National Institute Of Materials Physics - Romania

Publications

5975 articles found

5121. Ageing and barriers in tin dioxide gas sensors

Authors: Ionescu, R

Published: 1998, EUROSENSORS XII, VOLS 1 AND 2, 700, DOI:

The time-evolutions of both the electrical resistance in air, and of the response to reducing gases lead to the conclusion that the resistance of tin dioxide gas sensors is not governed by intergranular barriers. A conductance model is discussed, with a surface resistance and a bulk resistance connected in parallel. The long-termed evolution of the sensor resistance (ageing) is attributed to oxygen diffusion into the bulk.

5122. Change of the optical properties of porous silicon by post anodization treatments

Authors: Pavelescu, G; Ciurea, ML; Mihut, L; Galeata, G; Lengyel, E; Baltog, I; Roger, JP

Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 458, DOI:

Optical properties of as prepared porous silicon (PS) were compared with those of thermally treated and chemically cleaned samples. The change of the photoluminescence (PL) spectra correlated with ellipsometric. reflectance and Raman measurements leads us to conclude that the adsorbed species in the PS nanocrystalline structure play an important role in the origin of the PI emission, at least for as - anodized samples.

5123. Silicon linear image sensors for photometry

Authors: Cimpoca, V; Cengher, D; Crisan, C; Olariu, N; Oros, C; Cimpoca, M

Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 70, DOI:

The paper describes a new linear image sensor for photometry by applying bipolar technology (Standard Buried Collector-SEC) to the manufacture of self-scanning linear photodiode arrays. On a monolithic chip we have designed 128 to 1024 linear photodiodes, demultiplexing system and signals processing system. A dynamic simulation and a real-time measurement have been implemented, that allow to take into account every operational phase of detection. The dialogue between the various functions is established by message's transmission, using common data areas stored on disks or in central memory of PC compatible computer.

5124. Cobalt-manganese oxide thin films thermistors obtained by MOD

Authors: Dragoi, V; Alexe, M

Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 300, DOI:

Co1.4Mn1.6O4 (CMO) thin films were deposited onto silicon by Metalorganic Decomposition (MOD) method. Structure, composition and morphology were investigated by Electron Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Electrical measurements showed possible applications as negative temperature coefficient (NTC) thermistors.

5125. A new method for discriminating different reducing gases with SnO2 sensors

Authors: Ionescu, R; Vancu, A; Moise, C; Tomescu, A

Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 571, DOI:

By combining the changes induced by different reducing gases in electrical resistance with the corresponding changes of a second physical parameter it is possible to discriminate between groups off different reducing gases.

5126. XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulse laser deposition

Authors: Teodorescu, VS; Blanchin, MG; Champeaux, C; Garapon, C

Published: 1998, ELECTRON MICROSCOPY 1998, VOL 2: MATERIALS SCIENCE 1, 658, DOI:

5127. Mossbauer spectroscopy applied to radioactive waste processing

Authors: Filoti, G; Kuncser, V; Prisecaru, I; Rotaru, P; Turcanu, CN

Published: 1998, HYPERFINE INTERACTIONS, 112, 204, DOI: 10.1023/A:1011076522131

Two original evaluations of the embedding process and of the hydration promotion in cements using only Mossbauer data have been proposed. Quantitative factors connected with the Mossbauer parameters and describing the hydration degree, the quality of the precipitate bonds in the cement matrix, as well as the influence of the additional organic components on the hydration process were found.

5128. On the photoluminescence decay in porous silicon films

Authors: Baltog, I; Ciurea, ML; Pavelescu, G; Mihut, L; Baibarac, M

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 626, DOI: 10.1117/12.312818

The photoluminescence (PL) decay measurements were performed on porous silicon films. It was observed that the two components of FL, one of them fast (ns) and the other slow (mu s or ms sometimes) have different contributions to PL signal, depending on the wavelength of the excitation light. The slow component of PL was in details investigated. Time decay cures for different excitation (337.1 nm, 470 nm and 550nm) and emission (550, 650, 700, 800 and 860 nm) wavelengths and also for different excitation intensities were taken. All decay curves were fitted with a stretched exponential. The slow component of PL was proposed to be attributed to the radiative recombination on surfaces.

5129. Ionic space charge limited currents in natural quartz crystal

Authors: Enculescu, I; Iliescu, B

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 266, DOI: 10.1117/12.312762

Arrhenius plots and current-voltage characteristics were studied for natural quartz samples, in different conditions of air-sweeping time, of temperature, of electrodes (with or without any source of positive ions). Some observations about the influence of the ionic space charge limited current are made. Some dependencies of ionic current versus voltage were found.

5130. Collective modes and the far-infrared absorption of the two-dimensional electron gas in a periodic quantizing magnetic field

Authors: Manolescu, A; Gudmundsson, V

Published: 1998, SUPERLATTICES AND MICROSTRUCTURES, 23, 1180, DOI: 10.1006/spmi.1997.0557

We investigate the far-infrared (FIR) absorption of a two-dimensional electron gas in a periodically modulated quantizing magnetic field. The magnetic field varies along only one spatial direction and the external time-dependent electric field is linearly polarized along that axis. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. The effects of the magnetic material on top of the heterostructure as a grating coupler is included in the time-dependent incident FIR electric field. We show that, similar to an electric modulation, the absorption can be directly correlated to the underlying electronic energy bands. In addition, the magnetic modulation leads to absorption spectra with a richer structure due to the quite different static response of the electron density to the modulation. (C) 1998 Academic Press Limited.