Showing papers in "Physica Status Solidi (a) in 1998"
TL;DR: In this paper, a particular form of pulsed-laser-based thin-film crystallization method referred to as controlled super-lateral growth (C-SLG) is presented.
Abstract: This paper reviews a particular form of pulsed-laser-based thin-film crystallization method referred to as controlled super-lateral growth (C-SLG). By systematically manipulating and controlling the locations, shapes, and extent of melting induced by the incident laser pulses, the C-SLG approach — notably in a version referred to as sequential lateral solidification (SLS) — can lead to realization of a variety of microstructurally designed crystalline Si films with low structural defect densities, including 1. large-grained and grain-boundary-location controlled polycrystalline films, 2. directionally solidified microstructures, or 3. location-controlled single-crystal regions.
208 citations
TL;DR: In this paper, the LSDA + U method was used to obtain a better description of electron energy loss spectra, cohesive energies and elastic constants of both oxides compared with local spin density functional theory.
Abstract: We compare experimentally observed electron energy loss spectra (EELS) of uranium dioxide UO 2 and nickel monoxide NiO with the results of ab-initio calculations carried out by using a method combining the local spin density approximation and the Hubbard U term (the LSDA + U method). We show that by taking better account of strong Coulomb correlations between electrons in the 5f shell of uranium ions in UO 2 and in the 3d shell of nickel ions in NiO it is possible to arrive at a better description of electron energy loss spectra, cohesive energies and elastic constants of both oxides compared with local spin density functional theory. For NiO we also compare the LSDA + U results and EELS spectra with a self-interaction corrected LSDA calculation.
203 citations
TL;DR: In this article, the formation and structure of the as-pyrolyzed amorphous state and its devitrification into stable crystalline phases have been investigated by means of nuclear magnetic resonance spectroscopy, infrared spectrum analysis, thermogravimetry, mass spectroscopic, X-ray and neutron diffraction, and transmission electron microscopy.
Abstract: Pyrolysis of different polysilazanes has been used to prepare novel covalent amorphous ceramics composed of silicon, carbon, and nitrogen. The formation and structure of the as-pyrolyzed amorphous state and its devitrification into stable crystalline phases have been investigated by means of nuclear magnetic resonance spectroscopy, infrared spectroscopy, thermogravimetry, mass spectroscopy, X-ray and neutron diffraction, and by transmission electron microscopy. Additionally, the electrical conductivity and the compression creep behaviour of the as-received materials have been analyzed.
112 citations
TL;DR: In this article, two different triangular lattices of circular air rods with lattice constants of 2.3 and 1.5 μm were etched at least 75 μm deep in an n-type silicon substrate by electrochemical pore formation in aqueous hydrofluoric acid.
Abstract: We have fabricated macroporous silicon and proved its applicability as a two-dimensional photonic bandgap material in the near-infrared spectral range. Two different triangular lattices of circular air rods with lattice constants of 2.3 and 1.5 μm were etched at least 75 μm deep in an n-type silicon substrate by electrochemical pore formation in aqueous hydrofluoric acid. Photolithographic pre-patterning techniques and subsequent alkaline etching were used. In the case of the 1.5 μm lattice the photo-mask was modified so that series of etch pits were left out. These local perturbations of the initially regular lattice of air rods introduced photonic defects like waveguides. In the case of the 2.3 μm lattice we succeeded to micromechanically structure the macroporous layer to make 200 μm wide free-standing bars of porous material remain on the silicon substrate. These bars were used to measure the transmission of the photonic lattice dependent on the light polarization relative to the pore axes using FT infrared spectroscopy. The results excellently agree with theoretical calculations. The generation of KOH pits with lattice constants on a sub-μm length scale was demonstrated.
106 citations
TL;DR: In this paper, the authors investigated the radiative properties of thin films prepared by the rapid thermal process (RTP) and showed that three phases are present in the layers. But they did not investigate the properties of the three phases in terms of the conductivity of the layers and did not contribute to radiative recombinations.
