Dissertação de Mestrado #565: José Rivero

We predict the confinement of excitons in quantum dots generated by strain via the atomic force microscope (AFM) in atomically thin molybdenum disulfide (MoS2). We used an AFM probe to indent a monolayer of MoS2 over a poly-methyl methacrylate (PMMA) and thus generate an 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 review the electronic, mechanical and optical features of MoS2 and determine how the exciton is affected by a strain field. We use the deformation potential theory and combine with a k.p perturbation theory to describe the exciton energy and wavefunctions as a function of the biaxial strain. Using the method of finite elements we find that the most feasible conditions for achieving exciton confinement at 10 K are 15 nm – size and 2%-3% average strained indentations. We measure the mechanical response of PMMA to deformation via AFM and obtain the stress-strain curve, showing that the substrate behaves plastically at the same regime in which MoS2 is elastic. We perform Raman and photoluminescence spectroscopy of the strained MoS2 at room and low temperatures. We introduce the hyperspectrum which allows us to map the indented sample with sub-micron resolution and observe the local phenomena associated to the nanoindentation. We observed both a redshift of the exciton emission due to the local strain generated in the monolayer, and a slant due to the shift of the populations of charged and neutral excitons.