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

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 degrees 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/cm(2). 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 sp(2) 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 similar to 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 similar to 30,000 S/cm).