Publications

A reactive DC magnetron discharge produced in a TIN deposition system was investigated using optical emission spectroscopy. The influence of He, Ne and Kr addition into an Ar + N-2 working atmosphere was investigated. Addition of small percentages of He or Ne in the working atmosphere of Ar + N-2, caused a decrease of the N-2(+) (B)/N-2(C) ratio, whle with Kr addition the ratio increased. The known decrease of the relative intensity of Ti lines for N-2 addition was also observed for He addition, while it increases when Ne and Kr are added. XRD analysis of TiN thin films revealed that He addition determines the same effect as N-2. This behavior is explained by N and N+ density increase for He addition. (C) 1999 Elsevier Science Ltd. All rights reserved.

We consider the class of Hamiltonians composed by a quadratic form in the canonical operators and a linear interaction term with time periodic external fields of an arbitrary strength. The Hamiltonian can be made time independent by a unitary transformation in the extended Hilbert space, which has the meaning of a time-dependent translation in the classical phase space. We solve the eigenvalue problem for the Floquet Hamiltonian and we find general expressions for the time-dependent wave functions, of interest for the optical and transport properties of quantum nanostructures.

Cyclic voltammetry and impedance spectroscopy were used for study of polyaniline in acid solutions. Impedance spectra were presented both as Bode diagrams and Nyquist representations. The capacitive charging behaviour and anion (ClO4-, HSO4-) insertion/elimination reaction of the polymer film were discussed on the basis of a simplified Randles circuit model. The examined scanning electron micrographs have also shown that the nature of dopant anion changes the film morphology.

Metal structures of diffusion limited aggregation type were obtained by controlled electrodifussion in quartz crystal without macroscopic damages, Conditions of temperature, applied voltage and the form, shape and dimension of electrodes were found, in order to obtain fractal branches. Similarity with fractal DLA structures are described and discussed.

The frustration of the trinuclear clusters with antiferromagnetic intracluster interaction was investigated at low temperature and in applied magnetic field, by Mossbauer, susceptibility and magnetisation measurements. The spin configuration and the electronic state are described as a function of the temperature and the intensity of the applied field. The values of the exchange integrals are provided. (C) 1999 Elsevier Science B.V. All rights reserved.

After being dispersed in liquid solvents (Ethanol, CHCl3), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.

Melt-spun Cu80Co10Fe10 ribbons are shown to exhibit a nanogranular structure with magnetic alpha-Fe(Co) grains segregated from the Cu-rich matrix after appropriate annealing. The Cu matrix purification as well as the magnetic properties of the alpha-Fe(Co) grains existing in a range of sizes are studied using X-ray diffraction, Mossbauer spectrometry and magnetic measurements. There is an optimum annealing for obtaining a high magnetoresistive effect. (C) 1999 Elsevier Science B.V. All rights reserved.

Two sets of p-type silicon thigh resistivity bulk and low resistivity epitaxial) samples and one set of n(+)-p junctions have been irradiated with fast neutrons up to 8 x 10(13) cm(-2). I-V and C-V characteristics as well as Thermally Stimulated Currents (TSC) and Hall Effect (HE) analyses have been performed on the irradiated samples and diodes in view to determine the radiation-induced damage and the change in the electrical properties. A change in the effective carrier concentration and in the leakage current after irradiation similar to the one found for p(+)-n detectors has been observed in p-type diodes. An increase with the fluence of the resistivity and Hall coefficient was measured at room temperature both for the low and high resistivity sets. This evidence has been explained in terms of a two-level model taking into account a linear increase in concentration with the fluence of the main radiation-induced defects observed with TSC, probably related to divacancy and carbon-oxygen complex. (C) 1999 Elsevier Science B.V. All rights reserved.

TiN/Si structures were deposited on Si wafers by pulsed laser deposition technique. The highly conductive TiN films were grown on heated (100) Si substrates by laser ablation of a high purity Ti target in nitrogen reactive atmosphere. Subsequently, the Si layer was deposited by laser ablation of a Si target in vacuum (down to 10(-6) mbar) or in low pressure inert gas. The nitrogen gas pressure and the substrate temperature were found to strongly influence the TiN film structure and orientation. The degree of crystallinity of the Si layer grown on the TiN film was found to depend on Si/TiN collector temperature. Values below 550 degrees C (the threshold of TiN oxidation activation) were used in the experiments. Techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Force Microscopy (SFM) have been used to characterize the deposited structures. The TiN/Si structure rectifying properties were tested. The obtained Si/TiN/Si structure could be suitable for the building of Permeable Base Transistor (PBT, vertical MESFET) devices. (C) 1999 Elsevier Science S.A. All rights reserved.

Multilayer Pb(ZrTi)O-3 (PZT)/TiN/Si structures were grown by two subsequent laser ablation processes in reactive atmosphere. First, a fee-oriented TiN film was deposited by laser ablation of a Ti target in high-purity nitrogen reactive gas. Subsequently, a crystalline, piezoelectric PZT film was grown by reactive ablation of a PZT target in oxygen atmosphere. Both deposition processes were conducted at quite low Si(100) substrate temperature: 350 degrees C for TiN and 370 degrees C for PZT, in the same experimental setup (Nd-YAG laser, lambda = 1060 nm, energy/pulse 0.3 J, t(FWHM) = 10 ns). TiN film properties were analyzed by XRD and electric measurements. After the deposition of the PZT layer, the obtained structure was first characterized by XRD, SEM and SIMS techniques. Testing measurements performed after the deposition by thermal evaporation of an Al layer as top electrode on the PZT/TiN/Si structure confirm that they can be used as sensor transducer element. The TiN (as high conductive nitride) layer replaces the former Au layer used as bottom electrode. In this way, the Au diffusion inside the Si substrate, as well as in the deposited layer, is avoided, as could be observed from a comparative study of the SIMS spectra recorded for PZT/TiN/Si and PZT/Au/Si configurations. (C) 1999 Elsevier Science S.A. All rights reserved.