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Morphological evolution accompanying a surface roughening and preferred orientation is an effective way to realize a high-performance gas sensor because of its significant potential as a chemical catalyst through chemical potentials and atomic energy states. In this work, we investigated a heterojunction of double-side-W-decorated NiO nanoigloos fabricated through radio frequency sputtering and a soft-template method. Interestingly, a morphological evolution characterized by a pyramidal rough surface and the preferred orientation of the (111) plane was observed upon decorating the bare NiO nanoigloos with W. The underlying mechanism of the morphological evolution was precisely demonstrated based on the van der Drift competitive growth model originating from the oxygen transport and chemical strain in the lattice. The gas sensing properties of W-decorated NiO show an excellent NO2 response and selectivity when compared to other gases. In addition, high response stability was evaluated under interference ga...

The utilization of edge sites in two-dimensional materials including transition-metal dichalcogenides (TMDs) is an effective strategy to realize high-performance gas sensors because of their high catalytic activity. Herein, we demonstrate a facile strategy to synthesize the numerous edge sites of vertically aligned MoS

The utilization of p–p isotype heterojunctions is an effective strategy to enhance the gas sensing properties of metal-oxide semiconductors, but most previous studies focused on p–n heterojunctions owing to their simple mechanism of formation of depletion layers. However, a proper choice of isotype semiconductors with appropriate energy bands can also contribute to the enhancement of the gas sensing performance. Herein, we report nickel oxide (NiO)-decorated cobalt oxide (Co3O4) nanorods (NRs) fabricated using the multiple-step glancing angle deposition method. The effective decoration of NiO on the entire surface of Co3O4 NRs enabled the formation of numerous p–p heterojunctions, and they exhibited a 16.78 times higher gas response to 50 ppm of C6H6 at 350 °C compared to that of bare Co3O4 NRs with the calculated detection limit of approximately 13.91 ppb. Apart from the p–p heterojunctions, increased active sites owing to the changes in the orientation of the exposed lattice surface and the catalytic ef...

Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.

Self-assembled WO3 thin film nanostructures with 1-dimensional villi-like nanofingers (VLNF) have been synthesized on the SiO2/Si substrate with Pt interdigitated electrodes using glancing angle deposition (GAD). Room-temperature deposition of WO3 by GAD resulted in anisotropic nanostructures with large aspect ratio and porosity having a relative surface area, which is about 32 times larger than that of a plain WO3 film. A WO3 VLNF sensor shows extremely high response to nitric oxide (NO) at 200 °C in 80% of relative humidity atmosphere, while responses of the sensor to ethanol, acetone, ammonia, and carbon monoxide are negligible. Such high sensitivity and selectivity to NO are attributed to the highly efficient modualtion of potential barriers at narrow necks between individual WO3 VLNF and the intrinsically high sensitivity of WO3 to NO. The theoretical detection limit of the sensor for NO is expected to be as low as 88 parts per trillion (ppt). Since NO is an approved biomarker of chronic airway inflammation in asthma, unprecedentedly high response and selectivity, and ppt-level detection limit to NO under highly humid environment demonstrate the great potential of the WO3 VLNF for use in high performance breath analyzers.