Showing papers on "Amorphous solid published in 1980"

Application of A-C Techniques to the Study of Lithium Diffusion in Tungsten Trioxide Thin Films

Abstract: The small signal a-c impedance of the cell Li]LiAsF6 (0.75M) in propylene carbonatel Lip V~O3 thin film on tin oxide covered glass substrate has been measured at room temperature as a function of frequency from 5  10 -4 Hz to 5 X l0 s Hz at various open-circuit voltages. The diffusion equations have been solved for the appropriate finite boundary conditions, and analysis of the impedance data by the complex plane method yields values for the chemical diffusion coefficient, the component diffusion coefficient, the partial ionic conductivity of lithium, and the thermodynamic enhancement factor for LiyWO3 as a function of y. The films of WO3 were prepared by vacuum evaporation and were largely amorphous to x-rays. The chemical diffusion coefficient has a value of 2.4  10 -12 cm2/sec at y _-- 0.1, increasing to 2.8 X 10 -11 cm2/sec at y ---- 0.26. At short times (t ~ 0.5 sec) the interracial charge transfer reaction is important, but at longer times the rate of lithium injection is determined by the diffusion kinetics.

The Structure of Non-Crystalline Materials: Liquids and Amorphous Solids

Abstract: There is an increasing need to understand thectructure and properties of non-crystalline materials, liquids and amorphous solids, because of the important role they play in metallurgical processes such as slag-metal reactions and in developing new engineering materials such as metallic glasses. The characterization for the structure of disordered systems is of major importance in pure and applied physics, chemistry, and engineering, and the research into non-crystalline materials has therefore been expanding rapidly in the past ten years. This book represents an extended introductory treatise on the structure of non-crystalline materials, liquids, and amorphous solids. It covers the current experimental information about the structure of many kinds of non-crystalline materials: liquid metals and alloys, metallic glasses, molten and glassy silicates, amorphous and liquid semiconductors, molten salts, water and solutions. It also gives an outline of the liquid state theory and the methods of structural analysis by diffraction experiments. The author also discusses how the observed structural data can be applied to relate the macroscopic properties and this should help the reader to find fuller understanding of various interesting properties of non-crystalline materials. Some selected examples are included which cover the application of structural data to estimate macroscopic properties, such as electrical resistivity, self-diffusion coefficient, vapour pressure, and activity. This book gives a critical, up-to-date evaluation covering current problems and future directions in the new field of the structure and its application to non-crystalline materials. In addition, the available numerical data on the structure of liquid metals (50 elements) at various temperatures and of binary alloys (25 systems) are compiled in the appendices. The author believes that these numerical data and the references (more than 400) provide an adequate help and guide for professional persons. This book will be of use primarily to nonspecialists such as graduate students in materials science and physics. However, it will also be very useful to those in other fields, such as chemistry, ceramics, metallusgy, and applied science and engineering, who wish to become acquainted with the subject.

Structural defects in amorphous solids A computer simulation study

Abstract: A definition of structural defects in amorphous solids in terms of the distribution of the internal stresses on the atomic level and of the symmetry of the environment of individual atoms is introduced. This definition does not require an ideal reference structure. The concept of the internal stresses on the atomic scale has been previously applied to describe the core structure of crystalline dislocations. In this paper it has been applied to the model amorphous structure generated by a computer simulation. It was found that there is a significant variation in the magnitude and direction of internal stresses, and that there are regions of 10 to 20 atoms over which the stresses remain either high or low. A method of calculating the symmetry coefficients at atomic sites has been proposed, and applied to the same system. It has been shown that there are significant correlations between the internal stresses and the local symmetry. The low-stress, high-symmetry regions resemble microcrystalline clus...

