宮前 孝行

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.

Electronic structure of perfluorotetracosane [n-CF3(CF2)(22)CF3; 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.

Various systems formed by carbon and fluorine were studied by UV photoelectron spectroscopy (UPS), vacuum-ultraviolet (VUV) optical spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy New data were measured for poly(hexafluoro-1,3-butadiene) (PHFBD), which is actually poly(hexafluoro-2-butyne), and fluorinated graphites CE C2F, and C6F These data were analyzed together with reported data for n-C24F50, poly(tetrafluoroethylene) (PTFE), and fluorinated fullerenes C60Fx and C70Fx. The electronic structures deduced from UPS, VUV optical spectra and MO calculations could be understood in terms of degree of sigma delocalization, inductive effects of F and CF3 groups, and the molecular conformation with possible steric hindrance. The ionization threshold energy of PHFBD (10.3eV) is the largest one for unsaturated systems. The well polarized NEXAFS spectra of CF and C2F were analyzed by the comparison with related compounds. The NEXAFS results of C6F showed that the F atoms are neither in molecular farm nor covalently bonded to carbon atoms.

The surface morphology of Si(111) was investigated using scanning tunneling microscopy after desorption of surface SiO2 by synchrotron radiation illumination. The surface shows large regions of an atomically flat Si(111)-7 x 7 structure, and is characterized by the formation of single bilayer steps nicely registered to the crystal structure. This is in sharp contrast to Si(111) surfaces after thermal desorption of SiO2 at temperatures of 880 degrees C and above, where the surface steps are much more irregular. X-ray photoemission spectroscopy is also used to investigate the process of synchrotron radiation stimulated desorption. (C) 2000 American Vacuum Society. [S0734-2101(00)04304-9].

The surface morphology of Si(111) was investigated using scanning tunneling microscopy after desorption of surface SiO2 by synchrotron radiation (SR) illumination. The surface shows large regions of atomically flat Si(111)-7x7 structure, and is characterized by the formation of single bilayer steps nicely registered to the underlying crystal structure. This is in sharp contrast to Si(111) surfaces after thermal desorption of SiO2 at temperatures 880 degrees C and above, where the surface steps are much more irregular. The registration of the surface steps to the underlying crystal structure indicates that the Si(111) surface reaches thermodynamic equilibrium under SR irradiation at temperatures much lower than that necessary for thermal desorption. (C) 2000 American Institute of Physics. [S0003-6951(00)00511-8].

Angle-resolved ultraviolet photoelectron spectra were measured for oriented films of perfluorotetracosane, n-CF3(CF2)(22)CF3, as a model compound of poly(tetrafluoroethylene) using synchrotron radiation. The main spectral features showed continuous changes in both peak positions and intensities with photon energy, incident angle, and photoelectron take-off angle. The intramolecular energy-band dispersion of poly(tetrafluoroethylene) was mapped from the photo-energy dependence of the normal emission spectra. (C) 2000 American Institute of Physics. [S0021-9606(00)70206-6].

Synchrotron radiation (SR) stimulated desorption of silicon dioxide thin films was studied using scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and Auger electron spectroscopy. Reconstructed Si(111)-7X7 patterns were observed by LEED after 2 h SR irradiation at a surface temperature of 700 degrees C. The STM images show an atomically flat Si(111)-7X7 surface. STM topographs of SR-irradiated surfaces suggest that the oxide desorption; mechanism is completely different from that of thermal desorption of SiO2 film. These results indicate that the atomically flat Si surface can be obtained at low temperatures by using this technique. (C) 1999 American Vacuum Society. [S0734-2101(99)04804-6].

Temperture dependence of reflection spectra of iodine doped polyacetylene have been studied at 298 K and 10 K For wide spectral range. The spectra showed remarkable change at low temperature indicating that the mid gap band is increased while the band due to the free carrier is diminished. The change of the spectra is explained by the increase of the charged soliton structure or the bond alternation at low temperature. The result is consistent with the temperature dependence of electrical conductivity of doped polyacetylene.

