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Highlights • Hydrogen permeation in a PdAg alloy is traced in situ by UHV and ambient XPS. • Spectral variations of the surface Ag atom are observed at the adsorption process. • Pd atoms were found to be reactive sites during hydrogen absorption. • The Pd segregation likely promotes the hydrogen permeation. Abstract The hydrogen permeation process is crucial for hydrogen purification through a metal alloy. At the initial stage, it is connected with the dissociation and adsorption of hydrogen on the surface; subsequently, the process involves hydrogen absorption in the bulk. On the PdAg 23 alloy, we investigated the mechanisms of adsorption and absorption by in-situ ultrahigh vacuum and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements, respectively. During the adsorption under a H 2 pressure of 5 × 10−8 Torr at 300–620 K, the surface Ag atoms act as adsorption sites for the hydrogen atoms. The AP-XPS results show that hydrogen absorption is significantly enhanced above 473 K under H 2 exposure at 1.5 Torr, which is likely correlated to the α - β hydride phase transition occurring around 473 K. Hydrogen preferentially bonds with the Pd atoms rather than the Ag atoms in the case of hydrogen absorption into the PdAg 23 alloy. The atomic fractions of Pd on the surface were enhanced after hydrogen absorption, and hydrogen adsorption at a hydrogen pressure of 5 × 10−8 Torr at 620 K. This surface segregation of Pd atoms provides more reactive sites for hydrogen absorption, which may promote the hydrogen permeability of a PdAg 23 alloy. [ABSTRACT FROM AUTHOR]

Growths of novel two-dimensional materials have recently attracted interests to develop chemistry and physics at surfaces. By the boron deposition on Cu(110), we discovered a 1D anisotropic ordered phase, 3 × 1, as a pattern of electron diffraction. The electronic analysis by photoelectron spectroscopy unveiled that the surface superstructure is a layer of the Cu boride with a component of the negatively charged boron atoms. This surface boron atoms likely form the chain structure that is isoelectronic to carbon polymers, such as bumulene that was recently reported on Cu(111). Considering the two-fold rotation symmetry of Cu(110) substrate, the novel surface phase likely becomes an ideal system to examine 1D boron materials. • A 3 × 1 ordered phase was discovered on the boron-deposited Cu(110) surface. • From the XPS measurement, 3 × 1-B/Cu(110) was found to be a Cu boride compound. • It holds similarity with 73 × 39 -B/Cu(111) that has unique 1D boron arrangement. • The new surface phase likely becomes an ideal system to examine 1D boron materials. [ABSTRACT FROM AUTHOR]

Time-resolved soft X-ray photoelectron spectroscopy is utilized to determine an energy level alignment and the photoexcited carrier dynamics at a C 60 /TiO 2 (110) interface. The interface electronic structure is characterized by a type II junction, which favors an injection of photoexcited electrons from C 60 to TiO 2 . Ultraviolet (UV) laser pulse irradiation induces transient shifts of both C 1s and Ti 2p core levels towards the higher binding energies. These energy shifts are caused by a laser-induced charge transfer between the C 60 layer and the TiO 2 (110) surface. Upon UV absorption, valence electrons of C 60 are promoted to unoccupied levels, followed by a resonant transfer to TiO 2 , leaving C 60 in a cationized state. On the TiO 2 (110) side, the electrons are injected into the conduction band to raise the carrier density so that downward bending of the TiO 2 band is induced. The UV-excited states of C 60 and TiO 2 have sufficiently longer lifetime than the lifetime of the electron–hole pairs in solid C 60 . The C 60 /TiO 2 (110) interface is, thus, proved to be efficient for separating the electron–hole pairs generated within the C 60 layer. [ABSTRACT FROM AUTHOR]

