Surface-enhanced Raman spectroscopy (SERS) is pivotal for trace-molecule detection; however, conventional noble-metal substrates face cost and stability limitations. Two-dimensional molybdenum disulfide (MoS2) has emerged as a promising alternative but suffers from inefficient charge transfer. Herein, we developed a vacancy-compensated Se-doping strategy for monolayer MoS2 via controlled Ar/O2 etching and in situ selenization. The resulting 8.0 at% Se-doped substrate achieved an ultralow detection limit of 10-12 M for rhodamine 6G and an enhancement factor of 104, attributed to the enhanced carrier density and interfacial charge transfer. The platform also demonstrates excellent stability, reproducibility, and generality, offering a viable path toward high-performance semiconductor-based SERS applications.

Trapping light and enhancing electromagnetic fields in plasmonic nanostructures are crucial for advanced applications, such as for surface-enhanced Raman scattering, surface-enhanced fluorescence and plasmon-enhanced second-harmonic generation (PESHG) at subwavelength scales. Expanding the spatial distribution of enhanced electromagnetic fields, i.e., hot spots, has become a vital strategy to significantly enhance the performance of advanced nanophotonic applications. In this work, we propose a strategy of hybrid metal-dielectric (MD) nanohole arrays by introducing low-loss silicon nitride (Si3N4) dielectric layers into aluminum (Al) nanohole arrays to realize the strong light-trapping and expand the spatial distribution of hot spots at MD interfaces by changing the diameter of nanohole. The mechanism governing these phenomena is deriving from the occurrence of dielectric-mediated plasmonic coupling, facilitating the translation of local light confinements governed by plasmon-driven resonances to dielectric components and LSPR-excited hot-spots redistribution in plane. Moreover, we introduce both label and label-free optical probes regarding the photoluminescence enhancement of MoS2 and PESHG to verify and quantify the effect of expanded hot-spot distribution in hybrid Al-Si3N4 nanohole arrays on the enhancement of light-matter interaction. This work may provide a theoretical and experimental mechanism for expanding the potential in characterizing and quantifying hot-spot distribution in advanced optical nanodevices.

In this paper, a tunable dual-function terahertz absorber is proposed by integrating the phase-transition property of vanadium dioxide (VO₂) with the Fermi-level tunability of graphene. Here, the dual functionality specifically refers to broadband absorption switching over 3.0–4.25 THz, with the absorptance tunable from nearly 0 to nearly 98%, and narrowband-to-broadband mode conversion over 4.25–5.50 THz. Electromagnetic-field analyses indicate that the broadband absorption is associated with the Fabry–Pérot (FP) cavity resonance between the graphene and VO₂ layers, together with dipolar and higher-order multipolar resonances induced by localized surface plasmon resonance (LSPR) in graphene, whereas the narrowband absorption mainly originates from the LSPR in the graphene layer. Further investigations show that the tunable absorptance can be realized through the electrically tunable properties of graphene and the thermally tunable properties of vanadium dioxide. In addition, in the broadband mode, absorptance above 90% can be maintained for incident angles from 0° to 50°, and polarization insensitivity can be achieved under normal incidence. The proposed absorber provides both broadband switching and broadband–narrowband mode switching, showing potential for multifunctional terahertz dynamic devices.

In this paper, a tunable multi-band graphene-based terahertz absorber is proposed. The proposed absorber is a sandwich structure which is comprised of a gold ground layer, a SiO2 dielectric interlayer, and a periodic patterned graphene as the surface. In the design of graphene patterns, catenary curves are introduced. Simulation results show that four distinct absorption peaks at frequencies of 4.19 THz, 5.78 THz, 7.60 THz, and 9.95 THz and a very low absorption at 8.77 THz for TE mode have been achieved, respectively. The absorption rates corresponding to most peaks exceed 92

MoS2 has recently garnered significant attention as a semiconductor-based surface-enhanced Raman scattering (SERS) substrate. However, SERS enhancement and sensitivity are comparatively lower than those of high-conductivity metals, limiting its practical applications. In this study, we report a facile plasma engineering approach to tune the atomic structure of monolayer MoS2 (ML-MoS2) SERS substrates. We demonstrate that Ar–O2 plasma treatment can induce oxygen incorporation and create physical defects, which alters its electronic properties and enhances the charge transfer efficiency between the MoS2 substrates and the probe molecules, ultimately leading to a significant enhancement in the SERS performance. When using R6G as a probe molecule, the enhancement factor reaches up to 1.14 × 104, with a minimum detection limit as low as 10−10 M. Our results open new avenues for optimizing SERS substrates in ML-MoS2 and other transition metal dichalcogenides films.