Measurement of saturation magnetostriction of a thin amorphous ribbon by means of small-angle magnetization rotation

Abstract: A new method was developed to measure the saturation magnetostriction of a thin amorphous ribbon. It is based on the use of small-angle magnetization rotation to measure the change in anisotropy field caused by the tensile stress. Measurements have been performed on Metglas 2826, 2605, and Co-Si-B amorphous ribbons. The maximum experimental error of the measurement was estimated to be about ±5 percent. It is shown that the sensitivity of the method depends on the shape anisotropy field. The estimated sensitivity was about 2 × 10-7for Metglas 2826 ribbon with 1.8 mm × 40 μm × 12 cm in dimensions.

Spectroscopic Analysis of the Interface Between Si and Its Thermally Grown Oxide

Abstract: Spectroscopic ellipsometric data from 1.5–5.8 eV has been analyzed to determine the in situ optical response of the interface between Si and its thermally grown oxide. Results for , , and sample orientations show an interface of width consisting of atomically mixed Si and O of average stoichiometry . The optical data are not consistent with either microroughness at the interface or an abrupt transition between crystalline Si and or a significant accumulation of amorphous Si at the interface, but rather support a gradual transition region. The thickness and the average λ5461 refractive index of this region are in agreement with the fixed‐wavelength results, and , of Taft and Cordes. The oxide on the surface is shown to have a density about 1.2% less than that of corresponding oxides on and surfaces.

Method of crystallizing amorphous material with a moving energy beam

Abstract: An improved method for crystallizing amorphous material with a moving beam of energy is disclosed. In this method, the energy beam is scanned in a manner to provide controlled, continuous motion of the crystallization front.

Preferential Reduction of Amorphous to Crystalline Iron Oxides by Bacterial Activity

Abstract: Reduction of pedogenic iron oxides by the activity of Clostridium butyricum was studied in model experiments under controlled conditions of pH, particle size (63 to 125 μm), glucose (2 percent), and anaerobic conditions. Three horizons—from a gley, pseudogley, and red clay soil, respectively—with different Feo:Fed ratios were selected as test material. Except for Fe(II) formation, pH and Eh were measured at regular intervals. In all soils the total amount of free iron oxides (Fed), as well as the crystalline Fe (Fed - Feo), decreased while Fe(II) increased. The amount of amorphous Fe (Feo) remained relatively constant in those soils low in Feo:Fed (0.1 to 0.19), but diminished in the sample with a relatively high amount of amorphous Fe (Feo:Fed = 0.78). This suggests that crystalline rather than amorphous Fe forms are dissolved preferentially by acting as terminal electron acceptors. Nevertheless, the reduction of crystalline 59Fe-labeled oxides (hematite and goethite) mixed with Fe-amorphous gley soil material (Feo:Fed = 0.78) clearly showed that oxalate-soluble Fe was attacked in preference to 59Fe-labeled crystalline Fe. The processes of Fe(III) reduction in a microsite are discussed in relation to the mechanism of Fe(II) formation in flooded soils.

Electrical and Structural Properties of Phosphorous-Doped Glow-Discharge Si:F:H and Si:H Films

Abstract: Doping of Si:F:H and Si:H with P has been performed by a glow-discharge technique using PH3/SiF4+H2, PF5/SiF4+H2, PH3/SiH4+H2 and PF5/SiH4+H2 gaseous mixtures, and high conductive films over 100 ?-1 cm-1 have been obtained. It has also been made clear from X-ray diffraction and Raman-scattering measurements that all the P-doped Si:F:H films (P/Si>5?10-4) as well as high conductive Si:H films deposited under high RF power condition are polycrystalline, while Si:H films prepared under low power remain amorphous and their conductivity is less than 10-2 ?-1 cm-1. It is likely that film conductivity amounting to 100 ?-1 cm-1 should be ascribed to its polycrystalline structure.

