Diamond turning of glass

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

Blackley, W.S.; Scattergood, R.O.

A new research initiative will be undertaken to investigate the critical cutting depth concepts for single point diamond turning of brittle, amorphous materials. Inorganic glasses and a brittle, thermoset polymer (organic glass) are the principal candidate materials. Interrupted cutting tests similar to those done in earlier research are Ge and Si crystals will be made to obtain critical depth values as a function of machining parameters. The results will provide systematic data with which to assess machining performance on glasses and amorphous materials

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

Volker, Arno; Hunter, Alan

Anisotropic materials are being used increasingly in high performance industrial applications, particularly in the aeronautical and nuclear industries. Some important examples of these materials are composites, single-crystal and heavy-grained metals. Ultrasonic array imaging in these materials requires exact knowledge of the anisotropic material properties. Without this information, the images can be adversely affected, causing a reduction in defect detection and characterization performance. The imaging operation can be formulated in two consecutive and reciprocal focusing steps, i.e., focusing the sources and then focusing the receivers. Applying just one of these focusing steps yields an interesting intermediate domain. The resulting common focusmore » point gather (CFP-gather) can be interpreted to determine the propagation operator. After focusing the sources, the observed travel-time in the CFP-gather describes the propagation from the focus point to the receivers. If the correct propagation operator is used, the measured travel-times should be the same as the time-reversed focusing operator due to reciprocity. This makes it possible to iteratively update the focusing operator using the data only and allows the material to be imaged without explicit knowledge of the anisotropic material parameters. Furthermore, the determined propagation operator can also be used to invert for the anisotropic medium parameters. This paper details the proposed technique and demonstrates its use on simulated array data from a specimen of Inconel single-crystal alloy commonly used in the aeronautical and nuclear industries.« less

Segregation effects during solidification in weightless melts. [effects of evaporation and solidification on crystalization

NASA Technical Reports Server (NTRS)

Li, C.

1975-01-01

Computer programs are developed and used in the study of the combined effects of evaporation and solidification in space processing. The temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation were mathematically formulated. Computer results are included along with an econotechnical model of crystal growth. This model allows: prediction of crystal size, quality, and cost; systematic selection of the best growth equipment or alloy system; optimization of growth or material parameters; and a maximization of zero-gravity effects. Segregation in GaAs crystals was examined along with vibration effects on GaAs crystal growth. It was found that a unique segregation pattern and strong convention currents exist in GaAs crystal growth. Some beneficial effects from vibration during GaAs growth were discovered. The implications of the results in space processing are indicated.

High-Mobility, Ultrathin Organic Semiconducting Films Realized by Surface-Mediated Crystallization.

PubMed

Vladimirov, I; Kellermeier, M; Geßner, T; Molla, Zarah; Grigorian, S; Pietsch, U; Schaffroth, L S; Kühn, M; May, F; Weitz, R T

2018-01-10

The functionality of common organic semiconductor materials is determined by their chemical structure and crystal modification. While the former can be fine-tuned via synthesis, a priori control over the crystal structure has remained elusive. We show that the surface tension is the main driver for the plate-like crystallization of a novel small organic molecule n-type semiconductor at the liquid-air interface. This interface provides an ideal environment for the growth of millimeter-sized semiconductor platelets that are only few nanometers thick and thus highly attractive for application in transistors. On the basis of the novel high-performance perylene diimide, we show in as-grown, only 3 nm thin crystals electron mobilities of above 4 cm 2 /(V s) and excellent bias stress stability. We suggest that the established systematics on solvent parameters can provide the basis of a general framework for a more deterministic crystallization of other small molecules.

SEMICONDUCTOR MATERIALS: Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

NASA Astrophysics Data System (ADS)

Xiaofeng, Chen; Nuofu, Chen; Jinliang, Wu; Xiulan, Zhang; Chunlin, Chai; Yude, Yu

2009-08-01

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Luminescence spectra of a cholesteric photonic crystal

NASA Astrophysics Data System (ADS)

Dolganov, P. V.

2017-05-01

The transmission and luminescence spectra of a cholesteric photonic crystal doped with an organic dye are measured. The density of photon states is calculated using the material parameters obtained from the comparison of the experimental and theoretical spectra. The shape of the luminescence spectra is modified with respect to the density of photon states owing to the difference in the structure of the normal modes of the photonic crystal near the short-wavelength and long-wavelength edges of the photonic quasi-band gap upon the "pushing" of the photon states from the gap and to the nonvanishing orientation ordering of the luminescent molecules. The luminescence spectrum calculated taking into account the chiral structure of the photonic crystal agrees with the experimental spectrum.

Band structure of comb-like photonic crystals containing meta-materials

NASA Astrophysics Data System (ADS)

Weng, Yi; Wang, Zhi-Guo; Chen, Hong

2007-09-01

We study the transmission properties and band structure of comb-like photonic crystals (PC) with backbones constructed of meta-materials (negative-index materials) within the frame of the interface response theory. The result shows the existence of a special band gap at low frequency. This gap differs from the Bragg gaps in that it is insensitive to the geometrical scaling and disorder. In comparison with the zero-average-index gap in one-dimensional PC made of alternating positive- and negative-index materials, the gap is obviously deeper and broader, given the same system parameters. In addition, the behavior of its gap-edges is also different. One gap-edge is decided by the average permittivity whereas the other is only subject to the changing of the permeability of the backbone. Due to this asymmetry of the two gap-edges, the broadening of the gap could be realized with much freedom and facility.

Extending of flat normal dispersion profile in all-solid soft glass nonlinear photonic crystal fibres

NASA Astrophysics Data System (ADS)

Siwicki, Bartłomiej; Kasztelanic, Rafał; Klimczak, Mariusz; Cimek, Jarosław; Pysz, Dariusz; Stępień, Ryszard; Buczyński, Ryszard

2016-06-01

The bandwidth of coherent supercontinuum generated in optical fibres is strongly determined by the all-normal dispersion characteristic of the fibre. We investigate all-normal dispersion limitations in all-solid oxide-based soft glass photonic crystal fibres with various relative inclusion sizes and lattice constants. The influence of material dispersion on fibre dispersion characteristics for a selected pair of glasses is also examined. A relation between the material dispersion of the glasses and the fibre dispersion has been described. We determined the parameters which limit the maximum range of flattened all-normal dispersion profile achievable for the considered pair of heavy-metal-oxide soft glasses.

Host Materials for Transition-Metal Ions

DTIC Science & Technology

1989-09-01

Spectra of 3d Transition Elements in KMgF3 Crystal, Soy. Phys. Solid State 19 (1977), 340. 21. H . Onuki , F. Sugawara, M. Hirano, and Y. Yamaguchi...on Cs2SnBr 6 .... h ............. 84 13.2 Crystal-Field Components, Anm, for Sn (Oh) Site .............. 814 13.3 Experimental Parameters...A.M VSg Kleef, Y. N. .3oshi, and R. P. Srivastava, Analysis of’ Cd V: I.--4Ida-id’ 5p Transitions, Physica 114IC (1982), 105. 15. H . Benschop, Y. N

Steps wandering on the lysozyme and KDP crystals during growth in solution

NASA Astrophysics Data System (ADS)

Rashkovich, L. N.; Chernevich, T. G.; Gvozdev, N. V.; Shustin, O. A.; Yaminsky, I. V.

2001-10-01

We have applied atomic force microscopy for the study in solution of time evolution of step roughness on the crystal faces with high (pottasium dihydrophosphate: KDP) and low (lysozyme) density of kinks. It was found that the roughness increases with time revealing the time dependence as t1/4. Step velocity does not depend upon distance between steps, that is why the experimental data were interpreted on the basis of Voronkov theory, which assume, that the attachment and detachment of building units in the kinks is major limitation for crystal growth. In the frame of this theoretical model the calculation of material parameters is performed.

Porous silicon photonic crystals as hosts for polymers, biopolymers, and magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Li, Yang Yang

This thesis describes the construction of one-dimensional photonic crystals of porous silicon by electrochemically etching and the use of these materials as hosts for polymers, biopolymers, and magnetic nanoparticles. The spectral features of the photonic crystals derive from a porosity gradient that is determined by the electrochemical etching parameters. Since the photonic crystals are constructed of a porous material, they can serve as hosts for other materials. The first chapter of the thesis provides an introduction to porous Si, templating techniques and the use of porous materials for controlled release of drugs. This latter section is added because much of the thesis work addresses the application of porous Si hosts for controlled release of drugs. In the second chapter, it is shown that the spectral properties of the porous Si photonic crystal template can be transferred to a variety of organic and biopolymers. It is demonstrated that these castings can be used as vapor sensors and as self-reporting, bioresorbable materials. If the template is not removed, porous Si polymer composites are formed. The third chapter discussed that by spray-coating a fine mist of polymer solution onto the porous Si film, robust and smooth micron-sized cylindrical photonic crystals suitable for bioassays can be prepared. The fourth chapter focuses on using porous Si photonic crystals as a host for magnetic nanoparticles. The magnetic nanoparticles in this work are found to adhere to the surface of the porous Si film as well to infiltrate the pore structure. In a demonstration of optical switching that may be useful for information display applications, flipping between the colored to dark sides by application of a magnetic field is found to occur at rates of as large as 175 Hz. As the host for soluble molecular species, porous Si photonic crystals can be impregnated from solution. The aggregates that form upon evaporation of solvent are found to scatter light from the resonant optical structure over a large solid angle. The spectrum of the scattered light provides a convenient means of monitoring the temporal release characteristics of the guest material. An application of the phenomenon is demonstrated for release of a drug (caffeine) into aqueous solution from a porous Si photonic crystal.

Hydrothermal crystal growth of oxides for optical applications

NASA Astrophysics Data System (ADS)

McMillen, Colin David

2007-12-01

The manipulation of light has proven to be an integral part of today's technology-based society. In particular, there is great interest in obtaining coherent radiation in all regions of the optical spectrum to advance technology in military, medical, industrial, scientific and consumer fields. Exploring new crystal growth techniques as well as the growth of new optical materials is critical in the advancement of solid state optics. Surprisingly, the academic world devotes little attention to the growth of large crystals. This shortcoming has left gaps in the optical spectrum inaccessible by solid state devices. This dissertation explores the hydrothermal crystal growth of materials that could fill two such gaps. The first gap exists in the deep-UV region, particularly below 200 nm. Some materials such as LiB3O5 and beta-BaB2O4 can generate coherent light at wavelengths as low as 205 nm. The growth of these materials was explored to investigate the feasibility of the hydrothermal method as a new technique for growing these crystals. Particular attention was paid to the descriptive chemistry surrounding these systems, and several novel structures were elucidated. The study was also extended to the growth of materials that could be used for the generation of coherent light as low as 155 nm. Novel synthetic schemes for Sr2Be2B2O7 and KBe2BO 3F2 were developed and the growth of large crystals was explored. An extensive study of the structures, properties and crystal growth of related compounds, RbBe2BO3F2 and CsBe2BO 3F2, was also undertaken. Optimization of a number of parameters within this family of compounds led to the hydrothermal growth of large, high quality single crystal at rates suitable for large-scale growth. The second gap in technology is in the area of high average power solid state lasers emitting in the 1 mum and eye-safe (>1.5 mum) regions. A hydrothermal technique was developed to grow high quality crystals of Sc 2O3 and Sc2O3 doped with suitable lanthanide activator ions. Preliminary spectroscopic studies were performed and large crystals were again grown at rates suitable for commercial production. The synthesis of ultra-high purity Ln2O3 (Ln = Sc, Y, La-Lu) nanoparticles was also explored to advance the development of ceramic-based solid state lasers. Crystal growth is a complex task involving a great number of intricacies that must be understood and balanced. This dissertation has advanced the art and science of growing crystals, and documented the development of large, high quality crystals of advanced optical materials The materials and hydrothermal crystal growth techniques developed over the course of this work represent important progress toward controlling the optical spectrum.

Vapor Growth of Binary and Ternary Chalcogenides in Preparation for Microgravity Experiments

NASA Technical Reports Server (NTRS)

Su, C.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

In the bulk crystal growth of some technologically important semiconducting chalcopyrites, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials. The realization of routine production of high-quality single crystals of these semiconductors requires a fundamental, systematic and in-depth study on the PVT growth process and crystal growth by vapor transport in low gravity offers a set of unique conditions for this study. Previously, two reasons have been put forward to account for this. The first is weight-related reductions in crystal strain and defects. These are thought to be caused by the weight of the crystals during processing at elevated temperatures and retained on cooling, particularly for materials with a low yield strength. The second, and more general, reason is related to the reduction in density-gradient driven convection. The PVT crystal growth process consists of essentially three processes: sublimation of the source material, transport of the vapor species and condensation of the vapor species to form the crystal. The latter two processes can be affected by the convection caused by gravitational accelerations on Earth. Reductions in such convection in low gravity is expected to yield a nearly diffusion-limited growth condition which results in more uniform growth rates (on the microscopic scale) and hence greater crystalline perfection and compositional homogeneity. The reduction of convective contamination by performing flight experiments in a reduced gravity environment will help to understand the relation between fluid phase processes (growth parameters) and defect and impurity incorporation in grown crystals.

Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment

NASA Technical Reports Server (NTRS)

Su, Ching-Hua

2014-01-01

A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). There are two sections of the flight experiment: (I) crystal growth of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT) and (II) melt growth of CdZnTe by directional solidification. The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

Pin-Hole Free Perovskite Film for Solar Cells Application Prepared by Controlled Two-Step Spin-Coating Method

NASA Astrophysics Data System (ADS)

Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.

2017-05-01

Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.

Growth, spectral, thermal, dielectric, mechanical, linear and nonlinear optical, birefringence, laser damage threshold studies of semi-organic crystal: dibrucinium sulfate heptahydrate.

PubMed

Krishnan, P; Gayathri, K; Bhagavannarayana, G; Jayaramakrishnan, V; Gunasekaran, S; Anbalagan, G

2013-08-01

Dibrucinium sulfate heptahydrate (DBSH), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from water-ethanol solution at room temperature up to dimensions of 10×7×2 mm(3). The unit cell parameters were determined from single crystal and powder X-ray diffraction studies. The structural perfection of the grown crystal has been analyzed by high-resolution X-ray diffraction (HRXRD) study. FTIR and Raman studies were performed to identify the functional groups present in the title compound. The activation energy (E), entropy (ΔS), enthalpy (ΔH) and Gibbs free energy (ΔG), of the thermal decomposition reaction have been derived from thermo gravimetric (TGA) and differential thermal (DTA) analysis curves, using Coats-Redfern method. The variation of dielectric properties of the grown crystal with respect to frequency has been investigated at different temperatures. Microhardness measurements revealed the mechanical strength of grown crystal. The optical parameters, the optical band gap E(g) and width of localized states Eu were determined using the transmittance data in the spectral range 200-800 nm. The relative second harmonic efficiency of the compound is found to be 1.4 times greater than that of KDP. Birefringence and Laser damage threshold studies were carried out for the grown crystal. Copyright © 2013 Elsevier B.V. All rights reserved.

Limit of validity of Ostwald's rule of stages in a statistical mechanical model of crystallization.

PubMed

Hedges, Lester O; Whitelam, Stephen

2011-10-28

We have only rules of thumb with which to predict how a material will crystallize, chief among which is Ostwald's rule of stages. It states that the first phase to appear upon transformation of a parent phase is the one closest to it in free energy. Although sometimes upheld, the rule is without theoretical foundation and is not universally obeyed, highlighting the need for microscopic understanding of crystallization controls. Here we study in detail the crystallization pathways of a prototypical model of patchy particles. The range of crystallization pathways it exhibits is richer than can be predicted by Ostwald's rule, but a combination of simulation and analytic theory reveals clearly how these pathways are selected by microscopic parameters. Our results suggest strategies for controlling self-assembly pathways in simulation and experiment.

Low cost solar array project. Task 1: Silicon material, gaseous melt replenishment system

NASA Technical Reports Server (NTRS)

Jewett, D. N.; Bates, H. E.; Hill, D. M.

1979-01-01

A system to combine silicon formation, by hydrogen reduction of trichlorosilane, with the capability to replenish a crystal growth system is described. A variety of process parameters to allow sizing and specification of gas handling system components was estimated.

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.

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

NASA Astrophysics Data System (ADS)

Zhou, Dong

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Characterisation and sintering of nanophase hydroxyapatite synthesised by a species of Serratia

NASA Astrophysics Data System (ADS)

LSammons, R.; Thackray, A. C.; Medina Ledo, H.; Marquis, P. M.; Jones, I. P.; Yong, P.; Macaskie, L. E.

2007-12-01

The bacterium Serratia sp. NCIMB40259, which grows as a biofilm on polymeric, glass and metal substrates, produces extracellular crystals of hydroxyapatite (HA) by enzymatic cleavage of β-glycerophosphate in the presence of calcium chloride. Following growth on polyurethane foam, biomineralisation and subsequent sintering, an HA scaffold is formed whose three-dimensional architecture replicates that of the foam and the biofilm. Serratia HA was characterised using X-ray diffraction (XRD), Fourier Transform Infra-Red Spectroscopy (FTIR), energy dispersive X-ray analysis (EDX) scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). The nascent, unsintered material consisted mainly of calcium-deficient HA (CDHA) with a Ca/P ratio of 1.61+/- 0.06 and crystal size (TEM) of 50 +/- 10nm length. ED of unsintered crystals and crystals sintered at 600° C showed resolvable ring (unsintered) or dot (600° C) patterns ascribed to (0002), (1122) and (0006) planes of crystalline HA. Material sintered at 1200° C consisted of needle-like crystals of length range 54-111nm (XRD) with lattice parameters of a = 9.441 Å and c = 6.875 Å, consistent with HA.

Ultrasonically controlled particle size distribution of explosives: a safe method.

PubMed

Patil, Mohan Narayan; Gore, G M; Pandit, Aniruddha B

2008-03-01

Size reduction of the high energy materials (HEM's) by conventional methods (mechanical means) is not safe as they are very sensitive to friction and impact. Modified crystallization techniques can be used for the same purpose. The solute is dissolved in the solvent and crystallized via cooling or is precipitated out using an antisolvent. The various crystallization parameters such as temperature, antisolvent addition rate and agitation are adjusted to get the required final crystal size and morphology. The solvent-antisolvent ratio, time of crystallization and yield of the product are the key factors for controlling antisolvent based precipitation process. The advantages of cavitationally induced nucleation can be coupled with the conventional crystallization process. This study includes the effect of the ultrasonically generated acoustic cavitation phenomenon on the solvent antisolvent based precipitation process. CL20, a high-energy explosive compound, is a polyazapolycyclic caged polynitramine. CL-20 has greater energy output than existing (in-use) energetic ingredients while having an acceptable level of insensitivity to shock and other external stimuli. The size control and size distribution manipulation of the high energy material (CL20) has been successfully carried out safely and quickly along with an increase in the final mass yield, compared to the conventional antisolvent based precipitation process.

A Polymer-Dispersed Liquid Crystal-Based Dynamic Gain Equalizer

NASA Astrophysics Data System (ADS)

Barge, M.; Battarel, D.; de Bougrenet de La Tocnaye, J. L.

2005-08-01

This paper presents results obtained with a spatial light modulator (SLM) using a polymer-dispersed liquid-crystal (LC) material to provide dynamic gain equalization (DGE) for wavelength-division multiplexing (WDM) networks. We show the benefit of using a nonchannelized approach to adjust some physical parameters such as the ripple and the maximum obtainable attenuation slope for the spectra to be equalized. Particular attention is paid here to polarization dependence that can result from parasitic anisotropic multiple path interferences as well as induced anisotropy due to a planar transverse field when using a free-space SLM structure. In this frame, we demonstrate an original approach using a depolarizing prism that is only appropriate to such choice of material and that mitigates these effects. Finally, material engineering to widen the operating temperature range is also shortly presented in this paper.

Photo-Induced Deformations of Liquid Crystal Elastomers

NASA Astrophysics Data System (ADS)

Dawson, Nathan; Kuzyk, Mark; Neal, Jeremy; Luchette, Paul; Palffy-Muhoray, Peter

2010-10-01

Over a century ago, Alexander Graham Bell transmitted mechanical information on a beam of light using the ``photophone.'' We report on the use of a Fabry-Perot interferometer to encode and detect mechanical information of an illuminated liquid crystal elastomer (LCE) that is placed at a critical point between the reflectors. Furthermore, we show that cascading of macroscopic LCE-interferometer devices is possible. These are the first steps in the creation of ultra smart materials. Such applications require materials with a large photomechanical response. Thus, understanding the underlying mechanisms is critical. Only limited studies of the mechanisms of photomechanical effects have been studied in azo-dye-doped LCEs. The focus of our present work is to use the Fabry-Perot transducer geometry to study the underlying mechanisms and to determine the relevant material parameters that are used to develop theoretical models of the response. We use various intensity-modulated optical wave forms to determine the frequency response of the material, which are used to predict the material response in the time domain.

Magnetic field controlled floating-zone single crystal growth of intermetallic compounds

NASA Astrophysics Data System (ADS)

Hermann, R.; Gerbeth, G.; Priede, J.

2013-03-01

Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.

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

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Ramachandran, N.

2013-01-01

Crystals of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, will be grown by physical vapor transport in the Material Science Research Rack (MSRR) on International Space Station (ISS). The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

Elaboration and characterization of solid materials of types zeolite NaA and faujasite NaY exchanged by zinc metallic ions Zn2+

NASA Astrophysics Data System (ADS)

Nibou, D.; Amokrane, S.; Mekatel, H.; Lebaili, N.

2009-11-01

The present work deals with the elaborated of NaA and faujasite NaY solid materials according to a hydrothermal crystallization of amorphous gels composed of solutions of silicon, aluminum and sodium. The process elaboration has been achieved in autoclaves made of steel lined in Teflon under different operating conditions of temperature of heating, time of contact and stirring. After crystallization, the samples were characterized by different techniques such as X ray diffraction, scanning electronic microscopy, infrared spectroscopy, thermal analysis, and chemical analysis. Pure solid materials NaA and NaY zeolites were obtained and were impregnated by (Zn2+) ions by ion exchange process. The effects of various parameters such as initial metal concentration, pH, solid-liquid ratio (R) and temperature on the exchange percentage are studied. The equilibrium isotherms of zinc ions sorption are also evaluated using Langmuir and Freundlich models. Thermodynamic parameters, i.e. enthalpy of adsorption ΔHads∘, entropy change ΔSads∘ and Gibbs free energy ΔGads∘ for the sorption of zinc ions on NaA and NaY zeolites were examined.

Monolayer Colloidal Crystals by Modified Air-Water Interface Self-Assembly Approach

PubMed Central

Ye, Xin; Huang, Jin; Zeng, Yong; Sun, Lai-Xi; Geng, Feng; Liu, Hong-Jie; Wang, Feng-Rui; Jiang, Xiao-Dong; Wu, Wei-Dong; Zheng, Wan-Guo

2017-01-01

Hexagonally ordered arrays of polystyrene (PS) microspheres were prepared by a modified air-water self-assembly method. A detailed analysis of the air-water interface self-assembly process was conducted. Several parameters affect the quality of the monolayer colloidal crystals, i.e., the colloidal microsphere concentration on the latex, the surfactant concentration, the polystyrene microsphere diameter, the microsphere polydispersity, and the degree of sphericity of polystyrene microspheres. An abrupt change in surface tension was used to improve the quality of the monolayer colloidal crystal. Three typical microstructures, i.e., a cone, a pillar, and a binary structure were prepared by reactive-ion etching using a high-quality colloidal crystal mask. This study provides insight into the production of microsphere templates with flexible structures for large-area patterned materials. PMID:28946664

Combining 27Al Solid-State NMR and First-Principles Simulations To Explore Crystal Structure in Disordered Aluminum Oxynitride.

PubMed

Tu, Bingtian; Liu, Xin; Wang, Hao; Wang, Weimin; Zhai, Pengcheng; Fu, Zhengyi

2016-12-19

The nuclear magnetic resonance (NMR) technique gives insight into the local information in a crystal structure, while Rietveld refinement of powder X-ray diffraction (PXRD) sketches out the framework of a crystal lattice. In this work, first-principles calculations were combined with the solid-state NMR technique and Rietveld refinement to explore the crystal structure of a disordered aluminum oxynitride (γ-alon). The theoretical NMR parameters (chemical shift, δ iso , quadrupolar coupling constants, C Q , and asymmetry parameter, η) of Al 22.5 O 28.5 N 3.5 , predicted by the gauge-including projector augmented wave (GIPAW) algorithm, were used to facilitate the analytical investigation of the 27 Al magic-angle spinning (MAS) NMR spectra of the as-prepared sample, whose formula was confirmed to be Al 2.811 O 3.565 N 0.435 by quantitative analysis. The experimental δ iso , C Q , and η of 27 Al showed a small discrepancy compared with theoretical models. The ratio of aluminum located at the 8a to 16d sites was calculated to be 0.531 from the relative integration of peaks in the 27 Al NMR spectra. The occupancies of aluminum at the 8a and 16d positions were determined through NMR investigations to be 0.9755 and 0.9178, respectively, and were used in the Rietveld refinement to obtain the lattice parameter and anion parameter of Al 2.811 O 3.565 N 0.435 . The results from 27 Al NMR investigations and PXRD structural refinement complemented each other. This work provides a powerful and accessible strategy to precisely understand the crystal structure of novel oxynitride materials with multiple disorder.

Growth of single crystals of mercuric iodide (HgI/sub 2/) in spacelab III

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

Van Den Berg, L.; Schnepple, W.F.

1981-01-01

Continued development of a system designed to grow crystals by physical vapor transport in the environment of Spacelab III will be described, with special emphasis on simulation of expected space conditions, adjustment of crystal growth parameters, and on board observation and control of the experiment by crew members and ground personnel. A critical factor in the use of mercuric iodide for semiconductor detectors of x-rays and gamma-rays is the crystalline quality of the material. The twofold purpose of the Spacelab III experiment is therefore to grow single crystals with superior electronic properties as an indirect result of the greatly reducedmore » gravity field during the growth, and to obtain data which will lead to improved understanding of the vapor transport mechanism. The experiments planned to evaluate the space crystals, including gamma-ray diffractometry and measurements of stoichiometry, lattice dimensions, mechanical strength, luminescense, and detector performance are discussed.« less

Thermal, optical, mechanical and electrical properties of a novel NLO active L-phenylalanine L-phenylalaninium perchlorate single crystals

NASA Astrophysics Data System (ADS)

Cyrac Peter, A.; Vimalan, M.; Sagayaraj, P.; Madhavan, J.

2010-01-01

Single crystals of L-phenylalanine L-phenylalaninium perchlorate (LPAPCl), a semiorganic nonlinear (NLO) material have been successfully grown up to a size of 14 mm×5 mm×3 mm. The lattice parameters of the grown crystals are determined by single crystal XRD. The UV-Vis-NIR spectrum of LPAPCl show less optical absorption in the entire visible region. Nonlinear optical study reveals that the SHG efficiency of LPAPCl is nearly 1.4 times that of KDP. The laser damage density is found to be 7.4 GW/cm 2. The crystals are subjected to microhardness studies and the variation of the microhardness with the applied load is studied. The response of dielectric constant in the frequency region of 50 Hz to 5 MHz has been investigated. AC and DC conductivity and photoconductivity experiments are also carried out and the results are discussed.

Effect of the temperature-rate parameters of directional solidification on the structure formation in high-temperature materials

NASA Astrophysics Data System (ADS)

Svetlov, I. L.; Neiman, A. V.

2017-03-01

The effect of the temperature gradient and the crystal growth rate on the structure formation in nickel and niobium superalloys is studied under the conditions of the flat, cellular, dendritic, or dendritic-cellular configuration of a solidification front during directional solidification.

Modeling dislocation generation in high pressure Czochralski growth of indium phosphide single crystals

NASA Astrophysics Data System (ADS)

Pendurti, Srinivas

InP is an important material for opto-electronic and high speed electronics applications. Its main use today is as the substrate material for epitaxy to produce GaInAsP lasers. The present technology for growing bulk InP is the high pressure Czochralski process. Bulk InP grown through this technique suffers from presence of a high density of line defects or dislocations, which are produced by thermal stresses the material goes through during its growth in the high temperature furnace. Modeling of these thermal stresses and the resulting plastic deformation, giving rise to dislocation densities, entails simulation of the entire thermal history of the crystal during its growth in the furnace, and studying the deformation of the crystal through suitable visco-plastic constitutive equations. Accordingly, a suitable visco-plastic model for deformation of InP was constructed, integrated with the ABAQUS finite element code, and verified through experimental data for uniaxial constant strain rate deformation tests available in literature. This was then coupled with a computation fluid dynamics model, predicting the entire temperature history in the furnace during crystal growth, to study the plastic deformation and dislocation density evolution in the crystal during growth. Growth in a variety of conditions was simulated and those conditions that generate minimum dislocation density identified. Macroscopic controllable parameters that affect the dislocation densities the most, have also been delineated. It was found that the strength of gas convection in the Czochralski furnace has the strongest effect on the dislocation densities in the fully grown crystal. Comparison of the simulated dislocation densities on wafers, with experimentally recorded etch pit profiles on as-grown crystals was reasonable. Finally some limitations in the work are discussed and avenues for future work identified.

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.

Proposed square spiral microfabrication architecture for large three-dimensional photonic band gap crystals.

PubMed

Toader, O; John, S

2001-05-11

We present a blueprint for a three-dimensional photonic band gap (PBG) material that is amenable to large-scale microfabrication on the optical scale using glancing angle deposition methods. The proposed chiral crystal consists of square spiral posts on a tetragonal lattice. In the case of silicon posts in air (direct structure), the full PBG can be as large as 15% of the gap center frequency, whereas for air posts in a silicon background (inverted structure) the maximum PBG is 24% of the center frequency. This PBG occurs between the fourth and fifth bands of the photon dispersion relation and is very robust to variations (disorder) in the geometrical parameters of the crystal.

Growth of ruby crystals by the heat exchanger method, phase 1: NSF small business innovation research

NASA Astrophysics Data System (ADS)

Schmid, F.; Khattak, C. P.

1980-03-01

Conditions for the growth of large, uniformly doped laser crystals by the heat exchanger method are explored. Determination of the melt point, selection of crucible material and establishment of furnace operating parameters are discussed. The melt point of ruby was found to be 2040 plus or minus 10 C. Molybdenum crucibles can be used to contain ruby in vacuum as well as under argon atmospheres at desired superheat temperatures over extended periods required for crystal growth. Thermodynamic analysis was conducted and vapor pressures of volatile species calculated. Experimentally, volatilization of chromium oxides was suppressed by using welded covers on crucibles and operating under an argon pressure in the furnace.

Efficient Parameter Searches for Colloidal Materials Design with Digital Alchemy

NASA Astrophysics Data System (ADS)

Dodd, Paul, M.; Geng, Yina; van Anders, Greg; Glotzer, Sharon C.

Optimal colloidal materials design is challenging, even for high-throughput or genomic approaches, because the design space provided by modern colloid synthesis techniques can easily have dozens of dimensions. In this talk we present the methodology of an inverse approach we term ''digital alchemy'' to perform rapid searches of design-paramenter spaces with up to 188 dimensions that yield thermodynamically optimal colloid parameters for target crystal structures with up to 20 particles in a unit cell. The method relies only on fundamental principles of statistical mechanics and Metropolis Monte Carlo techniques, and yields particle attribute tolerances via analogues of familiar stress-strain relationships.

Melt growth of organic 4-(2-Phenylisopropyl) phenol single crystal and its structural, thermal, dielectric permittivity and optical properties

NASA Astrophysics Data System (ADS)

Sadhasivam, S.; Rajesh, N. P.

2017-12-01

A nonlinear optical (NLO) organic crystal 4-(2-Phenylisopropyl) phenol has been grown by a top seeded melt growth technique. The melt growth kinetics of solid-liquid (molten) interface and facets formation in melt growth were studied. The melt grown crystal has the (001), (00 1 bar),(110)(1 bar 1 bar 0) ,(1 bar 20),(1 2 bar 0),(2 bar 10) and(2 1 bar 0) different morphological face. The morphological characteristics of melt grown crystal helps to better infer the kinetic influence of melt and hone growth of organic material. The rhombohedral lattice cell parameters were measured by single crystal X-ray diffraction. 4-(2-Phenylisopropyl) phenol crystallizes in space group of R 3 bar . Thermal study shows that solid to liquid transition occurring at 350 K and decomposes at 597 K. The grown crystal was optically transparent in the wavelength range of 300-1100 nm. The low dielectric constant (9-11) was measured in the [001] of 4-(2-Phenylisopropyl) phenol crystal.

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

Ji, Xiaoyu; Lei, Shiming; Yu, Shih -Ying

Semiconductor core optical fibers with a silica cladding are of great interest in nonlinear photonics and optoelectronics applications. Laser crystallization has been recently demonstrated for crystallizing amorphous silicon fibers into crystalline form. Here we explore the underlying mechanism by which long single-crystal silicon fibers, which are novel platforms for silicon photonics, can be achieved by this process. Using finite element modeling, we construct a laser processing diagram that reveals a parameter space within which single crystals can be grown. Utilizing this diagram, we illustrate the creation of single-crystal silicon core fibers by laser crystallizing amorphous silicon deposited inside silica capillarymore » fibers by high-pressure chemical vapor deposition. The single-crystal fibers, up to 5.1 mm long, have a very welldefined core/cladding interface and a chemically pure silicon core that leads to very low optical losses down to ~0.47-1dB/cm at the standard telecommunication wavelength (1550 nm). Furthermore, tt also exhibits a photosensitivity that is comparable to bulk silicon. Creating such laser processing diagrams can provide a general framework for developing single-crystal fibers in other materials of technological importance.« less

Crystalline structure of Cu4SSe

NASA Astrophysics Data System (ADS)

Amiraslanov, I. R.; Alieva, N. A.; Guseinov, G. G.

2016-12-01

Ternary compound Cu4SSe has been first synthesized by alloying the Cu, S, and Se elements taken in stoichiometric ratios. An X-ray diffraction study of polycrystalline samples has revealed the synthesized material to be crystallized into the trigonal system with unit-cell parameters a = 4.021(1) Å, c = 6.838(1) Å, and V = 95.75(4) Å3; sp. gr. P bar 3 m1; Z = 1; D x = 6.333(3) g/cm3. The crystal structure has been solved and refined to the reliability factor R Bragg = 0.40%.

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

DOE PAGES

Neupane, Madhab; Xu, Su-Yang; Sankar, R.; ...

2015-08-20

Here we report the evolution of the surface electronic structure and surface material properties of a topological crystalline insulator (TCI), Pb 1more » $${-}$$xSnxSe, as a function of various material parameters including composition x, temperature T , and crystal structure. Our spectroscopic data demonstrate the electronic ground-state condition for the saddle point singularity, the tunability of surface chemical potential, and the surface states’ response to circularly polarized light. Our results show that each material parameter can tune the system between the trivial and topological phase in a distinct way, unlike that seen in Bi 2Se 3 and related compounds, leading to a rich topological phase diagram. Our systematic studies of the TCI Pb 1$${-}$$xSnxSe are a valuable materials guide to realize new topological phenomena.« less

An Efficient Scheme for Crystal Structure Prediction Based on Structural Motifs

DOE PAGES

Zhu, Zizhong; Wu, Ping; Wu, Shunqing; ...

2017-05-15

An efficient scheme based on structural motifs is proposed for the crystal structure prediction of materials. The key advantage of the present method comes in two fold: first, the degrees of freedom of the system are greatly reduced, since each structural motif, regardless of its size, can always be described by a set of parameters (R, θ, φ) with five degrees of freedom; second, the motifs could always appear in the predicted structures when the energies of the structures are relatively low. Both features make the present scheme a very efficient method for predicting desired materials. The method has beenmore » applied to the case of LiFePO 4, an important cathode material for lithium-ion batteries. Numerous new structures of LiFePO 4 have been found, compared to those currently available, available, demonstrating the reliability of the present methodology and illustrating the promise of the concept of structural motifs.« less

An Efficient Scheme for Crystal Structure Prediction Based on Structural Motifs

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

Zhu, Zizhong; Wu, Ping; Wu, Shunqing

An efficient scheme based on structural motifs is proposed for the crystal structure prediction of materials. The key advantage of the present method comes in two fold: first, the degrees of freedom of the system are greatly reduced, since each structural motif, regardless of its size, can always be described by a set of parameters (R, θ, φ) with five degrees of freedom; second, the motifs could always appear in the predicted structures when the energies of the structures are relatively low. Both features make the present scheme a very efficient method for predicting desired materials. The method has beenmore » applied to the case of LiFePO 4, an important cathode material for lithium-ion batteries. Numerous new structures of LiFePO 4 have been found, compared to those currently available, available, demonstrating the reliability of the present methodology and illustrating the promise of the concept of structural motifs.« less

Transmittance properties of one dimensional ternary nanocomposite photonic crystals

NASA Astrophysics Data System (ADS)

Elsayed, Hussein A.

2018-03-01

In the present work, we have theoretically investigated the transmittance characteristics of one dimensional ternary photonic crystals that containing a nanocomposite layer. The nanocomposite layer was designed from metallic nanoparticles of (Ag) in a transparent matrix of a dielectric material (MgF2). The numerical results are obtained based on the theoretical modeling of the characteristic matrix method and Maxwell-Garnett model. The investigated results demonstrate the significant effect of the volume fraction of the nanoparticles on the effective permittivity of the nanocomposite material as well as the transmission characteristics of our design. Moreover, the roles played by other parameters such as the thickness of the nanocomposite layer, the permittivity of the host dielectric material and the spherical radius of the nanoparticles are included her. The proposed structure could be promising for many applications such as THz optical filters, reflectors and optical switches.

Single-crystal silicon optical fiber by direct laser crystallization

DOE PAGES

Ji, Xiaoyu; Lei, Shiming; Yu, Shih -Ying; ...

2016-12-05

Semiconductor core optical fibers with a silica cladding are of great interest in nonlinear photonics and optoelectronics applications. Laser crystallization has been recently demonstrated for crystallizing amorphous silicon fibers into crystalline form. Here we explore the underlying mechanism by which long single-crystal silicon fibers, which are novel platforms for silicon photonics, can be achieved by this process. Using finite element modeling, we construct a laser processing diagram that reveals a parameter space within which single crystals can be grown. Utilizing this diagram, we illustrate the creation of single-crystal silicon core fibers by laser crystallizing amorphous silicon deposited inside silica capillarymore » fibers by high-pressure chemical vapor deposition. The single-crystal fibers, up to 5.1 mm long, have a very welldefined core/cladding interface and a chemically pure silicon core that leads to very low optical losses down to ~0.47-1dB/cm at the standard telecommunication wavelength (1550 nm). Furthermore, tt also exhibits a photosensitivity that is comparable to bulk silicon. Creating such laser processing diagrams can provide a general framework for developing single-crystal fibers in other materials of technological importance.« less

Optical, structural, thermal and dielectric spectroscopy characterizations of seeded melt grown 2-hydroxy biphenyl single crystal.

PubMed

Sadhasivam, S; Rajesh, Narayana Perumal

2014-09-15

Organic single crystal of 2-hydroxy biphenyl (2-HB) was grown by top seeded melt growth method. Scanning electron microscopy studies has been carried out on the surface of the grown crystals to investigate the nature of growth and defects. The crystalline perfection and lattice parameters of 2-HB has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Fdd2. The functional groups and molecular associations were confirmed by FT-IR. The optical characteristics such as cut-off and transmittance were carried out using UV-Vis-NIR spectra. Absence of absorption in the region between 320 and 1100 nm makes the grown crystal desirable to optical applications. Thermal stability of grown crystals was characterized by thermogravimetric (TGA), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) analyses. Broadband dielectric studies reveals that dielectric constant of grown crystal is low. The resistivity of grown crystal was studied by impedance analysis. The second harmonic generation intensity of 3.8 mJ was studied. The grown crystal belongs to soft material studied by hardness test. Copyright © 2014 Elsevier B.V. All rights reserved.

Growth, structural, thermal, linear and nonlinear optical and laser damage threshold studies of picolinium tartrate monohydrate single crystals.

PubMed

Peramaiyan, G; Pandi, P; Sornamurthy, B M; Bhagavannarayana, G; Mohan Kumar, R

2012-09-01

Picolinium tartrate monohydrate (PTM), a novel organic nonlinear optical material was synthesized and bulk crystals were grown from aqueous solution by slow cooling technique. The cell parameters of the grown crystal were found by single and powder X-ray diffraction analyses. The crystalline perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The presence of functional groups in the grown crystal was identified by FTIR and FT-Raman spectral analyses. UV-Vis spectral studies reveal PTM crystals are transparent in the wavelength region of 295-1100 nm. The thermal characteristics of PTM were analyzed by TGA/DTA studies. The dielectric and mechanical behaviours of PTM crystals were investigated. Dislocation density was estimated to be 2.89 × 10(3) cm(-2) on the flat-surface of PTM crystals from the etching studies. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. Its second harmonic generation relative efficiency was measured by Kurtz and Perry powder technique and was observed to be comparable with KDP crystal. Copyright © 2012 Elsevier B.V. All rights reserved.

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

Wang, Bingnan

Photonic crystals and metamaterials, both composed of artificial structures, are two interesting areas in electromagnetism and optics. New phenomena in photonic crystals and metamaterials are being discovered, including some not found in natural materials. This thesis presents my research work in the two areas. Photonic crystals are periodically arranged artificial structures, mostly made from dielectric materials, with period on the same order of the wavelength of the working electromagnetic wave. The wave propagation in photonic crystals is determined by the Bragg scattering of the periodic structure. Photonic band-gaps can be present for a properly designed photonic crystal. Electromagnetic waves withmore » frequency within the range of the band-gap are suppressed from propagating in the photonic crystal. With surface defects, a photonic crystal could support surface modes that are localized on the surface of the crystal, with mode frequencies within the band-gap. With line defects, a photonic crystal could allow the propagation of electromagnetic waves along the channels. The study of surface modes and waveguiding properties of a 2D photonic crystal will be presented in Chapter 1. Metamaterials are generally composed of artificial structures with sizes one order smaller than the wavelength and can be approximated as effective media. Effective macroscopic parameters such as electric permittivity ϵ, magnetic permeability μ are used to characterize the wave propagation in metamaterials. The fundamental structures of the metamaterials affect strongly their macroscopic properties. By designing the fundamental structures of the metamaterials, the effective parameters can be tuned and different electromagnetic properties can be achieved. One important aspect of metamaterial research is to get artificial magnetism. Metallic split-ring resonators (SRRs) and variants are widely used to build magnetic metamaterials with effective μ < 1 or even μ < 0. Varactor based nonlinear SRRs are built and modeled to study the nonlinearity in magnetic metamaterials and the results will be presented in Chapter 3. Negative refractive index n is one of the major target in the research of metamaterials. Negative n can be obtained with a metamaterial with both ϵ and μ negative. As an alternative, negative index for one of the circularly polarized waves could be achieved with metamaterials having a strong chirality ?. In this case neither ϵ} nor μ negative is required. My work on chiral metamaterials will be presented in Chapter 4.« less

Luminescence and radiation resistance of undoped NaI crystals

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

Shiran, N., E-mail: shiran@isc.kharkov.com; Boiaryntseva, I.; Gektin, A.

2014-11-15

Highlights: • The performance of NaI scintillators depends on luminescence properties. • A criterion of crystals’ purity level is radiation colorability at room temperature. • The traces of the most dangerous impurities were detected. • Crucial role in efficiency of pure NaI scintillator play the crystal perfection. - Abstract: Undoped NaI single crystal is an excellent scintillator at low temperature. However, scintillation parameters of different quality crystals vary in a wide range, significantly exceeding measurement error. Experimental data demonstrate the features of luminescence, radiation induced coloration, and afterglow dependence on the quality of nominally pure crystals. It is found thatmore » defects level that allows to elucidate artefacts introduced by traces of harmful impurities corresponds to 3 × 10{sup 15} cm{sup −3} that significantly overhead accuracy of chemical and absorption analysis. It is shown that special raw material treatment before and during the single crystal growth allows to reach NaI purity level that avoids impurities influence to the basic luminescence data.« less

Synthesis, crystal growth and characterization of bioactive material: 2-amino-1H-benzo[d]imidazol-3-ium salicylate single crystal-a proton transfer molecular complex

NASA Astrophysics Data System (ADS)

Fathima, K. Saiadali; Anitha, K.

2017-05-01

The 1:1 molecular adducts 2-aminobenzimidazolium salicylate (ABIS) single crystal was synthesized and grown from 2-aminobenzimidazole (ABI) as a donor and salicylic acid (SA) as an acceptor. The cell parameter was determined using single crystal X-Ray diffraction method and the complex ABIS belongs to monoclinic system. The spectroscopic studies showed that ABIS crystal was an ion pair complex. The FTIR and Raman spectra showed that the presence of O-H, C=N, C=O vibration which confirms the proton transfer from SA to ABI. The UV-Vis spectrum exhibited a visible band at 359nm for ABIS due to the salicylate anion of the molecule. Further the antimicrobial activity of ABIS complex against Staphylococcus aureus, klebsiella pneumonia, Pseudomonas eruginos and E.coli pathogens was investigated. So the complex molecule inhibits both Gram positive and Gram negative bacterial. It is found that benzimidazole with aminogroup at position 2 increases the general antimicrobial activities of ABIS crystal.

Growth of micro-crystals in solution by in-situ heating via continuous wave infrared laser light and an absorber

NASA Astrophysics Data System (ADS)

Pathak, Shashank; Dharmadhikari, Jayashree A.; Thamizhavel, A.; Mathur, Deepak; Dharmadhikari, Aditya K.

2016-01-01

We report on growth of micro-crystals such as sodium chloride (NaCl), copper sulphate (CuSO4), potassium di-hydrogen phosphate (KDP) and glycine (NH2CH2COOH) in solution by in-situ heating using continuous wave Nd:YVO4 laser light. Crystals are grown by adding single walled carbon nanotubes (SWNT). The SWNTs absorb 1064 nm light and act as an in-situ heat source that vaporizes the solvent producing microcrystals. The temporal dynamics of micro-crystal growth is investigated by varying experimental parameters such as SWNT bundle size and incident laser power. We also report crystal growth without SWNT in an absorbing medium: copper sulphate in water. Even though the growth dynamics with SWNT and copper sulphate are significantly different, our results indicate that bubble formation is necessary for nucleation. Our simple method may open up new vistas for rapid growth of seed crystals especially for examining the crystallizability of inorganic and organic materials.

Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals

NASA Astrophysics Data System (ADS)

Zhang, F. H.; Wang, S. F.; An, C. H.; Wang, J.; Xu, Q.

2017-06-01

Large-aperture potassium dihydrogen phosphate (KDP) crystals are widely used in the laser path of inertial confinement fusion (ICF) systems. The most common method of manufacturing half-meter KDP crystals is ultra-precision fly cutting. When processing KDP crystals by ultra-precision fly cutting, the dynamic characteristics of the fly cutting machine and fluctuations in the fly cutting environment are translated into surface errors at different spatial frequency bands. These machining errors should be suppressed effectively to guarantee that KDP crystals meet the full-band machining accuracy specified in the evaluation index. In this study, the anisotropic machinability of KDP crystals and the causes of typical surface errors in ultra-precision fly cutting of the material are investigated. The structures of the fly cutting machine and existing processing parameters are optimized to improve the machined surface quality. The findings are theoretically and practically important in the development of high-energy laser systems in China.

Magnetotransport Properties in High-Quality Ultrathin Two-Dimensional Superconducting Mo2C Crystals.

