Micro- and nanorods of potassium acid phthalate grown in ion-track templates

Microand nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution crystallization in the channels of ion-track membranes. The template consists of a polymer foil irradiated with energetic heavy ions and subsequently track-etched to dissolve the tracks and create open cylindrical channels. The pores are then filled with the desired material by electrochemical or electroless methods (see, e.g. [1]. The solution crystallization method which we employ in the present study was already used for the growth of KCl or NaCl nanorods [2]. This project focuses on KAP as material which is very soluble in water and easily crystallizes under ambient conditions. Dye-doped KAP crystals show extremely interesting luminescence behaviour with exceedingly high and fast nonlinear optical response [3]. Their performance is linked to the good optical quality, which depends on the crystal structure and morphology. The size and density of nanorod assemblies in templates can easily be controlled, and they can directly be incorporated into devices. As template we used 100 and 30 μm thick polycarbonate (PC) foils and irradiated them at the UNILAC with heavy ions of 11.1 MeV/nucleon energy and fluences between 10 5 and 10 9 ions/cm 2 . The ion tracks were etched in an aqueous solution of 6M NAOH at 50°C. For these etching conditions the pore diameter increases with ~2μm/h. For crystal growth, the track-etched membranes were placed on top of the growth solution and left floating in ambient conditions for several days. The solution consisted of KAP dissolved in water up to 80% of the saturation solubility. Due to evaporation, the crystallization occurs in the solution as well as inside the pores and on the surface of the membrane.