The Conductive Silver Nanowires Fabricated by Two-beam Laser Direct Writing on the Flexible Sheet

Abstract

Flexible electrically conductive nanowires are now a key component in the fields of flexible devices. The achievement of metal nanowire with good flexibility, conductivity, compact and smooth morphology is recognized as one critical milestone for the flexible devices. In this study, a two-beam laser direct writing system is designed to fabricate AgNW on PET sheet. The minimum width of the AgNW fabricated by this method is 187 ± 34 nm with the height of 84 ± 4 nm. We have investigated the electrical resistance under different voltages and the applicable voltage per meter range is determined to be less than 7.5 × 10³ V/m for the fabricated AgNW. The flexibility of the AgNW is very excellent, since the resistance only increases 6.63% even after the stretched bending of 2000 times at such a small bending radius of 1.0 mm. The proposed two-beam laser direct writing is an efficient method to fabricate AgNW on the flexible sheet, which could be applied in flexible micro/nano devices.

Figure 1. Schematic diagram of the two-beam laser direct writing experiment setup.

Figure 2. Schematic illustration of preparation of the AgNW on the PET sheet using two-beam laser direct writing.

(a) Ag aqueous solution is dropped on the glass substrate and covered by PET sheet. (b) The sample is sandwiched between the glass substrate and the PET sheet, and the PET sheet is made to be parallel to the glass substrate. (c) Two beams are focused into the sample by the objective lens and to fabricate the AgNW on the PET sheet. (d) PET sheet is peeled off from glass substrate and the AgNWs are obtained after washing out the unreacted solution with ethanol.

Figure 3. SEM images and the corresponding width and height of the AgNWs on the PET sheet that fabricated under different experimental conditions.

(a) SEM image of AgNWs fabricated while varying the scanning speed from 1.0 μm/s to 3.5 μm/s. The laser powers of pulse beam and CW beam is 1.79 mW and 0.43 mW, respectively. (b) SEM image of AgNWs which were fabricated while the pulse beam power varied from 0.35 mW to 0.43 mW. The CW beam power and scanning speed are 1.79 mW and 3.0 μm/s. (c) SEM image of AgNWs which were fabricated under the CW beam power ranging from 1.55 mW to 1.79 mW. The pulse beam power is 0.43 mW and the scanning speed is 3.0 μm/s. (d) The dependence of width and height of the AgNWs in (a) on the scanning speed. (e) The dependence of width and height of the AgNWs in (b) on the pulse beam power. (f) The dependence of width and height of the AgNWs in (c) on the CW beam power.

Figure 4. Investigated the conductivity of the AgNW.

(a) SEM image of the AgNW between two silver electrodes. (b) AFM image of AgNW. (c) The cross-section profile of the AgNW in (b). (d) The schematic illustration of the electrical measurement. (e) The digital photographs of the electrical measurement setup. (f) The resistance variation of AgNW with the measured voltage. Inset: The I-V curve at the voltage of 0.6 V. (g) The resistance variation of the AgNW with the measured times. Inset: The AgNW I-V curve of the 1000^th time.

Figure 5. Investigated the flexibility of the AgNW.

(a) The schematic illustration of the resistance measurement setup under bending deformation. (b) The digital photograph of the resistance measurement setup under bending deformation. (c) The AgNW resistance variation with the different bending radii, the “Flat” on the right side and left side of the coordinate represent without bending and straightening after bending, respectively. Inset: The AgNW I-V curve when it was straightened. (d) The resistance variation of AgNW with the bending times. Inset: The AgNW I-V curve after it was stretched bending 2000 times.