Abstract: Cu-rich and nearly stoichiometric CuIn(Ga)Se2 thin films prepared by the rapid thermal process (RTP) are investigated by electrical and optical methods. The experiments yield that three phases are present in the layers. Cu2—xSe, which determines the conductivity of the layers but does not contribute to the radiative recombinations is observed. CuIn1—xGaxSe2 causes a broad unstructured radiative recombination with a peak energy in the range from 1.0 to 1.1 eV, dependent on x. Recombinations with zero-phonon lines at 0.96 and 0.90 eV arise from CuInSe2. They involve a shallow donor with a binding energy of (10 ± 5) meV and two acceptors with binding energies of (75 ± 10) meV and (140 ± 10) meV, respectively. All features of these recombinations are well described in the donor–acceptor pair recombination model.
91 citations
TL;DR: In this paper, Si crystallites on glass of several tens of mm in length were obtained via sequential lateral solidification using a copper vapor laser, and they were used to obtain Si crystallite on glass.
Abstract: Understanding nucleation and growth of crystalline Si films on glass is of prime importance in order to tailor and optimize semiconductor properties for electronic devices such as solar cells. Commercial glass limits the maximum processing temperature of Si films to 600 C. Solid phase and laser crystallization, or a combination of both techniques, are thus primarily used to crystallize Si films on glass. While random nucleation and growth processes always result in the formation of a log± normal size distribution, control of nucleation sites allows one to determine the location of grain growth or even the crystallographic orientation of grains. Via sequential lateral solidification using a copper vapor laser, we obtain Si crystallites on glass of several tens of mm in length.
86 citations
TL;DR: In this paper, the origin of transmission damage in PWO crystals is discussed and it is shown that both electron and hole centers created on the basis of structural defects in PbWO 4 crystals contributed to induced absorption of the crystals.
Abstract: The origin of the transmission damage in PWO crystals is discussed. It is shown that both electron and hole centers created on the basis of structural defects in PbWO 4 crystals contributed to the induced absorption of the crystals. The different aspects of the suppression of the recharge processes in PWO scintillation crystals are also discussed.
85 citations
83 citations
TL;DR: In this article, the authors discuss several examples progressing from cases where the limitation in spatial resolution is given by the microscopes or the nature of the sample, to one example of impurity atoms at a grain boundary, which show intensity and fine structure changes from atomic column to atomic column.
Abstract: Spatially resolved electron energy-loss spectroscopy (EELS) is rapidly developing into a unique and powerful tool to characterize internal interfaces. Because atomic column resolved Z-contrast imaging can be performed simultaneously with EELS in the scanning transmission electron microscope, this combination allows the atomic structure to be correlated with the electronic structure, and thus the local properties of interfaces or defects can be determined directly. However, the ability to characterize interfaces and defects at that level requires not only high spatial resolution but also the exact knowledge of the beam location, from where the spectrum is obtained. Here we discuss several examples progressing from cases where the limitation in spatial resolution is given by the microscopes or the nature of the sample, to one example of impurity atoms at a grain boundary, which show intensity and fine structure changes from atomic column to atomic column. Such data can be interpreted as changes in valence of the impurity, depending on its exact site in the boundary plane. Analysis of this nature is a valuable first step in understanding the macroscopic structural, optical and electronic properties of materials.
76 citations
TL;DR: In this paper, the phase formation, electrical conductivity and anti dielectric constant as a function of temperature and frequency for the samples with x = 0.9 and 0.8 which are isostructural to BiFeO 3.
Abstract: xBiFeO 3 -(1-x)BaTiO 3 form substitutional ferroelectromagnetic solid solutions with the rhomobohedral distortion up to 67% of BiFeO 3 . The paper reports data on phase formation, electrical conductivity anti dielectric constant as a function of temperature and frequency for the samples with x = 0.9 and 0.8 which are isostructural to BiFeO 3 . The conductivity is found to be dependent on both frequency and temperature in the range 30 to 400 °C. The temperatures of dielectric anomalies are found to be lower than that of BiFeO 3 . The complex impedance studies indicate relaxation effects.
