| AVS 60th International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | K. Yamakawa, Gakushuin University, Japan |
| Authors: | K. Yamakawa, Gakushuin University, Japan K. Fukutani, University of Tokyo, Japan |
| Correspondent: | Click to Email |
The origin of asymmetric line shapes appearing in spectroscopy were first discussed in terms of interaction between a discrete state and continuous states by Fano [1]. Thereafter this Fano effect has been observed in a variety of systems including the adsorbate–surface system such as H / W(100), CO / Cu(100), and CO / Cu(111) [2, 3], where metal electronic states of a continuous spectrum interact with the vibrational state of the adsorbate. In the present study we performed Fourier transform infrared spectroscopy (FTIRS) of CO2 adsorbed on TiO2 nanotubes to observe an asymmetric absorption peak in the range of the antisymmetric stretching vibration (v3). In contrast to previous studies on metallic substrates, the asymmetric peak was observed on a semiconductor substrate in this study.
TiO2 nanotubes were synthesized following the way described in the literature [4]. For evaluation of the nanotubes Raman spectroscopy, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM) were performed. From the TEM images the diameters of the tubes were estimated to be several nanometers. Then, the TiO2 nanotubes dispersed in ethyl alcohol were sprayed on a CaF2(111) surface, which was set on a liquid-nitrogen cooled cryostat in an ultra-high vacuum chamber with a base pressure of 2×10-8 Pa. Infrared spectra were recorded in a transmission configuration, using a FTIR spectrometer at a spectral resolution of 4 cm-1 with a liquid-nitrogen cooled HgCdTe detector. The substrate temperature was kept at 81 K.
In the spectral range of v3 an absorption peak grew around 2340 cm-1 first, as the exposure of CO2 was increased. After this peak was saturated, a new absorption peak grew at 2350 cm-1. Saturation of the latter peak was followed by formation of a CO2 multilayer. Noting that the former peak appeared to be only a slight shoulder at the saturation of the latter peak, the former was assigned to v3 of CO2 on oxygen vacancy sites, while the latter to that on terrace sites. Whereas the absorption peak at 2350 cm-1 exhibited a normal absorption feature, the peak at 2340 cm-1 revealed an asymmetric shape. Adsorption on defect sites is thought to play an important role for appearance of the asymmetric peak.
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[2]Y. J. Chabal, Phy. Rev. Lett. 55, 845 (1985).
[3]C. J. Hirschmugl et al., J. Electron Spectrosc. Relat. Phenom. 54, 109 (1990).
[4]T. Kasuga et al., Adv. Mater. 11, 1307 (1999).