Atomic reconstruction

X 1) to (1 X 5) surface reconstructions of the (Oil) and (001) surfaces of fee metals such as Au, Pt and Ir have also been successfully studied with the STM,19,20 with the transmission electron microscope (TEM)13,21 and with the field ion microscope.14,15,22 Some of the FIM surface atomic reconstruction studies will be described below. 

Fig. 4.16 (a) Computer simulated image of a silicon tip within a basic crystallographic triangle. In this image, no atomic reconstruction is assumed, (b) A map of the indices of the facets of the same surface. (c) A field ion image of the same triangular surface area. Note that all these surfaces are reconstructed. 

The divacancy is a stable defect in crystalline silicon. The six dangling bonds left by the removal of two adjacent atoms reconstruct to leave two strong bonds and a pair of weakly interacting dangling bonds which comprise the gap states. The defect has four electronic levels in the gap and its neutral state has paired electrons and is diamagnetic. The divacancy model was first proposed by Spear (1974) to explain the early field effect results. A two-fold coordinated silicon atom also has Az = — 2 and so is of the same type. Adler (1978) concluded from molecular orbital arguments that this defect has the lowest formation energy of any silicon coordination defect. 

The Atomic Reconstruction of Metabolism (ARM) software, developed by Arita at the University of Tokyo and Institute for Advanced Biosciences, realized the computer simulation of radioisotope tracer experiments.Each molecule was represented at the atomic scale to describe its structural features (mappings) within a database. Data from the ENZYME database (http //us.expasy.org/enzyme) were curated and precomiled with all reactions in KEGG, EcoCyc... 

Computational physics historically has grown more out of theoretical physics groups than from the experimental side, at least that is so in the field of electronic structure of solids. Over most of my scientific life computation has tended to be something tacked onto the end of a piece of theory to bolster its correctness and help get it past the referee. I exaggerate a bit in order to make the point that one has to see computation these days as a third mode different both from theory and experiment. It is a third investigative technique in its own right, often more akin to experiment than to theory. For example computation has been used, as I am sure we will hear in talks later in the Advanced Studies Institute, to investigate the atomic reconstruction... 

---