Size and Surface Control of Optical Properties in Silicon Nanoparticles (original) (raw)
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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 .
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.
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.
The Journal of Physical Chemistry B, 1997
Weblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization-controlled condensation technique. SEM micrographs show particles with ∼10 nm diameter but the Raman shift suggests the presence of particles as small as ∼4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending, and rocking vibrations of the Si-O-Si bonds, indicating the presence of a surface oxidized layer, SiO x (x < 2). Further oxidation of the Si core appears to be very slow and inefficient under ambient temperature, but annealing at higher temperatures facilitates the oxidation. The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiO x passivated coating. They show a short-lived blue emission characteristic of the SiO 2 coating and a biexponential longer-lived red emission. The short lifetime component of the red emission, about 12 µs, does not depend on emission wavelength. The longer-lived component has a lifetime that ranges from 80 to over 130 µs (at 300 K), increasing with emission wavelength. The results are consistent with the quantum confinement mechanism as the source of the red photoluminescence.
Optical Materials, 2005
Size-dependent optical properties of laser-synthesized Si-based nanopowders were investigated by photo-luminescence (PL) and photo-luminescence excitation (PLE) spectroscopy on powder samples annealed in air in the 700-1000°C temperature range. TEM analysis reveals that at increasing annealing temperature a progressive Si nanoparticle size reduction occurs as a consequence of crystalline core oxidation, and a corresponding blue-shift of the PL emission is observed. The subsequent step is the preparation of nanocomposite materials by nanopowders dispersion and integration into a continuous silica phase by sol-gel processing. Synthesis parameters are adjusted in order to preserve the PL red emission from Si nanostructures. An interesting application would consist in the Er incorporation into the nanocomposite glassy material aiming at the 1.54 lm Er emission sensitization by energy transfer from Si nanostructures to nearby Er ions. However, it was found that Si nanoparticles are completely oxidized at the processing temperatures (1400°C) required to activate Er emission. Here we demonstrate that better and promising results can be achieved introducing in the sol-gel Si-based nanopowders withstanding higher temperatures.
Facile production of ultra-fine silicon nanoparticles
Royal Society Open Science, 2020
A facile procedure for the synthesis of ultra-fine silicon nanoparticles without the need for a Schlenk vacuum line is presented. The process consists of the production of a (HSiO 1.5 ) n sol–gel precursor based on the polycondensation of low-cost trichlorosilane (HSiCl 3 ), followed by its annealing and etching. The obtained materials were thoroughly characterized after each preparation step by electron microscopy, Fourier transform and Raman spectroscopy, X-ray dispersion spectroscopy, diffraction methods and photoluminescence spectroscopy. The data confirm the formation of ultra-fine silicon nanoparticles with controllable average diameters between 1 and 5 nm depending on the etching time.
Applied Physics A, 2004
Silicon nanocrystals (Si-nc) embedded in SiO 2 matrix have been prepared by high temperature thermal annealing (1000-1250 C) of substoichiometric SiO x lms deposited by plasma-enhanced chemical vapor deposition (PECVD). Different techniques have been used to examine the optical and structural properties of Si-nc. Transmission electron microscopy analysis shows the formation of nanocrystals whose sizes are dependent on annealing conditions and deposition parameters. The spectral positions of room temperature photoluminescence are systematically blue shifted with reduction in the size of Si-nc obtained by decreasing the annealing temperature or the Si content during the PECVD deposition. A similar trend has been found in optical absorption measurements. X-ray absorption ne structure measurements indicate the presence of an intermediate region between the Si-nc and the SiO 2 matrix that participates in the light emission process. Theoretical observations reported here support these ndings. All these efforts allow us to study the link between dimensionality, optical properties, and the local environment of Si-nc and the surrounding SiO 2 matrix.