In Situ Localized Growth of Ordered Metal Oxide Hollow Sphere Array on Microheater Platform for Sensitive, Ultra-Fast Gas Sensing

A simple and versatile strategy is presented for the localized on-chip synthesis of an ordered metal oxide hollow sphere array directly on a low power microheater platform to form a closely integrated miniaturized gas sensor. Selective microheater surface modification through fluorinated monolayer self-assembly and its subsequent microheater-induced thermal decomposition enables the position-controlled deposition of an ordered two-dimensional colloidal sphere array, which serves as a sacrificial template for metal oxide growth via homogeneous chemical precipitation; this strategy ensures control in both the morphology and placement of the sensing material on only the active heated area of the microheater platform, providing a major advantage over other methods of presynthesized nanomaterial integration via suspension coating or printing. A fabricated tin oxide hollow sphere-based sensor shows high sensitivity (6.5 ppb detection limit) and selectivity toward formaldehyde, and extremely fast response (1.8 s) and recovery (5.4 s) times. This flexible and scalable method can be used to fabricate high performance miniaturized gas sensors with a variety of hollow nanostructured metal oxides for a range of applications, including combining multiple metal oxides for superior sensitivity and tunable selectivity

In Situ Localized Growth of Porous Tin Oxide Films on Low Power Microheater Platform for Low Temperature CO Detection

This paper reports a facile method for creating a nanostructured metal oxide film on a low power microheater sensor platform and the direct realization of this structure as a gas sensor. By fast annealing the deposited liquid precursors with the microheater, a highly porous, nanocrystalline metal oxide film can be generated in situ and locally on the sensor platform. With only minimal processing, a high performance, miniaturized gas sensor is ready for use. A carbon monoxide sensor using the in situ synthesized porous tin oxide (SnO₂) sensing film is made as a demonstration of this technique. The sensor exhibits a low detection limit and fast response and recovery time at a low operating temperature. This facile fabrication method is highly flexible and has great potential for large-scale gas sensor fabrication

Nanowire-Assembled Hierarchical ZnCo₂O₄ Microstructure Integrated with a Low-Power Microheater for Highly Sensitive Formaldehyde Detection

Nanowire-assembled 3D hierarchical ZnCo₂O₄ microstructure is synthesized by a facile hydrothermal route and a subsequent annealing process. In comparison to simple nanowires, the resulting dandelion-like structure yields more open spaces between nanowires, which allow for better gas diffusion and provide more active sites for gas adsorption while maintaining good electrical conductivity. The hierarchical ZnCo₂O₄ microstructure is integrated on a low-power microheater platform without using binders or conductive additives. The hierarchical structure of the ZnCo₂O₄ sensing material provides reliable electrical connection across the sensing electrodes. The resulting sensor exhibits an ultralow detection limit of 3 ppb toward formaldehyde with fast response and recovery as well as good selectivity to CO, H₂, and hydrocarbons such as <i>n</i>-pentane, propane, and CH₄. The sensor only consumes ∼5.7 mW for continuous operation at 300 °C with good long-term stability. The excellent sensing performance of this hierarchical structure based sensor suggests the advantages of combining such structures with microfabricated heaters for practical low-power sensing applications