石井 久夫

We have investigated in situ and in real-time the formation process of anodic porous alumina on silicon using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We have collected IR absorption spectra of the interface between a porous alumina film and a Si substrate to elucidate the chemical processes involved in the porous-alumina formation. On the basis of the detailed analysis of IRAS spectra together with the variation of the anodic current density, we demonstrate that the chemical process at the alumina-Si interface proceeds as follows: As the pore reaches the alumina-Si interfacial region, inhomogeneous etching takes place. It produces small holes or cracks in the "barrier layer" at the bottom of the alumina pore, and through those holes or cracks the electrolyte pours into the vicinity of the Si substrate surface to form SiO2 nanodots. With further anodization, oxidation of the Si substrate surface occurs and finally peels the porous alumina film off the Si substrate. IRAS data are consistent with the results of observation by a field emission scanning electron microscope. The present results show that MIR-IRAS is a powerful tool for in situ monitoring chemical processes at semiconductor-solution interfaces. (c) 2006 The Electrochemical Society.

In various organic electronic devices, interfaces formed by organic layers can play important roles. We have been studying various organic interfaces for clarifying their structure and electronic structure. In this talk, we will report our recent study of the effect of various types of doping for a variety of dopants - residual impurity, atmospheric gases, and metallic and organic intentional dopants. In particular, detailed and quantitative information about the effect of oxygen from the viewpoint of electronic structure was obtained for titanyl phthalocyanine (TiOPc), and the results corresponded well with the recent report of atmospheric effect on organic field effect transistor. © 2005 Materials Research Society.

We have developed a photoelectron yield Spectroscopy (PYS) apparatus which enables us to measure work functions of metal electrodes and ionization potentials (IPs) of organic electronic materials in both vacuum and atmospheric conditions. By using UV spectral light source purged by nitrogen gas and sub-pico ammeter for detecting photoelectrons, our apparatus can measure a wide range of IPs of organic materials including not only hole transporting materials but also electron transporting materials. We will report on the details of the apparatus as well as some examples of the measurements. In addition, the application of this technique to characterize the electronic structure of organic / metal interfaces will be also reported.

Well-ordered thin films of p-oligophenylenes, p-quaterphenyl (4P), p-quinquephenyl (5P) and p-sexiphenyl (6P), were prepared on a Cu(I 00) single crystal substrate by vacuum vapor deposition. Their structures were investigated by infrared reflection absorption spectroscopy (IRRAS) and low energy electron diffraction (LEED). In the monolayers, p-oligophenylenes are physisorbed with their axes parallel to the substrate and form a regular two-dimensional arrangement. This structure is unaltered even in multilayers up to a thickness of a few nanometers. In the potassium (K)-doped 4P films, on the other hand, the arrangement is disrupted due to the perturbation by the dopant. The IRRAS investigation including observed and calculated spectra suggests that the radical monoanions are formed upon low-level doping, followed by saturation of the radical monoanion concentration and appearance of the dianions on increasing the amount of K. (c) 2005 Elsevier B.V. All rights reserved.

In spite of recent extensive studies of organic field effect transistors (OFETs), the operation mechanism is not yet clear. Especially the origin of the carriers accumulated in channel of OFET should be clarified to discuss the performance of OFETs. We have to take care of impurity-induced-carriers as well as carriers injected from source and drain electrodes. The spread of the charge sheet at organic/dielectric interface is also critical to the FET performance. Thus an experimental technique to probe such behavior of carriers is highly required. In this study. we have proposed displacement current measurement (DCM) method as a tool to characterize OFETs. We found that this technique enables us to probe various properties in OFETs; the carrier injection from metal electrodes to organic materials, the effective area of charge sheet in the channel, and the amounts of carriers accumulated in the device. The results for pentacene and poly-3-hexylthiophene FETs are reported to discuss the relation between the carrier generation and FET performance.

