Reflectance anisotropy spectroscopy

Frederick B G, Power J R, Cole R J, Perry C C, Chen Q, Flaq S, Bertrams T, Richardson N V and Weightman P 1998 Adsorbate azimuthal orientation from reflectance anisotropy spectroscopy P/rys. Rev. Lett. 80 4490-3... 

Adsorption of pyridine on Au(llO) electrodes was also studied using reflection anisotropy spectroscopy [255]. Reflection anisotropy of pyridine/Au(110) system has been attributed to n-jT transitions, the band of which was shifted compared to their spectral position in the gas phase, due to the interaction of the lone electron pair orbitals at N atom with the gold surface. 

Spectroscopies such as UV-visible absorption and phosphorescence and fluorescence detection are routinely used to probe electronic transitions in bulk materials, but they are seldom used to look at the properties of surfaces [72]. As with other optical techniques, one of the main problems here is the lack of surface discrimination, a problem that has sometime been b q)assed by either using thin films of the materials of interest [73, 74], or by using a reflection detection scheme. Modulation of a parameter, such as electric or magnetic fields, stress, or temperature, which affects the optical properties of the sample and detection of the AC component of the signal induced by such periodic changes, can also be used to achieve good surface sensitivity [75]. This latter approach is the basis for techniques such as surface reflectance spectroscopy, reflectance difference spectroscopy/reflectance anisotropy spectroscopy, surface photoadsorption... 

Surface states were first detected by optical techniques in semiconductors and are now studied mainly by ARUPS, KRIPES, STM, SDR, and reflectance anisotropy spectroscopy (RAS). 

Surface anisotropy has given rise to the technique of reflectance anisotropy spectroscopy (RAS), in which linearly polarized light is modulated between two principal directions (of the surface tensor) and the difference... 

KRIPES K-resolved inverse photoelectron RAS reflectance anisotropy spectroscopy... 

Whereas SE measures the ratio of reflection coefficients for different polarizations, various reflection difference techniques probe relative differences in reflectivity. Among these techniques one distinguishes surface differential reflectivity (SDR), surface photoabsorption (SPA) and reflection anisotropy spectroscopy (RAS). 

Reflection anisotropy spectroscopy (RAS) probes the difference between the reflection coefficients measured at near-normal incidence for two mutually perpendicular polarizations. Let ip be an azimuthal angle between the plane of incidence and one of the principal axes of the sample surface. Then the RAS signal normalized to the mean reflection coefficient, r, can be written as... 

Frederick, B., Cole, R., Power, J., Perry, C., Chen, Q., Richardson, N., Weightman, R, Verdozzi, C., Jennison, D., Schultz, R, and Sears, M. (1998). Molecular orientation with visible light Reflectance-anisotropy spectroscopy of 3-thiophene carboxylate on Cu(llO) surfaces. Phys. Rev. B, 58 10883 -10889. 

Weightman, P. (2001). The potential of reflection anisotropy spectroscopy as a probe of molecular assembly on metal surfaces, phys. stat. sol. (a), 188 1443 -1453. 

Reflection anisotropy spectroscopy (RAS) probes the electronic structure of surfaces and interfaces using visible and near-ultraviolet photons. From its origins in the 1980s as an in situ real-time monitor of semiconductor growth processes, RAS has evolved into a technique that has been applied to surfaces in UHV, surfaces under high pressure of ambient gas and solid/liquid interfaces in the field of electrochemistry, together with more spedaUst applications such as liquid crystal devices. (Note that the technique was also known as reflection difference spectroscopy (RDS) in the early years.) Most optical probes are not surface sensitive... 

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