology of the as-grown crystals as well as the as-grown surface morphology of ZnSe and Cr doped ZnSe crystals; (2) the distribution of impurities and defects in ZnSe grown crystals; and (3) the axial segregation in ZnSeTe grown crystals.

Surface modification of LiNbO3 and KTa1-xNbxO3 crystals irradiated by intense pulsed ion beam

NASA Astrophysics Data System (ADS)

Cui, Xiaojun; Shen, Jie; Zhong, Haowen; Zhang, Jie; Yu, Xiao; Liang, Guoying; Qu, Miao; Yan, Sha; Zhang, Xiaofu; Le, Xiaoyun

2017-10-01

In this work, we studied the surface modification of LiNbO3 and KTa1-xNbxO3 irradiated by intense pulsed ion beam, which was mainly composed of H+ (70%) and Cn+ (30%) at an acceleration voltage of about 450 kV. The surface morphologies, microstructural evolution and elemental analysis of the sample surfaces after IPIB irradiation have been analyzed by scanning electron microscope, atomic force microscope, X-ray diffraction and energy dispersive spectrometer techniques, respectively. The results show that the surface morphologies have significant difference impacted by the irradiation effect. Regular gully damages range from 200 to 400 nm in depth appeared in LiNbO3 under 2 J/cm2 energy density for 1 pulse, block cracking appeared in KTa1-xNbxO3 at the same condition. Surface of the crystals have melted and were darkened with the increasing number up to 5 pulses. Crystal lattice arrangement is believed to be the dominant reason for the different experimental results irradiated by intense pulsed ion beam.

The surface stability and morphology of tobermorite 11 Å from first principles

NASA Astrophysics Data System (ADS)

Mutisya, Sylvia M.; Miranda, Caetano R.

2018-06-01

Tobermorite minerals are important in many industrial processes typically occurring in hydrous environment. Their functionality is therefore governed in various aspects by their morphology and surface stability/reactivity. Here, we present the results of the surface energies and morphology of normal tobermorite 11 Å in a water vapor environment investigated by employing first principles atomistic thermodynamic calculations. For the low index tobermorite surfaces studied, the calculated surface energies fall within a narrow range (0.41-0.97 J/m2) with the (0 0 4) surface being the most stable. The equilibrium morphology is a thin pseudohexagonal plate elongated along the b axis. The hydrated surfaces are more stable at high water vapor chemical potentials with the stability enhanced as the water partial pressures are varied from ambient to supercritical hydrothermal conditions. Increasing the water vapor chemical potential gives rise to a smaller size of the tobermorite crystal, with the equilibrium morphology remaining unaltered.

Morphology and orientation of β-BaB{sub 2}O{sub 4} crystals patterned by laser in the inside of samarium barium borate glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishii, Akihito; Shinozaki, Kenji; Honma, Tsuyoshi

Nonlinear optical β-BaB{sub 2}O{sub 4} crystal lines (β-BBO) were patterned in the inside of 8Sm{sub 2}O{sub 3}–42BaO–50B{sub 2}O{sub 3} glass by irradiations of continuous-wave Yb:YVO{sub 4} lasers with a wavelength of 1080 nm (power: P=0.8–1.0 W, scanning speed: S=0.2–2.5 μm/s), in which the laser focal position was moved gradually from the surface to the inside. The morphology, size, and orientation of β-BBO crystals were examined from polarization optical microscope and birefringence imaging observations. It was demonstrated that c-axis oriented β-BBO crystals with long lengths (e.g., 20 mm) were patterned in the inside of the glass. The morphology of β-BBO inmore » the cross-section of lines was a rectangular shape with rounded corners, and the volume of β-BBO formed increased with increasing laser power and with decreasing laser scanning speed. The maximum depth in the inside from the surface for β-BBO patterning increased with increasing laser power, e.g., D{sub max}∼100 μm at P=0.8 W, D{sub max}∼170 μm at P=0.9 W, and D{sub max}∼200 μm at P=1 W. The present study proposes that the laser-induced crystallization opens a new door for applied engineering in glassy solids. - Graphical abstract: This figure shows the POM photographs for β-BaB{sub 2}O{sub 4} crystal lines patterned by cw Yb:YVO{sub 4} fiber laser irradiations with a laser power of P=0.8 W and a laser scanning speed S=2 μm/s in the glass. The laser focal point was moved gradually from the surface into the inside. The results shown in Fig. 1 demonstrate that it is possible to pattern highly oriented β-BaB{sub 2}O{sub 4} crystals even in the inside of glasses. - Highlights: • β-BaB{sub 2}O{sub 4} crystal lines were patterned in the inside of a glass by lasers. • Laser focal position was moved gradually from the surface to the inside. • Birefringence imaging was observed. • Morphology, size, and orientation of crystals were clarified. • Crystal lines with long lengths (e.g., 20 mm) were patterned at the depth of 200 μm.« less

Formation of curved micrometer-sized single crystals.

PubMed

Koifman Khristosov, Maria; Kabalah-Amitai, Lee; Burghammer, Manfred; Katsman, Alex; Pokroy, Boaz

2014-05-27

Crystals in nature often demonstrate curved morphologies rather than classical faceted surfaces. Inspired by biogenic curved single crystals, we demonstrate that gold single crystals exhibiting curved surfaces can be grown with no need of any fabrication steps. These single crystals grow from the confined volume of a droplet of a eutectic composition melt that forms via the dewetting of nanometric thin films. We can control their curvature by controlling the environment in which the process is carried out, including several parameters, such as the contact angle and the curvature of the drops, by changing the surface tension of the liquid drop during crystal growth. Here we present an energetic model that explains this phenomenon and predicts why and under what conditions crystals will be forced to grow with the curvature of the microdroplet even though the energetic state of a curved single crystal is very high.

Kinetics-Driven Crystal Facets Evolution at the Tip of Nanowires: A New Implementation of the Ostwald-Lussac Law.

PubMed

Yin, Xin; Wang, Xudong

2016-11-09

Nanocrystal facets evolution is critical for designing nanomaterial morphology and controlling their properties. In this work, we report a unique high-energy crystal facets evolution phenomenon at the tips of wurtzite zinc oxide nanowires (NWs). As the zinc vapor supersaturation decreased at the NW deposition region, the NW tip facets evolved from the (0001) surface to the {101̅3} surface and subsequently to the {112̅2} surface and eventually back to the flat (0001) surface. A series of NW tip morphology was observed in accordance to the different combinations of exposed facets. Exposure of the high-energy facets was attributed to the fluctuation of the energy barriers for the formation of different crystal facets during the layer-by-layer growth of the NW tip. The energy barrier differences between these crystal facets were quantified from the surface area ratios as a function of supersaturation. On the basis of the experimental observation and kinetics analysis, we argue that at appropriate deposition conditions exposure of the crystal facets at NW growth front is not merely determined by the surface energy. Instead, the NW may choose to expose the facets with minimal formation energy barrier, which can be determined by the Ehrlich-Schwoebel barrier variation. This empirical law for the NW tip facet formation was in analogy to the Ostwald-Lussac law of phase transformation, which brings a new insight toward nanostructure design and controlled synthesis.

Effects of Humidity and Surfaces on the Melt Crystallization of Ibuprofen

PubMed Central

Lee, Dong-Joo; Lee, Suyang; Kim, Il Won

2012-01-01

Melt crystallization of ibuprofen was studied to understand the effects of humidity and surfaces. The molecular self-assembly during the amorphous-to-crystal transformation was examined in terms of the nucleation and growth of the crystals. The crystallization was on Al, Au, and self-assembled monolayers with –CH3, –OH, and –COOH functional groups. Effects of the humidity were studied at room temperature (18–20 °C) with relative humidity 33%, 75%, and 100%. Effects of the surfaces were observed at −20 °C (relative humidity 36%) to enable close monitoring with slower crystal growth. The nucleation time of ibuprofen was faster at high humidity conditions probably due to the local formation of the unfavorable ibuprofen melt/water interface. The crystal morphologies of ibuprofen were governed by the nature of the surfaces, and they could be associated with the growth kinetics by the Avrami equation. The current study demonstrated the effective control of the melt crystallization of ibuprofen through the melt/atmosphere and melt/surface interfaces. PMID:22949861

Surface morphology and structure of Ge layer on Si(111) after solid phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshida, Ryoma; Tosaka, Aki; Shigeta, Yukichi

2018-05-01

The surface morphology change of a Ge layer on a Si(111) surface formed by solid phase epitaxy has been investigated with a scanning tunneling microscope (STM). The Ge film was deposited at room temperature and annealed at 400 °C or 600 °C. The STM images of the sample surface after annealing at 400 °C show a flat wetting layer (WL) with small three-dimensional islands on the WL. After annealing at 600 °C, the STM images show a surface roughening with large islands. From the relation between the average height of the roughness and the deposited layer thickness, it is confirmed that the diffusion of Ge atoms becomes very active at 600 °C. The Si crystal at the interface is reconstructed and the intermixing occurs over 600 °C. However, the intermixing is fairly restricted in the solid phase epitaxy growth at 400 °C. The surface morphology changes with the crystallization at 400 °C are discussed by the shape of the islands formed on the WL surface. It is shown that the diffusion of the Ge atoms in the amorphous phase is active even at 400 °C.

Micro-nano zinc oxide film fabricated by biomimetic mineralization: Designed architectures for SERS substrates

NASA Astrophysics Data System (ADS)

Lu, Fei; Guo, Yue; Wang, Yunxin; Song, Wei; Zhao, Bing

2018-05-01

In this study, we have investigated the effect of the surface morphologies of the zinc oxide (ZnO) substrates on surface enhanced Raman spectroscopy (SERS). During synthetic process, the self-assembly monolayers (SAMs) with different terminal groups are used as templates to induce the nucleation and growth of Zn(NO3)2·6H2O crystals, then different morphologies micro-nano ZnO powders are obtained by annealing Zn(NO3)2·6H2O crystals at 450 °C. The products obtained at different conditions are characterized by means of X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and Raman spectra. The as-prepared ZnO micro-sized particles have been used the efficient Surface enhanced Raman scattering (SERS) substrates, and the SERS signals of 4-mercaptopyridine (Mpy) probe molecules are much influenced by the morphologies of the ZnO structures. Results indicated that the more (0001) facets appear in the of ZnO morphology, the greater degree of charge-transfer (PCT) for the SERS enhancement on the surface of semiconductors is achieved. The chemical interaction between ZnO structures and Mpy molecules plays a very important role in the SERS enhancement.

Heterogeneous Nucleation of Dicalcium Phosphate Dihydrate on Modified Silica Surfaces

PubMed Central

Miller, Carrie; Komunjer, Ljepša; Hlady, Vladimir

2012-01-01

Heterogeneous nucleation of dicalcium phosphate dihydrate, CaHPO4•2H2O (DCPD) was studied on untreated planar fused silica and on three modified silica surfaces: octadecylsilyl (OTS) modified silica, human serum albumin treated OTS silica, and UV-oxidized 3-mercaptopropyltriethoxysilyl (MTS) modified silica. The supersaturation ratio of calcium and phosphate solution with respect to DCPD was kept below ~10. The nucleated crystals were observed 24 hours and one week after initial contact between supersaturated solutions and substrate surfaces using bright field and reflectance interference contrast microscopy. No DCPD crystals nucleated on albumin-treated OTS-silica. Majority of the DCDP crystals formed on the other modified silica surfaces appeared to be morphologically similar irrespective of the nature of nucleating substrate. Reflectance interference contrast microscopy provided a proof that the majority of the crystals on these substrates do not develop an extended contact with the substrate surface. The images showed that the most extended contact planes were between the DCPD crystals and MTS modified silica surface. The crystals nucleated on OTS-treated and untreated silica surfaces showed only few or none well-developed contact planes. PMID:25264399

Solvothermal synthesis and surface chemistry to control the size and morphology of nanoquartz

DOE PAGES

Sochalski-Kolbus, Lindsay M.; Wang, Hsiu-Wen; Rondinone, Adam Justin; ...

2015-09-29

In this paper, we report a solvothermal synthesis method that allows the crystallization of quartz to occur at a relatively low temperature of 300°C in the form of isolated nanosized euhedral crystals. Transmission electron microscopy (TEM) and small area electron diffraction (SAED) were used to confirm the phases present and their particle sizes, morphologies, and crystallinity of the products. In conclusion, the results show that it is possible to control the size and morphology of the nanoquartz from rough nanospheres to nanorods using fluoride, which templates the nanocrystals and moderates growth.

Evolution of Morphology and Crystallinity of Silica Minerals Under Hydrothermal Conditions

NASA Astrophysics Data System (ADS)

Isobe, H.

2011-12-01

Silica minerals are quite common mineral species in surface environment of the terrestrial planets. They are good indicator of terrestrial processes including hydrothermal alteration, diagenesis and soil formation. Hydrothermal quartz, metastable low temperature cristobalite and amorphous silica show characteristic morphology and crystallinity depending on their formation processes and kinetics under wide range of temperature, pressure, acidity and thermal history. In this study, silica minerals produced by acidic hydrothermal alteration related to volcanic activities and hydrothermal crystallization experiments from diatom sediment are examined with crystallographic analysis and morphologic observations. Low temperature form of cistobalite is a metastable phase and a common alteration product occured in highly acidic hydrothermal environment around fumaroles in geothermal / volcanic areas. XRD analysis revealed that the alteration degree of whole rock is represented by abundance of cristobalite. Detailed powder XRD analysis show that the primary diffraction peak of cristobalite composed with two or three phases with different d-spacing and FWHM by peak profile fitting analysis. Shorter d-spacing and narrower FWHM cristobalite crystallize from precursor materials with less-crystallized, longer d-spacing and wider FWHM cristobalite. Textures of hydrothermal cristobalite in altered rock shows remnant of porphylitic texture of the host rock, pyroxene-amphibole andesite. Diatom has amorphous silica shell and makes diatomite sediment. Diatomite found in less diagenetic Quarternary formation keeps amorphous silica diatom shells. Hydrothermal alteration experiments of amorphous silica diatomite sediment are carried out from 300 °C to 550 °C. Mineral composition of run products shows crystallization of cristobalite and quartz progress depending on temperature and run durations. Initial crystallization product, cristobalite grains occur as characteristic lepispheres and granules with various surface structures. At the very initial stage of cristobalite crystallization within 2 days run duration, cristobalite shows lepispheres a few micron meters in diameter with irregular, submicron scale ridges and grooves on the surface. With the run duration up to 7 days, lepispheres change to granules with smooth surface remaining a few micron meters in diameter. Crystallinity of cristobalite lepispheres and granules corresponds to opal-CT. Euhedral quartz crystals grow with dissolution of cristobalite grains. Growth rate of cristobalite and quartz is controlled by crystallization kinetics with induction period strongly depending on temperature. Induction period of cristobalite crystallization from amorphous silica may exceed several million years at temperature below 100 °C. Crystallinity, morphology and growth rate of silica minerals occurred in various terrestrial and planetary processes are controlled by temperature and acidity of hydrothermal fluid and nucleation and growth kinetics of silica minerals.

Catalysts for electrochemical generation of oxygen

NASA Technical Reports Server (NTRS)

Hagans, P.; Yeager, E.

1979-01-01

Several aspects of the electrolytic evolution of oxygen for use in life support systems are analyzed including kinetic studies of various metal and nonmetal electrode materials, the formation of underpotential films on electrodes, and electrode surface morphology and the use of single crystal metals. In order to investigate the role of surface morphology to electrochemical reactions, a low energy electron diffraction and an Auger electron spectrometer are combined with an electrochemical thin-layer cell allowing initial characterization of the surface, reaction run, and then a comparative surface analysis.

Spectromicroscopy measurements of surface morphology and band structure of exfoliated graphene

NASA Astrophysics Data System (ADS)

Knox, Kevin; Locatelli, Andrea; Cvetko, Dean; Mentes, Tevfik; Nino, Miguel; Wang, Shancai; Yilmaz, Mehmet; Kim, Philip; Osgood, Richard; Morgante, Alberto

2011-03-01

Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. ~However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically flat surfaces. Thus, an understanding of the surface morphology of graphene is essential to making high quality devices and important for interpreting ARPES results. In this talk, we will describe a non-invasive approach to examining the corrugation in exfoliated graphene using a combination of low energy electron microscopy (LEEM) and micro-spot low energy electron diffraction (LEED). We will also describe how such knowledge of surface roughness can be used in the analysis of ARPES data to improve resolution and extract useful information about the band-structure.

Nanoimprinted ultrafine line and space nanogratings for liquid crystal alignment.

PubMed

Liu, Yan Jun; Loh, Wei Wei; Leong, Eunice Sok Ping; Kustandi, Tanu Suryadi; Sun, Xiao Wei; Teng, Jing Hua

2012-11-23

Ultrafine 50 nm line and space nanogratings were fabricated using nanoimprint lithography, and were further used as an alignment layer for liquid crystals. The surface morphologies of the nanogratings were characterized and their surface energies were estimated through the measurement of the contact angles for two different liquids. Experimental results show that the surface energies of the nanogratings are anisotropic: the surface free energy towards the direction parallel to the grating lines is higher than that in the direction perpendicular to the grating lines. Electro-optical characteristics were tested from a twisted nematic liquid crystal cell, which was assembled using two identical nanogratings. Experimental results show that such a kind of nanograting is promising as an alternative to the conventional rubbing process for liquid crystal alignment.

First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

NASA Astrophysics Data System (ADS)

Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang

2018-04-01

Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.

Effect of surfactant concentration on nifedipine crystal habit and its related pharmaceutical properties

NASA Astrophysics Data System (ADS)

Kumar, Dinesh; Thipparaboina, Rajesh; Modi, Sameer R.; Bansal, Arvind K.; Shastri, Nalini R.

2015-07-01

Crystallization in the presence of Polysorbate-80 (T-80), a non-ionic surfactant was explored for crystal habit modification of nifedipine polymorph I (Nif). A concentration dependent reduction in aspect ratio was observed with T-80. Generation of any new solvates/polymorphs was ruled out by Fourier Transform Infrared spectroscopy, differential scanning calorimetry, powder X-ray diffraction, and thermogravimetric analysis, while the absence of T-80 on the surface or bulk of the recrystallized samples was established by liquid chromatography mass spectroscopy. The dissolution rate order of the re-crystallized Nif habits was in the order of; Nif-D (Nif with 0.6%v/v T-80)>Nif-C (Nif with 0.4% v/v T-80)>Nif-B (Nif with 0.2% v/v T-80)>Nif-A (plain Nif). Wetting ability and surface free energy determination from contact angle measurements were used to explain the order of dissolution rate. The consequences of varying concentration of T-80 on Nif crystal habit was supported by means of molecular dynamics (MD) which was executed using COMPASS force field while modified attachment energy was computed to acquire the absolute morphology. The mechanism for alteration in the morphology was suggested based on the computed crystal surface chemistry. Nif-D crystal habit was nearly iso-diametric with majority of facets occupied by polar dominant surfaces {0 1 1} and {0 0 2} which ultimately resulted in higher dissolution rate. In Nif-B and Nif-C the dissolution rate was dependent on the proportion of polar and non-polar facet area. The methodology used in this study could be an influential tool for selection of concentration of habit-modifying additives in other crystallization studies.

Quantitative control of CaCO3 growth on quartz crystal microbalance sensors as a signal amplification method.

PubMed

Wu, Congcong; Sun, Zhaomei; Liu, Li-Shang

2017-07-10

The surface crystallization of CaCO 3 on gold was monitored by a quartz crystal microbalance (QCM). Quantitative control of the grown crystals was realized by adjusting the ratio of two functional groups, -N(CH 3 ) 3 and -COOH, on SAMs. Crystals with uniform size, morphology and polymorphism were obtained. The amount of crystals formed was found to increase with an increase in the -COOH group. The proposed quantitative control of crystallization can be an effective mass amplification strategy for QCM to enhance its assay sensitivity.

Growth of two-dimensional Ge crystal by annealing of heteroepitaxial Ag/Ge(111) under N2 ambient

NASA Astrophysics Data System (ADS)

Ito, Koichi; Ohta, Akio; Kurosawa, Masashi; Araidai, Masaaki; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

2018-06-01

The growth of a two-dimensional crystal of Ge atoms on an atomically flat Ag(111) surface has been demonstrated by the thermal annealing of a heteroepitaxial Ag/Ge structure in N2 ambient at atmospheric pressure. The surface morphology and chemical bonding features of heteroepitaxial Ag(111) grown on wet-cleaned Ge(111) after annealing at different temperatures and for various times have been systematically investigated to control the surface segregation of Ge atoms and the planarization of the heteroepitaxial Ag(111) surface.

Additive-mediated electrochemical synthesis of platelike copper crystals for methanol electrooxidation.

PubMed

Venkatasubramanian, Rajesh; He, Jibao; Johnson, Michael W; Stern, Ilan; Kim, Dae Ho; Pesika, Noshir S

2013-10-29

A room-temperature electrochemical approach to synthesizing anisotropic platelike copper microcrystals and nanocrystals in the presence of potassium bromide is presented. Morphological and elemental characterization was performed using SEM, TEM, and XRD to confirm the anisotropic morphology and crystal structure of the synthesized copper particles. A possible mechanism for explaining the anisotropic crystal growth is proposed on the basis of the preferential adsorption of bromide ions to selective crystal faces. The shape-dependent electrocatalytic property of copper particles is demonstrated by its enhanced catalytic activity for methanol oxidation. Further development of such anisotropic copper particles localized on an electrode surface will lead us to find a suitable alternative for noble metal-based electrocatalysts for the methanol oxidation reaction relevant to fuel cells.

Study of modulation property to incident laser by surface micro-defects on KH2PO4 crystal

NASA Astrophysics Data System (ADS)

Chen, Ming-Jun; Cheng, Jian; Li, Ming-Quan; Xiao, Yong

2012-06-01

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries (e.g., width, morphology, and depth of defects) are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 μm. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.

Nanosensors: towards morphological control of gas sensing activity. SnO2, In2O3, ZnO and WO3 case studies.

PubMed

Gurlo, Aleksander

2011-01-01

Anisotropy is a basic property of single crystals. Dissimilar facets/surfaces have different geometric and electronic structure that results in dissimilar functional properties. Several case studies unambiguously demonstrated that the gas sensing activity of metal oxides is determined by the nature of surfaces exposed to ambient gas. Accordingly, a control over crystal morphology, i.e. over the angular relationships, size and shape of faces in a crystal, is required for the development of better sensors with increased selectivity and sensitivity in the chemical determination of gases. The first step toward this nanomorphological control of the gas sensing properties is the design and synthesis of well-defined nanocrystals which are uniform in size, shape and surface structure. These materials possess the planes of the symmetrical set {hkl} and must therefore behave identically in chemical reactions and adsorption processes. Because of these characteristics, the form-controlled nanocrystals are ideal candidates for fundamental studies of mechanisms of gas sensing which should involve (i) gas sensing measurements on specific surfaces, (ii) their atomistic/quantum chemical modelling and (ii) spectroscopic information obtained on same surfaces under operation conditions of sensors.

Crystallization of copper metaphosphate glass

NASA Technical Reports Server (NTRS)

Bae, Byeong-Soo; Weinberg, Michael C.

1993-01-01

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3),independent of the (Cu sup 2+)/(Cu(total)). However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the (Cu sup 2+)/(Cu (total)) ratio in the glass. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, but small at high temperature. The glass transition temperature of the glass increases as the (Cu sup 2+)/(Cu(total)) ratio is raised. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.

Single Crystals Grown Under Unconstrained Conditions

NASA Astrophysics Data System (ADS)

Sunagawa, Ichiro

Based on detailed investigations on morphology (evolution and variation in external forms), surface microtopography of crystal faces (spirals and etch figures), internal morphology (growth sectors, growth banding and associated impurity partitioning) and perfection (dislocations and other lattice defects) in single crystals, we can deduce how and by what mechanism the crystal grew and experienced fluctuation in growth parameters through its growth and post-growth history under unconstrained condition. The information is useful not only in finding appropriate way to growing highly perfect and homogeneous single crystals, but also in deciphering letters sent from the depth of the Earth and the Space. It is also useful in discriminating synthetic from natural gemstones. In this chapter, available methods to obtain molecular information are briefly summarized, and actual examples to demonstrate the importance of this type of investigations are selected from both natural minerals (diamond, quartz, hematite, corundum, beryl, phlogopite) and synthetic crystals (SiC, diamond, corundum, beryl).

Effect of homolog doping on surface morphology and mass-loss rates from PETN crystals. Studies using atomic force microscope and thermo-gravimetric analysis

DOE PAGES

Bhattacharya, S. K.; Maiti, A; Gee, R. H.; ...

2012-08-28

Pentaerythritol tetranitrate (PETN) is an important energetic material and its performance as a secondary explosive depends strongly on the density as well as flow porosity of powdered material, which in turn is governed by the size and surface properties of the PETN crystallite particles. Historically there has been evidence that the surface properties of PETN particles can be strongly influenced by the presence of homolog impurities of PETN, in particular, dipentaerythritol hexanitrate (diPEHN) and tripentaerythritol octanitrate (triPEON), although not many systematic studies characterizing such influence exist. In this work we employ thermogravimetric analysis (TGA) to measure mass-loss rates at elevatedmore » temperatures and show that doping with a small amount of diPEHN and triPEON can reduce the mass-loss rate from PETN single-crystal surfaces by as much as 35 % as compared to undoped crystals. Arrhenius plots of mass-loss rates as a function of temperature suggest that the reduction in evaporation is not due to the change in activation barrier of the molecular evaporation process, but perhaps due to the impedance to the receding motion of the steps by the immobile impurities on the surface. Removal of surface impurities through gentle washing with ethanol leads to enhanced mass-loss rate relative to pure PETN suggesting a roughened surface morphology. Some surface roughening in doped crystals is supported by Atomic force microscopy (AFM) images of growth layers that show evidences of growth layer stacking and rough edges. Furthermore, we find that a larger amount of impurity added to the original solution does not necessarily lead to a more highly doped crystal, which could perhaps be interpreted as PETN crystals being able to accommodate only up to a certain weight percent of homolog impurities.« less

Effects of Molar Ratios and Sintering Times on Crystal Structures and Surface Morphology of Nd1+xFeO3 Oxide Alloy Prepared by using Solid Reaction Method

NASA Astrophysics Data System (ADS)

Sujiono, E. H.; Agus, J.; Samnur, S.; Triyana, K.

2018-05-01

The effects of molar ratios and sintering times on crystal structures and surface morphology on NdFeO3 oxide alloy have been studied. NdFeO3 oxide alloy formed by chemical preparation with solid reaction method using raw oxide Fe2O3 (99.9 %) and Nd2O3 (99.9 %) powders. In this article we reported the effects of molar ratios x = (–0.1, –0.2 and –0.3) and sintering times for 15 h and 20 h on crystal structures and surface morphology of Nd1+xFeO3 synthesized by solid-state reaction method. The results indicate that variation of molar ratio and sintering time has influenced the FWHM, crystalline size and grain size. The Nd1+xFeO3 have a major phase is NdFeO3, and other minor phases are Fe2O3, Nd2O3 and Nd(OH)3. The dominant intensity of hkl (121) with a value in FWHM, crystallite size, and grain size an indication the results will be applied as a gas sensor material as the focus of the further study.

Revealing Anisotropic Spinel Formation on Pristine Li- and Mn-Rich Layered Oxide Surface and Its Impact on Cathode Performance

DOE PAGES

Kuppan, Saravanan; Shukla, Alpesh Khushalchand; Membreno, Daniel; ...

2017-01-06

Surface properties of cathode particles play important roles in the transport of ions and electrons and they may ultimately dominate cathode's performance and stability in lithium-ion batteries. Through the use of carefully prepared Li 1.2Ni 0.13Mn 0.54Co 0.13O 2 crystal samples with six distinct morphologies, surface transition-metal redox activities and crystal structural transformation are investigated as a function of surface area and surface crystalline orientation. Complementary depth-profiled core-level spectroscopy, namely, X-ray absorption spectroscopy, electron energy loss spectroscopy, and atomic-resolution scanning transmission electron microscopy, are applied in the study, presenting a fine example of combining advanced diagnostic techniques with a well-definedmore » model system of battery materials. Here, we report the following findings: (1) a thin layer of defective spinel with reduced transition metals, similar to what is reported on cycled conventional secondary particles in the literature, is found on pristine oxide surface even before cycling, and (2) surface crystal structure and chemical composition of both pristine and cycled particles are facet dependent. Oxide structural and cycling stabilities improve with maximum expression of surface facets stable against transition-metal reduction. Finally, the intricate relationships among morphology, surface reactivity and structural transformation, electrochemical performance, and stability of the cathode materials are revealed.« less

Morphological Control of Co3O4 and Its Photocatalytic Properties

EPA Science Inventory

Cobaltosic oxide (Co3O4), a p-type semiconductor, belongs to the normal spinel crystal structure based on a cubic close packing array of oxide ions. The size, surface, geometry, and crystal phase of catalysts are important parameters for controlling their chemical, optical, and ...

The Influence of Surface Morphology and Diffraction Resolution of Canavalin Crystals

NASA Technical Reports Server (NTRS)

Plomp, M.; Thomas, B. R.; Day, J. S.; McPherson, A.; Chernov, A. A.; Malkin, A.

2003-01-01

Canavalin crystals grown from material purified and not purified by High Performance Liquid Chromatography were studied by atomic force microscopy and x-ray diffraction. After purification, resolution was improved from 2.55Angstroms to 2.22Angstroms and jagged isotropic spiral steps transformed into regular, well polygonized steps.

Pyroxenes as recorders of lunar basalt petrogenesis - Chemical trends due to crystal-liquid interaction.

NASA Technical Reports Server (NTRS)

Bence, A. E.; Papike, J. J.

1972-01-01

Review of the crystallization histories suggested by the chemical, crystallographic, morphological, and paragenetic relationships observed in pyroxenes from basalts collected on the Apollo 11, 12, 14, 15, and Luna 16 missions. Although the final stages of lunar basalt crystallization appear to be rapid near-surface events, the initial stages are shown to vary considerably among the different basalt types.

{112} Polar surfaces of copper(indium,gallium)selenide: Properties and effects on crystal growth

NASA Astrophysics Data System (ADS)

Liao, Dongxiang

Cu(In,Ga)Se2 (GIGS) are promising materials for thin film photovoltaic applications. This work studies the epitaxial growth of CIGS single crystal films on GaAs substrates of various orientations and characterizes the properties of the thin films. A surprising finding is the strong tendency of film surfaces to facet to {112} planes. The work attempted to establish the connections between the film morphology, the surface energies, the surface chemical compositions, and the reconstruction of polar surfaces. Using angle-resolved photoelectron emission spectroscopy, I found that there is a severe Cu depletion at the first 1-2 layer of the free surface of CuInSe2 and the surface is semiconducting. The results strongly support the model of a reconstructed non-stoichiometric polar surface and exclude the previously believed existence of a bulk second phase on the CIS surface. Unique features of the film morphology suggest that the properties and structure of the polar surfaces have great effects on the growth of the crystals, and probably on the incorporation of the large amount of point defects. Measured chemical composition profiles indicate that the Cu depletion observed on free CIGS surface remains at the CIGS/CdS heterojunction interface and Cd is incorporated into the surface of CIGS. It is proposed that this non-stoichiometric composition leads to charge imbalance at the interface and causes the type-inversion of the CIGS surface, which are favorable for the device performance.

Numerical simulation of flow and mass transfer for large KDP crystal growth via solution-jet method

NASA Astrophysics Data System (ADS)

Yin, Huawei; Li, Mingwei; Hu, Zhitao; Zhou, Chuan; Li, Zhiwei

2018-06-01

A novel technique of growing large crystals of potassium dihydrogen phosphate (KDP) named solution-jet method is proposed. The aim is to increase supersaturation on the pyramidal face, especially for crystal surface regions close to the rotation axis. The fluid flow and surface supersaturation distribution of crystals grown under different conditions were computed using the finite-volume method. Results indicate that the time-averaged supersaturation of the pyramidal face in the proposed method significantly increases and the supersaturation difference from the crystal center to edge clearly decreases compared with the rotating-crystal method. With increased jet velocity, supersaturation on the pyramidal face steadily increases. Rotation rate considerably affects the magnitude and distribution of the prismatic surface supersaturation. With increased crystal size, the mean value of surface supersaturation averaged over the pyramid gradually decreases; conversely, standard deviation increases, which is detrimental to crystal growth. Moreover, the significant roles played by natural and forced convection in the process of mass transport are discussed. Results show that further increased jet velocity to 0.6 m/s renders negligible the effects of natural convection around the pyramid. The simulation for step propagation indicates that solution-jet method can promote a steady step migration and enhance surface morphology stability, which can improve the crystal quality.

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

NASA Astrophysics Data System (ADS)

Chen, Chun-Long; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald N.; Deyoreo, James J.

2014-09-01

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions, with hydrophobic interactions playing the dominant role. While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the {104} faces, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of the {104} faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Chunlong; Qi, Jiahui; Tao, Jinhui

2014-09-05

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic interactions (EI) and hydrophobic interactions (HI), with HI playing the dominant role. While either strong EI or HI inhibit growth and suppress (104) face expression, correlations between peptoid-crystal binding energiesmore » and observed changes in calcite growth indicate moderate EI allow peptoids to weakly adsorb while moderate HI cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of (104) faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.« less

Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

PubMed Central

Chen, Chun-Long; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald N.; DeYoreo, James J.

2014-01-01

In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions, with hydrophobic interactions playing the dominant role. While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the {104} faces, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of the {104} faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications. PMID:25189418

The ion capturing effect of 5° SiOx alignment films in liquid crystal devices

NASA Astrophysics Data System (ADS)

Huang, Yi; Bos, Philip J.; Bhowmik, Achintya

2010-09-01

We show that SiOx, deposited at 5° to the interior surface of a liquid crystal cell allows for a surprisingly substantial reduction in the ion concentration of liquid crystal devices. We have investigated this effect and found that this type of film, due to its surface morphology, captures ions from the liquid crystal material. Ion adsorption on 5° SiOx film obeys the Langmuir isotherm. Experimental results shown allow estimation of the ion capturing capacity of these films to be more than an order of 10 000/μm2. These types of materials are useful for new types of very low power liquid crystal devices such as e-books.

Face-by-face growth of sucrose crystals from aqueous solutions in the presence of raffinose—II: Growth morphology and segregation

NASA Astrophysics Data System (ADS)

Sgualdino, G.; Aquilano, D.; Pastero, L.; Vaccari, G.

2007-10-01

Raffinose segregation into sucrose crystals is experimentally determined along with the modifications of the quantitative sucrose growth morphology, which are in turn related to the different growth conditions. ( Craff, σ) morphodromes nicely represent the conflict between the supersaturation and the raffinose concentration in the solution on the growth morphology, while the overall segregation rate is nearly proportional to the linear overall crystal growth rate. Chernov and Burton-Prim-Slichter models, checked to fit our keff and ln(keff-1-1) coefficients as a function of the supersaturation and of the mean linear overall growth rate, do not allow to know whether the segregation occurs either by a process dominated by surface integration, or by additive transfer dominated by volume diffusion within the boundary layer. The distribution of segregated raffinose strictly depends on the { h k l} growth sectors and doped crystals contain deformed lattice zones, as it comes out from X-ray powder diagrams.

Fast growth with crystal splitting of morphology-controllable Bi2S3 flowers on TiO2 nanotube arrays

NASA Astrophysics Data System (ADS)

Yang, L. X.; Ding, Y. B.; Luo, S. L.; Luo, Y.; Deng, F.; Li, Y.

2013-03-01

Bi2S3 crystals with flower-like morphologies are deposited on TiO2 nanotube arrays (NTs) by applying the cathodic pulse electrodeposition (PED) technique at 120 °C in 20 s. The highly oriented TiO2 NTs/Ti serving as substrate has high surface energy which is favorable for Gibbs free energy decreasing in nucleation process. Numerous boundaries between NTs are nucleation sites for atomic clusters, resulting in a fast nucleation velocity. Effective and fast heterogeneous nucleation initiates a thermodynamic control growth model and finally leads to the fast formation of highly crystallized Bi2S3 with a typical splitting property. Ethylene glycol (EG) was introduced into the electrolytes to inhibit the typical growth along the c axis ([0 0 1] plane) and facilitate the growth along the ab plane, producing Bi2S3 crystals with variable morphologies from sheaves to flowers by increasing EG contents.

Correlating Polymer Crystals via Self-Induced Nucleation

NASA Astrophysics Data System (ADS)

Reiter, Günter

Crystallizable polymers often form multiple stacks of uniquely oriented lamellae, which have good registry despite being separated by amorphous fold surfaces. These correlations require multiple synchronized, yet unidentified, nucleation events. Here, we demonstrate that in thin films of isotactic polystyrene, the probability of generating correlated lamellae is controlled by the branched morphology of a single primary lamella. The nucleation density ns of secondary lamellae is found to be dependent on the width of the branches of the primary lamella. This relation is independent of molecular weight, crystallization temperature, and film thickness. We propose a nucleation mechanism based on the insertion of polymers into a branched primary lamellar crystal. Even in single crystals, characterized by faceted structures with a well-defined envelope reflecting the underlying crystal unit cell, polymers are folded and thus in a meta-stable state. Annealing such meta-stable single crystals allowed to unveil the initial morphological framework of a dendritic single crystal, i.e. the initial stages of growth.

Rapid crystallization and morphological adjustment of zeolite ZSM-5 in nonionic emulsions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Ying, E-mail: yingzh1977@163.co; Jin Chao; Research Institute of Petroleum Processing, Beijing 100083

2011-01-15

Zeolite ZSM-5 was synthesized for the first time in a nonionic emulsion composed of polyoxyethylated alkylphenol, butanol, cyclohexane and tetraethylammonium hydroxide (TEAOH)-containing zeolite synthesis mixture. The crystallization kinetics in the emulsion was investigated and the ZSM-5 product was characterized in detail by XRD, SEM, FT-IR, TG, N{sub 2} adsorption and CHN analysis techniques. Compared with the conventionally hydrothermal synthesis with the same structure directing agent TEAOH, the emulsion system allows rapid crystallization of ZSM-5. The ZSM-5 product exhibits unusual agglomerated structure and possesses larger specific surface area. The FT-IR, TG results plus CHN analysis show the encapsulation of a tracemore » of emulsion components in the emulsion ZSM-5. Control experiments show the emulsion system exerts the crystallization induction and morphological adjustment effects mainly during the aging period. The effects are tentatively attributed to the confined space domains, surfactant-water interaction as well as surfactant-growing crystals interaction existing in the emulsion. -- Graphical abstract: The nonionic emulsion synthesis allows rapid crystallization and morphological adjustment of zeolite ZSM-5 compared with the conventional hydrothermal synthesis. Display Omitted« less

Influence of substrate material and surface finishing on the morphology of the calcium-phosphate coating.

PubMed

Leitão, E; Barbosa, M A; de Groot, K

1997-07-01

The formation of an apatite-like layer was achieved by immersing Ti-6A1-4V, Ti-Al-2.5Fe, and 316 L stainless-steel substrata in Hank's balanced salt solution (HBSS). The layer was characterized by surface analysis techniques, namely X-ray microanalysis and X-ray diffraction, and the morphology was observed by scanning electron microscopy and atomic force microscopy. The concentrations of Ca and P were monitored as a function of time. The morphology of the precipitate layer seems to be dependent both on the type of metal substrate and its surface finish. Polished Ti-6A1-4V and Ti-Al-2.5Fe surfaces exhibit a plate precipitate morphology, whereas rougher surfaces show scattered crystal-like precipitation. The results suggest that the layer produced by immersion of polished titanium alloys in HBSS is constituted by an amorphous apatite.

Growth Temperature Dependence of Morphology of GaN Single Crystals in the Na-Li-Ca Flux Method

NASA Astrophysics Data System (ADS)

Wu, Xi; Hao, Hangfei; Li, Zhenrong; Fan, Shiji; Xu, Zhuo

2018-02-01

In this paper, the effect of growth temperature on the morphology and transparency of the GaN crystals obtained by the Li-Ca-added Na Flux method was studied. Addition of Li-Ca was attempted to control the growth habit and further improve transparency of GaN crystals. The samples with wurtzite structure of GaN were confirmed by the x-ray powder diffraction analysis. GaN single crystal with maximum size of about 6 mm was grown at 750°C. As the growth temperature was increased from 700°C to 850°C, the morphology of the crystals changed from pyramid to prism, and their surfaces became smooth. It was found that high growth temperature was beneficial to obtain a transparent crystal, but the evaporation of sodium would suppress its further growth. The E 2 (high) mode in the Raman spectra was at 568 cm-1, and the full-width at half-maximum values of this peak for the crystals obtained at 700°C, 750°C, 800°C, and 850°C were 7.5 cm-1, 10.3 cm-1, 4.4 cm-1, and 4.0 cm-1, respectively. It indicates that all the crystals are stress free and the transparent crystal grown at high temperature has high structural quality or low impurity concentrations.

Application of two dimensional periodic molecular dynamics to interfaces.

NASA Astrophysics Data System (ADS)

Gay, David H.; Slater, Ben; Catlow, C. Richard A.

1997-08-01

We have applied two-dimensional molecular dynamics to the surface of a crystalline aspartame and the interface between the crystal face and a solvent (water). This has allowed us to look at the dynamic processes at the surface. Understanding the surface structure and properties are important to controlling the crystal morphology. The thermodynamic ensemble was constant Number, surface Area and Temperature (NAT). The calculations have been carried out using a 2D Ewald summation and 2D periodic boundary conditions for the short range potentials. The equations of motion integration has been carried out using the standard velocity Verlet algorithm.

Preparation and magnetic properties of magnetic photonic crystal by using monodisperse polystyrene covered Fe3O4 nanoparticles onto glass substrate

NASA Astrophysics Data System (ADS)

Azizi, Zahra Sadat; Tehranchi, Mohammad Mehdi; Vakili, Seyed Hamed; Pourmahdian, Saeed

2018-05-01

Engineering approach towards combined photonic band gap properties and magnetic/polymer composite particles, attract considerable attention of researchers due to their unique properties. In this research, two different magnetic particles were prepared by nearly monodisperse polystyrene spheres as bead with two concentrations of Fe3O4 nanoparticles to prepare magnetic photonic crystals (MPCs). The crystal surfaces and particles morphology were investigated employing scanning electron microscopy and transmission electron microscopy. The volume fraction of magnetic material embedded into colloidal spheres and their morphology was found to be a key parameter in the optical and magneto-optical properties of transparent MPC.

Laser damage initiation and growth of antireflection coated S-FAP crystal surfaces prepared by pitch lap and magnetorheological finishing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stolz, C J; Menapace, J A; Schaffers, K I

Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb{sup 3+}:Sr{sub 5}(PO{sub 4}){sub 3}F] crystals that received a final polish by both conventional pitch lap finishing as well as magnetorheological finishing (MRF). SEM images of the damage morphology reveals laser damage originates at scratches and at substrate coating interfacial absorbing defects. Previous damage stability tests on multilayer mirror coatings and bare surfaces revealed damage growth can occur at fluences below themore » initiation fluence. The results from this study suggest the opposite trend for AR coatings. Investigation of unstable HR and uncoated surface damage morphologies reveals significant radial cracking that is not apparent with AR damage due to AR delamination from the coated surface with few apparent cracks at the damage boundary. Damage stability tests show that coated Yb:S-FAP crystals can operate at 1057 nm at fluences around 20 J/cm{sup 2} at 10 ns; almost twice the initiation damage threshold.« less

Illusory spirals and loops in crystal growth

PubMed Central

Shtukenberg, Alexander G.; Zhu, Zina; Bhandari, Misha; Song, Pengcheng; Kahr, Bart; Ward, Michael D.

2013-01-01

The theory of dislocation-controlled crystal growth identifies a continuous spiral step with an emergent lattice displacement on a crystal surface; a mechanistic corollary is that closely spaced, oppositely winding spirals merge to form concentric loops. In situ atomic force microscopy of step propagation on pathological l-cystine crystals did indeed show spirals and islands with step heights of one lattice displacement. We show by analysis of the rates of growth of smaller steps only one molecule high that the major morphological spirals and loops are actually consequences of the bunching of the smaller steps. The morphology of the bunched steps actually inverts the predictions of the theory: Spirals arise from pairs of dislocations, loops from single dislocations. Only through numerical simulation of the growth is it revealed how normal growth of anisotropic layers of molecules within the highly symmetrical crystals can conspire to create features in apparent violation of the classic theory. PMID:24101507

Analysis of the convergence rules of full-range PSD surface error of magnetorheological figuring KDP crystal.

PubMed

Chen, Shaoshan; He, Deyu; Wu, Yi; Chen, Huangfei; Zhang, Zaijing; Chen, Yunlei

2016-10-01

A new non-aqueous and abrasive-free magnetorheological finishing (MRF) method is adopted for processing potassium dihydrogen phosphate (KDP) crystal due to its low hardness, high brittleness, temperature sensitivity, and water solubility. This paper researches the convergence rules of the surface error of an initial single-point diamond turning (SPDT)-finished KDP crystal after MRF polishing. Currently, the SPDT process contains spiral cutting and fly cutting. The main difference of these two processes lies in the morphology of intermediate-frequency turning marks on the surface, which affects the convergence rules. The turning marks after spiral cutting are a series of concentric circles, while the turning marks after fly cutting are a series of parallel big arcs. Polishing results indicate that MRF polishing can only improve the low-frequency errors (L>10  mm) of a spiral-cutting KDP crystal. MRF polishing can improve the full-range surface errors (L>0.01  mm) of a fly-cutting KDP crystal if the polishing process is not done more than two times for single surface. We can conclude a fly-cutting KDP crystal will meet better optical performance after MRF figuring than a spiral-cutting KDP crystal with similar initial surface performance.

Homoepitaxial growth of β-Ga{sub 2}O{sub 3} thin films by low pressure chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rafique, Subrina; Han, Lu; Zhao, Hongping, E-mail: hongping.zhao@case.edu

2016-05-02

This paper presents the homoepitaxial growth of phase pure (010) β-Ga{sub 2}O{sub 3} thin films on (010) β-Ga{sub 2}O{sub 3} substrate by low pressure chemical vapor deposition. The effects of growth temperature on the surface morphology and crystal quality of the thin films were systematically investigated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O{sub 2}) as precursors for gallium and oxygen, respectively. The surface morphology and structural properties of the thin films were characterized by atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. Material characterization indicates the growth temperature played anmore » important role in controlling both surface morphology and crystal quality of the β-Ga{sub 2}O{sub 3} thin films. The smallest root-mean-square surface roughness of ∼7 nm was for thin films grown at a temperature of 950 °C, whereas the highest growth rate (∼1.3 μm/h) with a fixed oxygen flow rate was obtained for the epitaxial layers grown at 850 °C.« less

Amelogenin Affects Brushite Crystal Morphology and Promotes Its Phase Transformation to Monetite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Dongni; Ruan, Qichao; Tao, Jinhui

2016-09-07

Amelogenin protein is involved in organized apatite crystallization during enamel formation. Brushite (CaHPO4·2H2O), which is one of the precursors for hydroxyapatite in in vitro mineralization, has been used for fabrication of biomaterials for hard tissue repair. In order to explore its potential application in biomimetic material synthesis, we studied the influence of amelogenin on brushite morphology and phase transformation to monetite. Our results show that amelogenin can adsorb onto surface of brushite, leading to the formation of layered structures on the (010) face. Amelogenin promoted the phase transformation of brushite into monetite (CaHPO4) in the dry state, presumably by interactingmore » with crystalline water layers in brushite unit cell. Changes to the crystal morphology by amelogenin continued even after the phase transformation to monetite forming an organized nanotextured structure of nano-sticks resembling the bundle structure in enamel.« less

Exploration of crystal simulation potential by fluconazole isomorphism and its application in improvement of pharmaceutical properties

NASA Astrophysics Data System (ADS)

Thakur, Amitha; Kumar, Dinesh; Thipparaboina, Rajesh; Shastri, Nalini R.

2014-11-01

Control of crystal morphology during crystallization is a paramount challenge in pharmaceutical processing. Hence, there is need to introduce computational methods for morphology prediction to manage production cost of drugs and improve related pharmaceutical and biopharmaceutical properties. Layer docking approach with molecular dynamics opens a new avenue for crystal habit prediction in presence of solvent. In the present study, attempts were made to correlate predicted and experimental crystal habits of fluconazole considering solvent interactions using layer docking approach. Simulated results from layer docking approach with methanol as solvent gave two dominant facets (0 1 1) and (1 0 1) with a surface area 22.43% and 19.82% respectively, which were in agreement with the experimental results. Experimentally grown modified crystal habit of fluconazole in methanol showed enhanced dissolution rate (p<0.05) when compared to plain drug. This was attributed to the increased surface area on the specified facets caused by interactions with the solvent. Furthermore, Differential Scanning Calorimetry, Fourier Transform Infrared (FTIR) Spectroscopy and powder X-ray Diffraction of recrystallized samples confirmed only a habit change and absence of any polymorphs, hydrates or solvates. Flow and compressibility of fluconazole recrystallized in methanol was significantly improved when compared to plain drug. This study demonstrates a methodical approach using computational tools for prediction and modification of crystal habit, to enhance dissolution of poorly soluble drugs, for future pharmaceutical applications.

Crystal truncation rods from miscut surfaces

DOE PAGES

Petach, Trevor A.; Mehta, Apurva; Toney, Michael F.; ...

2017-05-08

Crystal truncation rods are used to study surface and interface structure. Since real surfaces are always somewhat miscut from a low index plane, it is important to study the effect of miscuts on crystal truncation rods. We develop a model that describes the truncation rod scattering from miscut surfaces that have steps and terraces. We show that nonuniform terrace widths and jagged step edges are both forms of roughness that decrease the intensity of the rods. Nonuniform terrace widths also result in a broad peak that overlaps the rods. We use our model to characterize the terrace width distribution andmore » step edge jaggedness on three SrTiO 3 (001) samples, showing excellent agreement between the model and the data, confirmed by atomic force micrographs of the surface morphology. As a result, we expect our description of terrace roughness will apply to many surfaces, even those without obvious terracing.« less

A phase field crystal model simulation of morphology evolution and misfit dislocation generation in nanoheteroepitaxy

NASA Astrophysics Data System (ADS)

Zhang, J.; Chen, Z.; Cheng, C.; Wang, Y. X.

2017-10-01

A phase field crystal (PFC) model is employed to study morphology evolution of nanoheteroepitaxy and misfit dislocation generation when applied with enhanced supercooling, lattice mismatch and substrate vicinal angle conditions. Misfit strain that rises due to lattice mismatch causes rough surfaces or misfit dislocations, deteriorates film properties, hence, efforts taken to reveal their microscopic mechanism are significant for film quality improvement. Uniform islands, instead of misfit dislocations, are developed in subcritical thickness film, serving as a way of strain relief by surface mechanism. Misfit dislocations generate when strain relief by surface mechanism is deficient in higher supercooling, multilayers of misfit dislocations dominate, but the number of layers reduces gradually when the supercooling is further enhanced. Rough surfaces like islands or cuspate pits are developed which is ascribed to lattice mismatch, multilayers of misfit dislocations generate to further enhance lattice mismatch. Layers of misfit dislocations generate at a thickening position at enhanced substrate vicinal angle, this further enhancing the angle leading to sporadic generation of misfit dislocations.

Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells.

PubMed

Huang, Yu-Ching; Tsao, Cheng-Si; Cho, Yi-Ju; Chen, Kuan-Chen; Chiang, Kai-Ming; Hsiao, Sheng-Yi; Chen, Chang-Wen; Su, Chun-Jen; Jeng, U-Ser; Lin, Hao-Wu

2015-09-04

The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells

NASA Astrophysics Data System (ADS)

Huang, Yu-Ching; Tsao, Cheng-Si; Cho, Yi-Ju; Chen, Kuan-Chen; Chiang, Kai-Ming; Hsiao, Sheng-Yi; Chen, Chang-Wen; Su, Chun-Jen; Jeng, U.-Ser; Lin, Hao-Wu

2015-09-01

The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

Impact of plant matrix polysaccharides on cellulose produced by surface-tethered cellulose synthases.

PubMed

Basu, Snehasish; Omadjela, Okako; Zimmer, Jochen; Catchmark, Jeffrey M

2017-04-15

Surface immobilized BcsA-B cellulose synthases synthesize crystalline cellulose II under in vitro conditions and were used to explore the interaction between cellulose and hemicelluloses and pectin. The morphology of the cellulose microfibrils changed in the presence of xyloglucan and glucomannan, while pectin did not significantly impact morphology. X-ray diffractometry and FT-IR spectroscopy indicated that crystal size and crystallinity were significantly affected by xyloglucan and glucomannan but not altered by pectin. Glucomannan had the most significant impact on the structure of cellulose and inhibits crystallization. The presence of xyloglucan and glucomannan prevents the proper assembly of cellulose microfibrils and changes the crystalline properties of cellulose II in in vitro conditions, but did not have any impact on cellulose allomorph. Copyright © 2017 Elsevier Ltd. All rights reserved.

Microscopic structure and properties changes of cassava stillage residue pretreated by mechanical activation.

PubMed

Liao, Zhengda; Huang, Zuqiang; Hu, Huayu; Zhang, Yanjuan; Tan, Yunfang

2011-09-01

This study has focused on the pretreatment of cassava stillage residue (CSR) by mechanical activation (MA) using a self-designed stirring ball mill. The changes in surface morphology, functional groups and crystalline structure of pretreated CSR were examined by using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) under reasonable conditions. The results showed that MA could significantly damage the crystal structure of CSR, resulting in the variation of surface morphology, the increase of amorphous region ratio and hydrogen bond energy, and the decrease in crystallinity and crystalline size. But no new functional groups generated during milling, and the crystal type of cellulose in CSR still belonged to cellulose I after MA. Copyright © 2011 Elsevier Ltd. All rights reserved.

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe 2 As 2 Superconductors

DOE PAGES

Zou, Qiang; Wu, Zhiming; Fu, Mingming; ...

2017-02-03

Combined scanning tunneling microscopy, spectroscopy, and local barrier height (LBH) studies show that low-temperature-cleaved optimally doped Ba(Fe 1–xCo x) 2As 2 crystals with x = 0.06, with T c = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba- and As-dominated surface terminations, respectively. Magnetic impurities, possibly due to Co or Fe atoms, are believed to createmore » local in-gap state and, in addition, suppress the superconducting coherence peaks. Lastly, this study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors and its relation with the electronic structures.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Yoreo, J; Orme, C; Dove, P

Since the dawn of life on earth, organisms have directed the crystallization of inorganic ions from solution to form minerals that meet specific biological needs. The resulting materials often exhibit remarkable properties, making the processes involved in biomineralization of interest to a wide array of scientific disciplines. From a geochemical standpoint, perhaps the most important consequence is that CaCO{sub 3} biomineral formation occurs in the Oceans on such a large scale that it influences many aspects of seawater chemistry and results in sequestration of carbon in the form of carbonate sediments. In this manner, the products of biomineralization are preservedmore » in the rock record and serve as an extensive chronicle of the interplay between biota and the earth system environment. From the point of view of materials synthesis, biological control over epitaxy is an elegant example of self-organization in complex molecular systems. Through selective introduction of peptides and proteins, living organisms deterministically modify nucleation, step kinetics, surface morphologies, and facet stabilities to produce nanophase materials, topologically complex single-crystals, and multi-layer composite. The resulting materials have biological functions as diverse as structural supports, porous filtration media, grinding and cutting tools, lenses, gravity sensors and magnetic guidance systems. As Table I shows, calcium carbonate minerals are ubiquitous amongst these biomineral structures. In addition , calcium carbonate is a well studied material that is easily crystallized and has known solution chemistry. Consequently, the calcium carbonate system provides an excellent model for investigating biomineralization processes. Surprisingly, in spite of the identification of carbonate biogenesis as a critical contributor to the carbon reservoir mediating climate change, and the enormous potential of biomimetic synthesis for production of tailored, crystalline nano- and micro-structured materials, the fundamental physical controls on carbonate biomineral formation remain poorly understood. Carbonates are formed in diverse environments almost exclusively by living organisms. These naturally occurring marine and fresh water minerals most commonly occur as the polymorphs of calcite, aragonite and vaterite which are nucleated and grown in the exoskeletons and tissues of marine and freshwater organisms ranging from simple bacteria and algae to crustaceans, molluscs, or sponges. It is known that the soluble fraction associated with mineralizing parts of organisms plays a primary role in crystal formation. In the formation of molluscan shells, this fraction is distinguished by the common presence of aspartic acid rich amino acid mixtures. It is also known that carbonates exposed to different polyamino acids exhibit different crystal habits. Belcher et al. showed that exposing growing CaCO{sub 3} crystals alternately to solutions containing polyanionic proteins associated with the aragonitic and calcitic layers of mollusc shells led to sequential switching of the crystal structure of the newly grown material between that of aragonite and calcite. Further work has demonstrated that these protein mixtures alter the morphology of the calcite growth surface and that they contain two fractions effecting growth: a step-binding fraction that inhibits step advancement on calcite surfaces, and a surface binding fraction that appears to lead to the subsequent nucleation of aragonite. Wierzbicki et al. found that polyaspartate molecules (ASP{sub 20}) bind to calcite surfaces. Finally, modeling of ASP{sub 15} binding to calcite planes predicts large binding energies for well defined orientations. This and related evidence shows that systematic relationships between crystal morphology and surface interactions with the reactive groups of the organic molecules must exist. However, the interplay between surface chemistry and the physical processes of nucleation and crystal growth are poorly understood because, until recently only ex situ biochemical studies focusing on the effect of changes in solution chemistry and/or surface stereo-chemistry on macroscopic crystal morphology had been performed.« less

Structural, morphological and Raman studies on hybridized PVDF/BaTiO3 nanocomposites

NASA Astrophysics Data System (ADS)

Rajamanickam, N.; Jayakumar, K.; Ramachandran, K.

2017-05-01

Hybridized nanocomposites of polyvinylidene fluoride (PVDF) and nano - barium titanate (BaTiO3) were prepared using the solution casting method for different concentrations of nano-BaTiO3 and were characterized by X-ray diffraction and scanning electron microscopy. The flower like structure for morphology was observed in SEM. Raman analysis showed that the modified BaTiO3 particles, due to higher specific surfaces, induce, predominantly, the crystallization of the electrically active β-phase of PVDF, while the initial micron size particles induce the formation of the most common but non-polar α-crystal form.

Vapor Growth and Characterization of Cr-Doped ZnSe Crystals

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Feth, Shari; Volz, M. P.; Matyi, R.; George, M. A.; Chattopadhyay, K.; Burger, A.; Lehoczky, S. L.

1999-01-01

Cr-doped ZnSe single crystals were grown by a self-seeded physical vapor transport technique in both vertical (stabilized) and horizontal configurations. The source materials were mixtures of ZnSe and CrSe. Growth temperatures were in the range of 1140-1150 C and the furnace translation rates were 1.9-2.2 mm/day. The surface morphology of the as-grown crystals was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different features of the as-grown surface of the vertically and horizontally grown crystals suggest that different growth mechanisms were involved in the two growth configurations. The [Cr] doping levels were determined to be in the range of 1.8-8.3 x 10 (exp 19) cm (exp -3) from optical absorption measurements. The crystalline quality of the grown crystals were examined by high-resolution triple-crystal X-ray diffraction (HRTXD) analysis.

Fabrication of ZnO photonic crystals by nanosphere lithography using inductively coupled-plasma reactive ion etching with CH{sub 4}/H{sub 2}/Ar plasma on the ZnO/GaN heterojunction light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Shr-Jia; Chang, Chun-Ming; Kao, Jiann-Shiun

2010-07-15

This article reports fabrication of n-ZnO photonic crystal/p-GaN light emitting diode (LED) by nanosphere lithography to further booster the light efficiency. In this article, the fabrication of ZnO photonic crystals is carried out by nanosphere lithography using inductively coupled plasma reactive ion etching with CH{sub 4}/H{sub 2}/Ar plasma on the n-ZnO/p-GaN heterojunction LEDs. The CH{sub 4}/H{sub 2}/Ar mixed gas gives high etching rate of n-ZnO film, which yields a better surface morphology and results less plasma-induced damages of the n-ZnO film. Optimal ZnO lattice parameters of 200 nm and air fill factor from 0.35 to 0.65 were obtained from fittingmore » the spectrum of n-ZnO/p-GaN LED using a MATLAB code. In this article, we will show our recent result that a ZnO photonic crystal cylinder has been fabricated using polystyrene nanosphere mask with lattice parameter of 200 nm and radius of hole around 70 nm. Surface morphology of ZnO photonic crystal was examined by scanning electron microscope.« less

Hot Corrosion of Single-Crystal NiAl-X Alloys

NASA Technical Reports Server (NTRS)

Nesbitt, James A.

1998-01-01

Several single-crystal NiAl-X alloys (X=Hf, Ti, Cr, Ga) underwent hot corrosion testing in a Mach 0.3 burner rig at 900 deg. C for 300 1-hr cycles. The surface morphology after testing consisted of either mounds or an inward, uniform-type of attack which preserved surface features. It was observed that the surface morphology was affected by the surface preparation treatments. Microstructurally, the hot corrosion attack initiated as pits but evolved to a rampant attack consisting of the rapid inward growth of Al2O3. Electropolishing and chemical milling produced many pits and grooves on the surface. However, the presence of pits and grooves did not appear to strongly influence the hot corrosion response. Attack on many samples was strongly localized which was attributed to compositional inhomogeneity within the samples. It was found that increasing the Ti content from 1% to 5 % degraded the hot corrosion response of these alloys. In contrast, the addition of 1-2% Cr reduced the susceptibility of these alloys to hot corrosion attack and negated the deleterious effect of the 4-5% Ti addition.

Morphology Analysis and Optimization: Crucial Factor Determining the Performance of Perovskite Solar Cells.

PubMed

Zeng, Wenjin; Liu, Xingming; Guo, Xiangru; Niu, Qiaoli; Yi, Jianpeng; Xia, Ruidong; Min, Yong

2017-03-24

This review presents an overall discussion on the morphology analysis and optimization for perovskite (PVSK) solar cells. Surface morphology and energy alignment have been proven to play a dominant role in determining the device performance. The effect of the key parameters such as solution condition and preparation atmosphere on the crystallization of PVSK, the characterization of surface morphology and interface distribution in the perovskite layer is discussed in detail. Furthermore, the analysis of interface energy level alignment by using X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy is presented to reveals the correlation between morphology and charge generation and collection within the perovskite layer, and its influence on the device performance. The techniques including architecture modification, solvent annealing, etc. were reviewed as an efficient approach to improve the morphology of PVSK. It is expected that further progress will be achieved with more efforts devoted to the insight of the mechanism of surface engineering in the field of PVSK solar cells.

Recrystallization-Induced Surface Cracks of Carbon Ions Irradiated 6H-SiC after Annealing.

PubMed

Ye, Chao; Ran, Guang; Zhou, Wei; Shen, Qiang; Feng, Qijie; Lin, Jianxin

2017-10-25

Single crystal 6H-SiC wafers with 4° off-axis [0001] orientation were irradiated with carbon ions and then annealed at 900 °C for different time periods. The microstructure and surface morphology of these samples were investigated by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Ion irradiation induced SiC amorphization, but the surface was smooth and did not have special structures. During the annealing process, the amorphous SiC was recrystallized to form columnar crystals that had a large amount of twin structures. The longer the annealing time was, the greater the amount of recrystallized SiC would be. The recrystallization volume fraction was accorded with the law of the Johnson-Mehl-Avrami equation. The surface morphology consisted of tiny pieces with an average width of approximately 30 nm in the annealed SiC. The volume shrinkage of irradiated SiC layer and the anisotropy of newly born crystals during annealing process produced internal stress and then induced not only a large number of dislocation walls in the non-irradiated layer but also the initiation and propagation of the cracks. The direction of dislocation walls was perpendicular to the growth direction of the columnar crystal. The longer the annealing time was, the larger the length and width of the formed crack would be. A quantitative model of the crack growth was provided to calculate the length and width of the cracks at a given annealing time.

Unique isothermal crystallization behavior of novel polyphenylene sulfide/inorganic fullerene-like WS2 nanocomposites.

