Superior Functionality by Design: Selective Ozone Sensing Realized by Rationally Constructed High‐Index ZnO Surfaces

Abstract

A new technique is reported for the transformation of smooth nonpolar ZnO nanowire surfaces to zigzagged high-index polar surfaces using polycrystalline ZnO thin films deposited by atomic layer deposition (ALD). The c-axis-oriented ZnO nanowires with smooth nonpolar surfaces are fabricated using vapor deposition method and subsequently coated by ALD with a ZnO particulate thin film. The synthesized ZnO-ZnO core-shell nanostructures are annealed at 800 °C to transform the smooth ZnO nanowires to zigzagged nanowires with high-index polar surfaces. Ozone sensing response is compared for all three types of fabricated nanowire morphologies, namely nanowires with smooth surfaces, ZnO-ZnO core-shell nanowires, and zigzagged ZnO nanowires to determine the role of crystallographic surface planes on gas response. While the smooth and core-shell nanowires are largely non-responsive to varying O(3) concentrations in the experiments, zigzagged nanowires show a significantly higher sensitivity (ppb level) owing to inherent defect-rich high-index polar surfaces.

High Density Unaggregated Au Nanoparticles on ZnO Nanorod Arrays Function as Efficient and Recyclable Photocatalysts for Environmental Purification

“…In recent decades, zinc oxide (ZnO) nanostructures (e.g., nanodots, nanorods, nanobelts, and so forth) have been extensively studied due to their attractive properties, such as excellent optoelectronic properties, high surface area to volume ratio, and convenient surface tailorability 1–3. In particular, one‐dimensional ZnO nanostructures have drawn intensive attention by the fact that they constitute suitable building blocks for various promising applications in the fields of nanogenerators, nanosensors, light‐emitting diodes, photovoltaic cells, and photocatalysts in environmental purification 4–8. For photocatalytic degradation of hazardous pollutants, 1D ZnO nanostructures, comparing with film‐based ZnO, have been recognized as preferable materials for photocatalytic processes due to their high surface area, efficient charge transport, excellent photosensitivity and optical anti‐reflection ability 9–11.…”

Growth mechanism, optical and photocatalytic properties of ZnO nanorods@nanoflowers (quantum dots) hybrid nanostructures

“…ZnO QDs in our samples is smaller than 7 nm in dimension, and so this blue-shift behavior of PL peak position is naturally explained by the quantum confinement effect [28], which is in agreement with the results from Raman. The deep level emission (DLE) band in the range of 430−670 nm is known as defect luminescence band, which has been reported to originate from various intrinsic and extrinsic defects in ZnO crystals and also influenced by defects, impurities and absorbed molecules on the sample surface [29,30]. It's generally agreed that DLE emission is largely related to oxygen vacancies (V O ) and surface defects.…”

“…The inset of Fig. 7 displays a column graph of the DLE to 9 NBE ratio from the three samples, the higher value indicates higher defect density [30]. It can be seen that the hybrid nanostructures show a higher concentration of surface defects as a result of ZnO QDs or ZnO NFs assembled onto the nanorods surface.…”

Atomic Layer Deposition to Materials for Gas Sensing Applications

“…A hydrogen sensor based on a ZnO nanorod (NR) array was fabricated by impregnating an anodic aluminum oxide template, supported on a niobium electrode, by ZnO ALD followed by dissolution of the template in an acid . ZnO NWs displaying high‐index polar zigzagged surfaces were fabricating in three steps ( Figure a) . (i) c‐axis oriented single crystal NWs were grown by physical vapor deposition.…”

“…a) Scheme of the fabrication process of the zigzagged nanowires; b) TEM image of a single crystal ZnO nanowire core coated by polycrystalline ZnO ALD film; c,d) TEM and HRTEM images of a zigzagged nanowire after thermal annealing. Reproduced with permission …”