Research On The Effect Of Tilt Grain Boundary On Thermal Conductivity Of Nanocrystalline ZnO

Nano materials have superior performance compared to conventional materials.They have unprecedented application prospects in energy,environment,sensors and other fields.With the improvement of the preparation process level,nano-semiconductor as the main material of the chip,its integration has reached the order of billions,the heat dissipation problem has become the main reason affecting the use efficiency and life.In addition,the development of thermoelectric conversion technology further promotes the research on thermal transport for nano-semiconductor materials.In the process of synthesis,various types of grain boundaries,such as tilt grain boundaries,rotating grain boundaries,etc.,are produced due to mutual extrusion between grains.When the device size is reduced to the nanometer level,the volume fraction of the grain boundary increases,and the hindrance effect on the carrier heat transport is obvious.The different influences and mechanism of the grain boundary property on the material heat conduction need to be explored.This paper starts with the atomic scale and dynamics evolution process,and explains the transport law of carriers in the nano-semiconductor through tilt grain boundaries.The twin-crystal ZnO structure is used as a model to study the effect of tilt grain boundaries on the thermal transport of nano-semiconductor materials.The study of the thermodynamic properties of grain boundaries involves the structure of the grain boundary and the external environmental conditions.It is very difficult to propose a complete theoretical model.Molecular dynamics simulation has become the most effective method.The tilt grain boundary structures with small angle and large angle were established by the coincidence position lattice method,and the most stable atomic configurations were obtained by simulated annealing and energy minimization.The grain boundary energy and the Kapitza resistance of the twin-crystal ZnO with different tilt angles were simulated by non-equilibrium molecular dynamics.The effects of sample length and temperature on the Kapitza resistance and thermal conductivity were investigated.The simulation results show that the grain boundary energy increases with the increase of the tilt angle.When the tilt angle is greater than 36.86°,the change of grain boundary energy tends to be stable,which satisfies the calculated value of Read-Shockley formula.The change of the Kapitza resistance with the tilt angle is consistent with the grain boundary energy,which further proves that the Kapitza resistance is linearly related to the grain boundary energy.The results were quantum corrected at 300 K simulated temperature,and the Kapitza resistance increased by 23 % compared to the simulated value.The thermal transport of the twin-crystal ZnO structure has significant size and temperature effects.The thermal conductivity increases with the increase of the sample length,and the Kapitza resistance is opposite.However,with the increase of temperature,the thermal conductivity and the Kapitza resistance show a decreasing trend.By comparing the phonon state densities of different tilt grain boundaries,the reasons for the influence of the tilt angle on carrier transport are explained from a deep level.