Au-activated InAs nanowires were grown on Si substrates by solid source molecular beam epitaxy (SSMBE). Epitaxial growth of InAs nanowires turned out to be very sensitive to the surface condition of the Si substrates. InAs nanowires having a \langle 111 \rangle growth direction, a high crystalline quality and a high aspect ratio over 300 with a uniform lateral size along the growth direction were grown using a high-temperature pre-annealing process in the MBE growth chamber to remove residual oxides from the surface of the Si substrates.
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We achieved the repositioning of native In adatoms on the polar III–V semiconductor surface InAs(111)A-(2 × 2) with atomic precision in a scanning tunnelling microscope (STM) operated at 5 K. The repositioning is performed by vertical manipulation, i.e., a reversible transfer of an individual adatom between the surface and the STM tip. Surface-to-tip transfer is achieved by a stepwise vibrational excitation of the adsorbate–surface bond via inelastic electron tunnelling assisted by the tip-induced electric field. In contrast, tip-to-surface back-transfer occurs upon tip–surface point contact formation governed by short-range adhesive forces between the surface and the In atom located at the tip apex. In addition, we found that carrier transport through the point contact is not of ballistic nature but is due to electron tunnelling. The vertical manipulation scheme used here enables us to assemble nanostructures of diverse sizes and shapes with the In adatoms residing on vacancy sites of the (2 × 2)-reconstructed surface (nearest-neighbour vacancy spacing: 8.57 Å).