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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).

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.