AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Tuesday Sessions
       Session NS2-TuM

Paper NS2-TuM8
Scanning Potentiometry Studies of Charge Transport in Sexithiophene-based FETs using Conducting Probe Atomic Force Microscopy (CP-AFM)

Tuesday, October 26, 1999, 10:40 am, Room 6C

Session: Molecular Electronics
Presenter: K. Seshadri, University of Minnesota
Authors: K. Seshadri, University of Minnesota
T.W. Kelley, University of Minnesota
C.D. Frisbie, University of Minnesota
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Investigation of charge transport mechanisms in organic semiconductors is of immense importance to development of devices such as thin film transistors and organic-based LEDs. Of particular interest is @alpha@-sexithiophene (6T), with a hole mobility high enough for flexible, "all plastic" devices. Conducting Probe Atomic Force Microscopy (CP-AFM) has been used to measure electrical transport characteristics of 6T. The semiconductor was deposited as crystals, ranging from 1 to 6 molecules (2-14 nm) in thickness and from 1-2 µm in diameter by vacuum sublimation onto SiO2/p-Si substrates, with lithographically defined Au contacts. The semiconductor crystallite grows across the gap between two electrodes, with a capacitively coupled gate electrode, so as to achieve a field-effect transistor configuration (FET). A Au-coated conducting AFM probe is brought into contact with the electrically biased 6T crystallite, and the potential is measured as a function of position. This is a scanning potentiometry experiment, involving mapping the local potential over the surface of the organic semiconductor. Mesoscopic transport measurements, in combination with AFM imaging, are a useful strategy for elucidating charge transport across grain boundaries, charge trapping, and other structure-transport relationships in organic materials.