The reaction of CO on the vicinal Cu(997) surface at 340 K under CO gas pressure of 0.8 mbar was investigated by ambient pressure X-ray photoelectron spectroscopy. A main reaction product on the surface was identified as carbonate (CO), based on estimation of the composition ratio of oxygen to carbon. CO was produced on the surface through the reaction of CO with oxygen formed from CO dissociation. The amount of adsorbed CO was increased and saturated as time elapsed. After saturation of adsorbed CO, atomic oxygen appeared on the surface, indicating that CO dissociation into CO and O continued to take place. The present study shows the importance of CO intermediate in the CO chemistry on stepped Cu surfaces. [ABSTRACT FROM AUTHOR]

[Display omitted] • New insights into the interaction of MoS 2 surfaces and hydrogen gas. • The AP-XPS spectra for Pd/MoS 2 under H 2 gas showed an upward energy shift. • The dissociation of H 2 at Pd sites, and the hydrogen spillover to the MoS 2 surface. • Pd-deposition can activate the MoS 2 basal plane for molecular hydrogen. We investigated the effects of gaseous hydrogen exposure on the bare MoS 2 and Pd-deposited MoS 2 basal surfaces using ambient-pressure X-ray photoelectron spectroscopy. In the Mo 3d core-level, S 2p core-level, and valence-band photoelectron spectra of a bare MoS 2 surface, little change was observed in the energy shift before and after exposure to hydrogen gas. Upon hydrogen gas exposure on the Pd-deposited MoS 2 surface, each peak in the photoelectron spectra (Mo 3d, S 2p, and valence-band) shifted to a lower binding energy with 0.1 eV. When hydrogen gas was evacuated, the peak energy remained lower compared with that before hydrogen gas exposure. The Pd 3d XPS spectra changed upon hydrogen gas exposure, which can be interpreted as the adsorption of dissociated hydrogen atoms on the Pd sites. These results indicate that the dissociation of molecular hydrogen and the adsorption of atomic hydrogen occur on the Pd-deposited sites on MoS 2 , and thereafter hydrogen atoms spillover onto the MoS 2 surface. This study shows that the activation site for the dissociation of molecular hydrogen is created on an inert MoS 2 basal surface by Pd deposition. In addition, the electronic states of the MoS 2 substrate have been modulated by hydrogen atoms spilled over onto the MoS 2 surface. [ABSTRACT FROM AUTHOR]

The present study gives experimental evidence of two-dimensional electronic states localized in subsurface layers of a Ge(1 1 1) substrate, in which a monolayer of Pb adsorbed on a Ge(1 1 1) surface is used as a template. We observed three pairs of the subsurface states by angle-resolved photoelectron spectroscopy, which are closely related to bulk heavy-hole, light-hole and spin–orbit split-off bands of Ge(1 1 1). The heavy-hole- and light-hole-derived bands show the Rashba-type band crossing at the Γ ¯ point. A density functional theory calculation suggests that the branches of these bands exhibit the Rashba-type spin splitting. On the other hand, we observed peculiar spin polarization for the subsurface states attributed to the bulk spin–orbit split-off band by spin- and angle-resolved photoelectron spectroscopy, where spin polarization of each branch is inverted with respect to Γ ¯ and the degeneracy, expected for a normal Rashba spin-split surface state is lifted at Γ ¯ . [ABSTRACT FROM AUTHOR]

[Display omitted] • Diffusivity of hydrogen atoms from surface to subsurface was the rate-limiting process during hydrogen storage. • Weaken Pd-H bond caused by surface disordering enhanced the hydrogen diffusion in the small-sized NPs. • Active sites of hydrogen absorption on the Pd cube-shaped NPs were investigated by the combination of experimental and theoretical methods. • New insights into the behaviors of hydrogen interacting with Pd cube-shaped NPs were provided. The hydrogen absorption and diffusion processes in cube-shaped palladium (Pd) nanoparticles (NPs) were studied by the combination of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory (DFT) calculations. A size dependence of the subsurface hydrogen absorption was observed. More hydrogen atoms were absorbed in the subsurface of the smaller-sized Pd NPs owing to the enhancement of the diffusivity of H atoms from the surface into the subsurface rather than the adsorption or absorption rates at the initial stages. This results from the weakened Pd-H bond caused by surface disordering of Pd NPs with the reduction of the size of the particles. Furthermore, we discuss the H absorption sites in the bulk by comparing the relative Pd 3 d core-level binding energy shifts of the Pd atoms obtained from the AP-XPS results and the theoretical calculations. The octahedral (O) sites are shown to be more favorable than the tetrahedral (T) sites for hydrogen occupation by comparing the experimental results and theoretical calculations. Finally, we proposed an interaction model between hydrogen and the Pd NPs during H 2 absorption and diffusion to provide new insights into the hydrogen absorption process. [ABSTRACT FROM AUTHOR]

