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Here, we demonstrate that the density of oxygen vacancies generated by the doped transition metal (TM) ions at the surface of ZnO nanoparticles (TM-doped ZnO NPs; TM = Cr or Co) determines the photocatalytic degradation (PCD) activity for organic pollutants; to this end, we employ multimodal microscopy and spectroscopy that encompass material probing at multiple length scales, ranging from the atomic to mesoscale. Following the doping treatment of pristine ZnO NPs as a post-synthetic process, Cr ion doping leads to a significant enhancement of the PCD activity of the ZnO NPs, whereas Co ion doping results in a negative effect. Atomic-scale observations and site-specific spectroscopy confirm that these two TM ions substitute for Zn, in different valence states (Cr3+ and Co2+, respectively), without inducing a phase change of the host ZnO matrix (wurtzite structure). Cr-doped ZnO NPs have the highest density of oxygen vacancies originating from charge mismatch, which contributes to a notably enhanced PCD effect on the tested pollutants, whereas the other two samples (pristine and Co-doped ones) have similar amounts of oxygen vacancies. Our multimodal and multiscale spectroscopic probing provides a clear insight into the significant role of charge mismatch, induced by the substitution of the host cation by the doped cation, in controlling the oxygen vacancies. This can serve as a practical guideline for atomically precise control of oxygen vacancies toward the development of high-performance metal oxide photocatalysts.

The surface morphology and electronic structure of hexagonal graphene onion rings (HGORs), a modified graphene structure, were investigated to confirm the possibility as an efficient catalyst when compared to graphene. After confirming the formation of HGORs with a smaller width (~4.2 μm) from scanning electron microscopy (SEM) and optical microscopy images, we compared the catalytic activities of HGORs and graphene by measuring the rate of oxidation of thiophenol using high-resolution photoemission spectroscopy (HRPES). In addition, we also assessed in 4-chlorophenol degradation and the OH radical formation with a benzoic acid to confirm the possibility for photocatalytic activities of HGORs. As a result, we confirmed that HGORs, which has an increased active site due to its three-dimensional structure formed by the reaction of graphene with hydrogen, can act as an effective catalyst. In addition, we could also realize the possibility of optical applicability by observing the 0.13 eV of band gap opening of HGORs.

Nanoparticles (NPs) of the well-known photocatalysts TiO2 and ZnO each doped with noble metals (NM = Au, Pd, or Pt) were synthesized by applying a thermosynthetic method, and the catalytic activities of the resulting six samples were compared. After characterizing them by using high-resolution photoemission spectroscopy (HRPES), we evaluated the catalytic effects of the samples the oxidation of 4-aminothiophenol (4-ATP) by using HRPES under UV illumination and on the oxidation of 4-ATP in aqueous solution by taking electrochemistry measurements. In addition, we determined the rates of conversion of CO to CO2 in the presence of these catalysts by using a residual gas analyzer under an ultra-high vacuum condition. As a result, we found a good positive correlation between the numbers of defect structures induced by the doped noble metals and the catalytic activity, and showed that Pd-TiO2 and Pt-ZnO NPs can act as efficient catalysts due to their relatively large number of defect structures and corresponding oxygen vacancies.

This study explored the crystallographic characterization of zirconium, zirconium-based samples containing minor alloying elements, simulated Zircaloy-4, and simulated ZIRLO at a temperature range of 30–870 °C using in situ high-temperature X-ray diffraction. The results from Pawley refinement demonstrated that the lattice thermal expansion along the a-axis direction is suppressed by the tin element, in contrast to the other minor alloying elements. Moreover, the simulated ZIRLO possesses the enhanced resistance for lattice thermal expansion compared to the simulated Zircaloy-4, indicating that a ZIRLO cladding has a better performance in suppressing the change in the lattice constants under a thermal environment.

Here, we report thorough spectroscopic characterization of tungsten oxide (WO3) nanoparticles (NPs) and WO3 NPs surface doped with transition metal (TM) ions (TM@WO3; TM = Cr3+, Mn2+, Fe3+, Co2+, and Ni2+) by using various surface analysis techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), high-resolution X-ray photoelectron spectroscopy (HRXPS), and extended X-ray absorption fine structure (EXAFS). At first glance, the morphologically distinct features were not perceivable across TM dopants. However, the detailed XPS analysis confirmed that the WO3 NPs doped with Cr and Fe ions formed a relatively large number of surface defects. Moreover, we found through EXAFS analysis that the chromium and iron ions doping on WO3 NPs promoted the dramatic shortening of the W O bond length as compared to pristine WO3 and other metal ion doped WO3 NPs. Much enhanced photocatalytic and electrocatalytic activities of Cr@WO3 and Fe@WO3, which relied on the different density of surface defects created by the charge and size of the TM dopants, were demonstrated in the photocatalytic degradation reactions of 4-chlorophenol and the electrocatalytic hydrogen evolution reaction. The present result can serve as a practical guideline for atomically precise control of oxygen vacancy toward the development of high-performance metal oxide photocatalysts.

