The unique attributes of a Field Ion Microscope-(FIM) permit direct observation of the surface diffusion of a single atom and simple atomic clusters on perfect crystal planes. A brief review of the principles and techniques of such studies is presented along with a collection of existing experimental data. Included is a one and two dimensional random walk of a single adatom or di-atomic cluster on well defined crystal planes, the structure and configuration of an atomic cluster on crystal surfaces, the experimental demonstration of non-monotonic long-range interaction obtained from the distribution functionof the distance between two adatoms on a single-crystal surface, and an atomic view of surface self-diffusion of clean and well defined surfaces.
The atomistic understanding of chemistry is based on chemical structure, spectroscopic properties, and reaction kinetics. There is a large amount information on the kinetics of heterogeneous catalysis. Then, too, various different methods of spectroscopic amalysis have been ingeniously applied to problems in surface chemistry. It is the purpose of this paper to show how spectroscopic methods, particularly infrared and electron energy loss spectoroscopy, may help to identify the structure of surface species which are closely related to the heterogeneous catalysis of carbon monoxide hydroge-nation, formic acid decomposition, and olefin isomerization.
Adsorption and desorption processes of bismuth on Si (100) surfaces were studied using quadrupole mass spectrometry, LEED, and AES in an UHV system. At high substrate temperatures, only a two-dimensional phase with saturation coverage was formed on a surface, and the LEED pattern from this surface shows Si (100)2×1 structure with weak fractional order spots. At low temperatures, formation of the second phase was observed after the completion of the first phase. The results of LEED and AES experiments suggested that the second phase consisted of threedimensional islands. The peak of flash desorption spectrum for the second phase shifted to the higher temperature side with the increase of the initial coverage of bismuth. This phenomenon can be explained by considering the emitting processes of Bi atoms from the three-dimensional islands to the substrate surface and vacuum.
Tansmission electron microscope Observation was made of the epitaxy of Bi deposited onto the surfaces of long-chain stearic acid molecular crystals, Vacuum-depositions of Bi onto stearic acid substrates, cleaved in air and vacuum, carried out at deposttion rates ranging 13Å/min to 3000Å/min. The residual gas pressures were 10-6 Torr and 10-4 Torr. The temprature of the substrate during deposition was 15°C. The epitaxy of Bi did not depond upon the lattice misfit between the substrate and the Bi thin film. The morphologies of Bi deposited onto the air-cleaved and vacuum-cleaved surfaces showed similar features at a film thickness ot about 100Å. There was also no significant difference in the epitaxial structures of Bi deposited in residual gas pressures of 10-6Torr or 10 -4Torr. Typical morphology of the deposited Bi was observed to bc triangular and hexagonal-shaped islands. The number of the triangular shapes of Bi particles becomes larger as the deposition rate increases; the hexagonal shapes remarkably appeard as the deposition rate decreased. The three-dimensional shape of the triangular particles were those of trigonal pyramids, eud the hexagonal particles were found to be flat. The mechanism of Bi thin films on surfaces of molecular crystals has been discussed prviously.
The Pittsburgh activated carbons (Calgon Co.) were outgassed at 1, 000°C for 2 hours and then reduced with H2 at 1, 000°C or oxidized with O2 at 100 and 300°C to prepare three activated carbons with different surface oxygen content. The prepared activated carbons have almost the same specific surface areas, pore volumes and pore size distributions. On these activated carbons, adsorption isotherms of water, ethanol and benzene were obtained. The effect of oxygen present on the surface of the activated carbons upon the adsorbability of these molecules was discussed. The amount of both water and ethanol adsorbed increased with increasing surface oxygen content of the activated carbon. On the other hand, that of benzene was unchanged. It is thought that the increases of the adsorbability of water and ethanol with increasing surface oxygen content are due to the interactions between the surface oxygen sites and the polar groups of these molecules. The reason for the constant adsorbability of benzene on these carbons may be that the adsorption of the benzene molecule takes place, it is thought mainly on hexagonal planes of the activated carbon crystallites, and that benzene is a non-polar molecule and so may not interact with surface oxygen sites.
A review is given of the recent studies on the preferred orientation of the crystallographic axis of crystalline aggregates. Two results of by Bauer's model which are helpful in the understanding the growth of oriented films on amorphous substrates, are explained. They are the equilibrium form of a crystal in a film formation and the angular dependence of the condensation on a given surface configuration. It is also shown, following the latest studies by Wilman et al, that the distribution function f(φ) for the relative area of the film surface elements, corresponding to the Bragg reflection arcs, can be calculated from the observed relation between the tilt angle δ of the orientation axis and the incident angle i for cubic and hexagonal materials. This is followed by a discussion on of the new technique “graphoepitaxy”, growth of a single crystal film with a preferred orientation on an amorphous substrate having an artificially created surface-relief grating.