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Photocatalytic conversion of lignocellulose to valuable aromatics has significant potential for applications in biorefineries. The photocatalyst efficiency of lignocellulose conversion is typically...

Cu/ZnO/Al2O3 is an industrially important heterogeneous catalyst for the conversion of CO2 to methanol, which is in worldwide demand, and for the solution of the activation mechanism of catalytically inactive CO2. Recent studies have achieved numerous improvements in active sites of catalysts for this process, which can be described as “active copper with step sites” decorated with ZnOx. In spite of these improvements, the mechanism of this process is still unknown, and even its initial stage remains unclear. In this study, we simplified the catalytic system to bare Cu(111) and Cu(775) surfaces in order to systematically determine the mechanistic effects of step sites. The reaction was conducted by using a CO2/H2 gas mixture at 1 Torr at various temperatures and characterized with infrared reflection absorption spectroscopy (IRRAS). The initial activation of CO2 was found to occur only with the coadsorption of hydrogen; it cannot on its own be converted into other activated species. This coadsorbed hydrog...

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 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 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 ...

The discrepancy of geometric configuration between phenylalanine and tyrosine adsorbed on Ge(100) surfaces was investigated using scanning tunneling microscopy (STM) in conjunction with density functional theory (DFT) calculations and core-level photoemission spectroscopy (CLPES). The study focused on the role of nucleophilic group (hydroxyl group) on phenyl ring of tyrosine, and we elucidated the difference of the adsorption geometry between phenylalanine and tyrosine on Ge(100) surfaces. We first confirmed that the “O–H dissociated–N dative bonded structure” was the most favorable structure in both molecules at low coverage by results of CLPES and DFT calculations. Geometric differences for the adsorption configurations between phenylalanine and tyrosine were observed: the phenyl ring of phenylalanine was aligned axially with respect to the Ge(100) surface, whereas that of tyrosine was tilted, as determined by DFT calculations. In sequence, we found out the results of STM images to confirm DFT results. ...

The variation of the adsorption structures and geometric configurations among phenylalanine derivatives (2-amino-4-phenylpropanoic acid (PhenA), 2-amino-5-phenylpropanoic acid (PhenB), and 2-amino-6-phenylpropanoic acid (PhenC)) adsorbed on Ge(100) surfaces was investigated using density functional theory (DFT) calculations. The chain length of a linker bonded to the α-carbon of the phenylalanine derivatives influenced the preferred adsorption structure in self-assembled monolayers (SAMs). We confirmed that the “O–H dissociated-N dative bonded structure” is the most favorable structure among the five possible adsorption structures. Interestingly, geometric differences in the adsorption configurations indicated that the phenyl rings of PhenA and PhenB were tilted with respect to the Ge(100) surface, with an angle 30° from the surface normal. In contrast, the phenyl ring of PhenC was tilted with an angle of 60° with respect to the surface normal. We therefore confirmed that PhenA and PhenB are available to ...

The coverage-dependent attachment of multifunctional groups included in alanine and leucine molecules adsorbed to the Ge(100)-2×1 surface was investigated and compared using core-level photoemission spectroscopy (CLPES) and density functional theory (DFT) calculations. The bonding configuration, stability, and adsorption energies were evaluated for two different coverage levels. In both molecules, the core-level spectra at a low coverage indicated that both the carboxyl and amine groups participated in the bonding with the Ge(100) surface by “O–H dissociated and N-dative bonded structure”. This is consistent with the DFT calculation results showing that such adsorption geometry is the most stable and follows the minimum reaction pathway. However, at high coverage level, an additional adsorption geometry of “O–H dissociation bonded structure” appeared possibly to minimize the steric hindrance between adsorbed molecules.

We investigate the variation of the electronic properties and morphological surface change of epitaxial graphene (EG) by chemically functionalizing the graphene layer with a surface-adsorbed organic free radical, 2,2,6,6-tetramethyl-1-piperridinyloxy (TEMPO) using scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and core-level photoemission spectroscopy (CLPES). STM and LEED images revealed that the adsorption of TEMPO occurred at the interface regions, observed as surface roughness in STM images and haziness in the (6(31/2) × 6(31/2))R30° LEED patterns. TEMPO molecules adsorbed onto EG through the NO radical group, as confirmed by the binding energies of the N 1s and O 1s core-level spectra. Changes in the work function, as measured by secondary electron edge, indicated that the adsorption of NO free radicals onto EG acts as an n-type dopant.

We investigated the adsorption structures of serine on a Ge(100) surface by core-level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. The adsor...

