High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

3.1. Fundamental Characterization 6672 3.2. Photocurrent Action Spectroscopy 6673 3.3. Optical Characterization 6673 3.4. Characterization of Electron Transfer 6673 4. Electron Transport in Metal Oxide Films 6674 4.1. Mechanism of Photoinduced Carrier Transport 6674 4.2. Characterization of Diffusion Length 6675 4.3. One-Dimensional (1-D) Transport Architectures 6675 4.4. Electrolyte Interactions 6676 5. Recent Trends in Liquid-Junction Solar Cells 6676 5.1. Dye Sensitized Solar Cells 6677 5.2. Quantum Dot Sensitized Solar Cells 6678 5.3. Carbon Nanostructure Based Photochemical Solar Cells 6679

Beyond Photovoltaics: Semiconductor Nanoarchitectures for Liquid-Junction Solar Cells

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6–20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS–CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Properties and Application of Geopolymers Vol. 841 (/MSF.841 /book) Development and Investigation of Materials Using Modern Techniques Vol. 840 (/MSF.840/book) Superplasticity in Advanced Materials ICSAM 2015 Vols. 838-839 (/MSF.838-839/book) 12th International Conference on High Speed Machining Vols. 836-837 (/MSF.836-837/book) Sintering Fundamentals II Vol. 835 (/MSF.835/book) Advanced Machining Technologies: Traditions and Innovations Vol. 834 (/MSF.834/book) Applied Materials and Technologies Vol. 833 (/MSF.833/book) Emerging Functional Materials: Book (/MSF.841/book) Papers (/MSF.841)

Materials Science Forum

High Power Impulse Magnetron Sputtering (HiPIMS) is a coating technology that combines magnetron sputtering with pulsed power concepts. By applying power in pulses of high amplitude and a relatively low duty cycle, large fractions of sputtered atoms and near-target gases are ionized. In contrast to conventional magnetron sputtering, HiPIMS is characterized by self-sputtering or repeated gas recycling for high and low sputter yield materials, respectively, and both for most intermediate materials. The dense plasma in front of the target has the dual function of sustaining the discharge and providing plasma-assistance to film growth, affecting the microstructure of growing films. Many technologically interesting thin films are compound films, which are composed of one or more metals and a reactive gas, most often oxygen or nitrogen. When reactive gas is added, non-trivial consequences arise for the system because the target may become “poisoned,” i.e., a compound layer forms on the target surface affecting the sputtering yield and the yield of secondary electron emission and thereby all other parameters. It is emphasized that the target state depends not only on the reactive gas' partial pressure (balanced via gas flow and pumping) but also on the ion flux to the target, which can be controlled by pulse parameters. This is a critical technological opportunity for reactive HiPIMS (R-HiPIMS). The scope of this tutorial is focused on plasma processes and mechanisms of operation and only briefly touches upon film properties. It introduces R-HiPIMS in a systematic, step-by-step approach by covering sputtering, magnetron sputtering, reactive magnetron sputtering, pulsed reactive magnetron sputtering, HiPIMS, and finally R-HiPIMS. The tutorial is concluded by considering variations of R-HiPIMS known as modulated pulsed power magnetron sputtering and deep-oscillation magnetron sputtering and combinations of R-HiPIMS with superimposed dc magnetron sputtering.

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Tutorial: Reactive high power impulse magnetron sputtering (R-HiPIMS)

Alumina coatings were reactively deposited on steel substrates by pulsed magnetron sputtering at substrate temperatures (Ts) of 330–760 °C. Investigations into the structure and morphology of the layers were made via XRD and SEM techniques, respectively. As to the layer properties, the hardness was determined by nanoindentation, and the residual stresses were derived from the bending of the coated substrates. At substrate temperatures of less than 330 °C the Al2O3 layers are amorphous to X-rays, whereas γ-Al2O3 is detected at a substrate temperature Ts ≈ 480 °C. A further increase in substrate temperature to 560 °C results in the formation of a pronounced texture of γ-Al2O3. A phase mixture of textured γ- and α-Al2O3 is deposited at Ts ≈ 690 °C. At Ts ≈ 760 °C the layer consists completely of α-Al2O3 with crystallite sizes of about 1 μm. The occurrence of the crystalline γ phase at 480 °C is linked with a pronounced increase in hardness from 10 to 19 GPa. The layer hardness of pure α-Al2O3 amounts to 22 GPa and corresponds to the hardness of the bulk material.

