Near-field Enhancement Effect Research Articles

Near-field enhancement by plasmonic antennas for photocatalytic Suzuki-Miyaura cross-coupling reactions

It is well documented that placing a plasmonic antenna close to catalytically active nanoparticles can enhance their catalytic activity in chemical reactions via the near-field enhancement effect. Less known is whether and how the near-field enhances the reactivity of the reactant substrates involved in these reactions. Herein, we prepared an “antenna-reactor” catalyst with Au nanoparticles absorbing light as an optical antenna and the adjacent Pd nanoparticles acting as a chemical reactor to study the near-field enhancement effect in Suzuki–Miyaura cross-coupling reaction involving various substrates. The results showed that the activity of Pd nanoparticles were significantly enhanced in the presence of Au antennas. Excessively increasing the density of Au antennas, however, suppressed the reaction due to the interaction between neighboring electromagnetic hot spots. Moreover, the near-field affected different substrates in different extents, enhancing more to reactions that involve substrates with higher electron cloud density at the reactive center. The overall effect of the near-field to the catalytic reactions was proved to be an integrated result of the effect of Au nanoparticle density and reactive center electron cloud density. This study provides enriched understanding for the near-field enhancement effect in photocatalytic reactions with various substrates, and deepened insights for new “antenna-reactor” photocatalyst design.

Double-layer metasurface for enhanced photon up-conversion

We present a double-layer dielectric metasurface obtained by stacking a silicon nanodisk array and a silicon photonic crystal slab with equal periodicity on top of each other. We focus on the investigation of electric near-field enhancement effects occurring at resonant excitation of the metasurface and study its optical properties numerically and experimentally. We find that the major difference in multi-layer metasurfaces when compared to conventional single-layer structures appears to be in Rayleigh–Wood anomalies: they are split into multiple different modes, which are themselves spectrally broadened. As a proof of concept, we cover a double-layer metasurface with a lanthanide-doped up-conversion particle layer and study its interaction with a 1550 nm photoexcitation. We observe a 2.7-fold enhanced up-conversion photoluminescence by using the stacked metasurface instead of a planar substrate, although only around 1% of the up-conversion material is exposed to enhanced near fields. Two mechanisms are identified explaining this behavior: First, enhanced near fields when exciting the metasurface resonantly, and second, light trapping by total internal reflection in the particle layer when the metasurface redirects light into high angle diffraction orders. These results pave the way for low-threshold and, in particular, broadband photon up-conversion in future solar energy and biosensing applications.

Ultra-extraordinary optical transmission induced by cascade coupling of surface plasmon polaritons in composite graphene-dielectric stack.

Surface plasmon polaritons have been extensively studied owing to the promising characteristics of near fields. In this paper, the cascade coupling of graphene surface plasmon polaritons (GSPPs) originating from cascading excitation and multiple coupling within a composite graphene-dielectric stack is presented. GSPPs confined to graphene layers are distributed in the entire stack as waveguide modes. Owing to the near-field enhancement effect and large lifetime of the GSPPs, the terahertz wave-graphene interaction is significantly enhanced, which induces an ultra-extraordinary optical transmission (UEOT) together with the reported negative dynamic conductivity of graphene. Furthermore, owing to cascade coupling, the UEOT exhibits considerable transmission enhancement, up to three orders of magnitude, and frequency and angle selections. Based on the key characteristics of cascade coupling, the mode density and coupling intensity of GSPPs, the dependences of the number of graphene layers in the stack, the thickness of dielectric buffers, and the effective Fermi levels of the graphene on the UEOT are also analyzed. The proposed mechanism can pave the way for using layered plasmonic materials in electric devices, such as amplifiers, sensors, detectors, and modulators.

