Design rules for nanogap-based hydrogen gas sensors

Nanoscale gaps, which enable many research applications in fields such as chemical sensors, single-electron transistors, and molecular switching devices, have been extensively investigated over the past decade and have witnessed the evolution of related technologies. Importantly, nanoscale gaps employed in hydrogen-gas (H₂) sensors have been used to reversibly detect H ₂ in an On-Off manner, and function as platforms for enhancing sensing performance. Herein, we review recent advances in nanogap design for H₂ sensors and deal with various strategies to create these gaps, including fracture generation by H₂ exposure, deposition onto prestructured patterns, island formation on a surface, artificial manipulation methods, methods using hybrid materials, and recent approaches using elastomeric substrates. Furthermore, this review discusses a new nanogap design that advances sensing capabilities in order to meet the diverse needs of academia and industry. Mind the gap: Various approaches for the formation of nanogaps in palladium-based nanostructures (see picture) have been investigated during the last decade to realize an optimized hydrogen gas sensor. Despite multilateral approaches to create various types of nanogaps, however, critical issues remain to be solved. To tackle the existing issues with nanogaps, design rules and recent advances with nanogaps are reviewed.