Heterogeneous nucleation for synthesis of sub-20nm ZnO nanopods and their application to optical humidity sensing.
We present a novel method for colloidal synthesis of one-dimensional ZnO nanopods by heterogeneous nucleation on zero-dimensional ZnO nanoparticle 'seeds'. Ultra-small ZnO nanopods, multi-legged structures with sub-20 nm individual leg diameters, can be synthesized by hydrolysis of a Zn2+ precursor growth solution in presence of ∼4 nm ZnO seeds under hydrothermal conditions via microwave-assisted heating in as little as 20 min of reaction time. One-dimensional ZnO nanorods are initially generated in the reaction mixture by heterogeneous nucleation and growth along the [0001] direction of the ZnO crystal. Growth of one-dimensional nanorods subsequently yields to an 'attachment' and size-focusing phase where individual nanorods fuse together to form multi-legged nanopods having diameters ∼15 nm. ZnO nanopods exhibit broad orange-red defect-related photoluminescence in addition to a near-band edge emission at 373 nm when excited above the band-gap at 350 nm. The defect-related photoluminescence of the ZnO nanopods has been applied towards reversible optical humidity sensing at room temperature. The sensors demonstrated a linear response between 22% and 70% relative humidity with a 0.4% increase in optical intensity per % change in relative humidity. Due to their ultra-small dimensions, ZnO nanopods exhibit a large dynamic range and enhanced sensitivity to changes in ambient humidity, thus showcasing their ability as a platform for optical environmental sensing.
Materials Science and Engineering, Texas A&M University, TX, United States.
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R
Majithia
Department of Biomedical Engineering, Texas A&M University, TX, United States.
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S
Ritter
Materials Science and Engineering, Texas A&M University, TX, United States; Department of Biomedical Engineering, Texas A&M University, TX, United States. Electronic address: kmeissner@tamu.edu.
K E
KE
Meissner
D006813:Humidity; D046529:Microscopy, Electron, Transmission; D049329:Nanostructures; D015034:Zinc Oxide / Q000737:chemistry*
D015034:Zinc Oxide
Heterogeneous nucleation; Microwave-assisted; Optical gas sensing; ZnO nanostructures