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We have performed transport measurements on a multi-layer graphene device fabricated by conventional mechanical exfoliation. By using the zero-field resistance of our graphene device as a self-thermometer, we are able to determine the effective Dirac fermion temperature TDF at various driving currents I while keeping the lattice constant fixed. Interesting, it is found that TDF is proportional to Ia where a ~ 1. According to theoretical and experimental studies, the exponent a is given by 2/(2+p) where the charge-phonon scattering rate 1/τph is proportional to TP. Therefore our results yield p ~ 0, suggesting that there is little Dirac fermion-phonon scattering, a great advantage for applications in nanoelectronics.

We have performed magneto transport measurements on a multi-layer graphene device fabricated by conventional mechanical exfoliation. Suppression of weak localization (WL) as evidenced by the negative magnetoresistance (NMR) centered at zero field, and reproducible universal conductance fluctuations (UCFs) are observed. Interestingly, it is found that the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are longer than those determined from fitting the amplitudes of the UCFs to theory in the low temperature regime ( T ≤ 8 K). In the high temperature regime ( T > 8 K), the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory. Our new results therefore indicate a difference in the electron phase-breaking process between the two models of WL and UCFs in graphene. We speculate that the presence of the capping and bottom graphene layers, which leads the enhancement of disorder in-between, improves the localization condition for WL effect during carrier transportation in the low temperature regime. With increasing temperature, the localization condition for WL in multi-layer graphene becomes much weaker due to strong thermal damping. Therefore, the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory at high temperatures.