PubMed

Naffakh, Mohammed; Marco, Carlos; Gómez, Marián A; Jiménez, Ignacio

2008-11-27

The isothermal crystallization of polyphenylene sulfide (PPS) nanocomposites with inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2) has been studied from a thermal and morphological point of view, using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), polarized optical microscopy (POM) and time-resolved synchrotron X-ray diffraction. All the analyses revealed that the incorporation of the IF-WS2 altered significantly the crystallization behavior of PPS, in a way strongly dependent with the nanocomposite composition. The addition of IF-WS2 in 0.1 wt % proportion retarded the crystallization of PPS by increasing its fold surface free energy in a 10%. However, addition of the nanoparticles in excess of 1 wt % results in a promotion of the crystallization rate with reduction of the fold surface free energy to half the value of pure PPS.

Form follows function: morphological diversification and alternative trapping strategies in carnivorous Nepenthes pitcher plants.

PubMed

Bauer, Ulrike; Clemente, C J; Renner, T; Federle, W

2012-01-01

Carnivorous plants of the genus Nepenthes have evolved a striking diversity of pitcher traps that rely on specialized slippery surfaces for prey capture. With a comparative study of trap morphology, we show that Nepenthes pitcher plants have evolved specific adaptations for the use of either one of two distinct trapping mechanisms: slippery wax crystals on the inner pitcher wall and 'insect aquaplaning' on the wet upper rim (peristome). Species without wax crystals had wider peristomes with a longer inward slope. Ancestral state reconstructions identified wax crystal layers and narrow, symmetrical peristomes as ancestral, indicating that wax crystals have been reduced or lost multiple times independently. Our results complement recent reports of nutrient source specializations in Nepenthes and suggest that these specializations may have driven speciation and rapid diversification in this genus. © 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology.

Study on preferred crystal orientations of Mg-Zr-O composite protective layer in AC-PDP

NASA Astrophysics Data System (ADS)

Bingang, G.; Chunliang, L.; Zhongxiao, S.; Liu, L.; Yufeng, F.; Xing, X.; Duowang, F.

2006-11-01

In order to study the preferred crystal orientations of Mg-Zr-O composite protective layers in PDP, Mg-Zr-O composite protective layers were deposited by Electron-beam Evaporator using (MgO+ZrO{2}) powder mixture as evaporation source material. X-ray diffractometer (XRD) was used to determine preferred crystal orientations of Mg-Zr-O composite protective layers, surface morphologies of films were analyzed by FESEM and voltage characteristics were examined in a testing macroscopic discharge cell of AC-PDP. On the basis of experimental analysis, the influence of oxide addition and deposition conditions on preferred orientations of Mg-Zr-O composite protective layers were investigated. The results showed that the preferred orientations of Mg-Zr-O films were determined by lattice distortion of MgO crystal. The deposition conditions have great effects on the preferred orientations of Mg-Zr-O films. The preferred orientations affect voltage characteristics through affecting surface morphology of Mg-Zr-O films. A small amount of Zr solution in MgO can decrease firing voltage compared with using pure MgO film. Firing voltage is closely related with the [ ZrO{2}/(MgO+ZrO{2})] ratio of evaporation source materials.

Crystal Structure Variations of Sn Nanoparticles upon Heating

NASA Astrophysics Data System (ADS)

Mittal, Jagjiwan; Lin, Kwang-Lung

2018-04-01

Structural changes in Sn nanoparticles during heating below the melting point have been investigated using differential scanning calorimetry (DSC), x-ray diffraction (XRD) analysis, electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). DSC revealed that the heat required to melt the nanoparticles (28.43 J/g) was about half compared with Sn metal (52.80 J/g), which was attributed to the large surface energy contribution for the nanoparticles. ED and XRD analyses of the Sn nanoparticles revealed increased intensity for crystal planes having large interplaner distances compared with regular crystal planes with increasing heat treatment temperature (HTT). HRTEM revealed an increase in interlayer spacing at the surface and near joints between nanoparticles with the HTT, leading to an amorphous structure of nanoparticles at the surface at 220°C. These results highlight the changes that occur in the morphology and crystal structure of Sn nanoparticles at the surface and in the interior with increase of the heat treatment temperature.

Optical properties and surface morphology studies of palladium contacts on mercuric iodide single crystals

NASA Astrophysics Data System (ADS)

George, M. A.; Azoulay, M.; Burger, A.; Biao, Y.; Silberman, E.; Nason, D.

1993-04-01

Palladium is chemically suitable for electric contacts on mercuric iodide detectors for photon and nuclear radiation detection, so the understanding of palladium contacts is important for fundamental and practical scientific purposes. A study has been conducted on the surface morphology of evaporated contacts using atomic force microscopy (AFM) and optical transmission and reflection. Evaporated palladium coatings are typically nonuniform and may deposit selectively on mercuric iodide surface defects. Reflection measurements show that coating thickness and surface treatment affect intensity, position, and shape of a reflected peak characteristic of the mercuric iodide structure. Results indicate that the band gap energy in the surface of the mercuric iodide is lowered by palladium contacts.

Tridimensional morphology and kinetics of etch pit on the {l_brace}0 0 0 1{r_brace} plane of sapphire crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Lunyong; Sun Jianfei, E-mail: jfsun_hit@263.net; Zuo Hongbo

2012-08-15

The tridimensional morphology and etching kinetics of the etch pit on the C-{l_brace}0 0 0 1{r_brace} plane of sapphire crystal ({alpha}-Al{sub 2}O{sub 3}) in molten KOH were studied experimentally. It was shown that the etch pit takes on tridimensional morphologies with triangular symmetry same as the symmetric property of the sapphire crystal. Pits like centric and eccentric triangular pyramid as well as hexagonal pyramid were observed, but the latter is less in density. In-depth analyses show the side walls of the etch pits belong to the {l_brace}1 1{sup Macron} 0 2{sup Macron }{r_brace} family, and the triangular pit contains edgesmore » full composed by Al{sup 3+} ions on the etching surface so it is more stable than the hexagonal pit since its edges on the etching surface contains Al{sup 2+} ions. The etch pits developed in a manner of kinematic wave by the step moving with constant speed, which is controlled by the chemical reaction with activation energy of 96.6 kJ/mol between Al{sub 2}O{sub 3} and KOH. - Graphical abstract: Schematic showing the atomic configuration of the predicted side walls of regular triangular pyramid shaped etch pit on the C-{l_brace}0 0 0 1{r_brace} plane of sapphire crystal. Highlights: Black-Right-Pointing-Pointer Observed the tridimensional morphology of etch pits. Black-Right-Pointing-Pointer Figured out the atomic configuration origin of the etch pits. Black-Right-Pointing-Pointer Quantitatively determined the etch rates of the etch pits.« less

Surface alloying in Sn/Au(111) at elevated temperature

NASA Astrophysics Data System (ADS)

Sadhukhan, Pampa; Singh, Vipin Kumar; Rai, Abhishek; Bhattacharya, Kuntala; Barman, Sudipta Roy

2018-04-01

On the basis of x-ray photoelectron spectroscopy, we show that when Sn is deposited on Au(111) single crystal surface at a substrate temperature TS=373 K, surface alloying occurs with the formation of AuSn phase. The evolution of the surface structure and the surface morphology has been studied by low energy electron diffraction and scanning tunneling microscopy, respectively as a function of Sn coverage and substrate temperatures.

Fundamental Studies of Crystal Growth of Microporous Materials

NASA Technical Reports Server (NTRS)

Dutta, P.; George, M.; Ramachandran, N.; Schoeman, B.; Curreri, Peter A. (Technical Monitor)

2002-01-01

Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (1) Nature of the molecular units responsible for the crystal nuclei formation; (2) Nature of the nuclei and nucleation process; (3) Growth process of the nuclei into crystal; (4) Morphological control and size of the resulting crystal; (5) Surface structure of the resulting crystals; (6) Transformation of frameworks into other frameworks or condensed structures. The NASA-funded research described in this report focuses to varying degrees on all of the above issues and has been described in several publications. Following is the presentation of the highlights of our current research program. The report is divided into five sections: (1) Fundamental aspects of the crystal growth process; (2) Morphological and Surface properties of crystals; (3) Crystal dissolution and transformations; (4) Modeling of Crystal Growth; (5) Relevant Microgravity Experiments.

Infrared actuation-induced simultaneous reconfiguration of surface color and morphology for soft robotics.

PubMed

Banisadr, Seyedali; Chen, Jian

2017-12-13

Cephalopods, such as cuttlefish, demonstrate remarkable adaptability to the coloration and texture of their surroundings by modulating their skin color and surface morphology simultaneously, for the purpose of adaptive camouflage and signal communication. Inspired by this unique feature of cuttlefish skins, we present a general approach to remote-controlled, smart films that undergo simultaneous changes of surface color and morphology upon infrared (IR) actuation. The smart film has a reconfigurable laminated structure that comprises an IR-responsive nanocomposite actuator layer and a mechanochromic elastomeric photonic crystal layer. Upon global or localized IR irradiation, the actuator layer exhibits fast, large, and reversible strain in the irradiated region, which causes a synergistically coupled change in the shape of the laminated film and color of the mechanochromic elastomeric photonic crystal layer in the same region. Bending and twisting deformations can be created under IR irradiation, through modulating the strain direction in the actuator layer of the laminated film. Furthermore, the laminated film has been used in a remote-controlled inchworm walker that can directly couple a color-changing skin with the robotic movements. Such remote-controlled, smart films may open up new application possibilities in soft robotics and wearable devices.

Co-effects of amines molecules and chitosan films on in vitro calcium carbonate mineralization.

PubMed

Cui, Jifei; Kennedy, John F; Nie, Jun; Ma, Guiping

2015-11-20

Amines monomers, N,N-dimethylaminoethyl methacrylate (DMAEMA), N,N-dimethylethanolamine (DMEA), 2-dimethylaminoethylamine (DMEDA) and N-methiyldiethanolamine (MDEA) were used to induce the formation of calcium carbonate (CaCO3) crystals on chitosan films, by using (NH4)2CO3 diffusion method at ambient temperature. The obtained CaCO3 particles were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The influence of reaction variables, such as the additive concentration and their types were also investigated on the products. The morphologies of CaCO3 crystals, inter-grown in cube-shape, were controlled by DMAEMA and DMEA. It was observed that the morphologies of CaCO3 changed from the cube grown arms to massive calcite with a hole on the face by increasing the concentrations of DMEDA and MDEA. While the precipitation grew on chitosan film without any organic additive, only single cube-shaped crystals were obtained. By these results the possible mechanisms can be proposed that electronic movement of the groups on the monomer effected ions configuration and molecules absorbed on the exposed surface, resulted the change of the surface energy, which caused the change in the morphology of CaCO3. Copyright © 2015 Elsevier Ltd. All rights reserved.

Zeolite Crystal Growth (ZCG) Flight on USML-2

NASA Technical Reports Server (NTRS)

Sacco, Albert, Jr.; Bac, Nurcan; Warzywoda, Juliusz; Guray, Ipek; Marceau, Michelle; Sacco, Teran L.; Whalen, Leah M.

1997-01-01

The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure, and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, Beta, and Silicalite were grown during the 16 day - USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts. The external surfaces of zeolite A, X, and Silicalite crystals grown in microgravity were smoother (lower surface roughness) than their terrestrial controls. Catalytic studies with zeolite Beta indicate that crystals grown in space exhibit a lower number of Lewis acid sites located in micropores. This suggests fewer structural defects for crystals grown in microgravity. Transmission electron micrographs (TEM) of zeolite Beta crystals also show that crystals grown in microgravity were free of line defects while terrestrial/controls had substantial defects.

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films

DOE PAGES

Zhang, Fengjiao; Mohammadi, Erfan; Luo, Xuyi; ...

2017-10-02

It is well-known that substrate surface properties have a profound impact on morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution coated semiconducting polymers, as the substratedirected thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We performmore » in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing a donor-accepter (D-A) conjugated polymer. Here, we find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate lead to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step towards establishing design rules and understanding the critical role of substrates in determining morphology of solution coated thin films.« less

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fengjiao; Mohammadi, Erfan; Luo, Xuyi

It is well-known that substrate surface properties have a profound impact on morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution coated semiconducting polymers, as the substratedirected thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We performmore » in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing a donor-accepter (D-A) conjugated polymer. Here, we find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate lead to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step towards establishing design rules and understanding the critical role of substrates in determining morphology of solution coated thin films.« less

The assessment of pore connectivity in hierarchical zeolites using positron annihilation lifetime spectroscopy: instrumental and morphological aspects.

PubMed

Zubiaga, Asier; Warringham, Robbie; Boltz, Marilyne; Cooke, David; Crivelli, Paolo; Gidley, David; Pérez-Ramírez, Javier; Mitchell, Sharon

2016-04-07

Recent studies demonstrated the power of positron annihilation lifetime spectroscopy (PALS) to characterise the connectivity and corresponding effectiveness of hierarchical pore networks in zeolites. This was based on the fractional escape of ortho-positronium (Ps), formed within the micropore framework, to vacuum. To further develop this technique, here we assess the impact of the positron implantation energy and of the zeolite crystal size and the particle morphology. Conventional measurements using fast positrons and beam measurements applying moderated positrons both readily distinguish purely microporous ZSM-5 zeolites comprised of single crystals or crystal aggregates. Unlike beam measurements, however, conventional measurements fail to discriminate model hierarchical zeolites with open or constricted mesopore architectures. Several steps are taken to rationalise these observations. The dominant contribution of Ps diffusion to the PALS response is confirmed by capping the external surface of the zeolite crystals with tetraethylorthosilicate, which greatly enhances the sensitivity to the micropore network. A one-dimensional model is constructed to predict the out-diffusion of Ps from a zeolite crystal, which is validated experimentally by comparing coffin-shaped single crystals of varying size. Calculation of the trends expected on the application of fast or moderated positrons indicates that the distinctions in the initial distribution of Ps at the crystal level cannot explain the limited sensitivity of the former to the mesopore architecture. Instead, we propose that the greater penetration of fast positrons within the sample increases the probability of Ps re-entry from intercrystalline voids into mesopores connected with the external surface of zeolite crystals, thereby reducing their fractional escape.

Cylindrically symmetric Green's function approach for modeling the crystal growth morphology of ice.

PubMed

Libbrecht, K G

1999-08-01

We describe a front-tracking Green's function approach to modeling cylindrically symmetric crystal growth. This method is simple to implement, and with little computer power can adequately model a wide range of physical situations. We apply the method to modeling the hexagonal prism growth of ice crystals, which is governed primarily by diffusion along with anisotropic surface kinetic processes. From ice crystal growth observations in air, we derive measurements of the kinetic growth coefficients for the basal and prism faces as a function of temperature, for supersaturations near the water saturation level. These measurements are interpreted in the context of a model for the nucleation and growth of ice, in which the growth dynamics are dominated by the structure of a disordered layer on the ice surfaces.

Calcite crystal growth rate inhibition by polycarboxylic acids

USGS Publications Warehouse

Reddy, M.M.; Hoch, A.R.

2001-01-01

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

Habit modification of potassium acid phthalate (KAP) single crystals by impurities

NASA Astrophysics Data System (ADS)

Murugakoothan, P.; Mohan Kumar, R.; Ushasree, P. M.; Jayavel, R.; Dhanasekaran, R.; Ramasamy, P.

1999-12-01

Nonlinear optical materials potassium dihydrogen phosphate (KDP), urea and L-arginine phosphate (LAP)-doped KAP crystals were grown by the slow cooling method. The LAP-doped crystals show pronounced habit modification compared to KDP and urea doping. The effect of these impurities on growth kinetics, surface morphology, habit modification, structure, optical and mechanical properties have been studied. Among the three impurities, urea doping yields high mechanical stability and optical transmission and for KDP and LAP doping there is a decrease in optical transmission.

Bioleaching of incineration fly ash by Aspergillus niger - precipitation of metallic salt crystals and morphological alteration of the fungus.

PubMed

Xu, Tong-Jiang; Ramanathan, Thulasya; Ting, Yen-Peng

2014-09-01

This study examines the bioleaching of municipal solid waste incineration fly ash by Aspergillus niger , and its effect on the fungal morphology, the fate of the ash particles, and the precipitation of metallic salt crystals during bioleaching. The fungal morphology was significantly affected during one-step and two-step bioleaching; scanning electron microscopy revealed that bioleaching caused distortion of the fungal hyphae (with up to 10 μm hyphae diameter) and a swollen pellet structure. In the absence of the fly ash, the fungi showed a linear structure (with 2-4 μm hyphae diameter). Energy-dispersive X-ray spectroscopy and X-ray diffraction confirmed the precipitation of calcium oxalate hydrate crystals at the surface of hyphae in both one-step and two-step bioleaching. Calcium oxalate precipitation affects bioleaching via the weakening of the fly ash, thus facilitating the release of other tightly bound metals in the matrix.

Crystallization kinetics in Si-1 at%Sn during rapid solidification in undercooled melt

NASA Astrophysics Data System (ADS)

Kuribayashi, K.; Ozawa, S.; Nagayama, K.; Inatomi, Y.

2017-06-01

In order to elucidate the cause of the morphological transition of crystals growing in an undercooled melt of semiconducting materials, we carried out the containerless solidification of undoped Si and Si-1 at%Sn using a CO2 laser-equipped electromagnetic levitator (EML). The crystallization of these materials was successfully achieved under controlled undercooling. The relation between the shape of growing crystals and the degree of undercooling in Si-1 at%Sn was similar to that in undoped Si; that is, plate-like needle crystals were observed at low undercooling, whereas at medium and high undercooling the shape of growing crystals changed to massive dendrites. The grain-size of as-solidified samples of Si-1 at%Sn was remarkably small compared with that of undoped Si. The surface morphologies of samples solidified by dropping the melt onto a chill plate of mirror-polished silicon consisted of typical twin-related <110> dendrites. On the other hand, samples that were dropped from the undercooled state consisted of twin-free <100> dendrites. The nucleation rate of two-dimensional nuclei calculated on the basis of two mechanisms, which are the twin-plane re-entrant edge mechanism and the twin-free mechanism, suggested that the morphological transition to twin-free <100> dendrites from twin-related <110> dendrites occurs when the degree of undercooling becomes larger than the critical value. These results indicate that the cause of the morphological transition of Si growing in the undercooled melt is not the roughening transition of the crystal-melt interface but the transition of the nucleation kinetics to the twin-free mechanism from the twin-related mechanism.

Ice recrystallization inhibition in ice cream by propylene glycol monostearate.

PubMed

Aleong, J M; Frochot, S; Goff, H D

2008-11-01

The effectiveness of propylene glycol monostearate (PGMS) to inhibit ice recrystallization was evaluated in ice cream and frozen sucrose solutions. PGMS (0.3%) dramatically reduced ice crystal sizes in ice cream and in sucrose solutions frozen in a scraped-surface freezer before and after heat shock, but had no effect in quiescently frozen solutions. PGMS showed limited emulsifier properties by promoting smaller fat globule size distributions and enhanced partial coalescence in the mix and ice cream, respectively, but at a much lower level compared to conventional ice cream emulsifier. Low temperature scanning electron microscopy revealed highly irregular crystal morphology in both ice cream and sucrose solutions frozen in a scraped-surface freezer. There was strong evidence to suggest that PGMS directly interacts with ice crystals and interferes with normal surface propagation. Shear during freezing may be required for its distribution around the ice and sufficient surface coverage.

Photoluminescence of vapor and solution grown ZnTe single crystals

NASA Astrophysics Data System (ADS)

Biao, Y.; Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.; Su, C.-H.; Volz, M. E.; Szofran, F. R.; Gillies, D. C.

1994-04-01

ZnTe single crystals grown by horizontal physical vapor transport (PVT) and by vertical traveling heater method (THM) from a Te solution were characterized by photoluminescence (PL) at 10.6 K and by atomic force microscopy (AFM). Copper was identified by PL as a major impurity existing in both crystals, forming a substitutional acceptor, Cu Zn. The THM ZnTe crystals were found to contain more Cu impurity than the PVT ZnTe crystals. The formation of Cu Zn-V Te complexes and the effects of annealing, oxygen contamination and intentional Cu doping were also studied. Finally, the surface morphology analyzed by AFM was correlated to the PL results.

Effects of Saponification Rate on Electrooptical Properties and Morphology of Poly(vinyl alcohol)/Liquid Crystal Composite Films

NASA Astrophysics Data System (ADS)

Ono, Hiroshi; Kawatsuki, Nobuhiro

1995-03-01

The relationship between the saponification rate of poly(vinyl alcohol) (PVA), and the electrooptical properties and morphology of the PVA/liquid crystal (LC) composite films was investigated. Light transmission clazing and the LC droplet size were varied by changing the saponification rate or the blend ratio of two kinds of PVA with different saponification rates because the refractive index and surface tension could be controlled by the saponification rate of PVA. The threshold voltage decreased with increasing saponification rate though the extrapolation length was decreased. It was suggested that the electrooptical properties were strongly dependent on the droplet size.

A critical analysis of calcium carbonate mesocrystals

PubMed Central

Kim, Yi-Yeoun; Schenk, Anna S.; Ihli, Johannes; Kulak, Alex N.; Hetherington, Nicola B. J.; Tang, Chiu C.; Schmahl, Wolfgang W.; Griesshaber, Erika; Hyett, Geoffrey; Meldrum, Fiona C.

2014-01-01

The term mesocrystal has been widely used to describe crystals that form by oriented assembly, and that exhibit nanoparticle substructures. Using calcite crystals co-precipitated with polymers as a suitable test case, this article looks critically at the concept of mesocrystals. Here we demonstrate that the data commonly used to assign mesocrystal structure may be frequently misinterpreted, and that these calcite/polymer crystals do not have nanoparticle substructures. Although morphologies suggest the presence of nanoparticles, these are only present on the crystal surface. High surface areas are only recorded for crystals freshly removed from solution and are again attributed to a thin shell of nanoparticles on a solid calcite core. Line broadening in powder X-ray diffraction spectra is due to lattice strain only, precluding the existence of a nanoparticle sub-structure. Finally, study of the formation mechanism provides no evidence for crystalline precursor particles. A re-evaluation of existing literature on some mesocrystals may therefore be required. PMID:25014563

Lattice Boltzmann Simulation of Kinetic Isotope Effect During Snow Crystal Formation

NASA Astrophysics Data System (ADS)

Lu, G.; Depaolo, D. J.; Kang, Q.; Zhang, D.

2007-12-01

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically-symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over- saturation, determines crystal morphology, there are no quantitative models that relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be direct relationships between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D lattice Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. Crystal growth patterns can be varied between random growth and deterministic growth (along the maximum concentration gradient for example). The input parameters needed are the isotope- dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the condensation coefficient for ice is uncertain. The ratio D/k is a length (order 1 micron) that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). However, few natural crystals form under such conditions. At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, and kinetic effects control isotopic fractionation. Fractionation factors for dendritic crystals are similar to those predicted by the spherical diffusion model, but the model also gives estimates of crystal heterogeneity. Dendritic crystals are constrained to be relatively large, with dimension much greater than about 20D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. An approach using a larger scale simulation and the domain decomposition method can provide a vapor flux for a nested smaller scale calculation. The results clarify the controls on crystal growth, and the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation.

DOE Award No. FG02-93ER14331 Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartynski, Robert

We have studyed new aspects of the relationships between nanoscale surface features and heterogeneous catalysis or electrocatalysis. We concentrate on atomically rough and morphologically unstable surfaces of catalytic metal single crystals (Re, Ru, Ir) that undergo nanoscale faceting when interacting with strongly adsorbed species (e.g. O, N, C) at elevated temperatures.

Morphological diversity of nitroguanidine crystals with enhanced mechanical performance and thermodynamic stability

NASA Astrophysics Data System (ADS)

Luo, Zhilong; Cui, Yingdan; Dong, Weibing; Xu, Qipeng; Zou, Gaoxing; Kang, Chao; Hou, Baohong; Chen, Song; Gong, Junbo

2017-12-01

Nitroguanidine (NQ) is a commonly used explosive, which has been widely used for both civilian and military explosive applications. However, the weak flowability and mechanical performance limit its application. In this work, mechanical performance and thermodynamic stability of NQ crystals were improved by controlling crystal morphologies in the crystallization process. Typical NQ crystals with multiple morphologies and single crystal form were obtained in the presence of additives during the cooling crystallization. The morphology controlled NQ crystals showed higher density, unimodal crystal size distribution and enhanced flowability. The additives showed the inhibitory effect on the nucleation of NQ crystals by in-situ FBRM and PVM determination, and the mechanism was analyzed by means of morphological prediction and molecular simulation. Furthermore, the morphology controlled NQ crystals suggested higher thermodynamic stability according to the calculation of entropy, enthalpy, Gibbs free energy and apparent activation energy on the basis of DSC results.

Effects of Corroded and Non-Corroded Biodegradable Mg and Mg Alloys on Viability, Morphology and Differentiation of MC3T3-E1 Cells Elicited by Direct Cell/Material Interaction

PubMed Central

Mostofi, Sepideh; Bonyadi Rad, Ehsan; Wiltsche, Helmar; Fasching, Ulrike; Szakacs, Gabor; Ramskogler, Claudia; Srinivasaiah, Sriveena; Ueçal, Muammer; Willumeit, Regine; Weinberg, Annelie-Martina; Schaefer, Ute

2016-01-01

This study investigated the effect of biodegradable Mg and Mg alloys on selected properties of MC3T3-E1 cells elicited by direct cell/material interaction. The chemical composition and morphology of the surface of Mg and Mg based alloys (Mg2Ag and Mg10Gd) were analysed by scanning electron microscopy (SEM) and EDX, following corrosion in cell culture medium for 1, 2, 3 and 8 days. The most pronounced difference in surface morphology, namely crystal formation, was observed when Pure Mg and Mg2Ag were immersed in cell medium for 8 days, and was associated with an increase in atomic % of oxygen and a decrease of surface calcium and phosphorous. Crystal formation on the surface of Mg10Gd was, in contrast, negligible at all time points. Time-dependent changes in oxygen, calcium and phosphorous surface content were furthermore not observed for Mg10Gd. MC3T3-E1 cell viability was reduced by culture on the surfaces of corroded Mg, Mg2Ag and Mg10Gd in a corrosion time-independent manner. Cells did not survive when cultured on 3 day pre-corroded Pure Mg and Mg2Ag, indicating crystal formation to be particular detrimental in this regard. Cell viability was not affected when cells were cultured on non-corroded Mg and Mg alloys for up to 12 days. These results suggest that corrosion associated changes in surface morphology and chemical composition significantly hamper cell viability and, thus, that non-corroded surfaces are more conducive to cell survival. An analysis of the differentiation potential of MC3T3-E1 cells cultured on non-corroded samples based on measurement of Collagen I and Runx2 expression, revealed a down-regulation of these markers within the first 6 days following cell seeding on all samples, despite persistent survival and proliferation. Cells cultured on Mg10Gd, however, exhibited a pronounced upregulation of collagen I and Runx2 between days 8 and 12, indicating an enhancement of osteointegration by this alloy that could be valuable for in vivo orthopedic applications. PMID:27459513

Oxygen interaction with disordered and nanostructured Ag(001) surfaces

NASA Astrophysics Data System (ADS)

Vattuone, L.; Burghaus, U.; Savio, L.; Rocca, M.; Costantini, G.; Buatier de Mongeot, F.; Boragno, C.; Rusponi, S.; Valbusa, U.

2001-08-01

We investigated O2 adsorption on Ag(001) in the presence of defects induced by Ne+ sputtering at different crystal temperatures, corresponding to different surface morphologies recently identified by scanning tunneling microscopy. The gas-phase molecules were dosed with a supersonic molecular beam. The total sticking coefficient and the total uptake were measured with the retarded reflector method, while the adsorption products were characterized by high resolution electron energy loss spectroscopy. We find that, for the sputtered surfaces, both sticking probability and total O2 uptake decrease. Molecular adsorption takes place also for heavily damaged surfaces but, contrary to the flat surface case, dissociation occurs already at a crystal temperature, T, of 105 K. The internal vibrational frequency of the O2 admolecules indicates that two out of the three O2- moieties present on the flat Ag(001) surface are destabilized by the presence of defects. The dissociation probability depends on surface morphology and drops for sputtering temperatures larger than 350 K, i.e., when surface mobility prevails healing the defects. The latter, previously identified with kink sites, are saturated at large O2 doses. The vibrational frequency of the oxygen adatoms, produced by low temperature dissociation, indicates the formation of at least two different adatom moieties, which we tentatively assign to oxygen atoms at kinks and vacancies.

Inorganic and Protein Crystal Assembly in Solutions

NASA Technical Reports Server (NTRS)

Chernov, A. A.

2005-01-01

The basic kinetic and thermodynamic concepts of crystal growth will be revisited in view of recent AFM and interferometric findings. These concepts are as follows: 1) The Kossel crystal model that allows only one kink type on the crystal surface. The modern theory is developed overwhelmingly for the Kessel model; 2) Presumption that intensive step fluctuations maintain kink density sufficiently high to allow applicability of Gibbs-Thomson law; 3) Common experience that unlimited step bunching (morphological instability) during layer growth from solutions and supercooled melts always takes place if the step flow direction coincides with that of the fluid.

Rapid Growth of Nanocrystalline Diamond on Single Crystal Diamond for Studies on Materials under Extreme Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, Samuel L.; Samudrala, Gopi K.; Catledge, Shane A.

Early stage nucleation morphologies of spatially localized nanocrystalline diamond (NCD) micro-anvils grown on (100)-oriented single crystal diamond (SCD) anvil surfaces were analyzed and investigated for applications in high pressure studies on materials. NCD was grown on SCD using Microwave Plasma Chemical Vapor Deposition (MPCVD) for brief time intervals ranging from 1-15 minutes. Early stage film morphologies were characterized using scanning electron microscopy (SEM) and Raman spectroscopy and were compared to films grown for several hours. Rapid nucleation and growth of NCD on SCD is demonstrated without any pre-growth seeding of the substrate surface. As grown NCD diamond micro-anvils on SCDmore » were used to generate static pressure of 0.5 Terapascal (TPa) on a tungsten sample as measured by synchrotron x-ray diffraction in a diamond anvil cell. Atomic force microscopy (AFM) analysis after decompression from ultrahigh pressures showed that the detachment of the NCD stage occurred in the bulk of the SCD and not at the interface, suggesting significant adhesive bond strength between nanocrystalline and single crystal diamond.« less

Rapid Growth of Nanocrystalline Diamond on Single Crystal Diamond for Studies on Materials under Extreme Conditions

DOE PAGES

Moore, Samuel L.; Samudrala, Gopi K.; Catledge, Shane A.; ...

2018-01-23

Early stage nucleation morphologies of spatially localized nanocrystalline diamond (NCD) micro-anvils grown on (100)-oriented single crystal diamond (SCD) anvil surfaces were analyzed and investigated for applications in high pressure studies on materials. NCD was grown on SCD using Microwave Plasma Chemical Vapor Deposition (MPCVD) for brief time intervals ranging from 1-15 minutes. Early stage film morphologies were characterized using scanning electron microscopy (SEM) and Raman spectroscopy and were compared to films grown for several hours. Rapid nucleation and growth of NCD on SCD is demonstrated without any pre-growth seeding of the substrate surface. As grown NCD diamond micro-anvils on SCDmore » were used to generate static pressure of 0.5 Terapascal (TPa) on a tungsten sample as measured by synchrotron x-ray diffraction in a diamond anvil cell. Atomic force microscopy (AFM) analysis after decompression from ultrahigh pressures showed that the detachment of the NCD stage occurred in the bulk of the SCD and not at the interface, suggesting significant adhesive bond strength between nanocrystalline and single crystal diamond.« less

Modulation of polyepoxysuccinic acid on crystallization of calcium oxalate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yanqing; Tang, Yongming, E-mail: tangym@njtech.edu.cn; Xu, Jinqiu

The influence of polyepoxysuccinic acid (PESA) on the phase composition and crystal morphology of calcium oxalate was investigated in this paper. It was found that the presence of PESA inhibited the growth of the monoclinic calcium oxalate monohydrate (COM) crystal and promoted the nucleation of the tetragonal calcium oxalate dihydrate (COD). In addition, with the increase in PESA concentration, the aggregation of COD crystals was reduced but the particle size was increased. Under the conditions of low calcium-to-oxalate ratio and high CaOx concentration, PESA could not effectively stabilize the formation of COD. Based on molecular dynamic simulations, the adsorption ofmore » PESA on CaOx crystal faces was confirmed. - Graphical abstract: Introduction of PESA into crystallization solutions promotes the formation of calcium oxalate dehydrate and modifies the morphology of crystals. - Highlights: • PESA induces the formation of COD at low supersaturation. • Establishment of Ca-rich surface augments the adsorption of PESA. • At Ca/Ox=0.5 PESA cannot induce the formation of COD compared with Ca/Ox=2. • Interaction of PESA with COM faces is stronger than that with COD faces.« less

Recrystallization-Induced Surface Cracks of Carbon Ions Irradiated 6H-SiC after Annealing

PubMed Central

Ye, Chao; Ran, Guang; Zhou, Wei; Shen, Qiang; Feng, Qijie; Lin, Jianxin

2017-01-01

Single crystal 6H-SiC wafers with 4° off-axis [0001] orientation were irradiated with carbon ions and then annealed at 900 °C for different time periods. The microstructure and surface morphology of these samples were investigated by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Ion irradiation induced SiC amorphization, but the surface was smooth and did not have special structures. During the annealing process, the amorphous SiC was recrystallized to form columnar crystals that had a large amount of twin structures. The longer the annealing time was, the greater the amount of recrystallized SiC would be. The recrystallization volume fraction was accorded with the law of the Johnson–Mehl–Avrami equation. The surface morphology consisted of tiny pieces with an average width of approximately 30 nm in the annealed SiC. The volume shrinkage of irradiated SiC layer and the anisotropy of newly born crystals during annealing process produced internal stress and then induced not only a large number of dislocation walls in the non-irradiated layer but also the initiation and propagation of the cracks. The direction of dislocation walls was perpendicular to the growth direction of the columnar crystal. The longer the annealing time was, the larger the length and width of the formed crack would be. A quantitative model of the crack growth was provided to calculate the length and width of the cracks at a given annealing time. PMID:29068408

Surface phase separation, dewetting feature size, and crystal morphology in thin films of polystyrene/poly(ε-caprolactone) blend.

PubMed

Ma, Meng; He, Zhoukun; Li, Yuhan; Chen, Feng; Wang, Ke; Zhang, Qing; Deng, Hua; Fu, Qiang

2012-12-01

Thin films of polystyrene (PS)/poly(ε-caprolactone) (PCL) blends were prepared by spin-coating and characterized by tapping mode force microscopy (AFM). Effects of the relative concentration of PS in polymer solution on the surface phase separation and dewetting feature size of the blend films were systematically studied. Due to the coupling of phase separation, dewetting, and crystallization of the blend films with the evaporation of solvent during spin-coating, different size of PS islands decorated with various PCL crystal structures including spherulite-like, flat-on individual lamellae, and flat-on dendritic crystal were obtained in the blend films by changing the film composition. The average distance of PS islands was shown to increase with the relative concentration of PS in casting solution. For a given ratio of PS/PCL, the feature size of PS appeared to increase linearly with the square of PS concentration while the PCL concentration only determined the crystal morphology of the blend films with no influence on the upper PS domain features. This is explained in terms of vertical phase separation and spinodal dewetting of the PS rich layer from the underlying PCL rich layer, leading to the upper PS dewetting process and the underlying PCL crystalline process to be mutually independent. Copyright © 2012 Elsevier Inc. All rights reserved.

Crystallization of calcium oxalate monohydrate at dipalmitoylphosphatidylcholine monolayers in the presence of chondroitin sulfate A

NASA Astrophysics Data System (ADS)

Ouyang, Jian-Ming; Deng, Sui-Ping; Zhong, Jiu-Ping; Tieke, Bernd; Yu, Shu-Hong

2004-10-01

The growth and aggregation of calcium oxalate monohydrate (COM) crystals beneath dipalmitoylphosphatidylcholine (DPPC) monolayers in the presence of chondroitin sulfate A (C4S) was systematically examined under different surface pressure. The results indicated that the addition of C4S can inhibit the crystal growth and prevent the aggregation of COM crystals. Under a DPPC monolayer, well-defined three-dimensional hexagonal prisms and three-dimensional rhombus prisms with sharply angled tips were obtained. The DPPC monolayer at a surface pressure of 10 mN/m can match the Ca2+ distance of the (1 bar 0 1) face of COM better than at 20 mN/m. The addition of C4S could cooperatively modulate the interaction strength between the monolayer (or itself) with the specific morphology determining faces such as (1 bar 0 1) and (0 2 0), and thus results in remarkable stabilization of the (1 bar 0 1) faces. The dramatic changes in morphological details were due to the strong electrostatic interactions between the Ca2+-rich (1 bar 0 1) crystal faces of COM and the polyanionic polysaccharide C4S together with the negatively charged sites of the zwitterionic DPPC monolayers. The increase of the concentration of C4S can further enhance the stabilization of the (1 bar 0 1) face.

Calcite precipitates in Slovenian bottled waters.

PubMed

Stanič, Tamara Ferjan; Miler, Miloš; Brenčič, Mihael; Gosar, Mateja

2017-06-01

Storage of bottled waters in varying ambient conditions affects its characteristics. Different storage conditions cause changes in the initial chemical composition of bottled water which lead to the occurrence of precipitates with various morphologies. In order to assess the relationship between water composition, storage conditions and precipitate morphology, a study of four brands of Slovenian bottled water stored in PET bottles was carried out. Chemical analyses of the main ions and measurements of the physical properties of water samples were performed before and after storage of water samples at different ambient conditions. SEM/EDS analysis of precipitates was performed after elapsed storage time. The results show that the presence of Mg 2+ , SO 4 2- , SiO 2 , Al, Mn and other impurities such as K + , Na + , Ba and Sr in the water controlled precipitate morphology by inhibiting crystal growth and leading to elongated rhombohedral calcite crystal forms which exhibit furrowed surfaces and calcite rosettes. Different storage conditions, however, affected the number of crystallization nuclei and size of calcite crystals. Hollow calcite spheres composed of cleavage rhombohedrons formed in the water with variable storage conditions by a combination of evaporation and precipitation of water droplets during high temperatures or by the bubble templating method.

Subsurface Grain Morphology Reconstruction by Differential Aperture X-ray Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eisenlohr, Philip; Shanthraj, Pratheek; Vande Kieft, Brendan R.

A multistep, non-destructive grain morphology reconstruction methodology that is applicable to near-surface volumes is developed and tested on synthetic grain structures. This approach probes the subsurface crystal orientation using differential aperture x-ray microscopy on a sparse grid across the microstructure volume of interest. Resulting orientation data are clustered according to proximity in physical and orientation space and used as seed points for an initial Voronoi tessellation to (crudely) approximate the grain morphology. Curvature-driven grain boundary relaxation, simulated by means of the Voronoi implicit interface method, progressively improves the reconstruction accuracy. The similarity between bulk and readily accessible surface reconstruction errormore » provides an objective termination criterion for boundary relaxation.« less

Effect of nitrogen on the growth of boron doped single crystal diamond

DOE PAGES

Karna, Sunil; Vohra, Yogesh

2013-11-18

Boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using microwave plasma assisted chemical vapor deposition. A modification in surface morphology of the film with increasing boron concentration in the plasma has been observed using atomic force microscopy. Use of nitrogen during boron doping has been found to improve the surface morphology and the growth rate of films but it lowers the electrical conductivity of the film. The Raman spectra indicated a zone center optical phonon mode along with a few additional bands at the lower wavenumber regions. The change in the peak profilemore » of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. Furthermore, sharpening and upshift of Raman line was observed in the film that was grown in presence of nitrogen along with diborane in process gas.« less

Surfactant Effect on Hydrate Crystallization at the Oil-Water Interface.

PubMed

Dann, Kevin; Rosenfeld, Liat

2018-05-29

Gas hydrates pose economic and environmental risks to the oil and gas industry when plug formation occurs in pipelines. A novel approach was applied to understand cyclopentane clathrate hydrate formation in the presence of nonionic surfactant to achieve hydrate inhibition at low percent weight compared to thermodynamic inhibitors. The hydrate-inhibiting performance of low (CMC) concentrations of Span 20, Span 80, Pluronic L31, and Tween 65 at 2 °C on a manually nucleated 2 μL droplet showed a morphological shift in crystallization from planar shell growth to conical growth. Monitoring the internal pressure of the water droplet undergoing hydrate crystallization provides information on the change in interfacial tension during the crystallization process. The results of this study will provide information on the surfactant effect on hydrate crystallization and inhibition. At low surfactant concentrations (below CMC), a planar hydrate crystal was formed. Decreasing interfacial tension was observed, which can be related to the shrinking area of the water-cyclopentane interface. At high surfactant concentration, the crystal morphology was shifted to conical. Interfacial tension measurements reveal oscillations of the interfacial tension during the crystallization process. The oscillations of the interfacial tension result from the fact that once the crystal has reached a critical size a portion of the cone breaks free from the droplet surface, which results in a sudden increase in the available surface for the surfactant molecules. Hence, a temporary increase in the interfacial tension can be observed. The oscillatory behavior of the interfacial tension is a result of the growth and release of the hydrate cones from the surface of the droplet. We have found that the most efficient surfactant in hydrate inhibition would be the one with HLB closest to 10 (equal hydrophilic-hydrophobic parts). In this way, the surfactant molecules will stay at the interface as they observe equal affinities for both the oil and water phases. Surfactant molecules that have the strongest affinity to the interface will be able to inhibit the growth of the crystal as they will force the cones to break and will not allow them to grow.

Facile electrocatalytic redox of hemoglobin by flower-like gold nanoparticles on boron-doped diamond surface.

PubMed

Li, Mingfang; Zhao, Guohua; Geng, Rong; Hu, Huikang

2008-11-01

The flower-like gold nanoparticles together with spherical and convex polyhedron gold nanoparticles were fabricated on boron-doped diamond (BDD) surface by one-step and simple electrochemical method through easily controlling the applied potential and the concentration of HAuCl(4). The recorded X-ray diffraction (XRD) patterns confirmed that these three shapes of gold nanoparticles were dominated by different crystal facets. The cyclic voltammetric results indicated that the morphology of gold nanoparticles plays big role in their electrochemical behaviors. The direct electrochemistry of hemoglobin (Hb) was realized on all the three different shapes of nanogold-attached BDD surface without the aid of any electron mediator. In pH 4.5 acetate buffer solutions (ABS), Hb showed a pair of well defined and quasi-reversible redox peaks. However, the results obtained demonstrated that the redox peak potential, the average surface concentration of electroactive heme, and the electron transfer rates of Hb are greatly dependent upon the surface morphology of gold nanoparticles. The electron transfer rate constant of hemoglobin over flower-like nanogold/BDD electrode was more than two times higher than that over spherical and convex polyhedron nanogold. The observed differences may be ascribed to the difference in gold particle characteristics including surface roughness, exposed surface area, and crystal structure.

Surface morphological evolution of epitaxial CrN(001) layers

NASA Astrophysics Data System (ADS)

Frederick, J. R.; Gall, D.

2005-09-01

CrN layers, 57 and 230 nm thick, were grown on MgO(001) at Ts=600-800 °C by ultrahigh-vacuum magnetron sputter deposition in pure N2 discharges from an oblique deposition angle α=80°. Layers grown at 600 °C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 °C is characterized by dendritic ridge patterns extending along the orthogonal <110> directions superposed by square-shaped super mounds with <100> edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 °C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as Ts is raised from 600 to 700 to 800 °C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 °C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent β>0.5. In contrast, kinetic roughening controls the surface morphology for Ts=800 °C, as well as the epitaxial fraction of the layers grown at 600 and 700 °C, yielding relatively smooth surfaces and β<=0.27.

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite

PubMed Central

Benzerara, Karim; Menguy, Nicolas; Guyot, François; Dominici, Christian; Gillet, Philippe

2003-01-01

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation. PMID:12792020

Nano Liquid Crystal Droplet Impact on Solid Surfaces

NASA Astrophysics Data System (ADS)

Zhang, Rui; de Pablo, Juan; dePablo Team

2015-03-01

Liquid droplet impaction on solid surfaces is an important problem with a wide range of applications in everyday life. Liquid crystals (LCs) are anisotropic liquids whose internal structure gives rise to rich optical and morphological phenomena. In this work we study the liquid crystal droplet impaction on solid surfaces by molecular dynamics simulations. We employ a widely used Gay-Berne model to describe the elongated liquid crystal molecules and their interactions. Our work shows that, in contrast to isotropic liquids, drop deformation is symmetric unless an instability kicks in, in which case a nano scale liquid crystal droplet exhibits distinct anisotropic spreading modes that do not occur in simple liquids. The drop prefers spreading along the low viscosity direction, but inertia can in some cases overcome that bias. The effects of the director field of the droplet, preferred anchoring direction and the anchoring strength of the wall are investigated. Large scale (0.1 micron) simulations are performed to connect our nano scale results to the experiments. Our studies indicate that LCs could provide an interesting alternative for development of next-generation printing inks.

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite.

PubMed

Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

2003-06-24

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

Tailoring the nanoscale morphology of HKUST-1 thin films via codeposition and seeded growth

PubMed Central

Brower, Landon J; Gentry, Lauren K; Napier, Amanda L

2017-01-01

Integration of surface-anchored metal-organic frameworks (surMOFs) within hierarchical architectures is necessary for potential sensing, electronic, optical, or separation applications. It is important to understand the fundamentals of film formation for these surMOFs in order to develop strategies for their incorporation with nanoscale control over lateral and vertical dimensions. This research identified processing parameters to control the film morphology for surMOFs of HKUST-1 fabricated by codeposition and seeded deposition. Time and temperature were investigated to observe film formation, to control film thickness, and to tune morphology. Film thickness was investigated by ellipsometry, while film structure and film roughness were characterized by atomic force microscopy. Films formed via codeposition resulted in nanocrystallites anchored to the gold substrate. A dynamic process at the interface was observed with a low density of large particulates (above 100 nm) initially forming on the substrate; and over time these particulates were slowly replaced by the prevalence of smaller crystallites (ca. 10 nm) covering the substrate at a high density. Elevated temperature was found to expedite the growth process to obtain the full range of surface morphologies with reasonable processing times. Seed crystals formed by the codeposition method were stable and nucleated growth throughout a subsequent layer-by-layer deposition process. These seed crystals templated the final film structure and tailor the features in lateral and vertical directions. Using codeposition and seeded growth, different surface morphologies with controllable nanoscale dimensions can be designed and fabricated for integration of MOF systems directly into device architectures and sensor platforms. PMID:29181287

Tailoring the nanoscale morphology of HKUST-1 thin films via codeposition and seeded growth.

PubMed

Brower, Landon J; Gentry, Lauren K; Napier, Amanda L; Anderson, Mary E

2017-01-01

Integration of surface-anchored metal-organic frameworks (surMOFs) within hierarchical architectures is necessary for potential sensing, electronic, optical, or separation applications. It is important to understand the fundamentals of film formation for these surMOFs in order to develop strategies for their incorporation with nanoscale control over lateral and vertical dimensions. This research identified processing parameters to control the film morphology for surMOFs of HKUST-1 fabricated by codeposition and seeded deposition. Time and temperature were investigated to observe film formation, to control film thickness, and to tune morphology. Film thickness was investigated by ellipsometry, while film structure and film roughness were characterized by atomic force microscopy. Films formed via codeposition resulted in nanocrystallites anchored to the gold substrate. A dynamic process at the interface was observed with a low density of large particulates (above 100 nm) initially forming on the substrate; and over time these particulates were slowly replaced by the prevalence of smaller crystallites (ca. 10 nm) covering the substrate at a high density. Elevated temperature was found to expedite the growth process to obtain the full range of surface morphologies with reasonable processing times. Seed crystals formed by the codeposition method were stable and nucleated growth throughout a subsequent layer-by-layer deposition process. These seed crystals templated the final film structure and tailor the features in lateral and vertical directions. Using codeposition and seeded growth, different surface morphologies with controllable nanoscale dimensions can be designed and fabricated for integration of MOF systems directly into device architectures and sensor platforms.

Influence of the pH value of a colloidal gold solution on the absorption spectra of an LSPR-assisted sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Jin; Li, Wenbin; Zhu, Mao

2014-03-15

The localized surface plasmon resonances (LSPRs) of gold particles assembled on a crystal plate are a powerful tool for biological sensors. Here, we prepare gold colloids in different pH solutions. We monitor the effects of the particle radius and particle coverage on the absorption spectra of AT-cut (r-face dihedral angle of about 3°) crystal plates supporting gold nanoparticles. The surface morphologies were monitored on silicon dioxide substrates using ultraviolet and visible (UV-vis) spectroscopy, and atomic force microscopy (AFM). The results showed that the gold particle coverage decreases with increasing pH value of the gold colloid solution. This phenomenon demonstrates thatmore » self-assembled gold surfaces were formed via the electrostatic adsorption of gold particles on the positively charged, ionized amino groups on the crystal plates in the acidic solution. The spectrum of gold nanoparticles with different coverage degree on the crystal plates showed that the LSPR properties are highly dependent on pH.« less

Effect of surface tension anisotropy on cellular morphologies

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Sekerka, R. F.

1988-01-01

A three-dimensional weakly nonlinear analysis for conditions near the onset of instability at the crystal-melt interface was carried out to second order, taking into account the effects of latent heat generation and surface-tension anisotropy of the crystal-melt interface; particular consideration was given to the growth of a cubic crystal in the 001-, 011-, and 111-line directions. Numerical calculations by McFadden et al. (1987), performed for an aluminum-chromium alloy with the assumption of a linear temperature field and an isotropic surface tension, showed that only hexagonal nodes (and not hexagonal cells) occurred near the onset of instability. The results of the present analysis indicate that the nonlinear temperature field (which occurs when thermal conductivities of the crystal and the melt are different and/or the latent heat effects are not negligible) can modify this result and, for certain alloys and processing conditions, can cause the occurrence of hexagonal cells near the onset of instability.

Anisotropic Strain Relaxation of Graphene by Corrugation on Copper Crystal Surfaces.

PubMed

Deng, Bing; Wu, Juanxia; Zhang, Shishu; Qi, Yue; Zheng, Liming; Yang, Hao; Tang, Jilin; Tong, Lianming; Zhang, Jin; Liu, Zhongfan; Peng, Hailin

2018-05-01

Corrugation is a ubiquitous phenomenon for graphene grown on metal substrates by chemical vapor deposition, which greatly affects the electrical, mechanical, and chemical properties. Recent years have witnessed great progress in controlled growth of large graphene single crystals; however, the issue of surface roughness is far from being addressed. Here, the corrugation at the interface of copper (Cu) and graphene, including Cu step bunches (CuSB) and graphene wrinkles, are investigated and ascribed to the anisotropic strain relaxation. It is found that the corrugation is strongly dependent on Cu crystallographic orientations, specifically, the packed density and anisotropic atomic configuration. Dense Cu step bunches are prone to form on loose packed faces due to the instability of surface dynamics. On an anisotropic Cu crystal surface, Cu step bunches and graphene wrinkles are formed in two perpendicular directions to release the anisotropic interfacial stress, as revealed by morphology imaging and vibrational analysis. Cu(111) is a suitable crystal face for growth of ultraflat graphene with roughness as low as 0.20 nm. It is believed the findings will contribute to clarifying the interplay between graphene and Cu crystal faces, and reducing surface roughness of graphene by engineering the crystallographic orientation of Cu substrates. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Anatase TiO2 single crystals with dominant {0 0 1} facets: Synthesis, shape-control mechanism and photocatalytic activity

NASA Astrophysics Data System (ADS)

Tong, Huifen; Zhou, Yingying; Chang, Gang; Li, Pai; Zhu, Ruizhi; He, Yunbin

2018-06-01

Anatase TiO2 micro-crystals with 51% surface exposing highly active {0 0 1} facets are prepared by hydrothermal synthesis using TiF4 as Ti resource and HF as morphology control agent. In addition, anatase TiO2 single crystals exposing large {0 0 1} crystal facets are facilely synthesized with "green" NaF plus HCl replacing HF for the morphology control. A series of comparative experiments are carried out for separately studying the effects of F- and H+ concentrations on the growth of TiO2 crystals, which have not been understood very much in depth so far. The results indicate that both F- and H+ synergistically affect the synthesis of truncated anatase octahedrons, where F- is preferentially adsorbed on the {0 0 1} facets resulting in lateral growth of these facets and H+ adjusts the growth rate of anatase TiO2 along different orientations by tuning the hydrolysis rate. Based on this information, anatase TiO2 single crystals with small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are successfully prepared under optimal conditions ([H+]/[F-] = 20:1). Photocatalytic activities of the as-prepared products toward methylene blue photo-degradation are further tested. It is revealed that both crystal size and percentage of {0 0 1} facets are decisive for the photocatalytic performance, and the crystals with a small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are catalytically most active. This work has clarified the main factors that control the growth process and morphology of anatase TiO2 single crystals for achieving superior photocatalytic properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hou, Kun; Gao, Ziwei, E-mail: zwgao@snnu.edu.cn; Da, Min

Highlights: Black-Right-Pointing-Pointer Highly oriented and well-defined ZnO urchin-like crystals were successfully fabricated by a facile and effective hydrotherm method. Black-Right-Pointing-Pointer Polyvinylpyrrolidone- and hydrogen peroxide-assisted synthesis of ZnO could optimize its crystalline quality and the obtained ZnO have smooth surface, radial growth of morphology, obvious crystal edges and decreased defects. Black-Right-Pointing-Pointer The physicochemical properties of samples were studied by analysis of its structure, morphology, surface and optical properties. Black-Right-Pointing-Pointer This study represented a multistep mechanism based on [Zn(OH){sub 4}]{sup 2-} growth units about formation such urchin-like structure. -- Abstract: The urchin-like ZnO microcrystals with high crystallinity decomposed from [Zn(OH){sub 4}]{sup 2-}more » directly were obtained via a hydrothermal method. The morphology, particle size, crystalline structure and fluorescence of the as-prepared ZnO were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analyses. The results demonstrated that the urchin-like ZnO crystals with wurtzite structure had a narrow distribution in size, which could be adjusted in the range of 30-80 {mu}m by varying reaction time. Broad visible light emission peak was also observed in the PL spectra of the synthesized ZnO products. A multistep growth process about how to form such a structure was proposed.« less

Analysis of the Early Stages and Evolution of Dental Enamel Erosion.

PubMed

Derceli, Juliana Dos Reis; Faraoni, Juliana Jendiroba; Pereira-da-Silva, Marcelo Assumpção; Palma-Dibb, Regina Guenka

2016-01-01

The aim of this study was to evaluate by atomic force microscopy (AFM) the early phases and evolution of dental enamel erosion caused by hydrochloric acid exposure, simulating gastroesophageal reflux episodes. Polished bovine enamel slabs (4x4x2 mm) were selected and exposed to 0.1 mL of 0.01 M hydrochloric acid (pH=2) at 37 ?#61472;?#61616;C using five different exposure intervals (n=1): no acid exposure (control), 10 s, 20 s, 30 s and 40 s. The exposed area was analyzed by AFM in 3 regions to measure the roughness, surface area and morphological surface. The data were analyzed qualitatively. Roughness started as low as that of the control sample, Rrms=3.5 nm, and gradually increased at a rate of 0.3 nm/s, until reaching Rrms=12.5 nm at 30 s. After 40 s, the roughness presented increment of 0.40 nm only. Surface area (SA) increased until 20 s, and for longer exposures, the surface area was constant (at 30 s, SA=4.40 μm2 and at 40 s, SA=4.43 μm2). As regards surface morphology, the control sample presented smaller hydroxyapatite crystals (22 nm) and after 40 s the crystal size was approximately 60 nm. Short periods of exposure were sufficient to produce enamel demineralization in different patterns and the morphological structure was less affected by exposure to hydrochloric acid over 30 s.

Precipitation of thin-film organic single crystals by a novel crystal growth method using electrospray and ionic liquid film

NASA Astrophysics Data System (ADS)

Ueda, Hiroyuki; Takeuchi, Keita; Kikuchi, Akihiko

2018-04-01

We report an organic single crystal growth technique, which uses a nonvolatile liquid thin film as a crystal growth field and supplies fine droplets containing solute from the surface of the liquid thin film uniformly and continuously by electrospray deposition. Here, we investigated the relationships between the solute concentration of the supplied solution and the morphology and size of precipitated crystals for four types of fluorescent organic low molecule material [tris(8-hydroxyquinoline)aluminum (Alq3), 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), N,N‧-bis(3-methylphenyl)-N,N‧-diphenylbenzidine (TPD), and N,N-bis(naphthalene-1-yl)-N,N-diphenyl-benzidine (NPB)] using an ionic liquid as the nonvolatile liquid. As the concentration of the supplied solution decreased, the morphology of precipitated crystals changed from dendritic or leaf shape to platelike one. At the solution concentration of 0.1 mg/ml, relatively large platelike single crystals with a diagonal length of over 100 µm were obtained for all types of material. In the experiment using ionic liquid and dioctyl sebacate as nonvolatile liquids, it was confirmed that there is a clear positive correlation between the maximum volume of the precipitated single crystal and the solubility of solute under the same solution supply conditions.

Magnetic spherical cores partly coated with periodic mesoporous organosilica single crystals.

PubMed

Li, Jing; Wei, Yong; Li, Wei; Deng, Yonghui; Zhao, Dongyuan

2012-03-07

Core-shell structured materials are of special significance in various applications. Until now, most reported core-shell structures have polycrystalline or amorphous coatings as their shell layers, with popular morphologies of microspheres or quasi-spheres. However, the single crystals, either mesoscale or atomic ones, are still rarely reported as shell layers. If single crystals can be coated on core materials, it would result in a range of new type core-shell structures with various morphologies, and probably more potential applications. In this work, we demonstrate that periodic mesoporous organosilica (PMO) single crystals can partly grow on magnetic microspheres to form incomplete Fe(3)O(4)@nSiO(2)@PMO core-shell materials in aqueous solution, which indeed is the first illustration that mesoporous single-crystal materials can be used as shell layers for preparation of core-shell materials. The achieved materials have advantages of high specific surface areas, good magnetic responses, embedded functional groups and cubic mesopore channels, which might provide them with various application conveniences. We suppose the partial growth is largely decided by the competition between growing tendency of single crystals and the resistances to this tendency. In principle, other single crystals, including a range of atomic single crystals, such as zeolites, are able to be developed into such core-shell structures.

Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

NASA Astrophysics Data System (ADS)

Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

2006-12-01

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number: Da = kh/D, where h is the width of the 2D calculation domain. Varying the nondimensional Da in the model is equivalent to varying the scale (h) in the model. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, the isotopic fractionations are dominated by kinetic effects, and similar to those predicted by the spherical diffusion model. Dendritic crystals are constrained to be relatively large, with dimension much greater than D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. A different approach, using a larger scale simulation to derive boundary conditions for a nested smaller scale calculation is in progress. The results to date clarify the controls on dendritic crystal growth, the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation, and provide limits on the value of the accommodation coefficient.

Electromagnetic induction heating for single crystal graphene growth: morphology control by rapid heating and quenching

NASA Astrophysics Data System (ADS)

Wu, Chaoxing; Li, Fushan; Chen, Wei; Veeramalai, Chandrasekar Perumal; Ooi, Poh Choon; Guo, Tailiang

2015-03-01

The direct observation of single crystal graphene growth and its shape evolution is of fundamental importance to the understanding of graphene growth physicochemical mechanisms and the achievement of wafer-scale single crystalline graphene. Here we demonstrate the controlled formation of single crystal graphene with varying shapes, and directly observe the shape evolution of single crystal graphene by developing a localized-heating and rapid-quenching chemical vapor deposition (CVD) system based on electromagnetic induction heating. Importantly, rational control of circular, hexagonal, and dendritic single crystalline graphene domains can be readily obtained for the first time by changing the growth condition. Systematic studies suggest that the graphene nucleation only occurs during the initial stage, while the domain density is independent of the growth temperatures due to the surface-limiting effect. In addition, the direct observation of graphene domain shape evolution is employed for the identification of competing growth mechanisms including diffusion-limited, attachment-limited, and detachment-limited processes. Our study not only provides a novel method for morphology-controlled graphene synthesis, but also offers fundamental insights into the kinetics of single crystal graphene growth.

Synthesis of Hexagonal Boron Nitride Mono layer: Control of Nucleation and Crystal Morphology

DOE PAGES

Stehle, Yijing Y.; Meyer, III, Harry M.; Unocic, Raymond R.; ...

2015-11-10

Mono layer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies formore » the hBN nucleation process of similar to 5 eV and crystal growth of similar to 3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure chemical vapor deposition on copper using borazane as a precursor.« less

Crystalline desiccation patterns and film break up from evaporating drops on hydrophobic oxide surfaces

NASA Astrophysics Data System (ADS)

McBride, Samantha; Dash, Susmita; Khan, Sami; Varanasi, Kripa

2017-11-01

Solute-laden sessile drops evaporating on a substrate will often force crystallization of the solute at the triple phase contact line between the drop, substrate, and air in an effect similar to the ``coffee-ring'' deposition of particles from a particle-laden drop. We report new observations of ring-shaped desiccation patterns of gypsum crystals on hydrophobic oxide substrates; ceria, erbia, and silica. These surfaces have similar contact angles ( 105 degrees), and evaporation of sessile drops proceeds at the same rate and without contact angle hysteresis on all three substrates. However, despite the apparent similarity, the patterns of crystal deposits exhibit large differences across the substrates. The supersaturation and elapsed time at the onset of crystallization also varied across substrates, despite overall evaporation rates being identical. The differences in patterns can be explained in light of the position and morphology of the crystals just prior to completion of evaporation when the sessile drop has transitioned to a thin film spread over the deposit area. Break-up of this film occurs very differently on the different surfaces, and is simultaneously influenced by existing crystals while also influencing final crystalline patterns. This work was supported by the NSF GRFP.

Optical Constants of Crystallized TiO2 Coatings Prepared by Sol-Gel Process

PubMed Central

Wang, Xiaodong; Wu, Guangming; Zhou, Bin; Shen, Jun

2013-01-01

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO2 coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing. PMID:28811410

Optical Constants of Crystallized TiO₂ Coatings Prepared by Sol-Gel Process.

PubMed

Wang, Xiaodong; Wu, Guangming; Zhou, Bin; Shen, Jun

2013-07-12

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO₂ coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing.

Reconditioning perovskite films in vapor environments through repeated cation doping

NASA Astrophysics Data System (ADS)

Boonthum, Chirapa; Pinsuwan, Kusuma; Ponchai, Jitprabhat; Srikhirin, Toemsak; Kanjanaboos, Pongsakorn

2018-06-01

Perovskites have attracted considerable attention for application as high-efficiency photovoltaic devices owing to their low-cost and low-temperature fabrication. A good surface and high crystallinity are necessary for high-performance devices. We examine the negative effects of chemical ambiences on the perovskite crystal formation and morphology. The repeated cation doping (RCD) technique was developed to remedy these issues by gradually dropping methylammonium ions on top of about-to-form perovskite surfaces to cause recrystallization. RCD promotes pinhole-free, compact, and polygonal-like surfaces under various vapor conditions. Furthermore, it enhances the electronic properties and crystallization. The benefits of RCD extend beyond perovskites under vapor ambiences, as it can improve regular and wasted perovskites.

Miscut dependent surface evolution in the process of N-polar GaN(000 1 bar) growth under N-rich condition

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.; Turski, Henryk; Sawicka, Marta; Skierbiszewski, Czesław

2017-01-01

The evolution of surface morphology during the growth of N-polar (000 1 bar) GaN under N-rich conditions is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2° and 4°. The results are compared with experimentally observed surface morphologies of (000 1 bar) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000 1 bar) surface where both types of atoms, nitrogen and gallium, attach to the surface and diffuse independently shows that at relatively high rates of the step flow (miscut angle < 2 °) the low mobility of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4°), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions crystal growth is realized by the process of two-dimensional island nucleation and coalescence. Larger crystal miscut, lower growth rate or higher temperature results in similar effect of the surface smoothening. We show that the surface also smoothens for the growth conditions with very high N-excess. In the presence of large number of nitrogen atoms the mobility of gallium atoms changes locally thus providing easier coalescence of separated island.

Effect of Polyelectrolyte and Fatty Acid Soap on the Formation of CaCO3 in the Bulk and the Deposit on Hard Surfaces.

