Papers

ICMCTF1999 Session H1: New Horizons in Thin Films and Coatings

Monday, April 12, 1999 8:30 AM in Sunrise Room

Monday Morning

Start	Invited?	Item
10:30 AM		H1-7 Atomic Layer by Layer Growth of Complex Oxide Heterostructures J. Eckstein (University of Illinois) As a class of materials, complex oxides exhibit a very diverse set of physical properties. These range, for example, from superconductivity, to magnetism, to ferroelectricity. Furthermore, many examples of these phenomena occur within a single type of oxide, namely perovskites and closely related phases. The different behavior of the materials is determined by electronic states derived from oxygen orbital common to all of the materials and metal atom d-state orbitals that depend specifically on the particular metal atom composition of the oxide. In particular, the filling of these states with electrons and the relative importance of electron correlation's spell the difference between simple metals and highly correlated ground states with interesting properties. The coherence lengths characterizing spatial variability of these ground states is typically only one to a few lattice constants in size. In addition, the lattice constants of virtually all of these materials is principally determined by close packing of oxygen ions and is only weakly dependent on the particular metal ion involved. This means that it is possible to grow samples in which nearly lattice matched multilayers contain atomic oxide planes that each would show very different physical behavior in bulk. Thus, it is in principle possible to control electron state filling by modulation doping specific atomic oxide lanes. It is possible to bring two very different order parameters together and make them interact at atomically precise interfaces with little strain. To fabricate samples in which such atomic scale materials engineering is employed, we have developed atomic layer by layer molecular beam epitaxy. We have used this to make samples including superconducting, magnetic and ferroelectric layers. We have studied tunneling in a variety of systems and have found such samples to be useful in understanding the excitation spectrum of superconductors and magnetic oxides.
11:10 AM		H1-9 Elucidation of the Reaction Sequences of Binary and Ternary Systems of CIGS H.J. Moore, D.L. Olson (Colorado School of Mines); R. Noufi (National Renewable Energy Laboratory) The binary and ternary systems of the quarternary system of copper, indium, gallium and selenium have been studied, in the form of multilayer thin films, for the purpose of understanding thin film phase transformations that are relevant to the production of Cu(In,Ga)Se₂ (CIGS) photovoltaic solar cells. For example, the intermetallic phases that are present during selenization of precursor films will affect film microstructure and the resulting film properties. The effective heat of formation (EHF) model has been used to predict phase formation sequences of the binary systems. By expanding the EHF model, the ternary systems of CIGS were predicted. The accuracy of these predictions was explored experimentally. By using differential thermal analysis (DTA), the reaction kinetics of product film formation were examined. X-ray diffraction (XRD) was used to determine reactant and product phases. Energy dispersive spectroscopy (EDS) was also used to support the results.
11:30 AM		H1-10 Producing Thin Films Using Low Pressure Plama Spray E.J. Young (Colorado School of Mines); M. Loch (Sulzer Metco, Switzerland); T. Ohno, C. Suryanarayana, J.J. Moore (Colorado School of Mines) Low pressure plasma spray (LPPS) coatings became common in the turbine industry over twenty years ago. The coatings on turbine blades provide thermal protection and tend to be very thick. Today, thinner coatings are being produced by LPPS in an attempt to fill the gap between physical vapor deposition (PVD) processes and other thick coating technologies, such as air plasma spray (APS) coatings. Ten micron alumina, Al₂O₃, coatings were deposited by the LPPS process. These coatings were evaluated using optical microscopy, scanning electron microscopy (SEM), x-ray diffraction, Auger electron spectroscopy (AES), and scratch testing. Different substrate preparations were evaluated for these thin coatings. The coatings tested exhibited chemical homogeneity from one sample to the next. Examination of the coatings using SEM and x-ray diffraction showed phase homogeneity of α-alumina to γ-alumina in excess of 90 percent. The LPPS process has high depostion rates, which may enable thin coatings (slightly thicker than PVD coatings) to be produced with savings in process time and cost.
11:50 AM		H1-11 A Novel Pulsed Magnetron Sputter Source Utilizing Very High Target Power Densities V.M. Kouznetsov, K. Macák, J.M. Schneider, A. Hörling, U. Helmersson (Linköping University, Sweden); I. Petrov (University of Illinois) The power density usually employed in DC magnetron sputtering is up to16 W/cm². Recently average values for the target power density as high as 28 W/cm² were reported for medium frequency pulsed DC magnetron sputtering. We have designed a novel pulsed power-source / magnetron system where peak power density-and average power density values of 2 kW/cm² and 2 W/cm² can be reached in stable operation. We have varied the average target power density and have carried out time resolved plasma probe measurements. Both the plasma density and electron temperature were found to increase as the target power density was increased. Furthermore we will report the effect of the target power density on Cu trench filling experiments.