Surface-photovoltage spectroscopy

In conclusion, nanorods are a potentially interesting material, but present results still do not allow understanding of whether the nanostructure leads to an improvement of the intrinsic photocatalytic behaviour, or whether other factors (accessible surface area, enhanced adsorption, etc) are responsible for the observed differences. In ZnO nanorods have been shown quite recently by surface photovoltage spectroscopy that the built-in electrical field is the main driving force for the separation of the photogenerated electron-hole pairs.191 This indicates that the nano-order influences the photophysical surface processes after photogeneration of the electron-hole pairs. A similar effect could be expected for Titania nanorods. However, present data do not support this suggestion, mainly due to the absence of adequate photo-physical and -chemical characterization of the materials and surface processes. 

Surface photovoltage spectroscopy (SPS) in Fig. 6.5 was used to determine the surface acidity of JML-1 by measuring transition of electrons between the interface and the surface. The JML-I40 calcined at 550°C exhibited two peaks at 596 nm and 677 nm, whereas the sample without calcination had only one peak at 330 nm. The peak at 330 nm is assigned to the band-band electron transition and those at 596 nm and 677 nm are attributed to the surface-related transitions. The observation of these surface-related transitions indicates the presence of positive charges on the surface of the calcined sample, suggesting that the acidity of JML-1 catalyst is resulted from a large amount of SZ acidic sites on the silica surface. 

Lenzmann F., Krueger J., Burnside S., Brooks K., Gratzel M., Gal D., Ruehle S. and Cahen D. (2001), Surface photovoltage spectroscopy of dye-sensitized solar cells with Ti02, Nb205, and SrTiOs nanocrystalline photoanodes indication for electron injection from higher excited dye states , J. Phys. Chem. B 105, 6347-6352. 

Table 5-41. Other spectroscopic methods Multiwavelength analysis, NMR, raman spectroscopy, and surface photovoltage spectroscopy. ...

A cost effective experimental setup for optical modulettion experiments, recently built in our laboratory. Is shown in Fig. 8 (57). Similar setup was recently reported by Tian et al. (58). Experiments performed with this system include photoreflectance (PR), electrolyte electroreflectance (EER), surface photovoltage spectroscopy (SPV), 1st. and 2nd. harmonics photoinduced current-voltage characteristics, spectral response and d.c. current-voltage characteristics. One can switch electronically between experiments and perform any number of techniques without moving the cell or removing the electrode from the electrolyte. A variable neutral... 

Steady state surface photovoltage (SPV) spectroscopy is useful for determining the nature of the junction between the nanocrystalline film and substrate. SPV studies of Ti02 films on Sn02 confirm that an electric field exists at the interface, driving electrons into the substrate. This is consistent with the values of the work functions of the two materials in vacuum (4.85 eV for Sn02 F, 5.15 eV for... 

A variance that usually appears in the literature as Surtece Photovoltage Spectroscopy (21) uses either a vibrating metal electrode in close proximity to the surface of the semiconductor (Kelvin probe), or a semitransparent metal electrode with a modulated light source to make contact with the semiconductor, and monitors the spectral response of the photovoltage with subband gap illumination. This technique can also be viewed as a non-contact technique that can be used for in situ characterization during device fabrication. 

Photovoltage spectroscopy allows the determination of band bending, that is, the determination of the location of surface states in the band gap it is a powerful noncontact technique for the characterization of surface and interface states, especially in the case of heterostructures [89, 91, 92]. 

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