Adsorption of [(tBu)GaS]4 on GaAs(001)-(2×4)

Autor: R.I. Pelzel, B.O. Fimland, B.Z. Nosho, W.H. Weinberg
Rok vydání: 1999
Předmět:
Zdroj: Surface Science. 426:163-172
ISSN: 0039-6028
DOI: 10.1016/s0039-6028(99)00191-0
Popis: We have conducted an ultrahigh vacuum investigation of [( t Bu)GaS] 4 adsorption on GaAs(001)-(2×4). Adsorbing [( t Bu)GaS] 4 at a surface temperature of 650 K results in a carbon-free overlayer as judged by Auger electron spectroscopy. For submonolayer coverages, scanning tunneling microscopy (STM) images show the presence of protrusions on the surface. The height distribution of these protrusions, which is insensitive to bias voltage, is peaked between 0.7 and 1.4 A, i.e., less than would be expected for the adsorption of intact Ga 4 S 4 cubane cores, suggesting that the Ga 4 S 4 cubane core of the [( t Bu)GaS] 4 molecular precursor has dissociated upon adsorption at 650 K. Further exposure to [( t Bu)GaS] 4 results in a nearly complete overlayer which contains small domains of a (2×1) GaS-induced reconstruction as judged by STM. Residing on the overlayer with (2×1) domains are features with heights between 3 and 4 A suggesting that the Ga 4 S 4 cubane core of the [( t Bu)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 (2×1) reconstructed 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 Ga 4 S 4 cubane cores that were adsorbed intact at 650 K. By annealing to 830 K, it is possible to desorb the second layer of GaS and obtain a (2×1) surface. Our STM images of this (2×1) reconstruction are consistent with a previously proposed model consisting of GaS heterodimers. Further adsorption of [( t Bu)GaS] 4 on the (2×1) surface at a temperature of 650 K results in clustering of the Ga 4 S 4 cubane cores into anisotropic GaS islands. The distribution of island aspect ratios ( d [110] / d [110] ) is peaked between 2 and 3.
Databáze: OpenAIRE
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