The electronic structure and molecular orientation of a tetratetracontane (n-C44H90; TTC) ultrathin film on a Cu(100) surface were studied by angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) using synchrotron radiation. A well-oriented thin film of TTC was successfully prepared by vacuum evaporation in ultrahigh vacuum at room temperature. We observed a (2×1)-like low-energy electron-diffraction (LEED) pattern for the deposited TTC film. This result indicates that the TTC molecules lie on the Cu(100) surface in two types of domains, rectangular to each other, in which the alkyl-chain axes are along the [110] and [11¯0] directions of the Cu(100) surface. The application of the dipole selection rules to the normal-emission ARUPS spectrum revealed that the C–C–C plane of TTC is parallel to the Cu(100) surface plane (flat-on orientation). The intramolecular energy-band dispersion of TTC was examined by changing the take-off angle of emitted electron along the [110] direction of the Cu(100) surface. The observed results support the conclusion about the direction of alkyl-chain axes by LEED observation. In order to analyze the molecular orientation more quantitatively, we also performed theoretical simulations of the angle-resolved photoemission spectra using the independent-atomic-center (IAC) approximation combined with ab initio molecular-orbital (MO) calculations for various molecular orientations. The simulated spectra for flat-on orientation are in excellent agreement with the observed spectra. These results once again verify the deduced molecular orientation, and also demonstrate the reliability of theoretical simulation with the IAC/MO approximation for compounds without a p-electron system. Furthermore, we observed a work function change of about -0.3 eV by adsorption of TTC. Such a decrease of the work function indicates the formation of a dipole layer at the interface, in contrast to the traditional picture of energy-level alignment assuming a common vacuum level at the organic/metal interface. © 1999 The American Physical Society.

We have constructed a scanning tunneling microscopy (STM) system for the study of synchrotron radiation (SR) stimulated photochemical reactions. In order to eliminate the vibration and acoustic noise, the entire UHV chamber is mounted on a high-performance air-suspended vibration isolation table and was also covered by the soundproof mat. The mechanisms for SR stimulated desorption of SiO2 thin films on the Si(lll) surfaces have been investigated using the STM, low energy electron diffraction (LEED), and Auger electron spectroscopy. An atomically flat and clean Si(lll)-(7x7) surface was obtained after two hours SR irradiation at a surface temperature of 700 degrees C. The STM topograph suggests that the desorption mechanism may be completely different between thermal and SR stimulated desorption of SiO2 film.

Synchrotron radiation (SR) stimulated process, which has characteristics of high spatial, resolution and low damage, is suitable for nano-processes. Si (111) surface after removal of native oxide by SR stimulated desorption was atomically fiat with no damage. If the semiconductor surface is chemically modified and chemical bonds having a weak interaction with the substrate electronic states (a localized electronic state) are formed, for example, such as SiH2 and SiH3, they can be broken (etched) by the SR irradiations. Efficient site specific bond breaking, overwhelming the secondary electron effects, can be expected by a resonant excitations from a core electronic state to a dissociative valence electron state. The excitation energy and polarization tunability, which is unique characteristic of the SR process, will display its power in the nano-process applications which require the atom level control.

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 2x1-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. (C) 1999 Elsevier Science B.V. All rights reserved.

This is the first report of the use of scanning tunneling microscopy (STM) to study changes in the surface morphology during synchrotron-radiation (SR) stimulated desorption of SiO2 films on Si(111). An atomically flat surface was obtained after SR irradiation for 2 h at a surface temperature of 700 degrees C. The STM topograph indicates that the SR desorption mechanism is quite different from the thermal desorption of SiO2. The lack of formation of multi-step holes on the exposed silicon surface indicates that the desorption of oxygen atoms and molecules by SR excitation leaving volatile SiO is an important mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.

