Imaging of electronic structure of lead phthalocyanine films studied by combined use of PEEM and Micro-UPS

Yamamoto, Izumi; Matsuura, N.; Mikamori, Manabu; Yamamoto, Ryōta; Yamada, Takashi; Miyakubo, Keisuke; Ueno, Nobuo; Munakata, Toshiaki

doi:10.1016/j.susc.2008.04.037

Cited by 26 publications

(26 citation statements)

References 16 publications

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“…Thus, one must prepare a uniform molecular monolayer to attain high-resolution UPS. Although islands of molecules with orientations different to the monolayer region grow at defects/step bunches of the substrate surface, the islands may be selectively cleaned away by appropriate heat treatment after deposition of a thicker molecular layer, as observed with photoemission electron microscopy (PEEM) [31,32]. From our experience, the detection of vibration satellites with UPS, which appear as skewed asymmetric line shape as seen in Figs.…”

Section: How To Realize Fine Feature Measurementmentioning

confidence: 82%

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

Kera

Ueno

2015

Journal of Electron Spectroscopy and Related Phenomena

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a b s t r a c tUnderstanding of electron-phonon coupling as well as intermolecular interaction is required to discuss the mobility of charge carrier in functional molecular solids. This article summarizes recent progress in direct measurements of valence hole-vibration coupling in ultrathin films of organic semiconductors by using ultraviolet photoelectron spectroscopy (UPS). The experimental study of hole-vibration coupling of the highest occupied molecular orbital (HOMO) state in ordered monolayer film by UPS is essential to comprehend hole-hopping transport and small-polaron related transport in organic semiconductors. Only careful measurements can attain the high-resolution spectra and provide key parameters in holetransport dynamics, namely the charge reorganization energy and small polaron binding energy. Analyses methods of the UPS HOMO fine feature and resulting charge reorganization energy and small polaron binding energy are described for pentacene and perfluoropentacene films. Difference between thin-film and gas-phase results is discussed by using newly measured high-quality gas-phase spectra of pentacene. Methodology for achieving high-resolution UPS measurements for molecular films is also described.

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Section: How To Realize Fine Feature Measurementmentioning

confidence: 82%

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

Kera

Ueno

2015

Journal of Electron Spectroscopy and Related Phenomena

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“…Absolute work function data for graphene bilayers are scarce and only one other value for TaC (111) could be found [48]. For graphite a work function of 4.49 eV was reported recently [47] in good agreement with other work [37,49]. Obviously, the work function for graphene on graphite must be identical to the one of graphite implying a chemical shift of zero.…”

Section: Work Functionmentioning

confidence: 86%

Two-photon photoemission from image-potential states of epitaxial graphene

et al. 2015

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Using angle-and time-resolved two-photon photoelectron spectroscopy we observe a single series of image-potential states of graphene on monolayer (MLG) and bilayer graphene (BLG) on SiC(0001). The first image-potential state on MLG (BLG) has a binding energy of 0.93 eV (0.84 eV). Lifetimes of the first three image-potential states of MLG are 9, 44 and 110 fs. On hydrogen-intercalated, quasifreestanding graphene no unoccupied states are observed. We attribute this to the absence of occupied initial states for direct transitions into image-potential states at photon energies below the work function used in two-photon photoemission. The work function varies between 4.14 and 4.79 eV, but the vacuum level stays ∼4.5 eV above the Dirac point for all surfaces studied. This finding suggests that direct excitation of image-potential states cannot be achieved by doping and the electron dynamics for free-standing graphene is not accessible by two-photon photoemission using photon energies below the work function.

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“…These differences imply that both films are basically regarded as the same structure at the bilayer coverage δ, but the molecules in the AG bilayer film are much less ordered or oriented than in the AN bilayer film, 10 as has been observed also for PbPc/HOPG. 43 This structural difference in the initial film growth is a key for the resulting band bending in thicker AG films, as described below. Fig.…”

Section: Methodsmentioning

confidence: 98%

“…[33][34][35][36][37][38][39][40]42 Moreover, a combination study of microspot UPS and photoemission electron microscopy on a PbPc/HOPG system indicated that both the as-grown (AG) and annealed (AN) bilayer islands or domains have essentially the same stacked structure but with different molecular packing and domain sizes; the AG (AN) film can be regarded as short-range-ordered loosely packed (long-range-ordered closely packed) film. 43 In this paper, we aim to clarify how such a structural difference in ultrathin films of p-MPc influences the thicker film structure on HOPG and the resulting ELA as well as bandbending phenomena. Chlorogallium Pc [ClGaPc, Fig.…”

Section: Introductionmentioning

confidence: 99%

Impact of structural imperfections on the energy-level alignment in organic films

et al. 2011

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This paper reports that structural imperfection in an organic thin film modulates the electronic structure to result in a serious band bending and change in the energy-level alignment (ELA) at the organic-conductor interface. Ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) were adopted to investigate thickness dependences of the electronic structure of polar phthalocyanine (chlorogallium phthalocyanine) thin films grown on graphite with respect to the film structure. We observed a large bandbending-like shift of occupied molecular-orbital bands toward the Fermi level and a continuous increase in the vacuum level for the as-grown film, whereas these phenomena were considerably suppressed by annealing the film. Both the as-grown and annealed films were characterized as essentially the same stacked bilayer film structure; however, high-resolution UPS and MAES measurements evidenced that there are structural defects in the as-grown film but not clearly in the annealed film, indicating that the defects are the origin of the modulation of the ELA and the band bending. Controlling the structural imperfections is a key issue for the desired ELA in organic devices.

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Imaging of electronic structure of lead phthalocyanine films studied by combined use of PEEM and Micro-UPS

Cited by 26 publications

References 16 publications

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

Two-photon photoemission from image-potential states of epitaxial graphene

Impact of structural imperfections on the energy-level alignment in organic films

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