Atomic Layer-Modified 3D Pd Nanochannels for High-Performance Hydrogen Sensing

Palladium (Pd), known for its excellent H₂ adsorption properties and ability to form palladium hydride (PdH_<i>x</i>), is extensively utilized as a key material in hydrogen (H₂) sensing technologies. Nevertheless, conventional Pd-based H₂ sensors have shown limited performance enhancements due to challenges in precisely controlling the microscopic interfaces between Pd nanograins, which determine the total resistance signal of the sensors. This limitation arises from the lack of a technique capable of precisely manipulating these interfaces at the atomic level. In this study, we develop an atomic layer etching (ALE) technique to enhance the performance of Pd-based H₂ sensors by enabling precise atomic-scale control over the surface of Pd nanochannels. We fabricated 3D Pd nanopatterns with ultrasmall grain sizes through a top-down nanolithography process, followed by an ALE process that achieved atomic-level precision (10 Å resolution) without compromising material crystallinity. Our two-step ALE process, comprising surface modification with Cl₂ plasma and removal with NH₃ ligand addition, enables uniform etching across a 4 in. wafer with less than 1% variation in etch per cycle (EPC). This atomic-level modulation of Pd nanochannels resulted in significantly enhanced H₂ sensitivity, demonstrating a maximum 130-fold increase in response to 1% H₂ concentration compared to nonatomically controlled sensors. Such substantial enhancement has been difficult to achieve through conventional structural tuning methods and is attributed to the maximized volume change of PdH_<i>x</i> resulting from the expanded gaps between Pd grains. This platform provides a promising avenue for developing high-performance H₂ sensors and other noble-metal-based applications requiring atomic-level structural precision.