Showing papers on "Amorphous solid published in 1994"
TL;DR: In this article, the authors compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of these materials.
Abstract: We compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of the structure of these materials. For the full range of carbon‐hydrogen alloys, including so‐called ‘‘amorphous diamond,’’ hydrogenated ‘‘diamondlike’’ carbon, and plasma‐polymers, a simple parametrization of the Raman spectrum in the usual 1000 cm−1 to 2000 cm−1 range can be used as a reliable predictor of hydrogenation and other properties (e.g., optical gap, hardness). Raman features in the 200 cm−1 to 1000 cm−1 range, a spectral region not usually reported for carbon films, may also be used as an indicator of hydrogenation. These growth method independent correlations greatly enhance the utility of Raman spectroscopy as a non‐destructive characterization and process control tool.
915 citations
TL;DR: It was found that there is a rapid initial reduction in the glass transition temperature from the dry state as water is absorbed, followed by a gradual leveling off of the response at higher water contents, indicating that water acts as a plasticizer in a way similar to that of other small molecules and not through any specific or stoichiometric interaction process(es).
Abstract: The glass transition temperature of an amorphous pharmaceutical solid is a critical physical property which can dramatically influence its chemical stability, physical stability, and viscoelastic properties. Water frequently acts as a potent plasticizer for such materials, and since many amorphous solids spontaneously absorb water from their surroundings the relationship between the glass transition temperature and the water content of these materials is important. For a wide range of amorphous and partially amorphous pharmaceutical solids, it was found that there is a rapid initial reduction in the glass transition temperature from the dry state as water is absorbed, followed by a gradual leveling off of the response at higher water contents. This plasticization effect could generally be described using a simplified form of the Gordon–Taylor/ Kelley–Bueche relationships derived from polymer free volume theory. Most of the systems considered showed a nearly ideal volume additivity and negligible tendency to interact. This is consistent with the hypothesis that such mixtures behave as concentrated polymer solutions and indicates that water acts as a plasticizer in a way similar to that of other small molecules and not through any specific or stoichiometric interaction process(es).
689 citations
TL;DR: In this paper, the authors report the direct observation of crystallization within the shear bands of aluminium-based amorphous alloys induced by bending, and suggest that mechanical deformation might therefore be used to form high-strength ammorphous-nanocrystalline composites.
Abstract: AMORPHOUS alloys formed by rapid solidification of a metallic melt are of considerable technological interest as high-strength materials1–8. As they are not in thermodynamic equilibrium, these materials tend to crystallize on heating9,10. A high degree of crystallization leads to embrittlement, but if it can be arrested when the crystallites are of only nanometre dimensions, the resulting amorphous–nanocrystalline composite actually has greater strength than the original amorphous material11. There is consequently much interest in understanding the mechanisms of crystallization. Previous studies have suggested that mechanical deformation can induce crystallization12–16. Here we report the direct observation of crystallization within the shear bands of aluminium-based amorphous alloys induced by bending. The crystals are face-centred cubic aluminium, 7–10 nm in diameter, and seem to form as a consequence of local atomic rearrangements in regions of high plastic strain. We suggest that mechanical deformation might therefore be used to form high-strength amorphous–nanocrystalline composites.
487 citations
TL;DR: The structural transition from Iah to Ial is responsible for the diffusion and recombination of radicals in ultraviolet-photolyzed interstellar ices at low temperatures and can be used to explain hitherto anomalous properties of astrophysical ices.
Abstract: Selected area electron diffraction is used to monitor structural changes of vapor-deposited water ice in vacuum during warm-up from 15 to 188 K. A progression of three amorphous forms of water ice is found with well-defined transitions. The formation of a high-density amorphous form (Iah) at 15 K is confirmed, and the transition to the more familiar low-density form (Ial) occurs gradually over the range 38 to 68 K. At 131 K, the ice transforms into a third amorphous form (Iar), which precedes the crystallization of cubic ice (Ic) and coexists metastably with Ic from 148 K until at least 188 K. These structural transformations of amorphous water ice can be used to explain hitherto anomalous properties of astrophysical ices. The structural transition from Iah to Ial is responsible for the diffusion and recombination of radicals in ultraviolet-photolyzed interstellar ices at low temperatures. The occurrence and persistence of Iar explains anomalous gas retention and gas release from water-rich ices at temperatures above 150 K.
