LEEM Studies of Phase Separations and Surface Depletion of Co and Ni on Si(111)

Abstract

Low energy electron microscopy images of Si(111) surfaces during submonolayer deposition of Co or Ni at temperatures near 700 • C reveal a phase separation into a disordered "ring cluster" phase and the ordered 7 × 7 reconstruction. For Co/Si(111) we find that temperature-driven phase separations at a fixed dose are reversible and occur at a fixed surface coverage. The shape of the phase boundary reveals a repulsive interaction between Co-containing ring clusters in the disordered phase. For Ni/Si (111), dissolution into the bulk prevents reversible separations between surface phases. At coverages close to 1/7 ML an ordered close-packed √ 7 × √ 7 ring cluster phase forms for Co/Si(111), but not for Ni/Si(111). The √ 7 × √ 7 phase disappears irreversibly on heating, due to the nucleation and growth of stable silicide islands.

Formation of two-dimensional silicide on Ni(100) surface

“…19 -R23.4°, and (1 × 1)-ring cluster (RC) phases. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] These surface silicides are thought to be intermediate states before the formation of thick epitaxial silicides. It has been reported that ´n 2 and 2 2-R45°phases form on a Si(100) substrate depending on the Ni coverages and substrate temperatures.…”

Formation and stability of a two-dimensional nickel silicide on Ni(111): An Auger, LEED, STM, and high-resolution photoemission study

“…The Ni-Si interface is a typical example of a system in which appear a number of surface phases during reactive diffusion. The initial stages of nucleation and growth of 2D and 3D phases at the Ni/Si interface have been extensively studied by structural or microscopy surface techniques, such as low-energy electron diffraction (LEED), low-energy electron microscopy (LEEM), scanning tunnelling microscopy (STM) [9][10][11][12]. Several 2D phases are reported to appear during the reaction of an ultrathin Ni film with a Si (111) substrate, ( phases [13][14][15][16][17].…”

Scanning tunnelling microscopy studies of silicides

“…These RCs might well be thought of as surface molecules of silicide, since they exist as discrete units in which the bonding resembles crystalline silicide. Recent experiments using the high temperature in situ imaging capability of low energy electron microscopy (LEEM) have explored the kinetic properties of these RCs in terms of 2D phase transitions, surface diffusion and assimilation into true silicide structures [61][62][63][64][65].…”