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Sample records for amorphous molecular materials

  1. Molecular Dynamics Study of Crack Behavior in AN Amorphous Material

    NASA Astrophysics Data System (ADS)

    Ochoa, Oscar Romulo

    The fracture behavior of amorphous solids has received much attention due to the importance of these materials for a variety of applications in construction, transportation, including space vehicles, communications and computers, and under extreme environmental conditions, such as high temperatures, pressures and corrosive atmospheres. In this thesis, we strive to study the basic mechanisms of brittle fracture in amorphous solids and the atomic motions which affect brittle fracture and the onset of a mixed brittle/ductile behavior. The molecular dynamics technique was chosen to simulate a silica glass and study its behavior under different strain rates. This method was chosen because of its ability to probe the effect of atomic structure and atomic motions on the failure process, over a range of experimentally inaccessible strain rates. This investigation emphasizes the effects of vibrational relaxation on the material's strength. Experiments performed include strain rates in which no vibrational equilibration by the atoms is allowed and others in which the strain rates are low enough so that local rearrangements through vibrational motions are permitted but no other relaxation processes occur. Cases studied include flawless samples and samples with empty cracks and liquid filled cracks. It is found that molecular dynamics provides us with a unique method to determine the intrinsic strength of materials. In this study it is found unexpectedly that at low strain rates stresses in the samples are greatly relieved through vibrational motion which cause bond stretching and SiO(,4) tetrahedral rotation, thus, a material's strength is reduced by almost 60% through these vibrational rearrangements. The presence of voids in a material reduces their strength proportionally to the size of the cracks. A Lennard-Jones liquid added inside the voids proved to have negligible effect on the samples' strength, and it is postulated that a study of the phenomenon of slow crack growth

  2. Characterisation of amorphous and nanocrystalline molecular materials by total scattering

    SciTech Connect

    Billinge, Simon J.L.; Dykhne, Timur; Juhás, Pavol; Boin, Emil; Taylor, Ryan; Florence, Alastair J.; Shankland, Kenneth

    2010-09-17

    The use of high-energy X-ray total scattering coupled with pair distribution function analysis produces unique structural fingerprints from amorphous and nanostructured phases of the pharmaceuticals carbamazepine and indomethacin. The advantages of such facility-based experiments over laboratory-based ones are discussed and the technique is illustrated with the characterisation of a melt-quenched sample of carbamazepine as a nanocrystalline (4.5 nm domain diameter) version of form III.

  3. Cucurbit[7]uril: an Amorphous Molecular Material for Highly Selective Carbon Dioxide Uptake

    SciTech Connect

    Tian, Jian; Ma, Shengqian; Thallapally, Praveen K.; Fowler, Drew; McGrail, B. Peter; Atwood, Jerry L.

    2011-06-10

    Cucurbit[7]uril (CB[7]), in its amorphous solid state, shows one of the highest CO2 sorption capacities among the known organic molecular porous materials at 298 K and 0.1~ and 1 bar. Apart from the highest CO2 capacity, CB[7] shows a remarkable selectivity of CO2 over N2 and CH4. These properties along with the readily available precursors makes this materials a very attractive for CO2 sequestration particularly when considering the easy synthesis and low manufacturing costs.

  4. Bifunctional star-burst amorphous molecular materials for OLEDs: achieving highly efficient solid-state luminescence and carrier transport induced by spontaneous molecular orientation.

    PubMed

    Kim, Jun Yun; Yasuda, Takuma; Yang, Yu Seok; Adachi, Chihaya

    2013-05-21

    Bifunctional star-burst amorphous molecular materials displaying both efficient solid-state luminescence and high hole-transport properties are developed in this study. A high external electroluminescence quantum efficiency up to 5.9% is attained in OLEDs employing the developed amorphous materials. It is revealed that the spontaneous horizontal orientation of these light-emitting molecules in their molecular-condensed states leads to a remarkable enhancement of the electroluminescence efficiencies and carrier-transport properties.

  5. Surprising increase in photostability of organic amorphous materials by efficient molecular packing

    NASA Astrophysics Data System (ADS)

    Qiu, Yue; Antony, Lucas; de Pablo, Juan; Ediger, Mark

    Photochemically robust materials are desired for organic electronics. Previous work has demonstrated that crystal packing can strongly influence photochemical reactivity. In amorphous materials, however, similar efforts to tune photostability have not been successful. In this work, we show that organic glasses prepared by physical vapor deposition can be highly stable against photo-isomerization. Disperse orange 37 (DO37), an azobenzene derivative, is studied as a model molecule. The thickness and molecular orientation of DO37 thin films can be altered by the photo-isomerization reaction. We use spectroscopic ellipsometry to measure sample thickness and molecular orientation during light irradiation. By changing the substrate temperature during the deposition, photostability can increase 2 to 3 orders of magnitude relative to the liquid-cooled glass. We find that photostability correlates with density of packing, with density increases of up to 1.3%. Simulations also show that glasses with higher density can be significantly more photo-stable. These results show for the first time that photostability of glasses can be significantly modulated by molecular packing. And they may provide insight in designing organic photovoltaics and light emission devices with longer lifetimes.

  6. Formation of amorphous materials

    DOEpatents

    Johnson, William L.; Schwarz, Ricardo B.

    1986-01-01

    Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

  7. Amorphous Molecular Organic Solids for Gas Adsorption

    SciTech Connect

    Tian, Jian; Thallapally, Praveen K.; Dalgarno, Scott J.; McGrail, B. Peter; Atwood, Jerry L.

    2009-07-06

    We show that molecular organic compounds with large accessible internal cavities, as part of their rigid molecular structure, display exceptional ability for gas storage and separation in the amorphous solid state. This finding suggests for the first time that long-range molecular order is not a prerequisite for organic molecules to be engineered as porous materials

  8. Amorphous and Ultradisperse Crystalline Materials,

    DTIC Science & Technology

    The book sums up experimental and theoretical findings on amorphous and ultradisperse crystalline materials , massive and film types. Present-day... crystalline materials of metallic systems are presented. Emphasis is placed on inorganic film materials.

  9. Defect-induced solid state amorphization of molecular crystals

    NASA Astrophysics Data System (ADS)

    Lei, Lei; Carvajal, Teresa; Koslowski, Marisol

    2012-04-01

    We investigate the process of mechanically induced amorphization in small molecule organic crystals under extensive deformation. In this work, we develop a model that describes the amorphization of molecular crystals, in which the plastic response is calculated with a phase field dislocation dynamics theory in four materials: acetaminophen, sucrose, γ-indomethacin, and aspirin. The model is able to predict the fraction of amorphous material generated in single crystals for a given applied stress. Our results show that γ-indomethacin and sucrose demonstrate large volume fractions of amorphous material after sufficient plastic deformation, while smaller amorphous volume fractions are predicted in acetaminophen and aspirin, in agreement with experimental observation.

  10. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  11. Amorphous Organic Photorefractive Materials

    NASA Astrophysics Data System (ADS)

    Bittner, Reinhard; Meerholz, Klaus

    This chapter is structured in four main sections. First an introduction to the field of organic photorefractive (PR) materials will be given, which covers a brief historic overview as well as milestones achieved in the efforts made to improve the steady-state and dynamic performance of these promising new holographic materials.

  12. On Structure and Properties of Amorphous Materials

    PubMed Central

    Stachurski, Zbigniew H.

    2011-01-01

    Mechanical, optical, magnetic and electronic properties of amorphous materials hold great promise towards current and emergent technologies. We distinguish at least four categories of amorphous (glassy) materials: (i) metallic; (ii) thin films; (iii) organic and inorganic thermoplastics; and (iv) amorphous permanent networks. Some fundamental questions about the atomic arrangements remain unresolved. This paper focuses on the models of atomic arrangements in amorphous materials. The earliest ideas of Bernal on the structure of liquids were followed by experiments and computer models for the packing of spheres. Modern approach is to carry out computer simulations with prediction that can be tested by experiments. A geometrical concept of an ideal amorphous solid is presented as a novel contribution to the understanding of atomic arrangements in amorphous solids. PMID:28824158

  13. Physical stabilization of low-molecular-weight amorphous drugs in the solid state: a material science approach.

    PubMed

    Qi, Sheng; McAuley, William J; Yang, Ziyi; Tipduangta, Pratchaya

    2014-07-01

    Use of the amorphous state is considered to be one of the most effective approaches for improving the dissolution and subsequent oral bioavailability of poorly water-soluble drugs. However as the amorphous state has much higher physical instability in comparison with its crystalline counterpart, stabilization of amorphous drugs in a solid-dosage form presents a major challenge to formulators. The currently used approaches for stabilizing amorphous drug are discussed in this article with respect to their preparation, mechanism of stabilization and limitations. In order to realize the potential of amorphous formulations, significant efforts are required to enable the prediction of formulation performance. This will facilitate the development of computational tools that can inform a rapid and rational formulation development process for amorphous drugs.

  14. Modeling and Simulation of Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Pandey, Anup

    The general and practical inversion of diffraction data - producing a computer model correctly representing the material explored - is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this dissertation, we introduce a robust method, Force-Enhanced Atomic Refinement (FEAR), which jointly exploits the power of ab initio atomistic simulation along with the information carried by diffraction data. As a preliminary trial, the method has been implemented using empirical potentials for amorphous silicon (a-Si) and silica ( SiO2). The models obtained are comparable to the ones prepared by the conventional approaches as well as the experiments. Using ab initio interactions, the method is applied to two very different systems: amorphous silicon (a-Si) and two compositions of a solid electrolyte memory material silver-doped GeSe3. It is shown that the method works well for both the materials. Besides that, the technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. It offers a means to add a priori information in first principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. Moreover, the method has also been used to create a computer model of a-Si, using highly precise X-ray diffraction data. The model predicts properties that are close to the continuous random network models but with no a priori assumptions. In addition, using the ab initio molecular dynamics simulations (AIMD) we explored the doping and transport in hydrogenated amorphous silicon a-Si:H with the most popular impurities: boron and phosphorous. We investigated doping for these impurities and the role of H in the doping process. We revealed the network motion and H hopping induced by

  15. Photonic crystals, amorphous materials, and quasicrystals.

    PubMed

    Edagawa, Keiichi

    2014-06-01

    Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.

  16. Photonic crystals, amorphous materials, and quasicrystals

    PubMed Central

    Edagawa, Keiichi

    2014-01-01

    Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states. PMID:27877676

  17. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, R.B.

    1987-05-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  18. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, Raoul B.

    1988-01-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  19. Thermal transport in amorphous materials: a review

    NASA Astrophysics Data System (ADS)

    Wingert, Matthew C.; Zheng, Jianlin; Kwon, Soonshin; Chen, Renkun

    2016-11-01

    Thermal transport plays a crucial role in performance and reliability of semiconductor electronic devices, where heat is mainly carried by phonons. Phonon transport in crystalline semiconductor materials, such as Si, Ge, GaAs, GaN, etc, has been extensively studied over the past two decades. In fact, study of phonon physics in crystalline semiconductor materials in both bulk and nanostructure forms has been the cornerstone of the emerging field of ‘nanoscale heat transfer’. On the contrary, thermal properties of amorphous materials have been relatively less explored. Recently, however, a growing number of studies have re-examined the thermal properties of amorphous semiconductors, such as amorphous Si. These studies, which included both computational and experimental work, have revealed that phonon transport in amorphous materials is perhaps more complicated than previously thought. For instance, depending on the type of amorphous materials, thermal transport occurs via three types of vibrations: propagons, diffusons, and locons, corresponding to the propagating, diffusion, and localized modes, respectively. The relative contribution of each of these modes dictates the thermal conductivity of the material, including its magnitude and its dependence on sample size and temperature. In this article, we will review the fundamental principles and recent development regarding thermal transport in amorphous semiconductors.

  20. Relationship between nanocrystalline and amorphous microstructures by molecular dynamics simulation

    SciTech Connect

    Keblinski, P.; Phillpot, S.R.; Wolf, D.; Gleiter, H.

    1996-08-01

    A recent molecular dynamics simulation method for growth of fully dense nanocrystalline materials crystallized from melt was used with the Stillinger-Weber three-body potential to synthesize nanocrystalline Si with a grain size up to 75{Angstrom}. Structures of the highly constrained grain boundaries (GBs), triple lines, and point grain junctions were found to be highly disordered and similar to the structure of amorphous Si. These and earlier results for fcc metals suggest that a nanocrystalline microstructure may be viewed as a two-phase system, namely an ordered crystalline phase in the grain interiors connected by an amorphous, intergranular, glue-like phase. Analysis of the structures of bicrystalline GBs in the same materials reveals the presence of an amorphous intergranular equilibrium phase only in the high-energy but not the low-energy GBs, suggesting that only high-energy boundaries are present in nanocrystalline microstructures.

  1. Theoretical studies of amorphous silicon and hydrogenated amorphous silicon with molecular dynamics simulations

    SciTech Connect

    Kwon, I.

    1991-12-20

    Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) have been studied with molecular dynamics simulations. The structural, vibrational, and electronic properties of these materials have been studied with computer-generated structural models and compare well with experimental observations. The stability of a-si and a-Si:H have been studied with the aim of understanding microscopic mechanisms underlying light-induced degradation in a-Si:H (the Staebler-Wronski effect). With a view to understanding thin film growth processes, a-Si films have been generated with molecular dynamics simulations by simulating the deposition of Si-clusters on a Si(111) substrate. A new two- and three-body interatomic potential for Si-H interactions has been developed. The structural properties of a-Si:H networks are in good agreement with experimental measurements. The presence of H atoms reduces strain and disorder relative to networks without H.

  2. Theoretical studies of amorphous silicon and hydrogenated amorphous silicon with molecular dynamics simulations

    SciTech Connect

    Kwon, I.

    1991-12-20

    Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) have been studied with molecular dynamics simulations. The structural, vibrational, and electronic properties of these materials have been studied with computer-generated structural models and compare well with experimental observations. The stability of a-si and a-Si:H have been studied with the aim of understanding microscopic mechanisms underlying light-induced degradation in a-Si:H (the Staebler-Wronski effect). With a view to understanding thin film growth processes, a-Si films have been generated with molecular dynamics simulations by simulating the deposition of Si-clusters on a Si(111) substrate. A new two- and three-body interatomic potential for Si-H interactions has been developed. The structural properties of a-Si:H networks are in good agreement with experimental measurements. The presence of H atoms reduces strain and disorder relative to networks without H.

  3. Characterizing Amorphous Silicates in Extraterrestrial Materials

    NASA Astrophysics Data System (ADS)

    Fu, X.; Wang, A.; Krawczynski, M. J.

    2015-12-01

    Amorphous silicates are common in extraterrestrial materials. They are seen in the matrix of carbonaceous chondrites as well as in planetary materials. Tagish Lake is one of the most primitive carbonaceous meteorites in which TEM and XRD analyses found evidence for poorly crystalline phyllosilicate-like species; Raman spectra revealed amorphous silicates with variable degree of polymerization and low crystallinity. On Mars, CheMin discovered amorphous phases in all analyzed samples, and poorly crystalline smectite in mudstone samples. These discoveries pose questions on the crystallinity of phyllosilicates found by remote sensing on Mars, which is directly relevant to aqueous alteration during geologic history of Mars. Our goal is to use spectroscopy to better characterize amorphous silicates. We use three approaches: (1) using silicate glasses synthesized with controlled chemistry to study the effects of silicate polymerization and (2) using phyllosilicates synthesized with controlled hydrothermal treatment to study the effect of crystallinity on vibrational spectroscopy, finally (3) to use the developed correlations in above two steps to study amorphous phases in meteorites, and those found in future missions to Mars. In the 1st step, silicate glasses were synthesized from pure oxides in a range of NBO/T ratios (from 0 to 4). Depending on the targeted NBO/T and composition of mixed oxides, temperatures for each experiment fell in a range from 1260 to 1520 °C, run for ~ 4 hrs. The melt was quenched in liquid N2 or water. Homogeneity of glass was checked under optical microscopy. Raman spectra were taken over 100 spots on small chips free of bubbles and crystals. We have observed that accompanying an increase of NBO/T, there is a strengthening and a position shift of the Raman peak near 1000 cm-1 (Si-Onon-bridging stretching mode), and the weakening of broad Raman peaks near 500 cm-1 (ring breathing mode) and 700cm-1 (Si-Obridging-Si mode). We are building the

  4. Amorphous titania/carbon composite electrode materials

    DOEpatents

    Vaughey, John T.; Jansen, Andrew; Joyce, Christopher D.

    2017-05-09

    An isolated salt comprising a compound of formula (H.sub.2X)(TiO(Y).sub.2) or a hydrate thereof, wherein X is 1,4-diazabicyclo[2.2.2]octane (DABCO), and Y is oxalate anion (C.sub.2O.sub.4.sup.-2), when heated in an oxygen-containing atmosphere at a temperature in the range of at least about 275.degree. C. to less than about 400.degree. C., decomposes to form an amorphous titania/carbon composite material comprising about 40 to about 50 percent by weight titania and about 50 to about 60 percent by weight of a carbonaceous material coating the titania. Heating the composite material at a temperature of about 400 to 500.degree. C. crystallizes the titania component to anatase. The titania materials of the invention are useful as components of the cathode or anode of a lithium or lithium ion electrochemical cell.

  5. Electrically conducting ternary amorphous fully oxidized materials and their application

    NASA Technical Reports Server (NTRS)

    Giauque, Pierre (Inventor); Nicolet, Marc (Inventor); Gasser, Stefan M. (Inventor); Kolawa, Elzbieta A. (Inventor); Cherry, Hillary (Inventor)

    2004-01-01

    Electrically active devices are formed using a special conducting material of the form Tm--Ox mixed with SiO2 where the materials are immiscible. The immiscible materials are forced together by using high energy process to form an amorphous phase of the two materials. The amorphous combination of the two materials is electrically conducting but forms an effective barrier.

  6. Molecular dynamics simulations of gas selectivity in amorphous porous molecular solids.

    PubMed

    Jiang, Shan; Jelfs, Kim E; Holden, Daniel; Hasell, Tom; Chong, Samantha Y; Haranczyk, Maciej; Trewin, Abbie; Cooper, Andrew I

    2013-11-27

    Some organic cage molecules have structures with protected, internal pore volume that cannot be in-filled, irrespective of the solid-state packing mode: that is, they are intrinsically porous. Amorphous packings can give higher pore volumes than crystalline packings for these materials, but the precise nature of this additional porosity is hard to understand for disordered solids that cannot be characterized by X-ray diffraction. We describe here a computational methodology for generating structural models of amorphous porous organic cages that are consistent with experimental data. Molecular dynamics simulations rationalize the observed gas selectivity in these amorphous solids and lead to insights regarding self-diffusivities, gas diffusion trajectories, and gas hopping mechanisms. These methods might be suitable for the de novo design of new amorphous porous solids for specific applications, where "rigid host" approximations are not applicable.

  7. Inversion of diffraction data for amorphous materials

    PubMed Central

    Pandey, Anup; Biswas, Parthapratim; Drabold, D. A.

    2016-01-01

    The general and practical inversion of diffraction data–producing a computer model correctly representing the material explored–is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this paper, we describe a robust method to jointly exploit the power of ab initio atomistic simulation along with the information carried by diffraction data. The method is applied to two very different systems: amorphous silicon and two compositions of a solid electrolyte memory material silver-doped GeSe3. The technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. By direct calculation, we show that the method works for both poor and excellent glass forming materials. It offers a means to add a priori information in first-principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. PMID:27652893

  8. Inversion of diffraction data for amorphous materials

    NASA Astrophysics Data System (ADS)

    Pandey, Anup; Biswas, Parthapratim; Drabold, D. A.

    2016-09-01

    The general and practical inversion of diffraction data-producing a computer model correctly representing the material explored-is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this paper, we describe a robust method to jointly exploit the power of ab initio atomistic simulation along with the information carried by diffraction data. The method is applied to two very different systems: amorphous silicon and two compositions of a solid electrolyte memory material silver-doped GeSe3. The technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. By direct calculation, we show that the method works for both poor and excellent glass forming materials. It offers a means to add a priori information in first-principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information.

  9. Amorphous materials molded IR lens progress report

    NASA Astrophysics Data System (ADS)

    Hilton, A. R., Sr.; McCord, James; Timm, Ronald; Le Blanc, R. A.

    2008-04-01

    Amorphous Materials began in 2000 a joint program with Lockheed Martin in Orlando to develop molding technology required to produce infrared lenses from chalcogenide glasses. Preliminary results were reported at this SPIE meeting by Amy Graham1 in 2003. The program ended in 2004. Since that time, AMI has concentrated on improving results from two low softening glasses, Amtir 4&5. Both glasses have been fully characterized and antireflection coatings have been developed for each. Lenses have been molded from both glasses, from Amtir 6 and from C1 Core glass. A Zygo unit is used to evaluate the results of each molded lens as a guide to improving the molding process. Expansion into a larger building has provided room for five production molding units. Molded lens sizes have ranged from 8 mm to 136 mm in diameter. Recent results will be presented

  10. Quantifying Nanoscale Order in Amorphous Materials via Fluctuation Electron Microscopy

    ERIC Educational Resources Information Center

    Bogle, Stephanie Nicole

    2009-01-01

    Fluctuation electron microscopy (FEM) has been used to study the nanoscale order in various amorphous materials. The method is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function…

  11. Quantifying Nanoscale Order in Amorphous Materials via Fluctuation Electron Microscopy

    ERIC Educational Resources Information Center

    Bogle, Stephanie Nicole

    2009-01-01

    Fluctuation electron microscopy (FEM) has been used to study the nanoscale order in various amorphous materials. The method is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function…

  12. Electron beam recrystallization of amorphous semiconductor materials

    NASA Technical Reports Server (NTRS)

    Evans, J. C., Jr.

    1968-01-01

    Nucleation and growth of crystalline films of silicon, germanium, and cadmium sulfide on substrates of plastic and glass were investigated. Amorphous films of germanium, silicon, and cadmium sulfide on amorphous substrates of glass and plastic were converted to the crystalline condition by electron bombardment.

  13. Molecular modeling of amorphous, non-woven polymer networks.

    PubMed

    Krausse, Constantin A; Milek, Theodor; Zahn, Dirk

    2015-10-01

    We outline a simple and efficient approach to generating molecular models of amorphous polymer networks. Similar to established techniques of preparing woven polymer networks from quenching high-temperature molecular simulation runs, we use a molecular dynamics simulations of a generic melt as starting points. This generic melt is however only used to describe parts of the polymers, namely the cross-linker units which positions are adopted from particle positions of the quenched melt. Specific degrees of network connectivity are tuned by geometric criteria for linker-linker connections and by suitable multi-body interaction potentials applied to the generic melt simulations. Using this technique we demonstrate adjusting fourfold linker coordination in amorphous polymer networks comprising 10-20% under-coordinated linkers. Graphical Abstract Molecular modeling of amorphous, non-woven polymer networks.

  14. Thermodynamics, molecular mobility and crystallization kinetics of amorphous griseofulvin.

    PubMed

    Zhou, Deliang; Zhang, Geoff G Z; Law, Devalina; Grant, David J W; Schmitt, Eric A

    2008-01-01

    Griseofulvin is a small rigid molecule that shows relatively high molecular mobility and small configurational entropy in the amorphous phase and tends to readily crystallize from both rubbery and glassy states. This work examines the crystallization kinetics and mechanism of amorphous griseofulvin and the quantitative correlation between the rate of crystallization and molecular mobility above and below Tg. Amorphous griseofulvin was prepared by rapidly quenching the melt in liquid N2. The thermodynamics and dynamics of amorphous phase were then characterized using a combination of thermal analysis techniques. After characterization of the amorphous phase, crystallization kinetics above Tg were monitored by isothermal differential scanning calorimetry (DSC). Transformation curves for crystallization fit a second-order John-Mehl-Avrami (JMA) model. Crystallization kinetics below Tg were monitored by powder X-ray diffraction and fit to the second-order JMA model. Activation energies for crystallization were markedly different above and below Tg suggesting a change in mechanism. In both cases molecular mobility appeared to be partially involved in the rate-limiting step for crystallization, but the extent of correlation between the rate of crystallization and molecular mobility was different above and below Tg. A lower extent of correlation below Tg was observed which does not appear to be explained by the molecular mobility alone and the diminishing activation energy for crystallization suggests a change in the mechanism of crystallization.

  15. Mesoscale modeling of strain induced solid state amorphization in crystalline materials

    NASA Astrophysics Data System (ADS)

    Lei, Lei

    Solid state amorphization, and in particular crystalline to amorphous transformation, can be observed in metallic alloys, semiconductors, intermetallics, minerals, and also molecular crystals when they undergo irradiation, hydrogen gas dissolution, thermal interdiffusion, mechanical alloying, or mechanical milling. Although the amorphization mechanisms may be different, the transformation occurs due to the high level of disorder introduced into the material. Milling induced solid state amorphization is proposed to be the result of accumulation of crystal defects, specifically dislocations, as the material is subjected to large deformations during the high energy process. Thus, understanding the deformation mechanisms of crystalline materials will be the first step in studying solid state amorphization in crystalline materials, which not only has scientific contributions, but also technical consequences. A phase field dislocation dynamics (PFDD) approach is employed in this work to simulate plastic deformation of molecular crystals. This PFDD model has the advantage of tracking all of the dislocations in a material simultaneously. The model takes into account the elastic interaction between dislocations, the lattice resistance to dislocation motion, and the elastic interaction of dislocations with an external stress field. The PFDD model is employed to describe the deformation of molecular crystals with pharmaceutical applications, namely, single crystal sucrose, acetaminophen, gamma-indomethacin, and aspirin. Stress-strain curves are produced that result in expected anisotropic material response due to the activation of different slip systems and yield stresses that agree well with those from experiments. The PFDD model is coupled to a phase transformation model to study the relation between plastic deformation and the solid state amorphization of crystals that undergo milling. This model predicts the amorphous volume fraction in excellent agreement with

  16. Amorphous drug delivery systems: molecular aspects, design, and performance.

    PubMed

    Kaushal, Aditya Mohan; Gupta, Piyush; Bansal, Arvind Kumar

    2004-01-01

    The biopharmaceutical properties-especially the solubility and permeability-of a molecule contribute to its overall therapeutic efficacy. The newer tools of drug discovery have caused a shift in the properties of drug-like compounds, resulting in drugs with poor aqueous solubility and permeability, which offer delivery challenges, thus requiring considerable pharmaceutical manning. The modulation of solubility is a more viable option for enhancing bioavailability than permeability, because of the lack of "safe" approaches to enhance the latter. Solid-state manipulation in general, and amorphization in particular, are preferred ways of enhancing solubility and optimizing delivery of poorly soluble drugs. This review attempts to address the diverse issues pertaining to amorphous drug delivery systems. We discuss the various thermodynamic phenomenon such as glass transition, fragility, molecular mobility, devitrification kinetics, and molecular-level chemical interactions that contribute to the ease of formation, the solubility advantage, and the stability of amorphous drugs. The engineering of pharmaceutical alloys by solubilizing and stabilizing carriers, commonly termed solid dispersions, provide avenues for exploiting the benefits of amorphous systems. Carrier properties, mechanisms of drug release, and study of release kinetics help to improve the predictability of performance. The review also addresses the various barriers in the design of amorphous delivery systems, use of amorphous form in controlled release delivery systems, and their in vivo performance.

  17. Molecular dynamics simulation of wetting on modified amorphous silica surface

    NASA Astrophysics Data System (ADS)

    Chai, Jingchun; Liu, Shuyan; Yang, Xiaoning

    2009-08-01

    The microscopic wetting of water on amorphous silica surfaces has been investigated by molecular dynamics simulation. Different degrees of surface hydroxylation/silanization were considered. It was observed that the hydrophobicity becomes enhanced with an increase in the degree of surface silanization. A continuous transformation from hydrophilicity to hydrophobicity can be attained for the amorphous silica surfaces through surface modification. From the simulation result, the contact angle can exceed 90° when surface silanization percentage is above 50%, showing a hydrophobic character. It is also found that when the percentage of surface silanization is above 70% on the amorphous silica surface, the water contact angle almost remains unchanged (110-120°). This phenomenon is a little different from the wetting behavior on smooth quartz plates in previous experimental report. This change in the wettability on modified amorphous silica surfaces can be interpreted in terms of the interaction between water molecules and the silica surfaces.

  18. Amorphous Silicates in Primitive Meteoritic Materials: Acfer 094 and IDPs

    NASA Technical Reports Server (NTRS)

    Keller, L. P.; Nakamura-Messenger, K.; Messenger, S.; Walker, Robert M.

    2009-01-01

    The abundance of presolar grains is one measure of the primitive nature of meteoritic materials. Presolar silicates are abundant in meteorites whose matrices are dominated by amorphous silicates such as the unique carbonaceous chondrite Acfer 094. Presolar silicates are even more abundant in chondritic-porous interplanetary dust particles (CP-IDPs). Amorphous silicates in the form of GEMS (glass with embedded metal and sulfides) grains are a major component of CP IDPs. We are studying amorphous silicates in Acfer 094 matrix in order to determine whether they are related to the GEMS grains in CPIDPs

  19. Fracture of Carbon Nanotube - Amorphous Carbon Composites: Molecular Modeling

    NASA Technical Reports Server (NTRS)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    Carbon nanotubes (CNTs) are promising candidates for use as reinforcements in next generation structural composite materials because of their extremely high specific stiffness and strength. They cannot, however, be viewed as simple replacements for carbon fibers because there are key differences between these materials in areas such as handling, processing, and matrix design. It is impossible to know for certain that CNT composites will represent a significant advance over carbon fiber composites before these various factors have been optimized, which is an extremely costly and time intensive process. This work attempts to place an upper bound on CNT composite mechanical properties by performing molecular dynamics simulations on idealized model systems with a reactive forcefield that permits modeling of both elastic deformations and fracture. Amorphous carbon (AC) was chosen for the matrix material in this work because of its structural simplicity and physical compatibility with the CNT fillers. It is also much stiffer and stronger than typical engineering polymer matrices. Three different arrangements of CNTs in the simulation cell have been investigated: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. The SWNT and MWNT array systems are clearly idealizations, but the SWNT bundle system is a step closer to real systems in which individual tubes aggregate into large assemblies. The effect of chemical crosslinking on composite properties is modeled by adding bonds between the CNTs and AC. The balance between weakening the CNTs and improving fiber-matrix load transfer is explored by systematically varying the extent of crosslinking. It is, of course, impossible to capture the full range of deformation and fracture processes that occur in real materials with even the largest atomistic molecular dynamics simulations. With this limitation in mind, the simulation results reported here provide a plausible upper limit on

  20. Molecular mobility in amorphous state: Implications on physical stability

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Sunny Piyush

    Amorphous pharmaceuticals are desirable in drug development due to their advantageous biopharmaceutical properties of higher apparent aqueous solubility and dissolution rate. The main obstacle in their widespread use, however, is their higher physicochemical instability than their crystalline counterparts. The goal of the present research project was to investigate correlations between the molecular mobility and physical stability in model amorphous compounds. The objective was to identify the specific mobility which is responsible for the physical instability in each case. This will potentially enable the development of effective strategies for the stabilization of amorphous pharmaceuticals. Moreover, these correlations can be used to develop predictive models for the stability at the pharmaceutically relevant storage conditions. Subtraction of dc conductivity enabled the comprehensive characterization of molecular mobility in amorphous trehalose. This was followed by investigation of correlation between crystallization behavior and different relaxations. Global mobility was found to be strongly coupled to both crystallization onset time and rate. Different preparation methods imparted different mobility states to amorphous trehalose which was postulated to be the reason for the significant physical stability differences. Predictive models were developed and a good agreement was found between the predicted and the experimental crystallization onset times at temperatures around and below the glass transition temperature (Tg). Effect of annealing was investigated on water sorption, enthalpic recovery and dielectric relaxation times in amorphous trehalose. Global mobility was found to be linearly correlated to the water sorption potential which enabled the development of predictive models. Global mobility was also found to be strongly correlated to physical instability in amorphous itraconazole. Effect of polymer (PVP and HPMCAS) on itraconazole mobility and

  1. Amorphous material in high strain experimental fault gouges

    SciTech Connect

    Yund, R.A.; Blanpied, M.L.; Tullis, T.E.; Weeks, J.D. )

    1990-09-10

    The microstructures of gouges produced in room temperature, rotary shear sliding experiments were examined by transmission electron microscopy. Gouges were produced by sliding on ground surfaces of granite, quartzite, or marble except for one experiment in which a 1-mm-thick simulated gouge layer was used. Water was added to the sliding surfaces of all but one sample. Crystal plastic processes play no role in the granite and quartzite gouges and a minor role in the marbles. All of the gouges consist of mostly submicron crystalline fragments; in addition, the granite gouges contain 5-60% amorphous material, and the quartzite gouge contains {approximately}50% amorphous material. In the granite samples the composition of the amorphous material commonly lies between K-rich and Na, Ca-rich feldspars, although portions may be silica-rich. The microstructural relations suggest that the amorphous material forms by comminution of fragments rather than by melting. The amount of amorphous material increases, and the size of the largest crystalline fragments decreases, with an increase in average shear strain, although the microstructure is nearly uniform throughout each granite gouge layer. These observations suggest that after slip becomes localized on Y shear surfaces and/or R{sub 1} Riedel shears the entire gouge layer must continue to undergo deformation. It is suggested that cyclic deformation in the gouge must occur to accommodate the passage of geometric irregularities on the active slip surfaces.

  2. Propagating mode-I fracture in amorphous materials using the continuous random network model

    NASA Astrophysics Data System (ADS)

    Heizler, Shay I.; Kessler, David A.; Levine, Herbert

    2011-08-01

    We study propagating mode-I fracture in two-dimensional amorphous materials using atomistic simulations. We use the continuous random network model of an amorphous material, creating samples using a two-dimensional analog of the Wooten-Winer-Weaire Monte Carlo algorithm. For modeling fracture, molecular-dynamics simulations were run on the resulting samples. The results of our simulations reproduce the main experimental features. In addition to achieving a steady-state crack under a constant driving displacement (which has not yet been achieved by other atomistic models for amorphous materials), the runs show microbranching, which increases with driving, transitioning to macrobranching for the largest drivings. In addition to the qualitative visual similarity of the simulated cracks to experiment, the simulation also succeeds in reproducing qualitatively the experimentally observed oscillations of the crack velocity.

  3. Amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1984-01-01

    An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  4. A shear localization mechanism for lubricity of amorphous carbon materials

    PubMed Central

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  5. A shear localization mechanism for lubricity of amorphous carbon materials

    NASA Astrophysics Data System (ADS)

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  6. A shear localization mechanism for lubricity of amorphous carbon materials.

    PubMed

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-13

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  7. An amorphous magnetic bimetallic sensor material

    NASA Astrophysics Data System (ADS)

    Kraus, L.; Hašlar, V.; Závěta, K.; Pokorný, J.; Duhaj, P.; Polak, C.

    1995-11-01

    An amorphous bimetal ribbon consisting of magnetostrictive (Fe40Ni40B20) and nonmagnetostrictive (Co67Fe4Cr7Si8B12) layers was prepared by planar flow casting from a double-chamber crucible. The effect of applied tensile stress on hysteresis loops and the surface domain structures of the stress-relieved bimetal was investigated at room temperature. The hysteresis loops can be well explained by superpositions of hysteresis loops of the individual layers. Only the magnetostrictive layer is responsible for the influence of applied stress on magnetic behavior. At a certain stress, the magnetic anisotropy of the magnetostrictive layer abruptly changes from a hard-ribbon-axis to an easy-ribbon-axis type. This transition is accompanied by a change of domain structure and a sharp maximum of the coercive field. A simple model taking into account an interplay of the applied tensile stress with the compressive stress produced by thermal contraction after stress relief and/or by bending of the ribbon has been developed. The observed behavior can be well explained by the model.

  8. Molecular dynamics simulation of amorphous SiO2 nanoparticles.

    PubMed

    Hoang, Vo Van

    2007-11-08

    Molecular dynamics simulation of amorphous SiO2 spherical nanoparticles has been carried out in a model with different sizes, 2, 4, and 6 nm, under non-periodic boundary conditions. We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of amorphous nanoparticles obtained at 350 K have been studied via partial radial distribution functions (PRDFs), mean interatomic distances, coordination numbers, and bond-angle distributions, which are compared with those observed in the bulk. Calculations of the radial density profile in nanoparticles show the tendency of oxygen to concentrate at the surface as observed previously in other amorphous clusters or thin films. Size effects on structure of nanosized models are significant. The calculations show that if the size is larger than 4 nm, amorphous SiO2 nanoparticles have a distorted tetrahedral network structure with the mean coordination number ZSi-O approximately 4.0 and ZO-Si approximately 2.0 like those observed in the bulk. Surface structure, surface energy, and glass transition temperature of SiO2 nanoparticles have been obtained and presented.

  9. Amorphous and Nanocomposite Materials for Energy-Efficient Electric Motors

    NASA Astrophysics Data System (ADS)

    Silveyra, Josefina M.; Xu, Patricia; Keylin, Vladimir; DeGeorge, Vincent; Leary, Alex; McHenry, Michael E.

    2016-01-01

    We explore amorphous soft-magnetic alloys as candidates for electric motor applications. The Co-rich system combines the benefits of low hysteretic and eddy-current losses while exhibiting negligible magnetostriction and robust mechanical properties. The amorphous precursors can be devitrified to form nanocomposite magnets. The superior characteristics of these materials offer the advantages of ease of handling in the manufacturing processing and low iron losses during motor operation. Co-rich amorphous ribbons were laser-cut to build a stator for a small demonstrator permanent-magnet machine. The motor was tested up to ~30,000 rpm. Finite-element analyses proved that the iron losses of the Co-rich amorphous stator were ~80% smaller than for a Si steel stator in the same motor, at 18,000 rpm (equivalent to an electric frequency of 2.1 kHz). These low-loss soft magnets have great potential for application in highly efficient high-speed electric machines, leading to size reduction as well as reduction or replacement of rare earths in permanent-magnet motors. More studies evaluating further processing techniques for amorphous and nanocomposite materials are needed.

  10. Molecular structure of vapor-deposited amorphous selenium

    NASA Astrophysics Data System (ADS)

    Goldan, A. H.; Li, C.; Pennycook, S. J.; Schneider, J.; Blom, A.; Zhao, W.

    2016-10-01

    The structure of amorphous selenium is clouded with much uncertainty and contradictory results regarding the dominance of polymeric chains versus monomer rings. The analysis of the diffraction radial distribution functions are inconclusive because of the similarities between the crystalline allotropes of selenium in terms of the coordination number, bond length, bond angle, and dihedral angle. Here, we took a much different approach and probed the molecular symmetry of the thermodynamically unstable amorphous state via analysis of structural phase transformations. We verified the structure of the converted metastable and stable crystalline structures using scanning transmission electron microscopy. In addition, given that no experimental technique can tell us the exact three-dimensional atomic arrangements in glassy semiconductors, we performed molecular-dynamic simulations using a well-established empirical three-body interatomic potential. We developed a true vapor-deposited process for the deposition of selenium molecules onto a substrate using empirical molecular vapor compositions and densities. We prepared both vapor-deposited and melt-quenched samples and showed that the simulated radial distribution functions match very well to experiment. The combination of our experimental and molecular-dynamic analyses shows that the structures of vapor- and melt-quenched glassy/amorphous selenium are quite different, based primarily on rings and chains, respectively, reflecting the predominant structure of the parent phase in its thermodynamic equilibrium.

  11. Method of depositing wide bandgap amorphous semiconductor materials

    DOEpatents

    Ellis, Jr., Frank B.; Delahoy, Alan E.

    1987-09-29

    A method of depositing wide bandgap p type amorphous semiconductor materials on a substrate without photosensitization by the decomposition of one or more higher order gaseous silanes in the presence of a p-type catalytic dopant at a temperature of about 200.degree. C. and a pressure in the range from about 1-50 Torr.

  12. Containerless synthesis of amorphous and nanophase organic materials

    DOEpatents

    Benmore, Chris J.; Weber, Johann R.

    2016-05-03

    The invention provides a method for producing a mixture of amorphous compounds, the method comprising supplying a solution containing the compounds; and allowing at least a portion of the solvent of the solution to evaporate while preventing the solute of the solution from contacting a nucleation point. Also provided is a method for transforming solids to amorphous material, the method comprising heating the solids in an environment to form a melt, wherein the environment contains no nucleation points; and cooling the melt in the environment.

  13. Communication: broken-ergodicity and the emergence of solid behaviour in amorphous materials.

    PubMed

    Williams, Stephen R

    2011-10-07

    Using a combination of theory and molecular dynamics simulations, we show how solid behaviour emerges in amorphous materials from microscopic considerations. The effect on the systems response to a sudden change in strain, upon entering the history dependent glass state, is focused on. An important symmetry that is always present in a fluid state, is shown to be broken for a simulated history dependent amorphous solid. Details of how this applies to a single sample and an ensemble of independent samples are discussed, along with the dependence on the time scale the system is monitored on. © 2011 American Institute of Physics

  14. Amorphization of hard crystalline materials by electrosprayed nanodroplet impact

    SciTech Connect

    Gamero-Castaño, Manuel Torrents, Anna; Borrajo-Pelaez, Rafael; Zheng, Jian-Guo

    2014-11-07

    A beam of electrosprayed nanodroplets impacting on single-crystal silicon amorphizes a thin surface layer of a thickness comparable to the diameter of the drops. The phase transition occurs at projectile velocities exceeding a threshold, and is caused by the quenching of material melted by the impacts. This article demonstrates that the amorphization of silicon is a general phenomenon, as nanodroplets impacting at sufficient velocity also amorphize other covalently bonded crystals. In particular, we bombard single-crystal wafers of Si, Ge, GaAs, GaP, InAs, and SiC in a range of projectile velocities, and characterize the samples via electron backscatter diffraction and transmission electron microscopy to determine the aggregation state under the surface. InAs requires the lowest projectile velocity to develop an amorphous layer, followed by Ge, Si, GaAs, and GaP. SiC is the only semiconductor that remains fully crystalline, likely due to the relatively low velocities of the beamlets used in this study. The resiliency of each crystal to amorphization correlates well with the specific energy needed to melt it except for Ge, which requires projectile velocities higher than expected.

  15. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John W.; Srivastava, Deepak

    2008-04-01

    Amorphous carbonaceous char produced from burning polymer solids has insulating properties that make it valuable in thermal protection and fire-retardant systems. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated.

  16. Aging mechanisms in amorphous phase-change materials.

    PubMed

    Raty, Jean Yves; Zhang, Wei; Luckas, Jennifer; Chen, Chao; Mazzarello, Riccardo; Bichara, Christophe; Wuttig, Matthias

    2015-06-24

    Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

  17. Dielectric properties of amorphous phase-change materials

    NASA Astrophysics Data System (ADS)

    Chen, C.; Jost, P.; Volker, H.; Kaminski, M.; Wirtssohn, M.; Engelmann, U.; Krüger, K.; Schlich, F.; Schlockermann, C.; Lobo, R. P. S. M.; Wuttig, M.

    2017-03-01

    The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz-3 GHz) and optical spectroscopy from the far- (20 c m-1 , 0.6 THz) to the near- (12 000 c m-1 , 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and S b2T e3 . These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and S b2T e3 has been identified.

  18. Fluctuation Electron Microscopy of Amorphous and Polycrystalline Materials

    NASA Astrophysics Data System (ADS)

    Rezikyan, Aram

    Fluctuation Electron Microscopy (FEM) has become an effective materials' structure characterization technique, capable of probing medium-range order (MRO) that may be present in amorphous materials. Although its sensitivity to MRO has been exercised in numerous studies, FEM is not yet a quantitative technique. The holdup has been the discrepancy between the computed kinematical variance and the experimental variance, which previously was attributed to source incoherence. Although high-brightness, high coherence, electron guns are now routinely available in modern electron microscopes, they have not eliminated this discrepancy between theory and experiment. The main objective of this thesis was to explore, and to reveal, the reasons behind this conundrum. The study was started with an analysis of the speckle statistics of tilted dark-field TEM images obtained from an amorphous carbon sample, which confirmed that the structural ordering is sensitively detected by FEM. This analysis also revealed the inconsistency between predictions of the source incoherence model and the experimentally observed variance. FEM of amorphous carbon, amorphous silicon and ultra nanocrystalline diamond samples was carried out in an attempt to explore the conundrum. Electron probe and sample parameters were varied to observe the scattering intensity variance behavior. Results were compared to models of probe incoherence, diffuse scattering, atom displacement damage, energy loss events and multiple scattering. Models of displacement decoherence matched the experimental results best. Decoherence was also explored by an interferometric diffraction method using bilayer amorphous samples, and results are consistent with strong displacement decoherence in addition to temporal decoherence arising from the electron source energy spread and energy loss events in thick samples. It is clear that decoherence plays an important role in the long-standing discrepancy between experimental FEM and its

  19. Examining the Validity of the Phonon Gas Model in Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Lv, Wei; Henry, Asegun

    2016-12-01

    The idea of treating phonon transport as equivalent to transport through a gas of particles is termed the phonon gas model (PGM), and it has been used almost ubiquitously to try and understand heat conduction in all solids. However, most of the modes in disordered materials do not propagate and thus may contribute to heat conduction in a fundamentally different way than is described by the PGM. From a practical perspective, the problem with trying to apply the PGM to amorphous materials is the fact that one cannot rigorously define the phonon velocities for non-propagating modes, since there is no periodicity. Here, we tested the validity of the PGM for amorphous materials by assuming the PGM is applicable, and then, using a combination of lattice dynamics, molecular dynamics (MD) and experimental thermal conductivity data, we back-calculated the phonon velocities for the vibrational modes. The results of this approach show that if the PGM was valid, a large number of the mid and high frequency modes would have to have either imaginary or extremely high velocities to reproduce the experimental thermal conductivity data. Furthermore, the results of MD based relaxation time calculations suggest that in amorphous materials there is little, if any, connection between relaxation times and thermal conductivity. This then strongly suggests that the PGM is inapplicable to amorphous solids.

  20. Examining the Validity of the Phonon Gas Model in Amorphous Materials

    PubMed Central

    Lv, Wei; Henry, Asegun

    2016-01-01

    The idea of treating phonon transport as equivalent to transport through a gas of particles is termed the phonon gas model (PGM), and it has been used almost ubiquitously to try and understand heat conduction in all solids. However, most of the modes in disordered materials do not propagate and thus may contribute to heat conduction in a fundamentally different way than is described by the PGM. From a practical perspective, the problem with trying to apply the PGM to amorphous materials is the fact that one cannot rigorously define the phonon velocities for non-propagating modes, since there is no periodicity. Here, we tested the validity of the PGM for amorphous materials by assuming the PGM is applicable, and then, using a combination of lattice dynamics, molecular dynamics (MD) and experimental thermal conductivity data, we back-calculated the phonon velocities for the vibrational modes. The results of this approach show that if the PGM was valid, a large number of the mid and high frequency modes would have to have either imaginary or extremely high velocities to reproduce the experimental thermal conductivity data. Furthermore, the results of MD based relaxation time calculations suggest that in amorphous materials there is little, if any, connection between relaxation times and thermal conductivity. This then strongly suggests that the PGM is inapplicable to amorphous solids. PMID:27917868

  1. Neutron scattering from amorphous, disordered and nanocrystalline materials

    SciTech Connect

    Price, D.L.

    1994-10-01

    The author has described the power of neutron diffraction and inelastic scattering techniques for determining the structure and dynamics of disordered systems, using the archetypal glass SiO{sub 2} as a detailed example. Of course the field of amorphous and disordered systems contains a much greater variety of types of materials exhibiting a wide range of possible types of disorder. The author gives a brief review of the varieties of order and disorder exhibited by condensed matter.

  2. Molecular-dynamics simulation of thermal conductivity in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Lee, Young Hee; Biswas, R.; Soukoulis, C. M.; Wang, C. Z.; Chan, C. T.; Ho, K. M.

    1991-03-01

    The temperature-dependent thermal conductivity κ(T) of amorphous silicon has been calculated from equilibrium molecular-dynamics simulations using the time correlations of the heat flux operator in which anharmonicity is explicitly incorporated. The Stillinger-Weber two- and three-body Si potential and the Wooten-Weaire-Winer a-Si model were utilized. The calculations correctly predict an increasing thermal conductivity at low temperatures (below 400 K). The κ(T), for T>400 K, is affected by the thermally generated coordination-defect states. Comparisons to both experiment and previous calculations will be described.

  3. Resolving 2D Amorphous Materials with Scanning Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Burson, Kristen M.; Buechner, Christin; Lewandowski, Adrian; Heyde, Markus; Freund, Hans-Joachim

    Novel two-dimensional (2D) materials have garnered significant scientific interest due to their potential technological applications. Alongside the emphasis on crystalline materials, such as graphene and hexagonal BN, a new class of 2D amorphous materials must be pursued. For amorphous materials, a detailed understanding of the complex structure is necessary. Here we present a structural study of 2D bilayer silica on Ru(0001), an insulating material which is weakly coupled to the substrate. Atomic structure has been determined with a dual mode atomic force microscopy (AFM) and scanning tunneling microscopy (STM) sensor in ultra-high vacuum (UHV) at low temperatures, revealing a network of different ring sizes. Liquid AFM measurements with sub-nanometer resolution bridge the gap between clean UHV conditions and the environments that many material applications demand. Samples are grown and characterized in vacuum and subsequently transferred to the liquid AFM. Notably, the key structural features observed, namely nanoscale ring networks and larger holes to the substrate, show strong quantitative agreement between the liquid and UHV microscopy measurements. This provides direct evidence for the structural stability of these silica films for nanoelectronics and other applications. KMB acknowledges support from the Alexander von Humboldt Foundation.

  4. Bulk acoustic wave resonators made of amorphous materials

    NASA Astrophysics Data System (ADS)

    Breuzet, Michel

    1990-08-01

    The investigation of plates vibrating at radio frequency and made of amorphous conductive or insulating materials is carried out. Capacitive excitation was employed for this type of resonator made of non piezoelectric material. The advantage of using contour vibration modes is demonstrated, with particular reference to the Lame mode. The optimization of mountings designed to minimize resonator/mounting coupling is investigated. The finite element computing method was applied. The results obtained on resonators made of AU4G and vitreous silica (SiO2) are discussed.

  5. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John; Srivastava, Deepak

    2008-03-01

    Amorphous carbonaceous char produced from burning polymer solids has insulating properties that makes it valuable for aerospace thermal protection systems as well as for fire retardants. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated structure. Mechanisms of the char formation process and the morphology of the resulting structure are elucidated.

  6. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review.

    PubMed

    Morón, Carlos; Cabrera, Carolina; Morón, Alberto; García, Alfonso; González, Mercedes

    2015-11-11

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a "simple" and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc.

  7. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review

    PubMed Central

    Morón, Carlos; Cabrera, Carolina; Morón, Alberto; García, Alfonso; González, Mercedes

    2015-01-01

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a “simple” and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc. PMID:26569244

  8. Model for charge/discharge-rate-dependent plastic flow in amorphous battery materials

    NASA Astrophysics Data System (ADS)

    Khosrownejad, S. M.; Curtin, W. A.

    2016-09-01

    Plastic flow is an important mechanism for relaxing stresses that develop due to swelling/shrinkage during charging/discharging of battery materials. Amorphous high-storage-capacity Li-Si has lower flow stresses than crystalline materials but there is evidence that the plastic flow stress depends on the conditions of charging and discharging, indicating important non-equilibrium aspects to the flow behavior. Here, a mechanistically-based constitutive model for rate-dependent plastic flow in amorphous materials, such as LixSi alloys, during charging and discharging is developed based on two physical concepts: (i) excess energy is stored in the material during electrochemical charging and discharging due to the inability of the amorphous material to fully relax during the charging/discharging process and (ii) this excess energy reduces the barriers for plastic flow processes and thus reduces the applied stresses necessary to cause plastic flow. The plastic flow stress is thus a competition between the time scales of charging/discharging and the time scales of glassy relaxation. The two concepts, as well as other aspects of the model, are validated using molecular simulations on a model Li-Si system. The model is applied to examine the plastic flow behavior of typical specimen geometries due to combined charging/discharging and stress history, and the results generally rationalize experimental observations.

  9. Prediction of Charge Mobility in Amorphous Organic Materials through the Application of Hopping Theory.

    PubMed

    Lee, Choongkeun; Waterland, Robert; Sohlberg, Karl

    2011-08-09

    The application of hopping theory to predict charge (hole) mobility in amorphous organic molecular materials is studied in detail. Application is made to amorphous cells of N,N'-diphenyl-N,N'-bis-(3-methylphenylene)-1,1'-diphenyl-4,4'-diamine (TPD), 1,1-bis-(4,4'-diethylaminophenyl)-4,4-diphenyl-1,3,butadinene (DEPB), N4,N4'-di(biphenyl-3-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (mBPD), N1,N4-di(naphthalen-1-yl)-N1,N4-diphenylbenzene-1,4-diamine (NNP), and N,N'-bis[9,9-dimethyl-2-fluorenyl]-N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (pFFA). Detailed analysis of the computation of each of the parameters in the equations for hopping rate is presented, including studies of their convergence with respect to various numerical approximations. Based on these convergence studies, the most robust methodology is then applied to investigate the dependence of mobility on such parameters as the monomer reorganization energy, the monomer-monomer coupling, and the material density. The results give insight into what will be required to improve the accuracy of predictions of mobility in amorphous organic materials, and what factors should be controlled to develop materials with higher (or lower) charge (hole) mobility.

  10. On Failure in Polycrystalline and Amorphous Brittle Materials

    NASA Astrophysics Data System (ADS)

    Bourne, N. K.

    2009-12-01

    The performance of behaviour of brittle materials depends upon discrete deformation mechanisms operating during the loading process. The critical mechanisms determining the behaviour of armour ceramics have not been isolated using traditional ballistics. It has recently become possible to measure strength histories in materials under shock. The data gained for the failed strength of the armour are shown to relate directly to the penetration measured into tiles. Further the material can be loaded and recovered for post-mortem examination. Failure is by micro-fracture that is a function of the defects and then cracking activated by plasticity mechanisms within the grains and failure at grain boundaries in the amorphous intergranular phase. Thus it is the shock-induced plastic yielding of grains at the impact face that determines the later time penetration through the tile.

  11. Charge transport and injection in amorphous organic electronic materials

    NASA Astrophysics Data System (ADS)

    Tse, Shing Chi

    This thesis presents how we use various measuring techniques to study the charge transport and injection in organic electronic materials. Understanding charge transport and injection properties in organic solids is of vital importance for improving performance characteristics of organic electronic devices, including organic-light-emitting diodes (OLEDs), photovoltaic cells (OPVs), and field effect transistors (OFETs). The charge transport properties of amorphous organic materials, commonly used in organic electronic devices, are investigated by the means of carrier mobility measurements. Transient electroluminescence (EL) technique was used to evaluate the electron mobility of an electron transporting material--- tris(8-hydroxyquinoline) aluminum (Alq3). The results are in excellent agreement with independent time-of-flight (TOF) measurements. Then, the effect of dopants on electron transport was also examined. TOF technique was also used to examine the effects of tertiary-butyl (t-Bu) substitutions on anthracene derivatives (ADN). All ADN compounds were found to be ambipolar. As the degree of t-Bu substitution increases, the carrier mobilities decrease progressively. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap. In addition, from TOF measurements, two naphthylamine-based hole transporters, namely, N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) and 4,4',4"-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA) were found to possess electron-transporting (ET) abilities. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the hopping model will be discussed. Furthermore, the ET property of NPB applied in OLEDs will also be examined. Besides transient EL and TOF techniques, we also use dark-injection space-charge-limited current

  12. FORMATION OF MOLECULAR OXYGEN AND OZONE ON AMORPHOUS SILICATES

    SciTech Connect

    Jing Dapeng; He Jiao; Vidali, Gianfranco; Brucato, John Robert; Tozzetti, Lorenzo; De Sio, Antonio

    2012-09-01

    Oxygen in the interstellar medium is seen in the gas phase, in ices (incorporated in H{sub 2}O, CO, and CO{sub 2}), and in grains such as (Mg{sub x} Fe{sub 1-x} )SiO{sub 3} or (Mg{sub x} Fe{sub 1-x} ){sub 2}SiO{sub 4}, 0 < x < 1. In this investigation, we study the diffusion of oxygen atoms and the formation of oxygen molecules and ozone on the surface of an amorphous silicate film. We find that ozone is formed at low temperature (<30 K), and molecular oxygen forms when the diffusion of oxygen atoms becomes significant, at around 60 K. This experiment, besides being the first determination of the diffusion energy barrier (1785 {+-} 35 K) for oxygen atoms on a silicate surface, suggests bare silicates as a possible storage place for oxygen atoms in low-A{sub v} environments.

  13. Molecular dynamics modeling of microstructure evolution during growth of amorphous carbon films

    SciTech Connect

    Glosli, J.N.; Belak, J.; Philpott, M.R.

    1996-01-08

    Amorphous carbon films approximately 20 nm thick are used throughout the computer industry as protective coatings on magnetic storage disks. As storage densities increase, the role of the overcoat becomes increasingly important because of smaller spacings between the recording head and the spinning disk. Furthermore, future-generation disks call for an overcoat thickness of 5 nm or less. These small length scales and the high speed of the spinning disk (10-30 m/s) suggest that a molecular dynamics (MD) model might provide useful insight into friction and wear mechanisms when the head and disk make contact. One of the necessary inputs required to carry out such an MD model is a specification of the position of all the atoms in the simulation, i.e. a detailed model of the material microstructure. Such a detailed understanding of the microstructure of amorphous carbon overcoats does not presently exist. Neutron and electron diffraction studies demonstrate that the material is amorphous. Previous classical MD simulations yield pair distribution functions in qualitative agreement with the diffraction studies, but they all differ in detail. More recent, quantum-mechanical tight-binding MD (TBMD) studies give a better description of the interatomic interactions and the chemical hybridization (sp{sup 2}-graphite-like versus sp{sup 3}-diamond-like). However, these studies are presently limited to rather small system sizes and rapid quench rates. In this paper we present molecular dynamics simulations of the growth of amorphous carbon films deposited onto a diamond substrate using a bond-order potential model. This classical potential mimics the quantum mechanics allowing carbon to form strong chemical bonds with a variety of hybridizations. It was found that the system formed unphysical bonding configurations without an added torsional energy between sp{sup 2} hybridized carbon atoms. This torsional energy was included for all results presented here. 18 refs., 3 figs.

  14. Bio-Based Bisfuran: Synthesis, Crystal Structure and Low Molecular Weight Amorphous Polyester.

    PubMed

    Gaitonde, Vishwanath; Lee, Kyunghee; Kirschbaum, Kristin; Sucheck, Steven J

    2014-07-23

    Discovery of renewable monomer feedstocks for fabrication of polymeric demand is critical in achieving sustainable materials. In the present work we have synthesized bisfuran diol (BFD) monomer from furfural, over four steps. BFD was examined via X-ray crystallography to understand the molecular arrangement in space, hydrogen bonding and packing of the molecules. This data was further used to compare BFD with structurally related Bisphenol A (BPA), and its known derivatives to predict the potential estrogenic or anti-estrogenic activities in BFD. Further, BFD was reacted with succinic acid to generate polyester material, bisfuran polyester (BFPE-1). MALDI characterization of BFPE-1 indicates low molecular weight polyester and thermal analysis reveals amorphous nature of the material.

  15. Molecular Dynamics, Recrystallization Behavior, and Water Solubility of the Amorphous Anticancer Agent Bicalutamide and Its Polyvinylpyrrolidone Mixtures.

    PubMed

    Szczurek, Justyna; Rams-Baron, Marzena; Knapik-Kowalczuk, Justyna; Antosik, Agata; Szafraniec, Joanna; Jamróz, Witold; Dulski, Mateusz; Jachowicz, Renata; Paluch, Marian

    2017-03-07

    In this paper, we investigated the molecular mobility and physical stability of amorphous bicalutamide, a poorly water-soluble drug widely used in prostate cancer treatment. Our broadband dielectric spectroscopy measurements and differential scanning calorimetry studies revealed that amorphous BIC is a moderately fragile material with a strong tendency to recrystallize from the amorphous state. However, mixing the drug with polymer polyvinylpyrrolidone results in a substantial improvement of physical stability attributed to the antiplasticizing effect governed by the polymer additive. Furthermore, IR study demonstrated the existence of specific interactions between the drug and excipient. We found out that preparation of bicalutamide-polyvinylpyrrolidone mixture in a 2-1 weight ratio completely hinder material recrystallization. Moreover, we determined the time-scale of structural relaxation in the glassy state for investigated materials. Because molecular mobility is considered an important factor governing crystallization behavior, such information was used to approximate the long-term physical stability of an amorphous drug and drug-polymer systems upon their storage at room temperature. Moreover, we found that such systems have distinctly higher water solubility and dissolution rate in comparison to the pure amorphous form, indicating the genuine formulation potential of the proposed approach.

