Tailoring gas sensing properties of carbon nanotubes

An approach to tune the chemical properties (electronic density of states, chemical potential) of carbon nanotubes (CNTs) for gas/vapor sensing is presented. The technique involves infiltrating CNTs with transition metal as opposed to decorating the outer sidewalls. NO2 was chosen as a model gas to demonstrate the variable/tunable sensing behavior of the metal-CNT hybrids. By varying the nature of the transition metal infiltrated into the CNT, we observe dramatically different responses among the hybrid sensors upon exposure to ppm levels of the target analyte. These responses are manifested as simultaneous resistive and capacitive components of the CNT impedance. While some hybrid materials demonstrated superior sensitivity (approximately two-fold increase) to detection of NO2 at room temperature compared to the pristine SWCNT sensor, other hybrid sensors showed suppressed sensitivity (approximately 20-fold decrease) to NO2 relative to the single wall CNT sensor. These differential impedimetric responses created from a library of metal-CNT hybrid materials may function as a practical approach for offering enhanced sensitivity and selectivity for gas sensing. (c) 2008 American Institute of Physics.