Structure and thermomechanical behavior of bent GaN nanowires

The thermal and mechanical behaviors of bent GaN nanowires are investigated using molecular dynamics (MD) simulations. The nanowires considered have an axial orientation along the [0 0 0 1] crystalline direction and hexagonal cross sections with diameters of 2.91 and 3.55 nm. A phase transformation from wurtzite to a tetragonal structure occurs near the surfaces of the nanowires in the bending process. The thermal conductivity is evaluated using an analytical model. This model is based on the same atomistic potential used in the MD calculations and uses configurational information from the MD calculations as input. The method is 50 times more computationally efficient compared with the Green-Kubo method. It is found that the thermal conductivity decreases by 35% and 25%, respectively, for nanowires 2.91 and 3.55 nm in diameter during the phase transformation in the bending process. In contrast, the thermal conductivity does not change during unloading and is found to be independent of the bending angle. The overall trend in thermal and mechanical responses of the nanowire with a diameter of 3.55 nm is similar to that for the nanowire with a diameter of 2.91 nm. Results also show that the phase transformation due to bending cannot be reversed by simple unloading. The finding points out a mechanism for altering the structure and thermal conductivity of GaN nanowires through transverse mechanical loading.