447 citations
TL;DR: It was shown that in both samples significant crystallization to the most stable polymorphic form occurred over several days when stored below Tg, and in some cases this process was preceded by the relaxation of one amorphous form to the other.
433 citations
TL;DR: In this article, the influence of the process parameters on the optical properties of TiO2 films, such as index of refraction, scattering of light, and absorption, is discussed.
388 citations
TL;DR: The microstructural features of the Si-SiO2 system and the chemical physics of its defects are reviewed and examined in this paper, where the role of atomic and molecular sized entities is emphasized, and the latter are limited to those containing only Si, O, H or combinations thereof.
Abstract: The microstructural features of the Si-SiO2 system and the chemical physics of its defects are reviewed and examined. Topics are grouped by scientific commonality, rather than by the usual technological manifestations. The role of atomic and molecular sized entities is emphasized, and the latter are limited to those containing only Si, O, H, or combinations thereof. Most of the reported researches involve x-ray or electron diffraction, Auger or photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, or capacitance-voltage or deep-level transient spectroscopy. Several forms of crystalline and amorphous vitreous silica are considered as a basis for discussion of thin film thermal silica on silicon wafers. Local lattice symmetry, stoichiometry, bond lengths and angles, vacancies and voids, dangling orbital centres, and fixed and migratory hydrogen species are treated extensively. Elements of relevant theory are summarized. Overall, it is hoped to provide a solid data base for future development of general models for essential electronic phenomena in the Si-SiO2 system.
365 citations
TL;DR: A comprehensive understanding of radiation effects in zircon, ZrSiO4, over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural ZIRcon, Pu-doped Zircon and ion-beam irradiated Zrcon as discussed by the authors.
Abstract: A comprehensive understanding of radiation effects in zircon, ZrSiO4, over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural zircon, Pu-doped zircon, and ion-beam irradiated zircon. Radiation damage in zircon results in the simultaneous accumulation of both point defects and amorphous regions. The amorphization process is consistent with models based on the multiple overlap of particle tracks, suggesting that amorphization occurs as a result of a critical defect concentration. The amorphization dose increases with temperature in two stages (below 300 K and above 473 K) and is nearly independent of the damage source (α-decay events or heavy-ion beams) at 300 K. Recrystallization of completely amorphous zircon occurs above 1300 K and is a two-step process that involves the initial formation of pseudo-cubic ZrO2.
361 citations
Book•
01 Jan 1994
TL;DR: Soft magnetic alloys amorphous ferromagnetic alloys and ferrofluids ferrimagnetic materials permanent magnetic materials as mentioned in this paper are the most commonly used materials for soft magnetic materials.
Abstract: Soft magnetic alloys amorphous ferromagnetic alloys and ferrofluids ferrimagnetic materials permanent magnetic materials.
326 citations
TL;DR: In this article, a comprehensive assessment of such disorder has been carried out on predetermined mixtures of crystalline and amorphous samples, as well as on crystalline samples mechanically milled for various periods of time.
320 citations
TL;DR: In this article, the effects of pyrolysis temperature, post-pyrolyisation thermal treatments, and excess lead addition on the growth and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated.
Abstract: The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.
01 Jun 1994-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the effect of the irradiation temperature, the crystallographic orientation, the initial electrical resistivity and the oxygen stoichiometry on the damage morphology of oxide materials has been investigated.
