Showing papers by "Solid State Physics Laboratory published in 1984"

Liquid alloys with strong chemical interactions

Abstract: Information about basic chemical interactions and the electronic structure of liquid compounds can be obtained from the study of the appropriate solid compounds. Using this guideline, the properties of alkali-group 1B, IIIB, IVB and VB alloys are discussed and models for band structures are considered. Evidence is provided for a competition between simple octet and clustered configurations. In either of them the band structure appears to be largely determined by the anions. In charge-transfer clustered compounds both the crystal structure and the band structure are closely related to those of the pure elements in the next group of the periodic table.

Experimental results for liquid alkali-group IV alloys

Abstract: Neutron diffraction experiments and measurements of the Knight shift and the electrical resistivity are presented for the liquid systems LiSn, NaPb, NaSn, LiGe, KPb and RbPb. They provide strong evidence for compound formation. There are indications for the existence of anion-clusters in all of these systems, except in LiSn.

Order parameters of a nematic liquid-crystal with low optical anisotropy as determined by depolarized raman-scattering

Abstract: Depolarized Raman measurements are reported for the order parameters and of a partially hydrogenated nematic compound. Similar to the situation observed for some nematic compounds of large birefringence the value of is anomalously low compared with theoretical predictions. Furthermore, resonant Raman measurements are reported for coloured probe molecules dissolved in the nematic compound. The order parameters of the probe are not typical for the ordering of the host-material Mesure en diffusion Raman polarisee des parametres d'ordre et de composes nematiques partiellement hydrogenes. Comme dans le cas des composes possedant une birefringence elevee, est beaucoup plus petit que la prediction theorique. En utilisant l'effet Raman resonant, les parametres d'ordre d'une sonde coloree dissoute dans le compose nematique ne representent pas l'ordre orientationnel de l'hote

Mossbauer isomer-shifts and quadrupole splittings in the amorphous iron-boron system

Abstract: The isomer shifts and quadrupoole splittings of amorphous Fe x B 1−x alloys (10 a/o ⪅ × ⪅ 90 a/o) were studied by 57 Fe Mossbauer spectroscopy. The isomer shift vs. composition can be described by the ▵φ ∗− and ▵n WS -terms of Miedema's cellular model to predict the heat of formation of binary alloys and an additional volume mismatch term. This term is necessary for boron-rich alloys ( x ⪅ 50 a/o). We conclude that these samples have a strained atomic structure. The values of the quadrupole splittings at the boron-rich side increase strongly, indicating that the Fe-atoms are squeezed into asymmetric atomic surroundings. Implanted iron into crystalline boron has a comparable isomer shift and quadrupole splitting as the boron-rich alloys.

Mössbauer Studies on Hyperfine Interactions in Titanium Substituted Lithium Ferrites

Abstract: Mossbauer spectra of Li0.5so+0.5xTix Fe2.5-1.5xO4, with x ranging from 0 to 1.2 are obtained at 300 and 78 K. Well defined hyperfine Zeeman spectra are observed for samples with x ≦ 5 0.6 at 300 K and for x ≦ 0.8 at 78 K and resolved into two sextets corresponding to octahedral and tetrahedral sites. The samples with x = 0.2 to 0.6 show a central doublet a t both the temperatures which is attributed to the presence of superparamagnetic clusters. Relaxation effects are observed for the samples with r = 0.8 and 1.0 at 300 K and with x = 1.0 and 1.2 at 78 K, while the sample with x = 1.2 at 300 K exhibits paramagnetic behaviour. There is no change in isomer shift with increasing Ti4+ substitution. The decrease in the magnetic field at 57Fe nucleus is explained in terms of exchange interactions and a canted spin arrangement on the tetrahedral sublattice. Bei 300 und 78 K werden die Mosbauerspektren von Li0,5+0,5xTixFe2,5-1,5x,04 (x im Bereich von 0 bis 1,2) itufgenommen. Wohldefinierte Zeeman-Hyperfeinspektren werden fur Proben mit x = 0,6 bei 300 K und fur x = 0,8 bei 78 K beobachtet und in zwei Sextetts entsprechend den oktaedrisrhen nnd tetraedrischen Platzen aufgeliist. Die Proben mib x = 0,2 bis 0,6 zeigen ein zentrales Dublett bei beiden Temperaturen, das auf die Anweseneheit von superparamagnetischen Clustern zuruckgefiihrt wird. Relaxationseffekte werden fur Proben mit x = 0, s und 1,0 bei 300 K und mit z = 1,0 und 1,2 bei 78 K beobachtet, wahrend die Probe mit, x = 1,2 bei 300 K paramagnetisches Verhalten zeigt. Es gibt keine Andernng an der Isomerverschiebung mit an- steigender Ti4+-Substitution. Der Abfall des magnetischen Feldes am 57Fe-Kern w-ird mit Aus- twuschwechselwirkungen und gekippter Spinanordnung des tetraedrischen Untergitters erklart.