  16. Theoretical Models for Vibrational Lifetimes in Amorphous Materials.

    NASA Astrophysics Data System (ADS)

    Orbach, R.

    1996-03-01

    The lifetimes of high energy lattice vibrational states in amorphous or glassy materials are calculated on the basis of a model in which vibrational states are extended for energies ω < ω_c, and ``super-localized'' for ω > ω_c. This model can account for the plateau in the thermal conductivity κ(T), a feature which is nearly universal for amorphous and glassy materials. The increase of κ(T) for temperatures greater than the plateau temperature arises from anharmonicity-induced localized vibrational state hopping, the major contribution arising from states with energies in the vicinity of ω_c. The same anharmonicity vertex allows one to calculate the anharmonicity-induced vibrational lifetime τ(ω) which can be expressed in terms of the hopping contribution to the thermal conductivity. Though amorphous and glassy materials are certainly not in general mass fractals, the fracton model is a convenient approach to obtain quantitative results. At low temperatures, the high energy (ω>>ω_c) vibrational lifetime is found to be proportional to exp Bigl[Bigl(ω\\over ω_cBigr) ^d_φ/DBigr] where d_φ is the superlocalization exponent of the localized vibrational state, and D is the mass density scaling exponent (equal to the Euclidean dimension d for dense systems, and the fractal dimension for fractal systems). This behavior arises from the combined action of a decrease in localization length, and an increase in the most probable hop distance, with increasing ω. This dependence is quite opposite to that found for crystalline materials where τ(ω) ∝ ω-5. Experiments of Scholten et al.^1 on a-Si:H exhibit the predicted exponential increase of τ(ω) with increasing ω. Using measured values for the third order elastic constant C_111, quantitative agreement is obtained for the 480 cm-1 TO vibration, with τ(ω) = 70 ns. l *Supported by the National Science Foundation.l **In conjunction with Dr. A. Jagannathan, and dedicated to the memory of H. M. Rosenberg

  17. Semiconductor device PN junction fabrication using optical processing of amorphous semiconductor material

    SciTech Connect

    Sopori, Bhushan; Rangappan, Anikara

    2014-11-25

    Systems and methods for semiconductor device PN junction fabrication are provided. In one embodiment, a method for fabricating an electrical device having a P-N junction comprises: depositing a layer of amorphous semiconductor material onto a crystalline semiconductor base, wherein the crystalline semiconductor base comprises a crystalline phase of a same semiconductor as the amorphous layer; and growing the layer of amorphous semiconductor material into a layer of crystalline semiconductor material that is epitaxially matched to the lattice structure of the crystalline semiconductor base by applying an optical energy that penetrates at least the amorphous semiconductor material.

  18. Applications of Non-Crystalline Materials — A. APPLICATIONS OF GLASSES, AMORPHOUS AND DISORDERED MATERIALS

    NASA Astrophysics Data System (ADS)

    Ovshinsky, Stanford R.

    The following sections are included: * Introduction * Information Technology * History * Phase change erasable optical memory * Basic physical process * Materials * Direct-overwrite recording * Device configurations * Structural analysis * Thermal stability * Phase transformation kinetics induced by a laser diode * Media performance * Manufacturing * Commercial applications * The Ovonic threshold switch * The Ovonic electronic phase change memory * Data storage mechanism * Basic device operation * Commercial applications of Ovonic unified semiconductor memories * Amorphous silicon alloy diode and TFT AMLCD display addressing * Long-life amorphous silicon alloy copier drums * Energy Generation and Storage * Amorphous silicon alloy thin-film photovoltaics * Introduction * Using science and technology to break the cost barrier * Multi-phase disordered hydrogen storage materials * Ovonic nickel metal-hydride batteries * NiMH cell chemistry * Metal hydride alloy development * Positive electrode development * Hydrogen storage for fuel cell applications * Fuel cells * The fuel * Conclusion * Acknowledgments * References

  19. Time-dependent failure of amorphous poly-D,L-lactide: influence of molecular weight.

    PubMed

    Söntjens, Serge H M; Engels, Tom A P; Smit, Theo H; Govaert, Leon E

    2012-09-01

    The specific time-dependent deformation response of amorphous poly(lactic acid) (PLA) is known to lead to rapid failure of these materials in load-bearing situations. We have investigated this phenomenon in uniaxial compression on P(L)DLLA samples with various molecular weights. The experiments revealed a strong dependence of the yield stress on the applied strain rate. Lower molecular weights showed identical deformation kinetics as higher molecular weights, albeit at lower stress values. This dependence on molecular weight was incorporated into an Eyring-equation by introducing mobility through a virtual temperature that is shifted by the deviation of the T(g) from T(g,∞). Stress-dependent lifetime of polymer constructs was described by the use of this modified Eyring-equation, combined with a critical plastic strain. This model proves useful in predicting the molecular weight dependence of the time to failure, although it slightly overestimates life time at low stress levels for a material with very low molecular weight. The versatility of the model is demonstrated on e-beam sterilized PLDLLA, where the resulting reduction in molecular weight induces a substantial decrease in lifetime. A single T(g) measurement provides sufficient information to predict the decrease in lifetime.

  20. Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations.

    PubMed

    Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

    2017-02-14

    Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young's modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young's modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.

  1. Nanometric Cutting of Silicon with an Amorphous-Crystalline Layered Structure: A Molecular Dynamics Study.

    PubMed

    Wang, Jinshi; Fang, Fengzhou; Zhang, Xiaodong

    2017-12-01

    Materials with specific nanometric layers are of great value in both theoretical and applied research. The nanometric layer could have a significant influence on the response to the mechanical loading. In this paper, the nanometric cutting on the layered systems of silicon has been studied by molecular dynamics. This kind of composite structure with amorphous layer and crystalline substrate is important for nanomachining. Material deformation, stress status, and chip formation, which are the key issues in nano-cutting, are analyzed. A new chip formation mechanism, i.e., the mixture of extrusion and shear, has been observed. In addition, from the perspective of engineering, some specific composite models show the desired properties due to the low subsurface damage or large material removal rate. The results enrich the cutting theory and provide guidance on nanometric machining.

  2. Nanometric Cutting of Silicon with an Amorphous-Crystalline Layered Structure: A Molecular Dynamics Study

    NASA Astrophysics Data System (ADS)

    Wang, Jinshi; Fang, Fengzhou; Zhang, Xiaodong

    2017-01-01

    Materials with specific nanometric layers are of great value in both theoretical and applied research. The nanometric layer could have a significant influence on the response to the mechanical loading. In this paper, the nanometric cutting on the layered systems of silicon has been studied by molecular dynamics. This kind of composite structure with amorphous layer and crystalline substrate is important for nanomachining. Material deformation, stress status, and chip formation, which are the key issues in nano-cutting, are analyzed. A new chip formation mechanism, i.e., the mixture of extrusion and shear, has been observed. In addition, from the perspective of engineering, some specific composite models show the desired properties due to the low subsurface damage or large material removal rate. The results enrich the cutting theory and provide guidance on nanometric machining.

  3. Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

    PubMed Central

    Xiao, H. Y.; Weber, W. J.; Zhang, Y.; Zu, X. T.; Li, S.

    2015-01-01

    The response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations. PMID:25660219

  4. Modeling the amorphous-to-crystalline phase transformation in network materials

    NASA Astrophysics Data System (ADS)

    Kohary, K.; Burlakov, V. M.; Pettifor, D. G.

    2005-06-01

    We have developed a computationally efficient rate equation model to study transformations between amorphous and crystalline phases of network forming materials. Amorphous and crystalline phases are treated in terms of their atomic ring distributions. The transformation between the two phases is considered to be driven by the conversion of one set of rings into another, following the Wooten-Winer-Weaire bond-switching algorithm. Our rate equation model describes both the generation and collapse of amorphous regions in thin crystalline films, the processes crucial for phase-change data storage materials. It is found that the amorphous spot collapse is assisted by the motion of certain crystal facets.

  5. A Molecular-Level View of the Physical Stability of Amorphous Solid Dispersions

    NASA Astrophysics Data System (ADS)

    Yuan, Xiaoda

    Many pharmaceutical compounds being developed in recent years are poorly soluble in water. This has led to insufficient oral bioavailability of many compounds in vitro. The amorphous formulation is one of the promising techniques to increase the oral bioavailability of these poorly water-soluble compounds. However, an amorphous drug substance is inherently unstable because it is a high energy form. In order to increase the physical stability, the amorphous drug is often formulated with a suitable polymer to form an amorphous solid dispersion. Previous research has suggested that the formation of an intimately mixed drug-polymer mixture contributes to the stabilization of the amorphous drug compound. The goal of this research is to better understand the role of miscibility, molecular interactions and mobility on the physical stability of amorphous solid dispersions. Methods were developed to detect different degrees of miscibility on nanometer scale and to quantify the extent of hydrogen-bonding interactions between the drug and the polymer. Miscibility, hydrogen-bonding interactions and molecular mobility were correlated with physical stability during a six-month period using three model systems. Overall, this research provides molecular-level insights into many factors that govern the physical stability of amorphous solid dispersions which can lead to a more effective design of stable amorphous formulations.

  6. Amorphous silicene—a view from molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Van Hoang, Vo; Long, N. T.

    2016-05-01

    Models of amorphous silicene (a-silicene) containing 104 atoms are obtained by cooling from the melt via molecular dynamics (MD) simulation. The evolution of various kinds of structural and thermodynamic behavior in models upon cooling from the melt is found, including total energy, radial distribution function (RDF), interatomic distance, coordination number, and ring and bond-angle distributions. We also show the buckling distribution and a 2D visualization of the atomic configurations. The diffraction pattern shows that a glass state is indeed formed in the system. The glass transition temperature of 2D silicon ({{T}\\text{g}}=1350 K) has a reasonable value compared to that of its 3D counterpart. Calculations show that although most atoms in a-silicene obtained at 300 K have a three-fold coordination and mainly evolve into six-fold rings, a-silicene also contains various structural defects including those not found in crystalline silicene (c-silicene) such as adatoms, clusters of small-membered rings, large-membered rings and local linear defects. The concentration of defects in a-silicene is much higher than that of the crystalline version. We find that buckling is not unique for all the atoms in the model. The strong distorted structure of a-silicene compared to that of the crystalline version may lead to physico-chemical properties, including the possibility of opening the band gap in the former compared to the zero band gap of the latter. Note that due to the fixed length being equal to buckling of 0.44 Å in the z direction with the elastic reflection behavior boundary, our models are relevant for a-silicene formed in confinement between two planar simple hard walls.

  7. Ab initio charge-carrier mobility model for amorphous molecular semiconductors

    NASA Astrophysics Data System (ADS)

    Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Nitsche, Robert; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.

    2016-05-01

    Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α -NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α -NPD. We apply our mobility model to two types of hole-only α -NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.

  8. Polymorphic form of piroxicam influences the performance of amorphous material prepared by ball-milling.

    PubMed

    Naelapää, Kaisa; Boetker, Johan Peter; Veski, Peep; Rantanen, Jukka; Rades, Thomas; Kogermann, Karin

    2012-06-15

    The objective of this study was to investigate the influence of the starting solid state form of piroxicam (anhydrate form I: PRXAH I vs form II: PRXAH II) on the properties of the resulting amorphous material. The second objective was to obtain further insight into the impact of critical factors like thermal stress, dissolution medium and storage conditions on the thermal behavior, solid state transformations and physical stability of amorphous materials. For analysis differential scanning calorimetry (DSC), Raman spectroscopy and X-ray powder diffractometry (XRPD) were used. Pair-wise distribution function (PDF) analysis of the XRPD data was performed. PDF analysis indicated that the recrystallization behavior of amorphous samples was influenced by the amount of residual order in the samples. The recrystallization behavior of amorphous samples prepared from PRXAH I showed similarity to the starting material, whereas the recrystallization behavior of amorphous samples prepared from PRXAH II resembled to that of the PRX form III (PRXAH III). Multivariate data analysis (MVDA) helped to identify that the influence of storage time and temperature was more pronounced in the case of amorphous PRX prepared from PRXAH I. Furthermore, the wet slurry experiments with amorphous materials revealed the recrystallization of amorphous material as PRXMH in the biorelevant medium.

  9. Atomic scale insight into the amorphous structure of Cu doped GeTe phase-change material

    SciTech Connect

    Zhang, Linchuan; Sa, Baisheng; Zhou, Jian; Sun, Zhimei; Song, Zhitang

    2014-10-21

    GeTe shows promising application as a recording material for phase-change nonvolatile memory due to its fast crystallization speed and extraordinary amorphous stability. To further improve the performance of GeTe, various transition metals, such as copper, have been doped in GeTe in recent works. However, the effect of the doped transition metals on the stability of amorphous GeTe is not known. Here, we shed light on this problem for the system of Cu doped GeTe by means of ab initio molecular dynamics calculations. Our results show that the doped Cu atoms tend to agglomerate in amorphous GeTe. Further, base on analyzing the pair correlation functions, coordination numbers and bond angle distributions, remarkable changes in the local structure of amorphous GeTe induced by Cu are obviously seen. The present work may provide some clues for understanding the effect of early transition metals on the local structure of amorphous phase-change compounds, and hence should be helpful for optimizing the structure and performance of phase-change materials by doping transition metals.

  10. Imaging of Crystalline and Amorphous Surface Regions Using Time-of-Flight Secondary-Ion Mass Spectrometry (ToF-SIMS): Application to Pharmaceutical Materials.

    PubMed

    Iuraş, Andreea; Scurr, David J; Boissier, Catherine; Nicholas, Mark L; Roberts, Clive J; Alexander, Morgan R

    2016-04-05

    The structure of a material, in particular the extremes of crystalline and amorphous forms, significantly impacts material performance in numerous sectors such as semiconductors, energy storage, and pharmaceutical products, which are investigated in this paper. To characterize the spatial distribution for crystalline-amorphous forms at the uppermost molecular surface layer, we performed time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) measurements for quench-cooled amorphous and recrystallized samples of the drugs indomethacin, felodipine, and acetaminophen. Polarized light microscopy was used to localize crystallinity induced in the samples under controlled conditions. Principal component analysis was used to identify the subtle changes in the ToF-SIMS spectra indicative of the amorphous and crystalline forms for each drug. The indicators of amorphous and crystalline surfaces were common in type across the three drugs, and could be explained in general terms of crystal packing and intermolecular bonding, leading to intramolecular bond scission in the formation of secondary ions. Less intramolecular scission occurred in the amorphous form, resulting in a greater intensity of molecular and dimer secondary ions. To test the generality of amorphous-crystalline differentiation using ToF-SIMS, a different recrystallization method was investigated where acetaminophen single crystals were recrystallized from supersaturated solutions. The findings indicated that the ability to assign the crystalline/amorphous state of the sample using ToF-SIMS was insensitive to the recrystallization method. This demonstrates that ToF-SIMS is capable of detecting and mapping ordered crystalline and disordered amorphous molecular materials forms at micron spatial resolution in the uppermost surface of a material.

  11. Molecular dynamics simulation of amorphization in forsterite by cosmic rays

    SciTech Connect

    Devanathan, Ram; Durham, Philip; Du, Jincheng; Corrales, Louis R.; Bringa, Eduardo M.

    2007-02-16

    We have examined cosmic ray interactions with silicate dust grains by simulating a thermal spike in a 1.25 million atom forsterite (Mg2SiO4) crystal with periodic boundaries. Spikes were generated by giving a kinetic energy of 1 or 2 eV to every atom within a cylinder of radius 1.73 nm along the [001] direction. An amorphous track of radius ~3 nm was produced for the 2 eV/atom case, but practically no amorphization was produced for 1 eV/atom because of effective dynamic annealing. Chemical segregation was not observed in the track. These results agree with recent experimental studies of ion irradiation effects in silicates, and indicate that cosmic rays can cause the amorphization of interstellar dust.

  12. Molecular dynamics simulation of the recrystallization of amorphous Si layers: Comprehensive study of the dependence of the recrystallization velocity on the interatomic potential

    NASA Astrophysics Data System (ADS)

    Krzeminski, C.; Brulin, Q.; Cuny, V.; Lecat, E.; Lampin, E.; Cleri, F.

    2007-06-01

    The molecular dynamics method is applied to simulate the recrystallization of an amorphous/crystalline silicon interface. The atomic structure of the amorphous material is constructed with the method of Wooten, Winer, and Weaire. The amorphous on crystalline stack is annealed afterward on a wide range of temperature and time using five different interatomic potentials: Stillinger-Weber, Tersoff, EDIP, SW115, and Lenosky. The simulations are exploited to systematically extract the recrystallization velocity. A strong dependency of the results on the interatomic potential is evidenced and explained by the capability of some potentials (Tersoff and SW115) to correctly handle the amorphous structure, while other potentials (Stillinger-Weber, EDIP, and Lenosky) lead to the melting of the amorphous. Consequently, the interatomic potentials are classified according to their ability to simulate the solid or the liquid phase epitaxy.

  13. Amorphous Silk Nanofiber Solutions for Fabricating Silk-Based Functional Materials.

    PubMed

    Dong, Xiaodan; Zhao, Qun; Xiao, Liying; Lu, Qiang; Kaplan, David L

    2016-09-12

    As a functional material, silk has been widely used in tissue engineering, drug release, and tissue regeneration. Increasing subtle control of silk hierarchical structures and thus specific functional performance is required for these applications but remains a challenge. Here, we report a novel silk nanofiber solution achieved through tuning solvent systems used to generate the material. Unlike the β-sheet rich silk nanofibers reported previously, these new silk nanofibers are mainly composed of amorphous structures and maintain a solution state in aqueous environments. The amorphous silk nanofibers are stable enough for storage and also metastable, making them easy to use in the further fabrication of materials through various processes. Silk scaffolds, hydrogels, and films were prepared from these silk nanofiber solutions. These silk materials from amorphous nanofiber solutions show different properties and tunable performance features. Therefore, these amorphous silk nanofibers are suitable units or building blocks for designing silk-based materials.

  14. In situ real-time spectroscopic ellipsometry measurement for the investigation of molecular orientation in organic amorphous multilayer structures

    NASA Astrophysics Data System (ADS)

    Yokoyama, Daisuke; Adachi, Chihaya

    2010-06-01

    To investigate molecular orientation in organic amorphous films, in situ real-time spectroscopic ellipsometry measurements were performed during vacuum deposition. Three materials with different molecular shapes were adopted to confirm the generality of the molecular orientation. In all three cases, more than 200 000 values for the ellipsometric parameters measured during deposition were well simulated simultaneously over the entire spectral range and measurement period using a simple model where the films possessed homogeneous optical anisotropy. This demonstrated the homogeneity of the molecular orientation in the direction of film thickness. The molecular orientation can be controlled by the substrate temperature even in multilayer structures. It is also demonstrated that a "multilayer structure" can be fabricated using only one material, where each layer has different optical and electrical properties.

  15. Optimization of large amorphous silicon and silica structures for molecular dynamics simulations of energetic impacts

    NASA Astrophysics Data System (ADS)

    Samela, Juha; Norris, Scott A.; Nordlund, Kai; Aziz, Michael J.

    2011-07-01

    A practical method to create optimized amorphous silicon and silica structures for molecular dynamics simulations is developed and tested. The method is based on the Wooten, Winer, and Weaire algorithm and combination of small optimized blocks to larger structures. The method makes possible to perform simulations of either very large cluster hypervelocity impacts on amorphous targets or small displacements induced by low energy ion impacts in silicon.

  16. First-principles study of crystalline and amorphous AlMgB{sub 14}-based materials

    SciTech Connect

    Ivashchenko, V. I.; Shevchenko, V. I.; Turchi, P. E. A.; Veprek, S.; Leszczynski, Jerzy; Gorb, Leonid; Hill, Frances

    2016-05-28

    We report first-principles investigations of crystalline and amorphous boron and M1{sub x}M2{sub y}X{sub z}B{sub 14−z} (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm{sup −1}, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm{sup −1}. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B{sub 12} units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

  17. First-principles study of crystalline and amorphous AlMgB14-based materials

    NASA Astrophysics Data System (ADS)

    Ivashchenko, V. I.; Turchi, P. E. A.; Veprek, S.; Shevchenko, V. I.; Leszczynski, Jerzy; Gorb, Leonid; Hill, Frances

    2016-05-01

    We report first-principles investigations of crystalline and amorphous boron and M1xM2yXzB14-z (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called "BAM" materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm-1, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100-1250 cm-1. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B12 units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

  18. Differences between vacuum-deposited and spin-coated amorphous films of OLED materials (presentation video)

    NASA Astrophysics Data System (ADS)

    Yokoyama, Daisuke; Shibata, Maki

    2014-10-01

    To realize low-cost fabrication processes for high-performance OLED displays and lighting panels, the understanding of solution-processed films and devices is becoming more important nowadays. However, differences between vacuum- and solution-processed films have not been sufficiently discussed, and they are sometimes regarded as identical. In this presentation, we show and discuss the important differences between physical properties of vacuum-deposited and spin-coated films of small-molecule OLED materials, especially focusing on the differences in film densities and molecular orientation. Since they are fundamental factors affecting both electrical and optical properties of amorphous films used in OLEDs, we should consider their differences carefully when discussing device performances in detail.

  19. Sodium diffusion through amorphous silica surfaces: a molecular dynamics study.

    PubMed

    Rarivomanantsoa, Michaël; Jund, Philippe; Jullien, Rémi

    2004-03-08

    We have studied the diffusion inside the silica network of sodium atoms initially located outside the surfaces of an amorphous silica film. We have focused our attention on structural and dynamical quantities, and we have found that the local environment of the sodium atoms is close to the local environment of the sodium atoms inside bulk sodo-silicate glasses obtained by quench. This is in agreement with recent experimental results.

  20. Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System

    NASA Technical Reports Server (NTRS)

    Nuth, J. A.; Brearley, A. J.; Scott, E. R. D.

    2004-01-01

    Comets, fine-grained matrices of chondrites, and chondritic interplanetary dust particles (IDPs) are each composed of both crystalline and amorphous silicates. The primitive solar nebula, in which comets and asteroids accreted, was formed from the collapsed core of a Giant Molecular Cloud, that, in turn, condensed from materials present in the interstellar medium (ISM). Despite observations that reveal the presence of crystalline magnesium silicate minerals in the shells of very high mass-loss-rate stars [1,2], typical silicate grains in the ISM are most likely to be amorphous, given their relatively long residence time in such a high radiation environment. An upper limit of 3% crystalline grains can be derived from their non-detection in spectra of ISM solids [3]. If the vast majority of grains that enter the primitive solar nebula are amorphous, then the observation of crystalline dust in comets and primitive chondrite matrices indicates the action of specific processes required to transform the amorphous starting materials into the crystals that are observed.

  1. XRD Technique: A way to disseminate structural changes in iron-based amorphous materials

    SciTech Connect

    Saw, C K; Lian, T; Day, D; Farmer, J

    2007-05-24

    Prevention of corrosion is a vital goal for the Department of Defense when billions of dollars are spent every year. Corrosion resistant materials have applications in all sort of military vehicles, and more importantly in naval vessels and submarines which come in contact with the seawater. It is known that corrosion resistance property can be improved by the used of structurally designed materials in the amorphous state where the atoms are arranged in a non-periodic fashion and specific atoms, tailored to the required properties can be interjected into the matrix for specific application. The XRD techniques reported here is to demonstrate the optimal conditions for characterization of these materials. The samples, which normally contain different compositions of Fe, Cr, B, Mo, Y, Mn, Si and W, are in the form of powders, ribbons and coatings. These results will be compared for the different forms of the sample which appears to correlate to the cooling rate during sample processing. In most cases, the materials are amorphous or amorphous with very small amount of crystallinity. In the ribbon samples for different compositions we observed that the materials are essentially amorphous. In most cases, starting from an amorphous powder sample, the coatings are also observed to be amorphous with a small amount of iron oxide on the surface, probably due to exposure to air.

  2. Stability and solubility of celecoxib-PVP amorphous dispersions: a molecular perspective.

    PubMed

    Gupta, Piyush; Kakumanu, Vasu Kumar; Bansal, Arvind K

    2004-10-01

    The purpose of the current study is to evaluate the solubility advantage offered by celecoxib (CEL) amorphous systems and to characterize and correlate the physical and thermodynamic properties of CEL and its amorphous molecular dispersions containing poly(vinylpyrrolidone) (PVP). The measurement of crystalline content, glass transition temperatures, and enthalpy relaxation was performed using differential scanning calorimetry. Solubility and dissolutions studies were conducted at 37 degrees C to elucidate release mechanisms. Further, the amorphous systems were characterized by polarized light microscopy and X-ray powder diffraction studies. The PVP content has a prominent effect on the stability and solubility profiles of amorphous systems. A dispersion of 20% w/w PVP with CEL resulted in a maxima in terms of solubility enhancement and lowering of relaxation enthalpy. The release of drug from amorphous molecular dispersions was found to be drug-dependent and independent of the carrier. The solubility enhancement and enthalpy relaxation studies with respect to PVP concentration helped in a better prediction of role of carrier and optimization of concentration in the use of solid dispersions or amorphous systems. The drug release mechanism is drug-controlled rather than carrier-controlled.

  3. Molecular dynamics simulation of yttria-stabilized zirconia (YSZ) crystalline and amorphous solids.

    PubMed

    Lau, Kah Chun; Dunlap, Brett I

    2011-01-26

    An empirically fitted atomic potential allows a classical molecular dynamics study of the static and dynamic properties of both crystalline and amorphous yttria-stabilized zirconia (YSZ) with typical dilute Y(2)O(3) concentrations (i.e. 3.0-12.0 mol% Y(2)O(3)) in the temperature range 300-1400 K. Based on the rigid ion model approximation, we find, regardless of the distinctly different geometries, that the oxygen ionic conductivity shows a maximum at ∼ 8.0 mol% Y(2)O(3), close to the experimental maximum. A lower absolute ionic conductivity is found for the high density YSZ amorphous solid, relative to crystalline YSZ, consistent with the trends observed in crystalline and stabilized amorphous thin films of YSZ reported in experiments. Different from YSZ crystals, intriguing features of mutual diffusion among the heavy cations and mobile anions are found in the amorphous phase.

  4. Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

    DOE PAGES

    Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen; ...

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser,more » electron and ion irradiations.« less

  5. Crystallized and amorphous vortices in rotating atomic-molecular Bose-Einstein condensates

    PubMed Central

    Liu, Chao-Fei; Fan, Heng; Gou, Shih-Chuan; Liu, Wu-Ming

    2014-01-01

    Vortex is a topological defect with a quantized winding number of the phase in superfluids and superconductors. Here, we investigate the crystallized (triangular, square, honeycomb) and amorphous vortices in rotating atomic-molecular Bose-Einstein condensates (BECs) by using the damped projected Gross-Pitaevskii equation. The amorphous vortices are the result of the considerable deviation induced by the interaction of atomic-molecular vortices. By changing the atom-molecule interaction from attractive to repulsive, the configuration of vortices can change from an overlapped atomic-molecular vortices to carbon-dioxide-type ones, then to atomic vortices with interstitial molecular vortices, and finally into independent separated ones. The Raman detuning can tune the ratio of the atomic vortex to the molecular vortex. We provide a phase diagram of vortices in rotating atomic-molecular BECs as a function of Raman detuning and the strength of atom-molecule interaction. PMID:24573303

  6. Short- and medium-range structure of amorphous zircon from molecular dynamics simulations

    SciTech Connect

    Du, Jincheng; Devanathan, Ram; Corrales, Louis R.; Weber, William J.; Cormack, Alastair N.

    2006-12-18

    We have obtained new insights into the structure of amorphous zircon using classical molecular dynamics simulations with a partial charge model. We present detailed structural characterizations of the simulated high and low density amorphous zircon and compare our results with available neutron diffraction, EXAFS, NMR and other experimental results. The results show that amorphization leads to polymerization of the silicon-oxygen network and the formation of regions rich in zirconium. The average n value of Qn species is 1.6-1.8. A considerable percentage of the oxygen ions (around 20%) have only zirconium in the first coordination shell (free oxygen) in amorphous zircon. The Zr-O bond length (around 2.10?) is shorter and the oxygen coordination number around zirconium smaller (6-7) than those in crystalline zircon, in good agreement with the EXAFS results. The total structure factors of simulated amorphous zircon also agree well with neutron diffraction results. We have examined the effects of the simulation cell size and relative density on the amorphous structure. The general features such as polymerization of silicon-oxygen network and the formation of clustered zirconium rich regions appear to be independent of system size and volume expansion in the range of 11 to 18%. Based on the obtained amorphous zircon structure, experimentally observed lower chemical durability of amorphous zircon compared to its crystalline form can be explained by the existence of the silicon-oxygen networks and zirconium rich regions in amorphous zircon that provides diffusion channels and eases dissolution processes. Battelle operates PNNL for the USDOE

  7. Microstructural study of amorphous magnetic materials though the Barkhausen effect

    SciTech Connect

    Durin, G.; Beatrice, C.; Bertotti, G. |

    1994-03-01

    Within the frame of a Langevin description of Barkhausen effect (BE) phenomenology, a theoretical and experimental approach including the effect of longitudinal magnetic flux propagation is presented. Measurements of BE power spectra and of amplitude probability distributions of jumps are performed on amorphous ferromagnets either as-quenched or magnetic annealed. Theoretical curves are compared with experimental data and the microscopic theory parameters are discussed.

  8. Classical molecular dynamics and ab initio simulations of chemical-mechanical polishing of amorphous silica

    NASA Astrophysics Data System (ADS)

    Chagarov, Evgueni Anatolievich

    Chemical-mechanical polishing (CMP) is a widely accepted process in the semiconductor industry. Despite intense theoretical and experimental research on CMP, there is a serious lack of fundamental understanding of the physical-chemical processes of polishing. The present work is intended to investigate these fundamental processes on an atomistic level. To model CMP on the atomic scale, a model of the amorphous silica is prepared by applying Design of Experiments (DOE) techniques to systematically investigate molecular dynamics preparation. These simulations yield high-quality models of amorphous silica, which are in excellent agreement with experimental results and are defect-free. Molecular dynamics simulations are performed to investigate the mechanical deformation during CMP of silica for different geometries and relative velocities. The simulations clarify asperity shape evolution during the process of shear and reveal temperature distributions as a function of time. It is found that the ratio of radii of a particle and asperity strongly affects the amount of the material removed whereas the relative velocity has a weaker affect on it. During shear, a significant local temperature increase occurs. This temperature increase lasts for a short time (picoseconds), but it can have a major impact on the amount of material removed. It is found that there could be significant deposition of the material from the particle to the slab, which can fill surface trenches and thereby make the surface smoother. An analytic model is developed for describing the amount of material removed as a function of asperity and particle radii and relative velocity. Density-functional calculations of different surfaces of two silica polymorphs, alpha-quartz and beta-cristobalite, are performed. The surface energies are calculated as a function of oxygen partial pressure for several different surface reconstructions and terminations. The case of hydrogen passivation is investigated to

  9. Solid state amorphization of organic molecular crystals using a vibrating mill

    NASA Astrophysics Data System (ADS)

    Tsukushi, Itaru; Yamamuro, Osamu; Matsuo, Takasuke

    1995-06-01

    The solid-state amorphization of organic molecular crystals was studied by differential scanning calorimetry (DSC) and X-ray powder diffraction. Two clathrate compounds of tri- O-methyl-β-cyclodextrin (TMCD) containing p-nitrobenzoic acid (NBA) and p-hydroxybenzoic acid (HBA), and seven other organic compounds, sucrose (SUC), salicin (SAL), phenolphthalein (PP), 1,3,5-tri-α-naphthylbenzene (TNB), p-quaterphenyl ( p-QP), p-terphenyl ( p-TP) and 1,3,5-triphenylbenzene (TPB) were ground for 2-16 h with a vibrating mill at room temperature. A halo diffraction pattern and exothermic effect due to the crystallization were observed in TMCD-NBA, TMCD-HBA, SUC, SAL, PP and TNB, indicating amorphization of these crystals. The ability of solid-state amorphization in organic molecular crystals was discussed from a thermodynamic point of view.

  10. Process induced disorder in crystalline materials: differentiating defective crystals from the amorphous form of griseofulvin.

    PubMed

    Feng, Tao; Pinal, Rodolfo; Carvajal, M Teresa

    2008-08-01

    This research investigates milling induced disorder in crystalline griseofulvin. Griseofulvin was subjected to cryogenic milling for various lengths of time. For comparison, the amorphous form of griseofulvin was also prepared by the quench melt method. Different analytical techniques were used to study the differences between the cryomilled, amorphous and crystalline forms of the drug. Cryogenic milling of griseofulvin progressively reduces the crystallinity of the drug by inducing crystal defects, rather than amorphous materials. Raman analysis provides evidence of structural differences between the two. The differences between the defective crystals produced by milling and the amorphous form are significant enough as to be measurable in their bulk thermal properties. Defective crystals show significant decrease in the heat of fusion as a function of milling time but do not exhibit a glass transition nor recrystallization from the amorphous form. Crystal defects undergo recrystallization upon heating at temperatures well below the glass transition temperature (T(g)) in a process that is separate and completely independent from the crystallization of the amorphous griseofulvin, observed above T(g). Physical mixtures of defective crystals and amorphous drug demonstrate that the thermal events associated with each form persist in the mixtures, unaffected by the presence of the other form.

  11. Freeze-dried amorphous dispersions for solubility enhancement of thermosensitive API having low molecular lipophilicity.

    PubMed

    Kulthe, V V; Chaudhari, P D; Aboul-Enein, H Y

    2014-09-01

    The present study focuses on the development of an alternative 'thermally gentle' strategy such as freeze-drying to obtain not only solubility enhanced but also physically stabilised amorphous solid dispersions of acetazolamide, which melt with decomposition (M.P.~260°C). The solid dispersions were prepared by freeze-drying an aqueous dispersion of acetazolamide containing a lyoprotectant as sugar alcohol (mannitol) in 1:0.5, 1:1 and 1:2 proportions by weight. All the proportions of solid dispersions reported a marked increase in solubility characteristics compared to those of pure drug; with outstanding performance by 1:1 ratio of about 6 folds rise in saturation solubility and 90% drug release in about initial 30 minutes. This could be attributed to the formation amorphous molecular dispersions, cosolvent effect of mannitol on dispersed acetazolamide as well as its local solubilisation effect at the diffusion layer. During stability study also, 1:1 ratio of solid dispersions reported an insignificant change in solubility characteristics subjected to an unchanged amorphous nature. Such physical stability could be attributed to decreased molecular mobility of the drug molecules in amorphous carrier because of weaker drug-carrier interactions. Thus, it was demonstrated that freeze-drying is an effective method of forming dissolution-enhanced, amorphous solid dispersions of thermally degradable APIs.

  12. Physical stability and solubility advantage from amorphous celecoxib: the role of thermodynamic quantities and molecular mobility.

    PubMed

    Gupta, Piyush; Chawla, Garima; Bansal, Arvind K

    2004-01-01

    Glassy pharmaceuticals, characterized by excess thermodynamic properties, are theoretically more soluble than their crystalline counterparts. The practical solubility advantage of the amorphous form of celecoxib (CEL) is lost due to its proclivity to lose energy and undergo solvent-mediated devitrification. Theoretical assessment of solubility advantage using differences in isobaric heat capacities (Cp) revealed a 7-21-fold enhancement in the solubility of the amorphous form over that of the crystalline state of CEL. The present study attempts to unveil these differences between experimental and theoretical solubility using thermodynamic parameters such as free energy, enthalpy, and entropy. Amorphous CEL exhibited 1.3-1.5 times enhancement in Cp over that for the crystalline form. The zero and critical molecular mobility regions, represented by Kauzmann temperature (TK) and glass transition temperature (Tg), were found to lie near 246 and 323 K, respectively, for amorphous CEL. The fictive temperature (Tf), an indicator of the configurational entropy of glass, was determined for glassy CEL, signifying the retention of considerable molecular mobility in the glassy phase that may favor nucleation even below Tg. Further, the estimation of various thermodynamic quantities and strength/fragility parameters (D = 11.5 and m = 67.0) postulated the classification of glassy CEL into moderately fragile liquid, as per Angell's classification. A comprehensive understanding of such thermodynamic facets of amorphous form would help in rationalizing the approaches toward development of stable glassy pharmaceuticals with adequate solubility advantage.

  13. Applications of amorphous magnetic materials at very-high magnetization rates (invited)

    NASA Astrophysics Data System (ADS)

    Smith, Carl H.

    1990-05-01

    Amorphous ferromagnetic alloys are finding increased application in high-energy pulse-power systems and in high-frequency switched-mode power supplies. The peak powers in these applications differ by several orders of magnitude as do the core sizes; however, these applications do share similar very-high magnetization rates often measured in teslas per microsecond. In this paper the important characteristics of amorphous magnetic materials used at high magnetization rates are reviewed. Domain models for very-high magnetization rates are discussed. The effects on magnetic losses of differing voltage waveform excitations are calculated for applications which require nonconstant rates of dB/dt. Finally, several applications utilizing magnetic amorphous alloys at high magnetization rates, in both research devices and potential commercial applications, are described. Pulse-power devices based on amorphous alloy cores have already reached multiterawatt peak output power levels with pulses shorter than 100 ns. Petawatt peak-power devices are on the drawing boards.

  14. Photochemical route for accessing amorphous metal oxide materials for water oxidation catalysis.

    PubMed

    Smith, Rodney D L; Prévot, Mathieu S; Fagan, Randal D; Zhang, Zhipan; Sedach, Pavel A; Siu, Man Kit Jack; Trudel, Simon; Berlinguette, Curtis P

    2013-04-05

    Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe(100-y-z)Co(y)Ni(z)O(x) are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.

  15. Effect of carbon and nitrogen doping on the structure of amorphous GeTe phase change material

    NASA Astrophysics Data System (ADS)

    Raty, Jean-Yves; Ghezzi, Giada; Maitrejean, Sylvain; Noé, Pierre; Roule, Anne; Bichara, Christophe; Hippert, Françoise

    2012-02-01

    Carbon and Nitrogen-doped GeTe are promising materials for use in phase change memories since the addition of C or N increases the stability of the amorphous phase. By combining ab initio molecular dynamics and X-ray scattering experiments, we show that carbon deeply modifies the structure of the amorphous phase through long carbon chains, tetrahedral and triangular units centred on carbon. A clear signature of these units is the appearance of an additional interatomic distance around 3.3 A in the pair correlation function. Besides, the first Ge-Ge and Ge-Te distances are almost not affected by doping. The implications for the vibrational and thermal properties are finally discussed.

  16. Tribological properties of amorphous alloys and the role of surfaces in abrasive wear of materials

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    The research approach undertaken by the authors relative to the subject, and examples of results from the authors are reviewed. The studies include programs in adhesion, friction, and various wear mechanisms (adhesive and abrasive wear). The materials which have been studied include such ceramic and metallic materials as silicon carbide, ferrites, diamond, and amorphous alloys.

  17. Morphology of Polymerized Membranes on an Amorphous Substrate at Molecular Resolution by AFM

    DTIC Science & Technology

    1993-09-15

    POLYMERIZED MEMBRANES ON AN AMORPHOUS SUBSTRATE AT MOLECULAR RESOLUTION BY AFM DTIC by SELECTE M. Radmacher, B. M. Goettgens, R. W. Tillmann , AUG 3 1...1991)) pp. 144-153. Department of Physics University of California, Santa Barbara Santa Barbara , CA 93106 Approved for Public Release Reproduction in...Molecular Resolution By AFM S PERFORMIN On. REPORT um---’" 7. AUTHOR(@) 8. CONTRACT OR GRANT NUMUEU(e) M. Radmacher, B.M. Goettgens, R.W. Tillmann

  18. Improved amorphous metal materials for magnetic pulse compression

    SciTech Connect

    Smith, C.H. )

    1989-08-01

    This program was undertaken by Allied-Signal Inc., under contract from Sandia National Laboratories to examine methods to improve the performance of ferromagnetic amorphous metal alloys for magnetic pulse compression applications. The alloy studied was METGLAS{reg sign} alloy 2605CO, an alloy with maximum saturation induction used in magnetic pulse compression projects. In order to reduce losses under rapid pulse magnetization, the limits of casting thinner ribbons, both in air and in vacuum, were explored as well as methods of reducing thickness after casting. The magnetic properties of these ribbons were characterized as a function of thickness. The voltage hold off and the effects of conformal insulative coatings on magnetic properties were studied in an attempt to develop an annealable insulation capable of withstanding 100 volt pulses. Finally, recommendations were made based on this work for scaling up to larger quantities of thin ribbon. 17 refs., 17 figs., 9 tabs.

  19. Radiation Resistance Studies of Amorphous Silicon Alloy Photovoltaic Materials

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.

    1994-01-01

    The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys was investigated. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below lE14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

  20. Molecular dynamics simulation of amorphous indomethacin-poly(vinylpyrrolidone) glasses: solubility and hydrogen bonding interactions.

    PubMed

    Xiang, Tian-Xiang; Anderson, Bradley D

    2013-03-01

    Amorphous drug dispersions are frequently employed to enhance solubility and dissolution of poorly water-soluble drugs and thereby increase their oral bioavailability. Because these systems are metastable, phase separation of the amorphous components and subsequent drug crystallization may occur during storage. Computational methods to determine the likelihood of these events would be very valuable, if their reliability could be validated. This study investigates amorphous systems of indomethacin (IMC) in poly(vinylpyrrolidone) (PVP) and their molecular interactions by means of molecular dynamics (MD) simulations. IMC and PVP molecules were constructed using X-ray diffraction data, and force-field parameters were assigned by analogy with similar groups in Amber-ff03. Five assemblies varying in PVP and IMC composition were equilibrated in their molten states then cooled at a rate of 0.03 K/ps to generate amorphous glasses. Prolonged aging dynamic runs (100 ns) at 298 K and 1 bar were then carried out, from which solubility parameters, the Flory-Huggins interaction parameter, and associated hydrogen bonding properties were obtained. Calculated glass transition temperature (T(g)) values were higher than experimental results because of the faster cooling rates in MD simulations. Molecular mobility as characterized by atomic fluctuations was substantially reduced below the T(g) with IMC-PVP systems exhibiting lower mobilities than that found in amorphous IMC, consistent with the antiplasticizing effect of PVP. The number of IMC-IMC hydrogen bonds (HBs) formed per IMC molecule was substantially lower in IMC-PVP mixtures, particularly the fractions of IMC molecules involved in two or three HBs with other IMC molecules that may be potential precursors for crystal growth. The loss of HBs between IMC molecules in the presence of PVP was largely compensated for by the formation of IMC-PVP HBs. The difference (6.5 MPa(1/2)) between the solubility parameters in amorphous IMC

  1. XRD technique: a way to discriminate structural changes in iron-based amorphous materials [An Alternative Method of Synthesizing Iron-based Amorphous Alloys

    SciTech Connect

    Saw, Cheng K.; Day, Dan; Farmer, Joe C.; Bauer, William

    2008-02-06

    Prevention of corrosion is a vital goal for the Department of Defense when billions of dollars are spent every year. Corrosion resistant materials have applications in all sort of military vehicles, and more importantly in naval vessels and submarines which come in contact with the seawater. It is known that corrosion resistance property can be improved by the used of structurally designed materials in the amorphous state where the atoms are arranged in a non-periodic fashion and specific atoms, tailored to the required properties can be interjected into the matrix for specific application. The XRD techniques reported here is to demonstrate the optimal conditions for characterization of these materials. The samples, which normally contain different compositions of Fe, Cr, B, Mo, Y, Mn, Si and W, are in the form of powders, ribbons and coatings. These results will be compared for the different forms of the sample which appears to correlate to the cooling rate during sample processing. In most cases, the materials are amorphous or amorphous with very small amount of crystallinity. In the ribbon samples for different compositions we observed that the materials are essentially amorphous. In most cases, starting from an amorphous powder sample, the coatings are also observed to be amorphous with a small amount of iron oxide on the surface, probably due to exposure to air.

  2. Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations

    PubMed Central

    Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

    2017-01-01

    Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions. PMID:28195190

  3. Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations

    NASA Astrophysics Data System (ADS)

    Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

    2017-02-01

    Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.

  4. Molecular-dynamics study of amorphous SiO{sub 2} relaxation

    SciTech Connect

    Fadhilah, Irfan Muhammad; Rosandi, Yudi

    2015-09-30

    Using Molecular-Dynamics simulation we observed the generation of amorphous SiO{sub 2} target from a randomly distributed Si and O atoms. We applied a sequence of annealing of the target with various temperature and quenching to room temperature. The relaxation time required by the system to form SiO{sub 4} tetrahedral mesh after a relatively long simulation time, is studied. The final amorphous target was analyzed using the radial distribution function method, which can be compared with the available theoretical and experimental data. We found that up to 70% of the target atoms form the tetrahedral SiO{sub 4} molecules. The number of formed tetrahedral increases following the growth function and the rate of SiO{sub 4} formation follows Arrhenius law, depends on the annealing temperature. The local structure of amorphous SiO{sub 2} after this treatment agrees well with those reported in some literatures.

  5. Molecular-dynamics study of the amorphization of CuTi

    SciTech Connect

    Sabochick, M.J.; Lam, N.Q. . Dept. of Engineering Physics; Argonne National Lab., IL )

    1989-11-01

    Radiation-induced amorphization of the crystalline compound CuTi was investigated by molecular-dynamics simulations using new interatomic potentials derived from the embedded-atom method. Two different approaches to amorphization were tried: one in which Cu and Ti atoms were randomly exchanged, and another in which Frenkel pairs were introduced at random. The potential energy, volume expansion and pair-correlation function were calculated as functions of chemical disorder and atomic displacements. The results indicate that, although both chemical disordering and point-defect introduction increase the system energy and volume, the presence of Frenkel pairs is essential to trigger the crystalline-to-amorphous transition. 20 refs., 3 figs.

  6. First principles-based multiparadigm, multiscale strategy for simulating complex materials processes with applications to amorphous SiC films

    SciTech Connect

    Naserifar, Saber; Goddard, William A.; Tsotsis, Theodore T.; Sahimi, Muhammad

    2015-05-07

    Progress has recently been made in developing reactive force fields to describe chemical reactions in systems too large for quantum mechanical (QM) methods. In particular, ReaxFF, a force field with parameters that are obtained solely from fitting QM reaction data, has been used to predict structures and properties of many materials. Important applications require, however, determination of the final structures produced by such complex processes as chemical vapor deposition, atomic layer deposition, and formation of ceramic films by pyrolysis of polymers. This requires the force field to properly describe the formation of other products of the process, in addition to yielding the final structure of the material. We describe a strategy for accomplishing this and present an example of its use for forming amorphous SiC films that have a wide variety of applications. Extensive reactive molecular dynamics (MD) simulations have been carried out to simulate the pyrolysis of hydridopolycarbosilane. The reaction products all agree with the experimental data. After removing the reaction products, the system is cooled down to room temperature at which it produces amorphous SiC film, for which the computed radial distribution function, x-ray diffraction pattern, and the equation of state describing the three main SiC polytypes agree with the data and with the QM calculations. Extensive MD simulations have also been carried out to compute other structural properties, as well the effective diffusivities of light gases in the amorphous SiC film.

  7. First principles-based multiparadigm, multiscale strategy for simulating complex materials processes with applications to amorphous SiC films

    NASA Astrophysics Data System (ADS)

    Naserifar, Saber; Goddard, William A.; Tsotsis, Theodore T.; Sahimi, Muhammad

    2015-05-01

    Progress has recently been made in developing reactive force fields to describe chemical reactions in systems too large for quantum mechanical (QM) methods. In particular, ReaxFF, a force field with parameters that are obtained solely from fitting QM reaction data, has been used to predict structures and properties of many materials. Important applications require, however, determination of the final structures produced by such complex processes as chemical vapor deposition, atomic layer deposition, and formation of ceramic films by pyrolysis of polymers. This requires the force field to properly describe the formation of other products of the process, in addition to yielding the final structure of the material. We describe a strategy for accomplishing this and present an example of its use for forming amorphous SiC films that have a wide variety of applications. Extensive reactive molecular dynamics (MD) simulations have been carried out to simulate the pyrolysis of hydridopolycarbosilane. The reaction products all agree with the experimental data. After removing the reaction products, the system is cooled down to room temperature at which it produces amorphous SiC film, for which the computed radial distribution function, x-ray diffraction pattern, and the equation of state describing the three main SiC polytypes agree with the data and with the QM calculations. Extensive MD simulations have also been carried out to compute other structural properties, as well the effective diffusivities of light gases in the amorphous SiC film.

  8. Molecular dynamics study of the mechanical loss in amorphous pure and doped silica.

    PubMed

    Hamdan, Rashid; Trinastic, Jonathan P; Cheng, H P

    2014-08-07

    Gravitational wave detectors and other precision measurement devices are limited by the thermal noise in the oxide coatings on the mirrors of such devices. We have investigated the mechanical loss in amorphous oxides by calculating the internal friction using classical, atomistic molecular dynamics simulations. We have implemented the trajectory bisection method and the non-local ridge method in the DL-POLY molecular dynamics simulation software to carry out those calculations. These methods have been used to locate the local potential energy minima that a system visits during a molecular dynamics trajectory and the transition state between any two consecutive minima. Using the numerically calculated barrier height distributions, barrier asymmetry distributions, relaxation times, and deformation potentials, we have calculated the internal friction of pure amorphous silica and silica mixed with other oxides. The results for silica compare well with experiment. Finally, we use the numerical calculations to comment on the validity of previously used theoretical assumptions.

  9. Molecular dynamics study of the mechanical loss in amorphous pure and doped silica

    NASA Astrophysics Data System (ADS)

    Hamdan, Rashid; Trinastic, Jonathan P.; Cheng, H. P.

    2014-08-01

    Gravitational wave detectors and other precision measurement devices are limited by the thermal noise in the oxide coatings on the mirrors of such devices. We have investigated the mechanical loss in amorphous oxides by calculating the internal friction using classical, atomistic molecular dynamics simulations. We have implemented the trajectory bisection method and the non-local ridge method in the DL-POLY molecular dynamics simulation software to carry out those calculations. These methods have been used to locate the local potential energy minima that a system visits during a molecular dynamics trajectory and the transition state between any two consecutive minima. Using the numerically calculated barrier height distributions, barrier asymmetry distributions, relaxation times, and deformation potentials, we have calculated the internal friction of pure amorphous silica and silica mixed with other oxides. The results for silica compare well with experiment. Finally, we use the numerical calculations to comment on the validity of previously used theoretical assumptions.

  10. New Class of High Temperature Pseudo-Amorphous Oxide Materials

    DTIC Science & Technology

    2003-12-01

    Non- crystalline materials can be synthesized using a variety of techniques such as thermal evaporation, sputtering, glow-discharge decomposition... crystalline materials . Principals of Applied Thin Films, Inc (ATFI) have discovered new solution derived non- crystalline oxide materials which can resist

  11. Band-gap engineering by molecular mechanical strain-induced giant tuning of the luminescence in colloidal amorphous porous silicon nanostructures.

    PubMed

    Mughal, A; El Demellawi, J K; Chaieb, Sahraoui

    2014-12-14

    Nano-silicon is a nanostructured material in which quantum or spatial confinement is the origin of the material's luminescence. When nano-silicon is broken into colloidal crystalline nanoparticles, its luminescence can be tuned across the visible spectrum only when the sizes of the nanoparticles, which are obtained via painstaking filtration methods that are difficult to scale up because of low yield, vary. Bright and tunable colloidal amorphous porous silicon nanostructures have not yet been reported. In this letter, we report on a 100 nm modulation in the emission of freestanding colloidal amorphous porous silicon nanostructures via band-gap engineering. The mechanism responsible for this tunable modulation, which is independent of the size of the individual particles and their distribution, is the distortion of the molecular orbitals by a strained silicon-silicon bond angle. This mechanism is also responsible for the amorphous-to-crystalline transformation of silicon.

  12. Performance improvement in amorphous silicon based uncooled microbolometers through pixel design and materials development

    NASA Astrophysics Data System (ADS)

    Ajmera, Sameer; Brady, John; Hanson, Charles; Schimert, Tom; Syllaios, A. J.; Taylor, Michael

    2011-06-01

    Uncooled amorphous silicon microbolometers have been established as a field-worthy technology for a broad range of applications where performance and form factor are paramount, such as soldier-borne systems. Recent developments in both bolometer materials and pixel design at L-3 in the 17μm pixel node have further advanced the state-of-the-art. Increasing the a-Si material temperature coefficient of resistance (TCR) has the impact of improving NETD sensitivity without increasing thermal time constant (TTC), leading to an improvement in the NETD×TTC product. By tuning the amorphous silicon thin-film microstructure using hydrogen dilution during deposition, films with high TCR have been developed. The electrical properties of these films have been shown to be stable even after thermal cycling to temperatures greater than 300oC enabling wafer-level vacuum packaging currently performed at L-3 to reduce the size and weight of the vacuum packaged unit. Through appropriate selection of conditions during deposition, amorphous silicon of ~3.4% TCR has been integrated into the L-3 microbolometer manufacturing flow. By combining pixel design enhancements with improvements to amorphous silicon thin-film technology, L-3's amorphous silicon microbolometer technology will continue to provide the performance required to meet the needs to tomorrow's war-fighter.

  13. Ultrastable Amorphous Sb2Se3 Film.

    PubMed

    Zhang, Kai; Li, Yang; Huang, Quan; Wang, Bihan; Zheng, Xuerong; Ren, Yang; Yang, Wenge

    2017-08-31

    Increasing the thermostability of amorphous materials has been a long journey to improve their properties. The metastable nature of chalcogenide glasses limits their practical applications as an amorphous semiconductor in photovoltaic performance. Here, we report the formation and physical properties of ultrastable amorphous Sb2Se3 with an enhanced thermal stability compared to ordinary amorphous Sb2Se3 (ΔTx= 17 K). By in situ high temperature-high energy synchrotron X-ray diffraction, the difference in structure relaxation between ordinary and ultrastable amorphous Sb2Se3 was manifested by local structure evolution. Ultrastable amorphous Sb2Se3 showed the smallest surface roughness and highest refractive index, the mechanism behind was further discussed in terms of fast molecular mobility and molecular orientation during vapor deposition. Formation of ultrastable amorphous Sb2Se3 demonstrated a promising avenue to obtain novel functional amorphous semiconductor with modulated structure and property.

  14. Molecular dynamics simulation of effect of glycerol monostearate on amorphous polyethylene in the presence of water.

    PubMed

    Iwata, Shinya

    2017-04-01

    Polyethylene (PE) is used widely as an electrical insulating material. However, the deterioration of its insulating ability is accelerated by exposure to a humid environment. To prevent the influence of water molecules, mixing 2,3-dihydroxypropyl octadecanoate-known as glycerol monostearate (GMS)-into PE has been proposed. However, the physical mechanism underlying the effect of GMS remains unclear. In the present study, the behavior of water molecules in amorphous PE with and without GMS molecule(s) was investigated in terms of diffusion and clustering using molecular dynamics (MD) simulations. Analyzing the mean square displacement (MSD), diffusion coefficient and radial distribution function (RDF) of the water molecules revealed that GMS contributed to suppressing the diffusion and dispersion of water molecules. Furthermore, it was demonstrated that, in the case of 4 wt% GMS and less than 2 wt% water, GMS contributes to reducing the diffusion coefficient of water molecules but does not change the glass transition temperature (T g) of the system drastically.

  15. Electrostatic interactions in molecular materials

    NASA Astrophysics Data System (ADS)

    Painelli, Anna; Terenziani, Francesca

    2004-03-01

    Non-additive collective behavior appears in molecular materials as a result of intermolecular interactions. We present a model for interacting polar and polarizable molecules that applies to different supramolecular architectures of donor-π-acceptor molecules. We follow a bottom-up modeling strategy: the detailed analysis of spectroscopic data of solvated molecules leads to the definition of a simple two-state model for the molecular units. Classical electrostatic interactions are then introduced to model molecular clusters. The molecular properties are strickingly affected by supramolecular interactions, as demonstrated by spectroscopic studies. Brand new phenomena, like phase transitions and multielectron transfer, with no counterpart at the molecular level are observed as direct consequences of electrostatic intermolecular interactions.

  16. Study of local atomic order in amorphous materials in a computerized transmission electron microscope.

    PubMed

    Balossier, G; Garg, R K; Bonhomme, P; Thomas, X

    1989-03-01

    Experimental results obtained by electron diffraction (ED) and extended electron energy loss fine structure (EXELFS) techniques to study the local atomic order in amorphous materials such as carbon, silicon, and its oxides are described. Potential applications of ED and EXELFS techniques and their limitations are also discussed.

  17. Use of Amorphous Oxides as High Temperature Dielectric Material in Wound Capacitors (PREPRINT)

    DTIC Science & Technology

    2008-02-01

    produce a capacitor. Capacitors fabricated using amorphous silicon dioxide as the dielectric have been shown to have stable capacitance...a higher dielectric constant in order to improve the energy density. These materials include hafnium dioxide and zirconium dioxide . Initial results...TERMS capacitor, dissipation factor, breakdown threshold, silicon dioxide , zirconium dioxide and dielectric 16. SECURITY CLASSIFICATION OF: 17

  18. Molecular orbital calculations on atomic structures of Si-based covalent amorphous ceramics

    SciTech Connect

    Matsunaga, K.; Matsubara, H.

    1999-07-01

    The authors have performed ab-initio Hartree-Fock molecular orbital calculations of local atomic structures and chemical bonding states in Si-N covalent amorphous ceramics. Solute elements such as boron, carbon and oxygen were considered in the Si-N network, and the bonding characteristics around the solute elements were analyzed. When a nitrogen atom is substituted by a carbon atom, it was found that Si-C bonds reinforce the Si-N network due to strong covalency.

  19. Dental materials. Amorphous intergranular phases control the properties of rodent tooth enamel.

    PubMed

    Gordon, Lyle M; Cohen, Michael J; MacRenaris, Keith W; Pasteris, Jill D; Seda, Takele; Joester, Derk

    2015-02-13

    Dental enamel, a hierarchical material composed primarily of hydroxylapatite nanowires, is susceptible to degradation by plaque biofilm-derived acids. The solubility of enamel strongly depends on the presence of Mg(2+), F(-), and CO3(2-). However, determining the distribution of these minor ions is challenging. We show—using atom probe tomography, x-ray absorption spectroscopy, and correlative techniques—that in unpigmented rodent enamel, Mg(2+) is predominantly present at grain boundaries as an intergranular phase of Mg-substituted amorphous calcium phosphate (Mg-ACP). In the pigmented enamel, a mixture of ferrihydrite and amorphous iron-calcium phosphate replaces the more soluble Mg-ACP, rendering it both harder and more resistant to acid attack. These results demonstrate the presence of enduring amorphous phases with a dramatic influence on the physical and chemical properties of the mature mineralized tissue.

  20. Crystallization kinetics and molecular mobility of an amorphous active pharmaceutical ingredient: A case study with Biclotymol.

    PubMed

    Schammé, Benjamin; Couvrat, Nicolas; Malpeli, Pascal; Delbreilh, Laurent; Dupray, Valérie; Dargent, Éric; Coquerel, Gérard

    2015-07-25

    The present case study focuses on the crystallization kinetics and molecular mobility of an amorphous mouth and throat drug namely Biclotymol, through differential scanning calorimetry (DSC), temperature resolved X-ray powder diffraction (TR-XRPD) and hot stage microscopy (HSM). Kinetics of crystallization above the glass transition through isothermal and non-isothermal cold crystallization were considered. Avrami model was used for isothermal crystallization process. Non-isothermal cold crystallization was investigated through Augis and Bennett model. Differences between crystallization processes have been ascribed to a site-saturated nucleation mechanism of the metastable form, confirmed by optical microscopy images. Regarding molecular mobility, a feature of molecular dynamics in glass-forming liquids as thermodynamic fragility index m was determined through calorimetric measurements. It turned out to be around m=100, describing Biclotymol as a fragile glass-former for Angell's classification. Relatively long-term stability of amorphous Biclotymol above Tg was analyzed indirectly by calorimetric monitoring to evaluate thermodynamic parameters and crystallization behavior of glassy Biclotymol. Within eight months of storage above Tg (T=Tg+2°C), amorphous Biclotymol does not show a strong inclination to crystallize and forms a relatively stable glass. This case study, involving a multidisciplinary approach, points out the importance of continuing looking for stability predictors. Copyright © 2015 Elsevier B.V. All rights reserved.

