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

Microcantilevers were first introduced as imaging probes in Atomic Force Microscopy (AFM) due to their extremely high sensitivity in measuring surface forces The versatility of these probes, however, allows the sensing and measurement of a host of mechanical properties of various materials Sensor parameters such as resonance frequency, quality factor, amplitude of vibration and bending due to a differential stress can all be simultaneously determined for a cantilever When measuring the mechanical properties of materials, identifying and discerning the most influential parameters responsible for the observed changes in the cantilever response are important We will, therefore, discuss the effects of various force fields such as those induced by mass loading, residual stress, internal friction of the material, and other changes in the mechanical properties of the microcantilevers Methods to measure variations in temperature, pressure, or molecular adsorption of water molecules are also discussed Often these effects occur simultaneously, increasing the number of parameters that need to be concurrently measured to ensure the reliability of the sensors We therefore systematically investigate the geometric and environmental effects on cantilever measurements including the chemical nature of the underlying interactions To address the geometric effects we have considered cantilevers with a rectangular or circular cross section The chemical nature is addressed by using cantilevers fabricated with metals and/or dielectrics Selective chemical etching, swelling or changes in Young's modulus of the surface were investigated by means of polymeric and inorganic coatings Finally to address the effect of the environment in which the cantilever operates, the Knudsen number was determined to characterize the molecule-cantilever collisions Also bimaterial cantilevers with high thermal sensitivity were used to discern the effect of temperature variations When appropriate, we use continuum mechanics, which is justified according to the ratio between the cantilever thickness and the grain size of the materials We will also address other potential applications such as the ageing process of nuclear materials, building materials, and optical fibers, which can be investigated by monitoring their mechanical changes with time In summary, by virtue of the dynamic response of a miniaturized cantilever shaped material, we present useful measurements of the associated elastic properties

/pdf/measurement-of-mechanical-properties-of-cantilever-shaped-4sjli2d1sl.pdf

Measurement of Mechanical Properties of Cantilever Shaped Materials.

Silicon carbide films with different carbon concentrations xC have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH4/CH4/H2 gas mixture at a low substrate temperature of 500 °C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at xC = 49 at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6 nm. At a lower value of xC, polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of xC, amorphous carbon and silicon carbide coexist in the films.

https://iopscience.iop.org/article/10.1088/0957-4484/18/46/465601/pdf

Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition

Electrophysical properties of thin germanium/carbon layers produced on silicon using organometallic radio frequency plasma enhanced chemical vapor deposition process

The influence of CH4 addition on composition, structure and optical characteristics of SiCN thin films deposited in a CH4/N2/Ar/hexamethyldisilazane microwave plasma

In a structure zone model (SZM), the temperature and the sputtering gas pressure have been proposed as major factors explaining the structural properties of both evaporated and sputtered metals. Nevertheless, there is no evidence that such models can be applied to amorphous hydrogenated carbon films synthesized by radio frequency plasma enhanced chemical vapor deposition (rf PECVD). This paper reports on an original experiment designed to test by atomic force microscopy the hypothesis of an analogy between the rf PECVD amorphous materials and the existing SZM model for metals (amorphous and crystalline). Our results show that four zone morphologies called 1, M, T, and 2 can be obtained for amorphous materials according to the adatom mobility conditions. The parameters that control these morphologies are the plasma pressure, the surface temperature, and the plasma composition. The SZM model enables control of the a-C:H and a-C:D growth process. Zone T was found particularly interesting for the preparation ...

Structure of amorphous hydrogenated carbon films prepared by radio frequency plasma enhanced chemical vapor deposition. An analogy with the structure zone model developed for metals

Using a radio frequency remote plasma deposition process, hydrogenated amorphous carbon thin films were prepared from a variety of hydrocarbon precursors. Monomers were aliphatic chains (butane, trans-2-butene), rings (ethylcyclohexane), or aromatics (styrene, ethylbenzene), mixed with hydrogen. These films were elaborated in order to be used in inertial confinement fusion experiments with the future megajoule laser. Thickness and roughness were studied and optimized in relation of plasma parameters. Structural properties were analyzed by Fourier transform infrared, Raman diffusion, and others.

Comparative study of a-C:H films for inertial confinement fusion prepared with various hydrocarbon precursors by radio frequency-plasma enhanced chemical vapor deposition

French targets prepared for inertial confinement fusion experiments, to be shot on the Laser Megajoule facility, are organic (CHx) microshells. The microshell, that contains the deuterium–tritium mixture (DT), is placed in a gold holraum that converts the laser light into an x-ray flow. It is an indirect drive to reach ignition. This microshell, whose role is an ablator to initiate compression of the target, is fabricated by plasma polymerization of organic precursors. In these implosion experiments, it is necessary to control the preheat of the deuterium–tritium fusible mixture in the capsule, and the ablation front instability, by doping the ablator layer with a small quantity of high Z material. The germanium or bromine doping of the CHx enables the control of the microshell opacity to prevent the preheat of DT from high energetic x rays. Titanium is used to diagnostises the implosion of the target. The coating properties evolve with the amount of dopant incorporated in the CHx matrix. Evolution of the...

Doped CHx microshells prepared by radio frequency plasma enhanced chemical vapor deposition for inertial confinement fusion experiments

Amorphous hydrogenated carbon films are the nominal ablators to be used in French inertial confinement fusion (ICF) experiments These targets are developed for the future Megajoule laser (LMJ) of 

Properties of a-C:H Coatings Prepared by PECVD for Laser Fusion Targets

This article deals with the development of a radio frequency plasma enhanced chemical vapor deposition thick film (175 μm thickness) derived from aliphatic chains, trans-2-butene, monomer mixed with hydrogen and various noble gases (helium, argon, and krypton). The main purpose was to engineer an amorphous hydrocarbon film (a-C:H) with low surface roughness of less than 20 nm, designed for use on an “ablator” in a new “MegaJoule” laser facility. Morphology and roughness were characterized by atomic force microscopy. An improvement of 70% is obtained by adding a bias on the substrate.

Atomic force microscopy investigation of a-C:H films prepared by plasma enhanced chemical vapor deposition for inertial confinement fusion experiments

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