Silicon surface structure

The crystallographic face of silicon that is most important industrially is the Si(100) surface, followed by the Si(lll) surface. Both the (100) and (111) surfaces undergo extensive reconstructions, i.e., their surface atomic geometry differs significantly from that of the bulk. Moreover, the two surfaces have markedly different 

The different surface atoms on the Si(lll)-7 x 7 surface have chemically distinct properties. Because of the electron redistribution, each rest atom and corner hole is negatively charged, while each of the adatoms has a partial positive charge [19,47]. Consequently, the rest atoms and corner hole can be considered nucleophilic, and the adatoms electrophilic. An adjacent rest atom-adatom pair hence forms a dipolar or diradical entity although the closest rest atom-adatom spacing on Si(lll)-7 x 7 (4.5 A) is much larger than the dimer distance on Si(100)-2 x 1 (2.4 A) [48], this pair may be expected to show some similarities in reactivity to the dimer on the 

Si(100)-2 x 1 surface. Indeed, similarities in adsorption products between the two surfaces have been reported, as will be seen later in this chapter. 

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Robinson, A.L. Consensus on Silicon Surface Structure Near, Science, 232, 451-453 (1986),... 

J. L. Cantin, M. Schoisswohl, A. Grosman, S. Lebib, C. Ortega, H. J. von Bardeleben, fi. Vazsonyi, G. Jalsovszky, and J. Erostyak, Anodic oxidation of p and p -type porous silicon Surface structural transformations and oxide formation, Thin Solid Films 276, 76, 1996. 

Dry etching is a commonly used teclmique for creating highly anisotropic, patterned surfaces. The interaction of gas phase etchants with surfaces is of fundamental interest to understanding such phenomena as undercutting and the dependence of etch rate on surface structure. Many surface science studies aim to understand these interactions at an atomic level, and the next section will explore what is known about the etching of silicon surfaces. 

Tom H W K, Heinz T F and Shen Y R 1983 Second-harmonic reflection from silicon surfaces and its relation to structural symmetry Phys. Rev. Lett. 51 1983... 

Shank C V, Yen R and Hirlimann C 1983 Femtosecond-time-resolved surface structural dynamics of optically excited silicon Phys. Rev. Lett. 51 900-2... 

The interaction between particle and surface and the interaction among atoms in the particle are modeled by the Leimard-Jones potential [26]. The parameters of the Leimard-Jones potential are set as follows pp = 0.86 eV, o-pp =2.27 A, eps = 0.43 eV, o-ps=3.0 A. The Tersoff potential [27], a classical model capable of describing a wide range of silicon structure, is employed for the interaction between silicon atoms of the surface. The particle prepared by annealing simulation from 5,000 K to 50 K, is composed of 864 atoms with cohesive energy of 5.77 eV/atom and diameter of 24 A. The silicon surface consists of 45,760 silicon atoms. The crystal orientations of [ 100], [010], [001 ] are set asx,y,z coordinate axes, respectively. So there are 40 atom layers in the z direction with a thickness of 54.3 A. Before collision, the whole system undergoes a relaxation of 5,000 fsat300 K. 

Beton and co-workers extended the hydrogen bonding approach to two-component systems, generating a number of structures that utilise different molecular motifs.24 26 In the case of perylene tetracarboxylic diimide (PTCDI) co-adsorbed with melamine (1,3,5-triazine-2,4,6-triamine) on a silver-terminated silicon surface, a network is formed in which the straight edges correspond to PTCDI with melamine at the vertices (Figure 11.6). The network shows large-area pores that the authors used to trap heptamers of C6o molecules. 

The measurement of changes of the surface potential Vo at the interface between an insulator and a solution is made possible by incorporating a thin film of that insulator in an electrolyte/insulator/silicon (EIS) structure. The surface potential of the silicon can be determined either by measuring the capacitance of the structure, or by fabricating a field effect transistor to measure the lateral current flow. In the latter case, the device is called an ion-sensitive field effect transistor (ISFET). Figure 1 shows a schematic representation of an ISFET structure. The first authors to suggest the application of ISFETs or EIS capacitors as a measurement tool to determine the surface potential of insulators were Schenck (15) and Cichos and Geidel (16). 

This is the regime of anodic current densities below JPS. A hole approaching the interface initiates the divalent electrochemical dissolution of a silicon surface atom at the emitter. The dissolution proceeds under formation of H2 and electron injection, as shown in Fig. 4.3. The formation of PS structures is confined to this region. 

Also, from Fig. 5 it appears that the anodic current density with n-type Si is extremely low due to the buildup of the depletion layer with a more than 1 Mf2 resistance. In fact, obtaining a few mA cm with n-type Si in the dark needs a very high polarization potential, up to 6-10 V so as to induce breakdown within the highly resistant depletion layer. Nevertheless, PS structure can be obtained on n-type Si, either using heavily doped samples, alternatively under light activated silicon surfaces. 

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