Adsorption on semiconductor surfaces

From the theoretical standpoint the above issues are addressed by quantum chemistry. On the basis of calculations of various cluster models [191] the properties of surfaces of solid body are being studied as well as issues dealing with interaction of gas with the surface of adsorbent. However, fairly good results have been obtained in this area only to calculate adsorption on metals. The necessity to account for more complex structure of the adsorption value as well as availability of various functional groups on the surface of adsorbent in case of adsorption on semiconductors geometrically complicates such calculations. 

The conclusion of the study [89] concerning non-dissociated character of hydrogen adsorption on semiconductors of ZnO type at low temperatures (lower than 70 C) was based on experimental facts indicating that hydrogen atoms which independently arrive at the surface of semi-... 

As described in the preceding sections, fundamental studies of heterogeneous catalysis at the surface of catalysts are important for understanding reaction pathways and for the development of new or improved catalysts and processes. There have been earlier hypotheses proposed for selective oxidation catalysis for example, the multiplet theory which suggests that the activity depends upon correctly spaced groups (multiplets) of atoms to accommodate the reactant molecule (Balandin, 1969) and electronic theory based on the nature of adsorption on semiconductors and empirical correlations between activity, work function and electrical conductivity (Wolkenstein 1960). The importance... 

Adsorption on Metal Surfaces and Its Bearing on Catalysis Joseph A. Becker The Application of the Theory of Semiconductors to Problems of Heterogeneous Catalysis K. HAUFFE... 

Most studies on deposition of fullerenes on semiconductor surfaces have focused on silicon9 28 and, to a much less extent, on GaAs. Earlier experimental work using HREELS (high-resolution electron energy loss spectroscopy) on C60 adsorption on Si (100)2 x 1 surface suggested that the molecular attachment to the... 

Semiconductor surfaces first became of interest about twenty years ago, and came into sharp focus only in the late forties and early fifties when germanium and silicon surfaces were studied intensively by numerous large research and development groups in various countries. This unusually intense activity resulted from the discovery of the transistor by a team of scientists at the Bell Telephone Laboratories in 1948 but it is of interest to note that this discovery was itself a direct outgrowth of work on semiconductor surfaces by the same scientists. It is also of interest to note that just as work on semiconductor surfaces has contributed to modern solid state electronics, so work on metal surfaces has contributed heavily to vacuum-tube electronics. Outstanding in this case are Langmuir s studies on gas adsorption and vacuum techniques. 

THE FUNDAMENTAL CONCEPTS of the physics and chemistry of surfaces are considered starting with Langmuir s work on thermionic emission and adsorption on metal surfaces and ending with the simple surface or phase boundary that occurs at a p-n junction in a semiconductor. Future progress depends on measuring both physical and chemical changes on the same surfaces at the same time. 

Because adsorption equilibria can produce a substantially different population at the semiconductor-liquid interface than is present in solution, interfacial charge trapping can produce specific activation of the better adsorbate from a mixture. Thus adsorption pre-equilibria are likely to be important in controlling the relative rates of photooxidation of competing substrates on semiconductor surfaces. Because adsorption equilibria can be influenced by the addition of very small amounts of cosolvent additives, higher reactivity [36] and higher selectivity can often be simulta-... 

The term semiconductor covers a wide range of materials, including the elements silicon and germanium, and compounds such as oxides, sulphides, selenides, etc. A survey of the physics and chemistry of semiconductors is given in the book edited by Hannay and particular reference to semiconductivity and adsorption on oxide surfaces is to be found in an article by Gray . 

Atomic adsorption on elemental semiconductors 3.1.2.1. A tomic adsorption on (100) surfaces... 

Fig. (3). Possible ways of adsorption of CO2 on semiconductor surfaces. Reproduced with permission from Ref [23], 2014 WILEY-VCH Verlag GmbH Co. KGaA, Wcinhcim.

Whilst in a qualitative sense this theory has a certain basic validity, it does not provide very real physical insight into the electronic and structural effects now known to be associated with adsorption on semiconductors. In the following sections, we shall attempt to show how the subject has been developed from the much greater understanding of semiconductor surfaces which is now available. 

The second application is to the direct measurement of adsorption-desorption processes using the Auger peak height of the particular element as a monitor. The principal limitation is the possible influence of the electron beam on the adsorbate, which can result in beam-induced desorption, adsorption or dissociation. The basis of electron-stimulated desorption (ESD) was established some time ago independently be Menzel and Gomer [38] and Redhead [39]. Electron impact causes Franck—Condon transitions of bound electrons in the adsorbed species into excited states. There is, therefore, a probability of dissociation with subsequent desorption of the particular species involved. As an example of these effects on semiconductor surfaces, Joyce and Neave [40] have reported results on silicon, while Ranke and Jacobi [41] have discussed the electron-stimulated oxidation of GaAs. 

The aim of this section is to illustrate with definite examples the type of information which can be obtained on semiconductor surface structures. We will consider in some detail experimental and theoretical results for three specific surfaces, Si 111, Si 100 and GaAs 110, which typify most of the important effects in relation to both preparation and subsequent adsorption behaviour. 

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