Metal-insulator transition effect on Graphene/VO _2 heterostructure via temperature-dependent Raman spectroscopy and resistivity measurement

High-quality VO _2 films were fabricated on top of c -Al _2 O _3 substrates using Reactive Bias Target Ion Beam Deposition (RBTIBD) and the studies of graphene/VO _2 heterostructure were conducted. Graphene layers were placed on top of ∼ 50 and ∼ 100 nm VO _2 . The graphene layers were introduced using mechanical exfoliate and CVD graphene wet-transfer method to prevent the worsening crystallinity of VO _2 , to avoid the strain effect from lattice mismatch and to study how VO _2 can affect the graphene layer. Slight increases in graphene/VO _2 T _MIT compared to pure VO _2 by ∼ 1.9 ^∘ C and ∼ 3.8 ^∘ C for CVD graphene on 100 and 50 nm VO _2 , respectively, were observed in temperature-dependent resistivity measurements. As the strain effect from lattice mismatch was minimized in our samples, the increase in T _MIT may originate from a large difference in the thermal conductivity between graphene and VO _2 . Temperature-dependent Raman spectroscopy measurements were also performed on all samples, and the G-peak splitting into two peaks, G ^+ and G ^- , were observed on graphene/VO _2 (100 nm) samples. The G-peak splitting is a reversible process and may originates from in-plane asymmetric tensile strain applied under the graphene layer due to the VO _2 phase transition mechanism. The 2D-peak measurements also show large blue-shifts around 13 cm ^-1 at room temperature and slightly red-shifts trend as temperature increases for 100 nm VO _2 samples. Other electronic interactions between graphene and VO _2 are expected as evidenced by 2D-peak characteristic observed in Raman measurements. These findings may provide a better understanding of graphene/VO _2 and introduce some new applications that utilize the controllable structural properties of graphene via the VO _2 phase transition.