Active Light Control of the MoS2 Monolayer Exciton Binding Energy
Supporting Information
Active Light Control of the MoS2 Monolayer Exciton Binding Energy Ziwei Li1†, Yingdong Xiao1†, Yongji Gong3, Zongpeng Wang1, Yimin Kang1, Shuai Zu1, Pulickel M. Ajayan3, Peter Nordlander2, and Zheyu Fang1* 1
School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China 2
Department of Electrical and Computer Engineering, and Laboratory for Nanophotonics, Rice University, 6100 Main Street, Houston, Texas 77005, United States. 3
Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, United States
1. Schematic of the experimental measurement setup.
Figure S1. Schematic view of optical setup for the reflectance and photoluminescence spectra measurement.
2. Spectral properties of MoS2-Au hybrid film. 1
Figure S2. (a) PL spectra and (b) Raman spectra for the MoS2 monolayer with (red) and without (gray) Au NPs. The inset in (b) shows the Raman splitting of the E12g mode.
With 532 nm laser illumination, plasmonic hot electrons generated from the decay of Au NPs plasmon resonance were injected into the MoS2. The results is a redshift of the MoS2 PL spectrum, as shown in Fig. S2a, where the PL spectra with and without Au-NPs are compared. Figure S2b shows the Raman spectrum of the MoS2 structure using the 532 nm laser with and without Au NPs. For pristine MoS2, the in-plane (E12g) and out-of-plane (A1g) phonon modes are located at 392.5 cm-1 and 412.2 cm-1, and shift to 389.7 cm-1 and 410.6 cm-1, respectively after Au NPs are deposited. Hot electrons doping shifts the in-plane mode by ~2.8 cm-1. The localized MoS2 phase transition also can be induced by the plasmonic doping effect, as reported in our previous work,1 however this phase transition only can be happened and observed when the measurement was taken in the ultra-high vacuum and low temperature chamber. This is confirmed by the Raman spectrum in Fig. S2(b), where there are no obvious 1T phase characteristic peaks was recorded at the room temperature and atmospheric environment. The inset shows the peak splitting of E12g mode, which is the evidence of coupling between the Au NPs and MoS2 systems.
2
3. Scattering cross section and localized electric field distribution of Au NPs.
Figure S3. (a) Scattering cross section of Au NPs deposited on a MoS2 monolayer. (b) The local electric field distribution of Au NPs with dipole plasmon resonance mode.
The scattering cross section of 5 nm diameter Au NPs is shown in Figure S3a, which is calculated by FDTD solutions. The scattering peaks represent dipole (540 nm) resonance mode of Au NPs. Only for resonant excitation of the dipolar plasmon mode do we expect significant hot electrons doping and significant spectral shifts. Figure S3b shows the plot of local electric field distribution of Au NPs with dipole plasmon resonance.
Hot electron generation mechanism in metals is photoexcitation and plasmon decay.2 Because of the extremely large cross section of plasmonic nanoparticles, plasmon-decay-induced hot electron generation could be extremely efficient. If the ligands are surrounded the Au particles, it still has the possibility for the interface barrier tunneling.
4. The influence of optical absorption of MoS2 monolayers on substrate.
3
Figure S4. (a) Schematic view of MoS2-Au hybrid film on 30 nm SiO2/ 30 nm Au /Si substrate under light excitation. (b) Mapping of the optical absorption of MoS2 on substrate with various SiO2 film thickness.
Figure S4a shows a schematic view of the monolayer MoS2 coated with Au nanoparticles under the light excitation. The light-materials interaction of can be dramatically enhanced by several channels as indicated with the arrows. Plasmonic resonance induced LSP, which generates dramatically enhanced localized electric field improves the coupling of light and 2D materials. With the large scattering cross section of Au nanoparticles and large absorption cross section of monolayer MoS2, the near-field scattering enhancement enhances the absorption of monolayer MoS2. The Au film provides a reflection mirror resulting in multiple reflection and absorption.
