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Lateral heterostructures

Just as in bulk materials, charge carriers can be confined in lateral heterostructures of TMDs when areas of lower bandgap are surrounded by material of a higher bandgap. Such heterostructures could be used to fabricate a variety of photon sources or to confine electrons and excitons.

We explore fabrication of lateral heterostructures using two methods: selective area chemical vapor deposition (CVD) and modulation of the electrostatic environment. In the first method, either lateral overgrowth of exfoliated monolayers1 or selective chalcogene atom replacement is used to passivate the edges of the monolayers. Heterostructures of two different materials are used extensively for bulk materials. The second method is specific to the atomically thin materials. In this method, monolayers are deposited and covered by various dielectric materials, leading to changes in both single particle and optical bandgaps. By changing the dielectric constant, we are able to shift exciton and trion energies by as much as 40 meV.
Samples are investigated using a number of optical spectroscopy techniques, including Raman and photoluminescence mapping, photoexcitation spectroscopy and reflectance mapping. Structural changes in the materials on the atomic scale are studied using advanced transmission electron microscopy.

(a) Optical micrograph of a MoSe2 monolayer (whose borders are marked by a yellow broken line) lying partly on a SiO2 substrate and partly on a h-BN flake (blue broken line). Part of the MoSe2 monolayer on hBN is covered by another h-BN flake (magenta broken line). The scale bar is 20 µm. b) Spatial distribution of exciton emission energy of the TMD-ML. Only regions where the probe laser beam fitted on homogenous parts of the sample were analysed.c) Three representative spectra along the line marked by a red arrow in figure b) showing a gradual transition between hBN cover and vacuum above the MoSe2. d) Change of the ratio of the photoluminencence intensity from the hBN-MoSe2/vacuum and hBN-MoSe2/hBN parts of the heterojunction changes across a distance defined by the laser spot size.

Reference

T. Stoica, M. Stoica, M. Duchamp, A. Tiedemann, S. Mantl, D. Grützmacher, D. Buca and B. E. Kardynał, Vapor transport growth of MoS2 nucleated on SiO2 patterns and graphene flakes, Nano Research 9 (11), 3504-3514 (2016).


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