Probing Excitons, Trions, and Dark Excitons in Monolayer WS₂ Using Resonance Raman Spectroscopy

Abstract

We present temperature-dependent resonance Raman measurements on monolayer WS for the temperature range 4-295 K using excitation photon energies from 1.9 to 2.15 eV in ∼7 meV steps. These are analyzed to determine the resonance profiles of five previously assigned phonon based Raman peaks (A', E', 2ZA, LA, 2LA) and a previously unassigned peak at 485 cm whose possible attributions are discussed. The resonance profiles obtained are fitted to a perturbation theory derived model and it is shown that both excitons and trions are required to explain the profiles. The model is used to separate the contribution of exciton-exciton, trion-trion, and exciton-trion scattering to each of the Raman peaks at 4 K. This separation allows the ratios of the rates of scattering involving the A' and E' phonons for each of the three types of scattering to be determined. The explanation of the multiphonon Raman peaks requires the coupling of bright excitons and trions to large wavevector dark states. The fitting of the resonance Raman profiles for these Raman peaks demonstrates scattering of bright excitons to bright trions via these large wavevector dark states.

A WS2-gold nanoparticle heterostructure-based novel SERS platform for the rapid identification of antibiotic-resistant pathogens

“…The observed strong plasmon band is mainly due to the localized surface plasmonic resonance (LSPR) of the GNPs induced by the incident light. [13][14][15][16][17][18] 2D-WS 2 nanosheets were synthesized using a simple ultrasonication route from WS 2 powder. 16,[20][21][22] Briey, commercial WS 2 bulk powder was pelletised by a grinding miller for about 4 h, as shown in Scheme 1B.…”

“…[4][5][6][7][8][9][10] Due to its high sensitivity, nondestructive character and ngerprint identication capability, SERS is highly promising in biomedical technology. [13][14][15][16][17][18][19][20] In the last two decades we and others have reported that extremely weak Raman signals can be enhanced signicantly using a proper design of the SERS substrate via the electromagnetic mechanism (EM) and chemical mechanism (CM). [16][17][18][19][20][21][22][23][24] Zero dimensional plasmonic nanoparticles such as gold and silver nanoparticles have been used extensively as SERS materials, where Raman intensity can be enhanced by $10 6 via EM & CM.…”

“…[13][14][15][16][17][18][19][20] In the last two decades we and others have reported that extremely weak Raman signals can be enhanced signicantly using a proper design of the SERS substrate via the electromagnetic mechanism (EM) and chemical mechanism (CM). [16][17][18][19][20][21][22][23][24] Zero dimensional plasmonic nanoparticles such as gold and silver nanoparticles have been used extensively as SERS materials, where Raman intensity can be enhanced by $10 6 via EM & CM. [13][14][15][16][17][18][19][20] On the other hand, in the last few years SERS substrates based on two-dimensional (2D) transition-metal dichalcogenides (TMD) have been reported, where Raman intensity can be enhanced by $10 2 via CM as well as due to the resonance with near-and far-eld optical properties.…”

“…[16][17][18][19][20][21][22][23][24] Zero dimensional plasmonic nanoparticles such as gold and silver nanoparticles have been used extensively as SERS materials, where Raman intensity can be enhanced by $10 6 via EM & CM. [13][14][15][16][17][18][19][20] On the other hand, in the last few years SERS substrates based on two-dimensional (2D) transition-metal dichalcogenides (TMD) have been reported, where Raman intensity can be enhanced by $10 2 via CM as well as due to the resonance with near-and far-eld optical properties. 11,16,[20][21][22][23][24] To take the advantages of the EM and CM effect from both types of materials, in the current manuscript we have reported the development of novel heterostructure material-based SERS using 2D WS 2 TMD and 0D plasmonic gold nanoparticles (GNPs).…”

“…[13][14][15][16][17][18][19][20] On the other hand, in the last few years SERS substrates based on two-dimensional (2D) transition-metal dichalcogenides (TMD) have been reported, where Raman intensity can be enhanced by $10 2 via CM as well as due to the resonance with near-and far-eld optical properties. 11,16,[20][21][22][23][24] To take the advantages of the EM and CM effect from both types of materials, in the current manuscript we have reported the development of novel heterostructure material-based SERS using 2D WS 2 TMD and 0D plasmonic gold nanoparticles (GNPs). The reported data show a remarkably high SERS sensitivity of $10 À10 to 10 À11 M from the heterostructure.…”