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The electronic structure and molecular orientation of dibenzo-18-crown-6 deposited on graphite were studied by ultraviolet photoelectron spectroscopy and metastable atom electron spectroscopy. We observed an alternate orientation of the molecule in the first monolayer and second layer. Moreover, the energy separations of the three top π-bands containing the highest occupied molecular orbital in the first layer were found to be clearly different from those in the multilayers, indicating that the conformation of the molecules in the first layer markedly changes even with a weak molecule−substrate interaction.

Interchain interaction, i.e., pi-pi stacking, can benefit the carrier transport in conjugated regio-regular poly(3-hexylthiophene) (P3HT) thin films. However, the existence of the insulating side hexyl chains in the surface region may be detrimental to the charge transfer between the polymer backbone and overlayer molecules. The control of the molecular orientation in the surface region is expected to alter the distribution of the pi electron density at the surface to solve such problems, which can be achieved by controlling the solvent removal rate during solidification. The evidence that the pi-electron density distribution at the outermost surface can be controlled is demonstrated by the investigation using the powerful combination of near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and the most surface-sensitive technique: Penning ionization electron spectroscopy. From the spectroscopic studies, it can be deduced that the slower removal rate of the solvent makes the polymer chains even at the surface have sufficient time to adopt a more nearly equilibrium structure with edge-on conformation. Thus, the side hexyl chains extend outside the surface, which buries the pi-electron density contributed from the polymer backbone. Contrarily, the quench of obtaining a thermo-equilibrium structure in the surface region due to the faster removal of the solvent residual can lead to the surface chain conformation without persisting to the strong bulk orientation preference. Therefore, the face-on conformation of the polymer chain at the surface of thin films coated with high spin coating speed facilitate the electron density of the polymer backbone exposed outside the surface. Finally, thickness dependence of the surface electronic structure of P3HT thin films is also discussed.

Angle-resolved photoelectron spectra were measured for a well-ordered monolayer film of titanyl phthalocyanine (OTiPc) prepared on a cleaved graphite surface using synchrotron radiation. The observed photoelectron angular distributions were analyzed by a calculation using the single-scattering approximation combined with molecular orbital calculation. The molecular orientation of the OTiPc monolayer on graphite was estimated quantitatively.

We report the surface electronic structures of polythiophene derivatives (including polythiophene, poly(3-butylthiophene), poly (3-hexylthiophene)(P3HT)) thin films observed by ultraviolet photoelectron spectroscopy and Penning ionization electron spectroscopy. He*-impact-surface-modification was applied on the P3HT surface to control the distribution of the electron density.

The hole-vibration coupling of the highest occupied state in pentacene thin films on graphite was studied by high-resolution ultraviolet photoemission spectroscopy. It was found that vibration satellites in the film are more intense than that in the gas phase and the vibrational energy in the film is slightly lower than that in the gas phase. This demonstrates that the reorganization energy (hole mobility) in the pentacene thin film is slightly larger (smaller) than that expected from the photoemission spectrum of free pentacene molecules.

Angle-resolved photoelectron spectra were measured for a single-domain monolayer film of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTCDA) prepared on a cleaved GeS(0 0 1) surface using synchrotron radiation. The observed photoelectron angular distributions were analyzed by a calculation using the single-scattering approximation combined with molecular orbital calculation. With the help of the low-energy electron diffraction pattern, the structure of the NTCDA monolayer on GeS(0 0 1) was estimated quantitatively.

Angle-resolved ultra-violet photoelectron spectroscopy (ARUPS) has been studied using a multiple scattering theory. ARUPS spectra of adsorbed large molecules on surface have information of geometric and electronic structures for near neighbors of an excited molecule. In order to obtain useful information, analyses of scattering order are discussed in terms of real-space multiple scattering theory. The theory allows us to discuss geometric and electronic structures of the excited molecule and local structure of near-neighbor molecules. In this paper, we have studied ARUPS of copper phthalocyanine. The single-scattering calculations are enough to estimate main structures of the spectra. However, the single scattering results are not converged to infinite order multiple scattering results. Our scattering order analysis shows double-scattering processes are important to approximate the infinite-order multiple scattering results. Moreover, we also find that the results of double scattering processes including intermolecular scattering path improve the data of single scattering. If we want to discuss fine structures of ARUPS, we should consider higher order multiple scattering processes.

