Showing papers in "Philosophical Magazine Part B in 1989"
TL;DR: In this paper, the microstructure of polycrystalline materials is digitized by dividing the polycrystaline material into small volume elements and storing the spatial location and crystallographic orientation of each element.
Abstract: Computer modelling has been carried out to study normal grain growth in three dimensions. The approach consists of digitizing the microstructure by dividing the polycrystalline material into small volume elements and storing the spatial location and crystallographic orientation of each element. An energy is assigned between each element and its neighbours, such that neighbours having unlike orientations provide weaker bonding than neighbours of like orientations. The annealing treatment during which grain growth occurs is simulated using a Monte Carlo technique in which elements are selected at random and thermally activated transitions to other orientations are attempted. With time, the system evolves so as to reduce the total grain interface area. The microstructures produced are in good correspondence to observations of pure metals and ceramics which have undergone grain growth. Power-law kinetics ([Rbar] = ct n) are observed, with a growth exponent in three dimensions of n = 0·48 ±0·04 in the...
332 citations
TL;DR: The correlation between dangling-bond defect density and the slope of the Urbach tail in hydrogenated amorphous silicon is examined in this article, and it is shown that this correlation can be explained quantitatively by a spontaneous decay of the weakest bonding orbitals into non-bonding defects during deposition or annealing of a sample and that the same correlation holds for all types of disorder affecting the edge of the urbach edge.
Abstract: The correlation between the density of dangling-bond defects and the slope of the Urbach tail in hydrogenated amorphous silicon is examined. It is shown that this correlation can be explained quantitatively by a spontaneous decay of the weakest bonding orbitals into non-bonding defects during deposition or annealing of a sample and that the same correlation holds for all types of disorder affecting the slope of the Urbach edge. The temperature dependence of the defect density as well as the creation of metastable defects are discussed, and quantitative expressions are derived which can be used to estimate the quality and the stability of a given sample on the basis of the slope of its Urbach tail alone. Possible ways for future improvement of the material are indicated.
295 citations
TL;DR: In this paper, the authors developed two-dimensional vertex models which are expected to capture the essential ingredients of the long-time behaviour of 2D grain growth and permit efficient large-scale computer simulations.
Abstract: We develop two-dimensional vertex models which are expected to capture the essential ingredients of the long-time behaviour of two-dimensional grain growth and permit efficient large-scale computer simulations. Such simulations are carried out starting with the initial 24 000 randomly chosen Voronoi cells. We confirm the 1/2 power law for the growth of average grain size. We also find the normalized grain-size distribution and the edge number distribution which exhibit stationary behaviour at long times except for small-amplitude oscillatory behaviour for the latter.
198 citations
TL;DR: In this article, it was shown that ultrafine iron oxide particles with a mean diameter of 6.9 nm and a very narrow size distribution have been studied by electron microscopy, Mossbauer spectroscopy, and X-ray diffraction.
Abstract: Ultrafine iron oxide particles with a mean diameter of 6.9 nm and a very narrow size distribution have been studied by electron microscopy, Mossbauer spectroscopy, and X-ray diffraction. Electron micrographs and electron diffraction patterns show that the particles form ‘super crystals’, that is, three-dimensional ordered close-packed structures, with a nearest neighbour distance of 9.1 nm.
149 citations
TL;DR: In this paper, a number of models made of soft spheres freely relaxed through the Lennard-Jones potential, in the size range 500 < N < 6000 atoms, were presented.
Abstract: This paper presents a number of models made of soft spheres freely relaxed through the Lennard-Jones potential, in the size range 500 < N < 6000 atoms. The external shape and potential energy of se...
133 citations
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TL;DR: In this paper, a unified model for silicon oxidation in dry and wet conditions is presented, which goes beyond the current models of kinetics and of ellipsometric and spectroscopic data by explicitly addressing the issues raised by isotope experiments.
