Molecular Dynamics Simulation On Carbon/silicon Nanotube Pressure Sensors

Since the discovery of the carbon nanotubes(CNTs) and silicon nanotubes/nanowires(SiNTs/SiNWs), they have attracted great interest for their exceptional electro-mechanical properties. Especially if they can be applied to pressure sensor, both of the sensitivity and the measuring range will be greatly improved. The electro-mechanical properties of CNT-based, Si NT-based, and SiNW-based pressure sensors are especially investigated by combining the classical molecular dynamics(MD) simulation and the piezo-electricity theory. The following conclusions can be drawn from the present study:(1) Firstly, a novel type of pressure sensor utilizing single walled carbon nanotubes(SWCNTs) is proposed. When little pressure is applied to the top plate, high pressure is transferred to the SWCNT through the leg, and then the SWCNT is deflected by the high local contact pressure. The electromechanical properties of the SWCNT-based pressure sensors are investigated by combining the classical molecular dynamics simulations and the piezo-electricity theory, and compared with those of the pressure sensor based on graphene nanoribbons(GNRs). The critical flexural strengths of both SWCNTs with two kinds of chiralities and GNRs are estimated at different temperatures. The MD results show that both the flexural strengths and stability of armchair SWCNTs are better than those of helical SWCNTs and GNRs at the same temperature. The maximal sensitivity of the GNR-based pressure sensors is five times that of the SWCNT-based pressure sensors, while the measuring range of SWCNT-based pressure sensors is double times that of GNR-based pressure sensors at room temperature. Our results also show that the sensitivity, measuring range, and conductivity change of both SWCNT-based and GNR-based pressure sensors decrease with the increasing temperature.(2) Secondly, the practicability of the carbon nanotube bundle(CNBs-based) pressure sensors is discussed. We find that the critical flexural strengths of CNBs decrease with the increasing temperature, which is almost independent on the diameter. The carbon atoms from different tubes are trying to form new C-C bonds, which reduces the flexural strength and leads to the flexural strength of CNBs being about 80% of those of SWCNTs. The critical flexural strengths and fracture strains of the CNBs are less than those of the SWCNTs. Both the conductivity and sensitivity of CNB-based pressure sensor are smaller than those of the SWCNT-based pressure sensor.(3) Finally, the practicability of the SiNT-based, and SiNW-based pressure sensors is discussed. We focus on predicting the effects of different factors such as temperature and diameter on the pressure sensor measuring range, sensitivity and conductivity. We also analyze the evolution of atomic structure under pressure at the atom scale. The MD results show that the critical flexural strengths of SiNWs greater than those of SiNTs under bending at same temperature, and the critical flexural strengths of sp2 hybrid SiNTs are greater than those of sp3 hybrid SiNTs at the same temperature. The critical flexural strengths of SiNTs/SiNWs are almost independent on the diameter. The measuring range of SiNWs-based pressure sensors is higher than that of SiNTs-based pressure sensors. The sensitivity of sp3 hybrid SiNTs-based pressure sensors is higher than those of sp2 hybrid SiNTs-based pressure sensors and SiNWs-based pressure sensors under the same pressure. The results also show that the sensitivity, measuring range, and conductivity change of both SiNTs-based and SiNWs-based pressure sensors decrease with the increasing temperature.