Point contact current-voltage measurements on individual organic semiconductor grains by conducting probe atomic force microscopy

Conducting probe atomic force microscopy (CP-AFM) was used to make point co ntact current-voltage (I-V) measurements on individual microscopic grains o f the organic semiconductor sexithiophene (6T). The 6T grains ranged from 1 to 6 molecules (2-14 nm) in thickness, 1-2 mu m in length and width, and w ere deposited by thermal evaporation onto SiO2 substrates previously patter ned with 200 nm wide Au wires. Au-coated AFM probes were used to image the substrates in air to identify individual 6T grains which grew in contact wi th a wire. The same probes were used to record the I-V characteristics of s ingle grains. Analysis of the differential resistance as a function of prob e wire separation yielded typical grain resistivities of 100 Omega cm and c ontact resistances of similar to 100 M Omega. Over the 0-3 V range probed, the shape of the I-V curves can be attributed to a combination of the nonli near I-V characteristics of the Au-GT junctions and the ohmic response of t he grain. in general, we have shown that CP-AFM is a reliable method for co rrelating electrical transport properties with microscopic morphology in or ganic semiconductors. (C) 2000 American Vacuum Society. [S0734-211X(00)0150 3-X].