Shape deformation of colloidal titania nanoparticles by means of ion irradiation
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1087-V03-26
Shape deformation of colloidal titania nanoparticles by means of ion irradiation Juan-Carlos Cheang-Wong, and Ana-Lilia Díaz-Fonseca Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, México, D.F., 01000, Mexico ABSTRACT Spherical submicrometer-sized titanium dioxide (TiO2 or titania) particles were prepared by the sol-gel method from hydrolysis and condensation of titanium butoxide Ti(OC4H9)4 using ammonia as a catalyst in ethanol/acetonitrile and annealing in air at 100ºC. Subsequently, they were deposited onto silicon substrates, in order to form a monolayer of TiO2 particles. Then these samples were irradiated at room temperature with Si2+ ions at 4, 6 and 8 MeV, with fluences in the 2×1014-2×1015 Si/cm2 range, under an angle of 45° with respect to the sample surface. The titania particles were characterized by scanning electron microscopy to determine their size and shape before and after the ion irradiation. After the Si irradiation the spherical titania particles turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and the decrease in the direction parallel to the ion beam. This deformation effect increases monotonically with the ion fluence, and depends on the electronic energy loss of the impinging ion.
INTRODUCTION Titania (TiO2) powder is one of the most important particulate material used for many purposes such as pigment for paints, enamel or glazes of ceramics, solar cell, luminescent material, photocatalyst and for bactericidal action [1]. Due to its very high refractive index (n = 2.7) and transparency in the visible range rutile titanium dioxide particles with approximately 250 nm of diameter are the most effective white pigment in the paint industry. Opacity of white paint films is due to multiple light scattering processes on rutile TiO2 pigments embedded into the film. It is clear that the properties of TiO2 depend strongly on its crystal structure, shape and size. Even if some of these characteristics can be perfectly controlled by appropriate synthesis conditions, a lot of effort is still required in order to correlate the influence of particle shape on the optical properties. In the case of optical applications such as photonic crystals and waveguides, non-spherical colloids and their ordered arrays may be more attractive than their spherical counterparts due to their lower symmetries. A variety of chemical methods have been used to directly synthesize cubic, ellipsoidal and rod-shaped colloids in solution. However, for photonic applications, in most cases, the particles do not self-assemble into wellordered structures, and this is attributable to insufficient uniformity of the particle size and shape. Therefore, several alternative approaches must be explored in order to modify the shape of titania colloidal particles, not only when they are still in solution, but also when they are already deposited on a given substrate. Moreover, this method must be also useful for the formation of ordere
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