Publications

The present paper is a review of the data about the dislocations in the as-grown quartz crystal. The work presents some general considerations about dislocations, their origins and causes, methods of their observation and techniques to reduce the dislocations density. It is also shown a method to obtain a new shape crystal used in the positive X-seeds preparation.

Electron spin resonance (ESR) investigations of polyethylene, irradiated with accelerated sulphur ions, are reported- The temperature dependence of resonance line parameters in the range 20-260-degrees-C, has been studied. Additional ESR data on polyethylene irradiated with neutrons as well as on polyethylene thermally degraded in air are presented. The nature of the free radicals induced by irradiation is discussed.

A method for the single crystal growth of Yttrium Iron Garnet (YIG) in a PbO/PbF2/B2O3 flux mixture with a melt cooling rate of 1-2.5 degrees C/h is described. In order to keep constant the crystal stoichiometry as well as its specific structural and magnetic properties at such high rates of the cooling process, a previously sintered polycrystalline garnet has been used as raw material. The YIG single crystal quality was checked-up by metallographic analysis, X-ray diffraction, SEM, and magnetic susceptibility measurements.

Evidence for a frozen spin ground state and a mixed magnetic ordered and paramagnetic state at intermediate temperatures was found in Fe-57-doped LiNiO2, using Mossbauer spectroscopy. The magnetic measurements, in agreement with Mossbauer data, suggest short-range ferromagnetic correlations at low temperatures and the occurrence of a paramagnetic phase below the spin freezing temperature.

In-field Mossbauer studies have been performed on the Li-0.5(1+t)(l+r)Fe2.5-1.5tTitO4 system with 1.10 less than or equal to t less than or equal to 1.40. The disordered magnetic properties depend strongly on the chemical disorder and local order induced by thermal treatments. The results are in agreement with low- and high-field magnetization measurements. Locally canted states are observed, with the degree of magnetic disorder depending on the composition and (or) the local chemical disorder.

Photoluminescence studies on Si1-xGex layers exceeding the critical thickness show not only dislocation-related peaks D1,...,D4, but also in addition a broad band (T band), centered at similar to 110 meV below the strained alloy band gap. Depth profiling studies show that the T band is due to centers in the Si1-xGex. The excitation power dependence and high quantum efficiency of the T band can be explained by assuming that it is due to an isoelectronically trapped exciton. T-band line shapes were fitted by a model based on statistical fluctuations of the Ge content and their effect on the local gap energy.

In the presence of tin tetrachloride, the rate constant for the rebinding of CO to the triliganded hemoglobin, l'(4), is much increased and the number of molecules participating in the CO ligation is decreasing. The pH drops, but a proton consumption process also takes place at the same time. The heme and its environment do not seem to change much, but the tin complexing to protein is very probable. The oxidation of hemoglobin in the form of either oxy or carbonmonoxy occurs with rather high rate.

The uniform one-dimensional and square lattice hopping models are considered, where particles can be in one of two states at each site. Transport takes place by nearest neighborjumps between upper energy states. Trapping in lower energy states introduces correlations, the effect of which on the dc conductivity is estimated in the first step beyond the mean-field approximation.

Magnetic and Mossbauer experiments were performed on Fe100-xGdx thin films and on Fe80-xGdxB20 both in thin films and ribbons for x less-than-or-equal-to 20. The ferrimagnetic order is perturbed by the presence of B and Fe-interactions are.different. For small Gd content, the low anisotropy is in the film plane, while for greater Gd the anisotropy goes out of the plane giving typical features of hysteresis loops and strong decrease of Mossbauer hyperfine fields.