We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga 2 O 3 synthesized on liquid Ga metal. A comparison of temperature-dependent electrical measurements of millimeter-scale passivated and bare graphene on SiO 2 /Si indicates that the passivated graphene maintains its high field effect mobility desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in passivated graphene over a range of temperatures below 220 K, due to the interplay of screening of the surface optical phonon modes of the SiO 2 by highdielectric-constant Ga 2 O 3 and the relatively high characteristic phonon frequencies of Ga 2 O 3 . Raman spectroscopy and electrical measurements indicate that Ga 2 O 3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al 2 O 3 .

We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga2O3 synthesized on liquid Ga metal. A comparison of temperature-dependent electrical measurements of millimetre-scale passivated and bare graphene on SiO2/Si indicate that the passivated graphene maintains its high field effect mobility desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in passivated graphene over a range of temperatures below 220 K, due to the interplay of screening of the surface optical phonon modes of the SiO2 by high-dielectric-constant Ga2O3, and the relatively high characteristic phonon frequencies of Ga2O3. Raman spectroscopy and electrical measurements indicate that Ga2O3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al2O3.