Fabrication of nanoscale three-dimensional graphite stacked-junctions by focused-ion-beam and observation of anomalous transport characteristics

We report on the fabrication and transport characteristics of nanoscale stacked-junctions of thin graphite flake. The stacked-junctions were fabricated using a three-dimensional focused-ion-beam milling. By varying the effective in-plane area down to submicron scale, the stacked-junctions with in-plane area A (from 2 down to 0.25 μm²) and stack height-length (from 300 to 100 nm) along c-axis were fabricated. The nano-stack shows perfect c-axis transport characteristics in which we observed a semiconducting behavior for T > 65 K and metallic behavior for T < 65 K. The obtained results were well fitted with the c-axis electrical conduction mechanism. The stack with in-plane area A of 0.25 μm² showed nonlinear concave-like I-V characteristics even at 300 K; however the stack with A ≥ 1 μm² were shown an ohmic-like I-V characteristic at 300 K for both low and high-current biasing. It turned into nonlinear characteristics when the temperature goes down. The observation of this anomalous transport characteristics were discussed in detail with stack capacitance calculations. The nonlinear characteristics observed at 300 K for the stack with A of 0.25 μm² were shown best fit with Fowler-Nordheim tunneling model.