  1. Extensively Reversible Thermal Transformations of a Bistable, Fluorescence-Switchable Molecular Solid: Entry into Functional Molecular Phase-Change Materials.

    PubMed

    Srujana, P; Radhakrishnan, T P

    2015-06-15

    Functional phase-change materials (PCMs) are conspicuously absent among molecular materials in which the various attributes of inorganic solids have been realized. While organic PCMs are primarily limited to thermal storage systems, the amorphous-crystalline transformation of materials like Ge-Sb-Te find use in advanced applications such as information storage. Reversible amorphous-crystalline transformations in molecular solids require a subtle balance between robust supramolecular assembly and flexible structural elements. We report novel diaminodicyanoquinodimethanes that achieve this transformation by interlinked helical assemblies coupled with conformationally flexible alkoxyalkyl chains. They exhibit highly reversible thermal transformations between bistable (crystalline/amorphous) forms, along with a prominent switching of the fluorescence emission energy and intensity.

  2. Influence of density and environmental factors on decomposition kinetics of amorphous polylactide - Reactive molecular dynamics studies.

    PubMed

    Mlyniec, A; Ekiert, M; Morawska-Chochol, A; Uhl, T

    2016-06-01

    In this work, we investigate the influence of the surrounding environment and the initial density on the decomposition kinetics of polylactide (PLA). The decomposition of the amorphous PLA was investigated by means of reactive molecular dynamics simulations. A computational model simulates the decomposition of PLA polymer inside the bulk, due to the assumed lack of removal of reaction products from the polymer matrix. We tracked the temperature dependency of the water and carbon monoxide production to extract the activation energy of thermal decomposition of PLA. We found that an increased density results in decreased activation energy of decomposition by about 50%. Moreover, initiation of decomposition of the amorphous PLA is followed by a rapid decline in activation energy caused by reaction products which accelerates the hydrolysis of esters. The addition of water molecules decreases initial energy of activation as well as accelerates the decomposition process. Additionally, we have investigated the dependency of density on external loading. Comparison of pressures needed to obtain assumed densities shows that this relationship is bilinear and the slope changes around a density equal to 1.3g/cm(3). The conducted analyses provide an insight into the thermal decomposition process of the amorphous phase of PLA, which is particularly susceptible to decomposition in amorphous and semi-crystalline PLA polymers.

  3. Ordering the amorphous - Structures in PBD LED materials

    NASA Astrophysics Data System (ADS)

    Emmerling, Franziska; Orgzall, Ingo; Dietzel, Birgit; Schulz, Burkhard; Larrucea, Julen

    2012-12-01

    The class of 2,5 disubstituted-1,3,4-oxadiazoles containing a biphenyl unit on one side is intensively used as electron transport materials to enhance the performance of organic light emitting diodes (OLEDs). In contrast to the ongoing research on these materials insights in their structure-property relationships are still incomplete. To overcome the structural tentativeness and ambiguities the crystal structures of 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, that of the related compound 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole and of 2-(4-biphenylyl)-5-(2,6-dimethylphenyl)-1,3,4-oxadiazole are determined. A comparison with the results of GAUSSIAN03 calculations and similar compounds in the Cambridge Structural Database leads to a profound characterization.

  4. Development of improved amorphous materials for laser systems

    NASA Technical Reports Server (NTRS)

    Neilson, G. F.; Weinberg, M. C.

    1974-01-01

    Crystallization calculations were performed in order to determine the possibility of forming a particular type of laser glass with the avoidance of devitrification in an outer space laboratory. It was demonstrated that under the homogenuous nucleating conditions obtainable in a zero gravity laboratory this laser glass may be easily quenched to a virtually crystal-free product. Experimental evidence is provided that use of this material as a host in a neodymium glass laser would result in more than a 10 percent increase in efficiency when compared to laser glass rods of a similar composition currently commercially available. Differential thermal analysis, thermal gradient oven, X-ray diffraction, and liquidus determination experiments were carried out to determine the basics of the crystallization behavior of the glass, and small-angle X-ray scattering and splat-cooling experiments were performed in order to provide additional evidence for the feasibility of producing this laser glass material, crystal free, in an outer space environment.

  5. Amorphous and Nanocrystalline High Temperature Magnetic Material for PWR

    DTIC Science & Technology

    2006-03-01

    losses. Finite element software packages including FEMLAB©, FEMME © and FLEXPDE© were investigated to determine the fabrication parameters for the...analysis was based on a combination of NiZn ferrite as a core material with a spiral Cu coil. The geometry used in FEMME to simulate the effects of...various parameters and frequencies is shown in Figure III.4.5. FEMME © was chosen because it was simple to use and a planar inductor can be simulated

  6. Amino acids as co-amorphous stabilizers for poorly water-soluble drugs--Part 2: molecular interactions.

    PubMed

    Löbmann, Korbinian; Laitinen, Riikka; Strachan, Clare; Rades, Thomas; Grohganz, Holger

    2013-11-01

    The formation of co-amorphous drug-drug mixtures has proved to be a powerful approach to stabilize the amorphous form and at the same time increase the dissolution of poorly water-soluble drugs. Molecular interactions in these co-amorphous formulations can play a crucial role in stabilization and dissolution enhancement. In this regard, Fourier-transform infrared spectroscopy (FTIR) is a valuable tool to analyze the molecular near range order of the compounds in the co-amorphous mixtures. In this study, several co-amorphous drugs--low molecular weight excipient blends--have been analyzed with FTIR spectroscopy. Molecular interactions of the drugs carbamazepine and indomethacin with the amino acids arginine, phenylalanine, and tryptophan were investigated. The amino acids were chosen from the biological target site of both drugs and prepared as co-amorphous formulations together with the drugs by vibrational ball milling. A detailed analysis of the FTIR spectra of these formulations revealed specific peak shifts in the vibrational modes of functional groups of drug and amino acid, as long as one amino acid from the biological target site was present in the blends. These peak shifts indicate that the drugs formed specific molecular interactions (hydrogen bonding and π-π interactions) with the amino acids. In the drug-amino acid mixtures that contained amino acids which were not present at the biological target site, no such interactions were identified. This study shows the potential of amino acids as small molecular weight excipients in co-amorphous formulations to stabilize the amorphous form of a poorly water-soluble drug through strong and specific molecular interactions with the drug. Copyright © 2013 Elsevier B.V. All rights reserved.

  7. Crystal-amorphous transformation via defect-templating in phase-change materials

    NASA Astrophysics Data System (ADS)

    Nukala, Pavan

    Phase-change materials (PCM) such as GeTe and Ge-Sb-Te alloys are potential candidates for non-volatile memory applications, because they can reversibly and rapidly transform between a crystalline phase and an amorphous phase with medium-range order. Traditionally, crystal-amorphous transformation in these materials has been carried out via melt-quench pathway, where the crystalline phase is heated beyond its melting point by the rising edge of an electric pulse, and the melt phase is quenched by the falling edge into a glassy phase. Formation of an intermediate melt phase in this transformation pathway requires usage of large switching current densities, resulting in energy wastage, and device degradation issues. Furthermore, melt-quench pathway is a brute force strategy of amorphizing PCM, and does not utilize the peculiar structural properties in crystalline phase. It will be beneficial from a device perspective that crystal-amorphous transformation is carried out via subtler solid-state pathways. Single-crystalline nanowire phase-change memory, owing to its lateral geometry and large volumes of active material, offers a platform to construct a crystal-amorphous transformation pathway via gradually increasing disorder in the crystalline phase, and study it. Using in situ transmission electron microscopy on GeTe and Ge2Sb2Te5 systems, we showed that the application of an electric pulse (heat-shock) creates dislocations in the PCM that migrate with the hole-wind force, and interact with the already existing ferroelectric boundaries in case of GeTe, changing their nature. We adapted novel tools such as optical second harmonic generation polarimety to carefully study these defect interactions. These defects accumulate at a region of local inhomogeneity, and upon addition of defects beyond a critical limit to that region via electrical pulsing, an amorphous phase "nucleates". We also studied the effect of defect dynamics on carrier transport using temperature

  8. The Digital Material: Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Bailey, Nicholas P.; Cretegny, Thierry; Dolgert, Andrew J.; Myers, Christopher R.; Schiøtz, Jakob; Sethna, James P.

    2001-03-01

    We announce the release of the molecular dynamics component of the Digital Material. The Digital Material is our multiscale modeling software infrastructure, designed for flexibility, extensibility, and for compatibility between simulations on disparate length scales. We illustrate how we use the high-level scripting language Python to control our low-level numerical kernals, and to interface them with standard visualization and data repository tools. Our use of design-patterns methodology leads us to decompose the MD simulation into a few weakly-coupled classes, such as AtomsMover, NeighborLocator, Potential, Constraint, and BoundaryConditions.

  9. Structural Models of Amorphous Carbon and its Surfaces by Tight-Binding Molecular Dynamics

    SciTech Connect

    Haerle, R.; Baldereschi, A.; Galli, G.

    1999-10-26

    We use liner-scaling tight-binding molecular dynamics to generate three structural models of bulk amorphous carbon with different atomic density. Amorphous carbon surfaces are then obtained by imposing tensile strain on these computer generated networks until fracture occurs. Our results show that for a given density, the formation energy of surfaces obtained with different tensile strains differ by only a few 10{sup -1} eV/atom and their structural properties are qualitatively similar. The presence of sp sites at the surface is observed at all densities, but with different values of the concentration. The surface thicknesses obtained in our simulations agree with experimental data. Furthermore we find that surface roughness increases with the amount of graphitic component in the bulk sample. The same trends of the macroscopic properties are obtained when using a two-center tight-binding Hamiltonian, an environmental dependent one, and first principles calculations.

  10. Dose effects on amorphous silicon sputtering by argon ions: A molecular dynamics simulation

    SciTech Connect

    Marques, L.A.; Rubio, J.E.; Jaraiz, M.; Bailon, L.A.; Barbolla, J.J.

    1997-02-01

    We have investigated, using molecular dynamics techniques, the sputtering yield enhancement of amorphous silicon produced by argon ion accumulation within the target. Several amorphous silicon samples, with different argon contents, were bombarded with 1 keV argon ions at normal incidence. To study the influence of the target structure, we considered samples with different argon arrangements, either uniformly distributed or within solid bubbles. We have observed that silicon sputtering yield increases linearly with dose until steady state conditions are reached. This enhancement is produced by the shallow argon atoms through the weakening of Si{endash}Si bonds. We have also observed that argon release takes place even long after the end of the collisional phase, and it is produced by ion-induced desorption and bubble destabilization. This enhanced argon yield determines the dose where target saturation and steady state conditions are reached. {copyright} {ital 1997 American Institute of Physics.}

  11. Molecular Dynamics Investigation of Adhesion between TATB Surfaces and Amorphous Fluoropolymers

    SciTech Connect

    Gee, R H; Maiti, A; Bastea, S; Fried, L

    2007-01-25

    Atomistic simulations are used to study the adhesion properties of amorphous perfluoro- and fluoro-polymers onto two different crystal surfaces of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Properties of the bulk amorphous polymer melts are also investigated. The fluoropolymers studied in this article include Kel-F 800, Teflon{reg_sign} AF, Hyflon AD{reg_sign}, and Cytop{reg_sign}. Simulations of the bulk polymer melts were performed over a wide range of temperatures including the volumetric glass transition temperature, so as to validate the interaction parameters used. The computed glass transition temperatures and densities compare well with experiment. The solubility parameters for the various polymers also compare well with calculations based on group additive methods. The local molecular structure at the TATB interface, as well as the degree of adhesion varies from one polymer to another. All polymers except Hyflon show a propensity to readily wet the two TATB surfaces studied.

  12. Iron-Based Amorphous Metals: High-Performance Corrosion-Resistant Material Development

    NASA Astrophysics Data System (ADS)

    Farmer, Joseph; Choi, Jor-Shan; Saw, Cheng; Haslam, Jeffrey; Day, Dan; Hailey, Phillip; Lian, Tiangan; Rebak, Raul; Perepezko, John; Payer, Joe; Branagan, Daniel; Beardsley, Brad; D'Amato, Andy; Aprigliano, Lou

    2009-06-01

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was cosponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the U.S. Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition, materials synthesis, thermal stability, corrosion resistance, environmental cracking, mechanical properties, damage tolerance, radiation effects, and important potential applications. Amorphous alloys identified as SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) and SAM1651 (Fe48Mo14Cr15Y2C15B6) have been produced as meltspun ribbons (MSRs), dropcast ingots, and thermal-spray coatings. Chromium (Cr), molybdenum (Mo), and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of MSRs and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently, thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests; good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while the open-circuit corrosion potentials (OCPs) were simultaneously monitored; reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber and suitable for criticality-control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional stainless steel and Ni-based materials, and are proving to have excellent wear

  13. Iron-Based Amorphous Metals:The High Performance Corrosion Resistant Materials(HPCRM) Program

    SciTech Connect

    Farmer, J

    2007-07-09

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  14. Iron-Based Amorphous-Metals: High-Performance Corrosion-Resistant Material (HPCRM) Development

    SciTech Connect

    Farmer, J C; Choi, J S; Saw, C; Haslam, J; Day, D; Hailey, P; Lian, T; Rebak, R; Perepezko, J; Payer, J; Branagan, D; Beardsley, B; D'Amato, A; Aprigliano, L

    2008-01-09

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  15. Dynamic vapor sorption as a tool for characterization and quantification of amorphous content in predominantly crystalline materials.

    PubMed

    Sheokand, Sneha; Modi, Sameer R; Bansal, Arvind K

    2014-11-01

    It is well established that pharmaceutical processing can cause disruption of the crystal structure, leading to generation of amorphous content in crystalline materials. The presence of even a small amount of amorphous form, especially on the surface of crystalline material, can affect processing, performance, and stability of a drug product. This necessitates the need to quantify, monitor, and control the amorphous form. Numerous analytical techniques have been reported for the quantification of amorphous phase, but issues of sensitivity, suitability, limit of detection, and quantitation pose significant challenges. The present review focuses on use of dynamic vapor sorption (DVS) for quantification of amorphous content in predominantly crystalline materials. The article discusses (1) theoretical and experimental considerations important for developing a quantification method, (2) methods used for quantification of amorphous content, (3) basis for selecting a suitable methodology depending on the properties of a material, and (4) role of various instrument and sample-related parameters in designing a protocol for quantification of amorphous content. Finally, DVS-based hyphenated techniques have been discussed as they can offer higher sensitivity for quantification of amorphous content.

  16. Geometry and mechanics of two-dimensional defects in amorphous materials.

    PubMed

    Moshe, Michael; Levin, Ido; Aharoni, Hillel; Kupferman, Raz; Sharon, Eran

    2015-09-01

    We study the geometry of defects in amorphous materials and their elastic interactions. Defects are defined and characterized by deviations of the material's intrinsic metric from a Euclidian metric. This characterization makes possible the identification of localized defects in amorphous materials, the formulation of a corresponding elastic problem, and its solution in various cases of physical interest. We present a multipole expansion that covers a large family of localized 2D defects. The dipole term, which represents a dislocation, is studied analytically and experimentally. Quadrupoles and higher multipoles correspond to fundamental strain-carrying entities. The interactions between those entities, as well as their interaction with external stress fields, are fundamental to the inelastic behavior of solids. We develop analytical tools to study those interactions. The model, methods, and results presented in this work are all relevant to the study of systems that involve a distribution of localized sources of strain. Examples are plasticity in amorphous materials and mechanical interactions between cells on a flexible substrate.

  17. Stick-slip instabilities and shear strain localization in amorphous materials.

    PubMed

    Daub, Eric G; Carlson, Jean M

    2009-12-01

    We study the impact of strain localization on the stability of frictional slipping in dense amorphous materials. We model the material using shear transformation zone (STZ) theory, a continuum approximation for plastic deformation in amorphous solids. In the STZ model, the internal state is quantified by an effective disorder temperature, and the effective temperature dynamics capture the spontaneous localization of strain. We study the effect of strain localization on stick-slip instabilities by coupling the STZ model to a noninertial spring slider system. We perform a linear stability analysis to generate a phase diagram that connects the small scale physics of strain localization to the macroscopic stability of sliding. Our calculations determine the values of spring stiffness and driving velocity where steady sliding becomes unstable and we confirm our results through numerical integration. We investigate both homogeneous deformation, where no shear band forms, and localized deformation, where a narrow shear band spontaneously forms and accommodates all of the deformation. Our results show that at a given velocity, strain localization leads to unstable frictional sliding at a much larger spring stiffness compared to homogeneous deformation, and that localized deformation cannot be approximated by a homogeneous model with a narrower material. We also find that strain localization provides a physical mechanism for irregular stick-slip cycles in certain parameter ranges. Our results quantitatively connect the internal physics of deformation in amorphous materials to the larger scale frictional dynamics of stick-slip.

  18. Amorphous material of the skin in amyotrophic lateral sclerosis: a morphologic and biochemical study

    NASA Technical Reports Server (NTRS)

    Ono, S.; Nagao, K.; Yamauchi, M.

    1994-01-01

    We performed morphologic studies on skin from seven patients with ALS and seven control subjects. By light microscopy, the wide spaces that separated collagen bundles reacted strongly with colloidal iron and alcian blue in ALS patients. Electron microscopy revealed markedly increased amorphous material that was positive for ruthenium red in the ground substance. These findings were not present in controls. Quantitative amino acid analysis showed that the amount of total amino acids (nmoles per mg dry weight) was significantly decreased (p < 0.01) in ALS patients compared with that of controls, and there was a significant negative correlation between skin amino acid content and duration of illness in ALS patients (r = -0.83, p < 0.001). These morphologic findings and biochemical data indicate that the amorphous material, which is markedly increased in ALS skin, includes glycosaminoglycans.

  19. Amorphous material of the skin in amyotrophic lateral sclerosis: a morphologic and biochemical study

    NASA Technical Reports Server (NTRS)

    Ono, S.; Nagao, K.; Yamauchi, M.

    1994-01-01

    We performed morphologic studies on skin from seven patients with ALS and seven control subjects. By light microscopy, the wide spaces that separated collagen bundles reacted strongly with colloidal iron and alcian blue in ALS patients. Electron microscopy revealed markedly increased amorphous material that was positive for ruthenium red in the ground substance. These findings were not present in controls. Quantitative amino acid analysis showed that the amount of total amino acids (nmoles per mg dry weight) was significantly decreased (p < 0.01) in ALS patients compared with that of controls, and there was a significant negative correlation between skin amino acid content and duration of illness in ALS patients (r = -0.83, p < 0.001). These morphologic findings and biochemical data indicate that the amorphous material, which is markedly increased in ALS skin, includes glycosaminoglycans.

  20. Amorphous boron nanorod as an anode material for lithium-ion batteries at room temperature.

    PubMed

    Deng, Changjian; Lau, Miu Lun; Barkholtz, Heather M; Xu, Haiping; Parrish, Riley; Xu, Meiyue Olivia; Xu, Tao; Liu, Yuzi; Wang, Hao; Connell, Justin G; Smith, Kassiopeia A; Xiong, Hui

    2017-08-03

    We report an amorphous boron nanorod anode material for lithium-ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mA h g(-1) by alloying with Li to form B4Li5. However, experimental studies of the boron anode have been rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of the bulk crystalline boron anode material are poor at room temperature. In this work, we utilized an amorphous nanostructured one-dimensional (1D) boron material aiming at improving the electrochemical reactivity between boron and lithium ions at room temperature. The amorphous boron nanorod anode exhibited, at room temperature, a reversible capacity of 170 mA h g(-1) at a current rate of 10 mA g(-1) between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. The lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration techniques (GITTs). The sweep voltammetric analysis suggested that the contributions from lithium ion diffusion into boron and the capacitive process to the overall lithium charge storage are 57% and 43%, respectively. The results from GITT indicated that the discharge capacity at higher potentials (>∼0.2 V vs. Li/Li(+)) could be ascribed to a capacitive process and at lower potentials (<∼0.2 V vs. Li/Li(+)) to diffusion-controlled alloying reactions. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod. This work provides new insights into designing nanostructured boron materials for lithium-ion batteries.

  1. Geometry and mechanics of two-dimensional defects in amorphous materials

    PubMed Central

    Moshe, Michael; Levin, Ido; Aharoni, Hillel; Kupferman, Raz; Sharon, Eran

    2015-01-01

    We study the geometry of defects in amorphous materials and their elastic interactions. Defects are defined and characterized by deviations of the material’s intrinsic metric from a Euclidian metric. This characterization makes possible the identification of localized defects in amorphous materials, the formulation of a corresponding elastic problem, and its solution in various cases of physical interest. We present a multipole expansion that covers a large family of localized 2D defects. The dipole term, which represents a dislocation, is studied analytically and experimentally. Quadrupoles and higher multipoles correspond to fundamental strain-carrying entities. The interactions between those entities, as well as their interaction with external stress fields, are fundamental to the inelastic behavior of solids. We develop analytical tools to study those interactions. The model, methods, and results presented in this work are all relevant to the study of systems that involve a distribution of localized sources of strain. Examples are plasticity in amorphous materials and mechanical interactions between cells on a flexible substrate. PMID:26261331

  2. A novel composite material based on antimony(III) oxide and amorphous silica

    SciTech Connect

    Zemnukhova, Ludmila A.; Panasenko, Alexander E.

    2013-05-01

    The composite material nSb₂O₃·mSiO₂·xH₂O was prepared by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. It has been shown that the composition of the material is influenced by the ratio of the initial components and the acidity of the reaction medium. The morphology of the material particles and its specific surface area have been determined. The thermal and optic properties were also investigated. - Graphical abstract: Novel composite material containing amorphous silica and crystal antimony(III) oxide has been synthesized by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. Highlights: • The composite material nSb₂O₃·mSiO₂·xH₂O was prepared in an aqueous medium. • The composition of the material is controllable by a synthesis conditions. • The morphology of the material and its optic properties have been determined.

  3. Large deformation and amorphization of Ni nanowires under uniaxial strain: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Branício, Paulo S.; Rino, José-Pedro

    2000-12-01

    Molecular-dynamics simulations were employed to study deformations on nickel nanowires subjected to uniaxial strain at 300 K using a recently reported embedded-atom (many body) model potential. This embedded-atom model can reproduce exactly the experimental second-order and third-order elastic moduli as well as the phase stability, equation of state and phonon frequency spectra are also in good agreement with experiments. Strong influence was observed in the Young modulus and force constant due to surface effects when considering nanowires with different cross sections. Applying strain rates, from 0.05 to 15% ps-1, we found elastic behavior up to 11.5% strain with corresponding stress of 9.4 GPa. At low strain rates (<0.05% ps-1) the system passes through plastic deformations although keeping the crystalline structure. This ductile process is showed by several snapshots. At this low strain rate regime we observed that the nanowires shows superplasticity. For high strain rates (>=7% ps-1) the system changes continuously from crystalline to amorphous phase. Although this amorphization occurs with no use of liquid quenching or introduction of chemical or physical disorder, so being a different and interesting process, the amorphous resulted is unstable. We studied this instability monitoring the recrystallization process.

  4. Molecular dynamics study of oil detachment from an amorphous silica surface in water medium

    NASA Astrophysics Data System (ADS)

    Chen, Jiaxuan; Si, Hao; Chen, Wenyang

    2015-10-01

    In this paper, the mechanism of oil detachment from optical glass in water medium is studied by using molecular dynamics simulation. At the beginning, some undecane molecules are adsorbed on the amorphous silica surface to get contaminated glass. Upon addition of 6000 water molecules, most of the undecane molecules on the substrate surface can be detached from an amorphous silica surface through three stages. The formation of different directions of water channels is vital for oil detachment. The electrostatic interaction of water substrate contributes to disturbing the aggregates of undecane molecules and the H-bonding interaction between the water molecules is helpful for the oil puddle away from the substrate. However, there is still some oil molecules residue on the substrate surface after water cleaning. The simulation results showed that the specific ring potential well of amorphous silica surface will hinder the detachment of oil molecules. We also find that the formation of the specific ring potential well is related to the number of atoms and the average radius in silica atomic rings. Increasing the upward lift force, which acts on the hydrocarbon tail of oil molecules, will be benefit to clear the oil pollution residues from the glass surface.

  5. Amorphous boron nanorod as an anode material for lithium-ion batteries at room temperature

    DOE PAGES

    Deng, Changjian; Lau, Miu Lun; Barkholtz, Heather; ...

    2017-08-14

    We report an amorphous boron nanorod anode material for lithium ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mAh g-1 by alloying with Li to form B4Li5. However, experimental studies of boron anode were rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of bulk crystalline boron anode material are poor at room temperature. In this work, we developed amorphous nanostructured one-dimensional (1D) boron material aiming at improving lithium ion diffusion in boron at room temperature. The amorphous boronmore » nanorod anode exhibited, at room temperature, a reversible capacity of 170 mAh g-1 at a current rate of 10 mA g-1 between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. Lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration technique (GITT). The sweep voltammetric analysis suggested that the contributions from lithium ions diffusion into boron as well as the capacitive process are 42.44% and 57.56%, respectively. Results from GITT indicated that the discharge capacity at higher potentials (> ~ 0.2 V vs, Li/Li+) could be ascribed to a capacitive process and at lower potentials (< ~0.2 V vs, Li/Li+) to diffusion control. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod.« less

  6. Amorphization in the vicinity of a grain boundary: A molecular-dynamics approach

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Gonzalo; Kiwi, Miguel; Ramírez, Ricardo

    1996-10-01

    The dynamics of the melting process of a binary system (such as the one formed by Co and Zr) that contains a grain boundary is investigated by means of molecular dynamics using Lennard-Jones-type interatomic potentials. The evolution of the disordering sequence, as the temperature is increased, is quantitatively studied and graphically illustrated. It is found that the presence of the defect acts like a seed for the disordering, with the genesis of an intermediate amorphous phase. The latter is properly identified and characterized and constitutes an intermediate stage before the proper melting process sets in.

  7. Stability of Li-carbon materials: a molecular modeling study

    NASA Astrophysics Data System (ADS)

    Nicolau, Dan V.

    2004-03-01

    Materials with exceptionally high content of carbon are used in technologies with various degrees of added value, from quasi-amorphous materials for carbon electrodes used in e.g. lithium batteries to highly-organized materials comprising e.g. nanotubes and fullerenes. The present study aims to test the feasibility of predicting the properties of carbon based materials using (i) molecular modeling and simulation techniques for prediction of compositional stability; and (ii) experimental data regarding materials used for lithium batteries as validation data. It has been found that a higher H/C atomic ratio has a complex influence on lithium uptake. The decrease of the number of the aromatic rings will limit the number of lithium ions allowed in the pore and the increase in pore flexibility will induce a more energetically favorable mechanism for lithium ions uptake (folding/house-of-cards formation against pore expansion).

  8. Icosahedral short-range order in amorphous Cu80Si20 by ab initio molecular dynamics simulation study

    SciTech Connect

    Wu, S.; Kramer, Matthew J.; Fang, Xiaowei; Wang, Shy-Guey; Wang, Cai-Zhuang; Ho, Kai-Ming; Ding, Z.J.; Chen, L.Y.

    2012-04-26

    Short-range order in liquid and amorphous structures of Cu80Si20 is studied by ab initio molecular dynamics simulations. We performed the simulations at 1140 and 300 K respectively to investigate the local structure change from liquid to amorphous. The result of structure factor in comparison with experimental data indicates that our simulation of amorphous Cu80Si20 is reliable. By using the bond-angle distribution function, Honeycutt–Andersen index, Voronoi tessellation method, and the atomistic cluster alignment method, the icosahedral short-range order in the system is revealed. Strong Cu–Si interaction was also observed.

  9. Atomic structure of amorphous Mg40Cu35Ti25 alloy: An ab initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Durandurdu, Murat

    2013-01-01

    Ab initio molecular dynamics simulations are carried out to model amorphous Mg40Cu35Ti25 and its local structural packing are investigated using a variety of analyzing techniques. Cu-atoms commonly form 12 fold coordinated clusters and some of which are perfect or defective types icosahedrons, implying an icosohedral short range order around Cu atoms. Mg and Ti atoms, on the other hand, favor to structure in higher coordinated polyhedrons. The coordination number of Ti atoms is slightly less than Mg atoms. The immiscibility effect between Ti and Mg is reflected by a low fraction of Mg-Ti bonding in the model. The atomic packing of Mg40Cu35Ti25 appears to be noticeably different from that of Mg-Cu-X (X=Y and Gd) metallic glasses even though all these materials exhibit primarily the same type of bonding natures.

  10. Molecular Dynamics Study of the Disruption of H-BONDS by Water Molecules and its Diffusion Behavior in Amorphous Cellulose

    NASA Astrophysics Data System (ADS)

    Liao, Ruijin; Zhu, Mengzhao; Zhou, Xin; Zhang, Fuzhou; Yan, Jiaming; Zhu, Wenbin; Gu, Chao

    2012-06-01

    Hydrolysis is an important component of the aging of cellulose, and it severely affects the insulating performance of cellulosic materials. The diffusion behavior of water molecules in amorphous cellulose and their destructive effect on the hydrogen bonding structure of cellulose were investigated by molecular dynamics. The change in the hydrogen bonding structure indicates that water molecules have a considerable effect on the hydrogen bonding structure within cellulose: both intermolecular and intramolecular hydrogen bonds decreased with an increase in ingressive water molecules. Moreover, the stabilities of the cellulose molecules were disrupted when the number of intermolecular hydrogen bonds declined to a certain degree. Both the free volumes of amorphous cells and water molecule-cellulose interaction affect the diffusion of water molecules. The latter, especially the hydrogen bonding interaction between water molecules and cellulose, plays a predominant role in the diffusion behavior of water molecules in the models of which the free volume rarely varies. The diffusion coefficient of water molecules has an excellent correlation with water molecule-cellulose interaction and the average hydrogen bonds between each water molecule and cellulose; however, this relationship was not apparent between the diffusion coefficient and free volume.

  11. Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites.

    PubMed

    Favero-Longo, Sergio E; Turci, Francesco; Tomatis, Maura; Castelli, Daniele; Bonfante, Paola; Hochella, Michael F; Piervittori, Rosanna; Fubini, Bice

    2005-08-01

    A natural deactivation of chrysotile asbestos occurs on serpentinite rocks where lichens selectively grow on the fibres and secrete metabolites, including oxalic acid, which, in the long term, turn the fibres into a non-toxic amorphous material.

  12. Application of amorphous carbon based materials as antireflective coatings on crystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    da Silva, D. S.; Côrtes, A. D. S.; Oliveira, M. H.; Motta, E. F.; Viana, G. A.; Mei, P. R.; Marques, F. C.

    2011-08-01

    We report on the investigation of the potential application of different forms of amorphous carbon (a-C and a-C:H) as an antireflective coating for crystalline silicon solar cells. Polymeric-like carbon (PLC) and hydrogenated diamond-like carbon films were deposited by plasma enhanced chemical vapor deposition. Tetrahedral amorphous carbon (ta-C) was deposited by the filtered cathodic vacuum arc technique. Those three different amorphous carbon structures were individually applied as single antireflective coatings on conventional (polished and texturized) p-n junction crystalline silicon solar cells. Due to their optical properties, good results were also obtained for double-layer antireflective coatings based on PLC or ta-C films combined with different materials. The results are compared with a conventional tin dioxide (SnO2) single-layer antireflective coating and zinc sulfide/magnesium fluoride (ZnS/MgF2) double-layer antireflective coatings. An increase of 23.7% in the short-circuit current density, Jsc, was obtained using PLC as an antireflective coating and 31.7% was achieved using a double-layer of PLC with a layer of magnesium fluoride (MgF2). An additional increase of 10.8% was obtained in texturized silicon, representing a total increase (texturization + double-layer) of about 40% in the short-circuit current density. The potential use of these materials are critically addressed considering their refractive index, optical bandgap, absorption coefficient, hardness, chemical inertness, and mechanical stability.

  13. Low-temperature Amorphous and Nanocrystalline Silicon Materials and Thin-film Transistors

    NASA Astrophysics Data System (ADS)

    Sazonov, Andrei; Striakhilev, Denis; Nathan, Arokia

    Low-temperature processing and characterization of amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si) materials and devices are reviewed. An overview of silicon-based low-temperature thin-film dielectrics is given in the context of thin-film transistor (TFT) device operation. The low-temperature growth and synthesis of these materials are also presented and compared to conventionally fabricated high-temperature processed devices. The effect of using nc-Si contacts on a-Si:H TFTs and the stability of nc-Si TFTs is reviewed.

  14. Omni-directional selective shielding material based on amorphous glass coated microwires

    NASA Astrophysics Data System (ADS)

    Ababei, G.; Chiriac, H.; David, V.; Dafinescu, V.; Nica, I.

    2012-01-01

    The shielding effectiveness of the omni-directional selective shielding material based on CoFe-glass coated amorphous wires in 0.8 GHz-3 GHz microwave frequency range is investigated. The measurements were done in a controlled medium using a TEM cell and in the free space using horn antennas, respectively. Experimental results indicate that the composite shielding material can be developed with desired shielding effectiveness and selective absorption of the microwave frequency range by controlling the number of the layers and the length of microwires.

  15. Charge carrier mobility in organic molecular materials probed by electromagnetic waves.

    PubMed

    Seki, Shu; Saeki, Akinori; Sakurai, Tsuneaki; Sakamaki, Daisuke

    2014-06-21

    Charge carrier mobility is an essential parameter providing control over the performance of semiconductor devices fabricated using a variety of organic molecular materials. Recent design strategies toward molecular materials have been directed at the substitution of amorphous silicon-based semiconductors; accordingly, numerous measurement techniques have been designed and developed to probe the electronic conducting nature of organic materials bearing extremely wide structural variations in comparison with inorganic and/or metal-oxide semiconductor materials. The present perspective highlights the evaluation methodologies of charge carrier mobility in organic materials, as well as the merits and demerits of techniques examining the feasibility of organic molecules, crystals, and supramolecular assemblies in semiconductor applications. Beyond the simple substitution of amorphous silicon, we have attempted to address in this perspective the systematic use of measurement techniques for future development of organic molecular semiconductors.

  16. Thermodynamics of water-solid interactions in crystalline and amorphous pharmaceutical materials.

    PubMed

    Sacchetti, Mark

    2014-09-01

    Pharmaceutical materials, crystalline and amorphous, sorb water from the atmosphere, which affects critical factors in the development of drugs, such as the selection of drug substance crystal form, compatibility with excipients, dosage form selection, packaging, and product shelf-life. It is common practice to quantify the amount of water that a material sorbs at a given relative humidity (RH), but the results alone provide minimal to no physicochemical insight into water-solid interactions, without which pharmaceutical scientists cannot develop an understanding of their materials, so as to anticipate and circumvent potential problems. This research was conducted to advance the science of pharmaceutical materials by examining the thermodynamics of solids with sorbed water. The compounds studied include nonhygroscopic drugs, a channel hydrate drug, a stoichiometric hydrate excipient, and an amorphous excipient. The water sorption isotherms were measured over a range of temperature to extract the partial molar enthalpy and entropy of sorbed water as well as the same quantities for some of the solids. It was found that water-solid interactions spanned a range of energy and entropy as a function of RH, which was unique to the solid, and which could be valuable in identifying batch-to-batch differences and effects of processing in material performance.

  17. Molecular Syntheses of Extended Materials

    NASA Astrophysics Data System (ADS)

    Paley, Daniel W.

    Bottom-up molecular synthesis is a route to chemically and crystallographically uniform polymers and solid-state materials. Through the use of molecular precursors, we gain atomic-level control of functionality and fine-tuning of the collective properties of materials. This dissertation presents two studies that demonstrate this approach. Ring-opening alkyne metathesis polymerization is a possible approach to monodisperse conjugated polymers, but its applications have been limited by difficult syntheses and high air sensitivity of known organometallic ROAMP initiators. We designed a dimeric, air-stable molybdenum alkylidyne with a tris(phenolate) supporting ligand. The precatalyst is activated by addition of methanol and polymerizes cyclooctynes with excellent chemical selectivity and functional group tolerance. The Nuckolls and Roy groups have introduced a new family of solid-state compounds synthesized from cobalt chalcogenide clusters Co6Q 8(PR3)6 and fullerenes. The first examples of these materials crystallized in superatom lattices with the symmetry of simple inorganic solids CdI2 (P-3m1) and NaCl (Fm-3m). This dissertation reveals that further members of the family feature extraordinary diversity of structure, including a pseudo-trigonal array of fulleride dimers in [Co 6Te8(PEt3)6]2[C140 ][C70]2 and a heterolayered van der Waals cocrystal [Co6Se8(PEt2phen)6][C 60]5. In addition to these unusual crystal structures, this dissertation presents a method for assigning redox states from crystallographic data in Co6Q8 clusters. Finally, a detailed guide to the collection and solution of single-crystal X-ray data is presented. The guide is intended for independent study by new crystallographers.

  18. Mechanism of amorphous itraconazole stabilization in polymer solid dispersions: role of molecular mobility.

    PubMed

    Bhardwaj, Sunny P; Arora, Kapildev K; Kwong, Elizabeth; Templeton, Allen; Clas, Sophie-Dorothee; Suryanarayanan, Raj

    2014-11-03

    Physical instability of amorphous solid dispersions can be a major impediment to their widespread use. We characterized the molecular mobility in amorphous solid dispersions of itraconazole (ITZ) with each polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose acetate succinate (HPMCAS) with the goal of investigating the correlation between molecular mobility and physical stability. Dielectric spectra showed two mobility modes: α-relaxation at temperatures above the glass transition temperature (Tg) and β-relaxation in the sub-Tg range. HPMCAS substantially increased the α-relaxation time, with an attendant increase in crystallization onset time and a decrease in crystallization rate constant, demonstrating the correlation between α-relaxation and stability. The inhibitory effect on α-relaxation as well as stability was temperature dependent and diminished as the temperature was increased above Tg. PVP, on the other hand, affected neither the α-relaxation time nor the crystallization onset time, further establishing the link between α-relaxation and crystallization onset in solid dispersions. However, it inhibited the crystallization rate, an effect attributed to factors other than mobility. Interestingly, both of the polymers acted as plasticizers of β-relaxation, ruling out the latter's involvement in physical stability.

  19. Method of making amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1982-01-01

    The process comprises placing an amorphous metal in particulate form and a low molecular weight (e.g., 1000-5000) thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  20. Classical and ab-initio molecular dynamic simulation of an amorphous silica surface

    NASA Astrophysics Data System (ADS)

    Mischler, C.; Kob, W.; Binder, K.

    2002-08-01

    We present the results of a classical molecular dynamic simulation as well as of an ab-initio molecular dynamic simulation of an amorphous silica surface. In the case of the classical simulation we use the potential proposed by van Beest et al. (BKS) whereas the ab-initio simulation is done with a Car-Parrinello method (CPMD). We find that the surfaces generated by BKS have a higher concentration of defects (e.g., concentration of two-membered rings) than those generated with CPMD. In addition also the distribution functions of the angles and of the distances are different for the short rings. Hence we conclude that whereas the BKS potential is able to correctly reproduce the surface on the length scale beyond ≈5 Å, it is necessary to use an ab-initio method to reliably predict the structure at small scales.

  1. Growth and modelling of spherical crystalline morphologies of molecular materials.

    PubMed

    Shalev, O; Biswas, S; Yang, Y; Eddir, T; Lu, W; Clarke, R; Shtein, M

    2014-10-16

    Crystalline, yet smooth, sphere-like morphologies of small molecular compounds are desirable in a wide range of applications but are very challenging to obtain using common growth techniques, where either amorphous films or faceted crystallites are the norm. Here we show solvent-free, guard flow-assisted organic vapour jet printing of non-faceted, crystalline microspheroids of archetypal small molecular materials used in organic electronic applications. We demonstrate how process parameters control the size distribution of the spheroids and propose an analytical model and a phase diagram predicting the surface morphology evolution of different molecules based on processing conditions, coupled with the thermophysical and mechanical properties of the molecules. This experimental approach opens a path for exciting applications of small molecular organic compounds in optical coatings, textured surfaces with controlled wettability, pharmaceutical and food substance printing and others, where thick organic films and particles with high surface area are needed.

  2. Relation between bandgap and resistance drift in amorphous phase change materials.

    PubMed

    Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

    2015-12-01

    Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

  3. Relation between bandgap and resistance drift in amorphous phase change materials

    PubMed Central

    Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

    2015-01-01

    Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift. PMID:26621533

  4. Early stages of mechanical crystallization of amorphous FeZrBCu soft magnetic material

    NASA Astrophysics Data System (ADS)

    Friedrich, J.; Herr, U.; Samwer, K.

    2000-03-01

    Nanocrystalline Fe-base soft magnetic materials with high saturation magnetization have been obtained by crystallization of FeZrBCu amorphous precursors. In contrast to the conventional thermal crystallization, mechanical crystallization provides an alternative route for the generation of nanocrystalline materials using a high energy ball mill. Special emphasis is put here on the early stages of the transformation. X-ray diffraction, Mössbauer spectroscopy, and magnetization measurements are used to characterize the material. We find a continuous increase of the saturation magnetization accompanied by an increase of the crystalline fraction. The coercivity shows a different behavior with a large increase after very short milling within the amorphous state and a decrease for long milling duration. The influence of the deformation process on the magnetic anisotropy and the coercivity is discussed in terms of stresses and shear band formation. The results are compared with the phase formation and magnetic properties of thermally crystallized FeZrBCu samples and mechanical crystallization studies of other materials.

  5. Hydrogels from Amorphous Calcium Carbonate and Polyacrylic Acid: Bio-Inspired Materials for "Mineral Plastics".

    PubMed

    Sun, Shengtong; Mao, Li-Bo; Lei, Zhouyue; Yu, Shu-Hong; Cölfen, Helmut

    2016-09-19

    Given increasing environmental issues due to the large usage of non-biodegradable plastics based on petroleum, new plastic materials, which are economic, environmentally friendly, and recyclable are in high demand. One feasible strategy is the bio-inspired synthesis of mineral-based hybrid materials. Herein we report a facile route for an amorphous CaCO3 (ACC)-based hydrogel consisting of very small ACC nanoparticles physically cross-linked by poly(acrylic acid). The hydrogel is shapeable, stretchable, and self-healable. Upon drying, the hydrogel forms free-standing, rigid, and transparent objects with remarkable mechanical performance. By swelling in water, the material can completely recover the initial hydrogel state. As a matrix, thermochromism can also be easily introduced. The present hybrid hydrogel may represent a new class of plastic materials, the "mineral plastics". © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

    SciTech Connect

    Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen; Zu, X. T.; Li, Sean

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations.

  7. Mapping amorphous material on a partially crystalline surface: nanothermal analysis for simultaneous characterisation and imaging of lactose compacts.

    PubMed

    Dai, Xuan; Reading, Mike; Craig, Duncan Q M

    2009-04-01

    The use of nanothermal analysis for mapping amorphous and crystalline lactose at a nanoscale is explored. Compressed tablets of amorphous and crystalline lactose (alone and mixed) were prepared and localised thermomechanical analysis (L-TMA) performed using micro- and nanothermal analysis in a addition to single point variable temperature pull-off force measurements. L-TMA was shown to be able to identify the different materials at a nanoscale via measurement of the thermal events associated with the amorphous and crystalline regions, while pull off force measurements showed that the adhesion of the amorphous material increased on approaching the T(g). Imaging was performed isothermally using topographic and pulsed force mode (PFM) measurements; both approaches were capable of discriminating two regions which L-TMA conformed to correspond to the two materials. In addition, force volume imaging (FVI) is suggested as a further approach to mapping the surfaces. We demonstrate that performing heated tip PFM measurements at a temperature close to the T(g) allows greater discrimination between the two regions. We therefore suggest that the nanothermal approach allows both characterisation and imaging of partially amorphous surfaces, and also demonstrate that heated tip imaging allows greater discrimination between crystalline and amorphous materials than is possible using ambient studies.

  8. High pressure polymorphs and amorphization of upconversion host material NaY(WO4)2

    DOE PAGES

    Hong, Fang; Yue, Binbin; Cheng, Zhenxiang; ...

    2016-07-29

    The pressure effect on the structural change of upconversion host material NaY(WO4)2 was studied in this paper by using in-situ synchrotron X-ray diffraction. A transition from the initial scheelite phase to the M-fergusonite phase occurs near 10 GPa, and another phase transition is found near 27.5 GPa, which could be an isostructural transition without symmetry change. The sample becomes amorphous when the pressure is fully released from high pressure. Finally, this work demonstrates the possibility of synthesizing various polymorph structures for non-linear optical applications with a high pressure, chemical doping, or strained thin-film nanostructure process.

  9. Directed vapor deposition of amorphous and polycrystalline electronic materials: Nonhydrogenated a-Si

    SciTech Connect

    Groves, J.F.; Jones, S.H.; Globus, T.; Hsiung, L.M.; Wadley, H.

    1995-10-01

    A novel directed vapor deposition (DVD) process for creating amorphous and polycrystalline electronic materials is reported. Initial experimental results for DVD of nonhydrogenated a-Si indicate that growth rates at least between 0.02 and 1.0 {micro}m/min can be achieved. In this process, evaporated silicon is efficiently entrained in a previously formed low pressure supersonic He jet. The silicon is evaporated using a high energy, high voltage, electron beam. The collimated jet of He entrained with silicon is used to deposit thin films of a-Si at room temperature on glass substrates. Initial TEM microstructure analysis and optical absorption analysis is presented.

  10. Molecularly imprinted materials: synthesis, properties, applications

    NASA Astrophysics Data System (ADS)

    Lisichkin, Georgii V.; Krutyakov, Yu A.

    2006-10-01

    This review is devoted to the method of molecular imprinting. The physicochemical fundamentals and mechanisms of covalent and non-covalent molecular imprinting aimed at the development of organic polymeric sorbents capable of molecular recognition are considered. Attention is focused on the preparation of molecular imprints on mineral supports. The mechanisms of molecular recognition in adsorption are discussed. Application fields of materials with molecular imprints are briefly surveyed.

  11. Viewing Molecular and Interface Interactions of Curcumin Amorphous Solid Dispersions for Comprehending Dissolution Mechanisms.

    PubMed

    Li, Jing; Wang, Xin; Li, Chang; Fan, Na; Wang, Jian; He, Zhonggui; Sun, Jin

    2017-08-07

    Tautomeric curcumin amorphous solid dispersions (Cur ASDs) formulated with various typical polymers (polyethylene glycol 6000 (PEG), polyvinylpyrrolidone K30 (PVP), Eudragit EPO (EuD), EuD/hydroxypropylmethyl cellulose E50 (HPMC), and PVP/EuD) were probed using in situ Raman imaging plus spectroscopy and molecular modeling techniques, and dissolution mechanism of Cur ASDs were revealed mainly through molecular and interfacial interactions formed between Cur and polymer. The results demonstrated that Cur of keto form existed in Cur-PEG, Cur of enol form was shown in Cur-PVP, while Cur-EuD or Cur ASDs formulated with EuD as component had Cur of keto form and enol form. Hydrogen bond interactions were formed between OH group (PEG, HPMC) with C═O (Cur), and C═O (PVP or EuD) with the OH group (Cur). For Cur ASDs formulated with single polymer, the existed form of Cur was possibly related with the molecular interactions formed between drug and polymer. The wetting effect of excipient and Cur ASDs as well as their fitting equations of contact angle profiles should be seriously considered when analyzing the dissolution mechanism of Cur ASDs. Furthermore, dissolution of Cur-EuD with erosion dissolution pattern was higher than Cur-PVP with diffusion mechanism, and their crystallization pathway can ascribe to solution pathway and solid matrix pathway, respectively. Last but not least, turbidimetry method was effective in determining which excipient was superior and evaluating the function of polymers, including their abilities to improve amorphous Cur loading, drug dissolution, and supersaturation levels. Therefore, both the probing of tautomeric Cur in ASDs at intermolecular level and elucidation of its dissolution mechanism has tremendous value.

  12. Molecular dynamics study of tracer diffusion of argon adsorbed on amorphous surfaces

    NASA Astrophysics Data System (ADS)

    Riccardo, J. L.; Steele, W. A.

    1996-12-01

    An isokinetic molecular dynamics simulation of argon adsorbed on several model amorphous surfaces of titanium dioxide is carried out. The solid is represented by the Bernal Model in which the surface is taken to be the exposed face of a dense random packing of oxide ions. This surface is roughened by deleting varying numbers of oxides at random from the outer layer of the solid. Surface diffusion in the limit of very low coverage (tracer diffusion) is evaluated by following the dynamics of noninteracting single adatoms. The diffusion coefficient in the zero-density limit is calculated from velocity autocorrelation functions for adatoms at several temperatures ranging from 85 to 300 K. The temperature dependence of the diffusion constants obtained in this way shows nearly Arrhenius behavior in this temperature range. It is shown that surface roughening at the atomic scale give rise to a higher apparent activation energy for diffusion. A statistical characterization of the adsorptive field through distributions of local maxima and minima in the adsorption energy surface along the diffusion paths was performed in order to relate the surface diffusion of monatomic species on amorphous surfaces to the recently proposed Dual Site-Bond Description of Heterogeneous Surfaces (DSBD). Independent evidence supporting the theoretical hypothesis of the DSBD is also obtained.

  13. Laser annealing of amorphous/poly: Silicon solar cell material flight experiment

    NASA Technical Reports Server (NTRS)

    Cole, Eric E.

    1990-01-01

    The preliminary design proposed for the microelectronics materials processing equipment is presented. An overall mission profile, description of all processing steps, analysis methods and measurement techniques, data acquisition and storage, and a preview of the experimental hardware are included. The goal of the project is to investigate the viability of material processing of semiconductor microelectronics materials in a micro-gravity environment. The two key processes are examined: (1) Rapid Thermal Annealing (RTA) of semiconductor thin films and damaged solar cells, and (2) thin film deposition using a filament evaporator. The RTA process will be used to obtain higher quality crystalline properties from amorphous/poly-silicon films. RTA methods can also be used to repair radiation-damaged solar cells. On earth this technique is commonly used to anneal semiconductor films after ion-implantation. The damage to the crystal lattice is similar to the defects found in solar cells which have been exposed to high-energy particle bombardment.

  14. Preparation of Potassium-Posphate-embedded Amorphous Silicate Material from Rice Straw Waste

    NASA Astrophysics Data System (ADS)

    Nandiyanto, A. B. D.; Permatasari, N.; Sucahya, T. N.; Purwanti, S. T.; Munawaroh, H. S. H.; Abdullah, A. G.; Hasanah, L.

    2017-03-01

    Rice straw is one of the agricultural wastes that increased every year. Since rice straw ash contains 74.6% of silica, this material is potentially used to produce silica. Thus, the purpose of this study was to investigate the possibility process for generating potassium-phosphate-embedded amorphous silica material. To extract silica from rice straw waste, we used potassium hydroxide solution followed by an acid precipitation treatment. Based on the experimental results, the proposed method is potential to be used as an alternative technique for getting silica material. In addition, the method has a positive impact on the environment because this is potential for reducing the amount of rice straw waste, whereas at the same time this provides an added value to the rice straw waste itself.

  15. Surface patterning for brittle amorphous material using nanoindenter-based mechanochemical nanofabrication.

    PubMed

    Park, Jeong Woo; Lee, Chae Moon; Choi, Soo Chang; Kim, Yong Woo; Lee, Deug Woo

    2008-02-27

    This paper demonstrates a micro/nanoscale surface patterning technology for brittle material using mechanical and chemical processes. Fused silica was scratched with a Berkovich tip under various normal loads from several mN to several tens of mN with various tip rotations. The scratched substrate was then chemically etched in hydrofluoric solution to evaluate the chemical properties of the different deformed layers produced under various mechanical scratching conditions. Our results showed that either protruding or depressed patterns could be generated on the scratched surface after chemical etching by controlling the tip rotation, the normal load and the etching condition. In addition, the mask effect of amorphous material after mechanical scratching was controlled by conventional mechanical machining conditions such as contact area, chip formation, plastic flow and material removal.

  16. MSL SAM-Like Evolved Gas Analyses of Si-rich Amorphous Materials

    NASA Technical Reports Server (NTRS)

    McAdam, Amy; Knudson, Christine; Sutter, Brad; Andrejkovicova, Slavka; Archer, P. Douglas; Franz, Heather; Eigenbrode, Jennifer; Morris, Richard; Ming, Douglas; Sun, Vivian; Wilhelm, Mary Beth; Mahaffy, Paul

    2016-01-01

    Chemical and mineralogical analyses of several samples from Murray Formation mudstones and Stimson Formation sandstones by the Mars Science Laboratory (MSL) revealed the presence of Si-rich amorphous or poorly ordered materials. It is possible to identify the presence of high-SiO2 vs. lower SiO2 amorphous materials (e.g., basaltic glasses), based on the position of the resulting wide diffraction features in XRD patterns from the Chemistry and Mineralogy (CheMin) instrument, but it is not possible to distinguish between several candidate high-SiO2 amorphous materials such as opal-A or rhyolitic glass. In the Buckskin (BS) sample from the upper Murray Formation, and the Big Sky (BY) and Greenhorn (GH) samples from the Stimson Formation, analyses by the Sample Analysis at Mars (SAM) instrument showed very broad H2O evolutions during sample heating at temperatures >450-500degC which had not been observed from previous samples. BS also had a significant broad evolution <450-500degC. We have undertaken a laboratory study targeted at understanding if the data from SAM can be used to place constraints on the nature of the amorphous phases. SAM-like evolved gas analyses have been performed on several opal and rhyolitic glass samples. Opal-A samples exhibited wide <500degC H2O evolutions, with lesser H2O evolved above 500degC. H2O evolution traces from rhyolitic glasses varied, having either two broad H2O peaks, <300degC and >500degC, or a broad peak centered around 400degC. For samples that produced two evolutions, the lower temperature peak is more intense than the higher temperature peak, a trend also exhibited by opal-A. This trend is consistent with data from BS, but does not seem consistent with data from BY and GH which evolved most of their H2O >500degC. It may be that dehydration of opal-A and/or rhyolitic glass can result in some preferential loss of lower temperature H2O, to produce traces that more closely resemble BY and GH. This is currently under investigation

  17. Textured Sb2Te3 films and GeTe/Sb2Te3 superlattices grown on amorphous substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Boschker, Jos E.; Tisbi, E.; Placidi, E.; Momand, Jamo; Redaelli, Andrea; Kooi, Bart J.; Arciprete, Fabrizio; Calarco, Raffaella

    2017-01-01

    The realization of textured films of 2-dimensionally (2D) bonded materials on amorphous substrates is important for the integration of this material class with silicon based technology. Here, we demonstrate the successful growth by molecular beam epitaxy of textured Sb2Te3 films and GeTe/Sb2Te3 superlattices on two types of amorphous substrates: carbon and SiO2. X-ray diffraction measurements reveal that the out-of-plane alignment of grains in the layers has a mosaic spread with a full width half maximum of 2.8°. We show that a good texture on SiO2 is only obtained for an appropriate surface preparation, which can be performed by ex situ exposure to Ar+ ions or by in situ exposure to an electron beam. X-ray photoelectron spectroscopy reveals that this surface preparation procedure results in reduced oxygen content. Finally, it is observed that film delamination can occur when a capping layer is deposited on top of a superlattice with a good texture. This is attributed to the stress in the capping layer and can be prevented by using optimized deposition conditions of the capping layer. The obtained results are also relevant to the growth of other 2D materials on amorphous substrates.

  18. Study of the molecular mobility of (±)-methocarbamol in the amorphous solid state

    NASA Astrophysics Data System (ADS)

    Moura Ramos, Joaquim J.; Diogo, Hermínio P.

    2017-04-01

    The experimental techniques of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) were used to study the thermal behavior of the pharmaceutical drug (±)-methocarbamol and its slow molecular mobility (in the 10-3-10-2 Hz range) in the amorphous solid state. The possibility of polymorphism was considered based on the DSC results. The glass forming ability and the glass stability were investigated by DSC, and the general kinetic features of the main relaxation, including the fragility or steepness index, were studied by both experimental techniques. The secondary relaxations detected by TSDC revealed fast and slow (Johari-Goldstein) modes. These secondary relaxations of different nature were assigned based on physical aging studies.

  19. Improved Stability Of Amorphous Zinc Tin Oxide Thin Film Transistors Using Molecular Passivation

    SciTech Connect

    Rajachidambaram, Meena Suhanya; Pandey, Archana; Vilayur Ganapathy, Subramanian; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai; Herman, Gregory S.

    2013-10-21

    The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFT) have been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid (n-HPA) when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.

  20. Study of the molecular mobility of (±)-methocarbamol in the amorphous solid state

    NASA Astrophysics Data System (ADS)

    Moura Ramos, Joaquim J.; Diogo, Hermínio P.

    2016-10-01

    The experimental techniques of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) were used to study the thermal behavior of the pharmaceutical drug (±)-methocarbamol and its slow molecular mobility (in the 10-3-10-2 Hz range) in the amorphous solid state. The possibility of polymorphism was considered based on the DSC results. The glass forming ability and the glass stability were investigated by DSC, and the general kinetic features of the main relaxation, including the fragility or steepness index, were studied by both experimental techniques. The secondary relaxations detected by TSDC revealed fast and slow (Johari-Goldstein) modes. These secondary relaxations of different nature were assigned based on physical aging studies.

  1. Direct molecular dynamics simulation of Ge deposition on amorphous SiO2 at experimentally relevant conditions

    DOE PAGES

    Chuang, Claire Y.; Zepeda-Ruiz, Luis A.; Han, Sang M.; ...

    2015-06-01

    Molecular dynamics simulations were used to study Ge island nucleation and growth on amorphous SiO2 substrates. This process is relevant in selective epitaxial growth of Ge on Si, for which SiO2 is often used as a template mask. The islanding process was studied over a wide range of temperatures and fluxes, using a recently proposed empirical potential model for the Si–SiO2–Ge system. The simulations provide an excellent quantitative picture of the Ge islanding and compare well with detailed experimental measurements. These quantitative comparisons were enabled by an analytical rate model as a bridge between simulations and experiments despite the factmore » that deposition fluxes accessible in simulations and experiments are necessarily different by many orders of magnitude. In particular, the simulations led to accurate predictions of the critical island size and the scaling of island density as a function of temperature. Lastly, the overall approach used here should be useful not just for future studies in this particular system, but also for molecular simulations of deposition in other materials.« less

  2. Direct molecular dynamics simulation of Ge deposition on amorphous SiO2 at experimentally relevant conditions

    SciTech Connect

    Chuang, Claire Y.; Zepeda-Ruiz, Luis A.; Han, Sang M.; Sinno, Talid

    2015-06-01

    Molecular dynamics simulations were used to study Ge island nucleation and growth on amorphous SiO2 substrates. This process is relevant in selective epitaxial growth of Ge on Si, for which SiO2 is often used as a template mask. The islanding process was studied over a wide range of temperatures and fluxes, using a recently proposed empirical potential model for the Si–SiO2–Ge system. The simulations provide an excellent quantitative picture of the Ge islanding and compare well with detailed experimental measurements. These quantitative comparisons were enabled by an analytical rate model as a bridge between simulations and experiments despite the fact that deposition fluxes accessible in simulations and experiments are necessarily different by many orders of magnitude. In particular, the simulations led to accurate predictions of the critical island size and the scaling of island density as a function of temperature. Lastly, the overall approach used here should be useful not just for future studies in this particular system, but also for molecular simulations of deposition in other materials.

  3. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

  4. The effect of Ta interface on the crystallization of amorphous phase change material thin films

    SciTech Connect

    Ghezzi, G. E.; Noé, P. Marra, M.; Sabbione, C.; Fillot, F.; Bernier, N.; Ferrand, J.; Maîtrejean, S.; Hippert, F.

    2014-06-02

    The crystallization of amorphous GeTe and Ge{sub 2}Sb{sub 2}Te{sub 5} phase change material films, with thickness between 10 and 100 nm, sandwiched between either Ta or SiO{sub 2} layers, was investigated by optical reflectivity. Ta cladding layers were found to increase the crystallization temperature, even for films as thick as 100 nm. X-Ray diffraction investigations of crystallized GeTe films showed a very weak texture in Ta cladded films, in contrast with the strong texture observed for SiO{sub 2} cladding layers. This study shows that crystallization mechanism of phase change materials can be highly impacted by interface effects, even for relatively thick films.

  5. Synthesis of amorphous supermicroporous zirconium phosphate materials by nonionic surfactant templating

    SciTech Connect

    Zhao, G.L.; Yuan, Z.Y. . E-mail: zyyuan@mail.nankai.edu.cn; Chen, T.H.

