CO2 laser-driven pyrolysis synthesis of silicon nanocrystals and applications (original) (raw)
Related papers
2005
The synthesis of silicon nanocrystals (Si-NC) has attracted a great deal of interest due to their size-dependent optical properties. The appearance of a strong visible photoluminescence (PL) even at room temperature makes this kind of material very interesting for applications in optoelectronics and photonics. In this work, we report on the possibility to control the optical properties of silicon nanostructures by fine tuning of both preparation and processing parameters. Large amount of Si-based nano-powders were prepared by cw CO2 laser pyrolysis of gasphase precursors followed by annealing at different temperatures, in controlled atmosphere. After the heat treatment, the structural and optical analyses revealed the presence of size-controlled optical properties, characterized by the typical Si-NC red-IR emission with lifetime ranging from a hundred of μs to some ms. Next step was the nano-powder dispersion by several methodologies and their incorporation into a silica sol-gel matrix. The realization of a glassy material that preserves the powder luminescence opens the way to a wide range of applications. To this purpose we focused our attention on the study of the influence of the sol-gel processing steps on the optical properties of Si-nano-powders. Moreover, a study of 1.54 micron Er emission sensitizing effect from Si-based nanostructures in sol-gel glasses was performed and is presented here.
Advanced Laser Technologies 2004, 2005
The synthesis of silicon nanocrystals (Si-NC) has attracted a great deal of interest due to their size-dependent optical properties. The appearance of a strong visible photoluminescence (PL) even at room temperature makes this kind of material very interesting for applications in optoelectronics and photonics. In this work, we report on the possibility to control the optical properties of silicon nanostructures by fine tuning of both preparation and processing parameters. Large amount of Si-based nano-powders were prepared by cw CO 2 laser pyrolysis of gasphase precursors followed by annealing at different temperatures, in controlled atmosphere. After the heat treatment, the structural and optical analyses revealed the presence of size-controlled optical properties, characterized by the typical Si-NC red-IR emission with lifetime ranging from a hundred of µs to some ms. Next step was the nano-powder dispersion by several methodologies and their incorporation into a silica sol-gel matrix. The realization of a glassy material that preserves the powder luminescence opens the way to a wide range of applications. To this purpose we focused our attention on the study of the influence of the sol-gel processing steps on the optical properties of Si-nano-powders. Moreover, a study of 1.54 micron Er emission sensitizing effect from Si-based nanostructures in sol-gel glasses was performed and is presented here.
Localized Synthesis of Silicon Nanocrystals in Silicon-rich SiO2 by CO2 Laser Annealing
2007
: The optical properties of a SiOx film rapid-thermal-annealed "RTA" by CO2 laser are primarily investigated. The micro-photoluminescence "-PL" and HRTEM analysis indicate that the precipitation of random-oriented Si nanocrystals can be initiated when laser intensity "Plaser" larger than 4.5 kW/cm2. At Plaser of 6 kW/cm2, the Si nanocrystals exhibits a largest diameter of 8 nm and a highest density of 4.51016 cm-3, which emits strong PL at 790-825 nm. The micro-photoreflectance of the CO2 laser RTA SiOx film reveals a volume-density-product dependent refractive index increasing from 1.57 to 1.87 as the Plaser increases from 1.5 to 7.5 kW/cm2. Nonetheless, the laser ablation of SiOx film occurs with a linear ablation slope of 35 nm/kW/cm2 at beyond 7.5 kW/cm2, which terminates the enlargement of Si nanocrystals, degrades the near-infrared PL, and slightly reduces the refractive index of the CO2 laser RTA SiOx film.
Surface control of optical properties in silicon nanocrystals produced by laser pyrolysis
Applied Surface Science, 2006
Macroscopic quantities (g/h) of Si nanoparticles were prepared by laser pyrolysis of silane and showed photoluminescence (PL) emission in the range 700-1050 nm after oxidation in air at a temperature T ! 700 8C. Two different strategies were followed to reduce as-produced particle agglomeration which hinders most of the applications, namely etching with either acid or alkaline solutions. Well isolated single particles were detected after acid etching in HF. Disaggregation was also achieved by the combined effect of the high power sonication and alkaline etching by tetra-methyl ammonium hydroxide (TMAH), which leaves OH terminated surfaces. However, in both cases re-aggregation was observed within a few hours after oxide removal. Stable dispersions of Si nanoparticles in different solvents were obtained by treatments of H-terminated surfaces with the surfactant TOPO (C 24 H 51 P O, trioctylphospine oxide) and by treatment of OH-terminated surfaces with Na 3 PO 4 .
