IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Thursday Sessions
       Session SC+SS+EL-ThM

Paper SC+SS+EL-ThM7
Making Organic Molecules on Cu(100) and GaAs(100)

Thursday, November 1, 2001, 10:20 am, Room 111

Session: Interaction of Hydrogen and Organics with Silicon
Presenter: N.K. Singh, The University of New South Wales, Australia
Authors: N.K. Singh, The University of New South Wales, Australia
N. Paris, The University of New South Wales, Australia
P. Gatland, The University of New South Wales, Australia
Correspondent: Click to Email
Alkyl coupling reactions, to form longer chain hydrocarbons, form the basis of many catalysed industrial processes. Surface studies carried out to date to understand the mechanisms by which carbon-carbon bonds form during the coupling process have been restricted to reactions of alkyl halides on coinage metal surfaces. Our recent investigations have shown that GaAs(100), a compound semiconductor, is also capable of catalysing alkyl coupling reactions, which had not been realised previously. Coupling products form irrespective of whether the alkyl groups are derived from alkanethiols or alkyl halides. However, on GaAs(100) the respective higher alkenes form, whereas it is known higher alkanes form on coinage metals. In this paper the surface reactions of a select group of alkanethiols (propanethiol, 1,1,1-trifluoroethanethiol) and alkyl halides (iodoethane, 2-iodo-1,1,1-trifluoroethane) on GaAs(100) and Cu(100), studied by thermal desorption and X-ray photoelectron spectroscopies, will be presented in order to establish the trend in the product mixtures on the two surfaces. We will show that both surfaces exhibit disproportionation and coupling reactions. Disproportionation reactions of the adsorbed alkyl fragments form the corresponding gaseous alkene, alkane and hydrogen. The coupling reactions however on the two surfaces differ. So for example, on Cu(100) CF@sub 3@CH@sub 2@I forms CF@sub 3@CH@sub 2@CH@sub 2@CF@sub 3@ as the coupling product while on GaAs(100) it forms CF@sub 2@=CHCH@sub 2@CF@sub 3@, the corresponding alkene. In the case of coupling reactions of CF@sub 3@CH@sub 2@SH, on Cu(100) CF@sub 3@CH@sub 2@CH@sub 2@CH@sub 3@ is formed while on GaAs(100) , CF@sub 2@=CHCH@sub 2@CH@sub 3@ is formed. These products are inconsistent with the products formed by CF@sub 3@CH@sub 2@I reactions. We will discuss the mechanisms by which these coupling reactions occur, and postulate reasons for the differences in the observed product mixtures on GaAs(100) and Cu(100).