Surface chemistry of silicon-the behaviour of dangling bonds

The role of surface dangling bonds in controlling the surface chemistry of Si(100) and Si(111) has been investigated using surface science methods. The adsorption and decomposition of acetylene on Si(100) has been shown to occur by means of a mobile precursor mechanism, leading to a di- sigma chemisorbed ethylenic species occupying Si dimer sites on Si(100). This species decomposes at elevated temperatures to produce adsorbed carbon and hydrogen (800 K) and then silicon carbide (1000 K). The activity of Si(111) for the adsorption of species such as ammonia and atomic hydrogen can be significantly reduced by doping of the surface region with boron. It has been shown that subsurface boron significantly changes the structure of Si(111)-(7*7) to a square root 3* square root 3 R30 degrees structure. In addition, the local doping of the surface reduces the chemical activity of the dangling bonds so that neither the dissociation of NH3 nor the adsorption of atomic hydrogen will occur.