Abstract: We describe a unified model for silicon oxidation in dry and wet conditions. It goes beyond the current models of kinetics and of ellipsometric and spectroscopic data by explicitly addressing the issues raised by isotope experiments. The model concentrates especially on the problems indicated in recent discussions, notably the very early stages of oxidation, the reactions at the Si/oxide interface, and the origin and nature of stress. Three features emerge as central: first, the several roles of stress and stress relaxation; second, the specific properties of the oxide adjacent to the silicon and the concept of the ‘reactive’ layer different in structure and composition, and third, the processes which encourage the insertion of interstitial oxygen into the silicon/oxygen network of the oxide. This ‘reactive layer’ or ‘altered layer’ is central to our analysis of dry oxidation through its role in the conversion of interstitial oxygen molecules into network oxygens. This conversion can be stimulate...
130 citations
TL;DR: In this article, the characteristic properties of vitreous electrolytes are summarised for convenience under the three headings of continuity, variability and vulnerability, which cover respectively the tempe, stability and vulnerability.
Abstract: The characteristic properties of vitreous electrolytes are summarised for convenience under the three headings of ‘continuity’, ‘variability’ and ‘vulnerability’. These cover respectively the tempe...
121 citations
TL;DR: The glass transition and heat capacity of hyperquenched glassy water have been studied by differential scanning calorimetry and by isothermal measurements from 103 K to a temperature where its crystallization to cubic ice is complete as mentioned in this paper.
Abstract: The glass transition and heat capacity of hyperquenched glassy water have been studied by differential scanning calorimetry and by isothermal measurements from 103 K to a temperature where its crystallization to cubic ice is complete Glassy water shows a thermally reversible glass-liquid transition and has a Tg, of 136 ± 1 K The activation energy of structural relaxation in the transition range is ∼55kjmol−1 and is a reflection of the energy required to break two hydrogen bonds before a rotational-translational diffusion of a water molecule in the H-bonded network can occur The temperature width of the transition is ∼12°, and the increase in the heat capacity is 16±01JK−1 mol−1 Liquid water formed on heating the glassy water to 146 K is more stable against crystallization than that which exists near 232 K The hyperquenched glassy form of water can be thermodynamically continuous with liquid water, but whether or not it has the same structure as water above 273 K or supercooled water near t
102 citations
TL;DR: In this article, the diffusion-controlled relaxation model was applied to ionic transport in glasses and the detailed frequency-dependent behaviour predicted by this model, when an exact treatment of the diffusion due to Bordewijk is employed, was discussed.
Abstract: The diffusion-controlled relaxation model, originally proposed by Glarum for molecular liquids, is applied here to ionic transport in glasses. For the first time, the detailed frequency-dependent behaviour predicted by this model, when an exact treatment of the diffusion due to Bordewijk is employed, is discussed. It is shown that this theory is capable of explaining most aspects of the a.c. transport in ionically conducting glasses without arbitrarily assuming the existence of a distribution of relaxation times.
91 citations
TL;DR: In this paper, the electron energy-loss spectrum due to surface plasmon excitation was studied for objects with arbitrary shape and dielectric constant and both classical and quantum-mechanical approaches were used.
Abstract: The electron energy-loss spectrum due to surface plasmon excitation is studied for objects with arbitrary shape and dielectric constant. Both classical and quantum-mechanical approaches are used. The results are useful for prediction of the energy loss spectrum obtained when using a highly convergent incident electron beam as is generally the case in scanning transmission electron microscopy.
87 citations
TL;DR: In this article, an increase in density was observed on melting of β-cristobalite using the constant pressure molecular dynamics technique and the formation of vitreous silica from the melt and the structure of the glass formed were also studied.
Abstract: An increase in density is observed on melting of β-cristobalite using the constant-pressure molecular dynamics technique. The formation of vitreous silica from the melt and the structure of the glass formed are also studied.
TL;DR: The zero-temperature energies and equilibrium volume expansions of point-defect-free grain boundaries (GBs) on the two densest planes of b.c. metals have been determined using a Finnis-Sinclair potential for Mo and Johnson's potential for α-Fe.
