Influence of Liquid Medium on Optical Characteristics of the Si Nanoparticles Prepared by Submerged Electrical Spark Discharge

We have measured the size, structure, and optical properties for two sets of nanoparticles synthesized via electrical-spark discharge between two plane silicon electrodes immersed in deionized water (DI) and 97 % ethanol. The nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV)-visible absorption spectrometry, Raman spectrometry, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The size and optical features of the nanoparticles were studied as functions of nature of the liquid. Nearly spherical, single-crystal, and morphologically similar Si nanoparticles with diameters in the 3–8 and 6–13 nm ranges were formed in the colloidal solutions of water and ethanol, with estimated indirect bandgaps of approximately 1.5 and 1.3 eV, respectively. In both cases, the Raman peaks were blue shifted with respect to those of bulk silicon, a result consistent with the small diameters of the particles. The silicon nanoparticles synthesized in water exhibited strong emission in the violet-blue range, with a double peak near 417 and 439 nm. For those synthesized in ethanol, blue-green emission centered at 463 nm was detected.     

The effect of water-soluble polymers on the stability and rheological properties of suspensions of fibrous activated charcoal

The stability and rheological characteristics of polymer-containing aqueous suspensions of fibrous activated charcoal are determined. It is shown that the improved stability of suspensions is observed in the presence of carboxymethyl cellulose, oxypropyl methyl cellulose, polyvinylpyrrolidone, and a new water-soluble cellulose derivative, whereas the presence of polyacrylamide, poly(acrylic acid), poly(vinyl alcohol), and starch leads to the formation of unstable suspensions having a broad particle size distribution. A correlation between the concentration of dispersed-phase particles corresponding to the transition to non-Newtonian flow and the characteristics of suspension stability (such as the rate of sedimentation, the volume of the sediment, and the particle size distribution) is established. It is suggested that the high degree of charcoal particle surface hydrophilization by polyvinylpyrrolidone and by the water-soluble cellulose derivative is mainly responsible for the stability of the modified suspensions.     

Fabrication of Silicon Carbide Nanocrystals by Electrical Discharge and Laser-Induced Processes in Solution

Plasma Chemistry and Plasma Processing - The capabilities of the liquid assisted electrical discharge technique with additional laser irradiation of colloids for the synthesis of SiC nanocrystals...     

Optical properties of silicon nanoparticles synthesized via electrical spark discharge in water

In this paper, we report a simple and low-cost technique for fabrication of silicon nanoparticles via electrical spark discharge between two plane silicon electrodes immersed in deionized water (DI). The pulsed spark discharge with the peak current of 60 A and a duration of a single discharge pulse of 60 μs was used in our experiment. The structure, morphology, and average size of the resulting nanoparticles were characterized by means of X-Ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). TEM images illustrated nearly spherical and isolated Si nanoparticles with diameters in the 3–8 nm range. The Raman peaks of the samples were shifted to the lower wave numbers in comparison to this of bulk crystalline silicon indicating the existence of tiny particles. The optical absorption spectrum of the nanoparticles was measured in the violet–visible (UV–Vis) spectral region. By measuring of the band gap we could estimate the average size of the prepared particles. The silicon nanoparticles synthesized exhibited a photoluminescence (PL) band in the violet-blue region with a double peak at around 417 and 439 nm. It can be attributed to oxide-related defects on the surface of silicon nanoparticles, which can act as the radiative centers for the electron-hole pair recombination.     

Spectroscopic diagnostics for an electrical discharge plasma in a liquid

We conducted spectroscopic studies of an electrical discharge plasma in a liquid, used for synthesis of nanosized particles of metals and their compounds. From the intensity ratio of the copper lines, we estimated the electron temperature, and from the Stark broadening of the hydrogen lines H _α we determined the electron density in the electrical discharge plasma. Information about the concentration of copper atoms in the discharge was obtained from analysis of the spectra in the region of resonance lines of copper. We carried out a comparative analysis of the plasma parameters for spark and arc discharges in water, ethanol, and air. Based on the equation of state for an ideal plasma, taking into account the Debye correction, we estimated the pressure in the plasma channel.