PubMed

Wang, Hao; Alfredsson, Viveka; Tropsch, Juergen; Ettl, Roland; Nylander, Tommy

2015-09-30

The effects of sodium polyacrylate (NaPAA) as well as potassium oleate on the nucleation and calcium carbonate crystal growth on hard surfaces, i.e., stainless steel and silica, have been investigated at different temperatures. The relation between the surface deposition and the corresponding bulk processes has been revealed by combining dynamic light scattering (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and ellipsometry. The aim was to further our understanding of the crystal deposition/growth mechanism and how it can be controlled by the presence of polyelectrolytes (NaPAA) or soap (potassium oleate). The addition of polyelectrolytes (NaPAA) or soap (potassium oleate) decreases the size of CaCO3 particles in bulk solution and affects both crystal structure and morphology in the bulk as well as on hard surfaces. The amount of particles on hard surfaces decreases significantly in the presence of both potassium oleate and NaPAA. This was found to be a consequence of potassium oleate or NaPAA adsorption on the hard surface as well as on the CaCO3 crystal surfaces. Here, the polymer NaPAA exhibited a stronger inhibition effect on the formation and growth of CaCO3 particles than potassium oleate.

A comparative study of the influence of alpha-lactose monohydrate particle morphology on granule and tablet properties after roll compaction/dry granulation.

PubMed

Grote, Simon; Kleinebudde, Peter

2018-05-29

The influence of particle morphology and size of alpha-lactose monohydrate on dry granules and tablets was studied. Four different morphologies were investigated: Two grades of primary crystals, which differed in their particle size and structure (compact crystals vs. agglomerates). The materials were roll compacted at different specific compaction forces and changes in the particle size distribution and the specific surface area were measured. Afterwards, two fractions of granules were pressed to tablets and the tensile strength was compared to that from tablets compressed from the raw materials. The specific surface area was increased induced by roll compaction/dry granulation for all materials. At increased specific compaction forces, the materials showed sufficient size enlargement. The morphology of lactose determined the strength of direct compressed tablets. In contrast, the strength of granule tablets was leveled by the previous compression step during roll compaction/dry granulation. Thus, the tensile strength of tablets compressed directly from the powder mixtures determined whether materials exhibited a loss in tabletability after roll compaction/dry granulation or not. The granule size had only a slight influence on the strength of produced tablets. In some cases, the fraction of smaller granules showed a higher tensile strength compared to the larger fraction.

Surface Termination of the Metal-Organic Framework HKUST-1: A Theoretical Investigation.

PubMed

Amirjalayer, Saeed; Tafipolsky, Maxim; Schmid, Rochus

2014-09-18

The surface morphology and termination of metal-organic frameworks (MOF) is of critical importance in many applications, but the surface properties of these soft materials are conceptually different from those of other materials like metal or oxide surfaces. Up to now, experimental investigations are scarce and theoretical simulations have focused on the bulk properties. The possible surface structure of the archetypal MOF HKUST-1 is investigated by a first-principles derived force field in combination with DFT calculations of model systems. The computed surface energies correctly predict the [111] surface to be most stable and allow us to obtain an unprecedented atomistic picture of the surface termination. Entropic factors are identified to determine the preferred surface termination and to be the driving force for the MOF growth. On the basis of this, reported strategies like employing "modulators" during the synthesis to tailor the crystal morphology are discussed.

Li2MoO4 crystal growth from solution activated by low-frequency vibrations

NASA Astrophysics Data System (ADS)

Barinova, Olga; Sadovskiy, Andrey; Ermochenkov, Ivan; Kirsanova, Svetlana; Sukhanova, Ekaterina; Kostikov, Vladimir; Belov, Stanislav; Mozhevitina, Elena; Khomyakov, Andrew; Kuchuk, Zhanna; Zharikov, Eugeny; Avetissov, Igor

2017-01-01

The possibility of Li2MoO4 crystal growth from aqueous solutions activated by axial vibrational control (AVC) technique was investigated. It was found out that a low-frequency mechanical activation of the solution led to an increase of Li2MoO4 equilibrium solubility in aqueous solution for 11 rel% in the 25-29 °C temperature range. The changes in solution structure were analyzed in situ by Raman study of the solution. The AVC activation of solution resulted in a re-faceting of growing crystals, a smoothing of a face surface morphology and reduction of water content in the crystal.

Improved performance of mesostructured perovskite solar cells via an anti-solvent method

NASA Astrophysics Data System (ADS)

Hao, Jiabin; Hao, Huiying; Cheng, Feiyu; Li, Jianfeng; Zhang, Haiyu; Dong, Jingjing; Xing, Jie; Liu, Hao; Wu, Jian

2018-06-01

One-step solution process is a facile and widely used procedure to prepare organic-inorganic perovskite materials. However, the poor surface morphology of the films attributed to the uncontrollable nucleation and crystal growth in the process is unfavorable to solar cells. In this study, an anti-solvent treatment during the one-step solution process, in which ethyl acetate (EA) was dropped on the sample during spinning the precursor solution containing CH3NH3Cl, was adopted to fabricate perovskite materials and solar cells. It was found that the morphology of the perovskite film was significantly improved due to the rapid nucleation and slow crystal growth process. The modified process enabled us to fabricate the mesoporous solar cell with power conversion efficiency of 14%, showing an improvement of 40% over the efficiency of 9.7% of the device prepared by conventional one-step method. The controlling effect of annealing time on the morphology, crystal structure and transport properties of perovskite layer as well as the performance of device fabricated by the anti-solvent method were investigated and the possible mechanism was discussed.

Structural and optical properties of WTe2 single crystals synthesized by DVT technique

NASA Astrophysics Data System (ADS)

Dixit, Vijay; Vyas, Chirag; Pathak, V. M.; Soalanki, G. K.; Patel, K. D.

2018-05-01

Layered transition metal di-chalcogenide (LTMDCs) crystals have attracted much attention due to their potential in optoelectronic device applications recently due to realization of their monolayer based structures. In the present investigation we report growth of WTe2 single crystals by direct vapor transport (DVT) technique. These crystals are then characterized by energy dispersive analysis of x-rays (EDAX) to study stoichiometric composition after growth. The structural properties are studied by x-ray diffraction (XRD) and selected area electron diffraction (SAED) is used to confirm orthorhombic structure of grown WTe2 crystal. Surface morphological properties of the crystals are also studied by scanning electron microscope (SEM). The optical properties of the grown crystals are studied by UV-Visible spectroscopy which gives direct band gap of 1.44 eV for grown WTe2 single crystals.

Effect of heat treatment on surface hydrophilicity-retaining ability of titanium dioxide nanotubes

NASA Astrophysics Data System (ADS)

Sun, Yu; Sun, Shupei; Liao, Xiaoming; Wen, Jiang; Yin, Guangfu; Pu, Ximing; Yao, Yadong; Huang, Zhongbing

2018-05-01

The aim of this study is to investigate the effect of different annealing temperature and atmosphere on the surface wettability retaining properties of titania nanotubes (TNs) fabricated by anodization. The TNs morphology, crystal phase composition and surface elemental composition and water contact angle (WCA) were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and contact angle instrument, respectively. After the samples annealed at 200 °C, 450 °C, 850 °C have been stored in air for 28 days, the WCAs increase to 31.7°, 21.1° and 110.5°, respectively. The results indicate that crystal phase composition of TNs plays an important role in surface wettability. Compared with the WCA (21.1°) of the samples annealed in air after 28 days, the WCA of samples annealed in oxygen-deficient atmosphere is lower, suggesting the contribution of oxygen vacancy in the enhanced hydrophilicity-retaining ability. Our study demonstrates that the surface hydrophilicity-retaining ability of TNs is related to the ordered nanotubular structure, crystal structure, the amount of surface hydroxyl group and oxygen vacancy defects.

Cu-based metal-organic framework thin films: A morphological and photovoltaic study

NASA Astrophysics Data System (ADS)

Khajavian, Ruhollah; Ghani, Kamal

2018-06-01

This work explores the layer-by-layer (LbL) fabrication of [Cu2(bdc)2(bpy)]n thin films by using pyridine and acetic acid as capping agents onto mesoporous titania surface. While in the presence of acetic acid highly-ordered crystals with nanoplate morphology are formed, modulation with pyridine gives rise to formation of leaf-like crystals. In addition, processing sequence also matters when modulator is added. According to our results, modulators should be added to metal solution rather than linker/pillar during LbL assembly. These films were subsequently shown to generate photocurrent in a sandwich-type Grätzel solar cell device in response to simulated 1 sun illumination. The results also demonstrated that the device consisted of well-aligned nanoplates exhibits higher power conversion efficiency than the similar cell with disordered leaf-like crystals after iodine loading.

Chromatographic study of formation conditions of rhombododecahedral diamond crystals

NASA Astrophysics Data System (ADS)

Zhimulev, E. I.; Sonin, V. M.; Chepurov, A. I.; Tomilenko, A. A.

2009-06-01

The results of chromatographic study of the formation of rhombododecahedral diamonds synthesized in the Fe-Ni-(Ti)-C system at 5.5-6.0 GPa and 1350-1450°C are presented, including crystals with rounded surfaces of the rhombododecahedron with parallel striation, which are morphological analogues of natural diamonds abundant at various kimberlite, lamproite, and placer deposits. Chromatography was performed at 150°C with mechanical breakup of diamonds. The stable release of methane when diamonds of habit {110} are crushed is established. It is concluded that the appearance of the habit rhombododecahedron may be related not only to the effect of temperature and pressure on crystal growth but also to reductive conditions of crystallization. At the same time, the appearance of significant amounts of hydrocarbons in the system probably results in stopping of the growth of faces {110} and {100} and, instead, formation of specific surfaces that are composed of microscopic accessories faced by planes {111}.

Influence of lysozyme on the precipitation of calcium carbonate: a kinetic and morphologic study

NASA Astrophysics Data System (ADS)

Jimenez-Lopez, Concepcion; Rodriguez-Navarro, Alejandro; Dominguez-Vera, Jose M.; Garcia-Ruiz, Juan M.

2003-05-01

Several mechanisms have been proposed to explain the interactions between proteins and mineral surfaces, among them a combination of electrostatic, stereochemical interactions and molecular recognition between the protein and the crystal surface. To identify the mechanisms of interaction in the lysozyme-calcium carbonate model system, the effect of this protein on the precipitation kinetics and morphology of calcite crystals was examined. The solution chemistry and morphology of the solid were monitored over time in a set of time-series free-drift experiments in which CaCO 3 was precipitated from solution in a closed system at 25°C and 1 atm total pressure, in the presence and absence of lysozyme. The precipitation of calcite was preceded by the precipitation of a metastable phase that later dissolved and gave rise to calcite as the sole phase. With increasing lysozyme concentration, the nucleation of both the metastable phase and calcite occurred at lower Ω calcite, indicating that lysozyme favored the nucleation of both phases. Calcite growth rate was not affected by the presence of lysozyme, at least at protein concentrations ranging from 0 mg/mL to 10 mg/mL. Lysozyme modified the habit of calcite crystals. The degree of habit modification changed with protein concentration. At lower concentrations of lysozyme, the typical rhombohedral habit of calcite crystals was modified by the expression of {110} faces, which resulted from the preferential adsorption of protein on these faces. With increasing lysozyme concentration, the growth of {110}, {100}, and finally {001} faces was sequentially inhibited. This adsorption sequence may be explained by an electrostatic interaction between lysozyme and calcite, in which the inhibition of the growth of {110}, {100}, and {001} faces could be explained by a combined effect of the density of carbonate groups in the calcite face and the specific orientation (perpendicular) of these carbonate groups with respect to the calcite surface. Overgrowth of calcite in the presence of lysozyme demonstrated that the protein favored and controlled the nucleation on the calcite substrate. Overgrowth crystals nucleated epitaxially in lines which run diagonal to rhombohedral {104} faces.

Photocatalytic Active Bismuth Fluoride/Oxyfluoride Surface Crystallized 2Bi2O3-B2O3 Glass-Ceramics

NASA Astrophysics Data System (ADS)

Sharma, Sumeet Kumar; Singh, V. P.; Chauhan, Vishal S.; Kushwaha, H. S.; Vaish, Rahul

2018-03-01

The present article deals with 2Bi2O3-B2O3 (BBO) glass whose photocatalytic activity has been enhanced by the method of wet etching using an aqueous solution of hydrofluoric acid (HF). X-ray diffraction of the samples reveals that etching with an aqueous solution of HF leads to the formation of BiF3 and BiO0.1F2.8 phases. Surface morphology obtained from scanning electron microscopy show granular and plate-like morphology on the etched glass samples. Rhodamine 6G (Rh 6G) has been used to investigate the photocatalytic activity of the as-quenched and etched glasses. Enhanced visible light-driven photocatalytic activity was observed in HF etched glass-ceramics compared to the as-quenched BBO glass. Contact angle of the as-quenched glass was 90.2°, which decreases up to 20.02° with an increase in concentration of HF in the etching solution. Enhanced photocatalytic activity and increase in the hydrophilic nature suggests the efficient treatment of water pollutants by using the prepared surface crystallized glass-ceramics.

Laboratory studies of the growth, sublimation, and light- scattering properties of single levitated ice particles

NASA Astrophysics Data System (ADS)

Bacon, Neil Julian

2001-12-01

I describe experiments to investigate the properties of microscopic ice particles. The goal of the work was to measure parameters that are important in cloud processes and radiative transfer, using a novel technique that avoids the use of substrates. The experiments were conducted in two separate electrodynamic balance chambers. Single, charged ice particles were formed from frost particles or from droplets frozen either homogeneously or heteroge neously with a bionucleant. The particles were trapped at temperatures between -38°C and -4°C and grown or sublimated according to the temperature gradient in the cham ber. I describe observations of breakup of sublimating frost particles, measurements of light scattering by hexagonal crystals, and observations of the morphology of ice particles grown from frozen water droplets and frost particles. The breaking strength of frost particles was an order of magnitude less than that of bulk ice. Light scattering features not previously observed were analyzed and related to crystal dimension. Initial results from a computer model failed to reproduce these features. The widths of scattering peaks suggest that surface roughness may play a role in determining the angular distribution of scattered light. Ice particle mass evolution was found to be consistent with diffusion- limited growth. Crystals grown slowly from frozen droplets adopted isometric habits, while faster growth resulted in thin side-planes, although there was not an exact correspondence between growth conditions and particle morphology. From the morphological transition, I infer lower limits for the critical supersaturation for layer nucleation on the prism face of 2.4% at -15°C, 4.4% at -20°C, and 3.1% at -25°C. Analytic expressions for the size dependence of facet stability are developed, indicating a strong dependence of stability on both crystal size and surface kinetics, and compared with data. I discuss the role of complex particle morphologies in radiative transfer and highlight the need for further measurements.

Effect of Preparation Methods on Crystallization Behavior and Tensile Strength of Poly(vinylidene fluoride) Membranes

PubMed Central

Liu, Jie; Lu, Xiaolong; Wu, Chunrui

2013-01-01

Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDF membranes was investigated. Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD) were employed to examine the crystal form of the surface layers and the overall membranes, respectively. Spherulite morphologies and thermal behavior of the membranes were studied by polarized light optical microscopy (PLO) and differential scanning calorimetry (DSC) separately. It was found that the crystallization behavior of PVDF membranes was closely related to the preparation methods. For membranes prepared by the NIPS method, the skin layers had a mixture of α and β phases, the overall membranes were predominantly α phase, and the total crystallinity was 60.0% with no spherulite. For melt spinning membranes, the surface layers also showed a mixture of α and β phases, the overall membranes were predominantly α phase. The total crystallinity was 48.7% with perfect spherulites. Whereas the crystallization behavior of solution-cast membranes was related to the evaporation temperature and the additive, when the evaporation temperature was 140 °C with a soluble additive in the dope solution, obvious spherulites appeared. The crystalline morphology of PVDF exerted a great influence on the tensile strength of the membranes, which was much higher with perfect spherulites. PMID:24957064

Sponge-like nanoporous single crystals of gold

PubMed Central

Khristosov, Maria Koifman; Bloch, Leonid; Burghammer, Manfred; Kauffmann, Yaron; Katsman, Alex; Pokroy, Boaz

2015-01-01

Single crystals in nature often demonstrate fascinating intricate porous morphologies rather than classical faceted surfaces. We attempt to grow such crystals, drawing inspiration from biogenic porous single crystals. Here we show that nanoporous single crystals of gold can be grown with no need for any elaborate fabrication steps. These crystals are found to grow following solidification of a eutectic composition melt that forms as a result of the dewetting of nanometric thin films. We also present a kinetic model that shows how this nano-porous single-crystalline structure can be obtained, and which allows the potential size of the porous single crystal to be predicted. Retaining their single-crystalline nature is due to the fact that the full crystallization process is faster than the average period between two subsequent nucleation events. Our findings clearly demonstrate that it is possible to form single-crystalline nano porous metal crystals in a controlled manner. PMID:26554856

Faceting, composition and crystal phase evolution in III-V antimonide nanowire heterostructures revealed by combining microscopy techniques.

PubMed

Xu, Tao; Dick, Kimberly A; Plissard, Sébastien; Nguyen, Thanh Hai; Makoudi, Younes; Berthe, Maxime; Nys, Jean-Philippe; Wallart, Xavier; Grandidier, Bruno; Caroff, Philippe

2012-03-09

III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs(1-x)Sb(x) heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.

Characterization of hematite nanoparticles synthesized via two different pathways

NASA Astrophysics Data System (ADS)

Das, Soumya; Hendry, M. Jim

2014-08-01

Hematite is one of the most common and thermodynamically stable iron oxides found in both natural and anthropogenic systems. Owing to its ubiquity, stability, moderate specific surface area, and ability to sequester metals and metalloids from aquatic systems, it has been the subject of a large number of adsorption studies published during the past few decades. Although preparation techniques are known to affect the surface morphology of hematite nanoparticles, the effects of aging under environmentally relevant conditions have yet to be tested with respect to surface morphology, surface area, and adsorptive capacity. We prepared hematite via two different pathways and aged it under highly alkaline conditions encountered in many mill tailings settings. Crystal habits and morphologies of the hematite nanoparticles were analyzed via scanning electron microscopy and transmission electron microscopy. X-ray diffraction, Raman spectroscopy, and Brunauer-Emmett-Teller surface area analyses were also conducted on the hematite nanoparticles before and after aging. The hematite synthesized via an Fe(III) salt solution (average particle size 37 nm) was morphologically and structurally different from the hematite synthesized via ferrihydrite aging (average particle size 144 nm). Overall, our data demonstrate that the crystallinity of hematite produced via ferrihydrite transformation is susceptible to morphological alterations/modifications. In contrast, the hematite formed via hydrolysis of an Fe(III) salt solution remains very stable in terms of structure, size, and morphology even under extreme experimental conditions.

New simulation model of multicomponent crystal growth and inhibition.

PubMed

Wathen, Brent; Kuiper, Michael; Walker, Virginia; Jia, Zongchao

2004-04-02

We review a novel computational model for the study of crystal structures both on their own and in conjunction with inhibitor molecules. The model advances existing Monte Carlo (MC) simulation techniques by extending them from modeling 3D crystal surface patches to modeling entire 3D crystals, and by including the use of "complex" multicomponent molecules within the simulations. These advances makes it possible to incorporate the 3D shape and non-uniform surface properties of inhibitors into simulations, and to study what effect these inhibitor properties have on the growth of whole crystals containing up to tens of millions of molecules. The application of this extended MC model to the study of antifreeze proteins (AFPs) and their effects on ice formation is reported, including the success of the technique in achieving AFP-induced ice-growth inhibition with concurrent changes to ice morphology that mimic experimental results. Simulations of ice-growth inhibition suggest that the degree of inhibition afforded by an AFP is a function of its ice-binding position relative to the underlying anisotropic growth pattern of ice. This extended MC technique is applicable to other crystal and crystal-inhibitor systems, including more complex crystal systems such as clathrates.

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Brebrick, Robert F.; Volz, Martin P.; Burger, Arnold; Dudley, Michael; Matyi, Richard J.; Ramachandran, Narayanan; Sha, Yi-Gao; Volz, Martin P.; Shih, Hung-Dah

2001-01-01

Crystal growth by vapor transport has several distinct advantages over melt growth techniques. Among various potential benefits from material processing in reduced gravity the followings two are considered to be related to crystal growth by vapor transport: (1) elimination of the crystal weight and its influence on the defect formation and (2) reduction of natural buoyancy-driven convective flows arising from thermally and/ or solutally induced density gradient in fluids. The previous results on vapor crystal growth of semiconductors showed the improvements in surface morphology, crystalline quality, electrical properties and dopant distribution of the crystals grown in reduced gravity as compared to the crystals grown on Earth. But the mechanisms, which are responsible for the improvements and cause the gravitational effects on the complicated and coupled processes of vapor mass transport and growth kinetics, are not well understood.

Growth of sodium chlorate crystals in the presence of potassium sulphate

NASA Astrophysics Data System (ADS)

Kim, E. L.; Tsyganova, A. A.; Vorontsov, D. A.; Ovsetsina, T. I.; Katkova, M. R.; Lykov, V. A.; Portnov, V. N.

2015-09-01

In this work, we investigated the morphology and growth rates of NaClO3 crystals in solutions with K2SO4 additives. NaClO3 crystals were grown using the temperature gradient technique under concentration convection. We found that the crystal habitus changed from cubic to tetrahedral, and the growth of the cubic {100}, tetrahedral {111} and rhomb-dodecahedral {110} faces decelerated with an increase in the concentration of SO42- ions. The {110} face was the most and the {100} face was the least inhibited by sulphate ions. The mechanism of SO42- ions action is their adsorption on the crystal surface, which impedes attachment of the crystal's building units. We conclude that different atomic structure and charge state of various crystal faces determine their sensitivity to the action of the SO42- ions.

Preparation of poly(L-lactic acid) nanofiber scaffolds with a rough surface by phase inversion using supercritical carbon dioxide.

PubMed

Yang, Ding-Zhu; Chen, Ai-Zheng; Wang, Shi-Bin; Li, Yi; Tang, Xiao-Lin; Wu, Yong-Jing

2015-06-24

Phase inversion using supercritical carbon dioxide (SC-CO2) has been widely used in the development of tissue engineering scaffolds, and particular attention has been given to obtaining desired morphology without additional post-treatments. However, the main challenge of this technique is the difficulty in generating a three-dimensional (3D) nanofiber structure with a rough surface in one step. Here, a poly(L-lactic acid) (PLLA) 3D nanofiber scaffold with a rough surface is obtained via phase inversion using SC-CO2 by carefully choosing fabrication conditions and porogens. It is found that this method can effectively modulate the structure morphology, promote the crystallization process of semicrystalline polymer, and induce the formation of rough structures on the surface of nanofibers. Meanwhile, the porogen of ammonium bicarbonate (AB) can produce a 3D structure with large pores, and porogen of menthol can improve the interconnectivity between the micropores of nanofibers. A significant increase in the fiber diameter is observed as the menthol content increases. Furthermore, the menthol may affect the mutual transition between the α' and α crystals of PLLA during the phase separation process. In addition, the results of protein adsorption, cell adhesion, and proliferation assays indicate that cells tend to have higher viability on the nanofiber scaffold. This process combines the characteristic properties of SC-CO2 and the solubility of menthol to tailor the morphology of polymeric scaffolds, which may have potential applications in tissue engineering.

Flow induced/ refined solution crystallization of a semiconducting polymer

NASA Astrophysics Data System (ADS)

Nguyen, Ngoc A.

Organic photovoltaics, a new generation of solar cells, has gained scientific and economic interests due to the ability of solution-processing and potentially low-cost power production. Though, the low power conversion efficiency of organic/ plastic solar cells is one of the most pertinent challenges that has appealed to research communities from many different fields including materials science and engineering, electrical engineering, chemical engineering, physics and chemistry. This thesis focuses on investigating and controlling the morphology of a semi-conducting, semi-crystalline polymer formed under shear-flow. Molecular structures and processing techniques are critical factors that significantly affect the morphology formation in the plastic solar cells, thus influencing device performance. In this study, flow-induced solution crystallization of poly (3-hexylthiophene) (P3HT) in a poor solvent, 2-ethylnapthalene (2-EN) was utilized to make a paint-like, structural liquid. The polymer crystals observed in this structured paint are micrometers long, nanometers in cross section and have a structure similar to that formed under quiescent conditions. There is pi-pi stacking order along the fibril axis, while polymer chain folding occurs along the fibril width and the order of the side-chain stacking is along fibril height. It was revealed that shear-flow not only induces P3HT crystallization from solution, but also refines and perfects the P3HT crystals. Thus, a general strategy to refine the semiconducting polymer crystals from solution under shear-flow has been developed and employed by simply tuning the processing (shearing) conditions with respect to the dissolution temperature of P3HT in 2-EN. The experimental results demonstrated that shear removes defects and allows more perfect crystals to be formed. There is no glass transition temperature observed in the crystals formed using the flow-induced crystallization indicating a significantly different morphology formation in comparison to that of the pristine (as-received) P3HT. As a result, single P3HT crystals with high surface energy chain folds were analyzed and determined. Previous reported results of infinite melting enthalpy of extended chain P3HT crystals are much higher than the result discovered in this study. The findings in this study revealed that the infinite melting enthalpy of chain-folded P3HT crystals is considerably decreased due to the presence of this P3HT chain-folded surface energy. In this study, the kinetics and mechanism of P3HT crystallization under shear-flow was thoroughly investigated as well. A homogeneous nucleation of P3HT was observed that allows one dimensional fibril crystal growth. The micrometer long P3HT crystals are formed and limited by the contact time between the P3HT molecules. Furthermore, it was found that phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles inhibit the crystallization of P3HT under shear. However, the shear-flow leads to nanophase agglomeration of PCBM and creates percolation of P3HT fibril crystal networks and the PCBM phase separated domains that apparently present better pathways for transporting electrons and holes. Interestingly, the structured liquid was simply applied onto substrates with a paintbrush resulting in similar device performance to those made with current techniques in which the morphology is commonly formed during application or post-processing steps. These detailed findings are given and discussed in the thesis.

Real-time observation of morphological transformations in II-VI semiconducting nanobelts via environmental transmission electron microscopy

DOE PAGES

Agarwal, Rahul; Zakharov, Dmitri N.; Krook, Nadia M.; ...

2015-05-01

It has been observed that wurtzite II–VI semiconducting nanobelts transform into single-crystal, periodically branched nanostructures upon heating. The mechanism of this novel transformation has been elucidated by heating II–VI nanobelts in an environmental transmission electron microscope (ETEM) in oxidizing, reducing and inert atmospheres while observing their structural changes with high spatial resolution. The interplay of surface reconstruction of high-energy surfaces of the wurtzite phase and environment-dependent anisotropic chemical etching of certain crystal surfaces in the branching mechanism of nanobelts has been observed. Understanding of structural and chemical transformations of materials via in situ microscopy techniques and their role in designingmore » new nanostructured materials is discussed.« less

Crystal Growth of Undoped and Doped ZnSe

NASA Technical Reports Server (NTRS)

Davis, Swanson L.; Chen, K.-T.; George, M. A.; Shi, D. T.; Collins, W. E.; Burger, Arnold

1997-01-01

The surface morphology of freshly cleaved ZnSe single crystal grown by the physical vapor transport (PVT) method was investigated by Atomic Force Microscopy (AFM) and the results were correlated with Differential Scanning Calorimetry (DSC) data. Selenium precipitates have been revealed in undoped doped ZnSe crystals having a size of about 50 nm. A transition temperature around 221 C in the DSC measurements is interpreted as the eutectic temperature of Se-saturated ZnSe. The AFM images of doped ZnSe also show that possible Cr clusters are uniformly distributed and they have an estimated size of about 6 nm.

Nucleation and growth of hydroxyapatite on arc-deposited TiO2 surfaces studied by quartz crystal microbalance with dissipation

NASA Astrophysics Data System (ADS)

Lilja, Mirjam; Butt, Umer; Shen, Zhijian; Bjöörn, Dorota

2013-11-01

Understanding of nucleation and growth kinetics of biomimetically deposited hydroxyapatite (HA) on crystalline TiO2 surfaces is important with respect to the application and performance of HA as functional implant coatings. Arc-evaporation was used to deposit TiO2 coatings dominated by anatase phase, rutile phase or their mixtures. Subsequent formation of HA from phosphate buffered saline solution (PBS) was investigated in real-time using in situ quartz crystal microbalance with dissipation technique (QCM-D). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the presence, morphology and crystal structure of TiO2 coatings and the formed HA. Increasing temperature of the PBS, increasing flow rate and applying a higher ion concentration in solution were found to accelerate HA nucleation process and hence affect growth kinetics. Lower PBS temperature resulted in the formation of HA coatings with flake-like morphology and increasing HA porosity. All TiO2 coatings under study enabled HA formation at body temperature, while in contrast Ti reference surfaces only supported HA nucleation and growth at elevated temperatures. QCM-D technique is a powerful tool for studying the impact of process parameters during biomimetic coating deposition on coating structure evolution in real time and provides valuable information for understanding, optimizing as well as tailoring the biomimetic HA growth processes.

Preliminary observations of the effect of solutal convection on crystal morphology

NASA Technical Reports Server (NTRS)

Broom, M. Beth H.; Witherow, William K.; Snyder, Robert S.; Carter, Daniel C.

1988-01-01

Studies to examine the effect of solutal convection on crystal morphology using sucrose as a model system were initiated. Aspect ratios, defined as the width of the 100-plane-oriented face over the width of the 001-plane-oriented face, were determined for oriented crystals which were grown with either the 001-oriented or the 100-oriented face perpendicular to the convective flow. The dependence of the crystal morphology on orientation is much greater for crystals grown with one face occluded than for crystals grown suspended in solution. Many factors appear to interact in a complex fashion to influence crystal morphology.

Effect of In Situ Annealing Treatment on the Mobility and Morphology of TIPS-Pentacene-Based Organic Field-Effect Transistors.

PubMed

Yang, Fuqiang; Wang, Xiaolin; Fan, Huidong; Tang, Ying; Yang, Jianjun; Yu, Junsheng

2017-08-23

In this work, organic field-effect transistors (OFETs) with a bottom gate top contact structure were fabricated by using a spray-coating method, and the influence of in situ annealing treatment on the OFET performance was investigated. Compared to the conventional post-annealing method, the field-effect mobility of OFET with 60 °C in situ annealing treatment was enhanced nearly four times from 0.056 to 0.191 cm 2 /Vs. The surface morphologies and the crystallization of TIPS-pentacene films were characterized by optical microscope, atomic force microscope, and X-ray diffraction. We found that the increased mobility was mainly attributed to the improved crystallization and highly ordered TIPS-pentacene molecules.

Effect of In Situ Annealing Treatment on the Mobility and Morphology of TIPS-Pentacene-Based Organic Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Yang, Fuqiang; Wang, Xiaolin; Fan, Huidong; Tang, Ying; Yang, Jianjun; Yu, Junsheng

2017-08-01

In this work, organic field-effect transistors (OFETs) with a bottom gate top contact structure were fabricated by using a spray-coating method, and the influence of in situ annealing treatment on the OFET performance was investigated. Compared to the conventional post-annealing method, the field-effect mobility of OFET with 60 °C in situ annealing treatment was enhanced nearly four times from 0.056 to 0.191 cm2/Vs. The surface morphologies and the crystallization of TIPS-pentacene films were characterized by optical microscope, atomic force microscope, and X-ray diffraction. We found that the increased mobility was mainly attributed to the improved crystallization and highly ordered TIPS-pentacene molecules.

Effects of different crystal faces on the surface charge of colloidal goethite (α-FeOOH) particles: an experimental and modeling study

NASA Astrophysics Data System (ADS)

Gaboriaud, Fabien; Ehrhardt, Jean-Jacques

2003-03-01

The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range. We demonstrate a procedure for the removal of the carbonate ions that initially adsorb on goethite and strongly affect the titration curves and pzc determination. We also investigated the crystal-face-specific reactivity of two morphologically different goethites. The z-profiles obtained from atomic force microscopy (AFM) images showed that the goethite with the smallest specific surface area ( S = 49 m 2/g, denoted G49) exhibits 70% of the (001) face, whereas this value is only 30% for the goethite with largest specific surface area ( S = 95 m 2/g, denoted G95). This morphologic difference results in slightly different pzc values: 9.0 for G49 goethite and 9.1 for G95 geothite. These experimental pzc values have been correlated with multisite complexation calculations using both the full-site and the 1-pK approaches. We used the full-site approach to consider all of the configurations of hydrogen bond interactions with surface site. The resulting mean charges gave estimated pzc values of 8.9 and 9.2 for the (001) and (101) faces, respectively. Considering these theoretical pzc values for individual faces and the face distributions obtained from AFM analysis, the calculated pzc values are in full agreement with the experimental pzc values. However, this morphologic difference is more expressed in surface charge values than in the pzc values. Indeed, the surface charge of G49 goethite is much higher than that of G95 goethite, and the 1-pK calculations make it possible to fit the titration data satisfactorily.

Manipulating crystallization with molecular additives.

PubMed

Shtukenberg, Alexander G; Lee, Stephanie S; Kahr, Bart; Ward, Michael D

2014-01-01

Given the importance of organic crystals in a wide range of industrial applications, the chemistry, biology, materials science, and chemical engineering communities have focused considerable attention on developing methods to control crystal structure, size, shape, and orientation. Tailored additives have been used to control crystallization to great effect, presumably by selectively binding to particular crystallographic surfaces and sites. However, substantial knowledge gaps still exist in the fundamental mechanisms that govern the formation and growth of organic crystals in both the absence and presence of additives. In this review, we highlight research discoveries that reveal the role of additives, either introduced by design or present adventitiously, on various stages of formation and growth of organic crystals, including nucleation, dislocation spiral growth mechanisms, growth inhibition, and nonclassical crystal morphologies. The insights from these investigations and others of their kind are likely to guide the development of innovative methods to manipulate crystallization for a wide range of materials and applications.

Growth kinetics of white graphene (h-BN) on a planarised Ni foil surface

PubMed Central

Cho, Hyunjin; Park, Sungchan; Won, Dong-Il; Kang, Sang Ook; Pyo, Seong-Soo; Kim, Dong-Ik; Kim, Soo Min; Kim, Hwan Chul; Kim, Myung Jong

2015-01-01

The morphology of the surface and the grain orientation of metal catalysts have been considered to be two important factors for the growth of white graphene (h-BN) by chemical vapour deposition (CVD). We report a correlation between the growth rate of h-BN and the orientation of the nickel grains. The surface of the nickel (Ni) foil was first polished by electrochemical polishing (ECP) and subsequently annealed in hydrogen at atmospheric pressure to suppress the effect of the surface morphology. Atmospheric annealing with hydrogen reduced the nucleation sites of h-BN, which induced a large crystal size mainly grown from the grain boundary with few other nucleation sites in the Ni foil. A higher growth rate was observed from the Ni grains that had the {110} or {100} orientation due to their higher surface energy. PMID:26156068

Drug-polymer interactions at water-crystal interfaces and implications for crystallization inhibition: molecular dynamics simulations of amphiphilic block copolymer interactions with tolazamide crystals.

PubMed

Gao, Yi; Olsen, Kenneth W

2015-07-01

A diblock copolymer, poly(ethylene glycol)-block-poly(lactic acid) (PEG-b-PLA), modulates the crystal growth of tolazamide (TLZ), resulting in a crystal morphology change from needles to plates in aqueous media. To understand this crystal surface drug-polymer interaction, we conducted molecular dynamics simulations on crystal surfaces of TLZ in water containing PEG-b-PLA. A 130-ns simulation of the polymer in a large water box was run before initiating 50 ns simulations with each of the crystal surfaces. The simulations demonstrated differentiated drug-polymer interactions that are consistent with experimental studies. Interaction of PEG-b-PLA with the (001) face occurred more rapidly (≤10 ns) and strongly (total interaction energy of -121.1 kJ/mol/monomer) than that with the (010) face (∼35 ns, -85.4 kJ/mol/monomer). There was little interaction with the (100) face. Hydrophobic and van der Waals (VDW) interactions were the dominant forces, accounting for more than 90% of total interaction energies. It suggests that polymers capable of forming strong hydrophobic and VDW interactions might be more effective in inhibiting crystallization of poorly water-soluble and hydrophobic drugs in aqueous media (such as gastrointestinal fluid) than those with hydrogen-bonding capacities. Such in-depth analysis and understanding facilitate the rational selection of polymers in designing supersaturation-based enabling formulations. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Experimental Simulation of Cryomagmatic Processes. Water Ice, Clathrates and Salts

NASA Astrophysics Data System (ADS)

Muñoz-Iglesias, V.; Prieto-Ballesteros, O.; López, I.

2018-06-01

Study of diverse cryomagmatic processes based on the system H2O-CO2-MgSO4 with application to Europa. The type of the crystals formed is related to volume-temperature changes, while their morphology is associated with surface geological features.

Influence of lead ions on the macromorphology of electrodeposited zinc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsuda, Tetsuaki; Tobias, Charles W.

1981-09-01

The morphology of zinc as it is electrodeposited from acid solutions demonstrates a remarkable imprint of electrolyte flow conditions. The development of macromorphology of zinc deposits has been investigated under galvanostatic conditions on a rotating plantinum disk electrode by use of photomacrography, scanning electron microscopy, electron probe microanalysis and Auger microprobe analysis. Logarithmic spiral markings, which reflect the hydrodynamic flow on a rotating disk, appear in a certain region of current density well below the limiting current density. Morphological observations revealed the major influence of trace lead ions on the amplifications of surface roughness through coalescence and preferred growth ofmore » initial protrusions. Results obtained from ultra-pure electrolyte suggest preferred crystal growth towards well-mixed orientation in the concentration field caused by slight differences in crystallization overpotential. A qualitative model involving a coupling mechanism between the evolving surface roughness and instability phenomena in the boundary layer is advanced to explain the formation of spiral patterns.« less

Crystallinity, Surface Morphology, and Photoelectrochemical Effects in Conical InP and InN Nanowires Grown on Silicon.

PubMed

Parameshwaran, Vijay; Xu, Xiaoqing; Clemens, Bruce

2016-08-24

The growth conditions of two types of indium-based III-V nanowires, InP and InN, are tailored such that instead of yielding conventional wire-type morphologies, single-crystal conical structures are formed with an enlarged diameter either near the base or near the tip. By using indium droplets as a growth catalyst, combined with an excess indium supply during growth, "ice cream cone" type structures are formed with a nanowire "cone" and an indium-based "ice cream" droplet on top for both InP and InN. Surface polycrystallinity and annihilation of the catalyst tip of the conical InP nanowires are observed when the indium supply is turned off during the growth process. This growth design technique is extended to create single-crystal InN nanowires with the same morphology. Conical InN nanowires with an enlarged base are obtained through the use of an excess combined Au-In growth catalyst. Electrochemical studies of the InP nanowires on silicon demonstrate a reduction photocurrent as a proof of photovolatic behavior and provide insight as to how the observed surface polycrystallinity and the resulting interface affect these device-level properties. Additionally, a photovoltage is induced in both types of conical InN nanowires on silicon, which is not replicated in epitaxial InN thin films.

Crystal engineering of ibuprofen compounds: From molecule to crystal structure to morphology prediction by computational simulation and experimental study

NASA Astrophysics Data System (ADS)

Zhang, Min; Liang, Zuozhong; Wu, Fei; Chen, Jian-Feng; Xue, Chunyu; Zhao, Hong

2017-06-01

We selected the crystal structures of ibuprofen with seven common space groups (Cc, P21/c, P212121, P21, Pbca, Pna21, and Pbcn), which was generated from ibuprofen molecule by molecular simulation. The predicted crystal structures of ibuprofen with space group P21/c has the lowest total energy and the largest density, which is nearly indistinguishable with experimental result. In addition, the XRD patterns for predicted crystal structure are highly consistent with recrystallization from solvent of ibuprofen. That indicates that the simulation can accurately predict the crystal structure of ibuprofen from the molecule. Furthermore, based on this crystal structure, we predicted the crystal habit in vacuum using the attachment energy (AE) method and considered solvent effects in a systematic way using the modified attachment energy (MAE) model. The simulation can accurately construct a complete process from molecule to crystal structure to morphology prediction. Experimentally, we observed crystal morphologies in four different polarity solvents compounds (ethanol, acetonitrile, ethyl acetate, and toluene). We found that the aspect ratio decreases of crystal habits in this ibuprofen system were found to vary with increasing solvent relative polarity. Besides, the modified crystal morphologies are in good agreement with the observed experimental morphologies. Finally, this work may guide computer-aided design of the desirable crystal morphology.

Peculiarities of structure formation of layered metal-oxide system Ti-Ta-(Ti,Ta)xOy during electro-spark alloying and thermally stimulated modification

NASA Astrophysics Data System (ADS)

Fomina, Marina A.; Koshuro, Vladimir A.; Fomin, Aleksandr A.; Rodionov, Igor V.; Skaptsov, Aleksandr A.; Zakharevich, Andrey M.; Aman, Alexander; Oseev, Aleksandr; Hirsch, Soeren; Majcherek, Soeren

2016-04-01

The study focuses on high-performance combined electro-spark alloying of titanium and titanium alloy (VT1-0, VT16) surface and porous matrix structure oxidation. The metal-oxide coatings morphology is the result of melt drop transfer, heat treatment, and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity of biocompatible layered metal-oxide system Ti-Ta-(Ti,Ta)xOy. It was found that during electro-spark alloying the concentration of tantalum on the titanium surface ranges from 0.1 to 3.2 at.%. Morphology of the deposited splats is represented by uniformly grown crystals of titanium and tantalum oxides, which increase from nano- to submicron size.

Biogenic twinned crystals exhibiting unique morphological symmetry

NASA Astrophysics Data System (ADS)

Hirsch, Anna; Gur, Dvir; Palmer, Ben; Addadi, Lia; Leiserowitz, Leslie; Kronik, Leeor

Guanine crystals are widely used in nature as components of multilayer reflectors. Organisms control the size, morphology, and arrangement of these crystals, to obtain a variety of optical ''devices''. The reflection systems found in the lens of the scallop eye and in the copepod cuticle are unique in that the multilayered reflectors are tiled together to form a contiguous packed array. In the former, square crystals are tiled to form a reflecting mirror. In the latter, hexagonal crystals are closely packed to produce brilliant colors. Based on electron diffraction, morphology considerations, and density functional theory, these crystals were shown to possess similar monoclinic crystal symmetry, which we have previously identified as different from that of synthetic anhydrous guanine. However, the crystals are different in that multiple twinning about the {012} and the {011} crystallographic planes results in square and hexagonal morphology, respectively. This is a unique example where controlled twinning is used as a strategy to form a morphology with higher symmetry than that of the underlying crystal, allowing for tilling that facilitates optical functionality.

Theoretical and experimental morphologies of 4-aminobenzophenone (ABP) crystals

NASA Astrophysics Data System (ADS)

Wang, Qingwu; Sheen, D. B.; Shepherd, E. E. A.; Sherwood, J. N.; Simpson, G. S.; Hammond, R. B.

1997-11-01

The lattice energy (Elatt), slice energies (Eslice) and attachment energies (Eatt) of the different habit faces of ABP crystals have been calculated using the computer program HABIT. On the basis of the attachment energies of different crystal faces, the morphology was defined as {1 0 0}, {0 0 1}, {1 1 0}, {11bar0} and {1 01bar}. To confirm this theoretical prediction, we have grown ABP films and ABP crystals from the vapour phase. In both cases, the morphologically most important face was defined as {1 0 0} face using X-ray diffraction techniques. The remaining faces of the vapour-grown crystals were defined using a projection method, while the crystallites in the films were morphologically analysed by means of atomic force microscopy (AFM). The experimental morphologies are basically in agreement with the computation. Deviations from the equilibrium morphology can be ascribed to departure from equilibrium conditions during growth. For completeness, the results are compared with those for crystals grown from solutions for which deviations in morphology from the theoretical predictions can be ascribed to interaction between the crystal faces and solvent molecules.

The Impact of Chemical Substitutions on Interfacial Properties of REE Orthophosphates (Monazite, Xenotime)

NASA Astrophysics Data System (ADS)

Gamage McEvoy, J.; Thibault, Y.

2016-12-01

Mineral surface properties strongly influence liquid-solid interface behaviour in the presence of various ligands, and can significantly affect processes of natural (ex. fluids, melts) and industrial (ex. oil recovery) relevance. Many Rare Earth Element (REE)-bearing minerals display extensive solid solutions resulting in significant chemical variations which influence their crystal and surface properties and, can consequently impact the interfacial features of their interaction with substances such as organic molecules (i.e. reactivity and sorption). For example, the surface charge properties of some REE orthophosphates show an uncharacteristically wide variation in reported values, where large differences in literature are commonly attributed to compositional differences between samples. However the impact of these chemical substitutions remains largely unknown. As such, the aim of this research was to systematically investigate the influence of mineralogical variation within the compositional space of the REE orthophosphates on their surface chemistry and resulting interaction with organic molecules. To better isolate the chemical, structural, and morphological variables, the synthesis of REE orthophosphate crystals along a number of defined substitutions was conducted, and their surface chemistry characteristics benchmarked against well-characterized natural monazite and xenotime from various localities. The interaction of these crystal surfaces with model organic molecules (long chain carboxylic acids and alkyl hydroxamic acids, respectively) was then studied and characterized via surface (X-ray photoelectron) and near-surface (vibrational) spectroscopic techniques. The implications of crystal surface-organic molecule interactions to mineral processing through flotation were also experimentally investigated.

Surface design for controlled crystallization: the role of surface chemistry and nanoscale pores in heterogeneous nucleation.

PubMed

Diao, Ying; Myerson, Allan S; Hatton, T Alan; Trout, Bernhardt L

2011-05-03

Current industrial practice for control of primary nucleation (nucleation from a system without pre-existing crystalline matter) during crystallization from solution involves control of supersaturation generation, impurity levels, and solvent composition. Nucleation behavior remains largely unpredictable, however, due to the presence of container surfaces, dust, dirt, and other impurities that can provide heterogeneous nucleation sites, thus making the control and scale-up of processes that depend on primary nucleation difficult. To develop a basis for the rational design of surfaces to control nucleation during crystallization from solution, we studied the role of surface chemistry and morphology of various polymeric substrates on heterogeneous nucleation using aspirin as a model compound. Nucleation induction time statistics were utilized to investigate and quantify systematically the effectiveness of polymer substrates in inducing nucleation. The nucleation induction time study revealed that poly(4-acryloylmorpholine) and poly(2-carboxyethyl acrylate), each cross-linked by divinylbenzene, significantly lowered the nucleation induction time of aspirin while the other polymers were essentially inactive. In addition, we found the presence of nanoscopic pores on certain polymer surfaces led to order-of-magnitude faster aspirin nucleation rates when compared with surfaces without pores. We studied the preferred orientation of aspirin crystals on polymer films and found the nucleation-active polymer surfaces preferentially nucleated the polar facets of aspirin, guided by hydrogen bonds. A model based on interfacial free energies was also developed which predicted the same trend of polymer surface nucleation activities as indicated by the nucleation induction times.

A study on the probability of twin plane formation during the nucleation of AgBr and AgCl crystals in the aqueous gelatin solution

NASA Astrophysics Data System (ADS)

Ohzeki, Katsuhisa; Hosoya, Yoichi

2007-07-01

A study was made on the probability of twin plane formation during the nucleation of AgBr and AgCl crystals. The growth condition was controlled to keep the number of the nuclei, neither decreasing owing to their dissolution, nor increasing owing to the formation of a new nucleus during the growth process. Under the condition, the nuclei were grown to have {1 1 1} faces on their surfaces by controlling pAg in a reaction solution and by use of growth modifier in case of AgCl crystal formation. The number of twin planes in each crystal was judged according to a conventional way on the basis of its morphology. The dependence of the number of twin planes per crystal on the probability of twin plain formation was in accordance with Poisson distribution, indicating the random formation of a twin plane on the {1 1 1} faces of a nucleus. The result that the ratio of number of AgCl crystals with parallel twin planes to all the multiply twinned crystals was about 10% supports the random formation of a twin plane and suggests that the twin plane formation took place on {1 1 1} surfaces at the possible eight corner of a nucleus. On the other hand, the ratio of the number of AgBr crystals with parallel twin planes to all the multiply twinned crystals was more than 50%. The result was explained by the anisotropic growth of a singly twinned nucleus according to the higher growth rate of {1 0 0} surfaces than that of {1 1 1} surfaces.

Crystallization Mechanism and Charge Carrier Transport in MAPLE-Deposited Conjugated Polymer Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Ban Xuan; Strzalka, Joseph; Jiang, Zhang

Although spin casting and chemical surface reactions are the most common methods used for fabricating functional polymer films onto substrates, they are limited with regard to producing films of certain morphological characteristics on different wetting and nonwetting substrates. The matrix-assisted pulsed laser evaporation (MAPLE) technique offers advantages with regard to producing films of different morphologies on different types of substrates. Here, we provide a quantitative characterization, using X-ray diffraction and optical methods, to elucidate the additive growth mechanism of MAPLE-deposited poly(3-hexylthiophene) (P3HT) films on substrates that have undergone different surface treatments, enabling them to possess different wettabilities. We show thatmore » MAPLE-deposited films are composed of crystalline phases, wherein the overall P3HT aggregate size and crystallite coherence length increase with deposition time. A complete pole figure constructed from X-ray diffraction measurements reveals that in these MAPLE-deposited films, there exist two distinct crystallite populations: (i) highly oriented crystals that grow from the flat dielectric substrate and (ii) misoriented crystals that preferentially grow on top of the existing polymer layers. The growth of the highly oriented crystals is highly sensitive to the chemistry of the substrate, whereas the effect of substrate chemistry on misoriented crystal growth is weaker. The use of a self-assembled monolayer to treat the substrate greatly enhances the population and crystallite coherence length at the buried interfaces, particularly during the early stage of deposition. Furthermore, the evolution of the in-plane carrier mobilities during the course of deposition is consistent with the development of highly oriented crystals at the buried interface, suggesting that this interface plays a key role toward determining carrier transport in organic thin-film transistors.« less

Crystallization Mechanism and Charge Carrier Transport in MAPLE-Deposited Conjugated Polymer Thin Films

DOE PAGES

Dong, Ban Xuan; Strzalka, Joseph; Jiang, Zhang; ...

2017-11-23

Although spin casting and chemical surface reactions are the most common methods used for fabricating functional polymer films onto substrates, they are limited with regard to producing films of certain morphological characteristics on different wetting and nonwetting substrates. The matrix-assisted pulsed laser evaporation (MAPLE) technique offers advantages with regard to producing films of different morphologies on different types of substrates. Here, we provide a quantitative characterization, using X-ray diffraction and optical methods, to elucidate the additive growth mechanism of MAPLE-deposited poly(3-hexylthiophene) (P3HT) films on substrates that have undergone different surface treatments, enabling them to possess different wettabilities. We show thatmore » MAPLE-deposited films are composed of crystalline phases, wherein the overall P3HT aggregate size and crystallite coherence length increase with deposition time. A complete pole figure constructed from X-ray diffraction measurements reveals that in these MAPLE-deposited films, there exist two distinct crystallite populations: (i) highly oriented crystals that grow from the flat dielectric substrate and (ii) misoriented crystals that preferentially grow on top of the existing polymer layers. The growth of the highly oriented crystals is highly sensitive to the chemistry of the substrate, whereas the effect of substrate chemistry on misoriented crystal growth is weaker. The use of a self-assembled monolayer to treat the substrate greatly enhances the population and crystallite coherence length at the buried interfaces, particularly during the early stage of deposition. Furthermore, the evolution of the in-plane carrier mobilities during the course of deposition is consistent with the development of highly oriented crystals at the buried interface, suggesting that this interface plays a key role toward determining carrier transport in organic thin-film transistors.« less

Crystal morphology optimization of thiamine hydrochloride in solvent system: Experimental and molecular dynamics simulation studies

NASA Astrophysics Data System (ADS)

Yang, Yang; Han, Dandan; Du, Shichao; Wu, Songgu; Gong, Junbo

2018-01-01

Thiamine hydrochloride (THCL) was produced in methanol accompanied with agglomeration in industry, the plate like morphology of THCL in methanol was not deserve to have a good quality. Selecting a suitable solvent should be considered because solvent could be one of the essential factors to impact morphology. Methanol and methanol/ethyl acetate solvent (0.2 vol fraction of methanol) was selected as the solvent system in reactive crystallization of THCL. The experiment results show the THCL crystal morphology in methanol/ethyl acetate solvent system was granular and more regular than that in methanol. In order to explicate the different crystal morphology in different solvents, molecular dynamics (MD) simulation was introduced to simulate crystal morphology in different solvents. The attachment energy (AE) model was employed to investigate the morphology of THCL under vacuum conditions, methanol and methanol/ethyl acetate solvent conditions, respectively. The simulation crystal morphology was in a good agreement with that of experimented. The particle of THCL in methanol/ethyl acetate solvent has less tendency to agglomeration, and then it is favorable to the downstream process, such as filtration, storage and transportation.

Mechanisms of protein and virus crystal growth: An atomic force microscopy study of canavalin and STMV crystallization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Land, T.A.; De Yoreo, J.J.; Malkin, A.J.

1996-05-01

The evolution of surface morphology and step dynamics during growth of rhombohedral crystals of the protein canavalin and crystals of the cubic satellite tobacco mosaic virus (STMV) have been investigated for the first time by in situ atomic force microscopy. These two crystals were observed to grow by very different mechanisms. Growth of canavalin occurs on complex vicinal hillocks formed by multiple, independently acting screw dislocations. Small clusters were observed on the terraces. STMV on the other hand, was observed to grow by 2D nucleation of islands. No dislocations were found on the crystal. The results are used to determinemore » the growth mechanisms and estimate the fundamental materials parameters. The images also illustrate the important mechanism of defect incorporation and provide insight to the processes that limit the growth rate and uniformity of these crystals.« less

Effect of H{sup +} implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klyui, N. I.; Lozinskii, V. B., E-mail: lvb@isp.kiev.ua; Liptuga, A. I.

2017-03-15

The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interactionmore » of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.« less

Growth of L-Valinium Aluminium Chloride single crystal for OLED and super-capacitor applications

NASA Astrophysics Data System (ADS)

Kalaivani, D.; Vijayalakshmi, S.; Theras, J. Elberin Mary; Jayaraman, D.; Joseph, V.

2015-12-01

L-Valinium Aluminium Chloride (LVAC), a novel semi-organic material, was grown using slow evaporation under isothermal condition. The single crystal data reveal that the grown crystal belongs to monoclinic system. The SEM micrographs give clear picture about the surface morphology. Further, they confirm the inclusion of aluminium chloride into atomic sites of L-Valine. The compositional elements present in the crystal were identified through EDAX analysis. The mass spectral analysis was carried out to determine the molecular weight of the grown crystal. The optical transparency of the grown crystal was investigated by UV-vis-NIR spectrum. FTIR spectral study was used to identify the functional groups present in the grown material. The luminescence characteristics of grown material were analysed to confirm the effect of metal ion on the ligand. This property makes the material suitable for OLED application. The supercapacitive performance of the grown crystal was finally studied using cyclic voltammetry.

Effect of alkali ions (Na+, K+, Cs+) on reaction mechanism of CZTS nano-particles synthesis

NASA Astrophysics Data System (ADS)

Kumar, Suresh; Altosaar, Mare; Grossberg, Maarja; Mikli, Valdek

2018-04-01

The control of morphology, elemental composition and phase composition of Cu2ZnSnS4 (CZTS) nano-crystals depends on the control of complex formation and surface stabilization of nano-particles in solution-based synthesis in oleylamine. At temperatures ≥280 °C, the control of nano-crystal's morphology and homogenous growth is difficult because of fast poly-nuclear growth occurring at higher temperatures. In the present work the effect of oleylamine complex formation with different alkali ions (Na+, K+ and Cs+) on nano-crystals growth at synthesis temperature of 280 °C was studied. It was found that nano-powders synthesized in the presence of Na+ and K+ ions showed the formation of crystals of different sizes - small nano-particles (18 nm-30 nm), large aggregated crystals (few nm to 1 μm) and large single crystals (1 μm - 4 μm). The presence of Cs+ ions in the nano-powder synthesis in oleylamine-metal precursor-CsOH solution promoted growth of nano-crystals of homogenous size. It is proposed that the formed oleylamine-Cs complexes a) enhance the formation and stabilization of oleylamine-metal (Cu, Zn and Sn) complexes before the injection of sulphur precursor into the oleylamine-metal precursor solution and b) after addition of sulphur stabilize the fast nucleated nano-particles and promote diffusion limited growth.

Step-height standards based on the rapid formation of monolayer steps on the surface of layered crystals

NASA Astrophysics Data System (ADS)

Komonov, A. I.; Prinz, V. Ya.; Seleznev, V. A.; Kokh, K. A.; Shlegel, V. N.

2017-07-01

Metrology is essential for nanotechnology, especially for structures and devices with feature sizes going down to nm. Scanning probe microscopes (SPMs) permits measurement of nanometer- and subnanometer-scale objects. Accuracy of size measurements performed using SPMs is largely defined by the accuracy of used calibration measures. In the present publication, we demonstrate that height standards of monolayer step (∼1 and ∼0.6 nm) can be easily prepared by cleaving Bi2Se3 and ZnWO4 layered single crystals. It was shown that the conducting surface of Bi2Se3 crystals offers height standard appropriate for calibrating STMs and for testing conductive SPM probes. Our AFM study of the morphology of freshly cleaved (0001) Bi2Se3 surfaces proved that such surfaces remained atomically smooth during a period of at least half a year. The (010) surfaces of ZnWO4 crystals remained atomically smooth during one day, but already two days later an additional nanorelief of amplitude ∼0.3 nm appeared on those surfaces. This relief, however, did not further grow in height, and it did not hamper the calibration. Simplicity and the possibility of rapid fabrication of the step-height standards, as well as their high stability, make these standards available for a great, permanently growing number of users involved in 3D printing activities.

Microneedle crystals of cyano-substituted thiophene/phenylene co-oligomer epitaxially grown on KCl surface

NASA Astrophysics Data System (ADS)

Torii, Kazuki; Dokiya, Shohei; Tanaka, Yosuke; Yoshinaga, Shohei; Yanagi, Hisao

2017-06-01

A cyno-substituted thiophene/phenylene co-oligomer (TPCO), 5,5‧-bis(4‧-cyanobiphenyl-4-yl)-2,2‧-bithiophene (BP2T-CN), is vapor-deposited on KCl (001) surface kept at 220 °C by the mask-shadowing method. Transmission electron microscopy and fluorescence microscopy reveal that the deposited BP2T-CN crystallizes in two types of morphologies: microneedles and thin film crystallites. In particular, the predominant microneedles epitaxially grow in four directions in the manner that the BP2T-CN molecules align along the [110]KCl or [-110]KCl. X-ray diffraction patterns indicate that the BP2T-CN molecules in the microneedle lie parallel while those in the thin film crystallite obliquely stand on the KCl surface.

CRYSTAL AND MORPHOLOGICAL PHASE TRANSFORMATION OF LEAD IN THE PRESENCE OF ORTHOPHOSPHATE

EPA Science Inventory

The use of phosphates in the drinking water industry is well known. Orthophosphate is used to reduce lead levels at the consumer’s tap by forming a relatively insoluble divalent lead orthophosphate compounds on the surface of the lead source (e.g., lead service line, brass fixtur...

Preparation and Characterization of Cyclotrimethylenetrinitramine (RDX) with Reduced Sensitivity

PubMed Central

Wang, Yuqiao; Li, Xin; Chen, Shusen; Ma, Xiao; Yu, Ziyang; Jin, Shaohua; Li, Lijie; Chen, Yu

2017-01-01

The internal defects and shape of cyclotrimethylenetrinitramine (RDX) crystal are critical parameters for the preparation of reduced sensitivity RDX (RS-RDX). In the current study, RDX was re-crystallized and spheroidized to form the high-quality RDX that was further characterized by purity, apparent density, size distribution, specific surface area, impact sensitivity, and shock sensitivity. The effects of re-crystallization solvent on the growth morphology of RDX crystal were investigated by both theoretical simulation and experiment test, and consistent results were obtained. The high-quality RDX exhibited a high purity (≥99.90%), high apparent density (≥1.811 g/cm3), spherical shape, and relatively low impact sensitivity (6%). Its specific surface area was reduced more than 30%. Compared with conventional RDXs, the high-quality RDX reduced the shock sensitivities of PBXN-109 and PBXW-115 by more than 30%, indicating that it was a RS-RDX. The reduced sensitivity and good processability of the high-quality RDX would be significant in improving the performances of RDX-based PBXs. PMID:28825661

Formation of surface nanolayers in chalcogenide crystals using coherent laser beams

NASA Astrophysics Data System (ADS)

Ozga, K.; Fedorchuk, A. O.; El-Naggar, A. M.; Albassam, A. A.; Kityk, V.

2018-03-01

We have shown a possibility to form laser modified surface nanolayers with thickness up to 60 nm in some ternary chalcogenide crystals (Ag3AsS3, Ag3SbS3, Tl3SbS3) The laser treatment was performed by two coherent laser beams split in a space. As the inducing lasers we have applied continuous wave (cw) Hesbnd Cd laser at wavelength 441 nm and doubled frequency cw Nd: YAG laser at 532 nm. The spectral energies of these lasers were higher with respect to the energy gaps of the studied crystals. The optical anisotropy was appeared and defected by monitoring of birefringence at probing wavelength of cw Hesbnd Ne laser at λ = 3390 nm. The changes of the laser stimulated near the surface layer morphology was monitored by TEM and AFM methods as well as by the reflected optical second harmonic generation at fundamental wavelength of microsecond CO2 laser generating at wavelength 10600 nm. This technique may open a new approach for the formation of the near the surface nanolayers in chalcogenides using external cw laser illumination.

Growth of potassium sulfate crystals in the presence of organic dyes: in situ characterization by atomic force microscopy

NASA Astrophysics Data System (ADS)

Mauri, Andrea; Moret, Massimo

2000-01-01

In situ atomic force microscopy (AFM) has been used to observe potassium sulfate crystals growing in the presence of acid fuchsin and pyranine. These polysulfonated dyes are well known for their ability to adsorb onto the {1 1 0} and {0 1 0} (pyranine only) crystal faces. Using AFM, we analyzed the changes in surface micromorphology induced by the additives on advancing steps for the {1 1 0} and {0 1 0} surfaces. In situ AFM showed that layers grow by step flow at pre-existing steps by the addition of growth units at the step edges. It has been found that dye concentrations as low as ˜2×10 -6 M for pyranine and ˜4×10 -4 M for acid fuchsin produce significant changes in the step morphology and growth rates. The additive molecules attach to the terraces and pin the growing front. As a consequence, the edges of the growing steps become jagged as the dye molecules are adsorbed onto the crystal surface. At critical dye concentrations crystal growth is heavily hampered or even stopped along certain crystallographic directions producing, on a macroscopic scale, strong habit modifications. The formation of dye inclusions by means of macrosteps overgrowing the poisoned surface was also imaged. Interestingly, comparison of the in situ AFM experiments with previous habit modification studies showed acid fuchsin is also able to enter the {0 1 0} surfaces, a previously unnoticed phenomenon.

Structural morphology of crystals with the barite (BaSO 4) structure: A revision and extension

NASA Astrophysics Data System (ADS)

Hartman, P.; Strom, C. S.

1989-09-01

The structural morphology of crystals with the barite (BaSO 4) structure (sulphates, chromates, perchlorates, permanganates and tetrafluoroborates) has been determined with the use of computer programs. Uniquely defined F forms are {002}, {210}, {211}, {020} and {201}. Two different F slices were found for {101} and {200}, 33 for {011}. Attachment energies and specific surface energies have been calculated for an electrostatic point charge model as a function of the charge distribution in the anion. On this basis it is concluded that {101} behaves as an F form, {200} as an S form and {011} as a K form. The theoretical growth form shows {210}, {101} and {002} as main forms. A comparison is made with habits of natural and synthetic crystals. Experiments on KCIO 4 show that {011} appears at high supersaturations (>38; ;20%). It is shown that a broken bond model provides relative attachment energies that are higher by a factor of about three.

In Situ Monitoring the Uptake of Moisture into Hybrid Perovskite Thin Films.

