electromagnetic enhancement (EM) and chemical enhancement (CM). The EM involves the local electromagnetic field enhancement that is typically attributed to the localized surface plasmonic resonance (LSPR) of free charge carriers at the surface of the metal nanostructures induced by the incident light. The LSPR wavelength is determined primarily by the free charge carrier concentration of the metal with a minor effect of the dimension and shape of the metal nanostructures. Molecules positioned [2] close to the LSPR nanostructures experience an enhanced evanescent electromagnetic field as compared to the incident excitation. This EM enhancement directly depends on the morphology of the metal surface, the wavelength of the incident light, and the dielectric constant of the surrounding medium of the metal. The EM enhancement factor can reach over 10 8 to enable ultrasensitive SERS detection down to the single-molecule level. [4][5][6] The CM is induced by the charge transfer between the SERS substrate and molecule with an enhancement factor typically on the order of 10 1 to 10 3 . [7][8][9] The CM effect is dictated by the interface electronic structures between the analyte and substrate and can be optimized by selecting a substrate with favorable band alignment with the highestoccupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) at the interface where the analyte (or probe molecule) bond to the substrate. Thus, tuning of the substrate electronic structure is important to an enhanced CM effect. [10] This has prompted intensive research exploring graphene-based SERS substrates considering the unique 2D atomically flat surface with delocalized π bonds, chemical inertness, biological compatibility, superior electronic and photonic properties, and the intrinsic Fermi energy at ≈4.5 eV that is compatible, as well as tunable, for CM enhancement with a large number of probe molecules. [7,8,11,12] Therefore, graphene is an excellent SERS substrate primarily due to the CM effect with the adsorbed molecules and the enhancement factor is quantitatively affected by the alignment of the probe molecule electronic structure with the Fermi level of graphene. [3,8] The EM and CM enhancement factors may be combined by adding metal nanostructures on graphene. [7,13] Since the Two-dimensional transition metal dichalcogenides (TMDs)/graphene van der Waals (vdW) heterostructures integrate the superior light-solid interaction in TMDs and charge mobility in graphene, and therefore are promising for surface-enhanced Raman spectroscopy (SERS). Herein, a novel TMD (MoS 2 and WS 2 ) nanodome/graphene vdW heterostructure SERS substrate, on which an extraordinary SERS sensitivity is achieved, is reported. Using fluorescent Rhodamine 6G (R6G) as probe molecules, the SERS sensitivity is in the range of 10 −11 to 10 −12 m on the TMD nanodomes/ graphene vdW heterostructure substrates using 532 nm Raman excitation, which is comparable to the best sensitivity reported so far using plasmonic metal nanostructures/graphene ...

Localized surface plasmon resonance (LSPR) is shown to be effective in trapping light for enhanced light absorption and hence performance in photonic and optoelectronic devices. Implementation of LSPR in all‐inorganic perovskite nanocrystals (PNCs) is particularly important considering their unique advantages in optoelectronics. Motivated by this, the first success in colloidal synthesis of AuCu/CsPbCl3 core/shell PNCs and observation of enhanced light absorption by the perovskite CsPbCl3 shell of thickness in the range of 2–4 nm, enabled by the LSPR AuCu core of an average diameter of 7.1 nm, is reported. This enhanced light absorption leads to a remarkably enhanced photoresponse in PNCs/graphene nanohybrid photodetectors using the AuCu/CsPbCl3 core/shell PNCs, by more than 30 times as compared to the counterparts with CsPbCl3 PNCs only (8–12 nm in dimension). This result illustrates the feasibility in implementation of LSPR light trapping directly in core/shell PNCs for high‐performance optoelectronics.

A novel substrate consisting of a 2D MoS2/graphene van der Waals (vdW) heterostructure decorated with Au nanoparticles (AuNPs) was developed for surface-enhanced Raman spectroscopy (SERS). A transfer-free chemical vapor deposition process was employed for layer-by-layer fabrication of graphene, followed with MoS2 directly on wafers of SiO2/Si without any metal catalyst. AuNPs were deposited on the MoS2/graphene via in situ electron-beam evaporation of Au at an elevated temperature in the range of 300–350 °C under high vacuum. Rhodamine 6G (R6G) was used as an SERS probe molecule with a SERS sensitivity of 5 × 10–8 M using a nonresonance 633 nm laser, which is an order of magnitude higher than that reported on the AuNPs/graphene substrate using the same excitation. A higher SERS sensitivity of 5 × 10–10 M was obtained using resonance 532 nm laser excitation. The observed SERS sensitivity enhancement can be attributed to the combination of the electromagnetic mechanism of the plasmonic AuNPs and the chemical mechanism of the AuNPs/MoS2/graphene vdW heterostructure via enhanced interface dipole–dipole interaction as compared to graphene or MoS2 only as suggested by a density functional theory calculation. Therefore, this AuNPs/MoS2/graphene vdW heterostructure is advantageous to practical applications in optoelectronics and biosensing.

Two-dimensional material van der Waals (vdW) heterostructures provide an excellent platform for design of novel optoelectronics. In this work, transition-metal dichalcogenide WS 2 nanodiscs (WS 2 -NDs) of lateral dimension of 200−400 nm and layer number of 4−7 were synthesized on graphene using a layer-by-layer, transfer-free chemical vapor deposition. On this WS 2 -NDs/graphene vdW heterostructures, localized surface plasmonic resonance (LSPR) was achieved, resulting in remarkably enhanced light absorption as compared to the counterpart devices with a continuous WS 2 layer (WS 2 -CL/graphene). Remarkably, the photoresponsivity of 6.4 A/W on the WS 2 -NDs/graphene photodetectors is seven times higher than that (0.91 A/W) of the WS 2 -CL/graphene vdW heterostructures at an incident 550 nm light intensity of 10 μW/cm 2 . Furthermore, the WS 2 -NDs/graphene photodetectors exhibit higher sensitivity to lower lights. Under 550 nm light illumination of 3 μW/cm 2 , which is beyond the sensitivity limit of the WS 2 -CL/graphene photodetectors, high photoresponsivity of 8.05 A/W and detectivity of 2.8 × 10 10 Jones are achieved at V sd = 5 V. This result demonstrates that the LSPR WS 2 -NDs/graphene vdW heterostructure is promising for scalable high-performance optoelectronics applications.

Plasmonic metal nanostructures provide a promising strategy for light trapping and therefore can dramatically enhance photocurrent in optoelectronics only if the trapped light can be coupled effectively from plasmons to excitons, whereas the reverse transfer of energy, charge, and heat from excitons to plasmons can be suppressed. Motivated by this, this work develops a scheme to implement a metafilm with Ag nanoparticles (NPs) embedded in 10 nm thick silica (Ag NPs–silica metafilm) to the active device channel of a hybrid perovskite film/graphene photodetector. Remarkably, an enhancement factor of 7.45 in photoresponsivity, the highest so far among all the reports adopting plasmonic metal NPs in perovskite photodetectors, has been achieved on the photodetectors with the Ag NPs–silica metafilms. Considering that the synthesis of the Ag NPs–silica metafilms can be readily scaled up to coat both rigid and flexible substrates, this result provides a low-cost metaplatform for a variety of high-performance optoelectronic device applications.