Dual defects and build-in electric field mediated direct Z-scheme W18O49/g-C3N4−x heterojunction for photocatalytic NO removal and organic pollutant degradation

In this work, dual defects mediated W18O49/g-C3N4−x heterojunction was prepared by in-situ hydrothermal method. The conversion from Ⅱ-type to Z-scheme heterojunction was achieved due to the formation of build-in electric field from g-C3N4−x to W18O49. Tests results indicated that the LSPR hot electrons of W18O49 could directly drive oxygen reduction reaction to generate O2− species and the partial electrons of g-C3N4−x were captured by O defect states of W18O49 to stabilize its free charge density, resulting in the continuous generation of high-energy hot electrons. The photo-generated carriers had the stronger redox ability compared with g-C3N4−x and W18O49 due to the Z-scheme charge transfer paths. Combined with the promoted exciton dissociation induced by N vacancies, the enhanced light absorption and accelerated carriers’ separation induced by near-field enhancement effect in visible-NIR range of oxygen vacancies, W18O49/g-C3N4−x heterojunction exhibited enhanced photocatalytic performance for NO removal and full-solar-spectrum-driven pollutants degradation.

Further enhancement of the near-field on Au nanogap dimers using quasi-dark plasmon modes

Metallic nanogap dimers are extremely useful for enhancing surface-enhanced Raman scattering and various nonlinear optical effects employing near-field enhancement effects induced by the localized surface plasmon resonance. However, the metallic nanogap dimers exhibit an intense light scattering due to the strong dipole-dipole interaction between two metallic nanostructures and, therefore, are not necessarily a structural design that exhibits the highest near-field enhancement due to the radiation loss. Here, we propose further enhancement of the near-field on metallic nanogap dimers using quasi-dark plasmon modes. By coupling with gold (Au) nanorods having the same plasmon resonant wavelength, but completely different sizes, a quasi-dark plasmon mode, which reduces the radiation loss slightly, is induced, resulting in the elongation of the plasmon dephasing time. As a result, the signal of surface-enhanced Raman scattering of crystal violet molecules adsorbed on the Au nanogap dimer is enhanced up to about three times as compared to that measured using the Au nanogap dimer without the Au nanorods. Scattering spectrum measurements as well as electromagnetic simulations were performed to clarify the mechanism for further enhancement of the near-field. The proposed coupled plasmonic system is expected to be advantageous, especially in enhancing nonlinear optical effects using plasmonic enhancement effects.

Solar-driven plasmonic heterostructure Ti/TiO2-x with gradient doping for sustainable plasmon-enhanced catalysis.

Plasmon-enhanced harvesting of photons has contributed to the photochemical conversion and storage of solar energy. However, high dependence on noble metals and weak coupling in heterostructures constrain the progress towards sustainable plasmonic enhancement. Here earth-abundant Ti is studied to achieve the plasmonic enhancement of catalytic activity in a solar-driven heterostructure Ti/TiO2-x. The heterostructure was fabricated by engineering an intense coupling of a surface-etched Ti metal and a gradient-based TiO2-x dielectric via diffusion doping. Ti/TiO2-x exhibits a highly resonant light absorption band associated with surface plasmon resonances that exhibit strong near-field enhancement (NFE) and hot electron injection effects. In a photoelectrochemical system, intense interaction of the resonant plasmons with a vicinal TiO2-x dielectric accelerates the transfer of solar energy to charge carriers for plasmon-enhanced water splitting reactions. Moreover, the plasmonic Ti/TiO2-x structure presents sustained enhanced redox activities over 100 h. The intense coupling by gradient doping offers an effective approach to enable the plasmon resonances of Ti excited by visible light. The Ti-based plasmonic heterostructure potentially opens an alternative avenue towards sustainable plasmon-enhanced catalysis.

Chiroptical study of the bimetal-cysteine hybrid composite: interaction between cysteine and Au/Ag alloyed nanotubes.

The coupling between noble metal nanostructures and chiral molecules gives rise to strong chiroptical responses in the range from the ultraviolet (UV) to visible spectrum. In this work, cysteine-modified Au/Ag alloyed nanotubes (ANTs) have been prepared by coupling cysteine with Au/Ag ANTs. The chiroptical responses strongly depend on the chirality of cysteine and show clear mirrored behaviours. In contrast to Ag- or Au-cysteine chiral hybrid nanorods, the cysteine-modified Au/Ag ANTs exhibit higher chiroptical responses due to a stronger local electromagnetic field. The induced CD signals emerge in the interband absorption region of Au/Ag ANTs rather than in the local surface plasmon bands, which can be attributed to both the extended helical network conformation on the surface of Au/Ag ANTs and the near-field enhancement effect of plasmonic nanotubes. This confirms that Coulomb interaction induces coupling between cysteine and Au/Ag ANTs, which allows cysteine molecules to form an extended helical network on the surface of Au/Ag ANTs. Furthermore, the cysteine-modified Au/Ag ANTs also show excellent chiral recognition for amino acids in catalytic electrochemical reactions due to the presence of chiral active sites and the steric effect of large groups.

