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S.N. Sharma

Bio: S.N. Sharma is an academic researcher from University of Barcelona. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Glow discharge. The author has an hindex of 7, co-authored 8 publications receiving 165 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of the structure of silicon films prepared under particular glow discharge conditions conclusively showed that nanometer-size ordered regions can be present in the matrix of this disordered semiconductor.
Abstract: Detailed analysis of the structure of silicon films prepared under particular rf glow discharge conditions conclusively show that nanometer-size (∼2 nm) ordered regions can be present in the matrix of this disordered semiconductor. The obtaining of such a type of `nanostructured' silicon films, referred to as polymorphous silicon in the following, under a wide range of plasma conditions, is attributed to the contribution of silicon `nanoparticles' to the growth of the films.

77 citations

Journal ArticleDOI
TL;DR: In this article, thin films of nanostructured silicon (ns-Si:H) were deposited by plasmaenhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 °C substrate temperature using a silane and hydrogen gas mixture under continuous wave (cw) plasma conditions.
Abstract: Thin films of nanostructured silicon (ns-Si:H) were deposited by plasma-enhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 °C substrate temperature using a silane and hydrogen gas mixture under continuous wave (cw) plasma conditions. The nanostructure of the films has been demonstrated by diverse ways: transmission electron microscopy, Raman spectroscopy, and x-ray diffraction, which have shown the presence of ordered silicon clusters (1–2 nm) embedded in an amorphous silicon matrix. Because of the presence of these ordered domains, the films crystallize faster than standard hydrogenated amorphous silicon samples, as evidenced by electrical measurements during the thermal annealing.

28 citations

Journal ArticleDOI
01 Jan 1999-Vacuum
TL;DR: In this article, a SiC nanometric powder has been obtained in square-wave modulated radiofrequency glow discharges from CH 4 and SiH 4 gas mixtures, and the effects on the structure of the powder were examined by FTIR, EA, XPS and from optical transmittance measurements.
Abstract: SiC nanometric powder has been obtained in square-wave modulated radiofrequency glow discharges from CH 4 and SiH 4 gas mixtures. Chemical and structural characterization revealed that the as-deposited SiC:H powder underwent spontaneous oxidation when exposed to atmosphere. To stabilise the powder chemically, we carried out a thermal treatment under vacuum (10 −4 Pa) consisting of heating to 800°C (20°C/min). The effects on the structure of the powder were examined by FTIR, EA, XPS and from optical transmittance measurements. They can be summarized as follows: dehydrogenation of the powder that induces the formation of a SiC carbidic network and chemical stability under atmospheric conditions, further confirmed by exposure to air for more than 6 months. In addition, TEM images showed that the annealed powder presented a short-range order in β -SiC units, but there was no evidence of size changes due to sinterization or compactaction phenomena.

14 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a study involving the production and characterisation of silicon carbon nitride (SiC ǫ n) nanometric powder, obtained from square-wave modulated RF plasmas of SiH4+CH4+NH3 and SiH 4 + CH4 + N2 gas mixtures.
Abstract: Square-wave modulation of the electrical power supplied to low pressure and temperature radio frequency (RF) plasmas has been revealed as a suitable method to produce nanometric powder of high purity and nanometric size (10–100 nm). Here, we present a study involving the production and characterisation of silicon carbon nitride (SiCN) nanometric powder, obtained from square-wave modulated RF plasmas of SiH4+CH4+NH3 and SiH4 + CH4 + N2 gas mixtures. Electron diffraction patterns and transmission electron micrographs showed that the SiCN powder particles are amorphous and have a size distribution in the range 25–45 nm. X-ray photoelectron spectroscopy, elemental analysis and Fourier-transform infrared spectroscopy showed important differences in the structure, hydrogenation, chemical composition and bond distribution (SiC, SiN) of the samples owing to the use of different gas mixture. This powder could be used as a raw material to produce advanced ceramics and composites with higher thermal and chemical stability and improved mechanical properties.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported the production of SiN nanopowder at room temperature and low pressure by RF glow discharge decomposition of SiH 4 and NH 3 gases, where the RF power was modulated at 0.5 Hz with a duty cycle of 20% in order to control the size of the expelled particles.
Abstract: Square-wave modulated radio frequency (RF) plasmas have been shown to be a suitable source of nanometric size powder with high purity and controllable nanostructure. This paper reports the production of SiN nanopowder at room temperature and low pressure by RF glow discharge decomposition of SiH 4 and NH 3 gases. The RF power was modulated at 0.5 Hz with a duty cycle of 20% in order to control the size of the expelled particles. A study of the particle formation process using in-situ monitoring of the RF dissipated power is presented. Transmission electron microscopy showed a narrow size distribution of spherical particles from 25 to 45 nm and their electron diffraction provided evidence of a short range order in Si or SiN units depending on the precursor gas mixture. Analysis by Fourier transform infrared spectroscopy revealed the presence of SiN, NH and SiH bonds and the elemental analysis of the powder determined its chemical composition.

