Probing near-field heating effects on monolayer MoS2 photoluminescence via tip-enhanced Raman spectroscopy

Abstract

The photoluminescence (PL) intensity of monolayer MoS2 is limited by weak optical absorption due to its atomic scale thickness. To enhance PL intensity, field enhancement techniques, such as surface plasmon resonance (SPR) of metal nanoparticles, are often employed. However, SPR-induced light confinement at the nanoscale also leads to significant localized heating. In this study, we investigated the impact of near-field heating due to SPR using tip-enhanced Raman spectroscopy (TERS) and tip-enhanced photoluminescence studies. Our results reveal nearly an order-of-magnitude difference in the enhancement factors (EFs) for Raman and PL signals of monolayer MoS2, with a local temperature increase of approximately 147 °C under the TERS tip at a laser power of 10.57 mW. The reduced PL EF compared with Raman EF is attributed to additional near-field heating from SPR. We further observed that local temperature fluctuations critically affect the EFs and found that a high thermal conductivity substrate can effectively mitigate the near-field thermal effects associated with SPR.