PubMed

Schlipf, Johannes; Bießmann, Lorenz; Oesinghaus, Lukas; Berger, Edith; Metwalli, Ezzeldin; Lercher, Johannes A; Porcar, Lionel; Müller-Buschbaum, Peter

2018-04-19

Solution-processed hybrid perovskites are of great interest for use in photovoltaics. However, polycrystalline perovskite thin films show strong degradation in humid atmospheres, which poses an important challenge for large-scale market introduction. With in situ grazing incidence neutron scattering (GISANS) we analyzed water content, degradation products, and morphological changes during prolonged exposure to several humidity levels. In high humidity, the formation of metastable hydrate phases is accompanied by domain swelling, which transforms the faceted crystals to a round-washed, pebble-like form. The films incorporate much more water than is integrated into the hydrates, with smaller crystals being more affected, making the degradation strongly dependent on film morphology. Even at low humidity, water is adsorbed on the crystal surfaces without the formation of crystalline degradation products. Thus, although production in an ambient atmosphere is of interest for industrial production it might lead to long-term degradation without appropriate countermeasures like postproduction drying below 30% RH.

Morphology Controls on Calcite Recrystallization.

PubMed

Heberling, Frank; Paulig, Leonie; Nie, Zhe; Schild, Dieter; Finck, Nicolas

2016-11-01

Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10 -13 mol/(m 2 ·s).

Femtosecond laser-induced phase transformations in amorphous Cu77Ni6Sn10P7 alloy

NASA Astrophysics Data System (ADS)

Zhang, Y.; Liu, L.; Zou, G.; Chen, N.; Wu, A.; Bai, H.; Zhou, Y.

2015-01-01

In this study, the femtosecond laser-induced crystallization of CuNiSnP amorphous ribbons was investigated by utilizing an amplified Ti:sapphire laser system. X-ray diffraction and scanning electronic microscope were applied to examine the phase and morphology changes of the amorphous ribbons. Micromachining without crystallization, surface patterning, and selective crystallization were successfully achieved by changing laser parameters. Obvious crystallization occurred under the condition that the laser fluence was smaller than the ablation threshold, indicating that the structural evolution of the material depends strongly on the laser parameters. Back cooling method was used to inhibit heat accumulation; a reversible transformation between the disordered amorphous and crystalline phases can be achieved by using this method.

Surface structure of micro-diamond from ultrahigh-pressure felsic granulite, Bohemian Massif: AFM study of growth and resorption phenomena

NASA Astrophysics Data System (ADS)

Kotková, J.; Klapetek, P.

2012-04-01

Morphology, associated phases and retrogression phenomena of in-situ microdiamonds formed at extreme pressures in ultrahigh-pressure metamorphic terranes represent excellent tools to study character of diamond-forming media at great depths. Well-preserved microdiamonds discovered recently along with coesite in ultrahigh-pressure granulites of the north Bohemian crystalline basement, European Variscan belt (Kotková et al., 2011), provide unique material for such investigations. The diamonds are enclosed in major granulite phases, i.e. garnet both in felsic and intermediate lithologies and in kyanite in the felsic sample, as well as in zircon. Transmitted and reflected light microscopy of the felsic granulite sample, with peak mineral assemblage garnet, kyanite, feldspar and quartz, revealed presence of numerous, 5-20 μm-sized, perfectly preserved diamond crystals enclosed in kyanite grains. In contrast, diamonds within garnet are rare, can reach up to 30 μm in size, and graphite rims as well as polycrystalline graphite aggregates possibly representing complete diamond retrogression are common. We applied atomic force microscopy to study in-situ crystal morphology and surface microtopographic features, representing clues to the conditions and mechanisms of crystal formation as well as diamond resorption and retrogression. Both diamond enclosed in garnet and in kyanite of the felsic granulite occur exclusively as single crystals. The crystals have octahedral crystal shapes with straight but rounded edges and rounded corners. Concentric triangular terraces delimiting a flat triangular table on crystal scale and small micron-sized negatively oriented downward-pointing trigons developed on the octahedron crystal faces. Higher magnification reveals presence of discontinuous elongate hillocks oriented parallel to the octahedron face edge with positively oriented trigons. We suggest that the large-scale triangular terraces represent growth features. In contrast, the rounding of crystal edges and corners and development of negative trigons reflect diamond resorption. According to experimental works, such features are attributed to high temperature resorption, i.e. oxidation above ~ 950°C due to interaction with CO2 and/or H2O-bearing fluids (or fluid-bearing melts). Our results are consistent with presence of supercritical C-O-H fluid in the rocks in subduction zones documented from other ultrahigh-pressure metamorphic terranes, the resorption morphology corresponding rather to the interaction with water-rich than CO2-rich fluids. Kotková J., ÓBrien P., Ziemann M. (2011): Diamond and coesite discovered in Saxony-type granulite: Solution to the Variscan garnet peridotite enigma. Geology, 39, 7, 667-670.

Study of Polymer Crystallization by Physical Vapor Deposition

NASA Astrophysics Data System (ADS)

Jeong, Hyuncheol

When a polymer is confined under the submicron length scale, confinement size and interfaces can significantly impact the crystallization kinetics and resulting morphology. The ability to tune the morphology of confined polymer systems is of critical importance for the development of high-performance polymer microelectronics. The wisdom from the research on confined crystallization suggests that it would be beneficial to have a processing route in which the crystallization of polymers is driven by interface and temperature effects at a nanometer-scale confinement. In practice, for atomic and small-molecular systems, physical vapor deposition (PVD) has been recognized as the most successful processing route for the precise control of the film structure at surface utilizing confinement effects. While standard PVD technologies are not generally applicable to the deposition of the chemically fragile macromolecules, the development of matrix-assisted pulsed laser evaporation (MAPLE) now enables the non-destructive PVD of high-molecular weight polymers. In this thesis work, we investigated the use of MAPLE for the precise control of the crystallization of polymer films at a molecular level. We also sought to decipher the rules governing the crystallization of confined polymers, by using MAPLE as a tool to form confined polymer systems onto substrates with a controlled temperature. We first explored the early stages of film growth and crystallization of poly(ethylene oxide) (PEO) at the substrate surface formed by MAPLE. The unique mechanism of film formation in MAPLE, the deposition of submicron-sized polymer droplets, allowed for the manifestation of confinement and substrate effects in the crystallization of MAPLE-deposited PEO. Furthermore, we also focused on the property of the amorphous PEO film formed by MAPLE, showing the dependence of polymer crystallization kinetics on the thermal history of the amorphous phase. Lastly, we probed how MAPLE processing affected the semi-crystalline structure in MAPLE-deposited polyethylene (PE) films. Depositing PE at various temperatures remarkably allowed for the tunability of the melting temperature and crystallinity of the PE films, thus manipulating the semi-crystalline structure. By comparing the structure of PE formed by different processing routes, i.e., MAPLE and melt-crystallization, we discussed how processing routes affect the development of semi-crystalline phase in polymer films.

3D Micro-topography of Transferred Laboratory and Natural Ice Crystal Surfaces Imaged by Cryo and Environmental Scanning Electron Microscopy

NASA Astrophysics Data System (ADS)

Magee, N. B.; Boaggio, K.; Bancroft, L.; Bandamede, M.

2015-12-01

Recent work has highlighted micro-scale roughness on the surfaces of ice crystals grown and imaged in-situ within the chambers of environmental scanning electron microscopes (ESEM). These observations appear to align with theoretical and satellite observations that suggest a prevalence of rough ice in cirrus clouds. However, the atmospheric application of the lab observations are indeterminate because the observations have been based only on crystals grown on substrates and in pure-water vapor environments. In this work, we present details and results from the development of a transfer technique which allows natural and lab-grown ice and snow crystals to be captured, preserved, and transferred into the ESEM for 3D imaging. Ice crystals were gathered from 1) natural snow, 2) a balloon-borne cirrus particle capture device, and 3) lab-grown ice crystals from a diffusion chamber. Ice crystals were captured in a pre-conditioned small-volume (~1 cm3) cryo-containment cell. The cell was then sealed closed and transferred to a specially-designed cryogenic dewer (filled with liquid nitrogen or crushed dry ice) for transport to a new Hitachi Field Emission, Variable Pressure SEM (SU-5000). The cryo-cell was then removed from the dewer and quickly placed onto the pre-conditioned cryo transfer stage attached to the ESEM (Quorum 3010T). Quantitative 3D topographical digital elevation models of ice surfaces are reported from SEM for the first time, including a variety of objective measures of statistical surface roughness. The surfaces of the transported crystals clearly exhibit signatures of mesoscopic roughening that are similar to examples of roughness seen in ESEM-grown crystals. For most transported crystals, the habits and crystal edges are more intricate that those observed for ice grown directly on substrates within the ESEM chamber. Portions of some crystals do appear smooth even at magnification greater than 1000x, a rare observation in our ESEM-grown crystals. The transported crystals hint at some significant differences in roughness morphology, but they do provide evidence that crystals grown in air/water mixtures and with minimal substrate influence also exhibit mesoscopic roughness with similarity to that observed in ESEM-grown crystals.

Effects of Co contents on the microstructures and properties of the electrodeposited NiCo–Zr composite coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Fei; Jiang, Chuanhai, E-mail: chuanhaijiang1963@163.com; Zhao, Yuantao

2015-05-15

Highlights: • The novel NiCo–Zr coatings were prepared by electro-deposition. • Surface morphology, crystal structure, grain size and microstrain were examined. • Texture, residual stress and corrosion resistance were investigated. • Addition of Co increased the hardness and corrosion resistance of the coatings. - Abstract: In this study, the NiCo–Zr composite coatings were prepared from the electrolytes with different Co{sup 2+} concentrations by electrodeposition method. The effects of Co contents on the crystal structure, surface morphology, grain size, microstrain and residual stress were examined by X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDX) andmore » atomic force microscope (AFM). The corrosion resistance of the composite coatings was also examined by the potentiodynamic polarization and electrochemical impedance (EIS) measurements. The results revealed that the crystal structures of the coatings were dependent on the Co contents and addition of Co content of 58 wt% resulted in the formation of hexagonal (hcp) Co. The increasing Co contents in the NiCo–Zr composite coatings resulted in the smoother and more compact surface, decreased the grain size and increased the microstrain. The micro-hardness and residual stress also increased with increasing Co contents. The addition of Co increased the corrosion resistance of the NiCo–Zr composite coatings compared with the Ni–Zr coating while the corrosion resistance of the NiCo–Zr composite coatings decreased as the Co contents increased.« less

Effect of silver-doping on the crystal structure, morphology and photocatalytic activity of TiO2 nanofibers

NASA Astrophysics Data System (ADS)

Barakat, N. A. M.; Kim, H. Y.

2012-09-01

In this study, effect of sliver-doping on the crystal structure, the nanofibrous morphology and the photocatalytic activity of titanium oxide nanofibers have been investigated. Silver-doped TiO2 nanofibers having different silver contents were prepared by calcination of electrospun nanofiber mats consisting of silver nitrate, titanium isopropoxide and poly(vinyl acetate) at 600 °C. The results affirmed formation of silver-doped TiO2 nanofibers composed of anatase and rutile when the silver nitrate content in the original electrospun solution was more than 3 wt%. The rutile phase content was directly proportional with the AgNO3 concentration in the electrospun solution. Negative impact of the silver-doping on the nanofibrous morphology was observed as increase the silver content caused to decrease the aspect ratio, i.e. producing nanorods rather nanofibers. However, silver-doping leads to modify the surface roughness. Study of the photocatalytic degradation of methylene blue dye clarified that increase the silver content strongly enhances the dye oxidation process.

Theoretical modeling of zircon's crystal morphology according to data of atomistic calculations

NASA Astrophysics Data System (ADS)

Gromalova, Natalia; Nikishaeva, Nadezhda; Eremin, Nikolay

2017-04-01

Zircon is an essential mineral that is used in the U-Pb dating. Moreover, zircon is highly resistant to radioactive exposure. It is of great interest in solving both fundamental and applied problems associated with the isolation of high-level radioactive waste. There is significant progress in forecasting of the most energetically favorable crystal structures at the present time. Unfortunately, the theoretical forecast of crystal morphology at high technological level is under-explored nowadays, though the estimation of crystal equilibrium habit is extremely important in studying the physical and chemical properties of new materials. For the first time, the thesis about relation of the equilibrium shape of a crystal with its crystal structure was put forward in the works by O.Brave. According to it, the idealized habit is determined in the simplest case by a correspondence with the reticular densities Rhkl of individual faces. This approach, along with all subsequent corrections, does not take into account the nature of atoms and the specific features of the chemical bond in crystals. The atomistic calculations of crystal surfaces are commonly performed using the energetic characteristics of faces, namely, the surface energy (Esurf), which is a measure of the thermodynamic stability of the crystal face. The stable crystal faces are characterized by small positive values of Esurf. As we know from our previous research (Gromalova et al.,2015) one of the constitutive factors affecting the value of the surface energy in calculations is a choice of potentials model. In this regard, we studied several sets of parameters of atomistic interatomic potentials optimized previously. As the first test model («Zircon 1») were used sets of interatomic potentials of interaction Zr-O, Si-O and O-O in the form of Buckingham potentials. To improve playback properties of zircon additionally used Morse potential for a couple of Zr-Si, as well as the three-particle angular harmonic potential. The other sets of interatomic potentials («Zircon 2, Zircon 3») differed from the first in that parameters was found with the help of quantum-chemical calculations of the structure «ab initio».The surface energies for different faces of zircon were calculated using Metadise code (Watson et al., 1996) at P4-3000 personal computer with Windows XP operating system. The computation time for one simple form was from 30 minutes to 12 hours. Calculations have shown that depending on the chosen model the surface energy of zircons faces several changes. For example, Esurf of face (331) obtained using models of potentials «Zircon 2», «Zircon 3» sufficiently similar (2.82 and 3.01 J/mol2 respectively). Meaning of Esurf of this face, calculated on the basis of set «Zircon 1» significantly lower (1,54 J/mol2). With regard to the face (100), it has low surface energies when selecting all three models, with a minimum value (1,14 J/mol2) in the model «Zircon 1». References: Gromalova N.A., Eremin N.N., Urusov V.S. Atomistic computer modeling of the crystal-morpology of corundum group minerals // Zapiski RMO. V. 144. №4. 2015. p. 84-92. Watson G.W., Kelsey E.T., de Leeuw N.H., Harris D.J, Parker S.C. Atomistic simulation of dislocations, surfaces and interfaces in MgO. Journal of the Chemical Society Faraday Transactions. 1996. V.92 P. 433-438.

Imaging the surface morphology, chemistry and conductivity of LiNi 1/3 Fe 1/3 Mn 4/3 O 4 crystalline facets using scanning transmission X-ray microscopy

DOE PAGES

Zhou, Jigang; Wang, Jian; Cutler, Jeffrey; ...

2016-07-26

We have employed scanning transmission X-ray microscopy (STXM) using the X-ray fluorescence mode in order to elucidate the chemical structures at Ni, Fe, Mn and O sites from the (111) and (100) facets of micron-sized LiNi 1/3Fe 1/3Mn 4/3O 4 energy material particles. Furthermore, STXM imaging using electron yield mode has mapped out the surface conductivity of the crystalline particles. Our study presents a novel approach that visualizes local element segregation, chemistry and conductivity variation among different crystal facets, which will assist further tailoring of the morphology and surface structure of this high voltage spinel lithium ion battery cathode material.

Slip as the basic mechanism for formation of deformation relief structural elements

NASA Astrophysics Data System (ADS)

Lychagin, D. V.; Alfyorova, E. A.

2017-07-01

The experimental results of investigation of the nickel single crystal surface morphology after compression deformation are presented. The quasi-periodic character of the deformation profile, common for shear deformation of different types of relief structural elements, is found. It is demonstrated that the morphological manifestation of these structural elements is determined by local shear systems along octahedral planes. The regularities of the deformation structure in these regions defining the material extrusion and intrusion regions and the specific features of disorientation accumulation are established. If reorientation of local regions takes part in the relief element formation, along with octahedral slip, much stronger growth of the surface area is observed. The possibility of application of two-dimensional and three-dimensional surface roughness parameters for description of deformation relief is considered.

The effect of tailor-made additives on crystal growth of methyl paraben: Experiments and modelling

NASA Astrophysics Data System (ADS)

Cai, Zhihui; Liu, Yong; Song, Yang; Guan, Guoqiang; Jiang, Yanbin

2017-03-01

In this study, methyl paraben (MP) was selected as the model component, and acetaminophen (APAP), p-methyl acetanilide (PMAA) and acetanilide (ACET), which share the similar molecular structure as MP, were selected as the three tailor-made additives to study the effect of tailor-made additives on the crystal growth of MP. HPLC results indicated that the MP crystals induced by the three additives contained MP only. Photographs of the single crystals prepared indicated that the morphology of the MP crystals was greatly changed by the additives, but PXRD and single crystal diffraction results illustrated that the MP crystals were the same polymorph only with different crystal habits, and no new crystal form was found compared with other references. To investigate the effect of the additives on the crystal growth, the interaction between additives and facets was discussed in detail using the DFT methods and MD simulations. The results showed that APAP, PMAA and ACET would be selectively adsorbed on the growth surfaces of the crystal facets, which induced the change in MP crystal habits.

Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

DOE PAGES

Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian; ...

2017-04-12

The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal spacemore » analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. As a result, island nucleation spacing obeys a power-law dependence on growth rate, with exponents of –0.24 and –0.29 for the m- and c-plane, respectively.« less

Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian

The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal spacemore » analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. As a result, island nucleation spacing obeys a power-law dependence on growth rate, with exponents of –0.24 and –0.29 for the m- and c-plane, respectively.« less

Influence of crystal habit on trimethoprim suspension formulation.

PubMed

Tiwary, A K; Panpalia, G M

1999-02-01

The role of crystal habit in influencing the physical stability and pharmacokinetics of trimethoprim suspensions was examined. Different habits for trimethoprim (TMP) were obtained by recrystallizing the commercial sample (PD) utilizing solvent-change precipitation method. Four distinct habits (microscopic observation) belonging to the same polymorphic state (DSC studies) were selected for studies. Preformulation and formulation studies were carried out on suspension dosage forms containing these crystals. The freshly prepared suspensions were also evaluated for their pharmacokinetic behaviour on healthy human volunteers using a cross over study. Variation of crystallization conditions produces different habits of TMP. Among the different crystal habits exhibiting same polymorphic state, the most anisometric crystal showed best physical stability in terms of sedimentation volume and redispersibility. However, habit did not significantly affect the extent of TMP excreted in urine. Modification of surface morphology without significantly altering the polymorphic state can be utilized for improving physical stability of TMP suspensions. However, the pharmacokinetic profile remains unaltered.

Surface and subsurface cracks characteristics of single crystal SiC wafer in surface machining

NASA Astrophysics Data System (ADS)

Qiusheng, Y.; Senkai, C.; Jisheng, P.

2015-03-01

Different machining processes were used in the single crystal SiC wafer machining. SEM was used to observe the surface morphology and a cross-sectional cleavages microscopy method was used for subsurface cracks detection. Surface and subsurface cracks characteristics of single crystal SiC wafer in abrasive machining were analysed. The results show that the surface and subsurface cracks system of single crystal SiC wafer in abrasive machining including radial crack, lateral crack and the median crack. In lapping process, material removal is dominated by brittle removal. Lots of chipping pits were found on the lapping surface. With the particle size becomes smaller, the surface roughness and subsurface crack depth decreases. When the particle size was changed to 1.5µm, the surface roughness Ra was reduced to 24.0nm and the maximum subsurface crack was 1.2µm. The efficiency of grinding is higher than lapping. Plastic removal can be achieved by changing the process parameters. Material removal was mostly in brittle fracture when grinding with 325# diamond wheel. Plow scratches and chipping pits were found on the ground surface. The surface roughness Ra was 17.7nm and maximum subsurface crack depth was 5.8 µm. When grinding with 8000# diamond wheel, the material removal was in plastic flow. Plastic scratches were found on the surface. A smooth surface of roughness Ra 2.5nm without any subsurface cracks was obtained. Atomic scale removal was possible in cluster magnetorheological finishing with diamond abrasive size of 0.5 µm. A super smooth surface eventually obtained with a roughness of Ra 0.4nm without any subsurface crack.

Actively addressed single pixel full-colour plasmonic display

NASA Astrophysics Data System (ADS)

Franklin, Daniel; Frank, Russell; Wu, Shin-Tson; Chanda, Debashis

2017-05-01

Dynamic, colour-changing surfaces have many applications including displays, wearables and active camouflage. Plasmonic nanostructures can fill this role by having the advantages of ultra-small pixels, high reflectivity and post-fabrication tuning through control of the surrounding media. However, previous reports of post-fabrication tuning have yet to cover a full red-green-blue (RGB) colour basis set with a single nanostructure of singular dimensions. Here, we report a method which greatly advances this tuning and demonstrates a liquid crystal-plasmonic system that covers the full RGB colour basis set, only as a function of voltage. This is accomplished through a surface morphology-induced, polarization-dependent plasmonic resonance and a combination of bulk and surface liquid crystal effects that manifest at different voltages. We further demonstrate the system's compatibility with existing LCD technology by integrating it with a commercially available thin-film-transistor array. The imprinted surface interfaces readily with computers to display images as well as video.

Polyethylenimine-assisted seed-mediated synthesis of gold nanoparticles for surface-enhanced Raman scattering studies

NASA Astrophysics Data System (ADS)

Philip, Anish; Ankudze, Bright; Pakkanen, Tuula T.

2018-06-01

Large-sized gold nanoparticles (AuNPs) were synthesized with a new polyethylenimine - assisted seed - mediated method for surface-enhanced Raman scattering (SERS) studies. The size and polydispersity of gold nanoparticles are controlled in the growth step with the amounts of polyethylenimine (PEI) and seeds. Influence of three silicon oxide supports having different surface morphologies, namely halloysite (Hal) nanotubes, glass plates and inverse opal films of SiO2, on the performance of gold nanoparticles in Raman scattering of a 4-aminothiophenol (4-ATP) analyte was investigated. Electrostatic interaction between positively charged polyethylenimine-capped AuNPs and negatively charged surfaces of silicon oxide supports was utilized in fabrication of the SERS substrates using deposition and infiltration methods. The Au-photonic crystal of the three SERS substrate groups is the most active one as it showed the highest analytical enhancement factor (AEF) and the lowest detection limit of 1x10-8 M for 4-ATP. Coupling of the optical properties of photonic crystals with the plasmonic properties of AuNPs provided Au-photonic crystals with the high SERS activity. The AuNPs clusters formed both in the photonic crystal and on the glass plate are capable of forming more hot spots as compared to sparsely distributed AuNPs on Hal nanotubes and thereby increasing the SERS enhancement.

Effect of thermal treatment on Zn nanodisks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acuña-Avila, Pedro E., E-mail: pacunaa004@alumno.uaemex.mx; López, Roberto; Vigueras-Santiago, Enrique

2015-06-15

Metallic Zn nanodisks with hexagonal morphology were obtained onto glass substrate under vacuum thermal evaporation. A thermal characterization of Zn nanodiks showed a lower oxidation temperature than source powder Zn. Different thermal treatment on Zn nanodisks played an important role on the morphology, crystal size and surface vibrational modes of ZnO. The growth of ZnO nanoneedles started at the edge of metallic zinc hexagonal structures according with SEM images, the higher temperature the longer needles were grown. XRD diffractogram confirmed the wurtzite structure of ZnO with metallic nuclei. A wide band between 530 and 580 cm{sup −1} of Raman scatteringmore » corresponded at surface vibrational modes not observed at higher temperature.« less

Template-directed control of crystal morphologies.

PubMed

Meldrum, Fiona C; Ludwigs, Sabine

2007-02-12

Biominerals are characterised by unique morphologies, and it is a long-term synthetic goal to reproduce these synthetically. We here apply a range of templating routes to investigate whether a fascinating category of biominerals, the single crystals with complex forms, can be produced using simple synthetic methods. Macroporous crystals with sponge-like morphologies identical to that of sea urchin skeletal plates were produced on templating with a sponge-like polymer membrane. Similarly, patterning of individual crystal faces was achieved from the micrometer to nanometer scale through crystallisation on colloidal particle monolayers and patterned polymer thin films. These experiments demonstrate the versatility of a templating approach to producing single crystals with unique morphologies.

Preparation of atomically flat rutile TiO 2(001) surfaces for oxide film growth

DOE PAGES

Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; ...

2016-01-01

The availability of low-index rutile TiO 2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO 2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO 2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surfacemore » energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO 2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.« less

Effects of Nano-CeO₂ with Different Nanocrystal Morphologies on Cytotoxicity in HepG2 Cells.

PubMed

Wang, Lili; Ai, Wenchao; Zhai, Yanwu; Li, Haishan; Zhou, Kebin; Chen, Huiming

2015-09-02

Cerium oxide nanoparticles (nano-CeO₂) have been reported to cause damage and apoptosis in human primary hepatocytes. Here, we compared the toxicity of three types of nano-CeO₂ with different nanocrystal morphologies (cube-, octahedron-, and rod-like crystals) in human hepatocellular carcinoma cells (HepG2). The cells were treated with the nano-CeO₂ at various concentrations (6.25, 12.5, 25, 50, 100 μg/mL). The crystal structure, size and morphology of nano-CeO₂ were investigated by X-ray diffractometry and transmission electron microscopy. The specific surface area was detected using the Brunauer, Emmet and Teller method. The cellular morphological and internal structure were observed by microscopy; apoptotic alterations were measured using flow cytometry; nuclear DNA, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) and glutathione (GSH) in HepG2 cells were measured using high content screening technology. The scavenging ability of hydroxyl free radicals and the redox properties of the nano-CeO₂ were measured by square-wave voltammetry and temperature-programmed-reduction methods. All three types of nano-CeO₂ entered the HepG2 cells, localized in the lysosome and cytoplasm, altered cellular shape, and caused cytotoxicity. The nano-CeO₂ with smaller specific surface areas induced more apoptosis, caused an increase in MMP, ROS and GSH, and lowered the cell's ability to scavenge hydroxyl free radicals and antioxidants. In this work, our data demonstrated that compared with cube-like and octahedron-like nano-CeO₂, the rod-like nano-CeO₂ has lowest toxicity to HepG2 cells owing to its larger specific surface areas.

Morphology of single inhalable particle in the air polluted city of Shijiazhuang, China.

PubMed

Wang, Zanhong; Zhang, Lingzhi; Zhang, Yuliang; Zhao, Zhou; Zhang, Sumin

2008-01-01

In the typical air polluted city of Shijiazhuang, single inhalable particle samples in non-heating period, heating period, dust storm days, and snowy days were collected and detected by SEM/EDS (scanning electron microscopy and energy dispersive X-ray spectrometry). The particle morphology was characterized by the 6 shape clusters, which are: irregular square, agglomerate, sphere, floccule, column or stick, and unknown, by quantitative order. The irregular square particles are common in all kinds of samples; sphere particles are more, and column or stick are less in winter samples; in the wet deposit samples, agglomerate and floccule particles are not found. The surface of most particles is coarse with fractal edge, which can provide suitable chemical reaction bed in the polluted atmospheric environment. New formed calcium crystal is found to demonstrate the existence of neutralized reaction, explaining the reason for the high SO2 emission and low acid rain frequency in Shijiazhuang. The three sorts of surface patterns of spheres are smooth, semi-smooth, and coarse, corresponding to the element of Si-dominant, Si-Al-dominant, and Fe-dominant. The soot particle is present as floccule with average size around 10 microm, considerably larger than the former reported results, but wrapped or captured with other fine particles to make its appearance unique and enhance its toxicity potentially. The new formed calcium crystal, the 3 sorts of sphere surface patterns, and the unique soot appearance represent the single inhalable particle's morphology characteristics in Shijiazhuang City.

Modulation of calcium oxalate dihydrate growth by selective crystal-face binding of phosphorylated osteopontin and polyaspartate peptide showing occlusion by sectoral (compositional) zoning.

PubMed

Chien, Yung-Ching; Masica, David L; Gray, Jeffrey J; Nguyen, Sarah; Vali, Hojatollah; McKee, Marc D

2009-08-28

Calcium oxalate dihydrate (COD) mineral and the urinary protein osteopontin/uropontin (OPN) are commonly found in kidney stones. To investigate the effects of OPN on COD growth, COD crystals were grown with phosphorylated OPN or a polyaspartic acid-rich peptide of OPN (DDLDDDDD, poly-Asp(86-93)). Crystals grown with OPN showed increased dimensions of the {110} prismatic faces attributable to selective inhibition at this crystallographic face. At high concentrations of OPN, elongated crystals with dominant {110} faces were produced, often with intergrown, interpenetrating twin crystals. Poly-Asp(86-93) dose-dependently elongated crystal morphology along the {110} faces in a manner similar to OPN. In crystal growth studies using fluorescently tagged poly-Asp(86-93) followed by imaging of crystal interiors using confocal microscopy, sectoral (compositional) zoning in COD was observed resulting from selective binding and incorporation (occlusion) of peptide exclusively into {110} crystal sectors. Computational modeling of poly-Asp(86-93) adsorption to COD {110} and {101} surfaces also suggests increased stabilization of the COD {110} surface and negligible change to the natively stable {101} surface. Ultrastructural, colloidal-gold immunolocalization of OPN by transmission electron microscopy in human stones confirmed an intracrystalline distribution of OPN. In summary, OPN and its poly-Asp(86-93) sequence similarly affect COD mineral growth; the {110} crystallographic faces become enhanced and dominant attributable to {110} face inhibition by the protein/peptide, and peptides can incorporate into the mineral phase. We, thus, conclude that the poly-Asp(86-93) domain is central to the OPN ability to interact with the {110} faces of COD, where it binds to inhibit crystal growth with subsequent intracrystalline incorporation (occlusion).

Critical detonation thickness in vapor-deposited hexanitroazobenzene (HNAB) films with different preparation conditions

NASA Astrophysics Data System (ADS)

Tappan, Alexander; Knepper, Robert; Marquez, Michael; Ball, J.; Miller, Jill

2013-06-01

At Sandia National Laboratories, we have coined the term ``microenergetics'' to describe sub-millimeter energetic material studies aimed at gaining knowledge of combustion and detonation behavior at the mesoscale. Films of the high explosive hexanitroazobenzene (HNAB) have been deposited through physical vapor deposition. HNAB deposits in an amorphous state that crystallizes over time and modest heating accelerates this crystallization. HNAB films were prepared under different crystallization temperatures, and characterized with surface profilometry and scanning electron microscopy. The critical detonation thickness for HNAB at different crystallization conditions was determined in a configuration where charge width was large compared to film thickness, and thus side losses did not play a role in detonation propagation. The results of these experiments will be discussed in the context of small sample geometry, deposited film morphology, crystal structure, and density.

Structural characterization of oxidized titanium surfaces

NASA Astrophysics Data System (ADS)

Jobin, M.; Taborelli, M.; Descouts, P.

1995-05-01

Oxidized titanium surfaces resulting from various processes have been structurally characterized by means of scanning force microscopy, x-ray photoemission spectroscopy (XPS), x-ray diffraction, and electron energy-loss spectroscopy (EELS) with losses in the 0-100 eV range. It has been found that the surface morphology has a granular structure for electropolished titanium and for titanium evaporated on mica at low substrate temperature (570 K), but changes to flat terraces for the films evaporated at higher temperature (770 K). Angular-dependent XPS has revealed the presence of a Ti2O3 suboxide at the Ti/TiO2 interface for electropolished titanium. Dry oxidation has been performed at 770 and 970 K on both weakly and highly crystallized evaporated titanium films oriented along (0001). In the case of underlying crystallized metallic titanium, the resulting TiO2 films are crystallized with the anatase (004) orientation for oxidation at 770 K and with rutile (200) orientation for oxidation at 970 K. EELS spectra interpreted in terms of the molecular orbitals of a (TiO6)8- cluster show that the local octahedral environment of titanium atoms is preserved on native oxides, even if these oxides are not crystallized.

Calcium carbonate nucleation in an alkaline lake surface water, Pyramid Lake, Nevada, USA

USGS Publications Warehouse

Reddy, Michael M.; Hoch, Anthony

2012-01-01

Calcium concentration and calcite supersaturation (Ω) needed for calcium carbonate nucleation and crystal growth in Pyramid Lake (PL) surface water were determined during August of 1997, 2000, and 2001. PL surface water has Ω values of 10-16. Notwithstanding high Ω, calcium carbonate growth did not occur on aragonite single crystals suspended PL surface water for several months. However, calcium solution addition to PL surface-water samples caused reproducible calcium carbonate mineral nucleation and crystal growth. Mean PL surface-water calcium concentration at nucleation was 2.33 mM (n = 10), a value about nine times higher than the ambient PL surface-water calcium concentration (0.26 mM); mean Ω at nucleation (109 with a standard deviation of 8) is about eight times the PL surface-water Ω. Calcium concentration and Ω regulated the calcium carbonate formation in PL nucleation experiments and surface water. Unfiltered samples nucleated at lower Ω than filtered samples. Calcium concentration and Ω at nucleation for experiments in the presence of added particles were within one standard deviation of the mean for all samples. Calcium carbonate formation rates followed a simple rate expression of the form, rate (mM/min) = A (Ω) + B. The best fit rate equation "Rate (Δ mM/Δ min) = -0.0026 Ω + 0.0175 (r = 0.904, n = 10)" was statistically significant at greater than the 0.01 confidence level and gives, after rearrangement, Ω at zero rate of 6.7. Nucleation in PL surface water and morphology of calcium carbonate particles formed in PL nucleation experiments and in PL surface-water samples suggest crystal growth inhibition by multiple substances present in PL surface water mediates PL calcium carbonate formation, but there is insufficient information to determine the chemical nature of all inhibitors.

Calcium Carbonate Nucleation in an Alkaline Lake Surface Water, Pyramid Lake, Nevada, USA

USGS Publications Warehouse

Reddy, M.M.; Hoch, A.

2012-01-01

Calcium concentration and calcite supersaturation (??) needed for calcium carbonate nucleation and crystal growth in Pyramid Lake (PL) surface water were determined during August of 1997, 2000, and 2001. PL surface water has ?? values of 10-16. Notwithstanding high ??, calcium carbonate growth did not occur on aragonite single crystals suspended PL surface water for several months. However, calcium solution addition to PL surface-water samples caused reproducible calcium carbonate mineral nucleation and crystal growth. Mean PL surface-water calcium concentration at nucleation was 2.33 mM (n = 10), a value about nine times higher than the ambient PL surface-water calcium concentration (0.26 mM); mean ?? at nucleation (109 with a standard deviation of 8) is about eight times the PL surface-water ??. Calcium concentration and ?? regulated the calcium carbonate formation in PL nucleation experiments and surface water. Unfiltered samples nucleated at lower ?? than filtered samples. Calcium concentration and ?? at nucleation for experiments in the presence of added particles were within one standard deviation of the mean for all samples. Calcium carbonate formation rates followed a simple rate expression of the form, rate (mM/min) = A (??) + B. The best fit rate equation "Rate (?? mM/?? min) = -0.0026 ?? + 0.0175 (r = 0.904, n = 10)" was statistically significant at greater than the 0.01 confidence level and gives, after rearrangement, ?? at zero rate of 6.7. Nucleation in PL surface water and morphology of calcium carbonate particles formed in PL nucleation experiments and in PL surface-water samples suggest crystal growth inhibition by multiple substances present in PL surface water mediates PL calcium carbonate formation, but there is insufficient information to determine the chemical nature of all inhibitors. ?? 2011 U.S. Government.

In situ 3D topographic and shape analysis by synchrotron radiation X-ray microtomography for crystal form identification in polymorphic mixtures

PubMed Central

Yin, Xian-Zhen; Xiao, Ti-Qiao; Nangia, Ashwini; Yang, Shuo; Lu, Xiao-Long; Li, Hai-Yan; Shao, Qun; He, You; York, Peter; Zhang, Ji-Wen

2016-01-01

Polymorphism denotes the existence of more than one crystal structure of a substance, and great practical and theoretical interest for the chemical and pharmaceutical industries. In many cases, it is challenging to produce a pure crystal form and establish a sensitive detection method for the identification of crystal form in a mixture of polymorphs. In this study, an accurate and sensitive method based on synchrotron radiation X-ray computed microtomography (SR-μCT) was devised to identify the polymorphs of clopidogrel bisulphate (CLP). After 3D reconstruction, crystal particles were extracted and dozens of structural parameters were calculated. Whilst, the particle shapes of the two crystal forms were all irregular, the surface of CLP II was found to be rougher than CLP I. In order to classify the crystal form based on the quantitative morphological property of particles, Volume Bias Percentage based on Surface Smoothing (VBP) was defined and a new method based on VBP was successfully developed, with a total matching rate of 99.91% for 4544 particles and a lowest detectable limit of 1%. More important for the mixtures in solid pharmaceutical formulations, the interference of excipients can be avoided, a feature cannot achieved by other available analytical methods. PMID:27097672

Top-seeded solution growth and morphology change of RbTiOPO4:Ta single crystal

NASA Astrophysics Data System (ADS)

Li, Ziqing; Chen, Yang; Zhu, Pengfei; Ji, Nianjing; Duan, Xiulan; Jiang, Huaidong

2018-04-01

The RbTiOPO4:Ta single crystal with dimensions of 4 mm × 31 mm × 18 mm was successfully grown by Top Seeded Solution Growth Technique. It is concluded that the doping Ta element can strongly influence the growth and morphology of the RbTiOPO4 crystal. The evident morphology change of RbTiOPO4:Ta crystal with respect to RbTiOPO4 crystal has been observed and the (1 0 0) crystal face was more developed than any other crystal faces. The possible reasons of the morphology change were analyzed through experimental and theoretical methods. Several methods were tried to increase crystallographic a direction dimension of RbTiOPO4:Ta crystals. Finally, the RbTiOPO4:Ta single crystal with crystallographic a direction dimension up to 6 mm was obtained by using thicker seed crystal. This way makes it possible to get isometric RbTiOPO4:Ta crystals, which is beneficial for nonlinear optical applications due to larger area in x-y plane.

Polymer stabilized liquid crystals: Topology-mediated electro-optical behavior and applications

NASA Astrophysics Data System (ADS)

Weng, Libo

There has been a wide range of liquid crystal polymer composites that vary in polymer concentration from as little as 3 wt.% (polymer stabilized liquid crystal) to as high as 60 wt.% (polymer dispersed liquid crystals). In this dissertation, an approach of surface polymerization based on a low reactive monomer concentration about 1 wt.% is studied in various liquid crystal operation modes. The first part of dissertation describes the development of a vertical alignment (VA) mode with surface polymer stabilization, and the effects of structure-performance relationship of reactive monomers (RMs) and polymerization conditions on the electro-optical behaviors of the liquid crystal device has been explored. The polymer topography plays an important role in modifying and enhancing the electro-optical performance of stabilized liquid crystal alignment. The enabling surface-pinned polymer stabilized vertical alignment (PSVA) approach has led to the development of high-performance and fast-switching displays with controllable pretilt angle, increase in surface anchoring energy, high optical contrast and fast response time. The second part of the dissertation explores a PSVA mode with in-plane switching (IPS) and its application for high-efficiency and fast-switching phase gratings. The diffraction patterns and the electro-optical behaviors including diffraction efficiency and response time are characterized. The diffraction grating mechanism and performance have been validated by computer simulation. Finally, the advantages of surface polymerization approach such as good optical contrast and fast response time have been applied to the fringe-field switching (FFS) system. The concentration of reactive monomer on the electro-optical behavior of the FFS cells is optimized. The outstanding electro-optical results and mechanism of increase in surface anchoring strength are corroborated by the director field simulation. The density and topology of nanoscale polymer protrusions are analyzed and confirmed by morphological study. The developed high-performance polymer-stabilized fringe-field-switching (PS-FFS) could open new types of device applications.

Sensing of contaminants in potable water using TiO{sub 2} functional film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akshatha, N.; Poonia, Monika; Gupta, R. K., E-mail: raj@pilani.bits-pilani.ac.in

2016-04-13

The piezoelectric based quartz crystal microbalance is employed for sensing contaminants in potable water. A spin coated thin layer of TiO{sub 2} nanoparticles was formed at the sensing area of a 5 MHz AT-cut quartz wafer. The thin film of TiO{sub 2} nanoparticles forms a mesoporous functional layer for the trapping of water borne contaminants. The morphology of the thin film of TiO{sub 2} nanoparticles was studied using field emission scanning electron microscope (FESEM). The surface morphology of the TiO{sub 2} nanoparticles reveals the mesoporous structures indicating large number of defects and porous sites. Such film was employed for the detectionmore » of water borne contaminants by detecting the piezoelectric response from a quartz crystal microbalance. We found the film to be very sensitive to the contaminants. The minimum detection limit was found to be 330 ppb. The effect of surface recharging was also studied by altering the physical conditions so that the film can be used for repetitive usage.« less

High-temperature morphological evolution of lithographically introduced cavities in silicon carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narushima, Takayuki; Glaeser, Andreas M.

2000-12-01

Internal cavities of controlled geometry and crystallography were introduced in 6H silicon carbide single crystals by combining lithographic methods, ion beam etching, and solid-state diffusion bonding. The morphological evolution of these internal cavities (negative crystals) in response to anneals of up to 128 h duration at 1900 degrees C was examined using optical microscopy. Surface energy anisotropy and faceting have a strong influence on both the geometric and kinetic characteristics of evolution. Decomposition of 12{bar 1}0 cavity edges into 101{bar 0} facets was observed after 16 h anneals, indicating that 12{bar 1}0 faces are not components of the Wulff shape.more » The shape evolution kinetics of penny-shaped cavities were also investigated. Experimentally observed evolution rates decreased much more rapidly with those predicted by a model in which surface diffusion is assumed to be rate-limiting. This suggests that the development of facets, and the associated loss of ledges and terraces during the initial stages of evolution results in an evolution process limited by the nucleation rate of attachment/detachment sites (ledges) on the facets.« less

Surface analysis of Fe-Co-Mo electrolytic coatings

NASA Astrophysics Data System (ADS)

Yar-Mukhamedova, G. Sh; Sakhnenko, N. D.; Ved', M. V.; Yermolenko, I. Yu; Zyubanova, S. I.

2017-06-01

Coatings Fe-Co-Mo with a composition of 47 at.% iron, 28 at.% Cobalt and 25 at.% Molybdenum were deposited from citrate electrolyte using pulse electrolysis mode. Scanning electron and atomic force microscopy have established the surface morphology and topography. It was identified the parts with a globular structure which have an average size of 0.2-0.5μm and singly located sharp grains. Within the same scan area sites with developed surface were detected the topography of which is identical to the crystal structure of cobalt with the crystallites size of 0.2-1.75μm. The parameters Ra and Rq for parts with different morphology as well as average characteristics of coatings demonstrated the low roughness of the surface. It is found that the coercive force of Fe-Co-Mo films is 7-10 Oe, which allow us to classify the Fe-Co-Mo coatings as soft magnetic materials.

Influence of Synthesis Temperature on the Growth and Surface Morphology of Co₃O₄ Nanocubes for Supercapacitor Applications.

PubMed

Samal, Rashmirekha; Dash, Barsha; Sarangi, Chinmaya Kumar; Sanjay, Kali; Subbaiah, Tondepu; Senanayake, Gamini; Minakshi, Manickam

2017-10-31

A facile hydrothermal route to control the crystal growth on the synthesis of Co₃O₄ nanostructures with cube-like morphologies has been reported and tested its suitability for supercapacitor applications. The chemical composition and morphologies of the as-prepared Co₃O₄ nanoparticles were extensively characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Varying the temperature caused considerable changes in the morphology, the electrochemical performance increased with rising temperature, and the redox reactions become more reversible. The results showed that the Co₃O₄ synthesized at a higher temperature (180 °C) demonstrated a high specific capacitance of 833 F/g. This is attributed to the optimal temperature and the controlled growth of nanocubes.

Growth and characterization of cubic SiC single-crystal films on Si

NASA Technical Reports Server (NTRS)

Powell, J. Anthony; Matus, L. G.; Kuczmarski, Maria A.

1987-01-01

Morphological and electrical characterization results are presented for cubic SiC films grown by chemical vapor deposition on single-crystal Si substrates. The films, up to 40 microns thick, were characterized by optical microscopy, (SEM), (TEM), electron channeling, surface profilometry, and Hall measurements. A variety of morphological features observed on the SiC films are described. Electrical measurements showed a decrease in the electron mobility with increasing electron carrier concentration, similar to that observed in Si. Room-temperature electron mobilities up to 520 sq cm/V-s (at an electron carrier concentration of 5 x 10 to the 16th/cu cm) were measured. Finally, a number of parameters believed to be important in the growth process were investigated, and some discussion is given of their possible effects on the film characteristics.

Growth and characterization of cubic SiC single-crystal films on Si

NASA Astrophysics Data System (ADS)

Powell, J. Anthony; Matus, L. G.; Kuczmarski, Maria A.

1987-06-01

Morphological and electrical characterization results are presented for cubic SiC films grown by chemical vapor deposition on single-crystal Si substrates. The films, up to 40 microns thick, were characterized by optical microscopy, (SEM), (TEM), electron channeling, surface profilometry, and Hall measurements. A variety of morphological features observed on the SiC films are described. Electrical measurements showed a decrease in the electron mobility with increasing electron carrier concentration, similar to that observed in Si. Room-temperature electron mobilities up to 520 sq cm/V-s (at an electron carrier concentration of 5 x 10 to the 16th/cu cm) were measured. Finally, a number of parameters believed to be important in the growth process were investigated, and some discussion is given of their possible effects on the film characteristics.

Epicuticular Wax Crystals of Wollemia nobilis: Morphology and Chemical Composition

PubMed Central

Dragota, Simona; Riederer, Markus

2007-01-01

Background and Aims The morphology of the epicuticular leaf waxes of Wollemia nobilis (Araucariaceae) was studied with special emphasis on the relationship between the microstructure of epicuticular wax crystals and their chemical composition. Wollemia nobilis is a unique coniferous tree of the family Araucariaceae and is of very high scientific value as it is the sole living representative of an ancient genus, which until 1994 was known only from fossils. Methods Scanning electron microscopy (SEM), gas chromatography (GC) combined with mass spectrometry (GC–MS) and nuclear magnetic resonance spectroscopy (NMR) were used for characterizing the morphology and the chemical structure of the epicuticular wax layer of W. nobilis needles. Key Results The main component of the leaf epicuticular wax of W. nobilis is nonacosan-10-ol. This secondary alcohol together with nonacosane diols is responsible for the tubular habit of the epicuticular wax crystals. Scanning electron micrographs revealed differences in the fine structure of adaxial and abaxial leaf surfaces that could be explained by gas chromatographic studies after selective mechanical removal of the waxes. Conclusions SEM investigations established the tubular crystalline microstructure of the epicuticular wax of W. nobilis leaves. GC–MS and NMR experiments showed that nonacosan-10-ol is the major constituent of the epicuticular wax of W. nobilis leaves. PMID:17611192

The influence of additives on the crystal habit of gibbsite

NASA Astrophysics Data System (ADS)

Seyssiecq, Isabelle; Veesler, Stéphane; Pèpe, Gérard; Boistelle, Roland

1999-01-01

Crystallization of gibbsite (Al(OH) 3) is an important stage of the Bayer process, production of alumina from bauxite ores. In both pure or industrial supersaturated sodium aluminate solutions, gibbsite crystals are always agglomerated. In the present paper, we present results of a study concerning the influence of different polycarboxylic acids as crystal habit modifier for gibbsite. In pure solution, agglomerated hexagonal plates are observed. Whereas acicular and tabular morphologies are found in the presence of different additives. These results are discussed referring to the crystallographic structure of gibbsite. It is found that only oxygen atoms are present on gibbsite surface. This observation leads us to propose an additive way of acting by formation of a molecular complex between the growth unit and the carboxylic groups of the additive.

Ray trace visualization of negative refraction of light in two-dimensional air-bridged silicon photonic crystal slabs at 1.55 microm.

PubMed

Gan, Lin; Liu, Ya-Zhao; Li, Jiang-Yan; Zhang, Ze-Bo; Zhang, Dao-Zhong; Li, Zhi-Yuan

2009-06-08

We demonstrate design, fabrication, and ray trace observation of negative refraction of near-infrared light in a two-dimensional square lattice of air holes etched into an air-bridged silicon slab. Special surface morphologies are designed to reduce the impedance mismatch when light refracts from a homogeneous silicon slab into the photonic crystal slab. We clearly observed negative refraction of infrared light for TE-like modes in a broad wavelength range by using scanning near-field optical microscopy technology. The experimental results are in good agreement with finite-difference time-domain simulations. The results indicate the designed photonic crystal structure can serve as polarization beam splitter.

Changing Morphology of BaO/AI₂O₃ during NO₂ Uptake and Release

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szanyi, Janos; Kwak, Ja Hun; Hanson, Jonathan

2005-04-21

The changes in the morphology of Ba-oxide-based NOx storage/reduction catalysts were investigated using time resolved x-ray diffraction, transmission electron microscopy and energy dispersed spectroscopy. Large Ba(NO₃)₂ crystallites form on the alumina support when the catalyst is prepared by the incipient wetness method using an aqueous Ba(NO₃)₂ solution. Heating the sample to 873K in a He flow results in the decomposition of the Ba(NO₃)₂ phase and the formation of both a monolayer BaO film strongly interacting with the alumina support, and nano crystalline BaO particles. Upon NO₂ exposure of these BaO phases at room temperature, small (nano-sized) Ba(NO₃)₂ crystals and amore » monolayer of surface nitrate form. Heating this sample in NO₂ results in the coalescence of the nano crystalline Ba(NO₃)₂ particles into large crystals. The average crystal size in the re-formed Ba(NO₃)₂ layer is significantly smaller than that measured after the catalyst preparation. Evidence is also presented for the existence of a monolayer Ba(NO₃)₂ phase after thermal treatment in NO₂, in addition to these large crystals. These results clearly demonstrate the dynamic nature of the Ba-containing phases that are active in the NOx storage/reduction process. The proposed morphology cycle may contribute to the understanding of the changes observed in the performances of these catalysts during actual operating conditions.« less

Multipulse nanosecond laser irradiation of silicon for the investigation of surface morphology and photoelectric properties

NASA Astrophysics Data System (ADS)

Sardar, Maryam; Chen, Jun; Ullah, Zaka; Jelani, Mohsan; Tabassum, Aasma; Cheng, Ju; Sun, Yuxiang; Lu, Jian

2017-12-01

We irradiate the single crystal boron-doped silicon (Si) with different number of laser pulses at constant fluence (7.5 J cm-2) in ambient air using Nd:YAG laser and examine its surface morphology and photoelectric properties in details. The results obtained from optical micrographs reveal the increase in heat affected zone (HAZ) and melted area of laser irradiated Si with increasing number of laser pulses. The SEM micrographs evidence the formation of various surface morphologies like laser induced periodic surface structures, crater, microcracks, clusters, cavities, pores, trapped bubbles, nucleation sites, micro-bumps, redeposited material and micro- and nano-particles on the surface of irradiated Si. The surface profilometry analysis informs that the depth of crater is increased with increase in number of incident laser pulses. The spectroscopic ellipsometry reveals that the multipulse irradiation of Si changes its optical properties (refractive index and extinction coefficient). The current-voltage (I-V) characteristic curves of laser irradiated Si show that although the multipulse laser irradiation produces considerable number of surface defects and damages, the electrical properties of Si are well sustained after the multipulse irradiation. The current findings suggest that the multipulse irradiation can be an effective way to tune the optical properties of Si for the fabrication of wide range of optoelectronic devices.

The effect of environmentally friendly hot-dipping auxiliary on the morphology of alloy coatings

NASA Astrophysics Data System (ADS)

Chen, Suhong; Guo, Kai; Zhu, Yi; Gao, Feng; Han, Zhijun

2017-10-01

Zn-Al-Mg-RE hot-dip alloy coatings which prepared by the environmentally friendly plating auxiliary were investigated by X-ray diffraction (XRD), SEM analysis and salt spray measurement. Significant variation in coating surface morphology and element content are observed with increasing content of Al and Mg in this paper. A reinforced ternary eutectic Zn-Al-MgZn2 is confirmed which attribute to improvement metallographic structure derived from certain ternary eutectic reaction in alloy solidification. For Mg-containing coatings, the enhanced corrosion resistance is observed by corrosion resistance test in salt spray at 35°C with 5% NaCl in terms of corrosion weight changes. It is found that the incorporation of 3 wt.% Mg and 0.1 wt.% rare earth element in to Zn-Al-Mg-RE bath caused structural refinement of the crystal and also helped to achieve excellent surface morphology.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, B.; Renaut, R.W.

Complex calcite crystals are an integral component of precipitates that form around the orifices of the Loburu and Mawe Moto hot springs on the shores of Lake bogoria, Kenya. Two types of large (up to 4 cm long) noncrystallographic dendrites are important components of these deposits. Feather dendrites are characterized by multiple levels of branching with individual branches developed through crystal splitting and spherulitic growth. Scandulitic (from Latin meaning shingle) dendrites are formed of stacked calcite crystals and are generally more compact than feather dendrites. These developed through the incremental stacking of rectangular-shaped calcite crystals that initially grew as skeletalmore » crystals. Feather and scandulitic dendrites precipitated from the same waters in the same springs. The difference in morphology is therefore related to microenvironments in which they grew. Feather dendrites grew in any direction in pools of free-standing water provided that they were in constant contact with the solute. Conversely, scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water. Thus, each calcite crystal in these dendrites represents one episode of crystal growth. The orientation of the component crystals in scandulitic dendrites is controlled by the topography of the dam or surface, not crystallographic criteria. The noncrystallographic dendrites formed from spring waters with initial temperatures of 90--99 C. Surficial water cooling, loss of CO{sub 2}, and presence of other elements that can interfere with crystal growth contributed to the formation of these unusual crystals.« less

Optimisation of powders for pulmonary delivery using supercritical fluid technology.

PubMed

Rehman, Mahboob; Shekunov, Boris Y; York, Peter; Lechuga-Ballesteros, David; Miller, Danforth P; Tan, Trixie; Colthorpe, Paul

2004-05-01

Supercritical fluid technology exploited in this work afforded single-step production of respirable particles of terbutaline sulphate (TBS). Different crystal forms of TBS were produced consistently, including two polymorphs, a stoichiometric monohydrate and amorphous material as well as particles with different degrees of crystallinity, size, and morphology. Different solid-state and surface characterisation techniques were applied in conjunction with measurements of powder flow properties using AeroFlow device and aerosol performance by Andersen Cascade Impactor tests. Improved fine particle fraction (FPF) was demonstrated for some powders produced by the SCF process when compared to the micronised material. Such enhanced flow properties and dispersion correlated well with the reduced surface energy parameters demonstrated by these powders. It is shown that semi-crystalline particles exhibited lower specific surface energy leading to a better performance in the powder flow and aerosol tests than crystalline materials. This difference of the surface and bulk crystal structure for selected powder batches is explained by the mechanism of precipitation in SCF which can lead to surface conditioning of particles produced.

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

NASA Technical Reports Server (NTRS)

Malkin, Alexander J.

1998-01-01

During the past year we have focused on application of in situ Atomic Force Microscopy (AFM) for studies of the growth mechanisms and kinetics of crystallization for different macromolecular systems. Mechanisms of macrostep formation and their decay, which are important in understanding of defect formation, were studied on the surfaces of thaumatin, catalase, canavalin and lysozyme crystals. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. No step bunching arising from interaction of individual steps in the course of the experiment was observed. The molecular structure of the growth steps for thaumatin and lipase crystals were deduced. It was further shown that growth step advance occurs by incorporation of single protein molecules. In singular directions growth steps move by one-dimensional nucleation on step edges followed by lateral growth. One-dimensional nuclei have different sizes, less then a single unit cell, varying for different directions of step movement. There is no roughness due to thermal fluctuations, and each protein molecule which incorporated into the step remained. Growth kinetics for catalase crystals was investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. The influence of impurities on growth kinetics and cessation of macromolecular crystals was studied. Thus, for catalase, in addition to pronounced impurity effects on the kinetics of crystallization, we were also able to directly observe adsorption of some impurities. At low supersaturation we repeatedly observed filaments which formed from impurity molecules sedimenting on the surfaces. Similar filaments were observed on the surfaces of thaumatin, canavalin and STMV crystals as well, but the frequency was low compared with catalase crystallization. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Attachment: "An in situ AFM investigation of catalase crystallization", "Atomic force microscopy studies of living cells: visualization of motility, division, aggregation, transformation, and apoptosis", AFM studies on mechanisms of nucleation and growth of macromolecular crystals", and "In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization".

Protein-free formation of bone-like apatite: New insights into the key role of carbonation

PubMed Central

Deymier, Alix C.; Nair, Arun K.; Depalle, Baptiste; Qin, Zhao; Arcot, Kashyap; Drouet, Christophe; Yoder, Claude H.; Buehler, Markus J.; Thomopoulos, Stavros; Genin, Guy M.; Pasteris, Jill D.

2017-01-01

The nanometer-sized plate-like morphology of bone mineral is necessary for proper bone mechanics and physiology. However, mechanisms regulating the morphology of these mineral nanocrystals remain unclear. The dominant hypothesis attributes the size and shape regulation to organic-mineral interactions. Here, we present data supporting the hypothesis that physicochemical effects of carbonate integration within the apatite lattice control the morphology, size, and mechanics of bioapatite mineral crystals. Carbonated apatites synthesized in the absence of organic molecules presented plate-like morphologies and nanoscale crystallite dimensions. Experimentally-determined crystallite size, lattice spacing, solubility and atomic order were modified by carbonate concentration. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations predicted changes in surface energy and elastic moduli with carbonate concentration. Combining these results with a scaling law predicted the experimentally observed scaling of size and energetics with carbonate concentration. The experiments and models describe a clear mechanism by which crystal dimensions are controlled by carbonate substitution. Furthermore, the results demonstrate that carbonate substitution is sufficient to drive the formation of bone-like crystallites. This new understanding points to pathways for biomimetic synthesis of novel, nanostructured biomaterials. PMID:28279923

Application Of Empirical Phase Diagrams For Multidimensional Data Visualization Of High Throughput Microbatch Crystallization Experiments.

PubMed

Klijn, Marieke E; Hubbuch, Jürgen

2018-04-27

Protein phase diagrams are a tool to investigate cause and consequence of solution conditions on protein phase behavior. The effects are scored according to aggregation morphologies such as crystals or amorphous precipitates. Solution conditions affect morphological features, such as crystal size, as well as kinetic features, such as crystal growth time. Common used data visualization techniques include individual line graphs or symbols-based phase diagrams. These techniques have limitations in terms of handling large datasets, comprehensiveness or completeness. To eliminate these limitations, morphological and kinetic features obtained from crystallization images generated with high throughput microbatch experiments have been visualized with radar charts in combination with the empirical phase diagram (EPD) method. Morphological features (crystal size, shape, and number, as well as precipitate size) and kinetic features (crystal and precipitate onset and growth time) are extracted for 768 solutions with varying chicken egg white lysozyme concentration, salt type, ionic strength and pH. Image-based aggregation morphology and kinetic features were compiled into a single and easily interpretable figure, thereby showing that the EPD method can support high throughput crystallization experiments in its data amount as well as its data complexity. Copyright © 2018. Published by Elsevier Inc.

Procedures for analysis of debris relative to Space Shuttle systems

NASA Technical Reports Server (NTRS)

Kim, Hae Soo; Cummings, Virginia J.

1993-01-01

Debris samples collected from various Space Shuttle systems have been submitted to the Microchemical Analysis Branch. This investigation was initiated to develop optimal techniques for the analysis of debris. Optical microscopy provides information about the morphology and size of crystallites, particle sizes, amorphous phases, glass phases, and poorly crystallized materials. Scanning electron microscopy with energy dispersive spectrometry is utilized for information on surface morphology and qualitative elemental content of debris. Analytical electron microscopy with wavelength dispersive spectrometry provides information on the quantitative elemental content of debris.

Crystal Growth and Dissolution of Methylammonium Lead Iodide Perovskite in Sequential Deposition: Correlation between Morphology Evolution and Photovoltaic Performance.

PubMed

Hsieh, Tsung-Yu; Huang, Chi-Kai; Su, Tzu-Sen; Hong, Cheng-You; Wei, Tzu-Chien

2017-03-15

Crystal morphology and structure are important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electronic, and photovoltaic devices. In particular, crystal growth and dissolution are two major phenomena in determining the morphology of methylammonium lead iodide perovskite in the sequential deposition method for fabricating a perovskite solar cell. In this report, the effect of immersion time in the second step, i.e., methlyammonium iodide immersion in the morphological, structural, optical, and photovoltaic evolution, is extensively investigated. Supported by experimental evidence, a five-staged, time-dependent evolution of the morphology of methylammonium lead iodide perovskite crystals is established and is well connected to the photovoltaic performance. This result is beneficial for engineering optimal time for methylammonium iodide immersion and converging the solar cell performance in the sequential deposition route. Meanwhile, our result suggests that large, well-faceted methylammonium lead iodide perovskite single crystal may be incubated by solution process. This offers a low cost route for synthesizing perovskite single crystal.

A study of structural and mechanical properties of nano-crystalline tungsten nitride film synthesis by plasma focus

NASA Astrophysics Data System (ADS)

Hussnain, Ali; Singh Rawat, Rajdeep; Ahmad, Riaz; Hussain, Tousif; Umar, Z. A.; Ikhlaq, Uzma; Chen, Zhong; Shen, Lu

2015-02-01

Nano-crystalline tungsten nitride thin films are synthesized on AISI-304 steel at room temperature using Mather-type plasma focus system. The surface properties of the exposed substrate against different deposition shots are examined for crystal structure, surface morphology and mechanical properties using X-ray diffraction (XRD), atomic force microscope, field emission scanning electron microscope and nano-indenter. The XRD results show the growth of WN and WN2 phases and the development of strain/stress in the deposited films by varying the number of deposition shots. Morphology of deposited films shows the significant change in the surface structure with different ion energy doses (number of deposition shots). Due to the effect of different ion energy doses, the strain/stress developed in the deposited film leads to an improvement of hardness of deposited films.

Modelling morphology evolution during solidification of IPP in processing conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pantani, R., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it; De Santis, F., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it; Speranza, V., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it

During polymer processing, crystallization takes place during or soon after flow. In most of cases, the flow field dramatically influences both the crystallization kinetics and the crystal morphology. On their turn, crystallinity and morphology affect product properties. Consequently, in the last decade, researchers tried to identify the main parameters determining crystallinity and morphology evolution during solidification In processing conditions. In this work, we present an approach to model flow-induced crystallization with the aim of predicting the morphology after processing. The approach is based on: interpretation of the FIC as the effect of molecular stretch on the thermodynamic crystallization temperature; modelingmore » the molecular stretch evolution by means of a model simple and easy to be implemented in polymer processing simulation codes; identification of the effect of flow on nucleation density and spherulites growth rate by means of simple experiments; determination of the condition under which fibers form instead of spherulites. Model predictions reproduce most of the features of final morphology observed in the samples after solidification.« less

Investigation of the operating conditions to morphology evolution of β-L-glutamic acid during seeded cooling crystallization

NASA Astrophysics Data System (ADS)

Zhang, Fangkun; Liu, Tao; Huo, Yan; Guan, Runduo; Wang, Xue Z.

2017-07-01

In this paper the effects of operating conditions including cooling rate, initial supersaturation, and seeding temperature were investigated on the morphology evolution of β-L-glutamic acid (β-LGA) during seeded cooling crystallization. Based on the results of in-situ image acquisition of the crystal morphology evolution during the crystallization process, it was found that the crystal products tend to be plate-like or short rod-like under a slow cooling rate, low initial supersaturation, and low seeding temperature. In the opposite, the operating conditions of a faster cooling rate, higher initial supersaturation, and higher seeding temperature tend to produce long rod-like or needle-like crystals, and meanwhile, the length and width of crystal products will be increased together with a wider crystal size distribution (CSD). The aspect ratio of crystals, defined by the crystal length over width measured from in-situ or sample images, was taken as a shape index to analyze the crystal morphologies. Based on comparative analysis of the experimental results, guidelines on these operating conditions were given for obtaining the desired crystal shapes, along with the strategies for obtaining a narrower CSD for better product quality. Experimental verifications were performed to illustrate the proposed guidelines on the operating conditions for seeded cooling crystallization of LGA solution.

