Kevin Mcilwrath

High-performance lithium battery anodes using silicon nanowires

There is great interest in developing rechargeable lithium batteries with higher energy capacity and longer cycle life for applications in portable electronic devices, electric vehicles and implantable medical devices. Silicon is an attractive anode material for lithium batteries because it has a low discharge potential and the highest known theoretical charge capacity (4,200 mAh g(-1); ref. 2). Although this is more than ten times higher than existing graphite anodes and much larger than various nitride and oxide materials, silicon anodes have limited applications because silicons volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading. Here, we show that silicon nanowire battery electrodes circumvent these issues as they can accommodate large strain without pulverization, provide good electronic contact and conduction, and display short lithium insertion distances. We achieved the theoretical charge capacity for silicon anodes and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.

Interface Characterization for Vertically Aligned Carbon Nanofibers for On-chip Interconnect Applications

Nanostructure characterization of carbon nanofibers (CNFs) for on-chip interconnect applications is presented. We propose a novel technique for characterizing interfacial nanostructures of vertically aligned CNFs, optimally suited for cross-sectional imaging with scanning transmission electron microscopy (STEM). Using this technique, vertically aligned CNFs are selectively grown by plasma-enhanced chemical vapor deposition (PECVD), on a substrate comprising a narrow strip (width ~100nm) formed by focused ion beam (FIB). Using high-resolution STEM, we show that CNFs with diameters ranging from 10-100 nm exhibit very similar graphitic layer morphologies at the base contact interface