71 citations
TL;DR: In this paper, the structural and electrical properties of copper silicide precipitates in silicon were investigated using high-resolution transmission electron microscopy (TEM) and they showed that metastable platelets surrounded by extrinsic stacking faults form upon quenching from high temperatures.
Abstract: We report results of a detailed study of structural and electrical properties of copper silicide precipitates in silicon. Using conventional and high-resolution transmission electron microscopy: we observe that metastable platelets surrounded by extrinsic stacking faults form upon quenching from high temperatures. By ripening experiments at low temperatures as well as by a variation of cooling rates it is shown how homogeneous copper precipitation merges into the heterogeneous precipitation mode of colony growth. The application of recently developed criteria for the interpretation of deep level transient spectra from extended defects allows to conclude that deep electronic states associated with the precipitates have bandlike character.
TL;DR: In this article, the critical resolved shear stress for activating the (0001) (2110) slip system of monocrystalline 6H-SiC has been determined as a function of test temperature and strain rate via constant-displacement compression tests.
Abstract: The critical resolved shear stress for activating the (0001) (2110) slip system of monocrystalline 6H-SiC has been determined as a function of test temperature and strain rate via constant-displacement compression tests. Tests were conducted at temperatures between 550 and 1300°C at strain rates of 1.3×10 -4 , 6.3×10 -5 and 3.1×10 -5 s -1 . The current study shows that 6H-SiC crystals can be plastically deformed via relatively modest resolved shear stresses on the basal plane at temperatures as low as 550 °C. For temperatures below 1300 °C for the fast and intermediate strain rates, and for temperatures below 1100 °C for the slow strain rate, the stress exponent n, and the activation enthalpy H were estimated to be (3.0±0.7) and (2.1±0.7) eV, respectively. At higher temperatures at the slowest strain rate, the activation enthalpy was determined to be (4.5±1.2) eV. Subsequent to the deformation tests, transmission electron microscopy (TEM) was used to rationalize some of the results.
TL;DR: In this paper, the authors studied the charge transport mechanisms in both polarities of Schottky diodes, in which a donor-type deep level whose ionization energy varies with the applied voltage according to the Poole-Frenkel effect was used.
Abstract: Space-charge-limited Schottky diodes are fabricated by evaporation of gold on electrodeposited CdTe films. The charge transport mechanisms, in both polarities, are studied. Thermionic emission and space-charge-limited conduction theories can adequately describe the transport properties. The latter mechanism is controlled by a donor-type deep level whose ionization energy varies with the applied voltage according to the Poole-Frenkel effect. Bardeen's model in which the Fermi level is pinned to the interface states, can explain the voltage dependence of the barrier height in these devices. Some of the important parameters of CdTe films are measured from the characteristics of these diodes.
TL;DR: Amorphous magnetostrictive films of the composition (Tb 0.27 Dy 0.73 ) 0.3 Fe 0.7 have been prepared by ion-beam sputtering as discussed by the authors.
Abstract: Amorphous magnetostrictive films of the composition (Tb 0.27 Dy 0.73 ) 0.3 Fe 0.7 have been prepared by ion-beam sputtering. The films have been subjected to a subsequent heat treatment for i00 min at various temperatures. Annealing temperatures to 5500°C result in a significant enhancement of the magnetostriction while the microstructure of the films remains amorphous. For annealing temperatures in the range of 600 to 8000°C nano- and microcrystalline samples have been obtained. Films with a grain size around 10 nm exhibit an in-plane magnetostriction up to λ∥ = 860 x 10 -6 at 1 T with a minimum coercivity of μ 0 H c ∥ = 0l.12 T.
TL;DR: In this paper, interference patterns from overlapping beams of an intense pulsed laser are used to realize high-resolution thermal processing for direct structuring of semiconductor films, with periods down to 130 nm.