10 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the benefits and challenges of using plasma-based systems in nanofabrication of nanostructured silicon films, low-dimensional semiconducting quantum structures, ordered carbon nanotip arrays, highly crystalline ${\mathrm{TiO}}_{2}$ coatings, and nano-structured hydroxyapatite bioceramics are discussed.
Abstract: The underlying physics of the application of low-temperature, low-pressure reactive plasmas in various nanoassembly processes is described. From the viewpoint of the ``cause and effect'' approach, this Colloquium focuses on the benefits and challenges of using plasma-based systems in nanofabrication of nanostructured silicon films, low-dimensional semiconducting quantum structures, ordered carbon nanotip arrays, highly crystalline ${\mathrm{TiO}}_{2}$ coatings, and nanostructured hydroxyapatite bioceramics. Other examples and future prospects of plasma-aided nanofabrication are also discussed.

675 citations

Journal ArticleDOI
TL;DR: An overview of dynamic self-organization phenomena in complex ionized gas systems, associated physical phenomena, and industrial applications is presented in this paper, where the most recent experimental, theoretical, and modeling efforts to understand the growth mechanisms and dynamics of nano- and micron-sized particles, as well as the unique properties of the plasma-particle systems (colloidal, or complex plasmas) and the associated physical effects are reviewed and the major technological applications of micro- and nanoparticles are discussed.
Abstract: An overview of dynamic self-organization phenomena in complex ionized gas systems, associated physical phenomena, and industrial applications is presented. The most recent experimental, theoretical, and modeling efforts to understand the growth mechanisms and dynamics of nano- and micron-sized particles, as well as the unique properties of the plasma-particle systems (colloidal, or complex plasmas) and the associated physical phenomena are reviewed and the major technological applications of micro- and nanoparticles are discussed. Until recently, such particles were considered mostly as a potential hazard for the microelectronic manufacturing and significant efforts were applied to remove them from the processing volume or suppress the gas-phase coagulation. Nowadays, fine clusters and particulates find numerous challenging applications in fundamental science as well as in nanotechnology and other leading high-tech industries.

322 citations

Journal ArticleDOI
TL;DR: The fundamentals of nanocrystal formation in plasmas are discussed, practical implementations of plasma reactors are reviewed, the materials that have been produced with nonthermal plAsmas and surface chemistries that have be developed are surveyed, and an overview of applications of plasma-synthesized nanocrystals is provided.
Abstract: Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

292 citations

Journal ArticleDOI
TL;DR: In this article, a detailed structural characterization by Raman spectroscopy of hydrogenated amorphous silicon and of nanostructured silicon (ns-Si:H) thin films grown in radio-frequency plasma was presented.
Abstract: In this work we present a detailed structural characterization by Raman spectroscopy of hydrogenated amorphous silicon (a-Si:H) and of nanostructured silicon (ns-Si:H) thin films grown in radio-frequency plasma. The ns-Si:H thin films, also called polymorphous Si thin films, consist of a two-phase mixture of amorphous and ordered Si. The Raman spectra were measured at increasing laser intensities. Very low laser power densities (∼1 kW/cm2) were used to thoroughly analyze the structure of as-deposited thin films. Higher Raman laser powers were found to induce the crystallization of the films, which was characterized by the appearance of a sharp peak around 500 cm−1. This was attained faster in the ns-Si:H than in the conventional a-Si:H thin films because the silicon-ordered particles cause a heterogeneous nucleation process in which they act as seeds for crystallization. The laser power densities for film crystallization, crystal size, and surface temperature were determined from this Raman analysis. The ...

238 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the state of the art on materials produced by fluidized bed chemical vapor deposition (FBCVD) is presented, where the authors focus on the ways to ensure such contact and particularly on the formation of fluidized beds.
Abstract: Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique.

202 citations