Probing nano-heterogeneity and aging effects in lateral 2D heterostructures using tip-enhanced photoluminescence

Interest in two-dimensional (2D) transition metal dichalcogenide materials has recently grown due to their tunable band gap, large exciton binding energy, and flexibility in designing a wide range of optoelectronic devices. However, the presence of adsorbates, strain, and aging-induced heterogeneities can severely influence their excitonic photoluminescence (PL). Therefore, precise nanoscale correlation between the optical and structural heterogeneities is of paramount importance and needs further investigation. In this report, we used tip-enhanced photoluminescence (TEPL) imaging of the nanoscale exciton emission of air-aged monolayer MoSe2-WSe2 multijunction lateral heterostructures with subwavelength spatial resolution of 40 nm. Distinct regions corresponding to monolayer MoSe2 and WSe2 were identified. Near-field excitation was used for the quantitative evaluation of the optical transition width: 40 nm sharp transition (WSe2→MoSe2), and 230 nm smooth interface (MoSe2→WSe2). Nanoscale composition of the alloying properties of the junction was estimated using TEPL. Furthermore, localized optical fluctuations and the role of the aging-induced nanoparticles in the excitonic PL suppression were investigated. The observed linear dependence of the PL suppression as a function of the nanoparticle size indicates the contribution of the chemical aging effects. The correlation between the nanoscale optical and structural characteristics will be useful for controlling and manipulating excitons in the next-generation atomically thin devices.