| AVS 54th International Symposium | |
| Surface Science | Friday Sessions |
| Session SS2+EM+TF-FrM |
| Session: | Organic Films II: Semiconductors and C@sub 60@ |
| Presenter: | R. Bechstein, University of Osnabrueck, Germany |
| Authors: | R. Bechstein, University of Osnabrueck, Germany J. Schütte, University of Osnabrueck, Germany P. Rahe, University of Osnabrueck, Germany A. Kühnle, University of Osnabrueck, Germany |
| Correspondent: | Click to Email |
The (110) surface of TiO2 constitutes an interesting model substrate for molecular adsorption studies due to its importance in applications such as organic solar cells and light emitting diodes. Several experiments revealed that organic molecules can be anchored to the surface through carboxylic groups both under ultra-high vacuum conditions1 as well as from solution.2 We investigated a perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) derivative without carboxylic anchor groups by non-contact atomic force microscopy (NC-AFM) under ultra-high vacuum conditions. The molecules were deposited at room temperature onto TiO2 (110) by evaporation from a Knudsen cell. We achieved true atomic resolution on the bare substrate as well as submolecular resolution on individual molecules. The molecules were observed to align along the [001] direction with the ability to move along this direction. They are found to be homogeneously distributed on the terraces without any tendency to cluster at step edges even at elevated temperature. Two molecular contrast modes are clearly distinguished. In one mode the molecules appear cloudy and are observed to be centred on top of bright rows. In the other mode the molecules are imaged with a dark bone-shaped centre and a bright rim, centred on top of dark rows. Scanning tunnelling microscopy measurements allow to conclude that the molecules are always centred on top of the bridging oxygen rows, demonstrating a contrast reversal between the two NC-AFM imaging modes. By comparing these results with previous NC-AFM studies,3 we can assign the two modes to positive and negative terminated tips showing that in NC-AFM imaging strongly depends on the tip termination.
1 A. Sasahara, H. Uetsuka, and H. Onishi, J. Phys. Chem. B 105, 1 (2001)
2 C. L. Pang, T.-a. Ishibashi, and H. Onishi, Jpn. J. Appl. Phys. 44, 5438 (2005)
3 J. V. Lauritsen, et al., Nanotechnology 17(14), 3436 (2006).