Seminar Abstract:
New applications in electronics and optics require methods of forming micro- and nanostructures in ways that are applicable to different classes of materials and substrates. These methods should also be simple, inexpensive, and amenable to manufacturing. This seminar describes several unconventional methods of forming micro- and nanostructures for electronic, optical, and optoelectronic applications. These methods all have a mechanical process as a key step. 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 (by physical or chemical means) with ultrathin mechanical sectioning with an ultramicrotome. This seminar describes the constraints on the materials applicable to nanoskiving, and then describes several applications, including nanowire chemical sensors, addressable nanowire electrodes for electrodeposition, organic photodetectors, plasmonic waveguides, and near-IR filters. Supporting techniques developed include mechanical and magnetic methods to manipulate the structures produced by nanoskiving and transfer them to optical fibers and other optical structures. The first part of the seminar also discusses 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 “rubber” solar cell, and a stretchable sensor of pressure and strain. A stretchable organic solar cell was fabricated by spin-coating the transparent electrode and active layer on a pre-strained elastomeric membrane. Upon release of the pre-strain, the films formed topographic waves that imparted elasticity to the device when strained (up to 27%). The device exhibited similar photovoltaic properties when both stretched and unstretched. This seminar also describes 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 were rendered stretchable by an application of strain and release along each axis. This action produced spring-like structures in the nanotubes, which accommodated strains up to 70% with little change in resistance. When embedded in elastomeric membranes, the nanotube films functioned as electrodes in arrays of transparent, stretchable capacitors, which manifest applications of pressure or tension as increases in capacitance.