Unusual 3D lithography approaches for fabrication of polymeric photonic microstructures

Abstract

Novel and intriguing lithographic approaches based on instabilities of liquid polymers and electro-hydro-dynamic at nanoscale have been developed. The unusual fabrication methods were aimed at fabricating 3D polymeric microstructures. A variety of microstructures were fabricated and tested for applications in different fields LIQUID NANO DISPENSERA new opto-nanofluidic approach named Pyro-EHD is presented for dispensing liquid nano-pico-droplets through pyroelectric effect activated by hot tip source or an IR laser into a dielectric crystal using a non-invasive simple and powerful electrode-less configuration. The manipulation of small amounts of liquids at micro to nanometer scale is of great interest in many fields of technology: biotechnology, patterning by deposition of inorganic, organic and biological inks and photnics [1-4]. We show a new and simple system where the liquid actuation and dispensing has been achieved through electrode-less configurations using polar dielectric crystals such as Lithium Niobate (LN) crystal and by exploiting the pyroelectric effect [5,6]. The technique presented allows one to avoid the use of high-voltage power supplies and electrical circuits, and moreover there is no need to design and fabricate nanocapillary nozzles. The functionalization of the lithium niobate (LN) is obtained by micro-engineering the ferroelectric domains and by inducing the pyroelectric effect through the use of appropriate heat sources such as a IR laser beam [7]. The set-up consists basically of a polished 500-µm thick z-cut LN substrate (from Crystal Technology, Inc.) placed over a microscope glass slide at a specific distance fixed by appropriate spacers (Figure 1). A liquid drop or film is first deposited on the glass slide and successively the upper surface of the LN wafer is placed in contact with an heated-tip that can be scanned in order to induce point-wise thermal stimuli. The heated-tip is in axis with the droplet reservoir on the microscope glass slide. A conventional heated soldering tip was used as heated-tip-source. LN reacts to the thermal-stimuli by building-up an electric potential across the z-cut LN crystal's surfaces because of the pyroelectric effect, that consists in the spontaneous polarization change ∆Ps following to a temperature gradient ∆T. At equilibrium, the crystal Ps is fully screened by the external screening charge and no electric field exists [8]. When the heating source locally heats the crystal, a sudden surface charge density σ immediately appears given by neglecting losses, where Pc is the material-specific pyroelectric coefficient (Pc= -8.3 x 10 -5C/°C/m2 for LN @ 25°C). The electric field exerts an attractive force on the liquid . When the liquid starts to deform under the action of the electric field, two evolutions are possible. Case (I): if the liquid volume and the separation distance D between the two