UC Berkeley

By virtue of their atomically thin structure, layered van der Waals materials with two-dimensionality (2D) exhibit a strong tunability of material properties beyond what can be achieved in their bulk counterpart. In this dissertation, I aim to realize and control the novel phenomena that are unique in such 2D layered materials. We achieved the exquisite property control by rationally tailoring the structural design of the devices. Toward this end, nanofabrication techniques are extensively employed to perform precise positioning and layer-by-layer stacking of the individual components to manufacture nanodevices from these van der Waals materials. A suite of advanced characterization techniques encompassing electrical transport, scanning probe microscopy, and spectroscopy (laser-based and synchrotron-based) are then used to study the great degree of properties tunability in the samples.

Firstly, we show the use of dielectric environment as a control knob to tune the bandgap of monolayer MoS2 by realizing a lateral heterojunction with implications in transport phenomena and future electronics. Secondly, we show the structural control of graphene-based 2D materials into moiré lattices and superstructures and demonstrated the use of an ultra-high-resolution implementation of scanning microwave impedance microscopy (i.e., uMIM) to reveal the detailed structure of such moiré systems. Thirdly, we discuss the control of electronic band structure in magic angle twisted bilayer graphene (tBLG) with the emergence of flat band near the Fermi level as probed with angle-resolved photoemission spectroscopy with nanoscale resolution (nanoARPES). Lastly, we provided an overview of future perspective and a highlight of recent results where other material parameters can be used to control the 2D material behavior. The possibility to engineer the material properties provides a fascinating route for on-demand application of the 2D nanomaterials in new multifunctional device concepts in electronics, optoelectronics, and quantum information science.