A new technical method is developed for soft X-ray spectroscopy of near-edge x-ray absorption fine structure (NEXAFS). The measurement is performed with continuously rotating linearly polarized light over 2 π , generated by a segmented undulator. A demonstration of the rotational NEXAFS experiment was successfully made with a 2D film, showing detailed polarization-dependence in intensity of the molecular orbitals. The present approach provides varieties of technical opportunities that are compatible with the state-of-the-art experiments in nano-space and under the o p e r a n d o condition. • We developed a new method for X-ray absorption spectroscopy with a novel undulator. • The segmented undulator generates continuously rotating linearly polarized light. • The approach matches with advanced X-ray experiments, such as operando measurements. [ABSTRACT FROM AUTHOR]

Theoretically predicted materials are often synthesized in low yields, and unexpected relationships are often encountered between the target materials and byproducts. Recently, two-dimensional boron materials proposed on the basis of model simulations and first principles calculations and possessing abundant atomic structures have attracted considerable interest. Borophane or the hydrogen boride (HB) sheet has been predicted to be the Dirac nodal semimetal when it has a boron network of nonsymmorphic symmetry. Upgrading the standard method, we fabricated freestanding HB sheets possessing either an apparent Fermi edge, reduced spectral weight, or a Fermi-level energy gap, as confirmed by using microbeam photoemission spectroscopy. The gapless electronic structures were correlated with terminal B-H bonds at the sheet edges, indicating the electronic modification of the porous structure as directly microscopically observed. The gapped or insulating sheet was fabricated via oxidation. This research provides methods for regulating the structural morphology and electronic states of HB sheets during synthesis.

An unexplored material of copper boride has been realized recently in two-dimensional form at a (111) surface of the fcc copper crystal. Here, one-dimensional (1-D) boron growth was observed on the Cu(110) surface, as probed by atomically resolved scanning probe microscopy. The 1-D copper boride was composed of quasi-periodic atomic chains periodically aligned parallel to each other, as confirmed by Fourier transform analysis. The 1-D growth unexpectedly proceeded across surface steps in a self-assembled manner and extended over several 100 nm. The long-range formation of a 1-D quasi-periodic structure on a surface has been theoretically modeled as a 1-D quasi-crystal and the predicted conditions matched the structural parameters obtained by the experimental work here. The quasi-periodic 1-D copper boride system enabled a way to examine 1-D quasi-crystallinity on an actual material.

Sulfur vacancy on an MoS 2 basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS 2 basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Strong spin-charge interactions in several ferromagnets are expected to lead to subpicosecond (sub-ps) magnetization of the magnetic materials through control of the carrier characteristics via electrical means, which is essential for ultrafast spin-based electronic devices. Thus far, ultrafast control of magnetization has been realized by optically pumping a large number of carriers into the d or f orbitals of a ferromagnet; however, it is extremely challenging to implement by electrical gating. This work demonstrates a new method for sub-ps magnetization manipulation called wavefunction engineering, in which only the spatial distribution (wavefunction) of s (or p) electrons is controlled and no change is required in the total carrier density. Using a ferromagnetic semiconductor (FMS) (In,Fe)As quantum well (QW), instant enhancement, as fast as 600 fs, of the magnetization is observed upon irradiating a femtosecond (fs) laser pulse. Theoretical analysis shows that the instant enhancement of the magnetization is induced when the 2D electron wavefunctions (WFs) in the FMS QW are rapidly moved by a photo-Dember electric field formed by an asymmetric distribution of the photocarriers. Because this WF engineering method can be equivalently implemented by applying a gate electric field, these results open a new way to realize ultrafast magnetic storage and spin-based information processing in present electronic systems., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Solid-state electrolytes overcome many challenges of present-day lithium ion batteries, such as safety hazards and dendrite formation 1,2 . However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificity. Here we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet-second-harmonic-generation spectroscopy, we obtained a direct spectral signature of surface lithium ions, showing a distinct blueshift relative to bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1 s state to hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies to develop these electrochemical devices via interfacial engineering of lithium ions., (© 2023. The Author(s).)

