Special ChBE Seminar: Darren J. Lipomi
Wednesday, February 22, 2012
Room 1200, Jeong H. Kim Engineering Building
Professor Srinivasa Raghavan
Chemical-Mechanical Processes in Nanoscale Optics and Electronics: Plasmonic Antennae, Rubber Solar Cells, and Electronic Skin
Darren J. Lipomi
Department of Chemical Engineering
This seminar describes several applications of hybrid approaches of forming micro- and nanostructures. These approaches combine chemical methods (e.g., synthesis, thin-film deposition, and soft lithography) with mechanical methods (e.g., cutting and stretching). The first part of the seminar focuses on nanoskiving and several supporting techniques. Nanoskiving is a process of fabrication and replication that combines soft lithographic molding and the deposition of thin films with ultrathin mechanical sectioning with an ultramicrotome. I will describe the constraints on the materials applicable to nanoskiving, and then describe several applications, including nanowire chemical sensors, organic photodetectors, plasmonic waveguides, and arrays of near-IR plasmonic resonators. Supporting techniques developed include mechanical and magnetic methods to manipulate the structures produced by nanoskiving. I will also discuss two additional forms of unconventional fabrication: shadow evaporation, and fabrication using a commercial nanoindentation system. Proof-of-principle applications demonstrated using shadow evaporation include field-effect transistors and logic gates produced using a single step of photolithography, and applications of nanoindentation include substrates for surface-enhanced Raman spectroscopy.
The second part of the seminar describes two applications of elastic micro- and nanostructured devices: a stretchable organic solar cell, and a stretchable sensor of pressure and strain. A stretchable organic solar cell is fabricated by spin-coating the transparent electrode and active layer on a pre-strained elastomeric membrane. Upon release of the pre-strain, the films form topographic waves that impart elasticity to the device when strained (up to 27%). The device exhibits similar photovoltaic properties when stretched or unstretched. I will conclude by discussing the fabrication and properties of a transparent, elastic, skin-like sensor of pressure and strain comprising transparent patterns of spray-deposited films of carbon nanotubes, which are rendered stretchable by an application of strain and release along each axis. This action produces spring-like structures in the nanotubes, which accommodate strains up to 150% with little change in resistance. When embedded in elastomeric membranes, the nanotube filmswhich are the most stretchable, conductive materials yet reportedfunction as electrodes in arrays of transparent, stretchable capacitors, which register applications of pressure or tension as changes in capacitance.