Program Organizer: Dr. David E. Jesson, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6030
Wednesday, PM Room: Orange County 4
February 7, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: Brad Orr, Dept. of Physics, The University of Michigan, Ann Arbor, MI 48109-1120
2:00 pm Invited
AN AFM STUDY OF THE GROWTH MECHANISMS AND MORPHOLOGIES OF SOLUTION- BASED CRYSTALS, J. J. De Yoreo, A. J. Malkin, T. A. Land, Lawrence Livermore National Laboratory, Livermore, CA, 94550; Yu G. Kuznetsov, J. D. Lee, A McPherson, Department of Biochemistry, University of California, Riverside, CA, 92521
Most studies of the nanometer scale morphology of crystalline surfaces have focused on the growth of thin films by molecular beam epitaxy or sputter deposition where growth proceeds at high supersaturation and low flux through 2D nucleation and multi- layer growth and where the critical nucleus consists of as few as one atom. In contrast, many bulk single crystals, both organic and inorganic, are grown from vapors or solutions at much lower supersaturations and higher fluxes where stable islands consist of tens to hundreds of molecules. We describe the results of both freeze- and- look and in situ atomic force microscopy (AFM) on single crystal surfaces of both inorganic and macromolecular systems grown from solution. The lattice spacings in these systems range from less than 5 Å for KH2PO4 (KDP) and CaCO3 to over 80 Å for the protein Canavalin and 160 Å for the Sattelite Tobacco Mosaic Virus (STMV). We observe multiple growth mechanisms including step flow on hillocks formed by screw dislocations as well as 2D and 3D nucleation of islands. We compare the growth morphologies to the predictions of classic growth models and from measurements of step and island dynamics we calculate the step edge free energies and the kinetic coefficients of elementary steps. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W- 7405- ENG- 48.
2:30 pm
FASCINATING PHYSICS OF THE Pb/Ge(111) INTERFACE:, J. M. Carpinelli, Department of Physics, University of Pennsylvania, Philadelphia, PA 19104; H.H. Weitering, Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996; E.W. Plummer, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; Roland Stumpf, Sandia National Laboratory, Albuquerque, NM 87185
The morass of different phases of thin Pb films on Ge(111) exhibit a tremendous assortment of physical phenomena. We have investigated the structural and electronic properties of these films as a function of temperature and coverage using STM, LEED, and EELS. Two metal- nonmetal transitions are observed for the ([[radical]]3 x [[radical]]13)R30deg. T4 adatom structure. The first occurs at room temperature with increasing Pb coverage, as this interface evolves from the mosaic phase to the alpha phase. The second occurs gradually and reversibly with decreasing temperature (onset near - 50deg.C) on the alpha phase, accompanying the formation of a (3 x 3) surface charge density wave and corresponding structural rippling. First principles calculations of the alpha phase indicate that there is a basic instability in this interface that could lead to the observed low- temperature structure. However, this predicted instability is too low in energy and produces atomic displacements that are too small to fully explain our observations.
2:50 pm
PREPARATION AND CHARACTERIZATION OF TiO2 THIN FILMS BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION: In- Soon Lee, Yoon- Bong Hahn, Department of Chemical Engineering & Technology, Chonbuk National University, Duckjin- Dong lGa, Chonju 561- 756, Korea
Dielectric TiO2 thin films were prepared on p- Si(100) substrates by plasma enhanced chemical vapor deposition using titanium isopropoxide and oxygen. Experiments were carried out under various operation conditions. Properties of the films were characterized by Ellipsometer, Auger electron spectroscopy, X- ray diffraction, FTIR, SEM, EDX, and LCR meter. The deposition rate was little affected by oxygen flow rate, but much influenced by RF power, substrate temperature, gap distance between electrodes, and feed rate of precursor. Morphology of the film became coarser with increasing the deposition time, and the film showed less uniformity at high deposition rates. It was also found that the deposition rate is controlled by surface reaction below 200deg.C, but controlled by mass transfer at higher temperatures. The effect of plasma annealing on the electrical properties of as- deposited TiO2 films was also investigated.
3:10 pm
ATOMIC STRUCTURES AND GROWTH MORPHOLOGIES OF ELECTRODEPOSITED METAL THIN FILMS ON SINGLE CRYSTAL GOLD SURFACES OBSERVED BY IN- SITU ATOMIC FORCE MICROSCOPY: N. Ikemiya,S. Hara, Department of Materials Science and Processing, Faculty of Engineering, Osaka University, Yamadaoka 2- 1, Suita 565, Japan
We have investigated atomic structures as well as nucleation and growth mechanisms of electrodeposited Ag, Cu, and Te thin films on single crystal Au surfaces using in- situ atomic force microscopy. We have determined atomic structures of underpotentially deposited metal monolayers in acidic electrolytes. We have found the growth morphologies of bulk deposited metal thin films are controlled mainly by the surface diffusion processes of metal adatoms on substrates. We will discuss epitaxial relationships between metal thin films and substrates and the relaxation mechanisms of strained thin Te films with large lattice misfits.
