Probing depth-resolved electronic structure of two-dimensional layered materials and their heterostructures using standing-wave photoemission microscopy*

Atomically thin and ultra-flexible two-dimensional materials and their heterostructures have been extensively studied as alternative materials platforms for logic and memory devices. Here, we demonstrate the capability to extract depth-resolved electronic structural information from single monolayers of transition-metal dichalcogenides and their heterostructures using standing-wave photoemission microscopy [1-2]. Depth resolution in the measurements is achieved by generating an x-ray standing wave within the sample by using a W/C multilayer mirror substrate in the first-order Bragg reflection geometry. The standing wave is translated vertically through the samples consisting of single-layer WS₂ flakes and WSe₂/MoS₂ heterostructures deposited or transferred on top of such substrates. Both core-level and valence-band experimental results are analyzed using x-ray optical optimization code and compared to first-principles theoretical electronic-structure calculations.

[1] F. Kronast et al., Appl. Phys. Lett. 93, 243116 (2008)

[2] A. X. Gray et al., Appl. Phys. Lett. 97, 062503 (2010)