Device fabrication on curvilinear two-dimensional surfaces using polymer probes

Abstract

Deposition of molecules on flat surfaces with sub-100 nm features of a plethora of combinations of inks and substrates, using flexible and hard probes on flat surfaces is extensively demonstrated in literature. However, the studies on the deposition and removal of fluorescent molecules and metal patterning on curvilinear two-dimensional substrates are scarce. In this study, conical and pyramidal probes composed of polydimethylsiloxane and polyacrylamide were used to deposit and remove thin coatings on planar and curvilinear surfaces. Fabrication of micro-photodetector devices on curved surfaces is demonstrated by fabricating microscale inter-digitated electrodes using probe-based patterning. A comprehensive characterization utilizing optical, electron and atomic force microscopy, and x-ray spectroscopic measurements of the probes and patterned substrates is presented. Differences in pattern capacity, speed, and quality of patterns based on nano-porous and non-porous probes is discussed. The inherent porosity and flexibility of polyacrylamide hydrogels allowed storage of large amounts of etchants facilitating microscale patterning of fluorescent inks and silver films on planar and curvilinear surfaces. A single polyacrylamide probe containing 0.9–1.2 nmol of rhodamine 6G stored within the polymeric matrix, allowed microscale patterning of an area of approximately 2.1 mm2 at an areal speed of ~1800 μm2/s. The modulation of size of the patterns was accomplished by changing the tip-substrate contact area. The experimental results showed a linear correlation between the displacement of the probe in the z-axis and the patterned area which agreed well with a physical model presented here. Importantly, the quality of micro-patterns was found to depend upon probe-substrate interfacial surface energy — high-quality patterns were obtained on low surface energy substrates. Finally, we demonstrated the fabrication of micro-photodetectors on two-dimensional curvilinear surfaces that posssessed a radius of curvature (k) ≈ 0.14 mm−1 by selectively removing silver from the surfaces followed by deposition of organic electron donor-acceptor pairs. In general, polymer lithography editor allows fabrication of devices on both planar and non-planar surfaces — PLE is an alternative tool to conventional microfabrication techniques.