Jun Yoshinobu

Chemically homogeneous and thermally reversible oxidation of epitaxial graphene

With its exceptional charge mobility, graphene holds great promise for applications in next-generation electronics. In an effort to tailor its properties and interfacial characteristics, the chemical functionalization of graphene is being actively pursued. The oxidation of graphene via the Hummers method is most widely used in current studies, although the chemical inhomogeneity and irreversibility of the resulting graphene oxide compromises its use in high-performance devices. Here, we present an alternative approach for oxidizing epitaxial graphene using atomic oxygen in ultrahigh vacuum. Atomic-resolution characterization with scanning tunnelling microscopy is quantitatively compared to density functional theory, showing that ultrahigh-vacuum oxidization results in uniform epoxy functionalization. Furthermore, this oxidation is shown to be fully reversible at temperatures as low as 260 °C using scanning tunnelling microscopy and spectroscopic techniques. In this manner, ultrahigh-vacuum oxidation overcomes the limitations of Hummers-method graphene oxide, thus creating new opportunities for the study and application of chemically functionalized graphene.

The adsorbed states of ethylene on Si(100)c(4×2), Si(100)(2×1), and vicinal Si(100) 9°: Electron energy loss spectroscopy and low‐energy electron diffraction studies

The adsorbed states of ethylene on the Si(100)c(4×2), Si(100)(2×1), and the Si(100) 9° vicinal surfaces have been studied using high resolution electron energy loss spectroscopy (EELS) and low‐energy electron diffraction (LEED). Ethylene is nondissociatively chemisorbed on the Si(100) surface in the wide temperature range between 77 and ∼600 K, and is rehybridized to have a near sp3 hybridization state. The adsorbed structure is proposed in which ethylene is di‐σ bonded to two adjacent Si atoms of the dimer at the Si(100) surface. The thermal decomposition of chemisorbed ethylene and the influence of steps on the adsorbed states of ethylene are discussed.

The adsorption and thermal decomposition of acetylene on Si(100) and vicinal Si(100)9

The adsorption and decomposition of acetylene on Si(100) and vicinal Si(100)9° have been studied using high resolution electron energy loss spectroscopy and low-energy electron diffraction. Acetylene is predominantly chemisorbed molecularly in the temperature range between 80 and ~ 300 K; a small amount of acetylene is partially dissociated. The molecularly-chemisorbed acetylene is rehybridized, and has the hybridization state near sp 3 . It is proposed that molecular acetylene is di-σ bonded to adjacent Si atoms of a dimer on Si(100).The thermal decomposition of chemisorbed acetylene, and the (inactive) role played by steps are discussed.

Thermal excitation of oxygen species as a trigger for the CO oxidation on Pt(111)

Thermal excitation of adsorbed oxygen species is found to initiate the CO oxidation on Pt(111). We have prepared three different coadsorption systems to study the reactivity of different oxygen species; (1) CO on the O2 preadsorbed Pt(111) surface, (2) CO on the nearly perfect Pt(111) p(2×2)‐O surface, and (3) CO on the disordered atomic oxygen‐preadsorbed Pt(111) surface. Four CO2 desorption peaks (α‐CO2 at 125 K, β3‐CO2 at ∼225 K, β2‐CO2 at ∼260 K, and β1‐CO2 at 320 K) are observed. The desorption temperatures of CO2 strongly depend on the adsorbed states of oxygen species. We have shown that the α‐CO2 state, β2,3‐CO2 states, and β1‐CO2 state are correlated with adsorbed O2, disordered oxygen atoms, and p(2×2) oxygen atoms, respectively. The difference in CO2 desorption temperature is related to thermal excitation of each oxygen species, which is derived from the structural information of coadsorbed states during thermal evolution by means of low‐energy electron diffraction and infrared reflection absor...

