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We investigate the electronic transport at the internal interface within a selection of metallic bilayer nanostructures using the contact-free, all-optical method of THz time-domain spectroscopy. The Ru/Co, Ru/Pt, and Ru/Al bilayer nanostructures and their individual constituent metals are studied, with Ru representing an archetypal d-band metal, Co an archetypal ferromagnet, and Pt and Al archetypal heavy and light metals, respectively. The THz conductivity data were analyzed in terms of Drude and Bloch–Grüneisen models, and the interface current coefficient of the internal nanointerface was determined. Strong temperature dependency of the interface current coefficient in the Ru/Co nanostructure is revealed. [ABSTRACT FROM AUTHOR]

Concentric double metallic shells (CDMSs) are strong candidates for photothermal-based therapy, wherein they utilize their tuned plasmon resonance in the near-infrared region via particle coupling factor fitting. Tuning the resonance of CDMSs to the desired near-infrared region is crucial considering the shift caused by variations in their design parameters. In this study, we investigated the effects of these parameters using full-wave electromagnetic analysis to highlight the dominant factors affecting the resonance shift in the absorption spectra of CDMSs. With systematic variations, our simulation data outlined the direct influence of the outer and inner nanoshells' (NS2 and NS1) aspect ratios r2 and r1, respectively, on the coupling factor (rT) aptitude for resonance tuning. For example, a CDMS with r2 = r1 = 0.8 shows coupling manifestation between NS2 and NS1 with rT as low as 0.2. However, we need the value of rT to be at least 0.6 for a CDMS with r2 = r1 = 0.4. Moreover, the dominant factors of the localized surface plasmon resonance shifts were determined by examining the mismatched parameter values of the same particle and found them to be related to NS2. We demonstrated how these factors are related to the complexity of localized surface plasmon resonance peak shifting and splitting in the absorption spectra of CDMSs. Our findings are expected to greatly improve the design of nanoparticles to optimize their responses in photothermal-based applications. [ABSTRACT FROM AUTHOR]

New phenomena have been discovered at the nanoscale that allow us to manipulate light and design devices. Evanescent waves such as Surface Plasmon Polaritons are excited in dielectric–metal interfaces and propagate in the metal. If they reach other interfaces, they may be transmitted by the metal. It is a phenomenon known as Extraordinary Optical Transmission that occurs in nanostructures at the optical range. Depending on the metal it is possible to tune the wavelengths and incident angles where this phenomenon occurs. Gold, silver, aluminium and copper nanolayers are analysed on top of silicon (a-Si and c-Si) considering a sweep between 250 nm and 2500 nm. Considering a novel model based on Fresnel Coefficients in absorbing media, it is possible to improve energy harvesting in the ultraviolet–visible range, mainly due to the propagation of Surface Plasmon Polaritons. Then, the role of Surface Plasmon Polaritons in Air–Metal–Silicon nanostructures is analysed. The inclusion of the metal layer may decrease the reflectance by at least 10%, reaching values higher than 60%. The presented charts allow us to analyse the materials, wavelengths and incident angles where reflectance is decreased. There, the inclusion of metal layers brings benefits to the photodetection, since more energy is available in the absorbing layer. Considering this approach, the detection of specific wavelengths may be improved by introducing metals in the detectors.

In this study, a composite silver nanostructure is presented to serve as the platform for highly efficient plasmon-enhanced fluorescence (PEF). The composite nanostructure is realized by first employing nanosphere lithography (NPL) combined with reactive ion etching (RIE) technology to create a silver nanopyramid array, which is then further modified with silver nanoparticles. Utilizing DCJTB as the fluorophore, this composite nanostructure is found to outperform the use of either silver nanoparticles or silver nanopyramid array. Notably, it not only enhances the photoluminescence (PL) but also reduces the carrier lifetime. The influence of the particle size of silver nanoparticles and the height of the silver nanopyramids is also investigated. It is found that larger silver nanoparticles and higher silver nanopyramids lead to stronger local surface plasmon resonance (LSPR), thereby enhancing the PEF phenomenon. Compared with the performance of using bare glass substrate, the PL intensity of using the composite nanostructure is enhanced to 19.4 times and the carrier lifetime is shortened by 61%.

