As the semiconductor industry pushes transistors toward atomic dimensions, a long-standing measurement bottleneck has threatened progress: no reliable way to directly observe how charge carriers behave at the shrinking contact between metal and semiconductor. A research team led by Distinguished Professor Ya-Ping Chiu of the Department of Physics at National Taiwan University (NTU) has now overcome that barrier, developing a technique capable of probing a working chip at atomic-scale resolution. The findings were published in Nature on July 1, 2026 (Nature 655, 350–356).
The breakthrough centres on a method the team calls Operando Cross-sectional Scanning Tunneling Microscopy (Operando XSTM), which measures electron transport at the metal–semiconductor contact edge while the device is actually powered and operating. Drawing on nearly two decades of cross-sectional STM expertise, the team integrated functioning transistors into an ultra-high-vacuum platform, mechanically cleaved them to expose a clean cross-section, and scanned the contact region point by point under real operating voltages. This allowed the first direct measurement of the carrier transfer length—a core quantity governing contact resistance—without relying on model-based extrapolation. For a monolayer molybdenum disulphide transistor with a bismuth contact, the measured transfer length was roughly 2 nanometres, far below the 9.25 nanometres inferred by conventional models, confirming the design's promise for next-generation technology nodes.
The achievement reflects a genuinely international, cross-disciplinary partnership. NTU developed the operando inspection platform; National Taiwan Normal University fabricated and electrically characterised the two-dimensional devices; and the National University of Singapore, led by Professor Lain-Jong Li, contributed materials, structural analysis, and simulation—forming a collaboration spanning materials, devices, metrology, and theory. Validated across multiple material systems, the platform establishes a versatile new standard for direct semiconductor inspection and underscores Taiwan's deepening capacity to lead the frontier of advanced chip research on the global stage.