Surface morphology of silica nanowires at the nanometer scale

Nanowires used in these experiments were manufactured from commercial optical fibers by the "microheater brushing technique", a top-down technique originally developed to manufacture nanowires from glasses with low processing temperature [15]. A commercial telecom optical fiber (SMF-1300/1550-9/125-0.25-10641, manufactured from Oz Optics), was held by two clamps mounted on translational stages (WSX-300 provided by Rockwell Automation) and heated by a ceramic microheater (manufactured by NTT-AT) with a bore 20 mm long and 2 mm wide (Fig. 1a) in air. The fiber was pulled with speeds in the range of few µm/s at both extremities while being heated up. The stages motion was computer controlled and mass conservation allowed for a great degree of control over the taper shape. The microheater temperature (T) was estimated to be ~ 1280 °C and was controlled by adjusting the current (I) flowing through it. The current was stable within 0.01A and was kept at 0.01A above the level at which the fiber broke. Fig. 1b reports the microheater calibration curve performed after the samples were manufactured by inserting a wire thermocouple inside the microheater bore and coincided within ~ 20°C with the calibration curve provided by the manufacturer. Regression of the experimental data showed that the maximum T in the microheater is related to the current flowing through it by T = 373 + 328 * I, implying that during the nanowire manufacture T inside the microheater is stable within ~ ± 3 °C. The inset of Fig. 1b shows the temperature profile inside the microheater for two different currents: experimental data is fit by a parabola and shows a hot zone smaller than 3 mm.