The formation of right-handed and left-handed chiral nanopores within a single domain during amino acid self-assembly on Au(111).

We report the formation of both right- and left-handed chiral nanopores within a single domain during the self-assembly of an amino acid derivative on an inert Au(111) surface using STM. DFT calculations employed to rationalize this unusual result identified that intermolecular interactions between chiral, windmill-shaped tetramers are crucial for self-assembly.

Investigation of the interaction between a novel unnatural chiral ligand and reactant on palladium for asymmetric hydrogenation.

We report about the mechanistic studies of the reaction between a newly synthesized (S)-2-((R)-3H-dinaphtho[2,1-c:1',2'-e]azepin-4(5H)-yl)-2-phenylethanol based on the binaphthyl skeleton and (E)-2-methyl-5-phenylpent-2-enoic acid for the asymmetric hydrogenation of α,ß-unsaturated acids with heterogeneous palladium catalysts. The specific interactions between the chiral ligand and reactant were investigated in solution with palladium nanoparticles, as well as under ultrahigh vacuum (UHV) conditions on the palladium metal surface in the absence of hydrogen. The reactions were explored using nuclear magnetic resonance (NMR) spectroscopy, scanning tunneling microscopy (STM), and high-resolution photoemission spectroscopy (HRPES) combined with density functional theory (DFT) calculations. A NMR study identified the interaction between both molecules with palladium nanoparticles in solution. In addition, STM and HRPES studies revealed the spatial distribution and configuration of both compounds on the palladium metal surface under UHV conditions. The theoretical results support the experimental results with respect to the interaction energy value. It was found that the reaction between the ligand and reactant occurs with hydrogen bonding on palladium surface, simultaneously. The present study provides mechanistic details of the asymmetric hydrogenation reaction, which bears a correlation between the ligand, reactant, and catalyst during the reaction.

Confirmation of the coexistence of two tautomers of 2-mercaptothiazoline on the Ge(100) surface.

We confirmed the coverage dependent variation of tautomers of 2-mercaptothiazoline (the thiolate and thione forms) adsorbed on the Ge(100) surface under UHV conditions by using HRXPS measurements in conjunction with the DFT calculation method, which was studied before only in aqueous systems. The C 1s, S 2p, and N 1s core-level spectra obtained using HRXPS revealed the simultaneous presence of two distinct adsorption structures in different proportions at both low (0.15 ML) and high (0.65 ML) coverages. Moreover, we modelled the adsorption structures and geometric configurations of the bond states of 2-mercaptothiazoline on the Ge(100) surface by using the DFT calculation method, and found that the S dative bonded structure is the most stable adsorption structure for the thione form of 2-mercaptothiazoline and that the S-H dissociated-N dative bonded structure is the most stable adsorption structure for the thiolate form.

Interplay of Fermi Level Pinning, Marcus Inverted Transport, and Orbital Gating in Molecular Tunneling Junctions.

This Letter examines the interplay of important tunneling mechanisms-Fermi level pinning, Marcus inverted transport, and orbital gating-in a molecular rectifier. The temperature dependence of the rectifying molecular junction containing 2,2'-bipyridyl terminated n-alkanethiolate was investigated. A bell-shaped trend of activation energy as a function of applied bias evidenced the dominant occurrence of unusual Marcus inverted transport, while retention of rectification at low temperatures implied that the rectification obeyed the resonant tunneling regime. The results allowed reconciling two separately developed transport models, Marcus-Landauer energetics and Fermi level pinning-based rectification. Our work shows that the internal orbital gating can be substituted with the pinning effect, which pushes the transport mechanism into the Marcus inverted regime.

Transition metal doped Sb@SnO2 nanoparticles for photochemical and electrochemical oxidation of cysteine.

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

Determining the Catalytic Activity of Transition Metal-Doped TiO2 Nanoparticles Using Surface Spectroscopic Analysis.

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

Enhancement of Photo-Oxidation Activities Depending on Structural Distortion of Fe-Doped TiO2 Nanoparticles.

To design a high-performance photocatalytic system with TiO2, it is necessary to reduce the bandgap and enhance the absorption efficiency. The reduction of the bandgap to the visible range was investigated with reference to the surface distortion of anatase TiO2 nanoparticles induced by varying Fe doping concentrations. Fe-doped TiO2 nanoparticles (Fe@TiO2) were synthesized by a hydrothermal method and analyzed by various surface analysis techniques such as transmission electron microscopy, Raman spectroscopy, X-ray diffraction, scanning transmission X-ray microscopy, and high-resolution photoemission spectroscopy. We observed that Fe doping over 5 wt.% gave rise to a distorted structure, i.e., Fe2Ti3O9, indicating numerous Ti(3+) and oxygen-vacancy sites. The Ti(3+) sites act as electron trap sites to deliver the electron to O2 as well as introduce the dopant level inside the bandgap, resulting in a significant increase in the photocatalytic oxidation reaction of thiol (-SH) of 2-aminothiophenol to sulfonic acid (-SO3H) under ultraviolet and visible light illumination.

Ultrathin and Flat Layer Black Phosphorus Fabricated by Reactive Oxygen and Water Rinse.

Ultrathin black phosphorus (BP) is one of the promising two-dimensional (2D) materials for future optoelectronic devices. Its chemical instability in ambient conditions and lack of a bottom-up approach for its synthesis necessitate efficient etching methods that generate BP films of designed thickness with stable and high-quality surfaces. Herein, reporting a photochemical etching method, we demonstrate a controlled layer-by-layer thinning of thick BP films down to a few layers or a single layer and confirm their Raman and photoluminescence characteristics. Ozone molecules generated by O2 photolysis oxidize BP, forming P2O5-like oxides. When the resulting phosphorus oxides are removed by water, the surface of BP with preset thickness is highly flat and self-protective by surface oxygen functional groups. This method provides a fabrication strategy of BP and possibly other 2D semiconductors with band gaps tuned by their thickness.

Comparative study of photocatalytic activities of hydrothermally grown ZnO nanorod on Si(001) wafer and FTO glass substrates.

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

Coverage-dependent variation of adsorption configurations of methionine on Ge(100).

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.