While reduced graphene oxide (rGO) is used widely as a catalyst, its catalytic activity can be improved significantly by modifying it with a metal. In this study, we compared the photocatalytic and catalytic properties of base-treated rGO particles and transition-metal-ion-doped rGO based on the oxidation reaction of thiophenol and the photocatalytic degradation of 4-chlorophenol. Since the two catalytic activities are related to the changes in the electronic structure of rGO, X-ray photoemission spectroscopy, X-ray absorption spectroscopy, and Raman spectroscopy were performed. When rGO was doped with Mn2+ ions, its catalytic properties improved with respect to both reactions. The changes in the electronic structure of rGO are attributed to the formation of defect structures on the rGO surface via a reaction between the doped Mn2+ ions and oxygen of the rGO surface. Thus, the results show that the doping of rGO with Mn ions in the +2-charge state (stable oxide form: MnO) enhances its catalytic and photocatalytic activities. Hence, this study provides new insights into the use of defect-controlled rGO as a novel catalyst.

The modified TiO2 nanoparticles (NPs) to enhance their catalytic activities by doping them with the five transition metals (Cr, Mn, Fe, Co, and Ni) have been investigated using various surface analysis techniques such as scanning electron microscopy (SEM), Raman spectroscopy, scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). To compare catalytic activities of these transition metal-doped TiO2 nanoparticles (TM-TiO2) with those of TiO2 NPs, we monitored their performances in the catalytic oxidation of 2-aminothiophenol (2-ATP) by using HRPES and on the oxidation of 2-ATP in aqueous solution by taking electrochemistry (EC) measurements. As a result, we clearly investigate that the increased defect structures induced by the doped transition metal are closely correlated with the enhancement of catalytic activities of TiO2 NPs and confirm that Fe- and Co-doped TiO2 NPs can act as efficient catalysts.

To compare the catalytic oxidation activities of reduced graphene oxide (rGO) and rGO samples doped with five different transition metals (TM-rGO), we determine their effects on the oxidation of L-cysteine (Cys) in aqueous solution by performing electrochemistry (EC) measurements and on the photocatalytic oxidation of Cys by using high-resolution photoemission spectroscopy (HRPES) under UV illumination. Our results show that Cr-, Fe-, and Co-doped rGO with 3+ charge states (stable oxide forms: Cr3+, Fe3+, and Co3+) exhibit enhanced catalytic activities that are due to the charge states of the doped metal ions as we compare them with Cr-, Fe-, and Co-doped rGO with 2+ charge states. Graphical Abstract The SEM images and the corresponding EC measurements for (a) Cr3+, (b) Fe3+, and (c) Co3+ doped rGO

This study examined the catalytic activities of three distinct N–Pd@TiO 2 nanoparticles, post-annealed (at 700, 800, and 900 °C) after fabrication on silicon substrates. Systematically, HRPES and SPEM indicated that nitrogen was predominantly doped around PdO nanostructure. Particularly, we prove that photocatalytic activity in effective nitrogen doped surface area is far higher than in undoped area of Pd@TiO 2 nanoparticles by measuring for oxidation reaction of benzenethiol, thioacetic acid, and thiobenzoic acid. Besides to the band gap narrowing, nitrogen doping leads to generate Ti 3 + species or oxygen vacancies site of the surface, which leads to enhance the activity of surface photocatalysis.

The correlation between the defect structures of hydrothermally grown TiO2 nanorods (TNR) and their photocatalytic activity has been investigated by using various surface spectroscopic analysis techniques including scanning transmission X-ray microscopy (STXM) and high-resolution photoemission spectroscopy (HRPES). Defect states related to Ti3+ and oxygen vacancies in TNR were observed when the growth time was over 90 min (i.e., those over 500 nm in height), and these TNR samples showed photocatalytic oxidation activity with respect to the molecules 2-mercaptoethanol (2-ME) or 2-aminothiophenol (2-ATP), also confirmed by HRPES. The presence of defect structures on the TNR influences on the electronic states of titanium and oxygen, and thus can improve the catalytic oxidation reactions.

