Search

Cold spraying of hard Fe particles onto soft Al substrates increases the mechanical energy supplied to the interface of the two metals compared to previous Al coatings on Fe substrate. As a result, the irregular interfacial morphologies found in this study were on a larger scale. As in the case of the soft particle/hard substrate system, roll-up features that perfectly encapsulated the Fe particles were found, but their structure was larger and complicated. When the Fe/Al interface was investigated further, it was found to be amorphous. This amorphous layer had a composition gradient, which indicates intermixing on an atomic scale. As could be expected from the enhanced mechanical energy of the Fe particle/Al substrate system, the amorphous layer was also thicker than that of the reversed system. Cold spraying is an ambient-temperature processing technique that involves materials that can be plastically deformed, and therefore, an analogy can be found with the cold rolling (cold welding) of two metal sheets or wires, where similar interfacial characteristics are found. Hence, the mechanisms of bonding and interface formation can be thought of as similar.

We investigated the structural and optical properties of Cu-poor CuGaSe2 (CGSe) films depending on the use of different substrates: indium-doped tin oxide (ITO) coated soda-lime glass (SLG) and fluorine-doped tin oxide (FTO) coated SLG as back contacts, widely used Mo-coated SLG, and pure SLG. The Cu-poor phase is chosen as a counterpart of Cu-poor Cu(In,Ga)Se2 to show the highest efficiency in this class of materials, and also give a test board for parasitic phases which might influence on device properties. Although the Cu-poor CGSe thin-films were deposited on the four substrates at the same time in an identical condition, they showed differences in the morphology and grain size due to different CGSe/substrate interfaces and growth mechanisms depending on the substrates. These surface properties of the CGSe films were identified clearly by atomic force microscopy (AFM) measurements. X-ray diffraction (XRD) measurement also supported the result of the AFM analysis and showed that the preferred orientation of CGSe is (112), independent of the substrates. The existence of parasitic phases was examined by Raman and photoluminescence spectroscopic techniques. While defect compounds such as CuGa3Se5 and CuGa5Se8 were identified for all films, the signals related to these parasitic phases are strongest for the films on the pure SLG substrate. Furthermore, the absorption property was investigated by spectroscopic ellipsometry in a photon energy range of 0.7–5 eV. We found that the absorption coefficient values for the CGSe films are about 104–105 cm−1 in the visible region. The absorption coefficient is also changed according to the use of different substrates. This difference comes from the parasitic phase formation, which leads to an increase of the bandgap and suppression of the optical absorption strength. Our systematic study suggests clearly that the difference in distribution of parasitic phases in the CGSe films could originate primarily from the different substrates used for the film deposition.