NEXAFS spectroscopic studies of molecular orientation in α-sexithienyl evaporated thin films on metal films

Okajima, Toshihiro; Narioka, S.; Tanimura, Sachiko; Hamano, Kouji; Kurata, Tetsuyuki; Uehara, Yasushi; Araki, Tohru; Ishii, Hisao; Ouchi, Yukio; Seki, Kazuhiko; Ogama, Tetsuo; Koezuka, Hiroshi

doi:10.1016/s0368-2048(96)80103-4

Cited by 28 publications

(11 citation statements)

References 14 publications

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“…The TP molecule has π-electrons, and the NEXAFS spectrum of the TP molecule in the gas phase and multilayer film shows a strong π* transition peak at 285.8 eV. 18,33,34 However, the spectrum of the TP SAMs shown in Figure 3b shows a much weaker peak at this energy. This means that the π-electron system of TP molecules is significantly modified on the Au(111) surface, indicating strong interaction between the π orbital and the Au surface.…”

Section: Stm Images Inmentioning

confidence: 99%

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

2009

Bulletin of the Korean Chemical Society

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Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 × 2√3) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and π-conjugated TP ring in the SAMs were calculated to be about 30 o and 40 o , respectively, from the surface normal. It was also observed that the π* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between π-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.

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Section: Stm Images Inmentioning

confidence: 99%

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

2009

Bulletin of the Korean Chemical Society

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“…For instance, a-sexithiophene (6T) has been found to form well-ordered films with molecules flat-lying on Au films while tilted by about 701 with respect to the surface plane on Ag and Cu films, respectively. 15 Since the quality and the properties of these interfaces are substantially dominated by the adsorption of the first molecular layer, it is important to gain detailed information on its geometry. Although the adsorption behavior of 6T on different metal surfaces has been intensively studied, [16][17][18][19][20][21][22][23][24][25] so far only two recent scanning tunneling microscopy (STM) studies investigated the adsorption of 8T on Cu(111) 26 and Au(111).…”

Section: Introductionmentioning

confidence: 99%

Coverage-dependent adsorption geometry of octithiophene on Au(111)

Varene

Bogner

Meyer

et al. 2012

Phys. Chem. Chem. Phys.

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The adsorption behavior of α-octithiophene (8T) on the Au(111) surface as a function of 8T coverage has been studied with low-temperature scanning tunneling microscopy, high resolution electron energy loss spectroscopy as well as with angle-resolved two-photon photoemission and ultraviolet photoemission spectroscopy. In the sub-monolayer regime 8T adopts a flat-lying adsorption geometry. Upon reaching the monolayer coverage the orientation of 8T molecules changes towards a tilted configuration, with the long molecular axis parallel to the surface plane, facilitating attractive intermolecular π-π-interactions. The photoemission intensity from the highest occupied molecular orbitals (HOMO and HOMO - 1) possesses a strong dependence on the adsorption geometry due to the direction of the involved transition dipole moment for the respective photoemission process. The change in molecular orientation as a function of coverage in the first molecular layer mirrors the delicate balance between intermolecular and molecule/substrate interactions. Fine tuning of these interactions opens up the possibility to control the molecular structure and accordingly the desirable functionality.

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“…Exceptions from the interaction-strength model, such as the upright molecular orientation in films grown onto polycrystalline and non-oxidized metallic surfaces (Au, Ag, and Cu) were substantiated by the higher roughness of the polycrystalline surfaces compared to the single-crystal surfaces [33][34][35]. Though, the interaction-strength model implicates further inconsistencies.…”

Section: Control Of Molecular Orientationmentioning

confidence: 94%

Practical photoemission characterization of molecular films and related interfaces

Ivančo

2014

Preprint

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Even though the term 'organic electronics' evokes rather organic devices, a significant part of its scope deals with physical properties of 'active elements' such as organic films and interfaces. Examination of the film growth and the evolution of the interface formation are particularly needful for the understanding a mechanism controlling their final properties. Performing such experiments in an ultra-high vacuum allows both to 'stretch' the time scale for pseudo real-time observations and to control properties of the probed systems on the atomic level. Photoemission technique probes directly electronic and chemical structure and it has thereby established among major tools employed in the field.This review primarily focuses to electronic properties of oligomeric molecular films and their interfaces examined by photoemission. Yet, it does not aspire after a complete overview on the topic; it rather aims to otherwise standard issues encountered at the photoemission characterization and analysis of the organic materials, though requiring to consider particularities of molecular films in terms of the growth, electronic properties, and their characterization and analysis. In particular, the fundamental electronic parameters of molecular films such as the work function, the ionization energy, and the interfacial energy level alignment, and their interplay, will be pursued with considering often neglected influence of the molecular orientation. Further, the implication on the band bending in molecular films based on photoemission characterization, and a model on the driving mechanism for the interfacial energy level alignment will be addressed.

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NEXAFS spectroscopic studies of molecular orientation in α-sexithienyl evaporated thin films on metal films

Cited by 28 publications

References 14 publications

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

Coverage-dependent adsorption geometry of octithiophene on Au(111)

Practical photoemission characterization of molecular films and related interfaces

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