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  • Graphene Nanoribbons: Synthesis, Properties and Electronics
  • Release time:2011-05-17 clicks:1
  • Time: Sep 10th 10:00

    Place:A429

     

    1.Graphene Nanoribbons: Synthesis, Properties and Electronics


    Xinran Wang


    Stanford University, USA



     Abstract´╝ÜGraphene nano-electronics has been very attractive due to


    high carrier mobility. The semi-metallic nature of bulk graphene


    requires width confinement down to ~sub-10nm in order to induce adequate


    bandgap for room temperature logic applications. In this talk, I will


    present our recent works on graphene (nanoribbon) electronics.


     First, we developed a unique chemical route to synthesize high


    quality, ultra-smooth graphene nanoribbons (GNRs) with width below 10nm.


    Transport measurements show that the bandgap scales inversely with GNR


    widths, indicating that bandgap opens in narrow GNRs due to quantum


    confinement. The first room temperature p-type graphene field-effect


    transistor (FET) is demonstrated with our chemically derived sub-10nm


    GNR.


     We next access the performance of chemically derived sub-10nm GNR


    FETs. At on state, the current density could be as high as ~2000uA/um,


    with on/off ratio ~ 106, subthreshold slope ~210mV/dec. The performance


    of sub-10nm GNR FETs is comparable to small diameter (d<1.2nm) carbon


    nanotube (CNT) FETs. The intrinsic carrier mobility and scattering mean


    free path is ~200cm2/Vs and ~10nm, respectively. We discuss the possible


    scattering mechanisms in the GNRs.


     Compared to CNTs, GNRs have open edges with high chemical reactivity.


    We can take advantage of this fact and chemically modify the GNR edges


    to change the electronic properties. We found that individual GNRs could


    be covalently functionalized by nitrogen species through high-power


    electrical joule heating in NH3 gas, leading to n-type electronic doping


    consistent with theory. The formation of C-N bond occurs mostly at the


    edges of graphene where chemical reactivity is high. We fabricated an n-


    type N-doped graphene field-effect transistor (FET) that operates at


    room temperature.




    2.Ripple texturing of suspended graphene atomic membranes


     Wenzhong Bao


     University of California, Riverside


     Abstract´╝Ü We investigate one-dimensional (1D) and 2D periodic ripples


    in suspended graphene sheets, using spontaneously and thermally induced


    longitudinal strains on patterned substrates. By in-situ SEM imaging, we


    provide the first measurement of graphene’s thermal expansion


    coefficient, which is anomalously large and negative, ~-7x10-6 K-1 at


    300K. Latest progress towards transport measurement in these devices


    will be discussed