Abstract's Details

Combined Grazing Incidence X-ray Scattering and Near-Edge X-ray Absorption Fine Structure of Tetraceno[2,3-b]Thiophene Thin Films for Transistors Applications
Abstract ID	MAT-11
Presenter	Stefan Mannsfeld
Presentation Type	Poster
Full Author List	S. C. B. Mannsfeld (1), Q. Yuan (2), Y.-H. Sun (1), M. Tang (3), M. F. Toney (4), J. Luning (4), Z. Bao (1)
Affiliations	(1) Dept. of Chemical Engineering, Stanford University, CA 94305 (2) Dept. of Materials Science and Engineering, Stanford University, CA 94305 (3) Dept. of Chemistry, Stanford University, CA 94305 (4) Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, CA 94025
Category	Materials Science
Abstract	Understanding the structure-property relationship for organic semiconductors is crucial in rational molecular design and organic transistor process control. Charge carrier transport in organic field effect transistors predominantly occurs in a few semiconductor layers close to the interface in contact with the dielectric layer. Therefore, a better understanding of the impact of crystal packing and thin film morphology in the first few monolayers above the dielectric layer on charge transport is needed to improve the transistor performance. The charge transport properties in these thin films sensitively depend on the molecular alignment which is thus crucial for an understanding of the obtained performance in thin film transistor devices. In this paper, a combination of grazing incidence X-ray diffraction (GIXD) and near edge X-ray absorption spectra (NEXAFS) was used to investigate molecular packing details for 2nm and 20nm thick films of tetraceno[2,3-b]thiophene. The results are compared to the corresponding data for the chemically similar and widely used pentacene. Possible effects of the observed thin film structure on the carrier mobility are discussed. It was found that films with a thickness of less than 20 nm can be described by a single phase with herringbone packing and two molecules per unit cell with a = 5.96 Å, b = 7.71 Å, c = 15.16Å, a = 97.30o, b = 95.63o, g = 90°. The precise alignment of the molecules in this unit cell was extracted by crystallographic refinement using the diffraction intensities obtained from the GIXD measurements. It is found that the small difference in molecular structure (compared to pentacene one benzene ring is substituted for a thiophene ring) leads to a measurable change in crystallinity, molecular packing and charge carrier mobility.
Footnotes
Funding Acknowledgement