Silicon surface chemistry

Chemical bronchitis, 25 479 Chemical bulk analysis, of silicon surface chemistry, 22 373... 

An additional complication affecting silicon surface chemistry is the well-established fact that dimers tilt away from the symmetric position (c.f. Fig. 1(b)). Associated with dimer tilting is a charge transfer from the down atom to the up atom. Hence, the dimers exhibit somewhat zwit-terionic character, with one electron-poor atom and one electron-rich atom. Such a property of the Si(100)-(2 x 1) surface makes it possible to use nucleophilic and electrophilic attachment reactions. At temperatures less than 120 K, dimer tilting on Si(100)-(2 x 1) can be observed in STM experiments [3,9], while at higher temperatures the direction of the tilt oscillates on a time scale faster than the order milliseconds sampling times of the STM. 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

In Section V, a general discussion of how silicon surfaces can be used to obtain monolayers is presented. The functionalization of silicon surfaces using radical chemistry is an area of intense and active investigation because of the potential for a myriad of practical applications.In order to help those readers who are not familiar with silyl radical chemistry, we discuss some general aspects of silyl radicals in Section II, together with some recent findings. 

The radical-based functionalization of silicon surfaces is a growing area because of the potential practical applications. Although further knowledge is needed, the scope, limitations, and mechanism of these reachons are sufficiently well understood that they can be used predictably and reliably in the modification of hydrogen-terminated silicon surfaces. The radical chemistry of (TMSlsSiH has frequently served as a model in reactions of both hydrogen-terminated porous and flat silicon surfaces. We trust that the survey presented here will serve as a platform to expand silicon radical chemistry with new and exciting discoveries. 

More recently, it has been shown that DNA oligomers can be synthesized directly on modified semiconductor surfaces using automated methods (196). The silicon surfaces are first modified to give a terminal, protected, hydroxyl group at which automated phosphoramidite chemistry can be performed (Fig. 61). Semiconductor processing methods... 

Parbhoo, B. O Hare, L.-A. Leadley, S. R. Fundamental Aspects of Adhesion Technology in Silicones. In Surfaces, Chemistry Applications-, Chaudhury, M., Pocius, A. V., Eds. Elsevier Amsterdam, 2002 Chapter 14, pp 677-709. 

The surface chemistry of coesite and stishovite was studied by Stiiber (296). The packing density of hydroxyl groups was estimated from the water vapor adsorption. More adsorption sites per unit surface area were found with silica of higher density. Stishovite is especially interesting since it is not attacked by hydrofluoric acid. Coesite is dissolved slowly. The resistance of stishovite is ascribed to the fact that silicon already has a coordination number of six. Dissolution of silica to HaSiFg by hydrogen fluoride is a nucleophilic attack. It is not possible when the coordination sphere of silicon is filled completely. In contrast, stishovite dissolves with an appreciable rate in water buffered to pH 8.2. The surface chemistry of. stishovite should be similar to that of its analog, rutile. 

The surface chemistry of SAMs of silanes on planar substrates such as oxidized silicon wafers is comparable to the chemistry of silica gel, with the absence of a porous structure [47]. 

Figure 6. Example of ion-assisted gas-surface chemistry in the etching of silicon with Xep2. The Xep2 flow is 2 x 10 moles/sec and the argon energy and current are 450 eV and 2.5 ijlA, respectively. (Reproduced with permission from Ref. 31J...

See Scanning tunneling spectroscopy Superconductors 332—334 Surface Brillouin zone 92 hexagonal lattice 133 one-dimensional lattice 123, 128 square lattice 129 Surface chemistry 334—338 hydrogen on silicon 336 oxygen on silicon 334 Surface electronic structures 117 Surface energy 96 Surface potential 93 Surface resonance 91 Surface states 91, 98—107 concept 98... 

Fig. 26. Ion-assisted gas-surface chemistry using Ar and XeFj on silicon (Volatile reaction product.).

Several excellent reviews are available concerning both surface structure of semiconductors and surface chemistry of semiconductors, including Refs. [5-23]. Here, a comprehensive review is not attempted and the reader is referred instead to those references. The focus of this chapter is primarily on the surface chemistry of silicon and germanium, as these are the two most heavily studied systems. We strive to provide insight into the chemical reactivity of these two surfaces, and hence... 

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