Two-dimensional hydrogen boride (HB) sheets prepared via the ion-exchange reaction from magnesium diboride (MgB 2 ) are known to possess several intriguing properties for a wide range of applications; however, previous reports have shown that the sheets prepared using this method contain small amounts of reactive components, making them unsuitable for certain applications. Therefore, developing a method for preparing HB sheets that exhibit long-term stability and do not contain reactive species is essential. In this study, we developed an effective treatment method for achieving long-term stabilization of HB sheets. We found that by pre-treating the HB sheets with water and then filtering the dried product from an acetonitrile dispersion, we could achieve excellent long-term stability over nine months. This stability was maintained even outside of a glovebox, with no H 2 released by the decomposition and/or reaction. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) absorption spectroscopy measurements revealed that the sample exhibited pure HB characteristics with negatively charged boron and B-H-B and terminal B-H bonds, even after nine months of storage. Furthermore, based on thermal desorption spectroscopy (TDS) measurements, the presence of reactive species in the as-prepared HB sheets is attributed to fluctuating B-H bonds with relatively weak binding energies that can be removed using the method developed in this study.

High oxygen permeability of mixed conductive La 0.65 Ca 0.35 FeO 3-δ (LCF) is applicable to pure oxygen gas generators and cathodes for solid oxide fuel cells, etc.; however, lower surface exchange reactions at temperatures below 800 °C reduce permeability. To understand the microscopic surface reaction mechanism, operando soft X-ray photoelectron spectroscopy of an LCF film surface was conducted during the evolution and incorporation of oxygen. LCF film was prepared on yttria-stabilized zirconia and a current was applied throughout the film at ∼600 °C. From operando X-ray photoelectron spectra, surface oxide species involved in the surface exchange reaction obviously appeared on the film during the evolution of oxygen from the surface. The number of surface oxide species abruptly decreased during incorporation of oxygen. By applying the current from a negative to positive value, the numbers of surface oxide species and ligand holes near Fe 3+ ions on the surface both significantly increased. The results infer that ligand holes in the Fe 3d-O 2p hybrid orbitals correspond to active reaction sites at which surface oxide species change to oxygen molecules. Increasing the number of active reaction sites is key to improving oxygen evolution of mixed conductive oxides.

A soft X-ray ptychography system using a Wolter mirror for the illumination optics has been developed. By taking advantage of the achromaticity of the optics, the system is capable of seamlessly imaging at half-period resolution of 50 nm with a broad photon-energy range from 250 eV to 2 keV while maintaining the focal position. Imaging a mammalian cell at various wavelengths was demonstrated, and high-resolution visualization of organelle was achieved. Stereo imaging was also performed with a long working distance of 20 mm. In combination with in-situ/operando and tomographic measurements, this system will be a powerful tool for observing biological and material targets with complex features.

Hematite (α-Fe 2 O 3 ) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature.

