The Origin of Mo₂C Films for Surface-Enhanced Raman Scattering Analysis: Electromagnetic or Chemical Enhancement?

Abstract

The relatively weak Raman enhanced factors of semiconductor-based substrate limit its further application in surface-enhanced Raman scattering (SERS). Here, a kind of two-dimensional (2D) semimetal material, molybdenum carbide (Mo2C) film, is prepared via a chemical vapor deposition (CVD) method, and the origin of SERS is investigated for the first time. The detection limits of the prepared Mo2C films for crystal violet (CV) and rhodamine 6G (R6G) molecules are low at 10–6 M and 10–8 M, respectively. Our detailed theoretical analysis, based on density functional theory and the finite element method, demonstrates that the enhancement of the 2D Mo2C film is indeed CM in nature rather than the EM effects. Besides, the basic doping strategies are proposed to further optimize the SERS sensitivity of Mo2C for Fermi level regulation. We believe this work will provide a helpful guide for developing a highly sensitive semimetal SERS substrate.

Plasmonic Ag/ZnO Nanoscale Villi in Microstructure Fibers for Sensitive and Reusable Surface-Enhanced Raman Scattering Sensing

“…Real-time and label-free detection of molecules in solution is important for applications in the area of medical diagnostics, food safety testing, and environmental monitoring. Surface-enhanced Raman scattering (SERS) − is a phenomenon where the Raman signal of analytes around the nanostructures is amplified by several orders of magnitude owing to the electromagnetic enhancement mechanism (EM) and the chemical enhancement mechanism (CM), − which makes label-free single-molecule fingerprinting possible. − The EM is mainly attributed to the localized surface plasmon resonance (LSPR) in noble-metal nanostructures and is generally believed to contribute dominantly to SERS. , The CM is mainly caused by charge transfer between analyte molecules and SERS-active substrates. , Abundant materials have been proposed to have chemical enhancement, such as semiconductors, transition metal dichalcogenides, graphene, molybdenum carbide, and so on. Plasmon-free SERS materials do not require well-designed hot spots, thus showing good signal uniformity and reproducibility.…”

In Situ Growth of Mo2C Crystals Stimulating Sodium-Ion Storage Properties of MoO2 Particles on N-Doped Carbon Nanobundles

“…The results indicate that the coexistence of MoO 2 and Mo 2 C in the composite is successfully achieved by the two-step calcination, and the introduction of Mo 2 C is beneficial to improving the conductivity and structural stability of the composite. The Raman spectra are displayed in Figure b, and both composites contain obvious characteristic peaks of MoO 2 , especially at 997 and 820 cm –1 . , At MoO 2 @Mo 2 C/C, other characteristic peaks also appear, which can reflect the introduction of the Mo 2 C phase (such as at 196 cm –1 ). , Additionally, the characteristic peaks at 1336.5 and 1606.1 cm –1 correspond to the amorphous and graphitic carbon, respectively, and the ratios ( I D / I G ) are 1.03 (MoO 2 @Mo 2 C/C) and 1.15 (MoO 2 /C), indicating that the carbon components in composites are amorphous. , The TG curves of the samples are displayed in Figure c, from which the mass changes of each component can be obtained. The initial mass decrease of MoO 2 @Mo 2 C/C can belong to the adsorbed water, and the subsequent mass increase may be because the mass of MoO 3 after oxidation of MoO 2 and Mo 2 C in air is greater than that of carbon decomposition.…”

“…31,32 At MoO 2 @Mo 2 C/C, other characteristic peaks also appear, which can reflect the introduction of the Mo 2 C phase (such as at 196 cm −1 ). 33,34 Additionally, the characteristic peaks at 1336.5 and 1606.1 cm −1 correspond to the amorphous and graphitic carbon, respectively, and the ratios (I D /I G ) are 1.03 (MoO 2 @Mo 2 C/C) and 1.15 (MoO 2 / C), indicating that the carbon components in composites are amorphous. 35,36 The TG curves of the samples are displayed in Figure 3c, from which the mass changes of each component can be obtained.…”

Cathodoluminescence Spectroscopy of Complex Dendritic Au Architectures for Application in Plasmon‐Mediated Photocatalysis and as SERS Substrates

“…Within the electromagnetic theory for SERS, the SERS intensity scales with the forth power of the local electric field intensity, thus substrates with high hot‐spots density and strength are desirable, [ 8 ] while chemical enhancement could also affect the SERS performance. [ 9 ] The Raman signal of molecules within the hot‐spots can be routinely amplified by a factor of ≈10 5 –10 6 , [ 10 ] and plasmonic structures can be designed to achieve single molecule detection. [ 11 ] Hot‐spots can also modify intrinsic physical and chemical properties of molecular adsorbates, promoting and enhancing chemical reactions by altering the surface potential energy landscape.…”