Showing papers on "Amorphous solid published in 1993"

Foundations of Materials Science and Engineering

Abstract: 1 Introduction to Materials Science and Engineering 2 Atomic Structure and Bonding 3 Crystal and Amorphous Structures in Materials 4 Solidification, Crystalline Imperfections 5 Thermally Activated Processes and Diffusion in Solids 6 Mechanical Properties of Metals I 7 Mechanical Properties of Metals II 8 Phase Diagrams 9 Engineering Alloys 10 Polymeric Materials 11 Ceramics 12 Composite Materials 13 Corrosion 14 Electrical Properties of Materials 15 Optical Properties and Superconductive Materials 16 Magnetic Properties 17 Biological and Biomaterials

Phase transformation mechanisms involved in excimer laser crystallization of amorphous silicon films

Abstract: We have investigated the phase transformation mechanisms and the resulting microstructures of excimer laser‐induced crystallization of amorphous Si films on SiO2. It is shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density. It is found that at the transition between the two regimes, exceedingly large grain‐sized polycrystalline films can be obtained. We call this the super lateral growth phenomenon, and propose a model based on liquid‐phase regrowth from the residual solid seeds when near‐complete melting of the Si film occurs.

Bias‐stress‐induced stretched‐exponential time dependence of charge injection and trapping in amorphous thin‐film transistors

Abstract: The threshold voltage instabilities in nitride/oxide dual gate dielectric hydrogenated amorphous silicon (a‐Si:H) thin‐film transistors are investigated as a function of stress time, stress temperature, and stress bias. The obtained results are explained with a multiple trapping model rather than weak bond breaking model. In our model, the injected carriers from the a‐Si:H channel first thermalize in a broad distribution of localized band‐tail states located at the a‐Si:H/aSiNx:H interface and in the a‐SiNx:H transitional layer close to the interface, then move to deeper energies in amorphous silicon nitride at longer stress times, larger stress electric fields, or higher stress temperatures. The obtained bias‐stress‐temperature induced threshold voltage shifts are accurately modeled with a stretched‐exponential stress time dependence where the stretched‐exponent β cannot be related to the β=TST/T0 but rather to β≂TST/T0*−β0 for TST≤80 °C; for TST≥80 °C, the β is stress temperature independent. We have al...

Silicide formation and silicide‐mediated crystallization of nickel‐implanted amorphous silicon thin films

Abstract: The nucleation and growth of isolated nickel disilicide precipitates in Ni‐implanted amorphous Si thin films and the subsequent low‐temperature silicide‐mediated crystallization of Si was studied using in situ transmission electron microscopy. Analysis of the spatial distribution of the NiSi2 precipitates strongly suggested the occurrence of site saturation during nucleation. NiSi2 precipitates were observed in situ to migrate through the amorphous Si thin films leaving a trail of crystalline Si at temperatures as low as ∼484 °C. Initially, a thin region of epitaxial Si formed on {111} faces of the octahedral NiSi2 precipitates with a coherent interface which was shown by high‐resolution electron microscopy to be Type A. Migration of the NiSi2 precipitates led to the growth of needles of Si which were parallel to 〈111〉 directions. The growth rate of the crystalline Si was limited by diffusion through the NiSi2 precipitates, and an effective diffusivity was determined at 507 and 660 °C. A mechanism for the enhanced growth rate of crystalline Si is proposed.

Preparation of 16 mm Diameter Rod of Amorphous Zr65Al7.5Ni10Cu17.5 Alloy

Abstract: Bulky amorphous alloys in a cylindrical shape with diameters up to 16 mm were found to form by water quenching a Zr 65 Al 75 Ni 10 Cu 175 melt in a quartz tube The amorphous phase of this alloy has the widest temperature interval of supercooled liquid region before crystallization The glass transition temperature, crystallization temperature and Vickers hardness for the bulky amorphous alloy with a diameter of 16 mm are 625 K, 750 K and 465, respectively, being nearly the same as those for the corresponding melt-spun ribbon with a thickness of 30 μm The extremely large glass-forming ability is presumably due to a combination of significantly different atomic size ratios among the constituent elements and the necessity of redistribution of Al for the progress of crystallization

Non-aqueous secondary battery

Abstract: The present invention provides a non-aqueous secondary battery having an improved charge and discharge cycle property and high discharge voltage, high energy density, high capacity and increased stability as well as an excellent high electric current atitude by using a lithium-containing transition metal oxide as a positive electrode material and at least one of the specfified composite oxides as a negative electrode material Accordingly, the feature of the present invention consists in that the negative electrode material mainly consists of at least one member selected from the group consisting of amorphous chalcogen compounds and amorphous oxides containing at least three atoms selected from the group consisting of Group 13, 14, 15 and 2 atoms of Periodic Table