Second harmonic generation (SHG) spectroscopy ubiquitously enables the investigation of surface chemistry, interfacial chemistry, as well as symmetry properties in solids. Polarization-resolved SHG spectroscopy in the visible to infrared regime is regularly used to investigate electronic and magnetic order through their angular anisotropies within the crystal structure. However, the increasing complexity of novel materials and emerging phenomena hampers the interpretation of experiments solely based on the investigation of hybridized valence states. Here, polarization-resolved SHG in the extreme ultraviolet (XUV-SHG) is demonstrated for the first time, enabling element-resolved angular anisotropy investigations. In noncentrosymmetric LiNbO_{3}, elemental contributions by lithium and niobium are clearly distinguished by energy dependent XUV-SHG measurements. This element-resolved and symmetry-sensitive experiment suggests that the displacement of Li ions in LiNbO_{3}, which is known to lead to ferroelectricity, is accompanied by distortions to the Nb ion environment that breaks the inversion symmetry of the NbO_{6} octahedron as well. Our simulations show that the measured second harmonic spectrum is consistent with Li ion displacements from the centrosymmetric position while the Nb─O bonds are elongated and contracted by displacements of the O atoms. In addition, the polarization-resolved measurement of XUV-SHG shows excellent agreement with numerical predictions based on dipole-induced SHG commonly used in the optical wavelengths. Our result constitutes the first verification of the dipole-based SHG model in the XUV regime. The findings of this work pave the way for future angle and time-resolved XUV-SHG studies with elemental specificity in condensed matter systems.

Copper tungstate (CuWO 4 ) is an important semiconductor with a sophisticated and debatable electronic structure that has a direct impact on its chemistry. Using the PAL-XFEL source, we study the electronic dynamics of photoexcited CuWO 4 . The Cu L 3 X-ray absorption spectrum shifts to lower energy upon photoexcitation, which implies that the photoexcitation process from the oxygen valence band to the tungsten conduction band effectively increases the charge density on the Cu atoms. The decay time of this spectral change is 400 fs indicating that the increased charge density exists only for a very short time and relaxes electronically. The initial increased charge density gives rise to a structural change on a time scale longer than 200 ps., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Hematite, α-Fe 2 O 3 , is an important semiconductor for photoelectrochemical water splitting. Its low charge carrier mobility and the presence of midgap states provide favourable conditions for electron-hole recombination, hence affecting the semiconductor's photoelectrochemical efficiency. The nature of the excited state and charge carrier transport in hematite is strongly debated. In order to further understand the fundamental properties of the hematite photoexcited state, we conducted femtosecond 2p (L 3 ) X-ray absorption (XAS) and 2p3d resonant inelastic scattering (RIXS) measurements on hematite thin-films at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). The observed spectral changes and kinetic processes are in agreement with previous 3p XAS reports. The potential additional information that could be acquired from 2p3d RIXS experiments is also discussed.

Hydrogen boride nanosheets (HB sheets) are facilely synthesized via ion-exchange treatment on magnesium diboride (MgB 2 ) in an acetonitrile solution. Optical absorption and fluorescence spectra of HB sheets indicate that their bandgap energy is 2.8 eV. According to first-principles calculations, optical absorption seen at 2.8 eV is assigned to the electron transition between the σ-bonding states of B and H orbitals. In addition, density functional theory (DFT) calculations suggest the other allowed transition from the σ-bonding state of B and H orbitals to the antibonding state with the gap of 3.8 eV. Significant gaseous H 2 release is found to occur only under photoirradiation, which causes the electron transition from the σ-bonding state to the antibonding state even under mild ambient conditions. The amount of H 2 released from the irradiated HB sheets is estimated to be 8 wt%, indicating that the sheets have a high H 2 -storage capacity compared with previously reported metal H 2 -storage materials.

Ultrafast carrier dynamics in a graphene system are very important in terms of optoelectronic devices. Recently, a twisted bilayer graphene has been discovered that possesses interesting electronic properties owing to strong modifications in interlayer couplings. Thus, a better understanding of ultrafast carrier dynamics in a twisted bilayer graphene is highly desired. Here, we reveal the unbalanced electron distributions in a quasicrystalline 30° twisted bilayer graphene (QCTBG), using time- and angle-resolved photoemission spectroscopy on the femtosecond time scale. We distinguish time-dependent electronic behavior between the upper- and lower-layer Dirac cones and gain insight into the dynamical properties of replica bands, which show characteristic signatures due to Umklapp scatterings. The experimental results are reproduced by solving a set of rate equations among the graphene layers and substrate. We find that the substrate buffer layer plays a key role in initial carrier injections to the upper and lower layers. Our results demonstrate that QCTBG can be a promising element for future devices.

