Yoshiya Harada

Photoelectron spectroscopy of naphthacene crystal in the vacuum ultraviolet region

Abstract The energy distribution curves of the photoelectrons emitted from naphthacene (C 18 H 12 ) crystal in the vacuum ultraviolet region were measured by an ac modulated retarding potential method. The peaks in the curves, 5.8 3 , 7.2 8 , 8.2 9 , 8.7 0 and 9.4 0 eV, are considered to be associated with the valence bands of the naphthacene crystal.

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...

Penning Ionization Electron Spectoscopy: Its Application to Surface Characterization of Organic Solids

In Penning ionization electron spectroscopy, the kinetic energy of electrons ejected by collisions between targets T (gas or solid) and metastable rare gas atoms A* is analyzed. This electron spectroscopy is selectively sensitive to the outermost surface layer of solids, since metastable atoms do not penetrate into inner layers. Furthermore, it provides information on the local electron distribution of individual orbitals exposed outside the outermost surface layer. The application of these unique features of Penning spectroscopy to the surface characterization of organic solids, including Langmuir-Blodgett films, is discussed. Both a Penning spectroscopy technique and the process of Penning ionization of gas-phase molecules are briefly described.

Exterior electron model for Penning ionization. Unsaturated hydrocarbons

A simple theoretical model is described for Penning ionization (M+A*→M++A+e−) in which a metastable‐state rare gas atom (A*) extracts an electron from a target molecule (M) and ejects another electron into a continuum state. One of the most important factors governing Penning ionization is electron distributions of molecular orbitals which are directly connected with the electronic transition probabilities. Another key factor is the repulsive molecular surface which divides the unreactive electron densities in the interior region from the reactive electron densities in the exterior region, because the metastable atom A* cannot penetrate into the interior region. In the present model, exterior electron densities (EED) for individual molecular orbitals are considered to be proportional to Penning ionization branching ratios. Good agreements between ab initio MO calculations of EED’s and experimental branching ratios of Penning ionization were obtained for various unsaturated hydrocarbon molecules.

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.

Photoelectron spectroscopy of naphthacene and perylene crystals by the rare gas emission lines

Abstract The energy distribution curves (EDCs) of the photoelectrons emitted from naphthacene (C 18 H 12 ) and perylene (C 20 H 12 ) crystals were measured using the rare gas resonance emission lines (He 21.22 eV, Ne 16.85 and 16.67 eV and Ar 11.83 and 11.62 eV). The peaks in the higher kinetic energy regions agree well with the peaks obtained from molecular photoelectron spectroscopy studies if constant energy shifts are assumed. In the lower kinetic energy regions, however, fixed kinetic energy peaks are found which are independent of the incident photon energies.

Vacuum–ultraviolet photoelectron spectroscopy of hexatriacontane (n‐C36H74) polycrystal: A model compound of polyethylene

Photoelectron spectra of hexatriacontane (n‐C36H74) films evaporated in situ under vacuum were measured at 12 photon energies between 11.4 eV and 21.2 eV. The escape depth of the photoelectrons was found to be much less than 10 nm. Although five valence band features on the photoelectron spectra are expected in this region from the findings by the XPS method, only one or two valence band features were observed; four features from the conduction band were found to dominate the spectra. The short escape depth and the smearing out of the valence band structure are attributed to scattering, which includes the scattering by phonons, and the appearance of the conduction band structure is attributed to accumulation of the secondary electrons to the high density of states parts associated with the conduction bands. The threshold energy of photoemission was found to be 9.1±0.5 eV. The finding for the evaporated films of polyethylene, despite some degree of decomposition, gave essentially the same result. The resul...

Comparison of the relative intensities of penning electron spectra and photoelectron spectra. II. Heterocyclic aromatic molecules

Abstract Ultraviolet photoelectron spectra and Penning electron spectra, using neon or helium metastable species, have been recorded for pyridine, thiophene and

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...

Penning ionization electron spectroscopy of CO and Fe(CO)5. Study of electronic structure of Fe(CO)5 from electron distribution of individual molecular orbitals

The He* Penning ionization electron spectra (PIES) and He I UV photoelectron spectra (UPS) of CO and Fe(CO)5 were measured. The relative intensity of the bands in PIES was shown to give information on the spatial electron distribution of individual molecular orbitals. On the basis of the information together with the results of the population analysis, most of the bands in the UPS of Fe(CO)5 were assigned. The usefulness of PIES in the study of stereochemistry was indicated.