Control of nanoparticle film structure for colloidal lithography

Colloidal lithography utilises nanoparticles' ability to self-organise on surfaces, which make them suitable as lithographic masks for the production of nano sized surface features. Adsorption under the influence of electrostatic particle-particle interactions results in ordered structures with the particles separated an average distance described by the random sequential adsorption model (RSA). Large areas (CM2) with a high density of nanoparticles can be covered, which is very useful for application areas like biosensors, biomaterials and catalysis, where large numbers of nano sized features are often required. Feature size, shape and spacing can be systematically varied. In this work methods to control the deposition of films consisting of polystyrene particles on flat oxidised titanium surfaces for particle sizes between 20 and 500 nm and coverages of 0-0.45 are demonstrated and discussed. Experimental difficulties encountered were aggregation of particles at high coverage/large particles and a low coverage limit at low ionic strengths. Experimental solutions to overcome these limitations, maintaining the fast parallel processing advantage of colloidal lithography, are presented. They include heating to stabilize initial (i.e. after adsorption) particle arrangements, use of spacer silica particles, and plasma etching to reduce particle sizes. (C) 2002 Elsevier Science B.V. All rights reserved.