Electroreflectance signal

Figure 7. Potential sweep of the electroreflectance signal at 1.74 eV superimposed on potential sweep of chopped light photoresponse...

Electroreflectance spectra were measured for n-CdSe in the liquid junction configuration, and variations of the lineshape as a function of potential were observed. As the potential was reduced below the flatband potential, the electroreflectance signals changed sign. The potential at which this change occurs correlates well with the turn-on potential for light-induced photocurrent and with the intercept of the Mott-Schottky plot. 

The defect absorption is observed for polarization Ellb and responds to fields F Ib only. This clearly shows a correlation of the it-rr transitions of the polymer. It is present in all samples and develops with the thermal conversion to the polymer, very similar to the electroreflectance signal of the band transition near 2.4 eV which is small in partly polymerized samples but growth strongly in the autocatalytic range of conversion. 

Figure 14. Contours of the variations in carrier concentrations across the surface of GaAs utilizing the electrolyte electroreflectance signal at 8370A. The numbers in the contours indicate percentage variations relative to the lowest concentration (106).

The above considerations are illustrated by Fig. 38, which shows the dependences of electroreflection of a silicon electrode on its potential. In fact, the signal changes the sign at the flat band potential (the latter was measured independently by the differential capacity technique). 

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)... 

Whereas electroreflectance is conventionally used in the UV/visible region, in the 1980s Bewick et al.l2 14 developed the technique in the IR region. Since IR radiation interacts with the vibrations of chemical bonds, important information regarding bonds with adsorbed species has been obtained15, especially useful for research into electrocatalysts. New developments in signal processing, such as the Fourier transform (FT-IR), have veen very valuable. 

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. 6.14 Electroabsorption (top) and linear (bottom) spectra of PDA single crystals with PTS and DCDH side groups derived in Ref. 111 from reflectance and electroreflectance at 7 10 K. PTS signals are doubled owing to nonequivalent chains in the low temperature phase. The EA signal between 1.9 and 2.4 eV resembles the derivative of the linear absorption for a Stark shift of 10 /xeV. (Adapted from Ref. 111.)...

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