A fast response gas sensor based on fluorine plasma modified single wall carbon nanotubes

Single wall carbon nanotubes (SWCNTs) were synthesized from chemical vapor deposition (CVD) by decomposition of ethanol over a Fe+Co/MgO heterogeneous catalyst. The SWCNTs were treated by fluorine plasma from microwave plasma enhanced chemical vapor deposition (MPECVD) for surface modification, and developed as novel gas sensor materials. In gas-sensing tests, the SWCNT-based gas sensors treated by fluorine plasma have shown a p-type response with resistance enhancement upon exposure to 50-500 ppm ethanol at room temperature. Fluorine plasma modification can enhance the sensor response (100 ppm) from 1.15 to 1.28 on process duration of 60 s due to the apparent elimination of amorphous carbon, as demonstrated by Raman results. The sensitivity (100 ppm) increases two more times (from 0.0009 to 0.0019) and the linear range of measurement can also extend. In addition, the response and recovery time (100 ppm) can decrease apparently from 195 to 69 s and 374 to 202 s due to the existence of numerous fluorine-included functional groups, as demonstrated by the results of x-ray photoelectron spectroscopy and Auger electron spectroscopy. Therefore, the fluorinated SWCNTs can elevate the sensitivity and reactivity for room temperature ethanol sensing.