Large and Pressure-Dependent Axis Piezoresistivity of Highly Oriented Pyrolytic Graphite near Zero Pressure.

The axis piezoresistivity is a fundamental and important parameter of graphite, but its value near zero pressure has not been well determined. Herein, a new method for studying the axis piezoresistivity of van der Waals materials near zero pressure is developed on the basis of scanning electron microscopy and finite element simulation. The axis piezoresistivity of microscale highly oriented pyrolytic graphite (HOPG) is found to show a large value of 5.68 × 10 kPa near zero pressure and decreases by 2 orders of magnitude to the established value of ∼10 kPa when the pressure increases to 200 MPa. By modulating the serial tunneling barrier model on the basis of the stacking faults, we describe the axis electrical transport of HOPG under compression. The large axis piezoresistivity near zero pressure and its large decrease in magnitude with pressure are attributed to the rapid stiffening of the electromechanical properties under compression.