Highly doped wide band gap metal oxide nanocrystals have recently been proposed as building blocks for applications as transparent electrodes, electrochromics, plasmonics, and optoelectronics in general. Here we demonstrate the application of gallium-doped zinc oxide (GZO) nanocrystals as novel plasmonic and chemiresistive sensors for the detection of hazardous gases including hydrogen (H) and nitrogen dioxide (NO). GZO nanocrystals with a tunable surface plasmon resonance in the near-infrared are obtained using a colloidal heat-up synthesis. Thanks to the strong sensitivity of the plasmon resonances to chemical and electrical changes occurring at the surface of the nanocrystals, such optical features can be used to detect the presence of toxic gases. By monitoring the changes in the dopant-induced plasmon resonance in the near-infrared, we demonstrate that GZO thin films prepared depositing an assembly of highly doped GZO colloids are able to optically detect both oxidizing and reducing gases at mild (<100 °C) operating temperatures. Combined optical and electrical measurements show that trivalent dopants within ZnO nanocrystals enhance the gas sensing response compared to undoped ZnO. Moreover, improved sub-ppm of NO gas sensitivity is achieved by activating the sensors response through combined purple-blue (λ = 430 nm) light irradiation and mild heating at 75 °C. In addition, these thin films based on degenerately doped semiconductors are highly transparent in the visible range, enabling the fabrication of "invisible" gas sensors. The use of highly doped semiconductive nanocrystals for both IR plasmonic and chemiresistive sensors represent a marked advancement toward the development of highly sensitive and selective devices.
A bioinspired multilayer film made of a new silk–titanate nanocomposite material, showing a humidity-responsive behavior, has been fabricated. The multilayer structure mimics the structure of the cuticle of the Hoplia coerulea beetle and shows long-term stability over a very large relative humidity range.
We applied cathodoluminescence (CL) spectroscopy to evaluate the defect-induced luminescence within ZnO and Ga-doped ZnO (GZO) nanoparticles. The observed emissions from defect sites present in the GZO lattice exhibited a strong dependence on both dopant content and synthesis methods. The strong and broad defect-induced emissions and inhomogeneous population of intrinsic defects in nano-sized ZnO particles could effectively be suppressed by Ga doping, although large dopant amounts caused the generation of negatively-charged defects, VZn and Oi, with a subsequent increase of the luminescence. Upon deconvolution of the retrieved CL spectra into individual sub-bands, the physical origin of all the sub-bands could be clarified, and related to sample composition and synthesis protocol. This study lays the foundation of quantitative CL evaluation of defects to assess the quality of GZO optoelectronic devices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.