Atomically clean semiconductor surfaces

Such a surface provides a basis for the study of its interactions with other species the effect of particular surface perturbations, e.g. atomic steps, can be considered once the ideal surface behaviour is understood. 

This section will begin with a discussion of the fundamental concepts of the electronic and crystallographic structure of semiconductor surfaces, followed by a description of the methods used to prepare surfaces in as ideal a state as possible experimentally. The emphasis will be on Si and GaAs as typical examples of elemental and compound semiconductor, respectively, and with which the great majority of published work has been carried out. We will conclude with some examples of the determination, experimentally and theoretically, of the electronic and crystallographic structure of specific surfaces of elemental and compound semiconductors. 

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The result of such calculations show that, on a clean semiconductor, surface atomic sites in equilibrium always differ substantially from those of a semi-infinite lattice and there is an inward force on these surface atoms, since the presence of a dangling bond on a surface atom strengthens the back bonds to atoms in the second layer. This means that the back bonds assume some double bond character (i.e. the bond order becomes greater than unity). The consequent change in bond length leads to so-called surface relaxation (see Sect. 3.3). 

Thus to define the atomic geometry of a clean semiconductor surface, it is necessary to determine (1) the depth of the reconstructed layer, (2) its structure, and (3) its registry with respect to the underlying substrate. 

True reconstruction implies a variation in the atomic density in the topmost layer of the substrate if compared with the corresponding bulk plane. Such a situation is found not only with numerous clean semiconductor surfaces but also with the (10 0) and (11 0) surfaces of the fee 5d metals [18]. 

The invention of the STM was in fact a true revolution in the fields of surface science and microscopy. After extremely high atomic resolution was achieved on clean semiconductor and metal surfaces, further studies were carried on surfaces that were covered with molecules, to observe structural information. 

This chapter is organized as follows. First, in sect. 2, we consider the surfaces of metals. In sect. 2.1 we describe the structure of unreconstructed clean metal surfaces and then proceed, in sect. 2.2, to consider the reconstructed surfaces. The surface structure of ordered and disordered metallic alloys is described in sect. 2.3. In sect. 2.4 we describe the surface structures associated with atomic adsorption on metals and in sect. 2.5 we consider molecular adsorption on metals. The structure of semiconductor surfaces is... 

AES has been applied in three areas of semiconductor surface studies. The simplest is the assessment of amounts of contamination present on a surface, and the absence of peaks other than those associated with the substrate is used effectively to define an atomically clean surface. It should be realised, however, that there could still be up to 0.01 monolayer, or 1013 atoms cm-2 of any element (hydrogen cannot be detected) on the surface, even though no additional Auger features are present. 

Part 5 covers special structures such as liquid crystals, solid surfaces and mesoscopic and nanostructured materials. The chapter on liquid crystals covers physical properties of the most common liquid crystalline substances as well as some liquid crystalline mixtures. Data compiled in the chapter on solid surfaces refer to atomically clean and well characterized surfaces. The values reported are mainly averages from different authors where reference to the original papers is made. In the chapter on nanostructured materials emphasis is placed on size and confinement effects. The properties associated with electronic confinement are addressed and particular attention is drawn to semiconductor-doped matrices. The two main applications of nanostructured magnetic materials, spintronics and ultrahigh-density data storage media, are also treated. 

The Si(111) surface is probably the most studied semiconductor surface. Yet, the details of the atomic and electronic structure are still considered open subjects. Experimental interest remains high because it is possible to cleave Si in vacuum and produce clean surfaces which can be studied with a host of techniques. Theoretically, this surface is considered to be the prototype semiconductor surface. 

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