    2005-11-03

    Supermicroporous zirconium phosphate materials possessing wormhole-like pores in the size range 1.3-1.8 nm were synthesized by using nonionic poly(ethylene oxide) surfactant (e.g., C{sub 16}H{sub 33}(EO){sub 10}, C{sub 18}H{sub 35}(EO){sub 10}) as a structure directing agent. The textural and structural properties were characterized by powder X-ray diffraction, N{sub 2} adsorption analysis, differential thermal analysis, scanning and transmission electron microscopy, {sup 31}P MAS NMR and infrared spectroscopy. The synthesized materials are amorphous, exhibiting high surface areas, narrow pore size distributions, excellent thermal stabilities (over 800 deg. C) and acidic properties. The supermicropore size of the synthesized zirconium phosphate may be tunable by the variation of alkyl chain length of the surfactant.

  6. Formation, Structure and Properties of Amorphous Carbon Char from Polymer Materials in Extreme Atmospheric Reentry Environments

    NASA Technical Reports Server (NTRS)

    Lawson, John W.

    2010-01-01

    Amorphous carbonaceous char produced from the pyrolysis of polymer solids has many desirable properties for ablative heat shields for space vehicles. Molecular dynamics simulations are presented to study the transformation of the local atomic structure from virgin polymer to a dense, disordered char [1]. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated. Thermal conductivity and mechanical response of the resulting char are evaluated [2]. During reenty, the optical response and oxidative reactivity of char are also important properties. Results of ab initio computations of char optical functions [3] and char reactivity [4] are also presented.

  7. Collective nonaffine displacements in amorphous materials during large-amplitude oscillatory shear

    NASA Astrophysics Data System (ADS)

    Priezjev, Nikolai V.

    2017-02-01

    Using molecular dynamics simulations, we study the transient response of a binary Lennard-Jones glass subjected to periodic shear deformation. The amorphous solid is modeled as a three-dimensional Kob-Andersen binary mixture at a low temperature. The cyclic loading is applied to slowly annealed, quiescent samples, which induces irreversible particle rearrangements at large strain amplitudes, leading to stress-strain hysteresis and a drift of the potential energy towards higher values. We find that the initial response to cyclic shear near the critical strain amplitude involves disconnected clusters of atoms with large nonaffine displacements. In contrast, the amplitude of shear stress oscillations decreases after a certain number of cycles, which is accompanied by the initiation and subsequent growth of a shear band.

  8. Molecular Relaxations in Supercooled Liquid and Glassy States of Amorphous Quinidine: Dielectric Spectroscopy and Density Functional Theory Approaches.

    PubMed

    Schammé, Benjamin; Mignot, Mélanie; Couvrat, Nicolas; Tognetti, Vincent; Joubert, Laurent; Dupray, Valérie; Delbreilh, Laurent; Dargent, Eric; Coquerel, Gérard

    2016-08-04

    In this article, we conduct a comprehensive molecular relaxation study of amorphous Quinidine above and below the glass-transition temperature (Tg) through broadband dielectric relaxation spectroscopy (BDS) experiments and theoretical density functional theory (DFT) calculations, as one major issue with the amorphous state of pharmaceuticals is life expectancy. These techniques enabled us to determine what kind of molecular motions are responsible, or not, for the devitrification of Quinidine. Parameters describing the complex molecular dynamics of amorphous Quinidine, such as Tg, the width of the α relaxation (βKWW), the temperature dependence of α-relaxation times (τα), the fragility index (m), and the apparent activation energy of secondary γ relaxation (Ea-γ), were characterized. Above Tg (> 60 °C), a medium degree of nonexponentiality (βKWW = 0.5) was evidenced. An intermediate value of the fragility index (m = 86) enabled us to consider Quinidine as a glass former of medium fragility. Below Tg (< 60 °C), one well-defined secondary γ relaxation, with an apparent activation energy of Ea-γ = 53.8 kJ/mol, was reported. From theoretical DFT calculations, we identified the most reactive part of Quinidine moieties through exploration of the potential energy surface. We evidenced that the clearly visible γ process has an intramolecular origin coming from the rotation of the CH(OH)C9H14N end group. An excess wing observed in amorphous Quinidine was found to be an unresolved Johari-Goldstein relaxation. These studies were supplemented by sub-Tg experimental evaluations of the life expectancy of amorphous Quinidine by X-ray powder diffraction and differential scanning calorimetry. We show that the difference between Tg and the onset temperature for crystallization, Tc, which is 30 K, is sufficiently large to avoid recrystallization of amorphous Quinidine during 16 months of storage under ambient conditions.

  9. PREFACE: Fourh Workshop on Non-Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Andreozzi, Laura; Giordano, Marco; Leporini, Dino; Tosi, Mario

    2007-04-01

    This special issue of Journal of Physics: Condensed Matter presents the Proceedings of the Fourh Workshop on Non-Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials, held in Pisa from 17-22 September 2006. This was the fourth of a series of workshops on this theme started in 1995 as a joint initiative of the Università di Pisa and the Scuola Normale Superiore. The 2006 edition was attended by about 200 participants from Europe, Asia and the Americas. As for the earlier workshops, the main objective was to bring together scientists from different areas of science, technology and engineering, to comparatively discuss experimental facts and theoretical predictions on the dynamical processes that occur in supercooled fluids and other disordered materials in non-equilibrium states. The underlying conceptual unity of the field provides a common background for the scientific community working in its various areas. In this edition the number of sessions was increased to cover a wider range of topics of general and current interest, in a larger number of stimulating lectures. The core of the workshop was a set of general lectures followed by more specific presentations on current issues in the main areas of the field. The sessions were in sequence devoted to: non-equilibrium dynamics, aging and secondary relaxations, biomaterials, polyamorphism and water, polymer dynamics I, complex systems, pressure-temperature scaling, thin films, nanometre length-scale studies, folded states of proteins and polymer crystals, theoretical aspects and energy landscape approaches, relaxation and heterogeneous dynamics, rheology in fluids and entangled polymers, biopolymers, and polymer dynamics II. We thank the session chairmen and all speakers for the high quality of their contributions. The structure of this issue of the proceedings follows the sequence of the oral presentations in the workshop, complemented by some papers selected from the poster sessions. Two

  10. Computationally Designed Molecularly Imprinted Materials

    NASA Astrophysics Data System (ADS)

    Pavel, Dumitru; Lagowski, Jolanta; Faid, Karim

    2004-03-01

    Molecular dynamics simulations were carried out for different molecular systems in order to predict the binding affinities, binding energies, binding distances and the active site groups between the simulated molecular systems and different bio-ligands (theophylline and its derivatives), which have been designed and minimized using molecular simulation techniques. The first simulated molecular systems consisted of a ligand and functional monomer, such as methacrylic acid and its derivatives. For each pair of molecular systems, (10 monomers with a ligand and 10 monomers without a ligand) a total energy difference was calculated in order to estimate the binding energy between a ligand and the corresponding monomers. The analysis of the simulated functional monomers with ligands indicates that the functional group of monomers interacting with ligands tends to be either COOH or CH2=CH. The distances between the ligand and monomer, in the most stable cases as indicated above, are between 2.0-4.5 Å. The second simulated molecular systems consisted of a ligand and a polymer. The polymers were obtained from monomers that were simulated above. And similar to monomer study, for each pair of molecular systems, (polymer with a ligand and polymer without a ligand) a total energy difference was calculated in order to estimate the binding energy between ligand and the corresponding polymer. The binding distance between the active site of a polymer and a ligand will also be discussed.

  11. Molecular modeling of temperature dependence of solubility parameters for amorphous polymers.

    PubMed

    Chen, Xianping; Yuan, Cadmus; Wong, Cell K Y; Zhang, Guoqi

    2012-06-01

    A molecular modeling strategy is proposed to describe the temperature (T) dependence of solubility parameter (δ) for the amorphous polymers which exhibit glass-rubber transition behavior. The commercial forcefield "COMPASS" is used to support the atomistic simulations of the polymer. The temperature dependence behavior of δ for the polymer is modeled by running molecular dynamics (MD) simulation at temperatures ranging from 250 up to 650 K. Comparing the MD predicted δ value at 298 K and the glass transition temperature (T(g)) of the polymer determined from δ-T curve with the experimental value confirm the accuracy of our method. The MD modeled relationship between δ and T agrees well with the previous theoretical works. We also observe the specific volume (v), cohesive energy (U(coh)), cohesive energy density (E(CED)) and δ shows a similar temperature dependence characteristics and a drastic change around the T(g). Meanwhile, the applications of δ and its temperature dependence property are addressed and discussed.

  12. Diffusion of molecules in the bulk of a low density amorphous ice from molecular dynamics simulations.

    PubMed

    Ghesquière, P; Mineva, T; Talbi, D; Theulé, P; Noble, J A; Chiavassa, T

    2015-05-07

    The diffusion of molecules in interstellar ice is a fundamental phenomenon to take into account while studying the formation of complex molecules in this ice. This work presents a theoretical study on the diffusion of H2O, NH3, CO2, CO, and H2CO in the bulk of a low density amorphous (LDA) ice, while taking into account the physical conditions prevailing in space, i.e. temperatures below 150 K and extremely low pressure. This study was undertaken by means of molecular dynamics simulations. For CO2 for which no experimental data were available we conducted our own experiments. From our calculations we show that, at low temperatures, the diffusion of molecules in the bulk of a LDA ice is driven by the self-diffusion of water molecules in the ice. With this study we demonstrate that molecular dynamics allows the calculation of diffusion coefficients for small molecules in LDA ice that are convincingly comparable to experimentally measured diffusion coefficients. We also provide diffusion coefficients for a series of molecules of astrochemical interest.

  13. Addressing the Amorphous Content Issue in Quantitative Phase Analysis: The Certification of NIST Standard Reference Material 676a

    SciTech Connect

    J Cline; R Von Dreele; R Winburn; P Stephens; J Filliben

    2011-12-31

    A non-diffracting surface layer exists at any boundary of a crystal and can comprise a mass fraction of several percent in a finely divided solid. This has led to the long-standing issue of amorphous content in standards for quantitative phase analysis (QPA). NIST standard reference material (SRM) 676a is a corundum ({alpha}-Al{sub 2}O{sub 3}) powder, certified with respect to phase purity for use as an internal standard in powder diffraction QPA. The amorphous content of SRM 676a is determined by comparing diffraction data from mixtures with samples of silicon powders that were engineered to vary their specific surface area. Under the (supported) assumption that the thickness of an amorphous surface layer on Si was invariant, this provided a method to control the crystalline/amorphous ratio of the silicon components of 50/50 weight mixtures of SRM 676a with silicon. Powder diffraction experiments utilizing neutron time-of-flight and 25 keV and 67 keV X-ray energies quantified the crystalline phase fractions from a series of specimens. Results from Rietveld analyses, which included a model for extinction effects in the silicon, of these data were extrapolated to the limit of zero amorphous content of the Si powder. The certified phase purity of SRM 676a is 99.02% {+-} 1.11% (95% confidence interval). This novel certification method permits quantification of amorphous content for any sample of interest, by spiking with SRM 676a.

  14. Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials.

    PubMed

    Kalkan, B; Sen, S; Clark, S M

    2011-09-28

    The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. © 2011 American Institute of Physics

  15. Addressing the amorphous content issue in quantitative phase analysis: the certification of NIST standard reference material 676a.

    PubMed

    Cline, James P; Von Dreele, Robert B; Winburn, Ryan; Stephens, Peter W; Filliben, James J

    2011-07-01

    A non-diffracting surface layer exists at any boundary of a crystal and can comprise a mass fraction of several percent in a finely divided solid. This has led to the long-standing issue of amorphous content in standards for quantitative phase analysis (QPA). NIST standard reference material (SRM) 676a is a corundum (α-Al(2)O(3)) powder, certified with respect to phase purity for use as an internal standard in powder diffraction QPA. The amorphous content of SRM 676a is determined by comparing diffraction data from mixtures with samples of silicon powders that were engineered to vary their specific surface area. Under the (supported) assumption that the thickness of an amorphous surface layer on Si was invariant, this provided a method to control the crystalline/amorphous ratio of the silicon components of 50/50 weight mixtures of SRM 676a with silicon. Powder diffraction experiments utilizing neutron time-of-flight and 25 keV and 67 keV X-ray energies quantified the crystalline phase fractions from a series of specimens. Results from Rietveld analyses, which included a model for extinction effects in the silicon, of these data were extrapolated to the limit of zero amorphous content of the Si powder. The certified phase purity of SRM 676a is 99.02% ± 1.11% (95% confidence interval). This novel certification method permits quantification of amorphous content for any sample of interest, by spiking with SRM 676a.

  16. A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review

    PubMed Central

    Romero, Cristina; Noyola, Juan C.; Santiago, Ulises; Valladares, Renela M.; Valladares, Alexander; Valladares, Ariel A.

    2010-01-01

    We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists first of constructing crystalline supercells with a large number of atoms and a density close to the real value and then lowering the density by increasing the volume. The resulting supercells are subjected to either ab initio or parameterized—Tersoff-based—molecular dynamics processes at various temperatures, all below the corresponding bulk melting points, followed by geometry relaxations. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions without the need of incorporating ad hoc semiconducting atomic structural elements such as graphene-like sheets and/or chain-like patterns (reconstructive simulations) or of reproducing the experimental processes (mimetic simulations). We report radial (pair) distribution functions, nanoporous structures of C and Si, and some computational predictions for their vibrational density of states. We present numerical estimates and discuss possible applications of semiconducting materials for hydrogen storage in potential fuel tanks. Nanopore structures for metallic elements like Al and Au also obtained through the expanding lattice method are reported.

  17. Nonequilibrium thermodynamics of driven amorphous materials. I. Internal degrees of freedom and volume deformation.

    PubMed

    Bouchbinder, Eran; Langer, J S

    2009-09-01

    This is the first of three papers devoted to the nonequilibrium thermodynamics of amorphous materials. Our focus here is on the role of internal degrees of freedom in determining the dynamics of such systems. For illustrative purposes, we study a solid whose internal degrees of freedom are vacancies that govern irreversible volume changes. Using this model, we compare a thermodynamic theory based on the Clausius-Duhem inequality to a statistical analysis based directly on the law of increase of entropy. The statistical theory is used first to derive the Clausius-Duhem inequality. We then use the theory to go beyond those results and obtain detailed equations of motion, including a rate factor that is enhanced by deformation-induced noisy fluctuations. The statistical analysis points to the need for understanding how both energy and entropy are shared by the vacancies and their environments.

  18. Shear-transformation-zone theory of yielding in athermal amorphous materials

    DOE PAGES

    Langer, J. S.

    2015-07-22

    Yielding transitions in athermal amorphous materials undergoing steady-state shear flow resemble critical phenomena. Historically, they have been described by the Herschel-Bulkley rheological formula, which implies singular behaviors at yield points. In this paper, I examine this class of phenomena using an elementary version of the thermodynamic shear-transformation-zone (STZ) theory, focusing on the role of the effective disorder temperature, and paying special attention to scaling and dimensional arguments. I find a wide variety of Herschel-Bulkley-like rheologies but, for fundamental reasons not specific to the STZ theory, conclude that the yielding transition is not truly critical. Specifically, for realistic many-body models withmore » short-range interactions, there is a correlation length that grows rapidly but ultimately saturates near the yield point.« less

  19. New Order-Parameter-Based Method for Characterizing Radiation Damage in Amorphous Materials.

    PubMed

    Galanakis, Nikolaos; Travis, Karl P

    2017-10-02

    We present a new method of characterizing damage arising from α-recoil cascades in amorphous materials including glasses. The approach taken is topological, yielding information on atom connectivity and utilizing complete sets of orthogonal functions (spherical harmonics and Hermite functions) to compute order parameters. The utility of our new approach is demonstrated by first applying it to models of radiation-damaged crystalline zircon, enabling validation against the standard defect counting method (Wigner-Seitz). We then apply it to a simple model of a glass, obtained by supercooling a Lennard-Jones liquid, for which defect counting methods are inapplicable. The method shows great promise for use in characterizing damage in more complicated glasses, particularly those of interest in the immobilization of nuclear waste, and when used in conjunction with nonequilibrium computer simulation could be a powerful tool to elucidate experimental data on the radiation tolerance of such wasteforms.

  20. Shear-transformation-zone theory of yielding in athermal amorphous materials

    NASA Astrophysics Data System (ADS)

    Langer, J. S.

    2015-07-01

    Yielding transitions in athermal amorphous materials undergoing steady-state shear flow resemble critical phenomena. Historically, they have been described by the Herschel-Bulkley rheological formula, which implies singular behaviors at yield points. In this paper, I examine this class of phenomena using an elementary version of the thermodynamic shear-transformation-zone (STZ) theory, focusing on the role of the effective disorder temperature, and paying special attention to scaling and dimensional arguments. I find a wide variety of Herschel-Bulkley-like rheologies but, for fundamental reasons not specific to the STZ theory, conclude that the yielding transition is not truly critical. In particular, for realistic many-body models with short-range interactions, there is a correlation length that grows rapidly but ultimately saturates near the yield point.

  1. Shear-transformation-zone theory of yielding in athermal amorphous materials

    SciTech Connect

    Langer, J. S.

    2015-07-22

    Yielding transitions in athermal amorphous materials undergoing steady-state shear flow resemble critical phenomena. Historically, they have been described by the Herschel-Bulkley rheological formula, which implies singular behaviors at yield points. In this paper, I examine this class of phenomena using an elementary version of the thermodynamic shear-transformation-zone (STZ) theory, focusing on the role of the effective disorder temperature, and paying special attention to scaling and dimensional arguments. I find a wide variety of Herschel-Bulkley-like rheologies but, for fundamental reasons not specific to the STZ theory, conclude that the yielding transition is not truly critical. Specifically, for realistic many-body models with short-range interactions, there is a correlation length that grows rapidly but ultimately saturates near the yield point.

  2. Overview of Amorphous and Nanocrystalline Magnetocaloric Materials Operating Near Room Temperature

    NASA Astrophysics Data System (ADS)

    Ucar, Huseyin; Ipus, John J.; Franco, V.; McHenry, M. E.; Laughlin, D. E.

    2012-07-01

    The observation of a giant magnetocaloric effect in Gd5Ge1.9Si2Fe0.1 has stimulated the magnetocaloric research in the last two decades. However, the high price of Gd and its proclivity to corrosion of these compounds have prevented their commercial use. To reduce raw materials cost, transition metal-based alloys are investigated to replace rare earth-based materials. Environmental considerations, substitution for scarce and strategic elements, and cost considerations all speak to potential contributions of these new materials to sustainability. Fe-based soft amorphous alloys are believed to be promising magnetic refrigerants. Efforts in improving the refrigeration capacity (RC) of refrigerants mainly rely on broadening the magnetic entropy change. One promising technique is to couple two phases of magnetic materials with desirable properties. Second is the investigation of nanoparticle synthesis routes, with ball milling being the most widely used one. The motivation for the nanoparticles synthesis is rooted in their inherent tendency to have distributed exchange coupling, which will broaden the magnetic entropy curve. As proven with the cost analysis, the focus is believed to shift from improving the RC of refrigerants toward finding the most economically advantageous magnetic refrigerant with the highest performance.

  3. A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer binders.

    PubMed

    Sadat, Mohammad Rafat; Bringuier, Stefan; Asaduzzaman, Abu; Muralidharan, Krishna; Zhang, Lianyang

    2016-10-07

    In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.

  4. A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer binders

    NASA Astrophysics Data System (ADS)

    Sadat, Mohammad Rafat; Bringuier, Stefan; Asaduzzaman, Abu; Muralidharan, Krishna; Zhang, Lianyang

    2016-10-01

    In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.

  5. Stress effects on the Raman spectrum of an amorphous material: Theory and experiment on a -Si:H

    NASA Astrophysics Data System (ADS)

    Strubbe, David A.; Johlin, Eric C.; Kirkpatrick, Timothy R.; Buonassisi, Tonio; Grossman, Jeffrey C.

    2015-12-01

    Strain in a material induces shifts in vibrational frequencies. This phenomenon is a probe of the nature of the vibrations and interatomic potentials and can be used to map local stress/strain distributions via Raman microscopy. This method is standard for crystalline silicon devices, but due to the lack of calibration relations, it has not been applied to amorphous materials such as hydrogenated amorphous silicon (a -Si:H), a widely studied material for thin-film photovoltaic and electronic devices. We calculated the Raman spectrum of a -Si:H ab initio under different strains ɛ and found peak shifts Δ ω =(-460 ±10 cm-1)Tr ɛ . This proportionality to the trace of the strain is the general form for isotropic amorphous vibrational modes, as we show by symmetry analysis and explicit computation. We also performed Raman measurements under strain and found a consistent coefficient of -510 ±120 cm-1 . These results demonstrate that a reliable calibration for the Raman/strain relation can be achieved even for the broad peaks of an amorphous material, with similar accuracy and precision as for crystalline materials.

  6. Molecular mobility of amorphous S-flurbiprofen: a dielectric relaxation spectroscopy approach.

    PubMed

    Rodrigues, A C; Viciosa, M T; Danède, F; Affouard, F; Correia, N T

    2014-01-06

    Amorphous S-flurbiprofen was obtained by the melt quench/cooling method. Dielectric measurements performed in the isochronal mode, conventional and temperature modulated differential scanning calorimetry (TMDSC) studies showed a glass transition, recrystallization, and melting. The different parameters characterizing the complex molecular dynamics of amorphous S-flurbiprofen that can have influence on crystallization and stability were comprehensively characterized by dielectric relaxation spectroscopy experiments (isothermal mode) covering a wide temperature (183 to 408 K) and frequency range (10(-1) to 10(6) Hz): width of the α-relaxation (βKWW), temperature dependence of α-relaxation times (τα), fragility index (m), relation of the α-relaxation with the β-secondary relaxation, and the breakdown of the Debye-Stokes-Einstein (DSE) relationship between the structural relaxation time and dc-conductivity (σdc) at deep undercooling close to Tg. The β-relaxation, observed in the glassy as well as in the supercooled state was identified as the genuine Johari-Goldstein process, attributed to localized motions and regarded as the precursor of the α-relaxation as suggested in the coupling model. A separation of about 6 decades between the α- and β-relaxation was observed at Tg; this decoupling decreased on increasing temperature, and both processes merged at Tαβ = 295 K. The temperature dependence of the α-relaxation time, τα, was described by two Vogel-Fulcher-Tammann-Hesse equations, which intercept at a crossover temperature, TB = 290 K, close to the splitting temperature between the α- and β-relaxation. From the low temperature VFTH equation, a Tg(DRS) = 265.2 was estimated (at τα =100 s) in good agreement with the calorimetric value (Tg,onset,TMDSC = 265.6 K), and a fragility or steepness index m = 113 was calculated allowing to classify S-flurbiprofen as a fragile glass former. The α-relaxation spectra were found to be characterized by a

  7. Toward a Better Understanding of the Physical Stability of Amorphous Anti-Inflammatory Agents: The Roles of Molecular Mobility and Molecular Interaction Patterns.

    PubMed

    Rams-Baron, M; Wojnarowska, Z; Grzybowska, K; Dulski, M; Knapik, J; Jurkiewicz, K; Smolka, W; Sawicki, W; Ratuszna, A; Paluch, M

    2015-10-05

    The aim of this article is to examine the crystallization tendencies of three chemically related amorphous anti-inflammatory agents, etoricoxib, celecoxib, and rofecoxib. Since the molecular mobility is considered as one of the factors affecting the crystallization behavior of a given material, broadband dielectric spectroscopy was used to gain insight into the molecular dynamics of the selected active pharmaceutical ingredients. Interestingly, our experiments did not reveal any significant differences in their relaxation behavior either in the supercooled liquid or in the glassy state. Hence, as a possible explanation for the enhanced physical stability of etoricoxib, its ability to undergo a tautomerization reaction was recognized. The occurrence of intramolecular proton transfer in the disordered etoricoxib was proven experimentally by time-dependent dielectric and infrared (IR) measurements. Additionally, IR spectroscopy combined with density functional theory calculations pointed out that in the etoricoxib drug, being in fact a binary mixture of tautomers, the individual isomers may interact with each other through a hydrogen bonding network. A possible explanation of this issue was achieved by performing dielectric experiments at elevated pressure. Since compression results in etoricoxib recrystallization, the possible influence of pressure on the observed stabilization effect is also carefully discussed.

  8. Thermal grafting of fluorinated molecular monolayers on doped amorphous silicon surfaces

    SciTech Connect

    Sabbah, H.; Zebda, A.; Ababou-Girard, S.; Solal, F.; Godet, C.; Conde, J. P.; Chu, V.

    2009-03-15

    Thermally induced (160-300 deg. C) gas phase grafting of linear alkene molecules (perfluorodecene) was performed on hydrogenated amorphous silicon (a-Si:H) films, either nominally undoped or doped with different boron and phosphorus concentrations. Dense and smooth a-Si:H films were grown using plasma decomposition of silane. Quantitative analysis of in situ x-ray photoelectron spectroscopy indicates the grafting of a single layer of organic molecules. The hydrophobic properties of perfluorodecene-modified surfaces were studied as a function of surface coverage. Annealing experiments in ultrahigh vacuum show the covalent binding and the thermal stability of these immobilized layers up to 370 deg. C; this temperature corresponds to the Si-C bond cleavage temperature. In contrast with hydrogenated crystalline Si(111):H, no heavy wet chemistry surface preparation is required for thermal grafting of alkene molecules on a-Si:H films. A threshold grafting temperature is observed, with a strong dependence on the doping level which produces a large contrast in the molecular coverage for grafting performed at 230 deg. C.

  9. Diffusion mechanism of hydrogen in amorphous silicon - Ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Su, Y.-S.; Pantelides, S. T.

    2001-03-01

    Diffusion of hydrogen in hydrogenated amorphous silicon (a-Si:H) is an important process, but the mechanism is still not well understood and even controversial. The observed activation energy is only about 1.5 eV, whereas the energy to dissociate Si-H bonds is much larger ( 2.5 eV). H is generally believed to migrate as an interstitial, perhaps as in crystalline Si. We report first-principles density-functional molecular dynamics simulations and identify a wealth of processes that occur. The main mechanism for the release of H from Si-H bonds is the conversion of the Si atom to fivefold coordination by the arrival of a floating bond, as suggested by one of us (STP, Phys. Rev. Lett. 58, 1344 (1987)) but the H atom is not released in the interstitial regions. Migration occurs by a bond-interconversion process, with the H atom acting as the analog of a floating bond. Estimates of the diffusion constant are in agreement with observations. Work supported in part by NSF.

  10. Magnetic and Electrical Characteristics of Cobalt-Based Amorphous Materials and Comparison to a Permalloy Type Polycrystalline Material

    NASA Technical Reports Server (NTRS)

    Wieserman, William R.; Schwarze, Gene E.; Niedra, Janis M.

    2005-01-01

    Magnetic component designers are always looking for improved soft magnetic core materials to increase the efficiency, temperature rating and power density of transformers, motors, generators and alternators, and energy density of inductors. In this paper, we report on the experimental investigation of commercially available cobalt-based amorphous alloys which, in their processing, were subjected to two different types of magnetic field anneals: A longitudinal magnetic field anneal or a transverse magnetic field anneal. The longitudinal field annealed material investigated was Metglas 2714A. The electrical and magnetic characteristics of this material were investigated over the frequency range of 1 to 200 kHz and temperature range of 23 to 150 C for both sine and square wave voltage excitation. The specific core loss was lower for the square than the sine wave voltage excitation for the same maximum flux density, frequency and temperature. The transverse magnetic field annealed core materials include Metglas 2714AF and Vacuumschmelze 6025F. These two materials were experimentally characterized over the frequency range of 10 to 200 kHz for sine wave voltage excitation and 23 C only. A comparison of the 2174A to 2714AF found that 2714AF always had lower specific core loss than 2714A for any given magnetic flux density and frequency and the ratio of specific core loss of 2714A to 2714AF was dependent on both magnetic flux density and frequency. A comparison was also made of the 2714A, 2714AF, and 6025F materials to two different tape thicknesses of the polycrystalline Supermalloy material and the results show that 2714AF and 6025F have the lowest specific core loss at 100 kHz over the magnetic flux density range of 0.1 to 0.4 Tesla.

  11. Molecular characterization of energetic materials

    NASA Astrophysics Data System (ADS)

    Saraf, Sanjeev R.

    2003-06-01

    Assessing hazards due to energetic or reactive chemicals is a challenging and complicated task and has received considerable attention from industry and regulatory bodies. Thermal analysis techniques, such as Differential Scanning Calorimeter (DSC), are commonly employed to evaluate reactivity hazards. A simple classification based on energy of reaction (-DeltaH), a thermodynamic parameter, and onset temperature (To), a kinetic parameter, is proposed with the aim of recognizing more hazardous compositions. The utility of other DSC parameter in predicting explosive properties is discussed. Calorimetric measurements to determine reactivity can be resource consuming, so computational methods to predict reactivity hazards present an attractive option. Molecular modeling techniques were employed to gain information at the molecular scale to predict calorimetric data. Molecular descriptors, calculated at density functional level of theory, were correlated with DSC data for mono nitro compounds applying Quantitative Structure Property Relationships (QSPR) and yielded reasonable predictions. Such correlations can be incorporated into a software program for a priori prediction of potential reactivity hazards. Estimations of potential hazards can greatly help to focus attention on more hazardous substances, such as hydroxylamine (HA), which was involved in two major industrial incidents in the past four years. A detailed discussion of HA investigation is presented.

  12. Progress in molecular precursors for electronic materials

    SciTech Connect

    Buhro, W.E.

    1996-09-01

    Molecular-precursor chemistry provides an essential underpinning to all electronic-materials technologies, including photovoltaics and related areas of direct interest to the DOE. Materials synthesis and processing is a rapidly developing field in which advances in molecular precursors are playing a major role. This article surveys selected recent research examples that define the exciting current directions in molecular-precursor science. These directions include growth of increasingly complex structures and stoichiometries, surface-selective growth, kinetic growth of metastable materials, growth of size-controlled quantum dots and quantum-dot arrays, and growth at progressively lower temperatures. Continued progress in molecular-precursor chemistry will afford precise control over the crystal structures, nanostructures, and microstructures of electronic materials.

  13. Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy.

    PubMed

    Brás, Ana R; Noronha, João P; Antunes, Alexandra M M; Cardoso, Maria M; Schönhals, Andreas; Affouard, Frédéric; Dionísio, Madalena; Correia, Natália T

    2008-09-04

    The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as alpha, beta, gamma, and D, were detected and characterized, and a complete relaxation map was given for the first time. The gamma-process has activation energy E a = 31 kJ.mol (-1), typical for local mobility. The weak beta-relaxation, observed in the glassy state as well as in the supercooled state was identified as the genuine Johari-Goldstein process. The temperature dependence of the relaxation time of the alpha-process (dynamic glass transition) does not obey a single VFTH law. Instead two VFTH regimes are observed separated by a crossover temperature, T B = 265 K. From the low temperature VFTH regime, a T g (diel) (tau =100 s) = 226 K was estimated, and a fragility or steepness index m = 93, was calculated showing that ibuprofen is a fragile glass former. The D-process has a Debye-like relaxation function but the temperature dependence of relaxation time also follows the VFTH behavior, with a Vogel temperature and a pre-exponential factor which seem to indicate that its dynamics is governed by the alpha-process. It has similar features as the Debye-type process observed in a variety of associating liquids, related to hydrogen bonding dynamics. The strong tendency of ibuprofen to form hydrogen bonded aggregates such as dimers and trimers either cyclic or linear which seems to control in particular the molecular mobility of ibuprofen was confirmed by IR spectroscopy, electrospray ionization mass spectrometry, and MD simulations.

  14. Role of Inelastic Electron–Phonon Scattering in Electron Transport through Ultra-Scaled Amorphous Phase Change Material Nanostructures

    SciTech Connect

    Liu, Jie; Xu, Xu; Anantram, M.P.

    2014-09-01

    The electron transport through ultra-scaled amorphous phase change material (PCM) GeTe is investigated by using ab initio molecular dynamics, density functional theory, and non-equilibrium Green’s function, and the inelastic electron–phonon scattering is accounted for by using the Born approximation. It is shown that, in ultra-scaled PCM device with 6 nm channel length, < 4 % of the energy carried by the incident electrons from the source is transferred to the atomic lattice before reaching the drain, indicating that the electron transport is largely elastic. Our simulation results show that the inelastic electron–phonon scattering, which plays an important role to excite trapped electrons in bulk PCM devices, exerts very limited influence on the current density value and the shape of current–voltage curve of ultra-scaled PCM devices. The analysis reveals that the Poole–Frenkel law and the Ohm’s law, which are the governing physical mechanisms of the bulk PCM devices, cease to be valid in the ultra-scaled PCM devices.

  15. Yttrium Iron Garnet Thin Films with Very Low Damping Obtained by Recrystallization of Amorphous Material.

    PubMed

    Hauser, Christoph; Richter, Tim; Homonnay, Nico; Eisenschmidt, Christian; Qaid, Mohammad; Deniz, Hakan; Hesse, Dietrich; Sawicki, Maciej; Ebbinghaus, Stefan G; Schmidt, Georg

    2016-02-10

    We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping and extremely narrow linewidth can be observed. For a 56 nm thick layer a damping constant of α = (6.15 ± 1.50) · 10(-5) is found and the linewidth at 9.6 GHz is as small as 1.30 ± 0.05 Oe which are the lowest values for PLD grown thin films reported so far. Even for a 20 nm thick layer a damping constant of α = (7.35 ± 1.40) · 10(-5) is found which is the lowest value for ultrathin films published so far. The FMR linewidth in this case is 3.49 ± 0.10 Oe at 9.6 GHz. Our results not only present a method of depositing thin film YIG of unprecedented quality but also open up new options for the fabrication of thin film complex oxides or even other crystalline materials.

  16. Room temperature phosphorescence of metal-free organic materials in amorphous polymer matrices.

    PubMed

    Lee, Dongwook; Bolton, Onas; Kim, Byoung Choul; Youk, Ji Ho; Takayama, Shuichi; Kim, Jinsang

    2013-04-24

    Developing metal-free organic phosphorescent materials is promising but challenging because achieving emissive triplet relaxation that outcompetes the vibrational loss of triplets, a key process to achieving phosphorescence, is difficult without heavy metal atoms. While recent studies reveal that bright room temperature phosphorescence can be realized in purely organic crystalline materials through directed halogen bonding, these organic phosphors still have limitations to practical applications due to the stringent requirement of high quality crystal formation. Here we report bright room temperature phosphorescence by embedding a purely organic phosphor into an amorphous glassy polymer matrix. Our study implies that the reduced beta (β)-relaxation of isotactic PMMA most efficiently suppresses vibrational triplet decay and allows the embedded organic phosphors to achieve a bright 7.5% phosphorescence quantum yield. We also demonstrate a microfluidic device integrated with a novel temperature sensor based on the metal-free purely organic phosphors in the temperature-sensitive polymer matrix. This unique system has many advantages: (i) simple device structures without feeding additional temperature sensing agents, (ii) bright phosphorescence emission, (iii) a reversible thermal response, and (iv) tunable temperature sensing ranges by using different polymers.

  17. Yttrium Iron Garnet Thin Films with Very Low Damping Obtained by Recrystallization of Amorphous Material

    PubMed Central

    Hauser, Christoph; Richter, Tim; Homonnay, Nico; Eisenschmidt, Christian; Qaid, Mohammad; Deniz, Hakan; Hesse, Dietrich; Sawicki, Maciej; Ebbinghaus, Stefan G.; Schmidt, Georg

    2016-01-01

    We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping and extremely narrow linewidth can be observed. For a 56 nm thick layer a damping constant of α = (6.15 ± 1.50) · 10−5 is found and the linewidth at 9.6 GHz is as small as 1.30 ± 0.05 Oe which are the lowest values for PLD grown thin films reported so far. Even for a 20 nm thick layer a damping constant of α = (7.35 ± 1.40) · 10−5 is found which is the lowest value for ultrathin films published so far. The FMR linewidth in this case is 3.49 ± 0.10 Oe at 9.6 GHz. Our results not only present a method of depositing thin film YIG of unprecedented quality but also open up new options for the fabrication of thin film complex oxides or even other crystalline materials. PMID:26860816

  18. Yttrium Iron Garnet Thin Films with Very Low Damping Obtained by Recrystallization of Amorphous Material

    NASA Astrophysics Data System (ADS)

    Hauser, Christoph; Richter, Tim; Homonnay, Nico; Eisenschmidt, Christian; Qaid, Mohammad; Deniz, Hakan; Hesse, Dietrich; Sawicki, Maciej; Ebbinghaus, Stefan G.; Schmidt, Georg

    2016-02-01

    We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping and extremely narrow linewidth can be observed. For a 56 nm thick layer a damping constant of α = (6.15 ± 1.50) · 10‑5 is found and the linewidth at 9.6 GHz is as small as 1.30 ± 0.05 Oe which are the lowest values for PLD grown thin films reported so far. Even for a 20 nm thick layer a damping constant of α = (7.35 ± 1.40) · 10‑5 is found which is the lowest value for ultrathin films published so far. The FMR linewidth in this case is 3.49 ± 0.10 Oe at 9.6 GHz. Our results not only present a method of depositing thin film YIG of unprecedented quality but also open up new options for the fabrication of thin film complex oxides or even other crystalline materials.

  19. Molecular Mechanisms in Smart Materials

    NASA Astrophysics Data System (ADS)

    Newnham, Robert E.

    1997-03-01

    One of the qualities that distinguishes living systems from inanimate matter is the ability to adapt to changes in the environment. Smart materials have the ability to perform both sensing and actuating functions and are, therefore, capable of imitating this rudimentary aspect of life. Four of the most widely used smart materials are piezoelectric Pb(Zr,Ti)O3, electrostrictive Pb(Mg,Nb)O3, magnetostrictive (Tb,Dy)Fe2, and the shape memory alloy NiTi. All four are ferroic with active domain walls, and two phase transformations which help tune the properties of these active materials. Pb(Zr,Ti)O3 is a ferroelectric ceramic which is cubic at high temperature and becomes ferroelectric on cooling through the Curie temperature. At room temperature, it is poised on a rhombohedral-tetragonal phase boundary which enhances the piezoelectric coefficients. Terfenol, (Tb,Dy)Fe2, is also cubic at high temperature and then becomes magnetic on cooling through its Curie temperature. At room temperature, it too, is poised on rhombohedral-tetragonal transition which enhances its magnetostriction coefficients. Pb(Mg,Nb)O3 and Nitinol (NiTi) are also cubic at high temperatures, and on annealing, transform to a partially ordered state. On further cooling, Pb(Mg,Nb)O3 passes through a diffuse phase transformation at room temperature where it exhibits very large dielectric and electrostrictive coefficients. Just below room temperature, it transforms to a ferroelectric rhombohedral phase. The partially ordered shape memory alloy NiTi undergoes an austenitic (cubic) to martensitic (monoclinic) phase change just above room temperature. It is easily deformed in the martensitic state but recovers its original shape when reheated to austenite. The structural similarities between these four superb actuator materials are remarkable, and provide a key to the development of future smart materials. Remarkable results are also achieved with composite sensors and actuators in which two phases with

  20. Solid-State Spectroscopic Investigation of Molecular Interactions between Clofazimine and Hypromellose Phthalate in Amorphous Solid Dispersions.

    PubMed

    Nie, Haichen; Su, Yongchao; Zhang, Mingtao; Song, Yang; Leone, Anthony; Taylor, Lynne S; Marsac, Patrick J; Li, Tonglei; Byrn, Stephen R

    2016-11-07

    It has been technically challenging to specify the detailed molecular interactions and binding motif between drugs and polymeric inhibitors in the solid state. To further investigate drug-polymer interactions from a molecular perspective, a solid dispersion of clofazimine (CLF) and hypromellose phthalate (HPMCP), with reported superior amorphous drug loading capacity and physical stability, was selected as a model system. The CLF-HPMCP interactions in solid dispersions were investigated by various solid state spectroscopic methods including ultraviolet-visible (UV-vis), infrared (IR), and solid-state NMR (ssNMR) spectroscopy. Significant spectral changes suggest that protonated CLF is ionically bonded to the carboxylate from the phthalyl substituents of HPMCP. In addition, multivariate analysis of spectra was applied to optimize the concentration of polymeric inhibitor used to formulate the amorphous solid dispersions. Most interestingly, proton transfer between CLF and carboxylic acid was experimentally investigated from 2D (1)H-(1)H homonuclear double quantum NMR spectra by utilizing the ultrafast magic-angle spinning (MAS) technique. The molecular interaction pattern and the critical bonding structure in CLF-HPMCP dispersions were further delineated by successfully correlating ssNMR findings with quantum chemistry calculations. These high-resolution investigations provide critical structural information on active pharmaceutical ingredient-polymer interaction, which can be useful for rational selection of appropriate polymeric carriers, which are effective crystallization inhibitors for amorphous drugs.

  1. Influence of polymer molecular weight on in vitro dissolution behavior and in vivo performance of celecoxib:PVP amorphous solid dispersions.

    PubMed

    Knopp, Matthias Manne; Nguyen, Julia Hoang; Becker, Christian; Francke, Nadine Monika; Jørgensen, Erling B; Holm, Per; Holm, René; Mu, Huiling; Rades, Thomas; Langguth, Peter

    2016-04-01

    In this study, the influence of the molecular weight of polyvinylpyrrolidone (PVP) on the non-sink in vitro dissolution and in vivo performance of celecoxib (CCX):PVP amorphous solid dispersions were investigated. The dissolution rate of CCX from the amorphous solid dispersions increased with decreasing PVP molecular weight and crystallization inhibition was increased with increasing molecular weight of PVP, but reached a maximum for PVP K30. This suggested that the crystallization inhibition was not proportional with molecular weight of the polymer, but rather there was an optimal molecular weight where the crystallization inhibition was strongest. Consistent with the findings from the non-sink in vitro dissolution tests, the amorphous solid dispersions with the highest molecular weight PVPs (K30 and K60) resulted in significantly higher in vivo bioavailability (AUC0-24h) compared with pure amorphous and crystalline CCX. A linear relationship between the in vitro and in vivo parameter AUC0-24h indicated that the simple non-sink in vitro dissolution method used in this study could be used to predict the in vivo performance of amorphous solid dispersion with good precision, which enabled a ranking between the different formulations. In conclusion, the findings of this study demonstrated that the in vitro and in vivo performance of CCX:PVP amorphous solid dispersions were significantly controlled by the molecular weight of the polymer. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Molecular understanding and design of zwitterionic materials.

    PubMed

    Shao, Qing; Jiang, Shaoyi

    2015-01-07

    Zwitterionic materials have moieties possessing cationic and anionic groups. This molecular structure leads to unique properties that can be the solutions of various application problems. A typical example is that zwitterionic carboxybetaine (CB) and sulfobetaine (SB) materials resist nonspecific protein adsorption in complex media. Considering the vast number of cationic and anionic groups in the current chemical inventory, there are many possible structural variations of zwitterionic materials. The diversified structures provide the possibility to achieve many desired properties and urge a better understanding of zwitterionic materials to provide design principles. Molecular simulations and modeling are a versatile tool to understand the structure-property relationships of materials at the molecular level. This progress report summarizes recent simulation and modeling studies addressing two fundamental questions regarding zwitterionic materials and their applications as biomaterials. First, what are the differences between zwitterionic and nonionic materials? Second, what are the differences among zwitterionic materials? This report also demonstrates a molecular design of new protein-resistant zwitterionic moieties beyond conventional CB and SB based on design principles developed from these simulation studies. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Structural and thermoelastic properties of crystalline and amorphous TiSi2 phases by tight-binding molecular dynamics

    NASA Astrophysics Data System (ADS)

    Iannuzzi, M.; Miglio, Leo; Celino, M.

    2000-06-01

    We have characterized by total-energy calculations and molecular-dynamics simulations the two crystalline phases (C54 and C49) of TiSi2 in a wide range of temperatures. We have also produced and analyzed the amorphous and the liquid phases. Structural and thermoelastic properties are calculated and reported for all the phases. The molecular-dynamics simulations are based on an original set of parameters for the interatomic potential in the framework of the tight-binding approach. The intrinsic difference between the C54 and C49 phases is addressed and discussed by looking at the structural and the electronic properties.

  4. Molecular Volume and Electronic and Vibrational Polarizibilities for Amorphous LaAlO3

    DTIC Science & Technology

    2004-12-01

    sixfold coordinated stishovite phase, the density increases to 4–4.4 g cm−3. Unfortunately, to our knowledge, density measurements on the bulk amorphous...quartz. The data used to estimate the value of sael +avibd for stishovite were taken from calculations. It is clear, therefore, that one should not neglect...the polarizability of three phases of SiO2, amorphous, a-quartz, and stishovite , as determined from their dielectric constants.ume cannot be assumed

  5. Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase.

    PubMed

    Jeyasingh, Rakesh; Fong, Scott W; Lee, Jaeho; Li, Zijian; Chang, Kuo-Wei; Mantegazza, Davide; Asheghi, Mehdi; Goodson, Kenneth E; Wong, H-S Philip

    2014-06-11

    Phase change materials are widely considered for application in nonvolatile memories because of their ability to achieve phase transformation in the nanosecond time scale. However, the knowledge of fast crystallization dynamics in these materials is limited because of the lack of fast and accurate temperature control methods. In this work, we have developed an experimental methodology that enables ultrafast characterization of phase-change dynamics on a more technologically relevant melt-quenched amorphous phase using practical device structures. We have extracted the crystallization growth velocity (U) in a functional capped phase change memory (PCM) device over 8 orders of magnitude (10(-10) < U < 10(-1) m/s) spanning a wide temperature range (415 < T < 580 K). We also observed direct evidence of non-Arrhenius crystallization behavior in programmed PCM devices at very high heating rates (>10(8) K/s), which reveals the extreme fragility of Ge2Sb2Te5 in its supercooled liquid phase. Furthermore, these crystallization properties were studied as a function of device programming cycles, and the results show degradation in the cell retention properties due to elemental segregation. The above experiments are enabled by the use of an on-chip fast heater and thermometer called as microthermal stage (MTS) integrated with a vertical phase change memory (PCM) cell. The temperature at the PCM layer can be controlled up to 600 K using MTS and with a thermal time constant of 800 ns, leading to heating rates ∼10(8) K/s that are close to the typical device operating conditions during PCM programming. The MTS allows us to independently control the electrical and thermal aspects of phase transformation (inseparable in a conventional PCM cell) and extract the temperature dependence of key material properties in real PCM devices.

  6. High-field electrical transport in amorphous phase-change materials

    NASA Astrophysics Data System (ADS)

    Kaes, Matthias; Le Gallo, Manuel; Sebastian, Abu; Salinga, Martin; Krebs, Daniel

    2015-10-01

    Electrical transport in chalcogenide-based phase change materials is an active area of research owing to the prominent role played by these materials in the field of information technology. Here, we present transport measurements (IV curves) obtained on line-cells of as-deposited amorphous phase change materials (Ge2Sb2Te5, GeTe, Ag4In3Sb66Te27) over a wide voltage and temperature range (300 K to 160 K). The well defined geometry of our devices enables a description of the transport behavior in terms of conductivity vs. electric field. At higher temperatures (300 K ≥ T ≥ 220 K) and low to intermediate fields (F < 20 V/μm), the data can be described within the framework of a previously developed model, which is based on multiple trapping transport together with 3D Poole-Frenkel emission from a two-center Coulomb potential. Based on this model, we observe a temperature dependence of the inter-trap distance, which we can relate to a temperature dependence in the occupation of the defect creating the Coulomb potential governing Poole-Frenkel emission. At higher fields and lower temperatures, the dependency of the IV curve on the electric field can be described by ln(I/I0) = (F/Fc)2. By combining this contribution with that of the Poole-Frenkel emission, we can show that the slope at high fields, Fc, is independent of temperature. We argue that models based on direct tunneling or thermally assisted tunneling from a single defect into the valence band cannot explain the observed behavior quantitatively.

  7. Seebeck and thermal conductivity analysis in amorphous/crystalline {beta}-K{<_2}Bi{<_8}Se{<_13} nanocomposite materials.

    SciTech Connect

    Kyratsi, Th.; Hatzikraniotis, E.; Ioannou, M.; Chung, D. Y.; Tsiaoussis, I.

    2011-01-01

    In this work, ball milling is applied on {beta}-K{sub 2}Bi{sub 8}Se{sub 13} compounds in order to explore the potential of the process for the fabrication of nano-based material. Polycrystalline {beta}-K{sub 2}Bi{sub 8}Se{sub 13}, synthesized from melt, was ball milled under inert atmosphere. Powder x-ray diffraction showed a significantly increased disorder with ball milling time. TEM studies confirmed the presence of nanocrystalline material in an amorphous matrix, suggesting the development of crystalline/amorphous {beta}-K{sub 2}Bi{sub 8}Se{sub 13} nanocomposite material via ball milling process. Seebeck coefficient and thermal conductivity were analyzed based on the effective medium theory and show a significant contribution of a nanocrystalline phase.

  8. A molecular dynamics analysis of ion irradiation of ultrathin amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Qi, J.; Komvopoulos, K.

    2016-09-01

    Molecular dynamics (MD) simulations provide insight into nanoscale problems where continuum description breaks down, such as the modeling of ultrathin films. Amorphous carbon (a-C) films are commonly used as protective overcoats in various contemporary technologies, including microelectromechanical systems, bio-implantable devices, optical lenses, and hard-disk drives. In all of these technologies, the protective a-C film must be continuous and very thin. For example, to achieve high storage densities (e.g., on the order of 1 Tb/in.2) in magnetic recording, the thickness of the a-C film used to protect the magnetic media and the recording head against mechanical wear and corrosion must be 2-3 nm. Inert ion irradiation is an effective post-deposition method for reducing the film thickness, while preserving the mechanical and chemical characteristics. In this study, MD simulations of Ar+ ion irradiated a-C films were performed to elucidate the effects of the ion incidence angle and ion kinetic energy on the film thickness and structure. The MD results reveal that the film etching rate exhibits a strong dependence on the ion kinetic energy and ion incidence angle, with a maximum etching rate corresponding to an ion incidence angle of ˜20°. It is also shown that Ar+ ion irradiation mainly affects the structure of the upper half of the ultrathin a-C film and that carbon atom hybridization is a strong function of the ion kinetic energy and ion incidence angle. The results of this study elucidate the effects of important ion irradiation parameters on the structure and thickness of ultrathin films and provide fundamental insight into the physics of dry etching.

  9. Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

    SciTech Connect

    Guseva, D. V.; Komarov, P. V.; Lyulin, Alexey V.

    2014-03-21

    Constant temperature–constant pressure (NpT) molecular-dynamics computer simulations have been carried out for the united-atom model of a non-crosslinked (1,4) cis-polyisoprene (PI) melt confined between two amorphous, fully coordinated silica surfaces. The Lennard-Jones 12-6 potential was implemented to describe the polymer–silica interactions. The thickness H of the produced PI–silica film has been varied in a wide range, 1 < H/R{sub g} < 8, where R{sub g} is the individual PI chain radius of gyration measured under the imposed confinement. After a thorough equilibration, the PI film stratified structure and polymer segmental dynamics have been studied. The chain structure in the middle of the films resembles that in a corresponding bulk, but the polymer-density profile shows a pronounced ordering of the polymer segments in the vicinity of silica surfaces; this ordering disappears toward the film middles. Tremendous slowing down of the polymer segmental dynamics has been observed in the film surface layers, with the segmental relaxation more than 150 times slower as compared to that in a PI bulk. This effect increases with decreasing the polymer-film thickness. The segmental relaxation in the PI film middles shows additional relaxation process which is absent in a PI bulk. Even though there are fast relaxation processes in the film middle, its overall relaxation is slower as compared to that in a bulk sample. The interpretation of the results in terms of polymer glassy bridges has been discussed.

  10. Lithium potential variations for metastable materials: case study of nanocrystalline and amorphous LiFePO4.

    PubMed

    Zhu, Changbao; Mu, Xiaoke; Popovic, Jelena; Weichert, Katja; van Aken, Peter A; Yu, Yan; Maier, Joachim

    2014-09-10

    Much attention has been paid to metastable materials in the lithium battery field, especially to nanocrystalline and amorphous materials. Nonetheless, fundamental issues such as lithium potential variations have not been pertinently addressed. Using LiFePO4 as a model system, we inspect such lithium potential variations for various lithium storage modes and evaluate them thermodynamically. The conclusions of this work are essential for an adequate understanding of the behavior of electrode materials and even helpful in the search for new energy materials.

  11. Advanced amorphous materials for photovoltaic conversion. Annual report, October 1, 1978-September 30, 1979

    SciTech Connect

    Griffith, R.W.; Kampas, F.J.; Vanier, P.E.; Hirsch, M.D.

    1980-01-01

    The objectives of this project are twofold: (1) to investigate new amorphous semiconductor (a-SC) materials, in which recombination centers are passivated, using plasma deposition techniques; and (2) to characterize the optoelectronic properties pertaining to both majority-carrier and minority-carrier transport in as-deposited films and in devices. The electronic properties of plasma-deposited a-Si:H alloys were studied as functions of oxygen and nitrogen impurities. Over a wide range of processing conditions, features displayed by the data include: (1) anomalous behavior in photoconductivity versus temperature for films deficient in either, or both, impurities (peaks appear that are associated with thermal-quenching processes and supralinearity); and (2) modification to classic behavior in photoconductivity owing to synergistic effects of oxygen and nitrogen. Correlations with photoluminescence were observed. Within the context of an emerging spectroscopy, optical emission spectroscopy was found to be a useful technique for the detection of emitting reactive species in the plasma. The presence of impurities, such as N/sub 2/ and chlorosilanes, was diagnosed.

  12. Disorder-induced amorphization

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Li, Mo

    1997-03-01

    Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.

  13. The toxicological mode of action and the safety of synthetic amorphous silica-a nanostructured material.

    PubMed

    Fruijtier-Pölloth, Claudia

    2012-04-11

    Synthetic amorphous silica (SAS), in the form of pyrogenic (fumed), precipitated, gel or colloidal SAS, has been used in a wide variety of industrial and consumer applications including food, cosmetics and pharmaceutical products for many decades. Based on extensive physico-chemical, ecotoxicology, toxicology, safety and epidemiology data, no environmental or health risks have been associated with these materials if produced and used under current hygiene standards and use recommendations. With internal structures in the nanoscale size range, pyrogenic, precipitated and gel SAS are typical examples of nanostructured materials as recently defined by the International Organisation for Standardisation (ISO). The manufacturing process of these SAS materials leads to aggregates of strongly (covalently) bonded or fused primary particles. Weak interaction forces (van der Waals interactions, hydrogen bonding, physical adhesion) between aggregates lead to the formation of micrometre (μm)-sized agglomerates. Typically, isolated nanoparticles do not occur. In contrast, colloidal SAS dispersions may contain isolated primary particles in the nano-size range which can be considered nano-objects. The size of the primary particle resulted in the materials often being considered as "nanosilica" and in the inclusion of SAS in research programmes on nanomaterials. The biological activity of SAS can be related to the particle shape and surface characteristics interfacing with the biological milieu rather than to particle size. SAS adsorbs to cellular surfaces and can affect membrane structures and integrity. Toxicity is linked to mechanisms of interactions with outer and inner cell membranes, signalling responses, and vesicle trafficking pathways. Interaction with membranes may induce the release of endosomal substances, reactive oxygen species, cytokines and chemokines and thus induce inflammatory responses. None of the SAS forms, including colloidal nano-sized particles, were shown

  14. High-density amorphous ice: Molecular dynamics simulations of the glass transition at 0.3 GPa.

    PubMed

    Seidl, M; Loerting, T; Zifferer, G

    2009-09-21

    Based on several force fields (COMPASS, modified TIP3P and SPC/E) high-density amorphous ice is simulated by use of isothermal-isobaric molecular dynamics at a pressure of p approximately 0.3 GPa in the temperature range from 70 to 300 K. Starting at low temperature a large number of heating/cooling cycles are performed and several characteristic properties (density, total energy, and mobility) are traced as functions of temperature. While the first cycles are showing irreversible structural relaxation effects data points from further cycles are reproducible and give clear evidence for the existence of a glass-to-liquid transition. Although, the observed transition temperatures T(g) are dependent on the actual force field used and slightly dependent on the method adopted the results indicate that high-density amorphous ices may indeed be low-temperature structural proxies of ultraviscous high-density liquids.

  15. Characterizing the Phyllosilicates and Amorphous Phases Found by MSL Using Laboratory XRD and EGA Measurements of Natural and Synthetic Materials

    NASA Technical Reports Server (NTRS)

    Rampe, Elizabeth B.; Morris, Richard V.; Chipera, Steve; Bish, David L.; Bristow, Thomas; Archer, Paul Douglas; Blake, David; Achilles, Cherie; Ming, Douglas W.; Vaniman, David; hide

    2013-01-01

    The Curiosity Rover landed on the Peace Vallis alluvial fan in Gale crater on August 5, 2012. A primary mission science objective is to search for past habitable environments, and, in particular, to assess the role of past water. Identifying the minerals and mineraloids that result from aqueous alteration at Gale crater is essential for understanding past aqueous processes at the MSL landing site and hence for interpreting the site's potential habitability. X-ray diffraction (XRD) data from the CheMin instrument and evolved gas analyses (EGA) from the SAM instrument have helped the MSL science team identify phases that resulted from aqueous processes: phyllosilicates and amorphous phases were measure in two drill samples (John Klein and Cumberland) obtained from the Sheepbed Member, Yellowknife Bay Fm., which is believed to represent a fluvial-lacustrine environment. A third set of analyses was obtained from scoop samples from the Rocknest sand shadow. Chemical data from the APXS instrument have helped constrain the chemical compositions of these secondary phases and suggest that the phyllosilicate component is Mg-enriched and the amorphous component is Fe-enriched, relatively Si-poor, and S- and H-bearing. To refine the phyllosilicate and amorphous components in the samples measured by MSL, we measured XRD and EGA data for a variety of relevant natural terrestrial phyllosilicates and synthetic mineraloids in laboratory testbeds of the CheMin and SAM instruments. Specifically, Mg-saturated smectites and vermiculites were measured with XRD at low relative humidity to understand the behavior of the 001 reflections under Mars-like conditions. Our laboratory XRD measurements suggest that interlayer cation composition affects the hydration state of swelling clays at low RH and, thus, the 001 peak positions. XRD patterns of synthetic amorphous materials, including allophane, ferrihydrite, and hisingerite were used in full-pattern fitting (FULLPAT) models to help

  16. Iron-Based Amorphous-Metals: High-Performance Corrosion-Resistant Materials (HPCRM) Development Final Report

    SciTech Connect

    Farmer, J C; Choi, J; Saw, C; Haslem, J; Day, D; Hailey, P; Lian, T; Rebak, R; Perepezko, J; Payer, J; Branagan, D; Beardsley, B; D'Amato, A; Aprigliano, L

    2009-03-16

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal make this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of these iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  17. Effects of the Terminal Structure, Purity, and Molecular Weight of an Amorphous Conjugated Polymer on Its Photovoltaic Characteristics.

    PubMed

    Kuwabara, Junpei; Yasuda, Takeshi; Takase, Naoto; Kanbara, Takaki

    2016-01-27

    The photovoltaic characteristics of an amorphous polymer containing EDOT and fluorene units were investigated. In particular, the effects of the terminal structure, residual amount of Pd, and molecular weight were systematically investigated. Direct arylation polycondensation of EDOT followed by an established purification method readily afforded polymers with different terminal structures, Pd contents, and molecular weights. Of these factors, the terminal structure of the polymer was a crucial factor affecting the photovoltaic characteristics. For example, the polymer with a Br terminal had a PCE of 2.9% in bulk-heterojunction organic photovoltaics (BHJ OPVs) with a fullerene derivative, whereas the polymer without a Br terminal had a PCE of 4.6% in the same cell configuration. The decreased Pd residues and high molecular weights of the polymers increased the long-term stability of the devices. Moreover, BHJ OPVs containing the high-molecular-weight polymer could be fabricated with an environmentally friendly nonhalogenated solvent.

  18. Thermodynamic and kinetic studies of laser thermal processing of heavily boron-doped amorphous silicon using molecular dynamics

    NASA Astrophysics Data System (ADS)

    Wang, Liguo; Clancy, Paulette; Thompson, Michael O.; Murthy, Cheruvu S.

