Catalytic role of gold nanoparticle in GaAs nanowire growth: a density functional theory study
The energetics of Ga, As, and GaAs species on the Au(111) surface (employed as a model for Au nanoparticles) is investigated by means of density functional calculations. Apart from formation of the compound Au_7Ga_2, Ga is found to form a surface alloy with gold with comparable ΔH ∼ −0.5 eV for both processes. Dissociative adsorption of As2 is found to be exothermic by more than 2 eV on both clean Au(111) and AuGa surface alloys. The As−Ga species formed by reaction of As with the surface alloy is sufficiently stable to cover the surface of an Au particle in vacuo in contact with a GaAs substrate. The results of the calculations are interpreted in the context of Au-catalyzed growth of GaAs nanowires. We argue that arsenic is supplied to the growth zone of the nanowire mainly by impingement of molecules on the gold particle and identify a regime of temperatures and As_2 partial pressures suitable for Au-catalyzed nanowire growth in molecular beam epitaxy.
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