Structure and Properties of LPCVD Silicon Films

Abstract: Silicon films deposited by low pressure chemical‐vapor deposition over the temperature range from 525° to 725°C were investigated. It was found that polycrystalline films are formed above 600°C and are more stable than the amorphous films deposited at lower temperatures. Their crystal structure is a strong function of the deposition temperature and a weaker function of the deposition rate. Either the {110} or the {100} texture may dominate the structure, depending primarily on the deposition temperature. The electrical resistance obtained on doping the LPCVD films that are polycrystalline as deposited is maximum for films deposited at the lower temperatures (near 600°C), although this dependence on deposition temperature decreases after annealing at higher temperatures. Dopant atoms reversibly segregate to the grain boundaries during lower temperature heat‐treatments subsequent to doping and are dispersed at higher temperatures, with corresponding changes in resistivity. The oxidation rate is only a weak function of the deposition temperature, although the initially amorphous films may oxidize somewhat more rapidly. The index of refraction of amorphous films is significantly higher than that of polycrystalline films.

Method for optimizing photoresponsive amorphous alloys and devices

Abstract: The production of improved photoresponsive amorphous alloys and devices, such as photovoltaic, photoreceptive devices and the like; having improved wavelength threshold characteristics is made possible by adding one or more band gap adjusting elements to the alloys and devices. The adjusting element or elements are added at least to the active photoresponsive regions of amorphous devices containing silicon and fluorine, and preferably hydrogen. One adjusting element is germanium which narrows the band gap from that of the materials without the adjusting element incorporated therein. Other adjusting elements can be used such as tin. The silicon and adjusting elements are concurrently combined and deposited as amorphous alloys by vapor deposition, sputtering or glow discharge decomposition. The addition of fluorine bonding and electronegativity to the alloy acts as a compensating or altering element to reduce the density of states in the energy gap thereof. The fluorine bond strength allows the adjusting element(s) to be added to the alloy to adjust the band gap without reducing the electronic qualities of the alloy. Hydrogen also acts as a compensating or altering element to compliment fluorine when utilized therewith. The compensating or altering element(s) can be added during deposition of the alloy or following deposition. The addition of the adjusting element(s) to the alloys adjusts the band gap to a selected optimum wavelength threshold for a particular device to increase the photoabsorption efficiency to enhance the device photoresponsive without adding states in the gap which decrease the efficiency of the devices. The adjusting element(s) can be added in varying amounts, in discrete layers or in substantially constant amounts in the alloys and devices.

An isothermal–isobaric computer simulation of the supercooled‐liquid/glass transition region: Is the short‐range order in the amorphous solid fcc?

Abstract: It is demonstrated that one can easily distinguish between a supercooled liquid that becomes a glass and a supercooled liquid that nucleates to a defect crystal during a quench using the isothermal–isobaric Monte Carlo method.(AIP)

Dissolution and Analysis of Amorphous Silica in Marine Sediments

Abstract: The analytical estimation of amorphous silica in selected Atlantic and Antarctic Ocean sediments, the U.S.G.S. standard marine mud (MAG-1), A.A.P.G. clays, and samples from cultures of a marine diatom, Hemidiscus, has been examined. Quantitative recovery of sedimentary amorphous silica was achieved by reacting 2 M Na2CO3 with a sample for 4 hours at 90°-100° C; where necessary, aluminum analysis is used to correct for the extraction of non-amorphous silica. Oceanic sediments having an amorphous SiO2/clay ratio of 1.0 or more can be analyzed by a single extraction with 2 M Na2CO3, without correction for non-amorphous additions. Marine sediments having an amorphous SiO2/clay ratio of from 1.0 to 0.25 can be corrected for inputs of clay-derived silica using an aluminum determination and an empirical correction factor. Sediments with amorphous SiO2/clay ratios of less than 0.25, samples containing non-silica-bearing aluminous materials such as gibbsite, or materials having low absolute levels of amorphous silica require successive leaches to accurately correct for silica inputs from non-amorphous sources. Our values for amorphous silica-rich circum-Antarctic sediments are equal to or greater than literature values, whereas our values for a set of amorphous silica-poor sediments from a transect of the North Atlantic at 11°N, after appropriate correction for silica released from clays, are significantly lower than previous estimates from the same region.

