Adsorbate Isotherm Analysis by Reflection Anisotropy Spectroscopy on Copper (110) in Hydrochloric Acid.

Reflectance anisotropy spectroscopy (RAS) is a powerful optical probe that works on a polarization contrast basis. It can be operated in any environment, ranging from ultrahigh vacuum to vapor phases and liquids. The measured optical anisotropies are caused by several symmetry breaking effects and are exclusively assigned to the surface for otherwise bulk isotropic materials. In this work, we present a systematic study comprising in situ RAS-transient to assess the surface thermodynamics of the chloride adsorption on Cu(110) upon systematic variations of the applied electrode potentials in comparison to cyclic voltammetry (CV). Numerical time-derivatives of the measured RAS-transients are shown to be exclusively associated with electrical currents of those electrochemical reactions, which change the properties of the electrode surface. The recorded transient line-shapes track the Frumkin type isotherm properties related to chloride coverage. Both connections are theoretically discussed. Owing to the surface and interface specificity, RAS is shown to exhibit a high surface sensitivity. In particular, processes taking place in parallel, namely, the hydrogen evolution reaction (HER) as well as the copper dissolution as Cu+ and Cu2+, do not contribute to the RAS response.

Structural Characterization of a Capillary Microfluidic Chip Using Microreflectance.

The structural characterization of capillary microfluidic chips is important for reliable applications. In particular, nondestructive diagnostic tools to assess geometrical dimensions and their correlations with control processes are of much importance, preferably if they are implemented in situ. Several techniques to accomplish this task have been reported; namely, optical coherence tomography (OCT) jointly with confocal fluorescence microscopy (CFM) to investigate internal features of lab-on-a-chip technologies. In this paper, we report on the use of a simple optical technique, based on near-normal incidence microreflectance, which allows mapping internal features of a microfluidic chip in a straightforward way. Our setup is based on a charge-coupled device camera that allows a lateral resolution of ∼2.5 µm and allows us to measure in the wavelength range of 640-750 nm. The technique takes advantage of the Fabry-Perot interferences features in the reflectance spectra, which are further analyzed by a discrete Fourier transform. In this way, the amplitude of the Fourier coefficients is modulated by the presence of a microfluidic channel.