Wafer‐Scale 2H‐MoS₂ Monolayer for High Surface‐enhanced Raman Scattering Performance: Charge‐Transfer Coupled with Molecule Resonance

Abstract

in 1997, this technique has been becoming one of the key technologies in chemical analysis, chemosensors, biomedical applications, etc. [1] To reveal the mechanism and improve the enhancement factor (EF), a large number of experimental and theoretical works were carried out. [2] For the substrates with noble metal nanoparticles, the electromagnetic mechanism arising from localized surface plasmons is dominantly responsible for the ultrahigh EF. [3] While the chemical mechanism, which is originated from the charge transfer between the substrate and absorbed molecules, is attributed to the SERS mechanism in the semiconducting substrates. [1c,4] Additionally, the accompanied resonances in the charge transfer, such as molecule resonance and surface plasmon, have also attributed to the enhanced SERS in the molecule-semiconductor system. [2d,5] As semiconductors are abundant, cheap, and stable, and may be easily integrated into modern electronic devices, they have been widely investigated. However, their performance is still poorer than those of noble metals. Therefore, various strategies, such as doping, defect engineering, morphology optimization, hybridization, and phase-transition control, [6] have been explored to improve the charge transfer asThe surface-enhanced Raman scattering (SERS) as a novel and efficient analytic technique to probe molecules has attracted tremendous attention. Semiconducting substrates have been widely investigated for their applications into SERS because of their easy integration with electronic devices. In this work, a wafer-scale semiconducting MoS 2 monolayer (2H-MoS 2 -ML) without additional treatment is used as the SERS substrate, which shows the naturally formed MoS 2 ML has excellent chemical stability, high uniformity, and high sensitivity. It is found that the detection concentration limit can reach 1 × 10 −8 m and the enhancement factor is about 4.5 × 10 6 for the rhodamine 6G (R6G) under a 532 nm excitation laser, which is the highest SERS performance observed on 2H-MoS 2 -ML up to now. The experimental and computational studies reveal that the photo-enhanced charge transfer coupled with molecule resonance contribute to remarkable SERS. In addition to R6G, 2H-MoS 2 -ML shows good SERS signals on the detection of amaranth and crystal violet too. The findings not only provide an insightful understanding of the mechanism for the improved SERS performance of semiconducting transition-metal dichalcogenides (TMDs) MLs, but are helpful for the design of novel SERS substrates. It is expected that the wafer-scale TMDs may find practical applications in SERS.

Pressure-Induced SERS-Enhanced Sensing of 4-Mercaptobenzoic Acid Using Few-Layer WS2 Nanosheets

“…As illustrated in Figure a, the R6G concentration was changed from 10 –6 to 10 –8 mol/L, and we see clearly that the R6G molecules can be detected universally even when the concentration is down to 10 –8 mol/L. The SERS spectra show the characteristic peaks of R6G at 613.6, 775.9, 1186.8, 1365.1, 1510.9, 1575.9, and 1651.8 cm –1 , which are consistent with the previous reports . We see that the SERS intensity decreases as the R6G concentration decreases (Figure b).…”

“…The SERS spectra show the characteristic peaks of R6G at 613.6, 775.9, 1186.8, 1365.1, 1510.9, 1575.9, and 1651.8 cm −1 , which are consistent with the previous reports. 4 We see that the SERS intensity decreases as the R6G concentration decreases (Figure 2b). The concentration limit of detection reaches 10 −8 mol/L, which is lower than 2 orders of magnitude compared to that (10 −6 mol/L) of the CVD growth of few-layer WS 2 .…”

“…Surface-enhanced Raman spectroscopy (SERS) as an ultrasensitive detection and analytical technique has been widely applied in various fields due to the outstanding advantage of unique vibrational fingerprints. − To date, two representative mechanisms for SERS enhancement are widely accepted. The major contributor to SERS enhancement is the electromagnetic mechanism (EM), which originates from the electromagnetic field magnification through the excitation of localized surface plasmon resonances (LSPRs) of noble-metal materials .…”

Chemically Engineered Sulfur Vacancies on Few-Layered Molybdenum Disulfide Nanosheets for Remarkable Surface-Enhanced Raman Scattering Activity

“…The two resonances mentioned above can also induce photoinduced CT resonances of neighboring molecules via vibronic coupling. These two processes are critical components of the Raman amplification mechanism in MoS vacancies. , When the sample is irradiated with a 532 nm laser (2.33 eV), electrons from the HOMO level of the R6G molecules are injected into the neighboring conduction band of the MoS 2 NSs to produce electron–hole pairs . This is the photoinduced CT process.…”

“…41,43 When the sample is irradiated with a 532 nm laser (2.33 eV), electrons from the HOMO level of the R6G molecules are injected into the neighboring conduction band of the MoS 2 NSs to produce electron−hole pairs. 41 This is the photoinduced CT process. The excited electrons were subsequently pumped into the LUMO level by a second photoinduced CT procedure, resulting in a Raman enhancement effect due to the increased polarizability.…”