    2002-09-01

    Laser thermal processing (LTP) has been proposed as a means to avoid unwanted transient enhanced diffusion and deactivation of dopants, especially boron and arsenic, during the formation of ultrashallow junctions. Although experimental studies have been carried out to determine the efficacy of LTP for pure Si and lightly B-doped junctions, the effects of high concentrations of dopants (above 2% B) on the thermodynamic and kinetic properties of the regrown film are unknown. In this study, a classical interatomic potential model [Stillinger-Weber (SW)] is used with a nonequilibrium molecular dynamics computer simulation technique to study the laser thermal processing of heavily B-doped Si in the range 2-10 at. % B. We observe only a small effect of boron concentration on the congruent melting temperature of the B:Si alloy, and thus the narrowing of the "process window" for LTP is predicted to be small. No significant tendency for boron to segregate was observed at either the regrowth front or the buried c-Si interface during fast regrowth. The B-doped region regrew as defect-free crystal with full activation of the boron atoms at low boron concentrations (2%), in good agreement with experiments. As the concentration of boron increased, the number of intrinsic Si defects and boron interstitials in the regrown materials increased, with a minor amount of boron atoms in clusters (<2%). An instability limit for crystal regrowth was observed at around 8%-10% boron atoms during fast regrowth; systems with 10% B showed partial amorphization during regrowth. Comparison with tight-binding quantum mechanical calculations showed that the SW model gives similar diffusivities in the liquid and tendency to cluster, but the lifetimes of the SW clusters are considerably too long (>150 ps, compared to 5 ps in tight binding). The importance of adequate system size is discussed.

  19. Studies of molecular properties of polymeric materials

    NASA Technical Reports Server (NTRS)

    Harries, W. L.; Long, Sheila Ann T.; Long, Edward R., Jr.

    1990-01-01

    Aerospace environment effects (high energy electrons, thermal cycling, atomic oxygen, and aircraft fluids) on polymeric and composite materials considered for structural use in spacecraft and advanced aircraft are examined. These materials include Mylar, Ultem, and Kapton. In addition to providing information on the behavior of the materials, attempts are made to relate the measurements to the molecular processes occurring in the material. A summary and overview of the technical aspects are given along with a list of the papers that resulted from the studies. The actual papers are included in the appendices and a glossary of technical terms and definitions is included in the front matter.

  20. First-principles computation of mantle materials in crystalline and amorphous phases

    NASA Astrophysics Data System (ADS)

    Karki, Bijaya B.

    2015-03-01

    First-principles methods based on density functional theory are used extensively in the investigation of the behavior and properties of mantle materials over broad ranges of pressure, temperature, and composition that are relevant. A review of computational results reported during the last couple of decades shows that essentially all properties including structure, phase transition, equation of state, thermodynamics, elasticity, alloying, conductivity, defects, interfaces, diffusivity, viscosity, and melting have been calculated from first principles. Using MgO, the second most abundant oxide of Earth's mantle, as a primary example and considering many other mantle materials in their crystalline and amorphous phases, we have found that most properties are strongly pressure dependent, sometimes varying non-monotonically and anomalously, with the effects of temperature being systematically suppressed with compression. The overall agreement with the available experimental data is excellent; it is remarkable that the early-calculated results such as shear wave velocities of two key phases, MgO and MgSiO3 perovskite, were subsequently reproduced by experimentation covering almost the entire mantle pressure regime. As covered in some detail, the defect formation and migration enthalpies of key mantle materials increase with pressure. The predicted trend is that partial MgO Schottky defects are energetically most favorable in Mg-silicates but their formation enthalpies are high. So, the diffusion in the mantle is likely to be in the extrinsic regime. Preliminary results on MgO and forsterite hint that the grain boundaries can accommodate point defects (including impurities) and enhance diffusion rates at all pressures. The structures are highly distorted in the close vicinity of the defects and at the interface with excess space. Recent simulations of MgO-SiO2 binary and other silicate melts have found that the melt self-diffusion and viscosity vary by several orders of

  1. Investigation and correlation of drug polymer miscibility and molecular interactions by various approaches for the preparation of amorphous solid dispersions.

    PubMed

    Meng, Fan; Trivino, Anne; Prasad, Dev; Chauhan, Harsh

    2015-04-25

    Curcumin (CUR) was used as a poorly soluble drug whereas polyvinyl pyrrolidone K90 (PVP), Eudragit EPO (EPO), hydroxypropyl methylcellulose E5 (HPMC) and polyethylene glycol 8000 (PEG) were used as hydrophilic polymers. CUR polymer miscibility was evaluated by solubility parameter, melting point depression and glass transition temperature (Tg) measurements. Molecular interactions between CUR and polymers were determined by Fourier-transform infrared spectroscopy (FTIR) and Raman. Amorphous solid dispersions were prepared with CUR-polymer ratio of 70:30 (w/w) by solvent evaporation technique and were evaluated for dissolution enhancement using USP II method. Physical states of solid dispersions were characterized by X-ray diffraction (XRD) whereas thermal behaviors were investigated using modulated differential scanning calorimetry (MDSC). CUR-EPO system showed good miscibility through all the approaches, whereas immiscibility was found in other CUR-polymer systems. CUR-EPO and CUR-HPMC systems showed significant molecular interactions whereas CUR-PVP and CUR-PEG showed no molecular interactions. All solid dispersions showed significant dissolution enhancement with CUR-EPO showing highest dissolution rate during first 1h whereas CUR-HPMC was effective in maintaining high CUR concentrations for 6h. The study highlights the importance of investigating and correlating drug polymer miscibility and molecular interactions by various approaches for successful formulation of amorphous solid dispersions.

  2. Structural Relaxations and Thermodynamic Properties of Molecular Amorphous Solids by Mechanical Milling

    NASA Astrophysics Data System (ADS)

    Tsukushi, I.; Yamamuro, O.; Matsuo, T.

    The organic crystals of tri-O-methyl-β-cyclodextrin (TMCD) and its three clathrate compounds containing benzoic acid (BA), p-nitrobenzoic acid (NBA) and p-hydroxybenzoic acid (HBA), sucrose (SUC), salicin (SAL), phenolphthalein (PP), 1,3,5-tri-α-naphthylbenzene (TNB) were amorphized by milling with a vibrating mill for 2 ˜ 16 hours at room temperature. The amorphization was checked by differential scanning calorimetry (DSC) and X-ray powder diffraction. The heat capacities of crystals, liquid quenched glasses (LQG), and mechanically-milled amorphous solid (MMAS) of TMCD and TNB were measured with an adiabatic calorimeter in the temperature range between 12 and 375 K. For both compounds, the enthalpy relaxation of MMAS appeared in the wide temperature range below Tg and the released configurational enthalpy was much larger than that of LQG, indicating that MMAS is more disordered and strained than LQG.

  3. Solar Cosmic-ray Interaction with Protoplanetary Disks: Production of Short-lived Radionuclides and Amorphization of Crystalline Material

    NASA Astrophysics Data System (ADS)

    Trappitsch, R.; Ciesla, F. J.

    2015-05-01

    Solar cosmic-ray (SCR) interactions with a protoplanetary disk have been invoked to explain several observations of primitive planetary materials. In our own Solar System, the presence of short-lived radionuclides (SLRs) in the oldest materials has been attributed to spallation reactions induced in phases that were irradiated by energetic particles in the solar nebula. Furthermore, observations of other protoplanetary disks show a mixture of crystalline and amorphous grains, though no correlation between grain crystallinity and disk or stellar properties have been identified. As most models for the origin of crystalline grains would predict such correlations, it was suggested that amorphization by stellar cosmic-rays may be masking or erasing such correlations. Here we quantitatively investigate these possibilities by modeling the interaction of energetic particles emitted by a young star with the surrounding protoplanetary disk. We do this by tracing the energy evolution of SCRs emitted from the young star through the disk and model the amount of time that dust grains would spend in regions where they would be exposed to these particles. We find that this irradiation scenario cannot explain the total SLR content of the solar nebula; however, this scenario could play a role in the amorphization of crystalline material at different locations or epochs of the disk over the course of its evolution.

  4. SOLAR COSMIC-RAY INTERACTION WITH PROTOPLANETARY DISKS: PRODUCTION OF SHORT-LIVED RADIONUCLIDES AND AMORPHIZATION OF CRYSTALLINE MATERIAL

    SciTech Connect

    Trappitsch, R.; Ciesla, F. J.

    2015-05-20

    Solar cosmic-ray (SCR) interactions with a protoplanetary disk have been invoked to explain several observations of primitive planetary materials. In our own Solar System, the presence of short-lived radionuclides (SLRs) in the oldest materials has been attributed to spallation reactions induced in phases that were irradiated by energetic particles in the solar nebula. Furthermore, observations of other protoplanetary disks show a mixture of crystalline and amorphous grains, though no correlation between grain crystallinity and disk or stellar properties have been identified. As most models for the origin of crystalline grains would predict such correlations, it was suggested that amorphization by stellar cosmic-rays may be masking or erasing such correlations. Here we quantitatively investigate these possibilities by modeling the interaction of energetic particles emitted by a young star with the surrounding protoplanetary disk. We do this by tracing the energy evolution of SCRs emitted from the young star through the disk and model the amount of time that dust grains would spend in regions where they would be exposed to these particles. We find that this irradiation scenario cannot explain the total SLR content of the solar nebula; however, this scenario could play a role in the amorphization of crystalline material at different locations or epochs of the disk over the course of its evolution.

  5. Effect of horizontal molecular orientation on triplet-exciton diffusion in amorphous organic films

    NASA Astrophysics Data System (ADS)

    Sawabe, T.; Takasu, I.; Yonehara, T.; Ono, T.; Yoshida, J.; Enomoto, S.; Amemiya, I.; Adachi, C.

    2012-09-01

    Triplet harvesting is a candidate technology for highly efficient and long-life white OLEDs, where green or red phosphorescent emitters are activated by the triplet-excitons diffused from blue fluorescent emitters. We examined two oxadiazole-based electron transport materials with different horizontal molecular orientation as a triplet-exciton diffusion layer (TDL) in triplet-harvesting OLEDs. The device characteristics and the transient electroluminescent analyses of the red phosphorescent emitter showed that the triplet-exciton diffusion was more effective in the highly oriented TDL. The results are ascribed to the strong orbital overlap between the oriented molecules, which provides rapid electron exchange (Dexter energy transfer) in the TDL.

  6. Reduction of Photoluminescence Quenching by Deuteration of Ytterbium-Doped Amorphous Carbon-Based Photonic Materials.

    PubMed

    Hsu, Hui-Lin; Leong, Keith R; Teng, I-Ju; Halamicek, Michael; Juang, Jenh-Yih; Jian, Sheng-Rui; Qian, Li; Kherani, Nazir P

    2014-08-06

    In situ Yb-doped amorphous carbon thin films were grown on Si substrates at low temperatures (<200 °C) by a simple one-step RF-PEMOCVD system as a potential photonic material for direct integration with Si CMOS back end-of-line processing. Room temperature photoluminescence around 1 µm was observed via direct incorporation of optically active Yb(3+) ions from the selected Yb(fod)₃ metal-organic compound. The partially fluorinated Yb(fod)₃ compound assists the suppression of photoluminescence quenching by substitution of C-H with C-F bonds. A four-fold enhancement of Yb photoluminescence was demonstrated via deuteration of the a-C host. The substrate temperature greatly influences the relative deposition rate of the plasma dissociated metal-organic species, and hence the concentration of the various elements. Yb and F incorporation are promoted at lower substrate temperatures, and suppressed at higher substrate temperatures. O concentration is slightly elevated at higher substrate temperatures. Photoluminescence was limited by the concentration of Yb within the film, the concentration of Yb ions in the +3 state, and the relative amount of quenching due to the various de-excitation pathways associated with the vibrational modes of the host a-C network. The observed wide full-width-at-half-maximum photoluminescence signal is a result of the variety of local bonding environments due to the a-C matrix, and the bonding of the Yb(3+) ions to O and/or F ions as observed in the X-ray photoelectron spectroscopy analyses.

  7. Reduction of Photoluminescence Quenching by Deuteration of Ytterbium-Doped Amorphous Carbon-Based Photonic Materials

    PubMed Central

    Hsu, Hui-Lin; Leong, Keith R.; Teng, I-Ju; Halamicek, Michael; Juang, Jenh-Yih; Jian, Sheng-Rui; Qian, Li; Kherani, Nazir P.

    2014-01-01

    In situ Yb-doped amorphous carbon thin films were grown on Si substrates at low temperatures (<200 °C) by a simple one-step RF-PEMOCVD system as a potential photonic material for direct integration with Si CMOS back end-of-line processing. Room temperature photoluminescence around 1 µm was observed via direct incorporation of optically active Yb3+ ions from the selected Yb(fod)3 metal-organic compound. The partially fluorinated Yb(fod)3 compound assists the suppression of photoluminescence quenching by substitution of C–H with C–F bonds. A four-fold enhancement of Yb photoluminescence was demonstrated via deuteration of the a-C host. The substrate temperature greatly influences the relative deposition rate of the plasma dissociated metal-organic species, and hence the concentration of the various elements. Yb and F incorporation are promoted at lower substrate temperatures, and suppressed at higher substrate temperatures. O concentration is slightly elevated at higher substrate temperatures. Photoluminescence was limited by the concentration of Yb within the film, the concentration of Yb ions in the +3 state, and the relative amount of quenching due to the various de-excitation pathways associated with the vibrational modes of the host a-C network. The observed wide full-width-at-half-maximum photoluminescence signal is a result of the variety of local bonding environments due to the a-C matrix, and the bonding of the Yb3+ ions to O and/or F ions as observed in the X-ray photoelectron spectroscopy analyses. PMID:28788152

  8. Molecular Rotors Built in Porous Materials.

    PubMed

    Comotti, Angiolina; Bracco, Silvia; Sozzani, Piero

    2016-09-20

    Molecules and materials can show dynamic structures in which the dominant mechanism is rotary motion. The single mobile elements are defined as "molecular rotors" and exhibit special properties (compared with their static counterparts), being able in perspective to greatly modulate the dielectric response and form the basis for molecular motors that are designed with the idea of making molecules perform a useful mechanical function. The construction of ordered rotary elements into a solid is a necessary feature for such design, because it enables the alignment of rotors and the fine-tuning of their steric and dipolar interactions. Crystal surfaces or bulk crystals are the most suitable to adapt rotors in 2D or 3D arrangements and engineer juxtaposition of the rotors in an ordered way. Nevertheless, it is only in recent times that materials showing porosity and remarkably low density have undergone tremendous development. The characteristics of large free volume combine well with the virtually unhindered motion of the molecular rotors built into their structure. Indeed, the molecular rotors are used as struts in porous covalent and supramolecular architectures, spanning both hybrid and fully organic materials. The modularity of the approach renders possible a variety of rotor geometrical arrangements in both robust frameworks stable up to 850 K and self-assembled molecular materials. A nanosecond (fast dynamics) motional regime can be achieved at temperatures lower than 240 K, enabling rotor arrays operating in the solid state even at low temperatures. Furthermore, in nanoporous materials, molecular rotors can interact with the diffusing chemical species, be they liquids, vapors, or gases. Through this chemical intervention, rotor speed can be modulated at will, enabling a new generation of rotor-containing materials sensitive to guests. In principle, an applied electric field can be the stimulus for chemical release from porous materials. The effort needed to

  9. Pressure-induced structural change from low-density to high-density amorphous ice by molecular-dynamics simulations

    NASA Astrophysics Data System (ADS)

    Hoshino, K.; Yoshikawa, T.; Munejiri, S.

    2011-01-01

    We have investigated the pressure dependence of the structure of amorphous ices by molecular-dynamics simulations to clarify the characteristic features of the structural change from the low-density amorphous (LDA) ice to the high-density amorphous (HDA) ice. We have found that, with increasing pressure at the temperature of 77 K, (1) the mean-square-displacement and its fluctuation as a function of time decrease, (2) the second peak of the oxygen-oxygen (O sbnd O) correlation function g(r) shifts to shorter distances and changes its shape drastically, e.g. it splits into two peaks, though the first peak remains almost same, (3) the average coordination number estimated from the first peak of g(r) increases from 4 to 5, (4) the broad peak of the O sbnd O sbnd O bond-angle distribution around 110° decreases and shifts towards 60°. From these results we conclude that the four-fold coordinated tetrahedral local structure in LDA ice changes to the five-fold coordinated structure in HDA ice, where the 'fifth' neighboring water molecule corresponds to the 'interstitial' water molecule.

  10. Correlation of inhibitory effects of polymers on indomethacin precipitation in solution and amorphous solid crystallization based on molecular interaction.

    PubMed

    Chauhan, Harsh; Kuldipkumar, Anuj; Barder, Timothy; Medek, Ales; Gu, Chong-Hui; Atef, Eman

    2014-02-01

    To correlate the polymer's degree of precipitation inhibition of indomethacin in solution to the amorphous stabilization in solid state. Precipitation of indomethacin (IMC) in presence of polymers was continuously monitored by a UV spectrophotometer. Precipitates were characterized by PXRD, IR and SEM. Solid dispersions with different polymer to drug ratios were prepared using solvent evaporation. Crystallization of the solid dispersion was monitored using PXRD. Modulated differential scanning calorimetry (MDSC), IR, Raman and solid state NMR were used to explore the possible interactions between IMC and polymers. PVP K90, HPMC and Eudragit E100 showed precipitation inhibitory effects in solution whereas Eudragit L100, Eudragit S100 and PEG 8000 showed no effect on IMC precipitation. The rank order of precipitation inhibitory effect on IMC was found to be PVP K90 > Eudragit E100 > HPMC. In the solid state, polymers showing precipitation inhibitory effect also exhibited amorphous stabilization of IMC with the same rank order of effectiveness. IR, Raman and solid state NMR studies showed that rank order of crystallization inhibition correlates with strength of molecular interaction between IMC and polymers. Correlation is observed in the polymers ability to inhibit precipitation in solution and amorphous stabilization in the solid state for IMC and can be explained by the strength of drug polymer interactions.

  11. Investigating miscibility and molecular mobility of nifedipine-PVP amorphous solid dispersions using solid-state NMR spectroscopy.

    PubMed

    Yuan, Xiaoda; Sperger, Diana; Munson, Eric J

    2014-01-06

    Solid-state NMR (SSNMR) (1)H T1 and T1ρ relaxation times were used to evaluate the miscibility of amorphous solid dispersions of nifedipine (NIF) and polyvinylpyrrolidone (PVP) prepared by three different methods: melt quenching in the typical lab setting, spray drying and melt quenching in the NMR rotor while spinning. Of the five compositions prepared by melt quenching in the lab setting, the 95:5 and 90:10 NIF:PVP (w:w) amorphous solid dispersions were not miscible while 75:25, 60:40, and 50:50 NIF:PVP dispersions were miscible by the (1)H T1ρ measurements. The domain size of the miscible systems was estimated to be less than 4.5 nm. Amorphous solid dispersions with composition of 90:10 NIF:PVP prepared by spray drying and melt quenching in the NMR rotor showed miscibility by (1)H T1ρ values. Variable-temperature SSNMR (1)H T1ρ relaxation measurements revealed a change in relaxation time at approximately 20 °C below Tg, suggesting increased molecular mobility above that temperature.

  12. Computational Nanotechnology Molecular Electronics, Materials and Machines

    NASA Technical Reports Server (NTRS)

    Srivastava, Deepak; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    This presentation covers research being performed on computational nanotechnology, carbon nanotubes and fullerenes at the NASA Ames Research Center. Topics cover include: nanomechanics of nanomaterials, nanotubes and composite materials, molecular electronics with nanotube junctions, kinky chemistry, and nanotechnology for solid-state quantum computers using fullerenes.

  13. Spectroscopic characterization of the interaction of molecular hydrogen with germanosilicate materials

    NASA Astrophysics Data System (ADS)

    Metroke, Tammy Lauren

    1997-12-01

    Scope and method of study. The purpose of this study was to (a) develop a complete structural model for germanosilicate materials as a function of catalyst, germania concentration, and temperature and (b) spectroscopically study the interaction of molecular hydrogen with sol-gel derived germanosilicate materials. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and multinuclear (1H, 29Si CP/MAS, 29Si MAS, variable temperature 1H, and 73Ge) nuclear magnetic resonance spectroscopies were used. Findings and conclusions. The surface and bulk structures of acid- and base-catalyzed germanosilicate materials were found to be phase separated. Base-catalyzed germanosilicate materials were composed of small germania crystallites dispersed in an amorphous silica matrix, whereas acid-catalyzed materials were found to be composed of larger blocks of hexagonal crystalline germania dispersed in an amorphous silica matrix. After heating to 600oC, the surface of base-catalyzed germanosilicate materials contained primarily isolated Si-OH and Ge-OH groups. Acid-catalyzed germanosilicate materials contained higher concentrations of water and less isolated Si-OH and Ge-OH groups on the surface after heating to 600oC. A surface model illustrating the structure of acid- and base-catalyzed gels after heating to 600oC was presented. Acid-catalyzed materials reacted with molecular hydrogen to form molecular water. Base-catalyzed materials reacted with molecular hydrogen to form hydrogen-bonded water. Stable hydrides were not produced in the reaction with molecular hydrogen. A mechanism for the formation of water was proposed, based on the interaction of hydrogen with defect peroxy linkages, to explain the changes.

  14. Study of ice cluster impacts on amorphous silica using the ReaxFF reactive force field molecular dynamics simulation method

    SciTech Connect

    Rahnamoun, A.; Duin, A. C. T. van

    2016-03-07

    We study the dynamics of the collisions between amorphous silica structures and amorphous and crystal ice clusters with impact velocities of 1 km/s, 4 km/s, and 7 km/s using the ReaxFF reactive molecular dynamics simulation method. The initial ice clusters consist of 150 water molecules for the amorphous ice cluster and 128 water molecules for the crystal ice cluster. The ice clusters are collided on the surface of amorphous fully oxidized and suboxide silica. These simulations show that at 1 km/s impact velocities, all the ice clusters accumulate on the surface and at 4 km/s and 7 km/s impact velocities, some of the ice cluster molecules bounce back from the surface. At 4 km/s and 7 km/s impact velocities, few of the water molecules dissociations are observed. The effect of the second ice cluster impacts on the surfaces which are fully covered with ice, on the mass loss/accumulation is studied. These studies show that at 1 km/s impacts, the entire ice cluster accumulates on the surface at both first and second ice impacts. At higher impact velocities, some ice molecules which after the first ice impacts have been attached to the surface will separate from the surface after the second ice impacts at 7 km/s impact velocity. For the 4 km/s ice cluster impact, ice accumulation is observed for the crystal ice cluster impacts and ice separation is observed for the amorphous ice impacts. Observing the temperatures of the ice clusters during the collisions indicates that the possibility of electron excitement at impact velocities less than 10 km/s is minimal and ReaxFF reactive molecular dynamics simulation can predict the chemistry of these hypervelocity impacts. However, at impact velocities close to 10 km/s the average temperature of the impacting ice clusters increase to about 2000 K, with individual molecules occasionally reaching temperatures of over 8000 K and thus it will be prudent to consider the concept of electron excitation at

  15. Effects of chitosan molecular weight on the physical and dissolution characteristics of amorphous curcumin-chitosan nanoparticle complex.

    PubMed

    Yu, Hong; Nguyen, Minh-Hiep; Hadinoto, Kunn

    2017-09-11

    To investigate the effects of varying molecular weight (MW) of chitosan (CHI) used in the complexation with curcumin (CUR) on the physical and dissolution characteristics of the amorphous CUR-CHI nanoparticle complex produced. Amorphous CUR-CHI nanoparticle complex (or CUR nanoplex in short) recently emerged as a promising bioavailability enhancement strategy of CUR attributed to its fast dissolution, supersaturation generation capability, and simple preparation. Existing CUR nanoplex prepared using low MW CHI, however, exhibited poor colloidal stability during storage. Herein we hypothesized that the colloidal stability could be improved by using CHI of higher MW. The effects of this approach on the nanoplex's other characteristics were simultaneously investigated. The CUR nanoplex was prepared by electrostatically driven self-assembled complexation between CUR and oppositely charged CHI of three different MWs (i.e. low, medium, and high). Besides colloidal stability, the effects of MW variation were investigated for the nanoplex's (1) other physical characteristics (i.e. size, zeta potential, CUR payload, amorphous state stability), (2) preparation efficiency (i.e. CUR utilization rate, yield), and (3) dissolutions under sink condition and supersaturation generation. CUR nanoplex prepared using CHI of high MW exhibited improved colloidal stability, larger size, superior morphology, and prolonged supersaturation generation. On the other hand, the effects of MW variation on the payload, amorphous state stability, preparation efficiency, and dissolution under sink condition were found to be insignificant. Varying MW of CHI used was an effective means to improve certain aspects of the CUR nanoplex characteristics with minimal adverse effects on the others.

  16. Structural properties of Ge-S amorphous networks in relationship with rigidity transitions: An ab initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Boolchand, P.; Micoulaut, M.

    2017-09-01

    We investigate the amorphous GexS100 -x (with 10 ≤x ≤40 ) system from ab initio simulations. Results show a very good agreement with experimental findings from diffraction and the topology of the obtained structural models is further analyzed and compared with the selenide analog. Differences emerge, however, from a detailed molecular dynamics analysis showing that the ring statistics and the homopolar defects do not evolve similarly. The findings are also connected to rigidity theory, which provides a topological approach to decoding the physics of network glasses, and the effects of composition and temperature are analyzed.

  17. Preservation of amorphous ultrafine material: A proposed proxy for slip during recent earthquakes on active faults

    NASA Astrophysics Data System (ADS)

    Hirono, Tetsuro; Asayama, Satoru; Kaneki, Shunya; Ito, Akihiro

    2016-11-01

    The criteria for designating an “Active Fault” not only are important for understanding regional tectonics, but also are a paramount issue for assessing the earthquake risk of faults that are near important structures such as nuclear power plants. Here we propose a proxy, based on the preservation of amorphous ultrafine particles, to assess fault activity within the last millennium. X-ray diffraction data and electron microscope observations of samples from an active fault demonstrated the preservation of large amounts of amorphous ultrafine particles in two slip zones that last ruptured in 1596 and 1999, respectively. A chemical kinetic evaluation of the dissolution process indicated that such particles could survive for centuries, which is consistent with the observations. Thus, preservation of amorphous ultrafine particles in a fault may be valuable for assessing the fault’s latest activity, aiding efforts to evaluate faults that may damage critical facilities in tectonically active zones.

  18. Preservation of amorphous ultrafine material: A proposed proxy for slip during recent earthquakes on active faults

    PubMed Central

    Hirono, Tetsuro; Asayama, Satoru; Kaneki, Shunya; Ito, Akihiro

    2016-01-01

    The criteria for designating an “Active Fault” not only are important for understanding regional tectonics, but also are a paramount issue for assessing the earthquake risk of faults that are near important structures such as nuclear power plants. Here we propose a proxy, based on the preservation of amorphous ultrafine particles, to assess fault activity within the last millennium. X-ray diffraction data and electron microscope observations of samples from an active fault demonstrated the preservation of large amounts of amorphous ultrafine particles in two slip zones that last ruptured in 1596 and 1999, respectively. A chemical kinetic evaluation of the dissolution process indicated that such particles could survive for centuries, which is consistent with the observations. Thus, preservation of amorphous ultrafine particles in a fault may be valuable for assessing the fault’s latest activity, aiding efforts to evaluate faults that may damage critical facilities in tectonically active zones. PMID:27827413

  19. The Glass Transition of Driven Molecular Materials

    NASA Astrophysics Data System (ADS)

    Descamps, M.; Willart, J. F.; Aumelas, A.

    2008-02-01

    There are many cases of practical interest where materials are maintained in nonequilibrium conditions by some external dynamical forcing: typical examples of these driven materials are provided by irradiation, grinding, extrusion…Contrary to usual phase transitions which are properly addressed by thermal equilibrium states, equilibrium and irreversible thermodynamics, no such general framework is available for driven systems. The purpose of this paper is to show some examples of phase transformations in driven molecular materials. These materials are considered because they are extremely sensitive to external disturbances and are generally very good glass formers. This allows investigating more easily a broad range of the parameters which possibly influence the nature of the end product. We will examine mainly the effect of grinding. Contrary to other materials, metals or minerals, systematic investigations of transformations induced by grinding of molecular materials have not yet been done despite the practical and fundamental interests of such investigations in pharmaceutical and agro-chemical science. We will address several modes of interconversions between crystalline and glassy states of the same compound. We will further discuss specific processing effects on the physical state of the glass itself. It will be shown from these investigations that rationalization and possibilities of prediction are emerging. The use of effective temperature concepts to describe the end product of milling will be discussed. These findings may be of general concern for driven materials of any chemical nature.

  20. A Generalized Theory of Electrical Characteristics of Schottky Barriers for Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Gupta, H. M.

    1997-12-01

    In the present paper, we discuss a generalized theory of electrical characteristics for amorphous semiconductor (or insulator) Schottky barriers, considering: (i) surface states, (ii) doping impurity states at a single energy level and (iii) energetically distributed bulk impurity states. We also consider a thin oxide layer (10 Å) between metal and semiconductor. We develop current versus applied potential characteristics considering the variation of the Fermi level very close to contact inside the semiconductor and decrease in barrier height due to the image force effect as well as potential fall on the oxide layer. Finally, we discuss the importance of each parameter, i.e. surface states, distributed impurity states, doping impurity states, thickness of oxide layer etc. on the log I versus applied potential characteristics. The present theory is also applicable for intimate contact, i.e. metal-semiconductor contact, crystalline material structures or for Schottky barriers in insulators or polymers. Dans cet article nous proposons une théorie géneralisée pour les charactéristiques éléctriques de barrière Schottky en semiconducteurs amorphes (ou isolants), tout en considérant: (i) des états de surface, (ii) des états d'impuretés dopées dans un seul niveau d'énergie, (iii) des états d'impuretés massives distribuées en énergie. Nous considérons aussi une fine couche d'oxide (10 Å) entre le métal et le semiconducteur. Nous développons les charactéristiques du courrant versus potentiel appliquée tout en considérant des variations du niveau de Fermi très proche du contact à l'intérieur du semiconducteur et une décroissance de l'hauteur de la barrière dûe aux effects de la force d'image ainsi qu'au chute de potentiel dans la couche d'oxide. Finalement nous discutons l'importance de chaque paramètre, i.e. états de surface, états d'impuretés distribuées, états d'impuretés dopées, épaisseur de la couche d'oxide, etc. sur les charact

  1. Amorphous material from the rapid evaporation of basalt weathering solutions: Implications for Amazonian alteration

    NASA Astrophysics Data System (ADS)

    Smith, R.; Horgan, B. H. N.; Christensen, P. R.

    2016-12-01

    Amorphous silicates of ambiguous origin are detected on the Martian surface through orbiter and rover measurements. Secondary amorphous silicates might precipitate from rapidly evaporating weathering solutions under Amazonian ( 3 BYA - present) surface conditions. Yet, such phases are poorly understood and are underrepresented in infrared spectral libraries. Amazonian weathering was simulated by dissolving two basaltic tephra compositions in DI water under two different atmospheres (1: oxidizing and 2: simulated Martian). The resulting weathering solutions were rapidly evaporated into sample cups. Precipitate mineralogy was studied using visible and near-infrared (VNIR) and thermal-infrared (TIR) spectroscopy and x-ray diffraction (XRD). Solution compositions were analyzed using Ion Chromatography (IC) and Inductively Coupled Plasma Mass-Spectroscopy (ICP-MS). All experiments formed hydrated amorphous silicates and nanophase iron-oxides, but precipitates from solutions formed under a simulated Martian atmosphere also contain crystalline carbonate and sulfate minerals. The oxidizing atmosphere precipitates are also S-bearing, based on solution chemistry, but no crystalline sulfates were unambiguously detected. The TIR spectra of all samples exhibit a spectral feature at 460 cm-1 that was previously only known to be present in the spectra of basaltic glass and some terrestrial palagonitized basalt samples, indicating that the precipitates are new to spectral libraries. Ongoing characterization will help determine the composition and structure of the amorphous phases. TIR spectral and XRD instruments on the Spirit and Mars Science Laboratory (MSL) rovers both indicate high abundances of basaltic glass in rock and soil samples, despite chemical evidence for aqueous alteration. Our results suggest that these measurements are consistent with secondary amorphous silicates formed through the rapid evaporation of basalt weathering solutions. Thus, transient water

  2. Insights into Silicate and Oxide Melt Structure from Amorphous, Non-Glass-Forming Materials

    NASA Astrophysics Data System (ADS)

    Stebbins, J. F.

    2015-12-01

    Many silicate and oxide liquids of interest in the Earth sciences and in technology cannot readily be quenched to glasses, either because of low silica contents (and hence low viscosity at the melting point and accompanying liquid 'fragility') or because of liquid-liquid unmixing at high temperature. Although in-situ, high temperature structural tools have been in use for decades and are rapidly developing, many methods are still most informative for glass samples quenched to ambient pressure and temperature, e.g. high-resolution solid-state NMR. Amorphous oxides, including alumina and silicate compositions, have widespread technological applications. These are generally deposited by a variety of high-energy sputtering methods, as films of thicknesses of 10's to 100's of nm. Using Al-27, Si-29, and O-17 NMR, we have recently shown that for such films, very similar short-range structure is seen in materials made by very different kinetic pathways, such as sol-gel synthesis vs. ion-beam sputtering. This path-independent structure suggests that these materials pass through transient equilibrium states during their formation, probably that of deeply supercooled liquids just above glass transition temperatures. In the HfO2-SiO2 and ZrO2-SiO2 systems, for example, samples have well-resolved O-17 NMR spectra, allowing quantitation of O sites with only Hf(Zr) neighbors (so-called "free" oxide ions), with mixed Hf(Zr) and Si neighbors, and Si only. The observed oxygen speciation agrees well with a simple thermodynamic model of one of the most fundamental equilibria in silicate systems, namely the reaction of bridging (Si-O-Si) and "free" (e.g. OHf3 and OHf4) oxide ions to produce "non-bridging" oxygens (e.g. Si-OHf2). This new approach to sampling such structural equilibria in compositions far outside the range of normal glass-forming liquids may provide new insights into more geological compositions as well, as well as in more general models of silicate melt chemistry.

  3. Amorphous thin film ruthenium oxide as an electrode material for electrochemical capacitors

    SciTech Connect

    Jow, T.R.; Zheng, J.P.

    1995-12-31

    Ruthenium oxide thin films of an amorphous phase were successfully prepared on a titanium (Ti) substrate at temperatures below 160 C. The sol-gel process using metal alkoxide precursor in nonaqueous solvents was used to prepare these films. The preliminary results showed that a specific capacitance of 430 F/g can be achieved for amorphous ruthenium oxide electrode in sulfuric acid. Films prepared by this method are compared with the films prepared by the thermal decomposition of the aqueous ruthenium chloride solution at temperatures above 300 C. The specific capacitance, the crystalline structure, and the surface morphology of these films as a function of the preparation temperature were also discussed.

  4. Solubility of crystalline organic compounds in high and low molecular weight amorphous matrices above and below the glass transition by zero enthalpy extrapolation.

    PubMed

    Amharar, Youness; Curtin, Vincent; Gallagher, Kieran H; Healy, Anne Marie

    2014-09-10

    Pharmaceutical applications which require knowledge of the solubility of a crystalline compound in an amorphous matrix are abundant in the literature. Several methods that allow the determination of such data have been reported, but so far have only been applicable to amorphous polymers above the glass transition of the resulting composites. The current work presents, for the first time, a reliable method for the determination of the solubility of crystalline pharmaceutical compounds in high and low molecular weight amorphous matrices at the glass transition and at room temperature (i.e. below the glass transition temperature), respectively. The solubilities of mannitol and indomethacin in polyvinyl pyrrolidone (PVP) K15 and PVP K25, respectively were measured at different temperatures. Mixtures of undissolved crystalline solute and saturated amorphous phase were obtained by annealing at a given temperature. The solubility at this temperature was then obtained by measuring the melting enthalpy of the crystalline phase, plotting it as a function of composition and extrapolating to zero enthalpy. This new method yielded results in accordance with the predictions reported in the literature. The method was also adapted for the measurement of the solubility of crystalline low molecular weight excipients in amorphous active pharmaceutical ingredients (APIs). The solubility of mannitol, glutaric acid and adipic acid in both indomethacin and sulfadimidine was experimentally determined and successfully compared with the difference between their respective calculated Hildebrand solubility parameters. As expected from the calculations, the dicarboxylic acids exhibited a high solubility in both amorphous indomethacin and sulfadimidine, whereas mannitol was almost insoluble in the same amorphous phases at room temperature. This work constitutes the first report of the methodology for determining an experimentally measured solubility for a low molecular weight crystalline solute

  5. Mapping minerals, amorphous materials, environmental materials, vegetation, water, ice and snow, and other materials: The USGS tricorder algorithm

    NASA Technical Reports Server (NTRS)

    Clark, Roger N.; Swayze, Gregg A.

    1995-01-01

    One of the challenges of Imaging Spectroscopy is the identification, mapping and abundance determination of materials, whether mineral, vegetable, or liquid, given enough spectral range, spectral resolution, signal to noise, and spatial resolution. Many materials show diagnostic absorption features in the visual and near infrared region (0.4 to 2.5 micrometers) of the spectrum. This region is covered by the modern imaging spectrometers such as AVIRIS. The challenge is to identify the materials from absorption bands in their spectra, and determine what specific analyses must be done to derive particular parameters of interest, ranging from simply identifying its presence to deriving its abundance, or determining specific chemistry of the material. Recently, a new analysis algorithm was developed that uses a digital spectral library of known materials and a fast, modified-least-squares method of determining if a single spectral feature for a given material is present. Clark et al. made another advance in the mapping algorithm: simultaneously mapping multiple minerals using multiple spectral features. This was done by a modified-least-squares fit of spectral features, from data in a digital spectral library, to corresponding spectral features in the image data. This version has now been superseded by a more comprehensive spectral analysis system called Tricorder.

  6. Universal features of amorphous plasticity

    NASA Astrophysics Data System (ADS)

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-07-01

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon.

  7. Universal features of amorphous plasticity

    PubMed Central

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-01-01

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon. PMID:28671191

  8. Universal features of amorphous plasticity.

    PubMed

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-07-03

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon.

  9. Molecular dynamics simulation of benzene in graphite and amorphous carbon slit pores.

    PubMed

    Fomin, Yu D

    2013-11-15

    It is well known that confining a liquid into a pore strongly alters the liquid behavior. Investigations of the effect of confinement are of great importance for many scientific and technological applications. Here, we present a study of the behavior of benzene confined in carbon slit pores. Two types of pores are considered-graphite and amorphous carbon ones. We show that the effect of different pore structure is of crucial importance for the benzene behavior. Copyright © 2013 Wiley Periodicals, Inc.

  10. Molecular relaxation behavior and isothermal crystallization above glass transition temperature of amorphous hesperetin.

    PubMed

    Shete, Ganesh; Khomane, Kailas S; Bansal, Arvind Kumar

    2014-01-01

    The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg ). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg , whereas α-relaxation prominently emerged above Tg . β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg + 16.5 K), 373 K (Tg + 26.5 K), and 383 K (Tg + 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHN and αHN .βHN , were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association.

  11. Optical materials based on molecular nanoparticles.

    PubMed

    Patra, A; Chandaluri, Ch G; Radhakrishnan, T P

    2012-01-21

    A major part of contemporary nanomaterials research is focused on metal and semiconductor nanoparticles, constituted of extended lattices of atoms or ions. Molecular nanoparticles assembled from small molecules through non-covalent interactions are relatively less explored but equally fascinating materials. Their unique and versatile characteristics have attracted considerable attention in recent years, establishing their identity and status as a novel class of nanomaterials. Optical characteristics of molecular nanoparticles capture the essence of their nanoscale features and form the basis of a variety of applications. This review describes the advances made in the field of fabrication of molecular nanoparticles, the wide spectrum of their optical and nonlinear optical characteristics and explorations of the potential applications that exploit their unique optical attributes.

  12. Vibrational mean free paths and thermal conductivity of amorphous silicon from non-equilibrium molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Sääskilahti, K.; Oksanen, J.; Tulkki, J.; McGaughey, A. J. H.; Volz, S.

    2016-12-01

    The frequency-dependent mean free paths (MFPs) of vibrational heat carriers in amorphous silicon are predicted from the length dependence of the spectrally decomposed heat current (SDHC) obtained from non-equilibrium molecular dynamics simulations. The results suggest a (frequency)- 2 scaling of the room-temperature MFPs below 5 THz. The MFPs exhibit a local maximum at a frequency of 8 THz and fall below 1 nm at frequencies greater than 10 THz, indicating localized vibrations. The MFPs extracted from sub-10 nm system-size simulations are used to predict the length-dependence of thermal conductivity up to system sizes of 100 nm and good agreement is found with independent molecular dynamics simulations. Weighting the SDHC by the frequency-dependent quantum occupation function provides a simple and convenient method to account for quantum statistics and provides reasonable agreement with the experimentally-measured trend and magnitude.

  13. Ultrafast optical response of the amorphous and crystalline states of the phase change material Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Miller, T. A.; Rudé, M.; Pruneri, V.; Wall, S.

    2016-07-01

    We examine the ultrafast optical response of the crystalline and amorphous phases of the phase change material Ge2Sb2Te5 (GST) below the phase transformation threshold. Simultaneous measurement of the transmissivity and reflectivity of thin film samples yields the time-dependent evolution of the dielectric function for both phases. We then identify how lattice motion and electronic excitation manifest in the dielectric response. The dielectric response of both phases is large but markedly different. At 800 nm, the changes in amorphous GST are well described by the Drude response of the generated photocarriers, whereas the crystalline phase is better described by the depopulation of resonant bonds. We find that the generated coherent phonons have a greater influence in the amorphous phase than the crystalline phase. Furthermore, coherent phonons do not influence resonant bonding. For fluences up to 50% of the transformation threshold, the structure does not exhibit bond softening in either phase, enabling large changes of the optical properties without structural modification.

  14. Pressure-Induced Structural Transformation in Radiation-Amorphized Zircon

    SciTech Connect

    Trachenko, Kostya; Dove, Martin T.; Salje, E. K. H.; Brazhkin, V. V.; Tsiok, O. B.

    2007-03-30

    We study the response of a radiation-amorphized material to high pressure. We have used zircon ZrSiO{sub 4} amorphized by natural radiation over geologic times, and have measured its volume under high pressure, using the precise strain-gauge technique. On pressure increase, we observe apparent softening of the material, starting from 4 GPa. Using molecular dynamics simulation, we associate this softening with the amorphous-amorphous transformation accompanied by the increase of local coordination numbers. We observe permanent densification of the quenched sample and a nontrivial 'pressure window' at high temperature. These features point to a new class of amorphous materials that show a response to pressure which is distinctly different from that of crystals.

  15. Pressure-induced structural transformation in radiation-amorphized zircon.

    PubMed

    Trachenko, Kostya; Brazhkin, V V; Tsiok, O B; Dove, Martin T; Salje, E K H

    2007-03-30

    We study the response of a radiation-amorphized material to high pressure. We have used zircon ZrSiO4 amorphized by natural radiation over geologic times, and have measured its volume under high pressure, using the precise strain-gauge technique. On pressure increase, we observe apparent softening of the material, starting from 4 GPa. Using molecular dynamics simulation, we associate this softening with the amorphous-amorphous transformation accompanied by the increase of local coordination numbers. We observe permanent densification of the quenched sample and a nontrivial "pressure window" at high temperature. These features point to a new class of amorphous materials that show a response to pressure which is distinctly different from that of crystals.

  16. Magnetic sensors using amorphous metal materials: detection of premature ventricular magnetic waves

    PubMed Central

    Uchiyama, Tsuyoshi; Nakayama, Shinsuke

    2013-01-01

    The detection of magnetic activity enables noncontact and noninvasive evaluation of electrical activity in humans. We review the detection of biomagnetic fields using amorphous metal wire-based magnetic sensors with the sensitivity of a pico-Tesla (pT) level. We measured magnetic fields close to the thoracic wall in a healthy subject sitting on a chair. The magnetic sensor head was mounted perpendicularly against the thoracic wall. Simultaneous measurements with ECG showed that changes in the magnetic field were synchronized with the cardiac electric activity, and that the magnetic wave pattern changed reflecting electrical activity of the atrium and ventricle, despite a large variation. Furthermore, magnetic waves reflecting ventricular arrhythmia were recorded in the same healthy subject. These results suggest that this magnetic sensor technology is applicable to human physiology and pathophysiology research. We also discuss future applications of amorphous wire-based magnetic sensors as well as possible improvements. PMID:24303116

  17. Magnetic sensors using amorphous metal materials: detection of premature ventricular magnetic waves.

    PubMed

    Uchiyama, Tsuyoshi; Nakayama, Shinsuke

    2013-07-01

    The detection of magnetic activity enables noncontact and noninvasive evaluation of electrical activity in humans. We review the detection of biomagnetic fields using amorphous metal wire-based magnetic sensors with the sensitivity of a pico-Tesla (pT) level. We measured magnetic fields close to the thoracic wall in a healthy subject sitting on a chair. The magnetic sensor head was mounted perpendicularly against the thoracic wall. Simultaneous measurements with ECG showed that changes in the magnetic field were synchronized with the cardiac electric activity, and that the magnetic wave pattern changed reflecting electrical activity of the atrium and ventricle, despite a large variation. Furthermore, magnetic waves reflecting ventricular arrhythmia were recorded in the same healthy subject. These results suggest that this magnetic sensor technology is applicable to human physiology and pathophysiology research. We also discuss future applications of amorphous wire-based magnetic sensors as well as possible improvements.

  18. Molecular assembly on two-dimensional materials.

    PubMed

    Kumar, Avijit; Banerjee, Kaustuv; Liljeroth, Peter

    2017-02-24

    Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from

  19. Molecular assembly on two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Kumar, Avijit; Banerjee, Kaustuv; Liljeroth, Peter

    2017-02-01

    Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule–substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging

  20. Interaction potential for aluminum nitride: A molecular dynamics study of mechanical and thermal properties of crystalline and amorphous aluminum nitride

    NASA Astrophysics Data System (ADS)

    Vashishta, Priya; Kalia, Rajiv K.; Nakano, Aiichiro; Rino, José Pedro; CollaboratoryAdvanced Computing; Simulations

    2011-02-01

    An effective interatomic interaction potential for AlN is proposed. The potential consists of two-body and three-body covalent interactions. The two-body potential includes steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between atoms, charge-induced dipole-interactions due to the electronic polarizability of ions, and induced dipole-dipole (van der Waals) interactions. The covalent characters of the Al-N-Al and N-Al-N bonds are described by the three-body potential. The proposed three-body interaction potential is a modification of the Stillinger-Weber form proposed to describe Si. Using the molecular dynamics method, the interaction potential is used to study structural, elastic, and dynamical properties of crystalline and amorphous states of AlN for several densities and temperatures. The structural energy for wurtzite (2H) structure has the lowest energy, followed zinc-blende and rock-salt (RS) structures. The pressure for the structural transformation from wurtzite-to-RS from the common tangent is found to be 24 GPa. For AlN in the wurtzite phase, our computed elastic constants (C11 , C12 , C13 , C33 , C44 , and C66 ), melting temperature, vibrational density-of-states, and specific heat agree well with the experiments. Predictions are made for the elastic constant as a function of density for the crystalline and amorphous phase. Structural correlations, such as pair distribution function and neutron and x-ray static structure factors are calculated for the amorphous and liquid state.

  1. In situ molecular elucidation of drug supersaturation achieved by nano-sizing and amorphization of poorly water-soluble drug.

    PubMed

    Ueda, Keisuke; Higashi, Kenjirou; Yamamoto, Keiji; Moribe, Kunikazu

    2015-09-18

    Quantitative evaluation of drug supersaturation and nanoparticle formation was conducted using in situ evaluation techniques, including nuclear magnetic resonance (NMR) spectroscopy. We prepared a ternary complex of carbamazepine (CBZ) with hydroxypropyl methylcellulose (HPMC) and sodium dodecyl sulfate (SDS) to improve the drug concentration. Different preparation methods, including grinding and spray drying, were performed to prepare the ternary component products, ground mixture (GM) and spray-dried sample (SD), respectively. Although CBZ was completely amorphized in the ternary SD, CBZ was partially amorphized with the remaining CBZ crystals in the ternary GM. Aqueous dispersion of the ternary GM formed nanoparticles of around 150 nm, originating from the CBZ crystals in the ternary GM. In contrast, the ternary SD formed transparent solutions without a precipitate. The molecular-level evaluation using NMR measurements revealed that approximately half a dose of CBZ in the ternary GM dispersion was present as nanoparticles; however, CBZ in the ternary SD was completely dissolved in the aqueous solution. The characteristic difference between the solid states, followed by different preparation methods, induced different solution characteristics in the ternary GM and SD. The permeation study, using a dialysis membrane, showed that the CBZ concentration dissolved in the bulk water phase rapidly reduced in the ternary SD dispersion compared to the ternary GM dispersion; this demonstrated the advantage of ternary GM dispersion in the maintenance of CBZ supersaturation. Long-term maintenance of a supersaturated state of CBZ observed in the ternary GM dispersion rather than in the ternary SD dispersion was achieved by the inhibition of CBZ crystallization owing to the existence of CBZ nanoparticles in the ternary GM dispersion. Nanoparticle formation, combined with drug amorphization, could be a promising approach to improve drug concentrations. The detailed elucidation

  2. Molecular beam epitaxy for advanced gate stack materials and processes

    NASA Astrophysics Data System (ADS)

    Locquet, Jean-Pierre

    2005-03-01

    The material requirements for future CMOS generations - as given by the ITRS roadmap - are very challenging. This includes a high K dielectric without a low K interfacial layer, a high mobility channel and the appropriate metal gate. With the help of two projects INVEST and ET4US, we are building up a molecular beam epitaxy (MBE) infrastructure to grow this material set on large area wafers that can be further processed into small scale devices. In the INVEST project, we have developed an MBE system for the growth of complex oxides on semiconductors. The system follows the overall design of a production tool and is equipped with an RF atomic oxygen source, effusion cells, e-beam evaporators and a differential pumping stage. The oxide growth process starts with desorbing the initial surface oxide on the Si wafers in ultra-high vacuum and high temperature to create a clean reconstructed 2x1 surface. Using the atomic oxygen it is possible to oxidize the surface in a well controlled manner at low temperature and to grow very thin and dense SiOx layers, followed by the growth of 2-6 nm amorphous high K dielectrics. The process parameters permit to tune the interface layer from a SiOx rich to a silicide rich interface with a significant impact on the capacitance and the leakage. Initial focus is on developing an optimized growth recipe for high quality amorphous HfO2 and LaHfO3.5 films. This recipe was subsequently used to make wafers for a transistor batch that gave us the first N short channel MBE MOSFET's (100 nm) using an etched gate process flow. Some highlights of the first batch for 3nm HfO2 MOSFET are a high mobility (> 270 cm^2/Vs) with a corresponding low leakage current of 2 mA/cm^2). While there were some process issues for LaHfO3.5, the 3 nm MOSFET showed very low leakage currents below 10-6 A/cm^2. Interestingly all the LaHFO3.5 MOSFETs showed very low threshold voltage instabilities. In collaboration with C. Marchiori, M. Sousa, A.Guiller, H. Siegwart, D

  3. Kinetics of oxidation of azobenzene nitrene with molecular oxygen in amorphous polymers

    SciTech Connect

    Kondratenko, E.V.; Bolshakov, B.V.; Tolkatchev, V.A.

    1996-12-31

    Kinetics of disappearance of azobenzene nitrene at 115-120 K in polymethyl methacrylate, poly styrene, polycarbonate and polysulfone films saturated with oxygen has been studied. For condition of oxygen excess the disappearance of nitrous is shown to be a result only of the reaction with the dissolved gas. Kinetics of the process is identical to that of the oxidation of macro radicals in the same polymer. The nonexponential character of kinetic curves is shown to be related with the existence of the rate constant distribution. The values of the width of distribution range in the narrow interval being practically the same for various polymers. The data about the width of the distribution function for the oxidation of macro radicals in amorphous polymers known from literature also fit into this interval. All the particles participating in the reaction with the experimental accuracy have the same dependence of the rate constant on temperature. The activation energies of reactions in various amorphous polymers have very close values.

  4. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  5. Recent advances in co-amorphous drug formulations.

    PubMed

    Dengale, Swapnil Jayant; Grohganz, Holger; Rades, Thomas; Löbmann, Korbinian

    2016-05-01

    Co-amorphous drug delivery systems have recently gained considerable interest in the pharmaceutical field because of their potential to improve oral bioavailability of poorly water-soluble drugs through drug dissolution enhancement as a result of the amorphous nature of the material. A co-amorphous system is characterized by the use of only low molecular weight components that are mixed into a homogeneous single-phase co-amorphous blend. The use of only low molecular weight co-formers makes this approach very attractive, as the amount of amorphous stabilizer can be significantly reduced compared with other amorphous stabilization techniques. Because of this, several research groups started to investigate the co-amorphous formulation approach, resulting in an increasing amount of scientific publications over the last few years. This study provides an overview of the co-amorphous field and its recent findings. In particular, we investigate co-amorphous formulations from the viewpoint of solid dispersions, describe their formation and mechanism of stabilization, study their impact on dissolution and in vivo performance and briefly outline the future potentials.

  6. Growth of amorphous and epitaxial alternative gate dielectrics on silicon by molecular-beam epitaxy and their characterization

    NASA Astrophysics Data System (ADS)

    Edge, Lisa Friedman

    The continued scaling of SiO2 in metal-oxide-semiconductor field-effect transistors (MOSFETs) is approaching its fundamental limit and in the next few years will have to be replaced with an alternative gate dielectric if Moore's law is to continue. In a search for suitable alternative dielectrics, I have investigated the growth of amorphous and epitaxial LaAlO3, LaScO3, La2O3, and Sc2O3 thin films by molecular-beam epitaxy (MBE) on silicon. A major challenge in the growth of alternative gate dielectrics on silicon is the formation of SiO2 at the interface between silicon and the high- K gate dielectric. In this dissertation, I have established deposition conditions that yielded abrupt interfaces (< 0.1 A of SiO2) between amorphous LaAlO3 or LaScO3 thin films and silicon. These results demonstrate the thinnest gate dielectrics ever produced that are free of interfacial SiO2, despite exposure to air. The thermal stability between silicon and the abrupt amorphous LaAlO 3 and LaScO3 thin films was established for the first time. By 900°C, crystallization is clearly observed, but the LaAlO3/Si interface remains sharp with no detectable interfacial SiO2. The thermal stability results establish key processing windows for the integration of amorphous LaAlO3 and LaScO3 thin films into silicon-based MOSFETs. In this work, the following critical physical properties of amorphous LaAlO3 thin films deposited on silicon have been determined: dielectric constant (K = 16 +/- 2), bandgap (Eg = 6.2 +/- 0.1 eV), and band alignment (DeltaEc = 1.8 +/- 0.2 for electrons and DeltaEv = 3.2 +/- 0.1 eV for holes). The following critical physical properties of amorphous LaScO3 thin films deposited on silicon have been determined: bandgap (Eg = 5.7 +/- 0.1 eV) and band alignment (DeltaEc = 2.0 +/- 0.1 eV for electrons and DeltaEv = 3.1 +/- 0.1 eV for holes). In this dissertation, epitaxial (0001) La2O3 thin films with the hexagonal crystal structure were grown on (111) Si for the first time

  7. SORPTION BEHAVIOR OF MONOSODIUM TITANATE AND AMORPHOUS PEROXOTITANATE MATERIALS UNDER WEAKLY ACIDIC CONDITIONS

    SciTech Connect

    Hobbs, D.; Elvington, M.; Click, D.

    2009-11-11

    Inorganic, titanate-based sorbents are tested with respect to adsorption of a variety of sorbates under weakly acidic conditions (pH 3). Specifically, monosodium titanate (MST) and amorphous peroxotitanate (APT) sorption characteristics are initially probed through a screening process consisting of a pair of mixed metal solutions containing a total of 29 sorbates including alkali metals, alkaline earth metals, transition metals, metalloids and nonmetals. MST and APT sorption characteristics are further analyzed individually with chromium(III) and cadmium(II) using a batch method at ambient laboratory temperature, varying concentrations of the sorbents and sorbates and contact times. Maximum sorbate loadings are obtained from the respective adsorption isotherms.

  8. Left handed material based on amorphous ferromagnetic microwires tunable by dc current

    NASA Astrophysics Data System (ADS)

    García-Miquel, H.; Carbonell, J.; Sánchez-Dehesa, J.

    2010-08-01

    Tuning of the transmission characteristics of amorphous ferromagnetic microwires through a dc current is demonstrated. These structures are studied in the frequency region where they present double negative behavior. It is found that their frequency response shifts with small dc currents circulating along the wires. It is observed that the dc current tends to compensate and even cancels the resonant peak associated to the static magnetic field applied along the wire axis. The phenomenon behind these findings is discussed in terms of the torque exerted by the field created by the current on the plane perpendicular to the wire axis.

  9. Hot-Wire CVD Amorphous Si Materials for Solar Cell Application

    SciTech Connect

    Wang, Q.

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films and their application to solar cells fabricated using the hot-wire chemical vapor deposition (HWCVD) or (CAT)-CVD will be reviewed. This review will focus on the comparison to the standard plasma enhance (PE) CVD in the terms of deposition technique, film properties, and solar cell performance. The advantages of using HWCVD for a-Si:H solar cell research as well as the criteria for industry's adaptation of this technique for mass production will be addressed.

  10. Nonequilibrium thermodynamics of driven amorphous materials. III. Shear-transformation-zone plasticity.

    PubMed

    Bouchbinder, Eran; Langer, J S

    2009-09-01

    We use the internal-variable, effective-temperature thermodynamics developed in two preceding papers to reformulate the shear-transformation-zone (STZ) theory of amorphous plasticity. As required by the preceding analysis, we make explicit approximations for the energy and entropy of the STZ internal degrees of freedom. We then show that the second law of thermodynamics constrains the STZ transition rates to have an Eyring form as a function of the effective temperature. Finally, we derive an equation of motion for the effective temperature for the case of STZ dynamics.

  11. New Methods of Simulation of Mn(II) EPR Spectra: Single Crystals, Polycrystalline and Amorphous (Biological) Materials

    NASA Astrophysics Data System (ADS)

    Misra, Sushil K.

    Biological systems exhibit properties of amorphous materials. The Mn(II) ion in amorphous materials is characterized by distributions of spin-Hamiltonian parameters around mean values. It has a certain advantage over other ions, being one of the most abundant elements on the earth. The extent to which living organisms utilize manganese varies from one organism to the other. There is a fairly high concentration of the Mn(II) ion in green plants, which use it in the O2 evolution reaction of photosynthesis (Sauer, 1980). Structure-reactivity relationships in Mn(II)-O2 complexes are given in a review article by Coleman and Taylor (1980). Manganese is a trace requirement in animal nutrition; highly elevated levels of manganese in the diet can be toxic, probably because of an interference with iron homeostasis (Underwood, 1971). On the other hand, animals raised with a dietary deficiency of manganese exhibit severe abnormalities in connective tissue; these problems have been attributed to the obligatory role of Mn(II) in mucopolysaccharide metabolism (Leach, 1971). Mn(II) has been detected unequivocally in living organisms.

  12. Molecular mobility studies on the amorphous state of disaccharides. I-thermally stimulated currents and differential scanning calorimetry.

    PubMed

    Pinto, Susana S; Diogo, Hermínio P; Nunes, Teresa G; Moura Ramos, Joaquim J

    2010-08-16

    The relaxational processes in amorphous solid gentiobiose and cellobiose are studied by thermally stimulated depolarization currents (TSDC) in the temperature region from 108K up to 423K. The slow molecular mobility was characterized in the crystal and in the glassy state. The features of different motional components of the secondary relaxation have been monitored as a function of time as the glass structurally relaxes on aging. It is concluded that some modes of motion of this mobility are aging independent, while others are affected by aging. The value of the steepness index or fragility (T(g)-normalized temperature dependence of the relaxation time) was obtained by differential scanning calorimetry (DSC) from the analysis of the scanning rate dependency of T(g).

  13. Molecular Dynamic Simulations of Glass Transition Temperature and Mechanical Properties in the Amorphous Region of Oil-Immersed Transformer Insulation Paper

    NASA Astrophysics Data System (ADS)

    Wang, You-Yuan; Yang, Tao; Liao, Rui-Jin

    2012-07-01

    The glass transition temperature (Tg) in the amorphous region of an insulation paper is one of the most important characteristics for thermal stability. Molecular dynamic simulations have been performed on three micro-structural models, namely, amorphous pure cellulose, amorphous cellulose with water and amorphous cellulose with oil, to study the microscopic mechanism of the glass transition process for oil-immersed transformer insulation paper. Using the method of specific volume versus temperature curve, the Tg of amorphous pure cellulose, cellulose with water, and cellulose with oil was determined as 448, 418 and 440 K, respectively. The current study may provide some information for thermal aging. The simulation results show that during the glass transition process, both the chain motion and mechanical properties of cellulose changes significantly. Relative to the oil molecules, water molecules immersed in the amorphous region of insulation paper can disrupt hydrogen bonds between cellulose chains. This phenomenon results in a significant reduction in the glass transition temperature and affects the thermal stability of the insulation paper.

