Showing papers by "Solid State Physics Laboratory published in 1982"
TL;DR: In this paper, the authors described the reentrant behavior in nematic liquid crystals by the treatment of the system as a mixture of monomers and dimers interacting through attractive induced soft interactions as well as hard core repulsions.
Abstract: Reentrant behavior in nematic liquid crystals is described by the treatment of the system as a mixture of monomers and dimers interacting through attractive induced soft interactions as well as hard-core repulsions It is shown that the induced forces between dimers, monomers, and between monomers and dimers, respectively, under suitable conditions of temperature and density lead to a smectic layer structure with a period equal to the length of the dimer However, with decreasing temperature or increasing density, repulsive steric forces, due to the unfavorable packing of the dimers in the smectic planes, may take over and thus favor the nematic phase again In agreement with experiment the best conditions to get a reentrant nematic phase are predicted for the ratio of the length of the dimer to that of the monomer between 13 and 14 The predictions of the model are in good agreement with currently available experimental data In principle, the model applies also to discotic liquid crystals
109 citations
TL;DR: In this article, the diamagnetic anisotropy of thirteen nematic liquid crystals is measured and the critical behavior of S near the nematic-isotropic phase transition can be described by an exponent 03B2 of the order of 0.25.
Abstract: Measurements are presented for the diamagnetic anisotropy of thirteen nematic liquid crystals. As any bias in the rotation around the long molecular axis is most probably small, the results probe accurately the temperature variations of S, the degree of orientational order. The critical behaviour of S near the nematic-isotropic phase transition can be described by an exponent 03B2 of the order of 0.25. Procedures are considered to obtain the molecular magnetic anisotropy. By a systematic variation of the structure of the molecules an impression of the contributions of the various molecular groups can be obtained It turns out to be rather difficult to obtain accurate data for the molecular magnetic anisotropy. As a consequence the absolute scale of S can only be fixed with an accuracy of the order of 10 %. J. Physique 43 (1982) 361-367 FTVRIER 1982,
104 citations
TL;DR: In this paper, it was shown that the even part of the distribution of the dominant hyperfine interaction (hyperfine field or quadrupole splitting) can be obtained directly without using least-square fitting procedures.
40 citations
TL;DR: In this paper, the Penn model for the dielectric constant of semiconductors is used to construct a general interrelation between the energy band gap and high frequency refractive index.
29 citations
20 citations
TL;DR: In this article, the phase transition sequence of nematic-smectic A-reentrant nematic was studied and the first phase transition can be understood by a combination of pairing of the terminally strongly polar molecules and a simple extension of McMillan's theory of the smectic phase to asymmetric molecules.
15 citations
TL;DR: Theoretical expressions for both the forward current-induced voltage decay (FCVD) and the photovoltage decay (PVD) in a base-dominated back-surface field (BSF) solar cell of arbitrary thickness were derived in this article.
13 citations
TL;DR: In this article, the influence of defect concentration on the relaxation of space charges in solid solutions has been investigated with the ionic-thermocurrent technique, and a percolation model has been used to explain these shifts.
Abstract: The influence of the defect concentration on the relaxation of space charges in ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ solid solutions has been investigated with the ionic-thermocurrent technique. A concentration domain of 0.004 up to 45 mol% has been used. As in the system ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$ the space-charge relaxation band (high-temperature band) shifts to lower temperatures with increasing $R{\mathrm{F}}_{3}$ concentration. A percolation model has been used to explain these shifts. Most of the differences between the systems ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ and ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$ are reducible to different dipolelike jumps supporting the charge transport: nearest-neighbor dipolelike jumps in ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ and next-nearest-neighbor dipolelike jumps in ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$. The charge transport may be interpreted qualitatively with a percolation mechanism.
10 citations
TL;DR: In this paper, a semi-empirical model for the calculation of the Gibbs free energy of mixing via the entropy of mixing, proposed by Visser et al., is used to determine the activity coefficients and the long-wavelength limit of the structure factor, S CC (0).
Abstract: The semi-empirical model for the calculation of the Gibbs free energy of mixing via the entropy of mixing, proposed by Visser et al. [1], is used to determine the activity coefficients and the long-wavelength limit of the structure factor, S CC (0). For the liquid alloys systems NaK and KCs the method leads to fairly accurate results, indicating almost ideal behaviour. For the compound-forming liquid alloys systems LiPb the agreement with experiment is less favourable, but the calculations clearly demonstrate the important influence of the volume contraction on the entropy.
8 citations
TL;DR: In this article, a high injection theory of open circuit voltage decay in a p - n junction diode is given, which takes into account the saturation of junction voltage at high injections and coupling between emitter and base of the diode.
Abstract: A high injection theory of open circuit voltage decay in a p - n junction diode is given. The theory takes into account the saturation of junction voltage at high injections and coupling between emitter and base of the diode. The results are in qualitative agreement with the available experimental results. In particular the theory explains the plateau which has been observed in most experimental results on the open circuit voltage decay at high injections.
7 citations
TL;DR: In this article, the ionic conductivity of dilute Sr 1 −xYb x F 2 +x solid solutions has been studied as a function of temperature and a re-analysis of the conductivity data for SrF 2 leads to the value 2.70 eV for intrinsic defect formation, contrary to reported values which range from 2.2 to 2.3 eV.
TL;DR: In this article, the authors measured the lifetime of Si and Ge p-n-junction diodes using reverse recovery and forward current-induced voltage decay methods and found that the lifetime always increases with injection level if the effect of the finite thickness of the base of the diode is taken into account while interpreting the experimental results.