A multilayered-mirror (MLM) monochromator beam line designed specially for synchrotron radiation (SR) stimulated process experiments has been constructed for the first time. The beam line was designed by the criteria; a beam spot size on the sample surface greater than or equal to 3 x 3 mm(2), a density of total irradiated photons greater than or equal to 10(18) photons/cm(2) (for an irradiation time of a few tens of minutes to a few hours), and low-energy background less than or equal to 1% of the output. The performance of the beam line was evaluated by measuring the transmitted photon flux of an Al filter around the Al L-2,L-3 absorption edge and by measuring the photoemission spectra of Ta using the output beam as an excitation light source. The Al thin film deposition was successfully demonstrated by using the monochromatized output beam. We conclude that this MLM monochromator performs sufficiently well to study the excitation energy dependence in SR-stimulated processes. (C) 1999 American Institute of Physics. [S0034-6748(99)02606-4].

The electronic structure and molecular orientation of a tetratetracontane (n-C44H90; TTC) ultrathin film on a Cu(100) surface were studied by angle-resolved ultraviolet photoelectron spectroscopy (ARUPS using synchrotron radiation. A well-oriented thin film of TTC was successfully prepared by vacuum evaporation in ultrahigh vacuum at room temperature. We observed a(2x1)-like low-energy electron-diffraction (LEED) pattern for the deposited TTC film. This result indicates that the TTC molecules lie on the Cu(100) surface in two types of domains, rectangular to each other, in which the alkyl-chain axes are along the [110] and [1 (1) over bar 0] directions of the Cu(100) surface. The application of the dipole selection rules to the normal-emission ARUPS spectrum revealed that the C-C-C plane of TTC is parallel to the Cu(100) surface plane (flat-on orientation). The intramolecular energy-band dispersion of TTC was examined by changing the take-off angle of emitted electron along the [110] direction of the Cu(TOO) surface. The observed results support the conclusion about the direction of alkyl-chain axes by LEED observation. In order to analyze the molecular orientation more quantitatively, we also performed theoretical simulations of the angle-resolved photoemission spectra using the independent-atomic-center (LAC approximation combined with nb initio molecular-orbital th (MO) calculations for various molecular orientations. The simulated spectra for flat-on orientation are in excellent agreement with the observed spectra. These results once again verify the deduced molecular orientation, and also demonstrate the reliability of theoretical simulation with the LAC/MO approximation for compounds without a rr-electron system. Furthermore, we observed a work function change of about -0.3 eV by adsorption of TTC. Such a decrease of the work function indicates the formation of a dipole layer at the interface, in contrast to the traditional picture of energy-level alignment assuming a common vacuum level at the organic/metal interface.

The electronic structure and molecular orientation of tetratetracontane (n-C44H90; TTC) ultra-thin film on Cu(100) were studied by angle-resolved UPS (ARUPS). We observed 2x1 like LEED pattern at room temperature. This indicates that the TTC molecule lies on the Cu(100) surface with its chain asis parallel to the Cu[110] direction. The application of the dipole selection-rule to normal emission spectrum revealed that the C-C-C plane of TTC is parallel to the surface (flat-on orientation). We also examined the dependence of the photoemission spectra on the take-off angle, and observed clear one-dimensional intramolecular energy-band dispersion. The simulated spectra for flat-on orientation based on independent-atomic-center (IAC) approximation combined with ab initio MO calculations are in good agreement with the observed spectra. These results verify the deduced molecular orientation and demonstrate the reliability of theoretical simulation with IAC approximation.

The photon-energy dependences of photoemission intensities of C-60 were quantitatively calculated by the single-scattering approximation for the final state and the ab initio molecular orbital calculation for the initial state. The calculated results agreed well with the measured intensity oscillation in the photon-energy range of hv = 18-110 eV. The calculation by the plane-wave approximation for the final state also gave similar oscillations, which suggests that the oscillations are independent of the accuracy of the final state. These results indicated that the oscillations originate from the interference of photoelectron waves emanating from the 60 carbon atoms, i.e., the multicentered photoemission with the phase difference of each wave. Further, the analytical calculation with a simplified spherical-shell-like initial state revealed that the spherical structure of C-60 molecule and its large radius dominate the oscillations.

