Biography: Prof. Huan HU is a tenured associate professor at ZJU-UIUC institute. He received B.S and M.S degrees from Tsinghua University and Ph.D. in University of Illinois at Urbana-Champaign (UIUC) in Electrical and Computer Engineering. He did his postdoc training in IBM T. J. Watson Research Center. He focuses on advanced nanofabrication and measurement and highly engages in interdisciplinary research. He has published more than 76 peer-reviewed papers on 45 different journals covering electronics, mechanics, biomedicine, chemistry, and materials. He has filed 28 US patents (18 granted) and 10 CN patents (4 granted). He invented a novel nanofabrication technology of producing robust nano-spherical probes promising for accurate nanoscale interface and mechanical measurement in 2020 and received very positive feedback in both industry and academia. Based on this technology, he founded a startup company that is currently supplying nano-spherical probes to researchers in tribology, biomedicine, and 2-D materials. He also serves as an associate editor in Frontiers in Sensors, an ad-hoc member in IEEE Electron Device Society, a council member of MEMS & NEMS Society of China.

Improving van der Waals Heterostructure via Nano-spherical Atomic Force Microscopic Probe Scanning

Van der Waals (vdW) heterostructure integration is a promising technology route for next-generation electronic and optoelectronic devices in post Moore era. The vdW forces enables integration of a wide range of materials including bulk materials and low-dimensional materials such as 2-D materials, leading to a much larger freedom of material design and device innovation. However, the preparation of vdW heterostructures especially the vertical stacking heterostructures is far from ideal in which disorders such as strains, interface bubbles, surface roughness, absorbates, charged impurities, vacancy, etc. occur. Although existing methods such as annealing, plasma treatment, chemical bath could improve in certain extent, they still suffer from limited improvement, incapability of removing contaminations, and introduction of chemical contaminations.

Here, we report a unique method of applying an atomic force microscopic (AFM) probe with a super smooth nano-spherical tip to contact scan the vdW heterostructures to improve the properties. This is an advancement over previous sharp AFM probe in both the improvement efficiency and reduced mechanical damage to the vdW heterostructures. We demonstrated more than 5 times of photoluminescence signals increasing over a treated MoS₂/SiO₂ heterostructures. In addition, we observed reduced thickness from 3 nm to 1.4 nm over a double-layer MoS2 sheet. Finally, we observed improved interlayer excitons over a WS2/MoS2/hBN heterostructure by contact scanning the sample with increasing forces from 50 nN to 200 nN. This method has minimal damage to heterostructures due to super smooth surface roughness (~ 0.2 nm) of the spherical tip. This method holds great promise for vdW heterostructures-based electronic and optoelectronic devices due to its compatibility with the fabrication process as well as its on-site scanning feedback capability.