Current energy production habits deplete fossil fuels and accumulate atmospheric CO 2 , which contribute to the global climate change. Electrochemical fuel production via CO 2 reduction reaction is an idealistic yet an achievable process that mitigates CO 2 emissions and simultaneously satisfies energy demands. Here, the enhancement of CO 2 reduction activity and stability on size-controlled particulate Ag electrocatalysts derived from a simple, one-step cyclic voltammetry (CV) process by changing scan rates (1–200 mV/s) was demonstrated. Interestingly, larger nanoparticles prepared by slower scan rates (1–5 mV/s) have exhibited the most degree of enhancement for CO 2 reduction to CO product. Compared to untreated Ag foil, nanostructured Ag electrode has shown an anodic shift of approximately 200 mV in the onset potential of CO partial current density ( j CO ), 160 mV reduction of overpotential at j CO = 10 mA/cm 2 , and increased Faradaic efficiency (F.E.) for CO production especially at lower biased potentials (−0.89 to −1.19 V vs. RHE). Stability tests have demonstrated a drastic improvement in maintaining CO F.E. X-ray photoelectron spectroscopy suggests that the enhancement is associated with stable oxygen species incorporated on the nanoparticle Ag surfaces during the CV fabrication process.

Defect engineered Fe3O4 nanoparticles (NPs) with magnetic properties can act as efficient photocatalysts in spite of no intrinsically photocatalytic property of bare Fe3O4. The purpose of this study is to confirm the possibility whether the modified Fe3O4 NPs can be an efficient photocatalyst by engineering the surface defects without compromising the magnetic properties of Fe3O4 NPs. Herein, we report a facile method to introduce surface defects on Fe3O4 and Cr@Fe3O4 NPs without degrading their magnetic properties via simple pH treatments at moderate temperatures. Our results showed that Cr@Fe3O4 NPs fabricated under basic conditions, denoted as Cr@Fe3O4-B NPs, showed a clear electronic structural evidence for surface defects on Fe3O4. The presence of defects on Fe3O4 induced an alternative approach to solar activation via ligand-to-metal charge transfer to drive selective photocatalytic degradation of phenolic compound without losing its magnetic property. It is highly desirable to seek a strategy for achieving the recovery of catalysts using a magnet, while minimizing the loss of catalyst and the cost for a complicate recovery process.

Introduction of defect structures into Fe-doped TiO2 nanoparticles (Fe@TiO2 NPs) has been shown to endow NPs with improved photocatalytic properties. However, current strategies for the preparation of defect-containing NPs require high temperature or complicated treatments, which can induce unwanted phase transition. In this paper, we report a facile method to introduce surface oxygen vacancies into anatase-type Fe@TiO2 NPs without altering the crystalline phase via simple pH treatments at moderate temperatures. Furthermore, we present the effects of pH on the formation of surface oxygen vacancies. The optimized treatment under basic conditions is revealed to promote the formation of oxygen vacancies on the surface of anatase Fe@TiO2 NPs and effectively reduces the particle size by more than 25%, thereby causing a significant enhancement in the photocatalytic activities of the NPs (e.g. ~3.5 times better in photocatalytic degradation rate of 4-CP as compared to acid-treated Fe@TiO2). Comprehensive structural and chemical characterizations reveal that the point defects are predominantly formed on the surface of anatase NPs, and their population can be maximized by use of basic pH conditions. Our results pave a way toward the facile and efficient engineering of surface defect structures on catalytic metal oxide NPs for the design of high-performance photocatalysts.

Transition metal-doped SnO2 nanoparticles (TM-SnO2) were synthesized by applying a thermos-synthesis method, which first involved doping SnO2 with Sb and then with transition metals (TM = Cr, Mn, Fe, or Co) of various concentrations to enhance a catalytic effect of SnO2. The doped particles were then analyzed by using various surface analysis techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). We evaluated the catalytic effects of these doped particles on the oxidation of L-cysteine (Cys) in aqueous solution by taking electrochemical measurements and on the photocatalytic oxidation of Cys by using HRPES under UV illumination. Through the spectral analysis, we found that the Cr- and Mn-doped SnO2 nanoparticles exhibit enhanced catalytic activities, which according to the various surface analyses were due to the effects of the sizes of the particles and electronegativity differences between the dopant metal and SnO2.

