National Institute Of Materials Physics - Romania

Publications

5840 articles found

5071. Temperature induced surface transitions in liquid crystal planar-tilted hybrid cells

Authors: Moldovan, R; Frunza, S; Beica, T; Tintaru, M; Ghiordanescu, V

Published: 1997, CRYSTAL RESEARCH AND TECHNOLOGY, 32, 675, DOI: 10.1002/crat.2170320510

Temperature induced surface transitions in liquid crystal hybrid cells with asymmetrical anchoring, planar to one surface and tilted to the other, are experimentally studied. The results are theoretically explained by an elastic theory and the resulting values for the effective splay-bend elastic constant for a given liquid crystal, as well as the parameters characterising the anchoring on the boundary surface with tilted anchoring are compared with data from previous experiments, with good agreement.

5072. Radiation damage effects on X- and gamma-ray N+PP+ silicon detectors

Authors: Cimpoca, V; Petris, M; Ruscu, R; Moraru, R; Breten, M; Cimpoca, M

Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 518, DOI:

The paper describes some results concerning technology and behaviour of X-and gamma-ray N+PP+ silicon defectors used in physics research, industrial and medical radiography and non-destructive testing. Devices manufactured under this technology proved to be stable alter an exposure in high intensity 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.

5073. Structure and hardness modifications induced by UV light in Ge-As-S amorphous chalcogenide films

Authors: Popescu, M; Skordeva, E; Arsova, D; Vateva, E; Sava, F; Lorinczi, A

Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 470, DOI:

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 x<19 and film hardening for x>19. 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.

5074. Medium range order in chalcogenide glasses

Authors: Popescu, M

Published: 1997, PHYSICS AND APPLICATIONS OF NON-CRYSTALLINE SEMICONDUCTORS IN OPTOELECTRONICS, 36, 232, DOI:

5075. Ni-Zn ferrite nanoparticles prepared by ball milling

Authors: Nicoara, G; Fratiloiu, D; Nogues, M; Dormann, JL; Vasiliu, F

Published: 1997, SYNTHESIS AND PROPERTIES OF MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS, PTS 1 AND 2 - ISMANAM-96, 235-2, 150, DOI: 10.4028/www.scientific.net/MSF.235-238.145

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.

5076. Model predictions for the radiation damage in semiconductors

Authors: Lazanu, S; Lazanu, I; Biggeri, U; Borchi, E; Bruzzi, M

Published: 1997, INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, VOL 59, PT 1 AND 2, 59, 1530, DOI:

5077. Hydrogen implantation in polycrystalline ZnO thin films

Authors: Bogatu, V; Goldenblum, A; Logofatu, B

Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 52, DOI:

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.

5078. Diffractive investigation of the domain structure in amorphous semiconductors

Authors: Popescu, MA

Published: 1997, INTERNATIONAL CONFERENCE ON CORRELATION OPTICS, 3317, 293, DOI: 10.1117/12.295695

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.

5079. Large area pulsed laser deposition of aurivillius-type layered perovskite thin films

Authors: Pignolet, A; Welke, S; Curran, C; Alexe, M; Senz, S; Hesse, D

Published: 1997, FERROELECTRICS, 202, 298, DOI: 10.1080/00150199708213487

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.

5080. Temperature dependence of the pyroelectric voltage in a 2-2 connectivity pyroelectric bimorph

Authors: Pintilie, L; Pintilie, I

Published: 1997, FERROELECTRICS, 200, 235, DOI: 10.1080/00150199708008608

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.