PubMed

Wang, Libin; Xu, Chuan; Liu, Zhibo; Chen, Long; Ma, Xiuliang; Cheng, Hui-Ming; Ren, Wencai; Kang, Ning

2016-04-26

Ultrathin transition metal carbides are a class of developing two-dimensional (2D) materials with superconductivity and show great potentials for electrical energy storage and other applications. Here, we report low-temperature magnetotransport measurements on high-quality ultrathin 2D superconducting α-Mo2C crystals synthesized by a chemical vapor deposition method. The magnetoresistance curves exhibit reproducible oscillations at low magnetic fields for temperature far below the superconducting transition temperature of the crystals. We interpret the oscillatory magnetoresistance as a consequence of screening currents circling around the boundary of triangle-shaped terraces found on the surface of ultrathin Mo2C crystals. As the sample thickness decreases, the Mo2C crystals exhibit negative magnetoresistance deep in the superconducting transition regime, which reveals strong phase fluctuations of the superconducting order parameters associated with the superconductor-insulator transition. Our results demonstrate that the ultrathin superconducting Mo2C crystals provide an interesting system for studying rich transport phenomena in a 2D crystalline superconductor with enhanced quantum fluctuations.

Finite Element Analysis of a Copper Single Crystal Shape Memory Alloy-Based Endodontic Instruments

NASA Astrophysics Data System (ADS)

Vincent, Marin; Thiebaud, Frédéric; Bel Haj Khalifa, Saifeddine; Engels-Deutsch, Marc; Ben Zineb, Tarak

2015-10-01

The aim of the present paper is the development of endodontic Cu-based single crystal Shape Memory Alloy (SMA) instruments in order to eliminate the antimicrobial and mechanical deficiencies observed with the conventional Nickel-Titane (NiTi) SMA files. A thermomechanical constitutive law, already developed and implemented in a finite element code by our research group, is adopted for the simulation of the single crystal SMA behavior. The corresponding material parameters were identified starting from experimental results for a tensile test at room temperature. A computer-aided design geometry has been achieved and considered for a finite element structural analysis of the endodontic Cu-based single crystal SMA files. They are meshed with tetrahedral continuum elements to improve the computation time and the accuracy of results. The geometric parameters tested in this study are the length of the active blade, the rod length, the pitch, the taper, the tip diameter, and the rod diameter. For each set of adopted parameters, a finite element model is built and tested in a combined bending-torsion loading in accordance with ISO 3630-1 norm. The numerical analysis based on finite element procedure allowed purposing an optimal geometry suitable for Cu-based single crystal SMA endodontic files. The same analysis was carried out for the classical NiTi SMA files and a comparison was made between the two kinds of files. It showed that Cu-based single crystal SMA files are less stiff than the NiTi files. The Cu-based endodontic files could be used to improve the root canal treatments. However, the finite element analysis brought out the need for further investigation based on experiments.

Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla.

PubMed

Challa, Pavan K; Curtiss, O; Williams, J C; Twieg, R; Toth, J; McGill, S; Jákli, A; Gleeson, J T; Sprunt, S N

2012-07-01

We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(αβ)B(α)B(β)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field.

Automatic high-throughput screening of colloidal crystals using machine learning

NASA Astrophysics Data System (ADS)

Spellings, Matthew; Glotzer, Sharon C.

Recent improvements in hardware and software have united to pose an interesting problem for computational scientists studying self-assembly of particles into crystal structures: while studies covering large swathes of parameter space can be dispatched at once using modern supercomputers and parallel architectures, identifying the different regions of a phase diagram is often a serial task completed by hand. While analytic methods exist to distinguish some simple structures, they can be difficult to apply, and automatic identification of more complex structures is still lacking. In this talk we describe one method to create numerical ``fingerprints'' of local order and use them to analyze a study of complex ordered structures. We can use these methods as first steps toward automatic exploration of parameter space and, more broadly, the strategic design of new materials.

Interacting effects of strengthening and twin boundary migration in nanotwinned materials

NASA Astrophysics Data System (ADS)

Joshi, Kartikey; Joshi, Shailendra P.

Twin boundaries play a governing role in the mechanical characteristics of nanotwinned materials. They act as yield strengthening agents by offering resistance to non-coplanar dislocation slip. Twin boundary migration may cause yield softening while also enhancing the strain hardening response. In this work, we investigate the interaction between strengthening and twin boundary migration mechanisms by developing a length-scale dependent crystal plasticity framework for face-centered-cubic nanotwinned materials. The crystal plasticity model incorporates strengthening mechanisms due to dislocation pile-up via slip and slip-rate gradients and twin boundary migration via source-based twin partial nucleation and lattice dislocation-twin boundary interaction. The coupled effect of the load orientation and initial twin size on the speed of twin boundary is discussed and an expression for the same is proposed in terms of relevant material parameters. The efficacy of finite element simulations and the analytical expression in predicting evolution of nanotwinned microstructures comprising size and spatial distributions of twins is demonstrated.

Statistical Nature of Atomic Disorder in Irradiated Crystals.

PubMed

Boulle, A; Debelle, A

2016-06-17

Atomic disorder in irradiated materials is investigated by means of x-ray diffraction, using cubic SiC single crystals as a model material. It is shown that, besides the determination of depth-resolved strain and damage profiles, x-ray diffraction can be efficiently used to determine the probability density function (PDF) of the atomic displacements within the crystal. This task is achieved by analyzing the diffraction-order dependence of the damage profiles. We thereby demonstrate that atomic displacements undergo Lévy flights, with a displacement PDF exhibiting heavy tails [with a tail index in the γ=0.73-0.37 range, i.e., far from the commonly assumed Gaussian case (γ=2)]. It is further demonstrated that these heavy tails are crucial to account for the amorphization kinetics in SiC. From the retrieved displacement PDFs we introduce a dimensionless parameter f_{D}^{XRD} to quantify the disordering. f_{D}^{XRD} is found to be consistent with both independent measurements using ion channeling and with molecular dynamics calculations.

Statistical Nature of Atomic Disorder in Irradiated Crystals

NASA Astrophysics Data System (ADS)

Boulle, A.; Debelle, A.

2016-06-01

Atomic disorder in irradiated materials is investigated by means of x-ray diffraction, using cubic SiC single crystals as a model material. It is shown that, besides the determination of depth-resolved strain and damage profiles, x-ray diffraction can be efficiently used to determine the probability density function (PDF) of the atomic displacements within the crystal. This task is achieved by analyzing the diffraction-order dependence of the damage profiles. We thereby demonstrate that atomic displacements undergo Lévy flights, with a displacement PDF exhibiting heavy tails [with a tail index in the γ =0.73 - 0.37 range, i.e., far from the commonly assumed Gaussian case (γ =2 )]. It is further demonstrated that these heavy tails are crucial to account for the amorphization kinetics in SiC. From the retrieved displacement PDFs we introduce a dimensionless parameter fDXRD to quantify the disordering. fDXRD is found to be consistent with both independent measurements using ion channeling and with molecular dynamics calculations.

First evidence of non-locality in real band-gap metamaterials: determining parameters in the relaxed micromorphic model

PubMed Central

Barbagallo, Gabriele; d’Agostino, Marco Valerio; Placidi, Luca; Neff, Patrizio

2016-01-01

In this paper, we propose the first estimate of some elastic parameters of the relaxed micromorphic model on the basis of real experiments of transmission of longitudinal plane waves across an interface separating a classical Cauchy material (steel plate) and a phononic crystal (steel plate with fluid-filled holes). A procedure is set up in order to identify the parameters of the relaxed micromorphic model by superimposing the experimentally based profile of the reflection coefficient (plotted as function of the wave-frequency) with the analogous profile obtained via numerical simulations. We determine five out of six constitutive parameters which are featured by the relaxed micromorphic model in the isotropic case, plus the determination of the micro-inertia parameter. The sixth elastic parameter, namely the Cosserat couple modulus μc, still remains undetermined, since experiments on transverse incident waves are not yet available. A fundamental result of this paper is the estimate of the non-locality intrinsically associated with the underlying microstructure of the metamaterial. We show that the characteristic length Lc measuring the non-locality of the phononic crystal is of the order of 13 of the diameter of its fluid-filled holes. PMID:27436984

First evidence of non-locality in real band-gap metamaterials: determining parameters in the relaxed micromorphic model.

PubMed

Madeo, Angela; Barbagallo, Gabriele; d'Agostino, Marco Valerio; Placidi, Luca; Neff, Patrizio

2016-06-01

In this paper, we propose the first estimate of some elastic parameters of the relaxed micromorphic model on the basis of real experiments of transmission of longitudinal plane waves across an interface separating a classical Cauchy material (steel plate) and a phononic crystal (steel plate with fluid-filled holes). A procedure is set up in order to identify the parameters of the relaxed micromorphic model by superimposing the experimentally based profile of the reflection coefficient (plotted as function of the wave-frequency) with the analogous profile obtained via numerical simulations. We determine five out of six constitutive parameters which are featured by the relaxed micromorphic model in the isotropic case, plus the determination of the micro-inertia parameter. The sixth elastic parameter, namely the Cosserat couple modulus μ c , still remains undetermined, since experiments on transverse incident waves are not yet available. A fundamental result of this paper is the estimate of the non-locality intrinsically associated with the underlying microstructure of the metamaterial. We show that the characteristic length L c measuring the non-locality of the phononic crystal is of the order of [Formula: see text] of the diameter of its fluid-filled holes.

Direct Writing of Three-Dimensional Macroporous Photonic Crystals on Pressure-Responsive Shape Memory Polymers.

PubMed

Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Wang, Bingchen; Basile, Vito; Taylor, Curtis; Jiang, Peng

2015-10-28

Here we report a single-step direct writing technology for making three-dimensional (3D) macroporous photonic crystal patterns on a new type of pressure-responsive shape memory polymer (SMP). This approach integrates two disparate fields that do not typically intersect: the well-established templating nanofabrication and shape memory materials. Periodic arrays of polymer macropores templated from self-assembled colloidal crystals are squeezed into disordered arrays in an unusual shape memory "cold" programming process. The recovery of the original macroporous photonic crystal lattices can be triggered by direct writing at ambient conditions using both macroscopic and nanoscopic tools, like a pencil or a nanoindenter. Interestingly, this shape memory disorder-order transition is reversible and the photonic crystal patterns can be erased and regenerated hundreds of times, promising the making of reconfigurable/rewritable nanooptical devices. Quantitative insights into the shape memory recovery of collapsed macropores induced by the lateral shear stresses in direct writing are gained through fundamental investigations on important process parameters, including the tip material, the critical pressure and writing speed for triggering the recovery of the deformed macropores, and the minimal feature size that can be directly written on the SMP membranes. Besides straightforward applications in photonic crystal devices, these smart mechanochromic SMPs that are sensitive to various mechanical stresses could render important technological applications ranging from chromogenic stress and impact sensors to rewritable high-density optical data storage media.

Polarization-dependent transverse-stress sensing characters of the gold-coated and liquid crystal filled photonic crystal fiber based on Surface Plasmon Resonance

NASA Astrophysics Data System (ADS)

Liu, Hai; Zhu, Chenghao; Wang, Yan; Tan, Ce; Li, Hongwei

2018-03-01

A transverse-stress sensor with enhanced sensitivity based on nematic liquid crystal (NLC) filled photonic crystal fiber (PCF) is proposed and analyzed by using the finite element method (FEM). The central hole of the PCF is infiltrated with NLC material with an adjustable rotation angle to achieve the polarization-dependent wavelength-selective sensing. And the combined use of side-hole structure and Surface Plasmon Resonance (SPR) technology enhanced the transverse-stress sensitivity enormously. Results reveal that the sensor can achieve a high sensitivity based on the polarization filter characteristic at special wavelengths. Besides that, the temperature and the transverse-stress in either direction can be effectively discriminated through dual-parameter demodulation method by adjusting the rotation angle of the NLC to introduce a new degree of freedom for sensing.

Application of the anisotropic phase-field crystal model to investigate the lattice systems of different anisotropic parameters and orientations

NASA Astrophysics Data System (ADS)

Kundin, Julia; Ajmal Choudhary, Muhammad

2017-07-01

In this article, we present the recent advances in the development of the anisotropic phase-field crystal (APFC) model. These advances are important in basic researches for multiferroic and thermoelectric materials with anisotropic crystal lattices and in thin-film applications. We start by providing a general description of the model derived in our previous studies based on the crystal symmetry and the microscopic dynamical density functional theory for anisotropic interactions and show that there exist only two possible degrees of freedom for the anisotropic lattices which are described by two independent parameters. New findings concerning the applications of the APFC model for the estimation of the elastic modules of anisotropic systems including sheared and stretched lattices as well as for the investigation of the heterogeneous thin film growth are described. The simulation results demonstrate the strong dependency of the misfit dislocation formation during the film growth on the anisotropy and reveal the asymmetric behavior in the cases of positive and negative misfits. We also present the development of the amplitude representation for the full APFC model of two orientation variants and show the relationship between the wave vectors and the base angles of the anisotropic lattices.

Phenomenological model of spin crossover in molecular crystals as derived from atom-atom potentials.

PubMed

Sinitskiy, Anton V; Tchougréeff, Andrei L; Dronskowski, Richard

2011-08-07

The method of atom-atom potentials, previously applied to the analysis of pure molecular crystals formed by either low-spin (LS) or high-spin (HS) forms (spin isomers) of Fe(II) coordination compounds (Sinitskiy et al., Phys. Chem. Chem. Phys., 2009, 11, 10983), is used to estimate the lattice enthalpies of mixed crystals containing different fractions of the spin isomers. The crystals under study were formed by LS and HS isomers of Fe(phen)(2)(NCS)(2) (phen = 1,10-phenanthroline), Fe(btz)(2)(NCS)(2) (btz = 5,5',6,6'-tetrahydro-4H,4'H-2,2'-bi-1,3-thiazine), and Fe(bpz)(2)(bipy) (bpz = dihydrobis(1-pyrazolil)borate, and bipy = 2,2'-bipyridine). For the first time the phenomenological parameters Γ pertinent to the Slichter-Drickamer model (SDM) of several materials were independently derived from the microscopic model of the crystals with use of atom-atom potentials of intermolecular interaction. The accuracy of the SDM was checked against the numerical data on the enthalpies of mixed crystals. Fair semiquantitative agreement with the experimental dependence of the HS fraction on temperature was achieved with use of these values. Prediction of trends in Γ values as a function of chemical composition and geometry of the crystals is possible with the proposed approach, which opens a way to rational design of spin crossover materials with desired properties. This journal is © the Owner Societies 2011

Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE

NASA Astrophysics Data System (ADS)

Cziczo, D. J.; Murphy, D. M.; Hudson, P. K.; Thomson, D. S.

2004-02-01

The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters, anvil cirrus formed about the Florida peninsula. A counter flow virtual impactor (CVI) was used to separate cirrus ice from the unactivated interstitial aerosol particles and evaporate condensed-phase water. Residual material, on a crystal-by-crystal basis, was subsequently analyzed using the NOAA Aeronomy Laboratory's Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Sampling was performed from 5 to 15 km altitude and from 12° to 28° north latitude within cirrus originating over land and ocean. Chemical composition measurements provided several important results. Sea salt was often incorporated into cirrus, consistent with homogeneous ice formation by aerosol particles from the marine boundary layer. Size measurements showed that large particles preferentially froze over smaller ones. Meteoritic material was found within ice crystals, indicative of a relation between stratospheric aerosol particles and tropospheric clouds. Mineral dust was the dominant residue observed in clouds formed during a dust transport event from the Sahara, consistent with a heterogeneous freezing mechanism. These results show that chemical composition and size are important determinants of which aerosol particles form cirrus ice crystals.

Steady-state hydrodynamic instabilities of active liquid crystals: hybrid lattice Boltzmann simulations.

PubMed

Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M

2007-09-01

We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.

Crystallographic orientation and electrode nature are key factors for electric current generation by Geobacter sulfurreducens.

PubMed

Maestro, Beatriz; Ortiz, Juan M; Schrott, Germán; Busalmen, Juan P; Climent, Víctor; Feliu, Juan M

2014-08-01

We have investigated the influence of electrode material and crystallographic structure on electron transfer and biofilm formation of Geobacter sulfurreducens. Single-crystal gold-Au(110), Au(111), Au(210)-and platinum-Pt(100), Pt(110), Pt(111), Pt(210)-electrodes were tested and compared to graphite rods. G. sulfurreducens electrochemically interacts with all these materials with different attachment kinetics and final current production, although redox species involved in the electron transfer to the anode are virtually the same in all cases. Initial bacterial colonization was fastest on graphite up to the monolayer level, whereas gold electrodes led to higher final current densities. Crystal geometry was shown to have an important influence, with Au(210) sustaining a current density of up to 1442±101μAcm(-2) at the steady state, over Au(111) with 961±94μAcm(-2) and Au(110) with 944±89μAcm(-2). On the other hand, the platinum electrodes displayed the lowest performances, including Pt(210). Our results indicate that both crystal geometry and electrode material are key parameters for the efficient interaction of bacteria with the substrate and should be considered for the design of novel materials and microbial devices to optimize energy production. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of Co-60 gamma radiation on optical, dielectric and mechanical properties of strontium L-ascorbate hexahydrate NLO crystal

NASA Astrophysics Data System (ADS)

Dileep, M. S.; Suresh Kumar, H. M.

2018-04-01

A potentially useful nonlinear optical semi-organic single crystal of strontium L-ascorbate hexahydrate (SLAH) was grown by solution growth slow evaporation technique at room temperature. The grown crystal is semi transparent, yellowish in color with monoclinic crystal system having space group P21 and is stable up to 198 °C. Further, SLAH crystals were irradiated with gamma rays produced by 60Co with different doses of 10 KGy, 30 KGy and 50 KGy at room temperature and then studied the effect of gamma-rays on dielectric properties, optical absorption, microhardness and SHG efficiency. The absorption study reveals that the absorbance of the grown crystal is appeared to be low throughout the visible region with a lower cutoff wavelength of 277 nm and these parameters are not affected upon gamma irradiation. The luminescence intensity of the crystal is also not affected by the irradiation. There is noticeable changes were observed in dielectric properties and hardness of the materials for different doses of gamma irradiation. The second harmonic generation (SHG) efficiency of the grown crystal is 0.54 times that of the KDP crystal and is decreased moderately by increasing the dosage of gamma irradiation.

Synthesis and NLO studies of novel (2E)-1-(2-bromo-4,5-dimethoxyphenyL)-3-(3-Bromo-4-Fluorophenyl)Prop-2-en-1-one single crystal

NASA Astrophysics Data System (ADS)

Shruthi, C.; Ravindrachary, V.; Prasad, D. Jagadeesh; Guruswamy, B.; Hegde, Shreedatta

2017-05-01

A novel organic nonlinear optical (NLO) material (2E)-1-(2-Bromo-4,5-Dimethoxyphenyl)-3-(3-Bromo-4-Fluorophenyl)Prop-2-en-1-one has been synthesized using Claisen-Schmidth condensation method. The chemical structure of the compound was confirmed by recording its FT-IR spectrum and the functional groups were identified. Single crystals were grown by slow evaporation method and the single crystal XRD study reveals that the compound crystallizes in the monoclinic crystal system with a space group -P 2yn. The observed cell parameters are a = 9.346(5) A°, b = 12.953(7) A°, c = 14.355(8) A°, α = 90°, β = 108.379°(9), γ = 90°. UV-Visible study shows that the compound is transparent in the entire visible region and the absorption takes place in the UV range. The Non linear optical efficiency of the crystal was estimated and it is found to be 0.5 times that of standard KDP crystal.

Nitrogen-Rich Energetic Metal-Organic Framework: Synthesis, Structure, Properties, and Thermal Behaviors of Pb(II) Complex Based on N,N-Bis(1H-tetrazole-5-yl)-Amine

PubMed Central

Liu, Qiangqiang; Jin, Bo; Zhang, Qingchun; Shang, Yu; Guo, Zhicheng; Tan, Bisheng; Peng, Rufang

2016-01-01

The focus of energetic materials is on searching for a high-energy, high-density, insensitive material. Previous investigations have shown that 3D energetic metal–organic frameworks (E-MOFs) have great potential and advantages in this field. A nitrogen-rich E-MOF, Pb(bta)·2H2O [N% = 31.98%, H2bta = N,N-Bis(1H-tetrazole-5-yl)-amine], was prepared through a one-step hydrothermal reaction in this study. Its crystal structure was determined through single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, and elemental analysis. The complex has high heat denotation (16.142 kJ·cm−3), high density (3.250 g·cm−3), and good thermostability (Tdec = 614.9 K, 5 K·min−1). The detonation pressure and velocity obtained through theoretical calculations were 43.47 GPa and 8.963 km·s−1, respectively. The sensitivity test showed that the complex is an impact-insensitive material (IS > 40 J). The thermal decomposition process and kinetic parameters of the complex were also investigated through thermogravimetry and differential scanning calorimetry. Non-isothermal kinetic parameters were calculated through the methods of Kissinger and Ozawa-Doyle. Results highlighted the nitrogen-rich MOF as a potential energetic material. PMID:28773805

Theoretical study of production of unique glasses in space. [kinetic relationships describing nucleation and crystallization phenomena

NASA Technical Reports Server (NTRS)

Larsen, D. C.; Sievert, J. L.

1975-01-01

The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.

Experimental Plan for Crystal Accumulation Studies in the WTP Melter Riser

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

Miller, D.; Fowley, M.

2015-04-28

This experimental plan defines crystal settling experiments to be in support of the U.S. Department of Energy – Office of River Protection crystal tolerant glass program. The road map for development of crystal-tolerant high level waste glasses recommends that fluid dynamic modeling be used to better understand the accumulation of crystals in the melter riser and mechanisms of removal. A full-scale version of the Hanford Waste Treatment and Immobilization Plant (WTP) melter riser constructed with transparent material will be used to provide data in support of model development. The system will also provide a platform to demonstrate mitigation or recoverymore » strategies in off-normal events where crystal accumulation impedes melter operation. Test conditions and material properties will be chosen to provide results over a variety of parameters, which can be used to guide validation experiments with the Research Scale Melter at the Pacific Northwest National Laboratory, and that will ultimately lead to the development of a process control strategy for the full scale WTP melter. The experiments described in this plan are divided into two phases. Bench scale tests will be used in Phase 1 (using the appropriate solid and fluid simulants to represent molten glass and spinel crystals) to verify the detection methods and analytical measurements prior to their use in a larger scale system. In Phase 2, a full scale, room temperature mockup of the WTP melter riser will be fabricated. The mockup will provide dynamic measurements of flow conditions, including resistance to pouring, as well as allow visual observation of crystal accumulation behavior.« less

A facile strategy to design zeolite L crystals with tunable morphology and surface architecture.

PubMed

Lupulescu, Alexandra I; Kumar, Manjesh; Rimer, Jeffrey D

2013-05-01

Tailoring the anisotropic growth rates of materials to achieve desired structural outcomes is a pervasive challenge in synthetic crystallization. Here we discuss a method to selectively control the growth of zeolite crystals, which are used extensively in a wide range of industrial applications. This facile method cooperatively tunes crystal properties, such as morphology and surface architecture, through the use of inexpensive, commercially available chemicals with specificity for binding to crystallographic surfaces and mediating anisotropic growth. We examined over 30 molecules as potential zeolite growth modifiers (ZGMs) of zeolite L (LTL type) crystallization. ZGM efficacy was quantified through a combination of macroscopic (bulk) and microscopic (surface) investigations that identified modifiers capable of dramatically altering the cylindrical morphology of LTL crystals. We demonstrate an ability to tailor properties critical to zeolite performance, such as external porous surface area, crystal shape, and pore length, which can enhance sorbate accessibility to LTL pores, tune the supramolecular organization of guest-host composites, and minimize the diffusion path length, respectively. We report that a synergistic combination of ZGMs and the judicious adjustment of synthesis parameters produce LTL crystals with unique surface features, and a range of length-to-diameter aspect ratios spanning 3 orders of magnitude. A systematic examination of different ZGM structures and molecular compositions (i.e., hydrophobicity and binding moieties) reveal interesting physicochemical properties governing their efficacy and specificity. Results of this study suggest this versatile strategy may prove applicable for a host of framework types to produce unrivaled materials that have eluded more conventional techniques.

Real-time Crystal Growth Visualization and Quantification by Energy-Resolved Neutron Imaging.

PubMed

Tremsin, Anton S; Perrodin, Didier; Losko, Adrian S; Vogel, Sven C; Bourke, Mark A M; Bizarri, Gregory A; Bourret, Edith D

2017-04-20

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of "blind" processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production. This technique is widely applicable and is not limited to crystal growth processes.

Real-time Crystal Growth Visualization and Quantification by Energy-Resolved Neutron Imaging

NASA Astrophysics Data System (ADS)

Tremsin, Anton S.; Perrodin, Didier; Losko, Adrian S.; Vogel, Sven C.; Bourke, Mark A. M.; Bizarri, Gregory A.; Bourret, Edith D.

2017-04-01

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of “blind” processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production. This technique is widely applicable and is not limited to crystal growth processes.

Geometrically distributed one-dimensional photonic crystals for light-reflection in all angles.

PubMed

Alagappan, G; Wu, P

2009-07-06

We demonstrate that a series of one-dimensional photonic crystals made of any dielectric materials, with the periods are distributed in a geometrical progression of a common ratio, r < rc (theta,P), where rc is a structural parameter that depends on the angle of incidence, theta, and polarization, P, is capable of blocking light of any spectral range. If an omni-directional reflection is desired for all polarizations and for all incident angles smaller than thetao, then r < rc (theta(o),p), where p is the polarization with the electric field parallel to the plane of incidence. We present simple and formula like expressions for rc, width of the bandgap, and minimum number of photonic crystals to achieve a perfect light reflection.

Real-time Crystal Growth Visualization and Quantification by Energy-Resolved Neutron Imaging

PubMed Central

Tremsin, Anton S.; Perrodin, Didier; Losko, Adrian S.; Vogel, Sven C.; Bourke, Mark A.M.; Bizarri, Gregory A.; Bourret, Edith D.

2017-01-01

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of “blind” processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production. This technique is widely applicable and is not limited to crystal growth processes. PMID:28425461

Optimization and characterization of bulk hexagonal boron nitride single crystals grown by the nickel-chromium flux method

NASA Astrophysics Data System (ADS)

Hoffman, Tim

Hexagonal boron nitride (hBN) is a wide bandgap III-V semiconductor that has seen new interest due to the development of other III-V LED devices and the advent of graphene and other 2-D materials. For device applications, high quality, low defect density materials are needed. Several applications for hBN crystals are being investigated, including as a neutron detector and interference-less infrared-absorbing material. Isotopically enriched crystals were utilized for enhanced propagation of phonon modes. These applications exploit the unique physical, electronic and nanophotonics applications for bulk hBN crystals. In this study, bulk hBN crystals were grown by the flux method using a molten Ni-Cr solvent at high temperatures (1500°C) and atmospheric pressures. The effects of growth parameters, source materials, and gas environment on the crystals size, morphology and purity were established and controlled, and the reliability of the process was greatly improved. Single-crystal domains exceeding 1mm in width and 200microm in thickness were produced and transferred to handle substrates for analysis. Grain size dependence with respect to dwell temperature, cooling rate and cooling temperature were analyzed and modeled using response surface morphology. Most significantly, crystal grain width was predicted to increase linearly with dwell temperature, with single-crystal domains exceeding 2mm in at 1700°C. Isotopically enriched 10B and 11B hBN crystal were produced using a Ni-Cr-B flux method, and their properties investigated. 10B concentration was evaluated using SIMS and correlated to the shift in the Raman peak of the E2g mode. Crystals with enrichment of 99% 10B and >99% 11B were achieved, with corresponding Raman shift peaks at 1392.0 cm-1 and 1356.6 cm-1, respectively. Peak FWHM also decreased as isotopic enrichment approached 100%, with widths as low as 3.5 cm-1 achieved, compared to 8.0 cm-1 for natural abundance samples. Defect selective etching was performed using a molten NaOH-KOH etchant at 425°C-525°C, to quantify the quality of the crystals. Three etch pit shapes were identified and etch pit width was investigated as a function of temperature. Etch pit density and etch pit activation energy was estimated at 5x107 cm-2 and 60 kJ/mol, respectively. Screw and mixed-type dislocations were identified using diffraction-contrast TEM imaging.

Synthesis, characterization, Hirshfeld surface analysis and antioxidant activity of a novel organic-inorganic hybrid material 1-methylpiperazine-1,4-diium bis(nitrate)

NASA Astrophysics Data System (ADS)

Gatfaoui, Sofian; Mezni, Ali; Roisnel, Thierry; Marouani, Houda

2017-07-01

The new inorganic-organic hybrid material 1-methylpiperazine-1,4-diium bis(nitrate) (MPN) have been synthesized and crystallized to the orthorhombic system with space group Pnma and the lattice parameters obtained are a = 10.9385(9) Å, b = 6.5698 Å (4), c = 13.7021(10) Å, V = 984.68(12) Å3 and Z = 4. The trigonal (NO3-) anions are connected to the 1-methylpiperazine-1,4-diium cations via a large number of bifurcated and non-bifurcated Nsbnd H⋯O and Csbnd H⋯O hydrogen bonds. The diprotonated piperazine ring adopts a chair conformation, with the methyl group occupying an equatorial position. Intermolecular interactions in the crystal structure were quantified by Hirshfeld surface analysis. Infrared spectrum confirms the existence of the functional groups in the elaborated material. Optical absorption reveals an important band gap energy indicating stability of the title compound. The DTA/TGA and DSC curves indicate that the crystal is thermally stable up to 180 °C. The antioxidant properties were determined via the DPPH radical scavenging, the ABTS radical scavenging, hydroxyl radical scavenging and ferric reducing power (FRP).

Explanation of the cw operation of the Er3+ 3-μm crystal laser

NASA Astrophysics Data System (ADS)

Pollnau, M.; Graf, Th.; Balmer, J. E.; Lüthy, W.; Weber, H. P.

1994-05-01

A computer simulation of the Er3+ 3-μm crystal laser considering the full rate-equation scheme up to the 4F7/2 level has been performed. The influence of the important system parameters on lasing and the interaction of these parameters has been clarified with multiple-parameter variations. Stimulated emission is fed mainly by up-conversion from the lower laser level and in many cases is reduced by the quenching of the lifetime of this level. However, also without up-conversion a set of parameters can be found that allows lasing. Up-conversion from the upper laser level is detrimental to stimulated emission but may be compensated by cross relaxation from the 4S3/2 level. For a typical experimental situation we started with the parameters of Er3+:LiYF4. In addition, the host materials Y3Al5O12 (YAG), YAlO3, Y3Sc2Al3O12 (YSGG), and BaY2F8, as well as the possibilities of codoping, are discussed. In view of the consideration of all excited levels up to 4F7/2, all lifetimes and branching ratios, ground-state depletion, excited-state absorption, three up-conversion processes as well as their inverse processes, stimulated emission, and a realistic resonator design, this is, to our knowledge, the most detailed investigation of the Er3+ 3-μm crystal laser performed so far.

Crystallization features of normal alkanes in confined geometry.

PubMed

Su, Yunlan; Liu, Guoming; Xie, Baoquan; Fu, Dongsheng; Wang, Dujin

2014-01-21

How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins. In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine-formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D) confining environment. We have studied multiple parameters of these microencapsulated n-alkanes, including surface freezing, metastability of the rotator phase, and the phase separation behaviors of n-alkane mixtures using differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD), and variable-temperature solid-state nuclear magnetic resonance (NMR). Our investigations revealed new direct evidence for the existence of surface freezing in microencapsulated n-alkanes. By examining the differences among chain packing and nucleation kinetics between bulk alkane solid solutions and their microencapsulated counterparts, we also discovered a mechanism responsible for the formation of a new metastable bulk phase. In addition, we found that confinement suppresses lamellar ordering and longitudinal diffusion, which play an important role in stabilizing the binary n-alkane solid solution in microcapsules. Our work also provided new insights into the phase separation of other mixed system, such as waxes, lipids, and polymer blends in confined geometry. These works provide a profound understanding of the relationship between molecular structure and material properties in the context of crystallization and therefore advance our ability to improve applications incorporating polymeric and molecular materials.

Multiple electrical phase transitions in Al substituted barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Kar, Manoranjan

2017-12-01

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12-xAlxO19, x = 0.0-4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution.

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

DOE PAGES

McGuire, Michael A.; Cao, Huibo; Chakoumakos, Bryan C.; ...

2014-11-18

Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature T SR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropymore » of the atomic displacement parameters for Bi with increasing temperature above T SR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.« less

The shear instability energy: a new parameter for materials design?

NASA Astrophysics Data System (ADS)

Kanani, M.; Hartmaier, A.; Janisch, R.

2017-10-01

Reliable and predictive relationships between fundamental microstructural material properties and observable macroscopic mechanical behaviour are needed for the successful design of new materials. In this study we establish a link between physical properties that are defined on the atomic level and the deformation mechanisms of slip planes and interfaces that govern the mechanical behaviour of a metallic material. To accomplish this, the shear instability energy Γ is introduced, which can be determined via quantum mechanical ab initio calculations or other atomistic methods. The concept is based on a multilayer generalised stacking fault energy calculation and can be applied to distinguish the different shear deformation mechanisms occurring at TiAl interfaces during finite-temperature molecular dynamics simulations. We use the new parameter Γ to construct a deformation mechanism map for different interfaces occurring in this intermetallic. Furthermore, Γ can be used to convert the results of ab initio density functional theory calculations into those obtained with an embedded atom method type potential for TiAl. We propose to include this new physical parameter into material databases to apply it for the design of materials and microstructures, which so far mainly relies on single-crystal values for the unstable and stable stacking fault energy.

The Property, Preparation and Application of Topological Insulators: A Review

PubMed Central

Tian, Wenchao; Shi, Jing; Wang, Yongkun

2017-01-01

Topological insulator (TI), a promising quantum and semiconductor material, has gapless surface state and narrow bulk band gap. Firstly, the properties, classifications and compounds of TI are introduced. Secondly, the preparation and doping of TI are assessed. Some results are listed. (1) Although various preparation methods are used to improve the crystal quality of the TI, it cannot reach the industrialization. Fermi level regulation still faces challenges; (2) The carrier type and lattice of TI are affected by non-magnetic impurities. The most promising property is the superconductivity at low temperature; (3) Magnetic impurities can destroy the time-reversal symmetry of the TI surface, which opens the band gap on the TI surface resulting in some novel physical effects such as quantum anomalous Hall effect (QAHE). Thirdly, this paper summarizes various applications of TI including photodetector, magnetic device, field-effect transistor (FET), laser, and so on. Furthermore, many of their parameters are compared based on TI and some common materials. It is found that TI-based devices exhibit excellent performance, but some parameters such as signal to noise ratio (S/N) are still lower than other materials. Finally, its advantages, challenges and future prospects are discussed. Overall, this paper provides an opportunity to improve crystal quality, doping regulation and application of TI. PMID:28773173

Spectroscopic characterisation of Er-doped LuVO4 single crystals

NASA Astrophysics Data System (ADS)

Lisiecki, R.; Dominiak-Dzik, G.; Solarz, P.; Strzęp, A.; Ryba-Romanowski, W.; Łukasiewicz, T.

2010-12-01

The LuVO4:Er single crystals were grown by the Czochralski technique. The crystal-field split energy levels of Er3+ ion were derived experimentally employing absorption and emission spectra measured at T=10 K. The Judd-Ofelt phenomenological method was used to estimate intensity parameters, radiative lifetimes and branching ratios of luminescence. The excited state dynamics of the LuVO4:Er systems was investigated and experimental lifetimes of emitting levels were measured. The emission cross section of the 4I13/2→4I15/2 transition in the infrared was calculated by the Füchtbauer-Ladenburg method. The gain cross section, estimated for several inverse-population parameters, allowed us to evaluate a potential laser activity of the LuVO4:Er system at 1.6 μm. Also, the potential range of the optical pumping was assessed based on absorption spectra achieved at the room temperature. The optical losses related to the green up-converted emission, encountered under the 978 nm excitation between 300 and 670 K were indicated and discussed. Spectroscopic peculiarities of the Er3+-doped LuVO4 crystal were discussed in relation to optical properties of the YVO4:Er and GdVO4:Er crystals. Taking into account the high quantum efficiency of the 4I13/2 level, and satisfactory absorption and emission features, the LuVO4:Er crystal can be considered as a promising active material for laser operation near 1.6 μm.

Synthesis, purification and bulk crystal growth of radiation detector materials using melt growth technique

NASA Astrophysics Data System (ADS)

Surabhi, Raja Rahul Reddy

In the past decade, there has been new and increased usage of radiation-detection technologies for applications in homeland security, non-proliferation, and national defense. Most of these applications require a portable device with high gamma-ray energy resolution and detection efficiency, compact size, room-temperature operation, and low cost. Consequently, there is a renewed understanding of the material limitations for these technologies and a great demand to develop next-generation radiation-detection materials that can operate at room temperature. Mercuric iodide (HgI2), Lead iodide (PbI2), and CdZnTe (CZT) are the current leading candidates for radiation detector applications. This is because of their high atomic number and large band gap that makes them particularly well suited for fabrication of high resolution and high efficiency compact devices. PbI2 is a promising material for room temperature nuclear radiation detectors, characterized by its wide band gap (EG=2.32eV) and high-density (rho=6.2g/cm3). It has been reported that PbI2 crystal detectors are able to detect gamma-ray in the range of 1KeV-1MeV, with good energy resolution. However, PbI 2 detectors have not been studied in detail because of non-availability of high quality single crystals. This study presents the synthesis, purification, growth and characterization of PbI2 single crystals grown. In this research, solid-state synthesis technique has been utilized for obtaining PbI2 as a starting material. For the first time, a unique low-temperature purification technique has been developed to obtain high-purity starting material. The crystals were grown using 2-zone Bridgman-Stockbarger (B.S) technique wherein growth rate and temperature gradient at the solid-liquid interface were optimized. Single crystals of PbI2 were successfully grown in quartz glass ampoule under different growth conditions. Material purity was determined by measuring the elemental concentration using the Inductively coupled plasma-optical emission spectroscopy (ICP-OES). ICP-OES is utilized for estimating impurities present in the low-temperature purified material, zone refined material and melt grown PbI2 crystals. The zone-refined material contains no traceable amounts of impurities, whereas the low-temperature purified material and melt grown PbI2 crystals show very low concentration of K (potassium) and Na (sodium) impurities. Crystal characterization has been performed for determining optical properties by UV-VIS spectroscopy. The energy band gap (EG) is an important parameter for materials used for room temperature gamma-ray detector applications. The absorption peak at 530nm is a characteristic of PbI2 and corresponds to the onset of the transitions from the valence band to the exciton level. From this absorption spectrum the calculated indirect band gap of PbI 2 was 2.33+/-0.025 eV at room temperature. For measuring the electrical properties (Dielectric and I-V characteristics) of the crystal, Ag (silver) contacts are applied to both sides of the sample. Dielectric analysis on melt grown PbI2 showed that space charge polarization was dominant at lower frequencies but stabilizes at higher frequencies over different operating temperatures. On the other hand, dielectric analysis for zone-refined material space charge polarization was constant over the operating range resulting in fewer lattice defects. Therefore the low temperature purified material followed by zone-refined purification provides detector grade material with fewer lattice defects. The measured electrical resistivity for melt grown PbI2 and zone-refined material are 3.185 x 10 10 O-cm and 0.754 x 109 O-cm at room temperature along (001) plane respectively.

An ignored variable: solution preparation temperature in protein crystallization.

PubMed

Chen, Rui-Qing; Lu, Qin-Qin; Cheng, Qing-Di; Ao, Liang-Bo; Zhang, Chen-Yan; Hou, Hai; Liu, Yong-Ming; Li, Da-Wei; Yin, Da-Chuan

2015-01-19

Protein crystallization is affected by many parameters, among which certain parameters have not been well controlled. The temperature at which the protein and precipitant solutions are mixed (i.e., the ambient temperature during mixing) is such a parameter that is typically not well controlled and is often ignored. In this paper, we show that this temperature can influence protein crystallization. The experimental results showed that both higher and lower mixing temperatures can enhance the success of crystallization, which follows a parabolic curve with an increasing ambient temperature. This work illustrates that the crystallization solution preparation temperature is also an important parameter for protein crystallization. Uncontrolled or poorly controlled room temperature may yield poor reproducibility in protein crystallization.

NONLINEAR AND FIBER OPTICS: Conversion of pulsed laser radiation from the 9.3-9.6 μm range to the second harmonic in ZnGeP2 crystals

NASA Astrophysics Data System (ADS)

Andreev, Yu M.; Bykanov, A. N.; Gribenyukov, A. I.; Zuev, V. V.; Karyshev, V. D.; Kisletsov, A. V.; Kovalev, I. O.; Konov, Vitalii I.; Kuz'min, G. P.; Nesterenko, A. A.; Osorgin, A. E.; Starodumov, Yu M.; Chapliev, N. I.

1990-04-01

A pulsed TEA CO2 laser was used in an investigation of the influence of the pump radiation parameters (mode composition, wavelength, pulse duration), of the focusing conditions, of the properties of the material (absorption coefficient), and of the operating conditions (temperature) on the efficiency of conversion to the second harmonic and on the angular dependences of phase matching in ZnGeP2 crystals. The calculated results were found to be in good agreement with the experimental data.

On a simple molecular–statistical model of a liquid-crystal suspension of anisometric particles

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

Zakhlevnykh, A. N., E-mail: anz@psu.ru; Lubnin, M. S.; Petrov, D. A.

2016-11-15

A molecular–statistical mean-field theory is constructed for suspensions of anisometric particles in nematic liquid crystals (NLCs). The spherical approximation, well known in the physics of ferromagnetic materials, is considered that allows one to obtain an analytic expression for the free energy and simple equations for the orientational state of a suspension that describe the temperature dependence of the order parameters of the suspension components. The transition temperature from ordered to isotropic state and the jumps in the order parameters at the phase-transition point are studied as a function of the anchoring energy of dispersed particles to the matrix, the concentrationmore » of the impurity phase, and the size of particles. The proposed approach allows one to generalize the model to the case of biaxial ordering.« less

Efficient green luminescence of terbium oxalate crystals: A case study with Judd-Ofelt theory and single crystal structure analysis and the effect of dehydration on luminescence

NASA Astrophysics Data System (ADS)

Alexander, Dinu; Joy, Monu; Thomas, Kukku; Sisira, S.; Biju, P. R.; Unnikrishnan, N. V.; Sudarsanakumar, C.; Ittyachen, M. A.; Joseph, Cyriac

2018-06-01

Design and synthesis of Lanthanide based metal organic framework is a frontier area of research owing to their structural diversity enabling specific applications. The luminescence properties of rare earths, tuned by the structural features of Ln-MOFs are investigated extensively. Rare earth oxalates which can be synthesized in a facile method, ensuring the structural features of MOFs with excellent photoluminescence characteristics deserves much attention. This work is the first time report on the single crystal structure and Judd-Ofelt (JO) theoretical analysis - their correlation with the intense and sharp green luminescence of Terbium oxalate crystals. The intense green luminescence observed for Terbium oxalate crystals for a wide range of excitation from DUV to visible region despite the luminescence limiting factors are discussed. The absence of concentration quenching and lifting up of forbidden nature of f-f transitions, allowing direct excitation of Terbium ions is analysed with the help of JO theory and single crystal structure analysis. The JO analysis predicted the asymmetry of Terbium sites, allowing the electric dipole transitions and from the JO intensity parameters, promising spectroscopic parameters - emission cross section, branching ratio, gain band width and gain coefficient of the material were calculated. The single crystal structure analysis revealed the asymmetry of Tb sites and structure of Terbium oxalate is formed by the hydrogen bonded stacking of overlapped six Terbium membered rings connected by the oxalate ligands. The molecularly thick layers thus formed on the crystal surface are imaged by the atomic force microscopy. The presence of water channels in the structure and the effect of lattice water molecules on the luminescence intensity are also investigated.

Design and Growth of Novel Compounds for Radiation Sensors: Multinary Chalcogenides

NASA Technical Reports Server (NTRS)

Singh, N. B.; Su, Ching-Hua; Nagaradona, Teja; Arnold, Brad; Choa, Fow-Sen

2016-01-01

Increasing threats of radiological weapons have revitalized the researches for low cost large volume ?-ray and neutron ray sensors In the past few years we have designed and grown ternary and quaternary lead and thallium chalcogenides and lead selenoiodides for detectors to meet these challenges. These materials are congruent, can be tailored to enhance the parameters required for radiation sensors. In addition, this class of compounds can be grown by Bridgman method which promises for large volume productions. We have single crystals of several compounds from the melt including Tl3AsSe3, Tl3AsSe3-xSx, TlGaSe2, AgGaGe3Se8, AgxLi1-xAgGaGe3Se8 and PbTlI5-x Sex compounds. Experimental studies indicate that these have very low absorption coefficient, low defect density and can be fabricated in any shape and sizes. These crystals do not require post growth annealing and do not show any second phase precipitates when processed for electrode bonding and other fabrication steps. In this paper we report purification, growth and fabrication of large Tl3AsSe3 (TAS) crystals. We observed that TAS crystals grown by using further purification of as supplied high purity source materials followed by directionally solidified charge showed higher resistivity than previously reported values. TAS also showed constant value as the function of voltage. A low thermal gradient and high purity source material were used to reduce thermal stresses in large crystals. By improving the purification of the as supplied source materials very high quality thallium, selenium and arsenic was achieved for preparing stoichiometric Tl3AsSe3 compound. Low gradient (<20K/cm) and slow growth rate (1-2 cm/day) produced crystals with reduced stress. Crystals did not show any micro cracking during fabrication of crystals grown with high purity and at low thermal gradient. Since thallium is a major component and very sensitive to surface oxidation, removal of surface and bulk oxides is very important. Intentional increase in the growth rate from 1cm/day to higher speed (>5cm/day) showed very different morphologies on the surface of the crystals. Electrical resistivity was one order of magnitude higher than previously reported value and it was observed to be constant as the function of frequency.

Time-evolution of grain size distributions in random nucleation and growth crystallization processes

NASA Astrophysics Data System (ADS)

Teran, Anthony V.; Bill, Andreas; Bergmann, Ralf B.

2010-02-01

We study the time dependence of the grain size distribution N(r,t) during crystallization of a d -dimensional solid. A partial differential equation, including a source term for nuclei and a growth law for grains, is solved analytically for any dimension d . We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates, the distribution evolves in time into the logarithmic-normal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.

Characterization of Strain Due to Nitrogen Doping Concentration Variations in Heavy Doped 4H-SiC

NASA Astrophysics Data System (ADS)

Yang, Yu; Guo, Jianqiu; Raghothamachar, Balaji; Chan, Xiaojun; Kim, Taejin; Dudley, Michael

2018-02-01

Highly doped 4H-SiC will show a significant lattice parameter difference with respect to the undoped material. We have applied the recently developed monochromatic contour mapping technique for 4H-SiC crystals to a 4H-SiC wafer crystal characterized by nitrogen doping concentration variation across the whole sample surface using a synchrotron monochromatic x-ray beam. Strain maps of 0008 and - 2203 planes were derived by deconvoluting the lattice parameter variations from the lattice tilt. Analysis reveals markedly different strain values within and out of the basal plane indicating the strain induced by nitrogen doping is anisotropic in the 4H-SiC hexagonal crystal structure. The highest strain calculated along growth direction [0001] and along [1-100] on the closed packed basal plane is up to - 4 × 10-4 and - 2.7 × 10-3, respectively. Using an anisotropic elasticity model by separating the whole bulk crystal into numerous identical rectangular prism units, the measured strain was related to the doping concentration and the calculated highest nitrogen level inside wafer crystal was determined to be 1.5 × 1020 cm-3. This is in agreement with observation of double Shockley stacking faults in the highly doped region that are predicted to nucleate at nitrogen levels above 2 × 1019 cm-3.

Tailoring of the partial magnonic gap in three-dimensional magnetoferritin-based magnonic crystals

NASA Astrophysics Data System (ADS)

Mamica, S.

2013-07-01

We investigate theoretically the use of magnetoferritin nanoparticles, self-assembled in the protein crystallization process, as the basis for the realization of 3D magnonic crystals in which the interparticle space is filled with a ferromagnetic material. Using the plane wave method we study the dependence of the width of the partial band gap and its central frequency on the total magnetic moment of the magnetoferritin core and the lattice constant of the magnetoferritin crystal. We show that by adjusting the combination of these two parameters the partial gap can be tailored in a wide frequency range and shifted to sub-terahertz frequencies. Moreover, the difference in the width of the partial gap for spin waves propagating in planes parallel and perpendicular to the external field allows for switching on and off the partial magnonic gap by changing the direction of the applied field.

