Importance of dewetting in organic molecular-beam deposition: Pentacene on gold

Beernink, Gunda; Strunskus, Thomas; Witte, Gregor; Wöll, Christof

doi:10.1063/1.1775040

Cited by 95 publications

(89 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This observation is consistent with the formation of PEN multilayers, as photoelectrons from the PEN monolayer (peak 1) become attenuated by the molecules adsorbed on top. Island growth of PEN on Au is well-documented in the literature, [7,19,20] and, indeed, we still observe intensity from the substrate metal E F at MT = 110 Å. Consequently, feature 2 is related to the HOMO-derived emission of PEN multilayers. The peak center is at ca.…”

supporting

confidence: 50%

“…[18,21] As the relative emission intensity of peaks 1 and 2 are markedly different in Figure 1d, we propose that PEN multilayers do not exhibit a flat-lying adsorption geometry (molecular plane parallel to the surface). However, molecules in the multilayer do not exhibit a "standing-upright" geometry (as on SiO 2 [22] or in certain thick films on Au [20] ), as the emission from the PEN HOMO remains strongly suppressed for h e = 0° (Fig. 1b).…”

mentioning

confidence: 92%

See 1 more Smart Citation

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

Vollmer²,

et al. 2006

View full text Add to dashboard Cite

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...

show abstract

supporting

confidence: 50%

mentioning

confidence: 92%

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

Vollmer²,

et al. 2006

View full text Add to dashboard Cite

show abstract

“…In fact, a change of the orientation ͑relative to the substrate surface͒ of rodlike conjugated organic molecules in thin films as a function of film thickness is a rather common observation, related to the release of stress existing in the ML or few multilayer systems. 11,12,15,18 However, the changes in orientation are not well understood ͑in terms of a critical layer thickness that initiates these changes͒, and substantial changes in BE's derived from photoemission, such as those reported here, were not yet observed. The defined transition from lying to vertically inclined molecules observed for DH6T/Ag, combined with the insulating properties of the hexyl substituents, leads to fundamentally different electronic properties in comparison to unsubstituted 6T.…”

mentioning

confidence: 74%

Influence of alkyl chain substitution on sexithienyl-metal interface morphology and energetics

Duhm

Glowatzki

Rabe

et al. 2006

Applied Physics Letters

View full text Add to dashboard Cite

The interface between Ag͑111͒ and vacuum sublimated ␣ , -dihexylsexithienyl ͑DH6T͒ was investigated using ultraviolet photoelectron spectroscopy and atomic force microscopy. While the monolayer of DH6T is lying flat on the metal surface, we found that already in the second molecular layer the molecules are almost standing upright. This abrupt change in molecular orientation lowered the hole injection barrier ͑⌬ h ͒ of DH6T/Ag by 0.5 eV between monolayer and multilayer. ⌬ h for DH6T multilayers was even lowered by 0.8 eV compared to unsubstituted sexithienyl multilayers. The reduction of ⌬ h is attributed to the electronic decoupling of molecules in the first from those in the second layer via the hexyl chains.

show abstract

“…[13][14][15] However, with increasing film thickness the molecules often undergo an orientational transition. [16][17][18][19] In a previous ultraviolet photoelectron spectroscopy ͑UPS͒ study of PFP on Au͑111͒ a transition from a flat lying monolayer to herringbonelike multilayers was proposed, 12 and concomitant changes in the IE were reported, however, they could not be explained. The IPBs of PFP are expected to have a similar impact on the electronic structure of a PFP thin film irrespective whether it is composed of standing molecules or of molecules with their short axes tilted with respect to the substrate surface ͓Fig.…”

Section: Introductionmentioning

confidence: 95%

Influence of intramolecular polar bonds on interface energetics in perfluoro-pentacene on Ag(111)

et al. 2010

View full text Add to dashboard Cite

We investigated the structural and electronic properties of vacuum sublimed perfluoro-pentacene ͑PFP͒ thin films on Ag͑111͒ substrates using x-ray standing waves ͑XSW͒, x-ray diffraction ͑XRD͒ and ultraviolet photoelectron spectroscopy ͑UPS͒. XSW results reveal a flat adsorption geometry of the monolayer PFP/Ag͑111͒ with a relatively large bonding distance of 3.16 Å for both, the carbon and fluorine atoms. Multilayers PFP/Ag͑111͒ adopt a herringbone structure with the molecular long axis parallel to the substrate and a vertical lattice spacing of 3.06 Å as evidenced by XRD. The strong intramolecular polar bond character of the fluorine-carbon bonds in PFP leads to an orientation dependent ionization energy ͑IE͒ that is experimentally observed by UPS for the monolayer-multilayer transition: The inclined molecular plane orientation in the multilayer herringbone arrangement leads to an increase of the PFP IE by Ͼ0.4 eV compared to the flat lying monolayer.

show abstract

Importance of dewetting in organic molecular-beam deposition: Pentacene on gold

Cited by 95 publications

References 18 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

Influence of alkyl chain substitution on sexithienyl-metal interface morphology and energetics

Influence of intramolecular polar bonds on interface energetics in perfluoro-pentacene on Ag(111)

Contact Info

Product

Resources

About