ICMCTF2004 Session TS3: The Atomistics of Thin Film Growth: Computational and Experimental Studies

Monday, April 19, 2004 10:30 AM in Room Sunset

Monday Morning

Start	Invited?	Item
10:30 AM	Invited	TS3-1 From Ab-initio to Classical Computational Studies in Thin Film Science V. Chirita (Linköping University, Sweden) The successful synthesis of a new crystalline phase for boron suboxide thin films, based solely on ab-initio calculations, is discussed. An overview of the atomic processes, as observed in classical computer simulations, induced by low-energy ion irradiation on inter- and intralayer mass transport during the initial stages of growth, is also presented. This includes effects on single adatoms, two-dimensional clusters and adatom/vacancy interactions with clusters on metallic surfaces. The underlying features and applicability of the two computational methods to thin films research are highlighted. What’s good, what’s bad, what one can do and what one cannot do, are some of the questions addressed herein.
11:10 AM	Invited	TS3-3 Dynamic Microscopy of Surface and Interface Processes R. Tromp (IBM T.J. Watson Research Center) Over the last decade, in-situ dynamic microscopy has made significant contributions to our understanding of surface and interface processes. Examples include the dynamics and energetics of surface structures phase transitions, the stability and thermodynamics of clean surfaces, nucleation and growth of thin epitaxial films, interfacial alloying, the formation of inorganic-organic interfaces, etcetera. Microscopy techniques used at IBM include Low Energy Electron Microscopy (LEEM), Utra-High Vacuum Transmission Electron Microscopy (UHV-TEM), and Liquid Cell TEM (LC-TEM). The recent development of LC-TEM expands the range of processes that can be studied into the technologically and scientifically important solid-liquid interface area. In this talk I will give an overview of recent results, illustrated with video sequences of relevant dynamic surface and interfaces processes.
11:50 AM		TS3-5 Ab Initio Calculations and Experimental Determination of the Structure of Cr₂AlC J.M. Schneider, Z. Sun, R. Mertens, F. Uestel (RWTH Aachen, Germany); R. Ahuja (Uppsala University, Sweden) We have calculated the equilibrium volume and the density of states (DOS) of Cr₂AlC for antiferromagnetic (AFM), ferromagnetic (FM) and paramagnetic (PM) configurations by ab initio total energy calculations. Based on a comparison of the cohesive energies as well as the DOS for all three magnetic configurations we have identified the AFM configuration to be the most stable one. Furthermore, we report the structural characterisation of polycrystalline Cr₂AlC thin films grown by magnetron sputtering. Our calculated interplanar distances and equilibrium volume for the antiferromagnetic configuration are in excellent agreement with glancing incidence X-ray diffraction data of the as deposited Cr₂AlC thin films, which supports our theoretical prediction.
12:10 PM		TS3-6 Relative Stability of Alumina Phases: the Effect of Additives as Calculated by DFT J.M. Andersson, E. Wallin (Linköping University, Sweden); D. Music (RWTH Aachen University, Germany); V. Chirita, U. Helmersson (Linköping University, Sweden) Alumina (Al₂O₃) exists in a number of meta-stable polymorphs in addition to the thermodynamically stable α phase. Both the stable and meta-stable aluminas have found important applications, but their structural complexity can lead to technical problems. On the one hand, the use of meta-stable aluminas is limited by phase transformations at elevated temperatures. On the other hand, synthesis of α-alumina typically requires high temperatures (about 1000°C) which limits the choice of substrate material and can induce unwanted chemical reactions. Thus, understanding and controlling the stability of alumina phases is of great importance. We have shown previously [J.M. Andersson, Zs. Czigány, P. Jin, and U. Helmersson, submitted to J. Vac. Sci. Technol. A] that α-alumina can be grown at very low temperatures (280°C) by using a chromia nucleation layer, indicating that alumina growth is highly nucleation controlled. Furthermore, it is known that the transition aluminas have lower surface energies than α-alumina [see e.g. J.M. McHale, A. Auroux, A.J. Perotta, and A. Navrotsky, Science 277, 788 (1997)]. This difference in surface energy offers an explanation to why the meta-stable polymorphs often form instead of the α phase. In this work we investigate the effect of substitutional additives on the phase stability of α- and θ-alumina (as a representative of the transition aluminas) by means of density functional theory (DFT). Calculations are done by substituting various amounts of Al ions by other metal ions (e.g. Cr, Sc, Fe, B, Cu). Preliminary results show that 5 at.% of Cr or Sc shifts the total energy of the θ phase relative to the α form by -23 or -15 meV/atom, respectively, while 10 at.% of Cr yields a -98 meV shift. There is thus a clear trend that these substitutions stabilize the θ structure, and that it is possible to make it energetically favorable compared to the α phase.