(Color online) (a) RHEED image of HOPG(0001) substrate. (b) RHEED image for 5 nm EuO deposited on top of HOPG(0001) in the adsorption-limited growth regime. (c) Exfoliated single layer graphene flakewith Pd/Ti electrodes in a Hall geometry. (d) Graphene resistivity, ρ, as afunction of the back gate voltage. Maximum ρ corresponds with the charge neutrality point (CNP), sometimes called the Dirac point. Positive (negative) voltages beyond the CNP correspond to electron (hole) type carriers. (e) Quantum Hall effect in single layer graphene at T = 10 K and B = 7 T.
(Color online) (a) Gate dependent resistivity demonstrating the charging effect at room temperature for EuO deposited on graphene FET device. The back gate is swept from −40 V to +40 V and back again at a rate of 0.5 V/s. (b) Temperature dependence of the charging effect plotted as the relative difference in the charge neutrality point between up and down sweeps of the back gate voltage. (c) Comparison of the gate dependent resistance at T = 10 K for pristine and EuO deposited on top. (d) Quantum Hall effect at T = 10 K after EuO deposition. Black (red/grey) curve corresponds to B = +7 T (B = −7 T).
(Color online) (a) Schematic of the proposed experiment in which atomic hydrogen is carefully introduced in situ to nonlocal graphene spin valves in an MBE chamber with magnetotransport capability. (b) Gate dependent resistivity of a pristine nonlocal graphene spin valve before the introduction of atomic hydrogen. (c) Nonlocal resistance, R NL, as a function of in-plane applied field, Bapp ,y, along the axis of the magnetic electrodes for pristine graphene. The two state parallel and antiparallel behavior demonstrates spin injection and transport in the graphene channel. Data correspond with the channel in (b) maintained at VG = −15 V. (d) Hanle spin precession measurements in pristine graphene at VG = −15 V. (e) Gate dependence of the spin lifetime determined from fits to the spin precession data for pristine graphene with tunneling contacts using the Hanle equation. All data are taken at T = 12 K.
(Color online) (a) Gate dependent resistivity curves for pristine graphene (blue dashed) and graphene exposed to 2 s (black) and 8 s (red/grey) of atomic hydrogen. The pristine curve (blue dashed) corresponds to the data presented in Fig. 1(b) . (b) The electron (black) and hole (red/grey) mobilities for the graphene spin valve as a function of hydrogen exposure. (c) Nonlocal resistance, RNL at VG = −16 V for 2 s (left axis, black) and 8 s (right axis, red/grey) of atomic hydrogen exposure. Notably, the dip at zero field increases with increasing hydrogen exposure. (d) Gate dependence of the relative dip size compared to the high-field RNL values. This is defined quantitatively as RNL ( Bapp ,y = 0)/ RNL ( Bapp , y →∞); 100% corresponds with full spin scattering and zero spin signal at zero field.
(Color online) (a)–(c) Hanle spin precession curves for graphene spin valves exposed to 8 s atomic hydrogen at several gate voltages. Black open circles represent the measured RNL signal vs Bap p ,z. Red/grey line is the fit to the Hanle equation using fixed DC (determined from the experimentally measured resistance). The spin lifetime and electron g-factor are allowed to be free parameters. (d) g* values determined from Hanle fitting for 2 s (blue diamonds) and 8 s (red triangles) atomic hydrogen exposure. Dashed line indicates g = 2. (e) Spin lifetime obtained from Hanle fitting for pristine graphene (black squares), 2 s hydrogen doping (blue diamonds), 8 s hydrogen doping (red triangles). The pristine data are the same as shown in Fig. 3(e) with g = 2. The spin lifetimes after hydrogen doping for 2 and 8 s correspond with the g* values shown in (d).
(Color online) (a) Experimentally determined diffusion coefficient from the Einstein relation (DC ) (black curve) and the diffusion coefficient obtained from Hanle fitting with g = 2 (DS ) (black squares) plotted as a function of back gate voltage for 8 s hydrogen exposure. For comparison, the measured conductivity (blue dashed curve) is shown on the right axis. (b) Relative difference between DS and DC for 8 s hydrogen-doped (dark red squares) graphene.
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