The ceria-based catalyst incorporated with Cr and a trace amount of Rh (Cr 0.19 Rh 0.06 CeO z ) was prepared and the reversible redox performances and oxidation catalysis of CO and alcohol derivatives with O 2 at low temperatures (<373 K) were investigated. In situ X-ray absorption fine structure (XAFS), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)-EDS/EELS and temperature-programmed reduction/oxidation (TPR/TPO) revealed the structures and redox mechanisms of three metals in Cr 0.19 Rh 0.06 CeO z : dispersed Rh 3+δ species (<1 nm) and Cr 6-γ O 3-x nanoparticles (∼1 nm) supported on CeO 2 in Cr 0.19 Rh 0.06 CeO z were transformed to Rh nanoclusters, Cr(OH) 3 species and CeO 2-x with two Ce 3+ -oxide layers at the surface in a concerted activation manner of the three metal species with H 2 .

Atomic scale engineering of two-dimensional materials could create devices with rich physical and chemical properties. External periodic potentials can enable the manipulation of the electronic band structures of materials. A prototypical system is (3×3)-silicene/Ag(111), which has substrate-induced periodic modulations. Recent angle-resolved photoemission spectroscopy measurements revealed six Dirac cone pairs at the Brillouin zone boundary of Ag(111), but their origin remains unclear [Proc. Natl. Acad. Sci. USA 113, 14656 (2016)]. We used linear dichroism angle-resolved photoemission spectroscopy, the tight-binding model, and first-principles calculations to reveal that these Dirac cones mainly derive from the original cones at the K (K^{'}) points of free-standing silicene. The Dirac cones of free-standing silicene are split by external periodic potentials that originate from the substrate-overlayer interaction. Our results not only confirm the origin of the Dirac cones in the (3×3)-silicene/Ag(111) system, but also provide a powerful route to manipulate the electronic structures of two-dimensional materials.

The functionalization of graphene is important in practical applications of graphene, such as in catalysts. However, the experimental study of the interactions of adsorbed molecules with functionalized graphene is difficult under ambient conditions at which catalysts are operated. Here, the adsorption of CO2 on an oxygen-functionalized epitaxial graphene surface was studied under near-ambient conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). The oxygen-functionalization of graphene is achieved in situ by the photo-induced dissociation of CO2 with X-rays on graphene in a CO2 gas atmosphere. The oxygen species on the graphene surface is identified as the epoxy group by XPS binding energies and thermal stability. Under near-ambient conditions of 1.6 mbar CO2 gas pressure and 175 K sample temperature, CO2 molecules are not adsorbed on the pristine graphene, but are adsorbed on the oxygen-functionalized graphene surface. The increase in the adsorption energy of CO2 on the oxygen-functionalized graphene surface is supported by first-principles calculations with the van der Waals density functional (vdW-DF) method. The adsorption of CO2 on the oxygen-functionalized graphene surface is enhanced by both the electrostatic interactions between the CO2 and the epoxy group and the vdW interactions between the CO2 and graphene. The detailed understanding of the interaction between CO2 and the oxygen-functionalized graphene surface obtained in this study may assist in developing guidelines for designing novel graphene-based catalysts.

The electronic states of Au-induced atomic nanowires on Ge(0 0 1) (Au/Ge(0 0 1) NWs) have been studied by angle-resolved photoelectron spectroscopy with linearly polarized light. We have found three electron pockets around the [Formula: see text] line, where the Fermi surfaces are closed in a surface Brillouin zone (SBZ). The results indicate 2D Fermi surfaces of Au/Ge(0 0 1) NWs whereas the atomic structure is 1D. On the basis of the polarization-dependent spectra, the relation between SBZ and the direction of the atomic NW, and the symmetry of the surface state are clarified. These are very useful for further studies on the atomic structure of NWs.