It is widely accepted that atmospheric oxygen can work as an electron-accepting dopant mainly to p-type organic semiconductors. We have examined the effect of oxygen on a pentacene field effect transistor (FET) with and without exposure to light using the displacement current measurement. Under vacuum conditions, the change in the displacement current due to hole injection from the source and drain electrodes to the pentacene layer is clearly observed, suggesting that the origin of the mobile carriers in the pentacene FET is carrier injection. When the FET is exposed to oxygen under dark conditions, a very small change in the threshold gate voltage for hole injection is observed. In contrast, with exposure to both oxygen and light, we observed that the threshold voltage is lowered and shifted across the zero bias and even to the polarity against hole injection. This photoinduced doping effect induces a distinct increase in the drain current of the FET, and it is maintained for at least several hours even after the irradiation is turned off. This finding suggests that the performance of organic semiconductor devices is affected not only by atmospheric oxygen but also by ambient light even during the processing and storage of the devices. © 2005 American Institute of Physics.

Electronic structures of room-temperature ionic liquids (RILs) were studied by ultraviolet photoemission spectroscopy (UPS) with synchrotron radiation. The samples contain 1-buthyl-3-methylimidazolium ion [bmim](+) as the common organic cation, combined with fluorine-containing inorganic anions. We also performed molecular orbital (MO) calculations for the isolated ions. Comparing the calculated density of the states with the observed spectra, we found that the top of the valence states in the liquid salts is derived from the organic cation, although the highest occupied molecular orbitals (HOMOs) of the isolated anions are higher than that of the isolated cation. The Madelung energies at the surface region, which are probably responsible for this reversal, are estimated by comparison between UPS and MO calculation. We also simulated the observed spectra based on the independent-atomic-center (IAC) approximation. (c) 2005 Elsevier B.V. All rights reserved.

We report an ambipolar operation in field-effect transistors of C-60 and metallofullerene Dy @ C-82 by modification of semiconductor/metal electrode interface with perfluoroalkylsilane (FAS) molecules. Kelvin probe experiments revealed that the work function of the gold surface modified with FAS molecules increased by 0.55 eV as compared to the untreated gold. Hole injection into fullerenes is qualitatively understood in terms of this work-function change induced by the FAS molecules. The present results indicate that the charge injection from electrodes to organic semiconductors can be controlled simply by modification of semiconductor/metal interface without changing materials themselves. (c) 2005 American Institute of Physics.

In many organic electronic devices, interfaces formed by organic layers can play crucial roles. We have been studying various organic interfaces for clarifying the molecular arrangement and electronic structure. In this talk, we will report a few topics from our recent efforts for understanding these interfaces, namely (1) Theoretical calculations on interfaces formed by depositing long-chain alkanes on metals, and (2) Study of the effect of various types of doping for a variety of dopants - residual impurity, atmospheric gases, and metallic and organic intentional dopants. In particular, detailed and quantitative information about the effect of oxygen from the viewpoint of electronic structure was obtained for titanyl phthalocyanine (TiOPc), and the results corresponded well with the recent report of atmospheric effect on organic field effect transistor. © 2005 SID.

We investigated formation processes of a porous anodic alumina film on a p-type silicon (Si) substrate using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We observed drastic IR spectral changes when anodization took place near the interface between an aluminum (Al) layer and a Si substrate. The intensity of absorption peaks due to porous anodic alumina increased with a decrease in anodic current density and it decreased simultaneously with formation of silicon oxides (SiO2) at the interface between a porous anodic porous alumina film and a Si substrate after appearance of a spike of anodic current density which indicated changes of states of electric double layer at the interface between an electrolyte and an electrode due to contact between an electrolyte and a Si substrate. The results suggested that the formation of SiO2 nanodots on a Si substrate promoted penetration of electrolytes to peel the porous anodic alumina film from it. (C) 2004 Elsevier B.V. All rights reserved.

Recently high and persistent spontaneous buildup of a surface potential (SP) upon vacuum deposition of tris (8-hydroxyquinolinato) aluminum (III) (Alq(3)) which is widely used for organic light emitting devices, on a gold substrate under dark condition (28 V for 560-nm-thick Alq(3) film) has been reported. The removal of the giant surface potential by visible light irradiation has also been reported. These properties of Alq(3) film suggest potential applications to various organic devices such as memory. In this study, we investigated the retention time of the giant potential and the mechanism of the light-induced depolarization in order to discuss the feasibility of the device applications. The observed decay rate of the surface potential in vacuum condition was roughly 10% loss in 10 years, which is enough for memory devices. As to the decay rate by light-irradiation, the observed rate was successfully reproduced by a theoretical simulation based on the photo-induced randomization of oriented Alq(3) molecules. (C) 2004 Published by Elsevier B.V.

