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.

/pdf/colloquium-reactive-plasmas-as-a-versatile-nanofabrication-41yd8l1e03.pdf

Colloquium: Reactive plasmas as a versatile nanofabrication tool

Dynamic self-organization phenomena in complex ionized gas systems: new paradigms and technological aspects

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...

Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications

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 ...

Crystal size and temperature measurements in nanostructured silicon using Raman spectroscopy

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.

https://oatao.univ-toulouse.fr/649/1/Vahlas_649.pdf

Principles and applications of CVD powder technology

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.

Nanoparticle formation in low-pressure silane plasmas: bridging the gap between a-Si:H and μc-Si films

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.

/pdf/effect-of-the-nanoparticles-on-the-structure-and-23q63p3jy9.pdf

Effect of the nanoparticles on the structure and crystallization of amorphous silicon thin films produced by rf glow discharge

Nanometric powder of stoichiometric silicon carbide produced in square-wave modulated RF glow discharges

SiCN nanometric powder produced in square-wave modulated RF glow discharges

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.

S.N. Sharma

Papers

Nanoparticle formation in low-pressure silane plasmas: bridging the gap between a-Si:H and μc-Si films

Effect of the nanoparticles on the structure and crystallization of amorphous silicon thin films produced by rf glow discharge

Nanometric powder of stoichiometric silicon carbide produced in square-wave modulated RF glow discharges

SiCN nanometric powder produced in square-wave modulated RF glow discharges

Nanopowder of silicon nitride produced in radio frequency modulated glow discharges from SiH4 and NH3