Discovery of bicyclic borane molecule BH.

The discovery of fullerene following the synthesis of graphene marked a paradigm shift in chemistry. Here, we report the discovery of biycycloborane, arising from the synthesis of borophane (hydrogen boride). Uniquely, this synthesis method involves a decomposition mechanism rather than traditional atom-by-atom assembly, marking an unique approach to constructing complex borane structures.

Chemical process of hydrogen and formic acid on a Pd-deposited Cu(111) surface studied by high-resolution X-ray photoelectron spectroscopy and density functional theory calculations.

Formic acid (HCOOH) is one of the essential molecules for CO utilization including methanol synthesis and hydrogen carriers. In this study, we have investigated the chemical processes of hydrogen and HCOOH on a dilute-alloy Pd-Cu(111) surface using high-resolution X-ray photoelectron spectroscopy (HR-XPS) and density functional theory (DFT) calculations. The present Pd-Cu(111) surface was prepared at 500 K, and the observed core-level shifts of Pd 3d indicate that Pd atoms were located at the surface and subsurface sites: 335.

Ultra-broadband detection of coherent infrared pulses by sum-frequency generation spectroscopy in reflection geometry.

We have newly developed, to the best of our knowledge, a detection method for broadband infrared pulses based on sum-frequency generation spectroscopy in reflection geometry, which can avoid a restriction of the detection bandwidth originating from the phase mismatch that is inevitable for the upconversion in transmission geometry. Using a GaAs crystal, we successfully demonstrated the ultra-broadband detection of the infrared pulses generated from a two-color laser-induced air plasma filament in a region from 300 to 3300 cm. With the advantage of ultra-short infrared pulses, the present detection method holds promise for application to time-resolved, ultra-broadband vibrational spectroscopy.

Low-temperature dissociation of CO molecules on vicinal Cu surfaces.

The reaction of carbon dioxide on the vicinal Cu surfaces at low temperatures was investigated by infrared reflection absorption spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy, and quadrupole mass spectrometry. Dissociation of CO molecules into CO on the Cu(997) and Cu(977) surfaces was observed at temperatures between 80 K and 90 K, whereas it did not occur on Cu(111) under a similar condition. CO and physisorbed CO were the main adsorbates during the reaction.

Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection.

We report the first observation of the spin Hall conductivity spectrum in GaAs at room temperature. Our terahertz polarimetry with a precision of several μrads resolves the Faraday rotation of terahertz pulses arising from the inverse spin Hall effect of optically injected spin-polarized electrons. The obtained spin Hall conductivity spectrum exhibits an excellent quantitative agreement with theory, demonstrating a crossover in the dominant origin from impurity scattering in the dc regime to the intrinsic Berry-curvature mechanism in the terahertz regime.

Disentangling the Competing Mechanisms of Light-Induced Anomalous Hall Conductivity in Three-Dimensional Dirac Semimetal.

We experimentally elucidate the origin of the anomalous Hall conductivity in a three-dimensional Dirac semimetal, Cd_{3}As_{2}, driven by circularly polarized light. Using time-resolved terahertz Faraday rotation spectroscopy, we determine the transient Hall conductivity spectrum with special attention to its sign. Our results clearly show the dominance of direct photocurrent generation assisted by the terahertz electric field.

Hydrogen-induced Sulfur Vacancies on the MoS Basal Plane Studied by Ambient Pressure XPS and DFT Calculations.

Sulfur vacancy on an MoS 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 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.

Stimulated Rayleigh Scattering Enhanced by a Longitudinal Plasma Mode in a Periodically Driven Dirac Semimetal Cd_{3}As_{2}.

Using broadband (12-45 THz) multi-terahertz spectroscopy, we show that stimulated Rayleigh scattering dominates the transient optical conductivity of cadmium arsenide, a Dirac semimetal, under an optical driving field at 30 THz. The characteristic dispersive line shape with net optical gain is accounted for by optical transitions between light-induced Floquet subbands, strikingly enhanced by the longitudinal plasma mode. Stimulated Rayleigh scattering with an unprecedentedly large refractive index change may pave the way for slow light generation in conductive solids at room temperature.

Elucidation of the atomic-scale processes of dissociative adsorption and spillover of hydrogen on the single atom alloy catalyst Pd/Cu(111).

Hydrogen spillover is a crucial process in the selective hydrogenation reactions on Pd/Cu single atom alloy catalysts. In this study, we report the atomic-scale perspective of these processes on the single atom alloy catalyst Pd/Cu(111) based on the experimental and theoretical results, including infrared reflection absorption spectroscopy (IRAS), temperature programmed desorption (TPD), high-resolution X-ray photoelectron spectroscopy (HR-XPS), and density functional theory (DFT) calculations for core-level excitation. The hydrogen spillover onto Cu(111) was successfully observed in real time using time-resolved IRAS measurements at 80 K.

Substrate-Selective Intermolecular Interaction and the Molecular Self-Assemblies: 1,3,5-Tris(4-bromophenyl)benzene Molecules on the Ag(111) and Si(111) (√3 × √3)-Ag Surfaces.

We report the formation processes of the self-assembled layer of 1,3,5-tris(4-bromophenyl)benzene (TBB) molecules on the Ag(111) and Si(111) (√3 × √3)-Ag surfaces by STM measurements and density functional theory (DFT) calculations. The self-assembled layers on the surfaces show characteristic structures controlled by the interplay between the intermolecular interaction and the molecule-substrate interaction. Through the cooperative interplay between the molecule-substrate interaction and the intermolecular halogen bond (XB), the periodic arrangement of TBB molecules appears on the Ag(111) surface.

Tracking Ultrafast Change of Multiterahertz Broadband Response Functions in a Photoexcited Dirac Semimetal CdAs Thin Film.