The adsorption configurations of S-proline on Ge(100) were studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution photoemission spectroscopy (HRPES). We identified three adsorption structures of S-proline on Ge(100) through analysis of the STM images, DFT calculations, and HRPES results: (i) an “intrarow O−H dissociated and N dative bonded structure”, (ii) an “O−H dissociation structure”, and (iii) an “N dative bonded structure”. Moreover, because adsorption through the N atom of S-proline creates a new chiral center due to symmetry reduction produced by N dative bonding with the surface, the adsorption configurations of S-proline on Ge(100) have either (R,S) or (S,S) chirality. Through DFT calculations, we clearly demonstrated that the adsorption configurations have (R,S) chirality with a preference for reaction at the Re face. This work presents a novel method for generating stereoselective attachment using S-proline molecules adsorbed on a G...

The adsorption structure and surface reorientation of cysteine molecules on a Ge(100) surface were studied using high-resolution core-level photoemission spectroscopy and low-energy electron diffraction (LEED) to track the variation in adsorption structure as a function of cysteine coverage. Analysis of the S 2p, C 1s, N 1s, and O 1s core-level spectra revealed quite different adsorption behaviors as a function of cysteine coverage. At 0.4 ML (below half a monolayer), a single S 2p peak and a single N 1s peak were observed, consistent with an adsorption structure that contained one type of thiol conformation and a neutrally charged amino moiety. At 0.60 ML (over half a monolayer), two S 2p peaks emerged with a binding energy difference of 0.91 eV, indicative of two types of thiols, and two N 1s peaks were observed, which were consistent with the presence of both neutrally charged NH2 and positively charged NH2+ moieties. The relative populations of the two thiols induced a structural change in the orderin...

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).

Chemical doping of epitaxial graphene (EG) by organic free radicals (4-amino-2,2,6,6-tetramethyl-1-piperridinyloxy; 4-amino-TEMPO) was investigated using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and high resolution photoemission spectroscopy (HRPES). STM images revealed that the empty density of states near the adsorption site significantly decreased as a result of radical doping. STS indicated that 4-amino-TEMPO radicals acted as n-type dopants on monolayer graphene. The radicals adsorbed onto EG through the nitroxide groups, leaving the amine group unreacted, which was confirmed by the binding energies of N 1s and O 1s core-level spectra. Furthermore, the measured work function changes verified that increased adsorption of the radicals on EG showed n-type doping characteristics.

The adsorption geometry of cis-2-butene-1,4-diol (BEDO, HOCH(2)CH=CHCH(2)OH) on Si(100)-2 x 1 was studied using scanning tunneling microscopy (STM), high resolution X-ray photoemission spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Bias-voltage-dependent STM images exhibited features characteristic of two distinct BEDO adsorption geometries. One feature was a bright protrusion located on the center of a single dimer, indicating an on-top configuration. The low bias-voltage STM image clearly showed dark features indicative of the formation of Si-H bonds on adjacent dimers in the same dimer row. The other feature was a bright protrusion bridged on end between two adjacent dimers in the same dimer row, indicating an end-bridge configuration. Accompanying this feature, two dark features attributed to Si-H bonds were observed on opposite positions to the bridged protrusion. From the XPS results, the Si 2p core level spectra revealed that the dimer atoms are involved in the formation of Si-O and Si-H bonds. On the other hand, carbon K-edge NEXAFS spectra showed that the C=C bond does not participate in the adsorption reaction and remains as an unreacted group. Collectively, the experimental results indicate that the adsorption of BEDO on Si(100)-2 x 1 occurs through the formation of two Si-O bonds via nucleophilic reaction between the two OH groups of BEDO and two Si-Si dimers. Importantly, the maintenance of the C=C bond means that the C=C functional group can be utilized as a new reaction site for further surface chemical reactions.

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...

The synthesis and structural analysis of two novel families of three-component reversible redox cycles [(C(2)B(9)H(11))M(mu-SPh)(2)](2)(n)PPN(n) (M = Mo, n = 2-, 2; 1-, 3; 0, 4; and M = W, n = 2-, 6; 1-, 7; 0, 8), where the cleavage and re-formation of the carborane cage C-C bond is observed during the redox reaction, are reported. Electronic saturation of the metal center (18e center) and the lack of bulky substituents on the carborane cage suggest that the deformed carborane cages in 2.PPN(2), 6.PPN(2), and 7.PPN invoke a new kind of deformed cage ("semicloso" framework). The XPS results show that the unprecedented competition for electron density between the metal center and the carborane cage is involved in the cleavage and formation of the carborane C-C bond.

Chemically modified epitaxial graphene (EG) by azidotrimethylsilane (ATS) was investigated using high-resolution photoemission spectroscopy (HRPES). Through the spectral analysis, we clearly confirmed that EG is modified by thermally generated nitrene radicals and found that the bonding nature between the nitrene radicals and EG is covalent. As we observe bonding nature of N 1s peaks, we found that two distinct N peaks can be clearly distinguished in the spectra. Using a covalently bound stretched graphene (CSG) model, we elucidated that nitrene radicals adsorb on the graphene layer at two different adsorption sites. Moreover, we were able to control the band gap of EG using valence band spectra as we change the amount of the dosing of nitrene.

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.

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).