Dr. Yuebing Zheng and his team have developed a self-limiting optoelectronic thinning (SOET) technique to prepare atomic monolayers of transition metal dichalcogenides (TMDC) in a commercially scalable manner. Dr. Zheng is the Temple Foundation Endowed Teaching Fellowship in Engineering #2 and an associate professor at UT Austin, with primary interests in advanced material science/engineering, biomechanical/biomedicine engineering, clean energy technologies, nano/micro-scale engineering, robotics/AI, and thermal fluid systems/transport. Dr. Zheng has published numerous technical and journal articles and has received awards from DOD and NIH. The focus of his work has broad applicability in the health, life sciences, national security, energy, and manufacturing sectors.
The developed SOET technology for high-efficiency thinning of multi-layer TMDC flakes into atomic monolayers is not limited by the original thickness of the TMDC flakes. Thinning is achieved by optically pumping electrons only over the indirect band gap of the TMDC flakes, using a laser with photon energies less than the direct band gap but greater than the bilayer indirect band gap of the TMDC. The developed SOET technique will automatically terminate once the TMDC flakes are thinned into a single layer.
The technique was demonstrated on MoS2 flakes and was capable of being conducted with only minimal control over the operating conditions. By properly choosing the wavelength of the laser beam, electrons can be selectively excited between the indirect bandgap of the multi-layer MoS2 sample, resulting in thinning of the TMDC through electrochemical degradation to an atomic monolayer of MoS2. Once a monolayer of MoS2 is realized, the laser beam cannot further excite the electrons over the wider, direct bandgap, thereby stopping the electrochemical reaction.
Available top-down thinning technologies (e.g., plasma, ion beam, thermal, laser, electrochemical) used to create TMDC monolayer materials from thick flakes require careful control of the operating conditions, and result in monolayer flakes of inconsistent quality. Flakes with different thicknesses are also thinned at the same rate under the same operating conditions, limiting production throughput.
Atomic monolayer flakes of TMDC (e.g., MoS2, WS2, MoSe2, WSe2) show significant potential for use in photodetection, valleytronics, sensing, biomedical imaging, and drug delivery applications due to the materials’ superior electrical and optical properties as compared to alternatives. The developed UT SOET technology to prepare monolayer TMDC has not been previously reported and shows significant potential to create high-quality TMDC at high production rates for use in these applications.