Generation of quantum dots via nanoindentation in MoS2: via nanoindentation in MoS2

Abstract

We predict the confinement of excitons in quantum dots generated by strain via the atomic force microscope (AFM) in atomically thin molybdenum disulfide (MoS2). MoS2 is a transition metal dichalcogenide (TMDC) and a bidimensional material which is now being studied due to its potential applications for transistors, detectors, sensors and single-photon emitters. We used an AFM probe to indent a monolayerflake of MoS2 over a poly-methyl methacrylate (PMMA) and thus generatean energy funnel of nanometric scale in which the excitons can be confined. The PMMA substrate has elastic-plastic properties that allow the indentations to have the suitable size to generate quantum dots.We make a review of the electronic, mechanical, vibrational and optical features o MoS2 in order to describe the exciton and how it is affected by the presence of a strain field. We make use of the deformation potential theory, and combine it to the k p perturbation theory to describe the exciton energy and wavefunctions as a funcion of the biaxial strain. We also model the nanoindentation via the method of finite elements and find that the most feasible conditions for achieving exciton confinement at 10 K are 15 nm - size and 2% - 3% average strained indentations. We review the experimental aspects of the AFM technique such as the contact and non-contact mode, the properties of the cantilever and the tip in order to estimate the force applied on the material at each nanoindentation. We also measure the mechanical response of PMMA to the deformation via AFM and obtain the stress-strain curve, showing that the substrate behaves plastically at the same regime in which MoS2 is elastic, which is convenient for performing nanoindentations without damaging the TMDC. Additionally, we perform Raman spectroscopy and photoluminescence spectroscopy measurements to characterize the emission of