In this artice, we report on a reduced‐order model (ROM) based on the proper orthogonal decomposition (POD) technique for the system of 3‐D time‐domain Maxwell's equations coupled to a Drude dispersion model, which is employed to describe the interaction of light with nanometer scale metallic structures. By using the singular value decomposition (SVD) method, the POD basis vectors are extracted offline from the snapshots produced by a high order discontinuous Galerkin time‐domain (DGTD) solver. With a Galerkin projection and a second order leap‐frog (LF2) time discretization, a discrete ROM is constructed. The stability condition of the ROM is then analyzed. In particular, when the boundary is a perfect electric conductor condition, the global energy of the ROM is bounded, which is consistent with the characteristics of global energy in the DGTD method. It is shown that the ROM based on Galerkin projection can maintain the stability characteristics of the original high dimensional model. Numerical experiments are presented to verify the accuracy, demonstrate the capabilities of the POD‐based ROM and assess its efficiency for 3‐D nanophotonic problems. [ABSTRACT FROM AUTHOR]

Abstract As planar optical elements, metasurfaces confer an unprecedented potential to manipulate light, which benefits from the deep control of the interactions between nanostructures and light. In the past decade, considerable progress has been made in various metasurfaces for on‐demand functions, drawing great interest from the scientific community. However, it is a great challenge to integrate different functions into a single metasurface, due to the incapability of manipulating light at different dimensions and the lack of universal intelligent design strategy. Here, an intelligent design platform based on deep neural networks is proposed, which can map between structure parameters and optical response. The well‐trained network model can intelligently retrieve nanostructures to meet multidimensional optical requirements of metasurfaces. Four metalenses for chiral focusing are realized by the design platform and the simulation results are highly consistent with the design target. In addition, metalenses based on arbitrary polarization at various working wavelength are also demonstrated, showing that the method has powerful design ability. Various optical properties of nanostructures, such as phase shift and polarization, are manipulated by deep neural networks, which can greatly promote the development of multifunctional devices and further pave the way for optical display, communication, computing, sensing, and other applications.

The plasmonic resonance frequency of metal nanoparticles (NPs) strongly depend on the geometry, size, and separation between NPs. Here, a plasmonic structure is designed based on a film-coupled nanoparticle phenomenon and analytically investigated by a finite element method via COMSOL Multiphysics software tool. The optical behavior of the designed structure is studied and compared for two noble metals (gold and silver as a case study). Simulation results confirmed that structural elements such as dielectric layer thickness, metal film thickness, and metal nanoparticle separation distance significantly affect the plasmonic properties. Consequently, optimizing the dimensions of the mentioned structural elements results in a strong field enhancement in the dielectric gap layer. The simplicity of this structure, easy controlling of the dielectric gap layer thickness, strong field confinement in a limited area, and lack of incident light angle tunning are characteristic features of the proposed structure. Strong field enhancement in a limited volume makes this structure promising as plasmonic nanoantennas, SERS platforms, and sensing applications. [ABSTRACT FROM AUTHOR]

Abstract Flexible perovskite solar cells (FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given.

Focused electron beam-induced processing is a versatile method for the fabrication of metallic nanostructures with arbitrary shape, in particular, on top of two-dimensional (2D) organic materials, such as self-assembled monolayers (SAMs). Two methods, namely electron beam-induced deposition (EBID) and electron beam-induced surface activation (EBISA) are studied with the precursors Fe(CO)5 and Co(CO)3NO on SAMs of 1,1′,4′,1′′-terphenyl-4-thiol (TPT). For Co(CO)3NO only EBID leads to deposits consisting of cobalt oxide. In the case of Fe(CO)5 EBID and EBISA yield deposits consisting of iron nanocrystals with high purity. Remarkably, the EBISA process exhibits a strong time dependence, which is analyzed in detail for different electron doses. This time dependence is a new phenomenon, which, to the best of our knowledge, was not reported before. The electron-induced cross-linking of the SAM caused by the cleavage of C–H bonds and the subsequent formation of new C–C bonds between neighboring molecules also seems to play a crucial role in the EBISA process. Previous studies showed that iron nanostructures fabricated on top of a cross-linked SAM on Au/mica can be transferred to solid substrates and grids without any changes, aside from oxidation. Here we demonstrate that iron as well as cobalt oxide structures on top of a cross-linked SAM on Ag/mica do change more significantly. The Fe(NO3)3 solution used for etching of the Ag layer also dissolves the cobalt oxide structures and causes dissolution and reduction of the iron structures. These results demonstrate that the fabrication of hybrids of metallic nanostructures onto organic 2D materials is an intrinsically complex procedure. The interactions among the metallic deposits, the substrate for the growth of the SAM, and the associated etching/dissolving agent need to be considered and further studied.

