Extended Data Figure 4: Bending stiffness measurements.
From: Graphene kirigami
a, We also performed a rough measurement of the spring constant using the force of gravity on the gold pads. After lifting the cantilever off the surface, the vertical deflection xg is determined using the shallow depth of focus of the microscope, adjusted for the change in index of refraction. The gravitational force Fg (corrected for buoyancy) yields the spring constant: k = Fg/xg. For the 50-µm-long cantilever shown (scale bar is 10 μm) with a 2-pN gold pad and xg = 25 µm, we find that k = 8 × 10−8 N m−1. We repeated the measurement for a variety of devices of varying length L and width W = 10 µm. We have observed that the cantilevers sometimes curve downwards even in the absence of an applied force, presumably due to residual materials or strains in the graphene, so these gravitational measurements probably have a systematic offset. b, The measured spring constants of 10-µm-wide devices are shown on a plot of spring constant versus device length for the thermal fluctuation (black), gravitational deflection (blue), and laser force measurements (red). The data from all three techniques (plus additional laser data for devices with other widths, as in Fig. 2) are shown in the inset as a histogram. Data with stars are from the same device, using the three different measurement techniques.
