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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.

The adsorption configurations of methionine molecules on the Ge(100) surface have been studied by using DFT calculations, core-level photoemission spectroscopy (CLPES), and low-energy electron diffraction (LEED) to scrutinize the adsorption structure as a function of coverage. At first, we obtained two important and stable structures. One is the most stable structure between these structures described as an "O-H dissociated-N dative-S dative-bonded structure" and the other is a less stable adsorption structure of these indicating an "O-H dissociated-S dative-bonded structure" by using DFT calculations. We also performed CLPES to clarify our DFT calculation results. Through the spectral analysis of the S 2p, C 1s, N 1s, and O 1s core-level spectra, we acquired the reasonable results that also revealed quite different bonding configurations depending on the methionine coverage. At low coverage (ca. 0.30 ML), a single type of sulfur and charged nitrogen peaks, which indicate an "O-H dissociated-N dative-S dative-bonded structure", were observed. On the other hand, two types of sulfur peaks with thiol formation and two nitrogen peaks with neutralized and charged characteristics were monitored at a higher coverage (0.60 ML and above), which can be described as an "O-H dissociated-S dative-bonded structure". Hence, we can clearly demonstrate that our results obtained from CLPES spectra and DFT calculations are matched well with each other. Moreover, we additionally confirmed that the relative population of the two types of thiols and amines being included in methionine in between half monolayer induces a surface reorientation in the ordering from 2×1 to 1×1 employing LEED. This interesting variation of the methionine adsorbed on the Ge(100) surface by coverage dependence will be precisely discussed by using DFT calculations, CLPES, and LEED.

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.

The variations with coverage and annealing temperature in the adsorption structure of alanine on Ge(100) have been investigated using high-resolution core-level photoemission spectroscopy (HRCLPES). The C 1s, N 1s, and O 1s core-level spectra at a low initial coverage show that both the carboxyl and amine groups of the alanine molecules participate in bonding with the Ge(100) surface in an "intrarow O-H dissociated and N dative bonded structure". However, at higher coverage we found that in addition to this structure an "O-H dissociation structure" is present. Moreover, we systematically monitored the variation of the bonding features of alanine adsorbed on Ge(100) with annealing temperature and thus were able to track the desorption processes. By analyzing the C 1s, N 1s, and O 1s spectra at 420 K, we conclude that the principal adsorption structure at this temperature is the "O-H dissociation structure" because of the disconnection of Ge-N dative bonding. At higher temperatures, the "O-H dissociation structure" is converted into various fragments such as Ge oxide (or Ge-CO), Ge nitride (Ge cyanide), and Ge carbide.

The adsorption structure of glycine on Ge(100) was investigated using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES). We found a major adsorption feature of glycine on Ge(100) in the STM images. This feature appeared as a bright protrusion between two dimer rows with a dark adjacent dimer. The position of the bright protrusion located in the middle of the two dimer rows indicates a multibonding adsorption structure. The results of the theoretical calculations confirm that the adsorption structure of glycine on Ge(100) (between two possible multibonding adsorption structures) is an "intrarow O-H dissociated and N dative bonded structure". In the HRCLPES experiments, we found an N 1s peak (at 399.5 eV) and two O 1s peaks (at 531.1 and 532.0 eV), which represent strong evidence that the adsorption configuration of glycine on Ge(100) is composed of both O-H dissociation and N dative bonding. All our STM, DFT, and HRCLPES results suggest that the adsorption structure of glycine molecules on Ge(100) is an "intrarow O-H dissociated and N dative bonded structure".

The electronic structures of ${\text{SrMn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{3}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ have been investigated by using photoemission spectroscopy (PES), soft x-ray absorption spectroscopy, and soft x-ray magnetic circular dichroism (XMCD). Both Mn and Fe ions are found to be nearly tetravalent for the whole range of $x$ in ${\text{SrMn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{3}$. Valence-band PES measurements show the broader $\text{Fe}\text{ }3d$ $({t}_{2g}^{3}{e}_{g}^{1})$ bands than the $\text{Mn}\text{ }3d$ $({t}_{2g}^{3})$ bands and the finite metallic intensity near ${E}_{F}$ in the $\text{Fe}\text{ }3d$ PES of ${\text{SrFeO}}_{3}$ in agreement with the metallic ground state of ${\text{SrFeO}}_{3}$. The $\text{Fe}\text{ }2p$ XMCD spectra exhibit the enhanced XMCD effect for $0.6\ensuremath{\le}x\ensuremath{\le}0.8$ in ${\text{SrMn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{3}$, which is consistent with the spin-glass behavior in the intermediate substitution, while the $\text{Mn}\text{ }2p$ states exhibit the negligible XMCD effect.