We report the facile and green synthesis of activated carbon-supported palladium (Pd/AC) containing homogeneously dispersed Pd nanoparticles (Pd NPs) by using eco-friendly and naturally available cinchonidine (CD) as the capping agent. The Pd NPs in the synthesized Pd/AC hybrid are uniform with sizes predominantly in the range 4 to 7 nm. The synthesized Pd/AC was characterized with various methods, such as TEM, XRD, and XPS, and the influence of the synthetic conditions on its properties were investigated. The advantages of CD over conventional capping agents include its easy depletion after the synthesis with a simple rinsing process. Owing to the ultrafine, well-dispersed and purified Pd NPs, the synthesized hybrid exhibits excellent catalytic activities in the reduction of 4-nitrophenol and methylene blue. These findings further the development of novel stabilizing agents from naturally available sources for the preparation of heterogeneous catalysts with enhanced performance.

Graphene domains with different sizes and densities were successfully grown on Cu foils with use of a chemical vapor deposition method. We investigated the effects of volume ratios of argon to hydrogen during the annealing process on graphene growth, especially as a function of hydrogen partial pressure. The mean size and density of graphene domains increased with an increase in hydrogen partial pressure during the annealing time. In addition, we found that annealing with use of only hydrogen gas resulted in snowflake-shaped carbon aggregates. Energy-dispersive X-ray spectroscopy (EDX) and high-resolution photoemission spectroscopy (HRPES) revealed that the snowflake-shaped carbon aggregates have stacked sp2 carbon configuration. With these observations, we demonstrate the key reaction details for each growth process and a proposed growth mechanism as a function of the partial pressure of H2 during the annealing process.

The capacities of graphene oxide (GO) and reduced graphene oxide (rGO) films grown on silicon substrate to cause the aniline to azobenzene oxidation reaction were compared by using Raman spectroscopy, high-resolution photoemission spectroscopy (HRPES), and work function measurements as well as scanning electron microscopy (SEM). The oxygen carriers’ existence on GO film, which includes a lot of oxygen carriers, can facilitate the aniline to azobenzene oxidation reaction with slightly partial conversion of aniline to nitrobenzene, as determined by the Raman shifts and core-level spectra resulting from exposure to aniline. The work function of the GO film was found to change dramatically in comparison with rGO film, indicating that aniline exposed to a GO film produced n-type doping characteristics by electron charge transfer from GO to aniline. These results indicate that the oxygen carriers on a GO film oxidize aniline to azobenzene and show that GO film prefers to act as a reaction reagent rather than rGO.

The variations of electronic and magnetic properties of ultrathin Fe overlayers on a W(001) surface as a function of Fe film thickness (1.0–4.0 ML) has been investigated using X-ray magnetic circular dichroism (XMCD) in conjunction with ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED). We found that the ferromagnetic property of Fe film started to build up over 2.0 ML, as we confirmed the spin and angular moment contribution to the magnetic moment using XMCD experiments. We also confirmed that a thermally stable layer is over 2.0 ML of Fe film as we change the annealing temperature taken after Fe deposition at 300 K and at 400 K using UPS. We will systematically demonstrate that the occurrence of ferromagnetic property of Fe film on a W(001) surface is closely correlated to a thermally stable layer of Fe film on a W(001) surface.

The Mg capping inside p-tert-butylcalix[4]arene (p-TBCA) adsorbed onto a Ge(100) surface was investigated using high-resolution photoemission spectroscopy (HRPES) and their corresponding DFT calculation results. After 0.10 ML p-TBCA molecules had been adsorbed onto a Ge(100) surface, subsequent adsorption of a small amount of metallic Mg (∼0.10 ML) resulted in the formation of a capped structure inside the preadsorbed p-TBCA molecules. The adsorption structures resulting from further deposition of Mg (∼0.50 ML) onto the Ge(100) surface were monitored based on the surface charge state obtained from Mg 2s core level spectrum. We also clarified the evidence of the Mg capped inside p-TBCA adsorbed onto the Ge(100) surface as we monitored the work function change. Moreover, we confirmed that three different adsorption structures are experimentally favorable at room temperature through DFT calculation results.

