Showing papers by "Solid State Physics Laboratory published in 1989"
TL;DR: The structural properties of liquid equiatomic alkali-metal--lead alloys, with {ital A}=Na, K, Rb, and Cs, have been studied with neutron diffraction with satisfactory agreement with the experimental data.
Abstract: The structural properties of liquid equiatomic alkali-metal--lead alloys APb, with A=Na, K, Rb, and Cs, have been studied with neutron diffraction. The experimental data are reduced to the neutron-weighted total structure factors S(Q) and radial distribution functions n(r). In all the systems studied, S(Q) is characterized by a first sharp diffraction peak (FSDP) at Q\ensuremath{\sim}1 A\r{} $^{\mathrm{\ensuremath{-}}1}$ and n(r) by structure in the first coordination shell at r=3--4 A\r{}, both features indicating the presence of polyatomic structural units. Two types of structural models have been fitted to the experimental data, both based on consideration of such units: the random packing of structural units model, and the reference interaction site model. The structures of the units are derived from powder-diffraction measurements made with the same instrument on solid polycrystalline samples. Allowing for a slight expansion of the units on melting and using physically reasonable values for the adjustable parameters, both models give satisfactory agreement with the experimental data and are used to give the partial structure factors and pair distribution functions. Inelastic-scattering measurements have been made on one system, liquid KPb, using a spectrometer at the same source. These yield a value for the mean diffusion constant, D=1.2\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ ${\mathrm{cm}}^{2}$/sec, and a smoothly varying inelastic scattering spectrum with no indication of excitations of a molecular character. The FSDP remains well defined when the inelastic scattering is integrated over small energy transfers, indicating a lifetime of ${10}^{\mathrm{\ensuremath{-}}13}$ sec or longer for the intermediate-range order responsible for this peak.
69 citations
46 citations
TL;DR: In this paper, the structure of borate glasses with various contents of Li 2 O, LiCl and Cs 2 O has been simulated by use of molecular dynamics and velocity autocorrelation functions, Raman and infrared spectra have been calculated and compared with experimental spectra.
Abstract: The structures of borate glasses with various contents of Li 2 O, LiCl and Cs 2 O have been simulated by use of molecular dynamics. Calculated radial distribution functions are in agreement with X-ray diffraction studies. The structure of v-B 2 O 3 consists of randomly linked BO 3 triangles. Addition of Li 2 O invokes a change of BO 3 triangles into BO 4 tetrahedrals. Addition of liCl leads to a more open boron-oxygen glass network and consequently to a decrease of the boron coordination number. Velocity autocorrelation functions, Raman and infrared spectra have been calculated and compared with experimental spectra. The frequency spectra of the Li and Cs atoms are in agreement with far IR measurements. The dominant parts of the overall vibrational density of states (DOS) spectra are due to nearest neighbor B-O stretching modes. The calculated IR spectra show one main peak, with a maximum at about 1100 cm −1 . This maximum shifts towards lower frequencies upon addition of alkali oxide, but no significant changes are observed if LiCl is added. These results are in agreement with experiment. For the calculation of the Raman spectra, only autocorrelated B-O bonds were taken into account. These calculations fail to reproduce the dominant experimental bands at 780 and 800 cm −1 . For a proper calculation of the Raman spectra of borate glasses, apparently cross-correlated B-O bond stretching vibrations should be taken into account.
25 citations
TL;DR: In this paper, a modified vertical Bridgman growth was used to make the solid-liquid interface planar, where instead of the usual radial symmetrical temperature conditions, a linear temperature gradient was created along the diameter of the cooling ingot during the growth.
18 citations
TL;DR: In this article, three impurity peaks at 4032, 6184, and 13831 cm −1 in the absorption spectrum of the Ga 2 Se 3 :Co 2+ (0.1 mole %) single crystals were observed.
15 citations
TL;DR: In this article, the authors studied the power law behavior of a rough metal-electrolyte interface characterized by a self-similar fractal geometry and showed that local field effects play an important role and have to be included explicitly in the model.
Abstract: The impedance of a rough metal-electrolyte interface is known to show a complex impedance of type Z(ω) ∼ (iω)−gh at low frequencies. We study this problem for interfaces characterized by a self-similar fractal geometry. In contrast to previous theoretical studies we show that: (i) local field effects play an important role and have to be included explicitly in the model; (ii) power law behaviour is obtained for a broad range of parameters but other behaviours are also possible; (iii) the exponent η depends explicitly on various features of the model and not only on the fractal dimensions of the surface.
13 citations
TL;DR: In this paper, various implantation effects which influence the performance and reproducibility of direct implantation GaAs integrated circuits and methods used to overcome/minimize them are discussed.