The analysis and control of interfaces between organic molecules and Si surfaces are basic issues for developing organic-inorganic hybrid devices. In this study, the adsorption of cata-condensed aromatics such as naphthalene, anthracene and pentacene on a Si(1 0 0)-2 x 1 surface was investigated by infrared reflection absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). It was found that the adsorption configuration of naphthalene is strongly dependent on the surface coverage. In contrast, larger aromatics such as anthracene and pentacene show less surface coverage dependence. The details of the adsorption configurations are discussed on the basis of frequency calculations performed with a density functional theory. (C) 2004 Published by Elsevier B.V.

Photopolymerization of cadmium 10,12-pentacosadiynoate (CdDA) in Langmuir-Blodgett (LB) films, with the molecular packing well arranged by moderate preannealing, was investigated with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Greenish films of polydiacetylene with an absorption wavelength of 705 nm were obtained through the photopolymerization of preannealed monomer LB films, and this resulted in an extended pi-conjugate system based on the well-ordered monomer in a two-dimensional arrangement. The electronic structures of the polydiacetylenes were found to be correlated to the variation of the molecular arrangements in the films from the changes in the NEXAFS spectra through photopolymerization in the LB films. (C) 2004 Wiley Periodicals, Inc.

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF2)(n); PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hnu) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hnu dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V-0, which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of -10 eV estimated in our previous study using the experimentally observed hnu dependence of the peak intensity. The estimation of V-0 was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V-0 was set at about zero. This value of V-0 is much different from the value of V-0=-10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V-0 from the peak intensity variation with hnu. Using the presently obtained V-0, we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V-0=-10 eV. (C) 2004 American Institute of Physics.

Band bending is a fundamental issue for discussing organic devices. Band bending with Fermi level alignment between semiconductors and metals are often assumed, although the validity of this scheme in the case of organic semiconductors has been not yet established. In this paper, our recent efforts to examine band bending in organic semiconductors using Kelvin probe method (KPM) are reported. After discussing the applicability of KPM to organic thick film - metal substrate system, the results for C-60, TPD, and Alq(3) are shown to discuss band bending of the films without intentional doping in ultrahigh vacuum condition. Gradual band bending was observed for C-60/metal interfaces although the width of the space charge layer is in the order of 100 nm. In contrast, flat band feature was observed for TPD/metal interfaces probably because of its high purity. These results demonstrate that the frame work of band bending used in inorganic semiconductor interfaces is still valid for organic semiconductors although much thicker films are often necessary to achieve bulk Fermi level alignment. For Alq(3)/ metal interfaces formed in dark condition, we found a new type of band bending where the energy levels change as a linear function of the distance from the interface. The observed location of the vacuum level was far below the Fermi level of the metal substrates, clearly indicating that Fermi level varies place by place in the system. Such electronically non-equilibrium state was quite stable for the order of years. The concept of Fermi level alignment is also discussed in relation to the observed energy diagrams. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The interaction between n-alkane and metal surfaces has been studied by means of density-functional theoretical calculations within a generalized gradient approximation (GGA). We demonstrate that although the GGA cannot reproduce the physisorption energy well, our calculations can reproduce the experimentally observed work-function change and softening of the CH stretching mode reasonably well. We also show that the most significant factor determining their dependence on metal substrates is the distance between the molecule and the substrate. © 2004 The American Physical Society.

We investigated formation processes of a porous anodic alumina film on a p-type silicon (Si) substrate using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We observed drastic IR spectral changes when porous anodic alumina film approached interfaces between an aluminum (Al) layer and a Si substrate. The intensity of the IR absorption peaks due to water (H2O) molecules and silicon oxides (SiO2) increased simultaneously with a spike of anodic current density. The IR spectral changes indicated that the penetration of electrolytes brought about inhomogeneous oxidation of a Si substrate surface. We observed that the arrangement of the SiO2 nanodots closely reflected that of pores of a porous anodic alumina film. IR absorption peaks due to porous anodic alumina finally disappeared. The formation of SiO2 nanodots on a Si substrate promoted penetration of electrolytes to peel the porous anodic alumina film off it.