Amorphous Inorganic Materials and Glasses

Abstract: Methods of preparing amorphous solids and glasses thermodynamic description of the glassy state phase transformation processes and glass formation structure and chemical bonding in glasses and amorphous solids eletronic states in noncrystalline solids amorphous and glass-forming substances electrical conductivity and optical properties of glasses and amorphous solids applications of ion-conducting glasses optical glasses for IR transmission information storage based on structural changes of glasses.

Molecular design for nonpolymeric organic dye glasses with thermal stability : relations between thermodynamic parameters and amorphous properties

Abstract: The molecular structures of low-molecular-weight organic compounds and their amorphous properties have been investigated to obtain a design rule for uniform amorphous films with high thermal stability. The glass transition temperature (Te/K), maximum crystal-growth velocity (MCV/m s -1 ), and maximum crystal-growth temperature (T c,max /K) are key parameters for characterizing the amorphous properties of organic materials. Some quantitative relations between these parameters and thermodynamic parameters were examined from both theoretical and experimental viewpoints

Solution effects on the surface reactions of a bioactive glass.

Abstract: The in vitro surface reactions of a 45S5 bioactive glass in three simulated body fluids (SBF) are analyzed using Fourier transform infrared (FTIR) spectroscopy. Five reaction stages are observed. Calcium and phosphate ions in SBF accelerate to a small extent the repolymerization of silica (Stage 3) and formation of an amorphous calcium-phosphate (a-CP) layer (Stage 4) on the glass surface. The a-CaP layer is crystallized to form hydroxy-carbonate apatite (HCAp) (Stage 5) more rapidly in the Ca- and P-containing SBF solutions (in 90 min rather than 120 min). However, Mg ions in SBF slow down formation of the a-CaP layer and greatly retard crystallization of HCAp on the glass surface.

Semiconductors for Solar Cells

Abstract: Physical principles of photovoltaic energy conversion technology of solar cell devices fundamental material parameters structural and electrical properties of lattice defects single crystal and polycrystalline silicon single crystal and epitaxial compound semiconductors thin-film compound semiconductors amorphous thin-film semiconductors.

Structures and properties of electron-beam-evaporated indium tin oxide films as studied by x-ray photoelectron spectroscopy and work-function measurements

Abstract: Indium tin oxide (ITO) films deposited on single‐crystal Si wafers by the electron‐beam‐(EB) evaporation method have been investigated by x‐ray photoelectron spectroscopy (XPS) together with work‐function and resistivity measurements. The XPS studies suggest that all the ITO films consist of crystalline and amorphous phases. The amount of the crystalline phase with respect to the amorphous phase for the ITO films, deposited with the incident angle of the ITO vapor to the Si substrate θi at 0°, is smaller than that for the ITO films deposited at θi=45°. The amount of the crystalline phase hardly depends on the conditions of postdeposition heat treatments, while that of the amorphous phase increases by raising the temperature of the heat treatments. Metal indium present in the films deposited at θi=0° is transformed into amorphous indium oxide by heating at 450 °C in air. Metal tin is also present near the ITO/Si interface for the ITO films deposited at θi=0°. The work function of the ITO films deposited at...

Low temperature crystallization and patterning of amorphous silicon films on electrically insulating substrates

Abstract: A fabrication process polycrystalline silicon thin film transistors commences with the deposition of an ultra-thin nucleating-site forming layer onto the surface of an insulating substrate (e.g., 7059 glass). Next, an amorphous silicon film is deposited thereover and the combined films are annealed at temperatures that do not exceed 600° C. By patterning the deposition of the nucleating site forming material on the glass substrate, the subsequently deposited amorphous film can be selectively crystallized only in areas in contact with the nucleating-site forming material.

