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 NO 2 response and selectivity when compared to other gases. In addition, high response stability was evaluated under interference gas and humidity conditions. The synergistic effects on the sensing performance were interpreted on the basis of the morphological evolution of W-decorated NiO nanoigloos.

Gas sensors for Internet of Things applications should meet two requisites—low power consumption and easy mounting universally. To satisfy the conditions, gas sensors need to operate at lower temperature and...

extensively studied because of their remarkable advantages including low cost, simple fabrication, high response, and easy integration with electronic circuits. To ensure high response and reversible operation of chemiresistive gas sensors, high operating temperatures of 150-400 °C are inevitably required for adsorption and desorption of target molecules on and off of the sensing materials. [3,4] However, this high temperature degrades the sensor stability and lifetime due to thermally induced grain growth, which can damage interconnected electronics. [5,6] Moreover, high power consumption (over ≈100 mW) is required, which must be decreased for the development of future battery-powered wireless sensors for applications to the IoT. [7] To design high performance gas sensors that operate at room temperature, a variety of approaches including self-heating, ultraviolet (UV)-assisted measurements, and 2D materials have been used for high stability and low power consumption. [8][9][10] Despite these extensive efforts, challenges remain including poor response and incomplete recovery because of the restricted modulation in electronic conductivity by insufficient reaction energy between the analytes and sensing materials. Recently, the utilization of humidity has been reported as an effective method for improving gas sensing performance at low temperatures.The development of high performance gas sensors that operate at room temperature has attracted considerable attention. Unfortunately, the conventional mechanism of chemiresistive sensors is restricted at room temperature by insufficient reaction energy with target molecules. Herein, novel strategy for room temperature gas sensors is reported using an ionic-activated sensing mechanism. The investigation reveals that a hydroxide layer is developed by the applied voltages on the SnO 2 surface in the presence of humidity, leading to increased electrical conductivity. Surprisingly, the experimental results indicate ideal sensing behavior at room temperature for NO 2 detection with sub-parts-per-trillion (132.3 ppt) detection and fast recovery (25.7 s) to 5 ppm NO 2 under humid conditions. The ionic-activated sensing mechanism is proposed as a cascade process involving the formation of ionic conduction, reaction with a target gas, and demonstrates the novelty of the approach. It is believed that the results presented will open new pathways as a promising method for room temperature gas sensors. Sensors/BiosensorsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.