| 1. |
- Christodoulou, C., et al.
(författare)
-
Tuning the work function of graphene-on-quartz with a high weight molecular acceptor
- 2014
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:9, s. 4784-4790
-
Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet and X-ray photoelectron spectroscopies in combination with density functional theory (DFT) calculations were used to study the change in the work function (Φ) of graphene, supported by quartz, as induced by adsorption of hexaazatriphenylene-hexacarbonitrile (HATCN). Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and DFT modeling show that a molecular-density-dependent reorientation of HATCN from a planar to a vertically inclined adsorption geometry occurs upon increasing surface coverage. This, in conjunction with the orientation-dependent magnitude of the interface dipole, allows one to explain the evolution of graphene Φ from 4.5 eV up to 5.7 eV, rendering the molecularly modified graphene-on-quartz a highly suitable hole injection electrode.
|
|
| 2. |
- Vollmer, A., et al.
(författare)
-
Two dimensional band structure mapping of organic single crystals using the new generation electron energy analyzer ARTOF
- 2012
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:3-4, s. 55-60
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a novel type of photoemission detector, the Angle Resolved Time Of Flight electron energy analyzer (ARTOF 10k), which enables electronic band structure determination under measurement conditions that are ideal for radiation-sensitive samples. This is facilitated through the combination of very high electron transmission and wide accessible angular range in one geometry. These properties make the ARTOF 10k predestined to investigate specimens that strongly suffer from radiation damage during photoemission experiments under "standard" conditions, such as organic single crystals, as extremely low fluxes can be used while not compromising spectra accumulation times and signal-to-noise ratio. Even though organic single crystals are of increasing fundamental and applied scientific interest, knowledge of their electronic properties is still largely based on theoretical calculations due to major experimental challenges in measuring photoemission. In this work we show that the band structures of rubrene and tetracene single crystals can be obtained with unprecedented quality using the ARTOF 10k detector. The dispersion of the highest occupied band in rubrene is confirmed in accordance with an earlier report [1] and we disclose the absence of notable dispersion for the highest occupied energy level on the surface of tetracene single crystals.
|
|
| 3. |
- Oehzelt, M., et al.
(författare)
-
Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 124:5, s. 54711-
-
Tidskriftsartikel (refereegranskat)abstract
- The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77 K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333 K, at which point the size of individual crystallites typically exceeds 100 nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures. © 2006 American Institute of Physics.
|
|
| 4. |
- Usachov, D., et al.
(författare)
-
Nitrogen-Doped Graphene: Efficient Growth, Structure, and Electronic Properties
- 2011
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:12, s. 5401-5407
-
Tidskriftsartikel (refereegranskat)abstract
- A novel strategy for efficient growth of nitrogen-doped graphene (N-graphene) on a large scale from s-triazine molecules is presented. The growth process has been unveiled in situ using time-dependent photoemission. It has been established that a postannealing of N-graphene after gold intercalation causes a conversion of the N environment from pyridinic to graphitic, allowing to obtain more than 8096 of all embedded nitrogen in graphitic form, which is essential for the electron doping in graphene. A band gap, a doping level of 300 meV, and a charge-carrier concentration of similar to 8 x 10(12) electrons per cm 2, induced by 0.4 atom % of graphitic nitrogen, have been detected by angle-resolved photoeinission spectroscopy, which offers great promise for implementation of this system in next generation electronic devices.
|
|