The magnetic and structural properties of a series of VxCo1−x alloy films prepared in a variety of compositions on a W(110) surface were investigated using spin-resolved photoemission spectroscopy (SRPES) and low-energy electron diffraction (LEED) measurements. The epitaxial structures of the films were preserved over all V concentrations, despite the observation of a structural phase transition (SPT: hcp/bcc at x = 0.38), which was apparent from the LEED images. A magnetic phase transition (MPT) from ferromagnetic to paramagnetic occurred in the Co-rich region at x = 0.38. The SPT (from hcp and bcc) and MPT (from ferromagnetic to paramagnetic) were clearly correlated at x = 0.38, possibly due to changes in the electronic and magnetic structures of the valence band, as monitored by SRPES and LEED. The magnetization in the VxCo1−x alloy films on a W(110) surface varied systematically with the V concentration, and correlations between the structural changes and magnetic properties were revealed using SRPES and LEED.

Histotripsy uses high-intensity focused ultrasound pulses at low duty cycle to generate energetic bubble clouds inside tissue to fractionate a region. As a potential tumor treatment modality, this cavitation-based non-invasive technique has the advantages of easy monitoring and sharp borders. Aiming at therapy efficiency, we experimentally investigated the effects of pulse repetition frequency (PRF) and lateral scan step size on the dimensions of lesions formed through HIFU histotripsy in agar mimicking tissue in terms of mechanical (not acoustical) properties. The single-element spherically focused source (1.1 MHz, 6.34 cm focal length, f/1) was excited to reach the peak compressional and rarefactional pressures of ~102 and 17 MPa, respectively. A targeted rectangular block of 4.5 mm wide (lateral) and 6mm deep (axial) was scanned in a raster pattern with a constant axial step size of 3mm. The lateral step size was varied between 375, 750, 1500, 2250 and 4500 μm. Pulses at each treatment location consisted of 5000 20-cycle sine wave tone bursts with the PRF of 167, 333 or 1000 Hz. Results suggested that the bubble activity region could extend beyond the -3 dB region and that refining the lateral scan mesh and/or increasing PRF enlarged the lesion extent. The 1500 μm-333 Hz and the 1500 μm-1 kHz conditions were in a more favorable position to be viewed as optimal with regard to lesion volume generation rate, bubble activity region width, and the potential for thermal damage.

The modification of the electronic properties of a coverage-dependent graphene layer by nitrogen ions irradiation was investigated using core-level photoemission spectroscopy (CLPES). Here we describe preparation of monolayer and multilayer epitaxial graphene (EG) functionalized by nitrogen ions irradiation with 100 eV to minimize the damage of graphene layer as we annealed up to 1300 K to track the surface property changes using CLPES. As a result, on the monolayer EG, we found that pyridinic nitrogen mainly existed on the surface. On the multilayer EG, we observed the formation of graphitic nitrogen remaining as a major species confirmed using N 1s core-level spectra. Through a work function change (ΔΦ) measurement, both systems indicated p-type doping properties with 4.71 (monolayer EG) and 4.87 eV (multilayer EG) of work function values after N2 ion irradiation. Interestingly, we observed that monolayer EG maintained its p-type doping character, whereas multilayer EG changed the doping character from ...

In order to compare the catalytic activities of reduced graphene oxide (rGO), graphene oxide (GO), and graphene, we conducted oxidation of 2-aminothiophenol (2-ATP) and reduction of nitrobenzene (NB) in their presence by using high-resolution photoemission spectroscopy (HRPES). In addition, we determined conversion rates of CO to CO2 in the presence of these catalysts by performing a residual gas analyzer (RGA) under a UHV condition, Orange II and methylene blue degradations UV-vis spectrophotometry, and electrochemistry (EC) measurements in an aqueous solution, as well as by obtaining cyclic voltammograms and determining the change of the condition of electrodes before and after the oxidation of 2-ATP. We found that we can successively fabricate GO (oxidation) and graphene (reduction) from rGO by controlling the oxidation or reduction procedure time and then clearly comparing the critical properties among them as we perform various oxidation and reduction activities.

To design a high-performance photocatalytic system with TiO2, it is necessary to reduce the bandgap and enhance the absorption efficiency. The reduction of the bandgap to the visible range was investigated with reference to the surface distortion of anatase TiO2 nanoparticles induced by varying Fe doping concentrations. Fe-doped TiO2 nanoparticles (Fe@TiO2) were synthesized by a hydrothermal method and analyzed by various surface analysis techniques such as transmission electron microscopy, Raman spectroscopy, X-ray diffraction, scanning transmission X-ray microscopy, and high-resolution photoemission spectroscopy. We observed that Fe doping over 5 wt.% gave rise to a distorted structure, i.e., Fe2Ti3O9, indicating numerous Ti3+ and oxygen-vacancy sites. The Ti3+ sites act as electron trap sites to deliver the electron to O2 as well as introduce the dopant level inside the bandgap, resulting in a significant increase in the photocatalytic oxidation reaction of thiol (–SH) of 2-aminothiophenol to sulfonic acid (–SO3H) under ultraviolet and visible light illumination. Electronic supplementary material The online version of this article (doi:10.1186/s11671-016-1263-6) contains supplementary material, which is available to authorized users.