  14. Picosecond amorphization of SiO2 stishovite under tension

    PubMed Central

    Misawa, Masaaki; Ryuo, Emina; Yoshida, Kimiko; Kalia, Rajiv K.; Nakano, Aiichiro; Nishiyama, Norimasa; Shimojo, Fuyuki; Vashishta, Priya; Wakai, Fumihiro

    2017-01-01

    It is extremely difficult to realize two conflicting properties—high hardness and toughness—in one material. Nano-polycrystalline stishovite, recently synthesized from Earth-abundant silica glass, proved to be a super-hard, ultra-tough material, which could provide sustainable supply of high-performance ceramics. Our quantum molecular dynamics simulations show that stishovite amorphizes rapidly on the order of picosecond under tension in front of a crack tip. We find a displacive amorphization mechanism that only involves short-distance collective motions of atoms, thereby facilitating the rapid transformation. The two-step amorphization pathway involves an intermediate state akin to experimentally suggested “high-density glass polymorphs” before eventually transforming to normal glass. The rapid amorphization can catch up with, screen, and self-heal a fast-moving crack. This new concept of fast amorphization toughening likely operates in other pressure-synthesized hard solids. PMID:28508056

  15. Picosecond amorphization of SiO2 stishovite under tension.

    PubMed

    Misawa, Masaaki; Ryuo, Emina; Yoshida, Kimiko; Kalia, Rajiv K; Nakano, Aiichiro; Nishiyama, Norimasa; Shimojo, Fuyuki; Vashishta, Priya; Wakai, Fumihiro

    2017-05-01

    It is extremely difficult to realize two conflicting properties-high hardness and toughness-in one material. Nano-polycrystalline stishovite, recently synthesized from Earth-abundant silica glass, proved to be a super-hard, ultra-tough material, which could provide sustainable supply of high-performance ceramics. Our quantum molecular dynamics simulations show that stishovite amorphizes rapidly on the order of picosecond under tension in front of a crack tip. We find a displacive amorphization mechanism that only involves short-distance collective motions of atoms, thereby facilitating the rapid transformation. The two-step amorphization pathway involves an intermediate state akin to experimentally suggested "high-density glass polymorphs" before eventually transforming to normal glass. The rapid amorphization can catch up with, screen, and self-heal a fast-moving crack. This new concept of fast amorphization toughening likely operates in other pressure-synthesized hard solids.

  16. Molecular forensic science of nuclear materials

    SciTech Connect

    Wilkerson, Marianne Perry

    2010-01-01

    We are interested in applying our understanding of actinide chemical structure and bonding to broaden the suite of analytical tools available for nuclear forensic analyses. Uranium- and plutonium-oxide systems form under a variety of conditions, and these chemical species exhibit some of the most complex behavior of metal oxide systems known. No less intriguing is the ability of AnO{sub 2} (An: U, Pu) to form non-stoichiometric species described as AnO{sub 2+x}. Environmental studies have shown the value of utilizing the chemical signatures of these actinide oxides materials to understand transport following release into the environment. Chemical speciation of actinide-oxide samples may also provide clues as to the age, source, process history, or transport of the material. The scientific challenge is to identify, measure and understand those aspects of speciation of actinide analytes that carry information about material origin and history most relevant to forensics. Here, we will describe our efforts in material synthesis and analytical methods development that we will use to provide the fundamental science required to characterize actinide oxide molecular structures for forensics science. Structural properties and initial results to measure structural variability of uranium oxide samples using synchrotron-based X-ray Absorption Fine Structure will be discussed.

  17. Investigation of the impact of annealing on global molecular mobility in glasses: optimization for stabilization of amorphous pharmaceuticals.

    PubMed

    Luthra, Suman A; Hodge, Ian M; Pikal, Michael J

    2008-09-01

    The purpose of this research was to investigate the effect of annealing on the molecular mobility in lyophilized glasses using differential scanning calorimetry (DSC) and isothermal microcalorimetry (IMC) techniques. A second objective that emerged was a systematic study of the unusual pre-T(g) thermal events that were observed during DSC warming scans after annealing. Aspartame lyophilized with three different excipients; sucrose, trehalose and poly vinyl pyrrolidone (PVP) was studied. The aim of this work was to quantify the decrease in mobility in amorphous lyophilized aspartame formulations upon systematic postlyophilization annealing. DSC scans of aspartame:sucrose formulation (T(g) = 73 degrees C) showed the presence of a pre-T(g) endotherm which disappeared upon annealing. Aspartame:trehalose (T(g) = 112 degrees C) and aspartame:PVP (T(g) = 100 degrees C) showed a broad exotherm before T(g) and annealing caused appearance of endothermic peaks before T(g). This work also employed IMC to measure the global molecular mobility represented by structural relaxation time (tau(beta)) in both un-annealed and annealed formulations. The effect of annealing on the enthalpy relaxation of lyophilized glasses, as measured by DSC and IMC, was consistent with the behavior predicted using the Tool-Narayanaswamy-Moynihan (TNM) phenomenology (Luthra et al., 2007, in press). The results show that the systems annealed at T(g) -15 degrees C to T(g) -20 degrees C have the lowest molecular mobility.

  18. Characterization of Amorphous Silicon Advanced Materials and PV Devices: Final Technical Report, 15 December 2001--31 January 2005

    SciTech Connect

    Taylor, P. C.

    2005-11-01

    The major objectives of this subcontract have been: (1) understand the microscopic properties of the defects that contribute to the Staebler-Wronski effect to eliminate this effect, (2) perform correlated studies on films and devices made by novel techniques, especially those with promise to improve stability or deposition rates, (3) understand the structural, electronic, and optical properties of films of hydrogenated amorphous silicon (a-Si:H) made on the boundary between the amorphous and microcrystalline phases, (4) search for more stable intrinsic layers of a-Si:H, (5) characterize the important defects, impurities, and metastabilities in the bulk and at surfaces and interfaces in a-Si:H films and devices and in important alloy systems, and (6) make state-of-the-art plasma-enhanced chemical vapor deposition (PECVD) devices out of new, advanced materials, when appropriate. All of these goals are highly relevant to improving photovoltaic devices based on a-Si:H and related alloys. With regard to the first objective, we have identified a paired hydrogen site that may be the defect that stabilizes the silicon dangling bonds formed in the Staebler-Wronski effect.

  19. Laboratory Evolved Gas Analyses of Si-rich Amorphous Materials: Implications for Analyses of Si-rich Amorphous Material in Gale Crater by the Mars Science Laboratory Sample Analysis at Mars Instrument

    NASA Astrophysics Data System (ADS)

    McAdam, A.; Knudson, C. A.; Sutter, B.; Andrejkovicova, S. C.; Archer, P. D., Jr.; Franz, H. B.; Eigenbrode, J. L.; Morris, R. V.; Ming, D. W.; Sun, V. Z.; Milliken, R.; Wilhelm, M. B.; Mahaffy, P. R.; Navarro-Gonzalez, R.

    2016-12-01

    The Chemistry and Mineralogy (CheMin) instrument onboard the Mars Science Laboratory (MSL) rover detected Si-rich amorphous or poorly ordered materials in several samples from Murray Formation mudstones and Stimson Formation sandstones. High-SiO2 amorphous materials such as opal-A or rhyolitic glass are candidate phases, but CheMin data cannot be used to distinguish between these possibilities. In the Buckskin (BS) sample from the upper Murray Formation, and the Big Sky (BY) and Greenhorn (GH) samples from the Stimson Formation, evolved gas analyses by the Sample Analysis at Mars (SAM) instrument showed very broad H2O evolutions during sample heating at temperatures >450-500°C, which had not been observed from previous samples. BS also had a significant broad evolution <450-500°C. We have undertaken a laboratory study targeted at understanding if the data from SAM analyses can be used to place constraints on the nature of the amorphous phases. SAM-like evolved gas analyses have been performed on several opal and rhyolitic glass samples. Opal-A samples exhibited wide <500°C H2O evolutions, with lesser H2O evolved above 500°C. H2O evolution traces from rhyolitic glasses varied, having either two broad H2O peaks, <300°C and >500°C, or a broad peak centered around 400°C. For samples that produced two evolutions, the lower temperature peak was more intense than the higher temperature peak, a trend also exhibited by opal-A. This trend is consistent with data from BS, but does not seem consistent with data from BY and GH which evolved most of their H2O >500°C. It may be that dehydration of opal-A and/or rhyolitic glass can result in some preferential loss of lower temperature H2O, to produce traces that more closely resemble BY and GH. This is currently under investigation and results will be reported.

  20. Radiation-induced amorphization of intermetallic compounds: A molecular-dynamics study of CuTi and Cu sub 4 Ti sub 3

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R. ); Sabochick, M.J. . Dept. of Engineering Physics)

    1991-06-01

    In the present paper, important results of our recent computer simulation of radiation-induced amorphization in the ordered compounds CuTi and Cu{sub 4}Ti{sub 3} are summarized. The energetic, structural, thermodynamic and mechanical responses of these intermetallics during chemical disordering, point-defect production and heating were simulated, using molecular dynamics and embedded-atom potentials. From the atomistic details obtained, the critical role of radiation-induced structural disorder in driving the crystalline-to-amorphous phase transformation is discussed. 25 refs., 4 figs.

  1. Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

    PubMed

    Sibik, Juraj; Löbmann, Korbinian; Rades, Thomas; Zeitler, J Axel

    2015-08-03

    There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.

  2. Preface: Thin films of molecular organic materials

    NASA Astrophysics Data System (ADS)

    Fraxedas, J.

    2008-03-01

    This special issue is devoted to thin films of molecular organic materials and its aim is to assemble numerous different aspects of this topic in order to reach a wide scientific audience. Under the term 'thin films', structures with thicknesses spanning from one monolayer or less up to several micrometers are included. In order to narrow down this relaxed definition (how thin is thin?) I suggest joining the stream that makes a distinction according to the length scale involved, separating nanometer-thick films from micrometer-thick films. While the physical properties of micrometer-thick films tend to mimic those of bulk materials, in the low nanometer regime new structures (e.g., crystallographic and substrate-induced phases) and properties are found. However, one has to bear in mind that some properties of micrometer-thick films are really confined to the film/substrate interface (e.g. charge injection), and are thus of nanometer nature. Supported in this dimensionality framework, this issue covers the most ideal and model 0D case, a single molecule on a surface, through to the more application-oriented 3D case, placing special emphasis on the fascinating 2D domain that is monolayer assembly. Thus, many aspects will be reviewed, such as single molecules, self-organization, monolayer regime, chirality, growth, physical properties and applications. This issue has been intentionally restricted to small molecules, thus leaving out polymers and biomolecules, because for small molecules it is easier to establish structure--property relationships. Traditionally, the preparation of thin films of molecular organic materials has been considered as a secondary, lower-ranked part of the more general field of this class of materials. The coating of diverse surfaces such as silicon, inorganic and organic single crystals, chemically modified substrates, polymers, etc., with interesting molecules was driven by the potential applications of such molecular materials

  3. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGES

    Novikov, S. V.; Ting, M.; Yu, K. M.; ...

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  4. Enhanced catalyst-free nucleation of GaN nanowires on amorphous Al{sub 2}O{sub 3} by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Sobanska, Marta Klosek, Kamil; Borysiuk, Jolanta; Kret, Slawomir; Tchutchulasvili, Giorgi; Gieraltowska, Sylwia; Zytkiewicz, Zbigniew R.

    2014-01-28

    We report on plasma-assisted molecular beam epitaxial growth of GaN nanowires (NWs) on Si(111) substrates with a thin amorphous Al{sub 2}O{sub 3} buffer layer deposited by atomic layer deposition. Comparison of nucleation kinetics shows that presence of amorphous Al{sub 2}O{sub 3} buffer significantly enhances spontaneous nucleation of GaN NWs. Slower nucleation was observed on partially amorphous silicon nitride films. No growth of NWs was found on sapphire substrate under the same growth conditions which we explain by a low density of defects on monocrystalline substrate surface where NWs may nucleate. Our finding shows that tuning of substrate microstructure is an efficient tool to control rate of self-induced nucleation of GaN NWs.

  5. High pressure polymorphs and amorphization of upconversion host material NaY(WO{sub 4}){sub 2}

    SciTech Connect

    Hong, Fang; Yue, Binbin E-mail: chenbin@hpstar.ac.cn; Cheng, Zhenxiang; Kunz, Martin; Chen, Bin E-mail: chenbin@hpstar.ac.cn; Mao, Ho-Kwang

    2016-07-25

    The pressure effect on the structural change of upconversion host material NaY(WO{sub 4}){sub 2} was studied by using in-situ synchrotron X-ray diffraction. A transition from the initial scheelite phase to the M-fergusonite phase occurs near 10 GPa, and another phase transition is found near 27.5 GPa, which could be an isostructural transition without symmetry change. The sample becomes amorphous when the pressure is fully released from high pressure. This work demonstrates the possibility of synthesizing various polymorph structures for non-linear optical applications with a high pressure, chemical doping, or strained thin-film nanostructure process.

  6. Use of X-ray diffraction to quantify amorphous supplementary cementitious materials in anhydrous and hydrated blended cements

    SciTech Connect

    Snellings, R.; Salze, A.; Scrivener, K.L.

    2014-10-15

    The content of individual amorphous supplementary cementitious materials (SCMs) in anhydrous and hydrated blended cements was quantified by the PONKCS [1] X-ray diffraction (XRD) method. The analytical precision and accuracy of the method were assessed through comparison to a series of mixes of known phase composition and of increasing complexity. A 2σ precision smaller than 2–3 wt.% and an accuracy better than 2 wt.% were achieved for SCMs in mixes with quartz, anhydrous Portland cement, and hydrated Portland cement. The extent of reaction of SCMs in hydrating binders measured by XRD was 1) internally consistent as confirmed through the standard addition method and 2) showed a linear correlation to the cumulative heat release as measured independently by isothermal conduction calorimetry. The advantages, limitations and applicability of the method are discussed with reference to existing methods that measure the degree of reaction of SCMs in blended cements.

  7. High pressure polymorphs and amorphization of upconversion host material NaY(WO4)2

    SciTech Connect

    Hong, Fang; Yue, Binbin; Cheng, Zhenxiang; Kunz, Martin; Chen, Bin; Mao, Ho-Kwang

    2016-07-29

    The pressure effect on the structural change of upconversion host material NaY(WO4)2 was studied in this paper by using in-situ synchrotron X-ray diffraction. A transition from the initial scheelite phase to the M-fergusonite phase occurs near 10 GPa, and another phase transition is found near 27.5 GPa, which could be an isostructural transition without symmetry change. The sample becomes amorphous when the pressure is fully released from high pressure. Finally, this work demonstrates the possibility of synthesizing various polymorph structures for non-linear optical applications with a high pressure, chemical doping, or strained thin-film nanostructure process.

  8. On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1990-01-01

    Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous

  9. On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1990-01-01

    Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous

  10. Electrons and phonons in amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Prasai, Kiran; Biswas, Parthapratim; Drabold, D. A.

    2016-07-01

    The coupling between lattice vibrations and electrons is one of the central concepts of condensed matter physics. The subject has been deeply studied for crystalline materials, but far less so for amorphous and glassy materials, which are among the most important for applications. In this paper, we explore the electron-lattice coupling using current tools of a first-principles computer simulation. We choose three materials to illustrate the phenomena: amorphous silicon (a-Si), amorphous selenium (a-Se) and amorphous gallium nitride (a-GaN). In each case, we show that there is a strong correlation between the localization of electron states and the magnitude of thermally induced fluctuations in energy eigenvalues obtained from the density-functional theory (i.e. Kohn-Sham eigenvalues). We provide a heuristic theory to explain these observations. The case of a-GaN, a topologically disordered partly ionic insulator, is distinctive compared to the covalent amorphous examples. Next, we explore the consequences of changing the charge state of a system as a proxy for tracking photo-induced structural changes in the materials. Where transport is concerned, we lend insight into the Meyer-Neldel compensation rule and discuss a thermally averaged Kubo-Greenwood formula as a means to estimate electrical conductivity and especially its temperature dependence. We close by showing how the optical gap of an amorphous semiconductor can be computationally engineered with the judicious use of Hellmann-Feynman forces (associated with a few defect states) using molecular dynamics simulations. These forces can be used to close or open an optical gap, and identify a structure with a prescribed gap. We use the approach with plane-wave density functional methods to identify a low-energy amorphous phase of silicon including several coordination defects, yet with a gap close to that of good quality a-Si models.

  11. Scaling of slip avalanches in sheared amorphous materials based on large-scale atomistic simulations.

    PubMed

    Zhang, Dansong; Dahmen, Karin A; Ostoja-Starzewski, Martin

    2017-03-01

    Atomistic simulations of binary amorphous systems with over 4 million atoms are performed. Systems of two interatomic potentials of the Lennard-Jones type, LJ12-6 and LJ9-6, are simulated. The athermal quasistatic shearing protocol is adopted, where the shear strain is applied in a stepwise fashion with each step followed by energy minimization. For each avalanche event, the shear stress drop (Δσ), the hydrostatic pressure drop (Δσ_{h}), and the potential energy drop (ΔE) are computed. It is found that, with the avalanche size increasing, the three become proportional to each other asymptotically. The probability distributions of avalanche sizes are obtained and values of scaling exponents fitted. In particular, the distributions follow a power law, P(ΔU)∼ΔU^{-τ}, where ΔU is a measure of avalanche sizes defined based on shear stress drops. The exponent τ is 1.25±0.1 for the LJ12-6 systems, and 1.15±0.1 for the LJ9-6 systems. The value of τ for the LJ12-6 systems is consistent with that from an earlier atomistic simulation study by Robbins et al. [Phys. Rev. Lett. 109, 105703 (2012)]PRLTAO0031-900710.1103/PhysRevLett.109.105703, but the fitted values of other scaling exponents differ, which may be because the shearing protocol used here differs from that in their study.

  12. Scaling of slip avalanches in sheared amorphous materials based on large-scale atomistic simulations

    NASA Astrophysics Data System (ADS)

    Zhang, Dansong; Dahmen, Karin A.; Ostoja-Starzewski, Martin

    2017-03-01

    Atomistic simulations of binary amorphous systems with over 4 million atoms are performed. Systems of two interatomic potentials of the Lennard-Jones type, LJ12-6 and LJ9-6, are simulated. The athermal quasistatic shearing protocol is adopted, where the shear strain is applied in a stepwise fashion with each step followed by energy minimization. For each avalanche event, the shear stress drop (Δ σ ), the hydrostatic pressure drop (Δ σh ), and the potential energy drop (Δ E ) are computed. It is found that, with the avalanche size increasing, the three become proportional to each other asymptotically. The probability distributions of avalanche sizes are obtained and values of scaling exponents fitted. In particular, the distributions follow a power law, P (Δ U )˜Δ U-τ , where Δ U is a measure of avalanche sizes defined based on shear stress drops. The exponent τ is 1.25 ±0.1 for the LJ12-6 systems, and 1.15 ±0.1 for the LJ9-6 systems. The value of τ for the LJ12-6 systems is consistent with that from an earlier atomistic simulation study by Robbins et al. [Phys. Rev. Lett. 109, 105703 (2012)], 10.1103/PhysRevLett.109.105703, but the fitted values of other scaling exponents differ, which may be because the shearing protocol used here differs from that in their study.

  13. Fabrication and Characterization of Amorphous/Nanocrystalline Thin Film Composite

    NASA Astrophysics Data System (ADS)

    Newton, Benjamin S.

    Combining the absorption abilities of amorphous silicon and the electron transport capabilities of crystalline silicon would be a great advantage to not only solar cells but other semiconductor devices. In this work composite films were created using molecular beam epitaxy and electron beam deposition interchangeably as a method to create metallic precursors. Aluminum induced crystallization techniques were used to convert an amorphous silicon film with a capping layer of aluminum nanodots into a film composed of a mixture of amorphous silicon and nanocrystalline silicon. This layer was grown into the amorphous layer by cannibalizing a portion of the amorphous silicon material during the aluminum induced crystallization. Characterization was performed on films and metallic precursors utilizing SEM, TEM, ellipsometry and spectrophotometer.

  14. Comparison of induced damage, range, reflection, and sputtering yield between amorphous, bcc crystalline, and bubble-containing tungsten materials under hydrogen isotope and noble gas plasma irradiations

    NASA Astrophysics Data System (ADS)

    Saito, Seiki; Nakamura, Hiroaki; Tokitani, Masayuki

    2017-01-01

    Binary-collision-approximation simulation of hydrogen isotope (i.e., hydrogen, deuterium, and tritium) and noble gas (i.e., helium, neon, and argon) injections into tungsten materials is performed. Three tungsten structures (i.e., amorphous, bcc crystalline, and helium bubble-containing structures) are prepared as target materials. Then, the trajectories of incident atoms, the distribution of recoil atoms, the penetration depth range of incident atoms, the sputtering yield, and the reflection rate are carefully investigated for these target materials.

  15. Structure and Transformation of Amorphous Calcium Carbonate: A Solid-State 43Ca NMR and Computational Molecular Dynamics Investigation

    SciTech Connect

    Singer, Jared W.; Yazaydin, A. O.; Kirkpatrick, Robert J.; Bowers, Geoffrey M.

    2012-05-22

    Amorphous calcium carbonate (ACC) is a metastable precursor to crystalline CaCO{sub 3} phases that precipitates by aggregation of ion pairs and prenucleation clusters. We use {sup 43}Ca solid-state NMR spectroscopy to probe the local structure and transformation of ACC synthesized from seawater-like solutions with and without Mg{sup 2+} and computational molecular dynamics (MD) simulations to provide more detailed molecular-scale understanding of the ACC structure. The {sup 43}Ca NMR spectra of ACC collected immediately after synthesis consist of broad, featureless resonances with Gaussian line shapes (FWHH = 27.6 {+-} 1 ppm) that do not depend on Mg{sup 2+} or H{sub 2}O content. A correlation between {sup 43}Ca isotropic chemical shifts and mean Ca-O bond distances for crystalline hydrous and anhydrous calcium carbonate phases indicates indistinguishable maximum mean Ca-O bond lengths of {approx}2.45 {angstrom} for all our samples. This value is near the upper end of the published Ca-O bond distance range for biogenic and synthetic ACCs obtained by Ca-X-ray absorption spectroscopy. It is slightly smaller than the values from the structural model of Mgfree ACC by Goodwin et al. obtained from reverse Monte Carlo (RMC) modeling of X-ray scattering data and our own computational molecular dynamics (MD) simulation based on this model. An MD simulation starting with the atomic positions of the Goodwin et al. RMC model using the force field of Raiteri and Gale shows significant structural reorganization during the simulation and that the interconnected carbonate/water-rich channels in the Goodwin et al. model shrink in size over the 2 ns simulation time. The distribution of polyhedrally averaged Ca-O bond distances from the MD simulation is in good agreement with the {sup 43}Ca NMR peak shape, suggesting that local structural disorder dominates the experimental line width of ACC.

  16. Gold nanoparticles promote amorphous carbon to be ammonia gas sensor

    NASA Astrophysics Data System (ADS)

    Hsu, Hua-Shu; Ju, Shin-Pon; Sun, Shih-Jye; Chou, Hsiung; Chia, C. H.

    2016-05-01

    As gold-nanoparticles-embedded in amorphous carbon films the sp 3 carbon orbits near the interface will be partially transferred to sp 2. The Raman spectrum measurements as well as the molecular-dynamics simulations used the second reactive empirical bond order (REBO) potential simulating the interatomic force between carbon atoms both confirm the orbital transformations. The amorphous carbon films are initially inert to gases, while the films embedded with gold nanoparticles exhibit the increase of resistance in ammonia atmosphere. Namely, gold-nanoparticles-embedded amorphous carbon films become the candidate for ammonia gas sensor materials.

  17. Encapsulated Vanadium-Based Hybrids in Amorphous N-Doped Carbon Matrix as Anode Materials for Lithium-Ion Batteries.

    PubMed

    Long, Bei; Balogun, Muhammad-Sadeeq; Luo, Lei; Luo, Yang; Qiu, Weitao; Song, Shuqin; Zhang, Lei; Tong, Yexiang

    2017-09-12

    Recently, researchers have made significant advancement in employing transition metal compound hybrids as anode material for lithium-ion batteries and developing simple preparation of these hybrids. To this end, this study reports a facile and scalable method for fabricating a vanadium oxide-nitride composite encapsulated in amorphous carbon matrix by simply mixing ammonium metavanadate and melamine as anode materials for lithium-ion batteries. By tuning the annealing temperature of the mixture, different hybrids of vanadium oxide-nitride compounds are synthesized. The electrode material prepared at 700 °C, i.e., VM-700, exhibits excellent cyclic stability retaining 92% of its reversible capacity after 200 cycles at a current density of 0.5 A g(-1) and attractive rate performance (220 mAh g(-1) ) under the current density of up to 2 A g(-1) . The outstanding electrochemical properties can be attributed to the synergistic effect from heterojunction form by the vanadium compound hybrids, the improved ability of the excellent conductive carbon for electron transfer, and restraining the expansion and aggregation of vanadium oxide-nitride in cycling. These interesting findings will provide a reference for the preparation of transition metal oxide and nitride composites as well. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Materials and characterization using acoustic nonlinearity parameters and harmonic generation - Effects of crystalline and amorphous structures

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Yost, William T.

    1990-01-01

    The effects of material structure on the nonlinearity parameters are reviewed. Problems discussed include definition of nonlinearity parameters, square-law nonlinearity and collinear beam-mixing, structure dependence of the nonlinearity parameters, negative nonlinearity parameters, and implications for materials characterization.

  19. Materials and characterization using acoustic nonlinearity parameters and harmonic generation - Effects of crystalline and amorphous structures

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Yost, William T.

    1990-01-01

    The effects of material structure on the nonlinearity parameters are reviewed. Problems discussed include definition of nonlinearity parameters, square-law nonlinearity and collinear beam-mixing, structure dependence of the nonlinearity parameters, negative nonlinearity parameters, and implications for materials characterization.

  20. High-strength and high-ductility nanostructured and amorphous metallic materials.

    PubMed

    Kou, Hongning; Lu, Jian; Li, Ying

    2014-08-20

    The development of materials with dual properties of high strength and high ductility has been a constant challenge since the foundation of the materials science discipline. The rapid progress of nanotechnology in recent decades has further brought this challenge to a new era. This Research News highlights a few newly developed strategies to optimize advanced nanomaterials and metallic glasses with exceptional dual mechanical properties of high strength and high ductility. A general concept of strain non-localization is presented to describe the role of multiscale (i.e., macroscale, microscale, nanoscale, and atomic scale) heterogeneities in the ductility enhancement of materials reputed to be intrinsically brittle, such as nanostructured metallic materials and bulk metallic glasses. These nanomaterials clearly form a new group of materials that display an extraordinary relationship between yield strength and the uniform elongation with the same chemical composition. Several other examples of nanomaterials such as those reinforced by nanoprecipitates will also be described.

  1. Molecular forensic science analysis of nuclear materials

    NASA Astrophysics Data System (ADS)

    Reilly, Dallas David

    Concerns over the proliferation and instances of nuclear material in the environment have increased interest in the expansion of nuclear forensics analysis and attribution programs. A new related field, molecular forensic science (MFS) has helped meet this expansion by applying common scientific analyses to nuclear forensics scenarios. In this work, MFS was applied to three scenarios related to nuclear forensics analysis. In the first, uranium dioxide was synthesized and aged at four sets of static environmental conditions and studied for changes in chemical speciation. The second highlighted the importance of bulk versus particle characterizations by analyzing a heterogeneous industrially prepared sample with similar techniques. In the third, mixed uranium/plutonium hot particles were collected from the McGuire Air Force Base BOMARC Site and analyzed for chemical speciation and elemental surface composition. This work has identified new signatures and has indicated unexpected chemical behavior under various conditions. These findings have lead to an expansion of basic actinide understanding, proof of MFS as a tool for nuclear forensic science, and new areas for expansion in these fields.

  2. Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays

    SciTech Connect

    Ehm,L.; Antao, S.; Chen, J.; Locke, D.; Michel, F.; Martin, D.; Yu, T.; Parise, J.; Lee, P.; et al.

    2007-01-01

    The method of high-energy total elastic X-ray scattering to determine the atomic structure of nanocrystalline, highly disordered, and amorphous materials is presented. The current state of the technique, its potential, and limitations are discussed with two successful studies on the pressure induced phase transition in mackinawite (FeS) and the high-pressure behavior of liquid gallium.

  3. A rare cause of breast mass that mimics carcinoma: Foreign body reaction to amorphous surgical material.

    PubMed

    Yazici, Burhan; Sever, Ali Riza; Mills, Philippa; Fish, David; Jones, Susan; Jones, Peter

    2007-01-01

    A breast mass caused by foreign body type granulomatous reaction to surgical material is a very rare lesion and may mimic carcinoma. Reported foreign materials have included suture materials, silicone, paraffin, gunpowder and carbon particles used for localization of a nonpalpable breast lesions. To our knowledge, a foreign body reaction to gauze sponge has not been reported previously. A 58-year-old woman who had an enlarging mass that mimicked breast carcinoma, due to foreign body reaction to gauze sponge is presented here, and relevant literature is reviewed.

  4. Hydrogen in amorphous silicon

    SciTech Connect

    Peercy, P. S.

    1980-01-01

    The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH/sub 1/) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon.

  5. Quantitative Fermi level tuning in amorphous organic semiconductor by molecular doping: Toward full understanding of the doping mechanism

    SciTech Connect

    Yang, Jin-Peng E-mail: uenon@faculty.chiba-u.jp; Wang, Wen-Qing; Cheng, Li-Wen; Zeng, Xiang-Hua; Bussolotti, Fabio; Li, Yan-Qing; Tang, Jian-Xin; Kera, Satoshi; Ueno, Nobuo E-mail: uenon@faculty.chiba-u.jp

    2016-08-29

    The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN){sub 6}]. We observed that HOMO of α-NPD shifts to the Fermi level (E{sub F}) in two different rates with the doping concentration of HAT(CN){sub 6}, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ∼5 × 10{sup 18} cm{sup −3} eV{sup −1}. From the theoretical simulation of the HAT(CN){sub 6}-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN){sub 6} molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ∼0.40 eV towards E{sub F}, and MR dependence of HOMO changes abruptly at MR ∼ 0.01 to a weaker dependence for MR > 0.01 due to future of the dopant acceptor level.

  6. The Molecular Volcano Revisited: Determination of Crack Propagation and Distribution During the Crystallization of Nanoscale Amorphous Solid Water Films.

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2012-02-02

    Temperature programmed desorption (TPD) is utilized to determine the length distribution of cracks formed through amorphous solid water (ASW) during crystallization. This distribution is determined by monitoring how the thickness of an ASW overlayer alters desorption of an underlayer of O2. As deposited the ASW overlayer prevents desorption of O2. During crystallization, cracks form through the ASW overlayer and open a path to vacuum which allows O2 to escape in a rapid episodic release known as the 'molecular volcano'. Sufficiently thick ASW overlayers further trap O2 resulting in a second O2 desorption peak commensurate with desorption of the last of the ASW overlayer. The evolution of this trapping peak with overlayer thickness is the basis for determining the distribution of crystallization induced cracks through the ASW. Reflection adsorption infrared spectroscopy (RAIRS) and TPD of multicomponent parfait structures of ASW, O2 and Kr indicate that a preponderance of these cracks propagate down from the outer surface of the ASW.

  7. Amorphous drug dispersions with mono- and diacyl lecithin: On molecular categorization of their feasibility and UV dissolution imaging.

    PubMed

    Gautschi, Nicolas; Van Hoogevest, Peter; Kuentz, Martin

    2015-08-01

    There is a growing interest in drug-phospholipid complexes and similar formulations that are mostly solid dispersions with high drug load. This study aims to explore the feasibility of such phospholipid-based solid dispersions as well as to characterize them. A particular aim was to compare monoacyl phosphatidylcholine (PC) with the diacyl excipient. The solid dispersions were manufactured using a solvent evaporation technique and characterized by means of differential scanning calorimetry and X-ray diffractometry. Density functional theory was used to calculate molecular frontier orbitals of the different compounds. Finally, the dissolution properties were analyzed in a flow-through cell by means of UV imaging. It was found that the ability to form solid dispersions with the phospholipids containing amorphous or solubilized drug (at equimolar ratio with the lipid) was dependent on the drug's frontier orbital energy, the enthalpy of fusion, as well as the log P value. In a subsequent dissolution study, UV imaging revealed pronounced surface swelling of the solid dispersions. Only the monoacyl PC was found to substantially enhance in vitro dissolution compared to pure drug. The gained understanding will support a future development of solid drug dispersions using phospholipids as matrix components.

  8. Quantitative Fermi level tuning in amorphous organic semiconductor by molecular doping: Toward full understanding of the doping mechanism

    NASA Astrophysics Data System (ADS)

    Yang, Jin-Peng; Wang, Wen-Qing; Bussolotti, Fabio; Cheng, Li-Wen; Li, Yan-Qing; Kera, Satoshi; Tang, Jian-Xin; Zeng, Xiang-Hua; Ueno, Nobuo

    2016-08-01

    The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN)6]. We observed that HOMO of α-NPD shifts to the Fermi level (EF) in two different rates with the doping concentration of HAT(CN)6, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ˜5 × 1018 cm-3 eV-1. From the theoretical simulation of the HAT(CN)6-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN)6 molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ˜0.40 eV towards EF, and MR dependence of HOMO changes abruptly at MR ˜ 0.01 to a weaker dependence for MR > 0.01 due to future of the dopant acceptor level.

  9. An ab initio molecular-orbital study on hydrogen-abstraction reactions at the growing surface of hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Nakajima, Kenji; Miyazaki, Kaori; Koinuma, Hideomi; Sato, Kota

    1998-07-01

    Energy profiles have been evaluated by an ab initio molecular-orbital method for hydrogen-abstraction reactions from surface model compounds of growing hydrogenated amorphous silicon (a-Si:H) by a SiH3 radical, a presumed main precursor to a-Si:H, as well as by a hydrogen radical which should coexist in the silane plasma chemical vapor deposition. The activation energies calculated for these two reactions decrease as the cluster size of the film surface model SinH2n+2 increases from n=1 to n=4 to converge for n⩾4. This trend is in parallel with the variation of atomic charge delocalization. Both activation energies (0.22 and 0.28 eV, respectively) for the largest model, Si7H16, were low enough to induce the hydrogen abstractions from the surface to form dangling bonds, which spontaneously react with SiH3 radicals to form Si-Si bond. From thus produced H3Si-Si≡surface, hydrogen can be eliminated with SiH3 (or H) to reproduce a dangling bond. The initial step of the a-Si:H film growth is deduced by the calculation to proceed through sequential reactions of spontaneous addition of SiH3 to the dangling bonds, and the hydrogen abstraction to reproduce dangling bonds.

  10. Molecular-scale tribology of amorphous carbon coatings: effects of film thickness, adhesion, and long-range interactions.

    PubMed

    Gao, G T; Mikulski, Paul T; Harrison, Judith A

    2002-06-19

    Classical molecular dynamics simulations have been conducted to investigate the atomic-scale friction and wear when hydrogen-terminated diamond (111) counterfaces are in sliding contact with diamond (111) surfaces coated with amorphous, hydrogen-free carbon films. Two films, with approximately the same ratio of sp(3)-to-sp(2) carbon, but different thicknesses, have been examined. Both systems give a similar average friction in the load range examined. Above a critical load, a series of tribochemical reactions occur resulting in a significant restructuring of the film. This restructuring is analogous to the "run-in" observed in macroscopic friction experiments and reduces the friction. The contribution of adhesion between the probe (counterface) and the sample to friction was examined by varying the saturation of the counterface. Decreasing the degree of counterface saturation, by reducing the hydrogen termination, increases the friction. Finally, the contribution of long-range interactions to friction was examined by using two potential energy functions that differ only in their long-range forces to examine friction in the same system.

  11. Molecular dynamics simulations on the local order of liquid and amorphous ZnTe

    NASA Astrophysics Data System (ADS)

    Rino, José Pedro; Borges, Denilson; Mota, Rita C.; Silva, Maurício A. P.

    2008-05-01

    Molecular dynamics studies of structural and dynamical correlations of molten and vitreous states under several conditions of density and temperature were performed. We use an effective recently proposed interatomic potential, consisting of two- and three-body covalent interactions which has successfully described the structural, dynamical, and structural phase transformation induced by pressure in ZnTe [D. S. Borges and J. P. Rino, Phys. Rev. B 72, 014107 (2005)]. The two-body term of the interaction potential consists of Coulomb interaction resulting from charge transfer, steric repulsion due to atomic sizes, charge-dipole interaction to include the effect of electronic polarizability of anions, and dipole-dipole (van der Waals) interactions. The three-body covalent term is a modification of the Stillinger-Weber potential. Molecular dynamics simulations in isobaric-isenthalpic ensemble have been performed for systems amounting to 4096 and 64 000 particles. Starting from a crystalline zinc-blende (ZB) structure, the system is initially heated until a very homogeneous liquid is obtained. The vitreous zinc telluride phase is attained by cooling the liquid at sufficiently fast cooling rates, while slower cooling rates lead to a disordered ZB crystalline structure. Two- and three-body correlations for the liquid and vitreous phases are analyzed through pair distribution functions, static structure factors, and bond angle distributions. In particular, the neutron static structure factor for the liquid phase is in very good agreement with both the reported experimental data and first-principles simulations.

  12. Megavoltage image contrast with low-atomic number target materials and amorphous silicon electronic portal imagers.

    PubMed

    Orton, E J; Robar, J L

    2009-03-07

    Low-atomic number (Z) targets have been shown to improve contrast in megavoltage (MV) images when using film-screen detection systems. This research aims to quantify the effect of low-Z targets on MV image contrast using an amorphous silicon electronic portal image detector (a-Si EPID) through both experimental measurement and Monte Carlo (MC) simulation. Experimental beams were produced with the linac running in the 6 MeV electron mode and with a 1.0 cm aluminum (Al, Z = 13) target replacing flattening filtration in the carousel, (6 MeV/Al). A 2100EX Varian linac equipped with an aS500 EPID was used with the QC3 MV phantom for the majority of contrast measurements. The BEAMnrc/EGSnrc MC package was used to build a model of the full imaging system including beam generation (linac head), the a-Si detector and the contrast phantom. The model accurately reproduces contrast measurements to within 2.5% for both the standard 6 MV therapy beam and the 6 MeV/Al beam. The contrast advantage of 6 MeV/Al over 6 MV, as quantified with the QC3 phantom, ranged from a factor increase of 1.6 +/- 0.1 to 2.8 +/- 0.2. Only a modest improvement in contrast was seen when the incident electron energy was reduced to 4 MeV (up to factor of 1.2 +/- 0.1 over 6 MeV/Al) or with removal of the copper build-up layer in the detector, (up to factor of 1.2 +/- 0.1 over 6 MeV/Al). Further decreasing the target Z, to beryllium (Be, Z = 4), at 4 MeV showed no significant improvement over 4 MeV/Al. Experimentally, the contrast advantage of 6 MeV/Al over 6 MV was found to decrease with increasing patient thickness, as can be expected due to selective attenuation of low-energy photons. At head and neck-like thicknesses, the low-Z advantage is a factor increase of 1.7 +/- 0.1.

  13. Synthesis and electrochemical performances of amorphous carbon-coated Sn-Sb particles as anode material for lithium-ion batteries

    SciTech Connect

    Wang Zhong; Tian Wenhuai; Liu Xiaohe; Yang Rong; Li Xingguo

    2007-12-15

    The amorphous carbon coating on the Sn-Sb particles was prepared from aqueous glucose solutions using a hydrothermal method. Because the outer layer carbon of composite materials is loose cotton-like and porous-like, it can accommodate the expansion and contraction of active materials to maintain the stability of the structure, and hinder effectively the aggregation of nano-sized alloy particles. The as-prepared composite materials show much improved electrochemical performances as anode materials for lithium-ion batteries compared with Sn-Sb alloy and carbon alone. This amorphous carbon-coated Sn-Sb particle is extremely promising anode materials for lithium secondary batteries and has a high potentiality in the future use. - Graphical abstract: The amorphous carbon coating on the Sn-Sb particles was prepared from aqueous glucose solutions using a hydrothermal method. Because the outer layer carbon of composite materials is loose cotton-like and porous-like, it can accommodate the expansion and contraction of active materials to maintain the stability of the structure, and hinder effectively the aggregation of nano-sized alloy particles.

  14. Amorphous silica-like carbon dioxide

    NASA Astrophysics Data System (ADS)

    Santoro, Mario; Gorelli, Federico A.; Bini, Roberto; Ruocco, Giancarlo; Scandolo, Sandro; Crichton, Wilson A.

    2006-06-01

    Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations. Here we report the synthesis of an amorphous, silica-like form of carbon dioxide, a-CO2, which we call `a-carbonia'. The compression of the molecular phase III of CO2 between 40 and 48GPa at room temperature initiated the transformation to the non-molecular amorphous phase. Infrared spectra measured at temperatures up to 680K show the progressive formation of C-O single bonds and the simultaneous disappearance of all molecular signatures. Furthermore, state-of-the-art Raman and synchrotron X-ray diffraction measurements on temperature-quenched samples confirm the amorphous character of the material. Comparison with vibrational and diffraction data for a-SiO2 and a-GeO2, as well as with the structure factor calculated for the a-CO2 sample obtained by first-principles molecular dynamics, shows that a-CO2 is structurally homologous to the other group IV dioxide glasses. We therefore conclude that the class of archetypal network-forming disordered systems, including a-SiO2, a-GeO2 and water, must be extended to include a-CO2.

  15. Specific volume-hole volume correlations in amorphous carbohydrates: effect of temperature, molecular weight, and water content.

    PubMed

    Townrow, Sam; Roussenova, Mina; Giardiello, Maria-Isabelle; Alam, Ashraf; Ubbink, Job

    2010-02-04

    The specific volume and the nanostructure of the free volume of amorphous blends of maltose with a narrow molecular weight distribution maltopolymer were systematically studied as a function of temperature, water content, pressure, and blend composition. Correlations between the hole free volume and the specific volume were investigated in the glassy and rubbery phases and in solution using positron annihilation lifetime spectroscopy (PALS) and pressure-volume-temperature (PVT) measurements, with the aim to provide a consolidated mechanistic understanding of the relation between changes in molecular packing and at the molecular level and the behavior of the specific volume at the macrolevel. Both specific volume and hole volume show a linear dependence on the temperature, but with a slope which is higher in the rubbery state than in the glassy state. As a function of temperature, the hole volume and the specific volume are linearly related, with no discontinuity at the glass transition temperature (T(g)). In the glassy state, both the specific volume and the hole volume decrease nonlinearly with the addition of maltose to the maltopolymer matrix, due to a more efficient molecular packing. For variations in carbohydrate composition, a linear dependence between the hole volume and the specific volume was again observed. The role of water was found to be significantly more complex, with increasing water content causing an increase in density in both the glassy and rubbery phases indicating that water exists in a highly dispersed state with a significantly lower specific molar volume than in bulk water. At very low water contents, the hole volume and the specific volume both decrease with increasing water content, which suggests that water acts as both a hole filler and a plasticizer. In the glassy state at slightly higher water contents, the specific volume continues to slowly decrease, but the hole size passes through a minimum before it starts to increase. This

  16. Suppressing molecular motions for enhanced room-temperature phosphorescence of metal-free organic materials

    PubMed Central

    Kwon, Min Sang; Yu, Youngchang; Coburn, Caleb; Phillips, Andrew W.; Chung, Kyeongwoon; Shanker, Apoorv; Jung, Jaehun; Kim, Gunho; Pipe, Kevin; Forrest, Stephen R.; Youk, Ji Ho; Gierschner, Johannes; Kim, Jinsang

    2015-01-01

    Metal-free organic phosphorescent materials are attractive alternatives to the predominantly used organometallic phosphors but are generally dimmer and are relatively rare, as, without heavy-metal atoms, spin–orbit coupling is less efficient and phosphorescence usually cannot compete with radiationless relaxation processes. Here we present a general design rule and a method to effectively reduce radiationless transitions and hence greatly enhance phosphorescence efficiency of metal-free organic materials in a variety of amorphous polymer matrices, based on the restriction of molecular motions in the proximity of embedded phosphors. Covalent cross-linking between phosphors and polymer matrices via Diels–Alder click chemistry is devised as a method. A sharp increase in phosphorescence quantum efficiency is observed in a variety of polymer matrices with this method, which is ca. two to five times higher than that of phosphor-doped polymer systems having no such covalent linkage. PMID:26626796

  17. Suppressing molecular motions for enhanced room-temperature phosphorescence of metal-free organic materials

    NASA Astrophysics Data System (ADS)

    Kwon, Min Sang; Yu, Youngchang; Coburn, Caleb; Phillips, Andrew W.; Chung, Kyeongwoon; Shanker, Apoorv; Jung, Jaehun; Kim, Gunho; Pipe, Kevin; Forrest, Stephen R.; Youk, Ji Ho; Gierschner, Johannes; Kim, Jinsang

    2015-12-01

    Metal-free organic phosphorescent materials are attractive alternatives to the predominantly used organometallic phosphors but are generally dimmer and are relatively rare, as, without heavy-metal atoms, spin-orbit coupling is less efficient and phosphorescence usually cannot compete with radiationless relaxation processes. Here we present a general design rule and a method to effectively reduce radiationless transitions and hence greatly enhance phosphorescence efficiency of metal-free organic materials in a variety of amorphous polymer matrices, based on the restriction of molecular motions in the proximity of embedded phosphors. Covalent cross-linking between phosphors and polymer matrices via Diels-Alder click chemistry is devised as a method. A sharp increase in phosphorescence quantum efficiency is observed in a variety of polymer matrices with this method, which is ca. two to five times higher than that of phosphor-doped polymer systems having no such covalent linkage.

  18. Solid state amorphization of nanocrystalline nickel by cryogenic laser shock peening

    SciTech Connect

    Ye, Chang Ren, Zhencheng; Zhao, Jingyi; Hou, Xiaoning; Dong, Yalin; Liu, Yang; Sang, Xiahan

    2015-10-07

    In this study, complete solid state amorphization in nanocrystalline nickel has been achieved through cryogenic laser shock peening (CLSP). High resolution transmission electron microscopy has revealed the complete amorphous structure of the sample after CLSP processing. A molecular dynamic model has been used to investigate material behavior during the shock loading and the effects of nanoscale grain boundaries on the amorphization process. It has been found that the initial nanoscale grain boundaries increase the initial Gibbs free energy before plastic deformation and also serve as dislocation emission sources during plastic deformation to contribute to defect density increase, leading to the amorphization of pure nanocrystalline nickel.

  19. Crystallization of amorphous lactose at high humidity studied by terahertz time domain spectroscopy

    NASA Astrophysics Data System (ADS)

    McIntosh, Alexander I.; Yang, Bin; Goldup, Stephen M.; Watkinson, Michael; Donnan, Robert S.

    2013-02-01

    We report the first use of terahertz time-domain spectroscopy (THz-TDS) to study the hydration and crystallization of an amorphous molecular solid at high humidity. Lactose in its amorphous and monohydrate forms exhibits different terahertz spectra due to the lack of long range order in the amorphous material. This difference allowed the transformation of amorphous lactose to its monohydrate form at high humidity to be studied in real time. Spectral fitting of frequency-domain data allowed kinetic data to be obtained and the crystallization was found to obey Avrami kinetics. Bulk changes during the crystallization could also be observed in the time-domain.

  20. Amorphous silica modeled with truncated and screened Coulomb interactions: A molecular dynamics simulation study

    NASA Astrophysics Data System (ADS)

    Carré, Antoine; Berthier, Ludovic; Horbach, Jürgen; Ispas, Simona; Kob, Walter

    2007-09-01

    We show that finite-range alternatives to the standard long-range pair potential for silica by van Beest et al. [Phys. Rev. Lett. 64, 1955 (1990)] might be used in molecular dynamics simulations. We study two such models that can be efficiently simulated since no Ewald summation is required. We first consider the Wolf method, where the Coulomb interactions are truncated at a cutoff distance rc such that the requirement of charge neutrality holds. Various static and dynamic quantities are computed and compared to results from simulations using Ewald summations. We find very good agreement for rc≈10Å. For lower values of rc, the long-range structure is affected which is accompanied by a slight acceleration of dynamic properties. In a second approach, the Coulomb interaction is replaced by an effective Yukawa interaction with two new parameters determined by a force fitting procedure. The same trend as for the Wolf method is seen. However, slightly larger cutoffs have to be used in order to obtain the same accuracy with respect to static and dynamic quantities as for the Wolf method.

  1. Mechanical behavior of linear amorphous polymers: comparison between molecular dynamics and finite-element simulations.

    PubMed

    Solar, Mathieu; Meyer, Hendrik; Gauthier, Christian; Fond, Christophe; Benzerara, Olivier; Schirrer, Robert; Baschnagel, Jörg

    2012-02-01

    This paper studies the rheology of weakly entangled polymer melts and films in the glassy domain and near the rubbery domain using two different methods: molecular dynamics (MD) and finite element (FE) simulations. In a first step, the uniaxial mechanical behavior of a bulk polymer sample is studied by means of particle-based MD simulations. The results are in good agreement with experimental data, and mechanical properties may be computed from the simulations. This uniaxial mechanical behavior is then implemented in FE simulations using an elasto-viscoelasto-viscoplastic constitutive law in a continuum mechanics (CM) approach. In a second step, the mechanical response of a polymer film during an indentation test is modeled with the MD method and with the FE simulations using the same constitutive law. Good agreement is found between the MD and CM results. This work provides evidence in favor of using MD simulations to investigate the local physics of contact mechanics, since the volume elements studied are representative and thus contain enough information about the microstructure of the polymer model, while surface phenomena (adhesion and surface tension) are naturally included in the MD approach.

  2. [Research strategy on molecular identification of animal medical material].

    PubMed

    Huang, Luqi; Tang, Shihuan; Li, Junde; Zhao, Jingxue

    2011-02-01

    This paper summarized and analyzed the status quo and problems about molecular identification of animal medical material, based on the facts, we proposed some research strategies, including uniting to tackle key problems, expanding the research species, accelerating manufacture and generalization of molecular identification kit, priming the research project of DNA barcoding, and establishing standard database on animal medical material.

  3. Molecularly Imprinted Materials: Towards the Next Generation

    DTIC Science & Technology

    2002-04-05

    SCINTILLATION POLYMERS : A NEW SENSOR CONCEPT Although molecularly imprinted polymers ( MIPs ) often display high binding affinity and specificity mimicking... sensors have been demonstrated over the past years. In general, molecular imprinting can be defined as a process of target directed synthesis of...efficiency. For these reasons imprinted polymer beads are preferable. Although the well-established suspension and dispersion polymerization methods

  4. Sol-gel strategies for amorphous inorganic membranes exhibiting molecular sieving characteristics

    SciTech Connect

    Raman, N.K.; Delattre, L.; Prakash, S.S.; Brinker, C.J. |

    1994-12-31

    We have used several sol-gel strategies to prepare supported inorganic membranes by a process that combines the features of slip-casting and dip-coating. To be viable the deposited membranes must exhibit both high flux and high selectivity. For porous membranes these requirements are met by extremely thin, defect-free porous films exhibiting a narrow size distribution of very small pores. This paper considers the use of polymeric silica and hybrid-organosilyl precursor sols in the context of the underlying physics and chemistry of the membrane deposition process. Since the average membrane pore size is ultimately established by the collapse of the gel network upon drying, it is necessary to promote polymer interpenetration and collapse during membrane deposition in order to achieve the very small pore sizes necessary for molecular sieving. For polymeric sols, this is accomplished using rather weakly branched polymers characterized by fractal dimension D < 1.5 under deposition conditions in which the silica condensation rate is minimized. By analogy to organic polymer sols and gels, we believe that the breadth of the pore size distribution can be influenced by the occurrence of micro-phase separation during membrane deposition. Minimization of the condensation rate not only fosters polymer collapse but should inhibit phase separation, leading to a narrower pore size distribution. The formation of microporosity through collapse of the gel network requires that small pores are achieved at the expense of membrane porosity. Incorporation of organic template ligands within a dense silica matrix followed by their removal allows us to independently control pore size and pore volume through the size and volume fraction of the organic template. Such strategies can be used to create microporous films with large volume fraction porosities.

  5. Trehalose amorphization and recrystallization.

    PubMed

    Sussich, Fabiana; Cesàro, Attilio

    2008-10-13

    The stability of the amorphous trehalose prepared by using several procedures is presented and discussed. Amorphization is shown to occur by melting (T(m)=215 degrees C) or milling (room temperature) the crystalline anhydrous form TRE-beta. Fast dehydration of the di-hydrate crystalline polymorph, TRE-h, also produces an amorphous phase. Other dehydration procedures of TRE-h, such as microwave treatment, supercritical extraction or gentle heating at low scan rates, give variable fractions of the polymorph TRE-alpha, that undergo amorphization upon melting (at lower temperature, T(m)=130 degrees C). Additional procedures for amorphization, such as freeze-drying, spray-drying or evaporation of trehalose solutions, are discussed. All these procedures are classified depending on the capability of the undercooled liquid phase to undergo cold crystallization upon heating the glassy state at temperatures above the glass transition temperature (T(g)=120 degrees C). The recrystallizable amorphous phase is invariably obtained by the melt of the polymorph TRE-alpha, while other procedures always give an amorphous phase that is unable to crystallize above T(g). The existence of two different categories is analyzed in terms of the transformation paths and the hypothesis that the systems may exhibit different molecular mobilities.

  6. Observation of directly interacting coherent two-level systems in an amorphous material.

    PubMed

    Lisenfeld, Jürgen; Grabovskij, Grigorij J; Müller, Clemens; Cole, Jared H; Weiss, Georg; Ustinov, Alexey V

    2015-02-05

    Parasitic two-level tunnelling systems originating from structural material defects affect the functionality of various microfabricated devices by acting as a source of noise. In particular, superconducting quantum bits may be sensitive to even single defects when these reside in the tunnel barrier of the qubit's Josephson junctions, and this can be exploited to observe and manipulate the quantum states of individual tunnelling systems. Here, we detect and fully characterize a system of two strongly interacting defects using a novel technique for high-resolution spectroscopy. Mutual defect coupling has been conjectured to explain various anomalies of glasses, and was recently suggested as the origin of low-frequency noise in superconducting devices. Our study provides conclusive evidence of defect interactions with full access to the individual constituents, demonstrating the potential of superconducting qubits for studying material defects. All our observations are consistent with the assumption that defects are generated by atomic tunnelling.

  7. Amorphous pharmaceutical solids.

    PubMed

    Vranić, Edina

    2004-07-01

    Amorphous forms are, by definition, non-crystalline materials which possess no long-range order. Their structure can be thought of as being similar to that of a frozen liquid with the thermal fluctuations present in a liquid frozen out, leaving only "static" structural disorder. The amorphous solids have always been an essential part of pharmaceutical research, but the current interest has been raised by two developments: a growing attention to pharmaceutical solids in general, especially polymorphs and solvates and a revived interest in the science of glasses and the glass transition. Amorphous substances may be formed both intentionally and unintentionally during normal pharmaceutical manufacturing operations. The properties of amorphous materials can be exploited to improve the performance of pharmaceutical dosage forms, but these properties can also give rise to unwanted effects that need to be understood and managed in order for the systems to perform as required.

  8. Molecular dynamics at ambient and elevated pressure of the amorphous pharmaceutical: Nonivamide (pelargonic acid vanillylamide)

    NASA Astrophysics Data System (ADS)

    Wojnarowska, Z.; Hawelek, L.; Paluch, M.; Sawicki, W.; Ngai, K. L.

    2011-01-01

    Broadband dielectric spectroscopy was employed to investigate the relaxation dynamics of supercooled and glassy nonivamide—the synthetic form of capsaicin being the most spicy-hot substance known to man. The material is of great importance in the pharmaceutical industry because it has wide usage in the medical field for relief of pain, and more recently it has been shown to be effective in fighting cancers. Dielectric measurements carried out at various isobaric and isothermal conditions (pressure up to 400 MPa) revealed very narrow α-loss peak and unresolved secondary relaxations appearing in the form of an excess wing on the high frequency flank. Moreover, our studies have shown the shape of dielectric loss spectrum at any fixed loss peak frequency is invariant to different combinations of temperature and pressure, i.e., validity of the time-temperature-pressure superpositioning. We also found the fragility index is nearly constant on varying pressure. This property is likely due to the unusual structure of nonivamide, which has a part characteristic of van der Waals glass-former and another part characteristic of hydrogen-bonded glass-former.

  9. Reversible devitrification in amorphous A s2S e3 under pressure

    NASA Astrophysics Data System (ADS)

    Ahmad, Azkar Saeed; Lou, Hong-Bo; Lin, Chuan-Long; Li, Ai-Guo; Yang, Ke; Glazyrin, K.; Liermann, H. P.; Franz, Hermann; Stâhl, Kenny; Cui, Shuo; Bureau, Bruno; Zhang, Dong-Xian; Wang, Xiao-Dong; Cao, Qing-Ping; Greer, A. Lindsay; Jiang, Jian-Zhong

    2016-11-01

    In pressure-induced reversible structural transitions, the term "reversible" refers to the recovery of the virgin structure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitions have been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structure upon complete depressurization has been lacking. In amorphous A s2S e3 (a -A s2S e3 ) chalcogenide, however, we report a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidence that upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin (as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations, we elucidate that the amorphization is mediated by a surplus of total free energy in the high-pressure face-centered cubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphous phase is a consequence of an enhancement in covalent bonding character over interlayer forces upon complete decompression. Furthermore, we observed a two-dimensional to three-dimensional network transition under compression and its reversibility upon decompression.

  10. Molecular dynamics simulations of the tribological behaviour of a water-lubricated amorphous carbon-fluorine PECVD coating

    NASA Astrophysics Data System (ADS)

    Rullich, Markus; Weiss, Volker C.; Frauenheim, Thomas

    2013-07-01

    Hybrid bearings comprising ceramic balls and steel rings exhibit increased wear-resistance and a reduced coefficient of friction (COF) compared with standard steel bearings. Using plasma-enhanced chemical vapour deposition (PECVD) coatings to modify the surface properties, the performance of these bearings can be further improved. Fluorine-containing amorphous hydrogenated carbon (a-C : F : H) films are well suited to this purpose. To study the influence of such coatings on the friction characteristics of key parts of hybrid bearings, a model of an a-C : F : H film was constructed and employed in molecular dynamics simulations of two slabs sliding past each other, lubricated by water. With one slab being pulled by a virtual spring, the perpendicular force (load) was kept constant using a barostat. For comparison, a system of two silicon dioxide (cristobalite) slabs and a mixed system consisting of a cristobalite slab and an a-C : F : H slab were investigated. Our results indicate a linear dependence of the friction force on the perpendicular force. With an increasing amount of water between the slabs, the COFs decrease. A decrease in temperature leads to an increased COF, while a decrease in the relative velocity of the slabs does not influence the COF between two a-C : F : H slabs, but reduces the COF for the other two systems. Our results for the COF and its dependence on temperature and relative sliding velocity generally agree well both with experiments and with simulations for similar systems reported in the literature.

  11. Neutron Compton scattering investigation of sodium hydride: From bulk material to encapsulated nanoparticulates in amorphous silica gel

    NASA Astrophysics Data System (ADS)

    Seel, A. G.; Sartbaeva, A.; Mayers, J.; Ramirez-Cuesta, A. J.; Edwards, P. P.

    2011-03-01

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  12. Neutron Compton scattering investigation of sodium hydride: from bulk material to encapsulated nanoparticulates in amorphous silica gel.

    PubMed

    Seel, A G; Sartbaeva, A; Mayers, J; Ramirez-Cuesta, A J; Edwards, P P

    2011-03-21

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  13. Case Study: Somatic Sprouts and Halo-Like Amorphous Materials of the Purkinje Cells in Huntington's Disease.

