(Invited) Toward the Formation of Ordered Nanoparticle Films By Electrophoretic Deposition and the Subsequent Assessment of Order Via Voronoi Tessellation Analysis

Electrophoretic deposition (EPD) is a liquid phase, materials casting approach whose technological advantages range from ease of application to size scalability, cost effectiveness, and rapid performance.  Material coatings, casts, and films assembled by EPD can be fabricated in just a few minutes and can easily be produced in nanometer to centimeter thicknesses across square nanometer to square meter surfaces.  EPD and other liquid-phase casting techniques can yield various degrees of order among the fabricated supercrystals.  Recently, we observed the evolution of order among nanoparticles (NPs) of cobalt ferrite.  We uncovered evidence that the NPs not only arranged into hexagonal close packing arrays when deposited onto silicon substrates by EPD but also appeared to have their crystallographic axes to be oriented collinearly.  This discovery could have far reaching ramifications in the rapid assembly of nanomaterials for applications, such as magnetic recording media and catalysis, among others.  Further, recently developed statistical measurement tools, specifically Voronoi tessellation analysis, that can be used to quantify the degree of ordering in monolayers of nanoparticles have been applied to the cobalt ferrite and the iron oxide systems.  The evolution of order in cobalt ferrite NP monolayers are juxtaposed with that of iron oxide NPs to explore the underlying causes of the differences in ordering based and the physical properties of the NP films.