Control of plasmon dephasing time using stacked nanogap gold structures for strong near-field enhancement

The construction of metallic nanostructures with strong near-field enhancement is becoming increasingly significant for the practical use of plasmonic devices, such as plasmonic sensors and light-energy conversion systems. Importantly, the near-field enhancement effect depends on the plasmon dephasing time. Here, we propose a method for controlling plasmon dephasing time by utilizing plasmonic coupling for stronger near-field enhancement. Ordered arrays of stacked nanogap gold (Au) structures composed of a metal/insulator/metal nanostructure were fabricated by electron beam lithography and dry etching processes on a niobium-doped titanium dioxide substrate. The dark plasmon mode was excited by the near-field coupling between the upper and lower Au nanostructures separated by an alumina layer with a thickness of 15nm. A strong near-field enhancement effect was induced by the localization of the electromagnetic field between the upper and lower Au nanostructures and the longer plasmon dephasing time based on the excitation of the dark plasmon mode. It is noteworthy that the dephasing time of the dark plasmon mode measured by time-resolved photoemission electron microscopy was extended 3-fold compared with that of the plasmon mode of the Au nanoblock, which can be controlled by the structural design of the stacked nanogap Au structures.

Size-Dependent Plasmonic Mode Evolution and SERS Performance of β-Sn Nanoparticles

Well-crystallized β-Sn nanoparticles with different diameters have been prepared by a wet chemical method at different reaction temperatures. Both optical characterizations and finite element simulations confirmed that higher-order resonance modes will appear when the size of nanoparticles gets bigger and the plasmon resonance absorption peaks resulting from all resonance modes will keep red-shifting with the increase in the size of nanoparticles. In addition, surface-enhanced Raman scattering measurements and corresponding calculations indicate that β-Sn nanoparticles could reveal a near-field enhancement effect and therefore could be an alternative efficient plasmonic material for the Si-based optoelectronic and/or photovoltaic devices.

Nanophotonic-Enhanced Two-Photon-Excited Photoluminescence of Perovskite Quantum Dots

All-inorganic CsPbBr3 perovskite colloidal quantum dots have recently emerged as promising material for a variety of optoelectronic applications, among others for multi-photon-pumped lasing. Nevertheless, high irradiance levels are generally required for such multi-photon processes. One strategy to enhance the multi-photon absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photon-excited photoluminescence of CsPbBr3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than one order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significant decreasing the required irradiance levels for multi-photon processes being of advantage in applications like low-threshold lasing, biomedical imaging, lighting and solar energy.

CO2 Reduction by Plasmonic Au Nanoparticle-Decorated TiO2 Photocatalyst with an Ultrathin Al2O3 Interlayer

A well-designed nanocomposite structure, Au/Al2O3/TiO2, that is Au-decorated TiO2 with an atomic-layer-deposited Al2O3 interlayer between Au and TiO2, was synthesized to study the role of plasmonic Au nanoparticles on photocatalytic CO2 reduction as well as the influence of the interlayer. Localized surface plasmon resonance induced hot electron injection and near-field enhancement, together with the enhanced charge separation caused by the Au NPs were found responsible for the promoted photocatalytic CO2 reduction on Au-modified TiO2. The Al2O3 interlayer inhibited electron transfer and dampened the near-field enhancement effect; however, it also served as passivation layer to suppress electron–hole recombination on the TiO2 surface. To further identify the significance of each of the mechanisms, photocatalysts with tailored thickness of Al2O3 interlayer and varied size of Au NPs were carefully synthesized, characterized, and tested for CO2 photoreduction with water. A finite difference time domain simul...

Enhanced water splitting under modal strong coupling conditions.