The study of VOPc thin film transistors on modified substrates

NASA Astrophysics Data System (ADS)

Song, De; Xu, Qi; Cheng, Hongcang; Li, Bao-zeng; Shang, Yubin

2018-02-01

The vanadyl phthalocyanine (VOPc) organic thin film transistors (OTFTs) were fabricated on the various organosilane self-assembled monolayer (SAM) modified substrates. And the effect of the surface properties on the performance of these transistors was studied. The atomic force morphologies and X-ray diffraction (XRD) spectrums of vanadyl phthalocyanine films on different SAM-modified surfaces were studied. They reveal that the terminal functional groups of organosilane affect the growth of VOPc film and device performance. The VOPc film on octadecyltrichlorosilane (OTS) modified substrate has larger crystal size and effective crystal thickness than those on phenyltrichlorosilane (PTS), 1H,1H,2H,2H-Perfluorodec-yltrichlorosilane (FDTS) as well as non-modified substrate, which contributes the mobility of corresponding device several and several dozen times relative to other ones. The effective crystal thickness and crystal grain size of VOPc film on PTS is between that on OTS treated and that on non-modified substrate due to the stronger attractive force between VOPc and SiO2. The VOPc films' performance and effective crystal thickness on FDTS treated are worse than that on PTS due to the existents of attractive force between -CF3 and VOPc.

Zinc-Nucleated D 2 and H 2 Crystal Formation from Their Liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernat, T. P.; Petta, N.; Kozioziemski, B.

Calorimetric measurements at University of Rochester Laboratory for Laser Energetics of D 2 crystallization from the melt indicate that zinc can act as a heterogeneous nucleation seed with suppressed supercooling. We further studied in this paper this effect for a variety of zinc substrates using the optical-access cryogenic sample cell at Lawrence Livermore National Laboratory. Small supercoolings are observed, some as low as 5 mK, but results depend on the zinc history and sample preparation. In general, thin samples prepared by physical vapor deposition were not effective in nucleating crystal formation. Larger (several-millimeter) granules showed greater supercooling suppression, depending onmore » surface modification and granule size. Surfaces of these granules are morphologically varied and not uniform. Scanning electron microscope images were not able to correlate any particular surface feature with enhanced nucleation. Finally, application of classical nucleation theory to the observed variation of supercooling level with granule size is consistent with nucleation features with sizes <100 nm and with wetting angles of a few degrees.« less

Zinc-Nucleated D 2 and H 2 Crystal Formation from Their Liquids

DOE PAGES

Bernat, T. P.; Petta, N.; Kozioziemski, B.; ...

2016-09-01

Calorimetric measurements at University of Rochester Laboratory for Laser Energetics of D 2 crystallization from the melt indicate that zinc can act as a heterogeneous nucleation seed with suppressed supercooling. We further studied in this paper this effect for a variety of zinc substrates using the optical-access cryogenic sample cell at Lawrence Livermore National Laboratory. Small supercoolings are observed, some as low as 5 mK, but results depend on the zinc history and sample preparation. In general, thin samples prepared by physical vapor deposition were not effective in nucleating crystal formation. Larger (several-millimeter) granules showed greater supercooling suppression, depending onmore » surface modification and granule size. Surfaces of these granules are morphologically varied and not uniform. Scanning electron microscope images were not able to correlate any particular surface feature with enhanced nucleation. Finally, application of classical nucleation theory to the observed variation of supercooling level with granule size is consistent with nucleation features with sizes <100 nm and with wetting angles of a few degrees.« less

Biocompatibility of GaSb thin films grown by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Nishimoto, Naoki; Fujihara, Junko; Yoshino, Katsumi

2017-07-01

GaSb may be suitable for biological applications, such as cellular sensors and bio-medical instrumentation because of its low toxicity compared with As (III) compounds and its band gap energy. Therefore, the biocompatibility and the film properties under physiological conditions were investigated for GaSb thin films with or without a surface coating. GaSb thin films were grown on quartz substrates by RF magnetron sputtering, and then coated with (3-mercaptopropyl) trimethoxysilane (MPT). The electrical properties, surface morphology, and crystal structure of the GaSb thin film were unaffected by the MPT coating. The cell viability assay suggested that MPT-coated GaSb thin films are biocompatible. Bare GaSb was particularly unstable in pH9 buffer. Ga elution was prevented by the MPT coating, although the Ga concentration in the pH 9 buffer was higher than that in the other solutions. The surface morphology and crystal structure were not changed by exposure to the solutions, except for the pH 9 buffer, and the thin film properties of MPT-coated GaSb exposed to distilled water and H2O2 in saline were maintained. These results indicate that MPT-coated GaSb thin films are biocompatible and could be used for temporary biomedical devices.

Growth morphologies of wax in the presence of kinetic inhibitors

NASA Astrophysics Data System (ADS)

Tetervak, Alexander A.

Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphologies. Although the utility of these kinetic inhibitors has been well demonstrated in the field, few studies have directly monitored their effect at microscopic morphology, and the mechanisms by which they act remain poorly understood. Here we present a study of the effects of such additives on the crystallization of long-chain n-alkanes from solution. The additives change the growth morphology from plate-like crystals to a microcrystalline mesh. When we impose a front velocity by moving the sample through a temperature gradient, the mesh growth may form a macroscopic banded pattern and also exhibit a burst-crystallization behavior. In this study, we characterize these crystallization phenomena and also two growth models: a continuum model that demonstrates the essential behavior of the banded crystallization, and a simple qualitative cellular automata model that captures basics of the burst-crystallization process. Keywords: solidification; mesh crystallization; kinetic inhibitor; burst growth.

Unsteady Crystal Growth Due to Step-Bunch Cascading

NASA Technical Reports Server (NTRS)

Vekilov, Peter G.; Lin, Hong; Rosenberger, Franz

1997-01-01

Based on our experimental findings of growth rate fluctuations during the crystallization of the protein lysozym, we have developed a numerical model that combines diffusion in the bulk of a solution with diffusive transport to microscopic growth steps that propagate on a finite crystal facet. Nonlinearities in layer growth kinetics arising from step interaction by bulk and surface diffusion, and from step generation by surface nucleation, are taken into account. On evaluation of the model with properties characteristic for the solute transport, and the generation and propagation of steps in the lysozyme system, growth rate fluctuations of the same magnitude and characteristic time, as in the experiments, are obtained. The fluctuation time scale is large compared to that of step generation. Variations of the governing parameters of the model reveal that both the nonlinearity in step kinetics and mixed transport-kinetics control of the crystallization process are necessary conditions for the fluctuations. On a microscopic scale, the fluctuations are associated with a morphological instability of the vicinal face, in which a step bunch triggers a cascade of new step bunches through the microscopic interfacial supersaturation distribution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohri, Maryam, E-mail: mmohri@ut.ac.ir; Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe; Nili-Ahmadabadi, Mahmoud

The crystallization of Ni-rich/NiTiCu bi-layer thin film deposited by magnetron sputtering from two separate alloy targets was investigated. To achieve the shape memory effect, the NiTi thin films deposited at room temperature with amorphous structure were annealed at 773 K for 15, 30, and 60 min for crystallization. Characterization of the films was carried out by differential scanning calorimetry to indicate the crystallization temperature, grazing incidence X-ray diffraction to identify the phase structures, atomic force microscopy to evaluate surface morphology, scanning transmission electron microscopy to study the cross section of the thin films. The results show that the structure ofmore » the annealed thin films strongly depends on the temperature and time of the annealing. Crystalline grains nucleated first at the surface and then grew inward to form columnar grains. Furthermore, the crystallization behavior was markedly affected by composition variations. - Highlights: • A developed bi-layer Ni45TiCu5/Ni50.8Ti was deposited on Si substrate and crystallized. • During crystallization, The Ni{sub 45}TiCu{sub 5} layer is thermally less stable than the Ni-rich layer. • The activation energy is 302 and 464 kJ/mol for Cu-rich and Ni-rich layer in bi-layer, respectively.« less

Effects of B2O3 content and sintering temperature on crystallization and microstructure of CBS glass-ceramic coatings

NASA Astrophysics Data System (ADS)

Li, Pengyang; Wang, Shubin; Liu, Jianggao; Feng, Mengjie; Yang, Xinwang

2015-11-01

Borosilicate glass-ceramics precursors with varying compositional ratios in the CaO-SiO2-B2O3 (CBS) system were synthesized by sol-gel method. The precursors were calcined at 1200 °C for 2 h to form glass powders. The glass-ceramics were prepared by overlaying glass slurries on the substrates before sintering at different temperatures. The as-prepared glasses and glass-ceramics were characterized by differential scanning calorimetry and X-ray diffraction. The crystallization activation energies (Ec) were calculated using the Kissinger method from DSC results. The morphology and crystallization behavior of the glass-ceramics were monitored by scanning electron microscopy. Both glass transition and crystallization temperatures decreased, however, the metastable zone increased. The Ec values of CBS glasses and glass-ceramics were 254.1, 173.2 and 164.4 kJ/mol with increasing B2O3 content, whereas that of the calcined G3 glass was 104.9 kJ/mol. Finally, the coatings were prepared at a low temperature (700 °C). The crystals that grew on the surface of multilayer coatings demonstrated heterogeneous surface nucleation and crystallization after heat-treatment from 700 °C to 850 °C for 4 h.

Fractals and foods.

PubMed

Peleg, M

1993-01-01

Fractal geometry and related concepts have had only a very minor impact on food research. The very few reported food applications deal mainly with the characterization of the contours of agglomerated instant coffee particles, the surface morphology of treated starch particles, the microstructure of casein gels viewed as a product limited diffusion aggregation, and the jagged mechanical signatures of crunchy dry foods. Fractal geometry describes objects having morphological features that are scale invariant. A demonstration of the self-similarity of fractal objects can be found in the familiar morphology of cauliflower and broccoli, both foods. Processes regulated by nonlinear dynamics can exhibit a chaotic behavior that has fractal characteristics. Examples are mixing of viscous fluids, turbulence, crystallization, agglomeration, diffusion, and possibly food spoilage.

Abnormal growth kinetics of h-BN epitaxial monolayer on Ru(0001) enhanced by subsurface Ar species

NASA Astrophysics Data System (ADS)

Wei, Wei; Meng, Jie; Meng, Caixia; Ning, Yanxiao; Li, Qunxiang; Fu, Qiang; Bao, Xinhe

2018-04-01

Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a "fractal-to-compact" morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal "compact-to-fractal" morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology.

Influence of surface morphology on the immersion mode ice nucleation efficiency of hematite particles

NASA Astrophysics Data System (ADS)

Hiranuma, N.; Hoffmann, N.; Kiselev, A.; Dreyer, A.; Zhang, K.; Kulkarni, G.; Koop, T.; Möhler, O.

2014-03-01

In this paper, the effect of the morphological modification of aerosol particles with respect to heterogeneous ice nucleation is comprehensively investigated for laboratory-generated hematite particles as a model substrate for atmospheric dust particles. The surface-area-scaled ice nucleation efficiencies of monodisperse cubic hematite particles and milled hematite particles were measured with a series of expansion cooling experiments using the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud simulation chamber. Complementary offline characterization of physico-chemical properties of both hematite subsets were also carried out with scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS), and an electro-kinetic particle charge detector to further constrain droplet-freezing measurements of hematite particles. Additionally, an empirical parameterization derived from our laboratory measurements was implemented in the single-column version of the Community Atmospheric Model version 5 (CAM5) to investigate the model sensitivity in simulated ice crystal number concentration on different ice nucleation efficiencies. From an experimental perspective, our results show that the immersion mode ice nucleation efficiency of milled hematite particles is almost an order of magnitude higher at -35.2 °C < T < -33.5 °C than that of the cubic hematite particles, indicating a substantial effect of morphological irregularities on immersion mode freezing. Our modeling results similarly show that the increased droplet-freezing rates of milled hematite particles lead to about one order magnitude higher ice crystal number in the upper troposphere than cubic hematite particles. Overall, our results suggest that the surface irregularities and associated active sites lead to greater ice activation through droplet freezing.

Controlling periodic ripple microstructure formation on 4H-SiC crystal with three time-delayed femtosecond laser beams of different linear polarizations.

PubMed

He, Wanlin; Yang, Jianjun; Guo, Chunlei

2017-03-06

The control of laser-induced periodic ripple microstructures on 4H-SiC crystal surface is studied using temporally delayed collinear three femtosecond laser pulse trains linearly polarized in different directions. The ripple orientation appears to develop independent of the individual laser polarizations and exhibits non-monotonical change with variable time delays, whose variation tendency is also affected by the polarization intersection angles. Remarkably, the ripple period is observed to transfer from high- to low-spatial-frequency regions, accompanied by distinctly improved morphological uniformity and clearness. The results are satisfactorily interpreted based on a physical model of the surface wave excitation on a transient index metasurface, which is confirmed by further experiments. Our investigations indicate that transient noneqilibrium dynamics of the material surface provides an effective way to manipulate the laser-induced microstructures.

Influence of Synthesis Temperature on the Growth and Surface Morphology of Co3O4 Nanocubes for Supercapacitor Applications

PubMed Central

Samal, Rashmirekha; Dash, Barsha; Sarangi, Chinmaya Kumar; Subbaiah, Tondepu; Senanayake, Gamini; Minakshi, Manickam

2017-01-01

A facile hydrothermal route to control the crystal growth on the synthesis of Co3O4 nanostructures with cube-like morphologies has been reported and tested its suitability for supercapacitor applications. The chemical composition and morphologies of the as-prepared Co3O4 nanoparticles were extensively characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Varying the temperature caused considerable changes in the morphology, the electrochemical performance increased with rising temperature, and the redox reactions become more reversible. The results showed that the Co3O4 synthesized at a higher temperature (180 °C) demonstrated a high specific capacitance of 833 F/g. This is attributed to the optimal temperature and the controlled growth of nanocubes. PMID:29088061

Surface or internal nucleation and crystallization of glass-ceramics

NASA Astrophysics Data System (ADS)

Höland, W.; Rheinberger, V. M.; Ritzberger, C.; Apel, E.

2013-07-01

Fluoroapatite (Ca5(PO4)3F) was precipitated in glass-ceramics via internal crystallization of base glasses. The crystals grew with a needle-like morphology in the direction of the crystallographic c-axis. Two different reaction mechanisms were analyzed: precipitation via a disordered primary apatite crystals and a solid state parallel reaction to rhenanite (NaCaPO4) precipitation. In contrast to the internal nucleation used in the formation of fluoroapatite, surface crystallization was induced to precipitate a phosphate-free oxyapatite of NaY9(SiO4)6O2-type. Internal nucleation and crystallization have been shown to be a very useful tool for developing high-strength lithium disilicate (Li2Si2O5) glass-ceramics. A very controlled process was conducted to transform the lithium metasilicate glass-ceramic precursor material into the final product of the lithium disilicate glass-ceramic without the major phase of the precursor material. The combination of all these methods allowed the driving forces of the internal nucleation and crystallization mechanisms to be explained. An amorphous phosphate primary phase was discovered in the process. Nucleation started at the interface between the amorphous phosphate phase and the glass matrix. The final products of all these glass-ceramics are biomaterials for dental restoration showing special optical properties, e.g. translucence and color close to dental teeth.

Two temperature approach to femtosecond laser oxidation of molybdenum and morphological study

NASA Astrophysics Data System (ADS)

Kotsedi, L.; Kaviyarasu, K.; Fuku, X. G.; Eaton, S. M.; Amara, E. H.; Bireche, F.; Ramponi, R.; Maaza, M.

2017-11-01

The two-temperature model was used to gain insight into the thermal evolution of the hot electrons and the crystal lattice of the molybdenum thin coating during femtosecond laser treatment. The heat from the laser raised the bulk temperature of the sample through heat transfer from the hot electron to the crystal lattice of the material, which then led to the melting of the top layer of the film. This process resulted in the hot melt reacting ambient oxygen, which in turn oxidized the surface of molybdenum coating. The topological study and morphology of the oxidized film was conducted using high-resolution scanning electron microscope, with micrographs taken in both the cross-sectional geometry and normal incidence to the electron beam. The molybdenum oxide nanorods were clearly observed and the x-ray diffraction patterns showed the diffraction peaks due to molybdenum oxide.

Understanding Crystal Populations: The Role of Textural Analysis in Determining Magmatic Timescales

NASA Astrophysics Data System (ADS)

Jerram, D. A.

2006-12-01

Crystal populations in igneous rocks that erupt at the Earths surface act as records of magma chamber processes at depth, predominantly recording episodes of growth/nucleation and geochemical changes within the host body. Detailed inspection of such crystal populations, however, reveals a complex crystal cargo that comprises crystals which have grown directly from the host, crystals that have spent one or more protracted periods being isolated from the host magma and crystals that originated from a completely different magma body and/or country rock. To further interrogate this crystal cargo we can use textural analysis techniques to fully quantify the crystal population and gather important information about the population, such as crystal morphology, spatial distribution and size relationships. When quantified, such data can be used to better constrain the different components of the resultant crystal population and how they relate to each other. Additionally, by combining textural analysis information with geochemical analysis, a powerful measure of magma timescales and magma chamber processes results. In this contribution the different types of textural analysis techniques in 2D and 3D are introduced with examples from both plutonic and volcanic systems presented to highlight the roll of this approach to quantifying magma timescales.

Improving the diffraction of apoA-IV crystals through extreme dehydration.

PubMed

Deng, Xiaodi; Davidson, W Sean; Thompson, Thomas B

2012-01-01

Apolipoproteins are the protein component of high-density lipoproteins (HDL), which are necessary for mobilizing lipid-like molecules throughout the body. Apolipoproteins undergo self-association, especially at higher concentrations, making them difficult to crystallize. Here, the crystallization and diffraction of the core fragment of apolipoprotein A-IV (apoA-IV), consisting of residues 64-335, is presented. ApoA-IV(64-335) crystallized readily in a variety of hexagonal (P6) morphologies with similar unit-cell parameters, all containing a long axis of nearly 550 Å in length. Preliminary diffraction experiments with the different crystal morphologies all resulted in limited streaky diffraction to 3.5 Å resolution. Crystal dehydration was applied to the different morphologies with variable success and was also used as a quality indicator of crystal-growth conditions. The results show that the morphologies that withstood the most extreme dehydration conditions showed the greatest improvement in diffraction. One morphology in particular was able to withstand dehydration in 60% PEG 3350 for over 12 h, which resulted in well defined intensities to 2.7 Å resolution. These results suggest that the approach of integrating dehydration with variation in crystal-growth conditions might be a general technique to optimize diffraction. © 2012 International Union of Crystallography. All rights reserved.

Dissipating Step Bunches during Crystallization under Transport Control

NASA Technical Reports Server (NTRS)

Lin, Hong; Yau, S.-T.; Vekilov, Peter, G.

2003-01-01

In studies of crystal formation by the generation and spreading of layers, equidistant step trains are considered unstable---bunches and other spatiotemporal patterns of the growth steps are viewed as ubiquitous. We provide an example to the opposite. We monitor the spatiotemporal dynamics of steps and the resulting step patterns during crystallization of the proteins ferritin and apoferritin using the atomic force microscope. The variations in step velocity and density are not correlated, indicating the lack of a long-range attraction between the steps. We show that (i) because of its coupling to bulk transport, nucleation of new layers is chaotic and occurs at the facet edges, where the interfacial supersaturation is higher; (ii) step bunches self-organize via the competition for supply from the solution; and, (iii) bunches of weakly interacting steps decay as they move along the face. Tests by numerical modeling support the conclusions about the mechanisms underlying our observations. The results from these systems suggest that during crystallization controlled by transport, with weakly or noninteracting growth steps, the stable kinetic state of the surface is an equidistant step train, and step bunches only arise during nucleation of new layers. Since nucleation only occurs at a few sites on the surface, the surface morphology may be controllably patterned or smoothened by locally controlling nucleation.

Impact of interaction range and curvature on crystal growth of particles confined to spherical surfaces.

PubMed

Paquay, Stefan; Both, Gert-Jan; van der Schoot, Paul

2017-07-01

When colloidal particles form a crystal phase on a spherical template, their packing is governed by the effective interaction between them and the elastic strain of bending the growing crystal. For example, if growth commences under appropriate conditions, and the isotropic crystal that forms reaches a critical size, growth continues via the incorporation of defects to alleviate elastic strain. Recently, it was experimentally found that, if defect formation is somehow not possible, the crystal instead continues growing in ribbons that protrude from the original crystal. Here we report on computer simulations in which we observe both the formation of ribbons at short interaction ranges and packings that incorporate defects if the interaction is longer-ranged. The ribbons only form above some critical crystal size, below which the nucleus is disk-shaped. We find that the scaling of the critical crystal size differs slightly from the one proposed in the literature, and we argue that this is because the actual morphology transition is caused by the competition between line tension and elastic stress, rather than the competition between chemical potential and elastic stress.

Impact of interaction range and curvature on crystal growth of particles confined to spherical surfaces

NASA Astrophysics Data System (ADS)

Paquay, Stefan; Both, Gert-Jan; van der Schoot, Paul

2017-07-01

When colloidal particles form a crystal phase on a spherical template, their packing is governed by the effective interaction between them and the elastic strain of bending the growing crystal. For example, if growth commences under appropriate conditions, and the isotropic crystal that forms reaches a critical size, growth continues via the incorporation of defects to alleviate elastic strain. Recently, it was experimentally found that, if defect formation is somehow not possible, the crystal instead continues growing in ribbons that protrude from the original crystal. Here we report on computer simulations in which we observe both the formation of ribbons at short interaction ranges and packings that incorporate defects if the interaction is longer-ranged. The ribbons only form above some critical crystal size, below which the nucleus is disk-shaped. We find that the scaling of the critical crystal size differs slightly from the one proposed in the literature, and we argue that this is because the actual morphology transition is caused by the competition between line tension and elastic stress, rather than the competition between chemical potential and elastic stress.

Crystallization of Polymers in Confined Environments: Structural Development of Semi-crystalline Polymer-Layered Silicate Nanocomposites

NASA Astrophysics Data System (ADS)

Vaia, Richard A.; Lincoln, Derek M.; Wang, Zhi-Gang; Hsiao, Benjamin S.; Krishnamoorti, Ramanan

2000-03-01

Over the last decade, the utility of ultrafine dispersions of inorganic nanoparticles to enhance polymer performance and function as precursors to form self-passivating / self-healing inorganic coatings on the polymer surface has been established. Before developing the fundamental structure-property relationships though, a detailed understanding of processing / morphology relationships is necessary. As with other multiphase systems exhibiting nano (1-100 nm) and meso (100-500 nm) order (such as biopolymers, block-copolymers, colloidal suspensions, liquid crystals), physical properties ranging from toughness to optical clarity are determined by morphology on various length scales which in turn arise from processing history. This is anticipated to be especially important for blends containing two or more constituents with fundamental structural features on the nanoscale, such as crystal lamellae and aluminosilicate sheets. Small-angle x-ray scattering experiments with synchrotron radiation reveal the presence of ultra-long range (20-60 nm) mesoscopic ordering of the layered silicate in molten polyamide 6-layered silicate nanocomposites. This superstructure of these semi-rigid inorganic sheets provides a confined environment to examine the crystallization of polyamide 6 with traditional bulk characterization techniques. In addition to a change lamellae organization and lamellae size, the presence of the aluminosilicate layers and extent of interfacial interactions (end-tethered v. physiadsorbed chains) substantially alters the nucleation rate, growth kinetics and Brill transition of the crystal phase as revealed by isothermal crystallization experiments monitored in-situ with synchrotron radiation. These exfoliated nanocomposites provide new opportunities to investigate confined polymer crystallization as well as provide insight into the origin of various property enhancements in these systems.

Comparison study of PE epitaxy on carbon nanotubes and graphene oxide and PE/graphene oxide as amphiphilic molecular structure for solvent separation

NASA Astrophysics Data System (ADS)

He, Linghao; Zheng, Xiaoli; Xu, Qun; Chen, Zhimin; Fu, Jianwei

2012-03-01

Carbon nanotubes (CNTs) and graphene nanosheets, as one-dimensional and two-dimensional carbon-based nanomaterials respectively, have different abilities to induce the polymer crystallization. In this study, hybrid materials, polyethylene (PE) decorating on CNTs and graphene oxide (GO), were prepared by a facile and efficient method using supercritical carbon dioxide (SC CO2) as anti-solvent. And the morphology and crystallization behavior of PE on CNTs and GO were investigated by transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectra, wide angle X-ray diffraction, and differential scanning calorimetry. Although both CNTs and GO could act as nucleating agents to induce PE epitaxial growth, CNTs were decorated by PE lamellar crystals forming nanohybrid "shish-kebab" (NHSK) structure, whereas GO sheets were only decorated with petal-like PE crystals. The varying morphologies of the nanohybrids depend on the PE epitaxy and the interactions between polymer chains and substrates. High surface curvature and the perfect ordered crystal structure of CNTs make PE crystals periodically grow on CNTs. While PE crystals grow and form multiple orientation-lamellae on GO due to the lattice matching and complex interactions between PE chains and GO. In addition, our experimental results show an interesting and evident stratification phenomenon for the PE/GO hybrid material, implying that GO decorated by PE have a screening function for the solvents. We anticipate that this work can widen the area of functionalization of carbon-based nanomaterials with a controlled means by an environmentally benign method, which are important for the functional design in nanodevice applications.

A top-down approach to crystal engineering of a racemic Δ2-isoxazoline.

PubMed

Lombardo, Giuseppe M; Rescifina, Antonio; Chiacchio, Ugo; Bacchi, Alessia; Punzo, Francesco

2014-02-01

The crystal structure of racemic dimethyl (4RS,5RS)-3-(4-nitrophenyl)-4,5-dihydroisoxazole-4,5-dicarboxylate, C13H12N2O7, has been determined by single-crystal X-ray diffraction. By analysing the degree of growth of the morphologically important crystal faces, a ranking of the most relevant non-covalent interactions determining the crystal structure can be inferred. The morphological information is considered with an approach opposite to the conventional one: instead of searching inside the structure for the potential key interactions and using them to calculate the crystal habit, the observed crystal morphology is used to define the preferential lines of growth of the crystal, and then this information is interpreted by means of density functional theory (DFT) calculations. Comparison with the X-ray structure confirms the validity of the strategy, thus suggesting this top-down approach to be a useful tool for crystal engineering.

Femtosecond laser irradiation on Nd:YAG crystal: Surface ablation and high-spatial-frequency nanograting

NASA Astrophysics Data System (ADS)

Ren, Yingying; Zhang, Limu; Romero, Carolina; Vázquez de Aldana, Javier R.; Chen, Feng

2018-05-01

In this work, we systematically study the surface modifications of femtosecond (fs) laser irradiated Nd:YAG crystal in stationary focusing case (i.e., the beam focused on the target in the steady focusing geometry) or dynamic scanning case (i.e., focused fs-laser beam scanning over the target material). Micro-sized structures (e.g. micro-craters or lines) are experimentally produced in a large scale of parameters in terms of pulse energy as well as (effective) pulse number. Surface ablation of Nd:YAG surface under both processing cases are investigated, involving the morphological evolution, parameter dependence, the ablation threshold fluences and the incubation factors. Meanwhile, under specific irradiation conditions, periodic surface structures with high-spatial-frequency (<λ/2) can be generated. The obtained period is as short as 157 nm in this work. Investigations on the evolution of nanograting formation and fluence dependence of period are performed. The experimental results obtained under different cases and the comparison between them reveal that incubation effect plays an important role not only in the ablation of Nd:YAG surface but also in the processes of nanograting formation.

Nucleation and growth studies of crystalline carbon phases at nanoscale

NASA Astrophysics Data System (ADS)

Mani, Radhika C.

Understanding the nucleation and early stage growth of crystals from the vapor phase is important for realizing large-area single-crystal quality films, controlled synthesis of nanocrystals, and the possible discovery of new phases of materials. Carbon provides the most interesting system because all its known crystalline phases (diamond, graphite and carbon nanotubes) are technologically important materials. Hence, this dissertation is focused on studying the nucleation and growth of carbon phases synthesized from the vapor phase. Nucleation experiments were performed in a microwave plasma chemical vapor deposition (CVD) reactor, and the resulting carbon nanocrystals were analyzed primarily using electron nanodiffraction and Raman spectroscopy. These studies led to the discovery of two new crystalline phases of sp 3 carbon other than diamond: face-centered and body-centered cubic carbon. Nanodiffraction results revealed possible hydrogen substitution into diamond-cubic lattices, indicating that these new phases probably act as intermediates in diamond nucleation. Nucleation experiments also led to the discovery of two new morphologies for sp2 carbon: nanocrystals of graphite and tapered, hollow 1-D structures termed here as "carbon nanopipettes". A Kinetic Monte Carlo (KMC) algorithm was developed to simulate the growth of individual diamond crystals from the vapor phase, starting with small clusters of carbon atoms (or seeds). Specifically, KMC simulations were used to distinguish the kinetic rules that give rise to a star-shaped decahedral morphology compared to decahedral crystals. KMC simulations revealed that slow adsorption on the {111} step-propagation sites compared to kink sites leads to star-decahedral crystals, and higher adsorption leads to decahedral crystals. Since the surfaces of the nanocrystals of graphite and nanopipettes were expected to be composed primarily of edge-plane sites, the electrochemical behavior of both these materials were investigated with compounds requiring chemisorption, specifically biologically important species. Both these materials exhibited a stable and reversible voltammetric behavior for dopamine (a neurotransmitter) similar to that of graphite edge planes. Furthermore, a simple bottom-up concept utilizing the tapered morphology of the nanopipettes was developed to assemble a nanoarray sensor for fast cyclic voltammetry. In summary, the main outcomes of this dissertation include: the discovery of new crystalline carbon phases, understanding kinetic faceting of multiply twinned diamond crystals and tapered morphologies of carbon nanotubes, and development of new electrode materials based on sp2 carbon nanocrystals for sensing biologically important analytes.

Crystallization of Chicken Egg-White Lysozyme from Ammonium Sulfate

NASA Technical Reports Server (NTRS)

Forsythe, Elizabeth L.; Snell, Edward H.; Pusey, Marc L.

1997-01-01

Chicken egg-white lysozyme was crystallized from ammonium sulfate over the pH range 4.0-7.8, with protein concentrations from 100 to 150 mg/ml. Crystals were obtained by vapor-diffusion or batch-crystallization methods. The protein crystallized in two morphologies with an apparent morphology dependence on temperature and protein concentration. In general, tetragonal crystals could be grown by lowering the protein concentration or temperature. Increasing the temperature or protein concentration resulted in the growth of orthorhombic crystals. Representative crystals of each morphology were selected for X-ray analysis. The tetragonal crystals belonged to the P4(sub 3)2(sub 1)2 space group with crystals grown at ph 4.4 having unit-cell dimensions of a = b = 78.7 1, c=38.6 A and diffracting to beyond 2.0 A. The orthorhombic crystals, grown at pH 4.8, were of space group P2(sub 1)2(sub 1)2 and had unit-cell dimensions of a = 30.51, b = 56.51 and c = 73.62 A.

Equilibria Configurations for Epitaxial Crystal Growth with Adatoms

NASA Astrophysics Data System (ADS)

Caroccia, Marco; Cristoferi, Riccardo; Dietrich, Laurent

2018-05-01

The behavior of a surface energy F}(E,u)} , where E is a set of finite perimeter and u\\in L^1(partial^{*} E, R_+) , is studied. These energies have been recently considered in the context of materials science to derive a new model in crystal growth that takes into account the effect of atoms, the freely diffusing on the surface (called adatoms), which are responsible for morphological evolution through an attachment and detachment process. Regular critical points, the existence and uniqueness of minimizers are discussed and the relaxation of F in a general setting under the L 1 convergence of sets and the vague convergence of measures is characterized. This is part of an ongoing project aimed at an analytical study of diffuse interface approximations of the associated evolution equations.

Effect of pH on the morphology of kidney stones

NASA Astrophysics Data System (ADS)

Agarwal, Neelesh; Sova, Stacey; Singh, N. B.; Arnold, Brad; Choa, Fow-Sen; Cullum, Brian; Su, Ching-Hua

2016-05-01

The process for the formation of kidney stone is very complex phenomena and has some similarity to the crystal growth from a solution. It is very much dependent on the acidity pH of the fluids. This pH variation affects the content and amount of filtering residue and its morphology. In this study we have performed experiments using carbonate, oxides and urea to simulate and understand the morphologies of the residue filtered and coarsened in different conditions. We observed that different of morphologies of kidney stones can be explained on the basis of acidity and hydration conditions. At lower pH fat prism crystals are observed and as pH increases, long fat needle crystals with large aspect ratio are observed. The coarsening experiments showed further growth of crystals. The remelting experiments showed that during dissolution of kidney stones the joining material breaks first leaving the large faceted crystals undissolved when attempts are made to dissolve into small crystallites. However, the morphology did not change. It was also observed that impurities such as magnesium oxide (MgO) affect the morphology significantly.

Actively addressed single pixel full-colour plasmonic display

PubMed Central

Franklin, Daniel; Frank, Russell; Wu, Shin-Tson; Chanda, Debashis

2017-01-01

Dynamic, colour-changing surfaces have many applications including displays, wearables and active camouflage. Plasmonic nanostructures can fill this role by having the advantages of ultra-small pixels, high reflectivity and post-fabrication tuning through control of the surrounding media. However, previous reports of post-fabrication tuning have yet to cover a full red-green-blue (RGB) colour basis set with a single nanostructure of singular dimensions. Here, we report a method which greatly advances this tuning and demonstrates a liquid crystal-plasmonic system that covers the full RGB colour basis set, only as a function of voltage. This is accomplished through a surface morphology-induced, polarization-dependent plasmonic resonance and a combination of bulk and surface liquid crystal effects that manifest at different voltages. We further demonstrate the system's compatibility with existing LCD technology by integrating it with a commercially available thin-film-transistor array. The imprinted surface interfaces readily with computers to display images as well as video. PMID:28488671

Effect of Morphology and Manganese Valence on the Voltage Fade and Capacity Retention of Li[Li 2/12Ni 3/12Mn 7/12]O 2

DOE PAGES

Verde, Michael G.; Liu, Haodong; Carroll, Kyler J.; ...

2014-10-02

We have determined the electrochemical characteristics of the high voltage, high capacity Li-ion battery cathode material Li[Li 2/12Ni 3/12Mn 7/12]O 2 prepared using three different synthesis routes: sol-gel, hydroxide co-precipitation, and carbonate co-precipitation. Each route leads to distinct morphologies and surface areas while maintaining the same crystal structures. X-ray photoelectron spectroscopy (XPS) measurements reveal differences in their surface chemistries upon cycling, which correlate with voltage fading. As expected, we observed the valence state of Mn on the surface to decrease upon lithiation, and this reduction is specifically correlated to discharging below 3.6V. Furthermore, the data shows a correlation of themore » formation of Li 2CO 3 with Mn oxidation state from the« less

The effect of SiO 2-doped boron nitride multiple coatings on mechanical properties of quartz fibers

NASA Astrophysics Data System (ADS)

Zheng, Yu; Wang, Shubin

2012-01-01

SiO2-doped boron nitride multiple coatings (SiO2/BN multiple coatings) were prepared on quartz fibers surface at 700 °C. Single fiber tensile test was employed to evaluate fiber tensile strength; Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were employed to evaluate morphology and structure of the fibers. Fiber tensile test results indicated that the strength of quartz fibers with SiO2/BN multiple coatings was about twice of the fibers with BN coatings and original fibers which were heated at 700 °C for 10 h. The SiO2/BN multiple coatings would provide compressive stress on quartz fibers, which would help to seal the defects on fiber surface. Furthermore, TEM images showed that the nano-SiO2 powders crystallized in advance of quartz fibers, which would suppress crystallization of quartz fibers and reduce damage from crystallization. Thus, nano-SiO2 powders would help to keep mechanical properties of quartz fibers.

Laser Induced Damage of Potassium Dihydrogen Phosphate (KDP) Optical Crystal Machined by Water Dissolution Ultra-Precision Polishing Method

PubMed Central

Gao, Hang; Wang, Xu; Guo, Dongming; Liu, Ziyuan

2018-01-01

Laser induced damage threshold (LIDT) is an important optical indicator for nonlinear Potassium Dihydrogen Phosphate (KDP) crystal used in high power laser systems. In this study, KDP optical crystals are initially machined with single point diamond turning (SPDT), followed by water dissolution ultra-precision polishing (WDUP) and then tested with 355 nm nanosecond pulsed-lasers. Power spectral density (PSD) analysis shows that WDUP process eliminates the laser-detrimental spatial frequencies band of micro-waviness on SPDT machined surface and consequently decreases its modulation effect on the laser beams. The laser test results show that LIDT of WDUP machined crystal improves and its stability has a significant increase by 72.1% compared with that of SPDT. Moreover, a subsequent ultrasonic assisted solvent cleaning process is suggested to have a positive effect on the laser performance of machined KDP crystal. Damage crater investigation indicates that the damage morphologies exhibit highly thermal explosion features of melted cores and brittle fractures of periphery material, which can be described with the classic thermal explosion model. The comparison result demonstrates that damage mechanisms for SPDT and WDUP machined crystal are the same and WDUP process reveals the real bulk laser resistance of KDP optical crystal by removing the micro-waviness and subsurface damage on SPDT machined surface. This improvement of WDUP method makes the LIDT more accurate and will be beneficial to the laser performance of KDP crystal. PMID:29534032

Crystallization Kinetics of Barium and Strontium Aluminosilicate Glasses of Feldspar Composition

NASA Technical Reports Server (NTRS)

Hyatt, Mark J.; Bansal, Narottam P.

1994-01-01

Crystallization kinetics of BaO.Al2O3.2SiO2 (BAS) and SrO.Al2O3.2SiO2 (SAS) glasses in bulk and powder forms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ/mol for bulk samples and 560 and 534 kJ/mol for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder x-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl2Si2O8 (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.

Morphological, spectroscopic and thermal studies of samarium chloride coordinated single crystal grown by slow evaporation method

NASA Astrophysics Data System (ADS)

Slathia, Goldy; Raina, Bindu; Gupta, Rashmi; Bamzai, K. K.

2018-05-01

The synthesis of samarium chloride coordinated single crystal was carried out at room temperature by slow evaporation method. The crystal possesses a well defined hexagonal morphology with six symmetrically equivalent growth sectors separated by growth boundaries. The theoretical morphology has been established by structural approach using Bravaise-Friedele-Donnaye-Harker (BFDH) law. Fourier transform infra red spectroscopy was carried in order to study the geometry and structure of the crystal. The detailed thermogravimetric analysis elucidates the thermal stability of the complex.

Controlling the Morphology of Side Chain Liquid Crystalline Block Copolymer Thin Films through Variations in Liquid Crystalline Content

PubMed Central

Verploegen, Eric; Zhang, Tejia; Jung, Yeon Sik; Ross, Caroline; Hammond, Paula T.

2009-01-01

In this paper we describe methods for manipulating the morphology of side-chain liquid crystalline block copolymers through variations in the liquid crystalline content. By systematically controlling the covalent attachment of side chain liquid crystals to a block copolymer (BCP) backbone, the morphology of both the liquid crystalline (LC) mesophase and the phase segregated BCP microstructures can be precisely manipulated. Increases in LC functionalization lead to stronger preferences for the anchoring of the LC mesophase relative to the substrate and the inter-material dividing surface (IMDS). By manipulating the strength of these interactions the arrangement and ordering of the ultrathin film block copolymer nanostructures can be controlled, yielding a range of morphologies that includes perpendicular and parallel cylinders, as well as both perpendicular and parallel lamellae. Additionally, we demonstrate the utilization of selective etching to create a nanoporous liquid crystalline polymer thin film. The unique control over the orientation and order of the self-assembled morphologies with respect to the substrate will allow for the custom design of thin films for specific nano-patterning applications without manipulation of the surface chemistry or the application of external fields. PMID:18763835

Controlling the morphology of side chain liquid crystalline block copolymer thin films through variations in liquid crystalline content.

PubMed

Verploegen, Eric; Zhang, Tejia; Jung, Yeon Sik; Ross, Caroline; Hammond, Paula T

2008-10-01

In this paper, we describe methods for manipulating the morphology of side-chain liquid crystalline block copolymers through variations in the liquid crystalline content. By systematically controlling the covalent attachment of side chain liquid crystals to a block copolymer (BCP) backbone, the morphology of both the liquid crystalline (LC) mesophase and the phase-segregated BCP microstructures can be precisely manipulated. Increases in LC functionalization lead to stronger preferences for the anchoring of the LC mesophase relative to the substrate and the intermaterial dividing surface. By manipulating the strength of these interactions, the arrangement and ordering of the ultrathin film block copolymer nanostructures can be controlled, yielding a range of morphologies that includes perpendicular and parallel cylinders, as well as both perpendicular and parallel lamellae. Additionally, we demonstrate the utilization of selective etching to create a nanoporous liquid crystalline polymer thin film. The unique control over the orientation and order of the self-assembled morphologies with respect to the substrate will allow for the custom design of thin films for specific nanopatterning applications without manipulation of the surface chemistry or the application of external fields.

Effect of negative bias on the composition and structure of the tungsten oxide thin films deposited by magnetron sputtering

NASA Astrophysics Data System (ADS)

Wang, Meihan; Lei, Hao; Wen, Jiaxing; Long, Haibo; Sawada, Yutaka; Hoshi, Yoichi; Uchida, Takayuki; Hou, Zhaoxia

2015-12-01

Tungsten oxide thin films were deposited at room temperature under different negative bias voltages (Vb, 0 to -500 V) by DC reactive magnetron sputtering, and then the as-deposited films were annealed at 500 °C in air atmosphere. The crystal structure, surface morphology, chemical composition and transmittance of the tungsten oxide thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometer. The XRD analysis reveals that the tungsten oxide films deposited at different negative bias voltages present a partly crystallized amorphous structure. All the films transfer from amorphous to crystalline (monoclinic + hexagonal) after annealing 3 h at 500 °C. Furthermore, the crystallized tungsten oxide films show different preferred orientation. The morphology of the tungsten oxide films deposited at different negative bias voltages is consisted of fine nanoscale grains. The grains grow up and conjunct with each other after annealing. The tungsten oxide films deposited at higher negative bias voltages after annealing show non-uniform special morphology. Substoichiometric tungsten oxide films were formed as evidenced by XPS spectra of W4f and O1s. As a result, semi-transparent films were obtained in the visible range for all films deposited at different negative bias voltages.

Morphology and solubility of multiple crystal forms of Taka-amylase A

NASA Astrophysics Data System (ADS)

Ninomiya, Kumiko; Yamamoto, Tenyu; Oheda, Tadashi; Sato, Kiyotaka; Sazaki, Gen; Matsuura, Yoshiki

2001-01-01

An α-amylase originating from a mold Aspergillus oryzae, Taka-amylase A (Mr of 52 kDa, pI of 3.8), has been purified to an electrophoretically single band grade. Crystallization behaviors were investigated using ammonium sulfate and polyethleneglycol 8000 as precipitants. The variations in the morphology of the crystals obtained with changing crystallization parameters are described. Five apparently different crystal forms were obtained, and their morphology and crystallographic data have been determined. Solubility values of four typical forms were measured using a Michelson-type two-beam interferometer. The results of these experiments showed that this protein can be a potentially interesting and useful model for crystal growth study with a gram-amount availability of pure protein sample.

Factors affecting the morphology of isocitrate lyase crystals

NASA Technical Reports Server (NTRS)

Demattei, Robert C.; Feigelson, Robert S.; Weber, Patricia C.

1992-01-01

Isocitrate lyase crystals have been grown by the hanging drop vapor equilibration method in both 1-g and microgravity and by vapor equilibrium in small capillaries. The crystal morphologies obtained have ranged from dendritic to 'octagonal' prisms. Theoretical evaporation models have been applied to these growth regimes. The results of these analyses along with other experimental results, indicate the factors which must be controlled to produce good growth morphologies.

Effect of annealing temperatures on the morphology and structural properties of PVDF/MgO nanocomposites thin films

NASA Astrophysics Data System (ADS)

Rozana, M. D.; Arshad, A. N.; Wahid, M. H. M.; Habibah, Z.; Sarip, M. N.; Rusop, M.

2018-05-01

This study investigates the effect of annealing on the topography, morphology and crystal phases of poly(vinylideneflouride)/Magnesium Oxide (MgO) nanocomposites thin films via AFM, FESEM and ATR-FTIR. The nanocomposites thin films were annealed at temperatures ranging from 70°C to 170°C. The annealed PVDF/MgO nanocomposites thin films were then cooled at room temperature before removal from the oven. This is to restructure the crystal lattice and to reduce imperfection for the PVDF/MgO nanocomposites thin films. PVDF/MgO nanocomposites thin films with annealing temperatures of 70°C, 90°C and 110°C showed uniform distribution of MgO nanoparticles, relatively low average surface roughness and no visible of defects. High application of annealing temperature on PVDF/MgO nanocomposites thin films caused tear-like defects on the thin films surface as observed by FESEM. The PVDF/MgO nanocomposites thin films annealed at 70°C was found to be a favourable film to be utilized in this study due to its enhanced β-crystalites of PVDF as evident in ATR-FTIR spectra.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiusheng, Y., E-mail: qsyan@gdut.edu.cn; Senkai, C., E-mail: senkite@sina.com; Jisheng, P., E-mail: panjisheng@gdut.edu.cn

Different machining processes were used in the single crystal SiC wafer machining. SEM was used to observe the surface morphology and a cross-sectional cleavages microscopy method was used for subsurface cracks detection. Surface and subsurface cracks characteristics of single crystal SiC wafer in abrasive machining were analysed. The results show that the surface and subsurface cracks system of single crystal SiC wafer in abrasive machining including radial crack, lateral crack and the median crack. In lapping process, material removal is dominated by brittle removal. Lots of chipping pits were found on the lapping surface. With the particle size becomes smaller,more » the surface roughness and subsurface crack depth decreases. When the particle size was changed to 1.5µm, the surface roughness Ra was reduced to 24.0nm and the maximum subsurface crack was 1.2µm. The efficiency of grinding is higher than lapping. Plastic removal can be achieved by changing the process parameters. Material removal was mostly in brittle fracture when grinding with 325# diamond wheel. Plow scratches and chipping pits were found on the ground surface. The surface roughness Ra was 17.7nm and maximum subsurface crack depth was 5.8 µm. When grinding with 8000# diamond wheel, the material removal was in plastic flow. Plastic scratches were found on the surface. A smooth surface of roughness Ra 2.5nm without any subsurface cracks was obtained. Atomic scale removal was possible in cluster magnetorheological finishing with diamond abrasive size of 0.5 µm. A super smooth surface eventually obtained with a roughness of Ra 0.4nm without any subsurface crack.« less

Effects of surface diffusion on high temperature selective emitters

DOE PAGES

Peykov, Daniel; Yeng, Yi Xiang; Celanovic, Ivan; ...

2015-01-01

Using morphological and optical simulations of 1D tantalum photonic crystals at 1200K, surface diffusion was determined to gradually reduce the efficiency of selective emitters. This was attributed to shifting resonance peaks and declining emissivity caused by changes to the cavity dimensions and the aperture width. Decreasing the structure’s curvature through larger periods and smaller cavity widths, as well as generating smoother transitions in curvature through the introduction of rounded cavities, was found to alleviate this degradation. An optimized structure, that shows both high efficiency selective emissivity and resistance to surface diffusion, was presented.

The Influence of the Surface Neutralization of Active Impurities on the Field-Electron Emission Properties of p-Type Silicon Crystals

NASA Astrophysics Data System (ADS)

Yafarov, R. K.

2017-12-01

Correlation dependences between variations of the structural-phase composition, morphology characteristics, and field-electron-emission (FEE) properties of surface-structured p-type silicon singlecrystalline (100)-oriented wafers have been studied during their stepwise high-dose carbon-ion-beam irradiation. It is established that the stepwise implantation of carbon decreases the FEE threshold and favors an increase in the maximum FEE-current density by more than two orders of magnitude. Physicochemical mechanisms involved in this modification of the properties of near-surface layers of silicon under carbon-ion implantation are considered.

Phase study and surface morphology of beta-alumina

NASA Astrophysics Data System (ADS)

Tak, S. K.

2018-05-01

Beta alumina ceramic is well known as a polycrystalline ceramic material. The characteristic crystal structure of beta-alumina makes it useful as a separator in sodium sulphur batteries and other electrochemical devices requiring the passage of sodium ions. β"-alumina powders for this study were prepared by zeta process. The pellets were sintered at different microwave power levels and power schedule to optimize the sintering conditions to obtain preferred β" phase with improved microstructure. Phase identification was studied by X-ray diffraction (XRD). XRD analysis shows increase in β'' phase as the sintering temperature was increased from 1400°C to 1600°C. Surface morphology of the pellets was carried out by Scanning Electron microscopy (SEM). SEM studies revealed the formation and growth of platelet grains with interconnected porosity.

Experimental investigation on photoelectric properties of ZAO thin film deposited on flexible substrate by magnetron sputtering

NASA Astrophysics Data System (ADS)

Hao, Ming; Liu, Kun; Liu, Xinghua; Wang, Dongyang; Ba, Dechun; Xie, Yuanhua; Du, Guangyu; Ba, Yaoshuai

2016-12-01

Transparent conductive ZAO (Zinc Aluminum Oxide) films on flexible substrates have a great potential for low-cost mass-production solar cells. ZAO thin films were achieved on flexible PET (polyethylene terephthalate) substrates by RF magnetron sputtering technology. The surface morphology and element content, the transmittance and the sheet resistance of the films were measured to determine the optical process parameters. The results show that the ZAO thin film shows the best parameters in terms of photoelectric performance including sputtering power, working pressure, sputtering time, substrate temperature (100 W, 1.5 Pa, 60 min, 125 °C). The sheet resistance of 510 Ω and transmittance in visible region of 92% were obtained after characterization. Surface morphology was uniform and compact with a good crystal grain.

Gold surface plasmon crystal structure based-on polystyrene template for biosensor application.

PubMed

Cheng, Min-Zhuo; Zhang, Jing; Bao, Dequan; Huang, Xiwei

2018-05-21

In this communication, we assembled ordered polystyrene (PS) microsphere array as a template with the drop-coating method, and the oxygen plasma was used to etch the template to adjust the spacing between the PS microspheres. Nano-triangular gold array and silver nano-pyramid array were obtained by ion beam sputtering to deposit precious metal gold and silver. We observed the surface morphology of Au and Au/Ag composite films by scanning electron microscope and characterized the films by X-ray diffraction and ultraviolet/visible light spectrophotometer. The results show that the etching time of oxygen plasma has an obvious effect in adjusting the spacing between PSs and has a significant effect on the morphology of Au structure. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of gamma irradiation on the surface morphology, XRD and thermophysical properties of silicide hexoboride

NASA Astrophysics Data System (ADS)

Mirzayev, Matlab N.; Mehdiyeva, Ravan N.; Garibov, Ramin G.; Ismayilova, Narmin A.; Jabarov, Sakin H.

2018-05-01

In this study, compounds of B6Si were irradiated using a 60Co gamma source that have an energy line of 1.25 MeV at the absorbed dose rates from 14.6 kGy to 194.4 kGy. Surface morphology images of the sample obtained by Scanning Electron Microscope (SEM) show that the crystal structure at a high absorbed doses (D ≥ 145.8kGy) starts to be destroyed. X-ray diffraction studies revealed that with increasing radiation absorption dose, the spectrum intensity of the sample was decreased 1.96 times compared with the initial value. Thermal properties were studied by Differential scanning calorimetry (DSC) method in the temperature range of 30-1000∘C.

A study of thermal properties of sodium titanate nanotubes synthesized by microwave-assisted hydrothermal method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Preda, Silviu, E-mail: predas01@yahoo.co.uk; Rutar, Melita; Jožef Stefan International Postgraduate School, Jamova cesta 39, SI-1000 Ljubljana

2015-11-15

Highlights: • The microwave-assisted hydrothermal route was used for titanate nanotubes synthesis. • Conversion to single-phase nanotube morphology completes after 8 h reaction time. • The nanotube morphology is stable up to 600 °C, as determined by in-situ XRD and SEM. • Sodium ions migrate to the surface due to thermal motion and structure condensation. - Abstract: Sodium titanate nanotubes (NaTiNTs) were synthesized by microwave-assisted hydrothermal treatment of commercial TiO{sub 2}, at constant temperature (135 °C) and different irradiation times (15 min, 1, 4, 8 and 16 h). The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electronmore » microscopy, differential scanning calorimetry and specific surface area measurements. The irradiation time turned out to be the key parameter for morphological control of the material. Nanotubes were observed already after 15 min of microwave irradiation. The analyses of the products irradiated for 8 and 16 h confirm the complete transformation of the starting TiO{sub 2} powder to NaTiNTs. The nanotubes are open ended with multi-wall structures, with the average outer diameter of 8 nm and specific surface area up to 210 m{sup 2}/g. The morphology, surface area and crystal structure of the sodium titanate nanotubes synthesized by microwave-assisted hydrothermal method were similar to those obtained by conventional hydrothermal method.« less

Coarse-grained modeling of crystal growth and polymorphism of a model pharmaceutical molecule.

PubMed

Mandal, Taraknath; Marson, Ryan L; Larson, Ronald G

2016-10-04

We describe a systematic coarse-graining method to study crystallization and predict possible polymorphs of small organic molecules. In this method, a coarse-grained (CG) force field is obtained by inverse-Boltzmann iteration from the radial distribution function of atomistic simulations of the known crystal. With the force field obtained by this method, we show that CG simulations of the drug phenytoin predict growth of a crystalline slab from a melt of phenytoin, allowing determination of the fastest-growing surface, as well as giving the correct lattice parameters and crystal morphology. By applying meta-dynamics to the coarse-grained model, a new crystalline form of phenytoin (monoclinic, space group P2 1 ) was predicted which is different from the experimentally known crystal structure (orthorhombic, space group Pna2 1 ). Atomistic simulations and quantum calculations then showed the polymorph to be meta-stable at ambient temperature and pressure, and thermodynamically more stable than the conventional orthorhombic crystal at high pressure. The results suggest an efficient route to study crystal growth of small organic molecules that could also be useful for identification of possible polymorphs as well.

Growth of raspberry-, prism- and flower-like ZnO particles using template-free low-temperature hydrothermal method and their application as humidity sensors

NASA Astrophysics Data System (ADS)

Pál, Edit; Hornok, Viktória; Kun, Robert; Chernyshev, Vladimir; Seemann, Torben; Dékány, Imre; Busse, Matthias

2012-08-01

Zinc oxide particles with different morphologies were prepared by hydrothermal method at 60-90 °C. The structure formation was controlled by the addition rate and temperature of hydrolyzing agent, while the particles size (10 nm-2.5 μm) was influenced by the preparation (hydrothermal) temperature. Scanning electron microscopy studies showed that raspberry-, prism- and flower-like ZnO particles were prepared, whose average size decreased with increasing reaction temperature. X-ray diffraction investigations confirmed that ZnO particles with hexagonal crystal structure formed in all syntheses. The raspberry-, prism- and flower-like ZnO particles showed a weak UV-emission in the range of 390-395 nm and strong visible emission with a maximum at 586, 593 and 598 nm, respectively. Morphology effect on electrical and water vapour sensing properties of ZnO samples was investigated by impedance spectroscopy and quartz crystal microbalance, respectively. The absolute impedance of raspberry-, prism- and flower-like ZnO particles was found to be strong dependent on the morphology. Space-charge-limited conductivity transport mechanism was proved by the oscillatory behaviour of impedance. Humidity sensor tests also revealed morphology and specific surface area dependency on the sensitivity and water vapour adsorption property.

Subsurface Grain Morphology Reconstruction by Differential Aperture X-ray Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eisenlohr, Philip; Shanthraj, Pratheek; Vande Kieft, Brendan R.

A multistep, non-destructive grain morphology reconstruction methodology that is applicable to near-surface volumes is developed and tested on synthetic grain structures. This approach probes the subsurface crystal orientation using differential aperture X-ray microscopy (DAXM) on a sparse grid across the microstructure volume of interest. Resulting orientation data is clustered according to proximity in physical and orientation space and used as seed points for an initial Voronoi tessellation to (crudely) approximate the grain morphology. Curvature-driven grain boundary relaxation, simulated by means of the Voronoi Implicit Interface Method (VIIM), progressively improves the reconstruction accuracy. The similarity between bulk and readily accessible surfacemore » reconstruction error provides an objective termination criterion for boundary relaxation.« less

Structural, morphological and optical studies of F doped SnO2 thin films

NASA Astrophysics Data System (ADS)

Chandel, Tarun; Thakur, Vikas; Dwivedi, Shailendra Kumar; Zaman, M. Burhanuz; Rajaram, Poolla

2018-05-01

Highly conducting and transparent FTO (flourine doped tin Oxide) thin films were grown on the glass substrates using a low cost spray pyrolysis technique. The films were characterized for their structural, morphological and optical studies using XRD, SEM and UV-Vis spectroscopy. XRD studies show that the FTO films crystallize in Tetragonal cassiterite structure. Morphological analysis using SEM show that the films are uniformly covered with spherical grains albeit high in surface roughness. The average optical transmission greater than 80% in the visible region along with the appearance of interference fringes in the transmission curves confirms the high quality of the films. Electrical studies show that the films exhibit sheet resistance below 10 Ω ϒ-1.

Growth and dislocation studies of β-HMX.

PubMed

Gallagher, Hugh G; Sherwood, John N; Vrcelj, Ranko M

2014-01-01

The defect structure of organic materials is important as it plays a major role in their crystal growth properties. It also can play a subcritical role in "hot-spot" detonation processes of energetics and one such energetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (β-HMX). The as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, all with {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two of which could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact of the twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one type of etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgers vector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated with line dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristic of mechanical deformation by dislocation slip. Crystals of β-HMX grown from acetone show good morphological agreement with that predicted by modelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution. Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant at higher super saturations. The twin plane in β-HMX was identified as a (101) reflection plane. The low plasticity of β-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays. On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screw dislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pits are associated with pure screw dislocations with b = [010]. Graphical abstractEtch pits on the twinned (010) face of β-HMX.

Solvent effects on the crystal growth structure and morphology of the pharmaceutical dirithromycin

NASA Astrophysics Data System (ADS)

Wang, Yuan; Liang, Zuozhong

2017-12-01

Solvent effects on the crystal structure and morphology of pharmaceutical dirithromycin molecules were systematically investigated using both experimental crystallization and theoretical simulation. Dirithromycin is one of the new generation of macrolide antibiotics with two polymorphic forms (Form I and Form II) and many solvate forms. Herein, six solvates of the dirithromycin, including acetonitrile, acetonitrile/water, acetone, 1-propanol, N,N-dimethylformamide (DMF) and cyclohexane, were studied. Experimentally, we crystallized the dirithromycin molecules in different solvents by the solvent evaporating method and measured the crystal structures with the X-ray diffraction (XRD). We compared these crystal structures of dirithromycin solvates and analyzed the solvent property-determined structure evolution. The solvents have a strong interaction with the dirithromycin molecule due to the formation of inter-molecular interactions (such as the hydrogen bonding and close contacts (sum of vdW radii)). Theoretically, we calculated the ideal crystal habit based on the solvated structures with the attachment growth (AE) model. The predicted morphologies and aspect ratios of dirithromycin solvates agree well with the experimental results. This work could be helpful to better understand the structure and morphology evolution of solvates controlled by solvents and guide the crystallization of active pharmaceutical ingredients in the pharmaceutical industry.

Surface dislocation nucleation controlled deformation of Au nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roos, B.; Kapelle, B.; Volkert, C. A., E-mail: volkert@ump.gwdg.de

2014-11-17

We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of themore » deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.« less

Synergetic effect of Sn addition and oxygen-deficient atmosphere to fabricate active hematite photoelectrodes for light-induced water splitting

NASA Astrophysics Data System (ADS)

Freitas, Andre L. M.; Souza, Flavio L.

2017-11-01

This work describes the design of a microwave-assisted method using hydrothermal conditions to fabricate pure and Sn-doped hematite photoelectrodes with varied synthesis time and additional thermal treatment under air and N2 atmosphere. The hematite photoelectrode formed under N2 atmosphere, with Sn deposited on its surface—which is represented by material synthesized at 4 h —exhibits the highest performance. Hence, Sn addition followed by high temperature annealing conducted in an oxygen-deficient atmosphere seems to create oxygen vacancies, and to prevent the segregation of dopant to form the SnO2 phase at the hematite crystal surface, reducing its energy and suppressing the grain growth. The increased donor number density provided by the oxygen vacancies (confirmed by x-ray photoelectron data), and a possible reduction in the grain boundary energy or hematite crystal interface might favor charge separation, and increase the electron transfer through the hematite into the back contact (FTO substrate). In consequence, the light-induced water oxidation reaction efficiency of Sn-hematite photoelectrodes was significantly increased in comparison with pure ones, even though the vertical rod morphology was not preserved. This finding provides a novel insight into intentional Sn addition, revealing that dopant segregation at the hematite crystal surface (or at the grain boundaries) could—by increasing the electron mobility—be the more relevant factor in developing active hematite photoelectrodes than the control of columnar morphology.

The effect of cold-light-activated bleaching treatment on enamel surfaces in vitro

PubMed Central

Shi, Xin-Chang; Ma, He; Zhou, Jing-Lin; Li, Wei

2012-01-01

This in vitro study aims to evaluate the crystal and surface microstructure of dental enamel after cold-light bleaching treatment. Twelve sound human premolars were cross-split into four specimens, namely, mesio-buccal (Group LP), disto-buccal (Group P), mesio-lingual (Group NP) and disto-lingual (Group L) specimens. These four groups were treated using the standard cold-light bleaching procedure, a bleaching agent, a peroxide-free bleaching agent and cold-light, respectively. Before and after treatment, all specimens were analyzed by high-resolution, micro-area X-ray diffraction and scanning electron microscopy. Using a spectrometer, tooth color of all specimens was measured before and after treatment. The phase of the enamel crystals was identified as hydroxyapatite and carbonated hydroxyapatite. After treatment, specimens in Groups LP and P showed significantly weaker X-ray diffraction peaks, significant reduction in crystal size and crystallinity, significant increase in L* but decrease in a* and b*, and obvious alterations in the surface morphology. However, specimens in Groups NP and L did not show any significant changes. The cold-light bleaching treatment leads to demineralization in the enamel surface. The acidic peroxide-containing bleaching agent was the major cause of demineralization, whereas cold-light did not exhibit significant increase or decrease effect on this demineralization. PMID:23258380

Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering

DOE PAGES

Tolstova, Yulia; Omelchenko, Stefan T.; Shing, Amanda M.; ...

2016-03-17

The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use asmore » epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. Additionally, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.« less

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

NASA Astrophysics Data System (ADS)

Greenlee, Jordan D.; Feigelson, Boris N.; Anderson, Travis J.; Tadjer, Marko J.; Hite, Jennifer K.; Mastro, Michael A.; Eddy, Charles R.; Hobart, Karl D.; Kub, Francis J.

2014-08-01

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N2 overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E2 and A1 (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.

Large-scale synthesis and growth habit of 3-D flower-like crystal of PbTe

NASA Astrophysics Data System (ADS)

Zhou, Nan; Chen, Gang; Yang, Xi; Zhang, Xiaosong

2012-02-01

In this paper, 3-D flower-like crystal of PbTe was successfully synthesized using Pb(CH3COO)2·3H2O and Na2TeO3 as precursors under hydrothermal conditions, and characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction pattern (XRD). The reaction parameters that influenced the evolution of PbTe synthesis and morphology were investigated. It was shown that the flower-like crystal of PbTe was composed of a nucleus with eight pods. A possible growth mechanism was proposed based on the calculation of the surface energies of PbTe and the SEM observation. Furthermore, the temperature-dependent transport properties of 3-D flower-like crystal of PbTe specimen have been evaluated with an average thermoelectric power of 120 S cm-1 and electrical conductivity of 220 μV K-1 at 740 K.

