Observation of the quantum Hall effect in epitaxial graphene on SiC(0001) with oxygen adsorption

In this letter, we report on transport measurements of epitaxial graphene on SiC(0001) with oxygen adsorption. In a $50×50μm2$ size Hall bar, we observe the half-integer quantum Hall effect with a transverse resistance plateau quantized at filling factor around 2, an evidence of monolayer graphene. We find low electron concentration of $9×1011cm−2$ and we show that a doping of $1013cm−2$ which is characteristic of intrinsic epitaxial graphene can be restored by vacuum annealing. The effect of oxygen adsorption on carrier density is confirmed by local angle-resolved photoemission spectroscopy measurements. These results are important for understanding oxygen adsorption on epitaxial graphene and for its application to metrology and mesoscopic physics where a low carrier concentration is required.