Strong coupling between plasmons and optical modes, such as waveguide or resonator modes, gives rise to a splitting in the plasmon absorption band. As a result, two new hybrid modes are formed that exhibit near-field enhancement effects. These hybrid modes have been exploited to improve light absorption in a number of systems. Here we show that this modal strong coupling between a Fabry-Pérot nanocavity mode and a localized surface plasmon resonance (LSPR) facilitates water splitting reactions. We use a gold nanoparticle (Au-NP)/TiO2/Au-film structure as a photoanode. This structure exhibits modal strong coupling between the Fabry-Pérot nanocavity modes of the TiO2 thin film/Au film and LSPR of the Au NPs. Electronic excitation of the Au NPs is promoted by the optical hybrid modes across a broad range of wavelengths, followed by a hot electron transfer to TiO2. A key feature of our structure is that the Au NPs are partially inlaid in the TiO2 layer, which results in an enhancement of the coupling strength and water-oxidation efficiency. We observe an 11-fold increase in the incident photon-to-current conversion efficiency with respect to a photoanode structure with no Au film. Also, the internal quantum efficiency is enhanced 1.5 times under a strong coupling over that under uncoupled conditions.

In Situ Shape Change of Au Nanoparticles on TiO2 by CdS Photodeposition: Its Near-Field Enhancement Effect on Photoinduced Electron Injection from CdS to TiO2.

Hemisphere-like gold nanoparticles (NPs) were loaded on TiO2 (Au/TiO2) by the deposition–precipitation method. Subsequent photodeposition of CdS on the Au surface of Au/TiO2 at 50 °C yields Au(core)–CdS(shell) hybrid quantum dots with a heteroepitaxial (HEPI) junction on TiO2 (Au@#CdS/TiO2), whereas nonHEPI Au@CdS/TiO2 was formed by CdS photodeposition at 25 °C. In the HEPI system, the shape of the Au core changes to an angular shape, whereas it remains in a hemisphere-like shape in the nonHEPI system. The hot photodeposition technique was applied to the Au NP-loaded mesoporous TiO2 nanocrystalline film (Au/mp-TiO2). Using Au@CdS/mp-TiO2 and Au@#CdS/mp-TiO2 as the photoanodes, two-electrode quantum dot-sensitized photoelectrochemical cells were fabricated for hydrogen (H2) generation from water, and the performances of the cells were evaluated under illumination of simulated sunlight. In the photocurrent and the rate of H2 evolution, the Au@#CdS/mp-TiO2 photoanode cell surpasses the CdS/mp-TiO2 and Au@CdS/mp-TiO2 ones. Three-dimensional finite-difference time-domain calculations for the model systems indicated that the angular shape Au core generates an intense electric field at the corners and edges, extending the electric field distribution over the Au core–CdS shell interface. The striking shape effect on the cell performances can originate from the promotion of the CdS excitation and charge separation due to the near-field enhancement by the deformed Au core.

(Invited) Plasmon-Induced Photocurrent Generation for Exploring the Near-Field Ofstrongly Coupled Plasmonic Systems

