Chloride passivation of germanium

Germanium surface passivation by chloride termination inhibits oxide formation and maintains a well-ordered surface. The chloride-terminated surface can also be used as a reactive precursor for wet organic functionalization. For example, Cullen et al. [105] first demonstrated the reaction of a chloride-terminated Ge(lll) surface with ethyl Grignard as a means of ethylation for use in surface stabilization. The chlorination was performed by a mixture of Cl2 and HC1 gas with N2 above atmospheric pressures [105]. Although this resulted in approximately a one-to-one ratio of adsorbed chlorine atoms with Ge surface atoms, the high pressures resulted in severe etching of the substrate [105]. 

Lu [110] prepared the first solution phase Cl-terminated surface by immersing a Ge(l 11) sample in dilute HC1. This resulted in a well-ordered, atop adsorption, similar to the surface formed by Cl adsorption in vacuum [110]. The chloride-terminated surface product is thermodynamically favored over the hydride-terminated surface product, as the Ge-Cl bond and Ge-H bond strengths are 103 and 77kcal/mol, respectively [88]. The chloride-terminated surface demonstrates passivation in its stability against oxidation on the scale of hours in ambient air [104,111]. 

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