Willow glass

We investigated the electrical characteristics of the nanowires by sourcing voltages from −10 to 10 mV. The gauge factors of the nanowires were evaluated by applying small bending strains as follows. First, the nanowires were deposited on glass coverslips. Then, they were placed partially suspended over step edges (10 μm – 130 μm) made of photoresist (SU8 Microchem) on a glass slide. The glass coverslips were positioned such that the middle of the nanowire would ideally be sitting directly over the step edge. The coverslip was clamped to the supporting glass slide a small distance from the step edge itself, depicted in Figure 3a. The free end was deflected to the point where it touched the glass underneath the step edge, applying a bending moment on the glass slide (and corresponding tension along the elongated fibres.) Resistance was measured (Keithley 2400) by applying eutectic gallium-indium (EGaIn) drops to the evaporated contact pads, and placing copper wires inside. A continuous change in strain with time was also induced by placing the nanowire on thin 100 μm Willow glass (Corning) as a cantilever and deflecting it using a motorized test stand (Mark-10).

We began by depositing 100 nm of gold was onto a silicon wafer at an approximate deposition rate of 3 Å/s by electron-beam evaporation (Temescal BJD 1800-1). The gold was stripped from the silicon wafer by puddle-casting epoxy (Epo-fix, Electron Microscopy Sciences) on the gold surface. Upon curing at 60 °C for 6 h, we detached the epoxy, which stripped the gold from the silicon wafer. We then cut out long rectangular pieces (w = 1 mm, l = 5 mm) from the gold on epoxy using a razor blade and hammer. Finally we embedded these pieces in additional epoxy using a block mold made from PDMS on a petri dish, and sectioned the block using an ultramicrotome (Reichert-Jung Ultracut E) fitted with a 2.5 mm diamond knife (Diatome Ultra 35°) [4 (link)]. The diamond knife was fixed to a water bath, onto which the slabs slid as they were produced. We transferred the slabs using the Perfect Loop tool to silicon for microscopic characterization, thin glass slides (Corning Willow glass) for characterization of the electrical properties, and polyimide tape (Kapton) for human pulse monitoring.