Abstract: The zero-temperature energies and equilibrium volume expansions of point-defect-free grain boundaries (GBs) on the two densest planes of b.c.c. metals have been determined using a Finnis—Sinclair potential for Mo and Johnson's potential for α-Fe. The energies and volume expansions of the (100) boundaries are found to be about two to three times larger than those of the (110) boundaries. A close correlation between large volume expansion and high GB energy is observed. Since both potentials yield qualitatively very similar results it is concluded that the short-range repulsion between atoms is the dominating contribution to the energy in the GB region and therefore, electronic many-body effects arising from a local volume dependence of the interatomic interactions are relatively unimportant.
TL;DR: The structure of Al65Cu20Fe15 can be seen as an ordered F superstructure of the usual primitive quasilattice with, at least, two motifs in the 6D representation as mentioned in this paper.
Abstract: Electron microscopy observations of the newly discovered icosahedral phase in the Al‐Cu‐Fe ternary system show a domain structure as expected from a group‐subgroup formal decomposition from a primitive six-dimensional (6D) hypercubic unit cell to a face‐centred one with twice the lattice parameter, as suggested by Ebalard and Spaepen. The structure of Al65Cu20Fe15 can be seen as an ordered F superstructure of the usual primitive quasilattice with, at least, two motifs in the 6D representation. The smoothness of the observed antiphase boundaries and the relative weak intensities of the superstructure reflections suggest that the ordered motifs should share many geometrical features. A possibility could be that at least one of the orbits of a given atomic species arranges in space according to a 6D primitive skeleton and chemical ordering occurs on the remaining orbits.
TL;DR: In this article, the microstructure of nanocrystalline Pd was investigated by small-angle neutron scattering, and the strong scattering signal was interpreted as originating from crystallites embedded in a matrix formed by incoherent interfaces.
Abstract: The microstructure of nanocrystalline Pd was investigated by small-angle neutron scattering. The strong scattering signal is interpreted as originating from crystallites embedded in a matrix formed by incoherent interfaces. From the scattering curves size distributions were determined, which yield an average radius of 2.6 nm. The volume fraction of the crystallites was found to be about 0.3, and the atomic density in the matrix about one-half that of Pd crystals. Structural parameters varied from sample to sample. An appreciable volume fraction of voids or interconnected channels may exist in some of the specimens.
TL;DR: In this article, the application of X-ray absorption spectroscopy (XAS) to the study of diffusion properties of oxide glasses and glass surfaces is considered. And the importance of combining XAS with diffusion measurements and structural modelling is stressed if the interdependence of structure and ionic transport is to be properly elucidated.
Abstract: The application of X-ray absorption spectroscopy (XAS) to the study of diffusion properties of oxide glasses and glass surfaces is considered. Mixed alkali silicates, the chemical resistance of iron-lead-phosphate glasses and the surface structure of uranium in leached borosilicate glasses are discussed. Results are interpreted using the modified random network (MRN) model. The importance of combining XAS with diffusion measurements and structural modelling is stressed if the interdependence of structure and ionic transport is to be properly elucidated.
TL;DR: In this paper, Czochralski silicon samples have been heated at 750°C for periods of 48,96 and 431 h under clean conditions appropriate to device fabrication.
Abstract: Czochralski silicon samples have been heated at 750°C for periods of 48,96 and 431 h under clean conditions appropriate to device fabrication. The loss of oxygen from solution was measured from the strength of the 9 pm absorption band with the samples at 4·2 K; detailed information about the SiO2 precipitates was obtained by measurements on many foils using transmission electron microscopy, and by small-angle neutron scattering. The three techniques were applied to common samples. The measurements show excellent overall self-consistency and some new features have been found in the transmission electron microscopy analysis. In general, platelets are observed with length increasing from 12 to 26 nm, and with thicknesses of about 2 nm. The number density of particles drops from 2 × 1013 to 7 × 1012 cm−3 as the heating time is increased. We deduce a value of the oxide density to be 2·6 g cm−3, which is somewhat higher than the normally quoted value of 2·3 g cm−3 for amorphous silica.
