Sexithiophene films on ordered and disordered TiO2(110) surfaces: Electronic, structural and morphological properties

Ivančo, J.; Haber, Thomas; Krenn, Joachim R.; Netzer, F.P.; Resel, Roland; Ramsey, Michael G.

doi:10.1016/j.susc.2006.09.020

Cited by 65 publications

(76 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While variations of the ionization potential (IP; the molecular equivalent of the work function) depending on the molecular orientation on a substrate have been reported before [10][11][12][13][14][15][16] , the prevalent interpretation in terms of variable photo-hole screening could never be satisfactorily quantified. Here, we propose a qualitatively different and novel explanation for the intriguing observation that one and the same molecule can have different -still welldefined -IPs if part of an ordered supramolecular structure.…”

Section: S Duhm Et Al Nature Materials Acceptedmentioning

confidence: 99%

“…36 We thus conclude that the 0.6 eV [0.4 eV] difference in the IP between standing and lying DH6T [6T] can not be explained in terms of photo-hole screening effects alone, and that another mechanism must be involved. 8 S. Duhm et al, Nature Materials, accepted In order to understand the remarkable finding of one molecule having a different IP depending on its orientation in an ordered supramolecular structure [10][11][12][13][14][15][16] 28 , we performed plane-wave based DFT calculations employing periodic boundary conditions and the repeated-slab approach on single layers of standing and lying DH6T and 6T molecules based on available structural data (see Methodology section for details) 13, 29,[37][38][39] . The occupied density-of-states (DOS) for a lying (L) and standing (S) layer of DH6T is shown in Figure 1b.…”

mentioning

confidence: 99%

“…It may be speculated, however, that the photo-hole is more efficiently screened by surrounding standing molecules than by surrounding flat-lying molecules and, for similar organic compounds, the impact of molecular orientation on the IP has indeed been qualitatively rationalized in terms of the polarization energy depending on the packing density and/or morphology 10,11,15,16 . Here, we provide an upper limit for this proposed variation in polarization energy: A molecule in the topmost organic layer is surrounded by the metal substrate (at some distance), neighboring molecules in the half-space below, and by vacuum in the half-space above; a molecule deeper in the organic layer is additionally surrounded by molecules on top.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

et al. 2008

View full text Add to dashboard Cite

S. Duhm et al., Nature Materials, acceptedWhile an isolated individual molecule clearly has only one ionization potential, multiple values are found for molecules in ordered assemblies. Photoelectron spectroscopy of archetypical π-conjugated organic compounds on metal substrates combined with first-principles calculations and electrostatic modeling reveal the existence of a surface dipole built into molecular layers. Conceptually different from the surface dipole at metal surfaces, its origin lies in details of the molecular electronic structure and its magnitude depends on the orientation of molecules relative to the surface of an ordered assembly. Suitable pre-patterning of substrates to induce specific molecular orientations in subsequently grown films thus permits adjusting the ionization potential of one molecular species over up to 0.6 eV via control over monolayer morphology. In addition to providing in-depth understanding of this phenomenon, our study offers design guidelines for improved organic/organic heterojunctions, hole-or electron-blocking layers, and reduced barriers for charge-carrier injection in organic electronic devices. S. Duhm et al., Nature Materials, acceptedIt is well established that the work function (Φ) of metals depends on the crystal face 1-3 .Φ is defined as the energy difference between the Fermi level (E F ) and the electrostatic potential above the sample, the vacuum level (V vac ). For, e.g., copper, Φs of the (100), (110), and (111) surfaces are spread over a range of 0.5 eV 1,2 . As E F is constant, this observation has been explained by the difference in the intrinsic "surface dipole": Differences in the geometric and, consequently, electronic structure cause a different amount of the electronic cloud to spill out of the bulk into the vacuum 3, 4 . The resulting dipole raises V vac to a larger or smaller extent and thus impacts Φ 4, 5 . Note that this effect can only be observed for laterally extended surfaces, as the spatial region above the sample where V vac is raised reaches farther away from the surface with increasing sample size (i.e., area of the exposed surface) 6, 7 . Small metal clusters with multiple facets of different crystal orientations have only one well-defined work function 8, 9 .For van der Waals (i.e., non-covalent) crystals of non-dipolar molecules, surface dipoles and work-function anisotropy have not yet been explored 6 . While variations of the ionization potential (IP; the molecular equivalent of the work function) depending on the molecular orientation on a substrate have been reported before [10][11][12][13][14][15][16] , the prevalent interpretation in terms of variable photo-hole screening could never be satisfactorily quantified. Here, we propose a qualitatively different and novel explanation for the intriguing observation that one and the same molecule can have different -still welldefined -IPs if part of an ordered supramolecular structure. S. Duhm et al., Nature Materials, acceptedWe performed X-ray photoelectron spectroscopy (XPS) and u...