Modeling a photoinduced planar-to-homeotropic anchoring transition triggered by surface azobenzene units in a nematic liquid crystal

NASA Astrophysics Data System (ADS)

Oswald, Patrick; Ignés-Mullol, Jordi

2017-09-01

The performance of light-controlled liquid crystal anchoring surfaces depends on the nature of the photosensitive moieties and on the concentration of spacer units. Here, we study the kinetics of photosensitive liquid crystal cells that incorporate an azobenzene-based self-assembled monolayer. We characterize the photoinduced homeotropic-to-planar transition and the subsequent reverse relaxation in terms of the underlying isomerization of the photosensitive layer. We show that the response time can be precisely adjusted by tuning the lateral packing of azobenzene units by means of inert spacer molecules. Using simple kinetic assumptions and a well-known model for the energetics of liquid crystal anchoring we are able to capture the details of the optical microscopy experimental observations. Our analysis provides fitted values for all the relevant material parameters, including the zenithal and the azimuthal anchoring strength.

Growth and optical properties of Dy:Y3Al5O12 crystal

NASA Astrophysics Data System (ADS)

Pan, Yuxin; Zhou, Shidong; Li, Dongzhen; Liu, Bin; Song, Qingsong; Liu, Jian; Liu, Peng; Ding, Yuchong; Wang, Xiaodan; Xu, Xiaodong; Xu, Jun

2018-02-01

High optical quality Dy:Y3Al5O12 (Dy:YAG) crystal has been grown by the Czochralski method. Absorption spectra, fluorescence spectra and fluorescence decay curve of Dy:YAG have been recorded at room temperature. The strongest emission of Dy:YAG crystal is near 583 nm, corresponding to the 4F9/2 → 6H13/2 transition. The Judd-Ofelt parameters Ω2, Ω4 and Ω6 were calculated to be 1.49 × 10-20 cm2, 0.94 × 10-20 cm2 and 3.20 × 10-20 cm2, respectively. The radiative transition rates, branching ratios and the emission cross sections were calculated. The fluorescence and radiative lifetimes are 0.40 ms and 1.02 ms, respectively, resulting in a quantum efficiency of 39.2%. The results indicate that the Dy:YAG crystal would be a promising yellow solid state laser material.

Protein crystal growth in low gravity

NASA Technical Reports Server (NTRS)

Feigelson, Robert S.

1987-01-01

The solubility and growth mechanism of canavalin were studied, and the applicability of the Schlieren technique to protein crystal growth was investigated. Canavalin which may be crystallized from a basic solution by the addition of hydrogen (H+) ions was shown to have normal solubility characteristics over the range of temperatures (5 to 25 C) and pH (5 to 7.5) studied. The solubility data combined with growth rate data gathered from the seeded growth of canavalin crystals indicated that the growth mechanism at high supersaturation ratios (>1.28) is screw dislocation like. A Schlieren apparatus was constructed and flow patterns were observed in Rochelle salt (sodium potassium tartrate), lysozyme, and canavalin. The critical parameters were identified as the change in density with concentration (dp/dc) and the change in index of refraction with concentration (dn/dc). Some of these values were measured for the materials listed.

Computational research on lithium ion battery materials

NASA Astrophysics Data System (ADS)

Tang, Ping

Crystals of LiFePO4 and related materials have recently received a lot of attention due to their very promising use as cathodes in rechargeable lithium ion batteries. This thesis studied the electronic structures of FePO 4 and LiMPO4, where M=Mn, Fe, Co and Ni within the framework of density-functional theory. The first study compared the electronic structures of the LiMPO 4 and FePO4 materials in their electrochemically active olivine form, using the LAPW (linear augmented plane wave) method [1]. A comparison of results for various spin configurations suggested that the ferromagnetic configuration can serve as a useful approximation for studying general features of these systems. The partial densities of states for the LiMPO4 materials are remarkably similar to each other, showing the transition metal 3d states forming narrow bands above the O 2p band. By contrast, in absence of Li, the majority spin transition metal 3d states are well-hybridized with the O 2p band in FePO4. The second study compared the electronic structures of FePO4 in several crystal structures including an olivine, monoclinic, quartz-like, and CrVO4-like form [2,3]. For this work, in addition to the LAPW method, PAW (Projector Augmented Wave) [4], and PWscf (plane-wave pseudopotential) [5] methods were used. By carefully adjusting the computational parameters, very similar results were achieved for the three independent computational methods. Results for the relative stability of the four crystal structures are reported. In addition, partial densities of state analyses show qualitative information about the crystal field splittings and bond hybridizations and help rationalize the understanding of the electrochemical and stability properties of these materials.

Correlation of materials properties with the atomic density concept

NASA Technical Reports Server (NTRS)

1975-01-01

Based on the hypothesis that the number of atoms per unit volume, accurately calculable for any substance of known real density and chemical composition, various characterizing parameters (energy levels of electrons interacting among atoms of the same or different kinds, atomic mass, bond intensity) were chosen for study. A multiple exponential equation was derived to express the relationship. Various properties were examined, and correlated with the various parameters. Some of the properties considered were: (1) heat of atomization, (2) boiling point, (3) melting point, (4) shear elastic modulus of cubic crystals, (5) thermal conductivity, and (6) refractive index for transparent substances. The solid elements and alkali halides were the materials studied. It is concluded that the number of different properties can quantitively be described by a common group of parameters for the solid elements, and a wide variety of compounds.

Stochastic Multiscale Modeling of Polycrystalline Materials

DTIC Science & Technology

2013-01-01

The single-grid strategy is adopted. The crystal visco-plastic constitutive model proposed in [7] along with a Voce type hardening model described...in [97] is used with γ̇0 = 1s−1 and m = 0.1. The parameters in the Voce type hardening law are selected according to [97]: κ0 = 47.0MPa, κ1 = 86.0MPa

Generalized Finsler geometric continuum physics with applications in fracture and phase transformations

NASA Astrophysics Data System (ADS)

Clayton, J. D.

2017-02-01

A theory of deformation of continuous media based on concepts from Finsler differential geometry is presented. The general theory accounts for finite deformations, nonlinear elasticity, and changes in internal state of the material, the latter represented by elements of a state vector of generalized Finsler space whose entries consist of one or more order parameter(s). Two descriptive representations of the deformation gradient are considered. The first invokes an additive decomposition and is applied to problems involving localized inelastic deformation mechanisms such as fracture. The second invokes a multiplicative decomposition and is applied to problems involving distributed deformation mechanisms such as phase transformations or twinning. Appropriate free energy functions are posited for each case, and Euler-Lagrange equations of equilibrium are derived. Solutions are obtained for specific problems of tensile fracture of an elastic cylinder and for amorphization of a crystal under spherical and uniaxial compression. The Finsler-based approach is demonstrated to be more general and potentially more physically descriptive than existing hyperelasticity models couched in Riemannian geometry or Euclidean space, without incorporation of supplementary ad hoc equations or spurious fitting parameters. Predictions for single crystals of boron carbide ceramic agree qualitatively, and in many instances quantitatively, with results from physical experiments and atomic simulations involving structural collapse and failure of the crystal along its c-axis.

An ignored variable: solution preparation temperature in protein crystallization

PubMed Central

Chen, Rui-Qing; Lu, Qin-Qin; Cheng, Qing-Di; Ao, Liang-Bo; Zhang, Chen-Yan; Hou, Hai; Liu, Yong-Ming; Li, Da-Wei; Yin, Da-Chuan

2015-01-01

Protein crystallization is affected by many parameters, among which certain parameters have not been well controlled. The temperature at which the protein and precipitant solutions are mixed (i.e., the ambient temperature during mixing) is such a parameter that is typically not well controlled and is often ignored. In this paper, we show that this temperature can influence protein crystallization. The experimental results showed that both higher and lower mixing temperatures can enhance the success of crystallization, which follows a parabolic curve with an increasing ambient temperature. This work illustrates that the crystallization solution preparation temperature is also an important parameter for protein crystallization. Uncontrolled or poorly controlled room temperature may yield poor reproducibility in protein crystallization. PMID:25597864

Quantitative Phase Analysis of Plasma-Treated High-Silica Materials

NASA Astrophysics Data System (ADS)

Kosmachev, P. V.; Abzaev, Yu. A.; Vlasov, V. A.

2018-06-01

The paper presents the X-ray diffraction (XRD) analysis of the crystal structure of SiO2 in two modifications, namely quartzite and quartz sand before and after plasma treatment. Plasma treatment enables the raw material to melt and evaporate after which the material quenches and condenses to form nanoparticles. The Rietveld refinement method is used to identify the lattice parameters of SiO2 phases. It is found that after plasma treatment SiO2 oxides are in the amorphous state, which are modeled within the microcanonical ensemble. Experiments show that amorphous phases are stable, and model X-ray reflection intensities approximate the experimental XRD patterns with fine precision. Within the modeling, full information is obtained for SiO2 crystalline and amorphous phases, which includes atom arrangement, structural parameters, atomic population of silicon and oxygen atoms in lattice sites.

Synthesis, growth, structural characterization, Hirshfeld analysis and nonlinear optical studies of a methyl substituted chalcone

NASA Astrophysics Data System (ADS)

Prabhu, Shobha R.; Jayarama, A.; Chandrasekharan, K.; Upadhyaya, V.; Ng, Seik Weng

2017-05-01

A new chalcone compound (2E)-3-(3-methylphenyl)-1-(4-nitrophenyl)prop-2-en-1-one (3MPNP) with molecular formula C16H13NO3 has been synthesized and crystallized by slow solvent evaporation technique. The Fourier transform infrared, Fourier transform Raman and nuclear magnetic resonance techniques were used for structural characterization. UV-visible absorption studies were carried out to study the transparency of the crystal in the visible region. Differential scanning calorimetry study shows thermal stability of crystals up to temperature 122 °C. Single crystal X-ray diffraction and powder X-ray diffraction techniques were used to study crystal structure and cell parameters. The Hirshfeld surface and 2-D fingerprint analysis were performed to study the nature of interactions and their quantitative contributions towards the crystal packing. The third order non-linear optical properties have been studied using single beam Z-scan technique and the results show that the material is a potential candidate for optical device applications such as optical limiters and optical switches.

Growth, structural, thermal, dielectric and nonlinear optical properties of potassium hexachloro cadmate (IV) a novel single crystal

NASA Astrophysics Data System (ADS)

Umarani, P.; Jagannathan, K.

2018-02-01

The Potassium hexachloro cadmate (IV) (PHC) single crystal was grown from the aqueous of the solution by a controlled evaporation method. Single crystal XRD solved the structure. FTIR is used to identify the functional groups of grown crystal. The UV-Vis-NIR spectrometer was used to find out the UV cut off region and to calculate the optical band gap of the Potassium hexachloro cadmate (IV) single crystal. The EDAX spectrum has been used to identify the compounds present in title compound. The TG-DTA profile shows the thermal stability of the grown crystal of Potassium hexachloro cadmate (IV). The Vicker's hardness measurement was used to calculate the material hardness of the title compound. The dielectric loss and constant varied with frequencies and activation energy is also calculated. The solid state parameters like plasma energy, Penn gap, Fermi energy, electronic polarizability using Penn analysis and Clausius-Mossotti equation were also calculated for the title compound. The Z-scan technique is used to calculate the third order nonlinear susceptibility of a real and imaginary part.

Point defect disorder in high-temperature solution grown Sr6Tb0.94Fe1.06(BO3)6 single crystals

NASA Astrophysics Data System (ADS)

Velázquez, M.; Péchev, S.; Duttine, M.; Wattiaux, A.; Labrugère, C.; Veber, Ph.; Buffière, S.; Denux, D.

2018-08-01

New Sr6Tb0.94Fe1.06(BO3)6 single crystals were obtained from lithium borate high-temperature solution growth under controlled atmosphere. Their average crystal structure was found to adopt the trigonal R-3 space group with lattice parameters a = 12.2164 Å and c = 9.1934 Å. A combined multiscale characterization approach, involving diffuse reflectance, X-ray photoelectron (XPS) and Mössbauer spectroscopies, was undertaken to establish the exact nature of the point defect disorder in this crystal structure. The FeTb× antisite disorder in the Sr6Tb0.94Fe1.06(BO3)6 single crystals is different from the kind of point defect disorder known to exist in the powder phase material counterpart. The absence of Tb4+ cations in the crystal lattice was established by XPS, and that of any phase transition down to 4 K was checked by specific heat measurements. The magnetic susceptibility curve was found to follow a Curie-Weiss behaviour in the 4-354 K temperature range.

Determining Kinetic Parameters for Isothermal Crystallization of Glasses

NASA Technical Reports Server (NTRS)

Ray, C. S.; Zhang, T.; Reis, S. T.; Brow, R. K.

2006-01-01

Non-isothermal crystallization techniques are frequently used to determine the kinetic parameters for crystallization in glasses. These techniques are experimentally simple and quick compared to the isothermal techniques. However, the analytical models used for non-isothermal data analysis, originally developed for describing isothermal transformation kinetics, are fundamentally flawed. The present paper describes a technique for determining the kinetic parameters for isothermal crystallization in glasses, which eliminates most of the common problems that generally make the studies of isothermal crystallization laborious and time consuming. In this technique, the volume fraction of glass that is crystallized as a function of time during an isothermal hold was determined using differential thermal analysis (DTA). The crystallization parameters for the lithium-disilicate (Li2O.2SiO2) model glass were first determined and compared to the same parameters determined by other techniques to establish the accuracy and usefulness of the present technique. This technique was then used to describe the crystallization kinetics of a complex Ca-Sr-Zn-silicate glass developed for sealing solid oxide fuel cells.

Nanosecond liquid crystalline optical modulator

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

Borshch, Volodymyr; Shiyanovskii, Sergij V.; Lavrentovich, Oleg D.

2016-07-26

An optical modulator includes a liquid crystal cell containing liquid crystal material having liquid crystal molecules oriented along a quiescent director direction in the unbiased state, and a voltage source configured to apply an electric field to the liquid crystal material wherein the direction of the applied electric field does not cause the quiescent director direction to change. An optical source is arranged to transmit light through or reflect light off the liquid crystal cell with the light passing through the liquid crystal material at an angle effective to undergo phase retardation in response to the voltage source applying themore » electric field. The liquid crystal material may have negative dielectric anisotropy, and the voltage source configured to apply an electric field to the liquid crystal material whose electric field vector is transverse to the quiescent director direction. Alternatively, the liquid crystal material may have positive dielectric anisotropy and the voltage source configured to apply an electric field to the liquid crystal material whose electric field vector is parallel with the quiescent director direction.« less

Role of Polymorphism and Thin-Film Morphology in Organic Semiconductors Processed by Solution Shearing

PubMed Central

2018-01-01

Organic semiconductors (OSCs) are promising materials for cost-effective production of electronic devices because they can be processed from solution employing high-throughput techniques. However, small-molecule OSCs are prone to structural modifications because of the presence of weak van der Waals intermolecular interactions. Hence, controlling the crystallization in these materials is pivotal to achieve high device reproducibility. In this perspective article, we focus on controlling polymorphism and morphology in small-molecule organic semiconducting thin films deposited by solution-shearing techniques compatible with roll-to-roll systems. Special attention is paid to the influence that the different experimental deposition parameters can have on thin films. Further, the main characterization techniques for thin-film structures are reviewed, highlighting the in situ characterization tools that can provide crucial insights into the crystallization mechanisms. PMID:29503976

Layered water in crystal interfaces as source for bone viscoelasticity: arguments from a multiscale approach

PubMed Central

Eberhardsteiner, Lukas; Hellmich, Christian; Scheiner, Stefan

2012-01-01

Extracellular bone material can be characterised as a nanocomposite where, in a liquid environment, nanometre-sized hydroxyapatite crystals precipitate within as well as between long fibre-like collagen fibrils (with diameters in the 100 nm range), as evidenced from neutron diffraction and transmission electron microscopy. Accordingly, these crystals are referred to as ‘interfibrillar mineral’ and ‘extrafibrillar mineral’, respectively. From a topological viewpoint, it is probable that the mineralisations start on the surfaces of the collagen fibrils (‘mineral-encrusted fibrils’), from where the crystals grow both into the fibril and into the extrafibrillar space. Since the mineral concentration depends on the pore spaces within the fibrils and between the fibrils (there is more space between them), the majority of the crystals (but clearly not all of them) typically lie in the extrafibrillar space. There, larger crystal agglomerations or clusters, spanning tens to hundreds of nanometers, develop in the course of mineralisation, and the micromechanics community has identified the pivotal role, which this extrafibrillar mineral plays for tissue elasticity. In such extrafibrillar crystal agglomerates, single crystals are stuck together, their surfaces being covered with very thin water layers. Recently, the latter have caught our interest regarding strength properties (Fritsch et al. 2009 J Theor Biol. 260(2): 230–252) – we have identified these water layers as weak interfaces in the extrafibrillar mineral of bone. Rate-independent gliding effects of crystals along the aforementioned interfaces, once an elastic threshold is surpassed, can be related to overall elastoplastic material behaviour of the hierarchical material ‘bone’. Extending this idea, the present paper is devoted to viscous gliding along these interfaces, expressing itself, at the macroscale, in the well-known experimentally evidenced phenomenon of bone viscoelasticity. In this context, a multiscale homogenisation scheme is extended to viscoelasticity, mineral-cluster-specific creep parameters are identified from three-point bending tests on hydrated bone samples, and the model is validated by statistically and physically independent experiments on partially dried samples. We expect this model to be relevant when it comes to prediction of time-dependent phenomena, e.g. in the context of bone remodelling. PMID:22563708

Layered water in crystal interfaces as source for bone viscoelasticity: arguments from a multiscale approach.

PubMed

Eberhardsteiner, Lukas; Hellmich, Christian; Scheiner, Stefan

2014-01-01

Extracellular bone material can be characterised as a nanocomposite where, in a liquid environment, nanometre-sized hydroxyapatite crystals precipitate within as well as between long fibre-like collagen fibrils (with diameters in the 100 nm range), as evidenced from neutron diffraction and transmission electron microscopy. Accordingly, these crystals are referred to as 'interfibrillar mineral' and 'extrafibrillar mineral', respectively. From a topological viewpoint, it is probable that the mineralisations start on the surfaces of the collagen fibrils ('mineral-encrusted fibrils'), from where the crystals grow both into the fibril and into the extrafibrillar space. Since the mineral concentration depends on the pore spaces within the fibrils and between the fibrils (there is more space between them), the majority of the crystals (but clearly not all of them) typically lie in the extrafibrillar space. There, larger crystal agglomerations or clusters, spanning tens to hundreds of nanometers, develop in the course of mineralisation, and the micromechanics community has identified the pivotal role, which this extrafibrillar mineral plays for tissue elasticity. In such extrafibrillar crystal agglomerates, single crystals are stuck together, their surfaces being covered with very thin water layers. Recently, the latter have caught our interest regarding strength properties (Fritsch et al. 2009 J Theor Biol. 260(2): 230-252) - we have identified these water layers as weak interfaces in the extrafibrillar mineral of bone. Rate-independent gliding effects of crystals along the aforementioned interfaces, once an elastic threshold is surpassed, can be related to overall elastoplastic material behaviour of the hierarchical material 'bone'. Extending this idea, the present paper is devoted to viscous gliding along these interfaces, expressing itself, at the macroscale, in the well-known experimentally evidenced phenomenon of bone viscoelasticity. In this context, a multiscale homogenisation scheme is extended to viscoelasticity, mineral-cluster-specific creep parameters are identified from three-point bending tests on hydrated bone samples, and the model is validated by statistically and physically independent experiments on partially dried samples. We expect this model to be relevant when it comes to prediction of time-dependent phenomena, e.g. in the context of bone remodelling.

Synthesis, crystal structure, vibrational spectroscopy, optical properties and theoretical studies of a new organic-inorganic hybrid material: [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2.

PubMed

Ben Ahmed, A; Feki, H; Abid, Y

2014-12-10

A new organic-inorganic hybrid material, [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2, has been synthesized and characterized by X-ray diffraction, FT-IR, Raman spectroscopy and UV-Visible absorption. The studied compound crystallizes in the triclinic system, space group P1¯ with the following parameters: a=8.4749(6)(Å), b=17.1392(12)(Å), c=17.1392(12)(Å), α=117.339(0)°, β=99.487(0)°, γ=99.487(0)° and Z=2. The crystal lattice is composed of a two discrete (BiBr6)(3-) anions surrounded by six ((CH3)2NH2)(+) cations. Complex hydrogen bonding interactions between (BiBr6)(3-) and organic cations from a three-dimensional network. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The full geometry optimization of designed system is performed using DFT method at B3LYP/LanL2DZ level of theory using the Gaussian03. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data obtained from FT-IR and Raman spectra are assigned based on the results of the theoretical calculations. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV-Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO-LUMO boundary. Copyright © 2014 Elsevier B.V. All rights reserved.

Method for acquiring, storing and analyzing crystal images

NASA Technical Reports Server (NTRS)

Gester, Thomas E. (Inventor); Rosenblum, William M. (Inventor); Christopher, Gayle K. (Inventor); Hamrick, David T. (Inventor); Delucas, Lawrence J. (Inventor); Tillotson, Brian (Inventor)

2003-01-01

A system utilizing a digital computer for acquiring, storing and evaluating crystal images. The system includes a video camera (12) which produces a digital output signal representative of a crystal specimen positioned within its focal window (16). The digitized output from the camera (12) is then stored on data storage media (32) together with other parameters inputted by a technician and relevant to the crystal specimen. Preferably, the digitized images are stored on removable media (32) while the parameters for different crystal specimens are maintained in a database (40) with indices to the digitized optical images on the other data storage media (32). Computer software is then utilized to identify not only the presence and number of crystals and the edges of the crystal specimens from the optical image, but to also rate the crystal specimens by various parameters, such as edge straightness, polygon formation, aspect ratio, surface clarity, crystal cracks and other defects or lack thereof, and other parameters relevant to the quality of the crystals.

Surface porosity and roughness of micrographite film for nucleation of hydroxyapatite.

PubMed

Asanithi, Piyapong

2014-08-01

Heterogeneous nucleation of hydroxyapatite (HAp) can be facilitated by physical and chemical properties of material surface. In this article, we reported how effective surface porosity and roughness are for inducing nucleation of HAp crystal in simulated body fluid. Two types of micrographite film (MGF) prepared from assembly of micrographite flakes were used as seeds to induce HAp crystal: uncompressed (high surface porosity) and compressed (low surface porosity) MGFs. Compressed MGF was prepared by applying mechanical compression to the uncompressed MGF. Uncompressed and compressed MGFs have similar surface wettability with the water contact angles (θ) of 113° and 107°, respectively. The number density of HAp crystals on the uncompressed MGF was higher than that of the compressed MGF by a factor of 6. This result implied that surface porosity and roughness were more effective parameters for inducing HAp crystal than surface wettability. Uncompressed MGF also induced HAp nucleation better than a cover glass although the glass had high wettability (θ = 64°). The effectiveness of uncompressed MGF on inducing HAp crystals was as high as that of the SiO2 -coated Si substrate. Our finding suggests that we do not require to functionalize material surface to be an effective seed; a surface with pores or roughness of the right scale is enough. © 2013 Wiley Periodicals, Inc.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE PAGES

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

2017-04-14

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

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

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Real-time Crystal Growth Visualization and Quantification by Energy-Resolved Neutron Imaging

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

Tremsin, Anton S.; Perrodin, Didier; Losko, Adrian S.

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of "blind" processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production.more » This technique is widely applicable and is not limited to crystal growth processes.« less

Microstructure-sensitive Crystal Viscoplasticity for Ni-base Superalloys Targeting Long-term Creep-Fatigue Interaction Modeling

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

Neu, Richard W.

The aim of this project is to develop a microstructure-sensitive crystal viscoplasticity (CVP) model for single-crystal Ni-base superalloys to model the behavior of the material and components in the hot gas path sections of industrial gas turbines (IGT). Microstructure degradation associated with aging critical to predicting long-term creep-fatigue interactions will be embedded into the model through the γ' precipitate morphology evolution by coupling the coarsening drivers and kinetics into the constitutive equations of the CVP model. Model parameters will be determined using new experimental protocols that involve systematically artificially aging the alloy under different stress conditions to determine the relationshipmore » between the size and morphology g' precipitates on the creep and thermomechanical fatigue response.« less

Microstructure-sensitive Crystal Viscoelasticity for Ni-base Superalloys Targeting Long-term Creep-Fatigue Interaction Modeling

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

Neu, Richard W

The aim of this project is to develop a microstructure-sensitive crystal viscoplasticity (CVP) model for single-crystal Ni-base superalloys to model the behavior of the material and components in the hot gas path sections of industrial gas turbines (IGT). Microstructure degradation associated with aging critical to predicting long-term creep-fatigue interactions will be embedded into the model through the γ' precipitate morphology evolution by coupling the coarsening drivers and kinetics into the constitutive equations of the CVP model. Model parameters will be determined using new experimental protocols that involve systematically artificially aging the alloy under different stress conditions to determine the relationshipmore » between the size and morphology g' precipitates on the creep and thermomechanical fatigue response.« less

Real-time Crystal Growth Visualization and Quantification by Energy-Resolved Neutron Imaging

DOE PAGES

Tremsin, Anton S.; Perrodin, Didier; Losko, Adrian S.; ...

2017-04-20

Energy-resolved neutron imaging is investigated as a real-time diagnostic tool for visualization and in-situ measurements of "blind" processes. This technique is demonstrated for the Bridgman-type crystal growth enabling remote and direct measurements of growth parameters crucial for process optimization. The location and shape of the interface between liquid and solid phases are monitored in real-time, concurrently with the measurement of elemental distribution within the growth volume and with the identification of structural features with a ~100 μm spatial resolution. Such diagnostics can substantially reduce the development time between exploratory small scale growth of new materials and their subsequent commercial production.more » This technique is widely applicable and is not limited to crystal growth processes.« less

Growth of 4-(dimethylamino) benzaldehyde doped triglycine sulphate single crystals and its characterization

NASA Astrophysics Data System (ADS)

Rai, Chitharanjan; Sreenivas, K.; Dharmaprakash, S. M.

2009-11-01

Single crystals of triglycine sulphate (TGS) doped with 1 mol% of 4-(dimethylamino) benzaldehyde (DB) have been grown from aqueous solution at ambient temperature by slow evaporation technique. The effect of dopant on the crystal growth and dielectric, pyroelectric and mechanical properties of TGS crystal have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters. FTIR spectra were employed to confirm the presence of 4-(dimethylamino) benzaldehyde in TGS crystal, qualitatively. The dielectric permittivity has been studied as a function of temperature by cooling the sample at a rate of 1 °C/min. An increase in the Curie temperature Tc=51 °C (for pure TGS, Tc=48.5 °C) and decrease in maximum permittivity has been observed for doped TGS when compared to pure TGS crystal. Pyroelectric studies on doped TGS were carried out to determine pyroelectric coefficient. The Vickers's hardness of the doped TGS crystals along (0 1 0) face is higher than that of pure TGS crystal for the same face. Domain patterns on b-cut plates were observed using scanning electron microscope. The low dielectric constant, higher pyroelectric coefficient and higher value of hardness suggest that doped TGS crystals could be a potential material for IR detectors.

Carbon Nanotubes Blended Hydroxyapatite Ethanol Sensor

NASA Astrophysics Data System (ADS)

Anjum, S. R.; Khairnar, R. S.

2016-12-01

Nano crystals of Hydroxyapatite (HAp) were synthesized by a wet chemical precipitation method. The nano composite materials were developed by doping various weight concentrations of carbon nanotubes in HAp, followed by characterization using scanning electron microscopy, and X-ray diffraction. Thick films of these materials were prepared by using screen printing technique. The ethanol sensing properties of these nano crystals and nano composite films were investigated by two probe electrical method. The gas sensing features such as operating temperature, response and recovery time, maximum gas detection limit, etc. were studied, since these parameters are of prime importance for sensor. The results revealed that at room temperature, the composite materials exhibited improved sensing performance towards 100 ppm ethanol with fast response times. It also showed shorter recovery time with higher vapor uptake capacity. The ethanol adsorption processes on doped and undoped substrates can be explained by surface chemical reactions as well as providing the possible adsorption models. The novelty of this work lies in developing reusable sensor substrates for room temperature sensing.

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.

Mechanisms of Photo-Induced Deformations of Liquid Crystal Elastomers

NASA Astrophysics Data System (ADS)

Dawson, Nathan; Kuzyk, Mark; Neal, Jeremy; Luchette, Paul; Palffy-Muhoray, Peter

2010-03-01

Over a century ago, Alexander Graham Bell invented the photophone, which he used to transmit mechanical information on a beam of light. We report on the use of an active Fabry-Perot interferometer to encode and detect mechanical information using the photomechanical effect of a liquid crystal elastomer (LCE) that is placed at a critical point between the reflectors. These are the first steps in the creation of ultra smart materials which require a large photomechanical response. Thus, understanding the underlying mechanisms is critical. Only limited studies of the mechanisms of the photomechanical effect, such as photo-isomerization, photo-reorientation and thermal effects have been studied in azo-dye-doped LCEs and in azo-dye-doped polymer fibers have been reported. The focus of our present work is to use the Fabry-Perot transducer geometry to study the underlying mechanisms and to determine the relevant material parameters that are used to develop theoretical models of the response. We use various intensity-modulated optical wave forms to determine the frequency response of the material, which are used to predict the material response.

Thermal deformation of cryogenically cooled silicon crystals under intense X-ray beams: measurement and finite-element predictions of the surface shape

PubMed Central

Zhang, Lin; Sánchez del Río, Manuel; Monaco, Giulio; Detlefs, Carsten; Roth, Thomas; Chumakov, Aleksandr I.; Glatzel, Pieter

2013-01-01

X-ray crystal monochromators exposed to white-beam X-rays in third-generation synchrotron light sources are subject to thermal deformations that must be minimized using an adequate cooling system. A new approach was used to measure the crystal shape profile and slope of several cryogenically cooled (liquid nitrogen) silicon monochromators as a function of beam power in situ and under heat load. The method utilizes multiple angular scans across the Bragg peak (rocking curve) at various vertical positions of a narrow-gap slit downstream from the monochromator. When increasing the beam power, the surface of the liquid-nitrogen-cooled silicon crystal deforms from a concave shape at low heat load to a convex shape at high heat load, passing through an approximately flat shape at intermediate heat load. Finite-element analysis is used to calculate the crystal thermal deformations. The simulated crystal profiles and slopes are in excellent agreement with experiments. The parameters used in simulations, such as material properties, absorbed power distribution on the crystal and cooling boundary conditions, are described in detail as they are fundamental for obtaining accurate results. PMID:23765298

Computerized Liquid Crystal Phase Identification by Neural Networks Analysis of Polarizing Microscopy Textures

NASA Astrophysics Data System (ADS)

Karaszi, Zoltan; Konya, Andrew; Dragan, Feodor; Jakli, Antal; CPIP/LCI; CS Dept. of Kent State University Collaboration

Polarizing optical microscopy (POM) is traditionally the best-established method of studying liquid crystals, and using POM started already with Otto Lehman in 1890. An expert, who is familiar with the science of optics of anisotropic materials and typical textures of liquid crystals, can identify phases with relatively large confidence. However, for unambiguous identification usually other expensive and time-consuming experiments are needed. Replacement of the subjective and qualitative human eye-based liquid crystal texture analysis with quantitative computerized image analysis technique started only recently and were used to enhance the detection of smooth phase transitions, determine order parameter and birefringence of specific liquid crystal phases. We investigate if the computer can recognize and name the phase where the texture was taken. To judge the potential of reliable image recognition based on this procedure, we used 871 images of liquid crystal textures belonging to five main categories: Nematic, Smectic A, Smectic C, Cholesteric and Crystal, and used a Neural Network Clustering Technique included in the data mining software package in Java ``WEKA''. A neural network trained on a set of 827 LC textures classified the remaining 44 textures with 80% accuracy.

Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4

NASA Astrophysics Data System (ADS)

Carnicom, Elizabeth M.; Klimczuk, Tomasz; von Rohr, Fabian; Winiarski, Michal J.; Kong, Tai; Stolze, Karoline; Xie, Weiwei; Kushwaha, Satya K.; Cava, Robert J.

2017-08-01

The growth and characterization of CePtIn4, stabilized by 10% Zn substitution for In, is reported. The new material is orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.51751(4) Å, b = 16.7570(2) Å, and c = 7.36682(8) Å, and the refined crystal composition has 10% of Zn substituted for In, i.e., the crystals are CePt(In0.9Zn0.1)4. Crystals were grown using a self-flux method: only growths containing Zn yielded CePtIn4 crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic temperature-dependent magnetic susceptibilities for single crystals show that Zn-stabilized CePtIn4 orders magnetically at ˜1.9 K. High-temperature Curie-Weiss fits indicate an effective moment of ˜2.49 μB/Ce and a directionally averaged Weiss-temperature of approximately -31 K. Specific heat data shows a peak consistent with the ordering temperature seen in the magnetic susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no superconducting transition down to 0.14 K.

Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset

NASA Astrophysics Data System (ADS)

Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

2010-12-01

The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one reflects a structural modification of the material (e.g. crystal reorganization, crystal failure, micro-cracking). In the special case presented here, the time weakening effect is the translation of plagioclase breaking during the magma flow. About the ultimate failure of the sample, crystal bearing melts appear to follow the general visco -elastic theory. However a crystal contribution has been here detected and corelate with smaller Deborah numbers before failure. Our observation offer a new vision on volcanic transition and an implication on the 90-95 eruptive crisis of Mt Unzen volcano is presented here.

Calculation of photonic bandgap for 2D hexagonal and square structure base on hybrid polymer material

NASA Astrophysics Data System (ADS)

Hidayat, S.; Riveli, N.

2018-05-01

We have calculated 2D photonic crystal band gap using plane-wave expansion method. The studied model of structures is hexagonal lattice and square lattice of rod cylinder in air. We have simulated the dispersion relation of it structure using hybrid polymer as rod material. The parameter structures are nrod = 1.5, nhole = 1, and rrod = 0.25a, where a is lattice constant. We found the distributed feedback occurs at the edge of upper band or frequency at 0.66 (a/λ). In our experimental work, we have successfully fabricated the 2D photonic crystal from hybrid polymer incorporated with organic dye laser. The lasing characteristics ware investigated using strip-line excitation light of SHG Nd-YAG laser (λ=532 nm). The lasing wavelengths for hexagonal structure are observed at 606 nm and 621 nm for photonic crystal period of 400 nm and 410 nm, respectively. λ=532 nm). Whereas the square structure, the lasing wavelengths are observed at (588 nm ± 2) and (606 nm ± 2 nm) for grating period of 391 nm and 405 nm.

Synthesis and characterization of CuAlO(2) and AgAlO(2) delafossite oxides through low-temperature hydrothermal methods.

PubMed

Xiong, Dehua; Zeng, Xianwei; Zhang, Wenjun; Wang, Huan; Zhao, Xiujian; Chen, Wei; Cheng, Yi-Bing

2014-04-21

In this work, we present one-step low temperature hydrothermal synthesis of submicrometer particulate CuAlO2 and AgAlO2 delafossite oxides, which are two important p-type transparent conducting oxides. The synthesis parameters that affect the crystal formation processes and the product morphologies, including the selection of starting materials and their molar ratios, the pH value of precursors, the hydrothermal temperature, pressure, and reaction time, have been studied. CuAlO2 crystals have been synthesized from the starting materials of CuCl and NaAlO2 at 320-400 °C, and from Cu2O and Al2O3 at 340-400 °C, respectively. AgAlO2 crystals have been successfully synthesized at the low temperature of 190 °C, using AgNO3 and Al(NO3)3 as the starting materials and NaOH as the mineralizer. The detailed elemental compositions, thermal stability, optical properties, and synthesis mechanisms of CuAlO2 and AgAlO2 also have been studied. Noteworthy is the fact that both CuAlO2 and AgAlO2 can be stabilized up to 800 °C, and their optical transparency can reach 60%-85% in the visible range. Besides, it is believed the crystal formation mechanisms uncovered in the synthesis of CuAlO2 and AgAlO2 will prove insightful guildlines for the preparation of other delafossite oxides.

The Effect of Surface Chemical Functionality Upon Ice Adhesion

NASA Technical Reports Server (NTRS)

Smith, Joseph G., Jr.; Wohl, Christopher J.; Doss, Jereme; Spence, Destiny; Kreeger, Richard E.; Palacios, Jose; Knuth, Taylor; Hadley, Kevin R.; McDougal, Nicholas D.

2015-01-01

In nature, anti-freeze proteins present in fish utilize specific organic functionalities to disrupt ice crystal formation and propagation. Based on these structures, surfaces with controlled chemical functionality and chain length were evaluated both experimentally and computationally to assess the effect of both parameters in mitigating ice formation. Linear aliphatic dimethylethoxysilanes terminated with methyl or hydroxyl groups were prepared, characterized, and used to coat aluminum. The effect upon icing using a microdroplet freezing apparatus and the Adverse Environment Rotor Test Stand found hydroxyl-terminated materials exhibited a greater propensity for ice formation and adhesion. Molecular dynamics simulations of a silica substrate bearing functionalized species of similar composition were brought into contact with a pre-equilibrated ice crystal. Several parameters including chain mobility were monitored to ascertain the size of a quasi-liquid layer. The studies suggested that chain mobility affected the interface between ice and the surface more than terminal group chemical composition.

Microstructure and photovoltaic performance of polycrystalline silicon thin films on temperature-stable ZnO:Al layers

NASA Astrophysics Data System (ADS)

Becker, C.; Ruske, F.; Sontheimer, T.; Gorka, B.; Bloeck, U.; Gall, S.; Rech, B.

2009-10-01

Polycrystalline silicon (poly-Si) thin films have been prepared by electron-beam evaporation and thermal annealing for the development of thin-film solar cells on glass coated with ZnO:Al as a transparent, conductive layer. The poly-Si microstructure and photovoltaic performance were investigated as functions of the deposition temperature by Raman spectroscopy, scanning and transmission electron microscopies including defect analysis, x-ray diffraction, external quantum efficiency, and open circuit measurements. It is found that two temperature regimes can be distinguished: Poly-Si films fabricated by deposition at low temperatures (Tdep<400 °C) and a subsequent thermal solid phase crystallization step exhibit 1-3 μm large, randomly oriented grains, but a quite poor photovoltaic performance. However, silicon films deposited at higher temperatures (Tdep>400 °C) directly in crystalline phase reveal columnar, up to 300 nm big crystals with a strong ⟨110⟩ orientation and much better solar cell parameters. It can be concluded from the results that the electrical quality of the material, reflected by the open circuit voltage of the solar cell, only marginally depends on crystal size and shape but rather on the intragrain properties of the material. The carrier collection, described by the short circuit current of the cell, seems to be positively influenced by preferential ⟨110⟩ orientation of the grains. The correlation between experimental, microstructural, and photovoltaic parameters will be discussed in detail.

Special Workshop: Kolsky/Split Hopkinson Pressure Bar Testing of Ceramics

DTIC Science & Technology

2006-09-01

merit) control armor performance and how these properties are controlled/ influenced by intrinsic (crystal structure, phase transitions, and single...reproducibility uncertainties (estimates of precision) could be quantified and also identify key parameters that should be controlled in SHPB/Kolsky testing...control performance? Are there figures of merit? How are the mechanical properties influenced by intrinsic and extrinsic material characteristics

Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

DOE PAGES

Hu, Xiao Hua; Sun, X.; Hector, Jr., L. G.; ...

2017-04-21

Here, microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plasticmore » self-consistent (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.« less

Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

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

Hu, X. H.; Sun, X.; Hector, L. G.

2017-06-01

Microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plastic self-consistentmore » (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.« less

Growth mechanisms of MgO nanocrystals via a sol-gel synthesis using different complexing agents

PubMed Central

2014-01-01

In the preparation of nanostructured materials, it is important to optimize synthesis parameters in order to obtain the desired material. This work investigates the role of complexing agents, oxalic acid and tartaric acid, in the production of MgO nanocrystals. Results from simultaneous thermogravimetric analysis (STA) show that the two different synthesis routes yield precursors with different thermal profiles. It is found that the thermal profiles of the precursors can reveal the effects of crystal growth during thermal annealing. X-ray diffraction confirms that the final products are pure, single phase and of cubic shape. It is also found that complexing agents can affect the rate of crystal growth. The structures of the oxalic acid and tartaric acid as well as the complexation sites play very important roles in the formation of the nanocrystals. The complexing agents influence the rate of growth which affects the final crystallite size of the materials. Surprisingly, it is also found that oxalic acid and tartaric acid act as surfactants inhibiting crystal growth even at a high temperature of 950°C and a long annealing time of 36 h. The crystallite formation routes are proposed to be via linear and branched polymer networks due to the different structures of the complexing agents. PMID:24650322

The interpretation of polycrystalline coherent inelastic neutron scattering from aluminium

PubMed Central

Roach, Daniel L.; Ross, D. Keith; Gale, Julian D.; Taylor, Jon W.

2013-01-01

A new approach to the interpretation and analysis of coherent inelastic neutron scattering from polycrystals (poly-CINS) is presented. This article describes a simulation of the one-phonon coherent inelastic scattering from a lattice model of an arbitrary crystal system. The one-phonon component is characterized by sharp features, determined, for example, by boundaries of the (Q, ω) regions where one-phonon scattering is allowed. These features may be identified with the same features apparent in the measured total coherent inelastic cross section, the other components of which (multiphonon or multiple scattering) show no sharp features. The parameters of the model can then be relaxed to improve the fit between model and experiment. This method is of particular interest where no single crystals are available. To test the approach, the poly-CINS has been measured for polycrystalline aluminium using the MARI spectrometer (ISIS), because both lattice dynamical models and measured dispersion curves are available for this material. The models used include a simple Lennard-Jones model fitted to the elastic constants of this material plus a number of embedded atom method force fields. The agreement obtained suggests that the method demonstrated should be effective in developing models for other materials where single-crystal dispersion curves are not available. PMID:24282332

Effect of the raw material type and the reaction time on the synthesis of halloysite based Zeolite Na-P1

NASA Astrophysics Data System (ADS)

Meftah, Mahdi; Oueslati, Walid; Chorfi, Nejmeddine; Ben Haj Amara, Abdesslem

Zeolites are currently one of the most important classes of inorganic materials because of their multiple applications not only as ions exchangers and molecular sieves, but also as catalysts. This works focus the synthesis and the characterization of Zeolite Na-P1 using halloysite (collected near Ain Khemouda, western Tunisia) as the starting material. Two parameters, such as the host materials type (natural or treated) and the reaction time, involved in the synthesis process are investigated. The intermediate phases and final products were characterized by X-ray diffraction, Infrared IR spectroscopy, scanning electron microscopy and high-resolution 29Si and 27Al MAS NMR. Obtained results show that the hydrothermal synthesis from natural and heated-halloysite leads to formation of homogenous Zeolite Na-P1. The difference in the crystallization/transformation time process is explained by the effect of the dissolution rate of the starting materials in sodium hydroxide solution. In the case of heated halloysite, the synthesis reaction with alkali solution occurs very readily and achieved without prior thermal activation at high temperature. The optimal conditions of Zeolite Na-P1 crystallization, from heated-halloysite, are reached at 120 °C.

Advanced methods for preparation and characterization of infrared detector materials. [crystallization and phase diagrams of Hg sub 1-x Cd sub x Te

NASA Technical Reports Server (NTRS)

Lehoczy, S. L.

1979-01-01

Crystal growth of Hg sub 1-x Cd sub x Te and density measurements of ingot slices are discussed. Radial compositional variations are evaluated from the results of infrared transmission edge mapping. The pseudo-binary HgTe-CdTe phase diagram is examined with reference to differential thermal analysis measurements. The phase equilibria calculations, based on the 'regular association solution' theory (R.A.S.) are explained and, using the obtained R.A.S. parameters, the activities of Hg, Cd, and Te vapors and their partial pressures over the pseudo-binary melt are calculated.

Effect of counter-ion on packing and crystal density of 5,5'-(3,3'-bi[1,2,4-oxadiazole]-5,5'-diyl)bis(1 H -tetrazol-1-olate) with five different cations

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

Giles, Ian D.; DeHope, Alan J.; Zuckerman, Nathaniel B.

In energetic materials, the crystal density is an important parameter that affects the performance of the material. When making ionic energetic materials, the choice of counter-ion can have detrimental or beneficial effects on the packing, and therefore the density, of the resulting energetic crystal. Presented herein are a series of five ionic energetic crystals, all containing the dianion 5,5′-(3,3′-bi[1,2,4-oxadiazole]-5,5′-diyl)bis(1 H -tetrazol-1-olate), with the following cations: hydrazinium ( 1 ) (2N 2 H 5 + ·C 6 N 12 O 4 2− ), hydroxylammonium ( 2 ) 2NH 4 O + ·C 6 N 12 O 4 2− [Pagoria et al..more » (2017). Chem. Heterocycl. Compd , 53 , 760–778; included for comparison], dimethylammonium ( 3 ) (2C 2 H 8 N + ·C 6 N 12 O 4 2− ), 5-amino-1 H -tetrazol-4-ium ( 4 ) (2CH 4 N 5 + ·C 6 N 12 O 4 2− ·4H 2 O), and aminoguanidinium ( 5 ) (2CH 7 N 4 + ·C 6 N 12 O 4 2− ). Both the supramolecular interactions and the sterics of the cation play a role in the density of the resulting crystals, which range from 1.544 to 1.873 Mg m −1 . In 5 , the tetrazolate ring is disordered over two positions [occupancy ratio 0.907 (5):0.093 (5)] due to a 180° rotation in the terminal tetrazole rings.« less

Effect of counter-ion on packing and crystal density of 5,5'-(3,3'-bi[1,2,4-oxadiazole]-5,5'-diyl)bis(1 H -tetrazol-1-olate) with five different cations

DOE PAGES

Giles, Ian D.; DeHope, Alan J.; Zuckerman, Nathaniel B.; ...

2018-03-09

In energetic materials, the crystal density is an important parameter that affects the performance of the material. When making ionic energetic materials, the choice of counter-ion can have detrimental or beneficial effects on the packing, and therefore the density, of the resulting energetic crystal. Presented herein are a series of five ionic energetic crystals, all containing the dianion 5,5′-(3,3′-bi[1,2,4-oxadiazole]-5,5′-diyl)bis(1 H -tetrazol-1-olate), with the following cations: hydrazinium ( 1 ) (2N 2 H 5 + ·C 6 N 12 O 4 2− ), hydroxylammonium ( 2 ) 2NH 4 O + ·C 6 N 12 O 4 2− [Pagoria et al..more » (2017). Chem. Heterocycl. Compd , 53 , 760–778; included for comparison], dimethylammonium ( 3 ) (2C 2 H 8 N + ·C 6 N 12 O 4 2− ), 5-amino-1 H -tetrazol-4-ium ( 4 ) (2CH 4 N 5 + ·C 6 N 12 O 4 2− ·4H 2 O), and aminoguanidinium ( 5 ) (2CH 7 N 4 + ·C 6 N 12 O 4 2− ). Both the supramolecular interactions and the sterics of the cation play a role in the density of the resulting crystals, which range from 1.544 to 1.873 Mg m −1 . In 5 , the tetrazolate ring is disordered over two positions [occupancy ratio 0.907 (5):0.093 (5)] due to a 180° rotation in the terminal tetrazole rings.« less

Crucial role of molecular planarity on the second order nonlinear optical property of pyridine based chalcone single crystals

NASA Astrophysics Data System (ADS)

Menezes, Anthoni Praveen; Jayarama, A.; Ng, Seik Weng

2015-05-01

An efficient nonlinear optical material 2E-3-(4-bromophenyl)-1-(pyridin-3-yl) prop-2-en-1-one (BPP) was synthesized and single crystals were grown using slow evaporation solution growth technique at room temperature. Grown crystal had prismatic morphology and its structure was confirmed by various spectroscopic studies, elemental analysis, and single crystal X-ray diffraction (XRD) technique. The single crystal XRD of the crystal showed that BPP crystallizes in monoclinic system with noncentrosymmetric space group P21 and the cell parameters are a = 5.6428(7) Å, b = 3.8637(6) Å, c = 26.411(2) Å, β = 97.568(11) deg and v = 575.82(12) Å3. The UV-Visible spectrum reveals that the crystal is optically transparent and has high optical energy band gap of 3.1 eV. The powder second harmonic generation efficiency (SHG) of BPP is 6.8 times that of KDP. From thermal analysis it is found that the crystal melts at 139 °C and decomposes at 264 °C. High optical transparency down to blue region, higher powder SHG efficiency and better thermal stability than that of urea makes this chalcone derivative a promising candidate for SHG applications. Furthermore, effect of molecular planarity on SHG efficiency and role of pyridine ring adjacent to carbonyl group in forming noncentrosymmetric crystal systems of chalcone family is also discussed.

