Adsorption of [(Bu-t)GaS](4) on GaAs(001)-(2 x 4)

We have conducted an ultrahigh vacuum investigation of [(Bu-t)GaS](4) adsor ption on GaAs(001)-(2 x 4). Adsorbing [(tBu)GaS], at a surface temperature of 650 K results in a carbon-free overlayer as judged by Auger electron spe ctroscopy. For submonolayer coverages, scanning tunneling microscopy (STM) images show the presence of protrusions on the surface. The height distribu tion of these protrusions, which is insensitive to bias voltage, is peaked between 0.7 and 1.4 Angstrom, i.e., less than would be expected for the ads orption of intact Ga4S4 cubane cores, suggesting that the Ga4S4 cubane core of the [(Bu-t)GaS], molecular precursor has dissociated upon adsorption at 650 K. Further exposure to [(Bu-t)GaS](4) results in a nearly complete ove rlayer which contains small domains of a (2 x 1) GaS-induced reconstruction as judged by STM. Residing on the overlayer with (2 x 1) domains are featu res with heights between 3 and 4 Angstrom suggesting that the Ga4S4 cubane core of the [(Bu-t)GaS](4) molecular precursor remains intact as adsorption at 650 K proceeds to the second layer of GaS. Upon annealing the overlayer to 790 K, STM images show adsorbates on a well-ordered (2 x 1) reconstruct ed surface. The height distribution of these adsorbates is peaked between 0 .7 and 1.4 A, suggesting that annealing to temperatures above 700 K results in the dissociation of the second layer Ga4S4 cubane cores that were adsor bed intact at 650 K, By annealing to 830 K, it is possible to desorb the se cond layer of GaS and obtain a (2 x 1) surface. Our STM images of this (2 x 1) reconstruction are consistent with a previously proposed model consisti ng of GaS heterodimers. Further adsorption of [(Bu-t)GaS], on the (2 x 1) s urface at a temperature of 650 K results in clustering of the Ga4S4 cubane cores into anisotropic GaS islands. The distribution of island aspect ratio s (d([(1) over bar 10])/d([110])) is peaked between 2 and 3. (C) 1999 Publi shed by Elsevier Science B.V. All rights reserved.