Carbon nanotube resistors as gas sensors: Towards selective analyte detection with various metal-nanotubeinterfaces

This paper reports the fabrication of conductance-based gas sensors based on horizontal, dense carbon nanotube (CNT) arrays directly integrated between metal electrodes via a selective and directional catalytic growth process performed in-situ and at the wafer-scale. We originally propose to use a functionalization strategy focusing on the key role of the electrode-CNT junction, for increased selectivity. Devices based on CNT arrays have been fabricated using various designs and different metals: Pt, Pd and Au, to top-contact the CNT arrays so as to provide several types of metal-CNT junctions. The sensors have been exposed to low concentrations of H2 as well as NH₃, toluene, ethanol and relative humidity. We demonstrate that the CNT resistors responses to gases are hardly dependent on the design, the CNT surface developed between the electrodes, but very specific to the metal-CNT interface. Therefore, we postulate that gases interact in a metal-specific way and modify the metal-CNT contact resistance of the resistors but the device sensitivity cannot simply be ascribed to the modulation of Schottky barriers as reported in literature. Since the main issue with CNT sensors is their lack of selectivity, we believe that this method provides an easy to implement strategy and shows potential for room temperature discriminative gas detection.