Electron Microscope Studies of Some Vapor Deposited Materials: Nucleation, Epitaxial Growth and Surface Topography
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ELECTRON MICROSCOPE STUDIES OF SOME VAPOR DEPOSITED MATERIALS: NUCLEATION, EPITAXIAL GROWTH AND SURFACE TOPOGRAPHY WILLIAM KRAKOW IBM Research Division, T. J. Watson Research Center, P. 0. Box 218, Yorktown Heights, NY 10598, USA
ABSTRACT The nucleation and epitaxial growth of deposits at both low and high temperature substrate conditions and the resulting two and three dimensional growth modes have been investigated using electron diffraction and transmission electron microscopy. At high temperatures, the growth of small particles such as Au, Pt and Ge grown under low rate conditions similar to MBE are revealed by lattice imaging. Using an intermediate buffer layer Ag film, surface growth of(100) and (310) Au thin film layers are revealed by diffraction contrast to be in a step ledge growth regime. While the abovc investigations were performed cx situ to the microscope vacuum environment, an in situ evaporator has been also been installed on a high resolution electron microscope. Observations can be made in real time of cluster growth from atomic diameters on up. The resulting atomic motion around cluster edges is similar in appearance to surface melting.
INTRODUCTION For many years electron microscopy has been one of the principle methods for studying the epitaxial growth of thin films and characterizing defects associated with thin film microstructural evolution. It has been particularly valuable for the characterization of the initial stages of epitaxy which includes the nucleation, topology and structural characteristics of the first deposited layers. The major questions involve the different regimes of condensation which include both absorption onto and the diffusion of atoms to clusters on surfaces. these mechanisms have been reviewed by several authors. In this short report it is not possible to encompass the large number of electron microscope studies dealing with the initial stages of epitaxial growth, rather they will be discussed in the context of the discussion of the results.
PROCEDURES, RESULTS AND DISCUSSION For the epitaxial growth experiments, single crystal rocksalt was cut and polished such that various different faces were available such as (100), (110), (11I), (310). These samples are then placed in a UIIV chamber where the vacuum reached into the 10-9 Torr range. In the case of metal clusters (3D growth) the substrate temperature was elevated to 400°C and depositions were at rates of 0. 1A/sec with a nominal average coverage of 15A. Upon completion of the metal deposition, a thin carbon film < 1OA thick was arc deposited. The composite thin film is then readily removed from the NaCl. For thick films no carbon was used since the films were continuous.
Mat. Res. Soc. Symp. Proc. Vol. 237. ©1992 Materials Research Society
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Fig. 1
High resolution micrograph of a 15A average thickness Au deposit on NaC1 at 400'C. Original microscope magnification 600,000x.
Fig. 2
fHigh resolution micrograph of Au deposited on a < 110> NaC1 substrate. Original magnification 600,000x and average deposit
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