Multifunctional device based on ZnO:Fe nanostructured films with enhanced UV and ultra-fast ethanol vapour sensing

Physica Status Solidi (a)

et al. 2018

Self Cite

In this work, a simple method of ZnAl2O4‐functionalization of ZnO microstructures is presented. The different characterization methods (structural, chemical, and micro‐Raman) demonstrated the presence of only ZnO and ZnAl2O4 crystalline phases. ZnAl2O4 nano‐crystallites grow on the surfaces of ZnO 3D microstructures having diameters of 50–100 nm and with high density. Transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM) results clearly show ZnAl2O4 crystallites functionalizing zinc oxide tetrapod arms. The individual structures (microwires (MWs) and three‐dimensional (3D) tetrapods (Ts)) are integrated into functional devices, suitable for gas sensing applications. All devices show excellent hydrogen gas selectivity at relatively low operating temperature in the range of 25–100 °C. The highest gas sensing performances are obtained based on individual ZnAl2O4‐functionalized ZnO tetrapods (ZnAl2O4/ZnO‐T, with an arm diameter (D) of ≈400 nm) and a response of ≈2 at 25 °C to 100 ppm of hydrogen gas (H2), while a ZnAl2O4/ZnO‐MW (D ≈ 400 nm) shows only a response of ≈1.1. The Al‐doped ZnO MW (D ≈ 400 nm) without ZnAl2O4 elaborated in another work, chosen only for comparison reason, shows no response up to 800 ppm H2 gas concentration. A gas sensing mechanism is proposed for a single ZnAl2O4/ZnO‐T microstructure based sensor. The obtained results on ZnAl2O4/ZnO‐T‐based devices is superior to many reported performances of other individual metal oxide nanostructures with much lower diameter, showing promising results for room temperature H2 gas sensing applications.

Section: Resultsmentioning

confidence: 99%

ZnAl₂O₄‐Functionalized Zinc Oxide Microstructures for Highly Selective Hydrogen Gas Sensing Applications

Hoppe

Physica Status Solidi (a)

et al. 2018

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“…Lee et al also attributed p ‐type conductivity of α‐Fe 2 O 3 NW to strong surface adsorption owing to the oxygen vacancies and the high surface‐to‐volume ratio . It is well known that at higher temperatures (between 150 and 400 °C) the molecular oxygen dissociates to atomic oxygen (see Figure a)

{normalO}_{2} (normalads) + {normale}^{-} \leftrightarrow {normalO}_{2}^{-} (normalads)

{normalO}^{-}_{2} (normalads) \leftrightarrow 2 {normalO}_{}^{-} (normalads)

…”

Section: Resultsmentioning

confidence: 99%

Localized Synthesis of Iron Oxide Nanowires and Fabrication of High Performance Nanosensors Based on a Single Fe₂O₃ Nanowire

Wolff

et al. 2017

Small

Self Cite

116

A composed morphology of iron oxide microstructures covered with very thin nanowires (NWs) with diameter of 15-50 nm has been presented. By oxidizing metallic Fe microparticles at 255 °C for 12 and 24 h, dense iron oxide NW networks bridging prepatterned Au/Cr pads are obtained. X-ray photoelectron spectroscopy studies reveal formation of α-Fe O and Fe O on the surface and it is confirmed by detailed high-resolution transmission electron microscopy and selected area electron diffraction (SAED) investigations that NWs are single phase α-Fe O and some domains of single phase Fe O . Localized synthesis of such nano- and microparticles directly on sensor platform/structure at 255 °C for 24 h and reoxidation at 650 °C for 0.2-2 h, yield in highly performance and reliable detection of acetone vapor with fast response and recovery times. First nanosensors on a single α-Fe O nanowire are fabricated and studied showing excellent performances and an increase in acetone response by decrease of their diameter was developed. The facile technological approach enables this nanomaterial as candidate for a range of applications in the field of nanoelectronics such as nanosensors and biomedicine devices, especially for breath analysis in the treatment of diabetes patients.

“…[2][3] However, the rapid progress in nanotechnologies includes the continuous search of novel materials with new and unique functionalities, which is in focus of many research groups around the world. [1][2][3][4][5][6] In this context, fabrication of three-dimensional (3-D) networks of interconnected ZnO tetrapods (ZnO-T) has been a very important step for progress in engineering, science and nanotechnology. 1,[3][4][6][7][8] Recently the research group of Rainer Adelung has demonstrated a fast and simple synthesis of highly porous interconnected ZnO-T networks by a crucible flame transport synthesis (C-FTS) approach and burner flame transport synthesis (B-FTS).…”

Section: Introductionmentioning

confidence: 99%

Hybridization of Zinc Oxide Tetrapods for Selective Gas Sensing Applications

ACS Appl. Mater. Interfaces

Gröttrup

et al. 2017

136

113

In this work, the exceptionally improved sensing capability of highly porous 3-D hybrid ceramic networks with respect to reducing gases is demonstrated for the first time. The 3-D hybrid ceramic networks are based on metal oxides Me= Fe, Cu, Al) doped and alloyed zinc oxide tetrapods (ZnO-T) forming numerous heterojunctions. A change in morphology of the samples and formation of different complex microstructures is achieved by mixing the metallic (Fe, Cu, Al) microparticles with ZnO tetrapods grown by flame transport synthesis (FTS) approach with different weight ratios (ZnO:Me, e.g., 20:1) and followed by subsequent thermal annealing them in air. The gas sensing studies reveal the possibility to control and change/tune the selectivity of the materials, depending on the elemental content ratio and the type of the added metal oxide in 3-D ZnO-T hybrid networks.While pristine ZnO-T networks showed a good response to H2 gas, a change/tune in selectivity to ethanol vapour with a decrease in optimal operating temperature was observed in the networks hybridized with Fe-oxide and Cu-oxide. In case of hybridization with ZnAl2O4 an improvement of H2 gas response (to ≈ 7.5) was reached at lower doping concentrations (20:1), whereas the increasing in concentration of ZnAl2O4 (10:1), the selectivity changes to methane CH4 gas (response ≈ 28). Selectivity tuning to different gases is attributed to the catalytic properties of the metal oxides after hybridization, while the sensitivity improvement is mainly associated with additional modulation of resistance by the built-in potential barriers between n-n and n-p heterojunctions, during adsorption and desorption of gaseous species. Density functional theory based calculations provided the mechanistic insights into the interactions between different hybrid networks and gas molecules supporting the experimentally observed results. The studied materials and sensor structures would provide particular advantages in the field of fundamental research, industrial and ecological applications.