Fig. 1. Schematic diagrams of the Lorentz-force-actuated method for friction experiments inside TEM. The force diagrams in the framed region exhibit that the punch deflects by the Lorentz force and the cantilever deflects under the friction force.

Fig. 2. Silver asperity sliding against tungsten punch under TEM. (a) The schematic diagram shows the deflection of the tungsten punch and the silver cantilever. The inset shows the three-dimensional sketch of the silver cantilever. (b) The electromechanical coupling curve for one cycle of friction test. (c) The frame extracted from the in situ video illustrates tracking points of the punch and the cantilever marked by solid red and blue triangles, respectively. (d) The deflection of the tungsten punch and the silver cantilever with respect to the electric current, with the error bars from the standard deviation over six-time tracking measurements.

Fig. 3. The finite element analysis for the stiffness of the silver cantilever by the Multiphysics package, COMSOL. (a) The finite element model for the silver cantilever experiencing normal force in the z-axis and lateral force along the x-axis. (b) The color map for the deflection along the x-axis. (c) The lateral force versus the deflection along the x-axis at the tracking point marked by solid blue triangle in (b), respectively.

Fig. 4. The transition from static to dynamic friction for the submicron-sized silver-tungsten contact. (a) The frame extracted from the in situ video corresponding to the starting point of the constant normal force (20 μN). (b)-(f) Frames corresponding to the b-f points in (g), respectively. (g)-(h) The friction force and relative displacements with respect to the punch deflection, respectively, with error bars calculated by the standard deviation propagation equation.