WATER ADSORPTION ON PT(111) : FROM ISOLATED MOLECULE TO THREE-DIMENSIONAL CLUSTER

Abstract Water adsorption on Pt(111) at 84 K was investigated by infrared reflection absorption spectroscopy. At a low coverage (θ = 0.13 ML), D2O adsorption exhibited absorption bands of νOD at 2475 cm−1 and δD2O at 1184 cm−1. The species is assigned to isolated D2O bound to the surface through the oxygen lone-pair. With increasing coverage (0.13

Chemisorption and thermal decomposition of ethylene on Pd(110): electron energy loss spectroscopy, low-energy electron diffraction, and thermal desorption spectroscopy studies

The adsorbed state of ethylene on Pd(110) at 90 K and its thermal decomposition in the temperature region between 90 and 600 K have been studied by the use of high resolution electron energy loss spectroscopy (EELS), low‐energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). At 90 K, ethylene is π bonded to the Pd(110) surface and is adsorbed almost disorderedly. The c(2×2)‐C2H4 patches are formed near the saturation coverage (which corresponds to 0.58 C2H4 molecule per surface Pd atom). By heating the C2H4‐saturated Pd(110) surface to 260 K, some C2H4 admolecules are desorbed intact and the remaining admolecules rearrange their adsorbed sites to form the c(2×2)‐C2H4 structure. At above 300 K, almost all the C2H4 admolecules are dehydrogenated, and the ethynyl (CCH) species, H adatoms and unstable dehydrogenated species [possibly, vinyl (CHCH2) species] are formed; the C2H4 desorption occurs by the recombination of H adatoms and dehydrogenated species. The remaining H adatoms are d...

Clustering behavior of water (D2O) on Pt(111)

The structure and adsorption environment of water (D2O) on Pt(111) are investigated using infrared reflection absorption spectroscopy. The sample was prepared by the heat and quench technique at a heating temperature between 25 and 165 K. At 25 K, adsorbed water molecules exist as monomers and dimers, where the latter is evidenced for the first time. Upon annealing to 40 K, dimers dissociate and monomers cluster into bilayer ice at the terrace. At 105 K, a liquidlike phase is formed at the step. The liquidlike phase frozen in by quenching the surface to 25 K reveals itself measured in the measurements as amorphous ice. Until 125 K, bilayer ice at the terrace and the liquidlike phase at the step coexist. At 155 K, bilayer ice melts and the remaining molecules are converted to the liquidlike phase at the step. These phenomena are evidenced by the behavior of coadsorbed CO as a spectator molecule.

Interaction of ethylene with the Si(111)(7×7) surface- A vibrational study

Abstract The adsorption of ethylene on the Si(111)(7×7) surface has been studied at 300 K using high-resolution electron energy loss spectroscopy. Assignments of the observed loss peaks are attempted. Ethylene is predominantly adsorbed non-dissociatively and is rehybridized to have a near sp3 hybridization state. The adsorbed structure is proposed in which ethylene is di-σ bonded to two adjacent surface Si atoms saturating the dangling bonds.

Rehybridization of acetylene on the Si(111) (7 × 7) surface - a vibrational study

Abstract The adsorption of acetylene on a Si(111) (7 × 7) surface has been studied at 300 K using high-resolution electron energy loss spectroscopy. Acetylene is predominantly adsorbed non-dissociatively, and is rehybridized having a state of hybridization between sp2 and sp3. An adsorbed structure is proposed in which acetylene is di-σ bonded to two adjacent surface Si atoms saturating the dangling bonds.

Initial adsorption sites of CO on Pt(111) and Ni(100) at low temperature

Abstract Adsorption of CO on Pt(111) at 25 K and Ni(100) at 18 K has been studied by infrared reflection absorption spectroscopy (IRAS). The occupation ratio of terminal CO to bridged CO species on Pt(111) at 25 K ranges from ∼2.3 to 1.2 at total coverages from 0.03 to 0.13 ML, and that of bridged CO to terminal CO species on Ni(100) at 18 K ranges from ∼3.2 to 0.7 at total coverages from 0.003 to 0.15 ML. Such strong coverage dependence of the occupation ratio, even at small coverages, suggests that the substrate-mediated interaction between CO molecules operates at a relatively long range ( > 10 A ). The isotope experiments suggest that there is dynamic interaction between preadsorbed (accommodated) CO species and incoming (mobile) CO species.