Colloidal assemblies modified by ion irradiation

Spherical SiO2 and ZnS colloidal particles show a dramatic anisotropic plas tic deformation under 4 MeV Xe ion irradiation. that changes their shape in to oblate ellipsoidal, with an aspect ratio that can be precisely controlle d by the ion fluence. The 290 nm and 1.1 mum diameter colloids were deposit ed on a Si substrate and irradiated at 90 K, using fluences in the range 3 x 10(13)-8 x 10(14) cm(-2). The transverse particle diameter shows a linear increase with ion fluence, while the longitudinal diameter shrinks: the pa rticle volume remains constant, Size aspect ratios up to 3.1 are achieved. Applications of the ion beam deformation technique are shown in studies of liquid crystalline colloidal ordering, self-assembled two-dimensional collo idal lithographic masks for thin-film deposition, and in tuning the optical properties of three-dimensional colloidal crystals. (C) 2001 Elsevier Scie nce B.V. All rights reserved.