Angle resolved photoemission spectroscopy (ARPES)

Since the properties of a solid are dictated by its electronic band structure, it is essential to directly investigate the band structure in order to gain empirical understanding of the material properties as well as insight on how to control these properties by changing the band structure. ARPES, with a typical beam spot size of several hundreds of microns to a millimeter, has emerged as a powerful technique for investigating the band structure of macroscopic crystals or large area extended thin films. Until now, however, the use of ARPES to directly probe the energy-momentum information of mesoscopic sized high-quality single-layer exfoliated 2D materials and their heterostructures has been limited due to the relatively large spot size compared with the small sample size. Our group has a strong on-going collaboration with the state-of-the-art MASTERO beam line at Advanced Light Source (ALS), Berkeley to carry out photoemission studies of mesoscopic sized air-sensitive 2D materials and their devices. At MASTERO beamline, we are participating in the commissioning of nano-ARPES, which will have the capability to resolve electronic band structure with spatial resolution reaching 50 nm. With the advent of nano-ARPES, the exploration of exotic physical phenomenon in the vast library of emerging 2D materials, van der Waals heterostructures, and devices is just the beginning!!! In the past, we have made significant contributions to the understanding of correlations between structural and electronic properties in 2D materials and their heterostructures.

Related selected publications:

1) Jyoti Katoch*, Soren Ulstrup*, et. al.  "Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures", Nature Physics 14, 355-359 (2018). 

2) Roland J. Koch, Jyoti Katoch, et. al. "Electronic structure of exfoliated and epitaxial hexagonal boron nitride", Phys. Rev. Materials 2, 074006 (2018).

3) Soren Ulstrup*, Jyoti Katoch* et. al. "Spatially Resolved Electronic Properties of Single- Layer WS2 on Transition Metal Oxides", ACS Nano 10 (11), pp 10058 - 10067 (2016).