Auger electron–photoion coincidence (AEPICO) experiments have been performed for condensed water (H 2 O and D 2 O) at the 4a 1 ← O 1s resonant transition. Several kinds of isotope effects were observed in H + (D + ) desorption, they were, (1) the differences in ion kinetic energy for the selected Auger-final-states, (2) the relative intensity differences in AEPICO spectra, (3) peak shifts in AEPICO and resonant Auger electron spectra and (4) the intensity difference in prominent peak in ion yield spectra. Those isotope effects can be explained by a four-step ion desorption mechanism involving O–H (O–D) bond extension within the lifetime of the O 1s core-hole.

Anisotropic surface diffusion of In atoms was observed by photoelectron emission microscopy (PEEM) when a square-shaped microstructure of In metal was deposited onto thin films of perylene-3,4,9,10-tetracarboxyric acid-dianhydride (PTCDA) grown on cleaved MoS 2 and GeS surfaces. For In microstructure on PTCDA/MoS 2 system, the PEEM images showed a triangle pattern, although the deposited shape of the In microstructure was square, indicating that In atoms diffuse to three directions on PTCDA/MoS 2 . Such triangle pattern was not observed on PTCDA/GeS but an oval structure was observed, revealing that In atoms diffuse to two directions on PTCDA/GeS with different diffusion constant. The two directions correspond well with surface crystal axes of GeS. Since the unit cells of PTCDA adsorbed on these two crystal surfaces are nearly the same, it is suggested that different anisotropic diffusion of In in these systems is related to strong In-PTCDA interaction which may be affected by the surface structure of underlying substrate.

A diffusion-induced changes of indium microstructure was observed by photoelectron emission microscopy (PEEM) and scanning electron microscopy (SEM) for evaporated microstructure of In metal on a pelylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) thin film on MoS2 substrate. The PEEM and SEM images show a periodic triangle pattern, although deposited shape of the In microstructure was square. In contrast such an unusual images originating from anisotropic diffusion was not observed when deposition metals or substrate materials were changed. These results suggest that the peculiar phenomenon originates from (1) chemical reaction between PTCDA and In, and (2) the molecular packing structure which depends on substrate materials.

A combined metastable electron emission microscopy (MEEM) and photoelectron emission microscopy (PEEM) study has been performed for copper phthalocyanine (CuPc) thin films vacuum deposited on Si(100) with a lithographic SiO2 pattern. The MEEM image of SiO2 pattern edges changed considerably upon deposition of a very small amount of CuPc on the SiO2/Si(100) substrate, whereas no such changes were observed in the PEEM images. The different contrast features in MEEM and PEEM can be the result of different surface sensitivities of these microscopy techniques. The MEEM contrast characteristic for the pattern edges after the CuPc deposition may be ascribed to the difference of the molecular orientation of CuPc which cannot be observed by PEEM.

The molecular orientation at the surfaces of poly(9-vinylcarbazole) (PvCz) thin films was studied by angle-resolved ultraviolet photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The observed take-off angle (θ) dependence of photoelectron intensities from top π band peaks clearly at larger θ than the calculated one for the three-dimensional isotropic random orientation model. The results indicate that there are more pendant groups with large tilt angles than the three-dimensional isotropic random orientation model, which is in good agreement with the result obtained from NEXAFS spectroscopy. The surface electronic states of PvCz may be rather dominated by σ(C–H) states at the pendant carbazole group than π states

Structure of the self-assembled film of 4-mercaptohydrocynnamic acid (HOOC(CH 2 ) 2 C 6 H 4 SH) deposited on Au(111) surface was characterized by X-ray photoelectron spectroscopy (XPS). From the XPS spectrum of S 2p, it was found that there are the two types of sulfur atoms, which correspond to sulfur in thiolate bonded to Au(111) and sulfur in unbound thiol at the surface. This result supports the bilayer formation of 4-mercaptohydrocynnamic acid molecules on Au(111) substrate. Furthermore, the XPS results of the O 1s region suggest that carboxylic anhydride is formed at room temperature.

Radiation damage of poly(methylmethacrylate) (PMMA) caused by vacuum ultraviolet monochromatic synchrotron radiation was studied by ultraviolet photoelectron spectroscopy. An independent atomic center approximation combined with molecular orbital calculation was employed to study the radiation damage of PMMA quantitatively for the first time. The results of the analysis indicate that main photodegradation is ascribed to abstraction of ester groups and formation of double bonds in the polymer chain.

High-resolution electron energy loss spectra (HREELS) were measured for ultrathin films of chloroaluminum phthalocyanine (C1AIPc) deposited on a cleaved HOPG surface in order to investigate the molecular orientation and its thickness dependence. It was found that for the monolayer film C1AIPc molecules lie fiat on the HOPG surface without heat treatment. With increase in the film thickness, the molecules become oriented at a tilt. The result show a marked difference from the orientation of C1AIPc molecules on MoS2, where the molecules lie tilt on MoS2 in the as-grown monolayer. © 1998 Elsevier Science B.V.

