A facile method for preparation of uniformly decorated-spherical SnO2 by CuO nanoparticles for highly responsive toluene detection at high temperature

We reported a facile preparation of a uniform decoration of spherical n-type SnO2 by p-type CuO nanopa rticles as well as their utilization for enhanced performance on toluene gas detection.CuO nanoparticles and spherical SnO2 were synthesized by a facile non-hydrolytic solvothermal reaction,which could easily control their morphology.A uniform CuO nanoparticles decoration onto spherical SnO2 was achieved by a simple sonication and vigorous stirring at room tempe rature.We revealed orga nic solvents used in the oxide synthesis had a considerable influence on its surface charge that was beneficial for a uniformly electrostatic self-decoration between positively charged p-type CuO nanoparticles and negatively charged n-type spherical SnO2.Interestingly,CuO was partially reduced to Cu metal during high concentration of toluene exposure destroying p-n contact and developing new metal-semiconductor contact so-called ohmic junction,resulting in extraordinarily responsive and selective to toluene gas at 400℃as compared to a single p-CuO and n-SnO2.It was also found that the amount of particle decoration had an influence on sensor response and resistance.The optimum amount of CuO nanoparticle decoration was0.1 mmol on 0.5 mmol SnO2.The re s ponse(S=Ra/Rg)and selectivity of CuO/S nO2 based material toward the exposure of 75 ppm toluene had reached to such high as 540 and 5,respectively.The effect of p-n heterojunction and metal-semiconductor contact on the gas sensing mechanism of p-type CuO/n-type SnO2 was discussed.Furthermore,by decorating with CuO nanoparticles,CuO/SnO2 morphology was well-maintained after gas sensing evaluation demonstrated its excellency for high temperature toluene gas sensor application.

Coupling of plasmonic nanopore pairs: facing dipoles attract each other

Control of the optical properties of nano-plasmonic structures is essential for next-generation optical circuits and high-throughput biosensing platforms.Realization of such nano-optical devices requires optical couplings of various nanostructured elements and field confinement at the nanoscale.In particular,symmetric coupling modes,also referred to as dark modes,have recently received considerable attention because these modes can confine light energy to small spaces.Although the coupling behavior of plasmonic nanoparticles has been relatively well studied,couplings of inverse structures,that is,holes and pores,remain partially unexplored.Even for the most fundamental coupling system of two dipolar holes,comparison of the symmetric and antisymmetric coupling modes has not been performed.Here we present,for the first time,a systematic study of the symmetric and anti-symmetric coupling of nanopore pairs using cathodoluminescence by scanning transmission electron microscopy and electromagnetic simulation.The symmetric coupling mode,approximated as a pair of facing dipoles,is observed at a lower energy than that of the anti-symmetric coupling mode,indicating that the facing dipoles attract each other.The anti-symmetric coupling mode splits into the inner-and outer-edge localized modes as the coupling distance decreases.These coupling behaviors cannot be fully explained as inverses of coupled disks.Symmetric and anti-symmetric coupling modes are also observed in a short-range ordered pore array,where one pore supports multiple local resonance modes,depending on the distance to the neighboring pore.Accessibility to the observed symmetric modes by far field is also discussed,which is important for nanophotonic device applications.