The optical absorption of MoS2 monolayers for different SiO2 film thickness was analysed by FDTD as shown in Figure S3b. All the substrates with 30-100 nm and 270-300 nm SiO2 film show the dramatic enhancement of both absorption features. The substrate with 30 nm SiO2 and 30 nm Au was chosen to enhance the optical absorption of MoS2 monolayers. 5. PL mapping of MoS2 monolayers. 4
Figure S5. PL mapping of peak A (a) and peak B (b) of MoS2 monolayers with 532 nm excitation. The mapping spectra shows the uniformity of the MoS2 monolayers.
6. PL spectra with increasing powers (Without Au nanoparticles).
Figure S6. PL spectra of MoS2 monolayers (without Au NPs) when the incident 532 nm laser power was increased from 0.5 mW to 5 mW. The PL spectra keep the same peak postions with the increasing powers at room temperature.
7. The calculation of system Fermi level change. 5
The Fermi level rises with plasmonic hot electrons doping can be calculated as:
∆E =
π h2 2 m*
∆n
For the calculated doping density is 2.6×1011 cm-2, the estimated Fermi level rises 0.56 meV. Compared with exciton binding energy changing ~15 meV, the contribution of Fermi level rising in the conduction band can be ignored.
REFERENCES 1. Kang, Y.; Najmaei, S.; Liu, Z.; Bao, Y.; Wang, Y.; Zhu, X.; Halas, N. J.; Nordlander, P.; Ajayan, P. M.; Lou, J. Plasmonic Hot Electron Induced Structural Phase Transition in a MoS2 Monolayer. Adv. Mater. 2014, 26, 6467—6471. 2. Zheng, B. Y.; Zhao, H.; Manjavacas, A.; McClain, M.; Nordlander, P.; Halas, N. J. Distinguishing between Plasmon-Induced and Photoexcited Carriers in a Device Geometry. Nat. Comm. 2015, 6, 7797/1—7797/7.
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Active Light Control of the MoS2 Monolayer Exciton Binding Energy Ziwei Li1†, Yingdong Xiao1†, Yongji Gong3, Zongpeng Wang1, Yimin Kang1, Shuai Zu1, Pulickel M. Ajayan3, Peter Nordlander2, and Zheyu Fang1* 1
School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China 2
Department of Electrical and Computer Engineering, and Laboratory for Nanophotonics, Rice University, 6100 Main Street, Houston, Texas 77005, United States. 3
Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, United States
1. Schematic of the experimental measurement setup.
Figure S1. Schematic view of optical setup for the reflectance and photoluminescence spectra measurement.
2. Spectral properties of MoS2-Au hybrid film. 1
Figure S2. (a) PL spectra and (b) Raman spectra for the MoS2 monolayer with (red) and without (gray) Au NPs. The inset in (b) shows the Raman splitting of the E12g mode.
With 532 nm laser illumination, plasmonic hot electrons generated from the decay of Au NPs plasmon resonance were injected into the MoS2. The results is a redshift of the MoS2 PL spectrum, as shown in Fig. S2a, where the PL spectra with and without Au-NPs are compared. Figure S2b shows the Raman spectrum of the MoS2 structure using the 532 nm laser with and without Au NPs. For pristine MoS2, the in-plane (E12g) and out-of-plane (A1g) phonon modes are located at 392.5 cm-1 and 412.2 cm-1, and shift to 389.7 cm-1 and 410.6 cm-1, respectively after Au NPs are deposited. Hot electrons doping shifts the in-plane mode by ~2.8 cm-1. The localized MoS2 phase transition also can be induced by the plasmonic doping effect, as reported in our previous work,1 however this phase transition only can be happened and observed when the measurement was taken in the ultra-high vacuum and low temperature chamber. This is confirmed by the Raman spectrum in Fig. S2(b), where there are no obvious 1T phase characteristic peaks was recorded at the room temperature and atmospheric environment. The inset shows the peak splitting of E12g mode, which is the evidence of coupling between the Au NPs and MoS2 systems.