TL;DR: In this paper, a superposition of three components with Gaussian shapes at around 750,840 and 960 cm−1, and a N-atom related Si-H absorption is observed at around 2100cm−1.
Abstract: Amorphous SINx: H films have been prepared by r.f. glow discharge of SiH4–N 2–H2 mixtures at 300°C, and the dependence on x of the Si–N and Si–H absorption bands investigated by infrared absorption spectroscopy. The stretching absorption profiles due to Si–N bonds are reproduced by a superposition of three components with Gaussian shapes at around 750,840 and 960 cm−1, and a N-atom related Si–H absorption is observed at around 2100cm−1. The weak 750cm−1 band, observed at the lower levels of x, is assigned to isolated Si–N bonds. Clear changes in the dependence of these absorption bands on x are observed at around x = 0·5. Up to x = 0·5, the 840 and 2100cm−1 bands increase with x keeping a fixed peak wavenumber, and also giving agreement between the N and H contents estimated from the intensity of each band. This indicates selectively increased formation of N–Si–H bonds, responsible for both bands at 840 and 2100 cm−1. Above x = 0·5, the 960 cm−1 band occurs, and the peak wavenumbers of the 960 an...
TL;DR: In this paper, the first measurements of the d.c. electrical conductivity and the low-frequency (static) dielectric constant of samarium phosphate glasses (in the composition range 5 to 25 mol% Sm2O3) are reported.
Abstract: The first measurements of the d.c. electrical conductivity and the low-frequency (static) dielectric constant of samarium phosphate glasses (in the composition range 5 to 25 mol% Sm2O3) are reported. A break in the slope of the Arrhenius plot divides the conductivity data into two temperature regimes, the conductivity mechanism at low temperatures having a lower activation energy than that at higher temperatures. An increase of Sm2O3 glass modifier content results in a decrease in the absolute value of the conductivity. The data are consistent with small-polaron transport and hence small-polaron theory has been used to establish the characteristic energies of the carriers. The dielectric constants range from 5.4 for a glass containing 5mol% Sm2O3 to 8·1 for that with 2Smol% Sm2O3; the temperature dependences of the dielectric constants are linear and positive, as is usual for glasses.
TL;DR: In this paper, the temperature dependences of the d.c and a.c. conductivities for transition metal oxide (TMO) glasses are re-examined and a multiphonon tunnelling process with weak coupling is discussed.
Abstract: Although it is well established that small polarons are formed in transition metal oxide (TMO) glasses, no satisfactory quantitative analysis of d.c. and a.c. transport exists. The temperature dependences of the d.c. and a.c. conductivities for TMO glasses are re-examined. The charge transport cannot be explained quantitatively by the small-polaron model (strong electron-lattice coupling). An alternative possibility—a multiphonon tunnelling process with weak coupling—is also discussed. The a.c. conductivity, which is strongly correlated to the d.c. conductivity and which has never been explained by current theories based on the pair approximation, is interpreted in terms of the continuous-time random-walk approximation.
TL;DR: In this paper, a new definition of hypertwins (hypertwins) based on the reduction of the number of arithmetically independent lattice vectors is proposed, which can be easily interpreted in terms of quasilattices.
Abstract: Polycrystalline aggregates with overall icosahedral symmetry have been found in rapidly solidified Al—Mn—Fe—Si alloys. The orientation relationship between crystals is such that icosahedral motifs in all the crystals are parallel. Although the cubic axes undergo fivefold rotation about irrational 〈1, τ, 0〉 axes, only five orientations occur among hundreds of crystals. This is a special orientation relationship, but there is neither a coincidence nor a twin lattice (S = σ = ∞). The concepts of twinning and special grain boundaries are re-examined, and a new definition of special orientations (hypertwins) based on the reduction of the number of arithmetically independent lattice vectors is proposed. It includes both old and new special orientations and can be easily interpreted in terms of quasilattices.
TL;DR: In this article, the authors performed neutron and Brillouin scattering studies of ion conducting metal-halide-doped borate glasses (MX)x-(M2O-nB2O3)1-x glasses.
