Program Organizer: Dr. David E. Jesson, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6030
Thursday, AM Room: Orange County 4
February 8, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: David J. Srolovitz, Department of Materials Science and Engineering, The University of Michigan, 2300 Hayward, Ann Arbor, Michigan 48109
8:30 am Invited
INTERFACIAL FORCE MICROSCOPY MEASUREMENTS OF THE NANOMECHANICAL PROPERTIES OF MATERIALS, J. E. Houston, T. A. Michalske, Sandia National Laboratories, Albuquerque, NM 87185- 1413
Scanning probe techniques have shown dramatic growth over the last several years and are presently making significant impact on surface and interfacial problems in material science. Interfacial Force Microscopy (IFM) utilizes a self balancing force sensor which permits stable operation in both the attractive and repulsive modes with effectively a zero compliance. In recent studies, we have taken advantage of these unique sensor properties in applications to the study of the mechanical properties of materials at the nano- meter scale. In this presentation, we show results demonstrating the enhanced capabilities of the IFM in application to studies of the elastic and plastic deformation of single nano- scale grains in a polycrystalline films of Au as well as single- crystal Au surfaces. We show examples of superplastic behavior in polycrystalline films, the role of tip radius in nucleating dislocations leading to plasticity, and the effect on the measured nanomechanical properties of varying the crystalline surface for the single- crystal work. This work is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences under contract DE- AC04- 94AL85000.
9:00 am Invited
A FINITE ELEMENT APPROACH TO SIMULATING EVOLVING MICROSTRUCTURES IN THIN FILMS: Z. Suo, Mechanical and Environmental Engineering Department, University of California, Santa Barbara, CA 93106
This presentation describes a class of simulation methods for structural evolution in materials. The method is formulated on the basis of an integral form of the nonequilibrium thermodynamics, uses finite elements to model structural features (e.g., grain boundaries), and results in a set of ordinary differential equations that govern the time evolution. The method has been used to simulate diverse phenomena, including grain growth, surface diffusion, and ferroelectric domain evolution. This presentation uses epitaxial grain growth in thin films as example to illustrate the method. When a polycrystalline film is heated, the grains with small free energies enlarge at the expense of the grains with larger free energies. The process may eventually produce a single crystal film. A number of events, however, can happen to prevent the film to evolve to a single crystal. For example, surface grooving can break the film into droplets. The finite element method is used to study the competition among these and other kinetic processes.
9:30 am
EPITAXIAL DIAMOND FILMS ON SILICON (001) SURFACE: Chonglin Chen, Gary S. Song, Terence E. Mitchell CMS, MS- K765, Los Alamos National Laboratory, Los Alamos, NM 87545; Byungyou Hong, Robert Collins, Russel Messier Materials Research Laboratory, Pennsylvania State University, Pennsylvania, PA 16802
The nucleation and growth behavior of nanocrystalline diamond thin films on Si substrate, prepared by plasma- enhanced chemical vapor deposition in a Ch4/H2/O2 mixture gas atmosphere, has been studied using high- resolution transmission electron microscopy (HRTEM). Results show that an amorphous interlayer of ~150 Å was formed prior to diamond nucleation. Local epitaxial growth of nanocrystalline diamond grains in the thin films on Si (001) surface has been observed. HRTEM images reveal that the epitaxial orientation relationship follows either a 3:2- match cube on cube arrangement with an ~7deg. tilt and a small angle rotation between the diamond lattice and the substrate lattice, or a 1:1- match with (lll)diamond/(0ll)si and [001]diamond/[O1l]si.
9:50 am
THIN FILM TEXTURES OF Au, Ag, Pd, AND Au- Pd COUPLES: Young S. Chung, Keenan L. Evans, Motorola, 5005 E. McDowell Rd. P004, Phoenix, AZ 85008
The crystal textures of polycrystalline films of Au, Pd, Ag and Au- Pd couples before and after annealing at 400deg.C were investigated via the x- ray diffraction pole figure method. The extent of a specific plane texture exhibited a significant dependence on metallic species and composition. Interaction between the substrate surface and condensed metals during the initial nucleation process is important in determining the ultimate film texture. The {111} texture formation on Au- Pd thin film couples displayed a strong dependence on the nature of the underlying seed layer. Gold films deposited on a palladium seed layer revealed much less (111} texture, than Au films deposited directly on a silicon dioxide surface. On the contrary, Pd films deposited on polycrystalline Au films showed higher degree of {111} texture, compared to Pd films deposited directly on silicon dioxide. Annealing the films greatly enhanced the degree of {111} texture, and the order of deposition affects the texture of the Au- Pd alloy films after annealing
10:10 am BREAK
DEFECTS III
Session Chairperson: W. W. Gerberich, Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
10:30 am
GROWTH AND CHARACTERIZATION OF ALUMINUM FILMS ON SAPPHIRE (0001): K. F. McCarty, D. L. Medlin, R. Q. Hwang, P. B. Mirkarimi, S. E. Guthrie, N. R. Moody, M. I. Baskes, Sandia National Laboratories, Livermore, CA 94551
We are studying aluminum films on a- alumina as a model system for film/substrate effects in electronics packaging. In particular, we are investigating the texture and possible epitaxy of aluminum films grown on sapphire (0001) surfaces. Aluminum films are deposited on sapphire (0001) surfaces by both an energetic process (pulsed laser deposition) and a thermal process (evaporation). The film structure is characterized both in situ (reflection high- energy electron diffraction) and ex situ (high- resolution and conventional transmission electron microscopy and atomic force microscopy). The observed interface structure is compared to predictions of semi- empirical, atomistic calculations. The work of adhesion of the films to the substrate is determined by micro- scratch testing. We emphasize the relationships between the conditions of growth, the structure of the interface, and the resulting mechanical properties. This work was performed under U.S. DOE contract DE- AC04- 94AL85000.
