Justification for the subject matter

The general topic of chemisorption on semiconductors, which encompasses the processes described in the title, has generated a vast literature for which Peshev et al. [1] have provided a bibliography of almost 3000 papers covering the period 1946—1972. If we examine the nature of much of the work cited there, we find it to be predominantly chemically orientated, both in the description of the materials studied and in the mechanisms proposed. Discussion of the crystallography and electronic structure of the semiconductor surface tends to be in bulk terms and measurement techniques for electronic effects are often simple adaptations of those devised for the determination of bulk properties. 

In large part, this somewhat unsatisfactory approach stems from the use of oxide semiconductors as vehicles for study. From a chemical viewpoint, their choice is entirely logical since they are widely used as catalysts, but in every other respect they are unsuitable. Stone [2] has pointed out some of the limitations, which include the poor quality of oxide crystals in terms of structural perfection, stoichiometry and purity, the virtual absence of any theoretical or experimental evaluation of their surface electronic and crystallographic structure, except in the most elementary terms [3], and a very limited technology for clean surface preparation, such that part of the reported work may not have related to semiconductor surfaces at all because of the level of contamination. 

In one sense, therefore, this review will be much more limited in scope than most previous reviews on this subject, but we hope to show how the application of the more recently developed experimental and theoretical methods of surface physics is leading to results of general significance. First, though, we will summarize very briefly the more conventional chemical approaches. 

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