Publications

X-ray diffraction and transmission experiments as well as hardness measurements on virgin and ultra violet (UV)-irradiated amorphous films in the system GexAs40-xS60 have been performed. The W-light determines the plm softening for x19. The structure remains amorphous but the distance characteristic to medium range order (MRO) shows variations as a function of composition and irradiation time. The main effect of the UV light is the release of a significant amount of sulphur.

Samples consisting of Ni0.8Zn0.2Fe2O4 nanoparticles, both interconnected or dispersed in a matrix, were prepared by high energy ball milling, starting from bulk material previously synthesised by the conventional ceramic method at 1250 degrees C under O-2 flux. Samples with different grain size were performed. The as-milled samples were characterised by chemical analysis, X-ray diffraction and transmission electron microscopy (TEM). The nondispersed samples consist of grains with a mean size of 100 nm and a large size distribution. The dispersed powder in silica shows individual particles almost spherical with size ranging from 8 up to 50 nm. A good agreement was obtained between X-ray and TEM results. Because the as-milled powder showed after 200 hours of milling a high impurity degree, due to the stainless steel vial and balls, an original method was used to separate the phases. Magnetic measurements and Mossbauer spectra were performed.

The paper presents the first results obtained on-the hydrogen ion implantation in polycrystalline ZnO thin films. The ion implantation was carried out with a Kaufman type ion source. The results obtained after the experimental determination of the penetration depth are very close to the ones computed on the basis of the usual theory for monocrystals.

The non-crystalline semiconductors (amorphous tetrahedrally bonded Si, Ge, amorphous and vitreous chalcogenides) exhibit a domain structure. These domains (which we call amorphites) have very small size (1-3 nm) and are separated by abrupt interfaces with highly distorted covalent bonds. The diffraction effects produced by short-wavelength electromagnetic radiation (X-rays) in various simulated networks have been investigated.

Thin films of Aurivillius-type layered perovskites of Bi4Ti3O12 and SrBi2Ta2O9 have been epitaxially deposited by PLD on SrTiO3 single crystal substrates. Bi4Ti3O12 has been deposited as well on a CeO2/YSZ/Si(100) buffer layer, and on Pt-coated oxidized silicon for electrical measurements. Using a new technique for large area PLD, Bi4Ti3O12 has also been deposited on a whole (100)-oriented 3 '' Si wafer. The obtained films have a homogeneous thickness over the whole wafer corresponding to an area of about 45 cm(2). The composition, structure, and electrical properties of the films are presented.

Parallel and series pyroelectric bimorph structures, with 2-2 connectivity, are theoretically analysed to obtain the electric fields inside the two component phases. The proposed model takes into consideration the possibility of an electrical interaction between the two phases. It is demonstrated that the value of the internal electric field, due to the pyroelectric charge generated during heating of the bimorph structure, is considerably different than the case where each of the two phases is heated separately. It is shown that the value and the orientation of the electric fields inside the two phases of the bimorph depend on the value of the pyroelectric coefficients and dielectric constants of the two phases. The most interesting result is obtained in the case of the series bimorph, where the orientation of the electric field inside the phase with a lower pyroelectric coefficent is opposite to the orientation of spontaneous polarisation of this phase.

The crystal structure of Bi-2212 phase was studied by XRD, TEM, HREM and SAED. Bi-2212 specimens with different Sr/Ca ratios have the same displacive incommensurate Bi modulation vector q(1) approximate to 0.21b*+c* but exhibit different superconducting critical temperatures T-c. The structural modulation does not influence the T-c value which is controlled by the cation concentration and the oxygen content. A Pb addition leads to a superposition of the incommensurate Pb-modulation characterized by a modulation vector q(2) approximate to +/- 0.16 b*, on the already observed Bi modulation. Typical structural disordering (stacking faults, Bi-layer delineation effects, a-b plane misorientation) was found.

The paper describes some results concerning technology and behaviour of X-and gamma-ray N+PP+ silicon detectors used in physics research, industrial and medical radiography and non-destructive testing. These detectors work at the room-temperature and can be used individually to detect X-and soft gamma-rays, or coupled with scintillators for higher incoming energies. Electrical characteristics of these photodiodes, their modification after exposure to radiation and results of spectroscopic X-and gamma-ray measurements are discussed Devices manufactured under this technology proved to be stable after an exposure in high intensity gamma field with the dose range of 10 krad-5 Mrad: Nuclear radiation resistance was studied by irradiation with Co-60 gamma source (1.17, 1.33 MeV) at dose rates of 59 krad/hour and 570 krad/hour. Results indicate that proposed structures enable the development of reliable silicon detectors to be used in a high gamma-radiation environments encountered in a lot of applications.