[Introduction] Metallic nanostructures which show localized surface plasmon resonances (LSPRs) have received considerable attention as a light harvesting optical antenna for light-energy conversion systems such as solar cells as well as artificial photosynthesis [1,2]. To construct efficient light harvesting optical antennae, an optimization of structural design is one of the most important research topics in plasmon-induced light energy conversions. Coupled plasmonic systems such as nanogap heptamer, dolmen, metal-insulator-metal nanostructures, and so on is promising as a photoelectrode design because of their strong near-field enhancement and wide wavelength responsibility. In this study, a coupled plasmonic system based on a waveguide-LSPR coupling system is employed to investigate whether the photocurrent response extends over a wide wavelength range and is promoted by near-field enhancement in the plasmon-induced photocurrent generation using gold nanostructured titanium dioxide (TiO2) photoelectrodes. Near-field spectrum and photocurrent action spectrum are compared to elucidate the effect of near-field enhancement on the photocurrent generation. [Experimental] TiO2 photoelectrodes supporting periodic gold nanogratings (AuNGs) with different pitch sizes were fabricated by a deposition of TiO2 on a glass substrate with a thickness of 250 nm using an atomic layer deposition (ALD) reactor, and subsequent electron beam lithography and lift-off processes. A conventional photoelectrochemical measurement was performed. The AuNGs/TiO2 photoelectrode, a platinum wire and a saturated calomel electrode (SCE) were employed as working, counter and reference electrodes, respectively. An aqueous Ar-gas-bubbled KClO4 (0.1 mol/dm3) solution was used as a supporting electrolyte solution. A plasmon-induced water oxidation as a half reaction of water splitting was explored [3]. [Results and Discussion] Figure 1(a) shows a scanning microscope (SEM) image of AuNGs/TiO2 photoelectrode with a pitch size of 300 nm. Extinction spectra of the AuNGs/TiO2 photoelectrode with a different pitch size are shown in Fig. 1(b). There is only one peak corresponding to the LSPR mode of periodic Au-NGs with 200 nm and 225 nm pitch sizes. Starting with a pitch size of 250 nm, three peaks can be observed, and the peaks show a spectral shift with increasing the pitch size. The two outer peaks can be assigned as coupled modes (P+ and P-) deriving from the symmetric waveguide mode Ew and LSPR mode Ep as shown in the illustration of the waveguide-LSPR coupling system (Fig. 1(c)). The center peak can be considered as a coupling mode between the asymmetric waveguide mode and the waveguide-LSPR coupling system. Internal quantum efficiency (IQE) spectra and simulated near-field spectra of the AuNGs/TiO2 photoelectrodes with 300 nm and 350 nm pitch sizes are shown in Fig. 2. The near-field intensity in the spectra was calculated by monitoring at the interface between the AuNGs and the TiO2 film by the electromagnetic simulations using a finite-difference time-domain (FDTD) method. It was clearly elucidated that IQE spectrum has successfully reproduced the near-field spectrum under the coupling conditions. This indicates that the photocurrent response extended over a wide wavelength range utilizing the coupled plasmonic systems and near-field enhancement effects promoted the plasmon-induced water oxidation because IQE values increased responding to the near-field spectra [4]. References Ueno, K., Oshikiri, T., Sun, Q., Shi, X., Misawa, H. Chem. Rev., DOI: 10.1021/acs.chemrev.7b00235.Ueno, K., Oshikiri, T., H. Misawa, ChemPhysChem, 2016, 17, 199−215.Nishijima, Y., Ueno, K., Yokota, Y., Murakoshi, K., Misawa, H. J. Phys. Chem. Lett. 2010, 1, 2031−2036.Guo, J., Ueno, K., Shi, X., Oshikiri, T., Misawa, H. et al., J. Phys. Chem. C 2017, 121, 21627−21633. Figure 1

Solid-State Plasmonic Solar Cells.

Metallic nanoparticles such as silver and gold show localized surface plasmon resonances (LSPRs), which are associated with near-field enhancement effects in the vicinity of nanoparticles. Therefore, strong light-matter interaction is induced by the near-field enhancement effects of LSPRs. Because the resonant wavelength of LSPRs can be easily controlled by the size and shape of the metallic nanoparticles in the visible and near-infrared wavelength range, LSPRs have received considerable attention as optical antennae for light energy conversion systems such as solar cells. LSPRs decay very quickly as a result of light scattering and excitation of electron-hole pairs in the metal itself. However, in addition to the near-field enhancement effect, this light scattering and electron-hole pair excitation, which are known to cause loss of LSPRs, can be utilized as a solar cell enhancement mechanism. Here, we focus on plasmonic solid-state solar cells. The mechanisms of the light scattering by LSPRs, near-field enhancement, and plasmon-induced charge separation based on electron-hole pair excitations can be clarified. We review the related studies from the viewpoint of these mechanisms rather than material science.

Plasmonic Near-Field Effect on Visible and Near-Infrared Emissions from Self-Assembled Gold Nanoparticle Films

In this work, we have performed a systematic investigation of the plasmon near-field effect on photoluminescence (PL) behavior of the annealed self-assembled gold nanostructured films. For this purpose, PL spectra of the films in different morphologies are compared. This allows us to identify the role of plasmon near-field enhancement and coupling effects in visible and near-infrared emissions as modulating the energy transfer mechanism between excited electrons and emitted photons. Our results indicate that the films’ near-infrared emission is generated by allowed intraband transition related to the breakdown of the symmetry and momentum selection rules due to the strongly confined near-field distribution. In addition, it is found that the efficiency of the near-infrared emission is directly proportional to the strength of the coupled near-field effect. The observed visible emission of the films is well explained by the interband transition of electrons into the conduction band and subsequent radiation by particle plasmons. The influence of the coupled plasmon resonance of the samples on the characteristics of the visible PL emission is discussed. The observed emission properties of the gold nanostructured films can make them very attractive material for many bio-imaging and surface-enhanced Raman scattering (SERS) applications.

