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We studied the role of order of the OTS layer on performance of OTFTs. The Langmuir-Blodgett technique was employed to control the density and the phase of the OTS monolayer. We discovered that a dense, crystalline OTS layer is an excellent substrate for organic semiconductor growth. Many semiconductors grow two-dimensionally via a layer-by-layer growth on dense OTS surfaces, while they grow three-dimensionaly on less organized OTS surfaces.
Studying the Dielectric-semiconductor Interface in Organic Thin Film Transistors: the Importance of Order of the SAM Dielectric Modification Layer
Authors: Virkar, A.1, Ito, Y.1.2, Mannsfeld, S.1, Oh, J.H.1, Toney, M.5, Tan, Y.H.3, Liu, G.3, Scott, C.4, Miller, R.4, Bao, Z.1
1Stanford University, 2Toppan Printing Co., Japan, 3UC Davis, 4IBM ARC, 5Stanford SRL
Mobilities as high as 2.2 cm2/Vs and 5.2 cm2/Vs were demonstrated for pentacene and C60 on crystalline OTS, respectively, compared to 0.6 cm2/Vs and 0.4cm2/Vs for pentacene and C60, respectively, on amorphous disordered OTS. We attributed the increase in mobility on the crystalline OTS to the semiconductor growth mode and not crystal island size which has often been suggested. We also showed that on the crystalline OTS surface, there are more methyl groups to interact with the depositing semiconductor and that these interactions are energetically favorable. The favorable interactions tend to stabilize the nucleating semiconductor crystal and increase the nucleation density.
Fig.1 AFM images of pentacene submonolayers (norminal thickness 1 nm) deposited on (a) disordered OTS and (b) crystalline OTS. A higher monolayer coverage and more 2D-like growth is seen on crystalline OTS surface
Curtis W. Frank, Stanford University, DMR 0213618
Stanford University MRSEC 0213618 IRG 3