AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS+OF-WeA

Paper SS+OF-WeA5
Epitaxial Growth of Pentacene on Bi/Si(111) Films

Wednesday, November 5, 2003, 3:20 pm, Room 327

Session: Growth and Characterization of Organic Films
Presenter: G.E. Thayer, IBM T.J. Watson Research Center
Authors: G.E. Thayer, IBM T.J. Watson Research Center
J.T. Sadowski, Tohoku University, Japan
R.M. Tromp, IBM T.J. Waston Research Center
Correspondent: Click to Email
Electrical contacts between organics and metals have been known to limit charge injection in organic electronic devices. Thus it is not surprising that there is a considerable amount of current work modifying metal surfaces and interfaces in an effort to align conduction with organic molecular levels. The solution to this problem begins with understanding the fundamental mechanisms that control both the morphology and electronic structure at the interface between metal and organic materials. Although the interfaces of organic films grown on many clean substrates (semiconductors, insulators, and metals) are found to be poorly ordered, our work has revealed that pentacene grows epitaxially on Bismuth (a semimetal). Using LEEM, PEEM, LEED, AFM, and STM our efforts have focused on understanding how pentacene molecules order in Pn/Bi/Si(111) thin films (1ML-10MLs). In contrast to the frequently used Pn/Au system, in the first ML of Pn/Bi the pentacene molecules stand up and are highly ordered as seen by the sharp LEED patterns that we observe. Our LEED analysis finds that the structure of Pn/Bi/Si(111) thin films is similar to the bulk structure of Pentacene with lateral 2D cell dimensions of a=7.8Å, b=6.2Å, and @gamma@=84.9°. In one dimension, this structure is 1:1 commensurate in the sqrt(3) direction of the underlying hexagonal Bi surface structure. However, in the other direction it is rotated by a small angle and is incommensurate with the Bi lattice. Control of Pn crystal orientation on metal electrodes will enable the fabrication of organic FFT’s whose electrical characteristics are not degraded by large angle grain boundaries at the source and drain junctions.