Electroreflectance spectroscopy

The reflectivity of bulk materials can be expressed through their complex dielectric functions e(w) (i.e., the dielectric constant as a function of frequency), the imaginary part of which signifies absorption. In the early days of electroreflectance spectroscopy the spectra were often interpreted in terms of the dielectric functions of the participating media. However, dielectric functions are macroscopic concepts, ill suited to the description of surfaces, interfaces, or thin layers. It is therefore preferable to interpret the data in terms of the electronic transitions involved wherever possible. 

A detailed evaluation shows that the shift of the energies of the surface states with potential is surprisingly large, and approaches 1 eV/V for state B. A completely satisfactory explanation has not yet been given, but specific adsorption of the anion is likely to play a role. 

Electroreflectance spectroscopy has been successfully applied to numerous other systems such as oxide films or adsorbed dyes. It is most useful when the observed features can be related to specific electronic transitions. As an example we mention the reactions of a film of Prussian Blue adsorbed on gold or platinum. Prussian Blue can be oxidized to Berlin Green, or reduced to Prussian White. The appearance of the products gives rise to characteristic features in the electroreflectance spectra [11]. 

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Dadap J I, Hu X F, Anderson M H, Downer M C, Lowell J Kand Aktsiperov O A 1996 Optical second-harmonic electroreflectance spectroscopy of a Si(OOOI) metal-oxide-semiconductor structure Phys. Rev. B 53 R7607-9... 

Valence Band Spectroscopy. Optical and electronic properties of UPD metal flms on metal electrodes have been studied in situ by means of differential- and electroreflectance spectroscopy [98], Optical absorption bands, however, reflect a combined density of electronic states at a photon energy which is the energetic difference of... 

When Desilvestro and Pons used in situ IR reflection spectroelectrochemistry to observe the reduction of C02 to oxalate at Pt electrodes in acetonitrile [83], two different forms of oxalate were observed. Similarly, Aylmer-Kelly et al. studied C02 reduction in acetonitrile and propylene carbonate at Pb electrodes [84], by using modulated specular electroreflectance spectroscopy. Subsequently, two radical intermediates were observed which they determined to be the C02 radical anion, C02, and the product of the radical anion and C02, the (C02)2 adduct (see Equations 11.9 and 11.10). Vassiliev et al. also studied the reduction of C02 in... 

In the first study of its kind, second harmonic generation has been used to study potential induced reconstruction on Au(lll) and Au(100) by Kolb and coworkers [156]. These surfaces have been known to reconstruct in UHY when they are clean [153, 157], Surface reconstruction occurs when the surface atoms of a solid rearrange themselves in a structure different from that expected from simple termination of the bulk lattice. Various studies by cyclic voltammetry, electroreflectance spectroscopy and ex situ electron diffraction have suggested that flame-treated crystals form stable reconstructions in solution. Unfortunately, due to the lack of in situ probes, very little direct evidence for this reconstruction has been available. 

It has been shown that contactless electroreflectance spectroscopy is an excellent experimental technique to study the built-in electric field in AlGaN/GaN heterostructures as well as the band gap discontinuity in GalnNAsSb/GaAs quantum wells. 

Hutton and Peter (1993) in a study of G2li xA xAs compared the bandgap values derived from photocurrent and photovoltage spectra with those derived by electrolyte electroreflectance spectroscopy (EER). They concluded that EER gives the most reliable results, provided that the doping density is not too high. 

Hutton R. S. and Peter L. M. (1993), Characterization of n-Ga xAlxAs (x < 0.3) epitaxial layers by photocurrent, photovoltage and electrolyte electroreflectance spectroscopies . Semiconductor Sci. Technol. 8, 1309-1316. 

Hutton R. S., Peter L. M., Batchelor R. A. and Hamnett A. (1994), The potential distribution across the semicondnctor-electrolyte interface—a stndy by electrolyte electroreflectance spectroscopy of GaAs and Gai AbAs nnder conditions of photodissolution , J. Electroanal. Chem. 375, 193-201. 

One line in bioelectrochemistry is rooted in electrochemical techniques, spectroscopy, and other physical chemical techniques. Linear and cyclic voltammetry are central.Other electrochemical techniques include impedance and electroreflectance spectroscopy," ultramicro-electrodes, and chronoamperometry. To this come spectroscopic techniques such as infiared, surface enhanced Raman and resonance Raman,second harmonic generation, surface Plasmon, and X-ray photoelectron spectroscopy. A second line has been to combine state-of-the-art physical electrochemistry with corresponding state-of-the-art microbiology and chemical S5mthesis. The former relates to the use of a wide range of designed mutant proteins, " the latter to chemical synthesis or de novo designed synthetic redox metalloproteins. " " ... 

Fig. 5.15. Schematics of spectroelectrochemical cells for electroreflectance spectroscopy. Top Arrangement for measurements at various angles of incidence bottom Cell for measurement with electrodes in the dipping technique...

This method is sometimes called reflectance difference spectroscopy (RDS) and, because of considerable overlap, this method is sometimes also considered to be a variation of electroreflectance spectroscopy (see p. 50 for further details). 

Numerous studies employing both polycrystalline and single crystal metal electrodes and semiconductor surfaces have been reported for an overview, see [772]. The possible advantages of a simultaneous (double beam) application of electroreflectance spectroscopy and second harmonic generation have been pointed out [769]. 

For SAMs with attached redox molecules, k (units of s ) can be measured by cychc voltammetry, chronoamperome-try (CA), alternating current impedance spectroscopy (ACIS), alternating current voltammetry (AGV), AG electroreflectance spectroscopy, and an indirect laser-induced temperature (ILIT) jump method. 

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