Low Temperature Electrical Transport in 2D Layers of Graphene, Graphitic Carbon Nitride, Graphene Oxide and Boron-Nitrogen-Carbon
Date of Award
Doctor of Philosophy
In this work, we have investigated temperature dependent electrical transport properties of carbon based two-dimensional (2D) nanomaterials. Various techniques were employed to synthesize the samples. For instance, high quality large area graphene and boron, nitrogen doped graphene (BNC) were grown using thermal catalytic chemical vapor deposition (CVD) method. Liquid phase exfoliation technique was utilized to exfoliate graphene and graphitic carbon nitride samples in isopropyl alcohol. Chemical reduction technique was used to reduce graphene oxide (rGO) by utilizing ascorbic acid (a green chemical) as a reducing agent. Detailed structural and morphology characterization of these samples was performed using state of the art microscopy as well as spectroscopic techniques (for example; Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), UV-Visible spectroscopy as well as Raman Spectroscopy). The low temperature (5 K< T <400 K) electrical transport properties of these materials show substantial difference from sample to sample studied. For instance, CVD grown graphene film has displayed metallic behavior over a wide range of temperature (5 K < T <300 K). At higher temperatures, resistivity followed linearly with the temperature (ρ(T) ~T). A power law dependence (ρ(T) ~ T4) observed at lower temperatures. Where as liquid phase exfoliated graphene and graphitic carbon nitride samples displayed nonmetallic nature: increasing resistance with decrease in temperature over a wide range (8 K < T < 270 K) of temperature. Electrical transport behavior in these samples was governed by two different Arrhenius behaviors in the studied temperature range. In the case of rGO and BNC layers, electrical conduction show two different transport mechanisms in two different temperature regimes. At higher temperatures, Arrhenius-like temperature dependence of resistance was observed indicating a band gap dominating transport behavior. At lower temperatures, Mott's two dimensional-Variable Range Hopping (2D-VRH) behavior was observed.
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