The Shearing Behavior of Nanowire Contact Pairs in Air and the Role of Humidity

A new technique based on optical microscope nanomanipulation is developed to permit optical observation of the shearing process between cantilevered nanowires (NWs). Real‐time observation of the deflection shape of NWs during shearing under controlled environmental conditions enables their shear stress evolution to be evaluated with respect to relative humidity (RH). The average static and kinetic shear strengths, τ¯s=7.1±0.8 and τ¯k=5.2±1.1 MPa, are found to be insensitive to the RH within the range of 40–60%. When the RH increased to 74%, the shear strength values increase to τ¯s=18.7±3.0 and τ¯k=14.7±1.8 MPa. When the RH decreases to 20%, a dramatic increase in the static and kinetic shear strengths is observed: τ¯s=64.4±7.2 and τ¯k=49.6±5.8 MPa. Water films absorbed on the surface of NWs within the RH range of 40–60% can lubricate their frictional interface and thus dramatically decrease the shear strength. At high RH of above 60% , the viscous effects of a water meniscus condensed around the contact point between two NWs can significantly enhance the shear strength and dampen stick‐slip behavior. The detachment of two NWs is then controlled by the rupture of a meniscus bridge, leading to high ultimate shear strength value of several tens of MPa.