Abstract: Interference patterns from overlapping beams of an intense pulsed laser are used to realize high-resolution thermal processing for direct structuring of semiconductor films. Line and dot arrays have been realized, with periods down to 130 nm. In AlGaAs/GaAs systems, a two-dimensional electron gas could be modulated with a periodic lateral potential, sufficient to form barriers as determined by optical and magnetotransport measurements. The thermal patterning is also a very attractive means of physically structuring GaN and related materials, because rapid thermal decomposition with the evolution of nitrogen can be induced.
TL;DR: In this article, the authors describe the synthesis, characterization, and grain growth behavior of nanocrystalline Ni coatings generated using a novel synthesis approach, namely high velocity oxy-fuel (HVOF) thermal spraying.
Abstract: The present paper describes the synthesis, characterization, and grain growth behavior of nanocrystalline Ni coatings generated using a novel synthesis approach, namely high velocity oxy-fuel (HVOF) thermal spraying. In the present investigation, the feedstock powders were prepared by mechanical milling in a methanol environment which yielded agglomerates with a flake-shaped geometry and an average grain size of less than 100 nm. The milled powders were then introduced into the HVOF spray system in order to investigate the feasibility of generating a coating with grain sizes in the nanocrystalline range (e.g., <100 nm). Scanning electron microscopy and transmission electron microscopy were used to study the morphology of the nanometric particles and the microstructure of the milled powders and the as-sprayed coatings. Transmission electron microscopy analysis performed on cross sections of the coating revealed a mixture of fine nanocrystalline grains and elongated coarse grains.
TL;DR: In this paper, the authors describe the nucleation, growth and oxidation of the wires and a technique developed to control the wire diameter and position, which can make it possible to conduct optical and transport measurements on a single wire of known dimensions.
Abstract: Si nanowires as thin as 10 nm have been grown using silane gas as the source gas in the Vapour–Liquid–Solid (VLS) reaction. This paper describes the nucleation, growth and oxidation of the wires and a technique developed to control the wire diameter and position. A very thin layer of Au is deposited onto a Si(111) surface at room temperature. Silane gas is then introduced into the chamber as the VLS Si source gas and the temperature is raised to 300 to 700 °C. Initially a catalytically active Au surface phase which coats the surface leads to the growth of a defective epitaxial Si layer. As Au/Si molten alloy balls nucleate and grow in size to approach the threshold size for VLS wire growth, which is determined by the Gibbs-Thomson effect, the epitaxial layer growth rate decreases and a transition to Si nanowire growth occurs. The morphology and width of the wires is strongly dependent on the growth temperature and pressure. At low pressure and high temperature relatively thick well-formed wires grow straight up from the substrate surface along the [111] direction. As the temperature is decreased and the pressure is increased thinner wires grow which tend to exhibit growth defects. The Si nanowires can be thinned down by oxidation. A light oxidation yields Si cores which are of the order of 5 nm in diameter. A method to control the position of the Si wires which exploits the difference in Au sticking coefficient on Si and SiO2 surfaces at elevated temperature (T > 540 °C) has recently been developed. Using thermally oxidized Si(111) as a starting substrate, circular holes ≈1.5 μm in diameter were etched through the SiO2 to expose the Si. The sample was heated to 700 °C and exposed to a flux of Au atoms. For low Au fluxes (≈1×1014 atoms cm—2 s—1) the Au sticking coefficient on the SiO2 surface is negligible at 700 °C but remains unity on the exposed Si surface in the holes. The liquid alloy which forms in the holes during Au deposition is able to agglomerate to form a single ball in each hole. The quantity of Au which contributes to each ball can be controlled because it is determined by the hole size and the total Au dose. When silane gas is then introduced into the chamber each alloy ball grows to form a Si wire of controlled diameter whose position is quasi-controlled by the initial patterning. No wire growth occurs on the SiO2 surface due to the absence of Au. This ability to control the size and position of the Si wires should make it possible to conduct optical and transport measurements on a single wire of known dimensions.
