Simulation-guided nanofabrication of high-quality practical tungsten probes

Micro/nanoscale tungsten probes are widely utilized in the fields of surface analysis, biological engineering, etc. amongst several others. This work performs comprehensive dynamic simulations on the influences of electric field distribution, surface tension and the bubbling situation on electrochemical etching behaviors, and then the tip dimension. Results show that the etching rate is reliant on the electric field distribution determined by the cathode dimension. The necking position lies in the meniscus rather than at the bottom of the meniscus. A bubble-free condition is mandatory to stabilize the distribution of OH- and WO4 2- ions for a smooth tungsten probe surface. Such simulation-guidance enables the nanofabrication of probes with a high aspect ratio (10 : 1), ultra-sharp tip apex (40 nm) and ultra-smooth surface. These probes have been successfully developed for high-performance application with Scanning Tunneling Microscopy (STM). The acquired decent atomic resolution images of epitaxial bilayer graphene robustly verify the feasibility of the practical level application of these nanoscale probes. Therefore, these nanoscale probes would be of great benefit to the development of advanced analytical science and nano-to-atomic scale experimental science and technology.G. M. gratefully acknowledges funding from National Natural Science Foundation of China (51977169, 51607138) and the Fundamental Research Funds for the Central University (xzy012019030). Z. Y. gratefully acknowledges the support from the ANU Futures Scheme (Q4601024) and the Australian Research Council (DP190100295, LE190100014). Y. P. gratefully acknowledges the support from the National Natural Science Foundation of China (11704303) and the National Key R&D Program of China (2017YFA0206202). The authors also acknowledge funding supported by State Key Laboratory of Electrical Insulation and Power Equipment (EIPE19203)