In this specific case we found that our CVD graphene is “thermally equivalent”, for heat injection perpendicular to the graphene planes, to a coating material of conductivity keff = 2.5 ± 0.3 W/m K and thickness teff = 3.5 ± 0.3 nm in perfect contact with the substrate.
Then, by adopting a simple lumped-elements model, we developed a new method that allows determining, through a multistep numerical analysis, the equivalent thermal properties of thermally conductive coatings of nanometric thickness. We performed scanning thermal microscopy measurements on single layers of chemical-vapor-deposited (CVD) graphene supported by different substrates, namely, SiO2, Al2O3, and PET using a double-scan technique to remove the contribution to the heat flux through the air and the cantilever. Therefore, our experimental results correlated with the theoretical simulations based on the periodic density functional theory formalism and contributed to a deeper understanding of the charge/energy transfer processes occurring in the MTO/LNO/Si interfaces, and toward the exploitation of the close relationship between the structure and properties of these new functional materials. Surprisingly, for the MTO/LNO heterostructure, the PL emission profile exhibited a dual-color emission with an intense broad luminescence in the blue region (maximum centered at 454 nm) and an intense near-infrared emission (maximum centered at 754 nm), respectively, mainly because of the effect of interface defects, which induced a significant change in the PL behavior. Additionally, the results revealed that the LNO films did not have a significant photoluminescence (PL) emission, while an intense broad infrared luminescence centered at 724 nm appeared for the MTO nanostructured film. The MTO/LNO heterostructure was polycrystalline and exhibited the diffraction peaks of both the MTO and the LNO phases. The diffraction peaks corresponded to a rhombohedral structure, which was confirmed by micro-Raman spectroscopy for both nanostructured films. The structural characterizations obtained by X-ray diffraction revealed a preferred (003) orientation for the MTO film, while the LNO film was polycrystalline. This study systematically investigated the electronic, structural, and optical properties of MgTiO3 (MTO), LaNiO3 (LNO), and MgTiO3/LaNiO3 (MTO/LNO) nanostructured films grown on Si(100) substrates by the pulsed laser deposition method.
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