Detecting near-infrared (NIR) light with high efficiency is crucial for photodetectors that are applied in optical communication systems. Si hyperdoped with deep-level impurities provides a monolithic platform for infrared optoelectronics with room-temperature operation at telecommunication wavelengths. In this work, we present strongly enhanced NIR absorption via the hybridization between plasmon resonance and mid-gap states in Au-hyperdoped Si layers, prepared by ion implantation and pulsed laser melting. The Au-hyperdoped Si layers exhibit high-quality recrystallization with the substitution of Au atoms into the Si matrix and the formation of Au nanoparticles on the surface. Surprisingly, the Au-hyperdoped Si layers exhibit a NIR absorption with spectral response extending up to 1650 nm and a maximum absorptance up to 30%. According to electromagnetic simulations, the enhanced infrared photoresponse can be attributed to the mid-gap states induced by substitutional Au atoms and the localized surface plasmon resonance associated with the Au nanoparticles. This work presents a simplified one-step process to gain significant enhancement of NIR absorption, which paves a way for the realization of Si-based photodetectors with room-temperature operation and outstanding performance.

In this work, we performed a systematic investigation on the comparison of magnetic anisotropy between three III-Mn-V dilute ferromagnetic semiconductors (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P prepared by ion implantation and pulsed laser melting. Compressive strain induces in-plane magnetic anisotropy in (Ga,Mn)As and (Ga,Mn)P, while out-of-plane magnetic anisotropy is present in (In,Mn)As due to tensile strain introduced by Mn substitution. Interestingly, all materials prepared herein does not present strong in-plane uniaxial anisotropy, between [110] and [11¯0] directions, which always exhibits in low temperature molecular beam epitaxy (LT-MBE) grown (Ga,Mn)As samples. The reason is ascribed to the fact that the ultra-fast recrystallization induced by pulsed laser melting weakens the formation of Mn-Mn dimers along the [11¯0] direction which presents in LT-MBE grown (Ga,Mn)As.

Recent surface-enhanced Raman spectroscopy (SERS) developments involve using nonmetallic materials as substrates. Molybdenum disulfide (MoS2) is a notable nonmetal semiconductor surface-enhanced Raman scattering (SERS) substrate because of its low cost, abundance, remarkable stability, and considerable chemical activity. However, its limited SERS activity has significantly impeded its advancement in SERS research. Herein, we report a facile and efficient approach for rapidly producing monolayer MoS2 films with adjustable sulfur vacancies via nitrogen plasma treatment. Monolayer MoS2 films exhibit exceptional sensitivity for SERS detection by manipulating the vacancy density. The optimized MoS2 substrate achieved a detection limit of roughly 10(-10) M and an enhancement factor of 2.29 x 10(5) for rhodamine 6G (R6G) probe molecules. We further illustrated that introducing sulfur vacancies can alter the bandgap structure of MoS2, thereby facilitating the separation of internal charge carriers and intensifying interactions with the target components. The vacancy-assisted technique paves the path for the widespread use of semiconductor-based ultrasensitive molecular detection.

Optical logic gates play important roles in all-optical logic circuits, which lie at the heart of the next-generation optical computing technology. However, the intrinsic contradiction between compactness and robustness hinders the development in this field. Here, we propose a simple design principle that can possess multiple-input-output states according to the incident circular polarization and direction based on the metasurface doublet, which enables controlled-NOT logic gates in infrared region. Therefore, the directional asymmetric electromagnetic transmission can be achieved. As a proof of concept, a spin-dependent Janus metasurface is designed and experimentally verified that four distinct images corresponding to four input states can be captured in the far-field. In addition, since the design method is derived from geometric optics, it can be easily applied to other spectra. We believe that the proposed metasurface doublet may empower many potential applications in chiral imaging, chiroptical spectroscopy and optical computing.

Ultraviolet surface-enhanced Raman scattering (UV-SERS) typically occupies an important position because the electronic absorption bands of many biomolecules are located in the deep-ultraviolet (DUV) or ultraviolet (UV) region. Practical application of UV-SERS still relies on uniform, reproducible, and affordable substrates. The conventional aluminum (Al) plasmonic nanostructures are mostly applied to act as UV-SERS substrates, but their intrinsic ohmic loss hinders their practical application. In this study, wafer-scale hybrid metal-dielectric gratings (HMDGs) consisting of aluminum and silicon (Al-Si) have been successfully fabricated as UV-SERS substrates to reduce ohmic dissipation and elevate the detection performance. Well-defined HMDG substrates exhibit tunable hybrid resonant modes in the UV and the visible regions. The adenine biomolecules deposited on HMDG substrates are used to perform SERS measurement with an excitation wavelength of 325 nm. The HMDG nanostructures can obtain as high as 5 orders of magnitude compared with that of Al film as UV-SERS substrates. The proposed HMDG nanostructures have a great advantage in detecting important biomolecules as UV-SERS substrates.

