Electroreflectance spectra

Figure 15.10 Normal-incidence electroreflectance spectrum of Ag(100) in 0.5 M NaF solutions for various bias potentials. Reprinted from Ref. 10 with...

If eqn. (37) is valid, two predictions can be made immediately, the first is that the lineshape should depend solely on the third derivative of the dielectric function of the semiconductor. This has been verified for i-Ge as shown in Fig. 9 here, the dielectric function determined from spectroscopic ellip-sometry is differentiated numerically three times and the results compared with the electroreflectance spectrum. The second consequence of eqn. (37) is that the lineshape depends quadratically on 8 and, for a classical depletion layer, this means, in turn, that the electroreflectance spectrum should be independent of the d.c. potential provided 6 does not alter. 

This approach has been used by Tomkiewicz et al. [17] to rationalise the electroreflectance spectrum of CdIn2Se4 unfortunately, the crystal studied in this report disintegrated before measurement of the donor intensity could be carried out to verify that the experimental conditions were such that the low-field theories could reasonably be expected to hold. Nevertheless, the intensity of the electroreflectance peak showed a marked dependence on potential, decreasing by a factor of ten over a 1V range as shown in Fig. 10(a). 

The electroreflectance spectrum of p-GaP in PC is shown in Fig. 32 it clearly differs both in size and magnitude from that found in aqueous solution. A detailed analysis along the lines developed above suggests that a spectrum of this shape could only arise from a sample with very little potential dropped across the depletion layer, in agreement with the a.c. data, and the magnitude of the spectrum is consistent with the suggestion that the magnitude of the potential drop in the depletion layer is only a few tens of mV. 

Observation of l/Ro) dR/dE) at a fixed potential as a function of incident light wavelength gives an electroreflectance spectrum. When the adsorbed species are light absorbing, the electroreflectance spectrum at times exhibits characteristic peaks at the wavelengths of absorption maxima, thus providing further information on the adsorbed states of the species. 

When adsorbed species on the electrode surface is light absorbing, the electroreflectance technique seems to be effective in detecting them with high sensitivity. Furthermore the technique will serve as a tool for obtaining knowledge of the adsorbed species at the molecular level since the electroreflectance spectrum indicates the electronic states of the species. 

In Fig. 5.16 the electroreflectance spectrum of the Au(100)-(1 x 1) surface shows two derivative-like features around 3 and 4.2 eV assigned to transitions from the bulk d-band into the aforementioned unoccupied surface states [98]. These fea-... 

We will illustrate the difficulties and the opportunities which are associated with two complementary measuring techniques Relaxation Spectrum Analysis and Electrolyte Electroreflectance. Both techniques provide information on the potential distribution at the junction of a "real" semiconductor. Due to the individual characteristics of each system, care must be taken before directly applying the results which were obtained on our samples to other, similarly prepared crystals. 

Electrolyte Electroreflectance (EER) is a sensitive optical technique in which an applied electric field at the surface of a semiconductor modulates the reflectivity, and the detected signals are analyzed using a lock-in amplifier. EER is a powerful method for studying the optical properties of semiconductors, and considerable experimental detail is available in the literature. ( H, J 2, H, 14 JL5) The EER spectrum is automatically normalized with respect to field-independent optical properties of surface films (for example, sulfides), electrolytes, and other experimental particulars. Significantly, the EER spectrum may contain features which are sensitive to both the AC and the DC applied electric fields, and can be used to monitor in situ the potential distribution at the liquid junction interface. (14, 15, 16, 17, 18)... 

Photoluminescence excitation spectroscopy (PLE) is generally used to identify the excited-state structure in quantum wells. For GalnN/GaN quantum wells, Im et al [14] used PLE to study single wells of various widths. Similarly to the results from absorption, electro-absorption, and electroreflectance measurements, a large Stokes shift of the onset of the PLE spectrum with respect to the dominating photoluminescence peak was observed at low temperature [14]. 

The basis of electroreflectance is more subtle than thermoreflectance Fig. 109(b) shows that the main effect arises from the fact that the presence of an electric field destroys the translational symmetry along one of the directions of the crystal. This loss of symmetry means that k need no longer be conserved along that axis and optical transitions need no longer be vertical in the Elk diagram. As for thermoreflectance, this effect will be most marked at the critical points, again allowing the spectroscopist to extract the data of real interest from the otherwise rather shapeless absorption spectrum of the solid. 

Electroreflectance (ER) measurement is a powerful technique that provides information on the redox state of the substance adsorbed in a monomolecular layer on an electrode [46]. When the ER spectrum is measured with an ADH-modified gold electrode at... 

The spectrum of an ER signal, i.e. the plot of (AR/R)er as a function of k, is called the electroreflectance (ER) spectrum. Electroreflectance measurement can also be carried out during linear potential scan or potential step of Ejc- Under linear potential scan, one obtains the voltammogram of the ER signal, the so-called ER voltammogram. 

Fig. 10 Electroreflectance spectra (s and p polarized light) (solid line) for a single touch film of 12-AS adsorbed onto Au(l 1 1) and (dashed line) the background spectrum recorded without an adsorbed monolayer. Data taken from Ref. [25]...

Fig. 4. Simultaneous (a) electroreflectance and (b) capacity vs. potential curves during the first negative potential sweep and their reversal for adsorbed cytochrome 3 on a gold electrode in 0.02 M NaF solution. pH = 5.4 f = 15 Hz E (modulation) = 50 mV rms v (sweep rate) = 3 mVs" angle of incident 0 X = 405 nm. (c) Typical spectral structures in electroreflectance displayed at the peak potential. in the presence of adsorbed cytochrome c on a gold electrode in 0.02 M KCIO4 (solid line) at pH 6. Dotted line represents the ER spectrum at — 0.7 V (vs. SCE) and broken line at +0.1 V. Reproduced from [56], courtesy of the publisher).

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