Influence of support morphology on the bonding of molecules to nanoparticles

PubMed Central

Yim, Chi Ming; Pang, Chi L.; Hermoso, Diego R.; Dover, Coinneach M.; Muryn, Christopher A.; Maccherozzi, Francesco; Dhesi, Sarnjeet S.; Pérez, Rubén; Thornton, Geoff

2015-01-01

Supported metal nanoparticles form the basis of heterogeneous catalysts. Above a certain nanoparticle size, it is generally assumed that adsorbates bond in an identical fashion as on a semiinfinite crystal. This assumption has allowed the database on metal single crystals accumulated over the past 40 years to be used to model heterogeneous catalysts. Using a surface science approach to CO adsorption on supported Pd nanoparticles, we show that this assumption may be flawed. Near-edge X-ray absorption fine structure measurements, isolated to one nanoparticle, show that CO bonds upright on the nanoparticle top facets as expected from single-crystal data. However, the CO lateral registry differs from the single crystal. Our calculations indicate that this is caused by the strain on the nanoparticle, induced by carpet growth across the substrate step edges. This strain also weakens the CO–metal bond, which will reduce the energy barrier for catalytic reactions, including CO oxidation. PMID:26080433

ZnO nanodisk based UV detectors with printed electrodes.

PubMed

Alenezi, Mohammad R; Alshammari, Abdullah S; Alzanki, Talal H; Jarowski, Peter; Henley, Simon John; Silva, S Ravi P

2014-04-08

The fabrication of highly functional materials for practical devices requires a deep understanding of the association between morphological and structural properties and applications. A controlled hydrothermal method to produce single crystal ZnO hexagonal nanodisks, nanorings, and nanoroses using a mixed solution of zinc sulfate (ZnSO4) and hexamethylenetetramine (HMTA) without the need of catalysts, substrates, or templates at low temperature (75 °C) is introduced. Metal-semiconductor-metal (MSM) ultraviolet (UV) detectors were fabricated based on individual and multiple single-crystal zinc oxide (ZnO) hexagonal nanodisks. High quality single crystal individual nanodisk devices were fabricated with inkjet-printed silver electrodes. The detectors fabricated show record photoresponsivity (3300 A/W) and external quantum efficiency (1.2 × 10(4)), which we attribute to the absence of grain boundaries in the single crystal ZnO nanodisk and the polarity of its exposed surface.

Sub-nanometer glass surface dynamics induced by illumination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Duc; Nienhaus, Lea; Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

2015-06-21

Illumination is known to induce stress and morphology changes in opaque glasses. Amorphous silicon carbide (a-SiC) has a smaller bandgap than the crystal. Thus, we were able to excite with 532 nm light a 1 μm amorphous surface layer on a SiC crystal while recording time-lapse movies of glass surface dynamics by scanning tunneling microscopy (STM). Photoexcitation of the a-SiC surface layer through the transparent crystal avoids heating the STM tip. Up to 6 × 10{sup 4} s, long movies of surface dynamics with 40 s time resolution and sub-nanometer spatial resolution were obtained. Clusters of ca. 3-5 glass formingmore » units diameter are seen to cooperatively hop between two states at the surface. Photoexcitation with green laser light recruits immobile clusters to hop, rather than increasing the rate at which already mobile clusters hop. No significant laser heating was observed. Thus, we favor an athermal mechanism whereby electronic excitation of a-SiC directly controls glassy surface dynamics. This mechanism is supported by an exciton migration-relaxation-thermal diffusion model. Individual clusters take ∼1 h to populate states differently after the light intensity has changed. We believe the surrounding matrix rearranges slowly when it is stressed by a change in laser intensity, and clusters serve as a diagnostic. Such cluster hopping and matrix rearrangement could underlie the microscopic mechanism of photoinduced aging of opaque glasses.« less

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating.

PubMed

Liu, Danqing; Liu, Ling; Onck, Patrick R; Broer, Dirk J

2015-03-31

In this work we propose randomly ordered polydomain nematic liquid crystal polymer networks to reversibly generate notable jagged relief patterns at a polymer coating surface by light illumination. The domain size is controlled by the addition of traces of partly insoluble fluorinated acrylate. The photoresponse of the coating is induced by a small amount of copolymerized azobenzene monomers. Upon exposure to UV light, azobenzene undergoes trans to cis isomerization, resulting in a change in molecular order and packing within each domain. The extent of this effect and its directionality depends on the domain orientation. Localized to domain level, this morphological change forms large 3D spikes at the surface with a modulation amplitude of more than 20% of the initial thickness. The process is reversible; the surface topographical patterns erase within 10 s by stopping the light exposure. A finite element model is applied to simulate the surface topography changes of the polydomain coating. The simulations describe the formation of the topographic features in terms of light absorption and isomerization process as a function of the director orientation. The random director distribution leads to surface structures which were found to be in close agreement with the ones measured by interference microscopy. The effect of domain size on surface roughness and depth modulation was explored and related to the internal mechanical constraints. The use of nematic liquid crystal polydomains confined in a polymer network largely simplifies the fabrication of smart coatings with a prominent triggered topographic response.

Near surface mechanical properties of optical single crystals and surface response to deterministic microgrinding

NASA Astrophysics Data System (ADS)

Randi, Joseph A., III

2005-12-01

This thesis makes use of microindentation, nanoindentation and nanoscratching methods to better understand the mechanical properties of single crystalline silicon, calcium fluoride, and magnesium fluoride. These properties are measured and are used to predict the material's response to material removal, specifically by grinding and polishing, which is a combination of elastic, plastic and fracture processes. The hardness anisotropy during Knoop microindentation, hardness from nanoindentation, and scratch morphology from nanoscratching are reported. This information is related to the surface microroughness from grinding. We show that mechanical property relationships that predict the surface roughness from lapping and deterministic microgrinding of optical glasses are applicable to single crystals. We show the range of hardness from some of the more common crystallographic faces. Magnesium fluoride, having a tetragonal structure, has 2-fold hardness anisotropy. Nanoindentation, as expected provides higher hardness than microindentation, but anisotropy is not observed. Nanoscratching provides the scratch profile during loading, after the load has been removed, and the coefficient of friction during the loading. Ductile and brittle mode scratching is present with brittle mode cracking being orientation specific. Subsurface damage (SSD) measurements are made using a novel process known as the MRF technique. Magnetorheological finishing is used to polish spots into the ground surface where SSD can be viewed. SSD is measured using an optical microscope and knowledge of the spot profile. This technique is calibrated with a previous technique and implemented to accurately measure SSD in single crystals. The data collected are compared to the surface microroughness of the ground surface, resulting in an upper bound relationship. The results indicate that SSD is always less than 1.4 times the peak-to-valley surface microroughness for single crystals regardless of the grinding conditions or mechanical properties. Single crystals have greater strain rate effects associated than optical glasses. Hence, the strain rate is investigated during grinding by applying more aggressive process parameters and measuring the resulting surface finish. It is observed that while there are weak materials and crystallographic orientation effects from process parameters, the changes in strain rate do not affect the surface finish of these materials.

Surface Engineering of Polycrystalline Silicon for Long-Term Mechanical Stress Endurance Enhancement in Flexible Low-Temperature Poly-Si Thin-Film Transistors.

PubMed

Chen, Bo-Wei; Chang, Ting-Chang; Chang, Kuan-Chang; Hung, Yu-Ju; Huang, Shin-Ping; Chen, Hua-Mao; Liao, Po-Yung; Lin, Yu-Ho; Huang, Hui-Chun; Chiang, Hsiao-Cheng; Yang, Chung-I; Zheng, Yu-Zhe; Chu, Ann-Kuo; Li, Hung-Wei; Tsai, Chih-Hung; Lu, Hsueh-Hsing; Wang, Terry Tai-Jui; Chang, Tsu-Chiang

2017-04-05

The surface morphology in polycrystalline silicon (poly-Si) film is an issue regardless of whether conventional excimer laser annealing (ELA) or the newer metal-induced lateral crystallization (MILC) process is used. This paper investigates the stress distribution while undergoing long-term mechanical stress and the influence of stress on electrical characteristics. Our simulated results show that the nonuniform stress in the gate insulator is more pronounced near the polysilicon/gate insulator edge and at the two sides of the polysilicon protrusion. This stress results in defects in the gate insulator and leads to a nonuniform degradation phenomenon, which affects both the performance and the reliability in thin-film transistors (TFTs). The degree of degradation is similar regardless of bending axis (channel-length axis, channel-width axis) or bending type (compression, tension), which means that the degradation is dominated by the protrusion effects. Furthermore, by utilizing long-term electrical bias stresses after undergoing long-tern bending stress, it is apparent that the carrier injection is severe in the subchannel region, which confirms that the influence of protrusions is crucial. To eliminate the influence of surface morphology in poly-Si, three kinds of laser energy density were used during crystallization to control the protrusion height. The device with the lowest protrusions demonstrates the smallest degradation after undergoing long-term bending.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ke; De Andrade, Vincent; Feng, Zhange

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion-mineral interactions during dissolution under far-from equilibrium conditions remains limited. Here we show that calcite (CaCO 3) exhibits a rich array of dissolution features in the presence of Pb. During the initial stage, calcite exhibits non-classical surface features characterized as micro pyramids developed spontaneously in acidic Pb-bearing solutions. Subsequent pseudomorphic growth of cerussite (PbCO 3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded amore » cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution-precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing micro structures observed in naturally-occurring and synthetic carbonate minerals by dissolution. In addition, heterogeneous micro-environments created in transport limited reactions under pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.« less

Phosphatic precipitates associated with actinomycetes in speleothems from Grand Cayman, British West Indies

NASA Astrophysics Data System (ADS)

Jones, Brian

2009-07-01

Calcitic speleothems from a cave located on the north central coast of Grand Cayman commonly include corrosion surfaces that developed when calcite precipitation ceased and corrosion mediated by condensates became the operative process. Dissolution features associated with these surfaces, including etched crystal surfaces, microcavities, and solution-widened boundaries between crystals, are commonly occupied by microbes and microbial mats that have been replaced by calcium phosphate and/or coated with calcium phosphate. No mineralized microbes were found in the calcite crystals that form the speleothems. The morphology of the mineralized hyphae (eight morphotypes) and spores (nine morphotypes) are indicative of actinomycetes, a group of microbes that are ideally adapted to life in oligotrophic cave environs. Superb preservation of the delicate hyphae, aerial hyphae, and delicate ornamentation on the hyphae and spores indicate that the microbes underwent rapid mineralized while close to their original life positions. Although these actinomycetes were extremely susceptible to replacement by calcium phosphate, there is no evidence that they directly or indirectly controlled precipitation. Nevertheless, the association between the P-rich precipitates and microbes shows that the use of phosphorus as a proxy for seasonal climate changes in paleoclimate analyses must be treated with caution.

Morphological and ultrastructural comparative analysis of bone tissue after Er:YAG laser and surgical drill osteotomy.

PubMed

Panduric, Dragana Gabric; Juric, Ivona Bago; Music, Svetozar; Molčanov, Krešimir; Sušic, Mato; Anic, Ivica

2014-07-01

The purpose of this study was to analyze morphological, chemical, and crystallographic changes of bone tissue after osteotomy performed with an erbium:yttrium-aluminium-garnet (Er:YAG) laser and a low speed pilot drill. Bone blocks were prepared from porcine ribs, and on each block, two tunnel preparations were performed using the Er:YAG laser (pulse energy: 1000 mJ, pulse duration: 300 μs, pulse repetition rate: 20 Hz) or the low-speed surgical pilot drill. The morphological changes of the cortical and the spongious surface of the tunnel preparations were analyzed under the field emission scanning electron microscopy (FE-SEM) at low and high resolution. The distribution and the level of chemical elements in the treated surfaces were evaluated by qualitative and semiquantitative energy dispersive x-ray analysis (SEM-EDX). Diffraction x-ray analysis was used to detect any differences and thermally induced modifications of hydroxyapatite crystals. FE-SEM revealed sharp edges of the Er:YAG preparations, with empty intertrabecular spaces and no signs of carbonization. In the drill group, the surface of the preparations was smooth, completely covered with smear layer and microcracks, and with hairy-like irregularities on the edges. SEM-EDX analysis did not reveal any differences in the number of specific chemical elements between the laser and the drill group. There were no thermally induced modifications of hydroxyapatite crystal structure in the bone tissue in either group. The Er:YAG laser ablation did not cause any chemical or crystallographic changes of the bone tissue. Compared with the drill, Er:YAG laser created well-defined edges of the preparations, and cortical bone had no smear layer.

Branched Crystalline Patterns of Poly(ε-caprolactone) and Poly(4-hydroxystyrene) Blends Thin Films.

PubMed

Hou, Chunyue; Yang, Tianbo; Sun, Xiaoli; Ren, Zhongjie; Li, Huihui; Yan, Shouke

2016-01-14

The chain organization of poly(ε-caprolactone) (PCL) in its blend with poly(4-hydroxystyrene) (PVPh) in thin films (130 ± 10 nm) has been revealed by grazing incident infrared (GIIR) spectroscopy. It can be found that PCL chains orient preferentially in the surface-normal direction and crystallization occurs simultaneously. The morphology of the PCL/PVPh blends films can be identified by optical microscopy (OM). When crystallized at 35 °C, the blends film shows a seaweed-like structure and becomes more open with increasing PVPh content. In contrast, when crystallized at higher temperatures, i.e., 40 and 45 °C, dendrites with apparent crystallographically favored branches can be observed. This characteristic morphology indicates that the diffusion-limited aggregation (DLA) process controls the crystal growth in the blends films. The detailed lamellar structure can be revealed by the height images of atomic force microscopy (AFM), i.e., the crystalline branches are composed of overlayered flat-on lamellae. The branch width has been found to be dependent on the supercooling and PVPh content. This result differs greatly from pure PCL, in which case the crystal patterns controlled by DLA process developed in ultrathin film or monolayers of several nanometers. In the PCL/PVPh blends case, the strong intermolecular interactions and the dilution effect of PVPh should contribute to these results. That is to say, the mobility of PCL chains can be retarded and diffusion of them to the crystal growth front slows down greatly, even though the film thickness is far more than the lamellar thickness of PCL.

Uncovering molecular details of urea crystal growth in the presence of additives.

PubMed

Salvalaglio, Matteo; Vetter, Thomas; Giberti, Federico; Mazzotti, Marco; Parrinello, Michele

2012-10-17

Controlling the shape of crystals is of great practical relevance in fields like pharmacology and fine chemistry. Here we examine the paradigmatic case of urea which is known to crystallize from water with a needle-like morphology. To prevent this undesired effect, inhibitors that selectively favor or discourage the growth of specific crystal faces can be used. In urea the most relevant faces are the {001} and the {110} which are known to grow fast and slow, respectively. The relevant growth speed difference between these two crystal faces is responsible for the needle-like structure of crystals grown in water solution. To prevent this effect, additives are used to slow down the growth of one face relative to another, thus controlling the shape of the crystal. We study the growth of fast {001} and slow {110} faces in water solution and the effect of shape controlling inhibitors like biuret. Extensive sampling through molecular dynamics simulations provides a microscopic picture of the growth mechanism and of the role of the additives. We find a continuous growth mechanism on the {001} face, while the slow growing {110} face evolves through a birth and spread process, in which the rate-determining step is the formation on the surface of a two-dimensional crystalline nucleus. On the {001} face, growth inhibitors like biuret compete with urea for the adsorption on surface lattice sites; on the {110} face instead additives cannot interact specifically with surface sites and play a marginal sterical hindrance of the crystal growth. The free energies of adsorption of additives and urea are evaluated with advanced simulation methods (well-tempered metadynamics) allowing a microscopic understanding of the selective effect of additives. Based on this case study, general principles for the understanding of the anisotropic growth of molecular crystals from solutions are laid out. Our work is a step toward a rational development of novel shape-affecting additives.

Correlation between crystallization behaviour and interfacial interactions in plasticized PLA/POSS nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kodal, Mehmet, E-mail: mehmet.kodal@kocaeli.edu.tr; Şirin, Hümeyra; Özkoç, Güralp, E-mail: guralp.ozkoc@kocaeli.edu.tr

2016-03-09

In this study, the correlation between crystallization behavior and surface chemistry of polyhedral oligomeric silsesquioxanes (POSS) for plasticized poly(lactic acid) (PLA)/POSS nanocomposites was investigated. Four different kinds of POSS particles having different chemical structures were used. Poly(ethylene glycol) (PEG, 8000 g/mol) was utilized as the plasticiser. The nanocomposites were melt-compounded in an Xplore Instruments 15 cc twin screw microcompounder at 180°C barrel temperature and 100 rpm screw speed. Non-isothermal crystallization behaviour of PLA/PEG/POSS nanocomposites were evaluated from common kinetic models such as Avrami and Avrami-Ozawa and Kissinger by using the thermal data obtained from differantial scanning calorimetry (DSC). A polarized optical microscopemore » (POM) equipped with a hot-stage was used to examine the morphology during the crystal growth. In order to investigate the interfacial interactions between POSS particles and plasticized PLA, thermodynamic work of adhesion approach was adopted using the experimentally determined surface energies. A strong correlation was obtained between interfacial chemistry and the nucleation rate in plasticized PLA/POSS nanocomposites. It was found that the polar interactions were the dominating factor which determines the nucleation activity of the POSS particles.« less

Investigation and characterization of ZnO single crystal microtubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Naser, Qusay A.H.; Zhou, Jian, E-mail: jianzhou@whut.edu.cn; Liu, Guizhen

2016-04-15

Morphological, structural, and optical characterization of microwave synthesized ZnO single crystal microtubes were investigated in this work. The structure and morphology of the ZnO microtubes are characterized using X-ray diffraction (XRD), single crystal diffraction (SCD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The results reveal that the as-synthesized ZnO microtube has a highly regular hexagonal cross section and smooth surfaces with an average length of 650–700 μm, an average outer diameter of 50 μm and wall thickness of 1–3 μm, possessing a single crystal wurtzite hexagonal structure. Optical properties of ZnOmore » single crystal microtubes were investigated by photoluminescence (PL) and ultraviolet-visible (UV-vis) absorption techniques. Room-temperature PL spectrum of the microtube reveal a strong UV emission peak at around 375.89 nm and broad and a weak visible emission with a main peak identified at 577 nm, which was assigned to the nearest band-edge emission and the deep-level emission, respectively. The band gap energy of ZnO microtube was found to be 3.27 eV. - Highlights: • ZnO microtube length of 650–700 μm, diameter of 50 μm, wall thickness of 1–3 μm • ZnO microtube possesses a single crystal wurtzite hexagonal structure. • The crystal system is hexahedral oriented along a-axis with indices of (100). • A strong and sharp UV emission at 375.89 nm (3.29 eV) • One prominent absorption band around 378.88 nm (3.27 eV)« less

Containerless processing of single crystals in low-G environment

NASA Technical Reports Server (NTRS)

Walter, H. U.

1974-01-01

Experiments on containerless crystal growth from the melt were conducted during Skylab missions SL3 and SL4 (Skylab Experiment M-560). Six samples of InSb were processed, one of them heavily doped with selenium. The concept of the experiment is discussed and related to general crystal growth methods and their merits as techniques for containerless processing in space. The morphology of the crystals obtained is explained in terms of volume changes associated with solidification and wetting conditions during solidification. All samples exhibit extremely well developed growth facets. Analysis by X-ray topographical methods and chemical etching shows that the crystals are of high structural perfection. Average dislocation density as revealed by etching is of the order of 100 per sq cm; no dislocation clusters could be observed in the space-grown samples. A sequence of striations that is observed in the first half of the selenium-doped sample is explained as being caused by periodic surface breakdown.

Lithium niobate bulk crystallization promoted by CO2 laser radiation

NASA Astrophysics Data System (ADS)

Ferreira, N. M.; Costa, F. M.; Nogueira, R. N.; Graça, M. P. F.

2012-09-01

The crystallization induced by laser radiation is a very promising technique to promote glass/ceramic transformation, being already used to produce crystalline patterns on glass surfaces. In this work, a SiO2-Li2O-Nb2O5 glass, prepared by the sol-gel route, was submitted to CO2 laser radiation and conventional heat-treatments in order to induce the LiNbO3 crystallization. The structure and morphology of the samples prepared by both routes was analyzed as a function of exposure time, radiation power and heat-treatment temperatures by XRD, Raman spectroscopy and SEM. The results reveal a correlation between the crystallization degree of LiNbO3 particles and glass matrix with the heat treatment type and experimental parameters. An heat-treatment at 650 °C/4 h was necessary to induce crystallization in heat treatments samples while 4 W/500 s was enough for laser radiation ones, corresponding a reduction time processing of ˜14 000 s.

Synthesis of renewable diesel through hydrodeoxygenation reaction from nyamplung oil (Calophyllum Inophyllum oil) using NiMo/Z and NiMo/C catalysts with rapid heating and cooling method

NASA Astrophysics Data System (ADS)

Susanto, B. H.; Prakasa, M. B.; Shahab, M. H.

2016-11-01

The synthesis of metal nanocrystal was conducted by modification preparation from simple heating method which heating and cooling process run rapidly. The result of NiMo/Z 575 °C characterizations are 33.73 m2/gram surface area and 31.80 nm crystal size. By used NiMo/C 700 °C catalyst for 30 minutes which had surface area of 263.21 m2/gram, had 31.77 nm crystal size, and good morphology, obtained catalyst with high activity, selectivity, and stability. After catalyst activated, synthesis of renewable diesel performed in hydrogenation reactor at 375 °C, 12 bar, and 800 rpm. The result of conversion was 81.99%, yield was 68.08%, and selectivity was 84.54%.

Direct Growth of CdTe on a (211) Si Substrate with Vapor Phase Epitaxy Using a Metallic Cd Source

NASA Astrophysics Data System (ADS)

Iso, Kenji; Gokudan, Yuya; Shiraishi, Masumi; Murakami, Hisashi; Koukitu, Akinori

2017-10-01

We successfully performed epitaxial CdTe growth on a Si (211) substrate with vapor-phase epitaxy using a cost-effective metallic cadmium source as a group-II precursor. The thermodynamic data demonstrate that the combination of metallic Cd and diisopropyl-telluride (DiPTe) with a H2 carrier gas enables the growth of CdTe crystals. A CdTe single crystal with a (422) surface orientation was obtained when a growth temperature between 600°C and 650°C was employed. The surface morphology and crystalline quality were improved with increasing film thickness. The full-width at half-maximum of the x-ray rocking curves with a film thickness of 15.7 μm for the skew-symmetrical (422) and asymmetrical (111) reflection were 528 arcsec and 615 arcsec, respectively.

Effect of Mg2+ on acidic calcium phosphate phases grown by electrodeposition

NASA Astrophysics Data System (ADS)

Correia, Matheus Bento; Júnior, José Pedro Gualberto; Macedo, Michelle Cardinale S. S.; Resende, Cristiane Xavier; dos Santos, Euler Araujo

2017-10-01

In this work, the effect of Mg2+ ions on the electrodeposition of dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and calcium-deficient hydroxyapatite (CDHA) crystals on a commercially pure titanium (cp-Ti) substrate was evaluated. We demonstrated that Mg2+ ions could change the morphology of the coatings by inhibiting the growth rate of the OCP and CDHA crystals and diminishing the crystallite size of DCPD. The inhibition effect on OCP and CDHA was most likely due to a surface adsorption mechanism since no evidence of a doping process was observed using Rietveld refinement and electron diffraction analyses. Conversely, the presence of Mg2+ ions generated a favorable condition for the nucleation of a new Mg2+-rich DCPD crystal population, presenting smaller crystallite sizes.

[A study of bone-like apatite formation on calcium phosphate ceramics in different kinds of animals in vivo].

PubMed

Duan, Yourong; Wu, Yao; Wang, Chaoyuan; Chen, Jiyong; Zhang, Xingdong

2003-03-01

Bone-like apatite formation on the surface of calcium phosphate ceramics has been believed to be necessary for new bone to grow on the ceramics and to be related to the osteoinductivity of the material. The research of bone-like apatite formation is a great help to understanding the mechanism of osteoinduction. Synthetic porous calcium phosphate ceramics (HA/TCP = 70/30) were implanted intramuscularly in pigs, dogs, rabbits and rats to make a comparative study of the bone-like apatite formation onto the porous HA/TCP ceramics in different animals. Specimens were harvested at 14 days after implantation. Samples were detected for the surface morphology with SEM. The chemical composition of the sample surface after implantation was analyzed with reflection infrared (R-IR). Obvious bone-like apatite formation could be detected in the sections of porous specimens harvested from all animals after 14 days intramuscular implantation. Crystal deposition could be only observed on the surface of the concave regions of the samples collected from dogs, rabbits and rat. On the contrary, evenly distributed flake-shaped crystal could be found on the pore surface and also on the outer surface of the materials implanted in pigs. The morphology of bone-like apatite in pigs was different from that in the others animals. Bone-like apatite was not observed in dense specimen implanted intramuscularly. Bone-like apatite formed faster on specimens implanted in rabbit than that in other animals. This formation sequence is different from the sequence of osteoinductivity of biphasic calcium phosphate ceramics implanted in these animals. The results demonstrated that the formation of bone-like apatite on materials is a prerequisite condition to their osteoinduction but other factors also play important roles in osteoinduction.

Structure refinement for tantalum nitrides nanocrystals with various morphologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

2012-07-15

Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

MOCVD Growth and Characterization of n-type Zinc Oxide Thin Films

NASA Astrophysics Data System (ADS)

Ben-Yaacov, Tammy

In the past decade, there has been widespread effort in the development of zinc oxide as a II-V1 semiconductor material. ZnO has potential advantages in optoelectronip device applications due to its unique electrical and optical properties. What stands out among these properties is its wide direct bandgap of 3.37 eV and its high electrical conductivity and transparency in the visible and near-UV regions of the spectrum. ZnO can be grown heteroepitaxially on GaN under near lattice-matched conditions and homoepitaxially as well, as high-quality bulk ZnO substrates are commercially available. This dissertation focuses on the development of the growth of high-quality, single crystal n-type ZnO films, control of n-type conductivity, as well as its application as a transparent contact material in GaN-based devices. The first part of this dissertation is an extensive heteroepitaxial and homoepitaxial growth study presenting the properties of ZnO(0001) layers grown on GaN(0001) templates and ZnO(0001) substrates. We show that deposition on GaN requires a two-step growth technique involving the growth of a low temperature nucleation layer before growing a high temperature epitaxial layer in order to obtain smooth ZnO films with excellent crystal quality and step-flow surface morphology. We obtained homoepitaxial ZnO(0001) films of structural quality and surface morphology that is comparable to the as-received substrates, and showed that a high growth temperature (≥1000°C) is needed in order to achieve step-flow growth mode. We performed n-type doping experiments, and established the conditions for which Indium effectively controls the n-type conductivity of ZnO films grown on GaN(0001) templates. A peak carrier concentration of 3.22x 10 19cm-3 and minimum sheet resistance of 97 O/square was achieved, while simultaneously maintaining good morphology and crystal quality. Finally, we present In-doped ZnO films implemented as p-contacts for GaN-based solar cells and LEDs, and we investigate the n-ZnO/p-GaN interface. We show that ZnO has potential as an effective p-contact for these devices, and determine properties that still need improvement in order for ZnO to compete with other contact materials. We also compare the device performance to metal-contacted devices. In summary, this thesis describes the growth of ZnO(0001) films by MOCVD, the progress in developing ZnO material with excellent surface morphology, high crystal quality, and controllable n-type doping, as well as its application to GaN-based optoelectronic devices as a p-contact material.

Simple, Green, and High-Yield Production of Boron-Based Nanostructures with Diverse Morphologies by Dissolution and Recrystallization of Layered Magnesium Diboride Crystals in Water.

PubMed

Gunda, Harini; Das, Saroj Kumar; Jasuja, Kabeer

2018-04-05

Layered metal diborides that contain metal atoms sandwiched between boron honeycomb planes offer a rich opportunity to access graphenic forms of boron. We recently demonstrated that magnesium diboride (MgB 2 ) could be exfoliated by ultrasonication in water to yield boron-based nanosheets. However, knowledge of the fate of metal boride crystals in aqueous phases is still in its incipient stages. This work presents our preliminary findings on the discovery that MgB 2 crystals can undergo dissolution in water under ambient conditions to result in precursors (prenucleation clusters) that, upon aging, undergo nonclassical crystallization preferentially growing in lateral directions by two-dimensional (2D) oriented attachment. We show that this recrystallization can be utilized as an avenue to obtain a high yield (≈92 %) of boron-based nanostructures, including nanodots, nanograins, nanoflakes, and nanosheets. These nanostructures comprise boron honeycomb planes chemically modified with hydride and oxy functional groups, which results in an overall negative charge on their surfaces. This ability of MgB 2 crystals to yield prenucleation clusters that can self-seed to form nanostructures comprising chemically modified boron honeycomb planes presents a new facet to the physicochemical interaction of MgB 2 with water. These findings also open newer avenues to obtain boron-based nanostructures with tunable morphologies by varying the chemical milieu during recrystallization. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Protonation of Different Goethite Surfaces - Unified Models for NaNO3 and NaCl Media.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lutzenkirchen, Johannes; Boily, Jean F.; Gunneriusson, Lars

2008-01-01

Acid-base titration data for two goethites samples in sodium nitrate and sodium chloride media are discussed. The data are modelled based on various surface complexation models in the framework of the MUlti SIte Complexation (MUSIC) model. Various assumptions with respect to the goethite morphology are considered in determining the site density of the surface functional groups. The results from the various model applications are not statistically significant in terms of goodness of fit. More importantly, various published assumptions with respect to the goethite morphology (i.e. the contributions of different crystal planes and their repercussions on the “overall” site densities ofmore » the various surface functional groups) do not significantly affect the final model parameters. The simultaneous fit of the chloride and nitrate data results in electrolyte binding constants, which are applicable over a wide range of electrolyte concentrations including mixtures of chloride and nitrate. Model parameters for the high surface area goethite sample are in excellent agreement with parameters that were independently obtained by another group on different goethite titration data sets.« less

Polymer composites and porous materials prepared by thermally induced phase separation and polymer-metal hybrid methods

NASA Astrophysics Data System (ADS)

Yoon, Joonsung

The primary objective of this research is to investigate the morphological and mechanical properties of composite materials and porous materials prepared by thermally induced phase separation. High melting crystallizable diluents were mixed with polymers so that the phase separation would be induced by the solidification of the diluents upon cooling. Theoretical phase diagrams were calculated using Flory-Huggins solution thermodynamics which show good agreement with the experimental results. Porous materials were prepared by the extraction of the crystallized diluents after cooling the mixtures (hexamethylbenzene/polyethylene and pyrene/polyethylene). Anisotropic structures show strong dependence on the identity of the diluents and the composition of the mixtures. Anisotropic crystal growth of the diluents was studied in terms of thermodynamics and kinetics using DSC, optical microscopy and SEM. Microstructures of the porous materials were explained in terms of supercooling and dendritic solidification. Dual functionality of the crystallizable diluents for composite materials was evaluated using isotactic polypropylene (iPP) and compatible diluents that crystallize upon cooling. The selected diluents form homogeneous mixtures with iPP at high temperature and lower the viscosity (improved processability), which undergo phase separation upon cooling to form solid particles that function as a toughening agent at room temperature. Tensile properties and morphology of the composites showed that organic crystalline particles have the similar effect as rigid particles to increase toughness; de-wetting between the particle and iPP matrix occurs at the early stage of deformation, followed by unhindered plastic flow that consumes significant amount of fracture energy. The effect of the diluents, however, strongly depends on the identity of the diluents that interact with the iPP during solidification step, which was demonstrated by comparing tetrabromobisphenol-A and phthalic anhydride. A simple method to prepare composite surfaces that can change the wettability in response to the temperature change was proposed and evaluated. Composite surfaces prepared by nanoporous alumina templates filled with polymers showed surface morphology and wettability that depend on temperature. This effect is attributed to the significant difference in thermal conductivity and the thermal expansion coefficient between the alumina and the polymers. The reversibility in thermal response depends on the properties of the polymers.

Cooling and crystallization of rhyolite-obsidian lava: Insights from micron-scale projections on plagioclase microlites

NASA Astrophysics Data System (ADS)

Sano, Kyohei; Toramaru, Atsushi

2017-07-01

To reveal the cooling process of a rhyolite-obsidian flow, we studied the morphology of plagioclase microlites in the Tokachi-Ishizawa lava of Shirataki, northern Hokkaido, Japan, where the structure of the lava can be observed from obsidian at the base of the flow to the innermost rhyolite. Needle-like micron-scale textures, known as "projections", occur on the short side surfaces of the plagioclase microlites. Using FE-SEM we discovered a positive correlation between the lengths and spacings of these projections. On the basis of the instability theory of an interface between melt and crystal, and to understand the length and spacing data, we developed a model that explains the positive correlation and allows us to simultaneously estimate growth rates and growth times. Applying the model to our morphological data and the estimated growth rates and growth times, we suggest that the characteristics of the projections reflect the degree of undercooling, which in turn correlates with lava structure (the obsidian at the margin of the flow experienced a higher degree of undercooling than the interior rhyolite). The newly developed method provides insights into the degree of undercooling during the final stages of crystallization of a rhyolitic lava flow.

Sonication-assisted synthesis of a new cationic zinc nitrate complex with a tetradentate Schiff base ligand: Crystal structure, Hirshfeld surface analysis and investigation of different parameters influence on morphological properties.

PubMed

Mousavi, S A; Montazerozohori, M; Masoudiasl, A; Mahmoudi, G; White, J M

2018-09-01

A nanostructured cationic zinc nitrate complex with a formula of [ZnLNO 3 ]NO 3 (where L = (N 2 E,N 2' E)-N 1 ,N 1' -(ethane-1,2-diyl)bis(N 2 -((E)-3-phenylallylidene)ethane-1,2-diamine)) was prepared by sonochemical process and characterized by single crystal X-ray crystallography, scanning electron microscopy (SEM), FT-IR and NMR spectroscopy and X-ray powder diffraction (XRPD). The X-ray analysis demonstrates the formation of a cationic complex that metal center is five-coordinated by four nitrogen atom from Schiff base ligand and one oxygen atom from nitrate group. The crystal packing analysis demonstrates the essential role of the nitrate groups in the organization of supramolecular structure. The morphology and size of ultrasound-assisted synthesized zinc nitrate complex have been investigated using scanning electron microscopy (SEM) by changing parameters such as the concentration of initial reactants, the sonication power and reaction temperature. In addition the calcination of zinc nitrate complex in air atmosphere led to production of zinc oxide nanoparticles. Copyright © 2018. Published by Elsevier B.V.

Two-Dimensional Magnesium Phosphate Nanosheets Form Highly Thixotropic Gels That Up-Regulate Bone Formation.

PubMed

Laurenti, Marco; Al Subaie, Ahmed; Abdallah, Mohamed-Nur; Cortes, Arthur R G; Ackerman, Jerome L; Vali, Hojatollah; Basu, Kaustuv; Zhang, Yu Ling; Murshed, Monzur; Strandman, Satu; Zhu, Julian; Makhoul, Nicholas; Barralet, Jake E; Tamimi, Faleh

2016-08-10

Hydrogels composed of two-dimensional (2D) nanomaterials have become an important alternative to replace traditional inorganic scaffolds for tissue engineering. Here, we describe a novel nanocrystalline material with 2D morphology that was synthesized by tuning the crystallization of the sodium-magnesium-phosphate system. We discovered that the sodium ion can regulate the precipitation of magnesium phosphate by interacting with the crystal's surface causing a preferential crystal growth that results in 2D morphology. The 2D nanomaterial gave rise to a physical hydrogel that presented extreme thixotropy, injectability, biocompatibility, bioresorption, and long-term stability. The nanocrystalline material was characterized in vitro and in vivo and we discovered that it presented unique biological properties. Magnesium phosphate nanosheets accelerated bone healing and osseointegration by enhancing collagen formation, osteoblasts differentiation, and osteoclasts proliferation through up-regulation of COL1A1, RunX2, ALP, OCN, and OPN. In summary, the 2D magnesium phosphate nanosheets could bring a paradigm shift in the field of minimally invasive orthopedic and craniofacial interventions because it is the only material available that can be injected through high gauge needles into bone defects in order to accelerate bone healing and osseointegration.

Growth, crystalline perfection, spectral and optical characterization of a novel optical material: l-tryptophan p-nitrophenol trisolvate single crystal.

PubMed

Sivakumar, N; Srividya, J; Mohana, J; Anbalagan, G

2015-03-15

l-tryptophan p-nitrophenol trisolvate (LTPN), an organic nonlinear optical material was synthesized using ethanol-water mixed solvent and the crystals were grown by a slow solvent evaporation method. The crystal structure and morphology were studied by single crystal X-ray diffraction analysis. The crystalline perfection of the LTPN crystal was analyzed by high-resolution X-ray diffraction study. The molecular structure of the crystal was confirmed by observing the various characteristic functional groups of the material using vibrational spectroscopy. The cut-off wavelength, optical transmission, refractive index and band gap energy were determined using UV-visible data. The variation of refractive index with wavelength shows the normal behavior. The second harmonic generation of the crystal was confirmed and the efficiency was measured using Kurtz Perry powder method. Single and multiple shot methods were employed to measure surface laser damage of the crystal. The photoluminescence spectral study revealed that the emission may be associated with the radiative recombination of trapped electrons and holes. Microhardness measurements revealed that LTPN belongs to a soft material category. Copyright © 2014 Elsevier B.V. All rights reserved.

The effect of UV exposure and heat treatment on crystallization behavior of photosensitive glasses

NASA Astrophysics Data System (ADS)

Kıbrıslı, Orhan; Ersundu, Ali Erçin

2018-05-01

In this study, photosensitive glasses in the Na2O-ZnO-Al2O3-SiO2 system with photosensitizing agents (cerium, silver, tin, antimony) and halogenides (NaF and KBr) were synthesized through a conventional melt-quenching technique. The crystallization mechanism was investigated for solely heat-treated and UV-exposed + heat-treated samples using differential thermal analysis (DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques to understand the effect of UV exposure on crystallization behavior of photosensitive glasses. Accordingly, non-isothermal DTA measurements were performed at different heating rates to determine crystallization peak, T p, and onset, T c, temperatures. For solely heat-treated samples, the kinetic parameters such as the Avrami constant, n, and morphology index, m, were calculated as 1 from the Ozawa method indicating surface crystallization and the value of crystallization activation energy was calculated as 944 kJ/mol using modified Kissinger method. On the contrary, bulk crystallization was found to be predominant for UV exposed + heat-treated samples revealing that UV exposure is the primary cause of bulk crystallization in photosensitive glasses.

Probing Zeolite Crystal Architecture and Structural Imperfections using Differently Sized Fluorescent Organic Probe Molecules.

PubMed

Hendriks, Frank C; Schmidt, Joel E; Rombouts, Jeroen A; Lammertsma, Koop; Bruijnincx, Pieter C A; Weckhuysen, Bert M

2017-05-05

A micro-spectroscopic method has been developed to probe the accessibility of zeolite crystals using a series of fluorescent 4-(4-diethylaminostyryl)-1-methylpyridinium iodide (DAMPI) probes of increasing molecular size. Staining large zeolite crystals with MFI (ZSM-5) topology and subsequent mapping of the resulting fluorescence using confocal fluorescence microscopy reveal differences in structural integrity: the 90° intergrowth sections of MFI crystals are prone to develop structural imperfections, which act as entrance routes for the probes into the zeolite crystal. Polarization-dependent measurements provide evidence for the probe molecule's alignment within the MFI zeolite pore system. The developed method was extended to BEA (Beta) crystals, showing that the previously observed hourglass pattern is a general feature of BEA crystals with this morphology. Furthermore, the probes can accurately identify at which crystal faces of BEA straight or sinusoidal pores open to the surface. The results show this method can spatially resolve the architecture-dependent internal pore structure of microporous materials, which is difficult to assess using other characterization techniques such as X-ray diffraction. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Growth and spectroscopic, thermodynamic and nonlinear optical studies of L-threonine phthalate crystal

NASA Astrophysics Data System (ADS)

Theras, J. Elberin Mary; Kalaivani, D.; Jayaraman, D.; Joseph, V.

2015-10-01

L-threonine phthalate (LTP) single crystal has been grown using a solution growth technique at room temperature. Single crystal X-ray diffraction analysis reveals that LTP crystallizes in monoclinic crystal system with space group C2/c. The optical absorption studies show that the crystal is transparent in the entire visible region with a cut-off wavelength 309 nm. The optical band gap is found to be 4.05 eV. The functional groups of the synthesized compound have been identified by FTIR spectral analysis. The functional groups present in the material were also confirmed by FT-RAMAN spectroscopy. Surface morphology and the presence of various elements were studied by SEM-EDAX analysis. The thermal stability of LTP single crystal has been analyzed by TGA/DTA studies. The thermodynamic parameters such as activation energy, entropy, enthalpy and Gibbs free energy were determined for the grown material using TG data and Coats-Redfern relation. Since the grown crystal is centrosymmetric, Z-Scan studies were carried out for analyzing the third order nonlinear optical property. The nonlinear absorption coefficient, nonlinear refractive index and susceptibility have been measured using Z-Scan technique.

Growth and characterization of a new nonlinear optical organic crystal: 2,4,6-Trimethylacetanilide

NASA Astrophysics Data System (ADS)

Upadhyaya, V.; Prabhu, Sharada G.

2015-09-01

A new nonlinear optical organic material, 2,4,6-trimethylacetanilide (246TMAA), also known as N-[2,4,6- trimethylphenyl]acetamide, has been synthesized and grown as a single crystal by the slow evaporation technique by organic solvents. The grown crystals have been characterized by morphology study. The crystals are prismatic. Surface examination shows granular dendritic pattern in optical micrograph. The Scanning Electron Micrograph shows the layered growth of the crystal. The Differential Scanning Calorimeter plot shows no phase change until melting point (219°C). The density of the crystals is 1.1g/cc and the crystals are soft. The crystals are transparent in the visible region and in the ultra-violet region till 280 nm. 246TMAA crystallizes with 2 molecules in a monoclinic unit cell in the noncentrosymmetric point group m, space group Pn. Refractive indices of this optically biaxial crystal along the three crystallophysical axes have been measured at 633 nm. The optical second harmonic generation efficiency of the crystal at 1064 nm is about half that of the urea crystal, measured by powder method using Nd:YAG laser. The results show that the 246TMAA crystal can efficiently be used for up-conversion of infrared radiation into visible green light. The powder X-ray diffraction spectrum of the crystal has been obtained.

On the development of two characteristically different crystal morphology in SiO(2)-MgO-Al (2)O (3)-K (2)O-B (2)O (3)-F glass-ceramic system.

PubMed

Roy, Shibayan; Basu, Bikramjit

2009-01-01

The present work demonstrates how crystals with two different characteristic morphologies can be formed in SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass-ceramic system by adopting two sets of heat treatment experiments. In our study, single stage heat treatment experiments were performed at 1,000 degrees C for varying holding time of 8-24 h with 4 h time interval and as a function of temperature in the range of 1,000-1,120 degrees C with 40 degrees C temperature interval. The constant heating rate of 10 degrees C/min was employed for both sets of experiments. The microstructural changes were investigated using Fourier transformed infrared spectroscopy (FT-IR), SEM-EDS and XRD. For temperature variation batches, the microstructure is characterized by interlocked, randomly oriented mica plates ('house-of-cards' morphology). An important and new observation of complex crystal morphology is made in the samples heat treated at 1,000 degrees C for varying holding times. Such morphology appears to be the results of composite spherulitic-dendritic like growth of mica rods radiating from a central nucleus. The possible mechanism for such characteristic crystal growth morphology is discussed with reference to a nucleation-growth kinetics based model. The activation energy for crystal nucleation and Avrami index are computed to be 388 kJ/mol and 1.3 respectively, assuming Johnson-Mehl-Avrami model of crystallization. Another important result is that a maximum of around 70% of spherulitic-dendritic like crystal morphology can be obtained after heat treatment at 1,000 degrees C for 24 h, while a lower amount (approximately 58%) of interlocked plate like mica crystals is formed after heat treatment at 1,040 degrees C for 4 h.

Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

DOE PAGES

O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal; ...

2017-05-22

Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

Air-stable solution-processed n-channel organic thin film transistors with polymerenhanced morphology

DOE PAGES

He, Zhengran; Shaik, Shoieb; Bi, Sheng; ...

2015-05-04

N,N 0-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN 2) is an n-type semiconductor exhibiting high electron mobility and excellent air stability. However, the reported electron mobility based on spin-coated PDIF-CN 2 film is much lower than the value of PDIF-CN 2 single crystals made from vapor phase deposition, indicating significant room for mobility enhancement. In this study, various insulating polymers, including poly(vinyl alcohol), poly(methyl methacrylate) (PMMA), and poly(alpha-methylstyrene) (PaMS), are pre-coated on silicon substrate aiming to enhance the morphology of the PDIF-CN 2 thin film, thereby improving the charge transport and air stability. Atomic force microscopy images reveal that with the pre-deposition of PaMSmore » or PMMA polymers, the morphology of the PDIF-CN 2 polycrystalline films is optimized in semiconducting crystal connectivity, domain size, and surface roughness, which leads to significant improvement of organic thin-film transistor (OTFT) performance. Particularly, an electron mobility of up to 0.55 cm 2/V s has been achieved from OTFTs based on the PDIF-CN 2 film with the pre-deposition of PaMS polymer.« less

Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal

Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

Crystallization of 21.25Gd 2O 3-63.75MoO 3-15B 2O 3 glass induced by femtosecond laser at the repetition rate of 250 kHz

NASA Astrophysics Data System (ADS)

Zhong, M. J.; Han, Y. M.; Liu, L. P.; Zhou, P.; Du, Y. Y.; Guo, Q. T.; Ma, H. L.; Dai, Y.

2010-12-01

We report the formation of β'-Gd 2(MoO 4) 3 (GMO) crystal on the surface of the 21.25Gd 2O 3-63.75MoO 3-15B 2O 3 glass, induced by 250 kHz, 800 nm femtosecond laser irradiation. The morphology of the modified region in the glass was clearly examined by scanning electron microscopy (SEM). By micro-Raman spectra, the laser-induced crystals were confirmed to be GMO phases and it is found that these crystals have a strong dependence on the number and power of the femtosecond laser pulses. When the irradiation laser power was 900 mW, not only the Raman peaks of GMO crystals but also some new peaks at 214 cm -1, 240 cm -1, 466 cm -1, 664 cm -1 and 994 cm -1which belong to the MoO 3 crystals were observed. The possible mechanisms are proposed to explain these phenomena.

Metal Organic Framework Micro/Nanopillars of Cu(BTC)·3H₂O and Zn(ADC)·DMSO.

PubMed

Kojtari, Arben; Ji, Hai-Feng

2015-04-09

In this work, we report the optical and thermal properties of Cu(BTC)·3H₂O (BTC = 1,3,5-benzenetricarboxylic acid) and Zn(ADC)·DMSO (ADC = 9,10- anthracenedicarboxylic acid, DMSO = dimethyl sulfoxide) metal-organic frameworks (MOFs) micro/nanopillars. The morphologies of MOFs on surfaces are most in the form of micro/nanopillars that were vertically oriented on the surface. The size and morphology of the pillars depend on the evaporation time, concentration, solvent, substrate, and starting volume of solutions. The crystal structures of the nanopillars and micropillars are the same, confirmed by powder XRD. Zn(ADC)·DMSO pillars have a strong blue fluorescence. Most of ADC in the pillars are in the form of monomers, which is different from ADC in the solid powder.

“Skin-Core-Skin” Structure of Polymer Crystallization Investigated by Multiscale Simulation

PubMed Central

Ruan, Chunlei

2018-01-01

“Skin-core-skin” structure is a typical crystal morphology in injection products. Previous numerical works have rarely focused on crystal evolution; rather, they have mostly been based on the prediction of temperature distribution or crystallization kinetics. The aim of this work was to achieve the “skin-core-skin” structure and investigate the role of external flow and temperature fields on crystal morphology. Therefore, the multiscale algorithm was extended to the simulation of polymer crystallization in a pipe flow. The multiscale algorithm contains two parts: a collocated finite volume method at the macroscopic level and a morphological Monte Carlo method at the microscopic level. The SIMPLE (semi-implicit method for pressure linked equations) algorithm was used to calculate the polymeric model at the macroscopic level, while the Monte Carlo method with stochastic birth-growth process of spherulites and shish-kebabs was used at the microscopic level. Results show that our algorithm is valid to predict “skin-core-skin” structure, and the initial melt temperature and the maximum velocity of melt at the inlet mainly affects the morphology of shish-kebabs. PMID:29659516

Dynamics of solid thin-film dewetting in the silicon-on-insulator system

NASA Astrophysics Data System (ADS)

Bussmann, E.; Cheynis, F.; Leroy, F.; Müller, P.; Pierre-Louis, O.

2011-04-01

Using low-energy electron microscopy movies, we have measured the dewetting dynamics of single-crystal Si(001) thin films on SiO2 substrates. During annealing (T>700 °C), voids open in the Si, exposing the oxide. The voids grow, evolving Si fingers that subsequently break apart into self-organized three-dimensional (3D) Si nanocrystals. A kinetic Monte Carlo model incorporating surface and interfacial free energies reproduces all the salient features of the morphological evolution. The dewetting dynamics is described using an analytic surface-diffusion-based model. We demonstrate quantitatively that Si dewetting from SiO2 is mediated by surface-diffusion driven by surface free-energy minimization.

Independence of surface morphology and reconstruction during the thermal preparation of perovskite oxide surfaces

NASA Astrophysics Data System (ADS)

Jäger, Maren; Teker, Ali; Mannhart, Jochen; Braun, Wolfgang

2018-03-01

Using a CO2 laser to directly heat the crystals from the back side, SrTiO3 substrates may be thermally prepared in situ for epitaxy without the need for ex-situ etching and annealing. We find that the formation of large terraces with straight steps at 900-1100 °C is independent of the formation of the ideal surface reconstruction for epitaxy, which requires temperatures in excess of 1200 °C to complete. The process may be universal, at least for perovskite oxide surfaces, as it also works, at different temperatures, for LaAlO3 and NdGaO3, two other widely used oxide substrate materials.

A systematic examination of the morphogenesis of calcium carbonate in the presence of a double-hydrophilic block copolymer.

PubMed

Cölfen, H; Qi, L

2001-01-05

In this paper, a systematic study of the influence of various experimental parameters on the morphology and size of CaCO3 crystals after room-temperature crystallization from water in the presence of poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) is presented. The pH of the solution, the block copolymer concentration, and the ratio [polymer]/[CaCO3] turned out to be important parameters for the morphogenesis of CaCO3, whereas a moderate increase of the ionic strength (0.016 M) had no influence. Depending on the experimental conditions, the crystal morphologies can be tuned from calcite rhombohedra via rods, ellipsoids or dumbbells to spheres. A morphology map is presented which allows the prediction of the crystal morphology from a combination of pH, and CaCO3 and polymer concentration. Morphologies reported in literature for the same system but under different crystallization conditions agree well with the predictions from the morphology map. A closer examination of the growth of polycrystalline macroscopic CaCO3 spheres by TEM and time-resolved dynamic light scattering showed that CaCO3 macrocrystals are formed from strings of aggregated amorphous nanoparticles and then recrystallize as dumbbell-shaped or spherical calcite macrocrystal.

Complex and oriented ZnO nanostructures.

PubMed

Tian, Zhengrong R; Voigt, James A; Liu, Jun; McKenzie, Bonnie; McDermott, Matthew J; Rodriguez, Mark A; Konishi, Hiromi; Xu, Huifang

2003-12-01

Extended and oriented nanostructures are desirable for many applications, but direct fabrication of complex nanostructures with controlled crystalline morphology, orientation and surface architectures remains a significant challenge. Here we report a low-temperature, environmentally benign, solution-based approach for the preparation of complex and oriented ZnO nanostructures, and the systematic modification of their crystal morphology. Using controlled seeded growth and citrate anions that selectively adsorb on ZnO basal planes as the structure-directing agent, we prepared large arrays of oriented ZnO nanorods with controlled aspect ratios, complex film morphologies made of oriented nanocolumns and nanoplates (remarkably similar to biomineral structures in red abalone shells) and complex bilayers showing in situ column-to-rod morphological transitions. The advantages of some of these ZnO structures for photocatalytic decompositions of volatile organic compounds were demonstrated. The novel ZnO nanostructures are expected to have great potential for sensing, catalysis, optical emission, piezoelectric transduction, and actuations.

Influence of surfactants on the microstructure and electrochemical performance of the tin oxide anode in lithium ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yan-Hui, E-mail: sunyanhui0102@163.com; Guangzhou Key Laboratory of Materials for Energy Conversion and Storage, South China Normal University, Guangzhou 510006; Dong, Pei-Pei

2016-02-15

Highlights: • CTAB and SDS alter the formation of SnO{sub 2} from nanosheets to nanocubes during oxalate precipitation. • The CTAB concentration affects the SnO{sub 2} crystal growth direction, morphology and size. • The SnO{sub 2} anode synthesized using CTAB exhibited superior electrochemical performance. • Proposed a mechanism of influence of surfactant on SnO{sub 2} in the precipitation and annealing process. - Abstract: Different SnO{sub 2} micro–nano structures are prepared by precipitation using a surfactant-assisted process. The surfactants, such as cetyltriethylammonium bromide (CTAB) or sodium dodecyl benzene sulfonate (SDBS), can change the crystal growth direction and microstructure of SnO{sub 2}more » primary and secondary particles. Larger SnO{sub 2} nanosheets were synthesized without surfactant, and micro-fragments composed of small nanospheres or nanocubes were synthesized using CTAB and SDBS. The CTAB-assisted process resulted in smaller primary particles and larger specific surface area and larger pore volume, as a lithium-ion-battery anode that exhibits superior electrochemical performance compared to the other two anodes. Further investigation showed that the concentration of CTAB had a substantial influence on the growth of the crystal face, morphology and size of the SnO{sub 2} secondary particles, which influenced the electrochemical performance of the anode. A simple mechanism for the influence of surfactants on SnO{sub 2} morphology and size in the precipitation and annealing process is proposed.« less

Influence of the doping type and level on the morphology of porous Si formed by galvanic etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pyatilova, O. V., E-mail: 5ilova87@gmail.com; Gavrilov, S. A.; Shilyaeva, Yu. I.

The formation of porous silicon (por-Si) layers by the galvanic etching of single-crystal Si samples (doped with boron or phosphorus) in an HF/C{sub 2}H{sub 5}OH/H{sub 2}O{sub 2} solution is investigated. The por-Si layers are analyzed by the capillary condensation of nitrogen and scanning electron microscopy (SEM). The dependences of the morphological characteristics of por-Si (pore diameter, specific surface area, pore volume, and thickness of the pore walls), which determine the por-Si combustion kinetics, on the dopant type and initial wafer resistivity are established.

Optical and morphological properties of sol gel derived titanium dioxide films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, A. B.; Sharma, S. K.; M, Vishwas

2015-08-28

Titanium oxide (Titania) thin films were synthesized on different substrates via the sol-gel dip-coating method using alkoxide solution. Some selected samples were also prepared with different percentage of Lead (Pb). The influence of Pb addition in precursor sol on the optical properties of titanium dioxide thin films was studied. The optical transmittance in the visible region has increased with increase in weight percentage of lead. The refractive index was slightly decreased with Pb addition. Crystallization of these coatings was achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studiedmore » by Scanning Electron Microscopy. Increase in average grain size from 250 nm to 350 nm with increase in Pb concentration is observed. Films were appeared to more coarse with increase in Pb addition. An increase in Pb addition resulted increase in average roughness from 12 nm to 25 nm.« less

Structural, optical and field emission properties of urchin-shaped ZnO nanostructures.

PubMed

Al-Heniti, Saleh; Umar, Ahmad

2013-01-01

In this work, well-crystallized urchin-shaped ZnO structures were synthesized on silicon substrate by simple non-catalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen as source materials for zinc and oxygen, respectively. The synthesized ZnO structures were characterized in detail in terms of their morphological, structural, optical and field emission properties. The detailed morphological investigations revealed that the synthesized structures possess urchin-shape and grown in high-density over the substrate surface. The detailed structural and optical characterizations revealed that the synthesized urchin-shaped ZnO structures are well-crystallized and exhibiting good optical properties. The field emission analysis for urchin-shaped ZnO structures exhibits a turn-on field of 4.6 V/microm. The emission current density reached to 0.056 mA/cm2 at an applied electrical field of 6.4 V/microm and shows no saturation. The calculated field enhancement factor 'beta', from the F-N plot, was found to be approximately 2.2 x 10(3).

Synthesis of Coral-Like Tantalum Oxide Films via Anodization in Mixed Organic-Inorganic Electrolytes

PubMed Central

Yu, Hongbin; Zhu, Suiyi; Yang, Xia; Wang, Xinhong; Sun, Hongwei; Huo, Mingxin

2013-01-01

We report a simple method to fabricate nano-porous tantalum oxide films via anodization with Ta foils as the anode at room temperature. A mixture of ethylene glycol, phosphoric acid, NH4F and H2O was used as the electrolyte where the nano-porous tantalum oxide could be synthesized by anodizing a tantalum foil for 1 h at 20 V in a two–electrode configuration. The as-prepared porous film exhibited a continuous, uniform and coral-like morphology. The diameters of pores ranged from 30 nm to 50 nm. The pores interlaced each other and the depth was about 150 nm. After calcination, the as-synthesized amorphous tantalum oxide could be crystallized to the orthorhombic crystal system. As observed in photocatalytic experiments, the coral-like tantalum oxide exhibited a higher photocatalytic activity for the degradation of phenol than that with a compact surface morphology, and the elimination rate of phenol increased by 66.7%. PMID:23799106

CH₃NH₃PbI₃-based planar solar cells with magnetron-sputtered nickel oxide.

PubMed

Cui, Jin; Meng, Fanping; Zhang, Hua; Cao, Kun; Yuan, Huailiang; Cheng, Yibing; Huang, Feng; Wang, Mingkui

2014-12-24

Herein we report an investigation of a CH3NH3PbI3 planar solar cell, showing significant power conversion efficiency (PCE) improvement from 4.88% to 6.13% by introducing a homogeneous and uniform NiO blocking interlayer fabricated with the reactive magnetron sputtering method. The sputtered NiO layer exhibits enhanced crystallization, high transmittance, and uniform surface morphology as well as a preferred in-plane orientation of the (200) plane. The PCE of the sputtered-NiO-based perovskite p-i-n planar solar cell can be further promoted to 9.83% when a homogeneous and dense perovskite layer is formed with solvent-engineering technology, showing an impressive open circuit voltage of 1.10 V. This is about 33% higher than that of devices using the conventional spray pyrolysis of NiO onto a transparent conducting glass. These results highlight the importance of a morphology- and crystallization-compatible interlayer toward a high-performance inverted perovskite planar solar cell.

The effects of tungsten's pre-irradiation surface condition on helium-irradiated morphology

DOE PAGES

Garrison, Lauren M.; Kulcinski, Gerald L.

2015-07-17

Erosion is a concern associated with the use of tungsten as a plasma-facing component in fusion reactors. To compare the damage progression, polycrystalline tungsten (PCW) and (110) single crystal tungsten (SCW) samples were prepared with (1) a mechanical polish (MP) with roughness values in the range of 0.018–0.020 μm and (2) an MP and electropolish (MPEP) resulting in roughness values of 0.010–0.020 μm for PCW and 0.003–0.005 μm for SCW samples. Samples were irradiated with 30 keV He + at 1173 K to fluences between 3 × 10 21 and 6 × 10 22 He/m 2. The morphologies that developedmore » after low-fluence bombardment were different for each type of sample—MP SCW, MPEP SCW, MP PCW, and MPEP PCW. At the highest fluence, the SCW MPEP sample lost significantly more mass and developed a different morphology than the MP SCW sample. The PCW samples developed a similar morphology and had similar mass loss at the highest fluence. Surface preparation can have a significant effect on post-irradiation morphology that should be considered for the design of future fusion reactors such as ITER and DEMO.« less

Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement.

PubMed

Ge, Jian-Feng; Liu, Zhi-Long; Gao, Chun-Lei; Qian, Dong; Liu, Canhua; Jia, Jin-Feng

2015-05-01

Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO3 surface.

Phase-field study of grain boundary tracking behavior in crack-seal microstructures

NASA Astrophysics Data System (ADS)

Ankit, Kumar; Nestler, Britta; Selzer, Michael; Reichardt, Mathias

2013-12-01

In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.

Effect of silk sericin on morphology and structure of calcium carbonate crystal

NASA Astrophysics Data System (ADS)

Zhao, Rui-Bo; Han, Hua-Feng; Ding, Shao; Li, Ze-Hao; Kong, Xiang-Dong

2013-06-01

In this paper, silk sericin was employed to regulate the mineralization of calcium carbonate (CaCO3). CaCO3 composite particles were prepared by the precipitation reaction of sodium carbonate with calcium chloride solution in the presence of silk sericin. The as-prepared samples were collected at different reaction time to study the crystallization process of CaCO3 by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The results showed that silk sericin significantly affected the morphology and crystallographic polymorph of CaCO3. With increasing the reaction time, the crystal phase of CaCO3 transferred from calcite dominated to vaterite dominated mixtures, while the morphology of CaCO3 changed from disk-like calcite crystal to spherical vaterite crystal. These studies showed the potential of silk sericin used as a template molecule to control the growth of inorganic crystal.

Crystal growth, structure and morphology of hydrocortisone methanol solvate

NASA Astrophysics Data System (ADS)

Chen, Jianxin; Wang, Jiangkang; Zhang, Ying; Wu, Hong; Chen, Wei; Guo, Zhichao

2004-04-01

Hydrocortisone (HC), an important grucocorticoid, was crystallized from methanol solvent in the form of its methanol solvate. Its crystal structure belongs to orthorhombic, space group P2 12 12 1, with the unit cell parameters a=7.712(3) Å, b=14.392(5) Å, c=18.408(6) Å, Z=4. The methanol takes part in intermolecular hydrogen bonding, so if we change the solvent, the crystal habit of HC maybe different. The long parallelepiped morphology was also predicted by Cerius 2TM simulation program. The influence of intermolecular interaction was taken into account in the attachment energy model. The morphology calculation performed on the potential energy minimized model using a generic DREIDING 2.21 force field and developed minimization protocol with derived partial charges fits the experimental crystal shape well.

Solidification observations and sliding wear behavior of vacuum arc melting processed Ni-Al-TiC composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karantzalis, A.E., E-mail: akarantz@cc.uoi.gr; Lekatou, A.; Tsirka, K.

2012-07-15

Monolithic Ni{sub 3}Al and Ni-25 at.%Al intermetallic matrix TiC-reinforced composites were successfully produced by vacuum arc melting. TiC crystals were formed through a dissolution-reprecipitation mechanism and their final morphology is explained by means of a) Jackson's classical nucleation and growth phenomena and b) solidification rate considerations. The TiC presence altered the matrix microconstituents most likely due to specific melt-particle interactions and crystal plane epitaxial matching. TiC particles caused a significant decrease on the specific wear rate of the monolithic Ni{sub 3}Al alloy and the possible wear mechanisms are approached by means of a) surface oxidation, b) crack/flaws formation, c) materialmore » detachment and d) debris-counter surfaces interactions. - Highlights: Black-Right-Pointing-Pointer Vacuum arc melting (VAM) of Ni-Al based intermetallic matrix composite materials. Black-Right-Pointing-Pointer Solidification phenomena examination. Black-Right-Pointing-Pointer TiC crystal formation and growth mechanisms. Black-Right-Pointing-Pointer Sliding wear examination.« less

Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides

DOE PAGES

Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; ...

2015-10-29

Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and amore » thin surface layer on certain crystallographic facets. Finally and more specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.« less

Thermally controlled growth of surface nanostructures on ion-modified AIII-BV semiconductor crystals

NASA Astrophysics Data System (ADS)

Trynkiewicz, Elzbieta; Jany, Benedykt R.; Wrana, Dominik; Krok, Franciszek

2018-01-01

The primary motivation for our systematic study is to provide a comprehensive overview of the role of sample temperature on the pattern evolution of several AIII-BV semiconductor crystal (001) surfaces (i.e., InSb, InP, InAs, GaSb) in terms of their response to low-energy Ar+ ion irradiation conditions. The surface morphology and the chemical diversity of such ion-modified binary materials has been characterized by means of scanning electron microscopy (SEM). In general, all surface textures following ion irradiation exhibit transitional behavior from small islands, via vertically oriented 3D nanostructures, to smoothened surface when the sample temperature is increased. This result reinforces our conviction that the mass redistribution of adatoms along the surface plays a vital role during the formation and growth process of surface nanostructures. We would like to emphasize that this paper addresses in detail for the first time the topic of the growth kinetics of the nanostructures with regard to thermal surface diffusion, while simultaneously offering some possible approaches to supplementing previous studies and therein gaining a new insight into this complex issue. The experimental results are discussed with reference to models of the pillars growth, abutting on preferential sputtering, the self-sustained etch masking effect and the redeposition process recently proposed to elucidate the observed nanostructuring mechanism.