Nitrogen doping of highly tetrahedral amorphous carbon

Abstract: Successful control of the conductivity of tetrahedrally bonded amorphous carbon (ta-C) by incorporation of N during film growth is reported. N is introduced into the films during growth by injecting N 2 gas into a plasma stream formed by a carbon cathodic vacuum arc. X-ray-photoemission-spectroscopy studies of films prepared over a range of N 2 partial pressures show that the N concentration varies from 2% to below the detection limit. Spectroscopic studies using electron-energy-loss spectroscopy confirm that the ta-C films with N contents up to 1 at. % retain their predominantly tetrahedral amorphous structure

Melt-stable amorphous lactide polymer film and process for manufacture thereof

Abstract: An amorphous film comprised of a lactide polymer. The lactide polymer comprises a plurality of poly(lactide) polymer chains, residual lactide in concentration of less than about 2 percent and water in concentration of less than about 2000 parts-per-million. A process for manufacturing an amorphous film with the lactide polymer composition is also disclosed.

Statistical analysis of the intergranular film thickness in silicon nitride ceramics

Abstract: Silicon nitride materials typically reveal thin amorphous intergranular films along grain boundaries, with only the exception of special boundaries. It is known that such grain-boundary films strongly affect the high-temperature properties of the bulk material. High-resolution electron microscopy (HREM) was used to study these amorphous films in different Si[sub 3]N[sub 4] ceramics. The observed film thicknesses at grain boundaries in these materials varied between 5 and 15 [angstrom]. It was shown that the grain-boundary film thickness strongly depends on film chemistry. Careful inspections of film-thickness measurements across grain boundaries in a given material suggest that the film widths vary on the order of 1 [angstrom]. Therefore, a quantitative evaluation should allow for the determination of the standard deviation of the film thickness. The amorphous film widths along grain boundaries in four materials were measured over the entire length (up to 1 [mu]m) of the grain boundary between two triple points. Forty to fifty data points were evaluated for each boundary, giving a Gaussian-like distribution of the film thickness around a median value, which corresponded well with the film width measured from single HREM micrographs. The accuracy achieved by the statistical method was better than [plus minus] 1 [angstrom].

Optical functions of chemical vapor deposited thin‐film silicon determined by spectroscopic ellipsometry

Abstract: The optical functions of several forms of thin‐film silicon (amorphous Si, fine‐grain polycrystalline Si, and large‐grain polycrystalline Si) grown on oxidized Si have been determined using 2‐channel spectroscopic polarization modulation ellipsometry from 240 to 840 nm (∼1.5–5.2 eV). It is shown that the standard technique for simulating the optical functions of polycrystalline silicon (an effective medium consisting of crystalline Si, amorphous Si, and voids) does not fit the ellipsometry data.

Does C60 have a liquid phase

Abstract: Above a substance's liquid–vapour critical point (i>Tc), the distinction between the liquid and vapour phases disappears. Below the triple point (T t), meanwhile (at which solid, liquid and vapour coexist), only the solid and vapour are stable. The liquid range, T c/T t, depends on the nature of the intermolecular forces: for argon, T c/Tt = 1.8, whereas for sodium the ratio is 7.5. But might there be molecular substances that have no liquid phase at all? Here we present results which suggest that C60 is such a substance. We map out the phase diagram using computer simulations in which the C60 molecules are represented by spheres interacting via Lennard-Jones potentials summed over all 60 carbon atoms. We find that the sublimation line passes above the metastable liquid-vapour coexistence curve. By drawing an analogy with the aggregation of colloidal particles, we expect that solid C60 formed by nucleation from the vapour phase will be amorphous rather than crystalline.

Mapping sp2 and sp3 states of carbon at sub-nanometre spatial resolution

Abstract: THE potential for diverse applications of diamond1 has been enhanced by the discovery of the chemical vapour deposition process2,3 for film formation. The growth of hetero-epitaxial diamond films on silicon is a particularly attractive goal, but only polycrystalline films have so far been prepared in this way4. Because of the large lattice mismatch, thin intermediate layers (interlayers5) are formed between the diamond and silicon phases, which may contain crystalline SiC (refs 6, 7) or amorphous compounds (SiC, carbon8 and SiO2). An understanding of how diamond nucleates5,9–11, and the role of these interlayers, requires a detailed knowledge of the nature of carbon bonding (sp2 orsp3) at the interface. Here we report the use of transmission electron energy-loss spectroscopy (EELS) to obtain a map of sp2 and sp3 carbon at a spatial resolution of less than a nanometre across the silicon–diamond interface. We find that diamond nucleates on an amorphous carbon layer, with the transition from sp2to sp3 carbon occurring over less than one nanometre.

