Intrinsic Mechanical Strain in Chemical Vapor Deposition-Grown MoS₂/MoSe₂ Monolayer Heterostructures: Implications for Nanoelectronic Devices

Abstract

In this work, we have synthesized 2D MoS2/MoSe2 heterostructures by chemical vapor deposition (CVD) in a one-pot, two-step configuration: the second crystal was directly grown on top of the first, without mechanical transfer. Indeed, most vertically stacked HSs go through nanomechanical manipulations resulting in nonhomogeneous residual strain, polymer residues or mechanical fracture. Also, among others, an advantage of such heterostructures is that they can be considered as pristine vertical HS, since they have a clean interface between layers. Moreover, another interest in studying such material is that the bottom and top layers are almost the same. They only differ by the chemical nature of the chalcogen atom, and consequently the size of the metal-chalcogen bond is slightly different. The photoluminescence and vibrational analyses indicate shifts in the band positions when compared to monolayer MoS2 or MoSe2. We propose that this behavior is mainly driven by a mechanical strain that originates from the synthesis, since the HSs tend to counterbalance the lattice mismatch between the top and the bottom crystals. Our findings are corroborated by DFT calculations, where electron and phonon dispersions of strained materials reproduce qualitatively well the experimental data. Also this work permits us to compare the interaction between constituent layers of HS assembled by transfer or by direct growth and their role to tune the physical properties of those nanomaterials for specific applications in nanoelectronics.

Study of Punctual Defects in Monolayer WS2: Evidence of Correlations Between Raman and Photoluminescence Spectroscopy

“…The X 0 PL intensity is quite homogeneous suggesting the absence of segregated α and β defect domains, as observed in hexagonal-shaped WS 2 crystals. , The PL spectrum consists of two excitonic peaks: a neutral-charge exciton ( X 0 ) and a negatively charged trion ( X t ), around 1.96 and 1.93 eV, respectively. These values are slightly lower when compared to mechanically exfoliated layers of WS 2 but are very similar to other works where CVD-grown crystals were studied. , This small red shift is probably induced by either few defects in the structure or residual strain on the SiO 2 substrate, inherent to CVD-grown TMDs. , …”