Abstract: Ion implantation is the most widely used process in semiconductor industry for selectively introducing controlled amount of impurities inGaAs. Various implantation effects which influence the performance and reproducibility of direct implantation GaAs integrated circuits and methods used to overcome/minimize them are discussed in this review. Abrief account of the implantation work being carried out in our laboratory towards fabrication of GaAs MESFETs and improving their performance and uniformity is also included here.
13 citations
TL;DR: In this paper, a nonlinear version of the random β-model where the fragmentation probability of an eddy depends directly on the activity of the neighbouring regimes is considered. And the authors point out how this generalization might be important for developing a first principle theory based on Navier-Strokes equations.
Abstract: We consider a nonlinear version of the random β-model where the fragmentation probability of an eddy depends directly on the activity of the neighbouring regimes. We present an exact calculation for the complete multifractal spectrum. Inspired by concepts recently introduced in the theory of fractal growth, we point out how this generalization might be important for developing a first principle theory based on the Navier-Strokes equations.
12 citations
TL;DR: In this paper, the energy band effect or Hume-Rothery rule was applied to the quasicrystalline series Al80Mn20-xFex and the isomer shift of the Mossbauer spectra showed a maximum at x=9, where e/a=1.76.
Abstract: In 1926 Hume Rothery discovered that for some simple alloys the electron to atom ratio e/a is a stability determining factor. We applied this energy band effect or Hume-Rothery rule to the quasicrystalline series Al80Mn20-xFex. The isomer shift of the Mossbauer spectra shows a maximum at x=9, where e/a=1.76. This strongly indicates a relatively low s-electron density, in agreement with the energy band effect.
11 citations
TL;DR: In this article, the effect of variation of tin concentration on the various hyperfine interactions has been discussed and it is concluded that in the cationic distribution of this series all Sn4+ ions occupy octahedral sites.
8 citations
TL;DR: In this paper, Li-Ga alloys of 54 different compositions were measured and the maximum liquidus temperature (739 °C) was observed not at 50 at.% Li but at 47.1 at.%.
Abstract: DSC measurements were performed for Li-Ga alloys of 54 different compositions. The solid compound at the maximum liquidus temperature (739 °C) is observed not at 50 at.% Li (as reported in previous studies) but at 47.1 at.% Li. A eutectic point was detected at 97 at.% Li, in excellent agreement with the result of Thummel and Klemm and in disagreement with that of Yatsenko et al., Solid compounds were found at 22.1, 33.3, 47.1, 60 and 66.7 at.% Li, of which those at 47.1 and 66.7 at.% Li seem to be accompanied by a non-stoichiometric region. The compound at 22.1 at.% Li corresponds to LiGa3.42, the existence and structure of which have recently been clarified by Belin.
TL;DR: In this article, the energy levels of Ni2+ ion were deduced and illustrated schematically relative to the band edges of MgGa2Se4 in the visible and near-infrared region.
TL;DR: In this article, an external magnetic field Hext≈5T was applied to obtain the asymmetry parameter ν, where ν = 0.7 for decagonal Al7(Mn0.7Fe 0.3) and ν=0.8 for icosahedral Al6Cr0.3.
Abstract: Mossbauer spectra of AlTFe-alloys with T=Cr or Mn, show a quadrupole splitting QS≈0.4 mm/s. This shows that the iron atom is not in an icosahedral site. In order to investigate the local symmetry further, we applied an external magnetic field Hext≈5T, so that the asymmetry parameter ν can be obtained. Using a one site approximation the results are: ν=0.7 for decagonal Al7(Mn0.7Fe0.3)2 and ν=0.8 for icosahedral Al6Cr0.7Fe0.3. This means that the iron atoms are in sites with a symmetry lower than axially symmetric. Most of the vertices in a Penrose lattice show such a symmetry.
TL;DR: The theory of random walks in random barrier networks has been applied to describe the properties associated with the hopping motion of fluoride ions in single crystals as mentioned in this paper, and theoretically predicted features like anomalous diffusion, leveling off of the mean square displacement, and normal diffusion in the long-time limit can be observed for these crystals.
Abstract: The theory of random walks in random barrier networks has been applied to describe the properties associated with the hopping motion of fluoride ions in single crystals ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$. It appears that theoretically predicted features like anomalous diffusion, leveling off of the mean-square displacement, and normal diffusion in the long-time limit can be observed for these crystals.
TL;DR: In this article, the activated resistivity in the Hg08Cd02Te crystal was investigated and three activation energies were reported, all of which increase with increasing compensation, in conjunction with the variation of Hall coefficient and Hall mobility with temperature.