Surface-enhanced Raman scattering (SERS) is a powerful molecular vibrational spectrum characterization method, and has shown promising applications in surface science, life science, environmental monitoring, etc. Developing new simple processes to fabricate low-cost substrates is an essential prerequisite to promote and strengthen the practical application of the SERS technique. For this purpose, the present work reports on the development of a metal/insulator/metal (MIM) structure combined with polystyrene (PS) binary colloidal crystals (bCCs) based on nanosphere self-assembly and electron-beam evaporation technologies. The PS bCCs are used to form a dielectric layer sandwiched between a bottom Ag reflection layer and an upper Ag shell layer. Compared with single-sized colloidal spheres, the PS bCCs exhibit considerably richer morphologies and structures. In addition, the closely packed Ag shell arrays enhance the density of electromagnetic field "hot spots" thus increasing the SERS activity. The PS bCCs-based MIM substrate could achieve an enhancement factor (EF) of 1.10 x 108 and an ultralow detection limit for the Rhodamine 6G (R6G) molecule of about 10-14 M. The results demonstrate that the proposed substrates with a facile fabrication strategy, low cost, large area and high sensitivity have high potential applications of SERS sensors for bio- and chemical molecular analysis.

Although current 2D metasurfaces have emerged as a paradigm platform for electromagnetic (EM) manipulation with enhanced and flexible functions over conventional optical components, their performance is intrinsically limited by constrained interaction with the EM waves due to reduced dimensions. Besides, fabrication of 2D metasurfaces over large areas remains complex and high cost especially in the visible spectrum, further limiting their practical applications. Here, a kind of metal-insulator-metal (MIM) 2.5D metasurfaces is proposed with enriched EM manipulation capabilities in both near-field and far-field compared with their planar counterparts. Moreover, wafer-scale fabrication with high uniformity is also realized by a lithography-free method. As a proof of concept, we experimentally demonstrate three kinds of centimeter-scale metadevices achieving broadband EM absorption (average absorption over 91% within 400-1200 nm), structural color display (coverage of the primary colors red, green and blue (RGB)) and surface-enhanced Raman scattering (largest enhancement factor of 3.29 x 10(7) and relative standard deviation less than 9%), respectively. It is envisioned that the proposed 2.5D metasurfaces may empower many potential applications in EM absorption, sensing and optical displays.

Metasurface absorber (MA) has been a research hotspot in the field of artificial electromagnetic structural material due to its dual advantages of high performance and compact design. Usually, the design of MA depends on the designer's professional knowledge, experience and physical inspiration. The desired optical response can be obtained by using electromagnetic simulation software to carry out hundreds or thousands of numerical calculations. Thus, it is still a challenge to quickly retrieve the optimal structure according to the desired optical response and realize the on-demand inverse design. Besides, limited by the inner physics of the MA, it is not always possible to find the structural parameters corresponding to the desired spectrum. This paper not only takes the planar geometry and thickness of the structures into account but also realizes the probability classification of the desired spectra through the classification network. According to the classification results, the prediction network of the corresponding is selected to realize the on-demand inverse design of MA. The proposed network model can design MA rapidly and accurately in a data-driven way and can be flexibly applied to the design of other data-enabled photonic devices, which is promising to become a comprehensive and effective design tool.

In order to meet the demand for broadband absorbers in the infrared transparent window of the atmosphere, we designed an ultrabroadband metamaterial absorber (MA), which is composed of a germanium-zinc sulfide-chromium-zinc sulfide (Ge-ZnS-Cr-ZnS) disk periodic array and a chromium (Cr) bottom layer. In the infrared transparent window of the atmosphere, the average absorption of the MA is as high as 99.1%, and ultrabroadband near-perfect absorption is realized. Moreover, the absorber is polarization independent and insensitive to the angle of incidence. The ultrabroadband and high-absorption metamaterial absorber has broad application prospects in solar cells, photodetectors, thermophotovoltaics, and thermal emitters.

