C. I. Smith

A rapid reflectance anisotropy spectrometer

A 16 channel reflectance anisotropy (RA) spectrometer capable of simultaneously acquiring reflectance spectra and real and imaginary RA spectra on the 0.1 s time-scale is reported. Its performance was evaluated by monitoring the electrolytic deposition/growth and removal of copper on a gold(110) surface. The slow deposition enabled very low noise spectra to be obtained, which served as the yardstick with which the spectra obtained during the rapid removal could be compared. The spectra obtained over the 15 s removal mirrored those obtained during the 500 s deposition period. The spectra are discussed in terms of the copper growth being in the form of aligned islands.

Determination of the structure of adenine monolayers adsorbed at Au(110)/electrolyte interfaces using reflection anisotropy spectroscopy

Reflection anisotropy spectroscopy (RAS) has been used to show that at saturation coverage adenine adsorbs on the Au(110)/electrolyte interface in a base-stacking configuration with the plane of the bases orientated vertically on the surface and with the long axis of the molecules parallel to the [110] direction. Changes in the RAS observed from adsorbed adenine as a result of changes in the potential applied to the Au(110) electrode could arise from slight changes in the orientation of the molecules in the vertical plane.

Adsorption of Pyridine on Au(110) as Measured by Reflection Anisotropy Spectroscopy

The reflection anisotropy spectra of pyridine adsorbed onto a Au(110) surface in an electrochemical cell demonstrates that this system forms an ordered structure. The reflection anisotropy spectroscopy (RAS) of pyridine/Au(110) is attributed to n - π * transitions which are shifted from their position in gas-phase spectra by the effects of the interaction of the N lone pair orbitals with the Au(110) surface. The time dependence of the reflection anisotropy spectrum of the pyridine/Au(110) system shows that after the initial onset of pyridine adsorption it takes ∼5 min for the system to yield the spectrum of the equilibrium ordered structure. A similar time is required for the RAS signal to return to that of the Au(110) surface following the desorption of pyridine.

The adsorption of bipyridine molecules on Au(110) as measured by reflection anisotropy spectroscopy

The reflection anisotropy spectra of 2,-bipyridine and 4,-bipyridine adsorbed onto an Au(110) surface in an electrochemical cell demonstrate that both systems form ordered structures. It is shown that reflection anisotropy spectroscopy can be used to distinguish between structural isomers adsorbed on the Au(110) surface.

Detection of DNA hybridisation on a functionalised diamond surface using reflection anisotropy spectroscopy

The analysis of single-stranded DNA attached to a polycrystalline diamond surface by reflection anisotropy spectroscopy (RAS) demonstrates that the DNA is oriented essentially vertically to the surface. RAS is able to detect the hybridisation between the attached strand and the homologous sequence.

The nature and stability of the Au(110)/electrochemical interface produced by flame annealing.

It is shown using reflection anisotropy spectroscopy (RAS) that following flame annealing and immersion in pure water, the Au(110) surface adopts a (1×1) structure and that this structure is preserved in a 0.1 M H(2)SO(4) environment. The surface transforms to the (1×2) reconstruction following the application of a potential of 0.0 V versus SCE (a saturated calomel electrode). This surface is unstable and the RAS profile changes over periods of 15 min and 1 h in a manner which suggests that changes are occurring in the structure and distribution of [11(-)0] steps. Over longer periods the RAS transforms towards a profile attributed to a surface associated with the specific adsorption of anions.

Spectral signatures of the surface reconstructions of Au(110)/electrolyte interfaces

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).

Evidence for protein conformational change at a Au(110)/protein interface.

Evidence is presented that reflection anisotropy spectroscopy (RAS) can provide real-time measurements of conformational change in proteins induced by electron transfer reactions. A bacterial electron transferring flavoprotein (ETF) has been modified so as to adsorb on an Au(110) electrode and enable reversible electron transfer to the protein cofactor in the absence of mediators. Reversible changes are observed in the RAS of this protein that are interpreted as arising from conformational changes accompanying the transfer of electrons.

Azimuthal dependent reflection anisotropy spectroscopy of Ag(110) near the plasmon resonance energy

The reflection anisotropy (RA) of Ag(110) has been investigated near 3.9 eV as a function of azimuthal angle θ using a photoelastically modulated spectrometer. At 3.9 eV the RA signal was small and varied as sin 4θ. At photon energies away from 3.9 eV the signal increased and varied as cos 2θ. Jones vector modeling of the system showed that in addition to the commonly observed cos 2θ dependence, which disappears when the reflection is isotropic, there is a sin 4θ dependence that occurs when the underlying dielectric function is anisotropic; in cubic materials this term is small but for other materials it may be very large.

Observation of the Electrochemical Oxidation of Au ( 110 ) by Reflection Anisotropy Spectroscopy

The reflection anisotropy spectra (RAS) of a Au(110) surface in an HCIO 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 Au(110) (1 X 2) surface, that the oxidation of the Au( 110) surface is reversible, and that there are no significant kinetic barriers to any of the surface processes that occur as the potential is cycled.