Real-Space Measurement of the Potential Distribution Inside Organic Semiconductors

Kemerink, Martijn; Offermans, P.; Duren, van Jkj Jeroen; Koenraad, PM Paul; Janssen, Raj René; Salemink, H.W.M.

doi:10.1103/physrevlett.88.096803

Cited by 12 publications

(16 citation statements)

References 16 publications

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“…2,6,[22][23][24]26,28,29,[34][35][36][37][38]42,43,[53][54][55][56] These molecules have attracted attention in the context of charge transport as materials for molecular electronic device applications. Aromatic molecules, whose conductivity occurs via the π-system, can behave as either electron donors or acceptors, depending on their functionalization.…”

Section: Introductionmentioning

confidence: 99%

Self-Assembly of Small Polycyclic Aromatic Hydrocarbons on Graphite: A Combined Scanning Tunneling Microscopy and Theoretical Approach

et al. 2005

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Self-assembled monolayers of chrysene and indene on graphite have been observed and characterized individually with scanning tunneling microscopy (STM) at 80 K under low-temperature, ultrahigh vacuum conditions. These molecules are small, polycyclic aromatic hydrocarbons (PAHs) containing no alkyl chains or functional groups that are known to promote two-dimensional self-assembly. Energy minimization and molecular dynamics simulations performed for small groups of the molecules physisorbed on graphite provide insight into the monolayer structure and forces that drive the self-assembly. The adsorption energy for a single chrysene molecule on a model graphite substrate is calculated to be 32 kcal/mol, while that for indene is 17 kcal/mol. Two distinct monolayer structures have been observed for chrysene, corresponding to highand low-density assemblies. High-resolution STM images taken of chrysene with different bias polarities reveal distinct nodal structure that is characteristic of the molecular electronic state(s) mediating the tunneling process. Density functional theory calculations are utilized in the assignment of the observed electronic states and possible tunneling mechanism. These results are discussed within the context of PAH and soot particle formation, because both chrysene and indene are known reaction products from the combustion of small hydrocarbons. They are also of fundamental interest in the fields of nanotechnology and molecular electronics.

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Section: Introductionmentioning

confidence: 99%

Self-Assembly of Small Polycyclic Aromatic Hydrocarbons on Graphite: A Combined Scanning Tunneling Microscopy and Theoretical Approach

et al. 2005

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“…2 virtually inaccessible. 4,8,9 For a device that is connected to external terminals, the condition J = 0 by definition applies at zero bias. However, since the charge density in the vicinity of the contact is much higher than the densities associated with space-charge limited conduction ͑SCLC͒, it is reasonable to take the onset of SCLC, which occurs when flatband is reached in the bulk of the device, as a first-order approximation for the flatband condition ͓Fig.…”

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confidence: 99%

Temperature-dependent built-in potential in organic semiconductor devices

Kemerink

Kramer

Gommans

et al. 2006

Applied Physics Letters

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The temperature dependence of the built-in voltage of organic semiconductor devices is studied. The results are interpreted using a simple analytical model for the band bending at the electrodes. It is based on the notion that, even at zero current, diffusion may cause a significant charge density in the entire device, and hence a temperature dependent band bending. Both magnitude and temperature dependence of the built-in potential of various devices are consistently described by the model, as the effects of a thin LiF layer between cathode and active layer.

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“…The characteristic plateau and the threshold behavior have been observed for a series of molecular and conjugated-polymer organic materials. [6][7][8][9]26 Alvarado et al 6 have proposed that these thresholds mark the onset of charge-carrier injection into positive (negative) polaronic states, P + ͑P − ͒, at an energy E P + ͑E P − ͒ of the organic material, whereas the width of the plateau corresponds to E g,sp . Moreover, they argue that a necessary condition for the determination of barrier heights for hole and electron injection at organic/metal interfaces is that the electric field at the tip apex be high enough to induce dominant carrier injection from the tip, with a negligible injection of charges of opposite polarity from the counter electrode.…”

Section: Methodsmentioning

confidence: 99%

“…Our results extend and unify earlier interpretations of experimental data that are valid for either a very sharp 6 or a relatively blunt tip. 8 The relevance of these results is emphasized by the fact that many organic semiconductors exhibit a strong tendency to form highly inhomogeneous layers. [10][11][12] As the length scale of these inhomogeneities is typically between a few nanometers and 1 m, [10][11][12] scanning probes are essential tools in the study of organic semiconductor thin films.…”

Section: Introductionmentioning

confidence: 99%

“…Contact-mode tip displacement versus bias voltage ͑z-V͒ spectroscopy at a constant current has been demonstrated as a potential technique to probe the electronic properties of buried organic/metal interfaces, 6,7 as well as the charge transport within organic materials. 8,9 Here, we present the results of modeling calculations for charge injection from a sharp metallic tip into semiconducting organic materials.…”

Section: Introductionmentioning

confidence: 99%

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Scanning tunneling spectroscopy on organic semiconductors: Experiment and model

et al. 2004

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Scanning-tunneling spectroscopy experiments performed on conjugated polymer films are compared with three-dimensional numerical model calculations for charge injection and transport. It is found that if a sufficiently sharp tip is used, the field enhancement near the tip apex leads to a significant increase in the injected current, which can amount to more than an order of magnitude and can even change the polarity of the predominant charge carrier. We show that when charge injection from the tip into the organic material predominates, it is possible to probe the electronic properties of the interface between the organic material and a metallic electrode directly by means of tip height versus bias voltage measurements. Thus, one can determine the alignment of the molecular orbital energy levels at the buried interface, as well as the single-particle band gap of the organic material. By comparing the single-particle energy gap and the optical absorption threshold, it is possible to obtain an estimate of the exciton binding energy. In addition, our calculations show that by using a one-dimensional model, reasonable parameters can only be extracted from z-V and I-V curves if the tip apex radius is much larger than the tip height. In all other cases, the full three-dimensional problem needs to be considered.

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Real-Space Measurement of the Potential Distribution Inside Organic Semiconductors

Cited by 12 publications

References 16 publications

Self-Assembly of Small Polycyclic Aromatic Hydrocarbons on Graphite: A Combined Scanning Tunneling Microscopy and Theoretical Approach

Self-Assembly of Small Polycyclic Aromatic Hydrocarbons on Graphite: A Combined Scanning Tunneling Microscopy and Theoretical Approach

Temperature-dependent built-in potential in organic semiconductor devices

Scanning tunneling spectroscopy on organic semiconductors: Experiment and model

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