CNR-SPIN Institute for Superconductors, Innovative Materials and Devices, C.so Perrone 24, I-16152 Genova, Italy.
Nanoscale. 2017 Jun 8;9(22):7612-7624. doi: 10.1039/c7nr00625j.
We report the frictional response of few-layer graphene (FLG) flakes obtained by the liquid phase exfoliation (LPE) of pristine graphite. To this end, we inkjet print FLG on bare and hexamethyldisilazane-terminated SiO substrates, producing micrometric patterns with nanoscopic roughness that are investigated by atomic force microscopy. Normal force spectroscopy and atomically-resolved morphologies indicate reduced surface contamination by solvents after a vacuum annealing process. Notably, the printed FLG flakes show ultralow friction comparable to that of micromechanically exfoliated graphene flakes. Lubricity is retained on flakes with a lateral size of a few tens of nanometres, and with a thickness as small as ∼2 nm, confirming the high crystalline quality and low defects density in the FLG basal plane. Surface exposed step edges exhibit the highest friction values, representing the preferential sites for the origin of the secondary dissipative processes related to edge straining, wear or lateral displacement of the flakes. Our work demonstrates that LPE enables fundamental studies on graphene friction to the single-flake level. The capability to deliver ultralow-friction-graphene over technologically relevant substrates, using a scalable production route and a high-throughput, large-area printing technique, may also open up new opportunities in the lubrication of micro- and nano-electromechanical systems.
我们报告了通过原始石墨的液相剥离（LPE）获得的少层石墨烯（FLG）薄片的摩擦响应。为此，我们通过喷墨打印将 FLG 打印在裸的和六甲基二硅氮烷封端的 SiO 衬底上，产生具有纳米级粗糙度的微尺度图案，并用原子力显微镜进行了研究。法向力谱和原子分辨形貌表明，真空退火过程后溶剂的表面污染减少。值得注意的是，打印的 FLG 薄片表现出与机械剥离的石墨烯薄片相当的超低摩擦。在几十分纳米的横向尺寸的薄片上保持了润滑性，并且厚度小至约 2nm，这证实了 FLG 基面中的高结晶质量和低缺陷密度。暴露的表面台阶边缘表现出最高的摩擦值，这代表了与边缘应变、磨损或薄片横向位移相关的二次耗散过程起源的优先位置。我们的工作表明，LPE 能够实现对石墨烯摩擦的单薄片级别的基础研究。使用可扩展的生产路线和高通量、大面积打印技术在技术相关衬底上提供超低摩擦石墨烯的能力，也可能为微纳机电系统的润滑开辟新的机会。
