Publications

For a 2D electron system in a 1D periodic potential modulation, a complicated structure of Shubnikov-de Haas peaks has been measured and qualitatively explained by a transport calculation including interaction effects in the Hartree-Fock approximation.

Photoelectric properties of PbTiO3/Si heterostructures were investigated over a broad range of wavelengths. The spectral distribution of the a.c. open-circuit voltage was measured for wavelengths ranging from 0.35 mu m to 4 mu m. Two local peaks are observed at 0.38 mu m and 0.9 mu m which can be attributed to band-to-band excitations in PbTiO3 and Si respectively. The shape of the a.c. signal depends both on the light intensity and on the wavelength. When the heterojunction is reverse-biased, a d.c. photocurrent was observed which has a similar spectral distribution as the a.c. open-circuit voltage.

The a-Si:H/electrolyte interface was studied using impedance spectroscopy (IS) method. The measurements were made in the frequency range of 100 Hz - 300 kHz and the potential range of -0.6 V - +0.8 V. The equivalent circuit suggested by the experimental curves allowed us to calculate the main parameters which characterize the interface and the mechanism through which the space charge region supplies carriers to the interface.

We present the results of dielectric- and differential scanning calorimetry investigations on several homologous of 4-n- alkoxybenzoic acids: in particular the 4-n-heptyl-, -octyl-, -nonyloxybenzoic acids are studied. Our measurements confirm the existence in the nematic phase of a textural transition, which on cooling changes a well ordered state, f.i. a twisted state, to a highly distorted one, characterized by the appearance of a multidomain structure. Such a transition turns out to be reversible, with a small hysteresis. The transition exhibits a clear evidence for the 4-n-octyl- and the 4-n-nonyloxybenzoic acids. On the contrary, the presence of this transition in the 4-n-heptyloxybenzoic acid is suggested by a small peak only in the curve of the dielectric permittivity. The effect of the simultaneous presence in the nematic phase of open and closed dimers and of cybotactic clusters can explain the observed dielectric behavior.

Purifying methods of cesium iodide are presented along with the reasons of their choice. Fractional recrystallization, drying in vacuum, chemical treatment with iodine and refining zone were used in this sequence. Impurity analysis regarded chlorine, bromine, iron and heavy metals. Finally the results show very low halogen level and reasonable level for metal.

Dosimetry from I-125 emitting Auger electrons in the follicles of the thyroid will improve when their complete interaction with the molecular structure about the Auger emitting atoms is known to Angstrom distances. Extended x-ray absorption fine structure (EXAFS) can provide this information. EXAFS experiments gave intermolecular and intramolecular distance for pure solid L-thyroxine (T-4) (C15H11I4NO4) using a model based on crystalline T-4 hydrochloride monohydrate (C15H11I4NO4HCl.H2O). For a solution of L-thyroxine the structure consists of the intramolecular distances found for T-4 and an additional shell of four carbon atoms distances of 2.01 Angstrom. Atomic density functions from Fourier transformed EXAFS measurements are suitable for estimating very short range interactions of Anger electrons in thyroid thyroglobulin over a radial distance of 7.71 Angstrom. Examination of density functions provided a plausible argument for the difference in biological effect between I-131 and I-125 in the thyroid.

The paper presents the current density peaks during the heating-up phase for different kind of quartzes: clear natural from Brazil, smoky natural, and synthetic quartz from Sawyer Research Product (Electronic and Premium Q), Toyo, romanian and polish ones, and compares the phenomenon in vacuum and in air for the same applied electric field and gives a model, with which the process could be described.

Laser spectroscopy has been applied to systematically investigate the effect of MgO or ZnO codoping on the Nd3+ centres formed in LiNbO3. Both codopant oxides produce the same effect, so two new Nd3+ centres appear in both LiNbO3(MgO):Nd and LiNbO3(ZnO):Nd crystals. These new centres correspond to a small percentage (less than 1%) of Nd3+ ions, which are displaced from Li+ sites to a new lattice site. The possible sites for these Nd3+ centres are discussed.