Highlights: Convincing candidates of flexible transparent electrodes are discussed in detail from the views of fabrication, properties and device performance. The progresses of flexible opaque electrodes used in flexible perovskite solar cells are provided. The future directions and challenges in developing flexible electrodes are highlighted. Flexible perovskite solar cells (FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given. [ABSTRACT FROM AUTHOR]

Due to small optical mode volumes and linear polarizations of surface-plasmon-polariton (SPP) resonant modes in metallic antennas, it is very difficult to obtain complex emission patterns and polarizations for single-photon emitters. Herein, nonresonant enhancement in a silver nanowire is used to both enhance emission rates and extract a z-oriented dipole, and then the symmetry of metallic nanostructures is proposed to tailor the patterns and polarizations of single-photon emission. The emission pattern of a quantum dot located close to a metallic nanostructure with a symmetric axis is split into multiple flaps. The number of splitting flaps is equal to the order of the symmetric axis. Moreover, the electric vectors of the emitted photons become centrally symmetric about the symmetric axis. The above phenomena are well explained by both a simulation and an image dipole model. The structural-symmetry-tailoring mechanism may open up a new avenue in the design of multifunctional and novel quantum-plasmonic devices.

Multi-resonant plasmonic simple geometries like nanocylinders and nanorods are highly interesting for two-photon photoluminescence and second harmonic generation applications, due to their easy fabrication and reproducibility in comparison with complex multi-resonant systems like dimers or nanoclusters. We demonstrate experimentally that by using a simple gold nanocylinder we can achieve a double resonantly enhanced two-photon photoluminescence of quantum dots, by matching the excitation wavelength of the quantum dots with a dipolar plasmon mode, while the emission is coupled with a radiative quadrupolar mode. We establish a method to separate experimentally the enhancement factor at the excitation and at the emission wavelengths for this double resonant system. The sensitivity of the spectral positions of the dipolar and quadrupolar plasmon resonances to the ellipticity of the nanocylinders and its impact on the two-photon photoluminescence enhancement are discussed.

The plasmonic resonance frequency of metal nanoparticles (NPs) strongly depend on the geometry, size, and separation between NPs. Here, a plasmonic structure is designed based on a film-coupled nanoparticle phenomenon and analytically investigated by a finite element method via COMSOL Multiphysics software tool. The optical behavior of the designed structure is studied and compared for two noble metals (gold and silver as a case study). Simulation results confirmed that structural elements such as dielectric layer thickness, metal film thickness, and metal nanoparticle separation distance significantly affect the plasmonic properties. Consequently, optimizing the dimensions of the mentioned structural elements results in a strong field enhancement in the dielectric gap layer. The simplicity of this structure, easy controlling of the dielectric gap layer thickness, strong field confinement in a limited area, and lack of incident light angle tunning are characteristic features of the proposed structure. Strong field enhancement in a limited volume makes this structure promising as plasmonic nanoantennas, SERS platforms, and sensing applications.

Surface-enhanced Raman scattering (SERS) as a label-free, non-contact, highly sensitive, and powerful technique has been widely applied in determining bio- and chemical molecules with fingerprint recognitions. 2-dimensional (2D) materials with layered structures, tunable optical properties, good chemical/physical stabilities, and strong charge–transfer interaction with molecules have attracted researchers’ interests. Two-D materials with a large and flat surface area, as well as good biocompatibility have been considered promising candidates in SERS and widely applied in chemical and bio-applications. It is well known that the noble metallic nanostructures with localized surface plasmon effects dominate the SERS performance. The combination of noble metallic nanostructure with 2D materials is becoming a new and attractive research domain. Until now, the SERS substrates combined with 2D materials, such as 2D graphene/metallic NPs, 2D materials@metallic core-shell structures, and metallic structure/2D materials/metallic structure are intensely studied. In this review, we introduce different kinds of fabrication strategies of 2D and 3D SERS substrates combing with 2D materials as well as their applications. We hope this review will help readers to figure out new ideas in designing and fabricating SERS substrates with high SERS performance that could enlarge the applicable domains of SERS.

The generation of pigment‐free colors by nanostructures and subwavelength patterns has evolved in the last decade and outperformed the conventional paints in terms of durability, recyclability, and environmental friendliness. The recent progress in the field of structural coloration, particularly reflective coloration, offering a full‐color gamut, has realized high‐resolution printing, not attainable by the pigment paints. Herein, an overview of the various systems able to offer reflective coloration for a variety of optical applications with static and dynamic responses is presented. Specifically, an emphasis is given to recent works of the article's authors on the cooperative action of the disordered particles and dipoles that can generate specular reflective colors. In addition, further developments of reflective color nanosystems are discussed. In the first section, an overview of the recent progress in the field of plasmonic reflective structural coloration is provided. The second part of the article deals with the authors’ latest findings with respect to polarizonic color generation and its implementation in various areas ranging from environmental detection and biosensing to colored solar perfect absorbers. The report is wrapped up with an outlook and summary.