Detecting explosive molecules from nanoliter solution: A new paradigm of SERS sensing on hydrophilic photonic crystal biosilica.

PubMed

Kong, Xianming; Xi, Yuting; Le Duff, Paul; Chong, Xinyuan; Li, Erwen; Ren, Fanghui; Rorrer, Gregory L; Wang, Alan X

2017-02-15

We demonstrate a photonic crystal biosilica surface-enhanced Raman scattering (SERS) substrate based on a diatom frustule with in-situ synthesized silver nanoparticles (Ag NPs) to detect explosive molecules from nanoliter (nL) solution. By integrating high density Ag NPs inside the nanopores of diatom biosilica, which is not achievable by traditional self-assembly techniques, we obtained ultra-high SERS sensitivity due to dual enhancement mechanisms. First, the hybrid plasmonic-photonic crystal biosilica with three dimensional morphologies was obtained by electroless-deposited Ag seeds at nanometer sized diatom frustule surface, which provides high density hot spots as well as strongly coupled optical resonances with the photonic crystal structure of diatom frustules. Second, we discovered that the evaporation-driven microscopic flow combined with the strong hydrophilic surface of diatom frustules is capable of concentrating the analyte molecules, which offers a simple yet effective mechanism to accelerate the mass transport into the SERS substrate. Using the inkjet printing technology, we are able to deliver multiple 100pico-liter (pL) volume droplets with pinpoint accuracy into a single diatom frustule with dimension around 30µm×7µm×5µm, which allows for label-free detection of explosive molecules such as trinitrotoluene (TNT) down to 10 -10 M in concentration and 2.7×10 -15 g in mass from 120nL solution. Our research illustrates a new paradigm of SERS sensing to detect trace level of chemical compounds from minimum volume of analyte using nature created photonic crystal biosilica materials. Copyright © 2016 Elsevier B.V. All rights reserved.

Detecting explosive molecules from nanoliter solution: A new paradigm of SERS sensing on hydrophilic photonic crystal biosilica

PubMed Central

Kong, Xianming; Xi, Yuting; Le Duff, Paul; Chong, Xinyuan; Li, Erwen; Ren, Fanghui; Rorrer, Gregory L.; Wang, Alan X.

2017-01-01

We demonstrate a photonic crystal biosilica surface-enhanced Raman scattering (SERS) substrate based on a diatom frustule with in-situ synthesized silver nanoparticles (Ag NPs) to detect explosive molecules from nanoliter (nL) solution. By integrating high density Ag NPs inside the nanopores of diatom biosilica, which is not achievable by traditional self-assembly techniques, we obtained ultra-high SERS sensitivity due to dual enhancement mechanisms. First, the hybrid plasmonic-photonic crystal biosilica with three dimensional morphologies was obtained by electroless-deposited Ag seeds at nanometer sized diatom frustule surface, which provides high density hot spots as well as strongly coupled optical resonances with the photonic crystal structure of diatom frustules. Second, we discovered that the evaporation-driven microscopic flow combined with the strong hydrophilic surface of diatom frustules is capable of concentrating the analyte molecules, which offers a simple yet effective mechanism to accelerate the mass transport into the SERS substrate. Using the inkjet printing technology, we are able to deliver multiple 100 pico-liter (pL) volume droplets with pinpoint accuracy into a single diatom frustule with dimension around 30 μm × 7 μm × 5 μm, which allows for label-free detection of explosive molecules such as trinitrotoluene (TNT) down to 10−10 M in concentration and 2.7 × 10−15 g in mass from 120 nL solution. Our research illustrates a new paradigm of SERS sensing to detect trace level of chemical compounds from minimum volume of analyte using nature created photonic crystal biosilica materials. PMID:27471144

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

NASA Astrophysics Data System (ADS)

Panda, Bishnu P.; Mohanty, Smita; Nayak, Sanjay K.

2014-09-01

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.

Room-temperature growth of thin films of niobium on strontium titanate (0 0 1) single-crystal substrates for superconducting joints

NASA Astrophysics Data System (ADS)

Shimizu, Yuhei; Tonooka, Kazuhiko; Yoshida, Yoshiyuki; Furuse, Mitsuho; Takashima, Hiroshi

2018-06-01

With the eventual aim of forming joints between superconducting wires of YBa2Cu3O7-δ (YBCO), thin films of Nb were grown at room-temperature on SrTiO3 (STO) (0 0 1), a single-crystal substrate that shows good lattice matching with YBCO. The crystallinity, surface morphology, and superconducting properties of the Nb thin films were investigated and compared with those of similar films grown on a silica glass substrate. The Nb thin films grew with an (hh0) orientation on both substrates. The crystallinity of the Nb thin films on the STO substrate was higher than that on the silica glass substrate. X-ray diffraction measurements and observation of the surface morphology by atomic-force microscopy indicated that Nb grew in the plane along the [1 0 0] and [0 1 0] directions of the STO substrate. This growth mode relaxes strain between Nb and STO, and is believed to lead to the high crystallinity observed. As a result, the Nb thin films on the STO substrates showed lower electric resistivity and a higher superconducting transition temperature than did those on the silica glass substrates. The results of this study should be useful in relation to the production of superconducting joints.

Chitosan-Assisted Crystallization and Film Forming of Perovskite Crystals through Biomineralization.

PubMed

Yang, Yang; Sun, Chen; Yip, Hin-Lap; Sun, Runcang; Wang, Xiaohui

2016-03-18

Biomimetic mineralization is a powerful approach for the synthesis of advanced composite materials with hierarchical organization and controlled structure. Herein, chitosan was introduced into a perovskite precursor solution as a biopolymer additive to control the crystallization and to improve the morphology and film-forming properties of a perovskite film by way of biomineralization. The biopolymer additive was able to control the size and morphology of the perovskite crystals and helped to form smooth films. The mechanism of chitosan-mediated nucleation and growth of the perovskite crystals was explored. As a possible application, the chitosan-perovskite composite film was introduced into a planar heterojunction solar cell and increased power conversion efficiency relative to that observed for the pristine perovskite film was achieved. The biomimetic mineralization method proposed in this study provides an alternative way of preparing perovskite crystals with well-controlled morphology and properties and extends the applications of perovskite crystals in photoelectronic fields, including planar-heterojunction solar cells. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigating the Influence of Temperature on the Kaolinite-Base Synthesis of Zeolite and Urease Immobilization for the Potential Fabrication of Electrochemical Urea Biosensors.

PubMed

Anderson, David Ebo; Balapangu, Srinivasan; Fleischer, Heidimarie N A; Viade, Ruth A; Krampa, Francis D; Kanyong, Prosper; Awandare, Gordon A; Tiburu, Elvis K

2017-08-08

Temperature-dependent zeolite synthesis has revealed a unique surface morphology, surface area and pore size which influence the immobilization of urease on gold electrode supports for biosensor fabrication. XRD characterization has identified zeolite X (Na) at all crystallization temperatures tested. However, N₂ adsorption and desorption results showed a pore size and pore volume of zeolite X (Na) 60 °C, zeolite X (Na) 70 °C and zeolite X (Na) 90 °C to range from 1.92 nm to 2.45 nm and 0.012 cm³/g to 0.061 cm³/g, respectively, with no significant differences. The specific surface area of zeolite X (Na) at 60, 70 and 90 °C was 64 m²/g, 67 m²/g and 113 m²/g, respectively. The pore size, specific surface area and pore volumes of zeolite X (Na) 80 °C and zeolite X (Na) 100 °C were dramatically increased to 4.21 nm, 295 m²/g, 0.762 cm³/g and 4.92 nm, 389 m²/g, 0.837 cm³/g, in that order. The analytical performance of adsorbed urease on zeolite X (Na) surface was also investigated using cyclic voltammetry measurements, and the results showed distinct cathodic and anodic peaks by zeolite X (Na) 80 °C and zeolite X (Na) 100 °C. These zeolites' molar conductance was measured as a function of urea concentration and gave an average polynomial regression fit of 0.948. The findings in this study suggest that certain physicochemical properties, such as crystallization temperature and pH, are critical parameters for improving the morphological properties of zeolites synthesized from natural sources for various biomedical applications.

Investigating the Influence of Temperature on the Kaolinite-Base Synthesis of Zeolite and Urease Immobilization for the Potential Fabrication of Electrochemical Urea Biosensors

PubMed Central

Anderson, David Ebo; Balapangu, Srinivasan; Fleischer, Heidimarie N. A.; Viade, Ruth A.; Awandare, Gordon A.; Tiburu, Elvis K.

2017-01-01

Temperature-dependent zeolite synthesis has revealed a unique surface morphology, surface area and pore size which influence the immobilization of urease on gold electrode supports for biosensor fabrication. XRD characterization has identified zeolite X (Na) at all crystallization temperatures tested. However, N2 adsorption and desorption results showed a pore size and pore volume of zeolite X (Na) 60 °C, zeolite X (Na) 70 °C and zeolite X (Na) 90 °C to range from 1.92 nm to 2.45 nm and 0.012 cm3/g to 0.061 cm3/g, respectively, with no significant differences. The specific surface area of zeolite X (Na) at 60, 70 and 90 °C was 64 m2/g, 67 m2/g and 113 m2/g, respectively. The pore size, specific surface area and pore volumes of zeolite X (Na) 80 °C and zeolite X (Na) 100 °C were dramatically increased to 4.21 nm, 295 m2/g, 0.762 cm3/g and 4.92 nm, 389 m2/g, 0.837 cm3/g, in that order. The analytical performance of adsorbed urease on zeolite X (Na) surface was also investigated using cyclic voltammetry measurements, and the results showed distinct cathodic and anodic peaks by zeolite X (Na) 80 °C and zeolite X (Na) 100 °C. These zeolites’ molar conductance was measured as a function of urea concentration and gave an average polynomial regression fit of 0.948. The findings in this study suggest that certain physicochemical properties, such as crystallization temperature and pH, are critical parameters for improving the morphological properties of zeolites synthesized from natural sources for various biomedical applications. PMID:28786961

Structural and morphological study of Fe-doped Bi-based superconductor

NASA Astrophysics Data System (ADS)

Singh, Yadunath; Kumar, Rohitash

2018-05-01

In the present work, we report the study of iron-doped Bi-based superconductor sample with stoichiometric composition of Bi2Sr2Can-1(Cu1-x Fex)3O2n+4 where n=3 and x = 0.7. This sample was prepared by grinding the precursor oxides in the Ball mill for 6 hours continuous at the rate of 400 rpm for a proper mixing and to obtain the required grain size. Then the solid-state reaction method was used to prepare the sample. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray fluorescence analysis (EDX) were performed for determination of the crystal structure, surface morphology and trace the material elements of samples, respectively. The surface microscopy data were collected over a selected area of the surface of the material and a two-dimensional image generated that displays spatial variations in properties including chemical characterization and orientation of materials.

Nanoparticle induced piezoelectric, super toughened, radiation resistant, multi-functional nanohybrids.

PubMed

Tiwari, Vimal K; Shripathi, T; Lalla, N P; Maiti, Pralay

2012-01-07

We have developed multifunctional nanohybrids of poly(vinylidene fluoride-co-chlorotrifluoroethylene) (CTFE) with a small percentage of surface modified inorganic layered silicate showing dramatic improvement in toughness, radiation resistant and piezoelectric properties vis-à-vis pristine polymer. Massive intercalation (d(001) 1.8 → 3.9 nm) of polymer inside the nanoclay galleries and unique crystallization behavior of the fluoropolymer on the surface of individual silicate layer has been reported. Toughness in the nanohybrid increases more than three orders of magnitude as compared to pure CTFE. High energy radiation (80 MeV Si(+7)) causes chain session, amorphization and creates olefinic bonds in the pure polymer while the nanohybrids are radiation resistant at a similar dose. Nanoclay induces the metastable piezoelectric β-phase in CTFE, suitable for sensor and actuator application. Molecular level changes after irradiation and controlled morphology for smart membrane have been confirmed by using spectroscopy, sol-gel technique, surface morphology studies and in situ residual gas analysis.

Surfactant-Free Shape Control of Gold Nanoparticles Enabled by Unified Theoretical Framework of Nanocrystal Synthesis.

PubMed

Wall, Matthew A; Harmsen, Stefan; Pal, Soumik; Zhang, Lihua; Arianna, Gianluca; Lombardi, John R; Drain, Charles Michael; Kircher, Moritz F

2017-06-01

Gold nanoparticles have unique properties that are highly dependent on their shape and size. Synthetic methods that enable precise control over nanoparticle morphology currently require shape-directing agents such as surfactants or polymers that force growth in a particular direction by adsorbing to specific crystal facets. These auxiliary reagents passivate the nanoparticles' surface, and thus decrease their performance in applications like catalysis and surface-enhanced Raman scattering. Here, a surfactant- and polymer-free approach to achieving high-performance gold nanoparticles is reported. A theoretical framework to elucidate the growth mechanism of nanoparticles in surfactant-free media is developed and it is applied to identify strategies for shape-controlled syntheses. Using the results of the analyses, a simple, green-chemistry synthesis of the four most commonly used morphologies: nanostars, nanospheres, nanorods, and nanoplates is designed. The nanoparticles synthesized by this method outperform analogous particles with surfactant and polymer coatings in both catalysis and surface-enhanced Raman scattering. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[Apatite-forming ability of pure titanium implant after micro-arc oxidation treatment].

PubMed

Tian, Zhihui; Zhang, Yu; Wang, Lichao; Nan, Kaihui

2013-10-01

To investigate the apatite forming ability of pure titanium implant after micro-arc oxidation treatment in simulated body fluid (SBF) and obtain implants with calcium phosphate (Ca-P) layers. The implants were immersed in (SBF) after micro-arc oxidation treatment for different time lengths, and their apatite forming ability and the morphology and constituents of the Ca-P layers formed on the sample surface were analyzed using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive electron probe. After immersion in SBF, large quantities of Ca-P layers were induced on the surface of the samples. The Ca-P layers were composed of octacalcium phosphate and carbonated hydroxyapatite, and the crystals showed a plate-like morphology with an oriented growth. The implants with micro-arc oxidation treatment show good apatite forming ability on the surface with rich calcium and phosphorus elements. The formed layers are composed of bone-like apatite including octacalcium phosphate and carbonated hydroxyapatite.

Compositions of Mg and Se, surface morphology, roughness and Raman property of Zn1-xMgxSeyTe1-y layers grown at various substrate temperatures or dopant transport rates by MOVPE

NASA Astrophysics Data System (ADS)

Nishio, Mitsuhiro; Saito, Katsuhiko; Urata, Kensuke; Okamoto, Yasuhiro; Tanaka, Daichi; Araki, Yasuhiro; Abiru, Masakatsu; Mori, Eiichiro; Tanaka, Tooru; Guo, Qixin

2015-03-01

The growth of undoped and phosphorus (P)-doped Zn1-xMgxSeyTe1-y layers on (100) ZnTe substrates by metalorganic vapor phase epitaxy was carried out. The compositions of Mg and Se, surface morphology, roughness and Raman property were characterized as a function of substrate temperature. Not only the compositions of Mg and Se but also the crystal quality of undoped Zn1-xMgxSeyTe1-y layer strongly depended upon the substrate temperature. Furthermore, the growth of Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe substrate was achieved independent of the transport rate of trisdimethylaminophosphorus. Undoped Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe led to improvement of surface roughness. On the other hand, P doping brought about deterioration of crystalline quality.

The roles of fluid motion and other transport phenomena in the morphology of materials

NASA Technical Reports Server (NTRS)

Saville, D. A.

1993-01-01

Two crystallization problems were studied: the growth of protein crystals, in particular the influence of colloidal forces and convection, and the influence of interface resistance on the growth of dendritic crystals. The protein study involved both experimental and theoretical work; the work of dendrites was entirely theoretical. In the study of protein crystallization, experiments were carried out where crystals were grown in the presence and absence of natural convection. No evidence was found that convection retards crystal growth. The theoretical study focused on the influence of colloidal forces (electrostatic and London-van der Waals) on the interaction between a protein molecule and a flat crystal surface. It was shown that the interaction is extremely sensitive to colloidal forces and that electrostatic interactions play a strong role in deciding whether or not a molecule will find a favorable site for adsorption. In the study of dendritic growth, the role of an interfacial resistance on the selection processes was examined. Using a computational scheme, it was found that the selected velocity is strongly dependent on the magnitude of the interfacial resistance to heat transfer. This is a possible explanation for discrepancies between the theoretical and experimental results on succinonitrile.

The roles of fluid motion and other transport phenomena in the morphology of materials

NASA Astrophysics Data System (ADS)

Saville, D. A.

1993-11-01

Two crystallization problems were studied: the growth of protein crystals, in particular the influence of colloidal forces and convection, and the influence of interface resistance on the growth of dendritic crystals. The protein study involved both experimental and theoretical work; the work of dendrites was entirely theoretical. In the study of protein crystallization, experiments were carried out where crystals were grown in the presence and absence of natural convection. No evidence was found that convection retards crystal growth. The theoretical study focused on the influence of colloidal forces (electrostatic and London-van der Waals) on the interaction between a protein molecule and a flat crystal surface. It was shown that the interaction is extremely sensitive to colloidal forces and that electrostatic interactions play a strong role in deciding whether or not a molecule will find a favorable site for adsorption. In the study of dendritic growth, the role of an interfacial resistance on the selection processes was examined. Using a computational scheme, it was found that the selected velocity is strongly dependent on the magnitude of the interfacial resistance to heat transfer. This is a possible explanation for discrepancies between the theoretical and experimental results on succinonitrile.

Preliminary morphological and X-ray diffraction studies of the crystals of the DNA cetyltrimethylammonium salt.

PubMed

Osica, V D; Pyatigorskaya, T L; Polyvtsev, O F; Dembo, A T; Kliya, M O; Vasilchenko, V N; Verkin, B I; Sukharevskya, B Y

1977-04-01

Double-stranded DNA molecules (molecular weight 2.5 X 10(5) - 5 X 10(5) daltons) have been crystallized from water-salt solutions as cetyltrimethylammonium salts (CTA-DNA). Variation of crystallization conditions results in a production of different types of CTA-DNA crystals: spherulits, dendrites, needle-shaped and faceted rhombic crystals, the latter beeing up to 0.3 mm on a side. X-ray diffraction data indicate that DNA molecules in the crystals form a hexagonal lattice which parameters vary slightly with the morphological type of the crystal. Comparison of the melting curves of the DNA preparation before and after crystallization suggests that DNA molecules are partially fractionated in the course of crystallization. Crystals of the CTA-DNA-proflavine complex have also been obtained.

Preliminary morphological and X-ray diffraction studies of the crystals of the DNA cetyltrimethylammonium salt.

PubMed Central

Osica, V D; Pyatigorskaya, T L; Polyvtsev, O F; Dembo, A T; Kliya, M O; Vasilchenko, V N; Verkin, B I; Sukharevskya, B Y

1977-01-01

Double-stranded DNA molecules (molecular weight 2.5 X 10(5) - 5 X 10(5) daltons) have been crystallized from water-salt solutions as cetyltrimethylammonium salts (CTA-DNA). Variation of crystallization conditions results in a production of different types of CTA-DNA crystals: spherulits, dendrites, needle-shaped and faceted rhombic crystals, the latter beeing up to 0.3 mm on a side. X-ray diffraction data indicate that DNA molecules in the crystals form a hexagonal lattice which parameters vary slightly with the morphological type of the crystal. Comparison of the melting curves of the DNA preparation before and after crystallization suggests that DNA molecules are partially fractionated in the course of crystallization. Crystals of the CTA-DNA-proflavine complex have also been obtained. Images PMID:866188

Ultrafast synthesis and characterization of carbonated hydroxyapatite nanopowders via sonochemistry-assisted microwave process.

PubMed

Zou, Zhaoyong; Lin, Kaili; Chen, Lei; Chang, Jiang

2012-11-01

Herein, carbonated hydroxyapatite (CHAp) nanopowders were synthesized via sonochemistry-assisted microwave process. The influences of microwave and ultrasonic irradiation on the crystallinity, morphology, yield, Ca/P molar ratio, specific surface area and dispersibility were investigated and compared with the conventional precipitation method. The results showed that sonochemistry-assisted microwave process significantly increased the synthetic efficiency. The well-crystallized nanopowders could be obtained at high yield of 98.8% in ultra-short-period of 5min. In addition, the crystallization process was promoted with the increase of ultrasonic and microwave power and the reaction time during the sonochemistry-assisted microwave process. The sonochemistry assistance also remarkably increased the specific surface area and dispersibility of the as-obtained products. These results suggest that the sonochemistry-assisted microwave process is an effective approach to synthesize CHAp with high efficiency. Copyright © 2012 Elsevier B.V. All rights reserved.

Phase-field crystal modeling of compositional domain formation in ultrathin films.

PubMed

Muralidharan, Srevatsan; Haataja, Mikko

2010-09-17

Bulk-immiscible binary systems often form stress-induced miscible alloy phases when deposited on a substrate. Both alloying and surface dislocation formation lead to the decrease of the elastic strain energy, and the competition between these two strain-relaxation mechanisms gives rise to the emergence of pseudomorphic compositional nanoscale domains, often coexisting with a partially coherent single phase. In this work, we develop a phase-field crystal model for compositional patterning in monolayer aggregates of binary metallic systems. We first demonstrate that the model naturally incorporates the competition between alloying and misfit dislocations, and quantify the effects of misfit and line tension on equilibrium domain size. Then, we quantitatively relate the parameters of the phase-field crystal model to a specific system, CoAg/Ru(0001), and demonstrate that the simulations capture experimentally observed morphologies.

Electronic transport in graphene-based heterostructures

NASA Astrophysics Data System (ADS)

Tan, J. Y.; Avsar, A.; Balakrishnan, J.; Koon, G. K. W.; Taychatanapat, T.; O'Farrell, E. C. T.; Watanabe, K.; Taniguchi, T.; Eda, G.; Castro Neto, A. H.; Özyilmaz, B.

2014-05-01

While boron nitride (BN) substrates have been utilized to achieve high electronic mobilities in graphene field effect transistors, it is unclear how other layered two dimensional (2D) crystals influence the electronic performance of graphene. In this Letter, we study the surface morphology of 2D BN, gallium selenide (GaSe), and transition metal dichalcogenides (tungsten disulfide (WS2) and molybdenum disulfide (MoS2)) crystals and their influence on graphene's electronic quality. Atomic force microscopy analysis shows that these crystals have improved surface roughness (root mean square value of only ˜0.1 nm) compared to conventional SiO2 substrate. While our results confirm that graphene devices exhibit very high electronic mobility (μ) on BN substrates, graphene devices on WS2 substrates (G/WS2) are equally promising for high quality electronic transport (μ ˜ 38 000 cm2/V s at room temperature), followed by G/MoS2 (μ ˜ 10 000 cm2/V s) and G/GaSe (μ ˜ 2200 cm2/V s). However, we observe a significant asymmetry in electron and hole conduction in G/WS2 and G/MoS2 heterostructures, most likely due to the presence of sulphur vacancies in the substrate crystals. GaSe crystals are observed to degrade over time even under ambient conditions, leading to a large hysteresis in graphene transport making it a less suitable substrate.

Effect of film thickness on morphological evolution in dewetting and crystallization of polystyrene/poly(ε-caprolactone) blend films.

PubMed

Ma, Meng; He, Zhoukun; Yang, Jinghui; Chen, Feng; Wang, Ke; Zhang, Qin; Deng, Hua; Fu, Qiang

2011-11-01

In this Article, the morphological evolution in the blend thin film of polystyrene (PS)/poly(ε-caprolactone) (PCL) was investigated via mainly AFM. It was found that an enriched two-layer structure with PS at the upper layer and PCL at the bottom layer was formed during spinning coating. By changing the solution concentration, different kinds of crystal morphologies, such as finger-like, dendritic, and spherulitic-like, could be obtained at the bottom PCL layer. These different initial states led to the morphological evolution processes to be quite different from each other, so the phase separation, dewetting, and crystalline morphology of PS/PCL blend films as a function of time were studied. It was interesting to find that the morphological evolution of PS at the upper layer was largely dependent on the film thickness. For the ultrathin (15 nm) blend film, a liquid-solid/liquid-liquid dewetting-wetting process was observed, forming ribbons that rupture into discrete circular PS islands on voronoi finger-like PCL crystal. For the thick (30 nm) blend film, the liquid-liquid dewetting of the upper PS layer from the underlying adsorbed PCL layer was found, forming interconnected rim structures that rupture into discrete circular PS islands embedded in the single lamellar PCL dendritic crystal due to Rayleigh instability. For the thicker (60 nm) blend film, a two-step liquid-liquid dewetting process with regular holes decorated with dendritic PCL crystal at early annealing stage and small holes decorated with spherulite-like PCL crystal among the early dewetting holes at later annealing stage was observed. The mechanism of this unusual morphological evolution process was discussed on the basis of the entropy effect and annealing-induced phase separation.

Degradation of blue and red inks by Ag/AgCl photocatalyst under UV light irradiation

NASA Astrophysics Data System (ADS)

Daupor, Hasan; Chenea, Asmat

2017-08-01

Objective of this research, cubic Ag/AgCl photocatalysts with an average particle size of 500 nm has been successfully synthesized via a modified precipitation reaction between ZrCl4 and AgNO3. Method for analysis, the crystal structure of the product was characterized by X-ray powder diffraction (XRD). The morphology and composition were studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-vis diffuse-reflection spectra (DRS) and so on. The result showed that the optical absorption spectrum exhibited strong absorption in the visible region around 500-600 nm due to surface plasmon resonance (SPR) of metallic silver nanoparticles. SEM micrographs showed that the obtained Ag/AgCl had cubic morphology and appeared on the porous surface as the cubic cage morphology. As a result, this porous surface also positively affected the photocatalytic reaction. The photocatalytic activity of the obtained product was evaluated by the photodegradation of blue and red ink solutions under UV light irradiation, and it was interestingly, discovered that AgCl could degrade 0.25% and 0.10% in 7 hours for blue and red inks solution respectively, Which were higher than of commercial AgCl. The result suggested that the morphology of Ag/AgCl strongly affected their photocatalytic activities. O2-, OH- reaction. radicals and Cl° atom are main species during photocatalytic reaction.

Laboratory studies of crystal growth in magma

NASA Astrophysics Data System (ADS)

Hammer, J. E.; Welsch, B. T.; First, E.; Shea, T.

2012-12-01

The proportions, compositions, and interrelationships among crystalline phases and glasses in volcanic rocks cryptically record pre-eruptive intensive conditions, the timing of changes in crystallization environment, and the devolatilization history of eruptive ascent. These parameters are recognized as important monitoring tools at active volcanoes and interpreting geologic events at prehistoric and remote eruptions, thus motivating our attempts to understand the information preserved in crystals through an experimental appoach. We are performing laboratory experiments in mafic, felsic, and intermediate composition magmas to study the mechanisms of crystal growth in thermochemical environments relevant to volcanic environments. We target features common to natural crystals in igneous rocks for our experimental studies of rapid crystal growth phenomena: (1) Surface curvature. Do curved interfaces and spongy cores represent evidence of dissolution (i.e., are they corrosion features), or do they record the transition from dendritic to polyhedral morphology? (2) Trapped melt inclusions. Do trapped liquids represent bulk (i.e., far-field) liquids, boundary layer liquids, or something intermediate, depending on individual species diffusivity? What sequence of crystal growth rates leads to preservation of sealed melt inclusions? (3) Subgrain boundaries. Natural phenocrysts commonly exhibit tabular subgrain regions distinguished by small angle lattice misorientations or "dislocation lamellae" and undulatory extinction. Might these crystal defects be produced as dendrites undergo ripening? (4) Clusters. Contacting clusters of polymineralic crystals are the building blocks of cumulates, and are ubiquitous features of mafic volcanic rocks. Are plagioclase and clinopyroxene aligned crystallographically, suggesting an epitaxial (surface energy) relationship? (5) Log-normal size distribution. What synthetic cooling histories produce "natural" distributions of crystal sizes, and are phenocrystic textures uniquely attributed to staged cooling? In addition, we seek to explore the limitations of the experimental approach. Which aspects of natural crystallization sequences are adequately reproduced in experimental charges, and which are compromised by the obligatory reduced temporal and spatial scales of crystal growth experiments? What are the implications of synthetic starting materials and thermal pre-treatments for nucleation, growth, heterophase equilibria, and textural maturation?

LiCoO2 Concaved Cuboctahedrons from Symmetry-Controlled Topological Reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, H.; Wu, L.; Zhang, L.

2011-01-19

Morphology control of functional materials is generally performed by controlling the growth rates on selected orientations or faces. Here, we control particle morphology by 'crystal templating': by choosing appropriate precursor crystals and reaction conditions, we demonstrate that a material with rhombohedral symmetry - namely the layered, positive electrode material, LiCoO{sub 2} - can grow to form a quadruple-twinned crystal with overall cubic symmetry. The twinned crystals show an unusual, concaved-cuboctahedron morphology, with uniform particle sizes of 0.5-2 {micro}m. On the basis of a range of synthetic and analytical experiments, including solid-state NMR, X-ray powder diffraction analysis and HRTEM, we proposemore » that these twinned crystals form via selective dissolution and an ion-exchange reaction accompanied by oxidation of a parent crystal of CoO, a material with cubic symmetry. This template crystal serves to nucleate the growth of four LiCoO{sub 2} twin crystals and to convert a highly anisotropic, layered material into a pseudo-3-dimensional, isotropic material.« less

Microscopic analysis of "iron spot" on blue-and-white porcelain from Jingdezhen imperial kiln in early Ming dynasty (14th-15th century).

PubMed

Wang, Wenxuan; Zhu, Jian; Jiang, Jianxin; Xu, Changqing; Wu, Shurong; Guan, Li; Zhang, Zhaoxia; Wu, Menglei; Du, Jingnan

2016-11-01

"Sumali," as an imported cobalt ore from overseas, was a sort of precious and valuable pigment used for imperial kilns only, which produces characteristic "iron spot" to blue-and-white porcelain in early Ming Dynasty (A.D. 14th-15th century). Although there were some old studies on it, the morphology and formation of iron spot has not been fully investigated and understood. Therefore, five selected samples with typical spot from Jingdezhen imperial kiln in Ming Yongle periods (A.D. 1403-1424) were analyzed by various microscopic analysis including 3D digital microscope, SEM-EDS and EPMA. According to SEM images, samples can be divided into three groups: un-reflected "iron spot" without crystals, un-reflected "iron spot" with crystals and reflected "iron spot" with crystals. Furthermore, 3D micro-images revealed that "iron spots" separate out dendritic or snow-shaped crystals of iron only on and parallel to the surface of glaze for which "iron spot" show strong metallic luster. Combining with microscopic observation and microanalysis on crystallization and non-crystallization areas, it indicates that firing oxygen concentration is the ultimate causation of forming reflective iron spot which has a shallower distribution below the surface and limits crystals growing down. More details about characters of "iron spot" used "Sumali" were found and provided new clues to coloration, formation mechanism and porcelain producing technology of imperial kiln from 14th to 15th centuries of China. © 2016 Wiley Periodicals, Inc.

Colloidal crystal based plasma polymer patterning to control Pseudomonas aeruginosa attachment to surfaces.

PubMed

Pingle, Hitesh; Wang, Peng-Yuan; Thissen, Helmut; McArthur, Sally; Kingshott, Peter

2015-12-02

Biofilm formation on medical implants and subsequent infections are a global problem. A great deal of effort has focused on developing chemical contrasts based on micro- and nanopatterning for studying and controlling cells and bacteria at surfaces. It has been known that micro- and nanopatterns on surfaces can influence biomolecule adsorption, and subsequent cell and bacterial adhesion. However, less focus has been on precisely controlling patterns to study the initial bacterial attachment mechanisms and subsequently how the patterning influences the role played by biomolecular adsorption on biofilm formation. In this work, the authors have used colloidal self-assembly in a confined area to pattern surfaces with colloidal crystals and used them as masks during allylamine plasma polymer (AAMpp) deposition to generate highly ordered patterns from the micro- to the nanoscale. Polyethylene glycol (PEG)-aldehyde was grafted to the plasma regions via "cloud point" grafting to prevent the attachment of bacteria on the plasma patterned surface regions, thereby controlling the adhesive sites by choice of the colloidal crystal morphology. Pseudomonas aeruginosa was chosen to study the bacterial interactions with these chemically patterned surfaces. Scanning electron microscope, x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and epifluorescence microscopy were used for pattern characterization, surface chemical analysis, and imaging of attached bacteria. The AAMpp influenced bacterial attachment because of the amine groups displaying a positive charge. XPS results confirm the successful grafting of PEG on the AAMpp surfaces. The results showed that PEG patterns can be used as a surface for bacterial patterning including investigating the role of biomolecular patterning on bacterial attachment. These types of patterns are easy to fabricate and could be useful in further applications in biomedical research.

Precision Control of Thermal Transport in Cryogenic Single-Crystal Silicon Devices

NASA Technical Reports Server (NTRS)

Rostem, K.; Chuss, D. T.; Colazo, F. A.; Crowe, E. J.; Denis, K. L.; Lourie, N. P.; Moseley, S. H.; Stevenson, T. R.; Wollack, E. J.

2014-01-01

We report on the diffusive-ballistic thermal conductance of multi-moded single-crystal silicon beams measured below 1 K. It is shown that the phonon mean-free-path is a strong function of the surface roughness characteristics of the beams. This effect is enhanced in diffuse beams with lengths much larger than, even when the surface is fairly smooth, 510 nm rms, and the peak thermal wavelength is 0.6 microns. Resonant phonon scattering has been observed in beams with a pitted surface morphology and characteristic pit depth of 30 nm. Hence, if the surface roughness is not adequately controlled, the thermal conductance can vary significantly for diffuse beams fabricated across a wafer. In contrast, when the beam length is of order, the conductance is dominated by ballistic transport and is effectively set by the beam cross-sectional area. We have demonstrated a uniformity of +/-8% in fractional deviation for ballistic beams, and this deviation is largely set by the thermal conductance of diffuse beams that support the micro-electro-mechanical device and electrical leads. In addition, we have found no evidence for excess specific heat in single-crystal silicon membranes. This allows for the precise control of the device heat capacity with normal metal films. We discuss the results in the context of the design and fabrication of large-format arrays of far-infrared and millimeter wavelength cryogenic detectors.

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenlee, Jordan D., E-mail: jordan.greenlee.ctr@nrl.navy.mil; Feigelson, Boris N.; Anderson, Travis J.

2014-08-14

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N{sub 2} overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at halfmore » maximums of the E{sub 2} and A{sub 1} (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.« less

Using tethered triblock copolymers to mediate the interaction between substrates

NASA Astrophysics Data System (ADS)

Chern, Shyh-Shi; Zhulina, Ekaterina B.; Pickett, Galen T.; Balazs, Anna C.

1998-04-01

Using scaling analysis and a self-consistent field (SCF) theory, we compress two copolymer-coated surfaces and isolate conditions that yield multiple, distinct minima in the interaction profile. We focus on planar surfaces that are coated with ABC triblock copolymers. Tethered to the surface by the last monomer in the C block, the copolymers are grafted at relatively low densities. The surrounding solution is a poor solvent for both the A and C blocks, and is a good solvent for the B blocks. Through scaling theory, we pinpoint the parameters that yield two minima in the interaction profile. The SCF calculations reveal the changes in the morphology of the polymers as the layers are compressed. Through both studies, we determine how the morphological changes give rise to the observed surface interactions. The results provide guidelines for creating polymer-coated colloidal systems that can form two stable crystal structures. Such systems could be used for bistable, optical switches. The findings also yield a prescription for creating systems that exhibit additional minima in the free energy of interaction.

DNA-templated synthesis of Pt nanoparticles on single-walled carbon nanotubes.

PubMed

Dong, Lifeng

2009-11-18

A series of electron microscopy characterizations demonstrate that single-stranded deoxyribonucleic acid (ssDNA) can bind to nanotube surfaces and disperse bundled single-walled carbon nanotubes (SWCNTs) into individual tubes. The ssDNA molecules on the nanotube surfaces demonstrate various morphologies, such as aggregated clusters and spiral wrapping around a nanotube with different pitches and spaces, indicating that the morphology of the SWCNT/DNA hybrids is not related solely to the base sequence of the ssDNA or the chirality or the diameter of the nanotubes. In addition to serving as a non-covalent dispersion agent, the ssDNA molecules bonded to the nanotube surface can provide addresses for localizing Pt(II) complexes along the nanotubes. The Pt nanoparticles obtained by a reduction of the Pt2+-DNA adducts are crystals with a size of < or =1-2 nm. These results expand our understanding of the interactions between ssDNA and SWCNTs and provide an efficient approach for positioning Pt and other metal particles, with uniform sizes and without aggregations, along the nanotube surfaces for applications in direct ethanol/methanol fuel cells and nanoscale electronics.

Effect of fast mold surface temperature evolution on iPP part morphology gradients

NASA Astrophysics Data System (ADS)

Liparoti, Sara; Sorrentino, Andrea; Guzman, Gustavo; Cakmak, Mukerrem; Titomanlio, Giuseppe

2016-03-01

The control of mold surface temperature is an important factor that affects the sample surface morphology as well as the structural gradients (orientation crystal size, and type) as well as cooling stresses. The frozen layer thickness formed during the filling stage also has a very significant effect on the flow resistance and thus on the resulting pressure drop and flow length in thin wall parts. The possibility to have a hot mold during filling and a quick cooling soon afterward is a significant process enhancement particularly for specialized applications such as micro injection molding and for the reproduction of micro structured surfaces. Up to now, several methods (electromagnetic, infrared, hot vapor fleshing etc,) were tried to achieve fast temperature evolution of the mold. Unfortunately, all these methods require a complex balance between thermal and mechanical problems, equipment cost, energy consumption, safety, molding cycle time and part quality achievable. In this work, a thin electrical resistance was designed and used to generate a fast and confined temperature variation on mold surface (by joule effect). Since the whole temperature evolution can take place in a few seconds, one can couple the advantages of a high surface temperature during filling with the advantages of a low mold temperature, fast cooling and low heating dissipation. Some experiments were performed with a commercial iPP resin. The effects of the surface temperature and of the heating time (under constant electric power) on surface finishing and on the final morphology (thickness and structure of the different layers) are explored and discussed.

Effect of fast mold surface temperature evolution on iPP part morphology gradients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liparoti, Sara; Sorrentino, Andrea; Guzman, Gustavo

The control of mold surface temperature is an important factor that affects the sample surface morphology as well as the structural gradients (orientation crystal size, and type) as well as cooling stresses. The frozen layer thickness formed during the filling stage also has a very significant effect on the flow resistance and thus on the resulting pressure drop and flow length in thin wall parts. The possibility to have a hot mold during filling and a quick cooling soon afterward is a significant process enhancement particularly for specialized applications such as micro injection molding and for the reproduction of micromore » structured surfaces. Up to now, several methods (electromagnetic, infrared, hot vapor fleshing etc,) were tried to achieve fast temperature evolution of the mold. Unfortunately, all these methods require a complex balance between thermal and mechanical problems, equipment cost, energy consumption, safety, molding cycle time and part quality achievable. In this work, a thin electrical resistance was designed and used to generate a fast and confined temperature variation on mold surface (by joule effect). Since the whole temperature evolution can take place in a few seconds, one can couple the advantages of a high surface temperature during filling with the advantages of a low mold temperature, fast cooling and low heating dissipation. Some experiments were performed with a commercial iPP resin. The effects of the surface temperature and of the heating time (under constant electric power) on surface finishing and on the final morphology (thickness and structure of the different layers) are explored and discussed.« less

Fracture, roughness and phase transformation in CAD/CAM milling and subsequent surface treatments of lithium metasilicate/disilicate glass-ceramics.

PubMed

Alao, Abdur-Rasheed; Stoll, Richard; Song, Xiao-Fei; Abbott, John R; Zhang, Yu; Abduo, Jaafar; Yin, Ling

2017-10-01

This paper studied surface fracture, roughness and morphology, phase transformations, and material removal mechanisms of lithium metasilicate/disilicate glass ceramics (LMGC/LDGC) in CAD/CAM-milling and subsequent surface treatments. LMGC (IPS e.max CAD) blocks were milled using a chairside dental CAD/CAM milling unit and then treated in sintering, polishing and glazing processes. X-ray diffraction was performed on all processed surfaces. Scanning electron microscopy (SEM) was applied to analyse surface fracture and morphology. Surface roughness was quantitatively characterized by the arithmetic average surface roughness R a and the maximum roughness R z using desktop SEM-assisted morphology analytical software. The CAD/CAM milling induced extensive brittle cracks and crystal pulverization on LMGC surfaces, which indicate that the dominant removal mechanism was the fracture mode. Polishing and sintering of the milled LMGC lowered the surface roughness (ANOVA, p < 0.05), respectively, while sintering also fully transformed the weak LMGC to the strong LDGC. However, polishing and glazing of LDGC did not significantly improve the roughness (ANOVA, p > 0.05). In comparison of all applied fabrication process routes, it is found that CAD/CAM milling followed by polishing and sintering produced the smoothest surface with R a = 0.12 ± 0.08µm and R z = 0.89 ± 0.26µm. Thus , it is proposed as the optimized process route for LMGC/LDGC in dental restorations. This route enables to manufacture LMGC/LDGC restorations with cost effectiveness, time efficiency, and improved surface quality for better occlusal functions and reduced bacterial plaque accumulation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Total reflection infrared spectroscopy of water-ice and frozen aqueous NaCl solutions.

PubMed

Walker, Rachel L; Searles, Keith; Willard, Jesse A; Michelsen, Rebecca R H

2013-12-28

Liquid-like and liquid water at and near the surface of water-ice and frozen aqueous sodium chloride films were observed using attenuated total reflection infrared spectroscopy (ATR-IR). The concentration of NaCl ranged from 0.0001 to 0.01 M and the temperature varied from the melting point of water down to 256 K. The amount of liquid brine at the interface of the frozen films with the germanium ATR crystal increased with salt concentration and temperature. Experimental spectra are compared to reflection spectra calculated for a simplified morphology of a uniform liquid layer between the germanium crystal and the frozen film. This morphology allows for the amount of liquid observed in an experimental spectrum to be converted to the thickness of a homogenous layer with an equivalent amount of liquid. These equivalent thickness ranges from a nanometer for water-ice at 260 K to 170 nm for 0.01 M NaCl close to the melting point. The amounts of brine observed are over an order of magnitude less than the total liquid predicted by equilibrium thermodynamic models, implying that the vast majority of the liquid fraction of frozen solutions may be found in internal inclusions, grain boundaries, and the like. Thus, the amount of liquid and the solutes dissolved in them that are available to react with atmospheric gases on the surfaces of snow and ice are not well described by thermodynamic equilibrium models which assume the liquid phase is located entirely at the surface.

Langmuir and Langmuir-Blodgett films of multifunctional, amphiphilic polyethers with cholesterol moieties.

PubMed

Reuter, Sascha; Hofmann, Anna M; Busse, Karsten; Frey, Holger; Kressler, Jörg

2011-03-01

Langmuir films of multifunctional, hydrophilic polyethers containing a hydrophobic cholesterol group (Ch) were studied by surface pressure-mean molecular area (π-mmA) measurements and Brewster angle microscopy (BAM). The polyethers were either homopolymers or diblock copolymers of linear poly(glycerol) (lPG), linear poly(glyceryl glycidyl ether) (lPGG), linear poly(ethylene glycol) (lPEG), or hyperbranched poly(glycerol) (hbPG). Surface pressure measurements revealed that the homopolymers lPG and hbPG did not stay at the water surface after spreading and solvent evaporation, in contrast to lPEG. Because of the incorporation of the Ch group in the polymer structure, stable Langmuir films were formed by Ch-lPG(n), Ch-lPGG(n), and Ch-hbPG(n). The Ch-hbPG(n), Ch-lPEG(n), Ch-lPEG(n)-b-lPG(m), Ch-lPEG(n)-b-lPGG(m), and Ch-lPEG(n)-b-hbPG(m) systems showed an extended plateau region assigned to a phase transition involving the Ch groups. Typical hierarchically ordered morphologies of the LB films on hydrophilic substrates were observed for all Ch-initiated polymers. All LB films showed that Ch of the Ch-initiated homopolymers is able to crystallize. This strong tendency of self-aggregation then triggers further dewetting effects of the respective polyether entities. Fingerlike morphologies are observed for Ch-lPEG(69), since the lPEG(69) entity is able to undergo crystallization after transfer onto the silicon substrate.

Single crystalline thin films as a novel class of electrocatalysts

DOE PAGES

Snyder, Joshua; Markovic, Nenad; Stamenkovic, Vojislav

2013-01-01

The ubiquitous use of single crystal metal electrodes has garnered invaluable insight into the relationship between surface atomic structure and functional electrochemical properties. But, the sensitivity of their electrochemical response to surface orientation and the amount of precious metal required can limit their use. We present here a generally applicable procedure for producing thin metal films with a large proportion of atomically flat (111) terraces without the use of an epitaxial template. Thermal annealing in a controlled atmosphere induces long-range ordering of magnetron sputtered thin metal films deposited on an amorphous substrate. The ordering transition in these thin metal filmsmore » yields characteristic (111) electrochemical signatures with minimal amount of material and provides an adequate replacement for oriented bulk single crystals. Our procedure can be generalized towards a novel class of practical multimetallic thin film based electrocatalysts with tunable near-surface compositional profile and morphology. Annealing of atomically corrugated sputtered thin film Pt-alloy catalysts yields an atomically smooth structure with highly crystalline, (111)-like ordered and Pt segregated surface that displays superior functional properties, bridging the gap between extended/bulk surfaces and nanoscale systems.« less

Surface chemistry and wear behavior of single-crystal silicon carbide sliding against iron at temperatures to 1500 C in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron and Auger electron spectroscopy analyses and morphological studies of wear and metal transfer were conducted with a single-crystal silicon carbide 0001 surface in contact with iron at various temperatures to 1500 C in a vacuum of 10 to the minus 8th power pascal. The results indicate that below 800 C, carbide-carbon and silicon are primarily seen on the silicon carbide surface. Above 800 C the graphite increases rapidly with increase in temperature. The outermost surficial layer, which consists mostly of graphite and little silicon at temperatures above 1200 C is about 2 nm thick. A thicker layer, which consists of a mixture of graphite, carbide, and silicon is approximately 100 nm thick. The closer the surface sliding temperature is to 800 C, the more the metal transfer produced. Above 800 C, there was a transfer of rough, discontinuous, and thin iron debris instead of smooth, continuous and thin iron film which was observed to transfer below 800 C. Two kinds of fracture pits were observed on the silicon carbide surface: (1) a pit with a spherical asperity; and (2) multiangular shaped pits.

Controllable preparation of a nano-hydroxyapatite coating on carbon fibers by electrochemical deposition and chemical treatment.

PubMed

Wang, Xudong; Zhao, Xueni; Wang, Wanying; Zhang, Jing; Zhang, Li; He, Fuzhen; Yang, Jianjun

2016-06-01

A nano-hydroxyapatite (HA) coating with appropriate thickness and morphology similar to that of human bone tissue was directly prepared onto the surfaces of carbon fibers (CFs). A mixed solution of nitric acid, hydrochloric acid, sulfuric acid, and hydrogen peroxide (NHSH) was used in the preparation process. The coating was fabricated by combining NHSH treatment and electrochemical deposition (ECD). NHSH treatment is easy to operate, produces rapid reaction, and highly effective. This method was first used to induce the nucleation and growth of HA crystals on the CF surfaces. Numerous O-containing functional groups, such as hydroxyl (-OH) and carboxyl (-COOH) groups, were grafted onto the CF surfaces by NHSH treatment (NHSH-CFs); as such, the amounts of these groups on the functionalized CFs increased by nearly 8- and 12-fold, respectively, compared with those on untreated CFs. After treatment, the NHSH-CFs not only acquired larger specific surface areas but retained surfaces free from serious corrosion or breakage. Hence, NHSH-CFs are ideal depositional substrates of HA coating during ECD. ECD was successfully used to prepare a nano-rod-like HA coating on the NHSH-CF surfaces. The elemental composition, structure, and morphology of the HA coating were effectively controlled by adjusting various technological parameters, such as the current density, deposition time, and temperature. The average central diameter of HA crystals and the coating density increased with increasing deposition time. The average central diameter of most HA crystals on the NHSH-CFs varied from approximately 60 nm to 210 nm as the deposition time increased from 60 min to 180 min. Further studies on a possible deposition mechanism revealed that numerous O-containing functional groups on the NHSH-CF surfaces could associate with electrolyte ions (Ca(2+)) to form special chemical bonds. These bonds can induce HA coating deposition and improve the interfacial bonding strength between the HA coating and NHCH-CFs. The results of this study and the proposed preparation of uniform and dense nano-HA coating provide theoretical and practical guidance for future investigations of active HA coatings on fiber materials for medical products and implants. This work also lays the foundation for the wider use of HA-coated CFs/HA composite implants in clinical application. Copyright © 2016 Elsevier B.V. All rights reserved.

Crystalline order of a water/glycine film coadsorbed on the (104) calcite surface.

PubMed

Magdans, Uta; Torrelles, Xavier; Angermund, Klaus; Gies, Hermann; Rius, Jordi

2007-04-24

For biomineralization processes, the interaction of the surface of calcite crystals with organic molecules is of particular importance. Especially, biologically controlled biomineralization as in exoskeletons of mollusks and echinoderms, e.g., sea urchin with single-crystal-like spines and shells,1-3 requires molecular control of seed formation and growth process. So far, experiments showing the obvious influence of organic molecules on the morphology and habit of calcite crystals have demonstrated the molecular dimension of the interaction.4-7 Details of the kinetics of growth and dissolution of mineral surfaces influenced by additives are available,8,9 but other experimental data about the structure of the organic/inorganic interface on the atomic scale are rare. On the other hand, complicated organic macromolecules which are involved in biomineralization are numerous, with only a small fraction solved in structure and function so far.10-13 Therefore, model systems have to be designed to provide a basic understanding for the interaction process.14 Using grazing incidence X-ray diffraction combined with molecular modeling techniques, we show that glycine molecules order periodically on the calcite (104) face in competition with the solvent water when exposed to an aqueous solution of the most simple amino acid. In contrast to the general concept of the charge-matching fit of organic molecules on mineral surfaces,4,14 glycine is not attached to the calcite surface directly but substitutes for water molecules in the second hydration layer.

Solution processed deposition of electron transport layers on perovskite crystal surface-A modeling based study

NASA Astrophysics Data System (ADS)

Mortuza, S. M.; Taufique, M. F. N.; Banerjee, Soumik

2017-02-01

The power conversion efficiency (PCE) of planar perovskite solar cells (PSCs) has reached up to ∼20%. However, structural and chemicals defects that lead to hysteresis in the perovskite based thin film pose challenges. Recent work has shown that thin films of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) deposited on the photo absorption layer, using solution processing techniques, minimize surface pin holes and defects thereby increasing the PCE. We developed and employed a multiscale model based on molecular dynamics (MD) and kinetic Monte Carlo (kMC) to establish a relationship between deposition rate and surface coverage on perovskite surface. The MD simulations of PCBMs dispersed in chlorobenzene, sandwiched between (110) perovskite substrates, indicate that PCBMs are deposited through anchoring of the oxygen atom of carbonyl group to the exposed lead (Pb) atom of (110) perovskite surface. Based on rates of distinct deposition events calculated from MD, kMC simulations were run to determine surface coverage at much larger time and length scales than accessible by MD alone. Based on the model, a generic relationship is established between deposition rate of PCBMs and surface coverage on perovskite crystal. The study also provides detailed insights into the morphology of the deposited film.

Effect of synthesis conditions on the nanopowder properties of Ce{sub 0.9}Zr{sub 0.1}O{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zimicz, M.G.; Fabregas, I.O.; Lamas, D.G.

Graphical abstract: . The synthesis of nanocrystalline Ce{sub 0.9}Zr{sub 0.1}O{sub 2} powders via the gel-combustion method, using different fuels, and following either stoichiometric or non-stoichiometric pH-controlled routes is investigated. Research highlights: {yields} All samples exhibited the fluorite-type crystal structure, nanometric average crystallite size and negligible carbon content. {yields} Synthesis conditions strongly affect the average crystallite size, the degree of agglomeration, the specific surface area and the pore volume. {yields} Our results indicate that, by controlling the synthesis conditions it is possible to obtain solids with custom-made morphological properties. -- Abstract: In this work, the synthesis of nanocrystalline Ce{sub 0.9}Zr{sub 0.1}O{submore » 2} powders via the gel-combustion method, using different fuels, and following either stoichiometric or non-stoichiometric pH-controlled routes is investigated. The objective is to evaluate the effect of synthesis conditions on the textural and morphological properties, and the crystal structure of the synthesized materials. The solids were characterized by nitrogen physisorption, Scanning Electron Microscopy (SEM), X-ray powder diffraction (XPD), and Carbon-Hydrogen-Nitrogen Elemental Analysis (CHN). All the powders exhibited nanometric crystallite size, fluorite-type structure and negligible carbon content. Synthesis conditions strongly affect the average crystallite size, the degree of agglomeration, the specific surface area and the pore volume. Our results indicate that, by controlling the synthesis conditions it is possible to obtain solids with custom-made morphological properties.« less

Molecular dynamic simulation for nanometric cutting of single-crystal face-centered cubic metals.

PubMed

Huang, Yanhua; Zong, Wenjun

2014-01-01

In this work, molecular dynamics simulations are performed to investigate the influence of material properties on the nanometric cutting of single crystal copper and aluminum with a diamond cutting tool. The atomic interactions in the two metallic materials are modeled by two sets of embedded atom method (EAM) potential parameters. Simulation results show that although the plastic deformation of the two materials is achieved by dislocation activities, the deformation behavior and related physical phenomena, such as the machining forces, machined surface quality, and chip morphology, are significantly different for different materials. Furthermore, the influence of material properties on the nanometric cutting has a strong dependence on the operating temperature.

Effects of phosphoric acid on the lead-acid battery reactions

NASA Astrophysics Data System (ADS)

Ikeda, Osamu; Iwakura, Chiaki; Yoneyama, Hiroshi; Tamura, Hideo

1986-10-01

The addition of a small amount of phosphoric acid to 5 M H2SO4 (commercial electrolyte of lead-acid batteries) results in various positive effects on the lead-acid battery reactions: (1) depression of the corrosion rate of the lead substrate through a preferential formation of alpha-PbO2 on the substrate surface; (2) retardation of hard sulfate formation or of deactivation of active materials; and (3) change in the crystal morphology of PbSO2 formed on the discharge of PbO2. Most of these effects results from chemisorption of phosphoric acid on PbSO4 crystals produced in the discharge process of PbO2.

Preparation of Interconnected Biomimetic Poly(vinylidene fluoride-co-chlorotrifluoroethylene) Hydrophobic Membrane by Tuning the Two-Stage Phase Inversion Process.

PubMed

Zheng, Libing; Wang, Jun; Wu, Zhenjun; Li, Jie; Zhang, Yong; Yang, Min; Wei, Yuansong

2016-11-30

A facile strategy was applied for poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) hydrophobic membrane preparation by tuning the two-stage phase inversion process. The exposure stage was found to benefit the solid-liquid demixing process (gelation/crystallization) induced by the solvent evaporation and the subsequent phase inversion induced by immersion benefit the liquid-liquid demixing. It was confirmed that the electrospun nanostructure-like biomimetic surface and interconnected pore structure can be expected by controlling the exposure duration, and 300 s was considered as the inflection point of exposure duration for PVDF-CTFE membrane through which a tremendous variation would show. The micro/nanohierarchical structure in the membrane surface owing to the crystallization of PVDF-CTFE copolymer was responsible for the improvement of membrane roughness and hydrophobicity. Meanwhile, the interconnected pore structure in both the surface and the cross-section, which were formed because of the crystallization process, offers more mass transfer passages and enhances the permeate flux. The membrane then showed excellent MD performance with high permeate flux, high salt rejection, and relatively high stability during a 48 h continuous DCMD operation, according to the morphology, pore structure, and properties, which can be a substitute for hydrophobic membrane application.

Pb 2+–Calcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite

DOE PAGES

Yuan, Ke; De Andrade, Vincent; Feng, Zhange; ...

2018-01-04

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion-mineral interactions during dissolution under far-from equilibrium conditions remains limited. Here we show that calcite (CaCO 3) exhibits a rich array of dissolution features in the presence of Pb. During the initial stage, calcite exhibits non-classical surface features characterized as micro pyramids developed spontaneously in acidic Pb-bearing solutions. Subsequent pseudomorphic growth of cerussite (PbCO 3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded amore » cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution-precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing micro structures observed in naturally-occurring and synthetic carbonate minerals by dissolution. In addition, heterogeneous micro-environments created in transport limited reactions under pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.« less

Correlation of lattice defects and thermal processing in the crystallization of titania nanotube arrays

NASA Astrophysics Data System (ADS)

Hosseinpour, Pegah M.; Yung, Daniel; Panaitescu, Eugen; Heiman, Don; Menon, Latika; Budil, David; Lewis, Laura H.

2014-12-01

Titania nanotubes have the potential to be employed in a wide range of energy-related applications such as solar energy-harvesting devices and hydrogen production. As the functionality of titania nanostructures is critically affected by their morphology and crystallinity, it is necessary to understand and control these factors in order to engineer useful materials for green applications. In this study, electrochemically-synthesized titania nanotube arrays were thermally processed in inert and reducing environments to isolate the role of post-synthesis processing conditions on the crystallization behavior, electronic structure and morphology development in titania nanotubes, correlated with the nanotube functionality. Structural and calorimetric studies revealed that as-synthesized amorphous nanotubes crystallize to form the anatase structure in a three-stage process that is facilitated by the creation of structural defects. It is concluded that processing in a reducing gas atmosphere versus in an inert environment provides a larger unit cell volume and a higher concentration of Ti3+ associated with oxygen vacancies, thereby reducing the activation energy of crystallization. Further, post-synthesis annealing in either reducing or inert atmospheres produces pronounced morphological changes, confirming that the nanotube arrays thermally transform into a porous morphology consisting of a fragmented tubular architecture surrounded by a network of connected nanoparticles. This study links explicit data concerning morphology, crystallization and defects, and shows that the annealing gas environment determines the details of the crystal structure, the electronic structure and the morphology of titania nanotubes. These factors, in turn, impact the charge transport and consequently the functionality of these nanotubes as photocatalysts.

Study of TiO2 anatase nano and microstructures with dominant {001} facets for NO oxidation.

PubMed

Sofianou, Maria-Veronica; Trapalis, Christos; Psycharis, Vassils; Boukos, Nikos; Vaimakis, Tiverios; Yu, Jiaguo; Wang, Wenguang

2012-11-01

TiO(2) anatase nanoplates and hollow microspheres were fabricated by a solvothermal-hydrothermal method using titanium isopropoxide as a titanium precursor and hydrofluoric acid as a capping agent in order to enhance the formation of the {001} crystal facets of the anatase nanocrystals. These different morphological structures of TiO(2) anatase can be achieved by only changing the solvent, keeping the amount of the precursor and of the capping agent identical during the solvothermal-hydrothermal process. After calcination of the samples, the adsorbed fluoride atoms on the {001} crystal facets of the TiO(2) anatase nanocrystals were completely removed from their surface according to XPS analysis. The calcined TiO(2) anatase structures were higher crystallized and the specific surface area of the catalysts increased, enhancing their photocatalytic activity in comparison to the non-calcined TiO(2) anatase structures. All TiO(2) anatase samples with adsorbed as well as non-adsorbed fluoride atoms on their {001} crystal facets, exhibited a higher photonic efficiency than Degussa P25, which was used as a reference. The fluoride free TiO(2) anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO(2) and NO(3) (-).

Bottom-up Fabrication of Multilayer Stacks of 3D Photonic Crystals from Titanium Dioxide.

PubMed

Kubrin, Roman; Pasquarelli, Robert M; Waleczek, Martin; Lee, Hooi Sing; Zierold, Robert; do Rosário, Jefferson J; Dyachenko, Pavel N; Montero Moreno, Josep M; Petrov, Alexander Yu; Janssen, Rolf; Eich, Manfred; Nielsch, Kornelius; Schneider, Gerold A

2016-04-27

A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons.

Morphological evolution of Bi2Se3 nanocrystalline materials synthesized by microwave assisted solvothermal method

NASA Astrophysics Data System (ADS)

Bera, Sumit; Behera, P.; Mishra, A. K.; Krishnan, M.; Patidar, M. M.; Singh, D.; Gangrade, M.; Venkatesh, R.; Deshpande, U. P.; Phase, D. M.; Ganesan, V.

2018-04-01

Structural, morphological and spectroscopic properties of Bi2Se3 nanoparticles synthesized by microwave assisted solvothermal method were investigated systematically. A controlled synthesis of different morphologies by a small variation in synthesis procedure is demonstrated. Powder X-ray diffraction (XRD) confirmed the formation of single phase. Crystallite and particle size reductions were studied with XRD and AFM (Atomic Force Microscopy). Different morphologies such as hexagonal nanoflakes with cross section of around˜6µm, nanoflower and octahedral agglomerated crystals of nearly ˜60 nm size have been observed in scanning electron microscope while varying the microwave assisted synthesis procedures. A significant blue shift observed in diffuse reflectance spectroscopy evidences the energy gap tuning as a result of morphological evolution. The difference in morphology observed in this three fast, facile and scalable synthesis is advantageous for tuning the thermoelectric figure of merit and for probing the surface states of these topological insulators. Low temperature resistivity remains similar for all three variants depicting a 2D character as evidenced by a -lnT term of localization.

Growth morphology of flux-synthesized La4Ti3O12 particles

NASA Astrophysics Data System (ADS)

Hori, Shigeo; Orum, Aslihan; Takatori, Kazumasa; Ikeda, Tomiko; Yoshimura, Masamichi; Tani, Toshihiko

2017-06-01

Anisometric-shaped particles were required for preparation of oriented ceramics by the reactive-templated grain growth method. Hexagonal plate-like particles of La4Ti3O12, (111)-type layered perovskite, were prepared by a molten salt synthesis (MSS), and the relationship between the morphology and crystal structure of the particles was analysed. La4Ti3O12 phase was obtained in KCl and NaCl fluxes whereas not obtained in LiCl. The developed plane of the plate-like particles was determined to be the (00l) plane and the side planes of the particle were found to be parallel the {h0l} planes. Surface steps with a height of approx. 0.9 nm were measured on the developed plane. The step height corresponds to the distance between two adjacent interlayers, which indicates the lowest surface energy of the planes along the interlayers.

Particular Film Formation of Phenytoin at Silica Surfaces

PubMed Central

2014-01-01

Given the increasing number of poorly soluble and thus poorly bioavailable active pharmaceutical materials, there is a demand for innovative formulation platforms for such molecules. Thus a focus on enhancing dissolution properties of poorly soluble drugs exists. Within this study, the spin coating of acetone solutions containing 5,5-diphenyl-2,4-imidazolidinedione (phenytoin) in various concentrations is evaluated. The results reveal strong variations of the morphology of deposited phenytoin crystals at silica surfaces. Individual separated particles are obtained on low phenytoin concentrations, and closely packed particular films form when the concentration is increased. As the material is isomorphic, these various morphologies have the same crystalline structure. Dissolution experiments reveal that both the apparent maximum solubility and as the dissolution rate are strongly enhanced compared to bulk powder, suggesting that formulation based on this preparative technique will allow overcoming the low solubility problematic for a variety of drugs. PMID:24417472

Influence of copper morphology in forming nucleation seeds for graphene growth.

PubMed

Han, Gang Hee; Güneş, Fethullah; Bae, Jung Jun; Kim, Eun Sung; Chae, Seung Jin; Shin, Hyeon-Jin; Choi, Jae-Young; Pribat, Didier; Lee, Young Hee

2011-10-12

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts.