Growth and characterization of Melaminium bis (trichloroacetate) dihydrate

NASA Astrophysics Data System (ADS)

Kanagathara, N.; Renganathan, N. G.; Marchewka, M. K.; Sivakumar, N.; Gayathri, K.; Krishnan, P.; Gunasekaran, S.; Anbalagan, G.

2013-01-01

Single crystals of melaminium bis (trichloroacetate) dihydrate have been grown successfully by slow evaporation solution growth technique at room temperature. Single crystal X-ray diffraction analysis reveals that the compound crystallizes in monoclinic system with non -centrosymmetric space group C2 with lattice parameters a = 17.70 Å, b = 8.44 Å, c = 6.09 Å, α = 90°, β = 100.24°, γ = 90° and V = 900 (Å)3. The UV-Vis transmittance spectrum shows that the crystal has a good optical transmittance in the entire visible region with lower cutoff wavelength of 351 nm. The vibrational frequencies of various functional groups present in the crystal have been derived from FI-IR, FT-Raman and Confocal Raman analyses. The chemical structure of the compound was established by 1H and 13C NMR spectrum. TGA-DTA analysis reveals that the materials have good thermal stability and the melting point of the crystal is found to be 195 °C. The dielectric response of the crystals was studied in the frequency range 50 Hz to 5 MHz at different temperatures and the results are discussed. Etching studies show the growth pattern of the crystals. The second harmonic generation efficiency was measured in comparison with KDP by employing powder Kurtz method.

Method of making macrocrystalline or single crystal semiconductor material

NASA Technical Reports Server (NTRS)

Shlichta, P. J. (Inventor); Holliday, R. J. (Inventor)

1986-01-01

A macrocrystalline or single crystal semiconductive material is formed from a primary substrate including a single crystal or several very large crystals of a relatively low melting material. This primary substrate is deposited on a base such as steel or ceramic, and it may be formed from such metals as zinc, cadmium, germanium, aluminum, tin, lead, copper, brass, magnesium silicide, or magnesium stannide. These materials generally have a melting point below about 1000 C and form on the base crystals the size of fingernails or greater. The primary substrate has an epitaxial relationship with a subsequently applied layer of material, and because of this epitaxial relationship, the material deposited on the primary substrate will have essentially the same crystal size as the crystals in the primary substrate. If required, successive layers are formed, each of a material which has an epitaxial relationship with the previously deposited layer, until a layer is formed which has an epitaxial relationship with the semiconductive material. This layer is referred to as the epitaxial substrate, and its crystals serve as sites for the growth of large crystals of semiconductive material. The primary substrate is passivated to remove or otherwise convert it into a stable or nonreactive state prior to deposition of the seconductive material.

REVIEW: Optics of globular photonic crystals

NASA Astrophysics Data System (ADS)

Gorelik, V. S.

2007-05-01

The results of experimental and theoretical studies of the optical properties of globular photonic crystals - new physical objects having a crystal structure with the lattice period exceeding considerably the atomic size, are presented. As globular photonic crystals, artificial opal matrices consisting of close-packed silica globules of diameter ~200 nm were used. The reflection spectra of these objects characterising the parameters of photonic bands existing in these crystals in the visible spectral region are presented. The idealised models of the energy band structure of photonic crystals investigated in the review give analytic dispersion dependences for the group velocity and the effective photon mass in a globular photonic crystal. The characteristics of secondary emission excited in globular photonic crystals by monochromatic and broadband radiation are presented. The results of investigations of single-photon-excited delayed scattering of light observed in globular photonic crystals exposed to cw UV radiation and radiation from a repetitively pulsed copper vapour laser are presented. The possibilities of using globular photonic crystals as active media for lasing in different spectral regions are considered. It is proposed to use globular photonic crystals as sensitive sensors in optoelectronic devices for molecular analysis of organic and inorganic materials by the modern methods of laser spectroscopy. The results of experimental studies of spontaneous and stimulated globular scattering of light are discussed. The conditions for observing resonance and two-photon-excited delayed scattering of light are found. The possibility of accumulation and localisation of the laser radiation energy inside a globular photonic crystal is reported.

An 8-channel wavelength demultiplexer based on photonic crystal fiber

NASA Astrophysics Data System (ADS)

Malka, Dror

2017-05-01

We propose a novel 8-channel wavelength demultiplexer based on photonic crystal fiber (PCF) structures that operate at 1530nm, 1535nm, 1540nm, 1545nm, 1550nm, 1555nm, 1560nm and 1565nm wavelengths. The new design is based on replacing some air-holes zones with silicon nitride and lithium niobate materials along the PCF axis with optimization of the PCF size. The reason of using these materials is because that each wavelength has a different value of coupling length. Numerical investigations were carried out on the geometrical parameters by using a beam propagation method (BPM). Simulation results show that the proposed device can transmit 8-channel that works in the whole C-band (1530- 1565nm) with low crosstalk ((-16.88)-(-15.93) dB) and bandwidth (4.02-4.69nm). Thus, the device can be very useful in optical networking systems that work on dense wavelength division multiplexing (DWDM) technology.

Investigation on Surface Insulation Strength of Machinable Ceramic Material under Pulsed Voltage in Vacuum

NASA Astrophysics Data System (ADS)

Zhang, Guan-Jun; Zhao, Wen-Bin; Ma, Xin-Pei; Li, Guang-Xin; Ma, Kui; Zheng, Nan; Yan, Zhang

Ceramic material has been widely used as insulator in vacuum. Their high hardness and brittle property brings some difficulty in the application. A new kind of machinable ceramic was invented recently. The ceramic can be machined easily and accurately after being sintered, which provides the possibility of making the insulator with fine and complicated configuration. The paper studies its surface insulation performance and flashover phenomena under pulsed excitation in vacuum. The ceramic samples with different crystallization parameters are tested under the vacuum level of 10-4 Pa. The machinable ceramic behaves better surface insulation performance than comparative the Al2O3 and glass sample. The effect of crystallization level on the trap density and flashover current is also presented. After flashover shots many times, the surface microscopic patterns of different samples are observed to investigate the damage status, which can be explained by the thermal damage mechanism.

Flux growth and characterization of cuprorivaite: the influence of temperature, flux, and silica source

NASA Astrophysics Data System (ADS)

Bloise, A.; Abd El Salam, S.; De Luca, R.; Crisci, G. M.; Miriello, D.

2016-07-01

Single crystals of cuprorivaite (CaCuSi4O10), one of the oldest synthetic color pigments of Egyptian history, have been synthesized by slow-cooling flux method. Several runs were carried out at temperatures between 800 and 960 °C and with reaction times ranging from 10 to 72 h. The starting materials and run products were characterized by binocular microscope, X-ray powder diffraction, scanning electron microscopy with annexed energy-dispersive spectrometry, and μ-Raman spectroscopy. The effects of growth parameters (temperature, flux, silica source) on yield and size of crystals were studied. The growth of cuprorivaite depends greatly on the starting materials: they are observed as run products only using natron as flux. Furthermore, colorimetric analysis performed on the synthesizing pigment was compared with the archeological samples present in the literature in order to value similarities and differences.

Ti, Ni and TiNi nanoparticles physically synthesized by Ar+ beam milling.

PubMed

Torres Castro, A; López Cuéllar, E; José Yacamán, M; Ortiz Méndez, U

2008-12-01

When the size of a particle decreases around 100 nm or less, there is a change in properties from those shown in the bulk material. In this work approximately 3 nm nanoparticles of Ni, Ti and TiNi bimetallic are produced using physical vapor deposition (PVD). Nanoparticles are characterized by High Resolution Transmission Electron Microscopy (HRTEM), High Angle Annular Dark Field (HAADF), Electron Diffraction (ED). The results show that all nanoparticles maintain the same crystal structure of bulk material but a change in their lattice parameter is produced.

Photonic band gap templating using optical interference lithography

NASA Astrophysics Data System (ADS)

Chan, Timothy Y. M.; Toader, Ovidiu; John, Sajeev

2005-04-01

We describe the properties of three families of inversion-symmetric, large photonic band-gap (PBG) template architectures defined by iso-intensity surfaces in four beam laser interference patterns. These templates can be fabricated by optical interference (holographic) lithography in a suitable polymer photo-resist. PBG materials can be synthesized from these templates using two stages of infiltration and inversion, first with silica and second with silicon. By considering point and space group symmetries to produce laser interference patterns with the smallest possible irreducible Brillouin zones, we obtain laser beam intensities, directions, and polarizations which generate a diamond-like (fcc) crystal, a novel body-centered cubic (bcc) architecture, and a simple-cubic (sc) structure. We obtain laser beam parameters that maximize the intensity contrasts of the interference patterns. This optimizes the robustness of the holographic lithography to inhomogeneity in the polymer photo-resist. When the optimized iso-intensity surface defines a silicon to air boundary (dielectric contrast of 11.9 to 1), the fcc, bcc, and sc crystals have PBG to center frequency ratios of 25%, 21%, and 11%, respectively. A full PBG forms for the diamond-like crystal when the refractive index contrast exceeds 1.97 to 1. We illustrate a noninversion symmetric PBG architecture that interpolates between a simple fcc structure and a diamond network structure. This crystal exhibits two distinct and complete photonic band gaps. We also describe a generalized class of tetragonal photonic crystals that interpolate between and extrapolate beyond the diamond-like crystal and the optimized bcc crystal. We demonstrate the extent to which the resulting PBG materials are robust against perturbations to the laser beam amplitudes and polarizations, and template inhomogeneity. The body centered cubic structure exhibits the maximum robustness overall.

Porous media modeling and micro-structurally motivated material moduli determination via the micro-dilatation theory

NASA Astrophysics Data System (ADS)

Jeong, J.; Ramézani, H.; Sardini, P.; Kondo, D.; Ponson, L.; Siitari-Kauppi, M.

2015-07-01

In the present contribution, the porous material modeling and micro-structural material parameters determination are scrutinized via the micro-dilatation theory. The main goal is to take advantage of the micro-dilatation theory which belongs to the generalized continuum media. In the first stage, the thermodynamic laws are entirely revised to reach the energy balance relation using three variables, deformation, porosity change and its gradient underlying the porous media as described in the micro-dilatation theory or so-called void elasticity. Two experiments over cement mortar specimens are performed in order to highlight the material parameters related to the pore structure. The shrinkage due to CO2 carbonation, porosity and its gradient are calculated. The extracted values are verified via 14C-PMMA radiographic image method. The modeling of swelling phenomenon of Delayed Ettringite Formation (DEF) is studied later on. This issue is performed via the crystallization pressure application using the micro-dilatation theory.

In-plane g factor of low-density two-dimensional holes in a Ge quantum well.

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

Lu, Tzu-Ming; Harris, Charles Thomas; Huang, Shih-Hsien

High-mobility two-dimensional (2D) holes residing in a Ge quantum well are a new electronic system with potentials in quantum computing and spintronics. Since for any electronic material, the effective mass and the g factor are two fundamental material parameters that determine the material response to electric and magnetic fields, measuring these two parameters in this material system is thus an important task that needs to be completed urgently. Because of the quantum confinement in the crystal growth direction (z), the biaxial strain of epitaxial Ge on SiGe, and the valance band nature, both the effective mass and the g factormore » can show very strong anisotropy. In particular, the in-plane g factor (g ip) can be vanishingly small while the perpendicular g factor (g z) can be much larger than 2. Here we report the measurement of g ip at very low hole densities using in-plane magneto-resistance measurement performed at the NHMFL.« less

Ground Based Experiments in Support of Microgravity Research Results-Vapor Growth of Organic Nonlinear Optical Thin Film

NASA Technical Reports Server (NTRS)

Zugrav, M. Ittu; Carswell, William E.; Haulenbeek, Glen B.; Wessling, Francis C.

2001-01-01

This work is specifically focused on explaining previous results obtained for the crystal growth of an organic material in a reduced gravity environment. On STS-59, in April 1994, two experiments were conducted with N,N-dimethyl-p-(2,2-dicyanovinyl) aniline (DCVA), a promising nonlinear optical (NLO) material. The space experiments were set to reproduce laboratory experiments that yielded small, bulk crystals of DCVA. The results of the flight experiment, however, were surprising. Rather than producing a bulk single crystal, the result was the production of two high quality, single crystalline thin films. This result was even more intriguing when it is considered that thin films are more desirable for NLO applications than are bulk single crystals. Repeated attempts on the ground to reproduce these results were fruitless. A second set of flight experiments was conducted on STS-69 in September 1995. This time eight DCVA experiments were flown, with each of seven experiments containing a slight change from the first reference experiment. The reference experiment was programmed with growth conditions identical to those of the STS-59 mission. The slight variations in each of the other seven were an attempt to understand what particular parameter was responsible for the preference of thin film growth over bulk crystal growth in microgravity. Once again the results were surprising. In all eight cases thin films were grown again, albeit with varying quality. So now we were faced with a phenomenon that not only takes place in microgravity, but also is very robust, resisting all attempts to force the growth of bulk single crystals.

High efficiency machining technology and equipment for edge chamfer of KDP crystals

NASA Astrophysics Data System (ADS)

Chen, Dongsheng; Wang, Baorui; Chen, Jihong

2016-10-01

Potassium dihydrogen phosphate (KDP) is a type of nonlinear optical crystal material. To Inhibit the transverse stimulated Raman scattering of laser beam and then enhance the optical performance of the optics, the edges of the large-sized KDP crystal needs to be removed to form chamfered faces with high surface quality (RMS<5 nm). However, as the depth of cut (DOC) of fly cutting is usually several, its machining efficiency is too low to be accepted for chamfering of the KDP crystal as the amount of materials to be removed is in the order of millimeter. This paper proposes a novel hybrid machining method, which combines precision grinding with fly cutting, for crackless and high efficiency chamfer of KDP crystal. A specialized machine tool, which adopts aerostatic bearing linear slide and aerostatic bearing spindle, was developed for chamfer of the KDP crystal. The aerostatic bearing linear slide consists of an aerostatic bearing guide with linearity of 0.1 μm/100mm and a linear motor to achieve linear feeding with high precision and high dynamic performance. The vertical spindle consists of an aerostatic bearing spindle with the rotation accuracy (axial) of 0.05 microns and Fork type flexible connection precision driving mechanism. The machining experiment on flying and grinding was carried out, the optimize machining parameters was gained by a series of experiment. Surface roughness of 2.4 nm has been obtained. The machining efficiency can be improved by six times using the combined method to produce the same machined surface quality.

Complete Stokes polarimetry of magneto-optical Faraday effect in a terbium gallium garnet crystal at cryogenic temperatures.

PubMed

Majeed, Hassaan; Shaheen, Amrozia; Anwar, Muhammad Sabieh

2013-10-21

We report the complete determination of the polarization changes caused in linearly polarized incident light due to propagation in a magneto-optically active terbium gallium garnet (TGG) single crystal, at temperatures ranging from 6.3 to 300 K. A 28-fold increase in the Verdet constant of the TGG crystal is seen as its temperature decreases to 6.3 K. In contrast with polarimetry of light emerging from a Faraday material at room temperature, polarimetry at cryogenic temperatures cannot be carried out using the conventional fixed polarizer-analyzer technique because the assumption that ellipticity is negligible becomes increasingly invalid as temperature is lowered. It is shown that complete determination of light polarization in such a case requires the determination of its Stokes parameters, otherwise inaccurate measurements will result with negative implications for practical devices.

Morphology, stoichiometry, and crystal structure control via post-annealing for Pt-ZnO nanograin Schottky barrier interfaces

NASA Astrophysics Data System (ADS)

Chan, Yuet Ching; Yu, Jerry; Ho, Derek

2018-06-01

Nanointerfaces have attracted intensive research effort for advanced electronics due to their unique and tunable semiconducting properties made possible by metal-contacted oxide structures at the nanoscale. Although much work has been on the adjustment of fabrication parameters to achieve high-quality interfaces, little work has experimentally obtained the various correlations between material parameters and Schottky barrier electronic properties to accurately probe the underlying phenomenon. In this work, we investigate the control of Pt-ZnO nanograin interfaces properties by thermal annealing. Specifically, we quantitatively analyze the correlation between material parameters (such as surface morphology, crystallographic structure, and stoichiometry) and Schottky diode parameters (Schottky barrier height, ideality factor, and contact resistance). Results revealed strong dependencies of Schottky barrier characteristics on oxygen vacancies, surface roughness, grain density, d-spacing, and crystallite size. I-V-T data shows that annealing at 600 °C produces a nanograin based interface with the most rectifying diode characteristics. These dependencies, which have not been previously reported holistically, highlight the close relationship between material properties and Schottky barrier characteristics, and are instrumental for the performance optimization of nanostructured metal-semiconductor interfaces in advanced electronic devices.

Effect of L-Cysteine doping on growth and some characteristics of potassium dihydrogen phosphate single crystals

NASA Astrophysics Data System (ADS)

Mahadik, Ashwini; Soni, P. H.; Desai, C. F.

2017-12-01

Among quite a number of technologically important NLO materials, Potassium Dihydrogen Phosphate (KDP) is one of the most favourable ones for second harmonic generation applications, such as in electro-optic modulators, parametric oscillators and harmonic generators. The authors report here their studies on KDP crystals doped with L-Cysteine (1 mol% and 2 mol%). The dopant inclusion in the crystals was confirmed using Fourier transform infrared (FT-IR) spectroscopy and Powder X-Ray Diffraction (XRD). The XRD results also confirm the tetragonal structure with lattice parameters a = b = 7.45 Å and c = 6.98 Å. The presence of functional groups of crystals was analyzed using the FTIR spectra. For band gap evaluation, UV-Vis spectra were used and it was found to be 3.41 eV, 4.40eVand 4.50 eV, respectively in the cases of pure KDP, 1 mol% and 2 mol% L-Cysteine dopings. The spectra quality indicates good transparency of the doped crystals in the visible region, a feature quite desirable for applications in optoelectronics.

Measurement of helium-like and hydrogen-like argon spectra using double-crystal X-ray spectrometers on EAST

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

Lyu, B., E-mail: blu@ipp.ac.cn; Hefei Science Center, Chinese Academy of Sciences, Hefei 230031; Chen, J.

2016-11-15

A two-crystal assembly was deployed on the tangential X-ray crystal spectrometer to measure both helium-like and hydrogen-like spectra on EAST. High-quality helium-like and hydrogen-like spectra were observed simultaneously for the first time on one detector for a wide range of plasma parameters. Profiles of line-integrated core ion temperatures inferred from two spectra were consistent. Since tungsten was adopted as the upper divertor material, one tungsten line (W XLIV at 4.017 Å) on the short-wavelength side of the Lyman-α line (Lα1) was identified for typical USN discharges, which was diffracted by a He-like crystal (2d = 4.913 Å). Another possible Femore » XXV line (1.85 Å) was observed to be located on the long-wavelength side of resonance line (w), which was diffracted from a H-like crystal (2d = 4.5622 Å) on the second order. Be-like argon lines were also observable that fill the detector space between the He-like and H-like spectra.« less

Measurement of helium-like and hydrogen-like argon spectra using double-crystal X-ray spectrometers on EAST.

PubMed

Lyu, B; Chen, J; Hu, R J; Wang, F D; Li, Y Y; Fu, J; Shen, Y C; Bitter, M; Hill, K W; Delgado-Aparicio, L F; Pablant, N; Lee, S G; Ye, M Y; Shi, Y J; Wan, B N

2016-11-01

A two-crystal assembly was deployed on the tangential X-ray crystal spectrometer to measure both helium-like and hydrogen-like spectra on EAST. High-quality helium-like and hydrogen-like spectra were observed simultaneously for the first time on one detector for a wide range of plasma parameters. Profiles of line-integrated core ion temperatures inferred from two spectra were consistent. Since tungsten was adopted as the upper divertor material, one tungsten line (W XLIV at 4.017 Å) on the short-wavelength side of the Lyman-α line (Lα1) was identified for typical USN discharges, which was diffracted by a He-like crystal (2d = 4.913 Å). Another possible Fe XXV line (1.85 Å) was observed to be located on the long-wavelength side of resonance line (w), which was diffracted from a H-like crystal (2d = 4.5622 Å) on the second order. Be-like argon lines were also observable that fill the detector space between the He-like and H-like spectra.

Crystallization and preliminary X-ray analysis of a novel thermoalkalophilic poly(3-hydroxybutyrate) depolymerase (PhaZ7) from Paucimonas lemoignei

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

Kapetaniou, Evangelia G.; Braaz, Reinhard; Jendrossek, Dieter

2005-05-01

A novel thermoalkalophilic depolymerase, PhaZ7, from P. lemoignei was crystallized by the microdialysis technique. Crystals belong to space group C2 and diffract to 2.75 Å resolution at a synchrotron source. Polyhydroxyalkanoates (PHA) are biodegradable polyesters that have attracted commercial and academic interest as environmentally friendly materials. A number of enzymes are able to degrade polyhydroxyalkanoates to water-soluble products. PhaZ7 poly(3-hydroxybutyrate) (PHB) depolymerase (EC 3.1.1.75), a 342-amino-acid hydrolase from the PHA-degrading bacterium Paucimonas lemoignei, has been found to possess substrate specificity for amorphous PHA. PhaZ7 was crystallized by the microdialysis method. Thin rod-like crystals were grown in low ionic strength solutionmore » and found to belong to the monoclinic space group C2, with unit-cell parameters a = 225.8, b = 46.5, c = 171.3, β = 128.9°. A complete data set was collected to 2.75 Å resolution at 100 K using synchrotron radiation.« less

Crystal morphology variation in inkjet-printed organic materials

NASA Astrophysics Data System (ADS)

Ihnen, Andrew C.; Petrock, Anne M.; Chou, Tsengming; Samuels, Phillip J.; Fuchs, Brian E.; Lee, Woo Y.

2011-11-01

The recent commercialization of piezoelectric-based drop-on-demand inkjet printers provides an additive processing platform for producing and micropatterning organic crystal structures. We report an inkjet printing approach where macro- and nano-scale energetic composites composed of cyclotrimethylenetrinitramine (RDX) crystals dispersed in a cellulose acetate butyrate (CAB) matrix are produced by direct phase transformation from organic solvent-based all-liquid inks. The characterization of printed composites illustrates distinct morphological changes dependent on ink deposition parameters. When 10 pL ink droplets rapidly formed a liquid pool, a coffee ring structure containing dendritic RDX crystals was produced. By increasing the substrate temperature, and consequently the evaporation rate of the pooled ink, the coffee ring structure was mitigated and shorter dendrites from up to ∼1 to 0.2 mm with closer arm spacing from ∼15 to 1 μm were produced. When the nucleation and growth of RDX and CAB were confined within the evaporating droplets, a granular structure containing nanoscale RDX crystals was produced. The results suggest that evaporation rate and microfluidic droplet confinement can effectively be used to tailor the morphology of inkjet-printed energetic composites.

Controlled crystallization of the lipophilic drug fenofibrate during freeze-drying: elucidation of the mechanism by in-line Raman spectroscopy.

PubMed

de Waard, Hans; De Beer, Thomas; Hinrichs, Wouter L J; Vervaet, Chris; Remon, Jean-Paul; Frijlink, Henderik W

2010-12-01

We developed a novel process, "controlled crystallization during freeze-drying" to produce drug nanocrystals of poorly water-soluble drugs. This process involves freeze-drying at a relatively high temperature of a drug and a matrix material from a mixture of tertiary butyl alcohol and water, resulting in drug nanocrystals incorporated in a matrix. The aim of this study was to elucidate the mechanisms that determine the size of the drug crystals. Fenofibrate was used as a model lipophilic drug. To monitor the crystallization during freeze-drying, a Raman probe was placed just above the sample in the freeze-dryer. These in-line Raman spectroscopy measurements clearly revealed when the different components crystallized during freeze-drying. The solvents crystallized only during the freezing step, while the solutes only crystallized after the temperature was increased, but before drying started. Although the solutes crystallized only after the freezing step, both the freezing rate and the shelf temperature were critical parameters that determined the final crystal size. At a higher freezing rate, smaller interstitial spaces containing the freeze-concentrated fraction were formed, resulting in smaller drug crystals (based on dissolution data). On the other hand, when the solutes crystallized at a lower shelf temperature, the degree of supersaturation is higher, resulting in a higher nucleation rate and consequently more and therefore smaller crystals. In conclusion, for the model drug fenofibrate, a high freezing rate and a relatively low crystallization temperature resulted in the smallest crystals and therefore the highest dissolution rate.

Charge relaxation and dynamics in organic semiconductors

NASA Astrophysics Data System (ADS)

Kwok, H. L.

2006-08-01

Charge relaxation in dispersive materials is often described in terms of the stretched exponential function (Kohlrausch law). The process can be explained using a "hopping" model which in principle, also applies to charge transport such as current conduction. This work analyzed reported transient photoconductivity data on functionalized pentacene single crystals using a geometric hopping model developed by B. Sturman et al and extracted values (or range of values) on the materials parameters relevant to charge relaxation as well as charge transport. Using the correlated disorder model (CDM), we estimated values of the carrier mobility for the pentacene samples. From these results, we observed the following: i) the transport site density appeared to be of the same order of magnitude as the carrier density; ii) it was possible to extract lower bound values on the materials parameters linked to the transport process; and iii) by matching the simulated charge decay to the transient photoconductivity data, we were able to refine estimates on the materials parameters. The data also allowed us to simulate the stretched exponential decay. Our observations suggested that the stretching index and the carrier mobility were related. Physically, such interdependence would allow one to demarcate between localized molecular interactions and distant coulomb interactions.

Electron Microscopy Characterization of Vanadium Dioxide Thin Films and Nanoparticles

NASA Astrophysics Data System (ADS)

Rivera, Felipe

Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to five orders of magnitude and a reversible drop in infrared optical transmission of up to 80%, this material holds promise in several technological applications. Solid phase crystallization of VO_2 thin films was obtained by a post-deposition annealing process of a VO_{x,x approx 2} amorphous film sputtered on an amorphous silicon dioxide (SiO_2) layer. Scanning electron microscopy (SEM) and electron-backscattered diffraction (EBSD) were utilized to study the morphology of the solid phase crystallization that resulted from this post-deposition annealing process. The annealing parameters ranged in temperature from 300°C up to 1000°C and in time from 5 minutes up to 12 hours. Depending on the annealing parameters, EBSD showed that this process yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. In addition to these films on SiO_2, other VO_2 thin films were deposited onto a-, c-, and r-cuts of sapphire and on TiO_2(001) heated single-crystal substrates by pulsed-laser deposition (PLD). The temperature of the substrates was kept at ˜500°C during deposition. EBSD maps and orientation imaging microscopy were used to study the epitaxy and orientation of the VO_2 grains deposited on the single crystal substrates, as well as on the amorphous SiO_2 layer. The EBSD/OIM results showed that: 1) For all the sapphire substrates analyzed, there is a predominant family of crystallographic relationships wherein the rutile VO_2{001} planes tend to lie parallel to the sapphire's {10-10} and the rutile VO_2{100} planes lie parallel to the sapphire's {1-210} and {0001}. Furthermore, while this family of relationships accounts for the majority of the VO_2 grains observed, due to the sapphire substrate's geometry there were variations within these rules that changed the orientation of VO_2 grains with respect to the substrate's normal direction. 2) For the TiO_2, a substrate with a lower lattice mismatch, we observe the expected relationship where the rutile VO_2 [100], [110], and [001] crystal directions lie parallel to the TiO_2 substrate's [100], [110], and [001] crystal directions respectively. 3) For the amorphous SiO_2 layer, all VO_2 crystals that were measurable (those that grew to the thickness of the deposited film) had a preferred orientation with the the rutile VO_2[001] crystal direction tending to lie parallel to the plane of the specimen. The use of transmission electron microscopy (TEM) is presented as a tool for further characterization studies of this material and its applications. In this work TEM diffraction patterns taken from cross-sections of particles of the a- and r-cut sapphire substrates not only solidified the predominant family mentioned, but also helped lift the ambiguity present in the rutile VO_2{100} axes. Finally, a focused-ion beam technique for preparation of cross-sectional TEM samples of metallic thin films deposited on polymer substrates is demonstrated.

Direct observation of interface instability during crystal growth

NASA Technical Reports Server (NTRS)

Tiller, W. A.; Feigelson, R. S.; Elwell, D.

1982-01-01

The general aim of this investigation was to study interface stability and solute segregation phenomena during crystallization of a model system. Emphasis was to be placed on direct observational studies partly because this offered the possibility at a later stage of performing related experiments under substantially convection-free conditions in the space shuttle. The major achievements described in this report are: (1) the development of a new model system for fundamental studies of crystal growth from the melt and the measurement of a range of material parameters necessary for comparison of experiment with theory. (2) The introduction of a new method of measuring segregation coefficient using absorption of a laser beam by the liquid phase. (3) The comparison of segregation in crystals grown by gradient freezing and by pulling from the melt. (4) The introduction into the theory of solute segregation of an interface field term and comparison with experiment. (5) The introduction of the interface field term into the theories of constitutional supercooling and morphological stability and assessment of its importance.

Optimization of the crystal growth of the superconductor CaKFe4As4 from solution in the FeAs -CaFe2As2-KFe2As2 system

NASA Astrophysics Data System (ADS)

Meier, W. R.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.

2017-06-01

Measurements of the anisotropic properties of single crystals play a crucial role in probing the physics of new materials. Determining a growth protocol that yields suitable high-quality single crystals can be particularly challenging for multicomponent compounds. Here we present a case study of how we refined a procedure to grow single crystals of CaKFe4As4 from a high temperature, quaternary liquid solution rich in iron and arsenic ("FeAs self-flux"). Temperature dependent resistance and magnetization measurements are emphasized, in addition to the x-ray diffraction, to detect intergrown CaKFe4As4 , CaFe2As2 , and KFe2As2 within what appear to be single crystals. Guided by the rules of phase equilibria and these data, we adjusted growth parameters to suppress formation of the impurity phases. The resulting optimized procedure yielded phase-pure single crystals of CaKFe4As4 . This optimization process offers insight into the growth of quaternary compounds and a glimpse of the four-component phase diagram in the pseudoternary FeAs -CaFe2As2-KFe2As2 system.

Influence law of structural characteristics on the surface roughness of a magnetorheological-finished KDP crystal.

PubMed

Chen, Shaoshan; Li, Shengyi; Hu, Hao; Li, Qi; Tie, Guipeng

2014-11-01

A new nonaqueous 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 influence of structural characteristics on the surface roughness of MRF-finished KDP crystal. The material removal by dissolution is uniform layer by layer when the polishing parameters are stable. The angle between the direction of the polishing wheel's linear velocity and the initial turning lines will affect the surface roughness. If the direction is perpendicular to the initial turning lines, the polishing can remove the lines. If the direction is parallel to the initial turning lines, the polishing can achieve better surface roughness. The structural characteristic of KDP crystal is related to its internal chemical bonds due to its anisotropy. During the MRF finishing process, surface roughness will be improved if the structural characteristics of the KDP crystal are the same on both sides of the wheel. The processing results of (001) plane crystal show we can get the best surface roughness (RMS of 0.809 nm) if the directions of cutting and MRF polishing are along the (110) direction.

Reduction of Defects in Germanium-Silicon

NASA Technical Reports Server (NTRS)

Szofran, Frank R.; Benz, K. W.; Croell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar; Walker, John S.

1999-01-01

It is well established that crystals grown without contact with a container have far superior quality to otherwise similar crystals grown in direct contact with a container. In addition to float-zone processing, detached-Bridgman growth is often cited as a promising tool to improve crystal quality, without the limitations of float zoning. Detached growth has been found to occur quite often during microgravity experiments and considerable improvements of crystal quality have been reported for those cases. However, no thorough understanding of the process or quantitative assessment of the quality improvements exists so far. This project will determine the means to reproducibly grow Ge-Si alloys in the detached mode. Specific objectives include: (1) measurement of the relevant material parameters such as contact angle, growth angle, surface tension, and wetting behavior of the GeSi-melt on potential crucible materials; (2) determination of the mechanism of detached growth including the role of convection; (3) quantitative determination of the differences of defects and impurities among normal Bridgman, detached Bridgman, and floating zone (FZ) growth; (4) investigation of the influence of defined azimuthal or meridional flow due to rotating magnetic fields on the characteristics of detached growth; (5) control time-dependent Marangoni convection in the case of FZ-growth by the use of a rotating magnetic field to examine the influence on the curvature of the solid-liquid interface and the heat and mass transport; and (6) grow high quality GeSi-single crystals with Si-concentration up to 10 at% and diameters up to 20 mm.

Fission Product Separation from Pyrochemical Electrolyte by Cold Finger Melt Crystallization

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

Versey, Joshua R.

This work contributes to the development of pyroprocessing technology as an economically viable means of separating used nuclear fuel from fission products and cladding materials. Electrolytic oxide reduction is used as a head-end step before electrorefining to reduce oxide fuel to metallic form. The electrolytic medium used in this technique is molten LiCl-Li2O. Groups I and II fission products, such as cesium (Cs) and strontium (Sr), have been shown to partition from the fuel into the molten LiCl-Li2O. Various approaches of separating these fission products from the salt have been investigated by different research groups. One promising approach is basedmore » on a layer crystallization method studied at the Korea Atomic Energy Research Institute (KAERI). Despite successful demonstration of this basic approach, there are questions that remain, especially concerning the development of economical and scalable operating parameters based on a comprehensive understanding of heat and mass transfer. This research explores these parameters through a series of experiments in which LiCl is purified, by concentrating CsCl in a liquid phase as purified LiCl is crystallized and removed via an argon-cooled cold finger.« less

Ternary gradient metal-organic frameworks.

PubMed

Liu, Chong; Rosi, Nathaniel L

2017-09-08

Gradient MOFs contain directional gradients of either structure or functionality. We have successfully prepared two ternary gradient MOFs based on bMOF-100 analogues, namely bMOF-100/102/106 and bMOF-110/100/102, via cascade ligand exchange reactions. The cubic unit cell parameter discrepancy within an individual ternary gradient MOF crystal is as large as ∼1 nm, demonstrating the impressive compatibility and flexibility of the component MOF materials. Because of the presence of a continuum of unit cells, the pore diameters within individual crystals also change in a gradient fashion from ∼2.5 nm to ∼3.0 nm for bMOF-100/102/106, and from ∼2.2 nm to ∼2.7 nm for bMOF-110/100/102, indicating significant porosity gradients. Like previously reported binary gradient MOFs, the composition of the ternary gradient MOFs can be easily controlled by adjusting the reaction conditions. Finally, X-ray diffraction and microspectrophotometry were used to analyse fractured gradient MOF crystals by comparing unit cell parameters and absorbance spectra at different locations, thus revealing the profile of heterogeneity (i.e. gradient distribution of properties) and further confirming the formation of ternary gradient MOFs.

Modeling TiO2's refractive index function from bulk to nanoparticles

NASA Astrophysics Data System (ADS)

Jalava, Juho-Pertti; Taavitsainen, Veli-Matti; Lamminmäki, Ralf-Johan; Lindholm, Minna; Auvinen, Sami; Alatalo, Matti; Vartiainen, Erik; Haario, Heikki

2015-12-01

In recent decades, the use of nanomaterials has become very common. Different nanomaterials are being used in over 1600 consumer products. Nanomaterials have been defined as having at least one dimension in the range of 1-100 nm. Such materials often have unique properties. Despite some warnings of applying bulk optical constants for nano size materials, stated already in 1980s, bulk constants are still commonly used in the light scattering measurements of nano size particles. Titanium dioxide is one of the materials that is manufactured and used as an engineered nanomaterial in increasing quantities. Due to the aforementioned facts, it is quite crucial for successful research and production of nanoparticles to find out the dependence of the refractive index function (RIF) of the material on its crystal size. We have earlier performed several ab initio computations for obtaining the dependence of the RIF of TiO2 on the crystal or on the cluster size, for particles of size up to ca. 2 nm. Extending the calculations to greater sizes has turned out to be infeasible due to the unbearable increase in computational time. However, in this study we show how the crystal-size-dependent-RIF (CS-RIF), for both rutile and anatase can be modeled from measured extinction or turbidity spectra of samples with varying crystal and particle sizes. For computing the turbidity spectrum, we constructed a model including primary crystals whose distributions were parameterized by mean and standard deviation, and also including aggregates consisting of mean sized primary particles, parameterized just by mean aggregate size. Mainly because of the long computing times Mie calculation was used in the computation of extinction spectra. However, in practical process applications, the obtained RIF will be used together with the T-matrix method. We constructed the RIFs used in the model using generalized oscillator model (GOM) as expanded to crystal size dependence. The unknown parameters of the model were solved using nonlinear least squares estimation. When the crystal size becomes smaller than the bulk size the shape of the estimated CS-RIFs reveal two distinct regions for both rutile and anatase. In the first region, starting apparently already from ca. 200 nm, the height of both the real part and the imaginary part of CS-RIF decreases on crystal diameter. However, the band gap remains constant. In the second region, starting when the crystal diameter is decreased to ca. 3 nm, a blue shift starts to increase the band gap. The band gap dependence on crystal size is quite consistent with the existing experimental values. Consequently, it is of great importance to use CS-RIF in light scattering measurements for nanoparticle size determination. Neglecting this, the smaller particles in the size distribution will have too small values, already for sub-micrometer particles, naturally distorting also the mean value. To our knowledge, this is the first time ever that a CS-RIF from bulk to 1 nm size is determined for any material.

Studies on synthesis of diamond at high pressure and temperature

NASA Astrophysics Data System (ADS)

Kailath, Ansu J.

Diamond is an essential material of modern industry and probably the most versatile abrasive available today. It also has many other industrial applications attributable to its unique mechanical, optical, thermal and electrical properties. Its usage has grown to the extent that there is hardly a production process in modern industry in which industrial diamond does not play a part. Bulk diamond production today is a major industry. Diamonds can be produced in its thermodynamically stable regions either by direct static conversion, or shock-wave conversion. The pressures and temperatures required for direct static conversion are very high. In the catalyst-solvent method, the material used establishes a reaction path with lower activation energy than for direct transformation. This helps in a quicker transformation under more benign conditions. Hence, catalyst-solvent synthesis is readily accomplished and is now a viable and successful industrial process. Diamonds produced by shock wave are very small (approximately 60mu). Therefore this diamond is limited to applications such as polishing compounds only. The quality, quantity, size and morphology of the crystals synthesized by catalyst-solvent process depend on different conditions employed for synthesis. These details, because of commercial reasons are not disclosed in published literature. Hence, systematic studies have been planned to investigate the effect of various growth parameters on the synthesized crystals. During the growth of synthetic diamond crystals, some catalyst-solvent is retained into the crystals in some form and behaves like an impurity. Several physico-mechanical properties of the crystals are found to depend on the total quantity and distribution of these inclusions. Thus, detailed investigation of the crystallization medium and inclusions in synthesized diamonds was also undertaken in the present work. The work incorporated in this thesis has been divided into seven chapters. The first chapter is a general introduction incorporating the information regarding diamond together with a brief history of diamond synthesis. It also includes the details of the high pressure synthesis of diamond, the uses of diamond grits, the advantages of the synthetic diamond grit over natural grit and an outline to elucidate the reasons which prompted to undertake the present work. The details of the technique used in the present studies for synthesis of diamond grits by high-pressure high-temperature process are included in chapter II. The hydraulic press used for synthesis, the details of the reactant materials, stacking of the high pressure cell and the details of synthesis run have been described together with the separation procedure to isolate diamond grits from the frozen slug. Different analytical and characterization techniques used in the present studies for the analysis and characterization of the reactant materials, synthesized diamonds and the crystallization medium have been illustrated in chapter III. The effect of different synthesizing parameters on synthesized diamond crystals were studied. This study includes: (a) dependence of yield of diamond on temperature and pressure, (b) dependence of crystal size on cook length, (c) effect of variation of the relative amounts of carbonaceous material and catalyst on synthesis, (d) morphological variation and (e) effect of pressure pulse on synthesized crystals. Various observations made during this study and the results obtained have been compiled in chapter IV. The synthesized diamond crystals were characterized by X-ray Powder Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Optical Microscopy. The results obtained have been compiled in chapter V. In addition to these, the results obtained from the Infrared Spectra and the Electron Paramagnetic Spectra have also been included. Studies of crystallization medium and inclusions in the synthesized diamonds were carried out. This include: (a) X-ray diffraction study of the phase composition of crystallization medium and inclusions in synthesized diamonds, (b) metallographic examination of the initial catalyst-solvent and the frozen slug after synthesis, (c) temperature dependence of the magnetic susceptibility of the initial catalyst-solvent and the frozen catalyst-solvent after synthesis, (d) scanning electron microscopic examination of the inclusion on the mechanically polished cross-sections of the synthesized crystals, (e) EDAX analysis of these observed inclusions and the frozen catalyst-solvent matrix after growth, (f) temperature dependence of the magnetic susceptibility of the synthesized crystals and (g) the Mossbauer spectroscopic analysis of the synthesized crystals. Different observations and the results obtained from these studies have been compiled and presented in chapter VI. Chapter VII illustrates the various conclusions drawn from the present studies.

Thermoluminescence kinetic features of Lithium Iodide (LiI) single crystal grown by vertical Bridgman technique

NASA Astrophysics Data System (ADS)

Daniel, D. Joseph; Kim, H. J.; Kim, Sunghwan; Khan, Sajid

2017-08-01

Single crystal of pure Lithium Iodide (LiI) has been grown from melt by using the vertical Bridgman technique. Thermoluminescence (TL) Measurements were carried out at 1 K/s following X-ray irradiation. The TL glow curve consists of a dominant peak at (peak-maximum Tm) 393 K and one low temperature peak of weaker intensity at 343 K. The order of kinetics (b), activation energy (E), and the frequency factor (S) for a prominent TL glow peak observed around 393 K for LiI crystals are reported for the first time. The peak shape analysis of the glow peak indicates the kinetics to be of the first order. The value of E is calculated using various standard methods such as initial rise (IR), whole glow peak (WGP), peak shape (PS), computerized glow curve deconvolution (CGCD) and Variable Heating rate (VHR) methods. An average value of 1.06 eV is obtained in this case. In order to validate the obtained parameters, numerically integrated TL glow curve has been generated using experimentally determined kinetic parameters. The effective atomic number (Zeff) for this material was determined and found to be 52. X-ray induced emission spectra of pure LiI single crystal are studied at room temperature and it is found that the sample exhibit sharp emission at 457 nm and broad emission at 650 nm.

Cloning, overexpression, crystallization and preliminary X-ray crystallographic analysis of a slow-processing mutant of penicillin G acylase from Kluyvera citrophila.

PubMed

Varshney, Nishant Kumar; Ramasamy, Sureshkumar; Brannigan, James A; Wilkinson, Anthony J; Suresh, C G

2013-08-01

Kluyvera citrophila penicillin G acylase (KcPGA) has recently attracted increased attention relative to the well studied and commonly used Escherichia coli PGA (EcPGA) because KcPGA is more resilient to harsh conditions and is easier to immobilize for the industrial hydrolysis of natural penicillins to generate the 6-aminopenicillin (6-APA) nucleus, which is the starting material for semi-synthetic antibiotic production. Like other penicillin acylases, KcPGA is synthesized as a single-chain inactive pro-PGA, which upon autocatalytic processing becomes an active heterodimer of α and β chains. Here, the cloning of the pac gene encoding KcPGA and the preparation of a slow-processing mutant precursor are reported. The purification, crystallization and preliminary X-ray analysis of crystals of this precursor protein are described. The protein crystallized in two different space groups, P1, with unit-cell parameters a = 54.0, b = 124.6, c = 135.1 Å, α = 104.1, β = 101.4, γ = 96.5°, and C2, with unit-cell parameters a = 265.1, b = 54.0, c = 249.2 Å, β = 104.4°, using the sitting-drop vapour-diffusion method. Diffraction data were collected at 100 K and the phases were determined using the molecular-replacement method. The initial maps revealed electron density for the spacer peptide.

Nanoparticle Superlattice Engineering with DNA

NASA Astrophysics Data System (ADS)

Macfarlane, Robert J.; Lee, Byeongdu; Jones, Matthew R.; Harris, Nadine; Schatz, George C.; Mirkin, Chad A.

2011-10-01

A current limitation in nanoparticle superlattice engineering is that the identities of the particles being assembled often determine the structures that can be synthesized. Therefore, specific crystallographic symmetries or lattice parameters can only be achieved using specific nanoparticles as building blocks (and vice versa). We present six design rules that can be used to deliberately prepare nine distinct colloidal crystal structures, with control over lattice parameters on the 25- to 150-nanometer length scale. These design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (5 to 60 nanometers), periodicity, and interparticle distance. As such, this work represents an advance in synthesizing tailorable macroscale architectures comprising nanoscale materials in a predictable fashion.

Reciprocal Space Mapping of Macromolecular Crystals in the Laboratory

NASA Technical Reports Server (NTRS)

Snell, Edward H.; Boggon, T. J.; Fewster, P. F.; Siddons, D. P.; Stojanof, V.; Pusey, M. L.

1998-01-01

The technique of reciprocal space mapping applied to the physical measurement of macromolecular crystals will be described. This technique uses a triple axis diffractometer setup whereby the monochromator is the first crystal, the sample is the second and the third crystal (of the same material as the monochromator) analyzes the diffracted beam. The geometry is such that it is possible to separate mosaic volume effects from lattice strain effects. The deconvolution of the instrument parameters will also be addressed. Results from measurements at Brookhaven National Synchrotron Radiation Source carried out on microgravity and ground-grown crystals will be presented. The required beam characteristics for reciprocal space mapping are also ideal for topographic studies and the first topographs ever recorded from microgravity protein crystal samples will be shown. We are now working on a system which will enable reciprocal space mapping, mosaicity and topography studies to be carried out in the home laboratory. This system uses a rotating anode X-ray source to provide an intense beam then a Bartels double crystal, four reflection monochromator to provide the spectral and geometric beam conditioning necessary such that the instrument characteristics do not mask the measurement. This is coupled to a high precision diffractometer and sensitive detector. Commissioning data and first results from the system will be presented.

