Hiroyuki Setoyama

Near-Edge X-ray Absorption Fine-Structure, X-ray Photoemission, and Fourier Transform Infrared Spectroscopies of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films

The chemical bonding structure of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films prepared by pulsed laser deposition was examined by near-edge X-ray absorption fine-structure (NEXAFS), X-ray photoemission, and Fourier transform infrared (FTIR) spectroscopies. An intense sp3-CH peak was observed in the FTIR spectrum. This implies that the sp3-CH peak originates from the grain boundaries between UNCD crystallites, wherein dangling bonds are terminated with hydrogen atoms. The presence of an intense σ*C–C peak in the NEXAFS spectrum and a narrow sp3 peak in the photoemission spectrum was specific to UNCD/a-C:H films; these confirm the existence of UNCD crystallites.

Photoionization of small krypton clusters in the Kr 3d regime: evidence for site-specific photoemission.

Kr 3d ionization energies of small, variable size krypton clusters are investigated by photoelectron spectroscopy, where the size regime of clusters with an average size N< or =30 is studied. Characteristic shifts in Kr 3d ionization energies to lower binding energies are found compared to the bare atom. These are also different from those of large krypton clusters. Moreover, we find evidence for photoionization of the krypton dimer. Its 3d ionization energy is barely shifted relative to the atomic value. Results from model calculations considering different isomers and cluster sizes as well as defect sites give evidence that the experimental results can be related to photoionization from different surface sites in variable size krypton clusters. This can be related to site-specific photoemission in small Kr clusters. The results are compared to size effects in Kr 3d near-edge features of variable size Kr clusters as well as recent results on Kr 3d photoionization of large Kr clusters.

Structural and Physical Characteristics of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Deposited Using a Coaxial Arc Plasma Gun

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films were formed without initial nucleation using a coaxial arc plasma gun. The UNCD crystallite diameters estimated from the X-ray diffraction peaks were approximately 2 nm. The Fourier transform infrared absorption spectrum exhibited an intense sp3-CH peak that might originate from the grain boundaries between UNCD crystallites whose dangling bonds are terminated with hydrogen atoms. A narrow sp3 peak in the photoemission spectrum implied that the film comprises a large number of UNCD crystallites. Large optical absorption coefficients at photon energies larger than 3 eV that might be due to the grain boundaries are specific to the UNCD/a-C:H films.

Formation of p-Type Semiconducting Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films by Boron Doping

p-Type ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films were fabricated by pulsed laser deposition using boron-doped graphite targets. Thermal analysis confirmed the occurrence of p-type conduction. The electrical conductivity increased with the doped amount of boron. An activation energy estimated from the Arrhenius plot was approximately 0.1 eV. Near-edge X-ray absorption fine structure spectra revealed that the σ*C–H peak weakened and the σ*C–B peak strengthened with an increase in the doped amount of boron. Fourier transform infrared spectroscopy showed that the sp3 C–H peak weakened with the doped amount of boron. These probably indicate that the hydrogen atoms that terminate the dangling bonds of UNCD crystallites are partially replaced with boron atoms.

Near-edge X-ray absorption fine structure of ultrananocrystalline diamond/hydrogenated amorphous carbon films prepared by pulsed laser deposition

The atomic bonding configuration of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films prepared by pulsed laser ablation of graphite in a hydrogen atmosphere was examined by near-edge X-ray absorption fine structure spectroscopy. The measured spectra were decomposed with simple component spectra, and they were analyzed in detail. As compared to the a-C:H films deposited at room substrate-temperature, the UNCD/a-C:H and nonhydrogenated amorphous carbon (a-C) films deposited at a substrate-temperature of 550°C exhibited enhanced π* and σ*C≡C peaks. At the elevated substrate-temperature, the π* and σ*C≡C bonds formation is enhanced while the σ*C-H and σ*C-C bonds formation is suppressed. The UNCD/a-C:H film showed a larger σ*C-C peak than the a-C film deposited at the same elevated substratete-temperature in vacuum. We believe that the intense σ*C-C peak is evidently responsible for UNCD crystallites existence in the film.

