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SiC steps

4H-SiC substrate preparation - graphitization. annealing. Polished SiC substrate. Graphitized substrate. SiC steps. Patterning. e-beam lithography. Hall bar. FET. Quantum Interference loop. Epitaxial graphene grown on SiC. Highly ordered and well defined material

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SiC steps

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  1. 4H-SiCsubstrate preparation - graphitization annealing Polished SiCsubstrate Graphitized substrate SiC steps

  2. Patterning

  3. e-beam lithography Hall bar FET Quantum Interference loop

  4. Epitaxial graphene grown on SiC Highly ordered and well defined material Transport layer is protected Graphene properties : Dirac - chiral electrons Anomalous Berry’s phase Weak anti-localization Landau level spectrum Long electronic phase coherence length Ballistic properties, high mobility Anomalous transport : no quantum Hall effect periodic and fractal-like spectrum for high mobility samples AFM

  5. 0.3-4K Rxy (Ω) 400µm Rxx (Ω/sq) Field(T) Magneto-transport of a wide Hall bar (EG on Si-face) Shubnikov - de Haas magnetoresistance maxima

  6. 4 Energy 3 Landau index (n) Magnetic field 1/Bn (T-1) Energy Magnetic field Magneto-transport and Landau levels Dirac particles: linear E(k) n 3 2 EF 1 0 0 -1 -2 -3 Normal electrons: quadratic E(k) EF Landau plot : Slope gives carrier density ns= 1.3 1012cm-2 Intercept at n=0 indicates anomalous Berry’s phase see K. Novoselov et al. Nature 438, 197 (2005); Y. Zhang et al. Nature 438, 201 (2005) W.de Heer et al., cond-mat /0704.0285

  7. Temperature dependence of the SdH peaks Landau levels thermally populated Lifshitz-Kosevich equation : A(T)/Ao=u/sinh(u) where u=2π2kBT/∆E(B) Energy Magnetic field DE/kB(K) 1 ∆E(B)= vF=0.75 106m/s 0 T e m p e r a t u r e V. Gusynin, Phys. Rev. B 71,125124 (2005)

  8. Transport is graphene-like surprising 3 layers Low mobility µ=1100 cm2/Vs Disordered as seen in STM (graphene on Si-face) Phase coherence length lf(T=4K)~100nm In agreement with STM-STS Scattering by defects for graphene on the Si-face G. Rutter, J. Stroscio et al., Science to be published P. Mallet, J.-Y.Veuillen et al. cond-mat/0702406

  9. n~1010/cm2 TEM -cross section E n~1012/cm2 5 nm Daniel Ugarte, LNLS, Brasil Interface charging Interface layer dominates transport Neutral layers seen in Landau level IR spectroscopy Sadowski PRL97, 266405 (2006) Graphene layers SiC Workfunction graphite-Workfunction SiC V ~0.3 eV Built-in electric field E= V/L L is of order of screening length. Hence interface layer is chargedns~ E/0 ~1012/cm2 (Note: n~1010/cm2 for neutral graphite) See also photoemission ARPES - A. Botswick et al. Nature Physics 3, 36 (2007) E. Rolling et al. cond-mat/0512226 (2005) - J. Phys Chem Solid 67, 2172 (2006) T. Seyller et al. , Surface Science 600, 3906 (2006).

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