Influence of OH groups on charge transport across organic-organic interfaces: a systematic approach employing an "ideal" device.
ABSTRACT The charge transport across a pentacene/SAM interface has been studied by scanning tunnelling spectroscopy (STS) as a function of temperature and film thickness in order to obtain information on the transport mechanisms and in particular on the importance of interfacial OH-groups on n-transport in organic semiconductors. The current-voltage (I-V) characteristics of pentacene thin films deposited on a mercaptoundecanol self-assembled monolayer (SAM) on Au(111) reveal an asymmetric behaviour. At positive sample bias the onset currents shift towards higher voltages for decreasing temperatures, whereas such changes are not seen at negative bias. For lower temperatures, the variation of current onset with layer thickness is absent. These observations are explained by OH-groups at the SAM-surface effectively acting as charge traps. When electrons are caught in these traps at the organic-organic interface, charge transport is severely affected. Imaging of the SAM after loading the traps suggests that the attachment of electrons to the OH-groups exposed at the organic surface is a reversible process.
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ABSTRACT: Single-crystal field-effect transistors based on 2,3-dimethylpentacene have been used to probe the effect of surface modification of the insulating dielectric SiO(2) layer on the transistor characteristics. Self-assembled monolayers (SAMs) of different chain lengths and functional groups were used to systematically modify the structure and property of the semiconductor/dielectric interface. The charge carrier mobility as a function of SAM used for surface modification was analyzed. The character of the terminal functional group, as well as the mechanic treatment (rubbing) of the monolayer, much influences the carrier mobility. Introduction of a polar end group (donor or acceptor type) decreases the mobility compared to a nonpolar end group. Prerubbing of the monolayer serves to increase the charge carrier mobility by a factor of 2-4-fold. The results are interpreted in terms of the orderliness of the monolayer which affects the contact at the monolayer/semiconductor interface, which in turn affects the trapping sites' density or the smoothness of the potential surface that the carriers experience while transporting along the interface.ACS Applied Materials & Interfaces 06/2011; 3(6):2136-41. DOI:10.1021/am200349j · 5.90 Impact Factor
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ABSTRACT: A light-addressable gold electrode modified with CdS and FePt or with CdS@FePt nanoparticles via an interfacial dithiol linker layer is presented. XPS measurements reveal that trans-stilbenedithiol provides high-quality self-assembled monolayers compared to benzenedithiol and biphenyldithiol, in case they are formed at elevated temperatures. The CdS nanoparticles in good electrical contact with the electrode allow for current generation under illumination and appropriate polarization. FePt nanoparticles serve as catalytic sites for the reduction of hydrogen peroxide to water. Advantageously, both properties can be combined by the use of hybrid nanoparticles fixed on the electrode by means of the optimized stilbenedithiol layer. This allows a light-controlled analysis of different hydrogen peroxide concentrations.ACS Nano 11/2011; 5(12):9870-6. DOI:10.1021/nn2035582 · 12.03 Impact Factor
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ABSTRACT: We review basic concepts as well as recent examples and applications of organic-organic heterostructures. We organize the different types of heterostructures according to material A deposited on material B (A/B), A co-deposited with B (A:B), heterostructures in the monolayer regime including nanostructuring concepts and systems involving self-assembled monolayers, as well as various other architectures, including superlattices. While most examples are related to small-molecule organic semiconductors, many of the ideas can be applied to other systems. The central theme is growth and structure as well as optical and electronic properties. Finally, we comment on implications for device applications.ChemPhysChem 02/2012; 13(3):628-43. DOI:10.1002/cphc.201100737 · 3.36 Impact Factor