Various models have been proposed, to date, to explain the improvement in organic electroluminescent devices by the insertion of an insulating layer such as LiF between the light emitting tris-(8-hydroxyquinolinato) aluminum (Alq(3)) layer and the cathode metal deposited on it. Although the average thickness of the LiF for the optimal performance is typically only 0.5 nm, the layer structure of the inserted LiF has been assumed explicitly or implicitly. In order to clarify the growth mode and electronic structure of LiF in the system, the Alq(3)-LiF-Al system was investigated by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and metastable atom electron spectroscopy (MAES). We found island formation of LiF on the Al substrate, and also that the Al surface is only partly covered when a 0.5-nm-thick LiF layer is deposited on it. MAES measurements revealed that island-grown LiF has density of states similar to that of a thick LiF layer except for the existence of defect states, which is probably due to Li vacancies near the interface-MAES also suggested a slight difference in the spatial extention of the wave function of LiF between a 0.5-nm-thick island and a 2.0-nm-thick film, while a distinct difference was found between LiF and Alq(3) films. These findings are important in order to discuss their attenuation lengths in relationship to electron injection. We have constructed a realistic energy diagram of the interface, taking account of the island nature of the 0.5-nm-thick LiF layer. This energy diagram suggests it is necessary to reexamine the proposed models.

The film structures of the long chain n-alkane n-C44H90 on Cu(1 0 0) and Cu(1 1 0) were investigated by infrared. reflection. absorption spectroscopy (IRRAS) and low energy electron diffraction (LEED). The first layer on Cu(1 0 0) consists, of the molecules oriented with the flat-on geometry where the carbon skeleton plane is parallel to the substrate. The molecular axes are arranged along [0 1 1] and [0- 1 1] directions. On the other hand, the molecules in the first layer on Cu(1 1 0), which also, adopt the flat-on geometry, are arranged with their molecular axes along only [1 - 10] direction, reflecting the in-plane anisotropy of the, substrate surface. Noticeable difference in molecular orientation in the multilayers was not observed between the two, substrates. The substrates affect only the first layers, and the surface symmetry restricts the molecular arrangement. (C) 2003 Elsevier Science B.V. All rights reserved.

This paper addresses the question of band bending at the C-60/metal interface. The change in the energy of the vacuum level relative to the Fermi level of the metal substrate E-vac(F) upon the deposition of C-60 on various metal substrates (Au, Cu, and Ag) was examined by the Kelvin probe method under ultrahigh vacuum as a function of C-60 thickness d. We observed (1) an abrupt shift of epsilon(vac)(F) at d less than or equal to 1 nm, to a uniform value of about 4.65 eV at all of the interfaces examined, and (2) a slower shift with further deposition of C-60, which stopped at d 500 nm at another common value. These abrupt and gradual shifts were ascribed to the formation of an interfacial dipole layer and to band bending leading to Fermi level alignment, respectively. We also examined the effect of air-exposed metal substrate and purification of C-60.

Au/fullerene(C-60)/SiO2/Si field effect transistor (FET) has been investigated to examine the behavior of carrier injection by using displacement current measurement (DCM) and infrared absorption spectroscopy in the multiple internal reflection (MIR-IRAS). At the first scan of DCM, an increasing displacement current due to electron injection was clearly observed above a threshold voltage in forward scan, while no flow-back of the injected electrons was observed, indicating that almost all electrons injected in the scan were trapped. The capacitance obtained from the increasing current suggests that the electrons injected from a Au electrode spread laterally along C-60/SiO2 to some extent. At the further scans of DCM, the threshold voltage was shifted to higher voltage, and the lateral spread of the electron was quite suppressed due to the space charge of the filled traps. These results clearly demonstrate that DCM is a useful method to examine the behavior of carriers in field effect transistor (FET) devices. The spectral change in MIR-IRAS observed under bias voltage for electron injection is also reported.

