Laser-grown silicon nanoparticles and photoluminescence properties
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Laser-grown silicon nanoparticles and photoluminescence properties N. Herlin-Boime1, K. Jursikova1, E. Trave2, E. Borsella3, O. Guillois1, F. Fabbri3 J. Vicens4; C. Reynaud1 1 : Service des Photons, Atomes et Molécules, Laboratoire Francis Perrin, CEA-CNRS URA 2453, Bat. 522, CEA Saclay, 91191 Gif sur Yvette Cédex (France) 2 : INFM, Dipartimento di Fisica "G. Galilei", Università di Padova, Via Marzolo, 8, 35131 Padova (Italy) 3 : ENEA, UTS FIS, Via E. Fermi 45, I-00044 Frascati, Rome (Italy) 4 : SIFCOM - ENSICAEN, UMR CNRS 6176, 6 Bd du Maréchal-Juin, F-14050 Caen Cedex (France)
ABSTRACT : Light-emitting silicon nanocrystals (Si nc) have attracted much interest due to their possible application as optoelectronic devices. The interest for Si nanopowders is enhanced by their photoluminescence (PL) emission intensity that can be very strong at room temperature. Due to the intrinsic biocompatibility of Si nanoparticles, this strong optical emission intensity as well as the long decay time (mean life time around hundred microseconds) make these powders potential candidates as tracers for in-vivo applications. Si nanopowders were obtained in gram quantities by CO2 laser pyrolysis of silane. The particles in the produced powders are in the size range 10-15 nm. These nanoparticles exhibit strong red photoluminescence after heat treatment. The appearance of intense PL emission is clearly related to the surface oxidation of the powders which must be carefully controlled. Several steps have been identified in the oxidation process. This paper presents a detailed study of the evolution of both the photoluminescence intensity and spectral dependence and of the crystalline structure as a function of the heat treatment. We also show that the nanopowders can be dispersed in liquids and incorporated in gel samples while keeping their intense photoluminescence. This result opens a route towards the fabrication of novel devices INTRODUCTION A large number of studies are related to the photoluminescence properties of silicon, to the understanding of the origin of this effect, as well as the possible applications, for example in optoelectronic devices. Several techniques have been used to obtain such Si-based nanostructures, see for example Li [1] and references therein. Among the synthesis techniques, the CO2 laser synthesis has proved to be efficient for the production of photoluminescent size selected silicon nanoparticles [2] with very high quantum efficiency [3]. In this case a pulsed CO2 laser is used and photoluminescence appears just after natural oxidation in air. It was shown that the photoluminescence properties originate from quantum confinement effects without any contribution from interaction between particles[4]. However, the production rate is very low, which does not make the method suitable for efficient fabrication of devices. Using a continuous CO2 laser, silicon nanopowders were also obtained by several groups [5, 1], and thermal and/or chemical treatments are necessary to obtain photoluminescence propert
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