Diamond-like carbon films from a hydrocarbon helium plasma

Abstract: The present invention relates to an improved method of depositing a diamond-like carbon film onto a substrate by low temperature plasma-enhanced chemical vapor deposition (PECVD) from a hydrocarbon/helium plasma. More specifically, the diamond-like carbon films of the present invention are deposited onto the substrate by employing acetylene which is heavily diluted with helium as the plasma gas. The films formed using the process of the present invention are characterized as being amorphous and having dielectric strengths comparable to those normally observed for diamond films. More importantly, however is that the films produced herein are thermally stable, optically transparent, absorbent in the ultraviolet range and hard thus making them extremely desirable for a wide variety of applications.

Analytical electron microscopy and Raman spectroscopy studies of carbon nitride thin films

Abstract: Deposition of carbon nitride thin films on Si(100) and polycrystalline Zr substrates was performed by dc magnetron sputtering of a graphite target under a pure nitrogen ambient. The resulting carbon nitride films (CNx) are primarily amorphous with a small volume fraction of nanocrystallites. Both energy‐dispersive x‐ray analysis and electron energy loss spectroscopy measurements showed that the amorphous matrix has uniform nitrogen‐to‐carbon ratios ∼0.4–0.8 depending on deposition conditions. Carbon and nitrogen K edge structures obtained from electron energy loss spectroscopy studies suggest that the amorphous carbon nitride matrix is primarily sp2 bonded. Apart from the carbon–nitrogen stretching vibration, Raman spectra of CNx films closely resemble those of diamondlike carbon films. Intensity and peak width changes of Raman features in the 1300–1600 cm−1 range due to inorganic carbon (D and G peak) under different deposition conditions are explained in terms of the extent of structural disorder in the...

Laser Ablation and the Production of Polymer Films

Abstract: The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface.

Low core losses of nanocrystalline Fe-M-B (M=Zr, Hf, or Nb) alloys

Abstract: Magnetic core properties, core loss, permeability, and saturation magnetic induction of bcc‐nanocrystalline Fe–M–B (M=Zr, Hf, and Nb) alloys produced by annealing a melt‐spun amorphous phase were investigated in a ring‐shaped form with the aim of clarifying the application potential as a core material. The bcc alloys exhibit high saturation induction (Bs) from 1.49 to 1.63 T combined with high permeability (μe) from 22 000 to 32 000 at 1 kHz and 0.4 A/m. The bcc Fe–M–B (M=Zr, Hf, or Nb) alloys also show low core losses (W) from 1.4×10−1 to 2.1×10−1 W/kg at 50 Hz and 1.4 T and from 1.70 to 2.50 W/kg at 1 kHz and 1.0 T. The W values attained for the bcc Fe–M–B (M=Zr, Hf, and Nb) alloys are smaller by 60%– 90% at 50 Hz and 1.4 T and 50%–70% at 1 kHz and 1.0 T, as compared with those for an amorphous Fe78Si9B13 alloy in practical use as a transformer core material. The low W values for the bcc‐nanocrystalline alloys are presumably due to the small anomaly factor comparable to a Co‐based amorphous alloy. The c...

Nano‐indentation studies of ultrahigh strength carbon nitride thin films

Abstract: Carbon nitride (CNx) thin films were prepared by dc magnetron sputtering of a graphite target in a nitrogen ambient onto Si(100) substrates held at ambient temperatures. The films are amorphous with a small volume fraction of nanocrystallites. All CNx coatings grown to a thickness of 1.5 μm are adherent and smooth. Nanoindentation studies showed clear dependence of hardness and effective modulus on deposition process parameters (nitrogen pressure, target power, and substrate bias). Most striking is the observation that CNx films can be synthesized with yield strength exceeding 5 GPa.

Study of the effect of Sn doping on the electronic transport properties of thin film indium oxide

Abstract: High quality, low resistivity (2.6×10−4 Ω cm), 0.32‐μm‐thick amorphous and polycrystalline, pure and Sn‐doped, In2O3 films prepared by high density plasma‐assisted electron beam evaporation were used to investigate the effect of Sn doping on the electronic transport properties of this material. Amorphous films with high carrier density in the as‐deposited state showed no effect of Sn doping on resistivity (ρ), Hall mobility (μ), or carrier density (n) over the range 0 to 5.3 wt % Sn. After recrystallization by annealing in air at 180 or 250 °C for 20 min, n, μ, and ρ were seen to be strongly dependent on Sn concentration in the range 0 to 1.5 wt % with a decreasing effect of Sn doping in the range 1.5 to 5.3 wt %. The data presented in this study were analyzed based on charged and neutral impurity scattering models and suggest that increasing Sn concentration leads to the formation of defect complexes which act as scattering centers but which do not contribute carriers to the material.