Observing ordered states in transition-metal oxides has been one of the most important topics in contemporary condensed-matter physics because ordering phenomena is directly related to anomalous physical properties such as superconductivity, colossal magnetoresistance, multiferroicity, and metal-insulator transition. Resonant soft x-ray diffraction has emerged as a new experimental tool for investigating spin ordering, and is especially suitable for studying thin films. Here we show how we have successfully observed charge/spin ordered states in transition-metal-oxide thin films by combining hard and soft x-ray diffraction.
The magnetic and electronic structures of the Fe3O4(111) surface were investigated by conversion electron Mössbauer spectroscopy (CEMS) and ultraviolet photoemission spectroscopy (UPS), respectively. The CEMS results indicated that the Fe3O4(111) surface is covered by closure domains, and that the magnetization direction of the Fe(B) site is more parallel to the surface than the non-perpendicular easy axes while that of the Fe(A) site corresponds to the easy exes. This indicates that the spins of the Fe(A) and Fe(B) sites are non-collinear near the surface. By using UPS, we have discovered that the H atom adsorption on the Fe(A)-terminated Fe3O4(111) surface reduces the work function but does not induce charge transfer. On the O2-exposed Fe(A)-terminated Fe3O4(111) surface, on the other hand, H adsorption increases the Fe(B) t2g derived peak in the UPS spectrum and decreases the work function. This indicates that, on the O2-exposed Fe(A)-terminated Fe3O4(111) surface, H atoms adsorb as cations and dope electrons to the Fe(B) t2g orbital.
A hydrophobic TiO2 surface can be converted to a hydrophilic one by UV light irradiation. This phenomenon was discovered more than 20 years ago and has been used in a variety of coating applications. However, the mechanism is not well understood. In particular, it is still not clear whether and how the surface structure is involved. We studied the possible structural change of the rutile-TiO2(110) surface by using X-ray crystal truncation rod (CTR) scattering. We demonstrated the occurrence of a surface structural change during the photoirradiation by using the high-speed CTR scattering profile measurement in a wavelength dispersive mode. We determined the structure of the hydrophobic (non-irradiated) and hydrophilic (photoirradiated) surfaces based on static CTR data, and proposed a possible mechanism of the water wettability transition.
Gaining a thorough understanding of the electrochemical interface in lithium ion batteries is essential for the development of a common strategy for the material design. This paper presents the interfacial reaction analyses between intercalation electrodes and organic electrolytes using an epitaxial-film model electrode and in situ surface scattering techniques which directly detect crystal structures in 10 nm-regions from the top of the electrode surface. The crystal structures of the intercalation electrodes drastically change in the surface regions when soaked to the electrolyte and are reconstructed during the initial electrochemical reaction. The reconstructed surface regions have a pronounced effect on the power characteristics and the stability at the subsequent electrochemical cycles.