Abstract: We report first results on the activated resistivity inn- type Hg08Cd02Te crystals heavily compensated through native acceptor defects (double acceptor mercury vacancies) Three activation energies are reported, all of which increase with increasing compensation In conjunction with the variation of Hall coefficient and Hall mobility with temperature we conclude, i) formation of (donor+-acceptor−) pairs during stoichiometric annealing, ii) distortion of second acceptor states of the paired mercury vacancies to raise them near, or in the conduction band, and iii) the pair states, when occupied with electrons in the presence of excess unpaired donors, behave like localized donors, and when unoccupied, like electron traps and/or recombination centres
TL;DR: In this article, a method for the preparation of high Tc superconductor (HTSC) Bi/sub 2/CaSr/Sub 2/Cu/Sr 2/O/sub 3/ + CaO and SrCO/Sub 3/+ CuO was adopted, these were then mixed in the molar ratio 1:2.
TL;DR: In this article, a simple method to compute void distributions of random Cantor sets is developed, and a detailed calculation is presented for the void distribution of the random Cantor set used in a recent theory of fractal growth.
Abstract: A simple method to compute void distributions of random Cantor sets is developed. In particular, a detailed calculation is presented for the void distribution of the random Cantor set used in a recent theory of fractal growth. The exact results allow us to clarify and rediscuss some of the implicit assumptions made previously in this theory.
TL;DR: In this paper, the problem of 1/f noise in thin metal films and metal-insulator composites in the scaling fractal regime near percolation threshold is considered.
Abstract: The problem of 1/f noise in thin metal films and metal-insulator composites in the scaling fractal regime near percolation threshold is considered. The correspondence between a percolation transition and a second order phase transition is extended from the point of view of electronic polarization and electrical fluctuations. The charge fluctuations on finite fractal clusters are argued to be analogous to spontaneous order parameter fluctuations in phase transitions, being correlated upto percolation correlation length. The charge relaxation times are shown to be related to the cluster sizes having distribution function of the formg(τ)∝τ−b
, whereb is connected to Euclidean and fractal dimensionalities and critical exponents. This produces the 1/f noise spectrum. Below percolation threshold, the nodes-links-blobs picture is invoked such that the blobs represent metallic conductances of the finite clusters and the links are tunnelling conductances between them through narrowest barrier regions. Above threshold, the finite cluster network is visualized as connected to the infinite cluster through narrowest tunnelling regions. The correlated spontaneous charge fluctuation on finite fractal clusters is held responsible for conductance fluctuation on either side of the metal-insulator transition via tunnelling processes. Finally, the scaling behaviour of noise magnitude near percolation threshold is explained.
TL;DR: In this paper, a stoichiometric annealing treatment is proposed for removing the tellurium precipitates from Hg0.8Cd0.2Te crystals grown by solid state recrystallisation.
Abstract: A stoichiometric annealing treatment is proposed for removing the tellurium precipitates from Hg0.8Cd0.2Te crystals grown by solid state recrystallisation. The fact that the chemical potential of tellurium decreases with increasing x in Hg saturated Hg1−xCdxTe is high-lighted and utilized in evolving the treatment. An Hg–Hg0.7Cd0.3Te source is used for annealing the bulk grown Hg0.8Cd0.2Te wafers. The annealing was carried out isothermally first at 420 °C and subsequently at 260 °C. Because of the retrograde solubility of Te in MCT the Te microprecipitates are partly dissolved back into the matrix at 420 °C and the remaining excess of Te is driven out into the ambient under the chemical potential gradient provided by the source. The proposed treatment almost completely eliminates the wafer-to-wafer and batch-to-batch variation in electrical properties of the low-temperature annealed Hg0.8Cd0.2Te crystals.
Es wird ein stoichiometrisches Temperverfahren vorgeschlagen zur Beseitigung von Te-Prazipitaten in Hg0.8Cd0.2Te-Kristallen, die durch Festkorper-Rekristallisation hergestellt worden sind. Die Abnahme des chemischen Potentials des Tellurs mit wachsendem x in Hg-gesattigtem Hg1−x · CdxTe wird zur Optimierung des Verfahrens genutzt. Verwendet wird eine Hg-Hg0,7Cd0,3Te-Quelle zur Temperung der Hg0,8Cd0,2Te-Proben. Die Temperung erfolgt isothermisch zunachst bei 420 °C und danach bei 260 °C. Wegen der rucklaufigen Loslichkeit des Te in MCT werden die Te-Prazipitate bei 420 °C wieder partiell in der Matrix gelost, und der verbleibende Te-Uberschus wird durch den chemischen Potentialgradienten, der durch die Quelle aufrecht erhalten wird, in die Umgebung herausgetrieben. Das vorgeschlagene Verfahren eliminiert fast vollstandig die Schwankungen von Scheibe zu Scheibe und von Charge zu Charge in den elektrischen Eigenschaften der bei tiefen Temperaturen getemperten Hg0,8Cd0,2Te-Kristalle.
