Author: Dr. Elena Blundo, Semiconductor Nanostructures and Quantum Systems (SNQS) group - Walter Schottky Institut, Technische Universität München 

When: Wednesday, February, 26 - 11AM

Where: Sala de Seminarios, 182 (ICMM-CSIC)

Abstract: van der Waals (vdW) two-dimensional (2D) materials can be stacked with unprecedented flexibility to create heterostructures (HSs), offering extra degrees of freedom such as arbitrariness in the choice of the materials, the twist angle between the constituent materials, and the possibility to mechanically deform the HS. Here, we explore new avenues for vdW heterostructuring by focusing on two exemplary material systems.

  • Moiré-confinement in type-II HSs

When stacking 2D materials at an arbitrary twist angle, a so-called moiré pattern form. The latter results in a moiré potential and in the consequent trapping of interlayer excitons (where electron and hole lie in the two different constituent materials of the HS) in the moiré potential minima.

Here, we investigate the trapping dynamics of moiré-confined interlayer excitons.

By focusing on MoSe2/WSe2 HSs with nearly 0° twist angle, we show evidence of (i) exciton trapping in different potential minima of the moiré potential at cryogenic temperatures, (ii) exciton de-trapping from the moiré potential for temperatures above 100 K, leading to the observation of free interlayer excitons.

  • Strain-engineered type-I HSs.

The achievement of high-performance optoelectronic devices based on vdW HSs is hindered by the necessity to find materials with specific band alignments, momentum-space matching conduction band minima (CBM) and valence band maxima (VBM), and efficient charge transfer between different layers. Fine tuning mechanisms to design ideal HSs are missing.

Here, we propose to exploit the remarkable mechanical flexibility and strength of 2D materials to engineer the electronic properties of 2D HSs. Specifically, we selectively strain only one of the constituent materials of vdW HSs formed by MS2 (M = Mo or W) monolayers (MLs) and InSe thin flakes. We show how strain can be used to engineer the electronic properties of the HS, activating electron and hole tunnelling from the MS2 ML to InSe. The peculiar electronic configuration achieved through strain-engineering enables an efficient coupling between the two materials without any requirements on the twist angle, resulting in a giant light emission enhancement of InSe by about two orders of magnitude.