Plasma production of metallic nanoparticles
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Metallic iron and iron oxide particles were produced by injecting ferrocene into the afterglow region of a low pressure, low power, plasma generated using a microwave power source. This was done as part of an effort to explore the feasibility of using flow type microwave plasmas for the production of metal nanoparticles. It was found that two parameters had the largest impact on the particles: injection point and plasma composition. Analysis done using Mossbauer effect spectroscopy, transmission electron microscopy, and x-ray diffraction indicated that low yields of small particles (ca. 10 nm) resulted from injection into the afterglow region. Much higher yields of large particles (ca. 50 nm) formed if the ferrocene was injected through the coupler. In hydrogen plasmas the particles that were produced were metallic iron, whereas in oxygen and argon plasmas the particles were iron oxide. In all cases significant amounts of graphitic carbon formed around the metal particles.
I. INTRODUCTION There is increasing interest in producing and studying gas phase produced nanoparticles. Ceramic particles are of the greatest interest because of their potential use in making ceramic parts, for use in adiabatic engines, and in other high temperature applications.1"4 However, there is also strong interest in non-ceramic materials as it has been shown that nanoparticles often have different properties for light adsorption, magnetism, catalytic behavior, and conductivity than do larger particles of the same materials." For example, there is a strong interest in exploring the production of magnetic nanoparticles that would be useful for data storage applications. New technologies for the production of nanoparticles are being developed. One reason is that it is clear that the surface properties of nanoparticles are very much a function of the details of production. Surface properties of nanoparticles can strongly impact final properties, such as the tendency to agglomerate and resistance to surface oxidation.2'3 Also, different production techniques lead to different levels of purity. It is generally understood, for example, that production from gas phase species leads to the formation of particles of higher purity than production in the liquid phase. This is particularly important for ceramics because even minute impurity levels can significantly weaken the final product.8 There is also interest in developing techniques that are more easily controlled, lead to tighter size distributions, and yield a product with a more uniform crystallinity.
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)Author to whom correspondence should be addressed. J. Mater. Res., Vol. 7, No. 8, Aug 1992 http://journals.cambridge.org
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Various plasma techniques have recently been found to have promise as a means to produce unique ceramic nanoparticles.9^13 The success of those efforts suggests that similar techniques be applied to the production of other types of nanoparticles. Indeed, the following is a report on the use of one particular plasma technique, flow-type microwave
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