The electromagnetic response of Dirac semimetals in the infrared and terahertz frequency ranges is attracting growing interest for potential applications in optoelectronics and nonlinear optics. The interplay between the free-carrier response and interband transitions in the gapless, linear dispersion relation plays a key role in enabling novel functionalities. Here we investigate ultrafast dynamics in thin films of a photoexcited Dirac semimetal CdAs by probing the broadband response functions as complex quantities in the multiterahertz region (10-45 THz, 40-180 meV, or 7-30 μm), which covers the crossover between the inter- and intraband response.

Role of Intermolecular Interactions in the Catalytic Reaction of Formic Acid on Cu(111).

Formic acid (HCOOH) can be catalytically decomposed into H and CO and is a promising hydrogen storage material. As H production catalysts, Cu surfaces allow selective HCOOH decarboxylation; however, the on-surface HCOOH decomposition reaction pathway remains controversial. In this study, the temperature dependence of the HCOOH/Cu(111) adsorption structures is elucidated by scanning tunneling microscopy and non-contact atomic force microscopy, establishing the adsorbate chemical species using density functional theory.

Formation of BN-covered silicene on ZrB/Si(111) by adsorption of NO and thermal processes.

We have investigated the adsorption and thermal reaction processes of NO with silicene spontaneously formed on the ZrB/Si(111) substrate using synchrotron radiation x-ray photoelectron spectroscopy (XPS) and density-functional theory calculations. NO is dissociatively adsorbed on the silicene surface at 300 K. An atomic nitrogen is bonded to three Si atoms most probably by a substitutional adsorption with a Si atom of silicene (N≡Si).

The roles of step-site and zinc in surface chemistry of formic acid on clean and Zn-modified Cu(111) and Cu(997) surfaces studied by HR-XPS, TPD, and IRAS.

The adsorption, desorption, and decomposition of formic acid (HCOOH) on Cu(111), Cu(997), Zn-Cu(111), and Zn-Cu(997) were systematically studied by high-resolution x-ray photoelectron spectroscopy, temperature programmed desorption, and infrared reflection absorption spectroscopy. On the clean Cu(111) surface, 13% of formic acid molecules adsorbed at 83 K were dissociated to form bidentate formate species by heating at 300 K; however, on the Zn-Cu(111) surface, only 4% of adsorbed HCOOH molecules were dissociated into the bidentate formate species. On the contrary, 13% of adsorbed HCOOH molecules were already dissociated into monodentate formate species on Cu(997) even at 83 K and 17% of adsorbed formic acid molecules were transformed to bidentate formate species by heating at 300 K, indicating that the stepped Cu surface has higher reactivity for HCOOH dissociation at low temperature.

Reversible low-temperature redox activity and selective oxidation catalysis derived from the concerted activation of multiple metal species on Cr and Rh-incorporated ceria catalysts.

The ceria-based catalyst incorporated with Cr and a trace amount of Rh (CrRhCeO) was prepared and the reversible redox performances and oxidation catalysis of CO and alcohol derivatives with O 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 CrRhCeO: dispersed Rh species (<1 nm) and CrO nanoparticles (∼1 nm) supported on CeO in CrRhCeO were transformed to Rh nanoclusters, Cr(OH) species and CeO with two Ce-oxide layers at the surface in a concerted activation manner of the three metal species with H.

Intra-dimer row and inter-dimer row coupling of the vibrational modes of chemisorbed CO on Si(001)-c(4×2) observed by angle-dependent transmission infrared spectroscopy.

The vibrational modes of chemisorbed CO on a Si(001) surface are investigated by means of transmission Fourier-transform infrared absorption spectroscopy. We observed the three components corresponding to the stretching vibration of the terminal-site CO adsorbed on the down-dimer sites of a Si(001) surface. The symmetric stretching vibration and asymmetric stretching vibration are observed separately.

An Ethynylene-Bridged Pentacene Dimer: Two-Step Synthesis and Charge-Transport Properties.

A rigid and planar ethynylene-bridged pentacene dimer (PenD) was synthesized from pentacenequinone in two steps, skipping the conventional stepwise approach. A brickwork motif in the single crystal shows two-dimensionally extended electronic interaction in the solid state. Highly crystalline dip-coated films exhibited average hole mobility of 0.

Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111).

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 (HCat-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 HCat-BMT-TTF adlayer formations.

CO adsorption on the copper surfaces: van der Waals density functional and TPD studies.

We investigated the adsorption of CO on the flat, stepped, and kinked copper surfaces from density functional theory calculations as well as the temperature programmed desorption and X-ray photoelectron spectroscopy. Several exchange-correlation functionals have been considered to characterize CO adsorption on the copper surfaces. We used the van der Waals density functionals (vdW-DFs), i.

Photoelectrochemical water splitting enhanced by self-assembled metal nanopillars embedded in an oxide semiconductor photoelectrode.

Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is of great practical interest for developing a sustainable energy system. Various nanoscale designs such as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the energy conversion efficiency of photoelectrochemical water splitting. Here we demonstrate a self-organized nanocomposite material concept for enhancing the efficiency of photocarrier separation and electrochemical energy conversion.

Observation of Fano line shapes in infrared vibrational spectra of CO2 adsorbed on Cu(997) and Cu(111).

Adsorption states of carbon dioxide on the Cu(997) and Cu(111) surfaces were investigated by infrared reflection absorption spectroscopy, temperature programmed desorption, and X-ray photoelectron spectroscopy. CO2 molecules are physisorbed on the Cu(997) surface at temperatures below 70 K; neither chemisorption nor dissociation of CO2 occurs on the Cu(997) surface at this low temperature. However, the vibrational spectra of adsorbed CO2 depend significantly on the substrate temperature and coverage.

Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species.

Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53-75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.