S. Bakalova

Enhanced gas sensing of Au nanocluster-doped or -coated zinc oxide thin films

We demonstrated that doping or covering with Au nanoclusters boosts gas sensing effectiveness of optical metal oxide sensors. The sensing response of pulsed laser deposited ZnO films as sensing element was tested by m-line technique for low concentration (1000ppm) of butane in environmental N2. The optical interrogation was performed for three types of coatings: undoped ZnO, undoped ZnO structures partially covered with Au nanoclusters, or obtained from Au (0.5wt%) doped ZnO targets. Nanocluster coating tripled the sensitivity, while doping resulted in an increase of up to 45% as compared with simple structures.

VIS/IR spectroscopy of thin AIN films grown by pulsed laser deposition at 400?C and 800?C and various N2 pressures

The optical properties of pulsed-laser-deposited (PLD) AlN films on silicon are reported in the wide visible and infrared spectral range from 5×104 cm−1 to 350 cm−1. The films were deposited at 400 °C or 800 °C and in vacuum or nitrogen gas ambient at pressures from 0.1 Pa to 10 Pa. The optical constants of the films were determined by modelling the spectroscopic ellipsometry data recorded in both the visible and infrared spectral ranges. The PLD AlN films deposited in vacuum have a bandgap energy of 6.2 eV in a good agreement with the crystalline AlN material, while an effective bandgap narrowing was observed for films deposited in N2 ambient. This effect was most pronounced in films deposited at 400°C, where the optical absorption below the fundamental edge was the largest due to a larger degree of disorder in the films. Fourier transform infrared spectroscopy was used to identify AlN phonon modes and stress in the films. The shift and broadening of the E1(TO) peak towards the higher wave numbers indicates that an increased compressive stress is developed in the deposited films as the nitrogen pressure is increased.

XRD Study of Pulsed Laser Deposited AIN Films with Nanosized Crystallites

The structure of pulsed laser deposited AIN films was investigated by X-ray diffractometry. The AIN films were deposited on (111) single-crystalline Si wafers in ambient nitrogen at a pressure of 0.1 Pa via ablation of an AIN target using KrF* excimer laser radiation (248 nm wavelength, t >= 7 ns) with 3.7 J/cm2 incident fluence. The obtained films had a polycrystalline structure with cubic phase nanocrystallites. The size of the crystallites, as estimated from the Bragg peaks, was about 55 nm slightly depending on the post-deposition cooling rate.

Surface morphology of RF plasma immersion H+ ion implanted and oxidized Si(100) surface

The surface morphology of p-Si(100) wafers after RF plasma immersion (PII) H+ ion implantation into a shallow Si surface layer and after subsequent thermal oxidation was studied by atomic-force microscopic (AFM) imaging. After PII implantation of hydrogen ions with an energy of 2 keV and fluences ranging from 1013 cm−2 to 1015 cm−2 the Si wafers were oxidized in dry O2 at temperatures ranging from 700 °C to 800 °C. From the analysis of the AFM images, the surface amplitude parameters were evaluated and considered in terms of the technological conditions. The amplitude parameters showed a clear dependence on the H+ dose and the oxidation temperature, with the tendency of increasing with the increase of both the H+ ion fluence and the oxidation temperature. The implantation causes surface roughening, changing the RMS roughness value from 0.15 nm (typical for a polished Si(100) surface) to the highest value 0.6 nm for the H+ fluence of 1015 ions/cm2. Oxidation of the H+ implanted Si region, as the oxide is growing inward into Si, levels away the pits created by implants and results in a smoother surface, although keeping the RMS values larger than 0.2 nm.