Observation by ultrasonic atomic force microscopy of reversible displacement of subsurface dislocations in highly oriented pyrolytic graphite

Graphite is an important material for use as a solid lubricant that works even at high temperatures. Generally, the reason for the lubricity is that carbon layers easily slide against each other due to the layered structure with weak interlayer interaction. However, the atomic nature of the interlayer interaction is still not fully understood. To improve this understanding, we applied ultrasonic atomic force microscopy to highly oriented pyrolytic graphite and observed edge dislocations accompanied by extra half-planes. Through observation of the dislocation behaviour under different loads, we found that the dislocation moved laterally by 20 nm as the load increased by 80 nN, and it returned to the original position as the load decreased. To explain this result, we propose a model for the lateral motion of the dislocation, which includes a spring and pinning point. This finding of the large lateral motion confirms the extraordinarily easy sliding between carbon layers, which is relevant to the performance as a solid lubricant. It may also be relevant to the significant material transport in graphite intercalation compounds and in carbon nanotubes.