Silver Monolayer Defects, Vacancies and Impurities, Exhibit Dynamic Behavior under Electron Excitation

Atomic-scale defects in two-dimensional materials can dramatically alter their electronic properties, offering exciting possibilities for both fundamental research and technological applications. Van Dong Pham from the Paul-Drude-Institut für Festkörperelektronik, alongside Arpit Jain and Chengye Dong from The Pennsylvania State University, and colleagues, now demonstrate unprecedented control over these defects within a single layer of silver positioned between graphene and silicon carbide. Their investigation reveals distinct defects, identified as vacancies and impurities, each possessing a unique electronic signature, and importantly, exhibits their ability to move controllably under stimulation from a scanning tunneling microscope tip. This dynamic behaviour, reminiscent of molecular switching, allows the defects to function as atomic-scale switches, offering a pathway towards manipulating two-dimensional metals with atomic precision and opening new avenues for nanoelectronic devices.

Point defects or impurities can give rise to sharp local modifications in the structure and electronic properties of two-dimensional metals, serving as an intriguing atomic-level solid-state model for both fundamental and application research. This work investigates atomic-scale defects in a two-dimensional silver monolayer intercalated between epitaxial graphene and silicon carbide, focusing on understanding how these defects alter the material’s characteristics and potentially enable novel functionalities. By examining these imperfections at the atomic level, scientists aim to establish a clearer connection between structural defects and electronic behaviour in two-dimensional materials, contributing to the growing field of atomically thin multifunctional coatings and providing insights for future materials design.

Ag Monolayer Height and Defect Characterisation

Researchers characterized a silver monolayer intercalated between graphene and silicon carbide using scanning tunneling microscopy and spectroscopy to identify and observe the dynamic behavior of point defects. Imaging confirmed the presence of a silver monolayer with a height consistent with a single atomic layer. Detailed analysis revealed bright and dark defects within the silver layer, and crucially, these defects disappeared when examined with low-energy electrons, indicating they reside below the graphene layer and are not surface contaminants. Further investigation of the defects’ electronic properties showed minimal response to changes in tip-sample distance, suggesting they possess intrinsic electronic properties beyond simple charge accumulation. Quantitative height measurements tracked the movement of bright defects, revealing they hop between locations and transform into dark vacant sites, providing insight into their diffusion mechanisms.

Defect States Visualized in Silver Monolayer

Scientists investigated atomic-scale defects within a two-dimensional silver monolayer using a scanning tunneling microscope. The research revealed distinct dark and bright defects, identified as in-plane vacancies and substitutional impurities, each hosting a localized electronic state induced solely by the defect itself. Differential conductance spectroscopy confirmed that the bright defect exhibits an occupied electronic state, while the dark defect displays an unoccupied state, both near the material’s Fermi level. The team observed a moiré pattern resulting from a slight mismatch between the graphene and silver layers, but this pattern was disrupted by the presence of the defects. Bias-dependent topography measurements confirmed that these defects are related to the electronic structure of the silver monolayer. Remarkably, the defects exhibit inelastic hopping under excitation by tunneling electrons, analogous to switching behavior in organic molecules, allowing for reversible control of the defects using the scanning tunneling microscope tip and enabling their function as atomic-scale two-level conductance switches.

Defect Hopping and Transformation in Silver Monolayers

This research presents a detailed investigation of atomic-scale defects within a two-dimensional silver monolayer, revealing previously unobserved dynamic behavior and establishing a pathway toward precise defect control. Through scanning tunneling microscopy, the team demonstrated that bright defects exhibit a remarkable ability to hop between locations when stimulated by an applied voltage, a process reminiscent of molecular switching. Importantly, this hopping is not simply a relocation of the defect, but a transformation; a bright defect converts into a dark vacancy, differing from the initial dark defect species. Spectroscopic analysis confirms these changes in electronic structure during the hopping process, supporting the conclusion that bright and dark defects likely originate from different impurity substitutions within the silver lattice, potentially involving silicon or other unknown elements. This work provides fundamental insight into the origins and behavior of defects in two-dimensional metals, opening possibilities for manipulating these defects as atomic-scale switches in future nanoelectronic devices.