Materials Week '97: Wednesday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Wednesday afternoon, September 17.

BOUNDARIES AND INTERFACES IN MATERIALS: THE DAVID A. SMITH SYMPOSIUM: Session VI

Session Chair: Adrian P. Sutton, The University of Oxford, Oxford, UK

SOME APPLICATIONS OF MAZED MULTICRYSTAL FILMS IN INTERFACE RESEARCH: U. Dahmen, K.H. Westmacott, National Center for Electron Microscopy, LBNL, Berkeley, CA 94720

Polycrystalline thin films with extreme texture, containing only two, three or four different grain orientations, can be grown in a maze-like topology by heteroepitaxial deposition on single crystal substrates. Although the misorientation between grains is fixed, the inclination of the grain boundaries is variable and thus free to reach local equilibrium. Such mazed multicrystal films are excellent for fundamental studies of grain boundary behavior, especially in the important size range accessible only to electron microscopy. This talk will illustrate applications of this thin film geometry to the study of grain boundary phenomena such as faceting and dissociation reactions, segregation, second phase precipitation, color crystallography and the force balance at triple junctions. Research supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under contract #DE-ACO3-76SFOOO98.

2:30 pm INVITED

ROLE OF GRAIN BOUNDARIES AND INTERFACES IN THIN FILM REACTIONS: K. Barmak, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015

Interest in thin film reactions is driven by the importance of these reactions in technological applications. For example the formation of silicides and aluminides plays an important role in semiconductor metallization schemes. There is now growing evidence that accurate descriptions of these reactions must consider not only the growth stage, but also the nucleation stage for product phase formation. In this paper, experimental and theoretical studies of the role of interfaces and grain boundaries in nucleation and growth of product phases will be discussed. In addition, the evolution of grain structure of product phases and the similarities and differences of these structures to those classified in structure zone models for vapor-deposited films will be addressed.

3:00 pm INVITED

THIN FILM MICROSTRUCTURES PRODUCED BY NUCLEATION AND GROWTH TO IMPINGEMENT: H.J. Frost, C.V. Thompson^*, Thayer School of Engineering, Dartmouth College, Hanover, NH; ^*Department of Materials Science and Engineering, MIT, Cambridge, MA

Recent simulations of phase transformations involving nucleation and growth-to-impingement, in both two and three dimensions, have allowed substantial progress beyond the original analytic modeling of Johnson and Mehl, Avrami, and Kolmorgorov, in providing descriptions of the details of the topology and geometry which result from a wide variety of nucleation conditions and growth conditions. Careful experimental studies of the geometrical and topological properties of real microstructures have been far less common. Accurate studies of three dimensional structures are difficult because they require laborious cross-sectioning. In rare cases, a phase transformation within a thin film may be accurately described as a two-dimensional process. In this case the microstructure may be easily observed and compared directly with computer simulations, so as to quantitatively establish the conditions of the nucleation and growth processes. A classic example of this is provided by the experiments on the crystallization of films of amorphous silicides performed by Professor David A. Smith and co-workers. In this paper we will review both the experimental and the computer simulation literature describing the microstructures resulting from phase transformations involving nucleation and growth-to-impingement in thin films, focusing especially on the microstructures reported by Smith and coworkers.

3:30 pm BREAK

3:40 pm INVITED

MORPHOLOGY AND KINETICS OF CRYSTALLIZATION OF AMORPHOUS CoSi₂ THIN FILMS: K.N. Tu, J.M. Liang¹, L.J. Chen¹, L.T. Shi², Department of Materials Science and Engineering, University of California - Los Angeles, Los Angeles, CA 90095; ¹Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, China; ²IBM T.J. Watson Research Center, Yorktown Heights, NY 10598

The morphology and kinetics of crystallization of amorphous CoSi₂ thin films in the temperature range of 130 to 160°C were studied by using TEM, resistivity, and calorimetry techniques. The nucleation rate and growth rate of crystalline CoSi₂ particles were measured independently from TEM images. The rate of transformation was measured by resistivity changes, and the heat of transformation by differential scanning calorimetry. These data were combined to obtain an understanding of the kinetic behavior of the crystallization. An attempt to calculate the interfacial energy between the crystalline and amorphous CoSi₂ is given.

4:10 pm INVITED

STRUCTURE OF FUSED INTERFACES BETWEEN InP AND GaAs: L. Sagalowicz, A. Rudra, P.H. Jouneau, A. Sirbu, E. Kapon, Institute for Micro and Optoelectronics, Department of Physics, Ecole Polytechnique Fdrale de Lausanne, 1015 Lausanne, Switzerland

For some optoelectronic applications, it is necessary to grow (001) InP epitaxially onto (001) GaAs, with a cube on cube orientation relationship. There is a 3.9% mismatch between the two structures and geometrical theories predict that the easiest way to accomodate the misfit is through a square network of edge (Lomer) dislocations spaced by 104Å. Conventional epitaxial growth techniques lead to the development of threading dislocations. Wafer fusion is tested to see if it leads to a better confinement of the dislocations at the interface. TEM is used to study the structure of the interface and the dislocation content for various fusion conditions. high resolution transmission electron microscopy (HRTEM) reveals that the interface is made up either by edge dislocations, or by an amorphous intermediate layer for which the thickness is about 2 nm. It was determined by electron energy loss spectroscopy that this layer is made of indium oxide. In all cases, HRTEM and plan view electron microscopy indicate that the defects are confined at the fused interface.

4:40 pm

INTERPHASE INTERFACES AND THE FORMATION OF THE FERROMAGNETIC -PHASE IN MnAl-BASE PERMANENT MAGNET ALLOYS: D.P. Hoydick, W.A. Soffa, Department. of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, PA 15261

Recently, new electron microscopy studies of the (hcp)'(B19)(L1₀) transformation in MnAl-base permanent magnet alloys have shown that the formation of the ferromagnetic -phase involves a diffusional nucleation and growth process akin to the so-called "massive transformation". These results contradict the conventional wisdom that has been promulgated for nearly 30 years which identified the transformation mechanism as a shear or martensitic mode. The mechanism of transformation will be discussed with an emphasis on the nature of the interphase interfaces and the attendant transformation twinning involved. Work supported by the National Science Foundation (DMR).

5:00 pm

THE ROLE OF GRAIN BOUNDARY MOBILITY IN THE DEVELOPMENT OF GOSS TEXTURE IN Fe-3%Si: P. Lin^1,2, G. Palumbo¹, E.M. Lehockey¹, K.T. Aust², ¹Ontario Hydro Technologies, 800 Kipling Avenue, Toronto, Canada M8Z 5S4; ²Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada M5S 3E4

Coincidence site lattice (CSL) grain boundaries have been shown to play an important role in the development of the Goss texture in the early stages of secondary recrystallization in Fe-3%Si. A "deficit" of these CSL boundaries, relative to the determined probability of occurrence during random growth, was determined for interfaces bounding Goss grains. This deficit is rationalized on the basis of preferential replacement of CSL boundaries by general (or higher S) interfaces due to the enhanced mobility of low S CSL grain boundaries. A simple statistical approach is applied to assess the relative mobility of CSL and non-CSL interfaces.