Control methods in microspheres precision assembly for colloidal lithography

Abstract

Colloidal lithography based on the assembly of microspheres is a powerful tool for the creation of a large variety of two dimensional micro or nanostructures patterned. However very few studies examine the control, qualification and quantification of the ordering of the particles once deposited on the substrate. We have developed two unique methods working at microscopic and macroscopic scales, respectively called Microfixe® and Macrofixe®, for the analysis of grain morphology in the case of hexagonal closed packed (HCP) monolayers of spherical microparticles. The processing of the images taken at microscopic scale uses Delaunay triangulation and histograms of lengths and orientations of Delaunay triangles sides. At the macroscopic scale, six camera images are required of the sample illuminated under six different incidence angles. Image treatment consists in the comparison of the six images and eventually subdivision of these images to sharpen the analysis. At the end, the two softwares constitute artificial images of particle deposit, giving at microscopic and macroscopic scales significant information about grain size, grain morphology, orientation distributions, defaults (voids, stacking)… With these two new control methods, colloidal lithography is emerging as an industrial process.