Organic Molecular Beam Deposition of α-Sexithienyl

Hamano, Kouji; Kurata, Tetsuyuki; Kubota, Shigeru; Koezuka, Hiroshi

doi:10.1143/jjap.33.l1031

Cited by 62 publications

(35 citation statements)

References 21 publications

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“…If we now restrict the study to films with granular structure we have shown that during deposition the grain size and ordering within the grains increases rapidly with increasing substrate temperature [29,37,69]. In all cases, the height of the steps of the films morphology measured by AFM show that, whatever the dimensions of the grains, T 6 molecules are standing approximately upright on the substrate.…”

Section: Morphology-dependent Polarization Of Fluorescence and Electrmentioning

confidence: 92%

“…I 1,1 is the interaction exchange integral between translationally equivalent molecules I 1Y1 hU Ã 1 U 1 jV 1Y1 jU 1 U Ã 1 i, where the operator V 1,1 is the intermolecular potential energy), while I 1,2 , I 1,3 , and I 1,4 are the interaction exchange integrals between translationally non-equivalent molecules. The simplified excitonic molecule model [27] predicted a splitting as large as 1 eV of the 1 1 B u molecular level [28,29,156 6 Electronic Structure and Energy Transfer in Solid a-Sexithienyl 30]. A more refined approach uses the two-centers potential expansion, which considers the interaction between point multipoles located at the centers of the two charge distributions.…”

Section: Single Crystal Electronic Structurementioning

confidence: 99%

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Electronic Structure and Energy Transfer in Solid α‐Sexithienyl

Taliani¹,

Biscarini²,

Muccini³

1999

Semiconducting Polymers

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Semiconducting conjugated polymers have been widely studied over the last twenty years for their unique electronic and optical properties, which fundamentally reside on the delocalized p-electron structure. In the early stages of the study of conjugated polymers it was thought that the p-conjugated backbone would provide the pathway for coherent electronic transport within the macromolecular unit. Further studies showed, however, that real polymers have a finite distribution of conjugated chain lengths and it became clear that electron transport would ultimately be limited by interchain hopping. Other trapping centers for electron transport are chemical defects of the macromolecular ensemble as well as morphological disorder of the material. It was at this stage that the use of oligomers had the first impulse and was widely considered a valuable route to the understanding of the intrinsic properties of conjugated polymers. In the early nineties the development of organic field effect transistors (FET), based on a-sexithienyl (T 6 ) by Garnier et al. [1,2] and confirmed soon after by Ostoja et al. [3] and Dodabalapur et al. [4], clearly indicated that the availability of chemically pure and ordered solids was the requisite to achieve reasonable working conditions for the FET operation. This finding opened the avenue for the development of the so-called plastic electronics. Disorder moreover is detrimental not only to electric transport but also, to a lesser extent, energy transport. Both charge and energy transport are among the basic steps in the operation of the organic light emitting diodes (OLED) [5,6]. Recombination is followed by energy transfer within the manifold of the excited electronic states leading ultimately to an exciton. The notion of excitons as lowest excitations in conjugated solids is now universally accepted since the emission of OLED is molecular in character as opposed to band-to-band radiative electron-hole recombination. Excitons in molecular crystals were extensively studied over the last decades [7,8]. Anisotropic intermolecular interactions in the ordered molecular solids were shown to allow the formation of collective Bloch electronic excitations (Frenkel excitons) in which the excitation is strongly bound to the molecular entity and therefore is called tight bound exciton as opposed to the weakly bound exciton (Wannier exciton) in inorganic semiconductors. Nevertheless, the excitonic band structure of conjugated oligomers is not known and the relative energy of the lowest singlet Semiconducting Polymers: Chemistry, Physics and Engineering. Edited by G. Hadziioannou and P. F. van Hutten

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Section: Morphology-dependent Polarization Of Fluorescence and Electrmentioning

confidence: 92%

Section: Single Crystal Electronic Structurementioning

confidence: 99%

Electronic Structure and Energy Transfer in Solid α‐Sexithienyl

Taliani¹,

Biscarini²,

Muccini³

1999

Semiconducting Polymers

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“…3 The standing structure was also reported by other groups. 4 Compared with the oligothiophenes on insulating substrates, there has been little investigation of oligothiophenes on metal substrates. Recently, however, studies of organic films on metal substrates have begun to investigate the organic-metal interaction.…”

Section: Introductionmentioning

confidence: 99%

Temperature and thickness dependence of molecular orientation of α-sexithienyl on Cu(111)

