The force sensor was made by gluing a commercial atomic force microscope (AFM) cantilever with a sharp tip (Nanosensor ATEC-CONT cantilevers, Neuchatel, Switzerland, C = 0.2 N/m) to one of the prongs of a commercially available quartz tuning fork (QTF). The signal from the QTF was amplified by a lock-in amplifier (SR830, Stanford Research Systems, Sunnyvale, CA, USA) and
recorded through the ADC-DAC card (NI PCI-6036E, National Instruments, Austin, TX, USA). The typical values of the driving voltage were 20 to 50 mV, and the corresponding tip oscillation amplitude was in the order of 100 nm. The tip oscillated parallel to the sample surface, i.e. in the shear mode. During the experiments, the tip was positioned at about the half height of a ND above the substrate
surface. Each manipulation Selleckchem Compound Library experiment started with a displacement of the ND from its initial position by an abrupt Inhibitor Library manufacturer tip motion to reduce the initial adhesion. Initial displacement was followed by controlled manipulation of the ND by pushing it with the AFM tip with simultaneous force recording. During the manipulation, the tip moved parallel to the surface along a straight line without feedback loop. The point of the tip contact with ND was varied to investigate different scenarios of ND behaviour. More details about the nanomanipulation technique can be found in . The Solid Mechanics module in COMSOL Multiphysics (version 4.3b) was used to build a stationary physics model of a deflected dumbbell resting on a flat substrate. The material properties of Ag were taken from the COMSOL material library; only Young’s modulus was added manually, with the value 83 GPa. Results and discussion ND formation Oxalosuccinic acid process SEM investigation revealed that after laser processing, most of the Ag NWs have rounded ends (end bulbs), and a large number of spherical NPs and some NDs were produced (Figure 1). Similar nanostructures can be produced by laser processing of Au NWs (Additional file 1: Figure S1). ND formation is a complicated dynamic process, which involves extreme temperature gradients, and includes rapid heating and melting
of the ends of NWs, contraction of liquid droplets into spheroidal bulbs and followed by rapid solidification. Figure 1 Nanostructures produced by laser processing of Ag NWs. NWs with end bulb, NDs of different length and spherical particles are typically produced (a-c). Partial rising of NDs from the substrate, imaged at 52° SEM stage tilt (d). Central part of Ag NDs is completely suspended, imaged at 45° (e). Ag ND rests on one bulb only, imaged at 45° (f). Let us propose a mechanism of ND formation using SEM images of NDs frozen at different stages of formation. After absorption of laser pulse energy, a NW starts to melt; liquid droplets grow in volume and move towards the centre of a NW (Figure 2a,b). Surface tension tends to minimize the surface area of a droplet and makes it spherical.