Manipulation of Gold Nanoparticles: Influence of Surface Chemistry, Temperature, and Environment (Vacuum versus Ambient Atmosphere) † K. Mougin,* ,‡ E. Gnecco, § A. Rao, § M. T. Cuberes, | S. Jayaraman, ⊥ E. W. McFarland, # H. Haidara, ‡ and E. Meyer § ICSI-CNRS, 15 Rue Jean Starcky, 68057 Mulhouse, France, Institute of Physics, UniVersity of Basel and NCCR “Nanoscale Science”, Klingelbergstrasse 82, 4056 Basel, Switzerland, Laboratorio de Nanote ´ cnicas, UniVersidad de Castilla-La Mancha, Plaza Manuel Meca 1, 13400 Almade ´ n, Spain, Corning Incorporated, 1 Science Center Road, Corning, New York 14831, and Chemical Engineering Department, UniVersity of CaliforniasSanta Barbara, Santa Barbara, California 93106-5080 ReceiVed September 20, 2007. In Final Form: October 24, 2007 We have manipulated raw and functionalized gold nanoparticles (with a mean diameter of 25 nm) on silicon substrates with dynamic atomic force microscopy (AFM). Under ambient conditions, the particles stick to silicon until a critical amplitude is reached by the oscillations of the probing tip. Beyond that threshold, the particles start to follow different directions, depending on their geometry and adhesion to the substrate. Higher and lower mobility were observed when the gold particles were coated with methyl- and hydroxyl-terminated thiol groups, respectively, which suggests that the adhesion of the particles to the substrate is strongly reduced by the presence of hydrophobic interfaces. Under ultrahigh vacuum conditions, where the water layer is absent, the particles did not move, even when operating the atomic force microscope in contact mode. We have also investigated the influence of the temperature (up to 150 °C) and of the geometrical arrangement of the particles on the manipulation process. Whereas thermal activation has an important effect in enhancing the mobility of the particles, we did not find differences when manipulating ordered versus random distributions of particles. 1. Introduction Nanomanipulation is a complex problem, where mechanical and chemical properties of substrates, probing tools, and nano- objects (“particles”) are combined and different results are expected depending on the environmental conditions. Despite the fundamental and practical interest of this problem, systematic investigations on nanomanipulation are still scarce. A reason for that is the difficulties in quantifying the dynamical processes occurring while manipulating, that is, collisions between probing tips and particles, friction between particles and substrates, electrostatic interactions among all of them, and so forth. The most accurate manipulation studies of nanoparticles have been performed by scanning tunneling microscopy (STM). In a pioneer experiment, one of us moved single C 60 molecules along the steps of a Cu(111) surface using a scanning tunneling microscope in ultrahigh vacuum (UHV). 1 Unfortunately, despite the accurate level of control obtained with STM, the energy dissipated in the manipulation process cannot be estimated with this technique. Manipulation of large C 60 islands on NaCl was performed by Lu ¨ thi et al. using contact atomic force microscopy (AFM). 2 Even if the shear between the islands and crystal surface can be derived from the frictional forces experienced by the AFM tip while scanning, the applicability of contact AFM to nanomanipulation is limited to relatively large objects (tens of nanometers in size). A compromise between the two techniques is tapping mode AFM. Here, the phase shift of the cantilever oscillations with respect to the external periodic excitation can be used to estimate the dissipated energy. This method was recently used by Ritter and co-workers to manipulate antimony particles on a graphite surface in air. 3 Gold particles are very attractive for different reasons. For instance, they are ideal electrodes for molecular electronics. 4 Gold clusters below 5 nm in size deposited onto thin metal oxides also exhibit unexpected highly catalytic activity (not obtained with bulk metal) for different reactions, from combustion to hydrogenation, reduction, and so forth. 5,6 Coated with organic molecules, gold nanoparticles can be used for DNA assays in genomics, 7,8 as signal amplifiers for biological recognition or for quantitation of tags in biological assays. To utilize and optimize the chemical/physical properties of nanosized gold particles, a large spectrum of research has been done on the control of the size, 9,10 shape, 11-14 surface chemistry, 15-18 and aggregation † Part of the Molecular and Surface Forces special issue. ‡ ICSI-CNRS. § University of Basel and NCCR “Nanoscale Science”. | Universidad de Castilla-La Mancha. ⊥ Corning Incorporated. # University of CaliforniasSanta Barbara. (1) Cuberes, M. T.; Schlitter, R. R.; Gimzewski, J. K. Appl. Phys. Lett. 1996, 69, 3016. (2) Lu ¨thi, R.; Meyer, E.; Haefke, H.; Howald, L.; Gutmannsbauer, W.; Gu ¨ntherodt, H.-J. Science 1994, 266, 1979. (3) Ritter, C.; Heyde, M.; Stegemann, B.; Rademann, K.; Schwarz, U. D. Phys. ReV.B 2005, 71, 085405. (4) Adams, D. M.; Brus, L.; Chidsey, C. D.; Creager, S.; Creutz, C.; Kagan, C. R.; Kamat, P. V.; Lieberman, M.; Lindsay, S.; Marcus, R. A.; Metzger, R. M.; Michel-Beyerle, M. E.; Miller, J. R.; Newton, M. D.; Rolison, D. R.; Sankey, O.; Schanze, K. 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Commun. 1994, 801-802. 1577 Langmuir 2008, 24, 1577-1581 10.1021/la702921v CCC: $40.75 © 2008 American Chemical Society Published on Web 01/18/2008