Abstract: Damage induced in several oxide materials by swift heavy ions is presented. The discussion is based on results obtained on the following materials [Y3Fe5O12, AFe12O19 (A = Ba, Sr), BFe2O4 (B = Ni, Mg, Zn), ZrSi2O4, SiO2 quartz, Al2O3, high Tc superconductors (YBa2Cu3O7 − δ and Bi2Sr2CaCu2O8)] which have been irradiated by ions with atomic number ranging between 6 (12C) and 92 (238U) and energies between 0.05 GeV and 6 GeV. The damage cross section A has been deduced using several physical characterisations like Mossbauer spectrometry, saturation magnetisation measurements, channeling Rutherford backscattering, infrared absorption and electrical resistance measurements. Depending on the material and on the value of the electronic stopping power (dE/dx) the damage cross section varies between 10−17 and 10−12 cm2. Using medium and high resolution transmission electron microscopy and chemical etching of the latent track, an electronic stopping power evolution of the damage morphology has been observed leading to the definition of an effective radius Re of the latent track which can be linked to the damage (amorphous) cross section A by the relation Re = √A/π. Moreover there is a direct correlation between these values and the damage morphology: for Re > 3 nm the latent tracks are long and cylindrical, conversely for Re < 3 nm the damage is inhomogeneous along the latent track. The effect of the irradiation temperature, of the crystallographic orientation, of the initial electrical resistivity and of the oxygen stoichiometry will be presented. In opposition to what has been usually believed it will be shown that alumina (Al2O3) is indeed sensitive to the electronic stopping power. Moreover the velocity of the incident ion has a direct influence on the damage production: the lower the velocity, the higher the damage.
TL;DR: In this article, a theoretical analysis of the super lateral growth (SLG) phenomenon observed in the pulsed laser-induced solidification of amorphous thin Si films on SiO2 is presented.
Abstract: This letter reports on the experimental findings, and provides a theoretical description of the super lateral growth (SLG) phenomenon observed in the pulsed laser‐induced solidification of amorphous thin Si films on SiO2. Experimentally, we report and elaborate on the isolated single‐crystal disk structure that is observed at the upper threshold of the SLG regime; the structure is revealed as an important microstructural feature for understanding the phenomenon. A theoretical discussion of the SLG phenomenon is provided in terms of the key factors that are suggested by our model—the interface response function of the solid, the nucleation kinetics of the solid, and a highly transient lateral‐thermal profile near the solid‐melt interface. Our model and analysis point out the important inadequacies associated with the vertical solidification rate/temperature gradient model, which is currently being utilized to explain the excimer laser crystallization of thin Si films on SiO2.
Book•
31 May 1994
TL;DR: In this article, the design and optimization of Solid-State Batteries is discussed. But the authors focus on the application of solid-state Ionic materials in the field of energy storage.
Abstract: Preface. 1. Design and Optimization of Solid-State Batteries. 2. Materials for Electrolyte: Crystalline Compounds. 3. Materials for Electrolyte: Fast-Ion-Conducting Glasses. 4. Materials for Electrolyte: Thin Films. 5. Polymer Electrolytes. 6. Materials for Electrodes: Crystalline Compounds. 7. Materials for Electrodes: Amorphous and Thin-Films. 8. Applications of Solid-State Ionic Materials. Subject Index.
TL;DR: In this paper, a microcalorimeter for measuring heat capacity of thin films in the range 1.5-800 K is described, using amorphous silicon nitride membrane as the sample substrate, a Pt thin film resistor for temperatures greater than 40 K, and either a thin film ammorphous Nb-Si or a boron-doped polycrystalline silicon thermometer for lower temperatures.
Abstract: A new microcalorimeter for measuring heat capacity of thin films in the range 1.5–800 K is described. Semiconductor processing techniques are used to create a device with an amorphous silicon nitride membrane as the sample substrate, a Pt thin film resistor for temperatures greater than 40 K, and either a thin film amorphous Nb–Si or a novel boron‐doped polycrystalline silicon thermometer for lower temperatures. The addenda of the device, including substrate, is 4×10−6 J/K at room temperature and 2×10−9 J/K at 4.3 K, approximately two orders of magnitude less than any existing calorimeter used for measuring thin films. The device is capable of measuring the heat capacity of thin film samples as small as a few micrograms.
TL;DR: The density of amorphous Si has been measured Multiple Si implants, at energies up to 80 MeV, were made through a contact mask to produce alternating ammorphous/crystalline Si stripes with amomorphous thicknesses up to ∼50 μm as mentioned in this paper.
