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V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Secondary Ions emission from Alkanethiol-SAMs due to highly charged ions bombardment M Flores 1 , V. Esaulov 2 and Y. Yamazaki 3 1 Depto. de Física, Facultad de ciencias físicas y matemáticas, Universidad de Chile, casilla 110-V, Santiago, Chile. 2 Laboratoire des Collisions Atomiques et Moleculaires, Universite Paris-Sud, Orsay Cedex, France. 3 Atomic Physics Laboratory, Riken Institute, Wako, Saitama, Japan. email address corresponding author: mflorescarra@ing.uchile.cl Self-assembled monolayers (SAMs) are ordered molecular assemblies formed by the adsorption of an active surfactant on a solid surface. SAMs provide a convenient, flexible, and simple system with which to tailor the interfacial properties of metal, metal oxides and semiconductors [1]. The alkanethiols are a common type of molecules used to build SAMs. Several techniques have been used to study and characterize SAMs, for example SPM, optical and ion spectroscopies. In the latter case, the interaction of ions with SAM surfaces leads to the sputtering of molecules from the surface, with the detection of such molecules giving information on both the chemical and structural composition of the SAM. For this reason much experimental and theoretical effort has been directed towards ion-SAM collisions. Special case is the highly charged ions (HCI). For slow HCI, the potential energy stored in the projectile can far exceed its kinetic energy. In contrast to the kinetic sputtering process, which is due to momentum transfer from the ion to the surface, HCI may also transfer significant potential energy, removing ions and molecules from the surface in a process called potential sputtering. SAMs of the alkanethiol molecules Undecanethiol (UDT), HS(CH 2 ) 10 CH 3 , and Dodecanethiol (DDT), HS(CH 2 ) 11 CH 3 , were prepared on atomically flat Au(111) which was deposited as a thin film on freshly cleaved mica. The quality of the SAMs was confirmed by STM observations [2]. The samples were bombardment with Ar q+ ions. The q-dependence of the proton sputtering yield from hydrogen contaminated/covered surfaces has been found to follow a power law dependence and this was explained by the classical over barrier model. In this model a HCI approaching an atom/molecule induces multielectron transfer. In the case of our SAM it would induce electron transfer from the alkanethiol molecule terminal functional group. Removal of two electrons from the most external part of the SAM, would create a doubly charged chemical bond (C-H) 2+ . Because the molecule is a poor conductor, the reneutralization probability in the molecular layer should be lower than on a metal, and a proton may be released in the bond direction by Coulomb repulsion [3]. In general, in the above model the proton yield is then dependent on the probabilities of removal of the first and second electron and on reneutralization as the ion moves away from the surface, given a power law, Fig 1(a,b), and in the case under study the probabilities are strong dependent of the orientation of the terminal functional group, Fig. 1(c,d). Figure 1. Proton Yields from (a)UDT and (b)DDT under bombardment with Ar q+ ions. Top surface scheme of the SAMs corresponding to (c)UDT and (d)DDT. References [1] Love et al, Chem. Rev. 105 (2005) 1103. [2] O’Rourke et al, Appl. Phys. Lett., submitted. [3] Flores et al, Phys. Rev. A79 (2009) 022902. 54 Valparaíso, Chile

V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Structural characterization of Pb nanoislands in SiO 2 /Si interface synthesized by ion implantation through MEIS analysis D. F. Sanchez 1 , F. P. Luce 2 , Z. E. Fabrim 1 , M. A. Sortica 1 , P. F. P. Fichtner 1 and P. L. Grande 1 1 Institute of Physics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil email address corresponding author: dario.f.sanchez@gmail.com Recently, the Medium Energy Ion Scattering (MEIS) technique has been used as an additional tool for characterization of nanoparticles (NPs), where basically their shape, composition, size distribution, stoichiometry and the determination of depth distributions of different elements in a single NP have been successfully obtained. We have developed a Monte Carlo simulation and fitting software, the PowerMeis [1], that considers any geometry, size distribution, density of the nanostructures and also the asymmetry of the energy loss-distribution. In this work we investigate buried Pb NPs synthesized by ion implantation on SiO 2 /Si thin film, with low temperature and long aging time treatments followed by a high temperature thermal annealing. This process [2] leads to the formation of a dense 2D NPs array located at the SiO 2 /Si interface, as shown in Fig. 1. Through the 2D MEIS spectra (energy and angle), we have studied the nanostructure geometry, number density and mean NP size of such system. The present results are compared to transmission electron microscopy (TEM) measurements. Figure 1. (a) HRTEM micrograph from a [011] oriented sample presenting a cross-section view of the NPs partially embedded in the Si matrix; (b) Brightfield two-beam image, underfocus, demonstrating that the NPs are exclusively located at the SiO 2 /Si (100) interface. (c) Plan-view image (bright field, in focus) close to the (001) zone axis, showing square based NPs preferentially aligned parallel to the (011) planes of the matrix. In Fig. 2 is compared the experimental MEIS spectra to the simulation performed by the PowerMeis software using the NP geometrical shape described in Fig. 3 and number density of 3.5×10 11 cm -2 , close to 55 Valparaíso, Chile

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