Synthesis of Silicon Nanocrystals in Silicon-Rich SiO[sub 2] by Rapid CO[sub 2] Laser Annealing
Electrochemical and Solid-State Letters, 2005
Localized synthesis of 4.2-5.6 nm Si nanocrystals ͑nc-Si͒ in plasma enhanced chemical vapor deposition-grown Si-rich SiO x ͑x = 1.25͒ ͑SRSO͒ layer is demonstrated using a CO 2 laser annealing at intensity of 6.0 kW/cm 2. At an optimized surface temperature of 1285°C, the precipitated nc-Si in annealed SRSO results in near-infrared photoluminescence at 806 nm. The refractive index of the laser-annealed SRSO at 633 nm increases from 1.57 to 2.31 as the laser intensity increases from 1.5 to 6.0 kW/cm 2. Transmission electron microscopy analysis reveals that the average size and volume density of nc-Si embedded in the SRSO layer are about 5.2 nm and 1.08 ϫ 10 18 cm −3 .
Room temperature fabrication of silicon nanocrystals by pulsed laser deposition
Journal of Nanoparticle Research, 2014
n bulk 203 Volume fraction occupied by grains Vbulk grains Vfragment 3.2 9 10-3 Volumetric numerical density nbulk grains Vfragment 9.7 9 10 4 grains/ lm 3 Fraction of the full grains nbulk ntot 96 % CS-CSS grains Average crystal size d average 8.0 nm ± 1.5 nm Number of CS-CSS grains in the fragment n CS-CSS 9 Volume fraction occupied by grains VCSÀCSS grains Vfragment 1.1 9 10-3 Volumetric numerical density nCSÀCSS Vfragment 4.3 9 10 3 grains/ lm 3 Fraction of the CS-CSS grains nCSÀCSS ntot 4 % All grains Average crystal size d average 4.2 nm ± 1.7 nm Number of grains in the fragment n all grains 212 Volume fraction occupied by grains Vall grains Vfragment 3.9 9 10-3 Volume fraction occupied by grains nall grains Vfragment 1.0 9 10 5 grains/ lm 3
Journal of Nanoparticle Research, 1999
Pulsed CO 2 -laser-induced decomposition of different mixtures of SiH 4 and C 2 H 2 in a flow reactor has been employed to produce silicon carbide clusters and nanoparticles with varying content of carbon. The as-synthesized species were extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where, after having traversed a differential chamber, they were analyzed with a time-of-flight mass spectrometer. Thin films of silicon carbide nanoclusters were produced by depositing the clusters at low energy on potassium bromide and sapphire windows mounted into the differential chamber. At the same time, Si and SiC nanoparticles were collected in a filter placed into the exhaust line of the flow reactor. Both beam and powder samples were characterized by FTIR spectroscopy. The close resemblance of the spectra suggests that the composition of the beam and powder particles obtained during the same run is nearly identical. XRD spectroscopy could only be employed for the investigation of the powders. It was found that CO 2 laser pyrolysis is ideally suited to produce silicon carbide nanoparticles with a high degree of crystallinity. Nanopowders produced from the pyrolysis of a stoichiometric (2 : 1) mixture of SiH 4 /C 2 H 2 were found to contain particles or domains of pure silicon. The characteristic silicon features in the FTIR and XRD spectra, however, disappeared when C 2 H 2 was applied in excess.
Luminescent silicon nanostructures synthesized by laser ablation
physica status solidi (a), 2007
This paper describes the properties of silicon nanostructures synthesized by laser ablation. This is an extremely flexible technique allowing the fabrication of different kinds of nanostructures including porous films and Si nanocrystals embedded in Si oxide. Quantum confinement effects in nanostructures of indirect bandgap semiconductors have attracted great interest due to their new optical properties. This improvement of the efficiency of silicon in emitting light is a first step towards the integration of silicon in optoelectronics. Many groups are working on developing fabrication methods of Si nanocrystals and on the optimization of their luminescence properties. In particular, we describe in detail the mechanisms that govern nucleation and growth of these photoluminescent nanostructures.
Microstructural properties of laser synthesized Si/C/N nanoparticles
Applied Surface Science, 1996
Microstructural properties of nanosized particles produced by CO 2 laser synthesis from gaseous precursors, are studied by different techniques. Results on the characterization of binary (SiC and Si3N 4) and ternary (Si/C/N) ultrafine powders are presented. The evolution of the chemical composition and microstructure, after heat treatments in different atmospheres, is investigated in order to study and to improve the stability of these materials.
Journal of Nanoparticle Research, 2010
The preparation of sizeable quantities of luminescent Si nanoparticles (Si-np) with controlled morphology is a challenging task. Here, we describe two strategies aiming at size reduction of the Si-np produced in a laser-assisted silane pyrolysis reactor without detrimental effects on the process yield and on the nanoparticle structural and compositional properties. The first method is based on the addition of a sensitizer gas to dilute silane and consequently reduce the nucleation centres density without decreasing the reaction temperature. The second consists in the introduction of a collector at a variable distance from the irradiated region to freeze the particle growth and decrease the inter-particle sintering probability. We report on the characterization of the produced Si-np, and we show that by combining the two methods, we are able to prepare 4 nm crystalline core size nanoparticles with a productivity of 1 g per hour. We also describe the enhancement effect of the wet-chemical oxidation processes on the luminescence emission intensity of the Si-np.