Influence behavior and mechanism of double-layer Gr stacking configuration on mechanical strength and thermoelectric transport properties of Cu/Gr composites

The mechanical strength, electrical conductivity, and thermal conductivity of Cu/graphene (Gr) composites with Cu (111)/double-layer Gr/Cu (111) structure were investigated by using density functional theory and semi-classical Boltzmann transport theory. The results indicate that, the chemical bonds were generated between the two layers of Gr film, and the maximum charge densities of Gr-Top stacking configuration and Gr-Hollow stacking configuration are 0.104 and 0.118 e/ų, respectively. Gr-Hollow stacking configuration has the larger mechanical strength and plasticity than Gr-Top stacking configuration. Although the covalent characteristic for the two stacking configurations is identical, the ionic characteristic of Gr-Top stacking configuration is stronger than Gr-Hollow stacking configuration. Therefore, the electron localization of Gr-Top stacking configuration is much stronger, leading to the smaller number of free electrons. The electrical conductivity and thermal conductivity of Gr-Hollow stacking configuration are 2.55 times and 1.63 times those of Gr-Top stacking configuration was achieved. Moreover, as the external longitudinal strain from 0 % to 15 % applied on Cu (111)/double-layer Gr/Cu (111) structure, the thermoelectric transport properties of Gr-Hollow stacking configuration are greater than Gr-Top stacking configuration, while as the strain are 20 % and 25 %, Gr-Top stacking configuration has the larger electric conductivity and thermal conductivity instead.