Crystal-field effects in fluoride crystals for optical refrigeration

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

Hehlen, Markus P

2010-01-01

The field of optical refrigeration of rare-earth-doped solids has recently seen an important breakthrough. The cooling of a YLiF{sub 4} (YLF) crystal doped with 5 mol% Yb3+ to 155 K by Seletskiy et al [NPhot] has surpassed the lowest temperatures ({approx}170 K for {approx}100 mW cooling capacity) that are practical with commercial multi-stage thermoelectric coolers (TEC) [Glaister]. This record performance has advanced laser cooling into an application relevant regime and has put first practical optical cryocoolers within reach. The result is also relevant from a material perspective since for the first time, an Yb3+-doped crystal has outperformed an Yb3+-doped glass.more » The record temperature of 208 K was held by the Yb3+-doped fluorozirconate glass ZBLAN. Advanced purification and glass fabrication methods currently under development are expected to also advance ZBLAN:Yb3+ to sub-TEC temperatures. However, recent achievements with YLF:Yb3+ illustrate that crystalline materials may have two potentially game-changing advantajes over glassy materials. First, the crystalline environment reduces the inhomogeneous broadening of the Yb3+ electronic transitions as compared to a glassy matrix. The respective sharpening of the crystal-field transitions increases the peak absorption cross section at the laser excitation wavelength and allows for more efficient pumping of the Yb3+ ions, particularly at low temperatures. Second, many detrimental impurities present in the starting materials tend to be excluded from the crystal during its slow growth process, in contrast to a glass where all impurities present in the starting materials are included in the glass when it is formed by temperature quenching a melt. The ultra high purity required for laser cooling materials [PRB] therefore may be easier to realize in crystals than in glasses. Laser cooling occurs by laser excitation of a rare-earth ion followed by anti-Stokes luminescence. Each such laser-cooling cycle extracts thermal energy from the solid and carries it away as high-entropy light, thereby cooling the material. In the ideal case, the respective laser-cooling power is given by the pump wavelength ({lambda}{sub p}), the mean fluorescence wavelength ({bar {lambda}}{sub L}), and the absorption coefficient (a{sub r}) of the pumped transition. These quantities are solely determined by crystal field interactions. On one hand, a large crystal-field splitting offers a favorably large difference of {lambda}{sub p} - {bar {lambda}}{sub L} and thus a high cooling efficiency {eta}{sub cool} = ({lambda}{sub p} - {bar {lambda}}{sub L})/{bar {lambda}}{sub L}. On the other hand, a small crystal-field splitting offers a high thermal population (n{sub i}) of the initial state of the pumped transition, giving a high pump absorption coefficient and thus high laser cooling power, particularly at low temperatures. A quantitative description of crystal-field interactions is therefore critical to the understanding and optimization of optical refrigeration. In the case of Yb3+ as the laser cooling ion, however, development of a crystal-field model is met with substantial difficulties. First, Yb3+ has only two 4/multiplets, {sup 2}F{sub 7/2} and {sup 2}F{sub 5/2}, which lead to at most 7 crystal-field levels. This makes it difficult, and in some cases impossible, to evaluate the crystal-field Hamiltonian, which has at least 4 parameters for any Yb3+ point symmety lower than cubic. Second, {sup 2}F{sub 7/2}{leftrightarrow}{sup 2}F{sub 5/2} transitions exhibit an exceptionally strong electron-phonon coupling compared to 4f transitions of other rare earths. This makes it difficult to distinguish electronic from vibronic transitions in the absorption and luminescence spectra and to reliably identify the crystal-field levels. Yb3+ crystal-field splittings reported in the literature should thus generally be viewed with caution. This paper explores the effects of crystal-field interactions on the laser cooling performance of Yb3+-doped fluoride crystals. It is shown that the total crystal-field splitting of the {sup 2}F{sub 7/2} and {sup 2}F{sub 5/2} multiplets of Yb3+ can be estimated from crystal-field splittings of other rare-earth-doped fluoride crystals. This approach takes advantage of an extensive body of experimental work from which Yb3+ doped fluoride crystals with favorable laser cooling properties might be identified. Section 2 reviews the crystal-field splitting of the 4f electronic states and introduces the crystal-field strength as a means to predict the total crystal-field splitting of the {sup 2}F{sub 7/2} and {sup 2}F{sub 5/2} multiplets. Section 3 illustrates the effect of the total {sup 2}F{sub 7/2} crystal field splitting on the laser cooling power. Finally, Section 4 compiles literature data on crystal-field splittings in fluoride crystals from which the {sup 2}F{sub 7/2} splitting is predicted.« less

Surrogate Seeds For Growth Of Crystals

NASA Technical Reports Server (NTRS)

Shlichta, Paul J.

1989-01-01

Larger crystals of higher quality grown. Alternative method for starting growth of crystal involves use of seed crystal of different material instead of same material as solution. Intended for growing single-crystal proteins for experiments but applicable in general to growth of crystals from solutions and to growth of semiconductor or other crystals from melts.

A metamorphic inorganic framework that can be switched between eight single-crystalline states

NASA Astrophysics Data System (ADS)

Zhan, Caihong; Cameron, Jamie M.; Gabb, David; Boyd, Thomas; Winter, Ross S.; Vilà-Nadal, Laia; Mitchell, Scott G.; Glatzel, Stefan; Breternitz, Joachim; Gregory, Duncan H.; Long, De-Liang; MacDonell, Andrew; Cronin, Leroy

2017-02-01

The design of highly flexible framework materials requires organic linkers, whereas inorganic materials are more robust but inflexible. Here, by using linkable inorganic rings made up of tungsten oxide (P8W48O184) building blocks, we synthesized an inorganic single crystal material that can undergo at least eight different crystal-to-crystal transformations, with gigantic crystal volume contraction and expansion changes ranging from -2,170 to +1,720 Å3 with no reduction in crystallinity. Not only does this material undergo the largest single crystal-to-single crystal volume transformation thus far reported (to the best of our knowledge), the system also shows conformational flexibility while maintaining robustness over several cycles in the reversible uptake and release of guest molecules switching the crystal between different metamorphic states. This material combines the robustness of inorganic materials with the flexibility of organic frameworks, thereby challenging the notion that flexible materials with robustness are mutually exclusive.

Quantitative Probes of Electron-Phonon Coupling in an Organic Charge-Transfer Material

NASA Astrophysics Data System (ADS)

Rury, Aaron; Sorenson, Shayne; Driscoll, Eric; Dawlaty, Jahan

While organic charge transfer (CT) materials may provide alternatives to inorganic materials in electronics and photonics applications, properties central to applications remain understudied in these organic materials. Specifically, electron-phonon coupling plays a pivotal role in electronic applications yet this coupling in CT materials remains difficult to directly characterize. To better understand the suitability of organic CT materials for electronic applications, we have devised an experimental technique that can directly assess electron-phonon coupling in a model organic CT material. Upon non-resonant interaction with an ultrafast laser pulse, we show that coherent excitation of Raman-active lattice vibrations of quinhydrone, a 1:1 co-crystal of the hydroquinone and p-benzoquinone, modulates the energies of electronic transitions probed by a white light pulse. Using a well-established theoretical framework of vibrational quantum beat spectra across the probe bandwidth, we quantitatively extract the parameters describing these electronic transitions to characterize electron-phonon coupling in this material. In conjunction with temperature-dependent resonance Raman measurements, we assess the hypothesis that several sharp transitions in the near-IR correspond to previously unknown excitonic states of this material. These results and their interpretation set the foundation for further elucidation of the one of the most important parameters in the application of organic charge-transfer materials to electronics and photonics.

Investigation of Interrelation between Deformation, Composition and Structural Characteristics of Magnesium Oxychloride Cements

NASA Astrophysics Data System (ADS)

Averina, G. F.; Chernykh, T. N.; Kramar, L. Ya

2017-11-01

The paper studies the process of volume deformation changes in magnesium cement at its hardening in accordance with its composition and structural peculiarities, which result from the roasting parameters of the raw materials. The study has been carried out with the aim of broadening raw materials sources for production of magnesia cements and construction materials through the use waste products of ore-dressing and processing enterprises. The mineralogical and phase composition of magnesium cements, obtained on the basis of magnesite with high content of impurity minerals from the mine dumps, has been studied by the X-ray phase analysis and derivatography. The roasting of the initial raw materials was carried out at various temperature conditions in order to get cements of different activities. The typical content of hydrated phases has been found for the hardened magnesian stone obtained from cements with different activity degrees. The characteristics of volume deformations developed in the magnesian stone have been described in relation to its phase composition. The influence of low- and high-activity crystals and calcium oxide crystals on the soundness and the structural integrity of magnesian stone has been covered.

Thermal Decomposition Study on CuInSe2 Single Crystals

NASA Astrophysics Data System (ADS)

Chauhan, Sanjaysinh M.; Chaki, Sunil H.; Deshpande, M. P.; Malek, Tasmira J.; Tailor, J. P.

2018-01-01

The thermal analysis of the chemical vapor transport (CVT)-grown CuInSe2 single crystals was carried out by recording the thermogravimetric, differential thermogravimetric and differential thermal analysis curves. All the three thermo-curves were recorded simultaneously by thermal analyzer in the temperature range of ambient to 1080 K in inert nitrogen atmosphere. The thermo-curves were recorded for four heating rates of 5 K \\cdot min^{-1}, 10 K \\cdot min^{-1}, 15 K \\cdot min^{-1} and 20 K \\cdot min^{-1}. The TG curve analysis showed negligible mass loss in the temperature range of ambient to 600 K, stating the sample material to be thermally stable in this temperature range. Above 601 K to the temperature of 1080 K, the sample showed continuous mass loss. The DTG curves showed two peaks in the temperature range of 601 K to 1080 K. The corresponding DTA showed initial minor exothermic nature followed by endothermic nature up to nearly 750 K and above it showed exothermic nature. The initial exothermic nature is due to absorbed water converting to water vapor, whereas the endothermic nature states the absorption of heat by the sample up to nearly 950 K. Above nearly 950 K the exothermic nature is due to the decomposition of sample material. The absorption of heat in the endothermic region is substantiated by corresponding weight loss in TG. The thermal kinetic parameters of the CVT-grown CuInSe2 single crystals were determined employing the non-mechanistic Kissinger relation. The determined kinetic parameters support the observations of the thermo-curves.

Synthesis, growth, structural, optical, spectral, thermal and mechanical studies of 4-methoxy 4-nitrostilbene (MONS): a new organic nonlinear optical single crystal.

PubMed

Dinakaran, Paul M; Bhagavannarayana, G; Kalainathan, S

2012-11-01

4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based on the solubility data good quality single crystal with dimensions up to 38×11×3 mm(3) has been grown by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the crystalline property and also the diffraction planes have been indexed. The lattice parameters for the grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been analysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown crystal. The UV-vis absorption spectrum has been recorded in the range of 190-1100 nm and the cut off wavelength 499 nm has been determined. The optical constants of MONS have been determined through UV-vis-NIR spectroscopy. The MONS crystals were further subjected to other characterizations. i.e., (1)H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55× greater than that of KDP crystal. Copyright © 2012 Elsevier B.V. All rights reserved.

Remarkable features in lattice-parameter ratios of crystals. II. Monoclinic and triclinic crystals.

PubMed

de Gelder, R; Janner, A

2005-06-01

The frequency distributions of monoclinic crystals as a function of the lattice-parameter ratios resemble the corresponding ones of orthorhombic crystals: an exponential component, with more or less pronounced sharp peaks, with in general the most important peak at the ratio value 1. In addition, the distribution as a function of the monoclinic angle beta has a sharp peak at 90 degrees and decreases sensibly at larger angles. Similar behavior is observed for the three triclinic angular parameters alpha, beta and gamma, with characteristic differences between the organic and metal-organic, bio-macromolecular and inorganic crystals, respectively. The general behavior observed for the hexagonal, tetragonal, orthorhombic, monoclinic and triclinic crystals {in the first part of this series [de Gelder & Janner (2005). Acta Cryst. B61, 287-295] and in the present case} is summarized and commented. The data involved represent 366 800 crystals, with lattice parameters taken from the Cambridge Structural Database, CSD (294 400 entries), the Protein Data Bank, PDB (18 800 entries), and the Inorganic Crystal Structure Database, ICSD (53 600 entries). A new general structural principle is suggested.

Cholesteric liquid crystals doped with gold nanoparticles

NASA Astrophysics Data System (ADS)

Bitar, Rajaa; Agez, Gonzague; Mitov, Michel

2012-10-01

The reflection color of a cholesteric liquid crystal depends on material parameters such as the molecular chirality or the concentration of chiral dopant, the helical pitch of the twisted structure and the optical indices. We show that the color may be selected simply by varying the annealing time of an open cholesteric oligomer film with hybrid anchoring. The 3D representation of the structure is provided by combining complementary imaging techniques. The color selectivity is due to controlled changes of the orientation of the helix axis with respect to the air-material interface. Potential applications are chiral microreflectors and microlenses. Then, we demonstrate the symbiotic association of gold nanoparticles within such cholesteric textures and their long-range self-organized arrangements. We show that the nanoparticles can be patterned on demand only by playing with the film thickness and the interfacial properties of the CLC film. We investigate how the selective reflection is affected by the in situ organization of gold nanoparticles and what is the plasmon response of nanoparticle chains. Potential applications are envisioned in the field of soft nanotechnology and optical materials.

Transient Thermal Analysis of a Refractive Secondary Solar Concentrator

NASA Technical Reports Server (NTRS)

Geng, Steven M.; Macosko, Robert P.

1999-01-01

A secondary concentrator is an optical device that accepts solar energy from a primary concentrator and further intensifies and directs the solar flux. The refractive secondary is one such device; fabricated from an optically clear solid material that can efficiently transmit the solar energy by way of refraction and total internal reflection. When combined with a large state-of-the-art rigid or inflatable primary concentrator, the refractive secondary enables solar concentration ratios of 10,000 to 1. In support of potential space solar thermal power and propulsion applications, the NASA Glenn Research Center is developing a single-crystal refractive secondary concentrator for use at temperatures exceeding 2000K. Candidate optically clear single-crystal materials like sapphire and zirconia are being evaluated for this application. To support this evaluation, a three-dimensional transient thermal model of a refractive secondary concentrator in a typical solar thermal propulsion application was developed. This paper describes the model and presents thermal predictions for both sapphire and zirconia prototypes. These predictions are then used to establish parameters for analyzing and testing the materials for their ability to survive thermal shock and stress.

Electromechanical properties of a textured ceramic material in the (1 - x)PMN- xPT system: Simulation based on the effective-medium method

NASA Astrophysics Data System (ADS)

Aleshin, V. I.; Raevskiĭ, I. P.; Sitalo, E. I.

2008-11-01

A complete set of dielectric, piezoelectric, and elastic parameters for the textured ceramic material 0.67PMN-0.33PT is calculated by the self-consistency method with due regard for the anisotropy and piezoelectric activity of the medium. It is shown that the best piezoelectric properties corresponding to those of a single crystal are observed for the ceramic material with a texture in which all crystallites are oriented parallel to the [001] direction of the parent perovskite cubic cell. The simplest models of the polarization of an untextured ceramic material with a random initial orientation of crystallites are considered. The results obtained are compared with experimental data.

Superconductivity in CaBi 2

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

Winiarski, M. J.; Wiendlocha, B.; Golba, S.

We observed superconductivity with critical temperature T c = 2.0 K in self-flux-grown single crystals of CaBi 2. This material adopts the ZrSi 2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi 2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T c is ΔC/γT c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol -1 K -2 and the Debye temperature Θ D = 157 K. The electron–phonon coupling strength ismore » λ el–ph = 0.59, and the thermodynamic critical field H c is low, between 111 and 124 Oe CaBi 2 is a moderate coupling type-I superconductor. Our results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin–orbit coupling and electronic property anisotropy. Furthermore, we find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.« less

Superconductivity in CaBi 2

DOE PAGES

Winiarski, M. J.; Wiendlocha, B.; Golba, S.; ...

2016-07-12

We observed superconductivity with critical temperature T c = 2.0 K in self-flux-grown single crystals of CaBi 2. This material adopts the ZrSi 2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi 2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T c is ΔC/γT c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol -1 K -2 and the Debye temperature Θ D = 157 K. The electron–phonon coupling strength ismore » λ el–ph = 0.59, and the thermodynamic critical field H c is low, between 111 and 124 Oe CaBi 2 is a moderate coupling type-I superconductor. Our results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin–orbit coupling and electronic property anisotropy. Furthermore, we find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.« less

The crystal structure and morphology of NiO-YSZ composite that prepared from local zircon concentrate of Bangka Island

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

Rahmawati, F., E-mail: fitria@mipa.uns.ac.id; Apriyani, K.; Heraldy, E.

2016-03-29

In order to increase the economic value of local zircon concentrate from Bangka Island, NiO-YSZ was synthesized from Zirconia, ZrO{sub 2} that was prepared from local zircon concentrate. The NiO-YSZ composite was synthesized by solid state reaction method. XRD analysis equipped with Le Bail refinement was carried out to analyze the crystal structure and cell parameters of the prepared materials. The result showed that zirconia was crystallized in tetragonal structure with a space group of P42/NMC. Yttria-Stabilized-Zirconia (YSZ) was prepared by doping 8% mol yttrium oxide into zirconia and then sintered at 1250°C for 3 hours. Doping of 8% molmore » Yttria allowed phase transformation of zirconia from tetragonal into the cubic structure. Meanwhile, the composite of NiO-YSZ consists of two crystalline phases, i.e. the NiO with cubic structure and the YSZ with cubic structure. SEM analysis of the prepared materials shows that the addition of NiO into YSZ allows the morphology to become more roughness with larger grain size.« less

Ultra compact spectrometer apparatus and method using photonic crystals

NASA Technical Reports Server (NTRS)

Ting, David Z. (Inventor); Hill, Cory J. (Inventor); Bandara, Sumith V. (Inventor); Gunapala, Sarath D. (Inventor)

2009-01-01

The present invention is directed to methods of photonic crystal formation, and to methods and apparatus for using such photonic crystals, particularly in conjunction with detector arrays. Photonic crystal parameters and detector array parameters are compared to optimize the selection and orientation of a photonic crystal shape. A photonic crystal is operatively positioned relative to a plurality of light sensors. The light sensors can be separated by a pitch distance and positioned within one half of the pitch distance of an exit surface of the photonic crystals.

Piezo-optic and elasto-optic properties of monoclinic triglycine sulfate crystals.

PubMed

Mytsyk, Bogdan; Demyanyshyn, Natalya; Erba, Alessandro; Shut, Viktor; Mozzharov, Sergey; Kost, Yaroslav; Mys, Oksana; Vlokh, Rostyslav

2017-12-01

For the first time, to the best of our knowledge, we have experimentally determined all of the components of the piezo-optic tensor for monoclinic crystals. This has been implemented on a specific example of triglycine sulfate crystals. Based on the results obtained, the complete elasto-optic tensor has been calculated. Acousto-optic figures of merit (AOFMs) have been estimated for the case of acousto-optic interaction occurring in the principal planes of the optical indicatrix ellipsoid and for geometries in which the highest elasto-optic coefficients are involved as effective parameters. It has been found that the highest AOFM value is equal to 6.8×10 -15   s 3 /kg for the case of isotropic acousto-optic interaction with quasi-longitudinal acoustic waves in the principal planes. This AOFM is higher than the corresponding values typical for canonic acousto-optic materials, which are transparent in the deep ultraviolet spectral range.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1986-01-01

It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy. III - Weakly nonlinear theory

NASA Technical Reports Server (NTRS)

Wheeler, A. A.; Mcfadden, G. B.; Coriell, S. R.; Hurle, D. T. J.

1990-01-01

The effect of a constant electric current on the crystal-melt interface morphology during directional solidification at constant velocity of a binary alloy is considered. A linear temperature field is assumed, and thermoelectric effects and Joule heating are neglected; electromigration and differing electrical conductivities of crystal and melt are taken into account. A two-dimensional weakly nonlinear analysis is carried out to third order in the interface amplitude, resulting in a cubic amplitude equation that describes whether the bifurcation from the planar state is supercritical or subcritical. For wavelengths corresponding to the most dangerous mode of linear theory, the demarcation between supercritical and subcritical behavior is calculated as a function of processing conditions and material parameters. The bifurcation behavior is a sensitive function of the magnitude and direction of the electric current and of the electrical conductivity ratio.

Design and growth of novel compounds for radiation sensors: multinary chalcogenides

NASA Astrophysics Data System (ADS)

Singh, N. B.; Su, Ching-Hua; Nagaradona, Teja; Arnold, Brad; Choa, Fow-Sen

2016-05-01

Increasing threats of radiological weapons have revitalized the researches for low cost large volume γ-ray and neutron ray sensors In the past few years we have designed and grown ternary and quaternary lead and thallium chalcogenides and lead selenoiodides for detectors to meet these challenges. These materials are congruent, can be tailored to enhance the parameters required for radiation sensors. In addition, this class of compounds can be grown by Bridgman method which promises for large volume productions. We have single crystals of several compounds from the melt including Tl3AsSe3, Tl3AsSe3-xSx, TlGaSe2, AgGaGe3Se8, AgxLi1-xAgGaGe3Se8 and PbTlI5-x Sex compounds. Experimental studies indicate that these have very low absorption coefficient, low defect density and can be fabricated in any shape and sizes. These crystals do not require post growth annealing and do not show any second phase precipitates when processed for electrode bonding and other fabrication steps. In this paper we report purification, growth and fabrication of large Tl3AsSe3 (TAS) crystals. We observed that TAS crystals grown by using further purification of as supplied high purity source materials followed by directionally solidified charge showed higher resistivity than previously reported values. TAS also showed constant value as the function of voltage.

Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

DOE PAGES

Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; ...

2016-02-01

Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CPmore » models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.« less

Thermoelectric properties of nanocrystalline Sb2Te3 thin films: experimental evaluation and first-principles calculation, addressing effect of crystal grain size.

PubMed

Morikawa, Satoshi; Inamoto, Takuya; Takashiri, Masayuki

2018-02-16

The effect of crystal grain size on the thermoelectric properties of nanocrystalline antimony telluride (Sb 2 Te 3 ) thin films was investigated by experiments and first-principles studies using a developed relaxation time approximation. The Sb 2 Te 3 thin films were deposited on glass substrates using radio-frequency magnetron sputtering. To change the crystal grain size of the Sb 2 Te 3 thin films, thermal annealing was performed at different temperatures. The crystal grain size, lattice parameter, and crystal orientation of the thin films were estimated using XRD patterns. The carrier concentration and in-plane thermoelectric properties of the thin films were measured at room temperature. A theoretical analysis was performed using a first-principles study based on density functional theory. The electronic band structures of Sb 2 Te 3 were calculated using different lattice parameters, and the thermoelectric properties were predicted based on the semi-classical Boltzmann transport equation in the relaxation time approximation. In particular, we introduced the effect of carrier scattering at the grain boundaries into the relaxation time approximation by estimating the group velocities from the electronic band structures. Finally, the experimentally measured thermoelectric properties were compared with those obtained by calculation. As a result, the calculated thermoelectric properties were found to be in good agreement with the experimental results. Therefore, we can conclude that introducing the effect of carrier scattering at the grain boundaries into the relaxation time approximation contributes to enhance the accuracy of a first-principles calculation relating to nanocrystalline materials.

Thermoelectric properties of nanocrystalline Sb2Te3 thin films: experimental evaluation and first-principles calculation, addressing effect of crystal grain size

NASA Astrophysics Data System (ADS)

Morikawa, Satoshi; Inamoto, Takuya; Takashiri, Masayuki

2018-02-01

The effect of crystal grain size on the thermoelectric properties of nanocrystalline antimony telluride (Sb2Te3) thin films was investigated by experiments and first-principles studies using a developed relaxation time approximation. The Sb2Te3 thin films were deposited on glass substrates using radio-frequency magnetron sputtering. To change the crystal grain size of the Sb2Te3 thin films, thermal annealing was performed at different temperatures. The crystal grain size, lattice parameter, and crystal orientation of the thin films were estimated using XRD patterns. The carrier concentration and in-plane thermoelectric properties of the thin films were measured at room temperature. A theoretical analysis was performed using a first-principles study based on density functional theory. The electronic band structures of Sb2Te3 were calculated using different lattice parameters, and the thermoelectric properties were predicted based on the semi-classical Boltzmann transport equation in the relaxation time approximation. In particular, we introduced the effect of carrier scattering at the grain boundaries into the relaxation time approximation by estimating the group velocities from the electronic band structures. Finally, the experimentally measured thermoelectric properties were compared with those obtained by calculation. As a result, the calculated thermoelectric properties were found to be in good agreement with the experimental results. Therefore, we can conclude that introducing the effect of carrier scattering at the grain boundaries into the relaxation time approximation contributes to enhance the accuracy of a first-principles calculation relating to nanocrystalline materials.

Mesoporous Nb2O5/SiO2 material obtained by sol-gel method and applied as adsorbent of crystal violet dye.

PubMed

Umpierres, Cibele S; Prola, Lizie D T; Adebayo, Matthew A; Lima, Eder C; Dos Reis, Glaydson S; Kunzler, Diego D F; Dotto, G L; Arenas, Leliz T; Benvenutti, Edilson V

2017-03-01

In this work, SiO 2 /Nb 2 O 5 (SiNb) material was prepared using sol-gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption-desorption isotherms, FTIR spectroscopy, pH pzc , and SEM-EDS. The analysis of N 2 isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area as high as 747 m 2  g -1 . For the CV adsorption process, variations of several parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g -1 at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents - the material showed very good efficiency for decolorization of dye effluents.

Fluoride crystals: materials for near-infrared solid state lasers

NASA Astrophysics Data System (ADS)

Parisi, Daniela; Veronesi, Stefano; Volpi, Azzurra; Gemmi, Mauro; Tonelli, Mauro; Cassanho, Arlete; Jenssen, Hans P.

2013-07-01

In this work we present an overview of the best 2μm laser results obtained in Tm-doped fluoride hosts LiYF4(YLF), LiLuF4 (LLF) and BaY2F8 (BYF) and we report on the growth, spectroscopy and first laser test emission of a novel mixed material BaYLuF8 (BYLF), interesting as a variant of BYF material with a partial substitution of Y3+ ions by Lu3+. The novel host is interesting mainly because indications are that the mixed crystal would be sturdier than BYF. The addition of Lutetium would improve the thermo-mechanical properties going into the direction of high power applications, as suggest from works on YLF and its isomorph LLF. A detailed description of Czochralski growth of fluoride laser materials is provided, focusing on the growth parameters of the novel BYLF:Tm3+12% material grown. With regard of spectroscopy analysis, we report on the results obtained with BYLF host. Detailed absorption, fluorescence and lifetime measurements have been performed focusing on the 3H4 and 3F4 manifolds, the pumping and upper laser level. Moreover diode pumped CW laser emission at 2 μm has been achieved in BYLF: Tm3+12% sample obtaining a slope efficiency of about 28% with respect to the absorbed power.

Thermoelectric Properties of Bi2Te2Se Compensated by Native Defects and Sn Doping

NASA Astrophysics Data System (ADS)

Fuccillo, M. K.; Jia, Shuang; Charles, M. E.; Cava, R. J.

2013-06-01

In Bi2Te2Se the defect chemistry involves native defects that compete such that they can either exchange dominance or else significantly compensate each other. Here we show how the net carrier concentration, n - p, which depends on the relative amounts of these defects and is readily obtained from Hall data, can be used as a fundamental materials parameter to describe the varied behavior of the thermoelectric properties as a function of compensation. We report the effects of tuning this parameter over multiple orders of magnitude by hole-doping the n-type material Bi2Te2Se0.995, which is already significantly compensated because of its Se deficiency. Crystals with different levels of hole doping were achieved by two separate approaches, namely by selecting pieces from different locations in an undoped crystal in which a systematic carrier concentration gradient had been induced by its growth conditions, and alternatively by doping with Sn for Bi. The thermoelectric power factors for Bi2- x Sn x Te2Se0.995 for x = 0, 0.002, 0.005, 0.010, and 0.040 are reported, and the dependence of the transport properties on the extent of compensation is discussed.

Rhombohedral cubic semiconductor materials on trigonal substrate with single crystal properties and devices based on such materials

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

Growth conditions are developed, based on a temperature-dependent alignment model, to enable formation of cubic group IV, group II-V and group II-VI crystals in the [111] orientation on the basal (0001) plane of trigonal crystal substrates, controlled such that the volume percentage of primary twin crystal is reduced from about 40% to about 0.3%, compared to the majority single crystal. The control of stacking faults in this and other embodiments can yield single crystalline semiconductors based on these materials that are substantially without defects, or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. These methods can selectively yield a cubic-on-trigonal epitaxial semiconductor material in which the cubic layer is substantially either directly aligned, or 60 degrees-rotated from, the underlying trigonal material.

Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: Scavenger of free radicals

NASA Astrophysics Data System (ADS)

Fezai, Ramzi; Hemissi, Hanene; Mezni, Ali; Rzaigui, Mohamed

2017-12-01

Single crystal of the hybrid compound [p-(F)C6H4NH3]6P6O18·2H2O has been grown with sizes up to 0.65 × 0.45 × 0.3 mm3 by the slow evaporation method. The crystal structure of this material was determined by single crystal X-ray diffraction. It crystallizes in the triclinic space group P 1 bar with the lattice parameters a = 10.16(3) Å, b = 15.87(3) Å, c = 16.36(4) Å, α = 80.93(2)°, β = 85.92(18)°, γ = 85.31(2)°, V = 2591.1(12) Å3 and Z = 2. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a, c) planes. The cohesion of the structure is essentially ensured by a hydrogen bonding network as well as electrostatic and Van Der Waals interactions and also F…F interactions so as to increase the stability of the 3D-network. The effect of the nature of the substituent in para-position with respect to amine group on obtained structures and on other studied properties was discussed. Crystal symmetry is confirmed by 31P MAS-NMR. Furthermore, IR characteristics and thermal analysis are given. The luminescent properties of this material have been carried out at room temperature based on UV absorption spectroscopy data. AC conductivity of this compound has been investigated by means of impedance spectroscopy measurements in the 303-383 K temperature range. The antioxidant study was determined, in vitro, using 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical and reducing power and with ascorbic acid as a control. X-rays structural results are correlated with electrical and antioxidant findings.

Improved reproducibility of unit-cell parameters in macromolecular cryocrystallography by limiting dehydration during crystal mounting.

PubMed

Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H

2014-08-01

In macromolecular cryocrystallography unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amount of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking solution. Secondly, the looped crystal is transferred to a vial containing a small amount of the crystal soaking solution. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temperature unit-cell parameters and offers some new approaches to crystal handling and cryoprotection.

Improved reproducibility of unit-cell parameters in macromolecular cryocrystallography by limiting dehydration during crystal mounting

PubMed Central

Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H.

2014-01-01

In macromolecular cryocrystallography unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amount of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking solution. Secondly, the looped crystal is transferred to a vial containing a small amount of the crystal soaking solution. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temperature unit-cell parameters and offers some new approaches to crystal handling and cryoprotection. PMID:25084331

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

Soft Chemistry, Coloring and Polytypism in Filled Tetrahedral Semiconductors: Toward Enhanced Thermoelectric and Battery Materials.

PubMed

White, Miles A; Medina-Gonzalez, Alan M; Vela, Javier

2018-03-12

Filled tetrahedral semiconductors are a rich family of compounds with tunable electronic structure, making them ideal for applications in thermoelectrics, photovoltaics, and battery anodes. Furthermore, these materials crystallize in a plethora of related structures that are very close in energy, giving rise to polytypism through the manipulation of synthetic parameters. This Minireview highlights recent advances in the solution-phase synthesis and nanostructuring of these materials. These methods enable the synthesis of metastable phases and polytypes that were previously unobtainable. Additionally, samples synthesized in solution phase have enhanced thermoelectric performance due to their decreased grain size. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

NASA Astrophysics Data System (ADS)

Ranjan, Srikant

2005-11-01

Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

Negative refraction in molybdenum disulfide.

PubMed

Wang, Wenhui; Cui, Xudong; Yang, Erchan; Fan, Quanping; Xiang, Bin

2015-08-24

Recently, negative refractions have been demonstrated in uniaxial crystals with no necessary of negative permittivity and permeability. However, the small anisotropy parameterγin the uniaxial crystals limits the negative refraction occurrence only in a small range of the incident light angle, retarding its practical applications. In this paper, we report negative refraction induced by a pronounced anisotropic behavior in the bulk MoS(2). Using the first-principles, the dielectric function and refractive index calculations confirm a uniaxial trait of MoS(2) with a calculated anisotropy parameterγlarger than 2.5 in the entire range of visible wavelength. The critical incident angle to trigger a negative refraction in the bulk MoS(2) is calculated up to 90°. The finite-difference time-domain simulations prove that the incident light with a density of 59.5% can be negatively refracted in a MoS(2) slab with a thickness of 0.1 µm. Our results open up a new pathway for MoS(2)-like materials to a novel field of optical integration.

Manipulating transmission and reflection properties of a photonic crystal doped with quantum dot nanostructures

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

Solookinejad, G.; Panahi, M.; Sangachin, E. A.

The transmission and reflection properties of incident light in a defect dielectric structure is studied theoretically. The defect structure consists of donor and acceptor quantum dot nanostructures embedded in a photonic crystal. It is shown that the transmission and reflection properties of incident light can be controlled by adjusting the corresponding parameters of the system. The role of dipole–dipole interaction is considered as a new parameter in our calculations. It is noted that the features of transmission and reflection curves can be adjusted in the presence of dipole–dipole interaction. It is found that the absorption of weak probe light canmore » be converted to the probe amplification in the presence of dipole–dipole interaction. Moreover, the group velocity of transmitted and reflected probe light is discussed in detail in the absence and presence of dipole–dipole interaction. Our proposed model can be used as a new all-optical devices based on photonic materials doped with nanoparticles.« less

Effect of self-organization, defects, impurities, and autocatalytic processes on the parameters of ZnO films and nanorods

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

Mezdrogina, M. M., E-mail: Margaret.M@mail.ioffe.ru; Eremenko, M. V.; Levitskii, V. S.

The effects of the parameters of ZnO-film deposition onto different substrates using the method of ac magnetron sputtering in a gas mixture of argon and oxygen hare studied. The phenomenon of self-organization is observed, which leads to invariability of the surface morphology of the ZnO films upon a variation in the substrate materials and deposition parameters. The parameters of the macro- and micro-photoluminescence spectra of the films differ insignificantly from the parameters of the photoluminescence spectra of bulk ZnO crystals obtained by the method of hydrothermal growth. The presence of intense emission with a narrow full-width at half-maximum (FWHM) inmore » different regions of the spectrum allows ZnO films obtained by magnetron sputtering doped with rare-earth metal impurities (REIs) to be considered as a promising material for the creation of optoelectronic devices working in a broad spectral range. The possibility of the implementation of magnetic ordering upon legierung with REIs significantly broadens the functional possibilities of ZnO films. The parameters of the photoluminescence spectra of ZnO nanorods are determined by their geometrical parameters and by the concentration and type of the impurities introduced.« less

Bottom-up on-crystal in-chip formation of a conducting salt and a view of its restructuring: from organic insulator to conducting "switch" through microfluidic manipulation.

PubMed

Puigmartí-Luis, Josep; Paradinas, Markos; Bailo, Elena; Rodriguez-Trujillo, Romen; Pfattner, Raphael; Ocal, Carmen; Amabilino, David B

2015-06-01

The chemical modification of an immobilized single crystal in a fluid cell is reported, whereby a material with switching functions is generated in situ by generating a chemical reagent in the flow. Crystals of the insulating organic crystal of TCNQ (tetracyanoquinodimethane) were grown in a microfluidic channel and were trapped using a pneumatic valve, a nascent technique for materials manipulation. They were subsequently reduced using solution-deposited silver to provide a conducting material in situ by a heterogeneous reaction. Removal of the new material from the chip proved it to be the silver salt of reduced TCNQ. Uniquely, conducting atomic force microscope (CAFM) studies show three regions in the solid. The localized original neutral organic material crystal is shown to be an insulator but to produce areas with Ohmic conducting characteristics after reduction. This inhomogeneous doping provides an opportunity for probing electrical materials properties side by side. Measurements with the CAFM witness this conducting material where the TCNQ is fully transformed to the silver salt. Additionally, an intermediate phase is observed that exhibits bipolar resistive switching typical of programmable resistive memories. Raman microscopy proves the conversion of the material in specific regions and clearly defines the intermediate phase region that could be responsible for the switching effect in related materials. This kind of "on crystal chemistry" exploiting immobilization and masking by a pneumatic clamp in a microfluidic channel shows how material can be selectively converted to give different functionalities in the same material piece, even though it is not a single crystal to single crystal conversion, and beckons exploitation for the preparation of systems relevant for molecular electronics as well as other areas where chemical manipulation of single crystals could be beneficial.

Continuous Czochralski growth: Silicon sheet growth development of the large area sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Johnson, C. M.

1980-01-01

The growth of 100 kg of silicon single crystal material, ten cm in diameter or greater, and 150 kg of silicon single crystal material 15 cm or greater utilizing one common silicon container material (one crucible) is investigated. A crystal grower that is recharged with a new supply of polysilicon material while still under vacuum and at temperatures above the melting point of silicon is developed. It accepts large polysilicon charges up to 30 kg, grows large crystal ingots (to 15 cm diameter and 25 kg in weight), and holds polysilicon material for recharging (rod or lump) while, at the same time, growing crystal ingots. Special equipment is designed to recharge polysilicon rods, recharge polysilicon lumps, and handle and store large, hot silicon crystal ingots. Many continuous crystal growth runs were performed lasting as long as 109 hours and producing as many as ten crystal ingots, 15 cm with weights progressing to 27 kg.

Tight-Binding Study of Polarons in Two-Dimensional Systems: Implications for Organic Field-Effect Transistor Materials

NASA Astrophysics Data System (ADS)

Lei, Jie

2011-03-01

In order to understand the electronic and transport properties of organic field-effect transistor (FET) materials, we theoretically studied the polarons in two-dimensional systems using a tight-binding model with the Holstein type and Su--Schrieffer--Heeger type electron--lattice couplings. By numerical calculations, it was found that a carrier accepts four kinds of localization, which are named the point polaron, two-dimensional polaron, one-dimensional polaron, and the extended state. The degree of localization is sensitive to the following parameters in the model: the strength and type of electron--lattice couplings, and the signs and relative magnitudes of transfer integrals. When a parameter set for a single-crystal phase of pentacene is applied within the Holstein model, a considerably delocalized hole polaron is found, consistent with the bandlike transport mechanism.

Development of a DOI PET Detector Having the Structure of the X'tal Cube Extended in One Direction

NASA Astrophysics Data System (ADS)

Inadama, Naoko; Hirano, Yoshiyuki; Nishikido, Fumihiko; Murayama, Hideo; Yamaya, Taiga

2016-10-01

X'tal cube is the cubic depth of interaction (DOI) PET detector which our research group developed. In this work, aiming to get higher sensitivity, we developed the long rectangular shape X'tal cube (long-XC) by extending the cubic X'tal cube structure in one direction. We verified performance of this long-XC and also studied detector parameters for optimization. The same as the X'tal cube, the crystal block of the long-XC is composed of a 3D array of cubic scintillation crystal elements. Reflectors are not inserted between these crystal elements. The scintillation light then spreads without being obstructed by reflectors and is detected by multiple numbers of the multi-pixel photon counters (MPPCs) coupled on all six sides of the crystal block. For crystal element identification, a simple Anger-type calculation is used. In this study, we arranged 3.0 mm×3.0 mm×3.0 mm LGSO crystal elements in a 6 × 6 × 14 array for the long-XC. In a previous study, we had already confirmed that for the X'tal cube consisting of a 6 × 6 × 6 array of the same crystal elements and 54 MPPCs, identification of all 216 crystal elements was possible and the average energy resolution for all the elements was about 11 %. The long-XC contains more than twice the number of the crystal elements but less than twice the number of the MPPCs compared to the previous X'tal cube. The detector parameters investigated with the long-XC were: the number of MPPCs on both sides in the extended direction (edge MPPCs); the MPPC type, the MPPCs of 25 μm × 25 μm or 50 μm × 50 μm pixel sizes; the material between the crystal elements, an air gap or an optical glue having a closer refractive index to that of LGSO than air has; and the MPPC signals used in the Anger-type calculation. Results of the crystal element identification performance showed that reducing the number of the edge MPPCs caused performance degradation only at the part near the edge. For the MPPC type, the 50 μm type was better than the 25 μm type, and for the material, air was much better than the optical glue. We found that the choice of MPPC signals for the Anger-type calculation was effective in the optical glue condition. For the long-XC in the air gap condition and using the 50 μm type MPPCs, we observed it had good performance and there was no significant degradation at the central part which is far from the edge MPPCs. For irradiation of 662 keV gamma-rays, we measured approximately 11 - 13 % energy resolution for each crystal element and there was only a small difference in light outputs between crystal elements at the central part and at the edges. These results at the central part suggested the possibility of further extension of the long-XC for higher sensitivity.

Growth of NBT-BT single crystals by flux method and their structural, morphological and electrical characterizations

NASA Astrophysics Data System (ADS)

Kanuru, Sreenadha Rao; Baskar, K.; Dhanasekaran, R.; Kumar, Binay

2016-05-01

In this paper, one of the important, eco-friendly polycrystalline material, (1-x)(Na0.5Bi0.5)TiO3 (NBT) - xBaTiO3 (BT) of different compositions (x=0.07, 0.06 and 0.05 wt%) around the morphotropic phase boundary (MPB) were synthesized by solid state reaction technique. And the single crystals with 13×7×7 mm3, 12×12×7 mm3 and 10×7×4 mm3 dimensions were grown by self flux method. The morphology, crystal structure and unit-cell parameters have been studied and the monoclinic phase has been identified for 0.07 wt% of BT. Higher BT concentration changes the crystal habit and the mechanism has been studied clearly. Raman spectroscopy at room-temperature confirms the presence of functional groups. The quality of the as grown single crystals was examined by high resolution x-ray diffraction analysis. The dielectric properties of the as grown crystals were investigated in the frequency range of 20 Hz-2 MHz from room temperature to 450 °C. The broad dielectric peak and frequency dispersion demonstrates the relaxor behavior of grown crystals. The dielectric constant (εr), transition temperature (Tm), and depolarization temperature (Td) of the grown crystals are found to be comparatively good. The diffusive factor (γ) from Curie-Weiss law confirms the as grown NBT-BT single crystals are relaxor in nature.

Molecular theory of smectic ordering in liquid crystals with nanoscale segregation of different molecular fragments

NASA Astrophysics Data System (ADS)

Gorkunov, M. V.; Osipov, M. A.; Kapernaum, N.; Nonnenmacher, D.; Giesselmann, F.

2011-11-01

A molecular statistical theory of the smectic A phase is developed taking into account specific interactions between different molecular fragments which enables one to describe different microscopic scenario of the transition into the smectic phase. The effects of nanoscale segregation are described using molecular models with different combinations of attractive and repulsive sites. These models have been used to calculate numerically coefficients in the mean filed potential as functions of molecular model parameters and the period of the smectic structure. The same coefficients are calculated also for a conventional smectic with standard Gay-Berne interaction potential which does not promote the segregation. The free energy is minimized numerically to calculate the order parameters of the smectic A phases and to study the nature of the smectic transition in both systems. It has been found that in conventional materials the smectic order can be stabilized only when the orientational order is sufficiently high, In contrast, in materials with nanosegregation the smectic order develops mainly in the form of the orientational-translational wave while the nematic order parameter remains relatively small. Microscopic mechanisms of smectic ordering in both systems are discussed in detail, and the results for smectic order parameters are compared with experimental data for materials of various molecular structure.

Bulk Crystal Growth of Nonlinear Optical Organic Materials Using Inverted Vertical Gradient Freeze Method

NASA Technical Reports Server (NTRS)

Choi, J.; Cruz, Magda; Metzl, R.; Wang, W. S.; Aggarwal, M. D.; Penn, Benjamin G.; Frazier, Donald O.

1998-01-01

A new process for producing large bulk single crystals of benzil (C6H5COCOC6H5) is reported in this paper. Good quality crystals have been successfully grown using this approach to crystal growth. This method seems to be very promising for other thermally stable NLO organic materials also. The entire contents vycor crucible 1.5 inch in diameter and 2 inch deep was converted to single crystal. Purity of the starting growth material is also an important factor in the final quality of the grown crystals. The entire crystal can be very easily taken out of the crucible by simple maneuvering. Initial characterization of the grown crystals indicated that the crystals are as good as other crystals grown by conventional Bridgman Stockbarger technique.

Intrinsically incompatible crystal (ligand) field parameter sets for transition ions at orthorhombic and lower symmetry sites in crystals and their implications

NASA Astrophysics Data System (ADS)

Rudowicz, C.; Gnutek, P.

2010-01-01

Central quantities in spectroscopy and magnetism of transition ions in crystals are crystal (ligand) field parameters (CFPs). For orthorhombic, monoclinic, and triclinic site symmetry CF analysis is prone to misinterpretations due to large number of CFPs and existence of correlated sets of alternative CFPs. In this review, we elucidate the intrinsic features of orthorhombic and lower symmetry CFPs and their implications. The alternative CFP sets, which yield identical energy levels, belong to different regions of CF parameter space and hence are intrinsically incompatible. Only their ‘images’ representing CFP sets expressed in the same region of CF parameter space may be directly compared. Implications of these features for fitting procedures and meaning of fitted CFPs are categorized into negative: pitfalls and positive: blessings. As a case study, the CFP sets for Tm 3+ ions in KLu(WO 4) 2 are analysed and shown to be intrinsically incompatible. Inadvertent, so meaningless, comparisons of incompatible CFP sets result in various pitfalls, e.g., controversial claims about the values of CFPs obtained by other researchers as well as incorrect structural conclusions or faulty systematics of CF parameters across rare-earth ion series based on relative magnitudes of incompatible CFPs. Such pitfalls bear on interpretation of, e.g., optical spectroscopy, inelastic neutron scattering, and magnetic susceptibility data. An extensive survey of pertinent literature was carried out to assess recognition of compatibility problems. Great portion of available orthorhombic and lower symmetry CFP sets are found intrinsically incompatible, yet these problems and their implications appear barely recognized. The considerable extent and consequences of pitfalls revealed by our survey call for concerted remedial actions of researchers. A general approach based on the rhombicity ratio standardization may solve compatibility problems. Wider utilization of alternative CFP sets in the multiple correlated fitting techniques may improve reliability ( blessing) of fitted CFPs. This review may be of interest to a broad range of researchers from condensed matter physicists to physical chemists working on, e.g., high temperature superconductors, luminescent, optoelectronic, laser, and magnetic materials.

IR Bandwidth and Crystal Thickness Effects on THG Efficiency and Temporal Shaping of Quasi-Rectangular UV Pulses: Part II - Incident IR Ripple

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

Bolton, Paul R.; Limborg-Deprey, Cecile; /SLAC

We have investigated the effect of incident ir spectral bandwidth and crystal thickness, on uv pulses produced by third harmonic generation (THG) in a crystal pair. Our focus is on the third harmonic generation efficiency and longitudinal uv intensity profile parameters of SNLO predictions that are evaluated for three incident ir spectral bandwidths and a range of crystal thicknesses. These results represent a continuation of earlier work in which the effects of the same selected ir bandwidths and range of crystal thicknesses were investigated using a pair of BBO Type I crystals in a simplistic geometry for which the longitudinalmore » intensity plateau has a zero slope, 'flattop' profile. The current work is distinguished from the previous work by an imposed ripple on the ir intensity longitudinal profile and constitutes a portion of a Part II effort to which we have made reference. As with preceding work, all third harmonic data are net results at the exit of the second BBO crystal. Predictions are obtained with the modified SNLO code developed by Arlee Smith at the Sandia National Laboratories. This modification has allowed us to pursue the 'coupled' case in which the output of the first BBO crystal is used as input to the second one. This includes both the fundamental and second harmonic light. Defined parameters are consistent with previous work. The presented cases are best results. The criteria for selection of these reported cases are highest THG efficiency combined with minimum intensity ripple in the plateau. The incident ir pulse is quasi-rectangular with an imposed 5.2 % (rms) intensity ripple added to the plateau. The ir pulse bandwidth is centered at 800 nm. Second harmonic generation occurs in the first BBO crystal and THG occurs in the second crystal as a consequence of sum frequency generation. Type I phase matching is used throughout, so that for a negative uniaxial crystal: n{sub 2}{sup e}({theta}) = n{sub 1}{sup o};(SHG) (1.1) 3n{sub 3}{sup 3}({theta}) = 2n{sub 2}{sup o} + n{sub 1}{sup o};(THG) where n{sub 2}{sup e}({theta}) and n{sub 3}{sup e}({theta}) are the angle dependent extraordinary refractive indices for the second and third harmonics respectively, and n{sub 1}{sup 1} and n{sub 2}{sup o} are the ordinary refractive indices for the fundamental and second harmonic respectively. Although our goal at this stage has not been to comply with all the LCLS injector laser specifications, the results provided here represent a parameter study that can be used to determine candidate bandwidth dependent, crystal thickness combinations for the detailed design of compliant THG subsystems. This simplistic geometry better elucidates acceptance bandwidth limitations that are intrinsic to the crystal material.« less

Two distinct crystallization processes in supercooled liquid

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

Tane, Masakazu, E-mail: mtane@sanken.osaka-u.ac.jp; Kimizuka, Hajime; Ichitsubo, Tetsu

2016-05-21

Using molecular dynamics simulations we show that two distinct crystallization processes, depending on the temperature at which crystallization occurs, appear in a supercooled liquid. As a model for glass-forming materials, an Al{sub 2}O{sub 3} model system, in which both the glass transition and crystallization from the supercooled liquid can be well reproduced, is employed. Simulations in the framework of an isothermal-isobaric ensemble indicate that the calculated time-temperature-transformation curve for the crystallization to γ(defect spinel)-Al{sub 2}O{sub 3} exhibited a typical nose shape, as experimentally observed in various glass materials. During annealing above the nose temperature, the structure of the supercooled liquidmore » does not change before the crystallization, because of the high atomic mobility (material transport). Thus, the crystallization is governed by the abrupt crystal nucleation, which results in the formation of a stable crystal structure. In contrast, during annealing below the nose temperature, the structure of the supercooled liquid gradually changes before the crystallization, and the formed crystal structure is less stable than that formed above the nose temperature, because of the restricted material transport.« less

Modeling of Macroscopic/Microscopic Transport and Growth Phenomena in Zeolite Crystal Solutions Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Gatsonis, Nikos A.; Alexandrou, Andreas; Shi, Hui; Ongewe, Bernard; Sacco, Albert, Jr.

