Two-dimensional epitaxial ErSi2 grown on B-passivated Si(111)-root 3x root3R30 degrees surfaces

The growth of thin erbium silicide layers on boron-passivated Si(111)root 3 X root 3R30 degrees surfaces has been investigated by angle-resolved ultrav iolet photoemission spectroscopy, ion scattering spectroscopy (ISS), and sc anning tunneling microscopy (STM). In the (sub)monolayer range, deposition of Er at 500 degrees C results in a surface band structure that clearly rev eals the formation of a silicide similar to the well-known two-dimensional (2D) ErSi2 growth on the Si(111)7x7 surface. Yet, the 2D Fermi surface exhi bits a marked reduction in surface band filling that can be readily underst ood in terms of random substitution of similar to 0.13-monolayer B for Si i n the silicide structure. ISS demonstrates that this substitution does not take place in the buckled Si-layer termination but rather in the double lay er underneath the hexagonal Er plane. High-resolution STM images clearly re veal the perturbation due to the B impurities in the form of an additional undulation on a 10-20 Angstrom length scale superimposed on the p(1X1) surf ace periodicity. In contrast to the Er/Si(111)7x7 interface, STM shows only the formation of 2D silicide islands without any holes in the uncovered su bstrate or competing Er-induced 5x2, 2x1, or 2 root 3X2 root 3R30 degrees r econstructions or silicides. This indicates a strongly modified growth mode on Si(111)root 3X root 3-B as compared to Si(111)7X7. [S0163-1829(99)09539 -9].