2
3. Scattering cross section and localized electric field distribution of Au NPs.
Figure S3. (a) Scattering cross section of Au NPs deposited on a MoS2 monolayer. (b) The local electric field distribution of Au NPs with dipole plasmon resonance mode.
The scattering cross section of 5 nm diameter Au NPs is shown in Figure S3a, which is calculated by FDTD solutions. The scattering peaks represent dipole (540 nm) resonance mode of Au NPs. Only for resonant excitation of the dipolar plasmon mode do we expect significant hot electrons doping and significant spectral shifts. Figure S3b shows the plot of local electric field distribution of Au NPs with dipole plasmon resonance.
Hot electron generation mechanism in metals is photoexcitation and plasmon decay.2 Because of the extremely large cross section of plasmonic nanoparticles, plasmon-decay-induced hot electron generation could be extremely efficient. If the ligands are surrounded the Au particles, it still has the possibility for the interface barrier tunneling.
4. The influence of optical absorption of MoS2 monolayers on substrate.
3
Figure S4. (a) Schematic view of MoS2-Au hybrid film on 30 nm SiO2/ 30 nm Au /Si substrate under light excitation. (b) Mapping of the optical absorption of MoS2 on substrate with various SiO2 film thickness.
Figure S4a shows a schematic view of the monolayer MoS2 coated with Au nanoparticles under the light excitation. The light-materials interaction of can be dramatically enhanced by several channels as indicated with the arrows. Plasmonic resonance induced LSP, which generates dramatically enhanced localized electric field improves the coupling of light and 2D materials. With the large scattering cross section of Au nanoparticles and large absorption cross section of monolayer MoS2, the near-field scattering enhancement enhances the absorption of monolayer MoS2. The Au film provides a reflection mirror resulting in multiple reflection and absorption.
The optical absorption of MoS2 monolayers for different SiO2 film thickness was analysed by FDTD as shown in Figure S3b. All the substrates with 30-100 nm and 270-300 nm SiO2 film show the dramatic enhancement of both absorption features. The substrate with 30 nm SiO2 and 30 nm Au was chosen to enhance the optical absorption of MoS2 monolayers. 5. PL mapping of MoS2 monolayers. 4
Figure S5. PL mapping of peak A (a) and peak B (b) of MoS2 monolayers with 532 nm excitation. The mapping spectra shows the uniformity of the MoS2 monolayers.
6. PL spectra with increasing powers (Without Au nanoparticles).
Figure S6. PL spectra of MoS2 monolayers (without Au NPs) when the incident 532 nm laser power was increased from 0.5 mW to 5 mW. The PL spectra keep the same peak postions with the increasing powers at room temperature.
7. The calculation of system Fermi level change. 5
The Fermi level rises with plasmonic hot electrons doping can be calculated as:
∆E =
π h2 2 m*
∆n
For the calculated doping density is 2.6×1011 cm-2, the estimated Fermi level rises 0.56 meV. Compared with exciton binding energy changing ~15 meV, the contribution of Fermi level rising in the conduction band can be ignored.
REFERENCES 1. Kang, Y.; Najmaei, S.; Liu, Z.; Bao, Y.; Wang, Y.; Zhu, X.; Halas, N. J.; Nordlander, P.; Ajayan, P. M.; Lou, J. Plasmonic Hot Electron Induced Structural Phase Transition in a MoS2 Monolayer. Adv. Mater. 2014, 26, 6467—6471. 2. Zheng, B. Y.; Zhao, H.; Manjavacas, A.; McClain, M.; Nordlander, P.; Halas, N. J. Distinguishing between Plasmon-Induced and Photoexcited Carriers in a Device Geometry. Nat. Comm. 2015, 6, 7797/1—7797/7.
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