Solid State Phenomena Vols. 99-100

Abstract: The structural analysis of thin cerium dioxide films doped with Cu, produced by laser ablation for applications in catalytic and gas sensors, was the general aim of the study. The thin films deposited on a (100) silicon substrate were nanocrystalline structure with a well-developed texture. The morphology, as well as the preferred films orientation, is changed with the volume fraction of Cu. The observed changes affect the catalytic properties of the materials obtained which was confirmed by the catalytic tests undertaken with CH4.

Abstract: The paper presents the study of CdS0.2Se0.8 n-type films 0.50-0.65 µm thick manufactured by the RF sputtering technique and their electro-optical properties. The effects of the substrate texturing on the structure and properties of the films are discussed. Recrystallization of the films sputtered onto glass substrates coated with a continuous or island-like silver sublayer resulted in the formation of a nanosized grain structure with higher photosensivity than films deposited onto aluminium oxide ceramics.

Abstract: The successive ionic layer adsorption and reaction (SILAR) technique was used to grow double layer structures of CdS-PbS. The growth of thin films by the SILAR technique from diluted aqueous solutions was achieved, ionic layer by ionic layer, at room temperature and normal pressure. The thin films on silicon were characterized by XRD, AFM, XPS. It was established that a double layer could be grown on crystalline silicon and that the morphology and crystallinity of the films could be controlled by changing the lead precursor.

Abstract: Gallium arsenide coating by molecular layers is a of increasing interest both for its surface passivation and for its use as a chemical or biochemical sensor. The surface state of GaAs and the nature of the molecular functionality to be bound to the surface are very important to assure good and durable adhesion. This work, using both the vibrational and the electronic energy loss range of high resolution electron energy loss spectra, showed that the water content in the solvent – acetonitrile – has a dramatic effect on the amount of phenylphosphonic acid molecules adsorbed on the GaAs substrate. There is a poor molecular adsorption for water contents ranging from 0 to 4% volume: HREELS spectrum is always a combination of the substrate and the adsorbed molecule spectra. For a water content of 5% there is an abrupt jump in the HREELS spectra shape: they become typical of phenyl groups in the electronic region. In the vibrational region, the typical C-H stretching peaks of aliphatic chains disappear showing that the extreme surface is exclusively covered by phenyl functions. Also for the samples, where a large adsorption occurs, surfaces become negatively charged under electron irradiation showing the existence of a large number of traps for incident electrons. Sonication of such well covered substrates destroys intermolecular bonds but keeps molecules that are chemically bound to the substrate.

Abstract: The structure of thin films of tungsten-carbon, deposited onto monocrystalline silicon substrates by reactive magnetron sputtering (argon + benzene) in a wide range of preparation parameters has been investigated by GISAXS. Substrates were in a fixed position relative to the two adjacent cylindrical magnetrons. Benzene partial pressure was varied from 1% to 10% of the total working gas pressure. A series of samples were prepared, with the substrate held at room temperature and 400°C, and the substrate potential held at floating potential or biased -70 V with respect to the discharge plasma. The bulk particle contribution to the scattering was investigated outside of the specular plane, applying a two dimensional CCD detector. For higher values of benzene partial pressure, the generated films consist of densely packed tungsten carbide grains in an amorphous, carbon rich matrix, while, in some cases, the lower benzene pressure resulted in isolated carbon rich particles in tungsten carbide. From earlier work it is known that the preparation parameters influence the film’s chemical composition, the relatively complex dependence of particle sizes on benzene partial pressure can be explained as a function of the relative carbon content.

Abstract: The effect of annealing under enhanced hydrostatic pressure (HT-HP treatment) on the structural evolution of nano-structured buried He-enriched layers in silicon was investigated by photoluminescence and TEM methods. It has been stated that the HT-HP treatment can affect the defect structure of nano-structured He-containing layer. Enhanced creation of helium bubbles during the HP-HT treatment takes place at HT £ 600oC. Annealing at HT ³ 800oC results in the accumulation (gettering) of oxygen atoms in the He implanted layer in Czochralski grown silicon. HP treatment stimulates this effect.

Abstract: TiO2 thin films were prepared by spray pyrolysis method. The solution containing titanium(IV)isopropoxide, acetylacetone and ethanol was deposited onto n-type Si(100) and HD Si(100) wafers at substrate temperatures of 315 to 500 0C by pulsed spray solution feed. The films were characterized by FTIR, XRD, AFM, ellipsometry, impedance and I-V measurements. Asdeposited films prepared below 500 0C were amorphous, whereas crystalline films could be achieved at 500 0C. Subsequent annealing at 700 °C in air led to crystalline anatase formation for films deposited below 400 °C. Rutile phase appears in annealed films prepared at a growth temperature above 400 °C. Anatase TiO2 films show refractive index in the range 2.20 to 2.40 and exhibit a relative dielectric constant value of 75 in the range 1 to 100 kHz. Electric breakdown occurs for 120 nm thick film at 250 kV/cm.

Abstract: Preliminary results of Raman scattering measurements of multiwall carbon nanotubes (MWCNT) are presented. The nanotubes have been carefully dissolved, separated and then characterized by AFM. The micro-Raman spectra are taken with 514,5nm wavelength excitations in the range 4K - 400K. Basically the spectra are quite similar to the well known single wall carbon nanotube spectra, but the low frequency band is absent. The major Raman bands, observed in single wall nanotubes are found in the spectra. In particular the disorder effects are visible due to the pronounced D band at ~1350 cm-1. Metallic and semiconducting type of conductivity is distinguished through analysis of the G (LO) mode at ~1600 cm-1. A new feature in these spectra exists at ~843 cm-1. Low energy radial breathing mode absence has been explained.

Abstract: We present a study on the preparation of multiwalled carbon nanotubes (MWCNT) using chemical vapour deposition (CVD). The CVD produced MWCNT and single wall carbon nanotubes (SWCNT) produced with a laser ablation technique were then chemically modified by substituting carbon atoms with boron and nitrogen atoms. The morphology and the crystal structure of the new class of nanostructures were analyzed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Abstract: The formation of novel carbon nanostructures containing Fe-Nd-B nanocrystallites is reported. Tests were performed in a DC arc plasma reactor under He atmosphere using (Fe-Nd-B)- filled anodes. The influence of the operational parameters pressure and anode composition on the product morphology was studied. The products were analyzed by HR TEM, MFM and magnetic measurements. Emission spectroscopy was performed to determine the temperature and C2 radical distribution in the arc.