title: Fast and selective room-temperature ammonia sensors using silver nanocrystal-functionalized carbon nanotubes.
abstract: We report a selective, room-temperature NH(3) gas-sensing platform with enhanced sensitivity, superfast response and recovery, and good stability, using Ag nanocrystal-functionalized multiwalled carbon nanotubes (Ag NC-MWCNTs). Ag NCs were synthesized by a simple mini-arc plasma method and directly assembled on MWCNTs using an electrostatic force-directed assembly process. The nanotubes were assembled onto gold electrodes with both ends in Ohmic contact. The addition of Ag NCs on MWCNTs resulted in dramatically improved sensitivity toward NH(3). Upon exposure to 1% NH(3) at room temperature, Ag NC-MWCNTs showed enhanced sensitivity (~9%), very fast response (~7 s), and full recovery within several minutes in air. Through density functional theory calculations, we found that the fully oxidized Ag surface plays a critical role in the sensor response. Ammonia molecules are adsorbed at Ag hollow sites on the AgO surface with H pointing toward Ag. A net charge transfer from NH(3) to the Ag NC-MWCNTs hybrid leads to the conductance change in the hybrid.
authors.affiliation: Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, USA.
authors.forename: Shumao
authors.initials: S
authors.lastname: Cui
authors.forename: Haihui
authors.initials: H
authors.lastname: Pu
authors.forename: Ganhua
authors.initials: G
authors.lastname: Lu
authors.forename: Zhenhai
authors.initials: Z
authors.lastname: Wen
authors.forename: Eric C
authors.initials: EC
authors.lastname: Mattson
authors.forename: Carol
authors.initials: C
authors.lastname: Hirschmugl
authors.forename: Marija
authors.initials: M
authors.lastname: Gajdardziska-Josifovska
authors.forename: Michael
authors.initials: M
authors.lastname: Weinert
authors.forename: Junhong
authors.initials: J
authors.lastname: Chen
mesh_terms: D000641:Ammonia / Q000032:analysis*; D055664:Electrochemical Techniques; D004566:Electrodes; D006046:Gold / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry*; D037742:Nanotubes, Carbon / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D013696:Temperature
chemical_list: D037742:Nanotubes, Carbon; D012834:Silver; D006046:Gold; D000641:Ammonia