The valence and spin states of $\mathrm{Mn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ spinel oxide have been investigated by employing soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The measured $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}2p$ and $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}2p$ XAS spectra indicate that Mn and Fe ions are nearly divalent $({\mathrm{Mn}}^{2+})$ and trivalent $({\mathrm{Fe}}^{3+})$, respectively. Our XAS and XMCD spectra for $\mathrm{Mn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ do not show clear evidence of mixed-valent states but provide evidence for the inversion of both Mn and Fe ions, with ${T}_{d}∕{O}_{h}\ensuremath{\sim}0.8∕0.2$ for Mn ions and ${T}_{d}∕{O}_{h}\ensuremath{\sim}0.1∕0.9$ for Fe ions, respectively. Based on our data, $\mathrm{Mn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ can be described either by the single-valence states of ${({\mathrm{Mn}}_{0.8}^{2+}{\mathrm{Fe}}_{0.2}^{3+})}_{A}{[{\mathrm{Fe}}_{1.8}^{3+}{\mathrm{Mn}}_{0.2}^{2+}]}_{B}{\mathrm{O}}_{4}$ or by the mixed-valence states of ${({\mathrm{Mn}}_{0.8}^{2+}{\mathrm{Fe}}_{0.2}^{3+})}_{A}{[{\mathrm{Fe}}_{1.6}^{3+}{\mathrm{Fe}}_{0.2}^{2+}{\mathrm{Mn}}_{0.2}^{3+}]}_{B}{\mathrm{O}}_{4}$.

The adsorption geometry of thiophene on Ge(100) have been studied by high‐resolution core‐level photoemission spectroscopy (HRPES) using synchrotron radiation and scanning tunneling microscopy (STM). From the analysis of the Ge 3d, S 2p, and C 1s core‐level photoemission spectra, we found three different adsorption geometries, which were assigned to a dative bonding feature, a [4+2] cycloaddition reaction product, and a desulfurization reaction product. Furthermore, we investigated that the ratio of the components induced by three adsorption geometries changed depending on the molecular coverage and the annealing temperature. At low coverage, the kinetically favorable dative bonding features favorably form 1‐D molecular chains. Increasing the molecular coverage, the energetically more stable [4+2] cycloaddition reaction products are additionally created.

We have studied the adsorption and decomposition of thiophene (C4H4S) on Ge(100) using scanning tunneling microscopy (STM), high-resolution core-level photoemission spectroscopy (HRPES), and density functional theory (DFT) calculation. Analysis of S 2p core-level spectra reveals three adsorption geometries, which we assign to a Ge-S dative bonding state, a [4 + 2] cycloaddition bonding state, and a decomposed bonding state (desulfurization reaction product). Furthermore, we found that the number ratio of the three adsorption geometries depended on the molecular coverage and the annealing temperature. At low coverages, the kinetically favorable dative bonding state is initially formed at room temperature. As the molecular coverage increases, thermodynamically stable [4 + 2] cycloaddition reaction products are additionally produced. In addition, we found that as the surface temperature increased, the [4 + 2] cycloaddition reaction product either possibly desorbed as molecular thiophene or decomposed to form a metallocycle-like species (C4H4Ge2) and a sulfide (Ge2S). We systematically elucidate the changes in the bonding states of adsorbed thiophene on Ge(100) according to the thiophene coverage and annealing temperature.

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.

The lower $({H}_{c1})$ and upper $({H}_{c2})$ critical fields of ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{B}}_{2}$ single crystals (for $x=0$, $0.1$, and $\ensuremath{\gtrsim}0.2$) have been deduced from local magnetization and specific heat measurements, respectively. We show that ${H}_{c1}$ and ${H}_{c2}$ are both decreasing with increasing doping content. The corresponding anisotropy parameter ${\ensuremath{\Gamma}}_{{H}_{c2}}(0)={H}_{c2}^{ab}(0)∕{H}_{c2}^{c}(0)$ value also decreases from $\ensuremath{\sim}5$ in pure ${\mathrm{MgB}}_{2}$ samples down to $\ensuremath{\sim}1.5$ for $x\ensuremath{\gtrsim}0.2$ whereas ${\ensuremath{\Gamma}}_{{H}_{c1}}(0)={H}_{c1}^{c}(0)∕{H}_{c1}^{ab}(0)$ remains on the order of 1 in all samples. The small and large gap values have been obtained by fitting the temperature dependence of the zero-field electronic contribution to the specific heat to the two-gap model for the three Al concentrations. Very similar values have also been obtained by point contact spectroscopy measurements. The evolution of those gaps with Al concentration suggests that both band filling and interband scattering effects are present.

