corrugations are formed evidently faster at this potential, the average vertical distance between the lowest and the highest sites of the oxidized film is about 400 nm, mainly due to the shorter time of the positive pulse. The current versus time curve, shown in Figure 3B, indicates also that at short pulses discharging of the film is not complete. Thus, the induction time also becomes shorter because the film is not fully dis- charged. Similar to other results, the periodicity in the appear- ance of hills and valleys is close to 4±5 lm. Changes of the film morphology become significant several seconds after the oxidizing potential is applied. This may be the result of a relatively high internal resistance in the AFM cell causing current limitations. In addition, it is likely that a certain time is required to attain a minimum concentration of 6OT +. in the film. On the other hand, during the reduction pro- cess of the film this induction time required to stabilize the sur- face is evidently shorter. It is well-known, also from AFM mea- surements, [22,23] that during the doping process of conductive polymers, a significant increase of the polymer volume takes place. However, during the morphology changes observed in these studies, the resulting film volume seems to be unchanged, since the formation of hills is counterbalanced by the forma- tion of valleys. In fact, at a film thickness less than that typical- ly used in these studies (more than 1 lm) the observed effects are not reversible and the electrode surface is not stable. The observed phenomena may be interpreted using the fol- lowing model. The neutral molecules of 6OT form helical struc- tures, earlier observed by scanning tunneling microscopy (STM). [24] Due to equal interactions between the molecules in the solid phase, a flat layer is formed on the electrode surface. Upon oxidation of 6OT, producing successively the radical cat- ion and the dication species, the conformation of the molecules is changed from the twisted, helical form to a flat one. [24] This dramatically changes the structure of existing molecular interac- tions, mainly due to the formation of thermodynamically more stable p-dimers and/or subsequently due to the formation of p-stacks, as postulated by Miller and Mann. [25] The macroscopic effect of the molecular stack structure is the appearance of hills and valleys observed in our EC AFM measurements. Addition- ally, diffusion of the solvated anions must be involved in the pro- cess to compensate the charge of the oxidized form of 6OT. This in fact facilitates displacements of oxidized flat molecules. Our observations seem to be consistent with the mechanism of the electrode process proposed by Miller and Mann [25] for oligothiophenes. 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Cai, P. Liu, A. R. Zhu, Appl. Surf. Sci. 1992, 60/61, 342. [25] L. L. Miller, K. R. Mann, Acc. Chem. Res. 1996, 29, 417. [26] G. Bidan, A. De Nicola, V. EnØe, S. Guillerez, Chem. Mater. 1998, 10, 1052. Chemical Nanolithography with Electron Beams** By Armin Gölzhäuser,* Wolfgang Eck, Wolfgang Geyer, Volker Stadler, Thomas Weimann, Peter Hinze, and Michael Grunze The development of simple and rapid techniques for the site-specific immobilization of single molecules or molecular aggregates is a central objective in nanoscience. Such chemi- 806 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim,2001 0935-9648/01/1106-0806 $ 17.50+.50/0 Adv. Mater. 2001, 13, No. 11, June 5 COMMUNICATIONS ± [*] Dr. A. Gölzhäuser, Dr. W. Eck, W. Geyer, V. Stadler, Prof. M. Grunze Angewandte Physikalische Chemie Universität Heidelberg Im Neuenheimer Feld 253, D-69120 Heidelberg (Germany) E-mail: armin.goelzhaeuser@urz.uni-heidelberg.de Dr. T. Weimann,P. Hinze Physikalisch Technische Bundesanstalt Bundesallee 100, D-38116 Braunschweig (Germany) [**] We thank the Bundesministerium für Bildung und Forschung (BMBF) and the Deutsche Forschungsgemeinschaft (DFG) for financial support. W. Geyer thanks the state of Baden-Württemberg for a stipend.