Structural and Electronic Properties of Ho nanowires grown on Si(001)

Chigusa Ohbuchi¹, Jun Nogami², and Norman Birge¹

¹Dept. of Physics and Astronomy,

²Dept. of Chemical Engineering and Materials Science

Michigan State University, East Lansing 48824

We have studied the growth of Ho on Si(001) using scanning tunneling microscopy and low energy electron diffraction. For low metal coverage, < 0.4 monolayers (ML), Ho grows in a Stranski-Krastanov mode with highly elongated nanowires and a 4x2 reconstructed substrate surface. Above 0.4 ML, 3D compact silicide islands coexist with the nanowires. A 7x2 2D phase appears in the 0.4-0.55 ML coverage range, and it always co-exists with the 4x2 phase. Interestingly, as the 3D silicide islands appear, the 4x2 and 7x2 reconstructions are gradually swept away, and replaced by the 2x1 dimer rows of the clean Si surface. This means that Ho atoms move to 3D silicide islands from the reconstructed substrate surface.

We will report on our progress in transport measurements on macroscopic networks of these nanowires. Two major issues to be addressed are the electrical contacts, and surface passivation. Post growth deposited Al-Si Ohmic contacts are used in our initial measurements. TaSi₂ and TiSi₂ are candidates for pre-growth deposited contacts, since these silicides can survive the high temperature flash necessary to clean the Si(001) surface. It is known that deposition of hydrogen passivates clean Si surfaces. Our STM observations show that silicide nanowires survive after hydrogen is deposited. We will report on the effect of passivation on the atomic and electronic structure of the nanowires.