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FRANCO MARIO GELARDI

Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization

  • Authors: Panasci S.E.; Koos A.; Schiliro E.; Di Franco S.; Greco G.; Fiorenza P.; Roccaforte F.; Agnello S.; Cannas M.; Gelardi F.M.; Sulyok A.; Nemeth M.; Pecz B.; Giannazzo F.
  • Publication year: 2022
  • Type: Articolo in rivista
  • OA Link: http://hdl.handle.net/10447/533046

Abstract

In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800◦C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2–3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with respect to the substrate were observed for the ~4.2 nm one. Such different configurations indicate the prevalence of different mechanisms (i.e., vapour-solid surface reaction or S diffusion within the film) as a function of the thickness. The uniform thickness distribution of the few-layer and multilayer MoS2 was confirmed by Raman mapping. Furthermore, the correlative plot of the characteristic A1g-E2g Raman modes revealed a compressive strain (ε ≈ −0.78 ± 0.18%) and the coexistence of n-and p-type doped areas in the few-layer MoS2 on SiO2, where the p-type doping is probably due to the presence of residual MoO3 . Nanoscale resolution current mapping by C-AFM showed local inhomogeneities in the conductivity of the few-layer MoS2, which are well correlated to the lateral changes in the strain detected by Raman. Finally, characteristic spectroscopic signatures of the defects/disorder in MoS2 films produced by sulfurization were identified by a comparative analysis of Raman and photoluminescence (PL) spectra with CVD grown MoS2 flakes.