Metal-insulator transition effect on Graphene/VO$$_\text {2}$$ heterostructure via temperature-dependent Raman spectroscopy and resistivity measurement

Abstract

AbstractHigh-quality VO$$_2$$ 2 films were fabricated on top of c-Al$$_2$$ 2 O$$_3$$ 3 substrates using Reactive Bias Target Ion Beam Deposition (RBTIBD) and the studies of graphene/VO$$_2$$ 2 heterostructure were conducted. Graphene layers were placed on top of $$\sim$$ ∼  50 and $$\sim$$ ∼  100 nm VO$$_2$$ 2 . The graphene layers were introduced using mechanical exfoliate and CVD graphene wet-transfer method to prevent the worsening crystallinity of VO$$_2$$ 2 , to avoid the strain effect from lattice mismatch and to study how VO$$_2$$ 2 can affect the graphene layer. Slight increases in graphene/VO$$_2$$ 2 T$$_\text {MIT}$$ MIT compared to pure VO$$_2$$ 2 by $$\sim$$ ∼  1.9 $$^{\circ }$$ ∘ C and $$\sim$$ ∼  3.8 $$^{\circ }$$ ∘ C for CVD graphene on 100 and 50 nm VO$$_2$$ 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$$_\text {MIT}$$ MIT may originate from a large difference in the thermal conductivity between graphene and VO$$_2$$ 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$$_2$$ 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$$_2$$ 2 phase transition mechanism. The 2D-peak measurements also show large blue-shifts around 13 cm$$^{-1}$$ - 1 at room temperature and slightly red-shifts trend as temperature increases for 100 nm VO$$_2$$ 2 samples. Other electronic interactions between graphene and VO$$_2$$ 2 are expected as evidenced by 2D-peak characteristic observed in Raman measurements. These findings may provide a better understanding of graphene/VO$$_2$$ 2 and introduce some new applications that utilize the controllable structural properties of graphene via the VO$$_2$$ 2 phase transition.