Towards the evaluation of defects in MoS₂ using cryogenic photoluminescence spectroscopy

Abstract

Towards the evaluation of defects in MoS 2 using cryogenic photoluminescence spectroscopyWe reveal the power of cryogenic photoluminescence (PL) for exploring defects in transition metal dichalcogenides (TMDs) via characteristic relaxation mechanisms of the excitons involved. We demonstrate that the transfer process has enormous impact on amount, localization and type of defects within a single fl ake giving rise to signifi cant variation of electronic and optical properties of the TMD monolayers.Our study thus provides a new insight into the defect-driven phenomena in TMDs, with prospect for research of TMD-based heterostructures and superlattices.Characterization of the type and density of defects in two-dimensional (2D) transition metal dichalcogenides (TMDs) is important as the nature of these defects strongly influences the electronic and optical properties of the material, especially its photoluminescence (PL). Defect characterization is not as straightforward as it is for graphene films, where the D and D' Raman scattering modes easily indicate the density and type of defects in the graphene layer. Thus, in addition to the Raman scattering analysis, other spectroscopic techniques are necessary to perform detailed characterization of atomically thin TMD layers. We demonstrate that PL spectroscopy performed at liquid helium temperatures reveals the key fingerprints of defects in TMDs and hence provides valuable information about their origin and concentration.In our study, we address defects in chemical vapor deposition (CVD)-grown MoS 2 monolayers. A significant difference is observed between the as-grown monolayers compared with the CVD-grown monolayers transferred onto a Si/SiO 2 substrate, which contain extra defects due to the transfer process. We demonstrate that the temperature-dependent Raman and PL micro-spectroscopy techniques enable disentangling the contributions and locations of various defect types in TMD systems. † Electronic supplementary information (ESI) available: Additional details on the Raman and PL spectroscopies, decomposition of the Raman and PL spectra, and maps of the Raman and PL spectral parameters at different temperatures for the as-grown and transferred CVD MoS 2 . See

Transfer of large-scale two-dimensional semiconductors: challenges and developments

“…Characterization of interlayer coupling [86,87]. Photoluminescence spectroscopy Can determine: the quality of transferred TMD films [20,85,[106][107][108], layer number [65,109] tensile strain [110][111][112][113][114][115], charge-doping [75,116], defects [106][107][108] and interlayer coupling [85,87].…”

“…These peaks are often difficult to detect at room temperature, since they show a sharp decrease in the intensity as the temperature increases, as shown in figure 17(e). Thus, the stronger temperature sensitivity of PL over Raman confers an advantage of PL over that of Raman spectroscopy [107].…”

The improved photocatalytic activity of highly expanded MoS2 under visible light emitting diodes

“…Meanwhile, the A-trions peak was attributed to the transition resulting from charge impurities in MoS 2 layer [48]. Technically, non-radiative recombination originating from defect will cause the A and B emission intensities to vary [49,50]. To identify the defect density, the B/A intensity ratio was recorded in Table 1.…”

Applications of Raman spectroscopy in two-dimensional materials

“…9). 124 The temperature-dependent Raman spectroscopy was applied for testing performance of the sensors consist of few-layers SnSe 2 sheets. In the range of 80-593 K, the result showed the negative temperature coe±cient (NTC) and softening of Raman modes in SnSe 2 with temperature increasing.…”