Hydrogen-bonding heterogeneous bilayers on substrates have been studied as a base for new functions of molecular adlayers by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations. Here, we report the formation of the catechol-fused bis(methylthio)tetrathiafulvalene (H 2 Cat-BMT-TTF) adlayer hydrogen bonding with an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on Au(111). The heterogeneous bilayer is realized by sequential two-step immersions in solutions for the individual Im-SAM and H 2 Cat-BMT-TTF adlayer formations. In the measurements by AFM, a grained H 2 Cat-BMT-TTF adlayer on Im-SAM is revealed. The coverage and the chemical states of H 2 Cat-BMT-TTF on Im-SAM are specified by XPS. On the vibrational spectrum measured by IRAS, the strong hydrogen bonds between H 2 Cat-BMT-TTF and Im-SAM are characterized by the remarkably red-shifted OH stretching mode at 3140 cm -1 , which is much lower than that for hydrogen-bonding water (typically ∼3300 cm -1 ). The OH stretching mode frequency and the adsorption strength for the H 2 Cat-BMT-TTF molecule hydrogen bonding with imidazole groups are quantitatively examined on the basis of DFT calculations.

Weyl semimetals (WSMs) are classified into two types, type I and II, according to the topology of the Weyl point, where the electron and hole pockets touch each other. Tungsten ditelluride (WTe 2 ) has garnered a great deal of attention as a strong candidate to be a type-II WSM. However, the Weyl points for WTe 2 are located above the Fermi level, which has prevented us from identifying the locations and the connection to the Fermi arc surface states by using angle-resolved photoemission spectroscopy. Here, we present experimental proof that WTe 2 is a type-II WSM. We measured energy-dependent quasiparticle interference patterns with a cryogenic scanning tunneling microscope, revealing the position of the Weyl point and its connection with the Fermi arc surface states, in agreement with prior theoretical predictions. Our results provide an answer to this crucial question and stimulate further exploration of the characteristics of WSMs.

Time-dependent responses of materials to an ultrashort optical pulse carry valuable information about the electronic and lattice dynamics; this research area has been widely studied on novel two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs) and topological insulators (TIs). We report herein a time-resolved and angle-resolved photoemission spectroscopy (TRARPES) study of WSe 2 , a layered semiconductor of interest for valley electronics. The results for below-gap optical pumping reveal energy-gain and -loss Floquet replica valence bands that appear instantaneously in concert with the pump pulse. Energy shift, broadening, and complex intensity variation and oscillation at twice the phonon frequency for the valence bands are observed at time scales ranging from the femtosecond to the picosecond and beyond. The underlying physics is rich, including ponderomotive interaction, dressing of the electronic states, creation of coherent phonon pairs, and diffusion of charge carriers - effects operating at vastly different time domains.

Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn 4 , ZrSiS, TlTaSe 2 and PbTaSe 2 . However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu 2 Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu 2 Si form two concentric loops centred around the Γ point and are protected by mirror reflection symmetry. Our results establish Cu 2 Si as a platform to study the novel physical properties in two-dimensional Dirac materials and provide opportunities to realize high-speed low-dissipation devices.

Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β&#95;{12} sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β&#95;{12} sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices.

We report a case of a 71-year-old male with rectal cancer accompanied by liver metastases. Abdominal CT scan revealed a hepatic tumor (S2, 3) about 4 cm in diameter. We performed a Mile's operation and planned to resect the liver metastases after chemotherapy of modified FOLFOX6(mFOLFOX6)regimen: l-leucovorin (200 mg/m2) and oxaliplatin (85 mg/m/2) were given as a 2-hour infusion followed by bolus injection of 5-FU 400 mg/m2 and a 46-hour infusion 5-FU 2,400 mg/m2 every 2 weeks. An abdominal CT scan 6 months later demonstrated regression of the liver metastases. Hepatectomy was performed after chemotherapy, and no viable tumor cells were seen.