Superlubricity of graphite sliding against graphene can be easily attained at the nanoscale when it forms the incommensurate contact under a low contact pressure. However, the achievement of superlubricity under an ultrahigh contact pressure (>1 GPa), which has more applications in the lubrication of micromachine and nanomachine, remains unclear. Here, this problem is addressed and the robust superlubricity of graphite is obtained under ultrahigh contact pressures of up to 2.52 GPa, by the formation of transferred graphene nanoflakes on a silicon tip. The friction coefficient becomes as low as 0.0003, a state that is attributed to the extremely low shear strength of the graphene/graphite interface in the incommensurate contact. When the pressure exceeds some threshold, the superlubricity state collapses suddenly with the friction coefficient increasing ≈10 times. The failure of superlubricity originates from the delamination of the topmost graphene layers on graphite under ultrahigh contact pressures, which requires the tip to provide additional exfoliation energies during the sliding process. The results demonstrate that the superlubricity of graphite sliding against graphene can exist stably under ultrahigh contact pressure, which would appear to accelerate its application in nanoscale lubrication.

中文翻译：

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超高接触压力下石墨与石墨烯纳米片滑动的超润滑性

当石墨在低接触压力下形成不相称接触时，可以在纳米尺度上轻松实现石墨与石墨烯滑动的超润滑性。然而，在超高接触压力（>1 GPa）下实现超润滑，在微机械和纳米机械的润滑中有更多的应用，目前尚不清楚。在这里，这个问题得到了解决，通过在硅尖端上形成转移的石墨烯纳米薄片，在高达 2.52 GPa 的超高接触压力下获得了石墨的强大超润滑性。摩擦系数低至0.0003，这种状态归因于非相称接触中石墨烯/石墨界面的剪切强度极低。当压力超过某个阈值时，超润滑状态突然崩溃，摩擦系数增加约10倍。超润滑性的失效源于石墨上最顶层石墨烯层在超高接触压力下的分层，这需要尖端在滑动过程中提供额外的剥离能量。结果表明，石墨与石墨烯滑动的超润滑性可以在超高接触压力下稳定存在，这将加速其在纳米润滑中的应用。