Koji K. Okudaira

Structure of copper- and H2-phthalocyanine thin films on MoS2 studied by angle-resolved ultraviolet photoelectron spectroscopy and low energy electron diffraction

Angle-resolved ultraviolet photoelectron spectra (ARUPS) of copper phthalocyanine (CuPc) and metal-free phthalocyanine (H2Pc) films (thickness from monolayer to 50–80 A) on cleaved MoS2 substrates were measured using monochromatic synchrotron radiation. Observed take-off angle (θ) and azimuthal angle (φ) dependencies of the top π band intensity were analyzed quantitatively by the single-scattering approximation theory combined with molecular orbital calculations. The analysis indicated that the molecules lie flat on the MoS2 surface in monolayer films of CuPc and H2Pc. The azimuthal orientation of the molecules (angle between molecular axis and surface crystal axis of MoS2), was found to be about −7°, −37°, or −67° for both monolayer films of CuPc and H2Pc. In the azimuthal orientation, the analyses indicated that there are only molecules with conterclockwise rotation, although both clockwise and counterclockwise rotations are expected. From the low energy electron diffraction, the two-dimensional lattice...

Photoemission study of direct photomicromachining in poly(vinylidene fluoride)

Direct pattern transfer onto poly(vinylidene fluoride) was achieved by using x-ray photons from a synchrotron radiation source. Quadrupole mass spectrometry and ultraviolet photoemission spectroscopy, combined with ab initio molecular orbital calculations, were employed to investigate the mechanism of direct photomicromachining. The mass spectrometry identified H2, F, and HF as the etched products, with no carbon containing species being detected. The changes in photoemission spectra due to photodegradation were analyzed by comparison with ab initio molecular orbital calculations. This analysis indicated that a high degree of conjugation is generated in the degraded polymer due to the loss of fluorine atoms. It is concluded that the mechanism of direct photomicromachining is ascribable to the shrinking of the irradiated polymer region due to defluorination and the generation of conjugation.

Molecular Orientation and Aggregation of Titanyl Phthalocyanine Molecules on Graphite Substrates: Effects of Surface Topography of the Substrate

Penning ionization electron spectroscopy (PIES) was used to investigate the effects of crystallographic inperfection of the substrate surface on organic ultrathin-film growth. For titanyl phthalocyanine (OTiPc) evaporated on graphite, it was found that the molecular orientation and aggregation in the film depend significantly on the type of graphite substrate. On a highly oriented pyrolytic graphite (HOPG), OTiPc film prepared by 1-monolayer-equivalence (MLE) deposition consists of islands of double layers, while on Grafoil, the molecules do not aggregate as on the HOPG, and form a monolayer. This large difference originated from the surface topography of the two graphite substrates.

Angle-resolved ultraviolet photoelectron spectroscopy of thin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) on the MoS2 surface

In this paper we report on the angle-resolved ultraviolet photoelectron spectroscopy on ultrathin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) (BTQBT) deposited on a MoS2 surface with synchrotron radiation, and describe the quantitative analysis of the angular distribution of photoelectron from the highest occupied state. The observed angular distributions were better explained by those calculated with the single-scattering approximation combined with molecular orbital calculation considering intramolecularly scattered waves than the previously used independent-atomic-center approximation combined with molecular orbital calculation. Further, the low-energy-electron diffraction measurements were performed on the film. From the low-energy-electron diffraction, the two-dimensional lattice of the ultrathin films on the MoS2 was found to be MoS2(0001)−(13×13, R=±13.9°)-BTQBT, and from the analysis of the photoelectron angular distributions, it was found that at the lattice points the molecules lie...

Angle-resolved ultraviolet photoelectron spectroscopy of In-[perylene-3,4,9,10-tetracarboxylic dianhydride] system

The In-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] system, obtained by the sequential evaporation of PTCDA and In on cleaved MoS2 surfaces, was measured by means of angle-resolved ultraviolet photoelectron spectroscopy. The results indicate that the four In atoms react with one PTCDA molecule. Using a model compound of the reaction product, In4PTCDA, the quantitative analysis of the take-off angle (θ) dependence of the photoelectron intensity from the new band shows that the band originates from the π state involving In 5pz atomic orbitals, and the In4PTCDA molecules lie tilted at the averaged tilt angle of the molecular plane β≅10°.

Angle-resolved UV photoelectron spectra (UPS) of thin films of perylene-3,4,9,10-tetracarboxylic dianhydride on MoS2

Angle-resolved UV photoelectron spectra (ARUPS) were measured for thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) deposited on cleaved MoS(2) surfaces. The take-off angle (theta) dependence of the photoelectron intensity of the highest pi band showed a sharp maximum at theta = 32-34 degrees. A spectral feature of the binding energy at approximately 8.9 eV, which is believed to originate from a pi state, showed a remarkably different theta dependence from that of the pi band. A quantitative analysis of the observed theta dependencies clearly indicates that (a) the feature at approximately 8.9 eV originates from the oxygen 2p non-bonding states and (b) the molecules lie flat on the substrate surface.

Characterization of ultrathin films of titanyl phthalocyanine on graphite: PIES and UPS study

Abstract Penning ionization electron spectroscopy (PIES) and ultraviolet photoelectron spectroscopy (UPS) were used to characterize ultrathin films (0.2–3 MLE) of titanyl phthalocyanine (OTiPc) deposited on a graphite substrate. The change in the molecular orientation at the outermost surface layer was selectively probed by PIES during the variations of the thickness and temperature of the films.

PHOTODEGRADATION OF POLY(TETRAFLUOROETHYLENE) AND POLY(VINYLIDENE FLUORIDE) THIN FILMS BY INNER SHELL EXCITATION

Ion time-of-flight (TOF) mass spectra of poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) thin films near fluorine and carbon K-edges were observed. For PTFE thin films, peaks corresponding to F+, CF+, and appeared, while for PVDF F+ and H+ were mainly observed. They indicate that for PTFE the polymer chain (C–C bonds) as well as C–F bonds are broken by irradiation of photons near fluorine and carbon K-edges, while for PVDF the bond scission occurs mainly at the C–F and C–H bond. Partial ion yields (PIY) of these ions for PTFE and PVDF thin films show strong photon energy dependencies near fluorine and carbon K-edges. The excitation from fluorine 1s to σ(C–F)* is specially efficient for F+ ion production for both PTFE and PVDF.

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.

Characterization of thin films of chloroaluminum phthalocyanine on MoS2 : HREELS, LEET and PIES study

Abstract High-resolution electron energy loss spectra (HREELS), low-energy electron transmission spectra (LEET) and Penning ionization electron spectra (PIES) were measured for thin films of chloroaluminum phthalocyanine (ClAlPc) deposited on a cleaved MoS 2 surface in order to investigate the molecular orientation and aggregation in the monolayer range. It was found that the as-grown film of monolayer equivalence consists of ClAlPc islands and the substrate surface is not fully covered by the molecules. Upon heating the film, the molecules spread over the substrate surface to form a uniform monolayer with a flat-lie orientation, where the Cl atoms protrude outside the film.