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.