Satoru Suzuki

The response of a material to light is described by the complex dielectric function . Therefore, determining (E) at various photon energies E is crucial for the development of photosensitive and optical materials. Valence-band excitation electron energy loss spectroscopy (EELS) is a powerful analytical technique for determining  (E) from visible light to the vacuum ultraviolet. EELS is primarily used in conjunction with a transmission electron microscope and can achieve atomic-level spatial resolution. However, EELS generally requires thin-film processing of the sample, making it impossible to analyze a thin film supported on a substrate. In this study, we attempted EELS measurements using hard X-ray photoelectron spectroscopy (HAXPES). Here, we use core level photoelectrons as the electron source. First, the validity of the measurement was verified by analyzing Ar gas using Ar 1s photoelectrons as the electron source. Next, a thin film of ZEP520A resist on a Si substrate was analyzed using Si 1s photoelectrons from the Si substrate as the electron source. This enabled us to obtain EELS data for a thin film sample on a substrate without the thin-film processing.

The electrical charging of insulating samples is a common problem in photoelectron spectroscopy. Although heating has been suggested as a way to minimize surface charging, systematic studies of this are scarce. We have found that during 8 keV photoelectron spectroscopy using a synchrotron, the extent of charging of three highly insulating materials could be significantly reduced with increasing temperature. The charging of glass and LiNbO3 samples could be almost completely compensated at a moderate temperature of ∼400 °C. Based on the temperature dependence of charging-induced binding energy shift, the activation energies of the charge compensation were evaluated to be about 0.73, 0.65, and 0.21 eV for a glass slide, cover glass, and LiNbO3, respectively. Furthermore, charge compensation was achieved by surface conduction rather than bulk conduction.

Abstract Detection of a small amount of oxygen vacancies is often difficult. In this study, using near-ambient pressure hard X-ray photoelectron spectroscopy, oxygen vacancies were formed in situ in SnO_{2 − x} and WO_{3 − y} under a reducing gas atmosphere. The number of oxygen vacancies was so small that they could not be detected in the core-level photoelectron spectra. However, the effects of the vacancies were observed in the valence band spectra. This is because under the measurement conditions, the relative sensitivity of the metal outer orbitals (Sn 5s and W 5d) occupied when the oxygen vacancies are formed is significantly higher than that of the O 2p orbital predominantly forming the valence band. The x and y values were estimated to be ∼0.007–0.01 and ∼0.008–0.02, respectively, which correspond to vacancy ratios of sub-percent.