1999-01-01

Crystals grown from liquid solutions have important industrial applications. Zeolites, for instance, a class of crystalline aluminosilicate materials, form the backbone of the chemical process industry worldwide, as they are used as adsorbents and catalysts. Many of the phenomena associated with crystal growth processes are not well understood due to complex microscopic and macroscopic interactions. Microgravity could help elucidate these phenomena and allow the control of defect locations, concentration, as well as size of crystals. Microgravity in an orbiting spacecraft could help isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation. In addition, crystals will stay essentially suspended in the nutrient pool under a diffusion-limited growth condition. This is expected to promote larger crystals by allowing a longer residence time in a high-concentration nutrient field. Among other factors, the crystal size distribution depends on the nucleation rate and crystallization. These two are also related to the "gel" polymerization/depolymerization rate. Macroscopic bulk mass and flow transport and especially gravity, force the crystals down to the bottom of the reactor, thus forming a sedimentation layer. In this layer, the growth rate of the crystals slows down as crystals compete for a limited amount of nutrients. The macroscopic transport phenomena under certain conditions can, however, enhance the nutrient supply and therefore, accelerate crystal growth. Several zeolite experiments have been performed in space with mixed results. The results from our laboratory have indicated an enhancement in size of 30 to 70 percent compared to the best ground based controls, and a reduction of lattice defects in many of the space grown crystals. Such experiments are difficult to interpret, and cannot be easily used to derive empirical or other laws since many physical parameters are simultaneously involved in the process. At the same time, however, there is increased urgency to develop such an understanding in order to more accurately quantify the process. In order to better understand the results obtained from our prior space experiments, and design future experiments, a detailed fluid dynamic model simulating the crystal growth mechanism is required. This will not only add to the fundamental knowledge on the crystallization of zeolites, but also be useful in predicting the limits of size and growth of these important industrial materials. Our objective is to develop macro/microscopic theoretical and computational models to study the effect of transport phenomena in the growth of crystals grown in solutions. Our effort has concentrated so far in the development of separate macroscopic and microscopic models. The major highlights of our accomplishments are described.

Comparison of helical scan and standard rotation methods in single-crystal X-ray data collection strategies.

PubMed

Polsinelli, Ivan; Savko, Martin; Rouanet-Mehouas, Cecile; Ciccone, Lidia; Nencetti, Susanna; Orlandini, Elisabetta; Stura, Enrico A; Shepard, William

2017-01-01

X-ray radiation in macromolecular crystallography can chemically alter the biological material and deteriorate the integrity of the crystal lattice with concomitant loss of resolution. Typical alterations include decarboxylation of glutamic and aspartic residues, breaking of disulfide bonds and the reduction of metal centres. Helical scans add a small translation to the crystal in the rotation method, so that for every image the crystal is shifted to expose a fresh part. On beamline PROXIMA 2A at Synchrotron SOLEIL, this procedure has been tested with various parameters in an attempt to understand how to mitigate the effects of radiation damage. Here, the strategies used and the crystallographic metrics for various scenarios are reported. Among these, the loss of bromine from bromophenyl moieties appears to be a useful monitor of radiation damage as the carbon-bromine bond is very sensitive to X-ray irradiation. Two cases are focused on where helical scans are shown to be superior in obtaining meaningful data compared with conventional methods. In one case the initial resolution of the crystal is extended over time, and in the second case the anomalous signal is preserved to provide greater effective multiplicity and easier phasing.

Real-time measurements of crystallization processes in viscoelastic polymeric photonic crystals

NASA Astrophysics Data System (ADS)

Snoswell, David R. E.; Finlayson, Chris E.; Zhao, Qibin; Baumberg, Jeremy J.

2015-11-01

We present a study of the dynamic shear ordering of viscoelastic photonic crystals, based on core-shell polymeric composite particles. Using an adapted shear-cell arrangement, the crystalline ordering of the material under conditions of oscillatory shear is interrogated in real time, through both video imaging and from the optical transmission spectra of the cell. In order to gain a deeper understanding of the macroscopic influences of shear on the crystallization process in this solvent-free system, the development of bulk ordering is studied as a function of the key parameters including duty cycle and shear-strain magnitude. In particular, optimal ordering is observed from a prerandomized sample at shear strains of around 160%, for 1-Hz oscillations. This ordering reaches completion over time scales of order 10 s. These observations suggest significant local strains are needed to drive nanoparticles through energy barriers, and that local creep is needed to break temporal symmetry in such high-viscosity nanoassemblies. Crystal shear-melting effects are also characterized under conditions of constant shear rate. These quantitative experiments aim to stimulate the development of theoretical models which can deal with the strong local particle interactions in this system.

Refractive index dependence of Papilio Ulysses butterfly wings reflectance spectra

NASA Astrophysics Data System (ADS)

Isnaeni, Muslimin, Ahmad Novi; Birowosuto, Muhammad Danang

2016-02-01

We have observed and utilized butterfly wings of Papilio Ulysses for refractive index sensor. We noticed this butterfly wings have photonic crystal structure, which causes blue color appearance on the wings. The photonic crystal structure, which consists of cuticle and air void, is approximated as one dimensional photonic crystal structure. This photonic crystal structure opens potential to several optical devices application, such as refractive index sensor. We have utilized small piece of Papilio Ulysses butterfly wings to characterize refractive index of several liquid base on reflectance spectrum of butterfly wings in the presence of sample liquid. For comparison, we simulated reflectance spectrum of one dimensional photonic crystal structure having material parameter based on real structure of butterfly wings. We found that reflectance spectrum peaks shifted as refractive index of sample changes. Although there is a slight difference in reflectance spectrum peaks between measured spectrum and calculated spectrum, the trend of reflectance spectrum peaks as function of sample's refractive index is the similar. We assume that during the measurement, the air void that filled by sample liquid is expanded due to liquid pressure. This change of void shape causes non-similarity between measured spectrum and calculated spectrum.

Processing materials in space - The history and the future

NASA Technical Reports Server (NTRS)

Chassay, Roger; Carswell, Bill

1987-01-01

The development of materials processing in space, and some of the Soyuz, Apollo, Skylab, and Shuttle orbital materials experiments are reviewed. Consideration is given to protein crystal growth, electrophoresis, low-gravity isoelectric focusing, phase partitioning, a monodisperse latex reactor, semiconductor crystal growth, solution crystal growth, the triglycine sulfate experiment, vapor crystal growth experiments, the mercuric iodide experiment, electronic and electrooptical materials, organic thin films and crystalline solids, deep undercooling of metals and alloys, magnetic materials, immiscible materials, metal solidification research, reluctant glass-forming materials, and containerless glass formation. The space processing apparatuses and ground facilities, for materials processing are described. Future facilities for commercial research, development, and manufacturing in space are proposed.

Optimization of the crystal growth of the superconductor CaKFe 4 As 4 from solution in the FeAs - CaFe 2 As 2 - KFe 2 As 2 system

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

Meier, W. R.; Kong, T.; Bud'ko, S. L.

Measurements of the anisotropic properties of single crystals play a crucial role in probing the physics of new materials. Determining a growth protocol that yields suitable high-quality single crystals can be particularly challenging for multicomponent compounds. Here we present a case study of how we refined a procedure to grow single crystals of CaKFe 4As 4 from a high temperature, quaternary liquid solution rich in iron and arsenic (“FeAs self-flux”). Temperature dependent resistance and magnetization measurements are emphasized, in addition to the x-ray diffraction, to detect intergrown CaKFe 4As 4, CaFe 2As 2, and KFe 2As 2 within what appearmore » to be single crystals. Guided by the rules of phase equilibria and these data, we adjusted growth parameters to suppress formation of the impurity phases. The resulting optimized procedure yielded phase-pure single crystals of CaKFe 4As 4. In conclusion, this optimization process offers insight into the growth of quaternary compounds and a glimpse of the four-component phase diagram in the pseudoternary FeAs–CaFe 2As 2–KFe 2As 2 system.« less

Optimization of the crystal growth of the superconductor CaKFe 4 As 4 from solution in the FeAs - CaFe 2 As 2 - KFe 2 As 2 system

DOE PAGES

Meier, W. R.; Kong, T.; Bud'ko, S. L.; ...

2017-06-19

Measurements of the anisotropic properties of single crystals play a crucial role in probing the physics of new materials. Determining a growth protocol that yields suitable high-quality single crystals can be particularly challenging for multicomponent compounds. Here we present a case study of how we refined a procedure to grow single crystals of CaKFe 4As 4 from a high temperature, quaternary liquid solution rich in iron and arsenic (“FeAs self-flux”). Temperature dependent resistance and magnetization measurements are emphasized, in addition to the x-ray diffraction, to detect intergrown CaKFe 4As 4, CaFe 2As 2, and KFe 2As 2 within what appearmore » to be single crystals. Guided by the rules of phase equilibria and these data, we adjusted growth parameters to suppress formation of the impurity phases. The resulting optimized procedure yielded phase-pure single crystals of CaKFe 4As 4. In conclusion, this optimization process offers insight into the growth of quaternary compounds and a glimpse of the four-component phase diagram in the pseudoternary FeAs–CaFe 2As 2–KFe 2As 2 system.« less

Method for monitoring the crystallization of an organic material from a liquid

DOEpatents

Asay, Blaine W.; Henson, Bryan F.; Sander, Robert K.; Robinson, Jeanne M.; Son, Steven F.; Dickson, Peter M.

2004-10-05

Method for monitoring the crystallization of at least one organic material from a liquid. According to the method, a liquid having at least one organic material capable of existing in at least one non-centrosymmetric phase is prepared. The liquid is interrogated with a laser beam at a chosen wavelength. As at least a portion of the at least one organic material crystallizes from the liquid, the intensity of any light scattered by the crystallized material at a wavelength equal to one-half the chosen wavelength of the interrogating laser beam is monitored. If the intensity of this scattered light, increases, then the crystals that form include at least one non-cetrosymmetric phase.

Highly Non-Linear Optical (NLO) organic crystals

NASA Technical Reports Server (NTRS)

Harris, J. Milton

1987-01-01

This research project involves the synthesis and characterization of organic materials having powerful nonlinear optical (NLO) properties and the growth of highly ordered crystals and monomolecular films of these materials. Research in four areas is discussed: theoretical design of new materials, characterization of NLO materials, synthesis of new materials and development of coupling procedures for forming layered films, and improvement of the techniques for vapor phase and solution phase growth of high quality organic crystals. Knowledge gained from these experiments will form the basis for experiments in the growth of these crystals.

Crystal structure and phase transition of thermoelectric SnSe.

PubMed

Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

2016-06-01

Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

A classical mechanics model for the interpretation of piezoelectric property data

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

Bell, Andrew J., E-mail: a.j.bell@leeds.ac.uk

2015-12-14

In order to provide a means of understanding, the relationship between the primary electromechanical coefficients and simple crystal chemistry parameters for piezoelectric materials, a static analysis of a 3 atom, dipolar molecule has been undertaken to derive relationships for elastic compliance s{sup E}, dielectric permittivity ε{sup X}, and piezoelectric charge coefficient d in terms of an effective ionic charge and two inter-atomic force constants. The relationships demonstrate the mutual interdependence of the three coefficients, in keeping with experimental evidence from a large dataset of commercial piezoelectric materials. It is shown that the electromechanical coupling coefficient k is purely an expressionmore » of the asymmetry in the two force constants or bond compliances. The treatment is extended to show that the quadratic electrostriction relation between strain and polarization, in both centrosymmetric and non-centrosymmetric systems, is due to the presence of a non-zero 2nd order term in the bond compliance. Comparison with experimental data explains the counter-intuitive, positive correlation of k with s{sup E} and ε{sup X} and supports the proposition that high piezoelectric activity in single crystals is dominated by large compliance coupled with asymmetry in the sub-cell force constants. However, the analysis also shows that in polycrystalline materials, the dielectric anisotropy of the constituent crystals can be more important for attaining large charge coefficients. The model provides a completely new methodology for the interpretation of piezoelectric and electrostrictive property data and suggests methods for rapid screening for high activity in candidate piezoelectric materials, both experimentally and by novel interrogation of ab initio calculations.« less

Progressive freezing and sweating in a test unit

NASA Astrophysics Data System (ADS)

Ulrich, J.; Özoğuz, Y.

1990-01-01

Crystallization from melts is applied in several fields like waste water treatment, fruit juice or liquid food concentration and purification of organic chemicals. Investigations to improve the understanding, the performance and the control of the process have been carried out. The experimental unit used a vertical tube with a falling film on the outside. With an specially designed measuring technique process controlling parameters have been studied. The results demonstrate the dependency of those parameters upon each other and indicate the way to control the process by controlling the dominant parameter. This is the growth rate of the crystal coat. A further purification of the crystal layer can be achieved by introducing the procedure of sweating, which is a controlled partial melting of the crystal coat. Here again process parameters have been varied and results are presented. The strong effect upon the final purity of the product by an efficient executed sweating which is effectively tuned on the crystallization procedure should save crystallization steps, energy and time.

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

Ginley, Theresa P.; Wang, Yong; Law, Stephanie

In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V 2-VI 3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have amore » high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. Furthermore, we close by discussing the bright future for TI film growth by MBE.« less

Square array photonic crystal fiber-based surface plasmon resonance refractive index sensor

NASA Astrophysics Data System (ADS)

Liu, Min; Yang, Xu; Zhao, Bingyue; Hou, Jingyun; Shum, Ping

2017-12-01

Based on surface plasmon resonance (SPR), a novel refractive index (RI) sensor comprising a square photonic crystal fiber (PCF) is proposed to realize the detection of the annular analyte. Instead of hexagon structure, four large air-holes in a square array are introduced to enhance the sensitivity by allowing two polarization directions of the core mode to be more sensitive. The gold is used as the only plasmonic material. The design purpose is to reduce the difficulty in gold deposition and enhance the RI sensitivity. The guiding properties and the effects of the parameters on the performance of the sensor are numerically investigated by the Finite Element Method (FEM). By optimizing the structure, the sensor can exhibit remarkable sensitivity up to 7250 nm/RIU and resolution of 1.0638 × 10-5 RIU with only one plasmonic material, which is very competitive compared with the other reported externally coated and single-layer coated PCF-based SPR (PCF-SPR) sensors, to our best knowledge.

Study of Strength Characteristics of Steel Specimens after Selective Laser Melting of Powder Materials 17-4PH, 316L, 321

NASA Astrophysics Data System (ADS)

Zhukov, Anton; Barakhtin, Boris; Kuznetsov, Pavel

By the method of selective laser melting of powder materials nanostructured stainless steels 17-4PH, 316L, 321 were obtained. In all experiments the recorded hardness increase depending on the construction parameters. Obtained relationship of hardness increase with the carbon ratio, which explained by the chemical composition of the metal in the melting zone. It is suggested that the effect of hardness increase is associated with structural changes as to the formation and dissolution of hardening nanophases. Methods of metallography were performed in structural studies. Traces of interlayer segregation were detected inside the grains as turbulent eddies in the bands of different saturation tone caused by the migration of convective (mass transfer) metal atoms. It was visible signs of crystallization through the grain places the image (dendrite crystals). These facts revealed structural features suggest that the adhesion layers of melted powder was initiated by the colder layers and going mechanism epitaxy by coherently oriented groups of atoms from layers of melting.

Structural Characterization and Impedance Spectroscopy of Substituted, Fused-Ring Organic Semiconductors

NASA Astrophysics Data System (ADS)

Shaw, Charles Michael

Organic materials present a number of advantages over silicon that make them ideal candidates for modest performance devices like active matrix backplanes and RFID tags. The work detailed here describes both structural characterization of promising new materials, as well as the adaptation of impedance spectroscopy techniques to the study of organic transistors. Unit cells and solution casting behavior for dioctyl- and didodecyl-pentathienoacene are presented. Dioctyl pentathienoacene has an orthorhombic lattice with parameters a = 1.15 nm, b = 0.43 nm and c = 3.05 nm. Didodecyl pentathienoacene has an monoclinic lattice with parameters gamma = 92.2°, a = 1.10 urn, b = 0.42 nm and c = 3.89 nm. Additionally, thermotropic phase behavior is detailed. Both materials exhibit a "side chain melting" transition---characterized by a dramatic unit cell contraction of more than 20%---and smectic C liquid crystal phases. The side chain melting transition shows similarity to phase transitions elicited by exposing these materials to high energy electron flux. In both cases, disorder in the substitutions results in new phases for these materials. Dioctyl-pentathienoacene also exhibits a unique phase, which is intermediately ordered and shows a threefold increase in critical dose over the as-cast phase. Impedance spectroscopy of triisopropylsilyl pentacene transistors suggests these devices are well fit by a Voigt model equivalent circuit. The gate bias dependent resistor represents the channel conductance and the capacitor represents the drain-gate and source-gate capacitances. This in turn suggests that conduction occurs through delocalized states available in ordered regions, with disordered regions contributing localized, immobile states. Impedance spectroscopy of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) shows similar behavior. The use of variable temperature impedance spectroscopy is also demonstrated. This technique is used to measure the reduction in trap energy---from 200 meV to 140 meV---produced by annealing the material in its liquid crystal phase.

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.

High-pressure dielectric studies on 1,6-anhydro-β -D-mannopyranose (plastic crystal) and 2,3,4-tri-O-acetyl-1,6-anhydro-β -D-glucopyranose (canonical glass)

NASA Astrophysics Data System (ADS)

Heczko, Dawid; Kamińska, Ewa; Minecka, Aldona; Dzienia, Andrzej; Jurkiewicz, Karolina; Tarnacka, Magdalena; Talik, Agnieszka; Kamiński, Kamil; Paluch, Marian

2018-05-01

Broadband Dielectric Spectroscopy was applied to investigate molecular dynamics of two anhydrosaccharides, i.e., 1,6-anhydro-β-D-mannopyranose, anhMAN (hydrogen-bonded system) and 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-glucopyranose, ac-anhGLU (van der Waals material), at different thermodynamic conditions. Moreover, the reported data were compared with those recently published for two other H-bonded systems, i.e., 1,6-anhydro-β-D-glucopyranose (anhGLU) and D-glucose (D-GLU). A direct comparison of the dynamical behavior of the materials with a similar chemical structure but significantly differing by the degrees of freedom, complexity, and intermolecular interactions made it possible to probe the impact of compression on the fragility, Temperature-Pressure Superpositioning and pressure coefficient of the glassy crystal/glass transition temperatures (d Tg c/d p ; d Tg/d p ). Moreover, the correlation between d Tg c/d p determined experimentally from the high-pressure dielectric data and the Ehrenfest equation has been tested for the plastic crystals (anhGLU and anhMAN) for the first time. Interestingly, a satisfactory agreement was found between both approaches. It is a quite intriguing finding which can be rationalized by the fact that the studied materials are characterized by the low complexity (lower degrees of freedom with respect to the molecular mobility) as well as ordered internal structure. Therefore, one can speculate that in contrast to the ordinary glasses the dynamics of the plastic crystals might be described with the use of a single order parameter. However, to confirm this thesis further, pressure-volume-temperature (PVT) experiments enabling calculations of the Prigogine Defay ratio are required.

Single crystals of the fluorite nonstoichiometric phase Eu{0.916/2+}Eu{0.084/3+}F2.084 (conductivity, transmission, and hardness)

NASA Astrophysics Data System (ADS)

Sobolev, B. P.; Turkina, T. M.; Sorokin, N. I.; Karimov, D. N.; Komar'kova, O. N.; Sulyanova, E. A.

2010-07-01

The nonstoichiometric phase EuF2+ x has been obtained via the partial reduction of EuF3 by elementary Si at 900-1100°C. Eu{0.916/2+}Eu{0.084/3+}F2.084 (EuF2.084) single crystals have been grown from melt by the Bridgman method in a fluorinating atmosphere. These crystals belong to the CaF2 structure type (sp. gr. Fm bar 3 m) with the cubic lattice parameter a = 5.8287(2) Å, are transparent in the spectral range of 0.5-11.3 μm, and have microhardness H μ = 3.12 ± 0.13 GPa and ionic conductivity σ = 1.4 × 10-5 S/cm at 400°C with the ion transport activation energy E a = 1.10 ± 0.05 eV. The physicochemical characteristics of the fluorite phases in the EuF2 - EuF3 systems are similar to those of the phases in the SrF2 - EuF3 and SrF2 - GdF3 systems due to the similar lattice parameters of the EuF2 and SrF2 components. Europium difluoride supplements the list of fluorite components MF2 ( M = Ca, Sr, Ba, Cd, Pb), which are crystal matrices for nonstoichiometric (nanostructured) fluoride materials M 1 - x R x F2 + x ( R are rare earth elements).

Investigation on synthesis, growth, structure and physical properties of AgGa0.5In0.5S2 single crystals for Mid-IR application

NASA Astrophysics Data System (ADS)

Karunagaran, N.; Ramasamy, P.

2018-02-01

Silver Gallium Indium Sulfide (AgGa0.5In0.5S2) belongs to the family of AIBIIIC2VI ternary compound semiconductors which crystallize in the chalcopyrite structure. Synthesis of the polycrystalline material from the starting elements is achieved using melt temperature oscillation method. The AgGa0.5In0.5S2 single crystals have been grown by the vertical Bridgman technique. The synthesized AgGa0.5In0.5S2 polycrystalline charge was confirmed by powder XRD. The peak positions are in good agreement with the powder diffraction file. Thermal property was analyzed using differential scanning calorimetry (DSC) technique. The melting point of the crystal is 896 °C and freezing point is 862 °C. The unit cell parameters were confirmed by single crystal X-ray. The transmittance of the grown crystal is 55% in the NIR region and 60% in the mid-IR region. The optical band gap was found to be 2.0 eV. The stoichiometric composition of AgGa0.5In0.5S2 was measured using energy dispersive spectrometry (EDS). The photoluminescence behavior of AgGa0.5In0.5S2 has been analyzed. The resistivity of the grown single crystal has been measured.

The collection of MicroED data for macromolecular crystallography.

PubMed

Shi, Dan; Nannenga, Brent L; de la Cruz, M Jason; Liu, Jinyang; Sawtelle, Steven; Calero, Guillermo; Reyes, Francis E; Hattne, Johan; Gonen, Tamir

2016-05-01

The formation of large, well-ordered crystals for crystallographic experiments remains a crucial bottleneck to the structural understanding of many important biological systems. To help alleviate this problem in crystallography, we have developed the MicroED method for the collection of electron diffraction data from 3D microcrystals and nanocrystals of radiation-sensitive biological material. In this approach, liquid solutions containing protein microcrystals are deposited on carbon-coated electron microscopy grids and are vitrified by plunging them into liquid ethane. MicroED data are collected for each selected crystal using cryo-electron microscopy, in which the crystal is diffracted using very few electrons as the stage is continuously rotated. This protocol gives advice on how to identify microcrystals by light microscopy or by negative-stain electron microscopy in samples obtained from standard protein crystallization experiments. The protocol also includes information about custom-designed equipment for controlling crystal rotation and software for recording experimental parameters in diffraction image metadata. Identifying microcrystals, preparing samples and setting up the microscope for diffraction data collection take approximately half an hour for each step. Screening microcrystals for quality diffraction takes roughly an hour, and the collection of a single data set is ∼10 min in duration. Complete data sets and resulting high-resolution structures can be obtained from a single crystal or by merging data from multiple crystals.

Optimization of rare-earth-doped fluorides for infrared lasers

NASA Astrophysics Data System (ADS)

Peterson, Rita Dedomenico

2000-11-01

The rare-earth-doped fluoride crystals Tm,Dy:BaY2F8 (Tm,Dy:BYF), Yb,Pr:NaYF4 (Yb,Pr:NYF), and Nd:NYF show considerable promise as infrared laser materials, operating at 3 μm, 1.3 μm, and 1.06 μm respectively. Lasing has been reported previously on all three ionic transitions, but not in these crystals. Optimization of these materials for laser applications requires a more complete spectroscopic characterization than is currently available, particularly with regard to the key parameters of fluorescence lifetime and stimulated emission cross section. To further the optimization process, polarized absorption and emission have been measured for Tm,Dy:BYF, Yb,Pr:NYF, and Nd:NYF, and relevant fluorescence lifetimes have been measured or estimated. For Tm,Dy:BYF and Yb,Pr:NYF which rely upon sensitization, energy transfer parameters were calculated. Results were used in a mathematical model to determine the conditions in which lasing may be obtained. The long upper laser level lifetime in Tm,Dy:BYF translates into low threshold pump intensity, but the ability to reach threshold depends strongly on active ion concentration. The short lifetime in Yb,Pr:NYF leads to much higher threshold pump intensities, but lasing is still attainable if resonator loss is minimized. In Nd:NYF lasing was demonstrated, with a maximum of 60 mW output from an absorbed pump power of 345 mW, and a slope efficiency of 21%. Thresholds were high owing to resonator losses near 9%. Two chief issues involving the optimization of these laser materials were identified and explored. First, identification of the orientation for which emission cross section is highest is complicated in Tm,Dy:BYF by the presence of strong magnetic dipole radiation on the 3 μm transition. This effect makes it necessary to account for the polarization of both the electric and magnetic fields of the emitted radiation when determining an optimal crystal orientation, an accounting further complicated by the low symmetry of the monoclinic BYF host crystal. Second, the effect of host crystal on fluorescence lifetime was considered by comparing lifetime values for the same ionic manifolds in BYF, NYF, and other host crystals. NYF has especially low phonon energies, which leads to longer lifetimes on the longer wavelength transitions which are susceptible to multiphonon relaxation. This advantage is especially needed for lasing at 1.3 μm in Pr where the upper level lifetime is very short. On the shorter wavelength transitions in Tm and Nd, however, the role of phonons is negligible and lifetimes are somewhat shorter than in other fluoride hosts.

Low-Dimensional Material: Structure-Property Relationship and Applications in Energy and Environmental Engineering

NASA Astrophysics Data System (ADS)

Xiao, Hang

In the past several decades, low-dimensional materials (0D materials, 1D materials and 2D materials) have attracted much interest from both the experimental and theoretical points of view. Because of the quantum confinement effect, low-dimensional materials have exhibited a kaleidoscope of fascinating phenomena and unusual physical and chemical properties, shedding light on many novel applications. Despite the enormous success has been achieved in the research of low-dimensional materials, there are three fundamental challenges of research in low-dimensional materials: 1) Develop new computational tools to accurately describe the properties of low-dimensional materials with low computational cost. 2) Predict and synthesize new low-dimensional materials with novel properties. 3) Reveal new phenomenon induced by the interaction between low-dimensional materials and the surrounding environment. In this thesis, atomistic modelling tools have been applied to address these challenges. We first developed ReaxFF parameters for phosphorus and hydrogen to give an accurate description of the chemical and mechanical properties of pristine and defected black phosphorene. ReaxFF for P/H is transferable to a wide range of phosphorus and hydrogen containing systems including bulk black phosphorus, blue phosphorene, edge-hydrogenated phosphorene, phosphorus clusters and phosphorus hydride molecules. The potential parameters were obtained by conducting global optimization with respect to a set of reference data generated by extensive ab initio calculations. We extended ReaxFF by adding a 60° correction term which significantly improved the description of phosphorus clusters. Emphasis was placed on the mechanical response of black phosphorene with different types of defects. Compared to the nonreactive SW potential of phosphorene, ReaxFF for P/H systems provides a significant improvement in describing the mechanical properties of the pristine and defected black phosphorene, as well as the thermal stability of phosphorene nanotubes. A counterintuitive phenomenon was observed that single vacancies weaken the black phosphorene more than double vacancies with higher formation energy. Our results also showed that the mechanical response of black phosphorene is more sensitive to defects in the zigzag direction than that in the armchair direction. Since ReaxFF allows straightforward extensions to the heterogeneous systems, such as oxides, nitrides, the proposed ReaxFF parameters for P/H systems also underpinned the reactive force field description of heterogeneous P systems, including P-containing 2D van der Waals heterostructures, oxides, etc. Based on the evolutionary algorithm driven structural search, we proposed a new stable trisulfur dinitride (S3N2) 2D crystal that is a covalent network composed solely of S-N sigma bonds. S3N 2 crystal is dynamically, thermally and chemically stable as confirmed by the computed phonon spectrum and ab initio molecular dynamics simulations. GW calculations showed that the 2D S3N2 crystal is a wide, direct band-gap (3.92 eV) semiconductor with a small hole effective mass. The anisotropic optical response of 2D S3N 2 crystal was revealed by GW-BSE calculations. Our result not only marked the prediction of the first 2D crystal composed of nitrogen and sulfur, but also underpinned potential innovations in 2D electronics, optoelectronics, etc. Inspired by the discovery of S3N2 2D crystal, we proposed a new 2D crystal, diphosphorus trisulfide (P2S3), based on the extensive evolutionary algorithm driven structural search. The 2D P2S3 crystal was confirmed to be dynamically, thermally and chemically stable by the computed phonon spectrum and ab initio molecular dynamics simulations. This 2D crystalline phase of P 2S3 corresponds to the global minimum in the Born-Oppenheimer surface of the phosphorus sulfide monolayers with 2:3 stoichiometry. It is a wide band gap (4.55 eV) semiconductor with P-S ? bonds. The electronic properties of P2S3 structure can be tuned by stacking into multilayer P2S3 structures, forming P2S3 nanoribbons or rolling into P2S3 nanotubes, expanding its potential applications for the emerging field of 2D electronics. Then we showed that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules was investigated by ab initio method. For n = 1-5 water molecules, all the reactants follow a stepwise pathway to the transition state. For n = 6-8 water molecules, all the reactants undergo a direct proton transfer to the transition state with overall lower activation free energy. The activation free energy of the reaction is dramatically reduced from 10.4 to 2.4 kcal/mol as the number of water molecules increases from 1 to 6. Meanwhile, the degree of the hydrolysis of CO32- is significantly increased compared to the bulk water solution scenario. The incomplete hydration shells facilitate the hydrolysis of CO3 2- with few water molecules to be not only thermodynamically favorable but also kinetically favorable. We showed that the chemical kinetics is not likely to constrain the speed of CO2 air capture driven by the humidity-swing. (Abstract shortened by ProQuest.).

Angular non-critical phase-matching second-harmonic-generation characteristics of RECOB (RE = Tm, Y, Gd, Sm, Nd and La) crystals.

PubMed

Liu, Yanqing; Wang, Zhengping; Yu, Fapeng; Qi, Hongwei; Yang, Xiuqin; Yu, Xiaoqiang; Zhao, Xian; Xu, Xinguang

2017-05-15

For the first time, the angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) characteristics of a family of monoclinic oxoborate crystals, RECa 4 O(BO 3 ) 3 (RECOB, RE = Tm, Y, Gd, Sm, Nd and La), were comprehensively investigated. For all of the realizable A-NCPM SHG styles, the feature parameters including PM wavelength, angular, wavelength and temperature acceptance bandwidths, have been derived from the theory and verified by the experiments. We discovered that the closer the ion radius between RE 3+ and Ca 2+ , the smaller the birefringence, and the better the A-NCPM SHG properties. As a result, for the Type-I SHG on Y-axis which has the largest effective nonlinear optical coefficient (d eff ) among the three realizable A-NCPM styles, NdCOB crystal presents the longest PM wavelength (927 nm), the largest angular acceptance bandwidth (Δθ⋅l 1/2 = 84.3 mrad·cm 1/2 , Δϕ⋅l 1/2 = 58.8 mrad·cm 1/2 ), and the broadest wavelength acceptance bandwidth (8.7 nm). This discovery will contribute to the design of new NCPM materials, at the same time the parameter formula will be helpful for the theoretical prediction of NCPM performance.

Magnetorheological finishing (MRF) of potassium dihydrogen phosphate (KDP) crystals: nonaqueous fluids development, optical finish, and laser damage performance at 1064 nm and 532 nm

NASA Astrophysics Data System (ADS)

Menapace, J. A.; Ehrmann, P. R.; Bickel, R. C.

2009-10-01

Over the past year we have been working on specialized MR fluids for polishing KDP crystals. KDP is an extremely difficult material to conventionally polish due to its water solubility, low hardness, and temperature sensitivity. Today, KDP crystals are finished using single-point diamond turning (SPDT) tools and nonaqueous lubricants/coolants. KDP optics fabricated using SPDT, however, are limited to surface corrections due to tool/method characteristics with surface quality driven by microroughness from machine pitch, speed, force, and diamond tool character. MRF polishing offers a means to circumvent many of these issues since it is deterministic which makes the technique practical for surface and transmitted wavefront correction, is low force, and is temperature independent. What is lacking is a usable nonaqueous MR fluid that is chemically and physically compatible with KDP which can be used for polishing and subsequently cleaned from the optical surface. In this study, we will present the fluid parameters important in the design and development of nonaqueous MR fluid formulations capable of polishing KDP and how these parameters affect MRF polishing. We will also discuss requirements peculiar to successful KDP polishing and how they affect optical figure/finish and laser damage performance at 1064 nm and 532 nm.

Investigation of the multiplet features of SrTiO 3 in X-ray absorption spectra based on configuration interaction calculations

DOE PAGES

Wu, M.; Xin, Houlin L.; Wang, J. O.; ...

2018-04-24

Synchrotron-based L 2,3-edge absorption spectra show strong sensitivities to the local electronic structure and chemical environment. However, detailed physical information cannot be extracted easily without computational aids. Here in this study using the experimental Ti L 2,3-edges absorption spectrum of SrTiO 3as a fingerprint and considering full multiplet effects, calculations yield different energy parameters characterizing local ground state properties. The peak splitting and intensity ratios of the L 3 and L 2 set of peaks are carefully analyzed quantitatively, giving rise to a small hybridization energy around 1.2 eV, and the different hybridization energy values reported in the literature aremore » further addressed. Finally, absorption spectra with different linearly polarized photons under various tetragonal crystal fields are investigated, revealing a non-linear orbital–lattice interaction, and a theoretical guidance for material engineering of SrTiO 3-based thin films and heterostructures is offered. Finally, detailed analysis of spectrum shifts with different tetragonal crystal fields suggests that the e g crystal field splitting is a necessary parameter for a thorough analysis of the spectra, even though it is not relevant for the ground state properties.« less

Investigation of the multiplet features of SrTiO 3 in X-ray absorption spectra based on configuration interaction calculations

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

Wu, M.; Xin, Houlin L.; Wang, J. O.

Synchrotron-based L 2,3-edge absorption spectra show strong sensitivities to the local electronic structure and chemical environment. However, detailed physical information cannot be extracted easily without computational aids. Here in this study using the experimental Ti L 2,3-edges absorption spectrum of SrTiO 3as a fingerprint and considering full multiplet effects, calculations yield different energy parameters characterizing local ground state properties. The peak splitting and intensity ratios of the L 3 and L 2 set of peaks are carefully analyzed quantitatively, giving rise to a small hybridization energy around 1.2 eV, and the different hybridization energy values reported in the literature aremore » further addressed. Finally, absorption spectra with different linearly polarized photons under various tetragonal crystal fields are investigated, revealing a non-linear orbital–lattice interaction, and a theoretical guidance for material engineering of SrTiO 3-based thin films and heterostructures is offered. Finally, detailed analysis of spectrum shifts with different tetragonal crystal fields suggests that the e g crystal field splitting is a necessary parameter for a thorough analysis of the spectra, even though it is not relevant for the ground state properties.« less

Peculiar behavior of magnetoresistance in HgSe single crystal with low electron concentration

NASA Astrophysics Data System (ADS)

Lonchakov, A. T.; Bobin, S. B.; Deryushkin, V. V.; Okulov, V. I.; Govorkova, T. E.; Neverov, V. N.

2018-02-01

Magnetoresistive properties of the single crystal of HgSe with a low electron concentration were studied in a wide range of temperatures and magnetic fields. Some fundamental parameters of the spectrum and scattering of electrons were experimentally determined. Two important features of magnetic transport were found—strong transverse magnetoresistance (MR) and negative longitudinal MR, which can indicate the existence of the topological phase of the Weyl semimetal (WSM) in HgSe. Taking this hypothesis into account, we suggest a modified band diagram of mercury selenide at low electron energies. The obtained results are essential for the deeper understanding of both physics of gapless semiconductors and WSMs—promising materials for various applications in electronics, spintronics, computer, and laser technologies.

Liquid Photonic Crystals for Mesopore Detection.

PubMed

Zhu, Biting; Fu, Qianqian; Chen, Ke; Ge, Jianping

2018-01-02

Nitrogen adsorption-desorption for mesopore characterization requires the using of expensive instrumentation, time-consuming processes, and the consumption of liquid nitrogen. Herein, a new method is developed to measure the pore parameters through mixing a mesoporous substance with a supersaturated SiO 2 colloidal solution at different temperatures, and subsequent rapid measurement of reflection changes of the precipitated liquid photonic crystals. The pore volumes and diameters of mesoporous silica were measured according to the positive correlation between unit mass reflection change (Δλ/m) and pore volume (V), and the negative correlation between average absorption temperature (T) and pore diameter (D). This new approach may provide an alternative method for fast, convenient and economical characterization of mesoporous materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemically Stable Lipids for Membrane Protein Crystallization

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

Ishchenko, Andrii; Peng, Lingling; Zinovev, Egor

2017-05-01

The lipidic cubic phase (LCP) has been widely recognized as a promising membrane-mimicking matrix for biophysical studies of membrane proteins and their crystallization in a lipidic environment. Application of this material to a wide variety of membrane proteins, however, is hindered due to a limited number of available host lipids, mostly monoacylglycerols (MAGs). Here, we designed, synthesized, and characterized a series of chemically stable lipids resistant to hydrolysis, with properties complementary to the widely used MAGs. In order to assess their potential to serve as host lipids for crystallization, we characterized the phase properties and lattice parameters of mesophases mademore » of two most promising lipids at a variety of different conditions by polarized light microscopy and small-angle X-ray scattering. Both lipids showed remarkable chemical stability and an extended LCP region in the phase diagram covering a wide range of temperatures down to 4 °C. One of these lipids has been used for crystallization and structure determination of a prototypical membrane protein bacteriorhodopsin at 4 and 20 °C.« less

Controlled Synthesis and Understanding of Growth Mechanism – Parameters for Atmospheric Pressure Hydrothermal Synthesis of Ultrathin Secondary ZnO Nanowires

DOE PAGES

Jiao, Mingzhi; Nguyen, Duc; Nguyen, Van; ...

2015-11-10

We measured luminescence and scintillation in ZnO single crystals by photoluminescence and X-ray-induced luminescence (XRIL). XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. In the origin of green emission, the dominant trap emission in ZnO, was investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials or the surroundings. Moreover, the measurements showed the absence of positron traps inmore » the crystals and yielded a bulk positron lifetime value that is in complete agreement with the predicted theoretical value = thereby confirming the advantage of the GIPS method. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE.« less

Investigating Deformation and Mesoscale Void Creation in HMX Based Composites using Tomography Based Grain Scale Finite Element Modeling

NASA Astrophysics Data System (ADS)

Walters, David J.; Luscher, Darby J.; Manner, Virginia; Yeager, John D.; Patterson, Brian M.

2017-06-01

The microstructure of plastic bonded explosives (PBXs) significantly affects their macroscale mechanical characteristics. Imaging and modeling of the mesoscale constituents allows for a detailed examination of the deformation of mechanically loaded PBXs. In this study, explosive composites, formulated with HMX crystals and various HTPB based polymer binders have been imaged using micro Computed Tomography (μCT). Cohesive parameters for simulation of the crystal/binder interface are determined by comparing numerical and experimental results of the delamination of a polymer bound bi-crystal system. Similarly, polycrystalline samples are discretized into a finite element mesh using the mesoscale geometry captured by in-situ μCT imaging. Experimentally, increasing the stiffness of the HTPB binder in the polycrystalline system resulted in a transition from ductile flow with little crystal/binder delamination to brittle behavior with increased void creation along the interfaces. Simulating the macroscale compression of these samples demonstrates the effects that the mesoscale geometry, cohesive properties, and binder stiffness have on the creation and distribution of interfacial voids. Understanding void nucleation is critical for modeling damage in these complex materials.

Anisotropic ray trace

NASA Astrophysics Data System (ADS)

Lam, Wai Sze Tiffany

Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for anisotropic ray tracing. x. Chapter 4 presents the data reduction of the P matrix of a crystal waveplate. The diattenuation is embedded in the singular values of P. The retardance is divided into two parts: (A) The physical retardance induced by OPLs and surface interactions, and (B) the geometrical transformation induced by geometry of a ray path, which is calculated by the geometrical transform Q matrix. The Q matrix of an anisotropic intercept is derived from the generalization of s- and p-bases at the anisotropic intercept; the p basis is not confined to the plane of incidence due to the anisotropic refraction or reflection. Chapter 5 shows how the multiple P matrices associated with the eigenmodes resulting from propagation through multiple anisotropic surfaces can be combined into one P matrix when the multiple modes interfere in their overlapping regions. The resultant P matrix contains diattenuation induced at each surface interaction as well as the retardance due to ray propagation and total internal reflections. The polarization aberrations of crystal waveplates and crystal polarizers are studied in Chapter 6 and Chapter 7. A wavefront simulated by a grid of rays is traced through the anisotropic system and the resultant grid of rays is analyzed. The analysis is complicated by the ray doubling effects and the partially overlapping eigen-wavefronts propagating in various directions. The wavefront and polarization aberrations of each eigenmode can be evaluated from the electric field distributions. The overall polarization at the plane of interest or the image quality at the image plane are affected by each of these eigen-wavefronts. Isotropic materials become anisotropic due to stress, strain, or applied electric or magnetic fields. In Chapter 8, the P matrix for anisotropic materials is extended to ray tracing in stress birefringent materials which are treated as spatially varying anisotropic materials. Such simulations can predict the spatial retardance variation throughout the stressed optical component and its effects on the point spread function and modulation transfer function for different incident polarizations. The anisotropic extension of the P matrix also applies to other anisotropic optical components, such as anisotropic diffractive optical elements and anisotropic thin films. It systematically keeps track of polarization transformation in 3D global Cartesian coordinates of a ray propagating through series of anisotropic and isotropic optical components with arbitrary orientations. The polarization ray tracing calculus with this generalized P matrix provides a powerful tool for optical ray trace and allows comprehensive analysis of complex optical system. (Abstract shortened by UMI.).

Influence of nanomechanical crystal properties on the comminution process of particulate solids in spiral jet mills.

PubMed

Zügner, Sascha; Marquardt, Karin; Zimmermann, Ingfried

2006-02-01

Elastic-plastic properties of single crystals are supposed to influence the size reduction process of bulk materials during jet milling. According to Pahl [M.H. Pahl, Zerkleinerungstechnik 2. Auflage. Fachbuchverlag, Leipzig (1993)] and H. Rumpf: [Prinzipien der Prallzerkleinerung und ihre Anwendung bei der Strahlmahlung. Chem. Ing. Tech., 3(1960) 129-135.] fracture toughness, maximum strain or work of fracture for example are strongly dependent on mechanical parameters like hardness (H) and young's modulus of elasticity (E). In addition the dwell time of particles in a spiral jet mill proved to correlate with the hardness of the feed material [F. Rief: Ph. D. Thesis, University of Würzburg (2001)]. Therefore 'near-surface' properties have a direct influence on the effectiveness of the comminution process. The mean particle diameter as well as the size distribution of the ground product may vary significantly with the nanomechanical response of the material. Thus accurate measurement of crystals' hardness and modulus is essential to determine the ideal operational micronisation conditions of the spiral jet mill. The recently developed nanoindentation technique is applied to examine subsurface properties of pharmaceutical bulk materials, namely calcite, sodium ascorbate, lactose and sodium chloride. Pressing a small sized tip into the material while continuously recording load and displacement, characteristic diagrams are derived. The mathematical evaluation of the force-displacement-data allows for calculation of the hardness and the elastic modulus of the investigated material at penetration depths between 50-300 nm. Grinding experiments performed with a modified spiral jet mill (Type Fryma JMRS 80) indicate the strong impact of the elastic-plastic properties of a given substance on its breaking behaviour. The fineness of milled products produced at constant grinding conditions but with different crystalline powders varies significantly as it is dependent on the nanohardness and the elasticity of the feed material. The analysis of this correlation gives new insights into the size reduction process.

Correlates of individual, and age-related, differences in short-term learning.

PubMed

Zhang, Zhiyong; Davis, Hasker P; Salthouse, Timothy A; Tucker-Drob, Elliot M

2007-07-01

Latent growth models were applied to data on multitrial verbal and spatial learning tasks from two independent studies. Although significant individual differences in both initial level of performance and subsequent learning were found in both tasks, age differences were found only in mean initial level, and not in mean learning. In neither task was fluid or crystallized intelligence associated with learning. Although there were moderate correlations among the level parameters across the verbal and spatial tasks, the learning parameters were not significantly correlated with one another across task modalities. These results are inconsistent with the existence of a general (e.g., material-independent) learning ability.

Passive Sensor Materials Based on Liquid Crystals

DTIC Science & Technology

2011-03-12

REPORT Passive Sensor Materials based on Liquid Crystals 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: Research supported by this grant entitled “Passive...Sensor Materials Based on Liquid Crystals” revolved around an investigation of liquid crystalline materials for use in passive sensors for chemical... based on Liquid Crystals Report Title ABSTRACT Research supported by this grant entitled “Passive Sensor Materials Based on Liquid Crystals” revolved

Reduction of Defects in Germanium-Silicon

NASA Technical Reports Server (NTRS)

Szofran, Frank R.; Benz, K. W.; Cobb, Sharon D.; Croell, Anne; Dold, P.; Motafef, S.; Schweizer, M.; Volz, Martin P.; Walker, J. S.