Abstract: We have performed neutron and Brillouin scattering studies of ion conducting metal-halide-doped borate glasses (MX)x-(M2O-nB2O3)1-x glasses (MX[tbnd]LiCl, AgI). Neutron diffraction experiments and small-angle neutron scattering investigations were carried out in order to determine the short-, medium-, and long-range structure of the glasses. The small-angle experiments show no significant scattering from inhomogeneities of dimensions 10–100 A, which contradicts suggestions that MX tend to form microdomains of size 20–30 A in the glass. A marked change in the medium-range order (less than 10 A) is observed when MX is added to the binary M2O-nB2O3 glass. For AgI-doped glasses a substantial increase in the medium-range order is found, which is manifested in a diffraction peak at anomalously low Q values (Q = 0·8A−1). The peak increases in strength with increasing AgI content. In contrast, for the LiCl-doped glasses, the ordering of the medium-range structure is observed to decrease when the salt is ...
TL;DR: In this article, a polymorphous Clapeyron diagram for melting and glass transition is developed which displays a triple point between supersaturated crystal, undercooled liquid and glass, at which the crystal-to-glass transition becomes continuous in entropy.
Abstract: For the thermodynamic description of solid-state amorphization processes in binary alloy systems the T 0 concept has been combined with the isentropic condition for glass formation from the undercooled liquid and extended to the pressure variable. A polymorphous Clapeyron diagram for melting and glass transition is developed which displays a triple point between supersaturated crystal, undercooled liquid and glass. As an example, the polymorphous phase diagram has been calculated for the Ni-Zr alloy system based on available thermodynamic data. A triple point is found at 11·5at, % Ni and 638 K at which the crystal-to-glass transition becomes continuous in entropy.
TL;DR: In this article, the effects of rigid-band (i.e. static) and electron-phonon disorder on the photoluminescence of a-Si: N: H alloys were investigated.
Abstract: We present new results from photoluminescence studies of a-Si: N: H alloys which enable us to distinguish between the effects of rigid-band (i.e. static) and electron-phonon disorder. Using predictions of correlations between the M-band width, the Urbach slope and the Tauc gap, we show that static structural disorder determines the photoluminescence band width. Analysis of earlier work on the a-Si: C: H and a-Si: Ge: H systems supports these conclusions. By using subgap excitation of luminescence, we provide further evidence that in the nitrogen-rich alloys this disorder is predominantly due to long-range alloy compositional fluctuations.
TL;DR: In this article, the so-called R, Z, C and τ phases have been selected for structural studies because of their presumed relation with the Al-Cu-Li quasicrystal.
Abstract: Intermetallic compounds with compositions in the vicinity of Al0·6 (Cu, Zn), (Li, Mg)0·3, namely the so-called R, Z, C and τ phases, have been selected for structural studies because of their presumed relation with the Al-Cu-Li quasicrystal. Neutron diffraction data strongly suggest unicity for short- and medium-range arrangements in these phases. Transmission electron microscopy confirms the point and allows detailed modelling, based on connections of atomic clusters having icosahedral symmetries and taken from the crystallographic structure of the b.c.c. R-phase.
TL;DR: The incorporation of tungsten and molybdenum into barrier films on aluminium, formed to 5-350V at 5 mA cm−2 in 0·1 M tungstate and Molybdate electrolytes at 298 K, has been studied by Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM) as discussed by the authors.
Abstract: The incorporation of tungsten and molybdenum into barrier films on aluminium, formed to 5–350V at 5 mA cm−2 in 0·1 M tungstate and molybdate electrolytes at 298 K, has been studied by Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). RBS indicated that tungsten and molybdenum were incorporated at similar constant rates (2·9 × 1013 W atoms cm−2 V−1 and 2·7 · 1013 Mo atoms cm −2 V−1), with the surface layers of all films being enriched with either ∼5 × 1014 W atoms cm−2 or ∼9 × 1014 Mo atoms cm−2. The enrichment was a consequence of immersion in the electrolyte, since similar concentrations of tungsten were picked up by merely dipping electropolished aluminium or anodic alumina films into the tungstate electrolyte. TEM of film sections, assisted by the atomic-number contrast effect associated with incorporated species, revealed that tungsten incorporated into a 50 V film was distributed uniformly in the outer 0·3 of the thickness.
