Novel method for the synthesis of thin film coatings on particulate materials

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Novel method for the synthesis of thin film coatings on particulate materials J.M. Fitz-Gerald Naval Research Laboratory, Code 6372, Washington, District of Columbia 20375

R.K. Singh, H. Gao, D. Wright, and M. Ollinger Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611

J.W. Marcinka Department of Electrical Engineering, Florida Atlantic University, Boca Raton, Florida 33431

S.J. Pennycook Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (Received 8 September 1997; accepted 26 May 1999)

In this paper, we show the feasibility of the pulsed-laser ablation technique to grow 20–30-nm-thick, discrete and continuous coatings on particulate material systems so that the properties of the core particles can be suitably modified. Experiments were conducted with a pulsed excimer laser (␭ ⳱ 248 nm, pulse duration ⳱ 25 ns) to deposit nanoparticle coatings on Al2O3 and SiO2 core particles by irradiation of Ag and Y2O3–Eu3+ sputtering targets. Structural characterization was performed with scanning electron microscopy, wavelength dispersive x-ray mapping, transmission electron microscopy, and scanning transmission electron microscopy with z-contrast.

I. INTRODUCTION

Submicrometer- to micrometer-sized metallic and ceramic particles (100 nm to 10 ␮m) act as principal precursor materials for a wide range of existing and emerging products involving advanced ceramics, metals, and composites that span several industries such as aerospace, automobile, machining, vacuum electronics, batteries, data storage, catalysis.1,2 Particulate materials as core technologies influence over 1 trillion dollars yearly on a worldwide basis.3 To achieve desirable properties in the final product, typically the properties of the particles such as shape, size, composition, surface charge, flowability, etc., have been controlled. These characteristics play an important role in determining the final microstructure, and thus the product’s properties. However, with the rapid advancements in nonparticulate technologies such as computers, telecommunications, and electronics, there is a strong need to develop novel particulate systems, which can result in value-added products with enhanced properties.4 Increasing interest in recent years has been focused on a wide variety of nanostructured materials, which possess grain or phase structures modulated on a length scale of less than 100 nm, because it is anticipated that their properties will be different from and often superior to conventional materials that have phase or grain boundaries over a coarser size scale.5,6 J. Mater. Res., Vol. 14, No. 8, Aug 1999

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Using artificially engineered nanostructured materials, it may be possible to engineer the properties by controlling the size of the constituent domains and the manner in which they are assembled. Some of the recent efforts have been focused on synthesizing atom clusters, zero di