FORMATION CONDITIONS AND ATOMIC-STRUCTURE OF THE SI(111)-ROOT-19 NI SURFACE

We determined the formation conditions and atomic structure of the Si( 111)-root 19 Ni surface using Auger electron spectroscopy, reflection high-energy electron diffraction (RHEED) and scanning tunneling micros copy (STM). The root 19 phase can be produced by low temperature depos ition followed by annealing and quenching from above 860 degrees C. It tends to coexist with a variable density 1x1-RC (ring cluster) phase. The intrinsic coverage of the root 19 phase alone is approximately 0. 15 monolayers, corresponding to three Ni atoms per root 19 unit cell. Deposition at 550 degrees C suppresses the 1x1-RC phase and creates a well-ordered root 19 phase in coexistence with Si 7x7. Deposition at 3 50 degrees C produces silicide islands in a matrix of Si 7x7. From hig h resolution STM images we determined the lattice registration of the root 19 phase and present a model for its atomic structure.