Reversed double-beam photoacoustic spectroscopy of metal-oxide powders for estimation of their energy-resolved distribution of electron traps and electronic-band structure

Abstract

A novel instrumental methodology, reversed double-beam photoacoustic spectroscopy (RDB-PAS), was developed for measuring the energy-resolved distribution of electron traps (ERDT) of metal-oxide powders. In the RDB-PAS measurement, electrons in the valence band of a powder sample are directly excited to electron traps (ETs) and accumulated in the ETs from the deeper (anodic) side to the shallower (cathodic) side by wavelength-scanned continuous light, and the increase in photoabsorption of electron-filled ETs is measured by modulated light at a fixed wavelength by PAS. It was shown that ERDT/CBB (conduction-band bottom) patterns measured by RDB-PAS can be used for not only identification and detailed characterization of a wide range of metal-oxide powder samples but also estimation of difference in apparent valence-band top (VBT) position.

Correlation of the Photocatalytic Activities of Cu, Ce and/or Pt-Modified Titania Particles with their Bulk and Surface Structures Studied by Reversed Double-Beam Photoacoustic Spectroscopy

“…One is that the area density of ETs in the heteroatom-modified surfaces was lower than that of the unmodified titania surface. The other possible explanation was that the photoabsorption coefficient of the heteroatom-included electron-filled ETs, especially the ETs with Ce, was the same as that of the commercial titania particles since the present ET-density measurement assumed that the coefficient of detected photoabsorption [6]. The interpretation mentioned above of the RDB-PAS results is still speculative without any knowledge of the surface structures.…”

“…The double side of the carbon tape was used and attached on a stub, and then, the sample powder was dispersed on carbon tape. RDB-PAS analysis was performed on laboratory-made instruments to obtain the ERDT/CBB (conduction-band bottom) patterns following the reported procedure in References [5,6] with slight modification as follows. A sample powder was set in a stainless-steel sample holder in a PAS cell equipped with a MEMS (micro-electro-mechanical system; SparkFun MEMS Microphone Breakout, INMP401 (ADMP401)) microphone module.…”

“…Continued use of the BSM is because no methods have been developed to measure the surface structural properties using macroscopic measurements, rather than microscopic measurements such as transmission electron microscopy or atomic force microscopy. To the authors' knowledge, reversed double-beam photoacoustic spectroscopy (RDB-PAS) has been developed to analyze the energy-resolved distribution of electron traps (ERDT), which reflect the surface structure of semiconductor solids (powder), including a wide range of metal oxides as the sole macroscopic analytical method [5,6].A number of papers have been published on the preparation, characterization, and photocatalytic activities of titania photocatalysts modified through doping, loading, and/or mixing heteroatoms [1,2], in which characterization was performed by X-ray diffractometry (XRD), nitrogen-adsorption measurement, and/or scanning electron microscopy. That is, no surface-structural analysis has been conducted, and the photocatalytic activity-photocatalyst property correlation seems to have been discussed without using surface-structural information.In the present paper, copper [7,8] and cerium-modified [9,10] samples were synthesized using the sol-gel method, while the Pt-modified [11] sample was prepared using the impregnation method.…”

“…Continued use of the BSM is because no methods have been developed to measure the surface structural properties using macroscopic measurements, rather than microscopic measurements such as transmission electron microscopy or atomic force microscopy. To the authors' knowledge, reversed double-beam photoacoustic spectroscopy (RDB-PAS) has been developed to analyze the energy-resolved distribution of electron traps (ERDT), which reflect the surface structure of semiconductor solids (powder), including a wide range of metal oxides as the sole macroscopic analytical method [5,6].…”

Photocatalytic Nanoparticulate ZrxTi1‐xO2 Coatings with Controlled Homogeneity of Elemental Composition

“…In this connection, time‐resolved TRMC analysis can complement reversed steady‐state double‐beam photoacoustic spectroscopy measurements in elucidation of photocatalytic mechanisms and physical nature of the relevant electron traps, which are still under discussion …”