3D Hybrid Plasmonic Nanostructures with Dense Hot Spots Using Monolayer MoS₂ as Sub‐Nanometer Spacer

Abstract

some problems for the use of graphene. First, it has been demonstrated that the intensity of the EF generally increase as the gap decreases from 10 nm to 6.2 Å but fall off dramatically when the gap further decrease from 6.2 Å for the occurrence of quantum mechanical effects based on the results of the simulation and experiments. [16] The thickness of monolayer graphene is just 3.4 Å, which is so thin that the quantum mechanical electron tunneling emerge in a NP/G/NP or NP/G/ metal film structure. For such nanostructures, the electron tunneling can reduce the accumulation of opposite charges on the both sides of gap and further the EF in the "hot spots" would decrease. Second, the graphene film would tear and suspend inevitably in the transferring process and cannot be covered tightly on the top of the nanostructure with many sharp irregular shapes. [17] To realize the better plasmonic couplings, a kind of new spacer with superior optical property and stability should be introduced. Molybdenum disulfide (MoS 2 ), a semiconductor crystal, has a hexagonal crystal structure with the Mo atom in a trigonal biprism coordination sandwiched between two S atom layers. The MoS 2 films have drawn a lot of attention for applications in energy conversion, photocatalysis, and biochemical sensing for its low cost, good chemical performance, and high stability. [18][19][20][21] Consequently, many researches have reported MoS 2 combined with plasmonic structures and showed excellent photoelectrical properties recently. [22][23][24] In this work, we proposed a 3D hybrid structure using mono layer MoS 2 as spacer between adjacent metal NP. The direct growth of MoS 2 films on AuNP was first realized and the monolayer MoS 2 /AuNP was further obtained after the simple ultrasonic treatment. The AuNP and AgNP were used separately as the third metal nanostructure through the metal films sputtering and annealing process on the surface of the MoS 2 /AuNP. Then, the AuNP/MoS 2 /AuNP (AuMAu) and AgNP/MoS 2 /AuNP (AgMAu) hybrid assemblies were all fabricated and investigated, respectively. Although the hybrid structure seems to have some structural similarities with some works using graphene as spacer, there are several differences. First, the thickness of monolayer MoS 2 is around 6.5 Å close to the optimum gap size (6.2 Å), which is supposed to obtain the considerable enhancement of the EF. The monolayer MoS 2 can act as an insulating sub-nanometer spacer between two metal NP layers for its high vertical resistance and gap thickness to effectively prevent the emergence of the quantum Here, 3D hybrid plasmonic nanostructures using monolayer MoS 2 as subnanometer spacer with high density hot spots are fabricated. For the 3D hybrid assemblies, the hot spots exist not only on the 0.65 nm thick MoS 2 gap regions between large and small nanoparticles (NP) but also between small and small NP. The high-density hot spots induce prominently enhanced optical absorption, huge surface enhanced Raman scattering effect, excellent reproducibility, and ultr...

A spontaneously formed plasmonic-MoTe2 hybrid platform for ultrasensitive Raman enhancement

“…This ideal limit of detection (LoD) is four orders of magnitude improved in comparison with the individual 1T′ MoTe2 substrates, 11 and far surpasses the previously reported results on metal nanostructures hybridized with graphene, hBN, MoS2 and other 2D materials, whose fabrication processes are much more complicated, costly and time-consuming. 16,17,37,38 Detailed comparison between the present work and other plasmonic-2D material based SERS substrates can be found in Table S1.…”

FDTD Analysis of Hotspot-Enabling Hybrid Nanohole-Nanoparticle Structures for SERS Detection

“…A spacing of 1 nm or less may relate, in praxis, to the use of small biomolecules such as cysteamine [ 29 ] and DNA-assisted assemblies [ 30 ] to generate sub-nanometer gaps between metallic structures. Other studies have demonstrated the deposition of monolayers such as graphene [ 44 , 45 ] and MoS 2 [ 46 ] as sub-nanometer spacers between NP-NP structures. In real-world applications, such as the sensing of drugs [ 47 ], pollutants [ 48 ], and cancer diagnosis [ 49 ], having an e-field enhancement over large matrix volumes is highly desirable as it increases the probability of detection [ 6 ].…”

New Trends in Nanoarchitectured SERS Substrates: Nanospaces, 2D Materials, and Organic Heterostructures

“…MoS 2 / graphene heterostructure, serving as nanospacer, could avoid the quantum mechanical electron tunneling current, forming high-density hot spots. [103,104] These substrates could provide electron transfer between MoS 2 and metal NPs accompanied by thickness-controlled plasmonic coupling between two noble metal surfaces (Figure 13d). [103] However, the application of sandwich-like substrate has not yet been tested on real analyte sensing.…”

“…[103,104] These substrates could provide electron transfer between MoS 2 and metal NPs accompanied by thickness-controlled plasmonic coupling between two noble metal surfaces (Figure 13d). [103] However, the application of sandwich-like substrate has not yet been tested on real analyte sensing.…”