Photoluminescence enhancement of monolayer MoS₂ using plasmonic gallium nanoparticles

Abstract

2D monolayer molybdenum disulphide (MoS2) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency.

Plasmonic coupling in closed-packed ordered gallium nanoparticles

“…This band corresponds to the in-plane or longitudinal LSPR mode of the Ga NPs and redshifts as the Ga mass is increased. This shift is well stablished in the literature since the NP diameter is expected to be proportional to the evaporated Ga mass; whose calibration could be found elsewhere 31 . The out-of-plane mode is placed in the UV (>6 eV), out of our SE spectral range for this case.…”

“…The analysis has been focused on the imaginary part of the pseudodielectric constant (<ε 2 >) since it regards the extinction response of the whole substrate-NP system, which is a good indicator of the far-field of the LSPRs 55 , as analysed later on in the simulations. The typical SE spectrum of Ga NPs on flat Si consists of two resonant bands ascribed to the two different axes in its hemispherical geometry 18,22,31,39 . The out-of-plane resonant mode due to the vertical and shortest axis of the NPs, typically observed in the UV region and the in-plane resonant mode due to the longest and horizontal axis, typically observed in the VIS-IR region.…”

“…Ga (purity of 99.9999%) is evaporated in a tungsten filament (99.90% purity) at a power of 50 W. The Al template samples as well as Si (100) reference samples were placed 200 mm away from the Ga source. The size of the Ga NPs is controlled by the Ga mass added to the crucible as shown elsewhere 31 . In this work, the Ga mass has been varied from 15 mg to 310 mg that produces NPs with diameter from 20 to 400 nm.…”

“…surface enhanced Raman spectroscopy (SERS) [27][28][29] , surface enhanced fluorescence 30,31 , Li-ion batteries 32 , waveguiding 33,34 , optical switching 35,36 , phase-change memories 37 or the development of biosensors for the detection of different diseases 38,39 .…”

“…With the aim to advance in these applications, several recent works have reported different approaches that have improved the size distributions of Ga NPs using IR light 40,41 , corrugated Cu films 29 , polymer nanostructured templates 42 and even 2D materials 31 . Although in all the cases the NPs were aligned and the size distributions were more homogeneous, NPs of different sizes still coexist.…”