Bulge Tests. Prior to the bulge tests, the thickness of the membranes and the radius of the circular freestanding membrane sections were determined by AFM and optical microscopy, respectively. The bulge tests were conducted using the same experimental setup and methods as described in detail in our previous studies. The holey substrates with freestanding membranes were fixed onto custombuilt sample holders using double-sided sticky tape (Tesa 05338). Topographic data were acquired using an AFM (JPK Nanowizard 3) equipped with NSG01 cantilevers. Ten evenly spaced line scans of 512 pixels within the total scan area of 100 × 100 µm 2 were performed using the intermittent contact mode.