Optical response in subnanometer gaps due to nonlocal response and quantum tunneling Appl. Phys. Lett. 101, 233111 (2012) Determination of optical properties of percolated nanostructures using an optical resonator system J. Appl. Phys. 112, 103536 (2012) A two-dimensional nanopatterned thin metallic transparent conductor with high transparency from the ultraviolet to the infrared Appl.

Conductivity, carrier concentration and carrier mobility in graphene were investigated as a function of time in response to ionized donor and acceptor adsorbates. While a reduction in conductivity and hole density in graphene was observed upon exposure to a weak electron donor NH3, the carrier mobility was found to increase monotonically. The opposite behavior is observed upon exposure to NO2, which is expected based on its typical electron withdrawing property. Upon exposure to C9H22N2, a strong donor, it resulted in the transformation of graphene from p-type to n-type, although the inverse variation of carrier concentration and mobility was still observed. The variational trends remained unaltered even after intentional introduction of defects in graphene through exposure to oxygen plasma. The responses to C9H22N2, NH3 and NO2 exposures underline a strong influence by ionized surface adsorbates, that we explained via a simple model considering charged impurity scattering of carriers in graphene.

Engineering graphene into a particular shape is vital for potential industrial applications. To this end, better understanding of the growth mechanism is needed to control the growth behavior of graphene on a substrate surface with a specific shape. In this work, a tetragon-shaped graphene single crystal (TS_GSC) with millimeter-scale grain size was achieved on copper foil, which was annealed at oxygen-free conditions (AOF) prior to graphene growth. The TS_GSC grains are featured by two dendritic Frontiers at the shorter-edge (SE) sides and two sharp Frontiers at the longer-edge (LE) sides of graphene grain. By combining scanning electron microscopy, optical microscopy, and Raman mapping with carbon isotope labeling, we revealed for the first time an asymmetric growth behavior of TS_GSC grains on an AOF-treated copper substrate. It was supposed that the growth of graphene was determined by the diffusion-limited aggregation mechanism at the SE side, whereas it was governed by the edge-determined atom-attachment mechanism at the LE side of graphene grain. In addition to single-layer graphene, tetragon-shaped bilayered graphene with grain size over 200 μm was also achieved on the AOF-treated copper substrate.