Recycling of LiCl–KCl eutectic salt wastes containing radioactive rare earth oxychlorides or oxides was studied to recover renewable salts from the salt wastes and to minimize the radioactive wastes by using a vacuum distillation method. Vaporization of the LiCl–KCl eutectic salt was effective above 900 °C and at 5 Torr. The condensations of the vaporized salt were largely dependent on temperature gradient. Based on these results, a recycling system of the salt wastes as a closed loop type was developed to obtain a high efficiency of the salt recovery condition. In this system, it was confirmed that renewable salt was recovered at more than 99 wt.% from the salt wastes, and the changes in temperature and pressure in the system could be utilized to understand the present condition of the system operation.

The ring formation and electronic properties of furan adsorbed on graphene layers grown on 6H-SiC (0001) has been investigated using atomic force microscopy (AFM), near edge X-ray absorption fine structure (NEXAFS) spectra for the C K-edge, and core level photoemission spectroscopy (CLPES). Moreover, we observed that furan molecules adsorbed on graphene could be used for chemical functionalization via the lone pair electrons of the oxygen group, allowing chemical doping. We also found that furan spontaneously form rings with one of three different bonding configurations and the electronic properties of the ring formed by furan on graphene can be described using by AFM, NEXAFS and CLPES, respectively.

The Chemical Doping of epitaxial graphene (EG) due to p-tert-butylcalix[4]arene was investigated using high resolution photoemission spectroscopy (HRPES). The measured work function changes verified that increased adsorption of the p-tert-butylcalix[4]arene on EG showed p-type doping characteristics due to charge transfer from the graphene to the p-tert-butylcalix[4]arene through the hydroxyl group. A single oxygen bonding feature associated with the O 1s peak was clearly observed in the core-level spectra, indicating the presence of one equivalent adsorption state.

Graphene was epitaxially grown on a 6H-SiC(0001) substrate by thermal decomposition of SiC under ultrahigh vacuum conditions. Using scanning tunneling microscopy (STM), we monitored the evolution of the graphene growth as a function of the temperature. We found that the evaporation of Si occurred dominantly from the corner of the step rather than on the terrace. A carbon-rich (6√3 × 6√3)R30° layer, monolayer graphene, and bilayer graphene were identified by measuring the roughness, step height, and atomic structures. Defect structures such as nanotubes and scattering defects on the monolayer graphene are also discussed. Furthermore, we confirmed that the Dirac points (ED) of the monolayer and bilayer graphene were clearly resolved by scanning tunneling spectroscopy (STS).

By using soft X-ray adsorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD), we investigated the fabrication of a single-phase Fe3O4 film on W(110) via the co-deposition method of Fe and oxygen as we control the substrate temperature. Furthermore, we confirmed the formation of various Fe-oxide films at various annealing temperature after the fabrication of the Fe3O4 film.

We have investigated the possibility of an interface between MgO and Fe lms to explore the existence of an oxide layer at the MgO/Fe interface as a preliminary system of Fe/MgO/Fe magnetic tunnel junctions. By using photoemission spectroscopy and X-ray absorption spectroscopy, we found that no iron-oxide layer existed at the interface for the in-situ-grown epitaxial MgO(001)/Fe(001) bilayer on a W(001) substrate. Moreover, we showed that metal Mg could revivify the iron-oxide to metal Fe when MgO was formed. These results show we can make iron-oxide-free samples in the Mg-rich growth condition.

We synthesized Ge and Ge1−xMx (M = Mn, Co, and Fe, x ≤ 0.4) nanowires using the thermal vapor transport method. All of the nanowires consisted of single-crystalline Ge nanocrystals grown uniformly with the [111] direction. High-resolution X-ray diffraction showed no metal cluster formation for any of the Ge1−xMx nanowires, and the reduction of the lattice constant for the Mn-substituted nanowires. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements revealed that the Mn2+ ions preferentially occupy the tetrahedral sites, substituting for Ge. The magnetic moment of the Mn ions reaches a maximum for x = 0.1, which is much larger than that of the Fe or Co ions. The magnetic hysteresis confirms the room-temperature ferromagnetism of the Ge1−xMnx nanowires, which is also maximized at x = 0.1. We suggest that the Mn ions produce dopant−acceptor hybridization with host defects in the p-type Ge nanowires. The Mn substitution is more effective to form significant ferromagnetic Ge nanowi...