Kiguchi

Yoshikawa

Saiki

2003

Journal of Applied Physics

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Atomic and electronic structures of α-sexithienyl(6 T) films grown on Cu(111) were studied by near edge x-ray absorption fine structure (NEXAFS) and S 1s x-ray photoemission spectroscopies. The polarization dependent NEXAFS indicated highly ordered arrays of 6 T molecules, with their molecular long axes parallel to the surface, at substrate temperatures lower than 300 K. On the other hand, their molecular long axes became normal to the surface at 360 K, while they initially adsorbed with their long axes parallel to the surface. The film thickness and substrate temperature dependence of the molecular orientation is discussed in terms of the van der Waals interaction between 6 T and Cu(111) and the kinetics of the growth process. It is demonstrated that the molecular orientation of the promising organic semiconductor 6 T can be controlled by substrate temperature.

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“…Among organic molecules, ␣-hexathiophene (T6) is a well-characterized prototypical compound for polyconjugated systems. [5][6][7][8][9][10][11][12] Furthermore, T6 possesses interesting properties of hole injection into highly fluorescent polymers. 13 It is then of utmost importance, in order to engineer new materials with suitable optoelectronic properties, to understand the essential processes in which T6 molecules form solid structures and to what extent their order can be driven by the substrate structure.…”

mentioning

confidence: 99%

Ordering of a prototypical conjugated molecular system during monolayer growth on the (1×2)-Au(110) surface

et al. 1996

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The UHV deposition of ␣-hexathiophene (T6) oligomers on the 1ϫ2 reconstructed Au͑110͒ surface has been studied in situ. The evolution of the surface morphology during the deposition is followed by the He atom scattering method. A proliferation of Au monoatomic steps is observed during deposition, indicating a strong interaction between Au substrate and T6 molecules. The build-up of a well-ordered single monolayer is obtained with a rectangular unit cell. Its dimensions indicate that T6 molecules lie on the surface, aligned along the rows of close-packed Au atoms.Organic molecules with -conjugated electrons have been shown to have unique electronic properties 1 that offer exciting opportunities for applications in both photonics 2 and optoelectronics.3 In particular, the interaction with and the ordering processes of these molecules at metal surfaces are of basic interest for organic light-emitting diode 4 technologies. Among organic molecules, ␣-hexathiophene (T6) is a well-characterized prototypical compound for polyconjugated systems.5-12 Furthermore, T6 possesses interesting properties of hole injection into highly fluorescent polymers.13 It is then of utmost importance, in order to engineer new materials with suitable optoelectronic properties, to understand the essential processes in which T6 molecules form solid structures and to what extent their order can be driven by the substrate structure. In the context of growth mechanisms of organic monolayers, 12,14 -20 it is worth mentioning that organic structures grown quasiepitaxially under ultrahigh vacuum ͑UHV͒ have been claimed to show interesting optical properties. 21,22 In the present work we present a study of the formation of a single molecular layer of T6 by UHV deposition on the (1ϫ2)-Au͑110͒ surface. He atom scattering has been used to study the surface morphology during deposition. This method has been shown to be particularly suited for studying organic overlayers, 23,24 being a nonpenetrating and nondestructive technique with a very high surface sensitivity.The first stages of T6 deposition show substantial modification of the substrate with proliferation of up-down correlated monoatomic steps, but the step density substantially reduces when a highly ordered T6 monolayer with a rectangular unit cell is reached. In this layer, the T6 molecules lie flat on the surface and are aligned along the rows of close packed Au atoms with a periodicity of 27.4Ϯ0.5 Å and 16.3Ϯ0.2 Å, respectively, along the Au rows ͑⌫X direction͒ and perpendicular to them ͑⌫Y direction͒. The former distance is consistent with the length of a single molecule while the latter is twice that of the (1ϫ2)-Au͑110͒ missing row structure.The He beam apparatus, described in detail elsewhere, 25 has a fixed scattering geometry with angle of incidence i ϭ55°Ϫ␣ and exit angle out ϭ55°ϩ␣. The sample is mounted on a high-precision manipulator with six degrees of freedom and with an angular reproducibility better than 0.01°. The diffraction intensities are collected by scanning the angle ␣, ...

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Organic Molecular Beam Deposition of α-Sexithienyl

Cited by 62 publications

References 21 publications

Electronic Structure and Energy Transfer in Solid α‐Sexithienyl

Electronic Structure and Energy Transfer in Solid α‐Sexithienyl

Temperature and thickness dependence of molecular orientation of α-sexithienyl on Cu(111)

Ordering of a prototypical conjugated molecular system during monolayer growth on the (1×2)-Au(110) surface

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