Interference-Enhanced Raman Scattering of Very Thin Titanium and Titanium Oxide Films

Abstract: The Raman spectra of very thin evaporated films (\ensuremath{\sim}6 nm thick) of metallic titanium and oxidized titanium are obtained with a new technique called interference-enhanced Raman scattering. The results indicate that titanium films exhibit a crystalline hcp structure while the titanium oxide has an amorphous structure with local atomic bonding configurations similar to those in crystalline ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$.

Phase Transitions in Amorphous Si Produced by Rapid Heating

Abstract: Amorphous Si layers have been melted by pulsed electron irradiation. Implanted As has been used as a marker for determining melt duration. Systematic differences between As diffusion in initially amorphous or crystalline Si are interpreted in terms of different enthalpies of melting between amorphous (1220 J/g) and crystalline (1790 J/g) Si. The implanted amorphous layers melt and crystallize at significantly lower electron energies than those required to melt and recrystallize crystalline Si, indicating that amorphous Si melts at 1170 K compared to 1685 K for crystalline Si.

Stability and Several Physical Properties of Amorphous and Crystalline Forms of Indomethacin

Abstract: An X-ray diffraction method for determination of the degree of crystallinity of indomethacin was established, and the transition rate of indomethacin from amorphous to crystalline form was investigated. The transition of the amorphous form to crystalline form at 20°, 30°and 40°followed first-order kinetics and the Arrhenius plot showed good linearity. The amorphous form was shown to change to form I at 100% relative humidity (RH), to form I or II at 89% RH and to form I at 79% and 69% RH at 30°. The transition rate of the amorphous form to form II at 100% RH was larger than that at 89% RH. A good linear relation was observed between the maximum amount of water absorbed (log scale) and the degree of crystallinity at 100% or 89% RH at 30°. The dissolution rate of the amorphous form was higher than those of forms I and II. The amorphous form showed better tablet-forming properties than the crystalline form.

Hydrides of metallic glass alloys

Abstract: The hydrogen absorption properties of several metallic glass alloys of the general formulas Ti1−xCux and Zr1−xCux (x = 0.3–0.7) were investigated and were compared with the absorption properties of the corresponding crystalline intermetallic compounds. Under similar conditions of temperature and pressure the metallic glass alloys had larger absorption capacities than their crystalline counterparts. “Amorphous” TiCu, for example, absorbed 35% more hydrogen than crystalline TiCu (TiCuH1.35 compared with TiCuH). These results indicate the relative importance of electronic structure and crystal structure in hydrogen absorption; it appears that the maximum hydrogen absorption capacity is determined by the electronic structure but that the crystal structure, i.e. the type and size of interstitial sites in the lattice, may not always permit maximum absorption to take place readily.

Kinetic theory of crystallization of amorphous materials

Abstract: Careful analysis of the Avrami equation [ x = 1 −exp(− At n )] shows that an activation energy for crystallization ( E c ) for amorphous materials can be defined over a selected range of temperatures. This activation energy can be determined experimentally using non-isothermal differential scanning calorimetry (DSC) by determining the crystallization temperature ( T c ) as a function of heating rate (φ). A plot of (ln( φ / T c ) has a slope equal to E c / n . The activation energy for the crystallization of amorphous arsenic obtained by this non-isothermal method is found to be in fair agreement with that obtained from an isothermal DSC experiment.

Photovoltaic study on the photo-enhanced diffusion of Ag in amorphous films of Ge2S3

Abstract: The process of the photo-enhanced diffusion of Ag atoms has been studied from photovoltaic responses in evaporated films of Ge2S3 between semitransparent metal electrodes. In addition to the ordinary barrier photovoltaic responses, an electron flow toward the Ag electrode (or a hole flow in the opposite direction) is generated by illumination of light. The current increases with the diffusion of Ag and disappears abruptly when the forefront of the diffusion reaches the opposite electrode. A simple model for the mechanism of the diffusion is presented by assuming the existence of charged defect centers in Ge2S3 films.