The adsorption of thiophene on Ge(100) has been studied using scanning tunneling microscopy (STM), high-resolution core-level photoemission spectroscopy (HRPES), and density functional theory (DFT) calculations. Until now, thiophene is known to react with the Ge(100) dimer through a [4 + 2] cycloaddition reaction at room temperature, similar to the case of thiophene on Si(100). However, we found that thiophene has two adsorption geometries on Ge(100) at room temperature, such as a kinetically favorable Ge−S dative bonding configuration and a thermodynamically stable [4 + 2] cycloaddition adduct. Moreover, our STM results show that under 0.25 ML thiophene molecules preferentially produce one-dimensional molecular chain structures on Ge(100) via the Ge−S dative bonding configuration.

The angular dependence of the upper critical field ${H}_{c2}$ of ${\mathrm{MgB}}_{2}$ single crystals is studied at various temperatures by means of specific-heat and transport measurements in magnetic fields up to $17\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Clear deviations from Ginzburg--Landau behavior are observed at all temperatures and are explained by two-band effects. The angular dependence and temperature dependence of the deviations are in qualitative agreement with theoretical predictions based on band-structure calculations. Quantitative agreement is obtained with an interband coupling slightly stronger than the calculated one, enabling band-structure anisotropies and interband coupling strength to be experimentally estimated. This provides a pathway to the study of disorder and doping effects in ${\mathrm{MgB}}_{2}$.

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.

The superconducting phase diagram of ${\mathrm{MgB}}_{2}$ was determined from magnetization, magnetotransport, and single-crystal specific-heat measurements. A zero-temperature in-plane coherence length of 9.4 nm is determined. The superconducting anisotropy \ensuremath{\gamma} increases from a value around 2 near ${T}_{c}$ to above 4.5 at 22 K. For $H\ensuremath{\parallel}c$ a pronounced peak effect in the critical current occurs at the upper critical field. Evidence for a surface superconducting state is presented for $H\ensuremath{\parallel}c$ that might account for the widespread in reported values of \ensuremath{\gamma}.

The adsorption and decomposition of AlCl3 on Ge(100) was studied using scanning tunneling microscopy (STM) and high-resolution core-level photoemission spectroscopy (HRCLPES). Through the analysis of the STM image and Ge 3d and Cl 2p core-level spectra of AlCl3 on Ge(100), we found that an AlCl3 molecule reacts with two Ge atoms via a cycloaddition reaction, which forms Cl−Ge and AlCl2−Ge without breaking AlCl3. Additionally, by considering valence shell electron pair repulsion (VSEPR) arguments, the effect of molecular structure on the surface chemistry was explained. To our knowledge, the adsorption of Lewis acid molecules on a semiconductor surface has not been studied in detail. These are the first results for the adsorption structures of Lewis acid molecule on Ge(100).

We introduced nitrogen ions to modify the graphene surface and its property changes were investigated. A graphene layer grown on 6H-SiC(0001) was irradiated with 100 eV nitrogen ions. Surface property changes were studied using photoemission spectroscopy (PES), near edge x-ray adsorption spectroscopy (NEXAFS), and atomic force microscopy(AFM). N 1s core level spectra show that three kinds of nitrogen species, nitrogen gas, graphite-like and pyridine-like nitrogen were induced on the nitrogen ion implanted graphene surface.

The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p→3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d3) and that Ni ions are formally divalent (3d8). Mn and Ni 2p→3d RPES shows that the occupied Mn 3d3 (t2g3↑) states are sharp and located around 2 eV below EF, while the occupied Ni 3d8 (t2g3↑t2g3↓eg2↑) states are broader than the Mn 3d states and they extend from EF to ∼5 eV below EF.

The electronic structures of (Fe,Mn)3O4 spinel oxides have been investigated by employing soft-x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). We have determined the valence states as well as the occupation sites of Mn and Fe ions in Fe0.9Mn2.1O4 and MnFe2O4. Fe0.9Mn2.1O4 is found to be close to the inverse spinel (the inversion parameter y≈0.85), while MnFe2O4 is close to the normal spinel (y≈0.2). In Fe0.9Mn2.1O4, Fe ions are mainly trivalent and the majority of Fe3+ ions occupy the octahedral B sites, while Mn ions are mixed-valent with approximately 45% MnA2+ at the tetrahedral A sites and 55% MnB3+ ions at the octahedral B sites. In MnFe2O4, Mn ions are mainly divalent and the majority of Mn2+ ions occupy the tetrahedral A sites, while Fe ions are mainly trivalent and the majority of Fe3+ ions occupy the octahedral B sites.