We report on the recent progress of our continued effort for the preparation and characterization of well oriented films of tetratetracontane (n-C44H90) and perfluorotetracosane (n-C24F50), which are good model molecules of fundamental polymers, polyethylene (CH2)(n) and poly(tetrafluoroethylen) (CF2)(n), vacuum-deposited on metal surfaces. When the surface of the metal substrate was oxidized, the deposited chain molecules are aligned with their molecular axes vertically standing on the surface, while they lie flat on the surface when atomically clean Cu(100) surface was used. In the case of n-C44H90 on Cu (100), low-energy electron diffraction (LEED) studies revealed that the molecules were also azimuthally aligned with the chain axis almost parallel with the <100> and <010> axis, and infrared reflection-absorption spectroscopy (IR-RAS) enabled detailed studies of the film structure at increasing film thickness.-By applying the technique of angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) to these flat-lying molecules, the intramolecular energy-band dispersion relation could be determined, The results agreed well with the results deduced from the previous work using vertically standing molecules assuming an inner potential V-0. of -5 eV, confirming the validity of the estimation of V-0. Excellent agreement was found between the observed and simulated spectra using the independent-atomic-center (IAC) approximation. Also the value of the vacuum level shift by molecular deposition was deduced for TTC/Cu(100) system to be -0.3 cV. As for n-C24F50, the E(k) relation deduced in our previous study using vertically standing molecules showed discrepancy with band calculations. The detailed reexamination of the experimental data using IAC calculations for the previous report gave more realistic estimation of V-0, and the newly deduced E(k) relation using this data showed good correspondence with theoretical band calculations, thus removing the difficulty in the previous work.

Recently we found high and persistent spontaneous buildup of the surface potential upon vacuum vapor deposition of tris(8-hydroxyquinolinato) aluminum(III)(Alq(3)) on Au substrate under dark conditions (28 V for 560 nm thick Alq(3) film). Such giant potential is removed by visible-light irradiation. These natures of the film suggest the possible applications to various organic devices such as memory devices. In this study, we investigated the retention time of the giant potential and the mechanism of the light-induced depolarization in order to discuss the feasibility of the device applications. The observed decay rate of the surface potential in vacuum condition was roughly 10 % loss in 10 years, which is enough for memory devices. As to the decay rate by light-irradiation, the observed rate was successfully reproduced by a theoretical simulation based on the photo-induced randomization of oriented Alq(3) molecules.

Interfacial band offset and band bending of organic semiconductors are critical to understand and improve organic photovoltaic cells. In this study, the energy level alignment of fullerene(C-60)/metal-free phthalocyanine (H2Pc) interface which is one of the model interfaces of organic photovoltaic cells has been investigated using UV and X-ray photoemissions. For both 'H2Pc on C-60' and "C-60 on H2Pc' interfaces, 0.3 eV downward energy level shift was observed in XPS at the interface formation. This energy shift is quite steep in contrast to the band bending observed for metal interfaces in our previous study, where thickness of 500nm was required to achieve 0.21eV band bending to get Fermi level alignment between metal electrode and C-60. To clarify the origin of the band bending, the effect of the insertion Of C-60-H2Pc co-deposited layer between Go and H2Pc layers was also investigated. The result suggested that possible doping of H2Pc to C-60 is not main origin of the observed energy shift. We also found that the vacuum level shift at H2Pc/C-60 interface is strongly dependent on the deposition sequence of the interface formation.

Anisotropic alignment of polyimide chains induced by linearly polarized deep UV (LPDUV) irradiation was studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the total electron yield (TEY) and partial electron yield (PEY) acquisition modes. The degree of the alignment manifested by the intensity of O K-edge pi* resonance of a C=O group is noticeably higher in the PEY acquisition mode than in the TEY one. The maximum anisotropy (linear dichroic ratio similar to10%) in the former case is observed at a lower exposure (similar to0.6 J/cm(2)) than in the latter case (similar to2 J/cm(2)). Considering the difference in electron escape depth between PEY (similar to2 nm) and TEY (similar to3.5 nm), we can conclude that the LPDUV-irradiated polyimide film exhibits depth dependence of anisotropy. The irradiation dependence of the PEY-derived anisotropy and the order parameter of liquid crystals (LC) showed good agreement, indicating that the anisotropy in the surface region is of major importance for LC alignment.

