Imaging defect formation in the template growth of ${\mathrm{NiSi}}_2$/Si(111): An application of quantum size microscopy

The tunneling microscope is used to study the solid phase reaction of thin nickel films on silicon substrates to form epitaxial nickel disilicide. The initially flat Si(111)-7×7 substrate develops defects in the form of surface and interface steps as the silicide reaction proceeds, with the steps corresponding to domains of ${\mathrm{NiSi}}_2$(111) of varying thicknesses. For low-temperature growth, the nickel disilicide terraces are atomically flat, whereas below the surface there is substantial inhomogeneity. Annealing this surface to higher temperature reduces the subsurface inhomogeneity by diffusing residual silicon to the surface to form adatom islands, trading off volume defects for surface defects. We present resonant tunneling spectra for the resulting vacuum-metal-semiconductor quantum-well structure, and discuss the conditions under which quantum size effects occur for carriers within the thin ${\mathrm{NiSi}}_2$ metallic film.