Abstract: The density of amorphous Si has been measured Multiple Si implants, at energies up to 80 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼50 μm For layers up to 34 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed Height differences between the amorphous and crystalline regions were measured for as‐implanted, thermally relaxed, and partially recrystallized samples using a surface profilometer Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 18±01% less dense than crystalline Si (490×1022 atom/cm3 at 300 K) Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (<01% density difference)
TL;DR: Amorphous mixed valent manganese oxides, a new class of photocatalytic materials, were the most active catalysts studied at room temperature under visible light illumination.
Abstract: Amorphous manganese oxides, potassium oxalatomanganate complexes, and crystalline tunnel structure manganese oxides (hollandite, todorokite, pyrolusite) have been prepared and used as photocatalysts for the oxidation of 2-propanol to acetone. Amorphous mixed valent manganese oxides, a new class of photocatalytic materials, were the most active catalysts studied at room temperature under visible light illumination. High activities correlate with higher oxidation state manganese (Mn[sup 3+], Mn[sup 4+]) oxides, large surface oxygen concentrations, and the presence of hydroxyl groups on surfaces of these catalysts. BET (surface area analysis), XRD (X-ray diffraction), EDX (energy dispersive X-ray analysis), SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy), and FTIR (Fourier transform infrared) data support these correlations. A mechanism for these photooxidation flow reactions involving manganese oxide catalysts has been proposed. Photochemical and characterization data suggest that the design of active photocatalysts may rely on preparation of mixed valent amorphous oxides that release oxygen more readily than crystalline materials. Conversions as high as 8% and 100% selectivity to acetone have been realized with such systems. 45 refs., 9 figs., 1 tab.
IBM1
TL;DR: In this article, the authors studied computer-generated models of amorphous SiC and showed that there are two principal factors controlling the degree of chemical order in amorphized covalent alloys.
Abstract: While ordering in alloy crystals is well understood, short-range ordering in amorphous alloys remains controversial. Here, by studying computer-generated models of amorphous SiC, we show that there are two principal factors controlling the degree of chemical order in amorphous covalent alloys. One, the chemical preference for mixed bonds, is much the same in crystalline and amorphous materials. However, the other factor, the atomic size difference, is far less effective at driving ordering in amorphous material than in the crystal. As a result, the amorphous phase may show either strong ordering (as in GaAs), or weaker ordering (as in SiC), depending upon the relative importance of these two factors.
TL;DR: Isothermal microcalorimetry has been used to follow recrystallisation of amorphous regions of powder surfaces as mentioned in this paper, which can be used to characterise the properties of the material and to show how and when crystallisation will occur, and to aid predictions of the product of the crystallisation process.
TL;DR: In this article, the electrochemical properties of amorphous Mg5oNi5o-;t-),MxN), (M, N = Co, Al and Si) hydrogen storage alloys prepared by mechanical alloying (MA) were investigated.
Abstract: The electrochemical behaviours of some amorphous Mg5oNi5o-;t-),MxN), (M, N = Co, Al and Si) hydrogen storage alloys prepared by mechanical alloying (MA) were investigated. It is found that the MA amorphous alloys are easier to activate electrochemically than crystalline alloys. All MA amorphous alloys reach their respective maximum capacities at the first charge/discharge cycle. At a current density of 20 mA/g the MA Mg5oNi5o has a maximum discharging capacity around 500 mAh/g, which is ten times higher than that of the crystalline alloy. The partial substitution of Co, Si and Al for Ni in Mg5oNi50 alloy decreases its discharging capacity each to a different extent. However, the durability of the amorphous Mg5oNi5o-:t-,,M.tN), alloys is rather poor, and their capacity degradation rates amount to 10
TL;DR: In this article, ZrO2 thin films were grown by the atomic layer epitaxy (ALE) technique using ZrCl4 and water as reactants, at 500°C amorphous films with good thickness uniformities were deposited onto soda lime glass substrates.
TL;DR: The structural development of HfO2 thin films grown from HfCl4 and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy.
TL;DR: In this article, a transition metal chalcogenide was synthesized at 140°C and a catalyst compound was obtained when reacting the corresponding transition metal carbonyl compounds and elemental selenium in xylene solvent.
