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

The c- 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 c- axis piezoresistivity of van der Waals materials near zero pressure is developed on the basis of in situ scanning electron microscopy and finite element simulation. The c- axis piezoresistivity of microscale highly oriented pyrolytic graphite (HOPG) is found to show a large value of 5.68 × 10 -5 kPa -1 near zero pressure and decreases by 2 orders of magnitude to the established value of ∼10 -7 kPa -1 when the pressure increases to 200 MPa. By modulating the serial tunneling barrier model on the basis of the stacking faults, we describe the c- axis electrical transport of HOPG under compression. The large c- 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.