Ethylene-induced welding of single-walled carbon nanotube films to enhance mechanical and optoelectronic properties

Abstract

Single-walled carbon nanotube (SWCNT) free-standing films combine high electrical conductivity with exceptional mechanical stability and optical transparency, opening the road for various applications: bolometers, thermophones, filters, etc. Here, we improve the performance of SWCNT free-standing films by engineering the intersections between the nanotube bundles –the building blocks forming and defining the conductivity and mechanical performance of the material. Hence, we propose a new, rapid, and scalable technology for the tailorable treatment of SWCNT free-standing films with ethylene (C₂H₄) under resistive heating. The technology comprises the high-temperature Joule heating of SWCNT free-standing films (700–1200 °C) combined with an exposure to ethylene flow at a pressure below 0.3 mPa, with an energy consumption as low as ca. 10 W/cm². Using a set of methods (UV–vis–NIR and Raman spectroscopies, scanning and transmission electron microscopies, four-probe sheet resistance, temperature coefficient of resistance, and combined ultimate tensile strength/gauge factor measurements) combined with molecular dynamics simulations, we observe the film welding, i.e., the deposition of sp² carbon coating presumably on nanotube bundle junctions. We show the welded free-standing films to enhance the performance of the filters and transparent electrodes (after doping with HAuCl₄), strengthening the material up to an order of magnitude (ultimate tensile strength ∼ 22 MPa) and reaching one of the state-of-the-art performance values of 30 Ohm/sq at a transmittance of 90 % at 550 nm (electrical conductivity ∼ 30,000 S/cm).