High current injection into SiO2 from Si rich SiO2 films and experimental applications

Abstract: Chemically vapor deposited (CVD) Si rich SiO2 layers on thermal or CVD SiO2 layers incorporated into metal‐insulator‐semiconductor (MIS) capacitor structures are shown to give very large injected electron currents at low to moderate negative gate voltage biases. The dependence of this injection mechanism on the Si rich SiO2 composition and thickness, temperature, capacitor area, annealing conditions, gate metal (Al or Au), and underlying SiO2 thickness is described. Photocurrent measurements are discussed and are shown to give similar barrier energies as seen for ’’uniform’’ internal photoemission into SiO2. From the experimental electrical and photoelectrical measurements described here and transmission electron microscopy (TEM) and Auger studies of others, a possible model to explain this phenomenon based on electric field distortion caused by a two phase mixture of amorphous Si and SiO2 is presented. Two experimental applications of these structures are described. In one application, an electrically al...

Diffusion and structural relaxation in compositionally modulated amorphous metal films

Abstract: The interdiffusivity in compositionally modulated (λ≈25 A) amorphous (Pd85Si15)61/(Fe85B15)89 and (Pd80Au7Si13)70/Fe30 films has been measured by monitoring the satellite of the (000) x‐ray scattering peak during isothermal anneals in the range 210–250 °C. Diffusivities as low as 10−22 cm2 s−1 have been measured. It was observed that the diffusivity decreased continuously during the annealing as a result of structural relaxation and settled down to a constant value only after many hours of annealing. The activation energy of the isoconfigurational diffusivity in the Pd‐Au‐Si/Fe films is 167 kJ mol−1. This value and the time scale of the relaxation are similar to those observed in earlier viscosity measurements, indicating a similarity between the structural defects controlling both transport processes.

Semiconducting properties of amorphous V2O5 layers deposited from gels

Abstract: Colloidal solutions of amorphous V2O5 are used for preparing semiconducting layers. Reasons for the high measured conductivity (σ≃0.8–1.0 Ω−1 cm−1) are discussed. The temperature dependence of σ is analyzed in terms of a temperature‐dependent activation‐energy model based upon the assumption of a random distribution of the distances between hopping sites.

AMORPHOUS MoS 3 AND WS 3

Abstract: MoS 3 and WS 3 are examples of a group of transition metal chalcogenides which have only been prepared in amorphous form. Recently these compounds have been found to show interesting properties as cathode materials in ambient temperature alkali metal batteries. In particular, MoS 3 reacts readily and reversibly with lithium, giving a battery system with a high theoretical energy density. In this paper, we report results of structural studies of amorphous MoS 3 and WS 3 using X-ray radial distribution analysis, EXAFS, X-ray photoelectron spectroscopy, magnetic susceptibility measurements and vibrational spectroscopies. The results reveal that these amorphous compounds have a chain-like structure similar to that of the crystalline trichalcogenides of the neighboring IVB and VB elements. However, the combined formations of the metal dimers and polysulfide bonds along the chains are structural features unique to these amorphous compounds. The possible implications of this structure to the observed electrochemical behavior will be discussed.

Extinction coefficients of amorphous carbon grains from 2100 Å to 340 μm

Abstract: Extinction measurements were made for three kinds of amorphous carbon grains in the range 2100 A-340 μm. Absolute values of extinction coefficients from different sources vary by almost constant factors. Wavelength dependences of extinction curves show a λ−1 or less steep fall off, against a λ−2 or steeper fall off of graphite grains. Small humps are found around 6.3, 8, 13.3 and 90 μm, although their origins are not yet clear. The infrared properties of amorphous carbon grains suggest that they could supply a significant amount of far-infrared emission noted in recent astronomical observations.