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A B S T R A C T S TUESDAY, JUNE 29 N A N O S E A 2 0 1 0 will be presented and a description of the structure and morphology of Suzuki surfaces of as-UHV-cleaved crystals and additionally annealed crystals, which exhibit surfaces restructured by diffusion and evaporation processes, is given. A discussion about defects like dislocations is involved. Further, it will be discussed to what extend the nano-structured Suzuki surface can be used as a nano-template for molecules and metal nano-clusters. First-time experiments will be presented, which exemplify the nano-template effect of Suzuki Surfaces. [1] K. Suzuki, J. Phys. Soc. Jpn. 16, 67 (1961) [2] C. Barth and C. R. Henry, New J. Phys. 11, 043003 (2009) [3] C. Barth and C. R. Henry, Phys. Rev. Lett. 100, 096101 (2008) [4] A. S. Foster, C. Barth and C. R. Henry, Phys. Rev. Lett. 102, 256103 (2009) 9H30-9H50 Electrostatic assembly of colloidal nanoparticles by AFM nanoxerography. Etienne PALLEAU, Laurence RESSIER , Guillaume VIAU (LPCNO, INSA, Département Génie Physique 135 avenue de Rangueil 31077 Toulouse Cedex 4) etienne.palleau@insa-toulouse.fr, ressier@insatoulouse.fr 1 – Introduction Colloidal nanoparticles are promising building blocks to fabricate future nanodevices in various domains such as chemical and biologic sensing, electronics, optics... But their integration in functional devices requires their directed assembly at desired locations on substrates. Electrostatic nanopatterning by atomic force microscopy (AFM) is an emerging tool to tackle this technological challenge [1]. This so-called “AFM nanoxerography” process utilizes charged patterns obtained by AFM charge writing into electret thin films to generate strong electric fields above the surface which act, via electrostatic interactions, as self-assembly targets for any kinds of charged or polarizable colloids. We expose here the directed assembly of various colloidal nanoparticles onto charged patterns written by AFM into poly(methylmethacrylate) (PMMA) thin films under ambient conditions. We also investigate the contribution of the two electrostatic forces responsible of the selective deposition of these colloids onto charged patterns. 2 – Experiments and results The AFM nanoxerography process is a two step method. The first step consists in AFM charge writing into 100 nm PMMA (996 k molecular weight) thin films spin-coated on a p-doped (1016 cm-3) silicon substrate under ambient conditions (Fig. 1a)). The surface potentials of such charged patterns are measured by Kelvin Force Microscopy (KFM). The second step of the process consists in dipping the electrostatically patterned substrate into non polar solvents containing nanoparticles then rinsing it in fresh solvent to remove the loosely adsorbed nanoparticles and finally drying it in nitrogen stream (Fig. 1b)). The directed nanoparticle assembly is finally observed by AFM in tapping mode (Fig. 1c)). 37
A B S T R A C T S TUESDAY, JUNE 29 N A N O S E A 2 0 1 0 Figure 1. Principle of the AFM nanoxerography process The AFM ability to perform, with the same instrument, charge writing with a great flexibility of pattern design, high-resolution charge imaging by surface potential measurements (KFM) and topography imaging by tapping, is very useful for understanding and improving the nanoxerography process. AFM nanoxerography is a generic process since it can be used to trap any charged and/or polarizable colloids (nanoparticles, nanotubes [2], biomolecules [3]) on specific areas of surfaces. To illustrate this point, we present in this paper the directed assembly of various kinds of colloidal nanoparticles by AFM nanoxerography, such as 100 nm latex nanoparticles in isopropanol, 10 nm silver nanoparticles or 2-3 nm gold nanoparticles in hexane. Depending on the surface charge and the polarizability of the colloidal nanoparticles used, the electrophoretic (Coulomb) and dielectrophoretic forces lead to a specific attraction/repulsion on positively and/or negatively charged patterns. For instance, negatively charged latex nanoparticles are attracted by electrophoretic forces on positively charged patterns and are strongly repeled from negatively ones. Silver nanoparticles do not seem to carry an important effective charge but are extremely polarizable leading to their directed assembly on both positively and negatively charged patterns. We recently performed numerical simulations of KFM measurements after AFM charge writing, in correlation with KFM experiments [4]. These simulations allow us to quantify the strenght of the electric field generated by charged patterns when immersed into several solvents. These results are used to quantify the contribution of each electrostatic force during the immersion of the charged substrates in the different colloidal solutions. 3 – Conclusion The directed assembly of various kinds of colloidal nanoparticles on specific areas of surfaces are performed by AFM nanoxerography. Depending on the surface charge and the polarizability of colloidal nanoparticles, the electrophoretic (Coulomb) and dielectrophoretic forces lead to a specific attraction/repulsion on positively and/or negatively charged patterns. Numerical simulations were carried out to quantify these electrostatic forces in various experimental conditions. [1] L. Ressier, E. Palleau, C. Garcia, G. Viau and B. Viallet, IEEE T Nanotech. 2009, 8 (4), 487-491 [2] L. Seemann, A. Stemmer, and N. Naujoks, Nano. Lett. 2007, 7 (10), 3007-3012 [3] E. Macarena Blanco, S. A. Nesbitt, M. A. Horton, and P. Mesquida, Adv. Mater, 2007, 19, 2469–2473 [4] E. Palleau, L. Ressier, Ł. Borowik and T. Mélin, Nanotech., 2010, under submission 38
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