Angle-resolved UV photoelectron spectra were measured for thin films of chloroaluminum phthalocyanine deposited on cleaved MoS2 surfaces. The take-off angle (theta) dependence of the photoelectron intensity of the highest pi band showed a remarkable sharpening upon cooling the film, indicating that thermal excitation of molecular vibrations gives a considerable broadening of the photoelectron angular distribution. The theta dependence observed at similar to 120 K agrees well with that calculated.

Angle-resolved UV photoelectron spectra (ARUPS) were measured for thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) deposited on cleaved MoS2 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 similar to 8.9 eV, which is believed to originate from a pi state, showed a remarkably different a dependence from that of the pi band. A quantitative analysis of the observed a dependencies clearly indicates that (a) the feature at similar to 8.9 eV originates from the oxygen 2p non-bonding states and (b) the molecules lie flat on the substrate surface.

Ultraviolet photoelectron spectra of a higher fullerene C-102 has been measured with a synchrotron radiation light source. The photoelectron onset energy of pristine C-102 is 0.85 eV below the Fermi level (E-F), which is the smallest value among the pristine fullerenes reported so far. The spectra show intensity oscillation upon the incident photon energy change as do those of other fullerenes. Spectral change upon potassium doping has been observed with the hv = 20 and 40 eV incident photon energies. The 20 eV spectra reveal a formation of a new state between the E-F and the band derived from the highest occupied molecular orbital (HOMO) upon potassium doping. The onset position of the new state moves toward the E-F, but it does not cross the E-F. This indicates the semiconductive nature of potassium doped C-102. When the potassium is excessively doped to C-102, the lower binding energy bands above 5 eV become faint. In accordance with this phenomenon, the hv = 40 eV spectra show an appearance of four distinct structures between 5 and 14 eV, As these bands are considered to derive from pseudo pi-electrons, heavy potassium doping may correspond with reconstruction of the fullerene cage or decomposition of the cage structure. (C) 1998 Elsevier Science B.V.

The photon energy hv dependences of angle-resolved ultraviolet photoelectron spectra of C-60 were measured in the range of hv = 20-120 eV. They exhibited the same intensity oscillations as reported previously, and were compared with the calculated results. In the calculation we used the single-scattering approximation for the final state with the result of the STO-5G molecular orbital calculation for the initial state. The calculated hv dependences for the HOMO and NHOMO states agreed well with the measured results. This indicated that the oscillations originate from the interference of photoelectron waves emanating from the 60 carbon atoms. Farther, the analytical calculation with the simplified initial state revealed that the spherical shell like molecular structure of C-60 with its large radius is the essential factor for the oscillations. (C) 1998 Elsevier Science B.V.

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)-(root 13 x root 13, R = +/- 13.9 degrees)-BTQBT, and from the analysis of the photoelectron angular distributions, it was found that at the lattice points the molecules lie flat with azimuthal orientations of 19 degrees and 47 degrees with respect to each surface crystal axis of MoS2. On the basis of these results, the full structure of the thin film, the two-dimensional lattice, and full molecular orientations at the lattice points, is proposed. (C) 1997 American Institute of Physics.

