Radu Apetrei

Pulsed Regime of a Hollow-Cathode Discharge Used in a Sputter Source

The pulsed operation of a cavity hollow-cathode post-discharge sputtering source was proposed to facilitate the sputtering of low-conductivity materials. Self-oscillating and externally driven pulsed regimes were investigated. The plasma density, temperature and relative density of atomic species along the discharge axis were determined by optical emission spectroscopy and Langmuir probe diagnostics. The temporal evolution of these parameters and dynamic current–voltage characteristics of the discharge were recorded in both regimes as functions of gas pressure and discharge current. The results bring more insight into the utilization of the above-mentioned device as a small sputtering source.

Optical Emission Spectroscopy Diagnostic of Discharge Plasma in a Hollow-Cathode Sputtering Source

Experimental results of the characterization of a cavity hollow-cathode post-discharge sputtering source by optical emission spectroscopy are presented. The discharge parameters are similar to those currently used in sputter-deposited ferromagnetic (Ni, Fe) and nonferromagnetic targets (Cu, Ti): Ar pressures, 6×10-2–1×10-1 mbar and discharge currents, 5–60 mA. The spatial distribution of the relative electron density in front of the cathode nozzle was determined from the radial distribution of light intensity by applying the Abel transformation. Therefore, the optical data could be correlated with the electrical diagnostic results obtained under low-density plasma conditions. The radial and axial distributions of the emission spectra were also mapped in the 340 to 650 nm wavelength range for Ar and metal (Ni, Ti, Cu) species.

Investigations on Crystallinity and Surface Oxidation States of Nb:TiO 2 DC-Sputtered Films

Pure anatase-ordered Nb:TiO2 thin films were prepared using a pulsed-DC sputtering source with a composite (TiO2)0.94Nb0.06 cathode. A mixture of Ar and O2 was used as discharge environment, under the total pressures of 1.0 × 10−2 and 5.0 × 10−2 mbar. The related effects of these parameters on film properties, associated with different deposition rates were monitored. The DC discharge was supplied by a pulsed voltage supply with a repetition rate of max. 350 kHz working in constant power mode, for two values of the injected power into discharge, 100 W and 200 W. Polycrystalline Nb-doped TiO2 thin films with the thickness in the range of 300 and 1100 nm and Nb content ranging between 2.1 and 2.8 at.% were deposited on heated (100)Si and glass substrates. Their optical transmittance measurements were used to derive the optical band gap using the Tauc plots spectra. Data processing showed band gap energy, E g , values ranging between 3.21 and 3.31 eV. Upon increasing the dopant content, a decrease in surface roughness and film crystallinity were observed. The results were used to design conductive electrodes in dye-sensitized solar cells with improved performances.

Characterization of Rutile N-Doped TiO2 Films Prepared by RF Magnetron Sputtering

Rutile N-doped TiO2 thin films were grown by RF magnetron sputtering on amorphous and crystalline substrates at room temperature. The surface elemental analysis, investigated by X-ray photoelectron spectroscopy indicated that the nitrogen content of the films could be adjusted up to values as high as 4.1 at.%. As demonstrated by the X-ray diffraction data, the as-deposited films (100 200 nm thick) showed no detectable crystalline structure, while after successive annealing in air for one hour at 400°C, 500°C and 600°C, the (110) rutile peaks occurred gradually as dominant features. The rutile phase in the films was confirmed by the band gap values of the deposited materials, which stabilized at 3.1 eV, for the thin films having 200 nm thicknesses.