The molecular orientation in self-assembled monolayers (SAMs) of thiophenol chemisorbed on polycrystalline gold from aqueous solutions has been investigated by Penning ionization electron spectroscopy (PIES) and ultraviolet photoelectron spectroscopy (UPS). The analysis of the relative band intensity of the Penning spectrum indicates that the phenyl ring in phenyl thiolate stands perpendicular to the substrate plane at room temperature. Upon heating, the phenyl ring becomes tilted in the layer.

Penning ionization electron spectroscopy (PIES) was used to investigate the molecular orientation, aggregation of molecules, and electronic structure of ultrathin films of titanyl phthalocyanine (OTiPc) vapor deposited on graphite and MoS 2 substrates. For the monolayer film, the molecular orientation was remarkably different between the two substrates. At room temperature, molecules spread over and almost cover the substrate on graphite, whereas they aggregate and form islands on MoS 2 . The PIES band due to the nonbonding orbital of the oxygen atom extending perpendicular to the molecular plane is extraordinary strong for the He * (2 3 S) metastable atom but not for the He * (2 1 S), indicating that the potential for the entrance channel is quite different between the two species.

The ion desorption by carbon 1s electron excitation was studied for thin films of selectively deuterated polystyrene ([CD 2 CD(C 6 H 5 )-] n , [-CH 2 -CH(C 6 D 5 )(] n , and [-CD 2 -CD(C 6 D 5 )-] n ) using the ion time-of-flight method with monochromatic synchrotron radiation pulses. By comparing the photon energy dependence of partial ion yields (PIY's) of D + of these polymers, it was found that the observed D + originates mainly from the pendant phenyl group. Further we found that PIY spectra of D + are useful in discussing the origin of the absorption features by comparing with the total electron yield.

The polarization dependence of F K‐edge X‐ray absorption near edge structure (XANES) spectra of highly‐oriented thin‐film of polytetrafluoroethylene (PTFE) has been analyzed by using multiple scattering theory. The spectra show clear polarization dependence due to the highly‐oriented structure. The multiple scattering calculations reflects a local structure around an absorbing atom. The calculated results obtained by considering intermolecular‐interactions are in good agreement with the observed polarization‐dependence. We have also analyzed structural models of the radiation damaged PTFE films.

Changes in the work function (WF) and binding energy of the highest occupied molecular orbital (HOMO) level in a titanyl phthalocyanine-(OTiPc) graphite system were studied as a function of OTiPc coverage by ultraviolet photoelectron spectroscopy. We observed that the WF increases with the coverage of the oriented OTiPc until the formation of the monolayer, while the energy position of the HOMO level stays almost unchanged with respect to the Fermi level. By analyzing the observed coverage dependence of the WF using the Topping model, we estimated the electric dipole moment and polarizability of OTiPc in a monolayer.

The hole-vibration coupling of the highest occupied state in pentacene thin films on graphite is studied by high-resolution ultraviolet photoelectron spectroscopy. Vibration satellites in the film show a take-off-angle dependence, indicating that the Franck-Condon principle is not strictly satisfied in this system. They are more intense than in the gas phase and the vibrational energy in the film is slightly lower than that in the gas phase. This demonstrates that the reorganization energy in pentacene thin films is slightly larger than that estimated from the photoelectron spectrum of free pentacene molecules. Furthermore, it is pointed out that the electron hopping in the low-temperature film may occur in the femtosecond scale before the electronic polarization of the surrounding medium is completed. © 2005 The American Physical Society.

The effect of an interface dipole layer on the energy level alignment at organic-conductor interfaces is studied on a copper phthalocyanine (CuPc) monolayer/electric dipole layer/graphite system via ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy. An oriented monolayer of the OTi-phthalocyanine molecule, which has an electric dipole moment, is grown on graphite to yield a well-defined dipole layer with the vacuum side negatively charged. The CuPc monolayer is sequentially deposited on the dipole layer kept at $123\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This weakly interacting system made of a very thin organic layer on top of a very thin dipole layer is in thermodynamic equilibrium. The UPS data from the system grown with and without the interface dipole layer show that the binding energy of the highest occupied state of the CuPc monolayer decreases when the dipole layer is inserted. The binding energy shift is in excellent agreement with the increase in vacuum level energy of the graphite substrate upon deposition of the dipole layer. The results show that the Fermi level of the CuPc shifts toward the valence states when the interface dipole layer is inserted.

