PhD thesis - Evans Research Group - University of Wisconsin-Madison

34significantly lower than descending from the second to the first pentacene layers [29, 30].Because the third layer islands nucleate almost immediately, the second layer of islandsdoes not percolate as easily as the first monolayer.(a)10 -810 -910 -6 0 0.2 0.4 0.6 0.8 1 1.2 1.410 -70.72 ML- drain current (A)2 µm0.9 ML10 -1010 -11drain current (A)0-2 10 -9-4 10 -9-6 10 -9-8 10 -9-1 10 -8(b)V =-60 VG-70 V-80 V-80 -70 -60 -50 -40 -30 -20 -10 0drain voltage (V)coverage (ML)drain current (A)0-5 10 -9-1 10 -8-1.5 10 -8-2 10 -8-2.5 10 -8-3 10 -8-3.5 10 -8-4 10 -8(c)V =-60 VG-70 V-80 V-80 -70 -60 -50 -40 -30 -20 -10 0drain voltage (V)Fig. 2.3: (a) Drain current as a function of pentacene coverage. The drain current at eachcoverage was measured at a constant gate voltage (-80 V) and drain voltage (-50 V). Theinset shows AFM images at 0.72 ML and 0.9 ML. (b), (c) Transistor characteristic curvesat 0.72 ML and 0.9 ML.