Stanislav Tsoi1,Kathleen McCreary1,Marc Christophersen1,Hsun-Jen Chuang1,Igor Vurgaftman1
U.S. Naval Research Laboratory1
Stanislav Tsoi1,Kathleen McCreary1,Marc Christophersen1,Hsun-Jen Chuang1,Igor Vurgaftman1
U.S. Naval Research Laboratory1
Recent experimental studies have demonstrated that coupling monolayer transition metal dichalcogenides to plasmonic cavities can significantly enhance their photoluminescence (PL). The present work aims to determine experimentally the magnitude of the plasmonic enhancement in WSe<sub>2</sub>. Periodic arrays of gold nanodisks are fabricated using electron beam lithography on Si substrates. The localized plasmon resonance of the nanodisks is characterized using reflectivity measurements. Monolayer flakes of WSe<sub>2</sub> with a lateral size over 30 µm, grown by chemical vapor deposition on separate Si substrates, are transferred on top of the gold nanodisk arrays. Stretching of the flexible monolayer over individual nanodisks creates localized nanoscale regions of WSe<sub>2</sub> under tensile strain, separated by fully relaxed WSe<sub>2</sub> regions between the nanodisks. Accordingly, room-temperature PL recorded from the WSe<sub>2</sub> contains an emission band at 1.65 eV, characteristic of exciton recombination in the fully relaxed monolayer, as well as additional low-energy bands assigned to the strained nano-regions. The strained PL is strongly enhanced when the excitation wavelength approaches the plasmon resonance, consistent with the spatial co-location of the strained nano-regions and the localized plasmonic field. Comparison of the strained PL intensity under the excitation on and off the plasmonic resonance allows us to assess the magnitude of the plasmonic enhancement. The results obtained are in quantitative agreement with numerical simulations.