This study addresses the question of band bending at the C-60/metal interface. The change in the energy of the vacuum level upon the deposition of C-60 on various metal substrates (Au, Cu, and Ag) was examined by the Kelvin probe method under ultrahigh vacuum as a function of C-60 thickness d. We observed (1) an abrupt shift of the energy of the vacuum level relative to the Fermi level of the metal substrate epsilon(vac)(F) at dless than or equal to1 nm, to a uniform value of about 4.65 eV at all of the interfaces examined and (2) a slower shift with further deposition of C-60, which stopped at dsimilar to500 nm at another common value. These abrupt and gradual shifts can be ascribed to the formation of an interfacial dipole layer and to band bending leading to Fermi level alignment, respectively. The value of epsilon(vac)(F) for the thick region is ascribed to the bulk work function of the specific specimen studied, and it is noted that the values reported for a few monolayers in the literature should not actually be regarded as the bulk work function. These results clearly demonstrate the necessity of detailed measurements of epsilon(vac)(F) up to a large thickness of the organic film and of using various metal substrates to determine the bulk work function. The convergence of epsilon(vac)(F) to a common value at a large thickness indicates the existence of remaining impurity. Its concentration was estimated and the effect of purification by sublimation was examined. We note that the bulk work functions obtained as the convergent values in such measurements are characteristic of specific specimens and may still not correspond to the value of the really intrinsic material. (C) 2002 American Institute of Physics.

Structures of a film of a long-chain n-alkane, tetratetracontane (n-C44H90; TTC) on a Cu(100) single-crystal surface were investigated by a combination of infrared reflection absorption spectroscopy (IRRAS) and low energy electron diffraction (LEED). Vacuum vapor deposition was used to prepare epitaxially grown films. Measurements of the stepwise increase in film thickness revealed the structural changes in TTC film during film growth. IRRAS investigations revealed that three phases appear during film growth, as previously observed for TTC deposited on Au(111) and Ag(111) surfaces. In the first layer, which consists of TTC molecules directly adsorbed on a Cu(100) surface, the molecules assume a flat-on structure with the carbon skeleton plane of TTC parallel to the surface (flat-on phase). The next layer consists of slightly disordered molecules including a gauche conformation (gauche phase). Finally, a film with molecular packing close to that in the crystalline state is formed with further deposition (quasi-crystalline phase). LEED investigations indicated that (1) the first layer forms a regular unit cell with a lamellar structure, (2) the molecular arrangement shows a transition upon the completion of the first layer, which can be ascribed to subdivision of the lamella into antiphase domains, and (3) the surfaces of the gauche and quasi-crystalline phases do not have two dimensional order. Since the molecule itself has a one-dimensional periodic structure, it is necessary to consider both the intramolecular and intermolecular periodicity for detailed analysis by LEED. Simulation of the LEED pattern by a kinematic theory indicated that the intramolecular rather than the intermolecular periodicity dominates the LEED pattern. (C) 2002 Elsevier Science B.V. All rights reserved.

The interaction between Alq(3) and potassium was studied by using Raman and infrared spectroscopies. Infrared reflection absorption spectroscopy (MAS) spectra of Alq(3) films show significant changes after potassium deposition, such as the appearance of new bands and changes in relative intensity. Surface-enhanced Raman scattering (SERS) spectra obtained using the 413.1 nm. line of a Kr+ laser reveal similar changes. Changes are even more obvious when the 530.9 nm line was used for excitation. Changes in the SERS for excitation with the 413.1 nm line are less obvious due to a strong photoluminescence. The vibrational pattern of potassium-doped Alq(3) cannot be explained by the formation of radical anion by simple charge transfer, indicating the excess electron is not delocalized over the molecule. The observed spectral change suggests that the potassium atom interacts with both nitrogen and oxygen atoms of Alq(3) molecule. (C) 2002 Elsevier Science B.V. All rights reserved.