Effect of the substrate temperature on the structure and properties of Al2O3 layers reactively deposited by pulsed magnetron sputtering

Crystalline TiO 2 layers could be deposited on glass and silicon substrates by reactive pulse magnetron sputtering without additional substrate heating using a long-term stable process with high deposition rate. XRD investigations have revealed that the variation of pulse mode between unipolar and bipolar allows the deposition of layers with anatase and rutile structures, respectively. The SEM micrographs of anatase layers show faceted crystallites on the surface as well as in the fracture. In comparison the rutile layers have a smoother surface and a more glassy like fracture. Cross-section TEM investigations on samples with anatase or rutile phase have shown that the growth of the layers starts with an amorphous sub-layer. With increasing distance from the substrate the nucleation of first crystallites can be recognized. The lateral size of the columnar grains ranges between 100 and 200 nm for anatase and rutile films. In contrast, the defect density of the rutile phase is drastically higher than in films with anatase structure. Spectroscopic ellipsometry measurements have shown that no absorption is present in the visible spectrum range. The refractive index at 550 nm is approximately 2.55 for anatase and 2.68 for rutile phase, respectively. The hardness and Young's modulus measured by nanoindentation is approximately 8 and 170 GPa for anatase and 17 and 260 GPa for rutile layers. Layers with an anatase structure are well suited for photocatalytic applications using the hydrophilic, self-cleaning and antifogging properties. Rutile layers can be used as optical layers with high refractive index and as protective layers with good mechanical properties.

Structure and properties of crystalline titanium oxide layers deposited by reactive pulse magnetron sputtering

Al x Sc 1 − x N films were deposited by reactive pulse magnetron co-sputtering from aluminum and scandium targets without additional substrate heating at deposition rates between 100 and 150 nm/min. With increasing incorporation of scandium into the hexagonal wurtzite structure, the piezoelectric properties are drastically improved. The piezoelectric charge coefficient d 33 is increased from 8.4 pC/N for AlN up to 23.6 pC/N for Al x Sc 1 − x N with 33% scandium. Between 35 and 43% scandium content a relative broad maximum with high piezoelectric coefficients between 26.9 and 27.3 pC/N was detected. A further increase of scandium concentration above 50% results in the formation of the cubic and centrosymmetric rock salt structure and therefore the complete loss of piezoelectric properties. By FE-SEM, XRD and TEM investigations it was shown that up to up to 43% scandium concentration the wurtzite structure becomes more and more disordered and the c/a ratio is decreased from 1.6 to 1.27. Nevertheless, no aluminum or scandium segregation could be detected by high resolution TEM investigations. The Young's modulus of the wurtzite phase is reduced with increasing scandium concentration from 340 GPa to 185 GPa. The drastic improvement of the piezoelectric properties can be explained by weakening of the chemical bonding and by high distortion of the wurtzite structure.

Effect of scandium content on structure and piezoelectric properties of AlScN films deposited by reactive pulse magnetron sputtering

Titanium oxide layers were deposited by reactive electron beam evaporation with and without additional plasma activation by spotless arc discharge. The influence of substrate temperature and plasma activation on structure and properties of TiO 2 layers are presented. The layers were deposited with very high deposition rates between 40 and 70 nm/s. XRD investigations have revealed that structure of all layers deposited at substrate temperature ( T S ) below 150 °C is amorphous. Without plasma activation and at substrate temperature above 200 °C layers with anatase phase were deposited. On the other hand with plasma activation the degree of substrate ion bombardment controls the formation of anatase or rutile phase. Furthermore a drastic influence of plasma activation on the properties of the layers could be found. Without plasma activation the refractive index at 550 nm only amounts to between 2.02 and 2.29 depending on substrate temperature. With plasma activation a drastic raise of refractive indexes to values between 2.30 and 2.58 can be reached. In addition the hardness of the layer is obviously influenced by plasma activation. At T S below 150 °C hardness is raised from 2.0 to 6.7 GPa. The formation of the rutile phase in layers deposited with plasma activation is linked with a further increase of hardness up to 12 GPa. Measurements of the contact angle show a promising super hydrophilicity of anatase layers. Therefore these layers should be well-suited as coatings with self-cleaning or antifogging properties. At T S below 150 °C the plasma activation enables the deposition of dense, high-refractive layers at very high deposition rates for applications as optical layers.

Structure and properties of titanium oxide layers deposited by reactive plasma activated electron beam evaporation

We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of ≤340 ∘C, which is much lower than that used in conventional processes (>500 ∘C). The CdTe films were treated with the usual CdCl2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub≤ 340 ∘C) compared to high-temperature cells (Tsub = 520 ∘C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposi...

Olaf Zywitzki

Papers

Effect of the substrate temperature on the structure and properties of Al2O3 layers reactively deposited by pulsed magnetron sputtering

Structure and properties of crystalline titanium oxide layers deposited by reactive pulse magnetron sputtering

Effect of scandium content on structure and piezoelectric properties of AlScN films deposited by reactive pulse magnetron sputtering

Structure and properties of titanium oxide layers deposited by reactive plasma activated electron beam evaporation

12% efficient CdTe/CdS thin film solar cells deposited by low-temperature close space sublimation