Volume 7, Issue 5
December 1985, pages 411-511
pp 411-417 December 1985
The heterogeneous nucleation theory of silicon on SiO2 and Si3N4 substrates has been developed using classical theory. It is shown that the experimental observations can be explained on the basis of the bond energies of O-H, N-H and Si-H. A reaction model is proposed for the growth of silicon on silicon from silane, using hydrogen as a carrier gas in the temperature region 600–900°C. The growth rate of silicon is shown to be equal toPSiH4PH2 when the partial pressure of hydrogen is high, and is independent of the total pressure and the partial pressure of hydrogen in the lower region.
pp 419-422 December 1985
The experimental data on the Hall measurements have been used to characterize deep electron trapping levels in Cr doped semi-insulating GaAs crystals. The energy of the level below the conduction band edge has been found to be ∼ 0·8 eV and is thought to be related to Ga vacancies in the host crystal and Cr impurities.
pp 423-426 December 1985
The technique of high pressure is utilized to study the carrier transport behaviour in doped and undoped bulk amorphous (GeSe3·5)100−xBix (x=0, 2, 4, 10) down to liquid nitrogen temperature to observe impurity induced modifications in amorphous semiconductors. It is observed that pressure induced effects in lightly doped (2 at % Bi) and heavily doped (x=4, 10) semiconductors are markedly different. Results are discussed in view of the incorporation behaviour of the bismuth impurity.
pp 427-457 December 1985
Doping with alkaline earth impurities converts the alkali halides into very efficient phosphors. LiF doped with Mg is extensively used in radiation dosimetry. However, the phenomenon of thermoluminescence in these materials is far from clear. LiF-tld 100 is artificially separated from the rest of the alkali halide phosphors. The available experimental data are not fully utilised in building a model for thermoluminescence processes. In this review, thermoluminescence properties of LiF-tld 100 and other alkali halide phosphors are discussed. The comparative study which points out several common points could be useful in understanding thetl processes in these phosphors.
pp 459-463 December 1985
A technique has been worked out for stabilizing polycrystalline MnO against oxidation in air without dopants and without exceeding a temperature of 800°C in the process. The material is active though highly resistant to oxidation.
pp 465-473 December 1985
Monophase Fe2W and FeMo intermetallics have been prepared by hydrogen reduction of Fe2WO6 and FeMoO4 oxides respectively below 1050 K. The ternary intermetallics Fe2W0·9Mo0·1 and FeMo0·9W0·1 have also been prepared by a similar method from the respective substituted oxides. The oxides and the intermetallics have been characterized by x-ray powder diffraction, x-ray photoelectron and Mössbauer spectroscopies. The observed negative isomer shift of Fe in the intermetallics is attributed to an increase in the electron density in Fe by electron transfer from W or Mo to Fe.
pp 475-481 December 1985
Procedure for hydrothermal transformation of natural clinoptilolite at 160°C is described. The synthesis is carried out in the system Na2O-Al2O3-SiO2-H2O. Products of 24–168 hr runs are characterized by x-ray diffraction,ir spectroscopy, energy dispersive analysis of x-rays (edax), and electron microscopy. Presence of analcime-type and faujasite-type zeolites in the final products is established. Si/Al ratio of the final mixed phase is estimated as 2·91. Spheroid crystals of analcime, fibrous crystals of mordenite (on analcime), and well developed polyhedral crystals of analcime-faujasite mixed phase are illustrated and described. It is shown that crystals grow by two-dimensional nucleation mechanism.
pp 483-489 December 1985
The current voltage behaviour of polycrystalline Tm2O3 has been investigated at 77 K and 300 K to 350 K. At low voltages, the conduction is ohmic while at higher voltages the current has a quadratic dependence on voltage. The voltageVT at which the transition from ohmic to non-ohmic conduction takes place changes from 180 V to 100 V as temperature increases from 77 K to 350 K. The results are interpreted in terms of the Rose theory of space charge limited currents (sclc) in defect insulators containing shallow traps.
pp 491-497 December 1985
The electrical resistivities of organic charge transfer complexes namely dithionaphthalene-iodine (1:1), anthracene-trinitrobenzene (1:1), pyrene-2I2 and benzidine-tcnq (dichloromethane) have been studied upto 2–8 GPa pressure. An increase in the electrical resistivities shows that the conduction is due to a hopping mechanism involving localized levels near the band edges or is trap-limited. Pressure can increase both the density of defects and intermolecular orbital overlap as opposite effects.
pp 499-507 December 1985
The influence of incident beam divergence on the length of the streak intercepted by the Ewald sphere is considered, as a relpHK·L of a faulted hexagonal crystal, mounted about itsc-axis on the goniometer head attached to the ø-circle, is brought into diffracting condition for the bisecting setting of a 4-circle diffractometer. For the special crystal mounting correction factors required to convert the measured intensities corresponding to a fixed length of the streak are derived. A procedure for experimentally verifying the mathematical approach employed in these derivations is also presented.
pp 509-511 December 1985
The magnon contribution to the specific heat of ferromagnetic terbium is evaluated and the results are compared with the measurements from 90 K down to absolute zero.
Volume 42 | Issue 6
Click here for Editorial Note on CAP Mode