Laser-Based Lithography for Polymeric Nanocomposite Structures

Abstract

In recent years, the synthesis of polymeric nanocomposites has gained much interest in the scientific community thanks to their unique capability to combine the properties of the host polymer matrices, such as toughness, elasticity, processability, solubility, thermal stability, etc, with those of inorganic nanoparticles (NPs), such as hardness, chemical resistance, optical and electronic properties. Among a variety of nanofillers, semiconductor and metallic NPs are extensively studied and used, because of their unique properties especially in the nanoscale. In this work we deal with polymeric nanocomposites incorporating various nanofillers, each one of them having extremely attractive properties for technological applications. In particular we focus on titanium dioxide (TiO2) NPs due to their unique reversible wettability, iron oxide (Fe2O3) NPs due to their superparamagnetic nature, gold (Au) NPs due to their enhanced electronic conductivity, and cadmium sulphide (CdS) NPs due to their tuned photoemission in the quantum size regime. Nanocomposite materials are usually prepared by simple blending of the nanosized inorganic components into polymer solutions. Nevertheless, this method quite often leads to formation of aggregates or macroscopic phase separation, since the control of the dispersion and distribution of the nanofillers within the organic matrices is impossible. To obtain a higher compatibility between the filler and the host polymeric material, and achieve coatings with high content of inorganic particles, the use of polymerization techniques is widely adopted (Fouassier 1995, Decker et al 2005, Lee et al 2006, Wang & Ni 2008). From this point of view, several methods can be considered, depending on the type of monomers and nanomaterials, such as bulk polymerization, photoinitiated polymerization, emulsion polymerization, in situ thermal polymerization, or copolymerization in solution. Among them, the use of ultraviolet (UV) light in combination with proper photoinitiators to produce polymeric nanocomposite films is one of the most rapid and effective method, the main advantage being the creation of well defined patterned structures. Patterning of nanocomposites using UV polymerization, the so-called UV photolithography is ideal for the direct incorporation of nanocomposites into specific parts of systems and devices. Photolithographically prepared nanocomposite structures can be used for the selective deposition of molecules, which have specific affinity to the photopolymerized