TL;DR: A theoretical analysis of the experimental bulk modulus K e of both binary tellurite and binary phosphate glasses containing transition metal oxides V 2 O 5 or MoO 3 with different percentages has been done as mentioned in this paper.
Abstract: A theoretical analysis of the experimental bulk modulus K e of both binary tellurite and binary phosphate glasses containing transition metal oxides V 2 O 5 or MoO 3 with different percentages has been done. The main parameters in the analysis were the calculated bulk modulus K bc and Poisson's ratio σ bc . The calculations have been done according to the bond compression model. These parameters were calculated for every glass series and for every glass composition. Also the ring size of the glass network has been calculated by using the ring deformation model for every glass series.
TL;DR: In this paper, the concept of thermodynamic excesses at interfaces in multicomponent systems is generalised to crystalline materials in a way which makes it useful for practical atomistic calculations.
Abstract: The concept of thermodynamic excesses at interfaces in multicomponent systems is generalised to crystalline materials in a way which makes it useful for practical atomistic calculations. It is necessary to terminate the region around the defect on the atomic scale in a way which is consistent with macroscopic thermodynamics, and this problem is solved by introducing a tapered termination, equivalent to averaging over an ensemble of terminations distributed broadly on the atomic scale. The approach leads to a unique definition of excesses which generalises the notion of a charged interface or polar interface. Five different situations are distinguished: (i) grain boundaries, (ii) a heterogeneous interface with more than two components, (iii) a heterogeneous interface in a two component system, (iv) free surfaces, and (v) dislocations. The simple example of a magnetite (Fe304) (111) surface is treated. General formula are also given for excess free energies of extended planar defects and their dependence on the chemical potentials and excesses of the components.
TL;DR: In this article, a review of the properties of vacancies in high-purity α-iron and an original contribution is made, where it is shown that self-diffusion in high purity δ-iron occurs by the vacancy mechanism, that the sum of the monovacancy formation and migration enthalphies in the magnetically fully ordered state is HF1V + HM1V = (2.91 ± 0.04) eV, and that for the formation enthalpy 1.61 eV ≤ HF 1V ≤ 1.75 eV holds
Abstract: The paper is both a review of the properties of vacancies in high-purity α-iron and an original contribution. In the review part it is shown that self-diffusion in α-iron occurs by the vacancy mechanism, that the sum of the monovacancy formation and migration enthalphies in the magnetically fully ordered state is HF1V + HM1V = (2.91 ± 0.04) eV, and that for the monovacancy formation enthalpy 1.61 eV ≤ HF1V ≤ 1.75 eV holds. The result for the monovacancy migration energy, HM1V = (1.23 ± 0.11) eV, excludes with certainty the attribution of Stage-III recovery to vacancy migration and supports the view that the Stage-III defect is a self-interstitial. It is shown that at elevated temperatures positrons trapped in vacancies in body-centred cubic iron may escape from them. The binding energy of positrons to the vacancies is estimated to be about 1.1 eV. This estimate is in agreement with the analysis of the high-temperature trapping of positive muon by vacancies, which in the present case proved to be the most sensitive technique for detecting vacancies present in thermal equilibrium.
TL;DR: In this article, the lifetime of Er 3+ doped LiNbO 3 has been measured for different doping concentrations and geometries of luminescence collection, and it has been found that this emission suffers of a strong radiation trapping effect, which affects the measured lifetime depending on the concentration and the geometry adopted.
Abstract: The lifetime of the 1.5 μm transition of Er 3+ doped LiNbO 3 has been measured for different doping concentrations and geometries of luminescence collection. It has been found that this emission suffers of a strong radiation trapping effect, which affects the measured lifetime depending on the concentration and the geometry adopted.
TL;DR: In this paper, the authors report on studies of dynamic strain ageing (DSA) in f.c. solid solutions which refer to the problems: (i) mode of diffusion (pipe or lattice) generating the various DSA effects; (ii) process (saturation or exhaustion) limiting this diffusion; (iii) current ageing model describing best all results.