2003-01-01

Crystals grown without being in contact with a container have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in the crystals. In addition to float-zone processing, detached Bridgman growth, although not a completely crucible-free method, is a promising tool to improve crystal quality. It does not suffer from the size limitations of float zoning and the impact of thermocapillary convection on heat and mass transport is expected to be negligible. Detached growth has been observed frequently during g experiments. Considerable improvements in crystalline quality have been reported for these cases. However, neither a thorough understanding of the process nor a quantitative assessment of the quality of these improvements exists. This project will determine the means to reproducibly grow GeSi alloys in a detached mode and seeks to compare processing-induced defects in Bridgman, detached-Bridgman, and floating-zone growth configurations in GeSi crystals (Si less than or equal to 10 at%) up to 20mm in diameter. Specific objectives include: measurement of the relevant material parameters such as contact angle, growth angle, surface tension, and wetting behavior of the GeSi-melt on potential crucible materials; determination of the mechanism of detached growth including the role of convection; quantitative determination of the differences in defects and impurities for crystals grown using normal Bridgman, detached Bridgman, and floating zone (FZ) methods; investigation of the influence of a defined flow imposed by a rotating magnetic field on the characteristics of detached growth; control of time-dependent Marangoni convection in the case of FZ growth by the use of a rotating magnetic field to examine the influence on the curvature of the solid-liquid interface and the heat and mass transport; and growth of benchmark quality GeSi-single crystals.

Positron Interactions with Oriented Polymers and with Chiral Quartz Crystals

NASA Astrophysics Data System (ADS)

Wu, Fei

Positron annihilation in various materials has been applied to characterize microstructure for decades. In this work, PALS was used to study material nanostructure, with a focus on the size and density of free volume and hole relaxation properties in polycarbonate (PC) and polymethylmethacrylate (PMMA); fundamental studies of polarized positron interaction with chiral crystals were also studied. Free volume relaxation in PC and PMMA with different levels of simple shear orientation was studied by PALS. Effects of applied pressure on the free volume recovery were evaluated. Combining the bulk- and pressure-dependent PALS analyses, the removal of applied pressure led to free-volume relaxation in all samples studied. The alignment of the polymer chains and free-volume holes imposes molecular restrictions on the molecular mobility of both PC and PMMA in their glassy states. Results indicated that the relaxation of the free volume holes at temperatures below glass transition is mostly reversible. Longitudinally polarized positron particles were used to reveal asymmetric interactions in chiral quartz crystals. Experimental results showed a significant intensity difference in free positronium annihilation for left handed (LH) and right handed (RH) chiral quartz crystals. Doppler broadening energy spectra (DBES) of z-cut LH or RH quartz disks at different angles were also measured by an "S parameter" to probe the observed difference. It was found that obtained annihilation energy difference of DBES was in agreement with the result of positron annihilation in bulk chiral crystals. PALS was used to compare different orientations and confirm asymmetric interactions in natural versus synthetic quartz LH and RH crystals in z and non-z orientations. Significant lifetime and intensity differences in free positronium annihilation for LH and RH quartz crystals were observed. The trend was found to be same in the related crystallographic orientations of the LH or RH crystals; the direction of incident positrons, z or non-z, did not affect the observed differences in lifetime and intensity trends. The results confirmed the existence of differential interactions of positronium with the asymmetric lattice structures of LH and RH quartz crystals.

Automating the application of smart materials for protein crystallization.

PubMed

Khurshid, Sahir; Govada, Lata; El-Sharif, Hazim F; Reddy, Subrayal M; Chayen, Naomi E

2015-03-01

The fabrication and validation of the first semi-liquid nonprotein nucleating agent to be administered automatically to crystallization trials is reported. This research builds upon prior demonstration of the suitability of molecularly imprinted polymers (MIPs; known as `smart materials') for inducing protein crystal growth. Modified MIPs of altered texture suitable for high-throughput trials are demonstrated to improve crystal quality and to increase the probability of success when screening for suitable crystallization conditions. The application of these materials is simple, time-efficient and will provide a potent tool for structural biologists embarking on crystallization trials.

Crystal structures of CaSiO3 polymorphs control growth and osteogenic differentiation of human mesenchymal stem cells on bioceramic surfaces.

PubMed

Zhang, Nianli; Molenda, James A; Mankoci, Steven; Zhou, Xianfeng; Murphy, William L; Sahai, Nita

2013-10-01

The repair and replacement of damaged or diseased human bone tissue requires a stable interface between the orthopedic implant and living tissue. The ideal material should be both osteoconductive (promote bonding to bone) and osteoinductive (induce osteogenic differentiation of cells and generate new bone). Partially resorbable bioceramic materials with both properties are developed by expensive trial-and-error methods. Structure-reactivity relationships for predicting the osteoinductive properties of ceramics would significantly increase the efficiency of developing materials for bone tissue engineering. Here we propose the novel hypothesis that the crystal structure of a bioceramic controls the release rates, subsequent surface modifications due to precipitation of new phases, and thus, the concentrations of soluble factors, and ultimately, the attachment, viability and osteogenic differentiation of human Mesenchymal Stem Cells (hMSCs). To illustrate our hypothesis, we used two CaSiO 3 polymorphs, pseudo-wollastonite (psw, β-CaSiO 3 ) and wollastonite (wol, α-CaSiO 3 ) as scaffolds for hMSC culture. Polymorphs are materials which have identical chemical composition and stoichiometry, but different crystal structures. We combined the results of detailed surface characterizations, including environmental Scanning Electron Microscopy (SEM) back-scattered imaging, and spot-analysis and 2D elemental mapping by SEM-Energy Dispersive X-ray (SEM-EDX), High Resolution Transmission Electron Microscopy (HRTEM) and surface roughness analysis; culture medium solution analyses; and molecular/genetic assays from cell culture. Our results confirmed the hypothesis that the psw polymorph, which has a strained silicate ring structure, is more osteoinductive than the wol polymorph, which has a more stable, open silicate chain structure. The observations could be attributed to easier dissolution (resorption) of psw compared to wol, which resulted in concentration profiles that were more osteoinductive for the former. Thus, we showed that crystal structure is a fundamental parameter to be considered in the intelligent design of pro-osteogenic, partially resorbable bioceramics.

Optimal configuration of microstructure in ferroelectric materials by stochastic optimization

NASA Astrophysics Data System (ADS)

Jayachandran, K. P.; Guedes, J. M.; Rodrigues, H. C.

2010-07-01

An optimization procedure determining the ideal configuration at the microstructural level of ferroelectric (FE) materials is applied to maximize piezoelectricity. Piezoelectricity in ceramic FEs differs significantly from that of single crystals because of the presence of crystallites (grains) possessing crystallographic axes aligned imperfectly. The piezoelectric properties of a polycrystalline (ceramic) FE is inextricably related to the grain orientation distribution (texture). The set of combination of variables, known as solution space, which dictates the texture of a ceramic is unlimited and hence the choice of the optimal solution which maximizes the piezoelectricity is complicated. Thus, a stochastic global optimization combined with homogenization is employed for the identification of the optimal granular configuration of the FE ceramic microstructure with optimum piezoelectric properties. The macroscopic equilibrium piezoelectric properties of polycrystalline FE is calculated using mathematical homogenization at each iteration step. The configuration of grains characterized by its orientations at each iteration is generated using a randomly selected set of orientation distribution parameters. The optimization procedure applied to the single crystalline phase compares well with the experimental data. Apparent enhancement of piezoelectric coefficient d33 is observed in an optimally oriented BaTiO3 single crystal. Based on the good agreement of results with the published data in single crystals, we proceed to apply the methodology in polycrystals. A configuration of crystallites, simultaneously constraining the orientation distribution of the c-axis (polar axis) while incorporating ab-plane randomness, which would multiply the overall piezoelectricity in ceramic BaTiO3 is also identified. The orientation distribution of the c-axes is found to be a narrow Gaussian distribution centered around 45°. The piezoelectric coefficient in such a ceramic is found to be nearly three times as that of the single crystal. Our optimization model provide designs for materials with enhanced piezoelectric performance, which would stimulate further studies involving materials possessing higher spontaneous polarization.

Review of aragonite and calcite crystal morphogenesis in thermal spring systems

NASA Astrophysics Data System (ADS)

Jones, Brian

2017-06-01

Aragonite and calcite crystals are the fundamental building blocks of calcareous thermal spring deposits. The diverse array of crystal morphologies found in these deposits, which includes monocrystals, mesocrystals, skeletal crystals, dendrites, and spherulites, are commonly precipitated under far-from-equilibrium conditions. Such crystals form through both abiotic and biotic processes. Many crystals develop through non-classical crystal growth models that involve the arrangement of nanocrystals in a precisely controlled crystallographic register. Calcite crystal morphogenesis has commonly been linked to a ;driving force;, which is a conceptual measure of the distance of the growth conditions from equilibrium conditions. Essentially, this scheme indicates that increasing levels of supersaturation and various other parameters that produce a progressive change from monocrystals and mesocrystals to skeletal crystals to crystallographic and non-crystallographic dendrites, to dumbbells, to spherulites. Despite the vast amount of information available from laboratory experiments and natural spring systems, the precise factors that control the driving force are open to debate. The fact that calcite crystal morphogenesis is still poorly understood is largely a reflection of the complexity of the factors that influence aragonite and calcite precipitation. Available information indicates that variations in calcite crystal morphogenesis can be attributed to physical and chemical parameters of the parent water, the presence of impurities, the addition of organic or inorganic additives to the water, the rate of crystal growth, and/or the presence of microbes and their associated biofilms. The problems in trying to relate crystal morphogenesis to specific environmental parameters arise because it is generally impossible to disentangle the controlling factor(s) from the vast array of potential parameters that may act alone or in unison with each other.

Optical characteristics of novel bulk and nanoengineered laser host materials

NASA Astrophysics Data System (ADS)

Prasad, Narasimha S.; Sova, Stacey; Kelly, Lisa; Bevan, Talon; Arnold, Bradley; Cooper, Christopher; Choa, Fow-Sen; Singh, N. B.

2018-02-01

The hexagonal apatite single crystals have been investigated for their applications as laser host materials. Czochralksi and flux growth methods have been utilized to obtain single crystals. For low temperature processing (<100 0C), several techniques for crystal growth have been developed. The hexagonal apatite structure (space group P63/m) is characteristic of several compounds, some of which have extremely interesting and useful properties as laser hosts and bone materials. Calcium lanthanum silicate (Nd-doped) and lanthanum aluminate material systems were studied in detail. Nanoengineered calcium and lanthanum based silicates were synthesized by a solution method and their optical and morphological characteristics were compared with Czochralski grown bulk hydroxyapatite single crystals. Materials were evaluated by absorbance, fluorescence and Raman characteristics. Neodymium, iron and chromium doped crystals grown by a solution method showed weak but similar optical properties to that of Czochralski grown single crystals.

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

DOEpatents

Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

1998-07-07

A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

DOEpatents

Todt, Volker; Miller, Dean J.; Shi, Donglu; Sengupta, Suvankar

1998-01-01

A method of fabricating bulk YBa.sub.2 Cu.sub.3 O.sub.x where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa.sub.2 Cu.sub.3 O.sub.x are heated in the presence of a Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y seed crystal to a temperature sufficient to form a liquid phase in the YBa.sub.2 Cu.sub.3 O.sub.x while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa.sub.2 Cu.sub.3 O.sub.x material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material.

Crystal Graph Convolutional Neural Networks for an Accurate and Interpretable Prediction of Material Properties

NASA Astrophysics Data System (ADS)

Xie, Tian; Grossman, Jeffrey C.

2018-04-01

The use of machine learning methods for accelerating the design of crystalline materials usually requires manually constructed feature vectors or complex transformation of atom coordinates to input the crystal structure, which either constrains the model to certain crystal types or makes it difficult to provide chemical insights. Here, we develop a crystal graph convolutional neural networks framework to directly learn material properties from the connection of atoms in the crystal, providing a universal and interpretable representation of crystalline materials. Our method provides a highly accurate prediction of density functional theory calculated properties for eight different properties of crystals with various structure types and compositions after being trained with 1 04 data points. Further, our framework is interpretable because one can extract the contributions from local chemical environments to global properties. Using an example of perovskites, we show how this information can be utilized to discover empirical rules for materials design.

Understanding the glass-forming ability of active pharmaceutical ingredients for designing supersaturating dosage forms.

PubMed

Kawakami, Kohsaku; Usui, Toshinori; Hattori, Mitsunari

2012-09-01

Amorphous solid dispersions have great potential for enhancing oral absorption of poorly soluble drugs. Crystallization behavior during storage and after exposure to aqueous media must be examined in detail for designing stable and effective amorphous formulations, and it is significantly affected by the intrinsic properties of an amorphous drug. Many attempts have been made to correlate various thermodynamic parameters of pharmaceutical glasses with their crystallization behavior; however, variations in model drugs that could be used for such investigation has been limited because the amorphous characteristics of drugs possessing a high crystallization tendency are difficult to evaluate. In this study, high-speed differential scanning calorimetry, which could inhibit their crystallization using high cooling rates up to 2000°C/s, was employed for assessing such drugs. The thermodynamic parameters of the glasses, including glass transition temperature (T(g)) and fragility, were obtained to show that their crystallization tendency cannot be explained simply by the parameters, although there have been general thought that fragility may be correlated with crystallization tendency. Also investigated was correlation between the thermodynamic parameters and crystallization tendency upon contact with water, which influences in vivo efficacy of amorphous formulations. T(g) was correlated well with the crystallization tendency upon contact with water. Copyright © 2012 Wiley Periodicals, Inc.

Nanomechanical investigation of ion implanted single crystals - Challenges, possibilities and pitfall traps related to nanoindentation

NASA Astrophysics Data System (ADS)

Kurpaska, Lukasz

2017-10-01

Nanoindentation technique have developed considerably over last thirty years. Nowadays, commercially available systems offer very precise measurement in nano- and microscale, environmental noise cancelling (or at least noise suppressing), in situ high temperature indentation in controlled atmosphere and vacuum conditions and different additional options, among them dedicated indentation is one of the most popular. Due to its high precision, and ability to measure mechanical properties from very small depths (tens of nm), this technique become quite popular in the nuclear society. It is known that ion implantation (to some extent) can simulate the influence of neutron flux. However, depth of the material damage is very limited resulting in creation of thin layer of modified material over unmodified bulk. Therefore, only very precise technique, offering possibility to control depth of the measurement can be used to study functional properties of the material. For this reason, nanoindentation technique seems to be a perfect tool to investigate mechanical properties of ion implanted specimens. However, conducting correct nanomechanical experiment and extracting valuable mechanical parameters is not an easy task. In this paper a discussion about the nanoindentation tests performed on ion irradiated YSZ single crystal is presented. The goal of this paper is to discuss possible traps when studying mechanical properties of such materials and thin coatings.

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

Hansen, Benjamin L; Bronkhorst, Curt; Beyerlein, Irene

The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. Themore » elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.« less

Computational studies on the crystal structure, thermodynamic properties, detonation performance, and pyrolysis mechanism of 2,4,6,8-tetranitro-1,3,5,7-tetraazacubane as a novel high energy density material.

PubMed

Wang, Fang; Du, Hongchen; Zhang, Jianying; Gong, Xuedong

2011-10-27

Studies have suggested that octanitrocubane (ONC) is one of the most powerful non-nuclear high energy density material (HEDM) currently known. 2,4,6,8-Tetranitro-1,3,5,7-tetraazacubane (TNTAC) studied in this work may also be a novel HEDM due to its high nitrogen content and crystal density. Density functional theory and molecular mechanics methods have been employed to study the crystal structure, IR spectrum, electronic structure, thermodynamic properties, gas-phase and condensed-phase heat of formation, detonation performance, and pyrolysis mechanism of TNTAC. The TNTAC has a predicted density of about 2.12 g/cm(3), and its detonation velocity (10.42 km/s) and detonation pressure (52.82 GPa) are higher than that of ONC. The crystalline packing is P2(1)2(1)2(1), and the corresponding cell parameters are Z = 4, a = 8.87 Å, b = 8.87 Å, and c = 11.47 Å. Both the density of states of the predicted crystal and the bond dissociation energy of the molecule in gas phase show that the cage C-N bond is the trigger bond during thermolysis. The activation energy of the pyrolysis initiation reaction obtained from the B3LYP/6-311++G(2df,2p) level is 125.98 kJ/mol, which indicates that TNTAC meets the thermal stability request as an exploitable HEDM.

ZnSe(Te)-based crystals and detectors for nondestructive testing and cargo inspection

NASA Astrophysics Data System (ADS)

Seminozhenko, V. P.; Ryzhikov, V. D.; Opolonin, A. D.; Lisetska, O. K.; Galkin, S. N.; Voronkin, E. F.; Kostyukevich, S. A.

2006-08-01

Due to disadvantages of scintillator ZnSe(Te) - poor transparence to own emission (10 -1 cm -1), long decay time, low density and Z eff-this material had no practical applications in the ranges of X-ray energies about 120-140 keV. After the development of dual energy X-ray inspection scanners, CT and digital radiography situation changed on the contrary at whole. Both theory and experiments show that now it is the best material for low energy array detectors. The pilot-industrial production of ZnSe(Te) crystals is organized, their usage in CT and inspection X-rays scanners being already started. It has become possible to get tomography imaging simultaneously with automatic recognition of dangerous objects and substances, which is due to the unique parameters of ZnSe(Te). Presently several leading western companies look for possibilities to use ZnSe(Te) for medical X-ray CT. Our aim was to unveil the nature of luminescence centers and the emission mechanism in crystals of ZnSe(Te) compounds with isovalent dopants from the results of our studies of optical, spectroscopic and kinetic characteriestics of these crystals. Basing on the obtained understanding of the emission centers, we aimed at creation of a reproducible production technology of scintillators for application in inspection and medical equipment. The research described in this publication was made possible in part by INTAS Project Ref. Nr. 05-104-7519.

Preparation and characterization of functionalized single walled carbon nanotubes (fSWCNT)/ Hydroxyapatite (HAp)-Nylon hybridized composite biomaterial to study the mechanical properties

NASA Astrophysics Data System (ADS)

Khanal, Suraj; Leventouri, Theodora; Mahfuz, Hassan; Rondinone, Adam

2014-03-01

Synthetic hydroxyapatite (HAp) bears poor mechanical properties that limit its applicability in orthopedics. We study the possibility of overcoming such limitations by incorporating functionalized single walled carbon nanotubes (fSWCNT) in a biocompatible/bioactive nano-composite. We present results from synthesis and characterization of samples prepared under different processing parameters. Ultra sonication method was to disperse functionalized single walled carbon nanotubes (fSWCNT) in HAp followed by a simple hot assorting method to incorporate with polymerized ɛ-caprolactam. The fracture toughness of the composite materials was tested in compliance with the ASTM D-5045 standard. We have found that while the fracture toughness strongly depends on the processing parameters, a value comparable to the one for cortical bone is achieved. Mechanical properties, electron microscopy and crystal structure properties of the composite materials will be discussed.

Titanium-doped sapphire laser research and design study

NASA Technical Reports Server (NTRS)

Moulton, Peter F.

1987-01-01

Three main topics were considered in this study: the fundamental laser parameters of titanium-doped sapphire, characterization of commercially grown material, and design of a tunable, narrow-linewidth laser. Fundamental parameters investigated included the gain cross section, upper-state lifetime as a function of temperature and the surface-damage threshold. Commercial material was found to vary widely in the level of absorption of the laser wavelength with the highest absorption in Czochralski-grown crystals. Several Yi:sapphire lasers were constructed, including a multimode laser with greater than 50mJ of output energy and a single-transverse-mode ring laser, whose spectral and temporal characteristics were completely characterized. A design for a narrow-linewidth (single-frequency) Ti:sapphire laser was developed, based on the results of the experimental work. The design involves the use of a single-frequency, quasi-cw master oscillator, employed as an injection source for a pulsed ring laser.

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.

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.

Flux Crystal Growth of the RE 2Ru 3Ge 5 ( RE = La, Ce, Nd, Gd, Tb) Series and Their Magnetic and Metamagnetic Transitions

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

Bugaris, Daniel E.; Malliakas, Christos D.; Bud?ko, Sergey L.

Previously synthesized only as powders, single crystals of the RE 2Ru 3Ge 5 (RE = La, Ce, Nd, Gd, Tb) series of compounds have been now been obtained from molten In. We report that these materials crystallize with the U 2Co 3Si 5-type structure in orthorhombic space group Ibam with lattice parameters a ~ 10.00-9.77 Å (La-Tb), b ~ 12.51-12.35 Å, and c ~ 5.92-5.72 Å. The structure is a three-dimensional framework consisting of RuGe 5 and RuGe 6 units, as well as Ge-Ge zigzag chains. This structure type, along with the other five (Sc 2Fe 3Si 5, Lu 2Comore » 3Si 5, Y 2Rh 3Sn 5, Yb 2Ir 3Ge 5, and Yb 2Pt 3Sn 5) to compose the RE 2T 3X 5 phase space, are discussed in depth. For the three compounds with RE = Nd, Gd, and Tb, multiple magnetic transitions and metamagnetic behavior are observed. Lastly, electronic band structure calculations performed on La 2Ru 3Ge 5 indicate that these materials have a negative band gap and are semimetallic in nature.« less

Quartz Crystal Microbalance with Dissipation Monitoring: Enabling Real-Time Characterization of Biological Materials and Their Interactions

PubMed Central

Dixon, Matthew C.

2008-01-01

In recent years, there has been a rapid growth in the number of scientific reports in which the quartz crystal microbalance (QCM) technique has played a key role in elucidating various aspects of biological materials and their interactions. This article illustrates some key advances in the development of a special variation of this technique called quartz crystal microbalance with dissipation monitoring (QCM-D). The main feature and advantage of QCM-D, compared with the conventional QCM, is that it in addition to measuring changes in resonant frequency (Δf), a simultaneous parameter related to the energy loss or dissipation (ΔD) of the system is also measured. Δf essentially measures changes in the mass attached to the sensor surface, while ΔD measures properties related to the viscoelastic properties of the adlayer. Thus, QCM-D measures two totally independent properties of the adlayer. The focus of this review is an overview of the QCM-D technology and highlights of recent applications. Specifically, recent applications dealing with DNA, proteins, lipids, and cells will be detailed. This is not intended as a comprehensive review of all possible applications of the QCM-D technology, but rather a glimpse into a few highlighted application areas in the biomolecular field that were published in 2007. PMID:19137101

Flux Crystal Growth of the RE 2Ru 3Ge 5 ( RE = La, Ce, Nd, Gd, Tb) Series and Their Magnetic and Metamagnetic Transitions

DOE PAGES

Bugaris, Daniel E.; Malliakas, Christos D.; Bud?ko, Sergey L.; ...

2017-11-21

Previously synthesized only as powders, single crystals of the RE 2Ru 3Ge 5 (RE = La, Ce, Nd, Gd, Tb) series of compounds have been now been obtained from molten In. We report that these materials crystallize with the U 2Co 3Si 5-type structure in orthorhombic space group Ibam with lattice parameters a ~ 10.00-9.77 Å (La-Tb), b ~ 12.51-12.35 Å, and c ~ 5.92-5.72 Å. The structure is a three-dimensional framework consisting of RuGe 5 and RuGe 6 units, as well as Ge-Ge zigzag chains. This structure type, along with the other five (Sc 2Fe 3Si 5, Lu 2Comore » 3Si 5, Y 2Rh 3Sn 5, Yb 2Ir 3Ge 5, and Yb 2Pt 3Sn 5) to compose the RE 2T 3X 5 phase space, are discussed in depth. For the three compounds with RE = Nd, Gd, and Tb, multiple magnetic transitions and metamagnetic behavior are observed. Lastly, electronic band structure calculations performed on La 2Ru 3Ge 5 indicate that these materials have a negative band gap and are semimetallic in nature.« less

Molecular organic crystalline matrix for hybrid organic-inorganic (nano) composite materials

NASA Astrophysics Data System (ADS)

Stanculescu, A.; Tugulea, L.; Alexandru, H. V.; Stanculescu, F.; Socol, M.

2005-02-01

Metal-doped benzil crystals have been grown by thermal gradient solidification in a vertical transparent growth configuration to investigate the effect of metallic guest on the ordered organic host. We have identified the conditions for growing homogeneous, optically good crystals of benzil doped with sodium and silver, limiting the effect of supercooling, low thermal conductivity and anisotropy of the growth speed (temperature gradient at the liquid-solid interface: 10-25 °C, moving speed of the growth interface 2.0 mm/h). The nature and concentration of the dopant are parameters affecting, through the growth process, the crystalline perfection and the optical properties of the organic matrix. Bulk optical characterisation, by spectrophotometrical methods, has offered details on some intrinsic properties of the system metal particles/benzil crystalline matrix. Analytical processing of the experimental data emphasised that benzil is a wide optical band gap organic semiconductor Eg=2.65 eV. We also have investigated the effect of sodium and silver on the properties of benzil crystal as potential transparent semiconductor matrix for (nano)composite metal/molecular organic material. With the increase of sodium concentration from c=1 to 6 wt%, a small narrowing of the band gap has been remarked. The same behaviour has been found for benzil doped with silver (c=2 wt%) compared to pure benzil.

Three-dimensional bioactive glass implants fabricated by rapid prototyping based on CO(2) laser cladding.

PubMed

Comesaña, R; Lusquiños, F; Del Val, J; López-Álvarez, M; Quintero, F; Riveiro, A; Boutinguiza, M; de Carlos, A; Jones, J R; Hill, R G; Pou, J

2011-09-01

Three-dimensional bioactive glass implants were produced by rapid prototyping based on laser cladding without using moulds. CO(2) laser radiation was employed to melt 45S5 and S520 bioactive glass particles and to deposit the material layer by layer following a desired geometry. Controlled thermal input and cooling rate by fine tuning of the processing parameters allowed the production of crack-free fully dense implants. Microstructural characterization revealed chemical composition stability, but crystallization during processing was extensive when 45S5 bioactive glass was used. Improved results were obtained using the S520 bioactive glass, which showed limited surface crystallization due to an expanded sintering window (the difference between the glass transition temperature and crystallization onset temperature). Ion release from the S520 implants in Tris buffer was similar to that of amorphous 45S5 bioactive glass prepared by casting in graphite moulds. Laser processed S520 scaffolds were not cytotoxic in vitro when osteoblast-like MC3T3-E1 cells were cultured with the dissolution products of the glasses; and the MC3T3-E1 cells attached and spread well when cultured on the surface of the materials. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Research experiences on materials science in space aboard Salyut and Mir

NASA Technical Reports Server (NTRS)

Regel, Liya L.

1992-01-01

From 1980 through 1991 approximately 500 materials processing experiments were performed aboard the space stations Salyut 6, Salyut 7 and Mir. This includes work on catalysts, polymers, metals and alloys, optical materials, superconductors, electronic crystals, thin film semiconductors, super ionic crystals, ceramics, and protein crystals. Often the resulting materials were surprisingly superior to those prepared on earth. The Soviets were the first to fabricate a laser (CdS) from a crystal grown in space, the first to grow a heterostructure in space, the first super ionic crystal in space, the first crystals of CdTe and its alloys, the first zeolite crystals, the first protein crystals, the first chromium disilicide glass, etc. The results were used to optimize terrestrial materials processing operations in Soviet industry. The characteristics of these three space stations are reviewed, along with the advantages of a space station for materials research, and the problems encountered by the materials scientists who used them. For example, the stations and the materials processing equipment were designed without significant input from the scientific community that would be using them. It is pointed out that successful results have been achieved also by materials processing at high gravity in large centrifuges. This research is also continuing around the world, including at Clarkson University. It is recommended that experiments be conducted in centrifuges in space, in order to investigate the acceleration regime between earth's gravity and the microgravity achieved in orbiting space stations. One cannot expect to understand the influence of gravity on materials processing from only two data points, earth's gravity and microgravity. One must also understand the influence of fluctuations in acceleration on board space stations, the so-called 'g-jitter.' This paper is presented in outline and graphical form.

Production and Characterization of TiO2 Nanofilms for Hemocompatible and Photocatalytic Applications

NASA Astrophysics Data System (ADS)

Schvezov, C. E.; Vera, M. L.; Schuster, J. M.; Rosenberger, M. R.

2017-10-01

Titanium dioxide (TiO2) coatings are currently produced for hemocompatible and photocatalytic applications by using two techniques: sol-gel and anodic oxidation. In this review, the research advances on TiO2 nanofilms produced with these techniques are presented, with a focus on different aspects such as process parameters, morphology, roughness, crystal structure, adhesion, wear and erosion resistance, corrosion resistance, hemocompatibility, toxicity, plaque and bacterial adhesion, and heterogeneous photocatalysis of immobilized porous material. This review was presented at the 3rd Pan American Materials Congress at the 2017 TMS Annual Meeting and Exhibition in San Diego, California, USA.

Lidar inelastic multiple-scattering parameters of cirrus particle ensembles determined with geometrical-optics crystal phase functions.

PubMed

Reichardt, J; Hess, M; Macke, A

2000-04-20

Multiple-scattering correction factors for cirrus particle extinction coefficients measured with Raman and high spectral resolution lidars are calculated with a radiative-transfer model. Cirrus particle-ensemble phase functions are computed from single-crystal phase functions derived in a geometrical-optics approximation. Seven crystal types are considered. In cirrus clouds with height-independent particle extinction coefficients the general pattern of the multiple-scattering parameters has a steep onset at cloud base with values of 0.5-0.7 followed by a gradual and monotonic decrease to 0.1-0.2 at cloud top. The larger the scattering particles are, the more gradual is the rate of decrease. Multiple-scattering parameters of complex crystals and of imperfect hexagonal columns and plates can be well approximated by those of projected-area equivalent ice spheres, whereas perfect hexagonal crystals show values as much as 70% higher than those of spheres. The dependencies of the multiple-scattering parameters on cirrus particle spectrum, base height, and geometric depth and on the lidar parameters laser wavelength and receiver field of view, are discussed, and a set of multiple-scattering parameter profiles for the correction of extinction measurements in homogeneous cirrus is provided.

Effect of metallic silver nanoparticles on the alignment and relaxation behaviour of liquid crystalline material in smectic C* phase

NASA Astrophysics Data System (ADS)

Vimal, Tripti; Kumar Gupta, Swadesh; Katiyar, Rohit; Srivastava, Atul; Czerwinski, Michal; Krup, Katarzyna; Kumar, Sandeep; Manohar, Rajiv

2017-09-01

The influence of silver nanoparticles dispersed in a Ferroelectric Liquid Crystal (FLC) on the properties of the resultant composite system has been investigated by thermal, electro-optical, and dielectric methods. We show that the concentration of thiol capped silver nanoparticles is a critical factor in governing the alignment of nanoparticles (NPs) in the host FLC. The orientation of NPs in composite samples affects the ordering of the LC (Liquid Crystal) phase and consequently changes the various phase transition temperatures of the host LC. Formation of self-assembled 2D (two dimensional) arrays of nanoparticles is observed for high concentration of dopant in the LC, oriented perpendicular to the direction of rubbing. We propose that the molecular interaction between the thiol capped NPs and LC molecules is the key factor behind such an arrangement of NPs. Orientation of NPs has affected the relaxation behaviour and various other material parameters, significantly. A noteworthy change in DC conductivity articulates our proposed idea of the formation of 2D array of NPs perpendicular to the direction of rubbing. This comprehensive study endorses the importance of dopant concentration in modifying the properties of the host LC material.

Quantification of photoinduced bending of dynamic molecular crystals: from macroscopic strain to kinetic constants and activation energies.

PubMed

Chizhik, Stanislav; Sidelnikov, Anatoly; Zakharov, Boris; Naumov, Panče; Boldyreva, Elena

2018-02-28

Photomechanically reconfigurable elastic single crystals are the key elements for contactless, timely controllable and spatially resolved transduction of light into work from the nanoscale to the macroscale. The deformation in such single-crystal actuators is observed and usually attributed to anisotropy in their structure induced by the external stimulus. Yet, the actual intrinsic and external factors that affect the mechanical response remain poorly understood, and the lack of rigorous models stands as the main impediment towards benchmarking of these materials against each other and with much better developed soft actuators based on polymers, liquid crystals and elastomers. Here, experimental approaches for precise measurement of macroscopic strain in a single crystal bent by means of a solid-state transformation induced by light are developed and used to extract the related temperature-dependent kinetic parameters. The experimental results are compared against an overarching mathematical model based on the combined consideration of light transport, chemical transformation and elastic deformation that does not require fitting of any empirical information. It is demonstrated that for a thermally reversible photoreactive bending crystal, the kinetic constants of the forward (photochemical) reaction and the reverse (thermal) reaction, as well as their temperature dependence, can be extracted with high accuracy. The improved kinematic model of crystal bending takes into account the feedback effect, which is often neglected but becomes increasingly important at the late stages of the photochemical reaction in a single crystal. The results provide the most rigorous and exact mathematical description of photoinduced bending of a single crystal to date.

Transition of vertically aligned liquid crystal driven by fan-shaped electric field

NASA Astrophysics Data System (ADS)

Tsung, J. W.; Ting, T. L.; Chen, C. Y.; Liang, W. L.; Lai, C. W.; Lin, T. H.; Hsu, W. H.

2017-09-01

Interdigital electrodes are implemented in many commercial and novel liquid crystal devices to align molecules. Although many empirical principles and patents apply to electrode design, only a few numerical simulations of alignment have been conducted. Why and how the molecules align in an ordered manner has never been adequately explained. Hence, this investigation addresses the Fréedericksz transition of vertically aligned liquid crystal that is driven by fishbone electrodes, and thereafter identifies the mechanism of liquid crystal alignment. Theoretical calculations suggest that the periodic deformation that is caused by the fan-shaped fringe field minimizes the free energy in the liquid crystal cell, and the optimal alignment can be obtained when the cell parameters satisfy the relation p /2 d =√{k11/k33 } , where p is the spatial period of the strips of the electrode; d denotes the cell gap; and k11 and k33 are the splay and bend elastic constants of the liquid crystal, respectively. Polymer-stabilized vertical alignment test cells with various p values and spacings between the electrodes were fabricated, and the process of liquid crystal alignment was observed under an optical microscope. The degree of alignment was evaluated by measuring the transmittance of the test cell. The experimental results were consistent with the theoretical predictions. The principle of design, p /2 d =√{k11/k33 } , greatly improves the uniformity and stability of the aligned liquid crystal. The methods that are presented here can be further applied to cholesteric liquid crystal and other self-assembled soft materials.

Effect of the purity of starting materials on the growth and properties of potassium dihydrogen phosphate single crystals – A comparative study

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

Rajesh, P., E-mail: rajeshp@ssn.edu.in; Charoen In, Urit; Manyum, Prapun

2014-11-15

Highlights: • Bulk size KDP crystal has been grown with higher growth rate. • Systematic study on the effect of starting materials has been done. • Crystalline perfection is maintained in the entire crystal. - Abstract: A systematic study on the effect of purity of starting materials on the growth and properties of potassium dihydrogen phosphate single crystals is crucial for the future study of the material for nonlinear optical applications. Potassium dihydrogen phosphate crystals were grown using high pure (99.999%) and ordinary (99.9%) starting raw materials using slow cooling method in identical conditions. Their optical transparency and crystalline perfectionmore » are studied by UV and high resolution X-ray diffraction analyses respectively. The results are checked with the help of etching analyses. The full width at half maximum is 8″ which is close to that expected from the plane wave theory of dynamical X-ray diffraction for an ideally perfect crystal. Results of those studies are correlated with each other. The quantitative results show that the raw material plays an important role in the growth of good quality crystals.« less

Fabrication Equipment for Periodic Material Assemblies and Ph Assemblies and Photonic Crystals (DURIP FY06)

DTIC Science & Technology

2008-04-29

An exhaust hood is necessary for binder removal. Cooling requires a fan at a second speed setpoint . Firing profiles need to be precisely...29,935.06 from Ohio match. Plasmalab 80 Plus Compact etching system (left) and heater/ chiller unit (right). CAHN TherMax 500 High Pressure TGA...the current research is aimed to optimize parameters of the structure, in order to improve the resonant properties of the periodic layered structures

Minimizing radiation damage in nonlinear optical crystals

DOEpatents

Cooke, D.W.; Bennett, B.L.; Cockroft, N.J.

1998-09-08

Methods are disclosed for minimizing laser induced damage to nonlinear crystals, such as KTP crystals, involving various means for electrically grounding the crystals in order to diffuse electrical discharges within the crystals caused by the incident laser beam. In certain embodiments, electrically conductive material is deposited onto or into surfaces of the nonlinear crystals and the electrically conductive surfaces are connected to an electrical ground. To minimize electrical discharges on crystal surfaces that are not covered by the grounded electrically conductive material, a vacuum may be created around the nonlinear crystal. 5 figs.

Growing Organic Crystals By The Czochralski Method

NASA Technical Reports Server (NTRS)

Shields, Angela; Frazier, Donald O.; Penn, Benjamin G.; Aggarwal, M. D.; Wang, W. S.

1994-01-01

Apparatus grows high-quality single crystals of organic compounds by Czochralski method. In Czochralski process, growing crystal lifted from middle of molten material without touching walls. Because of low melting temperatures of organic crystals, glass vessels usable. Traditional method for inorganic semiconductors adapted to optically nonlinear organic materials.

Thermophysical Property Measurements of Molten Semiconductors in 1-g and Reduced-g Condition

NASA Technical Reports Server (NTRS)

Rhim, Won-Kyu

1999-01-01

Understanding and controlling the formation kinetics of varieties of crystal imperfections such as point defects, non uniform distribution of doping atoms, and impurity atoms in growing crystals are very important. Theoretical (numerical) modeling of the crystal growth process is an essential step to achieving these objectives. In order to obtain reliable modeling results, input parameters, i.e. various thermophysical parameters, must be accurate. The importance of accurate thermophysical properties of semiconductors in crystal growth cannot be overly emphasized. The total hemispherical emissivity, for instance, has a dramatic impact on the thermal environment. It determines the radiative emission from the surface of the melt which determines to a large extent the profile of the solidified crystal. In order to understand the convection and the turbulence in a melt, viscosity becomes an important parameter. The liquid surface tension determines the shape of the liquid-atmosphere interface near the solid-liquid-atmosphere triple point. Currently used values for these parameters are rather inaccurate, and this program intends to provide more reliable measurements of these thermophysical properties. Thus, the objective of this program is in the accurate measurements of various thermophysical properties which can be reliably used in the modeling of various crystal growth processes. In this program, thermophysical properties of molten semiconductors, such as Si, Ge, Si-Ge, and InSb will be measured as a function of temperature using the High Temperature Electrostatic Levitator at JPL. Each material will be doped by different kinds of impurities at various doping levels. Thermophysical properties which will be measured include: density, thermal expansion coefficient, surface tension, viscosity, specific heat, hemispherical total emissivity, and perhaps electrical and thermal conductivities. Many molten semiconductors are chemically reactive with crucibles. As a result, these dispersed impurities in the melts tend to substantially modify the properties of pure semiconductors. Sample levitation done in a vacuum clearly helps maintain the sample purity. However, in the 1-g environment, all gravity caused effects such as convection, sedimentation and buoyancy are still present in the sample. In addition, large forces needed to levitate a sample in the presence of the gravity can cause additional flows in the melt. The use of the High Temperature Electrostatic Levitator (HTESL) for the present research is a recent development and little is known about the flows induced by the electrostatic forces. In this ground base program, we will define the limits of HTESL technology as various thermophysical properties of molten semiconductors are measured.

Tunable top-down fabrication and functional surface coating of single-crystal titanium dioxide nanostructures and nanoparticles

NASA Astrophysics Data System (ADS)

Ha, Seungkyu; Janissen, Richard; Ussembayev, Yera Ye.; van Oene, Maarten M.; Solano, Belen; Dekker, Nynke H.

2016-05-01

Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale.Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale. Electronic supplementary information (ESI) available: Experimental details (ESI Methods) of the optic axis orientation of TiO2 nanocylinders, Cr etch mask fabrication, surface functionalization and its evaluation using fluorescence microscopy, preparation of DNA constructs, assembly of flow cells, bioconjugation of TiO2 nanocylinders, OTW instrumentation and measurements; TiO2 dry etching optimization and the etching parameters employed (Tables S1 and S2); dimensional analysis of TiO2 nanocylinders (Table S3); diverse applications of TiO2 at the nanoscale (Fig. S1); selection of etch mask material (Fig. S2); control of sidewall profiles in TiO2 etching (Fig. S3); size distributions of TiO2 nanocylinders (Fig. S4); quantitative comparisons of different surface linker molecules (Fig. S5); DLS measurements on TiO2 nanocylinders (Fig. S6); optical trap calibration (Fig. S7); and supplementary references. See DOI: 10.1039/c6nr00898d

Crystal growth of compound semiconductors in a low-gravity environment (InGaAs crystals) (M-22)

NASA Technical Reports Server (NTRS)

Tatsumi, Masami

1993-01-01

Compound semiconductor crystals, such as gallium arsenide and indium phosphide crystals, have many interesting properties that silicon crystals lack, and they are expected to be used as materials for optic and/or electro-optic integrated devices. Generally speaking, alloy semiconductors, which consist of more than three elements, demonstrate new functions. For example, values of important parameters, such as lattice constant and emission wavelength, can be chosen independently. However, as it is easy for macroscopic and/or microscopic fluctuations of composition to occur in alloy semiconductor crystals, it is difficult to obtain crystals having homogeneous properties. Macroscopic change of composition in a crystal is caused by the segregation phenomenon. This phenomenon is due to a continuous change in the concentration of constituent elements at the solid-liquid interfacing during solidification. On Earth, attempts were made to obtain a crystal with homogeneous composition by maintaining a constant melt composition near the solid-liquid interface, through suppression of the convection flow of the melt by applying a magnetic field. However, the attempt was not completely successful. Convective flow does not occur in microgravity because the gravity in space is from four to six orders of magnitude less than that on Earth. In such a case, mass transfer in the melt is dominated by the diffusion phenomenon. So, if crystal growth is carried out at a rate that is higher than the rate of mass transfer due to this phenomenon, it is expected that crystals having a homogeneous composition will be obtained. In addition, it is also possible that microscopic composition fluctuations (striation) may disappear because microscopic fluctuations diminish in the absence of convection. We are going to grow a bulk-indium gallium arsenide (InGaAs) crystal using the gradient heating furnace (GHF) in the first material processing test (FMPT). The structure of the sample is shown where InGaAs polycrystals in a crucible are doubly sealed in two quartz tubes for safety. The GHF consists of two zones, namely, high temperature and low temperature zones, which results in a large temperature gradient at the interface. Crystal growth is performed by moving the furnace (i.e. the temperature profile) from the left to right at a definite rate. Thus, we will grow crystals both on Earth and in space under the same conditions. As previously described, it is possible to obtain good quality crystals which are homogeneous in composition both macroscopically and microscopically due to the lack of convection in space. We are planning to study the effects of convection on crystal growth from a melt by comparing and characterizing the properties of crystals grown on Earth with those grown in space.

Calculation of Optical Parameters of Liquid Crystals

NASA Astrophysics Data System (ADS)

Kumar, A.

2007-12-01

Validation of a modified four-parameter model describing temperature effect on liquid crystal refractive indices is being reported in the present article. This model is based upon the Vuks equation. Experimental data of ordinary and extraordinary refractive indices for two liquid crystal samples MLC-9200-000 and MLC-6608 are used to validate the above-mentioned theoretical model. Using these experimental data, birefringence, order parameter, normalized polarizabilities, and the temperature gradient of refractive indices are determined. Two methods: directly using birefringence measurements and using Haller's extrapolation procedure are adopted for the determination of order parameter. Both approches of order parameter calculation are compared. The temperature dependences of all these parameters are discussed. A close agreement between theory and experiment is obtained.

The field theory of specific heat

NASA Astrophysics Data System (ADS)

Gusev, Yu. V.

2016-01-01

Finite temperature quantum field theory in the heat kernel method is used to study the heat capacity of condensed matter. The lattice heat is treated à la P. Debye as energy of the elastic (sound) waves. The dimensionless functional of free energy is re-derived with a cut-off parameter and used to obtain the specific heat of crystal lattices. The new dimensionless thermodynamical variable is formed as Planck's inverse temperature divided by the lattice constant. The dimensionless constant, universal for the class of crystal lattices, which determines the low temperature region of molar specific heat, is introduced and tested with the data for diamond lattice crystals. The low temperature asymptotics of specific heat is found to be the fourth power in temperature instead of the cubic power law of the Debye theory. Experimental data for the carbon group elements (silicon, germanium) and other materials decisively confirm the quartic law. The true low temperature regime of specific heat is defined by the surface heat, therefore, it depends on the geometrical characteristics of the body, while the absolute zero temperature limit is geometrically forbidden. The limit on the growth of specific heat at temperatures close to critical points, known as the Dulong-Petit law, appears from the lattice constant cut-off. Its value depends on the lattice type and it is the same for materials with the same crystal lattice. The Dulong-Petit values of compounds are equal to those of elements with the same crystal lattice type, if one mole of solid state matter were taken as the Avogadro number of the composing atoms. Thus, the Neumann-Kopp law is valid only in some special cases.

Purification, crystallization and preliminary X-ray diffraction analysis of a novel keto-deoxy-d-galactarate (KDG) dehydratase from Agrobacterium tumefaciens

PubMed Central

Taberman, Helena; Andberg, Martina; Parkkinen, Tarja; Richard, Peter; Hakulinen, Nina; Koivula, Anu; Rouvinen, Juha

2014-01-01

d-Galacturonic acid is the main component of pectin. It could be used to produce affordable renewable fuels, chemicals and materials through biotechnical conversion. Keto-deoxy-d-galactarate (KDG) dehydratase is an enzyme in the oxidative pathway of d-galacturonic acid in Agrobacterium tumefaciens (At). It converts 3-deoxy-2-keto-l-threo-hexarate to α-ketoglutaric semialdehyde. At KDG dehydratase was crystallized by the hanging-drop vapour-diffusion method. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 169.1, b = 117.8, c = 74.3 Å, β = 112.4° and an asymmetric unit of four monomers. X-ray diffraction data were collected to 1.9 Å resolution using synchrotron radiation. The three-dimensional structure of At KDG dehydratase will provide valuable information on the function of the enzyme and will allow it to be engineered for biorefinery-based applications. PMID:24419616

Synthesis, crystal structure, spectroscopic characterization and optical properties of bis(4-acetylanilinium) tetrachlorocobalt (II)

NASA Astrophysics Data System (ADS)

Abkari, A.; Chaabane, I.; Guidara, K.

2017-02-01

The chemical preparation, crystal structure, spectroscopic investigations and optical features are given for a novel organic-inorganic hybrid material [C8H10NO]2CoCl4.The compound is crystallized in the orthorhombic space group Cmca, with the following unit cell parameters: a=19.461(2) Å, b=15.523(2) Å, c=13.7436(15) Å, and Z=8. The atomic arrangement shows an alternation of organic and inorganic layers along the b-axis. The cohesion between these entities is performed by N-H…Cl and N-H…O hydrogen bonds and π-π stacking interactions. Infrared and Raman spectra at room temperature are recorded in the 4000-400 and 4000-0 cm-1 frequency regions, respectively and analyzed on the basis of literature data. This study confirms the presence of the organic cation [C8H10NO]+ and of the [CoCl4]2- anion. UV-vis spectroscopy results showed the indirect transition with band gap energy 2.98 eV.

High-Precision Temperature Control of a Crystal Growth Furnace at 1,500 C

NASA Technical Reports Server (NTRS)

Stenzel, Ch.; Hess, A.; Croell, A.; Breuer, D.; Sauermann, H.

2012-01-01

For crystal growth of semiconductor materials a short-term temperature stability of 0.1 C at 1500 C is one of the essential parameters to be addressed for achieving high-quality crystals. Hence, for temperature monitoring and control with high precision in a floating zone furnace two sets of thermo-sensors, type B thermocouples and optical fibre thermometers, have been implemented and successfully operated in the furnace for more than 2000 h. The optical fibre thermometers consist of an optical system made of sapphire (two fibres plus a prism in between for deflection) and transmit the infra-red radiation of the heater to the outside of the hot core of the furnace for pyrometric temperature measurement. A dedicated control algorithm has been set up which controlled the power settings to the individual heaters. Both sensor types showed no degradation after this period and yielded a short-term stability at 1200 C of 0.05 C (optical fibre thermometers), respectively 0.08 C (thermocouples).

Evaluation of General and Tailor Made Force Fields via X-ray Thermal Diffuse Scattering Using Molecular Dynamics and Monte Carlo Simulations of Crystalline Aspirin.