    PubMed

    Sakai, Kenji; Ishida, Chiho; Morinaga, Akiyoshi; Takahashi, Kazuya; Yamada, Masahito

    2015-12-01

    We described a 63-year-old Japanese female with genetically confirmed Huntington's disease who showed unusual pathological findings in the cerebellum. This case exhibited typical neuropathological features as Huntington's disease, including severe degeneration of the neostriatum and widespread occurrence of ubiquitin and expanded polyglutamine-positive neuronal intranuclear and intracytoplasmic inclusions. The cerebellum was macroscopically unremarkable; however, somatic sprouts and halo-like amorphous materials of Purkinje cell with a large amount of torpedoes were noteworthy. Furthermore, the Purkinje cells were found to have granular cytoplasmic inclusions. Somatic sprouting is a form of degenerated Purkinje cell exhibited in several specific conditions. Although this finding usually appeared in developmental brains, several neurodegenerative disorders, including Menkes kinky hair disease, familial spinocerebellar ataxia, acute encephalopathy linked to familial hemiplegic migraine, and several other conditions, have been reported showing sprouting from the soma of Purkinje cell. We propose that Huntington's disease is another degenerative condition associated with these distinct neuropathological findings of Purkinje cell. Abnormally accumulated huntingtin protein in the cytoplasm could be related to the development of these structures.

  14. Synthesis of quenchable amorphous diamond

    DOE PAGES

    Zeng, Zhidan; Yang, Liuxiang; Zeng, Qiaoshi; ...

    2017-08-22

    Diamond owes its unique mechanical, thermal, optical, electrical, chemical, and biocompatible materials properties to its complete sp3-carbon network bonding. Crystallinity is another major controlling factor for materials properties. Although other Group-14 elements silicon and germanium have complementary crystalline and amorphous forms consisting of purely sp3 bonds, purely sp3-bonded tetrahedral amorphous carbon has not yet been obtained. In this letter, we combine high pressure and in situ laser heating techniques to convert glassy carbon into “quenchable amorphous diamond”, and recover it to ambient conditions. Our X-ray diffraction, high-resolution transmission electron microscopy and electron energy-loss spectroscopy experiments on the recovered sample andmore » computer simulations confirm its tetrahedral amorphous structure and complete sp3 bonding. This transparent quenchable amorphous diamond has, to our knowledge, the highest density among amorphous carbon materials, and shows incompressibility comparable to crystalline diamond.« less

  15. Pressure-driven transformation of the ordering in amorphous network-forming materials

    NASA Astrophysics Data System (ADS)

    Zeidler, Anita; Salmon, Philip S.

    2016-06-01

    The pressure-induced changes to the structure of disordered oxide and chalcogenide network-forming materials are investigated on the length scales associated with the first three peaks in measured diffraction patterns. The density dependence of a given peak position does not yield the network dimensionality, in contrast to metallic glasses where the results indicate a fractal geometry with a local dimensionality of ≃5 /2 . For oxides, a common relation is found between the intermediate-range ordering, as described by the position of the first sharp diffraction peak, and the oxygen-packing fraction, a parameter that plays a key role in driving changes to the coordination number of local motifs. The first sharp diffraction peak can therefore be used to gauge when topological changes are likely to occur, events that transform network structures and their related physical properties.

  16. The photoexcitation of crystalline ice and amorphous solid water: A molecular dynamics study of outcomes at 11 K and 125 K

    SciTech Connect

    Crouse, J.; Loock, H.-P. Cann, N. M.

    2015-07-21

    Photoexcitation of crystalline ice Ih and amorphous solid water at 7-9 eV is examined using molecular dynamics simulations and a fully flexible water model. The probabilities of photofragment desorption, trapping, and recombination are examined for crystalline ice at 11 K and at 125 K and for amorphous solid water at 11 K. For 11 K crystalline ice, a fully rigid water model is also employed for comparison. The kinetic energy of desorbed H atoms and the distance travelled by trapped fragments are correlated to the location and the local environment of the photoexcited water molecule. In all cases, H atom desorption is found to be the most likely outcome in the top bilayer while trapping of all photofragments is most probable deeper in the solid where the likelihood for recombination of the fragments into H{sub 2}O molecules also rises. Trajectory analysis indicates that the local hydrogen bonding network in amorphous solid water is more easily distorted by a photodissociation event compared to crystalline ice. Also, simulations indicate that desorption of OH radicals and H{sub 2}O molecules are more probable in amorphous solid water. The kinetic energy distributions for desorbed H atoms show a peak at high energy in crystalline ice, arising from photoexcited water molecules in the top monolayer. This peak is less pronounced in amorphous solid water. H atoms that are trapped may be displaced by up to ∼10 water cages, but migrate on average 3 water cages. Trapped OH fragments tend to stay near the original solvent cage.

  17. Elastic and thermal expansion asymmetry in dense molecular materials

    NASA Astrophysics Data System (ADS)

    Burg, Joseph A.; Dauskardt, Reinhold H.

    2016-09-01

    The elastic modulus and coefficient of thermal expansion are fundamental properties of elastically stiff molecular materials and are assumed to be the same (symmetric) under both tension and compression loading. We show that molecular materials can have a marked asymmetric elastic modulus and coefficient of thermal expansion that are inherently related to terminal chemical groups that limit molecular network connectivity. In compression, terminal groups sterically interact to stiffen the network, whereas in tension they interact less and disconnect the network. The existence of asymmetric elastic and thermal expansion behaviour has fundamental implications for computational approaches to molecular materials modelling and practical implications on the thermomechanical strains and associated elastic stresses. We develop a design space to control the degree of elastic asymmetry in molecular materials, a vital step towards understanding their integration into device technologies.

  18. Elastic and thermal expansion asymmetry in dense molecular materials.

    PubMed

    Burg, Joseph A; Dauskardt, Reinhold H

    2016-09-01

    The elastic modulus and coefficient of thermal expansion are fundamental properties of elastically stiff molecular materials and are assumed to be the same (symmetric) under both tension and compression loading. We show that molecular materials can have a marked asymmetric elastic modulus and coefficient of thermal expansion that are inherently related to terminal chemical groups that limit molecular network connectivity. In compression, terminal groups sterically interact to stiffen the network, whereas in tension they interact less and disconnect the network. The existence of asymmetric elastic and thermal expansion behaviour has fundamental implications for computational approaches to molecular materials modelling and practical implications on the thermomechanical strains and associated elastic stresses. We develop a design space to control the degree of elastic asymmetry in molecular materials, a vital step towards understanding their integration into device technologies.

  19. Configuration diffusion in glassy, amorphous polymers: Effects of polymer structure and dynamics on permeation via molecular simulation

    NASA Astrophysics Data System (ADS)

    Boshoff, Jan H. D.

    The goals of this dissertation are to provide a basis for understanding the fundamental mechanisms of, and the effects of nano-confinement on, diffusion in glassy, amorphous polymers. These polymers are extensively used as membranes in numerous separation applications such as drug delivery devices, air separation and water desalination. Molecular simulation is used to elucidate the effects of the structure and dynamics of glassy polymers on small molecule permeation. Particularly, the effects of thermal fluctuations on the diffusion mechanism and anomalous diffusion regime is shown for small gas diffusion in atactic polypropylene. Furthermore, polymer backbone conformational statistics of three different polypropylene models show that the united atom approximation favors gauche conformations in the polymer backbone, leading to artificially high values for Cinfinity for stereo-regular polypropylene. Diffusion results of He and CH4 in the refined model is presented using a force-decomposed/replicated data parallel molecular dynamics algorithm on a pseudo-explicit atom model proposed in literature. Excellent agreement with experimental values of the diffusivity is obtained. These results constitute the most accurate a priori prediction of small molecule diffusion in atactic polypropylene to date. Finally, the effects of nano-confinement on the polymer structure and dynamics, and consequently the permeation and selectivity was probed by He and CH4 permeation in aPP "adsorbed" in idealized pores of size smaller than the radius of gyration of the polymer. The extent of polymer structural changes is found to be closely correlated with the local correlation length xi of the polymer. Within xi from the pore surface, the polymer has a lower density, aligns with the pore direction and is found to pack in layers, while the polymer structure is identical to the bulk further than xi from the pore surface. These changes in polymer structure lead to substantial increases (up to

  20. Hybrid materials chemistry: Spectroscopic studies of molecular materials, nanoscale materials and their combinations

    NASA Astrophysics Data System (ADS)

    Marlatt, Craig W.

    Materials chemistry is a widely-used label within the overall field of chemistry, with a diverse range of possible applications. In this report, two classes of materials are discussed. Host-guest molecular systems that operate under supramolecular principles are examined via Raman spectroscopy and electrochemistry, and a sensing application for such systems is offered in the proof-of-principle detection of nitroaromatic explosives via host-guest binding. Next, metallic nanostructures that have tunable optical properties are synthesized and characterized to demonstrate that tunable nature, and the way such structures might be used for surface-enhanced Raman studies of the previously described host-guest systems is discussed by examining the current literature. Lastly, strategies to couple molecular systems and nanostructure systems are discussed and developed, and speculation on possible applications utilizing these coupled systems is made based on recent literature and the established themes of the research in this report.

  1. Characterizing the Phyllosilicates and Amorphous Phases Found by MSL Using Laboratory XRD and EGA Measurements of Natural and Synthetic Materials (Invited)

    NASA Astrophysics Data System (ADS)

    Rampe, E. B.; Morris, R. V.; Chipera, S.; Bish, D. L.; Bristow, T.; Archer, P. D.; Blake, D.; Achilles, C.; Ming, D. W.; Vaniman, D.; Crisp, J. A.; Des Marais, D. J.; Downs, R.; Farmer, J. D.; Morookian, J.; Morrison, S.; Sarrazin, P.; Spanovich, N.; Treiman, A. H.; Yen, A. S.; Team, M.

    2013-12-01

    The Curiosity Rover landed on the Peace Vallis alluvial fan in Gale crater on August 5, 2012. A primary mission science objective is to search for past habitable environments, and, in particular, to assess the role of past water. Identifying the minerals and mineraloids that result from aqueous alteration at Gale crater is essential for understanding past aqueous processes at the MSL landing site and hence for interpreting the site's potential habitability. X-ray diffraction (XRD) data from the CheMin instrument and evolved gas analyses (EGA) from the SAM instrument have helped the MSL science team identify phases that resulted from aqueous processes: phyllosilicates and amorphous phases were measure in two drill samples (John Klein and Cumberland) obtained from the Sheepbed Member, Yellowknife Bay Fm., which is believed to represent a fluvial-lacustrine environment. A third set of analyses was obtained from scoop samples from the Rocknest sand shadow. Chemical data from the APXS instrument have helped constrain the chemical compositions of these secondary phases and suggest that the phyllosilicate component is Mg-enriched and the amorphous component is Fe-enriched, relatively Si-poor, and S- and H-bearing. To refine the phyllosilicate and amorphous components in the samples measured by MSL, we measured XRD and EGA data for a variety of relevant natural terrestrial phyllosilicates and synthetic mineraloids in laboratory testbeds of the CheMin and SAM instruments. Specifically, Mg-saturated smectites and vermiculites were measured with XRD at low relative humidity to understand the behavior of the 001 reflections under Mars-like conditions. Our laboratory XRD measurements suggest that interlayer cation composition affects the hydration state of swelling clays at low RH and, thus, the 001 peak positions. XRD patterns of synthetic amorphous materials, including allophane, ferrihydrite, and hisingerite were used in full-pattern fitting (FULLPAT) models to help

  2. Erbium-Doped Amorphous Carbon-Based Thin Films: A Photonic Material Prepared by Low-Temperature RF-PEMOCVD

    PubMed Central

    Hsu, Hui-Lin; Leong, Keith R.; Teng, I-Ju; Halamicek, Michael; Juang, Jenh-Yih; Jian, Sheng-Rui; Qian, Li; Kherani, Nazir P.

    2014-01-01

    The integration of photonic materials into CMOS processing involves the use of new materials. A simple one-step metal-organic radio frequency plasma enhanced chemical vapor deposition system (RF-PEMOCVD) was deployed to grow erbium-doped amorphous carbon thin films (a-C:(Er)) on Si substrates at low temperatures (<200 °C). A partially fluorinated metal-organic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Erbium(+III) or abbreviated Er(fod)3, was incorporated in situ into a-C based host. Six-fold enhancement of Er room-temperature photoluminescence at 1.54 μm was demonstrated by deuteration of the a-C host. Furthermore, the effect of RF power and substrate temperature on the photoluminescence of a-C:D(Er) films was investigated and analyzed in terms of the film structure. Photoluminescence signal increases with increasing RF power, which is the result of an increase in [O]/[Er] ratio and the respective erbium-oxygen coordination number. Moreover, photoluminescence intensity decreases with increasing substrate temperature, which is attributed to an increased desorption rate or a lower sticking coefficient of the fluorinated fragments during film growth and hence [Er] decreases. In addition, it is observed that Er concentration quenching begins at ~2.2 at% and continues to increase until 5.5 at% in the studied a-C:D(Er) matrix. This technique provides the capability of doping Er in a vertically uniform profile. PMID:28788530

  3. Molecular glass positive i-line photoresist materials containing 2,1,4-DNQ and acid labile group

    NASA Astrophysics Data System (ADS)

    Wang, Liyuan; Yu, Jinxing; Xu, Na

    2010-04-01

    Recent years increasing attention has been given to molecular glass resist materials. In this paper, maleopimaric acid, cycloaddition reaction product of rosin with maleic anhydride, was reacted with hydroxylamine and then further esterified with 2-diazo-1-naphthoquinone-4-sulfonyl chloride to give N-hydroxy maleopimarimide sulfonate. The carboxylic acid group of the compound was then protected by the reaction of this compound with vinyl ethyl ether or dihydropyran. Thus obtained compounds were amorphous. When irradiated with i-line light, the 2,1,4-DNQ group undergo photolysis not only to give off nitrogen gas but also generate sulfonic acid which can result in the decomposition of the acid labile group. So, a novel chemically amplified positive i-line molecular glass photoresists can be formed by the compound and other acidolytic molecular glass compounds. The lithographic performance of the resist materials is evaluated.

  4. Cluster adsorption on amorphous and crystalline surfaces - A molecular dynamics study of model Pt on Cu and model Pd on Pt

    NASA Technical Reports Server (NTRS)

    Garofalini, S. H.; Halicioglu, T.; Pound, G. M.

    1981-01-01

    Molecular dynamics was used to study the structure, dispersion and short-time behavior of ten-atom clusters adsorbed onto amorphous and crystalline substrates, in which the cluster atoms differed from the substrate atoms. Two adatom-substrate model systems were chosen; one, in which the interaction energy between adatom pairs was greater than that between substrate pairs, and the other, in which the reverse was true. At relatively low temperature ranges, increased dispersion of cluster atoms occurred: (a) on the amorphous substrate as compared to the FCC(100) surface, (b) with increasing reduced temperature, and (c) with adatom-substrate interaction energy stronger than adatom-adatom interaction. Two-dimensional clusters (rafts) on the FCC(100) surface displayed migration of edge atoms only, indicating a mechanism for the cluster rotation and shape changes found in experimental studies.

  5. Atomic packing and diffusion in Fe85Si2B9P4 amorphous alloy analyzed by ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2015-05-01

    In the work reported in this paper, ab initio molecular dynamics simulation was performed on Fe85Si2B9P4 amorphous alloy. Preferred atomic environment of the elements was analyzed with Voronoi polyhedrons. It showed that B and P atoms prefer less neighbors compared with Fe and Si, making them structurally incompatible with Fe rich structure and repulsive to the formation of α-Fe. However, due to the low bonding energy of B and P caused by low coordination number, the diffusion rates of them were considerably large, resulting in the requirement of fast annealing for achieving optimum nano-crystallization for its soft magnetic property. The simulation work also indicates that diffusion rate in amorphous alloy is largely determined by bonding energy rather than atomic size.

  6. Cluster adsorption on amorphous and crystalline surfaces - A molecular dynamics study of model Pt on Cu and model Pd on Pt

    NASA Technical Reports Server (NTRS)

    Garofalini, S. H.; Halicioglu, T.; Pound, G. M.

    1981-01-01

    Molecular dynamics was used to study the structure, dispersion and short-time behavior of ten-atom clusters adsorbed onto amorphous and crystalline substrates, in which the cluster atoms differed from the substrate atoms. Two adatom-substrate model systems were chosen; one, in which the interaction energy between adatom pairs was greater than that between substrate pairs, and the other, in which the reverse was true. At relatively low temperature ranges, increased dispersion of cluster atoms occurred: (a) on the amorphous substrate as compared to the FCC(100) surface, (b) with increasing reduced temperature, and (c) with adatom-substrate interaction energy stronger than adatom-adatom interaction. Two-dimensional clusters (rafts) on the FCC(100) surface displayed migration of edge atoms only, indicating a mechanism for the cluster rotation and shape changes found in experimental studies.

  7. Slow molecular mobility in the crystalline and amorphous solid states of pentitols: a study by thermally stimulated depolarisation currents and by differential scanning calorimetry.

    PubMed

    Diogo, Hermínio P; Pinto, Susana S; Moura Ramos, Joaquim J

    2007-05-21

    The molecular mobility of the pentitol isomers (xylitol, adonitol, D-arabitol and L-arabitol) was studied by thermally stimulated depolarisation currents (TSDC) in the crystalline and in the amorphous solid states. Differential scanning calorimetry (DSC) was used to characterise the phase transformations, to detect polymorphism and to analyse the dynamics of the structural relaxation in the glassy state (from the heating rate dependence of the onset temperature of the glass transition signal). The mobility in crystalline xylitol and adonitol displays features that are different compared with crystalline arabitols. No difference of the dynamic behaviour seems to emerge from our results on the primary and secondary relaxations in the amorphous isomeric pentitols. The values of the steepness index or fragility obtained in this work by TSDC and DSC are compared with the values reported in the literature obtained from other experimental techniques, and with values predicted by empirical formulae.

  8. Molecular and nanoscale materials and devices in electronics.

    PubMed

    Fu, Lei; Cao, Lingchao; Liu, Yunqi; Zhu, Daoben

    2004-12-13

    Over the past several years, there have been many significant advances toward the realization of electronic computers integrated on the molecular scale and a much greater understanding of the types of materials that will be useful in molecular devices and their properties. It was demonstrated that individual molecules could serve as incomprehensibly tiny switch and wire one million times smaller than those on conventional silicon microchip. This has resulted very recently in the assembly and demonstration of tiny computer logic circuits built from such molecular scale devices. The purpose of this review is to provide a general introduction to molecular and nanoscale materials and devices in electronics.

  9. Multimillion atom molecular dynamics simulations of glasses and ceramic materials

    NASA Astrophysics Data System (ADS)

    Vashishta, Priya; Kalia, Rajiv K.; Nakano, Aiichiro

    1999-11-01

    Molecular dynamics simulations are a powerful tool for studying physical and chemical phenomena in materials. In these lectures we shall review the molecular dynamics method and its implementation on parallel computer architectures. Using the molecular dynamics method we will study a number of materials in different ranges of density, temperature, and uniaxial strain. These include structural correlations in silica glass under pressure, crack propagation in silicon nitride films, sintering of silicon nitride nanoclusters, consolidation of nanophase materials, and dynamic fracture. Multimillion atom simulations of oxidation of aluminum nanoclusters and nanoindentation in silicon nitride will also be discussed.

  10. Estimation of the free energy of adsorption of a polypeptide on amorphous SiO2 from molecular dynamics simulations and force spectroscopy experiments.

    PubMed

    Meißner, Robert Horst; Wei, Gang; Ciacchi, Lucio Colombi

    2015-08-21

    Estimating the free energy of adsorption of materials-binding peptides is fundamental to quantify their interactions across bio/inorganic interfaces, but is difficult to achieve both experimentally and theoretically. We employ a combination of molecular dynamics (MD) simulations and dynamical force-spectroscopy experiments based on atomic force microscopy (AFM) to estimate the free energy of adsorption ΔGads of a (GCRL) tetrapeptide on amorphous SiO2 in pure water. The results of both equilibrium, advanced sampling MD and non-equilibrium, steered MD are compared with those of two different approaches used to extract ΔGads from the dependence of experimentally measured adhesion forces on the applied AFM loading rates. In order to obtain unambiguous peak forces and bond loading rates from steered MD trajectories, we have developed a novel numerical protocol based on a piecewise-harmonic fit of the adhesion work profile along each trajectory. The interpretation of the experiments has required a thorough quantitative characterization of the elastic properties of polyethylene glycol linker molecules used to tether (GCRL)15 polypeptides to AFM cantilevers, and of the polypeptide itself. All obtained ΔGads values fall within a relatively narrow window between -5 and -9 kcal mol(-1), but can be associated with large relative error bars of more than 50%. Among the different approaches compared, Replica Exchange with Solute Tempering simulations augmented with MetaDynamics (RESTMetaD) and fitting of dynamic force spectroscopy experiments with the model of Friddle and De Yoreo lead to the most reliable ΔGads estimates.

  11. Electrochemical performance of natural graphite coated by amorphous carbon using two step synthesis processes at various temperatures for anode material in Li-ion battery

    NASA Astrophysics Data System (ADS)

    Rohman, F.; Nikmah, S. M.; Triwibowo, J.

    2017-03-01

    Electrochemical performance of natural graphite as anode material in the Li-ion battery has been modified by coating this particle with amorphous carbon through two step synthesis process. Citric acid as the amorphous carbon source was mixed with natural graphite (NG) in the ethanol solvent at 80 °C using magnetic stirrer. In the first step, the mixture of NG and CA were dried at 350 °C for 5 hours under argon atmosphere to evaporate the solvent. This dried mixture was then sintered at different temperature i.e. 500 °C (labeled CNG500), 600 °C (CNG600) and 700 °C (CNG700) under argon atmosphere to form amorphous carbon layer on the surface of NG. The crystal structure and morphology of the particles were characterized by using XRD, SEM and TEM. Electrochemical performance and charge-discharge of amorphous carbon-coated graphite has been evaluated by cyclic voltammetry and WBCS 3000, respectively. Cyclic voltammogram showed the working potential and redox reaction peak of the sample. Charge-discharge data was obtained to determine the specific capacity of the sample at 0.1C.

  12. Self-Climbed Amorphous Carbon Nanotubes Filled with Transition Metal Oxide Nanoparticles for Large Rate and Long Lifespan Anode Materials in Lithium Ion Batteries.

    PubMed

    Li, Shuoyu; Liu, Yuyi; Guo, Peisheng; Wang, Chengxin

    2017-08-16

    A composed material of amorphous carbon nanotubes (ACNTs) and encapsulated transition metal oxide (TMOs) nanoparticles was prepared by a common thermophysics effect, which is named the Marangoni effect, and a simple anneal process. The prepared ropy solution would form a Marangoni convection and climb into the channel of anodic aluminum oxide template (AAO) spontaneously. The ingenious design of the preparation method determined a distinctive structure of TMOs nanoparticles with a size of ∼5 nm and amorphous carbon coated outside full in the ACNTs. Here we prepared the ferric oxide (Fe2O3) nanoparticles and Fe2O3 mixed with manganic oxide (Fe2O3&Mn2O3) nanoparticles encapsulated in ACNTs as two anode materials of lithium ion batteries' the TMOs-filled ACNTs presented an evolutionary electrochemical performance in some respects of highly reversible capacity and excellent cycling stability (880 mA h g(-1) after 150 cycles).

  13. Atomic layer deposition of amorphous oxygen-deficient TiO2-x on carbon nanotubes as cathode materials for lithium-air batteries

    NASA Astrophysics Data System (ADS)

    Yang, Jingbo; Ma, Dingtao; Li, Yongliang; Zhang, Peixin; Mi, Hongwei; Deng, Libo; Sun, Lingna; Ren, Xiangzhong

    2017-08-01

    The amorphous oxygen-deficient TiO2-x thin layer coated carbon nanotubes (CNTs) are synthesized by atomic layer deposition and employed as cathode materials for lithium-air battery. The cathode demonstrates high electrocatalytic activity toward electrode reactions, resulting from the introduction of oxygen-deficient TiO2-x into the nanocomposites. It is found that the intrinsically isotropic nature of amorphous TiO2 which a certain amount of Ti3.5+ and Ti3+ can improve the catalytic activity. Consequently, the battery with the corresponded CNT@TiO2-x cathode shows high discharge/charge capacities and good cycling performance, which the cyclic retention of more than 90 cycles are achieved, while with the pristine CNTs only 50 cycles are obtained. This study provides an approach to fabricate cathode materials for lithium-air battery and moreover clarifies the influence of oxygen vacancies of TiO2 on the electrochemical performance.

  14. Molecular recognition: from solution science to nano/materials technology.

    PubMed

    Ariga, Katsuhiko; Ito, Hiroshi; Hill, Jonathan P; Tsukube, Hiroshi

    2012-09-07

    In the 25 years since its Nobel Prize in chemistry, supramolecular chemistry based on molecular recognition has been paid much attention in scientific and technological fields. Nanotechnology and the related areas seek breakthrough methods of nanofabrication based on rational organization through assembly of constituent molecules. Advanced biochemistry, medical applications, and environmental and energy technologies also depend on the importance of specific interactions between molecules. In those current fields, molecular recognition is now being re-evaluated. In this review, we re-examine current trends in molecular recognition from the viewpoint of the surrounding media, that is (i) the solution phase for development of basic science and molecular design advances; (ii) at nano/materials interfaces for emerging technologies and applications. The first section of this review includes molecular recognition frontiers, receptor design based on combinatorial approaches, organic capsule receptors, metallo-capsule receptors, helical receptors, dendrimer receptors, and the future design of receptor architectures. The following section summarizes topics related to molecular recognition at interfaces including fundamentals of molecular recognition, sensing and detection, structure formation, molecular machines, molecular recognition involving polymers and related materials, and molecular recognition processes in nanostructured materials.

  15. Containerless processing of amorphous ceramics

    NASA Technical Reports Server (NTRS)

    Weber, J. K. Richard; Krishnan, Shankar; Schiffman, Robert A.; Nordine, Paul C.

    1990-01-01

    The absence of gravity allows containerless processing of materials which could not otherwise be processed. High melting point, hard materials such as borides, nitrides, and refractory metals are usually brittle in their crystalline form. The absence of dislocations in amorphous materials frequently endows them with flexibility and toughness. Systematic studies of the properties of many amorphous materials have not been carried out. The requirements for their production is that they can be processed in a controlled way without container interaction. Containerless processing in microgravity could permit the control necessary to produce amorphous forms of hard materials.

  16. Molecular dynamics study on low-energy sputtering of carbon material by Xe ion bombardment

    NASA Astrophysics Data System (ADS)

    Muramoto, T.; Hyakutake, T.

    2013-05-01

    The low-energy sputtering of carbon material under Xe ion bombardment is studied through the molecular dynamics (MD) simulation. For the normal incidence of Xe, the MD result of sputtering yield almost agrees with the experimental result by Williams et al. (AIAA-2004-3788). However, the experimental result shows a less incident angle dependence than the MD result because the experiment performed on a rough surface. It is found that the sputtered particles have memory of the projectile because the sputtered particles by the low-energy projectile undergo only a few collisions before the ejection. Low density of an amorphous carbon surface brings the decrease of the sputtering yield and the increase of high-energy sputtered atoms.

  17. Amorphous carbon nitride as an alternative electrode material in electroanalysis: simultaneous determination of dopamine and ascorbic acid.

    PubMed

    Medeiros, Roberta A; Matos, Roberto; Benchikh, Abdelkader; Saidani, Boualem; Debiemme-Chouvy, Catherine; Deslouis, Claude; Rocha-Filho, Romeu C; Fatibello-Filho, Orlando

    2013-10-03

    Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L(-1) KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656 μmol L(-1) for DA and 1.05 μmol L(-1) for AA, whereas with the BDD electrode these values were 0.283 μmol L(-1) and 0.968 μmol L(-1), respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis.

  18. Etch Properties of Amorphous Carbon Material Using RF Pulsing in the O2/N2/CHF3 Plasma.

    PubMed

    Jeon, Min Hwan; Park, Jin Woo; Yun, Deok Hyun; Kim, Kyong Nam; Yeom, Geun Young

    2015-11-01

    The amorphous carbon layer (ACL), used as the hardmask for the etching of nanoscale semi-conductor materials, was etched using O2/CHF3 in addition to O2/N2 using pulsed dual-frequency capacitively coupled plasmas, and the effects of source power pulsing for different gas combinations on the characteristics of the plasmas and ACL etching were investigated. As the etch mask for ACL, a patterned SiON layer was used. The etch rates of ACL were decreased with the decrease of pulse duty percentage for both O2/N2 and O2/CHF3 due to decrease of the reactive radicals, such as F and O, with decreasing pulse duty percentage. In addition, at the same pulse duty percentage, the etch selectivity of ACL/SiON with O2/CHF3 was also significantly lower than that with O2/N2. However, the etch profiles of ACL with O2/CHF3 was more anisotropic and the etch profiles were further improved with decreasing the pulse duty percentage than those of ACL with O2/N2. The improved anisotropic etch profiles of ACL with decreasing pulse duty percentage for O2/CHF3 were believed to be related to the formation of a more effective passivation layer, such as a thick fluorocarbon layer, on the sidewall of the ACL during the etching with O2/CHF3, compared to the weak C-N passivation layer formed on the sidewall of ACL when using O2/N2.

  19. First principles prediction of amorphous phases using evolutionary algorithms.

    PubMed

    Nahas, Suhas; Gaur, Anshu; Bhowmick, Somnath

    2016-07-07

    We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures. Applying this method, in conjunction with density functional theory based electronic, ionic and cell relaxation, we re-investigate two well known amorphous semiconductors, namely silicon and indium gallium zinc oxide. We find that characteristic structural parameters like average bond length and bond angle are within ∼2% of those reported by ab initio MD calculations and experimental studies.

  20. First principles prediction of amorphous phases using evolutionary algorithms

    NASA Astrophysics Data System (ADS)

    Nahas, Suhas; Gaur, Anshu; Bhowmick, Somnath

    2016-07-01

    We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures. Applying this method, in conjunction with density functional theory based electronic, ionic and cell relaxation, we re-investigate two well known amorphous semiconductors, namely silicon and indium gallium zinc oxide. We find that characteristic structural parameters like average bond length and bond angle are within ˜2% of those reported by ab initio MD calculations and experimental studies.

  1. Sculpting Molecular Potentials to Design Optimized Materials: The Inverse Design of New Molecular Structures

    DTIC Science & Technology

    2010-05-10

    REPORT Final Report on " Sculpting Molecular Potentials to Design Optimized Materials: The Inverse Design of New Molecular Structures" (Agreement...Beratan, Weitao Yang, Michael J. Therien, Koen Clays Duke University Office of Research Support Duke University Durham, NC 27705 - REPORT...Prescribed by ANSI Std. Z39.18 - 31-Jul-2009 Final Report on " Sculpting Molecular Potentials to Design Optimized Materials: The Inverse Design of New

  2. AB Initi Molecular Dynamics Simulation of the Amorphous Structure of Ca-Mg-Cu and Ca-Mg-Zn Alloys (Postprint)

    DTIC Science & Technology

    2012-09-26

    The Minerals , Metals & Materials Society and ASM International (outside the USA). The U.S. Government is joint author of the work and has the right...amorphous alloys. DOI: 10.1007/s11661-012-1406-z The Minerals , Metals & Materials Society and ASM International (outside the USA) 2012 I. INTRODUCTION...presence ofMRO in these alloys,[34,35] as well as the fluctuation in the atomic scattering cross-sections: the solutes , Cu, Zn and Mg, have larger neutron

  3. Optical and Structural Properties of Microcrystalline GaN on an Amorphous Substrate Prepared by a Combination of Molecular Beam Epitaxy and Metal-Organic Chemical Vapor Deposition

    SciTech Connect

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  4. Optical and structural properties of microcrystalline GaN on an amorphous substrate prepared by a combination of molecular beam epitaxy and metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  5. Materials for next-generation molecularly selective synthetic membranes

    NASA Astrophysics Data System (ADS)

    Koros, William J.; Zhang, Chen

    2017-03-01

    Materials research is key to enable synthetic membranes for large-scale, energy-efficient molecular separations. Materials with rigid, engineered pore structures add an additional degree of freedom to create advanced membranes by providing entropically moderated selectivities. Scalability -- the capability to efficiently and economically pack membranes into practical modules -- is a critical yet often neglected factor to take into account for membrane materials screening. In this Progress Article, we highlight continuing developments and identify future opportunities in scalable membrane materials based on these rigid features, for both gas and liquid phase applications. These advanced materials open the door to a new generation of membrane processes beyond existing materials and approaches.

  6. Materials for next-generation molecularly selective synthetic membranes.

    PubMed

    Koros, William J; Zhang, Chen

    2017-03-01

    Materials research is key to enable synthetic membranes for large-scale, energy-efficient molecular separations. Materials with rigid, engineered pore structures add an additional degree of freedom to create advanced membranes by providing entropically moderated selectivities. Scalability - the capability to efficiently and economically pack membranes into practical modules - is a critical yet often neglected factor to take into account for membrane materials screening. In this Progress Article, we highlight continuing developments and identify future opportunities in scalable membrane materials based on these rigid features, for both gas and liquid phase applications. These advanced materials open the door to a new generation of membrane processes beyond existing materials and approaches.

  7. Three Dimensional Molecular Imaging for Lignocellulosic Materials

    SciTech Connect

    Bohn, Paul W.; Sweedler, Jonathan V.

    2011-06-09

    The development of high efficiency, inexpensive processing protocols to render biomass components into fermentable substrates for the sequential processing of cell wall components into fuels and important feedstocks for the biorefinery of the future is a key goal of the national roadmap for renewable energy. Furthermore, the development of such protocols depends critically on detailed knowledge of the spatial and temporal infiltration of reagents designed to remove and separate the phenylpropenoid heteropolymer (lignin) from the processable sugar components sequestered in the rigid cell walls of plants. A detailed chemical and structural understanding of this pre-enzymatic processing in space and time was the focus of this program. We worked to develop new imaging strategies that produce real-time molecular speciation information in situ; extract sub-surface information about the effects of processing; and follow the spatial and temporal characteristics of the molecular species in the matrix and correlate this complex profile with saccharification. Spatially correlated SIMS and Raman imaging were used to provide high quality, high resolution subcellular images of Miscanthus cross sections. Furthermore, the combination of information from the mass spectrometry and Raman scattering allows specific chemical assignments of observed structures, difficult to assign from either imaging approach alone and lays the foundation for subsequent heterocorrelated imaging experiments targeted at more challenging biological systems, such as the interacting plant-microbe systems relevant to the rhizosphere.

  8. Radiation-induced amorphization of ordered intermetallic compounds CuTi, CuTi sub 2 , and Cu sub 4 Ti sub 3 : A molecular-dynamics study

    SciTech Connect

    Sabochick, M.J. ); Lam, N.Q. )

    1991-03-01

    Solid-state amorphization resulting from the introduction of chemical disorder and point defects in the ordered intermetallic compounds CuTi, CuTi{sub 2}, and Cu{sub 4}Ti{sub 3} was investigated, with use of the isobaric-isothermal molecular-dynamics method in conjunction with embedded-atom potentials. Antisite defects were produced by randomly exchanging Cu and Ti atoms, and vacancies and interstitials were created by removing atoms at random from their normal sites and inserting atoms at random positions in the lattice, respectively. The potential energy, volume expansion, and pair-correlation function were calculated as functions of the numbers of atom exchanges and point defects. The results indicated that, although both chemical disordering and point-defect introduction increased the system energy and volume, the presence of point defects was essential to trigger the crystalline-to-amorphous transition. By comparing the pair-correlation function calculated after the introduction of point defects with that of the quenched liquid alloy, the critical damage dose (in dpa, displacements per atom) for amorphization was estimated for each compound: {similar to}0.7 dpa for CuTi, {similar to}0.5 dpa for CuTi{sub 2}, and {similar to}0.6 dpa for Cu{sub 4}Ti{sub 3}. At the onset of amorphization, the volume expansions were found to be {similar to}1.9%, {similar to}3.7%, and {similar to}1.7% for these respective compounds. In general, the results obtained in the present work are in good agreement with experimental observations.

  9. Ab initio molecular dynamics with a classical pressure reservoir: simulation of pressure-induced amorphization in a Si35H36 cluster

    PubMed

    Martonak; Molteni; Parrinello

    2000-01-24

    We present a new constant-pressure ab initio molecular dynamics method suitable for studying, e.g., pressure-induced structural transformations in finite nonperiodic systems such as clusters. We immerse an ab initio treated cluster into a model classical liquid, described by a soft-sphere potential, which acts as a pressure reservoir. The pressure is varied by tuning the parameter of the liquid potential. We apply the method to a Si35H36 cluster, which undergoes a pressure-induced amorphization at approximately 35 GPa, and remains in a disordered state even upon pressure release.

  10. Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

    NASA Astrophysics Data System (ADS)

    Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Meded, Velimir; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.

    2017-03-01

    In this study, we investigate on the basis of ab initio calculations how the morphology, molecular on-site energies, reorganization energies, and charge transfer integral distribution affect the hopping charge transport and the exciton formation process in disordered organic semiconductors. We focus on three materials applied frequently in organic light-emitting diodes: α -NPD , TCTA, and Spiro-DPVBi. Spatially correlated disorder and, more importantly, superexchange contributions to the transfer integrals, are found to give rise to a significant increase of the electric field dependence of the electron and hole mobility. Furthermore, a material-specific correlation is found between the HOMO and LUMO energy on each specific molecular site. For α -NPD and TCTA, we find a positive correlation between the HOMO and LUMO energies, dominated by a Coulombic contribution to the energies. In contrast, Spiro-DPVBi shows a negative correlation, dominated by a conformational contribution. The size and sign of this correlation have a strong influence on the exciton formation rate.

  11. Differentiating amorphous mixtures of cefuroxime axetil and copovidone by X-ray diffraction and differential scanning calorimetry.

    PubMed

    Nicolaï, B; Perrin, M-A; Céolin, R; Rietveld, I B

    2014-03-01

    The amorphous, molecular solid dispersion of cefuroxime axetil and copovidone with the mass ratio 71/29 is compared to its pure components in the amorphous state and to an amorphous mechanical mixture with the same mass ratio. Calorimetric studies demonstrate that all these materials are vitreous. By using X-ray diffraction profiles, a clear difference can be observed between the local order of the solid dispersion and that of the mechanical mixture. More generally, it is shown how the presence or absence of additivity in the diffraction data can be used to distinguish between different amorphous mixtures.

  12. Reversibility and criticality in amorphous solids

    DOE PAGES

    Regev, Ido; Weber, John; Reichhardt, Charles; ...

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaoticmore » behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.« less

  13. Reversibility and criticality in amorphous solids

    SciTech Connect

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.

  14. Structural Amorphous Steels

    NASA Astrophysics Data System (ADS)

    Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

    2004-06-01

    Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

  15. Preparation of Al72Ni8Ti8Zr6Nb3Y3 amorphous powders and bulk materials

    NASA Astrophysics Data System (ADS)

    Wu, Yu; Wang, Xin-fu; Han, Fu-sheng

    2016-10-01

    Amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were successfully fabricated by mechanical alloying. The microstructure, glass-forming ability, and crystallization behavior of amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The isothermal crystallization kinetics was analyzed by the Johnson-Mehl-Avrami equation. In the results, the supercooled liquid region of the amorphous alloy is as high as 81 K, as determined by non-isothermal DSC curves. The activation energy for crystallization is as high as 312.6 kJ·mol-1 obtained by Kissinger and Ozawa analyses. The values of Avrami exponent ( n) imply that the crystallization is dominated by interface-controlled three-dimensional growth in the early stage and the end stage and by diffusion-controlled two- or three-dimensional growth in the middle stage. In addition, the amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were sintered under 2 GPa at temperatures of 673 K and 723 K. The results show that the Vickers hardness of the compacted powders is as high as Hv 1215.

  16. Amorphous Hole-Transporting Material based on 2,2'-Bis-substituted 1,1'-Biphenyl Scaffold for Application in Perovskite Solar Cells.

    PubMed

    Magomedov, Artiom; Sakai, Nobuya; Kamarauskas, Egidijus; Jokubauskaitė, Gabrielė; Franckevičius, Marius; Jankauskas, Vygintas; Snaith, Henry J; Getautis, Vytautas

    2017-03-16

    Perovskite solar cells are considered a promising technology for solar-energy conversion, with power conversion efficiencies currently exceeding 20 %. In most of the reported devices, Spiro-OMeTAD is used for positive-charge extraction and transport layer. Although a number of alternative hole-transporting materials with different aromatic or heteroaromatic fragments have already been synthesized, a cheap and well-performing hole-transporting material is still in high demand. In this work, a two-step synthesis of a carbazole-based hole-transporting material is presented. Synthesized compounds exhibited amorphous nature, good solubility and thermal stability. The perovskite solar cells employing the newly synthesized material generated a power conversion efficiency of 16.5 % which is slightly lower than that obtained with Spiro-OMeTAD (17.5 %). The low-cost synthesis and high performance makes our hole-transport material promising for applications in perovskite-based optoelectronic devices.

  17. Direct Simulation of Ion Beam Induced Stressing and Amorphization of Silicon

    SciTech Connect

    Beardmore, K.M.; Gronbech-Jensen, N.

    1999-05-02

    Using molecular dynamics (MD) simulation, the authors investigate the mechanical response of silicon to high dose ion-irradiation. The authors employ a realistic model to directly simulate ion beam induced amorphization. Structural properties of the amorphized sample are compared with experimental data and results of other simulation studies. The authors find the behavior of the irradiated material is related to the rate at which it can relax. Depending upon the ability to deform, the authors observe either the generation of a high compressive stress and subsequent expansion of the material, or generation of tensile stress and densification. The authors note that statistical material properties, such as radial distribution functions are not sufficient to differentiate between the different densities of the amorphous samples. For any reasonable deformation rate, the authors observe an expansion of the target upon amorphization in agreement with experimental observations. This is in contrast to simulations of quenching which usually result in a denser structure relative to crystalline Si. The authors conclude that although there is substantial agreement between experimental measurements and simulation results, the amorphous structures being investigated may have fundamental differences; the difference in density can be attributed to local defects within the amorphous network. Finally the authors show that annealing simulations of their amorphized samples can lead to a reduction of high energy local defects without a large scale rearrangement of the amorphous network. This supports the proposal that defects in a-Si are analogous to those in c-Si.

  18. Structure and dielectric properties of amorphous LaAlO3 and LaAlOxNy films as alternative gate dielectric materials

    NASA Astrophysics Data System (ADS)

    Lu, Xu-bing; Liu, Zhi-guo; Wang, Yi-ping; Yang, Ying; Wang, Xiao-ping; Zhou, Hong-wei; Nguyen, Bich-yen

    2003-07-01

    Amorphous LaAlO3 (LAO) and LAOxNy (LAON) films have been prepared by pulsed laser deposition technique on Si (100) substrates and Pt coated silicon substrates. X-ray diffraction, transmission electron microscopy and differential thermal analysis investigations showed that both kinds of films remain amorphous up to a high temperature of 860 °C. Atomic force microscopy study indicated that the surface of the deposited films is very smooth with a root mean square roughness of 0.14 nm for 8 nm LAO. LAON films have a smoother surface than that of LAO films. High-resolution transmission electron microscope studies showed there often exists interfacial reaction between LAO and Si. One LAON/Si structure nearly without interfacial layer has been obtained. For LAO films, high bandgap of 6.55 eV and medium dielectric constant of 25-27 have been obtained. The LAON films showed small equivalent oxide thickness of 1.1 nm with a low leakage of 0.074 A/cm2@Vg=+1 V. It is proposed that amorphous LAON films are very promising dielectric materials for high k gate dielectric applications.

  19. Effects of temperature and strain rate on the deformation of amorphous polyethylene: a comparison between molecular dynamics simulations and experimental results

    NASA Astrophysics Data System (ADS)

    Sahputra, I. H.; Echtermeyer, A. T.

    2013-09-01

    Molecular dynamics simulations are used to investigate the effects of temperature and strain rate on the deformation of amorphous polyethylene. The simulations predict the effects of temperature and strain rate on the stress-strain responses, Young's modulus and Poisson's ratio similar to those observed in laboratory experiments performed by other researchers. The time-temperature superposition principle is applied to the Young's modulus and Poisson's ratio to form a master curve to address the discrepancies in strain rates between the simulations and the experiments. Differences in the numbers of monomers and chains, the degree of crystallinity and molecular orientation lead to discrepancies in the Young's modulus and Poisson's ratio between simulations and experiments.

  20. Small organic molecular imprinted materials: their preparation and application.

    PubMed

    Jiang, Xiaoman; Jiang, Na; Zhang, Haixia; Liu, Mancang

    2007-09-01

    Molecular imprinting is a technique for preparing polymeric materials that are capable of recognizing and binding the desired molecular target with a high affinity and selectivity. The materials can be applied to a wide range of target molecules, even those for which no natural binder exists or whose antibodies are difficult to raise. The imprinting of small organic molecules (e.g., pharmaceuticals, pesticides, amino acids, steroids, and sugars) is now almost routine. In this review, we pay special attention to the synthesis and application of molecular imprinted polymer (MIPs) imprinted with small organic molecules, including herbicides, pesticides, and drugs. The advantages, applications, and recent developments in small organic molecular imprinted technology are highlighted.

  1. Micro-/nanostructured multicomponent molecular materials: design, assembly, and functionality.

    PubMed

    Yan, Dongpeng

    2015-03-23

    Molecule-based micro-/nanomaterials have attracted considerable attention because their properties can vary greatly from the corresponding macro-sized bulk systems. Recently, the construction of multicomponent molecular solids based on crystal engineering principles has emerged as a promising alternative way to develop micro-/nanomaterials. Unlike single-component materials, the resulting multicomponent systems offer the advantages of tunable composition, and adjustable molecular arrangement, and intermolecular interactions within their solid states. The study of these materials also supplies insight into how the crystal structure, molecular components, and micro-/nanoscale effects can influence the performance of molecular materials. In this review, we describe recent advances and current directions in the assembly and applications of crystalline multicomponent micro-/nanostructures. Firstly, the design strategies for multicomponent systems based on molecular recognition and crystal engineering principles are introduced. Attention is then focused on the methods of fabrication of low-dimensional multicomponent micro-/nanostructures. Their new applications are also outlined. Finally, we briefly discuss perspectives for the further development of these molecular crystalline micro-/nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Association of Presolar Grains with Molecular Cloud Material in IDPs

    NASA Technical Reports Server (NTRS)

    Messenger, S.; Keller, L. P.

    2005-01-01

    Anhydrous interplanetary dust particles (IDPs) collected in the stratosphere appear chemically, mineralogically, and texturally primitive in comparison to meteorites. Particles that escape significant atmospheric entry heating have highly unequilibrated mineralogy, are volatile element rich, and, overall, appear to have escaped significant parent body hydrothermal alteration. These IDPs are comprised of the building blocks of the solar system. The strongest evidence that anhydrous IDPs are primitive is that they contain abundant stardust and molecular cloud material. In particular, presolar silicates were first identified in IDPs and are present in abundances (450-5,500 ppm) that are well above that observed in primitive meteorites (less than 170 ppm). The most fragile (cluster) IDPs also commonly exhibit large H and N isotopic anomalies that likely originated by isotopic fractionation during extremely low temperature chemical reactions in a presolar cold molecular cloud. The D/H ratios exceed that of most primitive meteorites, and in rare cases reach values directly observed from simple gas phase molecules in cold molecular clouds. The most extreme D- and N-15-enrichments are usually observed at the finest spatial scales (0.5-2 microns) that can be measured. These observations suggest that D and N-15 hotspots are in fact preserved nuggets of molecular cloud material, and that the materials within them also have presolar origins. The advanced capabilities of the NanoSIMS ion microprobe now enable us to test this hypothesis. Here, we report two recent examples of presolar silicates found to be directly associated with molecular cloud material.

  3. Quantum Mechanics and First-Principles Molecular Dynamics Selection of Polymer Sensing Materials

    NASA Astrophysics Data System (ADS)

    Blanco, Mario; Shevade, Abhijit V.; Ryan, Margaret A.

    We present two first-principles methods, density functional theory (DFT) and a molecular dynamics (MD) computer simulation protocol, as computational means for the selection of polymer sensing materials. The DFT methods can yield binding energies of polymer moieties to specific vapor bound compounds, quantities that were found useful in materials selection for sensing of organic and inorganic compounds for designing sensors for the electronic nose (ENose) that flew on the International Space Station (ISS) in 2008-2009. Similarly, we present an MD protocol that offers high consistency in the estimation of Hildebrand and Hansen solubility parameters (HSP) for vapor bound compounds and amorphous polymers. HSP are useful for fitting measured polymer sensor responses with physically rooted analytical models. We apply the method to the JPL electronic nose (ENose), an array of sensors with conducting leads connected through thin film polymers loaded with carbon black. Detection relies on a change in electric resistivity of the polymer film as function of the amount of swelling caused by the presence of the analyte chemical compound. The amount of swelling depends upon the chemical composition of the polymer and the analyte molecule. The pattern is unique and it unambiguously identifies the compound. Experimentally determined changes in relative resistivity of fifteen polymer sensor materials upon exposure to ten vapors were modeled with the first-principles HSP model.

  4. On-top π-stacking of quasiplanar molecules in hole-transporting materials: inducing anisotropic carrier mobility in amorphous films.

    PubMed

    Wakamiya, Atsushi; Nishimura, Hidetaka; Fukushima, Tatsuya; Suzuki, Furitsu; Saeki, Akinori; Seki, Shu; Osaka, Itaru; Sasamori, Takahiro; Murata, Michihisa; Murata, Yasujiro; Kaji, Hironori

    2014-06-02

    Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top π-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the π-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on π-stacking, thus facilitating an out-of-plane carrier mobility. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Embrittlement of Metal by Solute Segregation-Induced Amorphization

    SciTech Connect

    Chen, H.-P.; Kalia, Rajiv K.; Nakano, Aiichiro; Nomura, Ken-ichi; Vashishta, Priya; Yuan, Zaoshi; Kaxiras, Efthimios; Lu, Gang; Duin, Adri C. T. van

    2010-04-16

    Impurities segregated to grain boundaries of a material essentially alter its fracture behavior. A prime example is sulfur segregation-induced embrittlement of nickel, where an observed relation between sulfur-induced amorphization of grain boundaries and embrittlement remains unexplained. Here, 48x10{sup 6}-atom reactive-force-field molecular dynamics simulations provide the missing link. Namely, an order-of-magnitude reduction of grain-boundary shear strength due to amorphization, combined with tensile-strength reduction, allows the crack tip to always find an easy propagation path.

  6. Computation of free-molecular flow in nuclear materials

    NASA Astrophysics Data System (ADS)

    Casella, Andrew M.; Loyalka, Sudarshan K.; Hanson, Brady D.

    2009-11-01

    Generally, the transport of gases and vapors in nuclear materials is adequately described by the diffusion equation with an effective diffusion coefficient. There are instances however, in which the flow pathway can be so restrictive that the diffusion description has limitations. In general, molecular transport is governed by intermolecular forces and collisions (interactions between multiple gas/vapor molecules) and by molecule-surface interactions. However, if nano-scale pathways exist within these materials, as has been suggested, then molecular transport can be characterized as being in the free-molecular flow regime where intermolecular interactions can be ignored and flow is determined entirely by molecule-surface collisions. Our purpose in this investigation is to focus on free-molecular transport in fine capillaries of a range of shapes and to explore the effect of geometry on this transport. We have employed Monte Carlo techniques in our calculations, and for simple geometries we have benchmarked our results against some analytical and previously available results. We have used Mathematica ® which has exceptional built-in symbolic and graphical capabilities, permitting easy handling of complicated geometries and good visualization of the results. Our computations provide insights into the role of geometry in molecular transport in nuclear materials with narrow pathways for flows, and also will be useful in guiding computations that include intermolecular collisions and more realistic gas-surface collision operators.

  7. Molecular beam source for high vapor pressure materials

    SciTech Connect

    Myers, T.H.; Schetzina, J.F.

    1982-02-01

    A molecular beam source for deposition of high vapor pressure materials in MBE systems is described. The source consists of a collimating effusion cell of original design which is heated by a temperature-controlled Radak II oven (Luxel Corporation). Construction details of the source are given along with calibration and performance data.

  8. Molecularly Imprinted Polymers and Highly Porous Materials in Sensing Applications

    DTIC Science & Technology

    2007-04-01

    materials with applications in synthesis and catalysis”, Tetrahedron 59, 2025- 2057 (2003). 4. J. J. Becker and M.R. Gagne , “Exploiting the synergy...Dong Min Wu, Nicolas Fang, Xiang Zhang, Joseph Roberts , and Kenneth J. Shea, “Functional Molecularly Imprinted Polymer Microstructures Fabricated Using

  9. Production and Characterization of Bulk MgB2 Material made by the Combination of Crystalline and Carbon Coated Amorphous Boron Powders

    NASA Astrophysics Data System (ADS)

    Hiroki, K.; Muralidhar, M.; Koblischka, M. R.; Murakami, M.

    2017-07-01

    The object of this investigation is to reduce the cost of bulk production and in the same time to increase the critical current performance of bulk MgB2 material. High-purity commercial powders of Mg metal (99.9% purity) and two types of crystalline (99% purity) and 16.5 wt% carbon-coated, nanometer-sized amorphous boron powders (98.5% purity) were mixed in a nominal composition of MgB2 to reduce the boron cost and to see the effect on the superconducting and magnetic properties. Several samples were produced mixing the crystalline boron and carbon-coated, nanometer-sized amorphous boron powders in varying ratios (50:50, 60:40, 70:30, 80:20, 90:10) and synthesized using a single-step process using the solid state reaction around 800 °C for 3 h in pure argon atmosphere. The magnetization measurements exhibited a sharp superconducting transition temperature with T c, onset around 38.6 K to 37.2 K for the bulk samples prepared utilizing the mixture of crystalline boron and 16.5% carbon-coated amorphous boron. The critical current density at higher magnetic field was improved with addition of carbon-coated boron to crystalline boron in a ratio of 80:20. The highest self-field Jc around 215,000 A/cm2 and 37,000 A/cm2 were recorded at 20 K, self-field and 2 T for the sample with a ratio of 80:10. The present results clearly demonstrate that the bulk MgB2 performance can be improved by adding carbon-coated nano boron to crystalline boron, which will be attractive to reduce the cost of bulk MgB2 material for several industrial applications.

  10. Atomistic Simulation on the Relation between Amorphization and Crystalline Transformation in Ni-Ti Alloy

    NASA Astrophysics Data System (ADS)

    Saitoh, Ken-Ichi; Kubota, Keisuke

    Ni-Ti alloys are typical shape-memory materials. It is suggested that the atomic-scale phase transformation between martensite and austenite crystalline phases is responsible for such function. However, it is reported that these alloys sometimes show also amorphization together with nanocrystal under severe deformation. The mechanism of amorphization should compete against martensitic (crystalline) transformation (MT). This study focuses on the atomistic relation between amorphization and MT in Ni-Ti alloys. Molecular dynamics simulation is performed by using our simplified potential built on the MEAM framework. The change in crystalline state is identified and traced mainly by developing common neighbor analysis (CNA) method. Under amorphization from B2 cubic structure, the characteristic topological change in CNA cluster around a transforming atom is detected. By applying simple shear in periodic specimen, it is found that the martensite phases appear first then amorphous phases are formed. The nucleation of amorphous phases is strongly dependent on choice of shear plane, e.g. {100}, {110} or {111} plane. When the shear direction does not match to the orientation of inherent slip system, amorphous phase is nucleated with relative ease and remains for a long time. It is recognized that dislocation slip (plastic deformation), MT and amorphization are closely related in atomic scale. The direction of phase transition is mostly "B2(austenite)"→"B19'(martensite)"→"amorphous", except for the case of {111} shear plane which possesses "pre-amorphous" structures. It is found that the "pre-amorphous" is once formed and then disappears, preceding martensite phase or principal and later formation of amorphous phase.

  11. Diffusion and aggregation process of oxygen embedded around an amorphous/crystal interface of Si(001) studied by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Hoshino, Yasushi

    2017-05-01

    I performed empirical molecular dynamics (MD) simulations to understand the peculiar migration behavior of oxygen embedded in an amorphous Si (a-Si) layer near the crystal/amorphous (c/a) Si interface and investigated the time evolution of the atomic configuration at high temperatures from 1200 to 1500 K. The previously proposed sweeping effect, which is demonstrated in terms of the oxygen migration and precipitation in silicon taking place along the moving c/a interface, was definitely confirmed in this MD simulation. [Hoshino et al., J. Phys. D: Appl. Phys. 49, 315106 (2016)] In the present study, I reproducibly found the theoretical evidence of the novel sweeping and aggregation phenomenon of oxygen occurring in the recrystallization process of a-Si. The temperature-dependence revealed that the relationship between the displacement velocity of the oxygen and the c/a interface plays an important role in interpreting the behavior. The oxide precipitations in the recrystallized Si as well as the sweeping effect were well reproduced in the simulation in which the systems containing several oxygen atoms were assumed. These facts significantly well explain and support my interpretation in the previous papers reported on the synthesis mechanism of the ultrathin silicon-on-insulator/buried oxide structure prepared by low-energy implantation followed by relatively low temperature annealing, compared to the ordinary separation by the implanted oxygen process.

  12. Low-temperature dynamics in amorphous polymers and low-molecular-weight glasses--what is the difference?

    PubMed

    Eremchev, Ivan Yu; Vainer, Yury G; Naumov, Andrei V; Kador, Lothar

    2011-02-07

    Numerous experiments have shown that the low-temperature dynamics of a wide variety of disordered solids is qualitatively universal. However, most of these results were obtained with ensemble-averaging techniques which hide the local parameters of the dynamic processes. We used single-molecule (SM) spectroscopy for direct observation of the dynamic processes in disordered solids with different internal structure and chemical composition. The surprising result is that the dynamics of low-molecular-weight glasses and short-chain polymers does not follow, on a microscopic level, the current concept of low-temperature glass dynamics. An extra contribution to the dynamics was detected causing irreproducible jumps and drifts of the SM spectra on timescales between milliseconds and minutes. In most matrices consisting of small molecules and oligomers, the spectral dynamics was so fast that SM spectra could hardly or not at all be recorded and only irregular fluorescence flares were observed. These results provide new mechanistic insight into the behavior of glasses in general: At low temperatures, the local dynamics of disordered solids is not universal but depends on the structure and chemical composition of the material.

  13. Optimization of the molecular sieving properties of amorphous SiCXNY:H hydrogen selective membranes prepared by PECVD

    NASA Astrophysics Data System (ADS)

    Haacké, M.; Coustel, R.; Rouessac, V.; Drobek, M.; Roualdès, S.; Julbe, A.

    2015-07-01

    In this work, low frequency PECVD a-SiCxNy:H thin films have been synthesized in the temperature range 25-300 °C from hexamethyldisilazane precursor mixed with ammonia at various concentrations. A relevant correlation has been evidenced between the [N]/[C] atomic ratio in the gaseous phase and in the deposited thin films, allowing both prediction and control of the film microstructure. A simple method based on the analysis of the films FTIR spectra was proposed to determine the value of the [N]/[C] ratio and thus predict or adjust the gas transport properties of the membrane materials. Attractive ideal selectivities α*He/N2 exceeding 90 with He permeance ΠHe > 3.10-7 mol.s-1.m-2.Pa-1 were measured at 150 °C for the films prepared at 300 °C with an optimum [N]/[C] atomic ratio in the range 0.1-1.5. These films behave as molecular sieve membranes with a thermally activated transport of helium.

  14. Large scale molecular simulations with application to polymers and nano-scale materials

    NASA Astrophysics Data System (ADS)

    Gao, Guanghua

    There remain practical problems to predicting structures and properties of materials from first principles, though the foundation, quantum mechanics, has been established for many years. The goals of this research are to develop methods and tools that are accurate and practical, and apply them to important problems. Two aspects of the methodology are focused. (1) The development of accurate force fields based on ab initio quantum mechanical calculations on prototype systems. Procedures were developed on polyvinyl chloride (PVC) and successfully applied on other types of polymers. They are very important to studying of amorphous polymers materials, for which current methods have not been useful in predicting important properties (e.g. moduli and glass temperature). (2) The development of Massive Parallel Simulation (MPSim) Software. MPSim is suitable for large systems (millions of atoms). It has the ability of including environmental variables (temperature, pressure, tension, and shear) and extracting physical properties (moduli and glass temperatures). The theories and algorithms implemented are summarized in the Appendix. These methods and tools are applied to the accurate simulation of structures and properties of amorphous polymer materials and nano-materials. Molecular dynamics (MD) simulation on polyethylene (chapter 6) was used to develop a general strategy for predicting glass transition temperatures which is expected to be very important in polymer industry. In chapter 7, these strategies were successfully applied to three important fluoro polymers. Single-walled carbon nanotubes (SWNT), recently discovered but not very well characterized, is an interesting new class of materials. Using an accurate force field, structures and mechanical properties of these systems are studied. Chapter 2 shows that the dominating factor for deciding stable structures and mechanical properties is the tube size, not chirality. The behavior of (10, 10) nano-tube under bending

  15. Molecular tools for the construction of peptide-based materials.

    PubMed

    Ramakers, B E I; van Hest, J C M; Löwik, D W P M

    2014-04-21

    Proteins and peptides are fundamental components of living systems where they play crucial roles at both functional and structural level. The versatile biological properties of these molecules make them interesting building blocks for the construction of bio-active and biocompatible materials. A variety of molecular tools can be used to fashion the peptides necessary for the assembly of these materials. In this tutorial review we shall describe five of the main techniques, namely solid phase peptide synthesis, native chemical ligation, Staudinger ligation, NCA polymerisation, and genetic engineering, that have been used to great effect for the construction of a host of peptide-based materials.