Abstract: The work reports on studies of dynamic strain ageing (DSA) in f.c.c. solid solutions which refer to the problems: (i) mode of diffusion (pipe or lattice) generating the various DSA effects; (ii) the process (saturation or exhaustion) limiting this diffusion; (iii) the current ageing model describing best all results. From experiments on _C_uMn and _C_uAl under precisely chosen conditions an additional enthalpy Δg is derived which phenomenologically describes the DSA effects observed. Its analysis on solute concentration and stress at low and high degrees of tensile deformation yields clear answers to the above questions.
TL;DR: In this paper, a planetary ball mill was used to mechanically alloy three types of powders, namely, Ti 45 Ni 55, Ti 50 Ni 50 and Ti 55 Ni 45, for alloying for up to 10 hours.
Abstract: There kinds of Ti-Ni elemental powders, Ti 45 Ni 55 , Ti 50 Ni 50 and Ti 55 Ni 45 , were mechanically alloyed by a planetary ball mill for alloying times up to 10 h, and the alloying process and the microstructures after heating at temperature of 1273 K were investigated by powder X-ray diffractometry. The Ti 55 Ni 45 powder formed an amorphous phase after mechanical alloying for 10 h, while the Ti 50 Ni 50 powders formed a disordered b.c.c.-TiNi phase. The Ti 45 Ni 55 powder also formed the disordered b.c.c.-TiNi phase at an intermediate stage of mechanical alloying but turned to an amorphous state with increasing alloying time. After heating at 1273 K, the Ti 2 Ni phase has been formed in all powders, and the ordered B2-TiNi (CsCl structure) phase was observed in the Ti 50 Ni 50 and Ti 45 Ni 55 powders, but a monoclinic TiNi phase in the Ti 55 Ni 45 powder. In the Ti 45 Ni 55 powder also the TiNi 3 phase has been formed. The amounts of these intermetallic phases are dependent on the chemical compositions of the starting powders.
PARC1
TL;DR: In this article, the authors show that laser-crystallized polysilicon exhibits a narrow peak in the average grain size as a function of the excimer laser energy density, with a corresponding peak in electron mobility.
Abstract: Pulsed excimer-laser processing of amorphous silicon on non-crystalline substrates is an important processing technology for large-area polysilicon electronics, such as flat-panel displays and two-dimensional imaging arrays. It also allows for the integration of amorphous silicon and polysilicon devices on the same glass substrate and provides procedures for the doping of self-aligned thin-film transistors. Materials studies show that laser-crystallized polysilicon exhibits a narrow peak in the average grain size as a function of the excimer laser energy density, with a corresponding peak in the electron mobility. This is of particular significance for devices since large grains imply high electron mobility. On the other hand, the peak in the grain size is very narrow and is also accompanied by a peak in the surface roughness of the film. These relationships force a compromise between large grain size for high mobility and homogeneous size distribution for uniformity of device characteristics. A window exists in process parameter space where good-quality devices with uniform characteristics have been obtained. Also, laser-processing enhancements, such as laser doping and fabrication of self-aligned transistors, provide additional tools to fabricate unique devices.
TL;DR: In this article, high-resolution transmission electron microscopy (HRTEM) images were used to image the grain boundaries in cross-sectional view, using specimens that were prepared from a macroscopic SrTiO 3 bicrystal.
Abstract: This paper presents the results of experimental and theoretical studies on the atomistic structure of Σ = 3, (111) grain boundaries in SrTiO3 (strontium titanate). By means of high-resolution transmission electron microscopy (HRTEM) we have imaged the structure of such grain boundaries in cross-sectional view, using specimens that we prepared from a macroscopic SrTiO 3 bicrystal. By quantitative evaluation of HRTEM images that we recorded along the common (110) direction of the two adjoining half crystals we have determined the positions of the atom (ion) columns near the grain boundary plane with an average precision of 0.015 nm. We compare the experimental structure with model structures we have obtained by molecular statics calculations, employing empirical potentials. The equilibrium structure obtained by the calculations reproduces the characteristic features of the experimental grain boundary structure. Concerning the atom positions close to the grain boundary plane, however, the theoretical structure and the experimental structure exhibit significant discrepancies, which we discuss at the end of this paper.