PubMed

Chan, Eric J; Neumann, Marcus A

2018-04-10

We have performed a comparison of the experimental thermal diffuse scattering (TDS) from crystalline Aspirin (form I) to that calculated from molecular dynamics (MD) simulations based on a variety of general force fields and a tailor-made force field (TMFF). A comparison is also made with Monte Carlo (MC) simulations which use a "harmonic network" approach to describe the intermolecular interactions. These comparisons were based on the hypothesis that TDS could be a useful experimental data in validation of such simulation parameter sets, especially when calculations of dynamical properties (e.g., thermodynamic free energies) from molecular crystals are concerned. Currently such a validation of force field parameters against experimental data is often limited to calculation of specific physical properties, e.g., absolute lattice energies usually at 0 K or heat capacity measurements. TDS harvested from in-house or synchrotron experiments comprises highly detailed structural information representative of the dynamical motions of the crystal lattice. Thus, TDS is a well-suited experimental data-driven means of cross validating theoretical approaches targeted at understanding dynamical properties of crystals. We found from the results of our investigation that the TMFF and COMPASS (from the commercial software "Materials Studio") parameter sets gave the best agreement with experiment. From our homologous MC simulation analysis we are able to show that force constants associated with the molecular torsion angles are likely to be a strong contributing factor for the apparent reason why these aforementioned force fields performed better.

Geochemistry, thermometry and isotope ratios on the same zircon crystals: the tandem use of quadrupole LA-ICPMS and CA-TIMS

NASA Astrophysics Data System (ADS)

Olin, P. H.; Schmitz, M. D.; Crowley, J. L.

2011-12-01

Current trends in igneous petrology include the extraction of diverse geochemical information from smaller sample targets by ever more efficient and cost effective means. Igneous zircons are repositories of several types of petrogenetic information, such as magmatic crystallization ages obtained using U-Pb geochronology, magmatic temperatures using Ti-in-zircon geothermometry, and magmatic differentiation and/or mixing trends using trace element contents. Here we demonstrate a tandem quadrupole LA-ICPMS and CA-TIMS approach on single zircon crystals and within domains in single crystals, which extracts all of these data from a single laser spot analysis and then guides the acquisition of CA-TIMS ages at precisions relevant to magmatic histories. We present data from zircon-bearing intrusive and extrusive rocks spanning the compositional spectrum, and highlight results from silicic volcanic rocks with different affinities. The utility of our approach is illustrated in zircons from the Temora diorite, a commonly used standard material which we analysed using 25-μm ablation spots placed on dozens of grains which had been previously annealed and chemically abraded prior to mounting in epoxy. Our LA-ICPMS results illustrate a 3- to 5-fold variation in trace element concentrations and trace element ratios over >150 degrees of cooling as estimated from Ti-in-zircon thermometry. Some geochemical parameters (e.g., Nb/Ta variations and Eu anomalies) are consistent with crystal fractionation during progressive crystallization, while others are bimodal (e.g., Hf and U contents), suggesting the mixing of crystal/magma batches prior to final solidification. LA-ICPMS U-Pb spot ages reproduce the accepted CA-TIMS age within 2% precision and accuracy, while our CA-TIMS results on the same grains constrain the development of the observed geochemical variability to within 100 ka. Other zircon standard materials to be presented include Plesovich syenite, FC1 gabbro, and R33 diorite. Analyses of zircons from selected western Snake River Plain silicic volcanic units further demonstrate the capability of our approach. These units are targeted with the overarching goal of better understanding magmatism in the region and to identify geochemical fingerprints to better distinguish among and to correlate between units. Several rhyolites distributed along the northern margin of the plain have LA-ICPMS ages of ca. 11 Ma, within error of each other and their CA-TIMS ages, and reveal differences in temperatures of crystallization and trace element contents and ratios. Individual units have crystallization temperatures that span 100 degrees or more, and show correlations with whole-rock major and trace element contents and ratios. In many cases, zircon geochemical parameters such as REE and Y contents, and Nb/Ta and Th/U ratios allow units proximal to each other to be distinguished from one another while also providing fingerprints to correlate to distal units on the south side of the plain or elsewhere in the province.

Selective crystallization with preferred lithium-ion storage capability of inorganic materials

PubMed Central

2012-01-01

Lithium-ion batteries are supposed to be a key method to make a more efficient use of energy. In the past decade, nanostructured electrode materials have been extensively studied and have presented the opportunity to achieve superior performance for the next-generation batteries which require higher energy and power densities and longer cycle life. In this article, we reviewed recent research activities on selective crystallization of inorganic materials into nanostructured electrodes for lithium-ion batteries and discuss how selective crystallization can improve the electrode performance of materials; for example, selective exposure of surfaces normal to the ionic diffusion paths can greatly enhance the ion conductivity of insertion-type materials; crystallization of alloying-type materials into nanowire arrays has proven to be a good solution to the electrode pulverization problem; and constructing conversion-type materials into hollow structures is an effective approach to buffer the volume variation during cycling. The major goal of this review is to demonstrate the importance of crystallization in energy storage applications. PMID:22353373

Photonic Switching Devices Using Light Bullets

NASA Technical Reports Server (NTRS)

Goorjian, Peter M. (Inventor)

1999-01-01

A unique ultra-fast, all-optical switching device or switch is made with readily available, relatively inexpensive, highly nonlinear optical materials. which includes highly nonlinear optical glasses, semiconductor crystals and/or multiple quantum well semiconductor materials. At the specified wavelengths. these optical materials have a sufficiently negative group velocity dispersion and high nonlinear index of refraction to support stable light bullets. The light bullets counter-propagate through, and interact within the waveguide to selectively change each others' directions of propagation into predetermined channels. In one embodiment, the switch utilizes a rectangularly planar slab waveguide. and further includes two central channels and a plurality of lateral channels for guiding the light bullets into and out of the waveguide. An advantage of the present all-optical switching device lies in its practical use of light bullets, thus preventing the degeneration of the pulses due to dispersion and diffraction at the front and back of the pulses. Another advantage of the switching device is the relative insensitivity of the collision process to the time difference in which the counter-propagating pulses enter the waveguide. since. contrary to conventional co-propagating spatial solitons, the relative phase of the colliding pulses does not affect the interaction of these pulses. Yet another feature of the present all-optical switching device is the selection of the light pulse parameters which enables the generation of light bullets in nonlinear optical materials. including highly nonlinear optical glasses and semiconductor materials such as semiconductor crystals and/or multiple quantum well semiconductor materials.

Relaxor-based ferroelectric single crystals: growth, domain engineering, characterization and applications

PubMed Central

Sun, Enwei; Cao, Wenwu

2014-01-01

In the past decade, domain engineered relaxor-PT ferroelectric single crystals, including (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) and (1-x-y)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3 (PIN-PMN-PT), with compositions near the morphotropic phase boundary (MPB) have triggered a revolution in electromechanical devices owing to their giant piezoelectric properties and ultra-high electromechanical coupling factors. Compared to traditional PbZr1-xTixO3 (PZT) ceramics, the piezoelectric coefficient d33 is increased by a factor of 5 and the electromechanical coupling factor k33 is increased from < 70% to > 90%. Many emerging rich physical phenomena, such as charged domain walls, multi-phase coexistence, domain pattern symmetries, etc., have posed challenging fundamental questions for scientists. The superior electromechanical properties of these domain engineered single crystals have prompted the design of a new generation electromechanical devices, including sensors, transducers, actuators and other electromechanical devices, with greatly improved performance. It took less than 7 years from the discovery of larger size PMN-PT single crystals to the commercial production of the high-end ultrasonic imaging probe “PureWave”. The speed of development is unprecedented, and the research collaboration between academia and industrial engineers on this topic is truly intriguing. It is also exciting to see that these relaxor-PT single crystals are being used to replace traditional PZT piezoceramics in many new fields outside of medical imaging. The new ternary PIN-PMN-PT single crystals, particularly the ones with Mn-doping, have laid a solid foundation for innovations in high power acoustic projectors and ultrasonic motors, hinting another revolution in underwater SONARs and miniature actuation devices. This article intends to provide a comprehensive review on the development of relaxor-PT single crystals, spanning material discovery, crystal growth techniques, domain engineering concept, and full-matrix property characterization all the way to device innovations. It outlines a truly encouraging story in materials science in the modern era. All key references are provided and 30 complete sets of material parameters for different types of relaxor-PT single crystals are listed in the Appendix. It is the intension of this review article to serve as a resource for those who are interested in basic research and practical applications of these relaxor-PT single crystals. In addition, possible mechanisms of giant piezoelectric properties in these domain-engineered relaxor-PT systems will be discussed based on contributions from polarization rotation and charged domain walls. PMID:25061239

Relaxor-based ferroelectric single crystals: growth, domain engineering, characterization and applications.

PubMed

Sun, Enwei; Cao, Wenwu

2014-08-01

In the past decade, domain engineered relaxor-PT ferroelectric single crystals, including (1- x )Pb(Mg 1/3 Nb 2/3 )O 3 - x PbTiO 3 (PMN-PT), (1- x )Pb(Zn 1/3 Nb 2/3 )O 3 - x PbTiO 3 (PZN-PT) and (1- x - y )Pb(In 1/2 Nb 1/2 )O 3 - y Pb(Mg 1/3 Nb 2/3 )O 3 - x PbTiO 3 (PIN-PMN-PT), with compositions near the morphotropic phase boundary (MPB) have triggered a revolution in electromechanical devices owing to their giant piezoelectric properties and ultra-high electromechanical coupling factors. Compared to traditional PbZr 1- x Ti x O 3 (PZT) ceramics, the piezoelectric coefficient d 33 is increased by a factor of 5 and the electromechanical coupling factor k 33 is increased from < 70% to > 90%. Many emerging rich physical phenomena, such as charged domain walls, multi-phase coexistence, domain pattern symmetries, etc., have posed challenging fundamental questions for scientists. The superior electromechanical properties of these domain engineered single crystals have prompted the design of a new generation electromechanical devices, including sensors, transducers, actuators and other electromechanical devices, with greatly improved performance. It took less than 7 years from the discovery of larger size PMN-PT single crystals to the commercial production of the high-end ultrasonic imaging probe "PureWave". The speed of development is unprecedented, and the research collaboration between academia and industrial engineers on this topic is truly intriguing. It is also exciting to see that these relaxor-PT single crystals are being used to replace traditional PZT piezoceramics in many new fields outside of medical imaging. The new ternary PIN-PMN-PT single crystals, particularly the ones with Mn-doping, have laid a solid foundation for innovations in high power acoustic projectors and ultrasonic motors, hinting another revolution in underwater SONARs and miniature actuation devices. This article intends to provide a comprehensive review on the development of relaxor-PT single crystals, spanning material discovery, crystal growth techniques, domain engineering concept, and full-matrix property characterization all the way to device innovations. It outlines a truly encouraging story in materials science in the modern era. All key references are provided and 30 complete sets of material parameters for different types of relaxor-PT single crystals are listed in the Appendix. It is the intension of this review article to serve as a resource for those who are interested in basic research and practical applications of these relaxor-PT single crystals. In addition, possible mechanisms of giant piezoelectric properties in these domain-engineered relaxor-PT systems will be discussed based on contributions from polarization rotation and charged domain walls.

Photonic crystal light source

DOEpatents

Fleming, James G [Albuquerque, NM; Lin, Shawn-Yu [Albuquerque, NM; Bur, James A [Corrales, NM

2004-07-27

A light source is provided by a photonic crystal having an enhanced photonic density-of-states over a band of frequencies and wherein at least one of the dielectric materials of the photonic crystal has a complex dielectric constant, thereby producing enhanced light emission at the band of frequencies when the photonic crystal is heated. The dielectric material can be a metal, such as tungsten. The spectral properties of the light source can be easily tuned by modification of the photonic crystal structure and materials. The photonic crystal light source can be heated electrically or other heating means. The light source can further include additional photonic crystals that exhibit enhanced light emission at a different band of frequencies to provide for color mixing. The photonic crystal light source may have applications in optical telecommunications, information displays, energy conversion, sensors, and other optical applications.

Degassing and microlite crystallization during pre-climactic events of the 1991 eruption of Mt. Pinatubo, Philippines

USGS Publications Warehouse

Hammer, J.E.; Cashman, K.V.; Hoblitt, R.P.; Newman, S.

1999-01-01

Dacite tephras produced by the 1991 pre-climactic eruptive sequence at Mt. Pinatubo display extreme heterogeneity in vesicularity, ranging in clast density from 700 to 2580 kg m-3. Observations of the 13 surge-producing blasts that preceded the climactic plinian event include radar-defined estimates of column heights and seismically defined eruptive and intra-eruptive durations. A comparison of the characteristics of erupted material, including microlite textures, chemical compositions, and H2O contents, with eruptive parameters suggests that devolatilization-induced crystallization of the magma occurred to a varying extent prior to at least nine of the explosive events. Although volatile loss progressed to the same approximate level in all of the clasts analyzed (weight percent H2O=1.26-1.73), microlite crystallization was extremely variable (0-22%). We infer that syn-eruptive volatile exsolution from magma in the conduit and intra-eruptive separation of the gas phase was facilitated by the development of permeability within magma residing in the conduit. Correlation of maximum microlite crystallinity with repose interval duration (28-262 min) suggests that crystallization occurred primarily intra-eruptively, in response to the reduction in dissolved H2O content that occurred during the preceding event. Detailed textural characterization, including determination of three-dimensional shapes and crystal size distributions (CSD), was conducted on a subset of clasts in order to determine rates of crystal nucleation and growth using repose interval as the time available for crystallization. Shape and size analysis suggests that crystallization proceeded in response to lessening degrees of feldspar supersaturation as repose interval durations increased. We thus propose that during repose intervals, a plug of highly viscous magma formed due to the collapse of vesicular magma that had exsolved volatiles during the previous explosive event. If plug thickness grew proportionally to the square root of time, and if magma pressurization increased during the eruptive sequence, the frequency of eruptive pulses may have been modulated by degassing of magma within the conduit. Dense clasts in surge deposits probably represent plug material entrained by each subsequent explosive event.

Effect of process parameters and crystal orientation on 3D anisotropic stress during CZ and FZ growth of silicon

NASA Astrophysics Data System (ADS)

Drikis, Ivars; Plate, Matiss; Sennikovs, Juris; Virbulis, Janis

2017-09-01

Simulations of 3D anisotropic stress are carried out in <100> and <111> oriented Si crystals grown by FZ and CZ processes for different diameters, growth rates and process stages. Temperature dependent elastic constants and thermal expansion coefficients are used in the FE simulations. The von Mises stress at the triple point line is 5-11% higher in <111> crystals compared to <100> crystals. The process parameters have a larger effect on the von Mises stress than the crystal orientation. Generally, the <111> crystal has a higher azimuthal variation of stress along the triple point line ( 8%) than the <100> crystal ( 2%). The presence of a crystal ridge increases the stress beside the ridge and decreases it on the ridge compared with the round crystal.

Recent advances in continuum plasticity: phenomenological modeling and experimentation using X-ray diffraction

NASA Astrophysics Data System (ADS)

Edmiston, John Kearney

This work explores the field of continuum plasticity from two fronts. On the theory side, we establish a complete specification of a phenomenological theory of plasticity for single crystals. The model serves as an alternative to the popular crystal plasticity formulation. Such a model has been previously proposed in the literature; the new contribution made here is the constitutive framework and resulting simulations. We calibrate the model to available data and use a simple numerical method to explore resulting predictions in plane strain boundary value problems. Results show promise for further investigation of the plasticity model. Conveniently, this theory comes with a corresponding experimental tool in X-ray diffraction. Recent advances in hardware technology at synchrotron sources have led to an increased use of the technique for studies of plasticity in the bulk of materials. The method has been successful in qualitative observations of material behavior, but its use in quantitative studies seeking to extract material properties is open for investigation. Therefore in the second component of the thesis several contributions are made to synchrotron X-ray diffraction experiments, in terms of method development as well as the quantitative reporting of constitutive parameters. In the area of method development, analytical tools are developed to determine the available precision of this type of experiment—a crucial aspect to determine if the method is to be used for quantitative studies. We also extract kinematic information relating to intragranular inhomogeneity which is not accessible with traditional methods of data analysis. In the area of constitutive parameter identification, we use the method to extract parameters corresponding to the proposed formulation of plasticity for a titanium alloy (HCP) which is continuously sampled by X-ray diffraction during uniaxial extension. These results and the lessons learned from the efforts constitute early reporting of the quantitative profitability of undertaking such a line of experimentation for the study of plastic deformation processes.

Ilmenite as Dual-Use Material

NASA Technical Reports Server (NTRS)

Kumar, A. A.; Pandey, R. K.; Fogarty, T. N.; Wilkins, R.

1994-01-01

This paper addresses the subject of dual-use space technology transfer of a novel, non-traditional material termed ilmenite, found in a large percentage in the moon rocks brought back by NASA's APOLLO missions. The paper is somewhat premature in the sense that though the material as a mineral has been known for a long time, very little is known about pure single crystal ilmenite and hence few applications have been demonstrated. Yet, in another sense, it is very timely due to the fact that ilmenite promises to be a very interesting competition to silicon, silicon carbide and other compound semiconductors, especially those that are employed in high power, high temperature and large data storage/retrieval applications. It seems to be an excellent example of a small investment-high return situation. While some of the applications of this material - for production of oxygen, for instance - have been well-known, electronic applications have received relatively little attention. One reason for this was the fact that growth of single crystal ilmenite requires precise process conditions and parameters. We believe for the first time these have been determined in the Center for Electronic Materials, Texas A&M University. The work being done at Texas A&M University and Prairie View A&M University (supported by Battelle Pacific Northwest Laboratories and the Center for Space Power) indicates the excellent potential this material has in space as well as in terrestrial applications. To mention a few: as a wide band gap semiconductor it has applications in high temperature, high power situations, especially when heat dissipation is a problem such as may occur in the Space Station; the possibility of this material radiating in the blue region, it has immense applications in optoelectronics; as a material with a high density of highly directional d-bands, it lends itself to novel processing conditions and perhaps even to 'tunability' of physical parameters; as a potential scintillating material, it has possible applications as a sensor in waste management; as an oxygen sensor it has possible applications in automotive electronics; and as a radiation resistant material, it has obvious applications in the space environment. Results - experimental and theoretical - obtained so far in our laboratories will be reported with particular emphasis on the transfer of technology involving this fascinating material.

Learning physical descriptors for materials science by compressed sensing

NASA Astrophysics Data System (ADS)

Ghiringhelli, Luca M.; Vybiral, Jan; Ahmetcik, Emre; Ouyang, Runhai; Levchenko, Sergey V.; Draxl, Claudia; Scheffler, Matthias

2017-02-01

The availability of big data in materials science offers new routes for analyzing materials properties and functions and achieving scientific understanding. Finding structure in these data that is not directly visible by standard tools and exploitation of the scientific information requires new and dedicated methodology based on approaches from statistical learning, compressed sensing, and other recent methods from applied mathematics, computer science, statistics, signal processing, and information science. In this paper, we explain and demonstrate a compressed-sensing based methodology for feature selection, specifically for discovering physical descriptors, i.e., physical parameters that describe the material and its properties of interest, and associated equations that explicitly and quantitatively describe those relevant properties. As showcase application and proof of concept, we describe how to build a physical model for the quantitative prediction of the crystal structure of binary compound semiconductors.

Recent advances in engineering science; Proceedings of the A. Cemal Eringen Symposium, University of California, Berkeley, June 20-22, 1988

NASA Technical Reports Server (NTRS)

Koh, Severino L. (Editor); Speziale, Charles G. (Editor)

1989-01-01

Various papers on recent advances in engineering science are presented. Some individual topics addressed include: advances in adaptive methods in computational fluid mechanics, mixtures of two medicomorphic materials, computer tests of rubber elasticity, shear bands in isotropic micropolar elastic materials, nonlinear surface wave and resonator effects in magnetostrictive crystals, simulation of electrically enhanced fibrous filtration, plasticity theory of granular materials, dynamics of viscoelastic media with internal oscillators, postcritical behavior of a cantilever bar, boundary value problems in nonlocal elasticity, stability of flexible structures with random parameters, electromagnetic tornadoes in earth's ionosphere and magnetosphere, helicity fluctuations and the energy cascade in turbulence, mechanics of interfacial zones in bonded materials, propagation of a normal shock in a varying area duct, analytical mechanics of fracture and fatigue.

High energy X-ray diffraction study of a dental ceramics–titanium functional gradient material prepared by field assisted sintering technique

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

Witte, K., E-mail: kerstin.witte@uni-rostock.de; Bodnar, W.; Schell, N.

A functional gradient material with eleven layers composed of a dental ceramics and titanium was successfully consolidated using field assisted sintering technique in a two-step sintering process. High energy X-ray diffraction studies on the gradient were performed at High Energy Material Science beamline at Desy in Hamburg. Phase composition, crystal unit edges and lattice mismatch along the gradient were determined applying Rietveld refinement procedure. Phase analysis revealed that the main crystalline phase present in the gradient is α-Ti. Crystallinity increases stepwisely along the gradient with a decreasing increment between every next layer, following rather the weight fraction of titanium. Themore » crystal unit edge a of titanium remains approximately constant with a value of 2.9686(1) Å, while c is reduced with increasing amount of titanium. In the layer with pure titanium the crystal unit edge c is constant with a value of 4.7174(2) Å. The lattice mismatch leading to an internal stress was calculated over the whole gradient. It was found that the maximal internal stress in titanium embedded in the studied gradient is significantly smaller than its yield strength, which implies that the structure of titanium along the whole gradient is mechanically stable. - Highlights: • High energy XRD studies of dental ceramics–Ti gradient material consolidated by FAST. • Phase composition, crystallinity and lattice parameters are determined. • Crystallinity increases stepwisely along the gradient following weight fraction of Ti. • Lattice mismatch leading to internal stress is calculated over the whole gradient. • Internal stress in α-Ti embedded in the gradient is smaller than its yield strength.« less

Field induced heliconical structure of cholesteric liquid crystal

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

Lavrentovich, Oleg D.; Shiyanovsii, Sergij V.; Xiang, Jie

A diffraction grating comprises a liquid crystal (LC) cell configured to apply an electric field through a cholesteric LC material that induces the cholesteric LC material into a heliconical state with an oblique helicoid director. The applied electric field produces diffracted light from the cholesteric LC material within the visible, infrared or ultraviolet. The axis of the heliconical state is in the plane of the liquid crystal cell or perpendicular to the plane, depending on the application. A color tuning device operates with a similar heliconical state liquid crystal material but with the heliconical director axis oriented perpendicular to themore » plane of the cell. A power generator varies the strength of the applied electric field to adjust the wavelength of light reflected from the cholesteric liquid crystal material within the visible, infrared or ultraviolet.« less

Quantum Effects at a Proton Relaxation at Low Temperatures

NASA Astrophysics Data System (ADS)

Kalytka, V. A.; Korovkin, M. V.

2016-11-01

Quantum effects during migratory polarization in multi-well crystals (including multi-well silicates and crystalline hydrates) are investigated in a variable electric field at low temperatures by direct quantum-mechanical calculations. Based on analytical solution of the quantum Liouville kinetic equation in the linear approximation for the polarizing field, the non-stationary density matrix is calculated for an ensemble of non-interacting protons moving in the field of one-dimensional multi-well crystal potential relief of rectangular shape. An expression for the complex dielectric constant convenient for a comparison with experiment and calculation of relaxer parameters is derived using the nonequilibrium polarization density matrix. The density matrix apparatus can be used for analytical investigation of the quantum mechanism of spontaneous polarization of a ferroelectric material (KDP and DKDP).

SEMICONDUCTOR TECHNOLOGY: An efficient dose-compensation method for proximity effect correction

NASA Astrophysics Data System (ADS)

Ying, Wang; Weihua, Han; Xiang, Yang; Renping, Zhang; Yang, Zhang; Fuhua, Yang

2010-08-01

A novel simple dose-compensation method is developed for proximity effect correction in electron-beam lithography. The sizes of exposed patterns depend on dose factors while other exposure parameters (including accelerate voltage, resist thickness, exposing step size, substrate material, and so on) remain constant. This method is based on two reasonable assumptions in the evaluation of the compensated dose factor: one is that the relation between dose factors and circle-diameters is linear in the range under consideration; the other is that the compensated dose factor is only affected by the nearest neighbors for simplicity. Four-layer-hexagon photonic crystal structures were fabricated as test patterns to demonstrate this method. Compared to the uncorrected structures, the homogeneity of the corrected hole-size in photonic crystal structures was clearly improved.

Radial Photonic Crystal for detection of frequency and position of radiation sources.

PubMed

Carbonell, J; Díaz-Rubio, A; Torrent, D; Cervera, F; Kirleis, M A; Piqué, A; Sánchez-Dehesa, J

2012-01-01

Based on the concepts of artificially microstructured materials, i.e. metamaterials, we present here the first practical realization of a radial wave crystal. This type of device was introduced as a theoretical proposal in the field of acoustics, and can be briefly defined as a structured medium with radial symmetry, where the constitutive parameters are invariant under radial geometrical translations. Our practical demonstration is realized in the electromagnetic microwave spectrum, because of the equivalence between the wave problems in both fields. A device has been designed, fabricated and experimentally characterized. It is able to perform beam shaping of punctual wave sources, and also to sense position and frequency of external radiators. Owing to the flexibility offered by the design concept, other possible applications are discussed.

Micromechanical properties of single crystals and polycrystals of pure α-titanium: anisotropy of microhardness, size effect, effect of the temperature (77-300 K)

NASA Astrophysics Data System (ADS)

Lubenets, S. V.; Rusakova, A. V.; Fomenko, L. S.; Moskalenko, V. A.

2018-01-01

The anisotropy of microhardness of pure α-Ti single crystals, indentation size effect in single-crystal, course grained (CG) pure and nanocrystalline (NC) VT1-0 titanium, as well as the temperature dependences of the microhardness of single-crystal and CG Ti in the temperature range 77-300 K were studied. The minimum value of hardness was obtained when indenting into the basal plane (0001). The indentation size effect (ISE) was clearly observed in the indentation of soft high-purity single-crystal iodide titanium while it was the least pronounced in a sample of nanocrystalline VT1-0 titanium. It has been demonstrated that the ISE can be described within the model of geometrically necessary dislocations (GND), which follows from the theory of strain gradient plasticity. The true hardness and others parameters of the GND model were determined for all materials. The temperature dependence of the microhardness is in agreement with the idea of the governing role of Peierls relief in the dislocation thermally-activated plastic deformation of pure titanium as has been earlier established and justified in macroscopic tensile investigations at low temperatures. The activation energy and activation volume of dislocation motion in the strained region under the indenter were estimated.

[Flexible Guidance of Ultra-Short Laser Pulses in Ophthalmic Therapy Systems].

PubMed

Blum, J; Blum, M; Rill, M S; Haueisen, J

2017-01-01

In the last 20 years, the role of ultrashort pulsed lasers in ophthalmology has become increasingly important. However, it is still impossible to guide ultra-short laser pulses with standard glass fibres. The highly energetic femtosecond pulses would destroy the fibre material, and non-linear dispersion effects would significantly change beam parameters. In contrast, photonic crystal fibres mainly guide the laser pulses in air, so that absorption and dispersive pulse broadening have essentially no effect. This article compares classical beam guidance with mirrors, lenses and prisms with photonic crystal fibres and describes the underlying concepts and the current state of technology. A classical mirror arm possesses more variable optical properties, while the HCF (Hollow-Core Photonic Crystal Fibre) must be matched in terms of the laser energy and the laser spectrum. In contrast, the HCF has more advantages in respect of handling, system integration and costs. For applications based on photodisruptive laser-tissue interaction, the relatively low damage threshold of photonic crystal fibres compared to classic beam guiding systems is unacceptable. If, however, pulsed laser radiation has a sufficiently low peak intensity, e.g. as used for plasma-induced ablation, photonic crystal fibres can definitely be considered as an alternative solution to classic beam guidance. Georg Thieme Verlag KG Stuttgart · New York.

Graphene as a protein crystal mounting material to reduce background scatter.

PubMed

Wierman, Jennifer L; Alden, Jonathan S; Kim, Chae Un; McEuen, Paul L; Gruner, Sol M

2013-10-01

The overall signal-to-noise ratio per unit dose for X-ray diffraction data from protein crystals can be improved by reducing the mass and density of all material surrounding the crystals. This article demonstrates a path towards the practical ultimate in background reduction by use of atomically thin graphene sheets as a crystal mounting platform for protein crystals. The results show the potential for graphene in protein crystallography and other cases where X-ray scatter from the mounting material must be reduced and specimen dehydration prevented, such as in coherent X-ray diffraction imaging of microscopic objects.

Graphene as a protein crystal mounting material to reduce background scatter

PubMed Central

Wierman, Jennifer L.; Alden, Jonathan S.; Kim, Chae Un; McEuen, Paul L.; Gruner, Sol M.

2013-01-01

The overall signal-to-noise ratio per unit dose for X-ray diffraction data from protein crystals can be improved by reducing the mass and density of all material surrounding the crystals. This article demonstrates a path towards the practical ultimate in background reduction by use of atomically thin graphene sheets as a crystal mounting platform for protein crystals. The results show the potential for graphene in protein crystallography and other cases where X-ray scatter from the mounting material must be reduced and specimen dehydration prevented, such as in coherent X-ray diffraction imaging of microscopic objects. PMID:24068843

Phononic crystal devices

DOEpatents

El-Kady, Ihab F [Albuquerque, NM; Olsson, Roy H [Albuquerque, NM

2012-01-10

Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.

Structure and optical properties of evaporated films of the Cr- and V-group metals

NASA Technical Reports Server (NTRS)

Nestell, J. E., Jr.; Christy, R. W.; Cohen, M. H.; Ruben, G. C.

1980-01-01

Thin films of Cr, Mo, and W rapidly evaporated in high vacuum (5 x 10 to the -7th torr) onto room-temperature substrates show anomalously low reflectance (compared to bulk samples). From electron and X-ray diffraction and electron microscopy, the normal bcc crystal structure is found, but with very fine grains. Columnar grains about 100 A in diameter were separated by a less dense grain-boundary network about 10-A wide. The measured optical conductivity agrees with an inhomogeneous-medium model that assumes the normal crystalline conductivity for the grain interiors, with model parameters that correlate to the observed columnar grain size. In contrast, V and Nb films rapidly evaporated onto room-temperature substrates have the reflectance of bulk crystalline material. On liquid-nitrogen temperature substrates, however, V and Nb have normal bcc crystal structure but with small flat-plate grains, and the same model, with appropriate parameters, accounts for the optical conductivity. The difference between these two groups apparently depends on residual gases segregated at the grain boundaries in the Cr-group films.

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.

Structural comparative studies on new Mn(II), Cr(III) and Ru(III) complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ).

PubMed

Al-Assy, Waleed H; El-Askalany, Abdel Moneum H; Mostafa, Mohsen M

2013-12-01

The structure of a new Mn(II) complex, [Mn(TPTZ)Cl2(H2O)]⋅H2O, was established by a single crystal X-ray diffraction. Crystal data are as follow: monoclinic, P21/c,a = 8.7202 (3)Å, b = 11.5712 (4)Å, c = 20.8675 (9)Å, β=11 (18) × 1010, V = 2029.27 (13)Å(3), Z = 4. The HOMO, LUMO and other DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and its complexes using material studio program. The complexes were characterized by elemental analyses, spectral, magnetic, thermal and cyclic voltammetry measurements. Electronic spectra and magnetic moments of the complexes suggest distorted-octahedral structures around the metal ions (Mn(II), Cr(III) and Ru(III)). The redox properties were investigated by cyclic voltammetry. Kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. The results of DNA studies of the metal complexes promised to be effective in tumour treatment. Copyright © 2013 Elsevier B.V. All rights reserved.

Structural comparative studies on new MnII, CrIII and RuIII complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ)

NASA Astrophysics Data System (ADS)

Al-Assy, Waleed H.; El-Askalany, Abdel Moneum H.; Mostafa, Mohsen M.

2013-12-01

The structure of a new MnII complex, [Mn(TPTZ)Cl2(H2O)]ṡH2O, was established by a single crystal X-ray diffraction. Crystal data are as follow: monoclinic, P21/c, a = 8.7202 (3) Å, b = 11.5712 (4) Å, c = 20.8675 (9) Å, β = 11 (18) × 1010, V = 2029.27 (13) Å3, Z = 4. The HOMO, LUMO and other DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and its complexes using material studio program. The complexes were characterized by elemental analyses, spectral, magnetic, thermal and cyclic voltammetry measurements. Electronic spectra and magnetic moments of the complexes suggest distorted-octahedral structures around the metal ions (MnII, CrIII and RuIII). The redox properties were investigated by cyclic voltammetry. Kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. The results of DNA studies of the metal complexes promised to be effective in tumour treatment.

Spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics.

PubMed

Yu, Yunlong; Chen, Daqin; Ma, En; Wang, Yuansheng; Hu, Zhongjian

2007-07-01

In this paper, the spectroscopic properties of Nd(3+) doped transparent oxyfluoride glass ceramics containing LaF(3) nano-crystals were systematically studied. The formation and distribution of LaF(3) nano-crystals in the glass matrix were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on Judd-Ofelt theory, the intensity parameters Omega(t) (t=2, 4, 6), spontaneous emission probability, radiative lifetime, radiative quantum efficiency, width of the emission line and stimulated emission cross-section of Nd(3+) were evaluated. Particularly, the effect of Nd(3+) doping level on them was discussed. With the increase of Nd(3+) concentration in the glass ceramic, the experimental luminescence lifetime, radiative quantum efficiency and stimulated emission cross-section vary from 353.4 micros, 78.3% and 1.86 x 10(-20)cm(2) to 214.7 micros, 39.9% and 1.52 x 10(-20)cm(2), respectively. The comparative study of Nd(3+) spectroscopic parameters in different hosts suggests that the investigated glass ceramic system is potentially applicable as laser materials for 1.06 microm emission.

The fracture strength of cryomilled 99.7 Al nanopowders consolidated by high frequency induction sintering

NASA Astrophysics Data System (ADS)

El-Danaf, Ehab A.; Baig, Muneer; Almajid, Abdulhakim A.; Soliman, Mahmoud S.

2014-08-01

Mechanical Attrition of metallic powders induces severe plastic deformation and consequently reduces the average grain size. Powders of 99.7 Al (45μm particle size), cryomilled for 7 hrs having a crystal size of ~ 20 nm, were consolidated by high frequency induction sintering under a constant pressure of 50 MPa and at two temperatures of 500 and 550 °C for two sintering dwell times of 1 and 3 minutes at a constant heating rate of 400 °C/min. The bright field TEM image and X-ray line broadening technique, for the cryomilled powders, were used to measure-the crystallite size. Simple compression at an initial strain rate of 10-4 s-1 was conducted at room temperature, 373 and 473 K, and the yield strength was documented and correlated with the sintering parameters. The as-received 99.7 Al powders-consolidated using one of the sintering parameters was used as a reference material to compare the mechanical properties. Hardness, density and crystal size of the consolidated sample, that gave the highest yield and fracture strength, were measured.

Influence of Surrounding Dielectrics on the Data Retention Time of Doped Sb2Te Phase Change Material

NASA Astrophysics Data System (ADS)

Jedema, Friso; in `t Zandt, Micha; Wolters, Rob; Gravesteijn, Dirk

2011-02-01

The crystallization properties of as-deposited and laser written amorphous marks of doped Sb2Te phase change material are found to be only dependent on the top dielectric layer. A ZnS:SiO2 top dielectric layer yields a higher crystallization temperature and a larger crystal growth activation energy as compared to a SiO2 top dielectric layer, leading to superior data retention times at ambient temperatures. The observed correlation between the larger crystallization temperatures and larger crystal growth activation energies indicates that the viscosity of the phase change material in the amorphous state is dependent on the interfacial energy between the phase change material and the top dielectric layer.

Single-crystal equations of state of magnesiowüstite at high pressures

DOE PAGES

Finkelstein, Gregory J.; Jackson, Jennifer M.; Sturhahn, Wolfgang; ...

2017-08-01

Solid solutions of (Mg,Fe)O with high iron enrichment may be an important component of ultralow-velocity zones at Earth’s core-mantle boundary. However, to date there have been few high-precision studies on the elastic properties of these materials. In this study we present results on the compression of (Mg 0.22Fe 0.78)O magnesiowüstite in both neon and helium pressure media using single-crystal diffraction to ~55 GPa. In addition, our sample was characterized by time-domain synchrotron Mössbauer spectroscopy at ambient pressure using an extended time range that resulted in vastly improved energy resolution. The combination of these high-resolution techniques tightly constrains the presence ofmore » a defect-structure component at room pressure due to 4.7 mol% tetrahedrally-coordinated ferric iron, resulting in a renormalized composition of (Mg 0.215Fe 0.762⟂ 0.023)O. Both high-pressure diffraction datasets are well described by a 3rd-order Birch-Murnaghan equation of state. The best fit-parameters for a crystal with cubic structure in helium are K 0T = 148(3) GPa, K' 0T = 4.09(12), and V 0 = 78.87(6) Å 3. Increasing differential stress in the neon-containing sample chamber was correlated with increasing apparent distortion of the initially cubic unit cell, requiring a lower-symmetry hexagonal cell to fit the data above ~20 GPa. For fit equations of state, we determine the pressure-dependent correlation ellipses for the equation of state parameters and compare with previously published single-crystal diffraction data from (Mg,Fe)O crystals in a helium medium. We make two main observations from the datasets using a helium pressure medium: K 0T decreases as a function of increasing iron content from periclase to wüstite and K' 0T is consistent with an approximately constant value of 4.0 that is independent of iron content, at least up to (Mg,Fe)O containing ~78 mol% FeO. Finally, in combination with previously reported thermal parameters, we compute the density of Mw78 at core-mantle boundary conditions and discuss the implications.« less

Single-crystal equations of state of magnesiowüstite at high pressures

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

Finkelstein, Gregory J.; Jackson, Jennifer M.; Sturhahn, Wolfgang

Solid solutions of (Mg,Fe)O with high iron enrichment may be an important component of ultralow-velocity zones at Earth’s core-mantle boundary. However, to date there have been few high-precision studies on the elastic properties of these materials. In this study we present results on the compression of (Mg 0.22Fe 0.78)O magnesiowüstite in both neon and helium pressure media using single-crystal diffraction to ~55 GPa. In addition, our sample was characterized by time-domain synchrotron Mössbauer spectroscopy at ambient pressure using an extended time range that resulted in vastly improved energy resolution. The combination of these high-resolution techniques tightly constrains the presence ofmore » a defect-structure component at room pressure due to 4.7 mol% tetrahedrally-coordinated ferric iron, resulting in a renormalized composition of (Mg 0.215Fe 0.762⟂ 0.023)O. Both high-pressure diffraction datasets are well described by a 3rd-order Birch-Murnaghan equation of state. The best fit-parameters for a crystal with cubic structure in helium are K 0T = 148(3) GPa, K' 0T = 4.09(12), and V 0 = 78.87(6) Å 3. Increasing differential stress in the neon-containing sample chamber was correlated with increasing apparent distortion of the initially cubic unit cell, requiring a lower-symmetry hexagonal cell to fit the data above ~20 GPa. For fit equations of state, we determine the pressure-dependent correlation ellipses for the equation of state parameters and compare with previously published single-crystal diffraction data from (Mg,Fe)O crystals in a helium medium. We make two main observations from the datasets using a helium pressure medium: K 0T decreases as a function of increasing iron content from periclase to wüstite and K' 0T is consistent with an approximately constant value of 4.0 that is independent of iron content, at least up to (Mg,Fe)O containing ~78 mol% FeO. Finally, in combination with previously reported thermal parameters, we compute the density of Mw78 at core-mantle boundary conditions and discuss the implications.« less

Growth and characterization of struvite-Na crystals

NASA Astrophysics Data System (ADS)

Chauhan, Chetan K.; Joshi, Mihirkumar J.

2014-09-01

Sodium magnesium phosphate heptahydrate [NaMgPO4·7H2O], also known as struvite-Na, is the sodium analog to struvite. Among phosphate containing bio-minerals, struvite has attracted considerable attention, because of its common occurrence in a wide variety of environments. Struvite and family crystals were found as urinary calculi in humans and animals. Struvite-Na crystals were grown by a single diffusion gel growth technique in a silica hydro gel medium. Struvite-Na crystals with different morphologies having transparent to translucent diaphaneity were grown with different growth parameters. The phenomenon of Liesegang rings was also observed with some particular growth parameters. The powder XRD study confirmed the structural similarity of the grown struvite-Na crystals with struvite and found that struvite-Na crystallized in the orthorhombic Pmn21 space group with unit cell parameters such as a= 6.893 Å, b=6.124 Å, c=11.150 Å, and α=β=γ=90°. FT-IR spectra of struvite-Na crystals revealed the presence of functional groups. The TGA, DTA and DSC were carried out simultaneously. The kinetic and thermodynamic parameters of dehydration/decomposition process were calculated. The variation of dielectric constant with frequency of applied field was studied in the range from 400 Hz to 100 kHz.

Crystallization kinetic of Sb-V2O5-TeO2 glasses investigated by DSC and their elastic moduli and Poisson's ratio

NASA Astrophysics Data System (ADS)

Souri, Dariush

2015-01-01

Ternary tellurate glasses of the form xSb-(60-x)V2O5-40TeO2 (0≤x≤15 in mol%) were prepared by using the usual melt quenching method. Differential scanning calorimetry (DSC) at different heating rates (φ) was used to thermal analyze and to gain more insight in to the thermal stability, glass forming tendency and so calorimetric behavior of the present glasses. The glass transition temperature (Tg), the temperature corresponding to the onset of crystallization (Tx) and also the crystallization temperature (TCr) were obtained at different heating rates, to estimate the key kinetic parameter of activation energy of crystallization (ΔE) by using different empirical formulas. Also some other thermal parameters such as thermal stability and glass forming tendency were determined. It was found that Tg, Tx and TCr increase with increase in Sb content and also with increase in heating rate. Moreover, Makishima-Makenzie's theory was employed to evaluate the Poisson's ratio and elastic moduli, indicating a strong relation between elastic properties and the structure of glass. From the mechanical and thermal data and also the values of oxygen molar volume ( V O *), it was founded that the glass systems can be divided in to "two compositional regions"; so, results indicate that glasses with 10≤x≤15 (especially for x=12) are more thermal stable and strong glasses, which make them as more useful and promising materials in technological advantages and device manufacturing.

Growth and photo-response of NbSe2 and NbS2 crystals

NASA Astrophysics Data System (ADS)

Patel, Kunjal; Solanki, G. K.; Pataniya, Pratik; Patel, K. D.

2018-05-01

Transition metal dichalcogenides(TMDCs) have attracted intense research efforts due to their drastic properties change as we move towards ultra-thin crystalline layers from their bulk counterparts. Many well studied members of this family such as MoS2, WS2, WSe2, WS2 etc. have shown potential for flexible electronic devices including photovoltaic applications. The TMDCs like NbSe2 and NbS2 are relatively less studied layered compounds consisting of staked sandwiches of Se-Nb-Se/S-Nb-Se tri-layers with strong covalent/ionic intra layer bonds and weak Van der Waals interlayer interactions. In the present work, author have grown the crystals of NbSe2 and NbS2 by Direct Vapour Transport (DVT) technique and the material composition is confirmed using EDAX data. Photoelectrochemical (PEC) solar cell measurements are performed under monochromatic light illumination at different intensities and various solar cell parameters are calculated. These crystalline semiconductor electrodes were also analysed by photocurrent-voltage characteristics in a PEC solar cell structure (Cu/NbSe2/(0.1M K4Fe(CN)6 + 0.1M K3Fe(CN)6) and Cu/NbS2/(0.1M K4Fe(CN)6 +0.1M K3Fe(CN)6)). Blue coloured light gave the maximum efficiency. For further analysis of photodetection properties of the grown crystals, Ag painted broad low contact resistance electrical contacts were drawn from the crystals and its transient photoresponse was studied to evaluate different detector parameters.

Improved luminescence properties of MoS2 monolayers grown via MOCVD: role of pre-treatment and growth parameters

NASA Astrophysics Data System (ADS)

Andrzejewski, D.; Marx, M.; Grundmann, A.; Pfingsten, O.; Kalisch, H.; Vescan, A.; Heuken, M.; Kümmell, T.; Bacher, G.

2018-07-01

Fabrication of transition metal dichalcogenides (TMDCs) via metalorganic chemical vapor deposition (MOCVD) represents one of the most attractive routes to large-scale 2D material layers. Although good homogeneity and electrical conductance have been reported recently, the relation between growth parameters and photoluminescence (PL) intensity—one of the most important parameters for optoelectronic applications—has not yet been discussed for MOCVD TMDCs. In this work, MoS2 is grown via MOCVD on sapphire (0001) substrates using molybdenum hexacarbonyl (Mo(CO)6, MCO) and di-tert-butyl sulphide as precursor materials. A prebake step under H2 atmosphere combined with a reduced MCO precursor flow increases the crystal grain size by one order of magnitude and strongly enhances PL intensity with a clear correlation to the grain size. A decrease of the linewidth of both Raman resonances and PL spectra down to full width at half maxima of 3.2 cm‑1 for the E 2g Raman mode and 60 meV for the overall PL spectrum indicate a reduced defect density at optimized growth conditions.

Protein crystal nucleation in pores.

PubMed

Nanev, Christo N; Saridakis, Emmanuel; Chayen, Naomi E

2017-01-16

The most powerful method for protein structure determination is X-ray crystallography which relies on the availability of high quality crystals. Obtaining protein crystals is a major bottleneck, and inducing their nucleation is of crucial importance in this field. An effective method to form crystals is to introduce nucleation-inducing heterologous materials into the crystallization solution. Porous materials are exceptionally effective at inducing nucleation. It is shown here that a combined diffusion-adsorption effect can increase protein concentration inside pores, which enables crystal nucleation even under conditions where heterogeneous nucleation on flat surfaces is absent. Provided the pore is sufficiently narrow, protein molecules approach its walls and adsorb more frequently than they can escape. The decrease in the nucleation energy barrier is calculated, exhibiting its quantitative dependence on the confinement space and the energy of interaction with the pore walls. These results provide a detailed explanation of the effectiveness of porous materials for nucleation of protein crystals, and will be useful for optimal design of such materials.

ptchg: A FORTRAN program for point-charge calculations of electric field gradients (EFGs)

NASA Astrophysics Data System (ADS)

Spearing, Dane R.

1994-05-01

ptchg, a FORTRAN program, has been developed to calculate electric field gradients (EFG) around an atomic site in crystalline solids using the point-charge direct-lattice summation method. It uses output from the crystal structure generation program Atoms as its input. As an application of ptchg, a point-charge calculation of the EFG quadrupolar parameters around the oxygen site in SiO 2 cristobalite is demonstrated. Although point-charge calculations of electric field gradients generally are limited to ionic compounds, the computed quadrupolar parameters around the oxygen site in SiO 2 cristobalite, a highly covalent material, are in good agreement with the experimentally determined values from nuclear magnetic resonance (NMR) spectroscopy.

Crystallographic Characterization of Extraterrestrial Materials by Energy-Scanning X-ray Diffraction

NASA Technical Reports Server (NTRS)

Hagiya, Kenji; Mikouchi, Takashi; Ohsumi, Kazumasa; Terada, Yasuko; Yagi, Naoto; Komatsu, Mutsumi; Yamaguchi, Shoki; Hirata, Arashi; Kurokawa, Ayaka; Zolensky, Michael E. (Principal Investigator)

2016-01-01

We have continued our long-term project using X-ray diffraction to characterize a wide range of extraterrestrial samples. The stationary sample method with polychromatic X-rays is advantageous because the irradiated area of the sample is always same and fixed, meaning that all diffraction spots occur from the same area of the sample, however, unit cell parameters cannot be directly obtained by this method though they are very important for identification of mineral and for determination of crystal structures. In order to obtain the cell parameters even in the case of the sample stationary method, we apply energy scanning of a micro-beam of monochromatic SR at SPring-8.