Gas sensors with carbon nanotubes (CNTs) and tin dioxide (SnO2) nanoparticles for nitrogen dioxide (NO2) detection are fabricated using a two-step dielectrophoretic (DEP) assembly method, and the NO2 gas detection properties are investigated. For the fabrication of the sensor, CNTs assemble between electrodes by a DEP force, followed by SnO2 nanoparticle decoration also by a DEP assembly method, and the assembled CNTs act as high electric field electrodes. The formed CNT/SnO2 gas sensors exhibit a sharp increase in resistance followed by a gradual decrease upon NO2 exposure. pn hetero-junctions are formed between the CNTs and the SnO2 nanoparticles, and the resistance shift of the depletion region in the CNTs at the pn hetero-junction induces the sharp increase in the resistance.
