Platinum nanoparticles growth by means of pulsed laser ablation
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N11.25.1
Platinum nanoparticles growth by means of pulsed laser ablation R. Dolbec, E. Irissou, F. Rosei, D. Guay, M. Chaker and M.A. El Khakani* INRS-Énergie, Matériaux et Télécommunications, 1650 Boul. Lionel-Boulet, C.P. 1020, Varennes, Québec, J3X 1S2, Canada. *Corresponding author: [email protected] ABSTRACT Platinum nanoparticles were deposited onto Highly Oriented Pyrolitic Graphite (HOPG) substrate by laser ablating a Pt target at room temperature into a vacuum chamber. By varying the helium background pressure (from 10-5 to 0.5 Torr) and the target-to-substrate distance (from 3 to 6 cm), we were able to explore a large range of kinetic energies (i.e., from ~4 to ~130 eV/atom) of the Pt ablated neutrals species impinging on the HOPG substrates. Thus, the effect of the kinetic energy on the size and the surface density of Pt nanoparticles has been investigated ex-situ by means of scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The pulsed laser deposition technique is shown to produce Pt nanoparticles (of which diameter in the 1 - 4 nm range) with a relatively narrow size distribution. While the size of the PLD Pt nanoparticles is shown to be mainly influenced by the number of laser pulses, their shape is found to be more sensitive to kinetic energy of the Pt ablated species. INTRODUCTION The pulsed laser deposition (PLD) is a powerful and versatile method that has been used to deposit a variety of nanostructured materials under a very wide range of deposition conditions [1-3]. The extremely high instantaneous deposition rate of PLD together with the highly energetic ablated species are among the unique features that distinguish PLD from other conventional deposition methods [4,5]. In the early stages of growth, the supersaturated flux of the energetic ablated species leads to a high density of nucleation sites on the substrate and consequently to the formation of nano-islands or nanoparticles of the material being deposited. As the deposition process continues, the PLD leads to the formation of thin films (up to few 100s nm-thick) which are generally found to be nanostructured [2-7]. Nevertheless, the nanostructural characteristics of PLD thin films have been shown to be greatly influenced by the deposition conditions (e.g. background gas and pressure, laser fluence, target-to-substrate distance, substrate temperature, etc…). As an illustration, we have demonstrated that the grain size and nanoporosity of PLD nanostructured SnO2 thin films can be monitored, to some extent, by controlling the substrate deposition temperature and the oxygen background pressure in the deposition chamber [6,7]. On the other hand, it has been shown that the nanocrystalline structure of PLD gold thin films can be correlated to the kinetic energy (KE) of the ablated species [8, 9]. Despite the numerous studies reported on the PLD growth of thin films, much less effort has been dedicated so far to the study of the early stages of PLD growth that leads to the formati
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