Plasmon-Free Surface-Enhanced Raman Spectroscopy Using Metallic 2D Materials

Abstract

Two dimensional (2D) materials-based plasmon-free surface-enhanced Raman scattering (SERS) is an emerging field in nondestructive analysis. However, impeded by the low density of state (DOS), an inferior detection sensitivity is frequently encountered due to the low enhancement factor of most 2D materials. Metallic transition-metal dichalcogenides (TMDs) could be ideal plasmon-free SERS substrates because of their abundant DOS near the Fermi level. However, the absence of controllable synthesis of metallic 2D TMDs has hindered their study as SERS substrates. Here, we realize controllable synthesis of ultrathin metallic 2D niobium disulfide (NbS 2 ) (<2.5 nm) with large domain size (>160 μm). We have explored the SERS performance of as-obtained NbS 2 , which shows a detection limit down to 10 −14 mol•L −1 . The enhancement mechanism was studied in depth by density functional theory, which suggested a strong correlation between the SERS performance and DOS near the Fermi level. NbS 2 features the most abundant DOS and strongest binding energy with probe molecules as compared with other 2D materials such as graphene, 1T-phase MoS 2 , and 2H-phase MoS 2 . The large DOS increases the intermolecular charge transfer probability and thus induces prominent Raman enhancement. To extend the results to practical applications, the resulting NbS 2 -based plasmon-free SERS substrates were applied for distinguishing different types of red wines.

Defect engineering in semiconductor-based SERS

“…A special type of semiconductors must be mentioned here, namely metallic semiconductors which exhibit LSPR activity. Metallicity in semiconductors refers to their property to transport electrons, which becomes prominent when the charge carrier density and density of states near the Fermi level increases 73 . Metallicity is of interest to SERS as CT-based enhancement as well as plasmonic resonance-based enhancement is directly influenced by the metallicity of the semiconductor.…”

Surface Enhanced Raman Scattering Revealed by Interfacial Charge-Transfer Transitions

“…Hence, new types of metallic TMDs with abundant DOS near the Fermi level are now developed as efficient SERS substrates. Song et al used the CVD method to realize the controllable synthesis of metallic 2D niobium disulfide (NbS 2 ) nanosheets (<2.5 nm) with a large domain size (>160 mm), 46 and obtained superior SERS activities with respect to other 2D materials such as graphene, 1T-phase MoS 2 , and 2H-phase MoS 2 . A low LOD of 10 À14 M and an EF of approximately 10 3 were obtained with an NbS 2 substrate for the detection of an MB analyte, based on the increased intermolecular CT probability.…”

Initiating VB‐Group Laminated NbS2 Electromagnetic Wave Absorber toward Superior Absorption Bandwidth as Large as 6.48 GHz through Phase Engineering Modulation

“…Nevertheless, since the discovery of NbS 2 in the 1970s, [25] the inevitable high temperature and complex processes in the synthesis of NbS 2 have hindered its applications, resulting in the current NbS 2 researches that are mainly focused on theoretical calculations. [19,23,26,27] The currently available preparation methods for NbS 2 nanosheets are mainly based on hightemperature solid-state reactions (such as calcination [28,29] and chemical vapor deposition [30][31][32] ), resulting in the products that are excessively crystalline and require post-processing (such as defect engineering) to exhibit good catalytic and energy storage properties. The high-yield electrochemical exfoliation [33,34] method usually suffers from poor controllability, and is difficult to realize heteroatom doping [6] or compound with other materials [35] due to the top-down process involved.…”