| Miniaturized gas sensors that rapidly and accurately detect and differentiate trace amount of individual gases or gas mixtures are extremely attractive for many applications, including environmental monitoring, medical diagnosis, food processing, detection of explosives for national security, and lab-on-a-chip analytical devices. The objective of this study is to fabricate and characterize miniaturized gas sensors using tin oxide aerosol nanoparticles and hybrid structures of tin oxide nanoparticles supported on carbon nanotubes (CNTs).; A mini-arc plasma source has been developed to synthesize nonagglomerated and crystalline pure/doped tin oxide nanoparticles with controlled size. The nanoparticles are formed by direct vaporization of solid precursors followed by a rapid quenching. The electrical charges carried by as-produced aerosol nanoparticles facilitate the manipulation of nanoparticles using electrostatic force. An electrostatic precipitator (ESP) has been designed and constructed to perform electrostatic force directed assembly (ESFDA) of aerosol nanoparticles onto various substrates. The collection efficiency of the ESP has been predicted using simplified analytical models. The ESFDA technique has been used to successfully assemble nanoparticles onto random or vertically-aligned CNTs. An intrinsic nanoparticle size selection has been observed during the assembly process. The size distribution and the areal density of nanoparticles on CNTs can be controlled with electric field, flow residence time, and assembly time.; Miniaturized gas sensors based on tin oxide nanoparticles alone and tin oxide nanoparticle-CNT hybrid structures have been successfully fabricated by the ESFDA assembly of tin oxide nanoparticles onto electron-beam lithographically patterned interdigitated electrodes with or without CNTs. The nanoparticle gas sensor demonstrates good response and sensitivity at elevated operating temperatures around 250°C when exposed to low concentration ethanol vapor and hydrogen in air. The multiwalled CNT (MWCNT)-electrode contact can be improved by local Joule heating and annealing in an inert gas. The nanoparticle-MWCNT device shows great potential to sense low concentration gases (NO2,H 2, and CO) at room temperature. |
