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We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T3-(CH2)4-HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.

Two-terminal thin films of poly(3-hexylthiophene) (P3HT) with a wide electrode separation (150 μ m) has been studied using current–voltage characteristics at different temperatures. Space-charge-limited conduction (SCLC) with high injection barriers (1.3 eV) has been observed at all temperatures in the low electric field regime. A possible transition from SCLC to injection-limited conduction (ILC) is reported. The experimental results have been compared with the disorder-controlled injection model proposed by Arkhipov et al. [V.I. Arkhipov, H. von Seggern, E.V. Emilianova, Appl. Phys. Lett. 83 (2003) 5074; V.I. Arkhipov, E.V. Emilianova, Y.-H. Tak, H. Bassler, J. Appl. Phys. 84 (1998) 848; V.I. Arkhipov, U. Wolf, H. Bassler, Phys. Rev. B 59 (1999) 7514].

Charge injection from metal electrodes to organics is a subject of intense scientific investigation for organic electronics. Ballistic electron emission microscopy (BEEM) enables spectroscopy and imaging of buried interfaces with nanometer resolution. Spatial non-uniformity of carrier injection is observed for both Ag–PPP (poly-paraphenylene) and Ag–MEHPPV (poly-2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) interfaces. BEEM current images are found to correlate only marginally with the surface topography of the Ag film.

We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag–AgSe structures.

In this work, we present an investigation of the Ag-PPP (polyparaphenylene) interface using ballistic electron emission microscopy. Our work is the first successful application of the BEEM technique to metal-organic interfaces. We observe nanometer scale injection inhomogeneities. They have an electronic origin, since we find corresponding Schottky barrier variations. We also determine the transmission function of Ag-PPP interface and find that it agrees qualitatively with the theoretical calculations for a metal-phenyl ring interface. We conclude that charge transport across inhomogeneous barriers needs to be considered for understanding electronic transport across metal-organic interfaces and organic device characteristics.

The silver-p-phenylene (Ag-PPP) interface is investigated using ballistic electron emission microscopy (BEEM). Multiple injection barriers and spatial nonuniformity of carrier injection over nanometer length scales are observed. No unique injection barrier is found. Physical reasons for these features are discussed. BEEM current images and the surface topography of the silver film are uncorrelated., Comment: To appear in Applied Physics Letters

Metal organic interfaces have been under intensive scientific investigation over the past few years with the objective of improving devices based on organic materials. In this study, we report the first results on spectroscopy and imaging of a buried metal-organic interface using ballistic electron emission microscopy (BEEM). Unlike photoexcitation-based experiments, which typically average over large interfacial areas, BEEM enables direct observation of local interface band structure with nanometer resolution. The interface of silver (Ag) - polyparaphenylene (PPP, a blue emitter with high photoluminescence efficiency) is investigated. Multiple injection barriers and spatial non-uniformity of carrier injection are observed. Possible causes for these features will be discussed. The BEEM current images are found to correlate marginally with the surface topography of the silver film.