It is demonstrated using reflection anisotropy spectroscopy that the adsorption of cytosine and cytidine -monophosphate at the Au(110) 1 x 2/electrolyte interface gives rise to ordered structures in which the base is oriented vertical to the surface and parallel to the [110] axis of the Au(110) plane.

It is demonstrated that the (1 × 1) structure and the (1 × 2) and (1 × 3) surface reconstructions that occur at Au(110)/electrolyte interfaces have unique optical fingerprints. The optical fingerprints are potential, pH and anion dependent and have potential for use in monitoring dynamic changes at this interface. We also observe a specific reflection anisotropy spectroscopy signature that may arise from anions adsorbed on the (1 × 1) structure of Au(110).

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The reflection anisotropy spectra ͑RAS͒ of a Au͑110͒ surface in an HClO 4 electrolyte have been measured as the potential is cycled into the oxidation region. RAS spectral signatures are obtained for the adsorption of OH − and the oxidation of the surface. RA spectra indicate that both processes destroy surface states associated with the Au͑110͒ ͑1 ϫ 2͒ surface, that the oxidation of the Au͑110͒ surface is reversible, and that there are no significant kinetic barriers to any of the surface processes that occur as the potential is cycled.Given the scientific and industrial importance of electrochemistry, it is important to develop in situ probes of electrochemical reactions in order to obtain a better understanding of the processes involved. The oxidation of gold surfaces has been studied extensively by a variety of techniques, including cyclic voltammetry ͑CV͒, 1,2 rotating disk electrochemistry, 3 X-ray diffraction, 4 scanning tunnelling microscopy ͑STM͒, 5 X-ray photoelectron spectroscopy ͑XPS͒, and low-energy electron diffraction ͑LEED͒. 6 The oxidation is thought to proceed via the consecutive transfer of two electrons. The first stage is the chemisorption of the hydroxide ion, which is then oxidized to form a Au-OH species first identified by electroreflectance spectra, 7 though this technique was not able to identify the oxidation state of the adsorbed OH − . Submonolayer adsorption of the OH − species has been suggested by CV studies in acid solutions 8,9 and also by surface oxygen bands in surface enhanced raman spectroscopy ͑SERS͒. 10 A detailed chronocoulometry study coupled with subtractively normalized interfacial Fourier transform infrared ͑SNIFTIRS͒ measurements have shown that the adsorbed OH − forms a polar bond to the surface. 11 These infrared spectroscopy results confirm that for oxide formation to proceed, 1/3 of a monolayer has to form on the surface.The Au͑110͒ surface has also been studied by the optical techniques of electroreflectance 12 and second harmonic generation. 13 In this paper we apply the relatively new technique of reflection anisotropy spectroscopy ͑RAS͒ 14 to the study of the oxidation of an Au͑110͒ electrode. RAS has been extensively applied to the study of semiconductors 15 and as a monitor of semiconductor growth. 16 Recently, it has been applied to the study of metal surfaces in ultrahigh vacuum ͑UHV͒. 14,17 It has also been used to study the Au͑110͒ surface in an electrochemical environment, 18-22 to determine the orientation of cytosine and cytidine 5Ј-monophosphate adsorbed at Au͑110͒/electrolyte interfaces, 23 and to monitor the reversible reaction of cysteine ↔ cystine at Au͑110͒/electrolyte interfaces as a function of the potential applied to the Au͑110͒ electrode. 24 ExperimentalThe Au͑110͒ single crystal ͑purity 99.999%͒ was a disk with diameter 10 mm and a thickness of 2 mm, with an exposed area of 0.5 cm 2 . The crystal was orientated to an accuracy of 0.1°using X-ray diffraction, mechanically polished to 0.25 m with diamond paste, and cleaned in an ultrasonic b...

We compare the RAS of the Au(110)1x2 surface and the RAS of surfaces formed by depositing and then annealing two monolayers of Pd deposited on the Au(110)1x2 surface. The similarities and differences between the RAS of the Au(110) 1x2 surface and the annealed Pd/Au(110) surface are consistent with the view that annealing gives rise to the formation of a Au overlayer on top of a mixed Pd/Au layer. The RAS suggests that the Au overlayer gives rise to the surface states found on the Au(110) 1x2 surface.