Abstract: Minority-carrier lifetime as a function of level of injection has been measured for a number of Si and Ge p-n-junction diodes using reverse recovery and forward current-induced voltage decay methods. It is found that the lifetime always increases with injection level if the effect of the finite thickness of the base of the diode is taken into account while interpreting the experimental results. The decrease in the life-time values reported in the literature appears to be due to erroneous interpretation of the experimental data.
TL;DR: The magnetization and magnetoresistance of ferromagnetic melt-quenched amorphous Fe x B 1−x has been measured in this article and the magnetization indicates no saturation to fields above 30 tesla.
TL;DR: In this paper, the frequency dependence of free carrier relaxation time in the plasma reflectivity studies of semiconductors is accounted for on a two-carrier model by including the energy dependence of carrier relaxation times.
TL;DR: In this article, the pitch is temperature independent, which is a general result, and does not influence the discontinuity of the main (nematic) order parameter at the isotropic-cholesteric transition.
Abstract: The cholesteric state is discussed in terms of a model consisting of the Maier-Saupe and a twist interaction. The model can be easily solved in the mean field approximation. In the practical case of a large pitch analytical expressions are obtained for relevant quantities like the order parameters and the free energy. Then it appears that the pitch is temperature independent, which is a general result, and does not influence the discontinuity of the main (nematic) order parameter at the isotropic-cholesteric transition. Interactions giving rise to a temperature-dependent pitch are discussed briefly.
TL;DR: In this paper, the liquidus and solidus temperatures of Li-Cd alloys with compositions between 35 and 100 at % Cd have been determined by means of resistivity measurements and differential scanning calorimetry.
TL;DR: In this article, an analysis of gate failures in GaAs field effect transistors (FETs) was carried out and the volume changes and lattice mismatch gave rise to mechanical strains causing metallurgical failure of the Ti/Pt layers and consequently the formation of Au-Al intermetallics.
TL;DR: In this paper, the decomposition kinetics of the crystalline Fe3B intermetallic compound to α-Fe and Fe2B were investigated and the exponents characteristic of the kinetic processes in the crystallization and decomposition transformation were determined.
TL;DR: In this article, the diffusion length and lifetime of minority carriers in n+p Si-solar cells were measured based on capacitance measurements in forward bias condition at room and liquid air temperatures, where the solar cell was not biased by an external dc source, but was forwardbiased by its own photovoltage generated by illumination.
Abstract: Many methods have been developed for the measurement of the diffusion length and lifetime of minority carriers in p-n junction solar cells. This paper presents a new technique for the measurement of these parameters, based on capacitance measurements in forward-bias condition at room and liquid air temperatures. In this experiment the solar cell was not biased by an external dc source, but was forward-biased by its own photovoltage generated by illumination. The results give 135 um diffusion length and 5.2 µsec lifetime of the minority carriers in a n+-p Si-solar cell.
TL;DR: In this paper, the 7Li Knight shift in liquid Li-Mg alloys is found to be a linear, decreasing function of the magnesium concentration, which is explained qualitatively in terms of transfer of Fermi electrons from the Li to the Mg cells, in agreement with calculations of the local density of states in solid LiMg.
Abstract: The 7Li Knight shift in liquid Li-Mg alloys is found to be a linear, decreasing function of the magnesium concentration. This result is explained qualitatively in terms of transfer of Fermi electrons from the Li to the Mg cells, in agreement with calculations of the local density of states in solid LiMg by Inglesfield. The Korringa enhancement increases monotonically when magnesium is added to lithium.
TL;DR: In this paper, it was shown that there are significant chemical interactions between the transition metal atoms and metalloids which are stronger between Ni and B than between Fe and B, and that Ni prefers neighbourhoods with more B neighbours than Fe as deduced from the Mossbauer studies.
TL;DR: In this paper, the process-dependent behavior of such heterostructures is explained on the basis of surface states at the insulator-semiconductor interface and fixed charge in the insulating oxide layer, and calculated efficiencies of various heterostructure solar cells which have indium tin oxide as one of the constituents are also presented.
TL;DR: In this paper, the influence of entropies and specific heats on the experimental structure factors used in the calculations was investigated and the applicability to liquid metallic elements with a non-simple liquid structure.
Abstract: Some further calculations of entropies, S , and specific heats, C p , have been carried out within the framework of the Percus-Yevick phonon theory. In particular, the following points were investigated: (1) the influence on S and C p of the experimental structure factors used in the calculations and (2) the applicability to liquid metallic elements with a non-simple liquid structure.
01 Jan 1982
01 Jan 1982
TL;DR: In this article, the ideality factor of Si02 passivated Ni-(n) GaAs Schottky barrier diodes was found to lie between 1.07 and 1.13 irrespective of the structural variations, including SiO2 passivation.
Abstract: The non-ideal I vs V and 1/C2 vs V plots of Si02 passivated Ni-(n) GaAs Schottky barrier diodes are primarily due to formation of an interfacial layer at the metal-semiconductor interface during Ni Evaporation and due to excess capacitance of the MOS structure appearing parallel to the junction capacitance, respectively. The ideality factor, η, of the diodes is found to lie between 1.07 and 1.13 irrespective of the structural variations inclusive of SiO2 passivation. The effect of impurity gradation in the active GaAs epitaxial layer of C-V characteristics is also discussed.
TL;DR: In this paper, a constant coupling theory based on exact solutions of some one-dimensional systems is proposed, which is applied to the Humpries-James-Luckhurst model of nematic liquid crystals.
TL;DR: In this paper, it was shown that steep forward or reverse biased nn+ junctions can affect microwave device performance due to their in-built high field oven before a stationary Gunn domain needs to be considered.
Abstract: It is shown that steep forward or reverse biased nn+ junctions can affect microwave device performance due to their in–built high field oven before a stationary Gunn domain needs to be considered (which up to now has been viewed as the main cause, for the observed high field regions).