National Institute Of Materials Physics - Romania

Ceramic compounds of ferroelectric lead zirconate titanate (PZT) and ferroelectric barium titanate (BT) were prepared from nanopowders corresponding to the formula (1-x)PZT.xBT with x = 0; 0.1; 0.2 ... 0.9; 1. The samples were investigated by X-ray diffraction and electron microscopy and the piezoelectric properties were determined by means of an impedance analyzer. The sintering process is complex since samples densify at different temperatures depending on the composition resulting in different morphostructures. Accordingly, the piezoelectric properties show unusual behavior discussed in terms of different grain size and composition. A remarkably high enhancement of the relative dielectric constant, epsilon(r) coupled with maxima in both, piezoelectric charge constant d(33) and the piezoelectric voltage constant g(33), is observed for x = 0.4 while the values of the coupling coefficient kp are still high similar to those of pure PZT.

We report on the formation of the Ti3SiC2 nanolaminate phase in the Ti-Si-C thin film system, using a UHV magnetron sputtering technique with top mounted sample holder, from elemental and compound targets. The formation of the Ti3SiC2 (or 312 phase) has been evidenced by detailed X-ray diffraction analysis followed by full-profile quantitative analysis of the obtained diffractograms. It has been proven that for deposition temperatures as low as 500 degrees C, there is a significant amount of 312 phase obtained in the deposited films, in co-existence with the majority TiC phase. This amount increased to about 21% when the deposition temperature was raised to 650 degrees C. The ternary 312 phase becomes predominant at around 60% relative abundance for slight off-stoichiometric, Si increased, content of the alloy, for temperatures as low as 650 degrees C. The conditions for improving the relative abundance of the 312 phase within our experimental setup are pointed out and explained in terms of a nucleation and growth model of nanostructure formation from the amorphous precursor (?).

Low carbon Fe-C steel surface has been studied before and after electrolytic galvanization. The corrosion products formed under atmospheric conditions on the Fe-C steel were identified and characterised by X-ray diffraction (XRD), transmission Mossbauer spectroscopy, conversion electron Mossbauer spectroscopy (CEMS), and conversion X-ray Mossbauer spectroscopy (CXMS). In decreasing order of abundance the found corrosion phases were magnetite, hematite, and goethite. After the surface preparation, an electrolytic galvanization process was applied. A magnetic anisotropy was evidenced after preparation, in the superficial layer of around 250 nm thickness. Scanning electron microscopy (SEM) analyses evidenced the formation of a uniform thin Zn film of 8 mu m at the surface of steel. No other Fe-Zn phases were identified at the steel-Zn interface.

Triglycine sulphate (TGS) is a crystal having a typical second order ferroelectric transition and the Curie point around 49 degrees C. It is quite easy to grow and to analyse its properties. Our TGS crystals were grown by slow solvent evaporation in paraelectric phase, around 54 degrees C, where no mechanical tensions due to ferroelectric domains were present. Dielectric properies of TGS crystals were continuously measured at a pace of 0.6 degrees C/min, starting from 65 degrees C, crossing down the Curie point until zero Celsius, on the frequency range 1 divided by 10(7) Hz. The two component of permittivity were measured and the parameters vs. temperature were estimated and analysed.

Polysaccharides irradiation is usually used for their decontamination of fungi, pathogenic bacteria, toxigenic molds, parasitic organisms. ESR studies are performed just to evidence their irradiation. Therefore the accent is put on radical stability in time and ESR signal intensity dependence on irradiation dose. Less attention is given to radical nature and their dependence on plant nature. In this report a study of gamma irradiated pectin is given. Dose dependence of double integrated ESR signal is analyzed in terms of a recombination reaction during the radiation period. Radical stability dependence on water content is put in evidence.

GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).

Investigations of barium strontium titanate (BST) layers deposited on MgO and Si substrates are presented. Since the Sr content determines the dielectric and optical properties of the BST layers at room temperature, accurate compositional analysis was performed by using Rutherford Backscattering technique at 3.041 Mev.

Pd-Ge based ohmic contacts on III-V semiconductor e.g.Pd-Ge on n-GaAs are viewed as a viable alternative to low contact resistance metallization. As it was remarked [11, together with the device dimensions decrease, the AuGeNi metallization system becomes inadequate for shallow-junction devices. This characteristic is related to the formation of a low melting point beta- AuGa phase that leads to a poor contact thermal stability. Gallium Antimonide is anIII-V semiconductor compound that can be used in a photovoltaic convertor of GaAs/GaSb tandem stack With a predicted efficiency of 30%. Reduced series resistance on GaSb cells can be achieved by the improving of contact metallization properties. The present study is dedicated to the preparation conditions and structural analyzing of PdGe based contacts on n-GaSb, namely: Pd/Au/Ge. There are presented the depth profiling for PdGe metallization obtained from XPS measurements, and morphologic studies arisen from SEM technique and AFM technique.

In the current work we present AlN/Si based Surface Acoustic Wave (SAW) devices exploited as high sensitivity temperature sensors. The experimental results show that the resonance frequency varies between 3.2 and 5.5 GHz, depending on the finger/Interdigit spacing width and metal thickness. The temperature measurements were performed between -250 degrees C and +150 degrees C in a cryostat. The sensitivities were investigated between 24-150 degrees C and the values were compared to the results obtained for similar GaN/Si based SAW structures.

The films of SiGe nanocrystals in SiO2 on Si substrate were obtained by co-sputtering Si, Ge, and SiO2 followed by rapid thermal annealing. The films structure and morphology together with electrical and photoelectrical properties were studied by x-ray diffraction, transmission electron microscopy, current - voltage and spectral photocurrent measurements. The photocurrent spectra at 300, 200 and 100 K were correlated with results obtained from X-ray diffractograms and transmission electron microscopy. The photocurrent spectra show an extension in near infrared due to the enriching SiGe nanocrystals in Ge.