Publications

A quantum confinement model is proposed to explain the carriers transport in a nanowire network of porous silicon. The electron Hamiltonian is written as the sum of the longitudinal and the transversal contributions. The last one corresponds to a two-dimensional infinite cylindrical quantum well, whose energy levels determine the activation energies observed in the temperature dependence of the dark current. The model is in excellent agreement with the experimental data.

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.

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.

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.

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.

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.

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.

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.

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.