Reconfigurable electromagnetic (EM) devices with simultaneous small-footprint and high-efficiency are urgently on demand in the fields of optics and nanophotonics. However, it is still a great challenge to achieve this goal based on current design methods especially in infrared and visible bands. Here, a generalized methodology is proposed for highly efficient reconfigurable EM manipulation via the combination of subwavelength-scale metasurface with tunable phase-change material (PCM). As a proof of concept, several broadband metadevices operating in the infrared region are theoretically and numerically investigated. When PCM is in the amorphous state (corresponding to the phase manipulation mode), these devices can, respectively, achieve beam deflection, focusing and meta-holography. When PCM changes to crystalline state (corresponding to the amplitude control mode), they all behave as perfect absorbers with angular tolerance up to 40°. Further investigations also indicate that the designed devices can operate predictably and usefully across the continuous variation in crystal fraction. It is believed that the provided versatile metasurface platform may enable many fascinating applications such as dynamic beam steering, information encryption and active display.

As the 2D counterpart of metamaterials, metasurfaces have drawn wide attentions in recent years due to their unique electromagnetic (EM) properties and subwavelength footprints. Although great efforts have been made in metasurface‐based full vectorial manipulation of EM waves, the realization of multifunctional devices with high compactness is still challenging. Here, by employing the mutual coupling between the meta‐atoms to induce spin‐selective magnetic resonance, a generalized design principle based on single‐layered metasurface is proposed that can achieve giant chiral absorption with average circular dichroism larger than 80%. In addition, arbitrary wavefront manipulation for reflected waves can also be realized with operation efficiency larger than 88%. As a proof of concept, three kinds of chiral devices including beam deflector, vortex beam generator, and meta‐hologram are numerically investigated in infrared region with high performance. It is believed that these multifunctional devices with simple geometry have great potentials in the field of chiral imaging, chiroptical spectroscopy, and EM communication.

Compared with conventional mirrors that behave as isotropic electromagnetic (EM) reflectors, metamirrors composed of periodically aligned artificial meta-atoms exhibit increased degrees of freedom for EM manipulations. However, the functionality of most metamirrors is fixed by design, and how to achieve active EM control is still elusive. Here, we propose a multistate metamirror based on the nonvolatile phase change material Ge2Sb2Te5 (GST) with four distinct functionalities that can be realized in the infrared region by exploiting the temperature-activated phase transition. When varying the crystallinity of GST, the metamirror has the capability to perform as a right-handed circular polarization chiral mirror, a narrowband achiral mirror, a left-handed circular polarization chiral mirror, or a broadband achiral mirror, respectively. The inner physics is further explained by the construction or cancellation of extrinsic two-dimensional chirality. As a proof of concept, experimental verification is carried out and the measured results agree well with their simulated counterparts. Such a multifunctional tunable metamirror could address a wide range of applications from sensing and spectroscopy to analytical chemistry and imaging.

In this paper, a metamaterial absorber is proposed, which is constructed by graphene rings and a gold film separated by an ultrathin S i O 2 layer. The feature of this absorber is that the absorption bands can be adjusted either by applying external electric fields or by rotating the polarization angles of the incident electromagnetic waves. The calculation results show that the continuous tunable or two- to multi-band absorptions can be realized by the above two methods. Through equivalent medium theory and impedance-matching condition, the anisotropic absorption mechanism of this absorber is explained. Moreover, the simple specific design makes the absorption bands able to be further tuned by adjusting various parameters, such as the geometry sizes and relaxation times of graphene rings. Our results indicate that the absorber has great adjustability and great potential application in filtering, terahertz signal detection, signal parameter estimation, smart sensing, tunable absorbers, and cloaking.

Efficient control of the phase and polarization of light is of significant importance in modern optics and photonics. However, traditional methods are often accompanied with cascaded and bulky designs that cannot fulfill the ongoing demand for further integrations. Here, a single-layered metasurface composed of nonvolatile phase-change material Ge2Sb2Se4Te1 (GSST) is proposed with tunable spin-orbit interactions in subwavelength scale. According to the spin-dependent destructive or constructive interference, asymmetric transmission for circularly polarized incidence (extinction ratio > 8:1) can be achieved when GSST is in an amorphous state. Moreover, when GSST changes to crystalline state, reversed chiral transmission (extinction ratio > 12:1) can be observed due to the existence of intrinsic chirality. In addition, as the average cross-polarized transmitted amplitude is larger than 85%, arbitrary wavefront manipulations can be achieved in both states simultaneously based on the theory of Pancharatnam-Berry phase. As a proof of concept, several functional metasurface devices are designed and characterized to further demonstrate the validation of our design methodology. It is believed that these multifunctional devices with ultrahigh compactness are promising for various applications including chiroptical spectroscopy, EM communication, chiral imaging, and information encryption.