We investigate the temperature-dependent surface etching process induced by Ce silicide on Si(1 0 0) using scanning tunneling microscopy and X-ray photoelectron spectroscopy. We found that step edges on the Si(1 0 0) surface are gradually roughened due to the formation of Ce silicide as a function of substrate temperature. Unlike the Si(1 1 1) surface, however, terrace etching also occurs in addition to step roughening at 500 °C. Moreover, we found that Si(1 0 0) dimers are released and formed dimer vacancy lines because bulk diffusion of Ce silicide into Si(1 0 0) surface occurs the defect-induced strain at higher temperature (∼600 °C).

ZnO nanorods have been grown on Si(001) wafer and fluorine-doped tin oxide (FTO) glass substrates for 1 and 4 h with the hydrothermal methods. The morphologies and photocatalytic activities of the ZnO nanorods were found to depend on the substrates. We investigated their properties by using spectroscopic analysis and demonstrated that the shape of nanorod and the ratios of external defects can be controlled by varying the substrates. Our experiments revealed that the nanorods grown on Si(001) have a single-crystalline wurtzite structure with (002) facets and that the number of surface oxygen defects increases with their length as the growth time increases. The nanorods grown on Si(001) have different facets, in particular wider (002) facets, and a higher ratio of the oxygen defect than the nanorods on FTO glass substrate. Moreover, the photocatalytic activities with respect to 2-aminothiophenol (2-ATP) of these nanorods were investigated with high-resolution photoemission spectroscopy (HRPES). We demonstrated that their photocatalytic activity is influenced by the ratios of surface oxygen defects, which varies with the substrate surface.

One-dimensional Ce nanowires have been grown on a single-domain vicinal Si(1 0 0) surface. The growth mode, including the structural and electronic properties as a function of the substrate temperature and Ce coverage, was studied using scanning tunneling microscopy and scanning tunneling spectroscopy. The results show the formation of Ce nanowires along the step edges on the vicinal Si(1 0 0) substrate at 580 °C.

Using magnetization, magneto-transport and single-crystal specific heat measurements we have determined the superconducting phase diagram of MgB 2 . The superconducting anisotropy γ changes monotonously from a value of around 2 near T c to above 4.5 at 22 K. For H||c a pronounced peak effect in the critical current occurs at the upper critical field. We present a strong evidence for a surface superconducting state for H||c which might account for the wide spread in reported values of the superconducting anisotropy γ.

Graphene layers grown on 6H-SiC(0001) were irradiated with 1 MeV electron beam to functionalize its surface. A surface analysis using atomic force microscopy, the near edge X-ray adsorption fine structure spectra of C K-edge, and photoemission spectroscopy suggests that the electron beam irradiation in ambient condition can induce oxidation of the graphene layer.

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology. Published version

Using low-energy electron diffraction and scanning tunnelling microscopy, we studied the formation of Mg silicide and metallic Mg islands on a Si(111)-7 × 7 surface at room temperature as a function of Mg coverage. We found that the mechanism by which Mg islands grew on the Si(111)-7 × 7 surface, and the morphology of the islands that formed, depended on whether the Mg deposition was performed in a stepwise or continuous manner. When Mg was deposited in a stepwise manner, with 1 h between deposition events, an amorphous Mg silicide overlayer formed on the Si(111)-7 × 7 surface during the initial stage of deposition (up to 2.0 ML Mg coverage), as shown by the observation of δ7 × 7 and 1 × 1 low-energy electron diffraction patterns. Upon further stepwise Mg deposition, round-shaped Mg islands grew on the amorphous Mg silicide layer, as shown by scanning tunnelling microscopy and the emergence of a 1 × 1 low-energy electron diffraction pattern. If, on the other hand, the Mg was deposited continuously in a single step, hexagonal Mg islands formed on the flat Mg silicide layers, and a [Formula: see text] and 1 × 1 mixed phase was observed. Moreover, using scanning tunnelling spectroscopy, we confirmed the semiconducting and metallic nature of the Mg silicide layer and hexagonal Mg islands on the Si(111)-7 × 7 surface depending on their Mg coverage, respectively.

