The stability of graphene band structures against an external periodic perturbation; Na on Graphene

We report that the $\pi$ band of graphene sensitively changes as a function of an external potential induced by Na especially when the potential becomes periodic at low temperature. We have measured the band structures from the graphene layers formed on the 6H-SiC(0001) substrate using angle-resolved photoemission spectroscopy with synchrotron photons. With increasing Na dose, the $\pi$ band appears to be quickly diffused into background at 85 K whereas it becomes significantly enhanced its spectral intensity at room temperature (RT). A new parabolic band centered at $k\sim$1.15 \AA$^{-1}$ also forms near Fermi energy with Na at 85 K while no such a band observed at RT. Such changes in the band structure are found to be reversible with temperature. Analysis based on our first principles calculations suggests that the changes of the $\pi$ band of graphene be mainly driven by the Na-induced potential especially at low temperature where the potential becomes periodic due to the crystallized Na overlayer. The new parabolic band turns to be the $\pi$ band of the underlying buffer layer partially filled by the charge transfer from Na adatoms. The five orders of magnitude increased hopping rate of Na adatoms at RT preventing such a charge transfer explains the absence of the new band at RT.Comment: 6 pages and 6 figure

A plausible method of preparing the ideal p-n junction interface of a thermoelectric material by surface doping

Recent advances in two-dimensional (2D) crystals make it possible to realize an ideal interface structure that is required for device applications. Specifically, a p-n junction made of 2D crystals is predicted to exhibit an atomically well-defined interface that will lead to high device performance. Using angle-resolved photoemission spectroscopy, a simple surface treatment was shown to allow the possible formation of such an interface. Ta adsorption on the surface of a p-doped SnSe shifts the valence band maximum towards higher binding energy due to the charge transfer from Ta to SnSe that is highly localized at the surface due to the layered structure of SnSe. As a result, the charge carriers of the surface are changed from holes of its bulk characteristics to electrons, while the bulk remains as a p-type semiconductor. This observation suggests that the well-defined interface of a p-n junction with an atomically thin {\it n}-region is formed between Ta-adsorbed surface and bulk.Comment: 4 figure

A Study on the Relationship between Electronic Structure and Corrosion Characteristics of Zirconium Alloy in High-temperature Hydrogenated Water

The corrosion behavior of zirconium alloy was investigated using synchrotron scanning transmission X-ray microscopy and X-ray absorption spectroscopy. Scanning transmission X-ray micrographs showed different electronic structures at the oxide/metal interface of Zr???Nb???Sn alloy after exposure to high-temperature hydrogenated water. The orbital hybridization structure at the oxide/metal interface exhibited weaker t2g and eg peaks in X-ray absorption spectra, suggesting that zirconium suboxide can form just above the oxide/metal interface. The suboxide layer that formed at a high dissolved hydrogen concentration is thicker than the suboxide layer that formed at a normal dissolved hydrogen concentration after 100 d of oxidation

Additional file 1: of Enhancement of Photo-Oxidation Activities Depending on Structural Distortion of Fe-Doped TiO2 Nanoparticles

Supplementary material. Digital images and SEM images of Fe@TiO2 nanoparticles, XRD, and Raman intensity plot. Figure S1. Digital images of the Fe@TiO2 dispersed solution with several of Fe dopant concentration. Figure S2. SEM images as the morphologies varying the doping level of Fe: (a) 1 wt %, (b) 3 wt %, (c) 5 wt %; and their high-resolution images (a′), (b′), and (c′), respectively. Figure S3. EDX spectra with Fe peak (marked by black arrows) of big particles: (a) 1 wt% Fe@TiO2, (b) 3 wt% Fe@TiO2, and (c) 5 wt% Fe@TiO2. Figure S4. (a) XRD peak position and correspond lattice constant of (101) plane of anatase TiO2 structure and (b) Raman intensity ratio of I410 (α-Fe2O3 Eg) to I144 (anatase TiO2 Eg). Figure S5. Spectral subtraction of valence band spectra by bare TiO2 peak: (a) 1 wt% Fe@TiO2, (b) 3 wt% Fe@TiO2, and (c) 5 wt% Fe@TiO2

Spectromicroscopic observation of a live single cell in a biocompatible liquid-enclosing graphene system

On-the-spot visualization of biochemical responses of intact live cells is vital for a clear understanding of cell biology. The main obstacles for instant visualization of biochemical responses of living cells arise from the lack of a sophisticated detecting technique which can simultaneously provide chemical analysis tools and the biocompatible wet conditions. Here we introduce scanning transmission X-ray microscopy (STXM) combined with a liquid-enclosing graphene system (LGS), offering biocompatible conditions and improved X-ray absorption spectra to probe the chemical responses of live cells under wet conditions. This set-up enables us to probe a subtle change in absorption spectra depending on the oxidation state of a miniscule amount of oxygen in the functional groups present in each cell and its surroundings containing a minimal amount of liquid water. As an example of in situ biochemical responses of wet cells, chemical responses of a single Colo 205 cell are visualized and analyzed using X-ray absorption near the oxygen K-edge. This spectromicroscopic method using LGS can be applied to diverse biological samples under wet conditions for the analysis of their biochemical responses

Nanometer-scale local probing of X-ray absorption spectra of Co/Pt multilayer film

We report our local X-ray absorption spectra (XAS) measurement mapping for a Co/Pt multilayer using scanning transmission microscopy with 25-nm spatial resolution and 0.1-eV spectral resolution. We have systematically analyzed the two-dimensional XAS intensity variation over the corresponding magnetic domain patterns, revealing a XAS profile across the magnetic domain wall as well as the simultaneous high-throughput measurement of local XAS spectra.11sciescopu