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.

We found that Ce on the Si(111) system exhibited nonmetallic behavior at a critical coverage of 4.0 ML. We observed a large binding energy shift of 2.5 eV in x-ray photoelectron spectroscopy (XPS), and a band gap of 0.6 eV in scanning tunneling spectroscopy (STS), whereas normal metallic behavior was observed at other coverages. Moreover, a strong downward surface relaxation was observed at this critical coverage with increased surface roughness. We expect that this phase transition at a critical coverage is due to the breakdown of bulk modulus as a result of the release of tensile stress along the in-plane direction.

We investigated the adsorption and decomposition of thiophene (C4H4S) on Ge(100) using high-resolution photoemission spectroscopy. We found that the Ge 3d and C 1s core-level spectra revealed three adsorption geometries, which we assigned to a weakly bound state (i.e., a Ge–S dative bonding state), a [4+2] cycloaddition bonding state, and a decomposed bonding state (a desulfurization reaction product) as functions of the molecular coverage and the annealing temperature. In this study, we systematically elucidated the changes occurring in the bonding states of thiophene species adsorbed on a Ge(100) substrate.

We report the experimental evidence of significant change of the valence band structure during crystallization of Ge2Sb2Te5 (GST). Amorphous GST, prepared by sputter deposition at room temperature (RT), transforms successively into face-centered-cubic (fcc) and a hexagonal-close-packed (hcp) structures at around 150 and 300°C, respectively, during a stepwise temperature increase from RT to 350°C. During temperature increase, ultraviolet photoemission spectra were in vacuo obtained using synchrotron radiation. The measurement of the amorphous and fcc GST shows that the difference between the maximum valence band edge and the Fermi level reduces by 0.35eV during crystallization. For the fcc to hcp phase transformation, no band gap reduction was observed.

We investigated the formation of Pt silicide nanowires on a Si(100) surface using scanning tunnelling microscopy and high-resolution photoemission spectroscopy. Pt silicide nanowires with a tetragonal Pt2Si structure are formed along the step edges of Si(100). Pt-induced c(4 × 2) reconstructions also appear adjacent to the tetragonal Pt2Si nanowires. Formation of the Pt2Si nanowires is attributed to the anisotropic lattice mismatches between the tetragonal Pt2Si structure and Si(100). Scanning tunnelling spectroscopy data show that the nanowires are metallic. The stoichiometry of Pt silicide is confirmed by high-resolution photoemission spectroscopy.

Epitaxial Fe-rich alloy films of formulas Fe1−xNix, Fe1−xCox, and Fe1−xVx were grown on a W(110) substrate with a bcc structure without any structural transition at x

Purpose: An air bubble‐free flood phantom with grid patterns is fabricated to measure extrinsic resolution and linearity of PET scanner. It is designed to implement a 99m‐Tc flood phantom with motorized water pump to reduce the shaking procedure as well as reduce radiation exposure to workers. Method and Materials: The flood phantom is fabricated with circular (50cm diameter) and rectangular shapes (60cm*40cm) to measure the extrinsic resolution of conventional gamma camera. It has a handle in which an air pocket and water pump are placed. The air pocket is made of two chambers with conical valve between them. During the shaking procedure, the air bubbles are sucked into to the air pocket due to gravity effect and water perturbation. Once the air bubbles are trapped in the air pocket. They could not escape from it. After the radioisotopes are injected through a pin hole in the air pocket, water pump is turned on. The shaking procedure starts. In order to estimate the effectiveness of the shaking mechanism, the survey meter with well‐guided collimator is manually rotated on the flood phantom until uniformity of 3% is reached. It take approximately 5 minutes to mix the water with radioisotopes thoroughly. Results: The phantom is used to evaluate the extrinsic resolution and to estimate the uniformity/linearity of gamma camera or SPECTcamera.. The images are analyzed to quantitatively measure the integral and differential uniformity and the non‐linearity of the imaging system. The detailed data will be presented in the meeting. Conclusion: The phantom was very handy and effective to minimize radiation exposure to an operator. The multi‐channel ionization chamber will be replaced manual rotation procedure to design fully automatic monitoring system.