Nanostencil patterning of In and Sn on atomically clean Si(001)

N To, S Dobrin and J Nogami

Materials Science and Engineering, University of Toronto

A self-aligning nanostencil mask was used to pattern circular features of tin and indium over an atomically clean Si(001) substrate. The shadow mask limits material to deposit only where the membrane is open, leaving adjacent clean surfaces for material to diffuse. STM is used to study the surface diffusion of these metals in UHV. The diffusion of tin is found to be relatively limited in comparison with indium, and remains so even at increasing coverage. Indium forms unstable 3D islands that dissolve over time and contribute to the spreading of a single layer thick film on the surrounding clean surface. The difference in behaviour between the two metals can be attributed to the difference in activation energy for diffusion of atoms on top of the first atomic layer of metal.

Density Functional Theory (DFT) calculations were used to determine the activation barrier for a Sn or In atom traveling over occupied 2 × 2 reconstructed metal surfaces. Equilibrium positions are shown as 1,1’ and 32. Transition states are labeled 2 and 2’. The calculated Sn and In atoms diffusion along and across the direction of the underlying Si dimer rows are listed in following table.

	Activation barrier
Direction of the diffusion:	Sn	In
along dimer row	0.6 eV	0.2 eV
across dimer row	1.0 eV	0.4 eV

Presented at: the 22nd Canadian Conference on Surfaces, 13-16 May 2011, Simon Fraser University

Burnaby, British Columbia, s“Nanostencil patterning of In and Sn on atomically clean Si(001)”, N. To, S. Dobrin, J. Nogami