Polarized near-edge x-ray-absorption fine structure spectroscopy of C60-functionalized 11-amino-1-undecane thiol self-assembled monolayer: Molecular orientation and Evidence for C60 aggregation

Near-edge x-ray-absorption fine structure (NEXAFS) spectroscopy was adopted to probe the unoccupied electronic states of C60 anchored onto an organized assembly of 11-amino-1-undecane thiol on Au(111). The polarization dependence of the intensity of pi* resonance associated with C60 pi network revealed the self-assembled monolayer (SAM) system to be oriented with an average molecular tilt angle of 57 degrees with respect to the surface normal. Invoking the absence of solid-state band dispersion effects and in comparison to solid C60 and /or 1-ML C60/Au(111), the electronic structure of the resulting assembly was found dominated by spectral position shift and linewidth and intensity changes of the lowest unoccupied molecular orbital (LUMO), LUMO+1, and LUMO+2 orbitals. The latter implied hybridization between N Pz of -NH2 group of thiolate SAM and pi levels of C60, resulting in a nucleophilic addition with a change in the symmetry of C60 from Ih to C1 in the SAM. Occurrence of a new feature at 285.3 eV in the NEXAFS spectrum, assigned previously to pi* graphitic LUMO, signified the formation of aggregated clusters, (C60)n of C60 monomer. Low tunneling current scanning tunneling microscopy confirmed them to be spherical and stable aggregates with n approximately 5.

Full Picture of Valence Band Structure of Rubrene Single Crystals Probed by Angle-Resolved and Excitation-Energy-Dependent Photoelectron Spectroscopy

The valence band structure of rubrene single crystals was experimentally determined by high-resolution angle-resolved and excitation-energy-dependent photoelectron spectroscopy at room temperature. The energy position of the peak derived from the highest occupied molecular orbital did not depend on the excitation energy, reflecting an absence of energy dispersion along the surface normal direction. A two-dimensional valence band dispersion relation over the surface Brillouin zone obtained by angle-resolved photoemission to three critical points was reproduced excellently by a two-dimensional tight binding approximation. Highly anisotropic values of intermolecular transfer integrals to four adjacent molecules were obtained from the present results.

Direct observation of S-Au bonding state of self-assembled monolayers by outermost-surface spectroscopy using metastable atom beam

Abstract Temperature dependencies of metastable atom electron spectra (MAES) and ultraviolet photoelectron spectra (UPS) were measured for 8-bromo-1-octanethiol (8BRT) SAMs prepared on Au (111) surfaces in ethanol (EtOH) and n-hexane solutions. For both 8BRT SAMs, it was found that molecules stand upright to the substrate and the film surfaces consist of Br atoms. However, we found that 8BRT SAM prepared in n-hexane solution mainly consists of physisorbed molecules and they almost desorb at 100°C, while 8BRT SAM prepared in EtOH solution involves both physisorbed and chemisorbed molecules. For the SAM prepared in EtOH solution, we observed the valence electronic states which can be ascribed to S–Au bond of the chemisorbed ones after the desorption of the physisorbed molecules.

Surface/interface electronic structure in C60 anchored aminothiolate self-assembled monolayer: An approach to molecular electronics

Electronic structure in self-assembled monolayers (SAMs) of C(60) anchored 11-amino-1-undecane thiol (C(60)-11-AUT) on Au(111) was studied by means of ultraviolet photoelectron spectroscopy and hybrid density functional theory calculations. Valence band features of the molecular conformation revealed the interface electronic structure to be dominated by sigma(S-Au), localized at the thiolate anchor to Au. Formation of a localized covalent bond as a result of hybridization between N P(z) orbital of -NH(2) group of the thiolate SAM and the pi level of C(60) resulted in a symmetry change from I(h) in C(60) to C1 in C(60)-11-AUT SAM. Appearance of low, but finite amplitude surface electronic states of bonded C(60), much beyond the Fermi level, ruled out Au-C(60) end group contact. The band gap E(g) of the SAM, determined to be 2.7 eV, was drastically reduced from the insulating alkanethiol SAMs ( approximately 8.0 eV) and fell intermediate between the C(60) ground state (N electrons, 1.6 eV) and C(60) solid (N+/-1 electrons, 3.7 eV).

Electronic structure and molecular orientation at thin film surfaces of pendant-group polymers studied by outermost surface spectroscopy using metastable atoms

Abstract Metastable-atom electron spectroscopy (MAES) and ultraviolet photoelectron spectroscopy (UPS) were used to study the outermost surface of thin films of pendant group polymers: polystyrene, poly(2-vinylnaphthalene), and poly(9-vinylcarbazole). MAES is selectively sensitive to the outermost surface, and indicated that the surfaces of the polymer films were very clean, even though they were prepared by spin-casting in a room atmosphere. By comparison with gas-phase spectra and molecular orbital calculations of model molecules with pendant groups, it was confirmed that the principal constituent at the outermost surface of these polymer films is the pendant groups. Furthermore, it was observed that the intensity for σ(C–H) states of the pendant group is stronger in MAES spectra than in UPS spectra, indicating many pendant groups are inclined at large tilt angles.