Nanometric Dry Powder Coatings Using a Novel Process

Abstract

A wide range of advanced technology for existing and emerging products based on high temperature metal-ceramic composites used in aircrafts, cutting tools, lithium-ion based rechargeable batteries, superconductors, field emission based flat-panel displays, etc. employ micron to submicron sized (0.1-10 microns) particulate precursors in their manufacturing process. Although there has been a significant emphasis given to control of the particle characteristics (shape, size, surface chemistry, adsorption, etc.), relatively little or no attention has been paid to concomitant designing desirable surface and bulk properties at the particulate level, which can ultimately lead to enhanced properties of the product. By attaching atomic to nano-sized inorganic, multi-elemental clusters either in discrete or continuous from onto the surface of the core particles, i.e. nano-functionalization of the particulate surface, materials and products with significantly enhanced properties can be obtained. In this paper, we demonstrate for the first time the synthesis of artificially structured, nano-functionalized particulate materials with unique optical, cathodoluminescent, superconducting and electrical properties. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Experiments were conducted for laser deposition of Ag nano particles on Al₂O₃ and SiO₂ core particles by pulsed excimer laser (wavelength =248 nm and pulse duration =25 nanosecond) irradiation of a Ag, Y₂O₃:Eu³⁺, and TaSi₂ sputtering targets.
Analytical techniques using scanning electron microscopy (SEM), wavelength dispersive x-ray mapping (WDX) , transmission electron microscopy (TEM) , scanning transmission electron microscopy with z contrast (STEMZ), and photoluminesence (PL) were utilized to examine the structural, chemical, and morphological characteristics of the nanometric coatings. Qualitative surface uniformity measurements by WDX mapping techniques showed a high degree of coating uniformity on the core particulate. Structural TEM and STEMZ imaging showed both continuous and discrete polycrystalline, multiply twinned nano particle coatings ranging from 5-40 nm in thickness.