High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO2thin films using dc dual magnetron (DM) sputtering in Ar + O2mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature Tsurfmeasured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency frwas investigated in detail. It was found that the increase of frfrom 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate aDof sputtered TiO2films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO2films can be sputtered on unheated glass substrates at aD = 80 nm/min, Tsurf < 180 °C when high value of fr = 350 kHz was used. Properties of a thin hydrophilic TiO2film deposited on a polycarbonate substrate are given

Scientific complications and controversies noted in the field of CdS/CdTe thin film solar cells and the way forward for further development

Cadmium telluride-based solar cell is the most successfully commercialised thin film solar cell today. The laboratory-scale small devices have achieved ~ 22%, and commercial solar panels have reached ~ 18% conversion efficiencies. However, there are various technical complications and some notable scientific contradictions that appear in the scientific literature published since the early 1970s. This review paper discusses some of these major complications and controversies in order to focus future research on issues of material growth and characterisation, post-growth processing, device architectures and interpretation of the results. Although CdTe can be grown using more than 14 different growth techniques, successful commercialisation has been taken place using close-space sublimation and electrodeposition techniques only. The experimental results presented in this review are mainly based on electrodeposition. Historical trends of research and commercial successes have also been discussed compared to the timeline of novel breakthroughs in this field. Deeper understanding of these issues may lead to further increase in conversion efficiencies of this solar cell. Some novel ideas for further development of thin film solar cells are also discussed towards the end of this paper

High resolution EBIC and TEM investigations on CdTe solar cells

By the use of an ion beam preparation technique polished cross sections of cadmium telluride thin film solar cells are prepared, which enables a high resolution FE-SEM imaging of microstructure and interfaces and simultaneously the measurement of the electron beam induced current (EBIC). The effect of electron beam accelerating voltage on EBIC signal distribution was investigated. The best lateral resolution of the EBIC signal could be obtained for a relative low EB accelerating voltage of 2 keV. After increasing the accelerating voltages to 5 and 10 keV the lateral resolution is deteriorated, which can be explained by the increasing electron range. EBIC results with high lateral resolution show that mainly areas near to the grain boundaries of the CdTe crystallites contribute to the measured signal, which can be interpreted as evidence for grain boundary near states passivation. Further it could be shown that especially small CdTe grains near the CdS interface possesses to a high EBIC signal. These results can be discussed as an effect of the chlorine diffusion during activation treatment. Because of small volume diffusion coefficient of chlorine in CdTe the diffusion occurs preferably along the grain boundaries. By the further slow volume diffusion mainly the outer regions of the grains are affected

New coatings on metal sheets and strips produced using EB PVD technologies

EB PVD coatings on large metal sheets and metal strips are discussed and used since many years. Recently developed plasma activated technologies opened a fresh ground to think about new applications. The new coatings produced by EB PVD represent an outstanding supplement to existing products. lt could be verified that the deposition cost are low enough in comparison to competitive technologies. Dense Ti layers are produced with high deposition rates up to 1000 nm/s by EB evaporation in combination with an effective plasma activation by a spotless arc (SAD process). The corrosion resistance of the coatings deposited with SAD process and an additional bias voltage can be drastically improved in comparison to a deposition without plasma activation. Aluminum oxide coatings were deposited by reactive EB evaporation at deposition rates between 50 and 100 nm/s. The influence of the plasma activation by hollow cathode low-voltage electron beam (HAD process) on the structure and properties of Al(2)O(3) coatings have been investigated. lt could be shown that the coatings deposited with HAD process have a drastically increased hardness, a higher density and an improved chemical stability in comparison to the coatings deposited without plasma activation. The stone-blasting resistance of galvanized steel sheets can be improved with simultaneously maintained good formability by a thin Fe layer. The Fe layer is deposited by high rate EB evaporation. Via a subsequent annealing process an intermetallic compound top layer occurs

Effect of annealing procedure on phase formation in zinc magnesium alloy coatings on steel sheets

Zinc magnesium alloy coatings on steel sheets have excellent properties regarding the corrosion protection both in case of painted and unpainted state. The preparation of the zinc magnesium coatings was done by physical vapor deposition using an inline vacuum coater for sheets and metal strips. About 650 nm thick magnesium layers were deposited onto hot-dip galvanized steel sheets followed by a short-time heat treatment. The effect of annealing procedure on the diffusion behavior of the magnesium into the zinc layer was systematically investigated in the temperature range between 300 and 400 deg C. The composition depth profiles after the annealing procedure were determined by glow discharge optical emission spectrometry (GD-OES). In dependence on the annealing temperature the formation of intermetallic phases MgZn2 and Mg2Zn11 could be identified by X-ray diffraction (XRD). The development of microstructure with increasing annealing temperature was characterized by SEM investigations on metallographic cross-sections

Nanocomposite oxide and nitride hard coatings produced by pulse magnetron sputtering

In this work, the composition and the microstructure of two-phase hard coatings have been varied by reactive pulsed co-sputtering of two target materials to produce nanocomposite structures. Two material systems have been studied for their potential of improved properties induced by phase segregation: the nitride system Ti-Al-N and the oxide system Al-Zr-O. Both systems combine well-established hard coating materials and hold the potential for nanocomposite formation. The nitride system is known to exhibit enhanced properties when the composition Ti1-xAlxN is in the range x = 0.5 ... 0.7. Pulse magnetron sputtering allows tuning of the composition in this range by varying the pulse durations of the two materials sputtered. nc-(Ti,Al)N/nc-AlN films with hardness up to 38 GPa have been produced by optimising composition and microstructure. In the oxide system, nc-Al2O3/ZrO2 coatings with ?-phase Al2O3 of hardness about 30 GPa are obtained only when the ZrO2 content is below 8 at.%. With increasing zirconia content the films become amorphous and exhibit hardness of 10 GPa. At low alumina content, crystalline zirconia is stabilized in its tetragonal phase exhibiting hardness of 17 GPa

Effect of pulse mode in reactive magnetron sputtering on structure and properties of titanium dioxide films

The state of the art to obtain crystalline TiO2 layers by vacuum deposition methods is the use of elevated substrate temperature during deposition or annealing after deposition above 250 °C. Therefore these processes are limited to temperature resistant substrates like glass. On the other hand there is a call for photocatalytic and hydrophilic layers on temperature sensitive materials. An innovative reactive pulse magnetron sputtering (PMS) system allowing to change the pulse mode (unipolar pulse, bipolar pulse or pulse packet) has been used for the sputter deposition of transparent TiO2 films. Investigations were carried out to determine the influence of the pulse mode on the substrate peak temperature during deposition for different substrate materials, on the film structure and on different film properties (hardness, Young's modulus, refractive index and surface roughness). The experimental results show that it is possible to achieve crystalline TiO2 films by pulse sputtering without heating the substrate prior to or annealing the substrate after the coating procedure. Bipolar powering as well as pulse packet powering tend to affect the structure of the layers towards rutile. On thermal sensitive polycarbonate substrates we deposited 500 nm thick amorphous TiO2 films by unipolar pulse sputtering. To deposit crystalline TiO2 layers on these substrates is still a challenge