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Session Chairs: D.J. Srolovitz, Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136; D.P. Adams, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185
8:30 am INVITED
CORRECTION FACTORS TO THE CLASSICAL NUCLEATION RATE: David T. Wu, Dept. of Mechanical Engineering, Yale University, New Haven, CT 06520
The rate of nucleation can have a strong influence on the microstructure of thin films. This talk discusses corrections to the classical expression for nucleation rate. For heterogeneous nucleation's spherical cap model a new contact-angle dependence for the prefactor is presented, while in homogeneous nucleation the self-consistency correction is reconsidered using the idea of "kinetic potential." Both corrections can increase the nucleation rate significantly.
9:10 am INVITED
EVOLUTION OF THIN FILM MICROSTRUCTURE AND MORPHOLOGY DURING CHEMICAL VAPOR DEPOSITION: D.P.Adams, T.M. Mayer, E. Chason, B.S. Swartzentruber, Sandia National Laboratories, P.O. Box 5800, Albuquerque, N.M. 87185
We present a study of thin film growth by thermal chemical vapor deposition (CVD). In this investigation of metal growth onto Si substrates, the effects of chemical kinetic processes on both film structure and morphology are determined. Scanning tunneling microscopy is used to identify the nucleation sites and to monitor island growth during the submonolayer regime. Analysis of measured island size distributions reveals the importance of site-specific chemical reactions and precursor molecule diffusion. Also, we monitor the development of surface roughness of thicker films by x-ray reflectivity. These experiments demonstrate the influence of nucleation rate on surface morphology. Finally, we show how CVD kinetics can be manipulated by use of adsorbates which passivate chemically - reactive substrate sites. Adsorbate layers have been used to modify the nucleation rate and fabricate nanometer - size structures via selective - area growth. This work was supported by the U.S. Department of Energy under contract DE-AC04-94AL85000.
TEM INVESTIGATION OF CVD ALUMINA MULTILAYER COATINGS: M. Halvarsson, Department of Physics, Chalmers University of Technology, S-412 96 Göteborg, Sweden; S. Vuorinen, Research and Development, Seco Tools AB, S-737 82 Fagersta, Sweden
Chemically vapour deposited (CVD) alumina is frequently used as a wear-resistant coating on cemented carbide cutting tool inserts. Two crystallographic modifications of alumina are used, a-Al2O3 and k-Al2O3, often in combination with TiN, TiC, and Ti(C,N). In this paper, the microstructures of single and multilayer coatings of CVD k-Al2O3 have been investigated. The aim of this work was to describe the detailed microstructure of the coatings and relate this to mechanical properties and tool life. Deposition of the experimental coatings was carried out in a computer-controlled hot-wall CVD reactor. The coatings were examined by analytical scanning and transmission electron microscopy (SEM/EDX and TEM/EDX).
10:10 am BREAK
10:30 am INVITED
MOLECULAR VIEW OF CVD DIAMOND FILM GROWTH: David J. Srolovitz, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136; Corbett Battaile*, James E. Butler, DDGas/Surface Dynamics Section, Code 6174, Naval Research Laboratory, Washington DC 20375-0001
Kinetic Monte Carlo computer simulations of the growth of diamond thin films are presented as a function of hot filament chemical vapor deposition reactor conditions. The model includes chemical reactions between surface atoms, gaseous hydrogen and hydrocarbons, and between species on adjacent surface sites. Gas phase hydrocarbon composition is varied over six orders of magnitude. The effects of surface atomic structure and morphology on growth behavior are included explicitly. The evolution of surface structure (including reconstruction) during growth and evidence for step-flow growth and surface roughening will be presented. Model predictions for the growth rates of high symmetry facets will be presented and the influence of these growth rates on surface roughness, microstructure, point defect incorporation and texture will be discussed.
MICROSTRUCTURAL INVESTIGATION OF THE GROWTH OF YBa2Cu3O7-x /Nd2CuO4/YbA2Cu3O7-x TRILAYERED FILMS ON LaSrGaO4 SUBSTRATES: Y.H.Li, A.E. Staton-Bevan, Department of Materials, Imperial College, London SW7 2BP, UK; Z. Trajanovic, I. Takeuchi, T. Venkatesan, Department of Physics, University of Maryland, MD 20742
A HRTEM study of an YBCO/Nd2CuO4/YBCO trilayered films on LaSrGaO4 substrate with PBCO as a template layer has shown that in-plane aligned a-axis oriented YBCO films may be grown on (100) LaSrGaO4 substrates by pulsed laser deposition, which contain some domains with the c-axis misaligned by 90° in plane of the films. A Nd2CuO4 insulating layer, with a thickness of approximately 10nm, may be grown epitaxially between a-axis oriented YBCO layers with its c-axis parallel to the c-axis of the YBCO layers. A 90°-misoriented a-axis YBCO grain in the lower YBCO layer can nucleate a 90°-misoriented Nd2CuO4 grain in the a-axis oriented Nd2CuO4 layer and this grain can further nucleate a 90°-misoriented YBCO grain in the top YBCO layer. Narrow vertical Nd2O3 plates were observed in 90°-misoriented Nd2CuO4 grains formed epitaxially with the Nd2CuO4 grains. The interface between the PBCO template layer and the LaSrGaO4 substrate is quite rough with some amorphous islands in the template layer.
ADVANCES IN THE PROCESSING AND APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTING FILMS: M. Sisodia, R.K. Yadava, Dept. of Metallurgical Engineering, Malaviya Regional Engineering College, Jaipur 302 017, India
High critical temperature (high-Tc) superconductors have captured the interest of engineers and scientists world wide. For its commercial utilization in the field of microelectronics and electronic systems, they must be fabricated into desirable configurations, thin and thick films. During studies it has been observed that these superconducting thin films operating at liquid N2 temperature offer great possibilities for faster, more sensitive and precise electronics devices. Present paper reviews the fabrication techniques of high-Tc superconducting thin films which primarily includes Pulsed-Laser Deposition, Molecular ion beam epitaxy, Chemical Vapour Deposition (CVD) by using epitaxial growth on single crystal substrates (YSZ, MgO, Si, etc.) with excellent microstructural control and properties relationship. In addition to it, thick film fabrication is also discussed with major techniques like Screen Printing and Plasma Spraying along with associated processing parameters. Furthermore, advanced applications of each are enumerated at length.
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