TL;DR: In this paper, a detailed discussion of experimental (TOF) transit time, the moment when the center of charge leaves the sample at the back contact, and the physical interpretation of activation energies calculated from log(μeff) against 1/T plots is presented.
Abstract: Time-of-flight (TOF) experiments of a-Si: H, in which carrier transport proceeds via multiple trapping in, and re-emission from, a continuous distribution of localized states below the mobility edge, have been analysed using a computer simulation technique based on a numerical inversion of the Laplace transform. A detailed discussion of experimental (TOF) transit time, the moment when the centre of charge leaves the sample at the back contact, and the physical interpretation of activation energies calculated from log(μeff) against 1/T plots is presented. The activation energy is used to determine the trapping region of the tail-state distribution which dominates carrier transport and it is shown that the experimental transit time is approximately the free-carrier transit time plus the total resting time of carriers in traps visited at least once. TOF experiments have been carried out over a wide range of temperature and electric field. Experimental drift mobility data are evaluated to calculate t...
TL;DR: The characteristics of composite polymer electrolytes obtained by adding doped β″-A12 −O3 powders having a regular spherical shape with a mean diameter of 15 μm, to a poly(ethylene oxide)-sodium io...
Abstract: The characteristics of composite polymer electrolytes obtained by adding doped β″-A12 −O3 powders having a regular spherical shape with a mean diameter of 15 μm, to a poly(ethylene oxide)-sodium io...
TL;DR: In this article, an order parameter functional method is proposed which permits description of structural order-disorder phase transitions, where the probabilities of all atomic groups are represented in terms of a distribution function that is immediately related to the long-range order parameters.
Abstract: An order parameter functional method is proposed which permits description of structural order-disorder phase transitions. A feature peculiar to the method is that the probabilities of all atomic groups (clusters) are represented in terms of a distribution function that is immediately related to the long-range order parameters. Consideration is given to applications of the proposed method to describe atomic ordering in non-stoichiometric niobium and tantalum carbides.
TL;DR: In this paper, a detailed description of these arcs is presented, and two existing theoretical models, transition-state theory and the icosahedral glass, predict arcs in qualitative agreement with the observations but disagree with the details of their observed shapes and positions.
Abstract: In diffraction from some icosahedral quasicrystals, diffuse scattering is concentrated on finite geometrical loci in reciprocal space. This diffuse scattering typically appears as arcs in transmission electron microscopy diffraction patterns. The new Ti—Mn icosahedral phase produces much more intense arcs than previously observed in quasicrystals, allowing a significantly deeper study of them. In this paper, we present a detailed description of these arcs. Two existing theoretical models, transition-state theory and the icosahedral glass, predict arcs in qualitative agreement with the observations but disagree with the details of their observed shapes and positions.
PARC1
TL;DR: In this paper, the sweep-out experiment was used to measure the density of band-tail carriers in hydrogenated amorphous silicon (a-Si:H) and the results were related to the transport, the density-of-states distribution and the thermal equilibration of the localized states.
Abstract: The sweep-out experiment, used to measure the density of band-tail carriers in hydrogenated amorphous silicon (a-Si:H) is described. The experimental configuration, sample structure and analysis are discussed in some detail. The band-tail carrier density nBT is obtained with good accuracy from the charge collection, but their energy distribution is not easily deduced from the time dependence of the current. The sweep-out technique is applied to doped material and the results are related to the transport, the density-of-states distribution and the thermal equilibration of the localized states. In the equilibrium regime, nBT is activated with a doping-dependent energy, which is explained by the thermodynamics of the defect and dopant states. The measurements of nBT are combined with conductivity data and the density of states, to give the drift mobility of doped material. Sweep-out measurements also prove that the doping efficiency of a-Si: H depends on the position of the Fermi energy, as predicte...