Freestanding semiconductor nanowires have an enormous potential in becoming the building blocks of future devices in physics, chemistry and biology [1]. Au nano particles are commonly used to physically catalyze the growth of nanowires but the mechanism for this is not yet fully understood [2]. The Au seed particles can be formed either by deposition of a homogenous film of Au which upon annealing condenses to droplets or by aerosol methods. Substrate diffusion [3] is important for the growth of nanowires and it is therefore of great interest to study if the presence of Au affects the substrate surface structure since this could lead to dramatic differences in diffusion coefficients and unexpected growth behavior. We have used STM and LEED to conduct studies on the atomic scale and have recently [4] shown that on GaAs(111)B Au, present as film or aerosol nano particles, forms a thin wetting layer at temperatures relevant for nanowire growth. When a Au film was evaporated on to InAs(111)B and annealed to the same temperatures no such wetting layer was found. The Au film instead condenses into well defined and separated hexagonal islands. We have obtained atomically resolved images both on the reconstruction of the clean InAs(111)B surface as well as on the islands. These results interestingly show the qualitative differences in interaction with Au among III-V substrate materials: No Au wetting layer is observed on the InAs(111)B in contrast to the GaAs(111)B. We will discuss the possible reasons for these differences and the fundamental consequences it can have for nanowire growth.
[1] L. Samuelson, Mater. Today 6(10), 22 (2003)
[2] J. B. Hannon et al, Nature 440, 7080 (2006)
[3] L. E. Jensen et al, Nano Letters 4(10) , 1961 (2004)
[4] E. Hilner et al, Appl. Phys. Lett. 89, 251912 (2006)
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