Surface-enhanced Raman scattering (SERS) spectroscopy is applied to study in situ the interface formation of silver on thin Alq(3) films. The changes in the frequencies of Alq(3) vibrational modes are moderate and their line-shape is preserved upon Ag deposition. Moreover, a good correspondence appears between the SERS and powder spectra and frequencies predicted by density functional calculations for the meridianal isomer. The behaviour of Raman spectra indicates that no chemical interaction occurs between the Ag atoms and Alq(3) Molecules. (C) 2002 Elsevier Science B.V. All rights reserved.

The interface of the tris (8-hydroxyquinoline) aluminum (Alq(3))/LiF/Al system was investigated with ultraviolet photoelectron spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and X-ray photoelectron spectroscopy (XPS). Strong chemical interaction was observed at Alq(3) on Al interface. By inserting a LiF layer, this interaction is suppressed and interface energy level alignment is changed to reduce a barrier for electron injection. The enhancement of device efficiency is ascribed to these phenomena. The importance of the combined use of various techniques on the same interface is stressed.

Electronic structure of perfluorotetracosane [n- CF ₃ ( CF ₂)₂₂ CF ₃; PFT], which is an oligomer of poly(tetrafluoroethylene) (PTFE), was investigated by angle-resolved photoemission spectroscopy (ARUPS) with synchrotron radiation. Theoretical simulations of ARUPS spectra were also performed by the independent atomic center (IAC) approximation combined with ab initio molecular orbital (MO) calculations. Measured normal-emission spectra for end-on oriented (the long-chain axis of PFT is perpendicular to the surface) films showed an incident photon energy dependence due to the intramolecular energy band dispersion. The energy band structure along the long-chain direction of PFT obtained from measured and calculated spectra is also discussed.

In near edge X-ray absorption fine structure (NEXAFS) spectra of carbon (C) and nitrogen (N) K-edge regions were measured for the stable radical compound lithium phthalocyanine (LiPc). The observed spectra were compared with those of metal free Pc ( H ₂ Pc ), copper Pc (CuPc), and zinc Pc (ZnPc). The spectral features in the C K-edge region of LiPc were different from those of other Pcs in the low photon energy region. An additional peak around 283.5 eV was observed only in the spectrum of LiPc. On the other hand, the spectral features of these MPcs in the N K-edge region were similar and did not show a corresponding extra peak. These results were explained by the patterns of molecular orbitals of these Pcs and the selection rules of X-ray absorption in the localized core-hole picture. The extra peak observed in the C K-edge region is assigned to the excitation from C1s to the highest occupied molecular orbital (HOMO), which is only singly occupied due to the radical nature of the phthalocyanine ring. Group-theoretical consideration indicated that the transition from N1s to the HOMO is not allowed, and this explains the lack of an extra peak at the N K-edge.

The molecular alignments in transfered films of comb polymers with fluorocarbon side chains of various lengths and various atoms were investigated. The polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used for investigating the X- and Z-type monolayers and multilayer films. The characteristics of the fluorinated polymers are related to the orientation of fluorocarbons in films.

Layer structures and the molecular packing in the two-dimensional lattice were studied by using the in-plane X-ray diffractions in addition to the conventional small-angle XRD, and the polarized near-edge X-ray absorption fine structure (NEXAFS) spectra for the multilayers of fluorinated amphiphiles with vinyl groups and their comb-polymers containing fluorocarbons as the side-chains. These molecular lattices were significantly different from the bulk crystals due to the film compression.. and NEXAFS results show that the molecular arrangements of the fluorocarbon sidechains were strongly influenced by atoms at the omega -position of the fluorocarbon-chains. (C) 2001 Elsevier Science B.V. All rights reserved.

The average near-surface orientation of the main and side chains of polyimide (Pl) for liquid crystal (L-C) alignment has been studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A detailed analysis of the angular dependences of resonance intensities revealed that rubbing causes the inclination of the main chain with respect to the surface, the angle of which decreases with increasing rubbing strength. This variation was found to agree with the decrease of the LC pretilt angle in the cell fabricated with this PI surface. The relation between the surface tilt of the main chain and the pretilt of LC is almost the same for PI films with side chains. Thus, it is concluded that the main chain alignment is strongly correlated with the pretilt angle even in the side-chain PI alignment layer.