Tunable Crystal Nanostructures of Pentacene Thin Films on Gate Dielectrics Possessing Surface-Order Control

Authors

  • Do Hwan Kim,

    1. Department of Chemical Engineering Pohang University of Science and Technology Pohang, 790-784 (Korea)
    2. Display Device & Processing Lab., Samsung Advanced Institute of Technology, Yongin-si, Gyeonggi-do, 449-712, Korea.
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  • Hwa Sung Lee,

    1. Department of Chemical Engineering Pohang University of Science and Technology Pohang, 790-784 (Korea)
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  • Hoichang Yang,

    Corresponding author
    1. Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute Troy, NY 12180 (USA)
    • Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute Troy, NY 12180 (USA).
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  • Lin Yang,

    1. National Synchrotron Light Source Brookhaven National Laboratory Upton, NY 11973 (USA)
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  • Kilwon Cho

    Corresponding author
    1. Department of Chemical Engineering Pohang University of Science and Technology Pohang, 790-784 (Korea)
    • Department of Chemical Engineering Pohang University of Science and Technology Pohang, 790-784 (Korea).
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  • D. H. Kim and H. S. Lee contributed equally to this work. This work was supported by a grant (F0004022-2007-23) from the Information Display R&D Center, ERC Program (R11-2003-006-05004-0) of the MOST/KOSEF, and the Regional Technology Innovation Program of MOCIE of Korea (RTI04-01-04), POSTECH Core Research Program, and the Pohang Acceleratory Laboratory for providing the 4C2, 3C2, 8C1, and 10C1 beamlines used in this study. H. Yang and L. Yang thank the support from the NSF (DMR 0117792), the United States Department of Energy, and Office of Basic Energy Sciences (DE-AC02-98CH1-886).

Abstract

To enhance the electrical performance of pentacene-based field-effect transistors (FETs) by tuning the surface-induced ordering of pentacene crystals, we controlled the physical interactions at the semiconductor/gate dielectric (SiO2) interface by inserting a hydrophobic self-assembled monolayer (SAM, CH3-terminal) of organoalkyl-silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano-layers in contact with the SAM could adopt two competing crystalline phases—a “thin-film phase” and “bulk phase” – which affected the π-conjugated nanostructures in the ultrathin and subsequently thick films. The field-effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm2 V−1 s−1 for the disordered SAM-treated SiO2 gate-dielectric. This remarkable change in device performance can be explained by the production of well π-conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.

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