Browsing by Author "Zhang, Q."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields
    (American Physical Society, 2012) Booshehri, L.G.; Mielke, C.H.; Rickel, D.G.; Crooker, S.A.; Zhang, Q.; Ren, L.; Haroz, E.H.; Rustagi, A.; Stanton, C.J.; Jin, Z.; Sun, Z.; Yan, Z.; Tour, J.M.; Kono, J.
    Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.
  • Thumbnail Image
    Item
    Collective antenna effects in the terahertz and infrared response of highly aligned carbon nanotube arrays
    (The American Physical Society, 2013) Ren, L.; Zhang, Q.; Pint, C.L.; Wójcik, A.K.; Bunney, M. Jr; Arikawa, T.; Kawayama, I.; Tonouchi, M.; Hauge, R.H.; Belyanin, A.A.; Kono, J.
    We study macroscopically aligned single-wall carbon nanotube arrays with uniform lengths via polarization-dependent terahertz and infrared transmission spectroscopy. Polarization anisotropy is extreme at frequencies less than ∼100 cm−1 with no sign of attenuation when the polarization is perpendicular to the alignment direction. The attenuation for both parallel and perpendicular polarizations increases with increasing frequency, exhibiting a pronounced and broad peak around 450 cm−1 in the parallel case. We model the electromagnetic response of the sample by taking into account both radiative scattering and absorption losses. We show that our sample acts as an effective antenna due to the high degree of alignment, exhibiting much larger radiative scattering than absorption in the mid/far-infrared range. Our calculated attenuation spectrum clearly shows a non-Drude peak at ∼450 cm−1 in agreement with the experiment.
  • Thumbnail Image
    Item
    Intrinsic carrier mobility of multi-layered MoS2 field-effect transistors on SiO2
    (American Institute of Physics, 2013) Pradhan, N.R.; Rhodes, D.; Zhang, Q.; Talapatra, S.; Terrones, M.; Ajayan, P.M.; Balicas, L.
  • Thumbnail Image
    Item
    Magnetotransport in type-enriched single-wall carbon nanotube networks
    (American Physical Society, 2018) Wang, X.; Gao, W.; Li, X.; Zhang, Q.; Nanot, S.; Hároz, E.H.; Kono, J.; Rice, W.D.
    Single-wall carbon nanotubes (SWCNTs) exhibit a wide range of physical phenomena depending on their chirality. Nanotube networks typically contain a broad mixture of chiralities, which prevents an in-depth understanding of SWCNT ensemble properties. In particular, electronic-type mixing (the simultaneous presence of semiconductor and metallic nanotubes) in SWCNT networks remains the single largest hurdle to developing a comprehensive view of ensemble nanotube electrical transport, a critical step toward their use in optoelectronics. Here, we systematically study temperature-dependent magnetoconductivity (MC) in networks of highly enriched semiconductor and metal SWCNT films. In the semiconductor-enriched network, we observe two-dimensional variable-range hopping conduction from 5 to 290 K. Low-temperature MC measurements reveal a large, negative MC from which we determine the wave-function localization length and Fermi energy density of states. In contrast, the metal-enriched film exhibits positive MC that increases with decreasing temperature, a behavior attributed to two-dimensional weak localization. Using this model, we determine the details of the carrier phase coherence and fit the temperature-dependent conductivity. These extensive measurements on type-enriched SWCNT networks provide insights that pave the way for the use of SWCNTs in solid-state devices.