We investigated the Hall effect, the transverse magnetoresistance, the optical reflectivity and the ultraviolet photoelectron spectra for Ist and 2nd stage KOx-GICs (G(4n)KO(x), stage number n = 1,2;x similar to 2) in order to clarify the transport properties and the electronic structures. The Hall effect and the magnetoresistance indicate that the electrical conduction in KOx-GICs is governed by the majority electron carriers with low mobility in graphitic rr bands and the minority hole carriers with high mobility in the intercalate bands, the latter of which originates mainly from the oxygen bands as suggested by the incident photon energy dependence of the ultraviolet photoelectron spectra. The optical reflectance spectra give the estimates of the Fermi energies, 1.9 eV and 1.35 eV for 1st and 2nd stage compounds, respectively, on the basis of the Drude-Lorentz model. The contribution of the intercalate hole carriers to the plasma frequency is small in good agreement with the Hall effect indicating the presence of minority hale carriers. These experimental findings suggest the contribution of the intercalate layer to the transport properties and the electronic structure around the Fermi level.

Ultraviolet photoelectron spectra were measured using synchrotron radiation for four kinds of pi-conjugated polymers, poly(pyridine-2,5-diyl)[Ppy], poly(2,2'-bipyridine-5,5'-diyl)[Pbpy], poly(2-methylantraquinone-1,4-diyl)[P(2Me-1,4-AQ)], and poly(antraquinone-1,5-diyl)[P(1,5-AQ)], which exhibit n-type electrically conducting properties. Upon K-doping of Pbpy, two new states appeared in the originally empty energy gap. This finding indicates that the bipolaron bands are formed in K-doped Pbpy. While K-doped Ppy also shows similar gap states, it requires higher dopant concentration to create bipolaron bands than in the case of K-doped Pbpy. The UPS spectra of K-doped P(2Me-1,4-AQ) also show similar gap states, while it is almost absent in K-doped P(1,5-AQ). The changes in electronic structure of these polymers are discussed based on the conformational difference between these polymers.

Photoelectron spectroscopy (XPS and UPS) studies have been applied to the investigation of active oxygen species of solid solution series LixNi2-xO2 with wide range of 0<x less than or equal to 1 for understanding the origin of high activity and C-2-selectivity of the oxidative coupling of methane. From the comparison of these spectral features, the surface oxygen of Li0.3Ni1.7O2 with a cubic structure was assigned to O2- species, while that of LiNiO2 with a hexagonal structure was attributed to O- species associated with the catalytic activity for the oxidative coupling of methane. From the relationship between these structures and the catalytic activity, it was inferred that the anisotropic layered superstructure of LiNiO2 largely affected the formation of the active oxygen species for the oxidative coupling reaction.

The UPS spectra of cis- and trans-polyacetylene were measured by careful treatment of fresh samples. This is the first UPS measurement of cis-polyacetylene (cis-transoid). Assignments of the observed spectra are given by comparing with energy levels of cis- and trans-C20H22 obtained by ab initio MO calculation. The change of UPS spectra upon stepwise perchlorate doping was measured; at first the intensity of the C2p pi band decreased and the whole band shifted to higher binding energy. By further doping, a new C2p pi band appeared close to the Fermi level E(F) when the conductivity reached 11 000 S/cm. These changes show insulator to metal transition accompanied with structural transformation. The UPS spectrum near E(F) showed a strong correlational effect characteristic of a low-dimensional conductor. The spectra of heavily perchlorate doped and potassium-doped polyacetylene near E(F) are analyzed by a theory of Kopietz, Meden, and Schonhammer (Phys. Rev. Lett. 1995, 74, 2997).

Sodium- and potassium-doped highly conducting polyacetylenes were studied by ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. Upon doping, the UPS spectra immediately show a large shift toward the higher binding energy side relative to E(F). At intermediate doping level, a new state is created in the empty energy gap region. The gap state in the UPS spectra is assigned to the charged soliton band. This is the first direct observation of emission from the charged soliton state in doped polyacetylene. At heavily doped level, the quasi-metallic density of states is found just below the Fermi level and the broadening of the UPS spectra occurs at the regions of C 2(p) and C 2(s) levels. However, no finite density of states was observed at the Fermi level in the case of unoriented polyacetylene. This result is in contrast to the case of oriented polyacetylene doped with perchlorate, where the existence of a finite density of states at E(F) is reported. The spectral shape of UPS near the Fermi level is in accordance with Tomonaga-Luttinger liquid model of strong electron correlated system. Ab initio molecular orbital calculations taking account of nearest-neighbor chain effect gives a good description of the UPS for all the C 2s, C 2p sigma, and C 2p pi bands.