[Display omitted] • The Ag nanopyramid array modified with Ag NPs are fabricated on glass substrate. • PL intensity of DCJTB can be enhanced to 19.4 times. • PL's lifetime of DCJTB is reduced by 61%. In this study, a composite silver nanostructure is presented to serve as the platform for highly efficient plasmon-enhanced fluorescence (PEF). The composite nanostructure is realized by first employing nanosphere lithography (NPL) combined with reactive ion etching (RIE) technology to create a silver nanopyramid array, which is then further modified with silver nanoparticles. Utilizing DCJTB as the fluorophore, this composite nanostructure is found to outperform the use of either silver nanoparticles or silver nanopyramid array. Notably, it not only enhances the photoluminescence (PL) but also reduces the carrier lifetime. The influence of the particle size of silver nanoparticles and the height of the silver nanopyramids is also investigated. It is found that larger silver nanoparticles and higher silver nanopyramids lead to stronger local surface plasmon resonance (LSPR), thereby enhancing the PEF phenomenon. Compared with the performance of using bare glass substrate, the PL intensity of using the composite nanostructure is enhanced to 19.4 times and the carrier lifetime is shortened by 61%. [ABSTRACT FROM AUTHOR]

The ability of metallic nanostructures to confine light at the sub-wavelength scale enables new perspectives and opportunities in the field of nanotechnology. Making use of this unique advantage, nano-optical trapping techniques have been developed to tackle new challenges in a wide range of areas from biology to quantum optics. In this work, starting from basic theories, we present a review of research progress in near-field optical manipulation techniques based on metallic nanostructures, with an emphasis on some of the most promising advances in molecular technology, such as the precise control of single biomolecules. We also provide an overview of possible future research directions of nanomanipulation techniques.

Recently, nanotechnology has emerged as a tool for the development in the biological synthesis of noble metal nanoparticles. Among other conventional synthesis methods, biological synthesis methods have received great significance due to cost-effective and less hazardous nature which is due to the presence of plentiful as well as diversified biomolecules acting as capping and reducing agents. Biosynthesized silver nanoparticles (Ag NPs) manifest potential applications in several fields because of its safe and environment friendliness. Reported researches on the green synthesis of Ag NPs using different parts of stem, fruits, and seeds has been summarized along with the impact on the morphological properties. This review is important to find a way toward the cheaper, environmentally friendly and controlled synthesis of Ag NPs hence is of special concern. [ABSTRACT FROM AUTHOR]

The penetration of decimeter, centimeter, and millimeter electromagnetic waves through magnetic metallic nanostructures is considered in this work. Detailed information on the microwave giant magnetoresistive effect is presented. The manifestations of ferromagnetic and spin-wave resonances upon the transmission of microwaves through nanostructures are considered. [ABSTRACT FROM AUTHOR]

In this work, the effects of geometries of stainless steel electrodes used inelectrolytic analysis cells were studied. These cells are used for preparation ofmetallic nanostructures. These effects can be observed by studying energy transfercharacteristics of electrolytic cell as the electric field and current density aredetermined by its electrode geometry. Four electrode geometries were used in thiswork.

This review is focused on recent developments of surface-enhanced Raman scattering (SERS) applications in Analytical Chemistry. The work covers advances in the fabrication methods of SERS substrates, including nanoparticles immobilization techniques and advanced nanopatterning with metallic features. Recent insights in quantitative and sampling methods for SERS implementation and the development of new SERS-based approaches for both qualitative and quantitative analysis are discussed. The advent of methods for pre-concentration and new approaches for single-molecule SERS quantification, such as the digital SERS procedure, has provided additional improvements in the analytical figures-of-merit for analysis and assays based on SERS. The use of metal nanostructures as SERS detection elements integrated in devices, such as microfluidic systems and optical fibers, provided new tools for SERS applications that expand beyond the laboratory environment, bringing new opportunities for real-time field tests and process monitoring based on SERS. Finally, selected examples of SERS applications in analytical and bioanalytical chemistry are discussed. The breadth of this work reflects the vast diversity of subjects and approaches that are inherent to the SERS field. The state of the field indicates the potential for a variety of new SERS-based methods and technologies that can be routinely applied in analytical laboratories. Image 1 • This review covers recent advances of SERS applications in analytical chemistry. • Progresses in substrate development are discussed. • New types of devices that use SERS as a detection platform have been introduced. • SERS for bioanalytical applications is the area with most activity in the field. • New SERS quantification techniques are now available. [ABSTRACT FROM AUTHOR]

