Ammonia plasma induced n-type doping of semiconducting carbon nanotube films: thermoelectric properties and ambient effects

We explore an n-type doping strategy of semiconducting single-walled carbon nanotubes (sc-SWCNTs) by a covalent functionalization in low pressure ammonia plasma and elucidate the effect of air exposure on thermoelectric properties of the sc-SWCNTs before and after doping. Without doping, the sc-SWCNT films have a Seebeck coefficient of 125 μV/K and a power factor of 95 µW/mK2, in ambient conditions. Heating of such films in air up to 100°C and above is not changing their thermoelectric properties noticeably, however the films can be converted to an n-type material simply by gas desorption at low pressure and a high temperature, showing an outstanding negative Seebeck coefficient of ‒133 μV/K and power factor of 55 µW/mK2 at 220°C. Doping of the sc-SWCNTs films with ammonia plasma leads to the reduction of Seebeck coefficient down to 40 μV/K in ambient condition, which is the result of two competing effects: attachment of electron donating functional groups during plasma treatment and adsorption of water a...