3:30 pm BREAK
3:50 pm Invited
LOW TEMPERATURE EPITAXIAL GROWTH OF Si: S. M. Yalisove, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109- 2136
Homoepitaxial growth of Si has been shown to occur at temperatures far below traditional epitaxial temperatures via a limited thickness epitaxy pathway. The atomistic mechanisms which control limited thickness epitaxy are not yet understood. Many factors, such as impurities, surface roughness, temperature, and energy of the arriving species can alter the kinetics of the mechanism. Work will be presented which suggests that the phenomenon is intrinsic and controlled via a specific nucleation site. Data from studies on patterned substrates are consistent with the idea that the nucleation site for the crystalline to amorphous phase is at the intersection of (111) microfacets. The density of the microfacets can be controlled and shown to have a strong effect on the process of limited thickness epitaxial growth. These data will be discussed in the context of other systems which display similar phenomena.
4:20 pm Invited
EVOLUTION OF SURFACE MORPHOLOGY OF EPITAXIAL CALCIUM FLUORIDE FILMS: L. J. Schowalter, Byong Kim, Dept. Physics and Ctr. Integrated Electronics and Electronis Manufacturing, Rensselaer Polytechnic Institute, Troy, NY 12180
The growth of CaF2 on Si(111) vicinal substrates (tilted towards the [1 1 - 2] azimuth) has been studied using RHEED, AFM, and SEM. For growth at 770deg.C, the CaF2 grows in a layer- by- layer fashion for the first two monolayers as indicated by RHEED intensity oscillations. After two monolayers, CaF2 strongly prefers to nucleate at the Si step edges and grow laterally with constant height. The Si step edges will form step bands for this substrate orientation (~5 nm for 20 miscut substrates). Interestingly, once the CaF2 nucleates at a step band, it immediately grows to the same height as the step band and then grows out and along the step band will maintaining a uniform height. Eventually these thick islands coalesce and form a relatively flat overlayer. These results can be understood if the relative energy (per molecule) to form a third layer is very high and can not be explained as due to relative mobility differences between thick and thin CaF2.
4:50 pm
CHARACTERIZATION OF LOW TEMPERATURE GROWTH OF A HETEROEPITAXIAL SYSTEM: G.Vidali, Hong Zeng, and Chi Liu, The Solid State Science and Technology. Program and Physics Department, Syracuse University, Syracuse, NY 13244
In- situ and in real time characterization by atom beam scattering of deposition of Pb on Cu(001) at 150 K gives the opportunity to study the growth of a heteroepitaxial system with large lattice mismatch from submonolayer coverage to hundreds of layers. The first Pb layer forms a high order commensurate square symmetry phase; this is followed by double- stepped islands growth in the [001] Pb direction. From the fourth layer to the 16th layer, there is a quasi layerby- layer growth of Pb(111); this is to be contrasted with cluster growth for deposition at room temperature. Then the film roughens, with the vertical width growing as ~ t0.3; the average domain size decreases and Pb(111) mounds start to form. After the 40th layer the growth of the vertical width saturates. This is attributed to the fact that the size of the base of the mounds approaches the typical size of the coherent domains imposed by the mosaic structure of the first Pb layers. At this point the lateral correlation length has reached the lateral dimension of domains. The growth then continues with no further significant change of mounds upto 450 layers.
5:10 pm
THE STRUCTURE AND MORPHOLOGY OF EPITAXIAL DyP ON GaAs: L. P. Sadwick, P. P. Lee, M. Patel, M. Nikols, R. J. Hwu Department of Electrical Engineering, The University of UT, 3280 MEB, Salt Lake City, Utah; R. Alvis, One AMD Place, MS 32, Sunnyvale, CA 94088; R. Gedridge, Jr., T. Groshens Naval Air Warfare Center, China Lake, CA
The structure and morphology of epitaxial dsyprosium phosphide (DyP) on (001)
gallium arsenide (GaAs) has been studied by double crystal and two theta X-
ray
diffraction coupled with high resolution transmission electron microscopy
(TEM). DyP was grown by molecular beam epitaxy (MBE) as a function of substrate
temperature and phosphorus overpressure. The room temperature lattice constants
of DyP and GaAs are 5.6534 and 5.6533 Angstroms, respectively. DyP on GaAs
could be easily identified as it has significantly different structure factors
than that of GaAs. As an example, the 002 peak is larger by a factor of 20
compared to the 004 peak for DyP; whereas the 004 peak is a 100 times stronger
than the 002 peak for GaAs. X-
ray,
TEM, SEM, and high resolution microscope results show a strong dependence of
the crystal structure and orientation and morphology of DyP as a function of
substrate growth temperature and phosphorus pressure. Details of the DyP
structure and morphological properties will be presented.
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