Laser-Grown Silicon Nanoparticles and Photoluminescence Properties

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 CO 2 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

Biomedical and Sensor Applications of Silicon Nanoparticles

“…Based on the wet chemistry, Si NPs can be produced in inverse micelles [17,18] by synthesis in high-temperature supercritical solutions [19] and by reduction of alkylsilicon halides [20]. Gas-phase approaches are based on silane or disilane decomposition either via laser light irradiation, such as photolysis [21] and pyrolysis [22][23][24][25], or via electron impact [26]. In addition, Si NPs can be obtained via wet electrochemical etching of Si wafer in hydrofluoric acid, followed by ultrasound treatment [27][28][29].…”

“…Si NPs with an oxide surface passivation typically show a dipole-forbidden, moderately intense, PL emission ranging from yellow-orange to IR [22][23][24]. For example, in Figure 18.1 PL spectra measured under UV excitation on size-selected Si nanoparticles prepared by laser pyrolysis and exposed to air are shown [23].…”

“…In fact, Si NPs produced by laser pyrolysis are agglomerated due to particle coagulation and coalescence during the growth process [22,24,39], with typical aggregate size of some tens of nanometers, as measured by dynamic light scattering on nanopowder suspensions. Etching of Si and SiO 2 is well established thus far.…”

“…The results suggested that the surface modification of Si nanoparticles by SiÀO bonds did not affect the luminescence behavior of the Si cores. Recently, we found that oxidation by heating under air can turn pyrolytic Si NPs luminescent in the red [24,32]. However, this luminescence arises mainly from the dangling unsaturated bonds of SiÀO on the NP surfaces rather than from the Si core [12,13].…”

“…Bearing this in mind, in the framework of the BONSAI Project, 1 we tried to evaluate the initial phase of NPs-cell membrane interaction, addressing, in particular, the standard viability tests and their correlation with alteration in transendo-/epithelial resistance. Biocompatibility tests were performed on Si NPs prepared by laser pyrolysis [22,24,73].…”