Self-assembly of dithiol monolayers on Au(III)
MacDairmid, Allan Robert
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This thesis compares the self-assembly of octanethiol, a representative n-alkanethiol, with dithiothreitol (DTT) on Au (lll). Octanethiol is on eight carbon n-alkanethiol while DTT is a four carbon Q ,(i) dithiol with hydroxyl groups on the second and third carbons. We find that octanethiol forms a densely packed c(4x2) superlattice of the (/3*/3)R30deg. structure characteristic of n-alkanethiols. DTT forms a less dense monolayer, possibly c(2/3x/3). Both monolayers exhibit pits 2.5 A deep equivalent to the height of one gold layer. The time evolution of pitting is investigated in both systems using scanning tunneling microscopy (STM). The fraction of the surface that is covered by these pits is found to be in the range of 0.05-0.10 for both systems and consistent with previous n-alkanethiol studies. The mean pit radius approaches an equilibrium value of ~19 A for both thiol species. It has been observed that DTT modified systems do not reach this equilibrium value as quickly as octanethiol modified systems. The nature of the binding of DTT to gold is also investigated using STM and Auger electron spectroscopy (AES) studies. AES studies involving Eliman's Reagent, a marker species, suggest that a significant fraction of the DTT binds to the gold surface via two Au-S bonds.
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