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The complementary techniques of in-situ infrared spectroscopy and scanning tunneling microscopy (STM) have been used in this study to build detailed structural models for the chemisorbed forms of uracil, thymine, and 3-methyl uracil on Au(111) electrodes. The infrared spectra, in water and D2O electrolytes, show that both uracil and thymine adopt similar coordination forms with the surface with both exocyclic oxygen atoms and a deprotonated N3 facing in toward the surface in a vertically oriented chemisorbate. 3-Methyl uracil cannot exhibit such a surface coordination and its IR signature in the carbonyl stretching region is quite different. This is interpreted as the chemisorbate interacting through its deprotonated N1 and C2O. STM has been used to characterize and compare the molecular ordering of the three respective adsorbates. Uracil exhibits the highest coverage structure c(3 × ), while thymine exhibits smaller ordered domains which are expanded in one direction to allow for the spatial requirements of the methyl group on thymine. The domain size for the thymine chemisorbate could be improved by temperature annealing the electrode in-situ and a “pseudo c( × 4)” structure was observed. Both the uracil and thymine chemisorbate structures feature chains of molecules, stacked like “rolls of coins”, close enough for π-stacking to occur. The structure of thymine overlayers differs from uracil, since there are a number of different possible orientations of adjacent molecular rows, which results in a high frequency of stacking faults. These differences are discussed. 3-Methyl uracil is quite different, exhibiting a rather low coverage, albeit a highly ordered structure (5 × 2 ) which cannot allow π-stacking. On the basis of these observations, the factors governing the formation of the respective chemisorbed phases are discussed.

Organised multilayers were formed from the controlled self-assembly of ferrocene alkyl thiols on Au(111) surfaces. The control was accomplished by increasing the concentration of the thiol solutions used for the assembly. Cyclic voltammetry, ellipsometry, scanning probe microscopy (STM and AFM) and in situ FTIR spectroscopy were used to probe the di †erences between mono-and multilayers of the same compounds. Electrochemical desorption studies conÐrmed that the multilayer structure is attached to the surface via one monolayer. The electrochemical behaviour of the multilayers indicated the presence of more than one controlling factor during the oxidation step, whereas the reduction was kinetically controlled which contrasts with the behaviour of monolayers, which exhibit kinetic control for the oxidation and reduction steps. Conventional and imaging ellipsometry conÐrmed that multilayers with well-deÐned increments in thickness could be produced. However, STM indicated that at the monolayer stage, the thiols used promote the mobility of Au atoms on the surface. It is very likely that the multilayer structure is held together through hydrogen bonding. To the best of out knowledge, this is the Ðrst example of a controlled one-step growth of multilayers of ferrocenyl alkyl thiols using self-assembly techniques.

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