ABSTRACT
As the final piece of a broader study on structure-property performance of SnO2 sensors, this study examines the performance of sensors created from tin(IV) oxide (SnO2) nanowires and nanoparticles as a function of temperature for untreated (UT) devices as well as those treated using Ar/O2 and H2O plasmas. Nanoparticle and nanowire sensors were exposed to air, carbon monoxide (CO), or benzene (C6H6) to determine sensor response (Rair/Rgas) and sensitivity (Rair/Rgas > 1 or Rgas/Rair > 1). Although both Ar/O2 and H2O plasma modification minimally increase sensor sensitivity toward CO and C6H6 under most conditions, this study explores initial plasma parameters of a wide array of plasma precursors to better understand the materials properties and gas-phase species that lead to specific sensing capabilities. In particular, certain Ar/O2 and H2O plasma treatment conditions resulted in increased sensitivity over UT nanomaterials at 25 and 50 °C, but of greatest importance is the knowledge gained from the combined materials, gas-phase, and sensor performance analysis that provide greater insight for effectively selecting future materials and modification systems to achieve optimal gas sensor performance.
ABSTRACT
Strategic application of an array of complementary imaging and diffraction techniques is critical to determine accurate structural information on nanomaterials, especially when also seeking to elucidate structure-property relationships and their effects on gas sensors. In this work, SnO2 nanowires and nanobrushes grown via chemical vapor deposition (CVD) displayed the same tetragonal SnO2 structure as revealed via powder X-ray diffraction bulk crystallinity data. Additional characterization using a range of electron microscopy imaging and diffraction techniques, however, revealed important structure and morphology distinctions between the nanomaterials. Tailoring scanning transmission electron microscopy (STEM) modes combined with transmission electron backscatter diffraction (t-EBSD) techniques afforded a more detailed view of the SnO2 nanostructures. Indeed, upon deeper analysis of individual wires and brushes, we discovered that, despite a similar bulk structure, wires and brushes grew with different crystal faces and lattice spacings. Had we not utilized multiple STEM diffraction modes in conjunction with t-EBSD, differences in orientation related to bristle density would have been overlooked. Thus, it is only through a methodical combination of several structural analysis techniques that precise structural information can be reliably obtained.