Fabrication and Characterization of Metal-Semiconductor Schottky Barrier Junctions

Abstract: Metal-semiconductor contacts showing rectifying properties are finding more and more applications in modern semiconductor devices technology(1) Apart from the fact that they are comparatively easy to fabricate and incorporate into integrated circuits, the main reason for their wide usage is that they do not exhibit minority carrier effects (e.g., long reverse recovery time, diffusion capacitance, etc.) similar to those observed in p-n junction devices. Various metal-semiconductor systems, investigated during the last two decades, are tabulated in Table 1. It can be seen from this table that the investigations are mainly centered round Schottky contacts based on Si and GaAs. Amongst the two, Si-based Schottky contacts are at present being used in a wide variety of devices and integrated circuits. Recent advances in GaAs material and processing techniques have, however, shown that not only can all of the semiconductor device structures realized in Si be fabricated in GaAs, but optical and very high speed integrated circuits can also be realized in the not-too-distant future. It is because of this as well as metallurgical and reliability considerations that the activity pertaining to GaAs-based Schottky contacts has increased appreciably during the last few years.

On the microhardness of some organic molecular solids

Abstract: Microhardness measurements have been carried out on the (001) cleavage surfaces of anthracene, Phenanthrene and benzoic acid single crystals. The variation of the Vicker's Hardness Number (VHN) with load (P) shows a decrease in hardness with increasing load. Plots of load (P) vs the square of the diagonal (d2) and logarithm of load (log P) vs logarithm of diagonal (log d) are found to be linear. These observations are being explained in terms of the geometrical packing of molecules in these crystals which play an important role in causing slip.

Curie temperatures and 0°K magnetic moments of zinc-substituted lithium ferrites

Abstract: Because of their several attractive features including relatively high Curie temperatures, substituted lithium ferrites have become important for applications at microwave frequencies. Neel collinear arrangement of spins onA andB sublattices is unable to satisfactorily explain the 0°K saturation moments and the observed Curie temperatures of the zinc-substituted lithium ferrites, especially at concentrations of zincz>0·3 in the formula Li0·5−z/2ZnzFe2·5−z/2O4. Rosencaig’s localized canting model has been extended and used to compute 0°K magnetic moments and Curie temperatures of these ferrites with substitution levels up toz=0·7. Reasonably good agreement between the calculated and experimental values, both for the 0°K magnetic moments and the Curie temperatures, has been obtained using exchange parameters ratios based on the valuesJaa=−20°K,Jbb=−8°K andJab=Jba=−29°K.

