Luminescent nanocrystal modified photoresin for fabrication of high-aspect ratio three-dimensional microstructures
The organic polymers incorporating inorganic nanoparticles can result in material possessing with unique size-dependent properties, such as mechanical, optical, electrical, thermal and magnetic, that can be istinctively conveyed into the composite by the suitable nanoparticles. When nano-objects such as luminescent nanocrystals (NCs) particles are embedded into photostructurable polymer materials, they provide a new, highly processable material, which enables the engineering of novel, highly integrated micro/nanosystems (MEMS/NEMS) with enhanced intrinsic functional properties. The current effort aims, on one side, to the incorporation of the functional nanoparticles into the polymer matrix and, on the other side, to preserve the characteristic structurability of photosensitive polymers by UV lithography. In this paper we present a novel composite material obtained from the combination of luminescent nanocrystals (NCs) of cadmium selenide coated by a shell of zinc sulfide (CdSe@ZnS) with epoxy-based photosensitive resins. This class of material is well-known for polymer MEMS applications due to its unique structurability by UV lithography and mechanical properties. Luminescent CdSe@ZnS NCs with tuneable size, exhibiting size-dependent optoelectronic properties have been synthesized by means of colloidal routes methods. The presence of an organic ligand shell makes the NCs soluble in different types of solvents and thus enables their processing and incorporation into polymers. For this purpose a range on different solvents were tested in order to optimize the incorporation of the luminescent NCs (4.7 nm) in the epoxy-based resin. Spectroscopical and microscopical investigation were performed on the prepared composite samples and the effects of the NC concentration, size, surface chemistry and solvent composition were investigated in order to evaluate their role on the spectroscopical and structural behaviour of the nanocomposite properties. The NC-doped resin was then spin-coated on a silicon wafer, baked, exposed to UV light through a mask and developed. The results confirm the overall UV-structuring capability of the modified polymer and the NC emission properties were demonstrated to be retained. Furthermore, the luminescent properties of the NCs were retained after patterning by UV photolithography, although some aggregation of NCs was observed. The presence of organic ligand shell at the colloidal NC surface shows to be relevant for the subsequent processing of the doped photo-resin. The presented route looks promising for the microfabrication of polymer MEMS with inherent functionalities. Further optimization needs to be implemented also in view of a possible extension to incorporation of different types of colloidal NCs.
Record created on 2007-02-08, modified on 2016-08-08