Stress-engineered palladium nanowires for wide range (0.1%-3.9%) of H detection with high durability.

Pd nanowire-based H sensors have attracted significant attention because of their superior sensing performance. However, when exposed to H concentrations of more than 2%, Pd experiences volume expansion over 10%, resulting in a significant amount of mechanical stress. Thus, exposure to such high H concentrations causes physical destruction of Pd nanowires, such as breaks and peel-offs, leading to severe difficulty in the reliable detection of H over a wide concentration range. Here, we proposed a structural approach to resolve this issue by introducing a partially anchored Pd nanowire (PA-PdNW) structure. In this configuration, most of the structure was air-suspended, leaving a small portion anchored to the substrate. Air-suspension enabled PA-PdNW to expand freely, thus relieving the mechanical stress; therefore, the Pd nanowires could withstand numerous exposures to high H concentrations. To demonstrate the PA-PdNW structure, we developed a nano-fabrication method based on conventional semiconductor processes and successfully manufactured H sensor devices with uniform, perfectly aligned PA-PdNW arrays stably air-suspended with designed gaps from the substrate. The fabricated sensors achieved reliable detection of H in the 0.1%-3.9% concentration range with a significant resistance change. In addition, compared with fully anchored Pd nanowire (FA-PdNW) sensors, the PA-PdNW sensors showed superior durability, and the nanowires retained their initial structures even after 300 exposures to high H concentrations. Furthermore, it was confirmed that the PA-PdNW sensor can stably operate even in extremely humid environments at 85% relative humidity.