TL;DR: In this paper, the optical absorption spectra of SbSI: Ni single crystal were investigated, and also the electronic states of nickel impurity in the Sb SI: Ni crystal were identified.
TL;DR: In this paper, a densification suffisante permet d'ameliorer les proprietes supraconductrices des composes is proposed, i.e., les conditions de recuit permettent l'alignement des cristallites le long de la direction preferentielle de suprAConductivite.
Abstract: La densification suffisante permet d'ameliorer les proprietes supraconductrices des composes. Ceci semble du a une meilleure connection entre les grains supraconducteurs. Si les conditions de recuit permettent l'alignement des cristallites le long de la direction preferentielle de supraconductivite, les proprietes se trouvent ameliorees
TL;DR: In this article, gate oxides for MOS devices were grown in the presence of 1,1,1 trichloroethane (TCA) as a chlorine source.
TL;DR: In this paper, the two-step gate oxidation process is studied for growing highly reliable gate oxides for MOS devices using 1,1,1-trichloroethane as a chlorine source.
TL;DR: In this article, the authors measured inelastic neutron scattering spectra of the molten alloys Au 0.4 Cs 0.5 and AU 0.6 using the time-of-flight spectrometer IN5 at the Institut Laue-Langevin.
Abstract: We have measured inelastic neutron scattering spectra of the molten alloys Au 0.5 Cs 0.5 and Au 0.4 Cs 0.6 using the time-of-flight spectrometer IN5 at the Institut Laue-Langevin. Only small differences are observed between the spectra of the two samples, despite the fact that the former has a typically ionic conductivity, and the latter a typically metallic conductivity, two orders of magnitude higher. These results are consistent with a model where the Au 0.4 Cs 0.6 melt consists of segregated ionic (Au - Cs + ) regions and metallic (Cs + e - ) regions.
TL;DR: In this article, the infrared and Raman spectra of crystalline samples of NdP5O14, NaNdP4O12 and KNdP 4O12 are recorded.
Abstract: The infrared and Raman spectra of crystalline samples of NdP5O14, NaNdP4O12 and KNdP4O12 are recorded. The spectra are analysed on the basis of vibrations of P=O, P-O, PO2 and P-O-P groups. The P4O 12 4− ion has cyclic structures both in NaNdP4O12 and KNdP4O12 crystals. It has been inferred that the P-O-P bridges are stronger in metaphosphates.
TL;DR: In this paper, Li-Ga alloys of 54 different compositions were measured and the maximum liquidus temperature (739 °C) was observed not at 50 at.% Li but at 47.1 at.%.
Abstract: DSC measurements were performed for Li-Ga alloys of 54 different compositions. The solid compound at the maximum liquidus temperature (739 °C) is observed not at 50 at.% Li (as reported in previous studies) but at 47.1 at.% Li. A eutectic point was detected at 97 at.% Li, in excellent agreement with the result of Thummel and Klemm and in disagreement with that of Yatsenko et al., Solid compounds were found at 22.1, 33.3, 47.1, 60 and 66.7 at.% Li, of which those at 47.1 and 66.7 at.% Li seem to be accompanied by a non-stoichiometric region. The compound at 22.1 at.% Li corresponds to LiGa3.42, the existence and structure of which have recently been clarified by Belin.
01 Jan 1989
TL;DR: This approach clarifies the origin of fractal structures in these models and provides a systematic method for the calculation of the fractal dimension and the multifractal properties and makes clear why the usual renormalization schemes are not very suitable for these problems.
Abstract: In order to understand the physical origin of fractal structures the first step is to formulate models of fractal growth based on physical mechanisms like the Diffusion Limited Aggregation and the more General Dielectric Breakdown Model. They are based on a simple iterative process governed by the Laplace equation and a stochastic field and they give rise to patterns that spontaneously evolve into random fractal structures of great complexity. In addition one would like to achieve a theoretical understanding of these models similar to that provided by the Renormalization Group for Ising-type models. Recently we have introduced a new theoretical framework for intrinsically critical growth models. This method is based on a Fixed Scale Transformation (with respect to the dynamical evolution) that defines a functional iteration for the distribution of elementary configurations that appear in a coarse graining process. This allows to include screening effects in terms of convergent series and to describe the intrinsic fluctuations of the boundary conditions. This approach clarifies the origin of fractal structures in these models and provides a systematic method for the calculation of the fractal dimension and the multifractal properties. It also makes clear why the usual renormalization schemes are not very suitable for these problems. Here we describe the basic ideas of this new approach and report about recent developments including the application to the fractal dimension of the percolating cluster interpreted as a problem of fractal growth.