Observation of the microwave near-field enhancement effect in suspensions comprising single-walled carbon nanotubes

The strong polarization of isolated finite-length single-walled carbon nanotubes (CNTs) or bundles of CNTs has been predicted to lead to a strong near field enhancement effect that provokes additional electromagnetic energy dissipation in a conductive host (Shuba et al 2010 J. Appl. Phys. 108 114302). Here, we theoretically and experimentally show that this effect can be observed in the microwave frequency range via measurements of the spectra of the effective permittivity of CNT-based suspensions. Microwave effective permittivity of the suspensions comprising both annealed and doped CNTs has been measured in the temperature range from 300 to 330 K. The experimental data gives evidence of the unique properties of CNTs—to enhance electromagnetic fields in a volume as much as 100 times larger than the volume occupied by the nanotube itself.

Near-field wave enhancement and ‘quasi-surface’ longitudinal waves in a segmented thick-walled hollow cylindrical waveguide

Thick-walled structures with varying geometry are challenging for guided wave inspection due to the multimodal behaviour and the complex scattering of the wave modes. This article investigates the influence of the geometrical transitions on the propagation of the elastic waves in thick-walled cylindrical structures and proposes a structural evaluation technique based on the identified wave phenomena. In particular, a near-field wave enhancement effect caused by the crack-wave interaction and by the thickness changes in a waveguide is explored. Additionally, formation and propagation of the so-called longitudinal ‘quasi-surface’ waves are investigated, as they are found to be a main contributor to the observed wave enhancement phenomenon. The proposed new damage identification technique utilising the enhancement effect is validated numerically and experimentally on a beam and a hollow cylindrical structure.

Plasmonic enhancement of third-order nonlinear optical susceptibilities in self-doped Cu_2-xS nanoparticles

Heavily doped Cu2-xS nanoparticles with hole densities of ~1021 cm−3 were chemically synthesized and their localized surface plasmon resonance (LSPR) in the near-infrared region was investigated by nonlinear optical spectroscopy. We found that their third-order susceptibility χ(3) exhibits resonant enhancement around LSPR, similar to that in plasmonic noble metal nanoparticles. It was found that the maximum χ(3) value of Cu2-xS nanoparticles was comparable to that of Au nanoparticles with the same dimensions and concentrations. Our results indicate that Cu2-xS nanoparticles can be used as nonlinear optical materials operating in the near-infrared region, even though their near-field enhancement effect is slightly weaker than that of Au nanoparticles.

Improving All-Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect.

All-inorganic perovskites have high carrier mobility, long carrier diffusion length, excellent visible light absorption, and well overlapping with localized surface plasmon resonance (LSPR) of noble metal nanocrystals (NCs). The high-performance photodetectors can be constructed by means of the intrinsic outstanding photoelectric properties, especially plasma coupling. Here, for the first time, inorganic perovskite photodetectors are demonstrated with synergetic effect of preferred-orientation film and plasmonic with both high performance and solution process virtues, evidenced by 238% plasmonic enhancement factor and 106 on/off ratio. The CsPbBr3 and Au NC inks are assembled into high-quality films by centrifugal-casting and spin-coating, respectively, which lead to the low cost and solution-processed photodetectors. The remarkable near-field enhancement effect induced by the coupling between Au LSPR and CsPbBr3 photogenerated carriers is revealed by finite-difference time-domain simulations. The photodetector exhibits a light on/off ratio of more than 106 under 532 nm laser illumination of 4.65 mW cm-2 . The photocurrent increases from 0.67 to 2.77 μA with centrifugal-casting. Moreover, the photocurrent rises from 245.6 to 831.1 μA with Au NCs plasma enhancement, leading to an enhancement factor of 238%, which is the most optimal report among the LSPR-enhanced photodetectors, to the best of our knowledge. The results of this study suggest that all-inorganic perovskites are promising semiconductors for high-performance solution-processed photodetectors, which can be further enhanced by Au plasmonic effect, and hence have huge potentials in optical communication, safety monitoring, and biological sensing.