Optimized Fabrication and Characterization of W Tips for High-Performance Atomic-Resolution Scanning Tunneling Microscope

Scanning tunneling microscope (STM) is a powerful technique for atomic-resolution surface characterization that relies on quantum tunneling through sharp conductive probes. The preparation of high-quality STM tips represents a critical aspect of instrument performance, where tip sharpness determines imaging resolution and mechanical stability ensures measurement reproducibility. Tungsten (W) is widely used for STM tips due to its exceptional mechanical strength and excellent electrical conductivity. In this study, we optimized the fabrication of W tips through electrochemical etching by systematically investigating etching time, wire immersion depth, and applied voltage. Multiple tips were fabricated and evaluated based on their curvature radius and sharpness. The imaging performance of these tips was assessed through atomic-resolution STM measurements on highly oriented pyrolytic graphite (HOPG) at room temperature using a home-built STM system. Among the fabricated tips, the sharpest specimens demonstrated outstanding performance under extreme conditions, including low temperatures and high magnetic fields, confirming their suitability for advanced applications. These findings establish a reliable framework for fabricating high-performance W tips, which are essential for precise STM imaging and function effectively as antennas in terahertz (THz)-driven STM systems for exploring ultrafast nanoscale dynamics.