Photoemission from Azobenzene Alkanethiol Self-Assembled Monolayers

Weber, R.; Winter, and B.; Hertel, I. V.; Stiller, B.; Schrader, and S.; Brehmer, L.; Koch, Norbert

doi:10.1021/jp0226681

Cited by 33 publications

(28 citation statements)

References 28 publications

(71 reference statements)

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“…This assignment is based on the high photoemission cross section of F and earlier assignments for fluorinated conjugated molecules. [24] It is noteworthy that ARUPS spectra for normal and off-normal emission closely resemble what was described above for PEN/Au(111), that is, an intense peak at ca. 1 eV BE, which is almost completely suppressed at h e = 0°for all MTs.…”

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confidence: 71%

The Effect of Fluorination on Pentacene/Gold Interface Energetics and Charge Reorganization Energy

Vollmer²,

et al. 2006

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The energy level alignment at interfaces between conjugated organic semiconductors and metals is recognized as a key factor determining the performance of organic-based (opto)-electronic devices. [1,2] Experimentally, the hole-injection barriers (HIBs) at organic/metal interfaces can be directly determined by using ultraviolet photoelectron spectroscopy (UPS).In addition, angle-resolved UPS (ARUPS) allows molecular orientations at surfaces to be assessed. In the work reported here, we used this method to investigate interfaces between two prototypical organic semiconductors, pentacene (PEN) and perfluoropentacene (PFP), and Au. PEN can be used as the active material in organic field-effect transistors (OFETs) with a high hole mobility of up to 5.5 cm 2 V -1 s -1 .[3] The fabrication of integrated circuits also requires high-electron-mobility OFETs; this is difficult to achieve with PEN, which has reported electron mobilities of up to 0.04 cm 2 V -1 s -1 .[4] One approach to improving n-type performance of OFETs is to use PFP, resulting in high electron mobilities of more than 0.2 cm 2 V -1 s -1 . [5] Commonly, Au is used as the source and drain contact metal in OFETs. Therefore, the interface energetics between organic semiconductors and Au are of interest, since charges have to be transported across these interfaces and minimized contact resistance is aimed at. While a number of reports are already available on PEN/Au interfaces, nothing is yet known about PFP/Au. Moreover, published work on PEN/Au interfaces reveals controversial values for the HIB, ranging from ca. 0.5 to 0.9 eV for various polycrystalline [6][7][8][9] and single-crystal [10,11] Au surfaces. Even larger differences of the HIB were found for PEN on pristine and molecularly modified Au [9] and Ag [12] surfaces. At present, molecular-layer thickness and orientation, polarization, and thin-film polymorphism-and combinations thereof, as these parameters are interdependent-are being discussed as possible reasons for the observed variation. [8,9,12] The molecular-charge reorganization energy is yet another important parameter for efficient transport of charge carriers across interfaces and can also be assessed with UPS. [13][14][15] The present comparative ARUPS study for PEN and PFP on Au(111) highlights with unprecedented accuracy i) the effect of perfluorination (of PEN) on the interface energy levels, and ii) the effect of molecular-layer thickness on organic semiconductor/metal interface energetics. In short, the HIB for a monolayer of each organic material on the metal was almost identical, despite the very different ionization energies of PEN and PFP. In addition, we found distinctly different molecular level energies as a function of layer thickness, attributed to different polarization energies. The photoemission spectra for monolayers of the two organic materials corroborated that the charge-reorganization energy of PEN/Au (111) is significantly larger than for PEN in the gas phase, and even larger for PFP/Au(111).First, we discuss the inte...

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confidence: 71%

The Effect of Fluorination on Pentacene/Gold Interface Energetics and Charge Reorganization Energy

Vollmer²,

et al. 2006

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“…As shown above, even physisorbed molecules induce significant changes of f. In addition, some adsorbed species may have permanent dipoles with some preferred orientation relative to the surface, thus leading to additional changes in f (Df) according to the Helmholtz equation [Eq. (2)]: [32,33] …”

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Organic Electronic Devices and Their Functional Interfaces

2007

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A most appealing feature of the development of (opto)electronic devices based on conjugated organic materials is the highly visible link between fundamental research and technological advances. Improved understanding of organic material properties can often instantly be implemented in novel device architectures, which results in rapid progress in the performance and functionality of devices. An essential ingredient for this success is the strong interdisciplinary nature of the field of organic electronics, which brings together experts in chemistry, physics, and engineering, thus softening or even removing traditional boundaries between the disciplines. Naturally, a thorough comprehension of all properties of organic insulators, semiconductors, and conductors is the goal of current efforts. Furthermore, interfaces between dissimilar materials-organic/organic and organic/inorganic-are inherent in organic electronic devices. It has been recognized that these interfaces are a key for device function and efficiency, and detailed investigations of interface physics and chemistry are at the focus of research. Ultimately, a comprehensive understanding of phenomena at interfaces with organic materials will improve the rational design of highly functional organic electronic devices.

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“…However, there are some differences in peak intensity distribution. Most notably, the peaks near 13 eV and 16 eV binding energy observed in the GTCF spectra could be assigned to the C 2s valence emission from sp 3 hybridized carbon species [10]. The presence of such types of defects in the otherwise sp 2 hybridized carbon in graphite has been proposed to exist in thermally reduced graphite oxide samples on the edges of zigzag edges [8].…”

Section: Resultsmentioning

confidence: 98%

Electronic and structural properties of graphene-based transparent and conductive thin film electrodes

et al. 2008

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We demonstrate that graphene-based transparent and conductive thin films (GTCFs), fabricated by thermal reduction of graphite oxide, have very similar electronic and structural properties as highly oriented pyrolytic graphite (HOPG). Electron spectroscopy results suggest that the GTCFs are also semi-metallic and that the individual graphene sheets of the film are predominantly oriented parallel to the substrate plane. These films may therefore be considered as a technologically relevant analogue to HOPG electrodes, which cannot be easily processed into thin films.

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Photoemission from Azobenzene Alkanethiol Self-Assembled Monolayers

Cited by 33 publications

References 28 publications

The Effect of Fluorination on Pentacene/Gold Interface Energetics and Charge Reorganization Energy

The Effect of Fluorination on Pentacene/Gold Interface Energetics and Charge Reorganization Energy

Organic Electronic Devices and Their Functional Interfaces

Electronic and structural properties of graphene-based transparent and conductive thin film electrodes

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