The Applications of Channeling (conventional and Transmission) in Surface and Interface Studies.

The Si(100)(2 x 1) reconstructed surface was studied by conventional channeling, and, for the first time, by transmission channeling. Model predictions have been compared to the experimental results by use respectively of Monte -Carlo simulation and flux peaking effects. The atomic displacement perpendicular to the (110) plane, the distortion in the subsurface layers, and the domain effect are discussed. The Au/Si(100) interface was studied by transmission channeling as the Au coverage increases from 0.1 monolayer (ML). The bare Si surface identified by a (2 x 1) MEED pattern. The results indicate an important role of Au -Au atom interaction in the submonolayer region, and that cluster formation is a possible mechanism for the interface growth. A threshold thickness of (DBLTURN)4 ML is required to stimulate the room-temperature Au-Si interfacial reaction. A transition thickness of (DBLTURN)6 ML has been observed during which, on the average, every two deposited Au atoms interact with one Si atom until an amorphous Au-Si cover layer is formed. The Au-Si interfacial reaction ceases at (DBLTURN)10 ML, and further buildup of the gold layer is not epitaxial with the substrate crystal. Experimental results on the angular dependence of energy loss for 2 Mev channeled He('+) ions along the Si <100> axis by use of transmission channeling are here presented for the first time. The measured FWHM of this dependence (0.52 (+OR-) 0.02(DEGREES)) is significantly smaller than the corresponding experimental value for the nuclear encounter probability. Based on a two component assumption, and separating the contributions from valence electrons and core electrons, a simple empirical expression for the energy loss of channeled ions is here proposed. A method is developed to extract the average L shell electron density distribution in the channel from the measured angular dependence. The peak of the distribution is at 0.18 A.