Study On Nanofriction Properties Of Suspended Graphene Surface Based On Atomic Force Microscopy

Graphene has a wide range of potential applications in micro/nano electromechanical systems(MEMS/NEMS)due to its excellent lubrication and electrical properties.In suspension,various factors affecting graphene substrate can be eliminated and its intrinsic friction properties can be retained.Therefore,studying the tribological properties of suspended graphene has great advantages in improving the tribological properties of related microelectronic devices.In this paper,the traditional micromachining technology was used to prepare microporous arrays on Si O₂/Si substrate surface,and the graphene was transferred to etched through holes by mechanical stripping to form suspended structures.Based on atomic force microscopy(AFM)and high-precision rotating table,the surface nano-friction properties of graphene suspended in different directions and thicknesses,the thickness-dependent load friction hysteresis mechanism and the friction properties of graphene suspended in substrate electric field were investigated.The results show that:(1)The surface nano-friction of the graphene supported by the thickness of3.6nm shows Significant anisotropy but no periodic law,because the folding effect increases the deformation of the lattice direction.The surface nano-friction of 7.5nm and 14.7nm supported graphene exhibits period ic anisotropy of 180°and 90°,which is attributed to the combination of lattice orientation and folding effect.The surface nano-friction of graphene supported by a thickness of 24.5nm presents a periodic anisotropy of 60°,mainly due to the lattice orien tation,and the friction along the armchair lattice orientation is greater than that along the sawtooth lattice orientation.In the suspen sion state,the load applied by the tip is wrapped by the surface of graphene,which leads to no periodic law of frict ion anisotropy.(2)In the friction hysteresis experiment,the suspended graphene was thick-dependent.With the decrease of the thickness,the suspended graphene showed more obvious friction hysteresis.In addition,the friction hystere sis becomes more obvious with the increase of the maximum load.In the case of substrate support,no friction hysteresis was observed due to the strong adhe sion of substrate to graphene.The hysteresis of force-distance curves and deflection-load relationships measured by the tip on suspended and supported graphene surfaces is consistent with that found by friction hysteresis.(3)Under the action of the base electric field,the friction of the suspended graphene increases with the increase of the bias value,and the fricti on of the positive bias value is always greater than that of the negative bias value.Also,under the action of base electric field,the variation trend of adhesion force and friction force is consistent,and the observation of stick-slip behavior of tip on the surface of suspended graphene shows that friction energy consumption will increase.In addition,compared with the case of substrate support,the tip is significantly affected by electrostatic force when the oxide layer is missing in the suspension state of graphene,resulting in a larger increase in friction.