Michael S. Arnold
Department of Materials Science and Engineering,
University of Wisconsin-Madison

Overcoming long-standing challenges in carbon nanotubes and graphene nanoribbons to enable their application in transistors and photovoltaics

Carbon nanotubes and graphene nanoribbons are among the best charge transport materials ever discovered. The transformative potential of these materials in electronics and optoelectronics has already been demonstrated, on a single nanostructure level. However, implementing them in scaled, macroscopic applications involving many nanostructures has been much more difficult. My work addresses challenges – in controlling the growth, processing, ordering, and heterogeneity of carbon nanomaterials and in understanding phenomena beyond the scale of single nanostructures – that must be overcome to exploit these materials in (opto)electronics technology.

Along these lines, I will present on 3 inter-related areas: (1) Achieving highly monodisperse semiconducting carbon nanotubes without problematic metallic nanotubes and depositing these nanotubes into useful, organized arrays and assemblies. We have recently pioneered a scalable approach for depositing aligned arrays of ultrahigh purity semiconducting nanotubes called floating evaporative self-assembly (FESA) that has allowed us to create the highest performance carbon nanotube field effect transistors (FETs) ever demonstrated. (2) Unlocking the potential of carbon nanotubes as light absorbers in macroscopic, thin film photovoltaic photodetectors and solar cells. We have discovered how to efficiently harvest photons from thin films of nanotubes by driving the dissociation of photogenerated excitons using donor/acceptor heterojunctions. The efficiency of these devices is determined by the flow of energy in these films that we have temporally resolved and understood using a particularly broadband form of two-dimensional white light ultrafast spectroscopy. (3) Creating graphene nanostructures (e.g. nanoribbons) with smooth edges via a combination of top-down and bottom-up methods that can be extended to the large scales necessary for technology. We have recently discovered a new CVD-based synthesis for high aspect ratio, aligned armchair nanoribbons that are