National Institute Of Materials Physics - Romania

Publications

5840 articles found

5141. Electrical and structural properties of anodized porous silicon

Authors: Ciurea, ML; Pentia, E; Lazar, M; BeluMarian, A; Zavaliche, F; Manaila, R

Published: 1996, CAS '96 PROCEEDINGS - 1996 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 19TH EDITION, VOLS 1 AND 2, 236, DOI:

5142. The contribution to the non-uniform distribution of motion effects obtained for the SC-cut quartz plates

Authors: Mateescu, I; Zelenka, J; Mateescu, I

Published: 1996, PROCEEDINGS OF THE 1996 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM (50TH ANNIVERSARY), 411, DOI: 10.1109/FREQ.1996.559888

New experimental results related to the harmonic dependence of the characteristics of SC-cut quartz resonators on various material and electrode parameters are presented. On the basis of the analysis of SC-cut trapped-energy resonators vibrating in the coupled thickness-shear and thickness-twist in the vicinity of the fundamental and odd overtone thickness-shear frequency dependencies were established of effective mass-loading, effective coupling coefficient, motional capacitance and static capacitance on electrode material and dimensions. The results put into evidence the influence of the non-uniform distribution of motion on behaviour of the SC-cut resonators. The plane-parallel polished SC-cut quartz plate of 14mm diameter with different thickness Ag and CrAu electrodes and two values of electrode diameter were used for the experimental investigations.

5143. Optical and microstructural properties of TiO2(Ni2+) thin films

Authors: Parlog, C; Gartner, M; Osiceanu, P; Teodorescu, V; Moise, F; Ianculescu, A

Published: 1996, CERAMICS INTERNATIONAL, 22, 99, DOI: 10.1016/0272-8842(95)00062-3

Coloured TiO2(Ni2+) thin coatings doped with transitional metals (Ni) were deposited on different substrates (silicon wafers, glass, aluminum) by the sol-gel dip coating process. Complementary techniques (XPS, SE, TEM, XRD, Absorption Spectroscopy) were used to characterize the surface stoichiometry and optical properties, as well as the structure and texture of the thermally treated gels. The presence of fully oxidized film in the outer layers, crystallization in heat treatment to anatase and rutile, formation of porous and coloured films due to the influence of the dopant and the reaction with the substrate, as well as a decrease by three orders of magnitude of the resistivity of Ni-doped films, are reported.

5144. Thermal stability of Se/CdSe multilayers

Authors: Popescu, M; Sava, F; Lorinczi, A; Koch, PJ; Gutberlet, T; Uebach, W; Bradaczek, H; Vateva, E; Nesheva, D

Published: 1996, CAS '96 PROCEEDINGS - 1996 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 19TH EDITION, VOLS 1 AND 2, 304, DOI:

5145. On the determination of birefringence of liquid crystals by the interference method

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

Published: 1996, CRYSTAL RESEARCH AND TECHNOLOGY, 31, 955, DOI: 10.1002/crat.2170310724

A new method of processing the experimental data in the interference method for the determination of birefringence of liquid crystals which allows obtaining results in good agreement with those from prism or wedge methods, is presented.

5146. Polymer degradation within the glass transition range

Authors: Chipara, MI; Chipara, MD; Romero, JR

Published: 1996, IEEE 1996 ANNUAL REPORT - CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA, VOLS I & II, 820, DOI:

Polymer degradation around the glass transition temperature exhibits frequently an anomalous behaviour. Starting from the hypothesis that such anomalies are related to the glass transition phenomenon, the most relevant data reported in the literature are reviewed and a theoretical description, based on the free volume approximation is suggested. The degradation process is split in three steps. It is proved that the dominant contributions come from the defect's diffusion step and from the proper chemical stage, which may be supposed to be statistically independent. It is explain, using an extended WLF equation why these anomalies are not located exactly at the glass transition temperature. The agreement between theory and experimental data reported elsewhere is good.

5147. Coulomb interaction effects on the magnetoconductivity of laterally modulated two-dimensional electron systems

Authors: Manolescu, A; Gerhardts, RR; Tornow, M; Weiss, D; vonKlitzing, K; Weimann, G

Published: 1996, SURFACE SCIENCE, 361, 516, DOI: 10.1016/0039-6028(96)00458-X

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.

5148. Photoelectric properties of PbTiO3/Si heterostructures

Authors: Alexe, M; Pintilie, L; Pintilie, I; Pignolet, A; Senz, S; Hesse, D

Published: 1996, FERROELECTRIC THIN FILMS V, 433, 430, DOI: 10.1557/PROC-433-425

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.

5149. A study of hydrogenated amorphous silicon (a-Si:H)/electrolyte interface by means of impedance spectroscopy

Authors: Dragoe, D; Maracine, L; Popescu, V; Popescu, C

Published: SEP-OCT 1996, REVUE ROUMAINE DE CHIMIE, 41, 748, DOI:

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.

5150. Dielectric and DSC investigations of 4-n-substituted benzoic and cyclohexane carboxylic acids .1. Textural changes in homologous 4-n-alkoxybenzoic acids

Authors: Frunza, L; Frunza, S; Petrov, M; Sparavigna, A; Torgova, SI

Published: 1996, MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION C-MOLECULAR MATERIALS, 6, 223, DOI:

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.