Abstract
MoS2 micro-pyramids have demonstrated interesting properties in the fields of photonics and non-linear optics. In this work, we show the excitonic absorption and cathodoluminescence (CL) emission of MoS2 micro-pyramids grown by chemical vapor deposition (CVD) on SiO2 substrates. The excitonic absorption was obtained at room and cryogenic temperatures by taking advantage of the cathodoluminescence emission of the SiO2 substrate. We detected the CL emission related to defect intra-gap states, localized at the pyramid edges and with an enhanced intensity at the pyramid basal vertices. The photoluminescence and absorption analysis provided the Stokes shift of both the A and B excitons in the MoS2 pyramids. This analysis provides new insights into the optical functionality of MoS2 pyramids. This method can be applied to other 3D structures within the 2D materials family.
Highlights
In the last decade, the rise of monolayer (ML) transition metal dichalcogenides (TMDs) has changed the paradigm for the coupling of two-dimensional materials to a well-established platform without the constraints imposed by epitaxies such as crystal-lattice match or chemistry compatibility
We show the excitonic absorption and cathodoluminescence (CL) emission in MoS2 micro-pyramids grown by chemical vapor deposition (CVD) on SiO2 substrates
The excitonic absorption was obtained at room and cryogenic temperatures by taking advantage of the cathodoluminescence emission of the SiO2 substrate
Summary
The rise of monolayer (ML) transition metal dichalcogenides (TMDs) has changed the paradigm for the coupling of two-dimensional materials to a well-established platform without the constraints imposed by epitaxies such as crystal-lattice match or chemistry compatibility. The CL spectra of the pyramid and the substrate, from which the CL absorption-emission spectrum is obtained, are reported in Fig. S5 of the ESI.† The positive peaks are attributed to the absorption of the MoS2 A and B excitons, respectively, while the negative band is attributed to the light emission of the defect-related state excited by the electron beam.[36] The 1.70 eV CL emission band is broad (about 0.15 eV), implying a possible convolution of the two different emissions related to defect states, ruling out the possible attribution of such emissions to trionic states. With the same integration procedure as shown, it is possible to obtain the CL absorption-emission spectra of different areas of the MoS2 pyramid (Fig. 6)
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