Metal-insulator transition effect on Graphene/VO2 heterostructure via temperature-dependent Raman spectroscopy and resistivity measurement

Abstract

High-quality VO2 flms were fabricated on top of c-Al2O3 substrates using Reactive Bias Target Ion Beam Deposition (RBTIBD) and the studies of graphene/VO2 heterostructure were conducted. Graphene layers were placed on top of ∼50 and ∼100 nm VO2. The graphene layers were introduced using mechanical exfoliate and CVD graphene wet-transfer method to prevent the worsening crystallinity of VO2, to avoid the strain efect from lattice mismatch and to study how VO2 can afect the graphene layer. Slight increases in graphene/VO2 TMIT compared to pure VO2 by ∼1.9 ◦C and ∼3.8 ◦C for CVD graphene on 100 and 50 nm VO2, respectively, were observed in temperature-dependent resistivity measurements. As the strain efect from lattice mismatch was minimized in our samples, the increase in TMIT may originate from a large diference in the thermal conductivity between graphene and VO2. 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/VO2 (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 VO2 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 VO2 samples. Other electronic interactions between graphene and VO2 are expected as evidenced by 2D-peak characteristic observed in Raman measurements. These fndings may provide a better understanding of graphene/VO2 and introduce some new applications that utilize the controllable structural properties of graphene via the VO2 phase transition.