Surface structure and intrinsic wettability are both important for boiling heat transfer. While superhydrophilic micro, nano, and hierarchical surfaces are widely used for boiling enhancement, in which the surface structure and intrinsic wettability usually couple together. This study aims to decouple their influences on boiling heat transfer. Copper meshes are utilized as the microporous structures, and conformal superhydrophilic films of TiO₂ are deposited by atomic layer deposition (ALD). Although ALD coatings for boiling have been done on flat surfaces, this study separates the influence of surface structure from that of intrinsic wettability on a three-dimensional microporous surface. By comparing two and four layer meshes, we show that the surface structure has no obvious influence on the critical heat flux (CHF), but can significantly enhance the heat transfer coefficient (HTC). The intrinsic superhydrophilicity dramatically increases the CHF due to the fast rewetting of dryout regions. Our conclusion is that fast rewetting is critical to increase the CHF, while large surface areas are vital to enhance the HTC.

A novel low-temperature SnO₂ gas sensor was prepared and studied on silicon nanostructures formed by femtosecond laser irradiation. By applying a bias voltage on the silicon substrate to alter the charge distribution on the surface of the SnO₂, carbon monoxide (CO), and ammonia (NH₃) gas can be distinguished by the same sensor at room temperature. The experimental results are explained with a mechanism that the sensor works at low temperature because of adsorption of gas molecules that trap electrons to the surface of the SnO₂.