show abstract

Section: S Duhm Et Al Nature Materials Acceptedmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

et al. 2008

View full text Add to dashboard Cite

show abstract

“…20,22,24 Apart from the highly symmetric C60 molecule (forming at least one commensurate monolayer 28,29 ), the choice of planar molecules better matching the substrate lattice might allow improvement of the coherence of the growing film. This route has been attempted by deposition of uniaxial molecules like anthracene, 30 R-sexithiophene, 6T, 31 and para-sexiphenyl, 6P.…”

Section: Introductionmentioning

confidence: 99%

Planar Growth of Pentacene on the Dielectric TiO₂(110) Surface

Lanzilotto

Sánchez‐Sánchez

Bavdek³

et al. 2011

J. Phys. Chem. C

View full text Add to dashboard Cite

We have studied the growth of pentacene molecules on the unreconstructed and stoichiometric surface of TiO2(110). At variance with its characteristic homeotropic growth mode, pentacene is found to be physisorbed on this dielectric substrate with its long molecular axis oriented parallel to the surface and aligned along the [001] direction. Pentacene molecules couple side-by-side into long stripes running along the [11̅0] direction, where the overlayer preserves the substrate lattice periodicity (∼6.5 Å). In the opposite direction, head-to-head pentacene repulsion drives the ordering of the stripes, whose spacing simply depends on the surface coverage. By near-edge X-ray absorption, NEXAFS, we have determined the pentacene molecules to be tilted by ∼25° off the surface around their long axis. At the monolayer coverage, the pentacene orientation and spacing are very close to that of the (010) bulk planes (also called a−c planes) of pentacene crystals. We have observed that at least two additional layers can be grown on top of the monolayer following a planar configuration. Both the strong side-by-side intermolecular attraction and the full development of the bulklike electronic states, as probed by NEXAFS, suggest an optimal charge transport along the monolayer stripes of lying-down molecules.

show abstract

“…This kind of study was extended further, for instance, in several cases including 6P on mica [415], CuPc on indium tin oxide (ITO) [416], α-6P on TiO 2 [417], α-6T on TiO 2 [418], α-quinquethiophene on Cu [419], hexabenzocoronene (HBC) on Au [420], α-6P on KCl [421], and PTCDA on KCl [422]. However, many limited investigations were conducted on the fabrication of OFETs based on these crystals or thin films, which showed otherwise interesting morphologies and molecular alignments.…”

Section: Os Epitaxymentioning

confidence: 98%

Organic semiconductors for device applications: current trends and future prospects

Ahmad

2014

Journal of Polymer Engineering

View full text Add to dashboard Cite

Abstract:With the rich experience of developing silicon devices over a period of the last six decades, it is easy to assess the suitability of a new material for device applications by examining charge carrier injection, transport, and extraction across a practically realizable architecture; surface passivation; and packaging and reliability issues besides the feasibility of preparing mechanically robust wafer/substrate of single-crystal or polycrystalline/ amorphous thin films. For material preparation, parameters such as purification of constituent materials, crystal growth, and thin-film deposition with minimum defects/ disorders are equally important. Further, it is relevant to know whether conventional semiconductor processes, already known, would be useable directly or would require completely new technologies. Having found a likely candidate after such a screening, it would be necessary to identify a specific area of application against an existing list of materials available with special reference to cost reduction considerations in large-scale production. Various families of organic semiconductors are reviewed here, especially with the objective of using them in niche areas of large-area electronic displays, flexible organic electronics, and organic photovoltaic solar cells. While doing so, it appears feasible to improve mobility and stability by adjusting π-conjugation and modifying the energy bandgap. Higher conductivity nanocomposites, formed by blending with chemically conjugated C-allotropes and metal nanoparticles, open exciting methods of designing flexible contact/interconnects for organic and flexible electronics as can be seen from the discussion included here.

show abstract

Sexithiophene films on ordered and disordered TiO2(110) surfaces: Electronic, structural and morphological properties

Cited by 65 publications

References 38 publications

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Planar Growth of Pentacene on the Dielectric TiO₂(110) Surface

Organic semiconductors for device applications: current trends and future prospects

Contact Info

Product

Resources

About

Sexithiophene films on ordered and disordered TiO2(110) surfaces: Electronic, structural and morphological properties

Cited by 65 publications

References 38 publications

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Planar Growth of Pentacene on the Dielectric TiO2(110) Surface

Organic semiconductors for device applications: current trends and future prospects

Contact Info

Product

Resources

About

Planar Growth of Pentacene on the Dielectric TiO₂(110) Surface