OPTICAL SECOND HARMONIC SPECTROSCOPY OF THE ANATASE TiO₂(101) FACE

Abstract

We have investigated electronic levels of the H 2 O /anatase TiO 2 (101) interface by optical second harmonic spectroscopy. We see a sharp rise of SH intensity above the SH phonon energy 2ℏω~3.6 eV . According to our previous analysis, the SH signal from this face originates mainly from the H 2 O/TiO 2 (101) interface. The sum frequency intensity also shows a rise at ℏω1+ℏω2~3.6 eV . Thus the observed sharp rise of the SH intensity is due to a resonance of an interface band gap at 3.6eV. The energy of this interface band gap is larger than that of the bulk band gap, 3.2eV.

Investigation of Water Structure at the TiO2/Aqueous Interface

“…As an optical technique, it has been exploited for investigating vapor/liquid, solid/liquid, and liquid/liquid interfaces. While VSFS has yet to be applied to the TiO 2 /aqueous interface, studies have been conducted at other solid/aqueous interfaces including the SiO 2 /water, − Al 2 O 3 /water, and CaF 2 /water interfaces. , TiO 2 /aqueous interfaces have been observed, however, by second harmonic generation (SHG). , Furthermore, a catechol complex has been made on colloidal TiO 2 particles and a surface charge-transfer process was directly observed by SHG in aqueous solution in its presence. , In terms of nonaqueous titanium dioxide interfaces, VSFS has recently been exploited for investigating the photocatalytic reaction of poly(ethylene terephthalate) on TiO 2 . Also, the presence of trace hydrocarbon species has been monitored on nanoparticulate TiO 2 surfaces in the presence and absence of UV illumination …”

“…45,46 TiO 2 /aqueous interfaces have been observed, however, by second harmonic generation (SHG). 47,48 Furthermore, a catechol complex has been made on colloidal TiO 2 particles and a surface charge-transfer process was directly observed by SHG in aqueous solution in its presence. 49,50 In terms of nonaqueous titanium dioxide interfaces, VSFS has recently been exploited for investigating the photocatalytic reaction of poly(ethylene terephthalate) on TiO 2 .…”

Spectral, tensor, andab initiotheoretical analysis of optical second harmonic generation from the rutile TiO2(110) and (001) faces

“…When we calculate its nonlinear optical response we must consider the birefringence effect both for incident and SH waves. Some of the works have gone into details of this treatment for anisotropic media [13][14][15][16]. However, there has been no example of a systematic and simultaneous analysis of SH intensity patterns and spectra for an anisotropic nonlinear surface.…”

Ab initiocalculation of optical second harmonic generation at the rutileTiO2(110)surface

“…10 In addition to these experimental studies, optical second harmonic generation (SHG) has been used to analyze the electronic states of TiO 2 surfaces. [11][12][13][14][15] SHG is not only sensitive to the surface electronic structure, but also has attractive advantages such as high spectral resolution, nondestructive character, and insensitivity to ambient gas or liquid. Therefore, SHG can be used for in situ observation of surface electronic states of a TiO 2 sample showing catalytic activity in air or solution.…”

“…The SHG experiments for TiO 2 surfaces [13][14][15] have shown some outstanding results: the anisotropy of the SH response in the surface plane depends drastically on the incident photon energy, and the surface band gap estimated from a resonant peak in the SH intensity spectra is slightly larger than the bulk band gap. However, the interpretation of the experi-mental SHG data remained unsufficient, because of lacking knowledge on the underlying electronic transitions.…”