AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Thursday Sessions
       Session EM+AS+EN+TF-ThM

Paper EM+AS+EN+TF-ThM2
Scanning Tunneling Microscopy and Spectroscopy Study of Sliding Defects in α-6T Films on C60/Au(111)

Thursday, October 31, 2013, 8:20 am, Room 101 B

Session: Hybrid and Organic Electronics
Presenter: D.B. Dougherty, North Carolina State University
Authors: D.B. Dougherty, North Carolina State University
J. Wang, North Carolina State University
Correspondent: Click to Email
Compared to the Si-based traditional inorganic electronics, mechanical flexibility is a tremendous advantage for organic electronics. The origin of mechanical flexibility is the relatively weak intermolecular interactions. In addition to flexibility, these weak interactions can also lead to structural disorder in organic thin films that has a significant impact on carrier transport in organic electronic devices [1].A recent example can be seen in the analysis of the temperature dependence of carrier mobility in 2D α-sexithiophene (α-6T) field effect transistors (FET’s) [2] which differ from 3D counterparts due to different sources of disorder.

In an effort to understand the origin of disorder in sexithiophene films relevant to 2D FETs, we have grown single layer α-6T films on top of a C60 monolayer on Au (111). By utilizing Scanning Tunneling Microscopy and Spectroscopy, structural disorder effects in the α-sexitihophene layer have been observed. Sexithiophene molecules form islands on C60 monolayer with apparent height about equal to the length of one single molecule. The α-6T molecules assemble into “dimer strips” indicating the competition between interactions present in the α-6T bulk crystal and interactions with C60 substrate. Random apparent height variations are observed that can be explained by vertical sliding defects in the layer, similar to other standing molecular films [3]. Remarkably, these defects have a minimal effect on the HOMO energy level, which is instead only strongly influenced by random STM tip variations. This shows that intrinsic structural disorder in a-6T films does not have a strong electronic impact.

*This work was funded by NSF CAREER award DMR-1056861.

[1] Tessler et al., Adv. Mater. 21, 2741 (2009).

[2] Brondijk et al., Phys. Rev. Lett. 109, 056601 (2012).

[3]Kang et al., Appl. Phys. Lett. 86, 152115(2005).