A systematic study of the surface plasmon resonance (SPR)-dependent nonlinear optical response of Ag nanoplates is presented and discussed. The Ag nanoplates were synthesized using the well-known seed-mediated growth method. By performing the z-scan method with a nanosecond laser (532 nm, 5 ns), the optical nonlinearities of the Ag nanoplates, prepared tuning the SPR contribution in the 400–1000 nm range, were determined. The results showed a SPR-related competition between the saturable absorption and reverse saturable absorption mechanisms, while the nonlinear refraction changed from self-defocusing to self-focusing. Furthermore, the scattering effects contribute to determine the nature of the optical limiting response. The observed SPR-tunable third order optical nonlinearities make Ag nanoplates a suitable candidate to be used in different fields, i.e., laser pulse generation, optical limiting, or bio-imaging applications.

Nonlinear optics, when combined with microscopy, is known to provide advantages including novel contrast, deep tissue observation, and minimal invasiveness. In addition, special nonlinearities, such as switch on/off and saturation, can enhance the spatial resolution below the diffraction limit, revolutionizing the field of optical microscopy. These nonlinear imaging techniques are extremely useful for biological studies on various scales from molecules to cells to tissues. Nevertheless, in most cases, nonlinear optical interaction requires strong illumination, typically at least gigawatts per square centimeter intensity. Such strong illumination can cause significant phototoxicity or even photodamage to fragile biological samples. Therefore, it is highly desirable to find mechanisms that allow the reduction of illumination intensity. Surface plasmon, which is the collective oscillation of electrons in metal under light excitation, is capable of significantly enhancing the local field around the metal nanostructures and thus boosting up the efficiency of nonlinear optical interactions of the surrounding materials or of the metal itself. In this mini-review, we discuss the recent progress of plasmonics in nonlinear optical microscopy with a special focus on biological applications. The advancement of nonlinear imaging modalities (including incoherent/coherent Raman scattering, two/three-photon luminescence, and second/third harmonic generations that have been amalgamated with plasmonics), as well as the novel subdiffraction limit imaging techniques based on nonlinear behaviors of plasmonic scattering, is addressed.

In this study, a low-cost, simple, single-step low-voltage operation and a well-controlled method for deposition of uniformed and unique size distributions of silver nanoparticles (AgNPs) on the porous silicon (PS) layer were achieved via controlling the drift velocity of electrons in an aqueous solution of AgNO 3. The laser diode of 530 nm and 60 mW/cm2 laser wavelength and illumination power density was employed to prepare PS layer by a laser-assisted etching process. The PS layer was incorporated on the platinum disk cathode electrode, and a stainless steel plate as an anode was employed. Low applied operating voltage of about 3V DC at different drift currents of 10, 20, 30 and 40 mA for 2 min was applied to sustain the drift motion of Ag 2+ . Structural properties of AgNPs layer were examined via the field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) pattern. These measurements exposed that AgNPs were adjusted by controlling the drift current, and a uniform AgNPs with specific unique sizes were obtained. Grain size, specific surface area and nucleation sites of metallic AgNPs were intensely influenced by the drift current. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) was observed on irradiation of a symmetry-broken gold nanostructured surface with an ultrashort pulse of low input power. A metasurface consisting of lightning-bolt-like shaped gold (Au) nanostructures in a periodic arrangement was fabricated on a glass substrate and utilized to excite surface plasmons. The measured extinction spectrum had a dual band maximized at approximately 605 nm and 786 nm under illumination with linearly polarized light. The two-photon induced photoluminescence and SHG intensity were dependent on the polarization states and wavelength of the femtosecond laser pulse irradiation. Furthermore, the SHG intensity peak was linearly dependent on the input power of the incident laser beam, and the spectral property of the emitted second harmonic was correlated to the extinction spectrum of the nanostructured metasurface. The SHG peak over the pumping wavelengths was resonant with a transverse multipolar plasmon mode. The findings provide useful guidelines for efficient production of second harmonic luminescence. [ABSTRACT FROM AUTHOR]

