AVS 58th Annual International Symposium and Exhibition
    In Situ Spectroscopy and Microscopy Focus Topic Tuesday Sessions
       Session IS+AS+SS-TuM

Paper IS+AS+SS-TuM12
Fundamental Aspects of Organic Heterostructure Formation Examined using Supersonic Molecular Techniques and In Situ Real Time X-ray Synchrotron Radiation

Tuesday, November 1, 2011, 11:40 am, Room 106

Session: In Situ Studies of Organic and Soft Materials and Liquid-Solid Interfaces
Presenter: Edward Kish, Cornell University
Authors: E.R. Kish, Cornell University
T.V. Desai, Cornell University
A.R. Woll, Cornell University
J.R. Engstrom, Cornell University
Correspondent: Click to Email
Over the past several years significant advances have been made concerning our understanding of the growth of crystalline small molecule organic thin films consisting of a single component. An important challenge in organic electronics, photonics and photovoltaics is to develop and improve methods to integrate both p-type and n-type small molecule organic semiconductors into the same device microstructure. Thus, developing an understanding of the molecular scale events that lead to heterojunction formation is essential in these systems consisting of multiple components. Here we report on our examinations of the nucleation, growth, and dynamics of adsorption of a n-type organic semiconductor, N,Nʹ-ditridecylperlyene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13), on SiO2 surfaces modified by self-assembled monolayers (SAMs) and on a pre-deposited monolayer of pentacene (a p-type semiconductor) using supersonic molecular beam techniques, in situ synchrotron x-ray scattering and ex situ atomic force microscopy. From real-time x-ray scattering we find that PTCDI-C13 exhibits prolonged layer-by-layer growth for approximately the first 10 monolayers (MLs) of deposition on all three SAMs examined. Concerning the kinetics of growth we find that the adsorption probability of PTCDI-C13 on itself is similar to that observed on two SAMs that possess aromatic endgroups, but it differs significantly to that observed on a relatively short, methyl-terminated SAM. These differences could reflect mechanisms such as direct molecular insertion of PTCDI-C13 into either the existing PTCDI-C13 film, or the longer chain SAMs with aromatic endgroups. Concerning growth in the submonolayer regime, we find that nucleation is homogeneous, and that the absolute density of islands depends on the nature of the surface, while the relative change of the island density with increasing growth rate is essentially independent of the underlying SAM. From the latter we find that a critical island size of a single molecule of PTCDI-C13 can describe all the data. Finally, we will discuss our most recent results concerning the growth of heterostructures composed of a few to several monolayer stacks of PTCDI-C13 and pentacene. In this work we find that PTCDI-C13 grows in a smooth layer-by-layer fashion on pentacene, but the opposite is not true—pentacene grows in a purely 3D mode when deposited on PTCDI-C13. We will discuss the implications of this observation concerning the growth of organic heterostructures for applications in electronics, photonics and photovoltaics.