Effect of Ultrasonic on Copper Electroplating from the Non-Cyanide Alkaline Baths

NASA Astrophysics Data System (ADS)

Li, Minggang; Hu, Shuangshuang; Yang, Yejiong; Xu, Shuhan; Zhao, Xixi; Wei, Guoying

2014-06-01

Effects of the different ultrasonic powers on copper electrodeposition from non-cyanide alkaline baths by using pyrophosphate as complexing agent were investigated by different electrochemical methods. Cyclic voltammetry and current transient measurements were used to characterize the nucleation and growth mechanism. It is very obvious that the reduction potential moves to more positive one as the ultrasonic power increases. The quartz crystal microbalance (QCM) and chronoamperometric method were used to study the relationship between the mass change and the deposition time. It was found that the current efficiency of electrolyte under 0, 60, 80 and 100 W is 91.95%, 92.14%, 89.25% and 96.11%, respectively measured by QCM measurements. The surface morphology of the electrodeposited Cu films is analyzed by scanning electron microscopy (SEM). The morphology of copper films electrodeposited under the power of 60 W and 80 W presents a compact surface and the grains are fine and uniform.

Deformation analysis of vesicles in an alternating-current electric field.

PubMed

Tang, Yu-Gang; Liu, Ying; Feng, Xi-Qiao

2014-08-01

In this paper the shape equation for axisymmetric vesicles subjected to an ac electric field is derived on the basis of the liquid-crystal model. The equilibrium morphology of a lipid vesicle is determined by the minimization of its free energy in coupled mechanical and ac electric fields. Besides elastic bending, the effects of the osmotic pressure difference, surface tension, Maxwell pressure, and flexoelectric and dielectric properties of phospholipid membrane as well are taken into account. The influences of elastic bending, osmotic pressure difference, and surface tension on the frequency-dependent behavior of a vesicle membrane in an ac electric field are examined. The singularity of the ac electric field is also investigated. Our theoretical results of vesicle deformation agree well with previous experimental and numerical results. The present study provides insights into the physical mechanisms underpinning the frequency-dependent morphological evolution of vesicles in the electric and mechanical fields.

Morphological modification of alpha-MnO2 catalyst for use in Li/air batteries.

PubMed

Park, Min-Sik; Kim, Jae-Hun; Kim, Ki Jae; Jeong, Goojin; Kim, Young-Jun

2013-05-01

Single crystal alpha-MnO2 nanowires and nanopowders have been successfully synthesized in order to facilitate a comparison of their catalytic activity for use in Li-air batteries. The importance of the morphological modification of the alpha-MnO2 catalyst for facilitating electrochemical reactions between Li and O2 is addressed. Distinctive catalytic activity of alpha-MnO2 is observed, which is in line with its different morphologies. The catalytic activity significantly affects the reversible capacity of Li-air batteries. A high aspect ratio, large surface area and good dispersibility of alpha-MnO2 in the nanowire form are advantageous providing larger active surfaces for promoting the fundamental reactions in Li-air batteries. We also introduce a robustly designed air-electrode composed of highly porous carbon and nanostructured alpha-MnO2 catalysts, with employs a metal foam current collector to ensure sufficient air-permeability and to maximize electronic conduction during cycles. Our suggestions should prove helpful in forming a basis for further investigations in developing advanced Li-air batteries.

Crystallization, mechanical properties, and controlled enzymatic degradation of biodegradable poly(epsilon-caprolactone)/multi-walled carbon nanotubes nanocomposites.

PubMed

Qiu, Zhaobin; Wang, Huishan; Xu, Changling

2011-09-01

Biodegradable poly(epsilon-caprolactone) (PCL)/multi-walled carbon nanotubes containing carboxylic groups (f-MWNTs) nanocomposites were prepared via simple melt compounding at low f-MWNTs loading in this work. Scanning and transmission electron microscopy observations indicate a homogeneous and fine distribution of f-MWNTs throughout the PCL matrix. The effect of low f-MWNTs loading on the crystallization, mechanical properties, and controlled enzymatic degradation of PCL in the nanocomposites were studied in detail with various techniques. The experimental results indicate that the incorporation of f-MWNTs enhances both the nonisothermal crystallization peak temperature and the overall isothermal crystallization rate of PCL in the PCL/f-MWNTs nanocomposites relative to neat PCL; moreover, the incorporation of a small quantity of f-MWNTs has improved apparently the mechanical properties of the PCL/MWNTs nanocomposites compared to neat PCL. The enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites at low f-MWNTs loading was studied in detail. The variation of weight loss with enzymatic degradation time, the surface morphology change, the reduced film thickness, the appearance of f-MWNTs on the surface of the films, and the almost unchanged molecular weight after enzymatic degradation suggest that the enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites may proceed via surface erosion mechanism. The presence of f-MWNTs reduces the enzymatic degradation rate of the PCL matrix in the nanocomposites compared with that of the pure PCL film.

Purification and Crystal Growth of Lead Iodide by Physical Vapor Transport Method

NASA Technical Reports Server (NTRS)

Wright, G. W.; Cole, M.; Chen, Y.-F.; Chen, K.-T.; Chen, H.; Chattopadhyay, K.; Burger, A.

1998-01-01

Lead iodide (PbI2) is a layered compound semiconductor being developed as room temperature x- and gamma-ray detector. Compared to the more studied material, mercuric iodide, PbI2 has a higher melting temperature and no phase transition until liquid phase which are indications of better mechanical properties. In this study, the source material was purified by the zone-refining process, and the purest section was extracted from center of the the zone-refined ingot to be grown by physical vapor transport (PVT) method. The zone-refined material and as-grown crystals were characterized by optical microscopy and differential scanning calorimetry (DSC) to reveal the surface morphology, purity and stoichiometry. The results shows that both materials are near-stoichiometric composition, with the purity of the as-grown crystals higher than zone-refined materials. The resistivity of the as-grown crystal (10" Omega-cm) was derived from current-voltage (I-V) measurement, and is 10 times higher than the zone-refined materials. Detail results will be presented and discussed.

Control of p-type and n-type thermoelectric properties of bismuth telluride thin films by combinatorial sputter coating technology

NASA Astrophysics Data System (ADS)

Goto, Masahiro; Sasaki, Michiko; Xu, Yibin; Zhan, Tianzhuo; Isoda, Yukihiro; Shinohara, Yoshikazu

2017-06-01

p- and n-type bismuth telluride thin films have been synthesized by using a combinatorial sputter coating system (COSCOS). The crystal structure and crystal preferred orientation of the thin films were changed by controlling the coating condition of the radio frequency (RF) power during the sputter coating. As a result, the p- and n-type films and their dimensionless figure of merit (ZT) were optimized by the technique. The properties of the thin films such as the crystal structure, crystal preferred orientation, material composition and surface morphology were analyzed by X-ray diffraction, energy-dispersive X-ray spectroscopy and atomic force microscopy. Also, the thermoelectric properties of the Seebeck coefficient, electrical conductivity and thermal conductivity were measured. ZT for n- and p-type bismuth telluride thin films was found to be 0.27 and 0.40 at RF powers of 90 and 120 W, respectively. The proposed technology can be used to fabricate thermoelectric p-n modules of bismuth telluride without any doping process.

Morphology and formation mechanism in precipitation of calcite induced by Curvibacter lanceolatus strain HJ-1

NASA Astrophysics Data System (ADS)

Zhang, Chonghong; Li, Fuchun; Lv, Jiejie

2017-11-01

Precipitation of calcium carbobate induced by microbial activities is common occurrence in controlled solution, but the formation mechanism and morphology in precipitation of calcite in solution systems is unclear, and the role of microbes is disputed. Here, culture experiment was performed for 50 days using the Curvibacter lanceolatus strain HJ-1 in a M2 culture medium, and the phase composition and morphology of the precipitates were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) techniques. We show that the precipitation processes in our experiment lead to unusual morphologies of crystals corresponding to different growth stages, and the morphologies of the precipitated crystal aggregates ranging from the main rod-, cross-, star-, cauliflower-like morphologies to spherulitic structure. The complex and unusual morphologies of the precipitated calcite by strain HJ-1 may provide a reference point for better understanding the biomineralization mechanism of calcite, moreover, morphological transition of minerals revealed that the multi-ply crystals-aggregation mechanism for calcite growth in crystallisation media.

Superhydrophobic alumina surface based on stearic acid modification

NASA Astrophysics Data System (ADS)

Feng, Libang; Zhang, Hongxia; Mao, Pengzhi; Wang, Yanping; Ge, Yang

2011-02-01

A novel superhydrophobic alumina surface is fabricated by grafting stearic acid layer onto the porous and roughened aluminum film. The chemical and phase structure, morphology, and the chemical state of the atoms at the superhydrophobic surface were investigated by techniques as FTIR, XRD, FE-SEM, and XPS, respectively. Results show that a super water-repellent surface with a contact angle of 154.2° is generated. The superhydrophobic alumina surface takes on an uneven flowerlike structure with many nanometer-scale hollows distribute in the nipple-shaped protrusions, and which is composed of boehmite crystal and γ-Al2O3. Furthermore, the roughened and porous alumina surface is coated with a layer of hydrophobic alkyl chains which come from stearic acid molecules. Therefore, both the roughened structure and the hydrophobic layer endue the alumina surface with the superhydrophobic behavior.

Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment

NASA Astrophysics Data System (ADS)

Aguilar-Mamani, Wilson; Akhtar, Farid; Hedlund, Jonas; Mouzon, Johanne

2018-04-01

The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.

Synthesis and characterization of Ni doped ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Tamgadge, Y. S.; Gedam, P. P.; Ganorkar, R. P.; Mahure, M. A.; Pahurkar, V. G.; Muley, G. G.

2018-05-01

In this paper, we present synthesis of L-valine assisted surface modification of Ni doped ZnO nanoparticles (NPs) using chemical precipitation method. Samples were calcined at 500oC for 2h. Uncalcined and calcined samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet-visible (UV-vis) spectroscopy. Ni doped ZnO NPs with average particle size of 8 nm have been successfully obtained using L-valine as surface modifying agent. Increase in the particle size was observed after the calcination. XRD and TEM studies confirmed the purity, surface morphology and hexagonal wurtzite crystal structure of ZnO NPs. UV-vis spectroscopy indicated the blue shift of excitons absorption wavelength and surface modification by L-valine.

Crystal morphology modification by the addition of tailor-made stereocontrolled poly(N-isopropyl acrylamide).

PubMed

Munk, Tommy; Baldursdottir, Stefania; Hietala, Sami; Rades, Thomas; Kapp, Sebastian; Nuopponen, Markus; Kalliomäki, Katriina; Tenhu, Heikki; Rantanen, Jukka

2012-07-02

The use of additives in crystallization of pharmaceuticals is known to influence the particulate properties critically affecting downstream processing and the final product performance. Desired functionality can be build into these materials, e.g. via optimized synthesis of a polymeric additive. One such additive is the thermosensitive polymer poly(N-isopropyl acrylamide) (PNIPAM). The use of PNIPAM as a crystallization additive provides a possibility to affect viscosity at separation temperatures and nucleation and growth rates at higher temperatures. In this study, novel PNIPAM derivatives consisting of both isotactic-rich and atactic blocks were used as additives in evaporative crystallization of a model compound, nitrofurantoin (NF). Special attention was paid to possible interactions between NF and PNIPAM and the aggregation state of PNIPAM as a function of temperature and solvent composition. Optical light microscopy and Raman and FTIR spectroscopy were used to investigate the structure of the NF crystals and possible interaction with PNIPAM. A drastic change in the growth mechanism of nitrofurantoin crystals as monohydrate form II (NFMH-II) was observed in the presence of PNIPAM; the morphology of crystals changed from needle to dendritic shape. Additionally, the amphiphilic nature of PNIPAM increased the solubility of nitrofurantoin in water. PNIPAMs with varying molecular weights and stereoregularities resulted in similar changes in the crystal habit of the drug regardless of whether the polymer was aggregated or not. However, with increased additive concentration slower nucleation and growth rates of the crystals were observed. Heating of the crystallization medium resulted in phase separation of the PNIPAM. The phase separation had an influence on the achieved crystal morphology resulting in fewer, visually larger and more irregular dendritic crystals. No proof of hydrogen bond formation between PNIPAM and NF was observed, and the suggested mechanism for the observed dendritic morphology is related to the steric hindrance phenomenon. PNIPAM can be used as a crystallization additive with an obvious effect on the growth of NF crystals.

Unravelling merging behaviors and electrostatic properties of CVD-grown monolayer MoS{sub 2} domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Song; Yang, Bingchu, E-mail: bingchuyang@csu.edu.cn; Hunan Key Laboratory for Super-Microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha 410012

The presence of grain boundaries is inevitable for chemical vapor deposition (CVD)-grown MoS{sub 2} domains owing to various merging behaviors, which greatly limits its potential applications in novel electronic and optoelectronic devices. It is therefore of great significance to unravel the merging behaviors of the synthesized polygon shape MoS{sub 2} domains. Here we provide systematic investigations of merging behaviors and electrostatic properties of CVD-grown polycrystalline MoS{sub 2} crystals by multiple means. Morphological results exhibit various polygon shape features, ascribed to polycrystalline crystals merged with triangle shape MoS{sub 2} single crystals. The thickness of triangle and polygon shape MoS{sub 2} crystalsmore » is identical manifested by Raman intensity and peak position mappings. Three merging behaviors are proposed to illustrate the formation mechanisms of observed various polygon shaped MoS{sub 2} crystals. The combined photoemission electron microscopy and kelvin probe force microscopy results reveal that the surface potential of perfect merged crystals is identical, which has an important implication for fabricating MoS{sub 2}-based devices.« less

Nanoscale Structural Changes Upon Electrooxidation of Au(111) as Probed by Potentiodynamic Scanning Tunneling Microscopy

DTIC Science & Technology

1994-02-01

electrochemical formation and removal of oxide films is of broadbased practical as well as fundamental importance. Studies of noble metals, such as gold and...atomic level. At the current state of development of STM, monocrystalline gold electrodes provide efficacious choices of systems, partly in view of...several in-situ STM studies have focussed on the surface morphological changes attending oxidation and rereduction of single-crystal gold electrodes

Solidification of undercooled liquids

NASA Technical Reports Server (NTRS)

Perepezko, J. H.; Shiohara, Y.; Paik, J. S.; Flemmings, M. C.

1982-01-01

During rapid solidification processing (RSP) the amount of liquid undercooling is an important factor in determining microstructural development by controlling phase selection during nucleation and morphological evolution during crystal growth. While undercooling is an inherent feature of many techniques of RSP, the deepest undercoolings and most controlled studies have been possible in carefully prepared fine droplet samples. From past work and recent advances in studies of nucleation kinetics it has become clear that the initiation of crystallization during RSP is governed usually by heterogeneous sites located at surfaces. With known nucleant sites, it has been possible to identify specific pathways of metastable phase formation and microstructural development in alloys. These advances have allowed for a clearer assessment of the interplay between undercooling, cooling rate and particle size statistics in structure formation. New approaches to the examination of growth processes have been developed to follow the thermal behavior and morphology in small samples in the period of rapid crystallization and recalescence. Based upon the new experimental information from these studies, useful models can be developed for the overall solidification process to include nucleation behavior, thermodynamic constraints, thermal history, growth kinetics, solute redistribution and resulting structures. From the refinement of knowledge concerning the underlying factors that govern RSP a basis is emerging for an effective alloy design and processing strategy.

Phase conversion from hexagonal CuS(y)Se(1-y) to cubic Cu(2-x)S(y)Se(1-y): composition variation, morphology evolution, optical tuning, and solar cell applications.

PubMed

Xu, Jun; Yang, Xia; Yang, Qingdan; Zhang, Wenjun; Lee, Chun-Sing

2014-09-24

In this work, we report a simple and low-temperature approach for the controllable synthesis of ternary Cu-S-Se alloys featuring tunable crystal structures, compositions, morphologies, and optical properties. Hexagonal CuS(y)Se(1-y) nanoplates and face centered cubic (fcc) Cu(2-x)S(y)Se(1-y) single-crystal-like stacked nanoplate assemblies are synthesized, and their phase conversion mechanism is well investigated. It is found that both copper content and chalcogen composition (S/Se atomic ratio) of the Cu-S-Se alloys are tunable during the phase conversion process. Formation of the unique single-crystal-like stacked nanoplate assemblies is resulted from oriented stacking coupled with the Ostwald ripening effect. Remarkably, optical tuning for continuous red shifts of both the band-gap absorption and the near-infrared localized surface plasmon resonance are achieved. Furthermore, the novel Cu-S-Se alloys are utilized for the first time as highly efficient counter electrodes (CEs) in quantum dot sensitized solar cells (QDSSCs), showing outstanding electrocatalytic activity for polysulfide electrolyte regeneration and yielding a 135% enhancement in power conversion efficiency (PCE) as compared to the noble metal Pt counter electrode.

Crystallization of dicalcium phosphate dihydrate with presence of glutamic acid and arginine at 37 °C.

PubMed

Li, Chengfeng; Ge, Xiaolu; Li, Guochang; Bai, Jiahai; Ding, Rui

2014-08-01

The formations of non-metabolic stones, bones and teeth were seriously related to the morphology, size and surface reactivity of dicalcium phosphate dihydrate (DCPD). Herein, a facile biomimetic mineralization method with presence of glutamic acid and arginine was employed to fabricate DCPD with well-defined morphology and adjustable crystallite size. In reaction solution containing more arginine, crystallization of DCPD occurred with faster rate of nucleation and higher density of stacked layers due to the generation of more OH(-) ions after hydrolysis of arginine at 37 °C. With addition of fluorescein or acetone, the consumption of OH(-) ions or desolvation reaction of Ca(2+) ions was modulated, which resulted in the fabrication of DCPD with adjustable crystallite sizes and densities of stacked layers. In comparison with fluorescein-loading DCPD, dicalcium phosphate anhydrate was prepared with enhanced photoluminescence properties due to the reduction of self-quenching effect and regular arrangement of encapsulated fluorescein molecules. With addition of more acetone, DCPD was prepared with smaller crystallite size via antisolvent crystallization. The simulated process with addition of amino acids under 37 °C would shed light on the dynamic process of biomineralization for calcium phosphate compounds. Copyright © 2014 Elsevier B.V. All rights reserved.

Morphological stability of sapphire crystallization front

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baranov, V. V., E-mail: baranov.isc@gmail.com; Nizhankovskyi, S. V.

2016-03-15

The main factors and specificity of growth conditions for sapphire and Ti:sapphire crystals, which affect the morphological stability of the crystal–melt interface, have been investigated with allowance for the concentration and radiative melt supercooling. It is shown that the critical sapphire growth rate is determined to a great extent by the optical transparency of the melt and the mixing conditions near the crystallization front.

Spectroscopic analyses of Fe and water in clays: A Martian surface weathering study

NASA Technical Reports Server (NTRS)

Bishop, J. L.; Pieters, Carle M.; Edwards, J. O.; Coyne, L. M.; Chang, S.

1991-01-01

Martian surface morphology suggests the presence of liquid H2O on Mars in the past. Reflectance spectra of the Martian surface include features which correspond to the crystal field transitions of iron, as well as features supporting the presence of ice and minerals containing structural OH and surface water. Researchers initiated further spectroscopic studies of surface iron and water and structural OH in clays in order to determine what remotely obtained spectra can indicate about the presence of clays on Mars based on a clearer understanding of the factors influencing the spectral features. Current technology allows researchers to better correlate the low frequency fundamental stretching and bending vibrations of O-H bonds with the diagnostic near infrared overtone and combination bands used in mineral characterization and identification.

Factors influencing gypsum crystal morphology within a flue gas desulfurization vessel

NASA Astrophysics Data System (ADS)

Lewis, Kinsey M.

Flue gas desulfurization (FGD) is utilized by the coal--powered generating industry to safely eliminate sulfur dioxide. A FGD vessel (scrubber) synthetically creates gypsum crystals by combining limestone (CaCO3), SO2 flue gas, water and oxygen resulting in crystalline gypsum (CaSO4 · 2H2O), which can be sold for an economic return. Flat disk--like crystals, opposed to rod--like crystals, are hard to dewater, lowering economic return. The objectives were to investigate the cause of varying morphologies, understand the environment of precipitation, as well as identify correlations between operating conditions and resulting unfavorable gypsum crystal growth. Results show evidence supporting airborne impurities due to the onsite coal pile, the abundance and size of CaCO 3 and high Ca:SO4 ratios within the scrubber as possible factors controlling gypsum crystal morphology. In conclusion, regularly purging the system and incorporating a filter on the air intake valve will provide an economic byproduct avoiding costly landfill deposits.

Deposition of Cubic AlN Films on MgO (100) Substrates by Laser Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Mo, Z. K.; Yang, W. J.; Weng, Y.; Fu, Y. C.; He, H.; Shen, X. M.

2017-12-01

Cubic AlN (c-AlN) films were deposited on MgO (100) substrates by laser molecular beam epitaxy (LMBE) technique. The crystal structure and surface morphology of deposited films with various laser pulse energy and substrate temperature were investigated. The results indicate that c-AlN films exhibit the (200) preferred orientation, showing a good epitaxial relationship with the substrate. The surface roughness of c-AlN films increases when the laser pulse energy and substrate temperature increase. The film grown at laser pulse energy of 150 mJ and substrate temperature of 700 °C shows the best crystalline quality and relatively smooth surface.

Dissolution of uranophane: An AFM, XPS, SEM and ICP study

NASA Astrophysics Data System (ADS)

Schindler, Michael; Freund, Michael; Hawthorne, Frank C.; Burns, Peter C.; Maurice, Patricia A.

2009-05-01

Dissolution experiments on single crystals of uranophane and uranophane-β, Ca(H 2O) 5[(UO 2)(SiO 3(OH)] 2, from the Shinkolobwe mine of the Democratic Republic of Congo, were done in an aqueous HCl solution of pH 3.5 for 3 h, in HCl solutions of pH 2 for 5, 10 and 30 min, and in Pb 2+-, Ba-, Sr-, Ca- and Mg-HCl solutions of pH 2 for 30 min. The basal surfaces of the treated uranophane crystals were examined using atomic-force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Solutions after dissolution experiments on single crystals and synthetic powders were analysed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) and mass spectroscopy (ICP-MS). The morphology of the observed etch pits (measured by AFM) were compared to the morphology, predicted on the basis of the bond-valence deficiency of polyhedron chains along the edges of the basal surface. Etch pits form in HCl solutions of pH 2. Their decrease in depth with the duration of the dissolution experiment is explained with the stepwave dissolution model, which describes the lowering of the surrounding area of an etch pit with continuous waves of steps emanated from the etch pit into the rest of the crystal surface. Hillocks form in an HCl solution of pH 3.5, and the chemical composition of the surface (as indicated by XPS) shows that these hillocks are the result of the precipitation of a uranyl-hydroxy-hydrate phase. Well-orientated hillocks form on the surface of uranophane in a SrCl 2-HCl solution of pH 2. They are part of an aged silica coating of composition Si 2O 2(OH) 4(H 2O) n. An amorphous layer forms on the surface of uranophane in a MgCl 2-HCl solution of pH 2, which has a composition and structure similar to silicic acid. Small crystallites of uranyl-hydroxy-hydrate phases form on the surface of uranophane after treatment in Pb(NO 3) 2-HCl and BaCl 2-HCl solutions of pH 2. Dissolution experiments on synthetic uranophane powders show that in the early stage of the experiments, the dissolution rate of uranophane increase in the sequence Pb(NO 3) 2-HCl < BaCl 2-HCl < CaCl 2-HCl < HCl < SrCl 2-HCl < MgCl 2-HCl, indicating that the dissolution of uranophane is more enhanced in solutions containing divalent cations of small ionic radii and high Lewis acidity (Mg, MgCl +).

Effects of cyclic structure inhibitors on the morphology and growth of tetrahydrofuran hydrate crystals

NASA Astrophysics Data System (ADS)

Li, Sijia; Wang, Yanhong; Lang, Xuemei; Fan, Shuanshi

2013-08-01

Morphology and growth of hydrate crystals with cyclic structure inhibitors at a hydrate-liquid interface were directly observed through a microscopic manipulating apparatus. Tetrahydrofuran (THF) hydrate was employed as an objective. The effects of four kind of cyclic structure inhibitors, polyvinylpyrrolidone (PVP), poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine) (PVPP), poly(2-vinyl pyridine-co-N-vinylcaprolactam) (PVPC) and poly(N-vinylcaprolactam) (PVCap), were investigated. Morphological patterns between each hydrate crystal growth from hydrate-liquid interface into droplet were found differ significantly. Lamellar structure growth of hydrate crystal was observed without inhibitor, while with PVP was featheriness-like, PVPP was like long dendritic crystal, PVPC was Mimosa pudica leaf-like and PVCap was like weeds. The growth rate of hydrate crystal without inhibitor was 0.00498 mm3/s, while with PVPP, PVPC and PVCap, were 0.00339 mm3/s, 0.00350 mm3/s, 0.00386 mm3/s and 0.00426 mm3/s, respectively. Cyclic structure inhibitors can decrease the growth rate, degree of reduction in growth rate of hydrate crystals decrease with the increase of cylinder number.

Phase-field crystal simulation facet and branch crystal growth

NASA Astrophysics Data System (ADS)

Chen, Zhi; Wang, Zhaoyang; Gu, Xinrui; Chen, Yufei; Hao, Limei; de Wit, Jos; Jin, Kexin

2018-05-01

Phase-field crystal model with one mode is introduced to describe morphological transition. The relationship between growth morphology and smooth density distribution was investigated. The results indicate that the pattern selection of dendrite growth is caused by the competition between interface energy anisotropy and interface kinetic anisotropy based on the 2D phase diagram. When the calculation time increases, the crystal grows to secondary dendrite at the dimensionless undercooling equal to - 0.4. Moreover, when noise is introduced in the growth progress, the symmetry is broken in the growth mode, and there becomes irregular fractal-like growth morphology. Furthermore, the single crystal shape develops into polycrystalline when the noise amplitude is large enough. When the dimensionless undercooling is less than - 0.3, the noise has a significant effect on the growth shape. In addition, the growth velocity of crystal near to liquid phase line is slow, while the shape far away from the liquid adapts to fast growth. Based on the simulation results, the method was proved to be effective, and it can easily obtain different crystal shapes by choosing the different points in 2D phase diagram.

Time-Lapse, in Situ Imaging of Ice Crystal Growth Using Confocal Microscopy

PubMed Central

2016-01-01

Ice crystals nucleate and grow when a water solution is cooled below its freezing point. The growth velocities and morphologies of the ice crystals depend on many parameters, such as the temperature of ice growth, the melting temperature, and the interactions of solutes with the growing crystals. Three types of morphologies may appear: dendritic, cellular (or fingerlike), or the faceted equilibrium form. Understanding and controlling which type of morphology is formed is essential in several domains, from biology to geophysics and materials science. Obtaining, in situ, three dimensional observations without introducing artifacts due to the experimental technique is nevertheless challenging. Here we show how we can use laser scanning confocal microscopy to follow in real-time the growth of smoothed and faceted ice crystals in zirconium acetate solutions. Both qualitative and quantitative observations can be made. In particular, we can precisely measure the lateral growth velocity of the crystals, a measure otherwise difficult to obtain. Such observations should help us understand the influence of the parameters that control the growth of ice crystals in various systems. PMID:27917410

Time-Lapse, in Situ Imaging of Ice Crystal Growth Using Confocal Microscopy.

PubMed

Marcellini, Moreno; Noirjean, Cecile; Dedovets, Dmytro; Maria, Juliette; Deville, Sylvain

2016-11-30

Ice crystals nucleate and grow when a water solution is cooled below its freezing point. The growth velocities and morphologies of the ice crystals depend on many parameters, such as the temperature of ice growth, the melting temperature, and the interactions of solutes with the growing crystals. Three types of morphologies may appear: dendritic, cellular (or fingerlike), or the faceted equilibrium form. Understanding and controlling which type of morphology is formed is essential in several domains, from biology to geophysics and materials science. Obtaining, in situ, three dimensional observations without introducing artifacts due to the experimental technique is nevertheless challenging. Here we show how we can use laser scanning confocal microscopy to follow in real-time the growth of smoothed and faceted ice crystals in zirconium acetate solutions. Both qualitative and quantitative observations can be made. In particular, we can precisely measure the lateral growth velocity of the crystals, a measure otherwise difficult to obtain. Such observations should help us understand the influence of the parameters that control the growth of ice crystals in various systems.

Thin-walled nanoscrolls by multi-step intercalation from tubular halloysite-10 Å and its rearrangement upon peroxide treatment

NASA Astrophysics Data System (ADS)

Zsirka, Balázs; Horváth, Erzsébet; Szabó, Péter; Juzsakova, Tatjána; Szilágyi, Róbert K.; Fertig, Dávid; Makó, Éva; Varga, Tamás; Kónya, Zoltán; Kukovecz, Ákos; Kristóf, János

2017-03-01

Surface modification of the halloysite-10 Å mineral with tubular morphology can be achieved by slightly modified procedures developed for the delamination of kaolinite minerals. The resulting delaminated halloysite nanoparticles have unexpected surface/morphological properties that display, new potentials in catalyst development. In this work, a four-step intercalation/delamination procedure is described for the preparation of thin-walled nanoscrolls from the multi-layered hydrated halloysite mineral that consists of (1) intercalation of halloysite with potassium acetate, (2) replacement intercalation with ethylene glycol, (3) replacement intercalation with hexylamine, and (4) delamination with toluene. The intercalation steps were followed by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, thermogravimetry, and infrared spectroscopy. Delamination eliminated the crystalline order and the crystallite size along the 'c'-axis, increased the specific surface area, greatly decreased the thickness of the mineral tubes to a monolayer, and shifted the pore diameter toward the micropore region. Unexpectedly, the removal of residual organics from intercalation steps adsorbed at the nanoscroll surface with a peroxide treatment resulted in partial recovery of crystallinity and increase of crystallite size along the 'c'-crystal direction. The d(001) value showed a diffuse pattern at 7.4-7.7 Å due to the rearrangement of the thin-walled nanoscrolls toward the initial tubular morphology of the dehydrated halloysite-7 Å mineral.

Fundamental Studies of Crystal Growth of Microporous Materials

NASA Technical Reports Server (NTRS)

Singh, Ramsharan; Doolittle, John, Jr.; Payra, Pramatha; Dutta, Prabir K.; George, Michael A.; Ramachandran, Narayanan; Schoeman, Brian J.

2003-01-01

Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (a) Nature of the molecular units responsible for the crystal nuclei formation; (b) Nature of the nuclei and nucleation process; (c) Growth process of the nuclei into crystal; (d) Morphological control and size of the resulting crystal; (e) Surface structure of the resulting crystals; and (f) Transformation of frameworks into other frameworks or condensed structures.

Relationship between morphologies and orientations of Cu{sub 6}Sn{sub 5} grains in Sn3.0Ag0.5Cu solder joints on different Cu pads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Yanhong, E-mail: tianyh@hit.edu.cn; Zhang, Rui; Hang, Chunjin

2014-02-15

The morphologies and orientations of Cu{sub 6}Sn{sub 5} intermetallic compounds in the Sn3.0Ag0.5Cu solder joints both on polycrystalline and single crystal Cu pads under different peak reflow temperatures and times above liquids were investigated. The relationship between Cu{sub 6}Sn{sub 5} grain orientations and morphologies was clarified. At the interface of Sn3.0Ag0.5Cu/polycrystalline Cu pad, scalloped Cu{sub 6}Sn{sub 5} intermetallic compounds formed at 250 °C and roof shape Cu{sub 6}Sn{sub 5} formed at 300 °C. Both scalloped Cu{sub 6}Sn{sub 5} and roof shape Cu{sub 6}Sn{sub 5} had a preferred orientation of (0001) plane being parallel to polycrystalline Cu pad surface. Besides, themore » percentage of large angle grain boundaries increased as the peak reflow temperature rose. At the interface of Sn3.0Ag0.5Cu/(111) single crystal Cu pad, the Cu{sub 6}Sn{sub 5} intermetallic compounds were mainly scallop-type at 250 °C and were prism type at 300 °C. The prismatic Cu{sub 6}Sn{sub 5} grains grew along the three preferred directions with the inter-angles of 60° on (111) single crystal Cu pad while along two perpendicular directions on (100) single crystal Cu pad. The orientation relationship between Cu{sub 6}Sn{sub 5} grains and the single crystal Cu pads was investigated by electron backscatter diffraction technology. In addition, two types of hollowed Cu{sub 6}Sn{sub 5} intermetallic compounds were found inside the joints of polycrystalline Cu pads. The long hexagonal Cu{sub 6}Sn{sub 5} strips were observed in the joints reflowing at 250 °C while the hollowed Cu{sub 6}Sn{sub 5} strips with the ‘▪’ shape cross-sections appeared at 300 °C, which was attributed to the different grain growth rates of different Cu{sub 6}Sn{sub 5} crystal faces. - Highlights: • The orientation of interfacial Cu{sub 6}Sn{sub 5} grains was obtained by EBSD technology. • Two types of hollowed Cu{sub 6}Sn{sub 5} strips were found at different temperatures. • The formation mechanism of hollowed Cu{sub 6}Sn{sub 5} was elaborated based on Bravais law. • The relationship between Cu{sub 6}Sn{sub 5} grain orientations and morphologies was clarified.« less

Morphological stability and kinetics in crystal growth from vapors

NASA Technical Reports Server (NTRS)

Rosenberger, Franz

1990-01-01

The following topics are discussed: (1) microscopy image storage and processing system; (2) growth kinetics and morphology study with carbon tetrabromide; (3) photothermal deflection vapor growth setup; (4) bridgman growth of iodine single crystals; (5) vapor concentration distribution measurement during growth; and (6) Monte Carlo modeling of anisotropic growth kinetics and morphology. A collection of presentations and publications of these results are presented.

Fabrication and characterization of poly(L-lactic acid) gels induced by fibrous complex crystallization with solvents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsuda, Yasuhiro; Fukatsu, Akinobu; Wang, Yangyang

2014-01-01

Complex crystal induced gelation of poly(L-lactic acid) (PLLA) solutions was studied for a series of solvents, including N,N-dimethylformamide (DMF). By cooling the solutions prepared at elevated temperatures, PLLA gels were produced in solvents that induced complex crystals ( -crystals) with PLLA. Fibrous structure of PLLA in the gel with DMF was observed by polarizing optical microscopy, field emission electron microscopy, and atomic force microscopy. Upon heating, the crystal form of PLLA in the DMF gel changed from -crystal to a-crystal, the major crystal form in common untreated PLLA films, but the morphology and high elastic modulus of the gel remainedmore » until the a-crystal dissolved at higher temperature. In addition, a solvent exchanging method was developed, which allowed PLLA gels to be prepared in other useful solvents that do not induce -crystals without losing the morphology and mechanical properties.« less

On the tungsten single crystal coatings achieved by chemical vapor transportation deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, J.Q.; Shen, Y.B.; Yao, S.Y.

2016-12-15

The tungsten single crystal has many excellent properties, namely a high melting point, high anti-creeping strength. Chemical vapor transportation deposition (CVTD) is a possible approach to achieve large-sized W single crystals for high-temperature application such as the cathode of a thermionic energy converter. In this work, CVTD W coatings were deposited on the monocrystalline molybdenum substrate (a tube with < 111 > axial crystalline orientation) using WCl{sub 6} as a transport medium. The microstructures of the coatings were investigated by a scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The as-deposited coatings are hexagonal prisms—rough surfaces perpendicular to with alternating hill-like bulges and pits at the side edges of the prisms, and flat surfaces perpendicular to < 112 > with arc-shaped terraces at the side faces. This can be explained by two-dimensional nucleation -mediated lateral growth model. Some parts of the coatings contain hillocks of an exotic morphology (noted as “abnormal growth”). The authors hypothesize that the abnormal growth is likely caused by the defects of the Mo substrate, which facilitate W nucleation sites, cause orientation difference, and may even form boundaries in the coatings. A dislocation density of 10{sup 6} to 10{sup 7} (counts/cm{sup 2}) was revealed by an etch-pit method and synchrotron X-ray diffraction. As the depositing temperature rises, the dislocation density decreases, and no sub-boundaries are found on samples deposited over 1300 °C, as a result of atom diffusion and dislocation climbing. - Highlights: •The varied growth rate causes the different morphologies of different planes. •The W coating is a single crystal when only single hillocks appear. •The (110) plane tends to have the lowest dislocation density. •The dislocation density tends to decrease as the temperature increases.« less

The mode of emplacement of Neogene flood basalts in Eastern Iceland: The plagioclase ultraphyric basalts in the Grænavatn group

NASA Astrophysics Data System (ADS)

Óskarsson, Birgir V.; Andersen, Christina B.; Riishuus, Morten S.; Sørensen, Erik Vest; Tegner, Christian

2017-02-01

Plagioclase ultraphyric basalt lava with high fraction of solids have a mode of emplacement that is poorly understood. In this study we conduct detailed mapping of a PUB group in eastern Iceland, namely the Grænavatn group, and assess the group architecture, flow morphology and internal structure with additional constraints from petrography, petrology and crystal size distribution, to derive information on emplacement dynamics of plagioclase ultraphyric basalts. We also derive information on the plumbing system of the group with reference to the source of the macrocysts. The group is exposed in steep glacially carved fjords and can be traced for more than 70 km along strike. The flows have mixed architecture of simple and compound flows. Individual flow lobes have thicknesses in the range of 1-24 m and many reach widths and lengths exceeding 1000 m. The flows vary from rubbly to slabby pahoehoe, but are predominantly of pahoehoe type. The aspect ratio of the group and the nature of the flows indicate fissure-fed eruptions. The plagioclase macrocrysts (5-30 mm) are An-rich, exhibit bimodal size distribution and the modal proportions within the group varies from 15-40%. Clinopyroxene macrocrysts are also present ranging from 1-6%. The lowermost flow is thickest and carries the greatest crystal cargo load. The morphology of the lava flows suggests low viscous behavior, at odds with the high crystal content. The very calcic plagioclase macrocrysts (An80-85) are in disequilibrium with the groundmass and plagioclase microlaths therein (An50-70), meaning that the crystal-laden magmas quickly ascended from deeper crustal levels to the surface. The flows with highest crystal content may have maintained high temperatures by heat exchange with the primitive macrocrysts in the flows and developed non-Newtonian behavior such as shear thinning. Such conditions would have enabled the flows to advance rapidly during episodes with high effusion rates forming the simple flows, and subsequently maintained by insulated lobe-by-lobe emplacement. Occasionally surges disrupted the crust to form rubbly and slabby pahoehoe. A Herschel-Bulkley model is applied to the flows yielding effusion rates in the order of 103-104 m 3/s for the largest eruptions. Variation in crystal proportions within the group and individual flows is considered to be the result of magmas penetrating a crystal mush, followed by disaggregation and mobilization, sorting by flotation, mixing of magma batches and transportation of heterogeneous crystal-laden magmas to the surface with opportunities for staging en route.

Study of recrystallization and devitrification of lunar glass

NASA Technical Reports Server (NTRS)

Ulrich, D. R.

1974-01-01

The technique of differential thermal analysis (DTA) was applied to the study of the Apollo 17 orange soil (74220,63) and the Apollo 16 glass coated anorthite (64455,21). These glasses show accentuated exotherms of strain relief in the annealing range which is indicative of rapid cooling. These are amenable to interpretation by comparison to the known history of synthetic glasses. Synthetic glasses were prepared whose similarity in behavior between the lunar glasses and their synthetic analogs is striking. Approximate rates of cooling of the lunar glasses were determined from comparative DTA of lunar and synthetic glasses and from the determination of the relation of strain relief in the annealing range to quench rate. At higher temperatures the glasses show exotherms of crystallization. The crystallization products associated with the exothermic reactions have been identified by X-ray diffraction and the surface morphologies developed by strain relief and crystallization have been characterized with scanning electron microscopy.

Biomimetic whisker-shaped apatite coating of titanium powder.

PubMed

Sim, Young Uk; Kim, Jong Hee; Yang, Tae Young; Yoon, Seog Young; Park, Hong Chae

2010-05-01

Biomimetic apatite coatings on chemically modified titanium powder have been processed and the resulting coating layers evaluated in terms of morphology, composition and structure, using TF-XRD, XPS, SEM, TEM and FTIR analysis. After 7 days immersion in a simulated body fluid (SBF), nanometer-sized fine precipitates with an amorphous whisker-like phase and a Ca/P atomic ratio of 1.94 were obtained on the external surface of the titanium particles. When the immersion time in SBF was extended to 16 days, the coating layer consisted of the whisker-like nanostructured crystals of carbonated hydroxyapatite with a atomic ratio of 3; in such a case, a double coating layer was developed. The double layer could be divided into two regions and could be clearly distinguished: an inner dense region (approximately 200 nm in thickness) which may include hard agglomerated crystals and an outer less dense region (> 500 nm in thickness) in which crystals are loosely distributed.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

PubMed

Huang, Lizhen; Hu, Xiaorong; Chi, Lifeng

2015-09-15

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Formation mechanism of graphite hexagonal pyramids by argon plasma etching of graphite substrates

NASA Astrophysics Data System (ADS)

Glad, X.; de Poucques, L.; Bougdira, J.

2015-12-01

A new graphite crystal morphology has been recently reported, namely the graphite hexagonal pyramids (GHPs). They are hexagonally-shaped crystals with diameters ranging from 50 to 800 nm and a constant apex angle of 40°. These nanostructures are formed from graphite substrates (flexible graphite and highly ordered pyrolytic graphite) in low pressure helicon coupling radiofrequency argon plasma at 25 eV ion energy and, purportedly, due to a physical etching process. In this paper, the occurrence of peculiar crystals is shown, presenting two hexagonal orientations obtained on both types of samples, which confirms such a formation mechanism. Moreover, by applying a pretreatment step with different time durations of inductive coupling radiofrequency argon plasma, for which the incident ion energy decreases at 12 eV, uniform coverage of the surface can be achieved with an influence on the density and size of the GHPs.

Probing interlayer interactions in WS2 -graphene van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Chung, Ting Fung; Yuan, Long; Huang, Libai; Chen, Yong P.

Two-dimensional crystals based van der Waals coupled heterostructures are of interest owing to their potential applications for flexible and transparent electronics and optoelectronics. The interaction between the 2D layered crystals at the interfaces of these heterostructures is crucial in determining the overall performance and is strongly affected by contamination and interfacial strain. We have fabricated heterostructures consisting of atomically thin exfoliated WS2 and chemical-vapor-deposited (CVD) graphene, and studied the interaction and coupling between the WS2 and graphene using atomic force microscopy (AFM), Raman spectroscopy and femtosecond transient absorption measurement (TAM). Information from Raman-active phonon modes allows us to estimate charge doping in graphene and interfacial strain on the crystals. Spatial imaging probed by TAM can be correlated to the heterostructure surface morphology measured by AFM and Raman maps of graphene and WS2, showing how the interlayer coupling alters exciton decay dynamics quantitatively.

Effect of CeO2 on TiC Morphology in Ni-Based Composite Coating

NASA Astrophysics Data System (ADS)

Cai, Yangchuan; Luo, Zhen; Chen, Yao

2018-03-01

The TiC/Ni composite coating with different content of CeO2 was fabricated on the Cr12MoV steel by laser cladding. The microstructure of cladding layers with the different content of CeO2 from the bottom to the surface is columnar crystal, cellular crystal, and equiaxed crystal. When the content of CeO2 is 0 %, the cladding layer has a coarse and nonuniform microstructure and TiC particles gathering in the cladding layer, and then the wear resistance was reduced. Appropriate rare-earth elements refined and homogenised the microstructure and enhanced the content of carbides, precipitated TiC particles and original TiC particles were spheroidised and refined, the wear resistance of the cladding layer was improved significantly. Excessive rare-earth elements polluted the grain boundaries and made the excessive burning loss of TiC particles that reduced the wear resistance of the cladding layer.

NASA research Program: The roles of fluid motion and other transport phenomena in the morphology of materials

NASA Technical Reports Server (NTRS)

Saville, D. A.

1988-01-01

The influence of transport phenomena on the morphology of crystalline materials was investigated. Two problems were studied: the effects of convection on the crystallization of pure materials, and the crystallization of proteins from solution.

Dislocation, crystallite size distribution and lattice strain of magnesium oxide nanoparticles

NASA Astrophysics Data System (ADS)

Sutapa, I. W.; Wahid Wahab, Abdul; Taba, P.; Nafie, N. L.

2018-03-01

The oxide of magnesium nanoparticles synthesized using sol-gel method and analysis of the structural properties was conducted. The functional groups of nanoparticles has been analysed by Fourier Transform Infrared Spectroscopy (FT-IR). Dislocations, average size of crystal, strain, stress, the energy density of crystal, crystallite size distribution and morphologies of the crystals were determined based on X-ray diffraction profile analysis. The morphological of the crystal was analysed based on the image resulted from SEM analysis. The crystallite size distribution was calculated with the contention that the particle size has a normal logarithmic form. The most orientations of crystal were determined based on the textural crystal from diffraction data of X-ray diffraction profile analysis. FT-IR results showed the stretching vibration mode of the Mg-O-Mg in the range of 400.11-525 cm-1 as a broad band. The average size crystal of nanoparticles resulted is 9.21 mm with dislocation value of crystal is 0.012 nm-2. The strains, stress, the energy density of crystal are 1.5 x 10-4 37.31 MPa; 0.72 MPa respectively. The highest texture coefficient value of the crystal is 0.98. This result is supported by morphological analysis using SEM which shows most of the regular cubic-shaped crystals. The synthesis method is suitable for simple and cost-effective synthesis model of MgO nanoparticles.

The Particle Habit Imaging and Polar Scattering probe PHIPS: First Stereo-Imaging and Polar Scattering Function Measurements of Ice Particles

NASA Astrophysics Data System (ADS)

Abdelmonem, A.; Schnaiter, M.; Schön, R.; Leisner, T.

2009-04-01

Cirrus clouds impact climate by their influence on the water vapour distribution in the upper troposphere. Moreover, they directly affect the radiative balance of the Earth's atmosphere by the scattering of incoming solar radiation and the absorption of outgoing thermal emission. The link between the microphysical properties of ice cloud particles and the radiative forcing of the clouds is not as yet well understood and the influence of the shapes of ice crystals on the radiative budget of cirrus clouds is currently under debate. PHIPS is a new experimental device for the stereo-imaging of individual cloud particles and the simultaneous measurement of the polar scattering function of the same particle. PHIPS uses an automated particle event triggering system that ensures that only those particles are captured which are located in the field of view - depth of field volume of the microscope unit. Efforts were made to improve the resolution power of the microscope unit down to about 3 µm and to facilitate a 3D morphology impression of the ice crystals. This is realised by a stereo-imaging set up composed of two identical microscopes which image the same particle under an angular viewing distance of 30°. The scattering part of PHIPS enables the measurement of the polar light scattering function of cloud particles with an angular resolution of 1° for forward scattering directions (from 1° to 10°) and 8° for side and backscattering directions (from 18° to 170°). For each particle the light scattering pulse per channel is stored either as integrated intensity or as time resolved intensity function which opens a new category of data analysis concerning details of the particle movement. PHIPS is the first step to PHIPS-HALO which is one of the in situ ice particle and water vapour instruments that are currently under development for the new German research aircraft HALO. The instrument was tested in the ice cloud characterisation campaign HALO-02 which was conducted in December 2008 at the AIDA cloud chamber in the temperature range from -5°C to -70°C. In a series of experiments small externally generated seed ice crystals were grown in AIDA at distinct temperature and saturation ratio conditions. For these experiments the long known ice morphology diagram with the temperature dependent morphology changes and the supersaturation dependent structural complexity could clearly be reproduced by PHIPS. Structural details like hollow crystals, crystals with inclusions, and crystals with stepped surfaces (Hopper crystals) could be resolved by PHIPS. Moreover, the advantage of stereo-imaging in terms of habit classification and particle orientation deduction could be demonstrated. The scattering function measurement reveals ice particle orientation dependent specular reflection peaks which might contain information about the surface roughness. The presentation will describe the instrument set up in detail and highlight some preliminary results.

In Situ TEM and AFM Investigation of Morphological Controls during the Growth of Single Crystal BaWO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lili; Zhang, Shuai; Bowden, Mark E.

Barium tungstate (BaWO 4) is a widely investigated inorganic optical material due to its attractive emission properties. Because those properties strongly depend on crystal structure and morphology, numerous approaches to controlling growth have been pursued. However, an understanding of the growth mechanisms that lead to the wide range of morphologies obtained to date is largely lacking, and most attempts to develop that understanding have been based on post-growth analyses. Significantly, such analyses have led to the conclusion that certain BaWO 4 crystal morphologies result from a nonclassical growth process of oriented attachment. In this work, we systematically varied the morphologymore » of BaWO 4 crystals by adjusting the relative concentrations of solute, water, and ethanol. We then explored the growth mechanism leading to the observed range of morphologies through in situ TEM and in situ AFM. We find that even the most complex BaWO 4 morphologies occur through purely classical growth mechanisms largely controlled by the content of solute and ethanol. The latter acts as an impurity to poison growth at low concentrations and low solute levels, but leads to development of growth instabilities and eventual dendritic growth at high alcohol and moderate solute concentrations by driving up the supersaturation. These findings also highlight the necessity of in situ experiments to interpret ex situ observations of crystal growth and decipher the controlling mechanisms.« less

Application of atomic force microscopy to microbial surfaces: from reconstituted cell surface layers to living cells.

PubMed

Dufrêne, Y F

2001-02-01

The application of atomic force microscopy (AFM) to probe the ultrastructure and physical properties of microbial cell surfaces is reviewed. The unique capabilities of AFM can be summarized as follows: imaging surface topography with (sub)nanometer lateral resolution; examining biological specimens under physiological conditions; measuring local properties and interaction forces. AFM is being used increasingly for: (i) visualizing the surface ultrastructure of microbial cell surface layers, including bacterial S-layers, purple membranes, porin OmpF crystals and fungal rodlet layers; (ii) monitoring conformational changes of individual membrane proteins; (iii) examining the morphology of bacterial biofilms, (iv) revealing the nanoscale structure of living microbial cells, including fungi, yeasts and bacteria, (v) mapping interaction forces at microbial surfaces, such as van der Waals and electrostatic forces, solvation forces, and steric/bridging forces; and (vi) probing the local mechanical properties of cell surface layers and of single cells.

Agarose template for the fabrication of macroporous metal oxide structures.

PubMed

Zhou, Jingfang; Zhou, Meifang; Caruso, Rachel A

2006-03-28

Agarose gels have been applied as templates for the formation of macroporous metal oxide structures. The preparation of the agarose template is extremely simple, and with variation of the agarose content, control over morphology is demonstrated: The average pore size decreases from 180 to 55 nm and the surface area increases from 238 to 271 m2 g(-1) with increasing agarose content in the gel. The gelling temperature was also found to influence the final template morphology. Conducting sol-gel chemistry within the template structure followed by removal of the template by heating to 450 degrees C gives porous inorganic oxides. The technique has been demonstrated for the oxides of titanium, zirconium, niobium, and tin. The final morphology of the metal oxide is homogeneous and results from a coating of the agarose structure. The pore diameter decreased and the specific surface area of the titanium dioxide materials increased from 28 to 66 m2 g(-1) as the agarose content in the template is increased from 0.5 to 5.0 wt%. The overall pore size and surface area are lower than the original gel due to shrinkage occurring with the sol-gel process, as well as crystallization and a loss of microporosity in the final material.

Effect of precursor solutions on ZnO film via solution precursor plasma spray and corresponding gas sensing performances

NASA Astrophysics Data System (ADS)

Yu, Z. X.; Ma, Y. Z.; Zhao, Y. L.; Huang, J. B.; Wang, W. Z.; Moliere, M.; Liao, H. L.

2017-08-01

Solution precursor plasma spraying (SPPS) as a novel thermal spray method was employed to deposit nano-structured ZnO thin film using different formulations of the precursor solution. This article focuses on the influence of the solution composition on the preferential orientation of crystal growth, on crystal size and surface morphology of the resulting ZnO films. The trend of preferential growth along (002) lattice plane of ZnO film was studied by slow scanning X-ray diffraction using a specific coefficient P(002). It appears that the thermal spray process promotes the buildup of ZnO films preferentially oriented along the c-axis. The shape of single particle tends to change from round shaped beads to hexagonal plates by increasing the volume ratio of ethanol in the solvent. Both cauliflower and honeycomb-like surface morphologies featuring high specific surface area and roughness were obtained through the SPPS process by varying solution composition. These ZnO films are hydrophobic with contact angle as high as 136°, which is seemingly associated with micro reliefs developing high surface specific area. Then the gas sensing performances of ZnO films preferentially oriented along (002) face were tentatively predicted using the "first principle calculation method" and were compared with those of conventional films that are mainly oriented along the (101) face. The (002) face displays better hydrogen adsorption capability than the (101) face with much larger resulting changes in electrical resistance. In conclusion, the c-axis oriented ZnO films obtained through SSPS have favorable performances to be used as sensitive layer in gas sensing applications.

Controlled synthesis of BiVO{sub 4} with multiple morphologies via an ethylenediamine-assisted hydrothermal method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Xuemei, E-mail: qixuemei@shiep.edu.cn; School of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090; Zhu, Xinyuan

2014-11-15

Graphical abstract: BiVO{sub 4} samples with various morphologies were synthesized via a simple ethylenediamine (EN) assisted hydrothermal route. One of the mixed crystal phase with spherical and porous morphology showed excellent photocatalytic activity and about 90% Rhodamine B was degraded after 140 min visible light irradiation. - Highlights: • BiVO{sub 4} samples with various morphologies were synthesized by hydrothermal method. • Ethylenediamine mainly acts as alkaline source to adjust pH values of precursor. • BiVO{sub 4} with spherical morphology has excellent photocatalytic activity. - Abstract: In this work, BiVO{sub 4} particles with different crystal structures and morphologies including hexahedral, sphericalmore » porous and hyperbranched ones were fabricated in the presence of ethylenediamine by hydrothermal process. The as-fabricated samples were well characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and ultraviolet–visible absorption spectroscopy. The results showed that the morphology and crystal structure of BiVO{sub 4} particles could be well controlled by only changing the ethylenediamine content in the deionized water solution. Photocatalytic activity of the samples was evaluated by the degradation of Rhodamine B under visible-light irradiation. It was shown that BiVO{sub 4} sample with spherical porous morphology and mixed crystal phase exhibited the best photocatalytic performance after optimizing the ethylenediamine content. The best degradation ratio of Rhodamine B could reach about 87% after 140 min visible-light irradiation.« less

Occurrence and characterisation of calcium oxalate crystals in stems and fruits of Hylocereus costaricensis and Selenicereus megalanthus (Cactaceae: Hylocereeae).

PubMed

Viñas, María; Jiménez, Víctor M

2016-10-01

Detailed description about occurrence of calcium oxalate (CaOx) crystals in the edible vine cactus species Hylocereus costaricensis and Selenicereus megalanthus is scarce. Therefore, we evaluated and characterized the presence, morphology and composition of CaOx crystals in both species. Crystals were isolated from greenhouse and in vitro vegetative stems, and from ripe fruit peels and pulp by enzymatic digestion and density centrifugation and quantified with a haemocytometer. Morphologies were studied using scanning electron microscopy, elemental composition with energy-dispersive X-ray spectroscopy and salt composition with X-ray powder diffraction. Analyses conducted confirmed that isolated crystals were exclusively composed by CaOx, both mono- and dihydrated. Highest crystal contents were measured in greenhouse stems, followed by the fruit peels. While very few crystals were quantified in in vitro plants, they were not detected in the fruit pulp at all, which is of advantage for its human consumption and could be linked to mechanisms of seed dispersal through animals. Different crystal morphologies were observed, sometimes varying between genotypes and tissues analysed. This is the first work known to the authors with a detailed characterization of CaOx crystals in vine cacti. Copyright © 2016 Elsevier Ltd. All rights reserved.

Flow-induced crystallization in isotactic polypropylene

NASA Astrophysics Data System (ADS)

Hamad, Fawzi Ghassan

Brief intervals of strong flow stretch chains in a semicrystalline polymer melt, which results in an increase in the nuclei number density and a transformation of the crystal structure. This flow-induced crystallization (FIC) phenomenon is explored in this study using highly isotactic polypropylene (iPP) samples. Using one synthesized and five commercial linear isotactic polypropylene samples, we investigate the FIC behavior by imposing shear onto these samples in a rotational rheometer. Equipped with a good temperature control and flexible shear protocol, we apply different temperature and flow conditions. The magnitude of the FIC effect varies with basic processing parameters (shear rate, specific work, crystallization temperature, and shearing temperature) and material properties (totalistic, molecular weight distribution, and particle concentration in the polymer). The scope of this study is to systematically investigate the influences of these parameters on FIC. The FIC effects that are investigated in this dissertation are: crystallization kinetics, persistence time of flow-induced nuclei, and crystal morphology. The crystallization time was measured in the rheometer by monitoring the onset of crystallization after quenching samples sheared above Tm. These samples were subsequently used to study their flow-induced nuclei persistence time and crystal morphology. The lifetime of flow-induced nuclei was determined by measuring the time required to return from FIC back to quiescent crystallization using a differential scanning calorimeter. The crystal morphology was imaged using polarized optical microscopy and atomic force microscopy. We investigated the influence of specific work on the three FIC characteristics, and found three regimes that are separated by the critical work ( Wc) and the saturation work (Wsat) thresholds. Below the critical work threshold, the morphology is composed of mostly spherulite crystals, which keep a constant volume, and a small fraction of rice grain (anisotropic) crystals. The number of rice grain crystals increases with specific work, speeding up the crystallization time of the semicrystalline polymer. At critical work, spherulite formation stops, and the morphology consists only of rice grain structures. This morphology allows the sample to crystallize at higher temperatures when cooling at 5 C/min, with the sheared sample crystallizing at 129C compared to the unsheared sample at 113C. . Shearing isotactic polypropylene at higher temperatures reduced the FIC effect after subsequent quenching. Generally speaking, shearing at higher temperatures results in slower crystallization, but surprisingly, the influence of temperature is rather weak. Flow-induced crystallization persists even when shear is applied well above the equilibrium melting temperature (187C), finally weakening above the Hoffman-Weeks temperature (210C). This is likely due to the long lifetime of flow- induced precursors (crystallize to form rice grains), which remain stable at temperatures below 210C and only start to disappear slowly in prolonged annealing at temperatures above 210C (diminishing the FIC effect). Tacticity was found to govern the maximum nuclei number density in sheared samples; samples with lower isotactic content show a stronger FIC effect. Similarly, it was found that the concentration of particulates (mainly catalyst residue) are crucially important to FIC, samples with lower amounts of particles lowering the FIC nuclei number density. Data shows that the rate at which the crystallization time changes correlates with the prominence of the high molecular weight tail. A sample with a higher molecular weight tail in its distribution exhibits a faster change in crystallization time as a function of specific work. Similarly, increasing the molecular weight of the added component in a blend induces a larger change in the FIC behavior. (Abstract shortened by ProQuest.).

Crystal morphology of sunflower wax in soybean oil organogel

USDA-ARS?s Scientific Manuscript database

While sunflower wax has been recognized as an excellent organogelator for edible oil, the detailed morphology of sunflower wax crystals formed in an edible oil organogel has not been fully understood. In this study, polarized light microscopy, phase contrast microscopy, scanning electron microscopy ...

Crystallographic control of surface structure on the sectoral zoning of iron in a diopside from Orford nickel mine (Quebec), Canada

NASA Astrophysics Data System (ADS)

Paquette, J.; Zangooi, A.; Thornton, K.

2004-05-01

The influence of surface structure on partitioning between mineral and melt (or solution) has been noted by other workers in a handful of minerals, including calcite, dolomite, apatite, topaz and diamond. Each one of these minerals displays at least one crystallographic face where steps present during crystal growth are not equivalent by symmetry. When this is the case, sectors grown at the edge of these steps commonly show differential incorporation of minor or trace elements. In the diopside investigated here, electron probe microanalyses performed on the as-grown (100) surface of several crystals show concentric and sectoral zoning defined by variations in Fe content. Atomic force microscopy (AFM) was used to study the surfaces of the three crystallographic forms present on the diopside crystals, with the goal of relating the compositional zoning to the surface structure of the faces. The dominant {100} faces are covered with growth hillocks consisting of four vicinal faces defined by steps parallel to [010] and [001]. The steps are often bunched into macrosteps and the resulting hillocks are visible optically. The steps along the two crystallographic directions show significant differences in straightness and smoothness that indicate non-equivalent kinetics. The wavier steps correspond to Fe-enriched areas within the {100} sectors. The {010} faces, next in morphological importance, are dominated by a single step orientation and show no differential incorporation. They display topography related to polysynthetic twinning. The {110} faces are much smaller and very few show resolvable steps. Sector zoning (i.e. diffential partitioning among non-equivalent crystallographic faces) has been described in the past from pyroxenes. Explanations have invoked either differences in surface structure among non-equivalent faces or their unequal growth rates. This particular occurrence indicates that trace element incorporation is, in fact, highly site-specific and that significant compositioinal zoning can be induced on a single face without invoking the effect of growth rate. The natural diopside crystals from the Orford nickel mine (Brompton, Quebec) show a unusual bladed habit flattened on {100} faces. Exceptional fluid chemistry during crystallization may therefore be required for the persistence of steps responsible for differential incorporation. Nevertheless, whenever this zoning is present, the trace element involved cannot be expected to reflect thermodynamic equilibrium between the solid and the fluid from which it crystallized.

Method for estimating the morphological significance of simple forms of crystals from X-ray data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Treivus, E. B., E-mail: sbobr1@bk.ru

2010-09-15

When developing V.I. Mikheev and I.I. Shafranovskii's method for estimating the morphological significance of faces of different simple forms from X-ray reflection intensities, a way to approximately evaluate the morphological significance of simple forms on crystals from the structure amplitudes of the corresponding atomic planes is proposed. The potential for this approach is demonstrated by the examples of marcasite and zircon.

Hydroxyapatite-silver nanoparticles coatings on porous polyurethane scaffold.

PubMed

Ciobanu, Gabriela; Ilisei, Simona; Luca, Constantin

2014-02-01

The present paper is focused on a study regarding the possibility of obtaining hydroxyapatite-silver nanoparticle coatings on porous polyurethane scaffold. The method applied is based on a combined strategy involving hydroxyapatite biomimetic deposition on polyurethane surface using a Supersaturated Calcification Solution (SCS), combined with silver ions reduction and in-situ crystallization processes on hydroxyapatite-polyurethane surface by sample immersing in AgNO3 solution. The morphology, composition and phase structure of the prepared samples were characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. The data obtained show that a layer of hydroxyapatite was deposited on porous polyurethane support and the silver nanoparticles (average size 34.71 nm) were dispersed among and even on the hydroxyapatite crystals. Hydroxyapatite/polyurethane surface acts as a reducer and a stabilizing agent for silver ions. The surface plasmon resonance peak in UV-Vis absorption spectra showed an absorption maximum at 415 nm, indicating formation of silver nanoparticles. The hydroxyapatite-silver polyurethane scaffolds were tested against Staphylococcus aureus and Escherichia coli and the obtained data were indicative of good antibacterial properties of the materials. © 2013.

Aqueous film coating to reduce recrystallization of guaifenesin from hot-melt extruded acrylic matrices.

PubMed

Bruce, Caroline D; Fegely, Kurt A; Rajabi-Siahboomi, Ali R; McGinity, James W

2010-02-01

This study investigated the effect of aqueous film coating on the recrystallization of guaifenesin from acrylic, hot-melt extruded matrix tablets. After hot-melt extrusion, matrix tablets were film-coated with either hypromellose or ethylcellulose. The effects of the coating polymer, curing and storage conditions, polymer weight gain, and core guaifenesin concentration on guaifenesin recrystallization were investigated. The presence of either film coating on the guaifenesin-containing tablets was found to prolong the onset time of drug crystallization. The coating polymer was the most important factor determining the delay in the onset of crystallization, with the more hydrophilic polymer, hypromellose, having a higher solubilization potential for the guaifenesin and delaying crystallization for longer period (3 or 6 months in tablets stored at 40 degrees C or 25 degrees C, respectively) than the more hydrophobic ethylcellulose, which displayed a lower solubilization potential for guaifenesin (crystal growth on tablets cured for 2 hours at 60 degrees C occurred within 3 weeks, whereas uncoated tablets displayed surface crystal growth after 30 minutes). Crystal morphology was also affected by the film coating. Elevated temperatures during both curing and storage, incomplete film coalescence, and high core drug concentrations all contributed to an earlier onset of crystal growth.