We report on a systematic study of a number of structurally identical but chemically distinct transition metal oxides in order to determine how the material-specific properties such as the composition and the strain affect the properties at the interface of heterostructures. Our study considers a series of structures containing two layers of ferromagnetic SrRuO3, with antiferromagnetic insulating manganites sandwiched in between. The results demonstrate how to control the strength and relative orientation of interfacial ferromagnetism in correlated electron materials by means of valence state variation and substrate-induced strain, respectively. � 2010 The American Physical Society.

We investigated the structure and electronic properties of unidirectional Pt(2)Si nanowires (NWs) grown on a Si(100)-2 degrees off surface. We found that Pt(2)Si NWs were formed along the step edges of the Si(100)-2 degrees off surface with c(4x6) reconstructions that occurred on the terraces of Si(100) using scanning tunneling microscopy and the structure of formed NWs was found to be Pt(2)Si by core-level photoemission spectroscopy. Moreover, we confirmed that the electronic band structures of the NWs along the NW direction are different from those perpendicular to the NWs and the surface state induced by the Pt(2)Si NWs was observed with a small density of state using the angle-resolved photoemission spectra.

We investigate the quantum-well states (QWSs) of Ag on an $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ni}$ alloy film grown on a W(110) substrate, using spin- and angle-resolved photoemission spectroscopy (SPARPES). As the Ni content is increased, the $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ni}$ alloy undergoes a transition from a bcc (110) structure to a fcc (111) structure at a Ni concentration of 30%. In the bcc (110) region, we found that as the Ni concentration was increased, the binding energy shifted linearly toward higher binding energy in the QWSs of a thin Ag film, with a maximum shift of $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for a Ni concentration of 30%. Our SPARPES data and phase accumulation model calculation indicate that this shift is due to electron doping resulting from inserting Ni, which has two more electrons than Fe. In the fcc (111) region, by contrast, the binding energy shift in the QWSs is barely noticeable, indicating that the potential shift caused by electron doping is insufficiently large in this region. Moreover, as the Ni concentration is increased, a decrease in the polarization of QWSs is observed, which can be attributed to the reduced exchange splitting energy.

International audience; The point-contact spectroscopy is used to address the evolution of two superconducting energy gaps in the Al- and C-doped magnesium diboride polycrystals and single crystals with Tc's from 39 to 22 K prepared by different techniques. The obtained evolution of two gaps does not show any anomalous behavior but can be consistently described by the combination of the (prevailing) band filling effect and a (minor) increased interband scattering as proposed by Kortus et al. [Kortus et al., Phys. Rev. Lett. 94 (2005) 027002]. The approaching of two gaps is stronger in the Al-doped systems but interband scattering is still not large enough to merge two gaps. The full merging can expected only for higher dopings with Tc's below 10-15 K. In-magnetic-field measurements are used to analyze the intraband scatterings introduced by these two substitutions. It is shown that the carbon doping introduces significant disorder mainly by decreasing the diffusion coefficient in the p band while the Al substitution leaves the samples in the clean limit.

We demonstrate direct evidence of possible surface superconductivity on small, well-shaped ${\mathrm{MgB}}_{2}$ single crystals. Transport measurements in the range $Hl{1.6H}_{c2}^{c},$ where ${H}_{c2}^{c}$ is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular-dependent resistivity. Studies of the alignment of $\mathbf{H}$ with selected crystal surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.

We measure the resistivity of platinum-silicide nanowires (Pt2Si NWs) epitaxially formed on a Si(100) surface using double-scanning-probe tunneling microscope. Despite the large Schottky barrier height reported on a macroscopic Pt2Si∕n-Si interface, leakage current through the substrate is observed in the resistance measurement, and is quantitatively estimated to be separated from the current through the nanowire. The measured resistivity of Pt2Si NWs is about half the reported resistivity of thick Pt2Si films, which could be due to additional conduction paths through surface or interface states on NWs.

We investigated the electronic and structural properties of graphene layers grown on a 6H-SiC (Si-terminated) substrate by using core level photoemission spectroscopy (CLPES), low energy electron diffraction (LEED), and near edge x-ray absorption fine structure (NEXAFS). The angle between the plane of the graphene sheet and the SiC substrate was measured by monitoring the variation of the π* transition in the NEXAFS spectrum with the thickness of the graphene layers. As the thickness of the graphene layers increased, the angle gradually decreased.