Dipoles in solid-solutions sr1-xgdxf2+x

Abstract: In this paper we present new results on the dielectric relaxation behavior of solid solutions of the type ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x}{\mathrm{F}}_{2+x}$. Attention will be paid to dipole relaxation peaks associated with two different complexes: (a) the nearest-neighbor (NN) ${\mathrm{Gd}}^{3+}\ensuremath{-}{{\mathrm{F}}_{i}}^{\ensuremath{-}}$ dipole and (b) the next-nearest-neighbor (NNN) ${\mathrm{Gd}}^{3+}\ensuremath{-}{{\mathrm{F}}_{i}}^{\ensuremath{-}}$ center. The experiments have been carried out in the frequency range from 100 to ${3\ifmmode\times\else\texttimes\fi{}10}^{4}$ Hz. From the behavior of the NN and NNN dipole relaxation bands as a function of the excitation frequency, we have determined the energy difference between the two different dipole configurations to be about 0.050 eV. In addition, we have studied the intensity of the dipole bands as a function of the concentration ($x$) of ${\mathrm{Gd}}^{3+}$ ions. It is possible to explain the observed behavior of the intensity of the dipole relaxation peaks as a function of $x$ without the need of assuming that there is extensive clustering of ${\mathrm{Gd}}^{3+}$ impurities. We propose to divide the dipoles into two different groups: The first one contains dipoles that are not disturbed severely by extremely close dipoles, contributing to the dipole relaxation peak; the second group of dipoles, which are at close distances from at least a second dipole, contributes significantly to the dc-ionic-conduction process.

Electron microscope studies of phase transformations in thin films of Tin Diselenide

Abstract: The present investigations explore the structural characteristics of the thin films of tin diselenide (SnSe2). Unlike bulk, only sparse studies are available on the structural characteristics in the thin form. SnSe2 is known to exhibit almost exclusively the 2H CdI2 type structure in bulk (single crystal) form. Particular emphasis on phase formation and structural transformations obtained in the thin film form has been given. The results reveal that all as-deposited films are amorphous in nature and undergo an amorphous crystalline transformation upon pulse annealing (∼200 °C), the crystalline phase exhibiting the 2H bulk structure. Further pulse annealing at higher temperatures (∼300 to 500 °C) results in thermal decomposition of this 2H phase, giving rise to several other phases, namely SnSe (orthorhombic), SnSe (cubic) and Sn2Se3 (tetragonal) phases, the SnSe phases exhibiting variations in lattice parameters. In addition, a new incommensurate phase of SnSe has been obtained. A model is proposed for the formation of this phase from the orthorhombie SnSe phase. The final product of decomposition is found to be tetragonal tin. In dieser Arbeit werden die Struktureigenschaften von SnSe2 Dunnschichten untersucht. Im Gegensatz zum massiven Material existieren nur wenige Studien uber die Struktureigenschaften von Dunnschichten. SnSe2 hat meistens den 2H-CdI2 Strukturtyp in der Einkristallform. Besondere Betonung wurde auf die Phasenbildung und die strukturellen Umwandlungen, die in der Dunnschichtform auftreten, gelegt. Die Ergebnisse zeigen, das alle aufgedampften Schichten in der Natur amorph sind und sich von amorph nach kristallin unter Impulstemperung (∼200°C) umwandelt, wobei die Kristallphase die 2H-Struktur besitzt. Weitere Impulstemperung bei hoheren Temperaturen (∼300°C bis 500°C) verursacht eine thermische Zerlegung dieser 2H-Phase in mehrere verschiedene Phasen, namlich SnSe-(orthorhombisch), SnSe-(kubisch) und Sn2Se3-(tetragonal)-Phasen, wobei die SnSe-Phasen Anderungen in Gitterparametern zeigen. Zusatzlich wurde eine neue inkommensurable Phase von SnSe beobachtet. Ein Modell wurde fur die Bildung dieser Phase aus der orthorhombischen SnSe-Phase vorgeschlagen. Als Endprodukt der Zerlegung stellte sich das tetragonale Zinn heraus.

Current gain of silicon bipolar transistor with polysilicon emitter contact

Abstract: A two-region analysis is presented to predict the common-emitter current gain of a bipolar transistor with the polysilicon contact to the emitter for a case when the recombinations at the mono-poly interface are not negligible. The calculated current-gain enhancement for typical device parameters and for different values of interface recombination velocity show that the current-gain enhancement and its increase with decrease of emitter width is smaller for the interface with larger recombinations.

A Simple Solar Cell Characteristics Plotter

Abstract: A simple and economical system for the measurement of current voltage characteristics of solar cells has been described. Facility for the detection and marking of maximum power point on the I-V characteristic of the cell under illumination has also been added to facilitate the solar cell panel designer to avoid the hot spots in the panel.