ELSEVIER Surface Science 396 (1998) 40-51 surface science Ab initio HF/DFT studies of the chemisorption of hydrogen on the cluster simulated Si(111 )-(V3 x V )R30°-A1 and -Ga surfaces Sanwu Wang, M.W. Radny *, P.V. Smith Department of Physics, The Universityof Newcastle, Callaghan2308, Australia Received 9 June 1997; accepted for publication 31 July 1997 Abstract The chemisorption of atomic hydrogen on the Si( 111 )-(N/3 × ~/3)R30°-A1 and -Ga surfaces has been studied by first-principles all- electron Hartree-Fock/density functional theory (DFT) cluster calculations. It has been found that the hydrogen chemisorption behaviour on the Ga terminated cluster modelled surface is similar to that for the A1 terminated cluster. Hydrogen atoms chemisorbing near an adatom site are found to cause the breaking of SiAl (or S~Ga) bonds and the formation of H-Si bonds. The aluminium (or gallium) adatoms move from their original threefold sites to the adjacent bridge sites (one hydrogen atom), and then to the neighbouring on-top sites (two hydrogen atoms). Calculations of the binding energies have shown that aluminium or gallium adatoms occupying the bridge and on-top sites may be able to migrate on the real surface. This suggests the possible formation of A1 (or Ga) islands, together with a local (1 x 1)H surface reconstruction. Further exposure to hydrogen does not cause any further structural transformations and supports the ('x/3 x ~)-( 1 x 1) phase transition. © 1998 Elsevier Science B.V. Keywords: Ab initio quantum chemical methods and calculations; Aluminium; Chemisorption; Density functional calculations; Gallium; Hydrogen; Models of surface chemical reactions; Silicon 1. Introduction The properties of the interfaces formed by che- misorbed group-III elements on Si(111) surfaces have attracted a great deal of interest since Lander and Morrison [1] first performed a low-energy electron diffraction (LEED) study of the adsorp- tion of A1 onto the Si(lll) surface. This interest is primarily due to the technological and funda- mental importance of these Si( 111 ) group-III che- misorption systems, and has resulted in the atomic and electronic structures of the clean Si(lll)- (V~ x V~)R30°-B, -A1, -Ga and -In surfaces (here- * Corresponding author. Tel.: (+61)49 215447; fax: (+61) 49 216907; e-mail: phmwr@cc.newcastle.edu.au 0039-6028/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0039-6028 ( 97 ) 00657-2 after simply referred as ~/3 surfaces) now being fairly well understood [2]. A number of recent experiments have investi- gated the interaction of these "X/3 surfaces with atomic hydrogen [3-9] and shown that significant structural changes occur in the B, A1 and In surfaces following atomic hydrogen exposure. Landemark et al. [3] used the V~-In surface to obtain an unreconstructed H-terminated Si(111)- (1 x 1) surface by hydrogen exposure. A (1 x 1) LEED pattern was obtained after the hydrogen exposure exceeded 5000 L (1 L= 10 .6 Torr-s -1) at 350°C. Core-level and angle-resolved photo- electron spectroscopy (ARPES) suggested that the formation of the (1 x 1)H structure was accompa- nied by the breaking of Si-In bonds and their