  16. Nickel phosphate molecular sieve as electrochemical capacitors material

    NASA Astrophysics Data System (ADS)

    Yang, Jing-He; Tan, Juan; Ma, Ding

    2014-08-01

    The nickel phosphate molecular sieve VSB-5 as an electrode material for supercapacitors is investigated by cyclic voltammetry (CV) and chronopotentiometry in alkaline media. The VSB-5 shows high specific capacitance and excellent cycling stability. The specific capacitance of VSB-5 is 2740 F g-1 at a current density of 3 A g-1 and there is no significant reduction in Coulombic efficiency after 3000 cycles at 30 A g-1. In comparison with mesoporous nickel phosphate NiPO, porous nickel hydroxide and mesoporous nickel oxide, this remarkable electrochemical performance of VSB-5 will make nickel phosphate material a promising new electrode material for high performance supercapacitors.

  17. Molecularly Engineered Energy Materials, an Energy Frontier Research Center

    SciTech Connect

    Ozolins, Vidvuds

    2016-09-28

    Molecularly Engineered Energy Materials (MEEM) was established as an interdisciplinary cutting-edge UCLA-based research center uniquely equipped to attack the challenge of rationally designing, synthesizing and testing revolutionary new energy materials. Our mission was to achieve transformational improvements in the performance of materials via controlling the nano-and mesoscale structure using selectively designed, earth-abundant, inexpensive molecular building blocks. MEEM has focused on materials that are inherently abundant, can be easily assembled from intelligently designed building blocks (molecules, nanoparticles), and have the potential to deliver transformative economic benefits in comparison with the current crystalline-and polycrystalline-based energy technologies. MEEM addressed basic science issues related to the fundamental mechanisms of carrier generation, energy conversion, as well as transport and storage of charge and mass in tunable, architectonically complex materials. Fundamental understanding of these processes will enable rational design, efficient synthesis and effective deployment of novel three-dimensional material architectures for energy applications. Three interrelated research directions were initially identified where these novel architectures hold great promise for high-reward research: solar energy generation, electrochemical energy storage, and materials for CO2 capture. Of these, the first two remained throughout the project performance period, while carbon capture was been phased out in consultation and with approval from BES program manager.

  18. Applications of Non-Crystalline Materials — C. REAL TIME OPTICAL RECORDING ON THIN FILMS OF AMORPHOUS SEMICONDUCTORS

    NASA Astrophysics Data System (ADS)

    Mitkova, Maria

    The following sections are included: * Introduction * Amorphous Semiconductors as Optical Storage Medium * Principles and Results on Real-time Optical Recording * Digital optical recording * Digital optical recording due to ablation of the films by illumination with light * Digital optical recording due to coagulation of an island film * Digital optical recording due to phase transition * Digital optical recording due to photoinduced surface deposition of metallic silver * Principles of holographic recording * Recording and readout * Classification of the holograms * Diffraction efficiency * Results in holographic recording on chalcogenide glasses * Future Trends * Acknowledgments * References

  19. Photoelectron yield spectroscopy and inverse photoemission spectroscopy evaluations of p-type amorphous silicon carbide films prepared using liquid materials

    SciTech Connect

    Murakami, Tatsuya E-mail: mtakashi@jaist.ac.jp; Masuda, Takashi E-mail: mtakashi@jaist.ac.jp; Inoue, Satoshi; Shimoda, Tatsuya; Yano, Hiroshi; Iwamuro, Noriyuki

    2016-05-15

    Phosphorus-doped amorphous silicon carbide films were prepared using a polymeric precursor solution. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage, providing semiconducting properties in the films. The valence and conduction states of resultant films were determined directly through the combination of inverse photoemission spectroscopy and photoelectron yield spectroscopy. The incorporated carbon widened energy gap and optical gap comparably in the films with lower carbon concentrations. In contrast, a large deviation between the energy gap and the optical gap was observed at higher carbon contents because of exponential widening of the band tail.

  20. Calculation of absorption and secondary scattering of X-rays by spherical amorphous materials in an asymmetric transmission geometry.

    PubMed

    Bendert, J C; Blodgett, M E; Kelton, K F

    2013-03-01

    Expressions for absorption and the secondary scattering intensity ratio are presented for a small beam impinging off-center of a spherical amorphous sample. Large gradients in the absorption correction are observed from small offsets from the central axis. Additionally, the secondary scattering intensity ratio causes an intensity asymmetry in the detector image. The secondary scattering intensity ratio is presented in integral form and must be computed numerically. An analytic, small-angle, asymptotic series solution for the integral form of the absorption correction is also presented.

  1. Data supporting the role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells.

    PubMed

    Scuto, Andrea; Valenti, Luca; Pierro, Silvio; Foti, Marina; Gerardi, Cosimo; Battaglia, Anna; Lombardo, Salvatore

    2015-09-01

    Hydrogenated amorphous Si (a-Si:H) solar cells are strongly affected by the well known Staebler-Wronski effect. This is a worsening of solar cell performances under light soaking which results in a substantial loss of cell power conversion efficiency compared to time zero performance. It is believed not to be an extrinsic effect, but rather a basic phenomenon related to the nature of a-Si:H and to the stability and motion of H-related species in the a-Si:H lattice. This work has been designed in support of the research article entitled "Role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells" in Solar Energy Materials & Solar Cells (Scuto et al. [1]), which discusses an electrical method based on reverse bias stress to improve the solar cell parameters, and in particular the effect of temperature, electric field intensity and illumination level as a function of the stress time. Here we provide a further set of the obtained experimental data results.

  2. Data supporting the role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells

    PubMed Central

    Scuto, Andrea; Valenti, Luca; Pierro, Silvio; Foti, Marina; Gerardi, Cosimo; Battaglia, Anna; Lombardo, Salvatore

    2015-01-01

    Hydrogenated amorphous Si (a­Si:H) solar cells are strongly affected by the well known Staebler–Wronski effect. This is a worsening of solar cell performances under light soaking which results in a substantial loss of cell power conversion efficiency compared to time zero performance. It is believed not to be an extrinsic effect, but rather a basic phenomenon related to the nature of a­Si:H and to the stability and motion of H­related species in the a­Si:H lattice. This work has been designed in support of the research article entitled “Role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells” in Solar Energy Materials & Solar Cells (Scuto et al. [1]), which discusses an electrical method based on reverse bias stress to improve the solar cell parameters, and in particular the effect of temperature, electric field intensity and illumination level as a function of the stress time. Here we provide a further set of the obtained experimental data results. PMID:26966715

  3. Molecular deformation mechanisms of the wood cell wall material.

    PubMed

    Jin, Kai; Qin, Zhao; Buehler, Markus J

    2015-02-01

    Wood is a biological material with outstanding mechanical properties resulting from its hierarchical structure across different scales. Although earlier work has shown that the cellular structure of wood is a key factor that renders it excellent mechanical properties at light weight, the mechanical properties of the wood cell wall material itself still needs to be understood comprehensively. The wood cell wall material features a fiber reinforced composite structure, where cellulose fibrils act as stiff fibers, and hemicellulose and lignin molecules act as soft matrix. The angle between the fiber direction and the loading direction has been found to be the key factor controlling the mechanical properties. However, how the interactions between theses constitutive molecules contribute to the overall properties is still unclear, although the shearing between fibers has been proposed as a primary deformation mechanism. Here we report a molecular model of the wood cell wall material with atomistic resolution, used to assess the mechanical behavior under shear loading in order to understand the deformation mechanisms at the molecular level. The model includes an explicit description of cellulose crystals, hemicellulose, as well as lignin molecules arranged in a layered nanocomposite. The results obtained using this model show that the wood cell wall material under shear loading deforms in an elastic and then plastic manner. The plastic regime can be divided into two parts according to the different deformation mechanisms: yielding of the matrix and sliding of matrix along the cellulose surface. Our molecular dynamics study provides insights of the mechanical behavior of wood cell wall material at the molecular level, and paves a way for the multi-scale understanding of the mechanical properties of wood.

  4. TOPICAL REVIEW: Molecular materials for organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Mori, T.

    2008-05-01

    Organic field-effect transistors are important applications of thin films of molecular materials. A variety of materials have been explored for improving the performance of organic transistors. The materials are conventionally classified as p-channel and n-channel, but not only the performance but also even the carrier polarity is greatly dependent on the combinations of organic semiconductors and electrode materials. In this review, particular emphasis is laid on multi-sulfur compounds such as tetrathiafulvalenes and metal dithiolates. These compounds are components of highly conducting materials such as organic superconductors, but are also used in organic transistors. The charge-transfer complexes are used in organic transistors as active layers as well as electrodes.

  5. Molecular dynamics study of the effect of titanium ion energy on surface structure during the amorphous TiO2 films deposition

    NASA Astrophysics Data System (ADS)

    Chen, Xian; Wang, Yan-Wu; Liu, Xin; Wang, Xiao-Yan; Wang, Xiao-Bo; An, Shu-Dong; Zhao, Yu-Qing

    2015-08-01

    This paper has investigated the impact of the incident titanium ion energy on the surface structure formation mechanism and the film properties during the amorphous TiO2 thin film deposition process with the molecular dynamics simulation method. The results show that the increase of film density and the reduction of the surface roughness happen when the energy of incident titanium ions is increased. It is also found that the film growth mode is the Volmer-Weber (island) growth mode under the influence of the surface potential. The effect of surface potential is more significant if the incident ions energy becomes smaller. That will make the Volmer-Weber (island) growth mode promoted and the surface roughness of the deposited films become larger. Conversely, the Volmer-Weber growth mode is inhibited when the incident ion energy is higher. It will be conducive to the formation of more smooth film surface.

  6. Molecular modeling of protein materials: case study of elastin

    NASA Astrophysics Data System (ADS)

    Tarakanova, Anna; Buehler, Markus J.

    2013-09-01

    Molecular modeling of protein materials is a quickly growing area of research that has produced numerous contributions in fields ranging from structural engineering to medicine and biology. We review here the history and methods commonly employed in molecular modeling of protein materials, emphasizing the advantages for using modeling as a complement to experimental work. We then consider a case study of the protein elastin, a critically important ‘mechanical protein’ to exemplify the approach in an area where molecular modeling has made a significant impact. We outline the progression of computational modeling studies that have considerably enhanced our understanding of this important protein which endows elasticity and recoil to the tissues it is found in, including the skin, lungs, arteries and the heart. A vast collection of literature has been directed at studying the structure and function of this protein for over half a century, the first molecular dynamics study of elastin being reported in the 1980s. We review the pivotal computational works that have considerably enhanced our fundamental understanding of elastin's atomistic structure and its extraordinary qualities—focusing on two in particular: elastin's superb elasticity and the inverse temperature transition—the remarkable ability of elastin to take on a more structured conformation at higher temperatures, suggesting its effectiveness as a biomolecular switch. Our hope is to showcase these methods as both complementary and enriching to experimental approaches that have thus far dominated the study of most protein-based materials.

  7. EXPERIMENTAL INVESTIGATION OF THE ORTHO/PARA RATIO OF NEWLY FORMED MOLECULAR HYDROGEN ON AMORPHOUS SOLID WATER

    SciTech Connect

    Gavilan, L.; Lemaire, J. L.; Dulieu, F.; Congiu, E.; Chaabouni, H.; Vidali, G.; Chehrouri, M.; Fillion, J.-H.

    2012-11-20

    Several astronomical observations have shown that the ortho/para ratio (OPR) of H{sub 2} can differ from the expected statistical value of 3 or the local thermodynamic equilibrium (LTE) value at the gas or dust temperature. It is thus important to know the OPR of H{sub 2} newly formed on dust grain surfaces, in order to clarify the dependence of the observed OPR in space on the formation process. Using an experimental setup designed to mimic interstellar medium environments, we measured the OPR of H{sub 2} and D{sub 2} formed on the surface of porous amorphous water ice held at 10 K. We report for the first time the OPR value for newly formed D{sub 2}, consistent with the expected LTE value at the high-temperature limit found by previous theoretical and experimental works on the determination of the OPR upon H{sub 2} formation on surfaces at low temperature.

  8. Water sorption, glass transition, and protein-stabilizing behavior of an amorphous sucrose matrix combined with various materials.

    PubMed

    Imamura, Koreyoshi; Yokoyama, Toru; Fukushima, Atsushi; Kinuhata, Mitsunori; Nakanishi, Kazuhiro

    2010-11-01

    The effects of various additives on the physical properties of an amorphous sugar matrix were compared. Amorphous, sugar-additive mixtures were prepared by freeze-drying and then rehumidified at given RHs. Sucrose and eighteen types of substances were used as the sugar and the additive, respectively, and water sorption, glass-to-rubber transition, and protein stabilization during freeze-drying for the various sucrose-additive mixtures were examined. The additives were categorized into two groups according to their effects on T(g) and water sorption. Presence of polysaccharides, cyclodextrins, and polymers (large-sized additives) resulted in a decrease in equilibrium water content from the ideal value calculated from individual water contents for sucrose and additive, and in contrast, low MW substances containing ionizable groups (small-ionized additives) resulted in an increase. The increase in T(g) by the addition of large-sized additives was significant at the additive contents >50 wt.% whereas the T(g) was markedly increased in the lower additive content by the addition of small-ionized additives. The addition of small-ionized additives enhanced the decrease in T(g) with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives.

  9. Structure and Properties of Amorphous Transparent Conducting Oxides

    NASA Astrophysics Data System (ADS)

    Medvedeva, Julia

    Driven by technological appeal, the research area of amorphous oxide semiconductors has grown tremendously since the first demonstration of the unique properties of amorphous indium oxide more than a decade ago. Today, amorphous oxides, such as a-ITO, a-IZO, a-IGZO, or a-ZITO, exhibit the optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts, pushing the latter out of the market. Large-area uniformity, low-cost low-temperature deposition, high carrier mobility, optical transparency, and mechanical flexibility make these materials appealing for next-generation thin-film electronics. Yet, the structural variations associated with crystalline-to-amorphous transition as well as their role in carrier generation and transport properties of these oxides are far from being understood. Although amorphous oxides lack grain boundaries, factors like (i) size and distribution of nanocrystalline inclusions; (ii) spatial distribution and clustering of incorporated cations in multicomponent oxides; (iii) formation of trap defects; and (iv) piezoelectric effects associated with internal strains, will contribute to electron scattering. In this work, ab-initio molecular dynamics (MD) and accurate density-functional approaches are employed to understand how the properties of amorphous ternary and quaternary oxides depend on quench rates, cation compositions, and oxygen stoichiometries. The MD results, combined with thorough experimental characterization, reveal that interplay between the local and long-range structural preferences of the constituent oxides gives rise to a complex composition-dependent structural behavior in the amorphous oxides. The proposed network models of metal-oxygen polyhedra help explain the observed intriguing electrical and optical properties in In-based oxides and suggest ways to broaden the phase space of amorphous oxide semiconductors with tunable properties. The

  10. Metal-mediated molecular materials at the nano- and mesoscale

    NASA Astrophysics Data System (ADS)

    Arroyo, Itzia Zoraida

    The synthesis of materials via self-assembly is a powerful bottom-up approach for assembling matter from subnanometer up to micrometer scales. This methodology involves the spontaneous and reversible organization of small molecules to create larger structures driven by non-covalent interactions such as hydrogen bonding, hydrophobic forces and metal-ligand coordination interactions. In this dissertation we developed the synthetic methods to generate materials at the nano- and meso-scale using coordination-directed strategies for molecular self-assembly in solid-state and in water. In addition, we produced materials with a modular increased complexity with potential applications in advanced technologies and medicine. Molecular materials in the solid-state were engineered using the coordination directed approach by synthesizing organic ligands with well-defined geometries and symmetries that self-assembly with transition metals in aprotic media into supra-molecular arrays. These structures were crystallized and characterized by techniques such as X-ray Crystallography, Multi-Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), Infrared (IR) and Ultraviolet-Visible (UV-vis) Spectroscopies. Potential application as hydrogen storage systems was evaluated using 2H NMR spectroscopy. Coordination-directed molecular materials that self-assembly in water were achieved by combining coordination capable amphiphilic molecules and designing their chemistry so that they can rearrange in water to produce different lyotropic phases. We characterized these materials using Extended X-ray Absorbance Fine Structure Spectroscopy (EXAFS), Dynamic Light Scattering, Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Optical Microscopy and X-ray Photoelectron Spectroscopy (XPS). The new class of metallo-liposomes was used as a DNA delivery system and demonstrated to be effective for the transfection of pEGFP-N1 plasmid into HEK 293-T cells. Modular molecular

  11. Molecular shield - An orbiting low-density materials laboratory

    NASA Technical Reports Server (NTRS)

    Melfi, L. T., Jr.; Outlaw, R. A.; Hueser, J. E.; Brock, F. J.

    1976-01-01

    Analysis of a molecular shield orbited at 200 km utilizes the kinetic theory of a drifting Maxwellian gas, applied to a hemispherical shell geometry containing internal sources. The molecular shield provides very low gas density conditions for materials experiments at low gravity, while the hemispherical geometry minimizes the internal surface/volume ratio. Deployment of the shield in orbit is described. Contributions to density by shield outgassing, by experiment outgassing, and by interaction with the orbiter are discussed separately. A jettisonable closure plate sealing the hemisphere minimizes any risk of experiment contamination during deployment.

  12. Si K-edge XANES study of SiO{sub x}C{sub y}H{sub z} amorphous polymeric materials

    SciTech Connect

    Chaboy, J.; Barranco, A.; Yanguas-Gil, A.; Yubero, F.; Gonzalez-Elipe, A. R.

    2007-02-15

    This work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous SiO{sub x}C{sub y}H{sub z} polymers prepared by plasma-enhanced chemical-vapor deposition with different C/O ratios. SiO{sub 2} and SiC have been used as reference materials. The comparison of the experimental Si K-edge x-ray absorption near-edge structure spectra with theoretical computations based on multiple scattering theory has allowed us to monitor the modification of the local coordination around Si as a function of the overall C/O ratio in this kind of materials.

  13. Amorphic complexity

    NASA Astrophysics Data System (ADS)

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  14. HIGHWAY INFRASTRUCTURE FOCUS AREA NEXT-GENERATION INFRASTRUCTURE MATERIALS VOLUME I - TECHNICAL PROPOSAL & MANAGEMENTENHANCEMENT OF TRANSPORTATION INFRASTRUCTURE WITH IRON-BASED AMORPHOUS-METAL AND CERAMIC COATINGS

    SciTech Connect

    Farmer, J C

    2007-12-04

    The infrastructure for transportation in the United States allows for a high level of mobility and freight activity for the current population of 300 million residents, and several million business establishments. According to a Department of Transportation study, more than 230 million motor vehicles, ships, airplanes, and railroads cars were used on 6.4 million kilometers (4 million miles) of highways, railroads, airports, and waterways in 1998. Pipelines and storage tanks were considered to be part of this deteriorating infrastructure. The annual direct cost of corrosion in the infrastructure category was estimated to be approximately $22.6 billion in 1998. There were 583,000 bridges in the United States in 1998. Of this total, 200,000 bridges were steel, 235,000 were conventional reinforced concrete, 108,000 bridges were constructed using pre-stressed concrete, and the balance was made using other materials of construction. Approximately 15 percent of the bridges accounted for at this point in time were structurally deficient, primarily due to corrosion of steel and steel reinforcement. Iron-based amorphous metals, including SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been developed, and have very good corrosion resistance. These materials have been prepared as a melt-spun ribbons, as well as gas atomized powders and thermal-spray coatings. During electrochemical testing in several environments, including seawater at 90 C, the passive film stabilities of these materials were found to be comparable to that of more expensive high-performance alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. These materials also performed very well in standard salt fog tests. Chromium (Cr), molybdenum (Mo) and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation

  15. Self assembled molecular monolayers on high surface area materials as molecular getters

    DOEpatents

    King, David E.; Herdt, Gregory C.; Czanderna, Alvin W.

    1997-01-01

    The present invention relates to a gettering material that may be used as a filtration medium to remove pollutants from the environment. The gettering material comprises a high surface area material having a metal surface that chemically bonds n-alkanethiols in an organized manner thereby forming a molecular monolayer over the metal surface. The n-alkanethiols have a free functional group that interacts with the environment thereby binding specific pollutants that may be present. The gettering material may be exposed to streams of air in heating, ventilation, and air conditioning systems or streams of water to remove specific pollutants from either medium.

  16. Self assembled molecular monolayers on high surface area materials as molecular getters

    DOEpatents

    King, D.E.; Herdt, G.C.; Czanderna, A.W.

    1997-01-07

    The present invention relates to a gettering material that may be used as a filtration medium to remove pollutants from the environment. The gettering material comprises a high surface area material having a metal surface that chemically bonds n-alkanethiols in an organized manner thereby forming a molecular monolayer over the metal surface. The n-alkanethiols have a free functional group that interacts with the environment thereby binding specific pollutants that may be present. The gettering material may be exposed to streams of air in heating, ventilation, and air conditioning systems or streams of water to remove specific pollutants from either medium. 9 figs.

  17. Evaluation of different calorimetric methods to determine the glass transition temperature and molecular mobility below T(g) for amorphous drugs.

    PubMed

    Weuts, I; Kempen, D; Six, K; Peeters, J; Verreck, G; Brewster, M; Van den Mooter, G

    2003-06-18

    The purpose of the present study was to compare different calorimetric methods used to determine the glass transition temperature (T(g)) and to evaluate the relaxation behaviour and hence the stability of amorphous drugs below their T(g). Data showed that the values of the activation energy for the transition of a glass to its super-cooled liquid state qualitatively correlate with the values of the mean molecular relaxation time constant of ketoconazole, itraconazole and miconazole, three structurally related drugs. Estimation of the molecular mobility by activation energy calculation indicated that loperamide was more stable than its two building blocks T263 and R731. It was further shown that the most commonly used approach to determine T(g) (T(g (1/2 c(p))) leads to erroneous values when enthalpy recovery is significant. In this case, an alternative method based on enthalpic considerations leads to results in accordance to basic thermodynamics. Estimation of molecular mobility based on activation energy calculations is therefore considered to be a valuable alternative for the method based on measurement of the extent of relaxation. When enthalpy relaxation is important, the use of T(g 1/2c(p)) leads to an overestimation of the T(g).

  18. Segmented molecular design of self-healing proteinaceous materials

    PubMed Central

    Sariola, Veikko; Pena-Francesch, Abdon; Jung, Huihun; Çetinkaya, Murat; Pacheco, Carlos; Sitti, Metin; Demirel, Melik C.

    2015-01-01

    Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure–property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials. PMID:26323335

  19. Segmented molecular design of self-healing proteinaceous materials.

    PubMed

    Sariola, Veikko; Pena-Francesch, Abdon; Jung, Huihun; Çetinkaya, Murat; Pacheco, Carlos; Sitti, Metin; Demirel, Melik C

    2015-09-01

    Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure-property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.

  20. Segmented molecular design of self-healing proteinaceous materials

    NASA Astrophysics Data System (ADS)

    Sariola, Veikko; Pena-Francesch, Abdon; Jung, Huihun; Çetinkaya, Murat; Pacheco, Carlos; Sitti, Metin; Demirel, Melik C.

    2015-09-01

    Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure-property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.

  1. The thermodynamics of amorphous Cu and CuTi

    NASA Astrophysics Data System (ADS)

    Ashkenazy, Yinon; Averback, Robert S.; Granato, Andrew V.

    2002-03-01

    The changes in thermodynamic properties of amorphous metals as they are cooled from the liquid state provide revealing information about the nature of the amorphous state and the melting and glass transitions. We present here calculations on pure Cu and Cu-Ti of such properties as entropy and heat capacity using molecular dynamics computer simulations. Even though for pure Cu we find crystallization prior to formation of a glass, the results are consistent with a very low glass temperature and in part can be explained by Granatos interstitialcy model of melting [Phys. Rev. Lett. 68 (1992) 974]. Comparison of the calculations with experimental data as well as comparison between the pure amorphous material and the glass-forming alloy will be presented.

  2. Optical investigation of molecular structure of sophisticated materials for photonics

    NASA Astrophysics Data System (ADS)

    Gnyba, Marcin; Keraenen, Mikko

    2003-10-01

    Permanent development of photonics stimulates a searching for new materials, which have better optical, mechanical and electrical properties. One of the new classes of materials with large application and development potential are hybrid polymers, synthesized in sol-gel technology. Thanks to incorporation of organic components into an in organic network, a combination of advantages of both class of materials became available. Properties of hybrids may be formed in wide range. These materials can be used in photonics to produce planar waveguides, lenses, Bragg gratings and components for integrated optics. Moreover, dielectric layers, coatings and packaging are made from hybrids. Additionally, research to apply them in optical fiber sensors (including bio-sensors) and solid state lasers is underway. However, to obtain a high quality product, a strict control of its molecular structure must be ensured. This is a very difficult task, because of a sophisticated structure of hybrid polymers. To address these problems, optical, non-destructive measurement techniques such as Raman and infrared spectroscopy were used. They are compementary methods, so their simultaneous application, as it was shown in this paper, can significantly increase the amoung of information about molecular structure of materials and process of their synthesis.

  3. Molecular receptors in metal oxide sol-gel materials prepared via molecular imprinting

    DOEpatents

    Sasaki, Darryl Y.; Brinker, C. Jeffrey; Ashley, Carol S.; Daitch, Charles E.; Shea, Kenneth J.; Rush, Daniel J.

    2000-01-01

    A method is provided for molecularly imprinting the surface of a sol-gel material, by forming a solution comprised of a sol-gel material, a solvent, an imprinting molecule, and a functionalizing siloxane monomer of the form Si(OR).sub.3-n X.sub.n, wherein n is an integer between zero and three and X is a functional group capable of reacting with the imprinting molecule, evaporating the solvent, and removing the imprinting molecule to form the molecularly imprinted metal oxide sol-gel material. The use of metal oxide sol-gels allows the material porosity, pore size, density, surface area, hardness, electrostatic charge, polarity, optical density, and surface hydrophobicity to be tailored and be employed as sensors and in catalytic and separations operations.

  4. Unveiling the complex electronic structure of amorphous metal oxides

    PubMed Central

    Århammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmström, Erik; Araujo, C. Moyses; Gråsjö, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Föhlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Börje; Ahuja, Rajeev

    2011-01-01

    Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

  5. First-principles study of the amorphization of stishovite by isotropic volume expansion

    NASA Astrophysics Data System (ADS)

    Misawa, Masaaki; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    Simple synthesis of ceramics with high hardness and high toughness from Earth-abundant materials is one of the most important issues in materials science. Nishiyama et al. synthesized nano-crystalline stishovite with extremely high toughness and high hardness via compression and decompression of silica, and proposed fracture-induced amorphization mechanisms for the toughning. Furthermore, it was shown that the toughening mechanisms are effective even in nanoscale order. Our first-principles molecular dynamics simulations have shown rapid amorphization of stishovite within picoseconds under increasing volume, thus substantiating the proposed amorphization mechanisms. Furthermore, we have calculated the critical stress, energy difference, and energy barrier for the crystalline-to-amorphous structural transition.

  6. Polymeric and Molecular Materials for Advanced Organic Electronics

    DTIC Science & Technology

    2014-10-20

    easily reconfigurable. These new- generation products will require new types of semiconductors and other materials, less capital- intensive thin film ...based polymers with highly informative properties. vii This includes polymers where electron-poor BTI is co- polymerized with electron-rich R2Si...blocks for molecular and polymeric hole- and electron transporters. Based on these results and our expertise in imide-based semiconducting polymers

  7. Facile synthesis of amorphous FeOOH/MnO2 composites as screen-printed electrode materials for all-printed solid-state flexible supercapacitors

    NASA Astrophysics Data System (ADS)

    Lu, Qiang; Liu, Li; Yang, Shuanglei; Liu, Jun; Tian, Qingyong; Yao, Weijing; Xue, Qingwen; Li, Mengxiao; Wu, Wei

    2017-09-01

    More convenience and intelligence life lead by flexible/wearable electronics requires innovation and hommization of power sources. Here, amorphous FeOOH/MnO2 composite as screen-printed electrode materials for supercapacitors (SCs) is synthesized by a facile method, and solid-state flexible SCs with aesthetic design are fabricated by fully screen-printed process on different substrates, including PET, paper and textile. The amorphous FeOOH/MnO2 composite shows a high specific capacitance and a good rate capability (350.2 F g-1 at a current density of 0.5 A g-1 and 159.5 F g-1 at 20 A g-1). It also possesses 95.6% capacitance retention even after 10 000 cycles. Moreover, the all-printed solid-state flexible SC device exhibits a high area specific capacitance of 5.7 mF cm-2 and 80% capacitance retention even after 2000 cycles. It also shows high mechanical flexibility. Simultaneously, these printed SCs on different substrates in series are capable to light up a 1.9 V yellow light emitting diode (LED), even after bending and stretching.

  8. High performance amorphous-Si@SiOx/C composite anode materials for Li-ion batteries derived from ball-milling and in situ carbonization

    NASA Astrophysics Data System (ADS)

    Wang, Dingsheng; Gao, Mingxia; Pan, Hongge; Wang, Junhua; Liu, Yongfeng

    2014-06-01

    Amorphous-Si@SiOx/C composites with amorphous Si particles as core and coated with a double layer of SiOx and carbon are prepared by ball-milling crystal micron-sized silicon powders and carbonization of the citric acid intruded in the ball-milled Si. Different ratios of Si to citric acid are used in order to optimize the electrochemical performance. It is found that SiOx exists naturally at the surfaces of raw Si particles and its content increases to ca. 24 wt.% after ball-milling. With an optimized Si to citric acid weight ratio of 1/2.5, corresponding to 8.4 wt.% C in the composite, a thin carbon layer is coated on the surfaces of a-Si@SiOx particles, moreover, floc-like carbon also forms and connects the carbon coated a-Si@SiOx particles. The composite provides a capacity of 1450 mA h g-1 after 100 cycles at a current density of 100 mA g1, and a capacity of 1230 mA h g-1 after 100 cycles at 500 mA g1 as anode material for lithium-ion batteries. Effects of ball-milling and the addition of citric acid on the microstructure and electrochemical properties of the composites are revealed and the mechanism of the improvement in electrochemical properties is discussed.

  9. Primordial Molecular Cloud Material in Metal-Rich Carbonaceous Chondrites

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2016-03-01

    The menagerie of objects that make up our Solar System reflects the composition of the huge molecular cloud in which the Sun formed, a late addition of short-lived isotopes from an exploding supernova or stellar winds from a neighboring massive star, heating and/or alteration by water in growing planetesimals that modified and segregated the primordial components, and mixing throughout the Solar System. Outer Solar System objects, such as comets, have always been cold, hence minimizing the changes experienced by more processed objects. They are thought to preserve information about the molecular cloud. Elishevah Van Kooten (Natural History Museum of Denmark and the University of Copenhagen) and co-authors in Denmark and at the University of Hawai'i, measured the isotopic compositions of magnesium and chromium in metal-rich carbonaceous chondrites. They found that the meteorites preserve an isotopic signature of primordial molecular cloud materials, providing a potentially detailed record of the molecular cloud's composition and of materials that formed in the outer Solar System.

  10. Photophysics of Molecular Materials: From Single Molecules to Single Crystals

    NASA Astrophysics Data System (ADS)

    Lanzani, Guglielmo

    2005-12-01

    Carbon based pi-conjugated materials offer a broad range of applications, going from molecular electronics and single molecule devices to nanotechnology, plastic electronics and optoelectronics. The proper physical description of such materials is in between that of molecular solids and that of low-dimensional covalent semiconductors. This book is a comprehensive review of their elementary excitations processes and dynamics, which merges the two viewpoints, sometimes very different if not contrasting. In each chapter, a broad tutorial introduction provides a solid physical background to the topic, which is further discussed based on recent experimental results obtained via state-of-the-art techniques. Both the molecular, intra-chain character and the solid state, inter-molecular physics is addressed. Reports on single molecule and single polymer chain spectroscopy introduce the on-site phenomena. Several chapters are dedicated to nano-probes, steady state and transient spectroscopies. The highly ordered state, occurring in single crystals, is also discussed thoroughly. Finally, less conventional tools such as THz spectroscopy are discussed in detail. The book provides a useful introduction to the field for newcomers, and a valid reference for experienced researchers in the field.

  11. Photophysics of Molecular Materials: From Single Molecules to Single Crystals

    NASA Astrophysics Data System (ADS)

    Lanzani, Guglielmo

    2003-09-01

    Carbon based pi-conjugated materials offer a broad range of applications, going from molecular electronics and single molecule devices to nanotechnology, plastic electronics and optoelectronics. The proper physical description of such materials is in between that of molecular solids and that of low-dimensional covalent semiconductors. This book is a comprehensive review of their elementary excitations processes and dynamics, which merges the two viewpoints, sometimes very different if not contrasting. In each chapter, a broad tutorial introduction provides a solid physical background to the topic, which is further discussed based on recent experimental results obtained via state-of-the-art techniques. Both the molecular, intra-chain character and the solid state, inter-molecular physics is addressed. Reports on single molecule and single polymer chain spectroscopy introduce the on-site phenomena. Several chapters are dedicated to nano-probes, steady state and transient spectroscopies. The highly ordered state, occurring in single crystals, is also discussed thoroughly. Finally, less conventional tools such as THz spectroscopy are discussed in detail. The book provides a useful introduction to the field for newcomers, and a valid reference for experienced researchers in the field.

  12. Amorphous metallic foam

    NASA Astrophysics Data System (ADS)

    Schroers, Jan; Veazey, Chris; Johnson, William L.

    2003-01-01

    The bulk glass forming alloy Pd43Ni10Cu27P20 is processed into a low-density amorphous metallic foam. Pd43Ni10Cu27P20 is mixed with hydrated B2O3, which releases gas at elevated temperature and/or low pressure. Very homogeneous foams are achieved due to the high viscosity of the alloy even at its liquidus temperature. By processing at the liquidus temperature and decreasing the pressure to 10-2 mbar, well-distributed bubbles expand to foam the material. Foam densities as low as 1.4×103 kg/m3 were obtained, corresponding to a bubble volume fraction of 84%. The bubble diameter ranges between 2×10-4 and 1×10-3 m. Thermal analysis by differential scanning calorimetry confirms the amorphous nature of the foam. Furthermore, it reveals that the foam's thermal stability is comparable to the bulk material.

  13. Amorphous silicon solar cell allowing infrared transmission

    DOEpatents

    Carlson, David E.

    1979-01-01

    An amorphous silicon solar cell with a layer of high index of refraction material or a series of layers having high and low indices of refraction material deposited upon a transparent substrate to reflect light of energies greater than the bandgap energy of the amorphous silicon back into the solar cell and transmit solar radiation having an energy less than the bandgap energy of the amorphous silicon.

  14. Impact of Amorphous SiO2 Nanoparticles on a Living Organism: Morphological, Behavioral, and Molecular Biology Implications

    PubMed Central

    Ambrosone, Alfredo; Scotto di Vettimo, Maria Rosaria; Malvindi, Maria Ada; Roopin, Modi; Levy, Oren; Marchesano, Valentina; Pompa, Pier Paolo; Tortiglione, Claudia; Tino, Angela

    2014-01-01

    It is generally accepted that silica (SiO2) is not toxic. But the increasing use of silica nanoparticles (SiO2NPs) in many different industrial fields has prompted the careful investigation of their toxicity in biological systems. In this report, we describe the effects elicited by SiO2NPs on animal and cell physiology. Stable and monodisperse amorphous silica nanoparticles, 25 nM in diameter, were administered to living Hydra vulgaris (Cnidaria). The dose-related effects were defined by morphological and behavioral assays. The results revealed an all-or-nothing lethal toxicity with a rather high threshold (35 nM NPs) and a LT50 of 38 h. At sub lethal doses, the morphophysiological effects included: animal morphology alterations, paralysis of the gastric region, disorganization and depletion of tentacle specialized cells, increase of apoptotic and collapsed cells, and reduction of the epithelial cell proliferation rate. Transcriptome analysis (RNAseq) revealed 45 differentially expressed genes, mostly involved in stress response and cuticle renovation. Our results show that Hydra reacts to SiO2NPs, is able to rebalance the animal homeostasis up to a relatively high doses of SiO2NPs, and that the physiological modifications are transduced to gene expression modulation. PMID:25325055

  15. Impact of Amorphous SiO2 Nanoparticles on a Living Organism: Morphological, Behavioral, and Molecular Biology Implications.

    PubMed

    Ambrosone, Alfredo; Scotto di Vettimo, Maria Rosaria; Malvindi, Maria Ada; Roopin, Modi; Levy, Oren; Marchesano, Valentina; Pompa, Pier Paolo; Tortiglione, Claudia; Tino, Angela

    2014-01-01

    It is generally accepted that silica (SiO2) is not toxic. But the increasing use of silica nanoparticles (SiO2NPs) in many different industrial fields has prompted the careful investigation of their toxicity in biological systems. In this report, we describe the effects elicited by SiO2NPs on animal and cell physiology. Stable and monodisperse amorphous silica nanoparticles, 25 nM in diameter, were administered to living Hydra vulgaris (Cnidaria). The dose-related effects were defined by morphological and behavioral assays. The results revealed an all-or-nothing lethal toxicity with a rather high threshold (35 nM NPs) and a LT50 of 38 h. At sub lethal doses, the morphophysiological effects included: animal morphology alterations, paralysis of the gastric region, disorganization and depletion of tentacle specialized cells, increase of apoptotic and collapsed cells, and reduction of the epithelial cell proliferation rate. Transcriptome analysis (RNAseq) revealed 45 differentially expressed genes, mostly involved in stress response and cuticle renovation. Our results show that Hydra reacts to SiO2NPs, is able to rebalance the animal homeostasis up to a relatively high doses of SiO2NPs, and that the physiological modifications are transduced to gene expression modulation.

  16. Maxwell rigidity and topological constraints in amorphous phase-change networks

    SciTech Connect

    Micoulaut, M.; Otjacques, C.; Raty, J.-Y.; Bichara, C.

    2011-12-12

    By analyzing first-principles molecular-dynamics simulations of different telluride amorphous networks, we develop a method for the enumeration of radial and angular topological constraints, and show that the phase diagram of the most popular system Ge-Sb-Te can be split into two compositional elastic phases: a tellurium rich flexible phase and a stressed rigid phase that contains most of the materials used in phase-change applications. This sound atomic scale insight should open new avenues for the understanding of phase-change materials and other complex amorphous materials from the viewpoint of rigidity.

  17. Laser surface treatment of amorphous metals

    NASA Astrophysics Data System (ADS)

    Katakam, Shravana K.

    Amorphous materials are used as soft magnetic materials and also as surface coatings to improve the surface properties. Furthermore, the nanocrystalline materials derived from their amorphous precursors show superior soft magnetic properties than amorphous counter parts for transformer core applications. In the present work, laser based processing of amorphous materials will be presented. Conventionally, the nanocrystalline materials are synthesized by furnace heat treatment of amorphous precursors. Fe-based amorphous/nanocrystalline materials due to their low cost and superior magnetic properties are the most widely used soft magnetic materials. However, achieving nanocrystalline microstructure in Fe-Si-B ternary system becomes very difficult owing its rapid growth rate at higher temperatures and sluggish diffusion at low temperature annealing. Hence, nanocrystallization in this system is achieved by using alloying additions (Cu and Nb) in the ternary Fe-Si-B system. Thus, increasing the cost and also resulting in reduction of saturation magnetization. laser processing technique is used to achieve extremely fine nanocrystalline microstructure in Fe-Si-B amorphous precursor. Microstructure-magnetic Property-laser processing co-relationship has been established for Fe-Si-B ternary system using analytical techniques. Laser processing improved the magnetic properties with significant increase in saturation magnetization and near zero coercivity values. Amorphous materials exhibit excellent corrosion resistance by virtue of their atomic structure. Fe-based amorphous materials are economical and due to their ease of processing are of potential interest to synthesize as coatings materials for wear and corrosion resistance applications. Fe-Cr-Mo-Y-C-B amorphous system was used to develop thick coatings on 4130 Steel substrate and the corrosion resistance of the amorphous coatings was improved. It is also shown that the mode of corrosion depends on the laser processing

  18. Materials research at Stanford University. [composite materials, crystal structure, acoustics

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Research activity related to the science of materials is described. The following areas are included: elastic and thermal properties of composite materials, acoustic waves and devices, amorphous materials, crystal structure, synthesis of metal-metal bonds, interactions of solids with solutions, electrochemistry, fatigue damage, superconductivity and molecular physics and phase transition kinetics.

  19. The release of trapped gases from amorphous solid water films. I. "Top-down" crystallization-induced crack propagation probed using the molecular volcano.

    PubMed

    May, R Alan; Smith, R Scott; Kay, Bruce D

    2013-03-14

    In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the "molecular volcano." The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ∕mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization∕crack front into the film is in good agreement with the temperature programmed desorption results.

  20. The Release of Trapped Gases from Amorphous Solid Water Films: I. “Top-Down” Crystallization-Induced Crack Propagation Probed using the Molecular Volcano

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2013-03-14

    In this (Paper I) and the companion paper (Paper II) we investigate the mechanisms for the release of trapped gases from underneath of amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization ASW, a phenomenon that we termed the "molecular volcano". The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length and distribution are independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2 or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ/mol. This value is consistent with the crystallization growth rate reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization/crack front into the film is in good agreement with the temperature programmed desorption results.

  1. From molecular design and materials construction to organic nanophotonic devices.

    PubMed

    Zhang, Chuang; Yan, Yongli; Zhao, Yong Sheng; Yao, Jiannian

    2014-12-16

    CONSPECTUS: Nanophotonics has recently received broad research interest, since it may provide an alternative opportunity to overcome the fundamental limitations in electronic circuits. Diverse optical materials down to the wavelength scale are required to develop nanophotonic devices, including functional components for light emission, transmission, and detection. During the past decade, the chemists have made their own contributions to this interdisciplinary field, especially from the controlled fabrication of nanophotonic molecules and materials. In this context, organic micro- or nanocrystals have been developed as a very promising kind of building block in the construction of novel units for integrated nanophotonics, mainly due to the great versatility in organic molecular structures and their flexibility for the subsequent processing. Following the pioneering works on organic nanolasers and optical waveguides, the organic nanophotonic materials and devices have attracted increasing interest and developed rapidly during the past few years. In this Account, we review our research on the photonic performance of molecular micro- or nanostructures and the latest breakthroughs toward organic nanophotonic devices. Overall, the versatile features of organic materials are highlighted, because they brings tunable optical properties based on molecular design, size-dependent light confinement in low-dimensional structures, and various device geometries for nanophotonic integration. The molecular diversity enables abundant optical transitions in conjugated π-electron systems, and thus brings specific photonic functions into molecular aggregates. The morphology of these micro- or nanostructures can be further controlled based on the weak intermolecular interactions during molecular assembly process, making the aggregates show photon confinement or light guiding properties as nanophotonic materials. By adoption of some active processes in the composite of two or more

  2. Design Molecular Recognition Materials for Chiral Sensors, Separtations and Catalytic Materials

    SciTech Connect

    Jia, S.; Nenoff, T.M.; Provencio, P.; Qiu, Y.; Shelnutt, J.A.; Thoma, S.G.; Zhang, J.

    1998-11-01

    The goal is the development of materials that are highly sensitive and selective for chid chemicals and biochemical (such as insecticides, herbicides, proteins, and nerve agents) to be used as sensors, catalysts and separations membranes. Molecular modeling methods are being used to tailor chiral molecular recognition sites with high affinity and selectivity for specified agents. The work focuses on both silicate and non-silicate materials modified with chirally-pure fictional groups for the catalysis or separations of enantiomerically-pure molecules. Surfactant and quaternary amine templating is being used to synthesize porous frameworks, containing mesopores of 30 to 100 angstroms. Computer molecukw modeling methods are being used in the design of these materials, especially in the chid surface- modi~ing agents. Molecular modeling is also being used to predict the catalytic and separations selectivities of the modified mesoporous materials. The ability to design and synthesize tailored asymmetric molecular recognition sites for sensor coatings allows a broader range of chemicals to be sensed with the desired high sensitivity and selectivity. Initial experiments target the selective sensing of small molecule gases and non-toxic model neural compounds. Further efforts will address designing sensors that greatly extend the variety of resolvable chemical species and forming a predictive, model-based method for developing advanced sensors.

  3. Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

    NASA Technical Reports Server (NTRS)

    Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

  4. Rational Design of Molecular Ferroelectric Materials and Nanostructures

    SciTech Connect

    Ducharme, Stephen

    2012-09-25

    The purpose of this project was to gain insight into the properties of molecular ferroelectrics through the detailed study of oligomer analogs of polyvinylidene fluoride (PVDF). By focusing on interactions at both the molecular level and the nanoscale level, we expect to gain improved understanding about the fundamental mechanism of ferroelectricity and its key properties. The research consisted of three complementary components: 1) Rational synthesis of VDF oligomers by Prof. Takacs' group; 2) Detailed structural and electrical studies of thin by Prof. Ducharme's Group; and 3) First-principles computational studies by DOE Lab Partner Dr. Serge Nakhman-son at Argonne National Laboratory. The main results of the work was a detailed understanding of the relationships between the molecular interactions and macroscopic phenomenology of fer-roelectricity VDF oligomers. This is valuable information supporting the development of im-proved electromechanical materials for, e.g., sonar, ultrasonic imaging, artificial muscles, and compliant actuators. Other potential applications include nonvolatile ferroelectric memories, heat-sensing imaging arrays, photovoltaic devices, and functional biomimetic materials. The pro-ject contributed to the training and professional development of undergraduate students and graduate students, post-doctoral assistants, and a high-school teacher. Project personnel took part in several outreach and education activities each year.

  5. Nano-crystallization and magnetic mechanisms of Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} amorphous alloy by ab initio molecular dynamics simulation

    SciTech Connect

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2014-05-07

    Iron-based amorphous and nano-crystalline alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, fundamental understanding of the nano-crystallization mechanisms and magnetic features in the amorphous structure are still lack of knowledge. In the present work, we performed ab initio molecular dynamics simulation to clarify the ionic and electronic structure in atomic scale, and to derive the origin of the good magnetic property of Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} amorphous alloy. The simulation gave a direct evidence of the Cu-P bonding preference in the amorphous alloy, which may promote nucleation in nano-crystallization process. On the other hand, the electron transfer and the band/orbital features in the amorphous alloy suggests that alloying elements with large electronegativity and the potential to expand Fe disordered matrix are preferred for enhancing the magnetization.

  6. Amorphization and thermal stability of aluminum-based nanoparticles prepared from the rapid cooling of nanodroplets: effect of iron addition.

    PubMed

    Xiao, Shifang; Li, Xiaofan; Deng, Huiqiu; Deng, Lei; Hu, Wangyu

    2015-03-07

    Despite an intensive investigation on bimetallic nanoparticles, little attention has been paid to their amorphization in the past few decades. The study of amorphization on a nanoscale is of considerable significance for the preparation of amorphous nanoparticles and bulk metallic glass. Herein, we pursue the amorphization process of Al-based nanoparticles with classic molecular dynamics simulations and local structural analysis techniques. By a comparative study of the amorphization of pure Al and Fe-doped Al-based nanodroplets in the course of rapid cooling, we find that Fe addition plays a very important role in the vitrification of Al-based nanodroplets. Owing to the subsurface segregated Fe atoms with their nearest neighbors tending to form relatively stable icosahedral (ICO) clusters, the Fe-centred cluster network near the surface effectively suppresses the crystallization of droplets from surface nucleation and growth as the concentration of Fe attains a certain value. The glass formation ability of nanodroplets is suggested to be enhanced by the high intrinsic inner pressure as a result of small size and surface tension, combined with the dopant-inhibited surface nucleation. In addition, the effect of the size and the added concentration of nanoparticles on amorphization and the thermal stability of the amorphous nanoparticles are discussed. Our findings reveal the amorphization mechanism in Fe-doped Al-based nanoparticles and provide a theoretical guidance for the design of amorphous materials.

  7. Local structure of amorphous Ag5In5Sb60Te30 and In3SbTe2 phase change materials revealed by X-ray photoelectron and Raman spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Sahu, Smriti; Manivannan, Anbarasu; Shaik, Habibuddin; Mohan Rao, G.

    2017-07-01

    Reversible switching between highly resistive (binary "0") amorphous phase and low resistive (binary "1") crystalline phase of chalcogenide-based Phase Change Materials is accredited for the development of next generation high-speed, non-volatile, data storage applications. The doped Sb-Te based materials have shown enhanced electrical/optical properties, compared to Ge-Sb-Te family for high-speed memory devices. We report here the local atomic structure of as-deposited amorphous Ag5In5Sb60Te30 (AIST) and In3SbTe2 (IST) phase change materials using X-ray photoelectron and Raman spectroscopic studies. Although AIST and IST materials show identical crystallization behavior, they differ distinctly in their crystallization temperatures. Our experimental results demonstrate that the local environment of In remains identical in the amorphous phase of both AIST and IST material, irrespective of its atomic fraction. In bonds with Sb (˜44%) and Te (˜56%), thereby forming the primary matrix in IST with a very few Sb-Te bonds. Sb2Te constructs the base matrix for AIST (˜63%) along with few Sb-Sb bonds. Furthermore, an interesting assimilation of the role of small-scale dopants such as Ag and In in AIST, reveals rare bonds between themselves, while showing selective substitution in the vicinity of Sb and Te. This results in increased electronegativity difference, and consequently, the bond strength is recognized as the factor rendering stability in amorphous AIST.

  8. Cooling rate effects on structure of amorphous graphene

    NASA Astrophysics Data System (ADS)

    Van Hoang, Vo

    2015-01-01

    Simple monatomic amorphous 2D models with Honeycomb structure are obtained from 2D simple monatomic liquids with Honeycomb interaction potential (Rechtsman et al., Phys. Rev. Lett. 95, 228301 (2005)) via molecular dynamics (MD) simulations. Models are observed by cooling from the melt at various cooling rates. Temperature dependence of thermodynamic and structural properties including total energy, mean ring size, mean coordination number is studied in order to show evolution of structure and thermodynamics upon cooling from the melt. Structural properties of the amorphous Honeycomb structures are studied via radial distribution function (RDF), coordination number and ring distributions together with 2D visualization of the atomic configurations. Amorphous Honeycomb structures contain a large amount of structural defects including new ones which have not been previously reported yet. Cooling rate dependence of structural properties of the obtained amorphous Honeycomb structures is analyzed. Although amorphous graphene has been proposed theoretically and/or recently obtained by the experiments, our understanding of structural properties of the system is still poor. Therefore, our simulations highlight the situation and give deeper understanding of structure and thermodynamics of the glassy state of this novel 2D material.

  9. Shock induced crystallization of amorphous Nickel powders

    NASA Astrophysics Data System (ADS)

    Cherukara, Mathew; Strachan, Alejandro

    2015-06-01

    Recent experimental work has shown the efficacy of amorphous Ni/crystalline Al composites as energetic materials, with flame velocities twice that of a comparable crystalline Ni/crystalline Al system. Of further interest is the recrystallization mechanisms in the pure amorphous Ni powders, both thermally induced and mechanically induced. We present large-scale molecular dynamics simulations of shock-induced recrystallization in loosely packed amorphous Nickel powders. We study the time dependent nucleation and growth processes by holding the shocked samples at the induced pressures and temperatures for extended periods following the passage of the shock (up to 6 ns). We find that the nanostructure of the recrystallized Ni and time scales of recrystallization are dependent on the piston velocity. At low piston velocities, nucleation events are rare, leading to long incubation times and a relatively coarse nanostructure. At higher piston velocities, local variations in temperature due to jetting phenomena and void collapse, give rise to multiple nucleation events on time scales comparable to the passage of the shock wave, leading to the formation of a fine-grained nanostructure. Interestingly, we observe that the nucleation and growth process occurs in two steps, with the first nuclei crystallizing into the BCC structure, before evolving over time into the expected FCC structure. U.S. Defense Threat Reduction Agency, HDTRA1-10-1-0119 (Program Manager Suhithi Peiris).

  10. Monolithic integration of microelectronics and photonics using molecularly engineered materials

    NASA Astrophysics Data System (ADS)

    Kubacki, Ronald M.

    2005-03-01

    The monolithic integration of CMOS microelectronics with photonics is inevitable and benefits both technologies. Photonic integration to microelectronics provides such solutions as overcoming microprocessor communication roadblocks through the use of optical interconnection. Microelectronic integration can provide benefits to photonic structures by optimizing electronic signals generated by photonic biosensors for example. Photonic integration must complement, build on, and enhance the existing state of CMOS microelectronic technology. Photonic approaches that ignore the realities of CMOS architectures (such as power and thermal limitations), provide little benefit to the CMOS device performance, are incompatible with CMOS silicon manufacturing processes, or are incapable of achieving levels of long term reliability already well demonstrated by microelectronic devices, give little reason for photonic/microelectronic integration. Practical implementation of photonics on chip, monolithically with CMOS type microelectronic devices, remains in the laboratory. This work presents architectures to integrate photonics and microelectronics that address CMOS fabrication realities, increase performance of both the electronic and optical functions, and retain current levels of reliability. Fabricating these structures with the limited CMOS material set and/or typical photonic materials requires materials to be molecularly engineered to provide required properties. Materials have been investigated that enable economic fabrication of photonic structures for monolithic integration. Low loss self assembled silicon nanocomposite VIPIR waveguide structures are combined with long term stable non-linear poled polymers for fabrication of electro-optic active devices. Materials are fabricated using low temperature plasma enhanced chemical vapor deposition (PECVD).

  11. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    PubMed

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. High Pressure Materials Research: Novel Extended Phases of Molecular Triatomics

    SciTech Connect

    Yoo, C

    2004-05-26

    Application of high pressure significantly alters the interatomic distance and thus the nature of intermolecular interaction, chemical bonding, molecular configuration, crystal structure, and stability of solid [1]. With modern advances in high-pressure technologies [2], it is feasible to achieve a large (often up to a several-fold) compression of lattice, at which condition material can be easily forced into a new physical and chemical configuration [3]. The high-pressure thus offers enhanced opportunities to discover new phases, both stable and metastable ones, and to tune exotic properties in a wide-range of atomistic length scale, substantially greater than (often being several orders of) those achieved by other thermal (varying temperatures) and chemical (varying composition or making alloys) means. Simple molecular solids like H{sub 2}, C, CO{sub 2}, N{sub 2}, O{sub 2}, H{sub 2}O, CO, NH{sub 3}, and CH{sub 4} are bounded by strong covalent intramolecular bonds, yet relatively weak intermolecular bonds of van der Waals and/or hydrogen bonds. The weak intermolecular bonds make these solids highly compressible (i.e., low bulk moduli typically less than 10 GPa), while the strong covalent bonds make them chemically inert at least initially at low pressures. Carbon-carbon single bonds, carbon-oxygen double bonds and nitrogen-nitrogen triple bonds, for example, are among the strongest. These molecular forms are, thus, often considered to remain stable in an extended region of high pressures and high temperatures. High stabilities of these covalent molecules are also the basis of which their mixtures are often presumed to be the major detonation products of energetic materials as well as the major constituents of giant planets. However, their physical/chemical stabilities are not truly understood at those extreme pressure-temperature conditions. In fact, an increasing amount of experimental evidences contradict the assumed stability of these materials at high

  13. Beating the amorphous limit in thermal conductivity by superlattices design

    PubMed Central

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-01-01

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts. PMID:26374147

  14. Beating the amorphous limit in thermal conductivity by superlattices design.

    PubMed

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-09-16

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts.

  15. Structural Organization of {pi} Conjugated Highly Luminescent Molecular Material

    SciTech Connect

    Toudic, B.; Limelette, P.; Le Gac, F.; Moreac, A.; Rabiller, P.; Froyer, G.

    2005-11-18

    We report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below room temperature reveals a singular behavior suggesting a modification of the overlap between the electronic wave function induced by the nonplanarity. These results provide a new basis to answer fundamental issues related to molecular and electronic materials and, in particular, luminescent organic devices.

  16. Determine the permeability of an amorphous mixture of polydimethylsiloxane and dealuminated zeolite ZSM-5 to various ethanol-water solutions using molecular simulations.

    EPA Science Inventory

    An amorphous mixture of PDMS and multi-cellular fragments of ZSM-5 is brought together to approximate the properties of a mixed matrix membrane of PDMS with ZSM-5. The permeability coefficient of the amorphous mixture for pure water is the product of the diffusion coefficient of...

  17. Determine the permeability of an amorphous mixture of polydimethylsiloxane and dealuminated zeolite ZSM-5 to various ethanol-water solutions using molecular simulations.

    EPA Science Inventory

    An amorphous mixture of PDMS and multi-cellular fragments of ZSM-5 is brought together to approximate the properties of a mixed matrix membrane of PDMS with ZSM-5. The permeability coefficient of the amorphous mixture for pure water is the product of the diffusion coefficient of...

  18. Pressure-induced amorphization in crystalline silica: Soft phonon modes and shear instabilities in coesite

    SciTech Connect

    Dean, David W.; Wentzcovitch, Renata M.; Keskar, N.; Chelikowsky, James R.; Binggeli, N.

    2000-02-01

    Quartz and closely related materials will transform under pressure from crystalline states to amorphous forms. Here we examine coesite, a high-pressure form of silica which also undergoes pressure induced amorphization. We find that coesite, like quartz, possesses a shear instability closely coupled to a zone-edge phonon softening at pressures comparable to the amorphization transformation. The commonality of these features strongly suggests that a coupling between a shear and a phonon soft mode plays an important role in pressure induced amorphization. This mechanism is similar to that observed in martensitic transformations. The densities for the phases produced at high pressures, as calculated from variable cell shape molecular dynamics, follow the experimental glassy region joining coesite to stishovite. (c) 2000 The American Physical Society.

  19. Plastic Deformation, Amorphization, and Phase Changes in Extreme Laser Shock Compression of Ta and Si

    NASA Astrophysics Data System (ADS)

    Meyers, Marc

    2015-06-01

    High-amplitude pulsed lasers probe the response of materials at pressures up to 100s of GPa and strain rates of 108 s-1, revealing plastic deformation, phase transformations, and amorphization. Molecular dynamics simulations provide modeling at comparable strain rates and time durations. Shock compression of monocrystalline Ta reveals dislocations at low pressures and twinning at higher pressures (above 24 GPa). Results are compared with predictions from homogeneous dislocation generation and multiplication and the latter mechanism is dominant. The formation of an Omega phase was observed in monocrystalline tantalum at a shock amplitude of approximately 70 GPa. The shear stresses may play a role in the transformation. As shock energy increases, the following structural changes in monocrystalline Si are observed: dislocations and stacking faults; bands of amorphized Si forming on crystallographic orientations consistent with slip; broad regions of amorphized Si; nanocrystalline Si resulting from re-crystallization. MD simulations display similar amorphous regions. Funding: UCOP and DOE SSAP.

  20. Fractal evaluation of drug amorphicity from optical and scanning electron microscope images

    NASA Astrophysics Data System (ADS)

    Gavriloaia, Bogdan-Mihai G.; Vizireanu, Radu C.; Neamtu, Catalin I.; Gavriloaia, Gheorghe V.

    2013-09-01

    Amorphous materials are metastable, more reactive than the crystalline ones, and have to be evaluated before pharmaceutical compound formulation. Amorphicity is interpreted as a spatial chaos, and patterns of molecular aggregates of dexamethasone, D, were investigated in this paper by using fractal dimension, FD. Images having three magnifications of D were taken from an optical microscope, OM, and with eight magnifications, from a scanning electron microscope, SEM, were analyzed. The average FD for pattern irregularities of OM images was 1.538, and about 1.692 for SEM images. The FDs of the two kinds of images are less sensitive of threshold level. 3D images were shown to illustrate dependence of FD of threshold and magnification level. As a result, optical image of single scale is enough to characterize the drug amorphicity. As a result, the OM image at a single scale is enough to characterize the amorphicity of D.