TL;DR: In this article, the size dependence of phonon modes in the nanocrystals was observed and attributed to the internal stress arising from surface tension effects, and a relation between the frequency of the E 1 (1TO) mode and the crystallite size was established to be ω R = 89 - 440/R, and the critical size for PbTiO 3 was estimated to be 11.6 nm from the equation.
Abstract: PbTiO3 nanocrystals were investigated by using Raman spectroscopy. The phonon modes in the nanocrystals exhibited an obvious frequency downshift as compared with bulk single crystals, and the mode frequencies in nanocrystalline PbTiO 3 shifted up with annealing treatment. Size dependence of phonon modes in the nanocrystals was observed and attributed to the internal stress arising from surface tension effects. A relation between the frequency (ω R ) of the E 1 (1TO) mode and the crystallite size (R) was established to be ω R = 89 - 440/R, and the critical size for PbTiO 3 was estimated to be 11.6 nm from the equation.
TL;DR: In this article, the microstructure development and crystallization behavior of Si-C-N ceramics were characterized by transmission electron microscopy (TEM) and the results showed that the observed microstructures are closely related to the residual porosity of the system.
Abstract: Monolithic polymer-derived Si-C-N ceramics were processed by blending 70 vol% of both crosslinked and pyrolyzed Si-C-N powder particles with an oligomeric Si-C-N precursor (liquid polysilazane). The respective Si-C-N powder particles were prepared from the same liquid precursor, however, pre-heated at 300 and 1000 °C. Powder compacts were annealed at 300 °C, in order to crosslink the liquid precursor that acts as a binder phase between the powder particles. After crosslinking, an additional heat treatment was performed at 1540 °C to transform both the binder phase and the particles into a homogeneous ceramic matrix. Microstructure development and, in particular, crystallization behavior of the monoliths were characterized by transmission electron microscopy (TEM). In general, the two starting materials, which only differ with respect to the pre-heat treatment of the powder particles, evolved markedly different microstructures. The material prepared with 300 °C polymer powder and oligomeric binder revealed a homogeneous amorphous microstructure with only a small fraction of crystallized spherical inclusions after exposure to 1540 °C. In contrast, blending the powder particles annealed at 1000 °C with the same binder yielded a high degree of SiC crystallization within regions that were formerly filled by the polymeric binder. The Si-C-N powder particles, however, remained amorphous. As will be shown, the observed microstructure variations are closely related to the residual porosity of the system. Moreover, phase separation in the amorphous matrix can also affect the overall stability of such polymer-derived ceramics, when exposed to high temperatures. A distinction between open and closed systems allows to explain the observed microstructure variations and, more importantly, a correlation with the high-temperature stability of the materials.
Journal Article•
TL;DR: In this paper, the authors investigated the radiative recombinations of thin films prepared by the rapid thermal process (RTP) and showed that three phases are present in the layers.
Abstract: Cu-rich and nearly stoichiometric CuIn(Ga)Sc 2 thin films prepared by the rapid thermal process (RTP) are investigated by electrical and optical methods. The experiments yield that three phases are present in the layers. Cu 2-x Se, which determines the conductivity of the layers but does not contribute to the radiative recombinations is observed. CuIn 1-x Ga x -Se 2 causes broad unstructured radiative recombination with a peak energy in the range from 1.00 to 1.1 eV. dependent on x. Recombinations with zero-phonon lines at 0.96 and 0.90 cV arise from CuInSe 2 . They involve a shallow donor with a binding energy of (10±5)mev and two acceptors with binding energies of (75 ± 10) meV and (140 ± 10) mev, respectively. All features of these recombinations are well described in the donor acceptor pair recombination model.