This article introduces our recent study on solid surfaces by metastable electron emission microscopy (MEEM) which is in principle selectively sensitive to outermost-surface electronic states. Examples of surface images by MEEM are shown for a SiO2 pattern on Si(100) and a microstructured thin film of organic semiconductor, chloroaluminum phthalocyanine (ClAlPc), on a MoS2 surface. The latter result demonstrates that very large organic molecule can diffuse on the surface. For the ClAlPc film, the results obtained by photoemission electron microscopy (PEEM) using photons near the threshold ionization energy of the target are also shown.

Metastable atom electron spectroscopy and ultraviolet photoelectron spectroscopy were used to characterize orientation of bisazomethine dye molecules (DE2) in thin films deposited on graphite and ITO. We found that the molecular orientation of DE2 in multilayers is largely different on these substrates. On graphite, the molecules lie flat in a monolayer and become standing up with increasing the film thickness, while on ITO they lie nearly flat independent of the film thickness.

The effect of the molecular orientation on the molecular electronic structure is studied on the Cu-phthalocyanine∕graphite system via film thickness dependences of metastable-atom electron spectra and ultraviolet photoelectron spectra. We observed a decrease in the vacuum-level position and a corresponding band-bending-like shift in the highest occupied state only for thick films where the molecular tilt angle increases gradually with the film thickness. These shifts are explained by electric dipoles produced in the film by a gradient of the intermolecular electronic interaction along the surface normal due to the continuous increase in the molecular tilt angle. The result indicates that the change in the molecular orientation is an important origin of the band-bending-like shift in the molecular electronic states even if the molecule has no permanent electric dipole.

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.

The molecular orientation at the surfaces of poly(2-vinylnaphthalene) thin films was studied by angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS study showed that pendant naphthalene groups are oriented with a tilt angle ( β ) of 57°, while the ARUPS study gave information on the tilt-angle distribution as well as the mean value (∼58°) of β . The mean value of β determined by ARUPS agrees well with that found in the NEXAFS study.

Low-energy-electron transmission (LEET) spectra were measured for graphite using electron energies below 30 eV. The observed LEET spectra have broadened square-wave-like features, and comparison with the conduction-band density of states above the vacuum level measured by ultraviolet photoemission and inverse photoemission spectroscopies indicated that the conduction-band density of states was not observed in the LEET spectra except band gaps. It is concluded that band gaps are more strongly reflected in LEET spectra than other features in the density-of-states. It is expected that electron-interference effects along the surface normal dominate LEET features, even for a very thick sample, where the energy dependence of electron-transmission probability through a one-dimensional periodic potential along the surface normal does not reflect the variation of the density of states (except band gaps).

The electronic structure and molecular orientation of tetratetracontane (n-C44H90) films on Cu(100) and Au(111) surfaces were investigated by angle-resolved UV photoemission spectroscopy (ARUPS) and low energy electron diffraction (LEED). The observed ARUPS spectra showed the drastic take-off angle dependence due to intramolecular band dispersion. A 2×1-like LEED pattern was observed for both substrates. From these results and theoretical simulation of ARUPS spectra based on independent-atomic center (IAC) approximation, we found that the C–C–C plane of the adsorbed TTC molecule is parallel to the substrate surface and its molecular axis is along a [110] direction for both substrates. We also measured the work function change by adsorption of TTC. The observed values were c.a. −0.3eV and −0.7eV for Cu(100) and Au(111) systems, respectively. Such decrease of the work function indicates the existence of a dipole layer at the interfaces in contrast to the traditional picture of energy level alignment at organic/metal interface assuming a common vacuum level at the interface. The dipole formation in such physisorbed systems can be explained by the polarization of the TTC molecule due to an image force.

Photon stimulated ion desorption (PSID) of thin films of selectively deuterated polystyrene ([ CD2 CD(C6H5) ]n,[ CH2 CH(C6D5) ]n and[ CD2 CD(C6D5) ]n) have been investigated to reveal the mechanism of surface photochemical reactions following core excitation. Desorbing ions were measured using the time-of-flight mass spectrometer (TOF-MS) combined with a pulsed synchrotron radiation. From the total electron yield spectrum and partial ion yield spectrum of each sample, it is concluded that D+ ions are mainly desorbed from the phenyl group and the yield of D+ is enhanced at the C D* resonance. From the ion kinetic energy distribution obtained from analysis of the TOF spectrum, the ions desorbed from the phenyl group have different kinetic energy distribution. The results are discussed in connection with the mechanism of PSID.