Ac240tsa r3

We evaluated the mechanical properties of the nanofibers with a combined AFM/optical microscopy technique. The cover glass with the sample was placed on the microscope stage. The stage serves an inverted optical microscope (Olympus IX 73) and AFM (MFP-3D-Bio, Oxford Instruments-Asylum Research, Santa Barbara, CA, USA). We adjusted the stage before manipulations began, so that the sample was directly above the objective lens and beneath the AFM probe. The AFM was then put into contact mode to begin fiber manipulations. The probe was raised to hover above a specific fiber. The AFM probe was lowered in 500 nm steps until the apex of the tip was horizontally level with the desired fiber. By adjusting the lateral x-y-position, the AFM probe was placed at the middle of the suspended fiber. Only the tip of the AFM probe was in contact with the fiber. The fiber was pulled in the horizontal plane, perpendicular to the fiber length, parallel to the groove, at a speed of 350 nm/s, until it broke (Figure 1C,D). The AFM and the sample were checked regularly to ensure that they were level with each other. Asylum Research AFM Probes AC240TSA-R3 were used (resonance frequency f = 70 kHz, spring constant, k = 2 N/m, length L = 240 µm, width w = 40 µm, height h = 14 µm, nominal tip radius, r = 7 nm).