PR0362
The growth morphology of ultrathin films of perylene-3,4,9,10-tetracarboxylic
dianhydride (PTCDA) on rutile (110) titanium dioxide.
‫ۑ‬Richard Murdey1, Naoki Sato2
1Kyoto University Pioneering Research Unit for Next Generation
2Kyoto University Institute for Chemical Research

Introduction
Epitaxial growth of sexithiophene on rutile TiO2 (110) surfaces has been recentlyobserved.1 The sexithiophene molecules were oriented with the primary axis in the same
direction as the oxygen and titanium rows of the substrate. It has also been noted howeverthat surface defects on the (110) terraces can to act as anchor points for perylene derivatives,and possibly nucleation sites for the formation of larger clusters.2 In our work, we examine
the influence of the substrate on the morphology and electrical properties of PTCDA thinfilms and consider possible methods to chemically deactivate the nucleation sites in order toimprove film quality. Dienols are tested to discover if they can be made to selectively bind to
the surface defect sites as they are known to effectively bind to nanoparticle surfaces.3,4Finally, we look at whether this treatment has a measureable effect on the growth mode ofvacuum deposited PTCDA thin films.
Experimental
Rutile TiO2 (110) single crystals were obtained from Shinkosha. The offcut wasspecified to be a maximum of 0.05°. The crystals were washed in acetone, ethanol and hot
ultrapure water before being annealed to 1273 K for 5 hours under atmosphere and washedagain in either ultrapure water or acidified 10 mM solutions of L-ascorbic acid (Aldrich) orascorbic acid palmitate (Aldrich). AFM measurements were made on a Molecular ImagingPicoscan II+ instrument operated in contact mode. Contact angle measurements wereperformed

atroomtemperatureusing10mL

dropletsofultrapure

water.

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) was obtained from Aldrich andpurified by vacuum sublimation before use. Thin films were deposited from resistively heatedquartz crucibles in a UHV chamber with a base pressure of 10-10 mbar.

Results and Discussion
The AFM image of the annealed TiO2 (110) surface is shown in Figure 1. Regular, flat
terraces are observed consistent with the manufacturers stated offcut angle. The contact
angle measurements in Figure 2 clearly show the effect of the adsorbed dienol molecules.

Fig. 1.

Contact mode AFM image (left) of the TiO2 (110) rutile surface after annealing at 1273 K in airfor 5 hours. The profile (right) shows that the atomically flat, 400 nm wide terraces have a stepheight corresponding with the (110) axis repeat distance of 0.32 nm.5

Fig. 2.

Contact angle measurements of TiO2 (110) surfaces showing the effect of exposure to aqueous
solutions of hydrophopic and hydrophilic dienol molecules.

References
1. T. Haber, J. Ivanco, M.G. Ramsey, R. Resel, J. Cryst. Growth, 310 (2008) 101.
2. J. Schütte, R. Bechstein, P. Rahe, et. al. Phys. Rev. B, 79 (2009) 045428.
3. T. Lana-Villarreal, A. Rodes, J. M. Perez, R. Gomez J. Am. Chem. Soc., 127 (2005) 12601.
4. L. de la Garza, Z. V. Saponjic, N. M. Dimitrijevic, et. al. J. Phys. Chem. B, 110 (2006) 680.
5. H. Onishi, Y. Iwasawa, Surface Science 313 (1994) L783.