TL;DR: In this paper, a picosecond pump-probe technique is used to measure the room-temperature thermal conductivity and longitudinal sound velocity of amorphous diamond (a•D) and diamondlike carbon (DLC) thin films.
Abstract: A picosecond pump‐probe technique is used to measure the room‐temperature thermal conductivity κ and longitudinal sound velocity cl of amorphous diamond (a‐D) and diamondlike carbon (DLC) thin films. Both κ and cl were found to decrease with film hydrogen content. Depending on the film deposition technique, κ is in the range 5–10×10−2 W cm−1 K−1 for a‐D, and 3–10×10−3 W cm−1 K−1 for DLC. Values of cl were found to be in the range 14–18×105 cm s−1 for a‐D, and 6–9×105 cm s−1 for DLC.
TL;DR: In this paper, a study of the structure V2O5, GeO2, and Bi2O3 glasses by IR spectroscopy was performed to obtain information about the competitive role of each of the three components in the formation of the glass network.
Abstract: This paper reports a study of the structure V2O5GeO2Bi2O3 glasses by IR spectroscopy to obtain information about the competitive role of each of V2O5, GeO2 and Bi2O3 in the formation of the glass network. The amorphous samples were obtained by the twin-roller technique. Bi2O3 leads to transformation of the layered and chain vanadate structure and depolymerization of three-dimensional germanate lattice. The bismuthate complexes can be viewed as deformed BiO6 groups. It is established that with a decrease in the V2O5 content VO4 groups are formed. GeO4 structural unit with different degrees of polymerization arer present in the network in the entire concentration range.
TL;DR: In this article, a diamond-like form of hydrogenated amorphous carbon (a•C:H) with density 2.9 g cm−3, sp3 fraction of 0.75, and hardness of 61 GPa has been deposited from acetylene in a novel plasma beam source.
Abstract: A highly tetrahedral, diamond‐like form of hydrogenated amorphous carbon (a‐C:H) with density of 2.9 g cm−3, sp3 fraction of 0.75, and hardness of 61 GPa, the highest values so far attained from a hydrocarbon source gas, has been deposited from acetylene in a novel plasma beam source. The ion energy for highest sp3 fraction is measured to be about 100 eV per C atom, similar to that for a‐C, indicating that the subplantation deposition model of a‐C also describes a‐C:H.
TL;DR: In this article, Li3.3PO3.8N0.22 and LiMn 2O4 cells with open circuit voltages at full charge of about 2.5 V, 3.7 V, and 4.2 V, respectively, were fabricated and characterized.
01 Jan 1994
TL;DR: In this article, the mechanisms operative in diffusion and solubility of light gases in amorphous, dense polymer systems are discussed and two types of methods used, molecular dynamics simulation and an approach based on transition state theory, are described.
Abstract: The mechanisms operative in diffusion and solubility of light gases in amorphous, dense polymer systems are discussed. Two types of methods used, Molecular Dynamics simulation and an approach based on Transition State Theory, are described. The methods prove to be complementary and to yield identical results in the areas where both can be independently applied.
TL;DR: In this paper, the authors measured the transmission of infrared light through thin films of varying thickness over the frequency range from about 7000 to 500/cm at temperatures below 200 K. They used an iterative Kramers-Kronig technique to determine the optical constants which gave the best match between measured transmission spectra and those calculated for a variety of films of different thickness.
Abstract: We determined the infrared optical constants of nitric acid trihydrate, nitric acid dihydrate, nitric acid monohydrate, and solid amorphous nitric acid solutions which crystallize to form these hydrates. We have also found the infrared optical constants of H2O ice. We measured the transmission of infrared light throught thin films of varying thickness over the frequency range from about 7000 to 500/cm at temperatures below 200 K. We developed a theory for the transmission of light through a substrate that has thin films on both sides. We used an iterative Kramers-Kronig technique to determine the optical constants which gave the best match between measured transmission spectra and those calculated for a variety of films of different thickness. These optical constants should be useful for calculations of the infrared spectrum of polar stratospheric clouds.