The electrical conductivity of perchlorate doped polyacetylene was measured down to 1.5 K. The temperature dependence of conductivity was analyzed by Mott's three dimensional variable range hopping model. At the high (190 - 50 K) and low(15 K - 1.5 K) temperature regions, the plots of ln[sigma(T)T-1/2] showed linear relations to T--1/4 For the parallel direction to the stretching direction, the hopping distance and decay length of the localized state become larger with an increasing orientational order. The variable range hopping parameters indicate that the anisotropy of the conductivity arises from the hopping frequency factor.

The electrical conductivities of perchlorate-doped highly oriented polyacetylene films were measured from 290 to 1.5 K. The conductivity and its anisotropy were significantly enhanced by stretching. The value of the conductivity was 18000 S cm(-1) at 190 K, and remained at 14000 S cm(-1), even at 1.5 K. The extraordinary high conductivity at very low temperature showed that the him is really metallic. The temperature dependence of the conductivity could be expressed as the sum of two terms:One is almost a temperature-independent term, which may be due to a very weakly localized free carrier; the other is due to a three-dimensional variable-range hopping mechanism of a more localized carrier. The conduction mechanism is discussed in terms of the poison model of doped polyacetylene.

New-type polyacetylene, stretched and doped with perchlorate or iodine, shows a nearly metallic conductivity up to 2.5 × 104 S cm-1. The molecular structure of the heavily doped chain is discussed to understand the metallic state. Ab initio molecular orbital calculations of model complexes, reflection spectra and ultraviolet photoemission spectra (UPS) are studied at several dopant levels. The transitions from insulator to metal are discussed based on optical conductivity spectra (σ(ω)), which are obtained from the reflection spectra measured from the far-infrared to ultraviolet regions. The UPS of alkali metal-doped or perchlorate-doped polyacetylene thin films are measured finite density of states is found at the Fermi level in both heavily n-type and p-type doped films. The changes of UPS are correlated to the calculated energy levels of the charged soliton-antisoliton and polson-antipolson chains. These results are analyzed based on transitions in stages from pristine to charged soliton, then to polson chain in the isolated state, and finally to polson chains interacting three dimensionally. The importance of three-dimensional interaction is found in σ(ω), UPS and electrical conductivity analyzed by the variable range hopping model. © 1994.

The absorption, reflection and ultraviolet photoemission spectra (UPS) of thin films of polyacetylene doped with perchlorate ion or potassium are studied to find the mechanism of insulator to metal transition. The transition occurs by two steps, first the charged soliton chain showing the mid gap absorption is formed in the lightly doped film, and then the metallic state is found in the heavily doped film, which is composed of polson units. The strong far infrared absorption is spectral characteristic band of polson unit. The polson chain gives a metallic far infrared reflectance along the chain direction in the heavily doped film. In the heavily doped film a genuine metallic Fermi level is found in the UPS spectra. The results are interpretted by the molecular orbital calculation of doped polyacetylene which is presented in the accompanied paper.

Electronic structure of new type polyacetylene prepared by methods of Naarmann and Tsukamoto is studied by measuring absorption and reflection spectra from far infrared to visible regions. Optical conductivity spectra and dielectric functions are obtained by Kramers-Kronig transformation of reflectance. The spectra of stretched thin film show metallic behavior along the oriented chain. Since the metallic state is found only in the stretched film, not only one-dimensional interaction but the interaction between the chains seems important to realize metal. Dielectric function along the chain direction indicates that the screening effect may assist semiconductor to metal and metal to more metallic transitions in the oriented new polyacetylene.