10:50 am
HETEROGENEOUS GENERATION OF STACKING FAULTS IN SEMICONDUCTORS:, Y. Chen, S. Ruvimov, J. Jasinski Z. Liliental- Weber, and J. Washburn, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720
In our experiments, stacking faults were observed frequently in semiconductors in which there was nonstoichiometry. For example, in low- temperature grown, and in annealed As- implanted GaAs, a high density of stacking faults have been observed. An atomic model is proposed to explain that a stacking fault is induced in this case by the excess As during crystal growth. In ZnSe epilayers grown on GaAs substrates, stacking faults were also frequently observed, and the density of the stacking faults is influenced by the different types of interfacial structures (SeZn/AsGa or ZnSe/GaAs). The different stacking fault densities are explained by the local bonding between Ga/Se or Zn/As. Different densities of stacking faults were also observed in GaN bulk crystal for growth along [0001] compared to growth along [30-1]. In this case too the formation of stacking fault appears to be influenced by excess Ga. In general, the existence of nonstoichiometry, which can distort the local atomic bonding, seems to induce the formation of stacking faults during crystal growth.
11:10 am
GROWTH AND RELAXATION OF HETEROEPITAXIAL Si1- x- yGexCy FILMS ON Si(100): Harald Jacobsson, Nicole Herbots, Sean Hearne, Joan Xiang, Peihua Ye, Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287
The new group IV- IV- IV ternary semiconductor Si1-x-yGexcy offers new possibilities for strain modification and bandgap engineering on a Si substrate. In this work the growth kinetics and onset of relaxation for a cubic diamond, solid solution of Si1-x-yGexcy has been investigated. Epitaxial quality and defect nucleation has been studied using Rutherford backscattering combined with ion channeling (IC) in different axial directions, transmission electron microscopy (TEM) and infrared spectroscopy (IR). The results show that the films are epitaxial. The crystalline quality is fair at low carbon concentration but the defect density increases with increasing carbon concentration. The energy dependence of the minimum yield, combined with TEM observations, shows that dislocations dominate at lower carbon concentrations, whereas stacking faults dominate at higher carbon concentrations. Both IC and IR spectra indicate an increase in bondlength distribution with increasing carbon concentration. These observations suggest that carbon is detrimental to the elastic properties of Si1-xGex causing relaxation and defect nucleation when carbon concentrations exceed 2%.
11:30 am
LATTICE MISMATCH INDUCED ROUGHENING IN THE MBE GROWTH OF NbxTil- XO2 on TiO2 (110) and (100): Y. Gao, S. A. Chambers, Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, P.O. Box 999, MS K2- 12, Richland, WA 99352
We have grown single- crystal, mixed rutile phases of NbxTi1-xO2 on TiO2 (110) and (100) by molecular beam epitaxy for x ranging from 0.02 to 0.50. The resulting epitaxial films have been characterized by means of RHEED, LEED, UPS, XPS, XPD, AFM, and TEM. From the resulting analyses, we have determined that Nb goes in substitutionally to cation sites in the rutile lattice, displaces Ti, and assumes a +4 oxidation state. Surface roughening occurs as x increases for both crystal orientations. However, significant roughening occurs at x = 0.15 on (100) compared to a value of x = 0.30 for (110). This difference comes about because of the numerical values of the Ti- O and Nb- O bond lengths. The irregular octrahedral M- O bond lengths, R1 and R2, differ by 1% and 12% in going from TiO2 to NbO2, respectively. Significantly, only half the metal atoms in a given layer of the (110) growth surface have in- plane components of R2 whereas every metal atom in the (100) growth plane has such components. Thus, there is a substantially larger in- plane lattice mismatch when the growth surface is (100) compared to (110). Therefore, misfit dislocation nucleation and subsequent step formation at the surface occurs for a lower value of x on (100), leading to surface roughening. Pacific Northwest Laboratory is operated for the U.S. Departrnent of Energy by Battelle Memorial Institute under contract De- AcO6- 76RL0 1830.
11:50 am
EVOLUTION OF MISFIT DISLOCATION NETWORK AND MORPHOLOGY IN OMVPE GROWN (001) ZnSe/GaAs: S. Ruvimov, E. D. Bourret, J. Washburn, Y. Chen, W. Swider, and Z. Liliental- Weber, Lawrence Berkeley Laboratory, Berkeley, CA 94720
Transmission electron microscopy and X-
ray
diffraction techniques have been applied to study strain relaxation and the
evolution of the dislocation structure and morphology of ZnSe epilayers grown
by low pressure OMVPE on a (001) surface of semi-
insulating
GaAs. Before the ZnSe growth, the substrate surface was exposed at
650deg.C to a flow of tertiarybutyl arsine to form an As-
terminated
surface. This surface treatment is shown to result in a drastic decrease in the
SF density. For the first time formation of 60deg. misfit dislocations was
observed at a layer thickness of 0.05 um. This agrees well with the theoretical
critical thickness expected for misfit dislocation formation in the ZnSe/GaAs
system, but is much lower than the experimental critical thickness of 0.15-
0.2
um reported earlier. Various mechanisms of dislocation generation were observed
at different growth stages. The evolution of dislocation structure is discussed
in relation with layer morphology.
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