Thermal Transport in Graphene Oxide Films: Theoretical Analysis and Molecular Dynamics Simulation

Thermal Conductivity of Nano-Crystallized Indium-Gallium-Zinc Oxide Thin Films Determined by Differential Three-Omega Method

The temperature dependence thermal conductivity of the indium-gallium-zinc oxide (IGZO) thin films was investigated with the differential three-omega method for the clear demonstration of nanocrystallinity. The thin films were deposited on an alumina (α-Al₂O₃) substrate by direct current (DC) magnetron sputtering at different oxygen partial pressures ([PO₂] = 0%, 10%, and 65%). Their thermal conductivities at room temperature were measured to be 1.65, 1.76, and 2.58 Wm⁻¹K⁻¹, respectively. The thermal conductivities decreased with an increase in the ambient measurement temperature. This thermal property is similar to that of crystalline materials. Electron microscopy observations revealed the presence of nanocrystals embedded in the amorphous matrix of the IGZO films. The typical size of the nanocrystals was approximately 2–5 nm with the lattice distance of about 0.24–0.26 nm. These experimental results indicate that the nanocrystalline microstructure controls the heat conduction in the IGZO films.

Unveiling the mechanism of structure-dependent thermal transport behavior in self-folded graphene film: a multiscale study

Understanding the relationship between the microstructures and overall properties is one of the basic concerns for material design and applications. As a ubiquitous structural configuration in nature, the folded morphology is also widely observed in graphene-based nanomaterials, namely grafold. Recently, a self-folded graphene film (SF-GF) material has been successfully fabricated by the assembly of grafolds and exhibits promising applications in thermal management. However, the dependence of thermal properties of SF-GF on the structural features of grafold has remained unclear. We here develop a theoretical model to describe the thermal transport behavior in SF-GF. Our model demonstrates the relationship between the fold length of grafolds and thermal properties of SF-GF. It serves as an efficient and portable tool to predict the temperature profile and thermal conductivity of SF-GF with good validations by large-scale molecular dynamics simulations. Using this model, we further study the evolution of thermal conductivity of SF-GF with the unfolding deformation during the stretch. Moreover, the effect of geometrical irregularity of grafolds is uncovered. The model developed in this work not only provides practical guidelines for the manipulation and design of thermal properties of SF-GF, but also benefits the understanding of thermal transport behaviors in other two-dimensional nanomaterials with folded structures.