An optical carbon nanotube fibre probe for measurement of nano structures with large aspect ratio

With the development of imaging and measurement technologies, scanning near-field optical microscopy (SNOM) has achieved high signal-to-noise ratio. The resolution of a fibre probe-based SNOM system is capable of reaching 10 nm. However, SNOM applications are presently constrained to the measurement of near-field optical information to relatively straightforward structures, including quantum dots, carbon nanotubes, graphene, and so forth. The geometry of conventional fibre probes, with tips at an angle of 30°–60°, presents a challenge for accurately imaging complex surface structures. This paper proposes a carbon nanotube composite fibre probe (CNT-FP) with a large aspect ratio. The key point is that a carbon nanotube bundle is composited at the tip of conventional surface plasmon polaritons fibre probes (SPPs-FP), which are the fibre probes coated with gold film to excite the SPPs. The coupling, propagation, and focusing effects of SPPs on the carbon nanotube bundle are verified. CNT-FPs have been fabricated and applied to measure a grating with the depth of 400 nm and the width of 400 nm. The experimental results show that the measurement accuracy and imaging quality of CNT-FP are nearly one order of magnitude higher than that of conventional SPPs-FP, as evidenced by evaluation criteria such as line roughness and volatility index. Moreover, it achieves an optical resolution of 72.1 nm in the measurements of a nano structure with large aspect ratio. It provides an effective solution of measuring structures with larger aspect ratios.