Highly nonlinear optical 4-(4-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST) crystals have been successfully grown in micron scale and have been fixed in polymerized mixture of isodecyl acrylate (IDA) and trimethylolpropane ethoxylate (1 EO/OH) methyl ether diacrylate (TMP). The formation of DAST crystals in polymerized thin film (2 μm) was proceeded by three steps. Firstly, an evaporation of methanol during spincoating initiated crystalization. Secondly, polymerization by UV exposure in vacuum condition fixed crystals in matrix. Thirdly, annealing process at 80 °C completed crystals growth. It was evidenced that the ratio of IDA:TMP monomers strongly influenced on DAST crystals size (from 10 microns to submicron scale) and hence influenced on properties. The absorption and luminescence spectra and the second-harmonic generation signal confirmed surface morphology of DAST crystals, which is responsible for second-order nonlinear properties. Thus created thin film with DAST crystals is promising candidate for nonlinear optical applications, in particular those employing the quasi-phase matching method.
The aim of this work is the theoretical investigation of instability development of the nanoparticle surface shape during diffuse growth. The unperturbed surface is considered as an ideal sphere. The mass diffusion flux promotes increase of the sphere volume and development of free surface perturbations. The relaxation of these perturbations due to action of capillary forces is also considered along with development of small perturbations of a free surface at the expense of perturbation of a mass diffusion flux. We use the effective coefficient of viscosity μ and surface tension coefficient σ of nanoparticle to describe a surface shape relaxation. As a result there were revealed various modes at which the surface of nanoparticle loses the stability and investigated dynamics of instability development of surface.