Abstract The author reports spectroscopic characterization, and simulation of metallic nanoantennas consisting of arrays of Au nanostructures for enhancement of dye fluorescence. The molecular dye fluorescence was significantly enhanced by near-field interaction between plasmons excited from the Au nanostructures and the molecule. The resulting fluorescence enhancement caused by the near-field enhancement was attributed to plasmon resonances and correlated to the extinction of the metal nanostructure. The author also performed numerical calculations of the Purcell enhancement factors, simulating the spontaneous emission enhancement of a dipole emitter positioned near the nanostructure, and these are in good agreement with the measured fluorescence enhancement. Highlights • Fabrication of hybrid dye-doped nanostructured photoluminescent materials. • Numerical simulation of nanostructured antenna enhancing photoluminescence. • Optical characterization of hybrid dye-doped nanostructured photoluminescent materials. [ABSTRACT FROM AUTHOR]

We derive and analyze analytical expressions for the quantum electron current density and electromagnetic field distribution inside a metallic nanoslab. Besides, we obtain general explicit expressions for the surface impedances of both metal slab boundaries. We found that the phenomenon of Landau damping manifests itself in the frequency dependence of the surface impedances as resonances associated with the discretization of the electromagnetic and electron wave numbers inside the metal nanoslab. In particular, the quantum nonlocal resonances of the surface impedances are clearly discernible at slab thicknesses smaller than the electromagnetic skin depth. The predictions for the surface impedances in the quantum regime turn out to be radically different from those of the quantum local approach, the semiclassical Boltzmann kinetic equation formalism and the classical Drude–Lorentz local model. The analytical study completely agrees with the respective numerical calculations. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to improve the sensitivity and the performance of nano-sensors by using the simulation, which was done by finite element method in 2D plasmonic nanostructures. Meanwhile, the effects of geometric parameters of a hexagonal gold nanostructure, and the influence of two dielectrics Si 3 N 4 and SiO x were treated. In order to have better sensitivity, the nature and the thickness of a deposed dielectric were controlled. Whenever we change the geometric parameters of the metallic nanostructure, we see changes in nanoparticle's plasmonic response. Adjusting the theoretical curve to experimental LSPR curve allowed the geometry of the plasmonic interface to be fixed and evaluation of the change in the wavelength at resonance ( λ R ) as a function of the SiO x overlayers thickness. The theoretical data were compared with experimental results obtained on glass/Au nanowires/SiO x and glass/Au Nanowires/Si 3 N 4 interfaces. Highlights • We propose a new design structure with gold nanoparticles. • The effect of geometrical nanowires in the structure and evolution of plasmon resonance are studied. • The theoretical data were compared with experimental results obtained. • The LSPR parameters are optimized to improve the sensitivity and the performance of nano-sensors. [ABSTRACT FROM AUTHOR]

Tip-enhanced Raman spectroscopy (TERS) has experienced tremendous progress over the last two decades. Despite detecting single molecules and achieving sub-nanometer spatial resolution, attaining high TERS sensitivity is still a challenging task due to low reproducibility of tip fabrication, especially regarding very sharp tip apices. Here, we present an approach for achieving strong TERS sensitivity via a systematic study of the near-field enhancement properties in the so-called gap-mode TERS configurations using the combination of finite element method (FEM) simulations and TERS experiments. In the simulation study, a gold tip apex is fixed at 80 nm of diameter, and the substrate consists of 20 nm high gold nanodiscs with diameter varying from 5 nm to 120 nm placed on a flat extended gold substrate. The local electric field distributions are computed in the spectral range from 500 nm to 800 nm with the tip placed both at the center and the edge of the gold nanostructure. The model is then compared with the typical gap-mode TERS configuration, in which a tip of varying diameter from 2 nm to 160 nm is placed in the proximity of a gold thin film. Our simulations show that the tip-nanodisc combined system provides much improved TERS sensitivity compared to the conventional gap-mode TERS configuration. We find that for the same tip diameter, the spatial resolution achieved in the tip-nanodisc model is much better than that observed in the conventional gap-mode TERS, which requires a very sharp metal tip to achieve the same spatial resolution on an extended metal substrate. Finally, TERS experiments are conducted on gold nanodisc arrays using home-built gold tips to validate our simulation results. Our simulations provide a guide for designing and realization of both high-spatial resolution and strong TERS intensity in future TERS experiments.

Additive, direct-write manufacturing via a focused electron beam has evolved into a reliable 3D nanoprinting technology in recent years. Aside from low demands on substrate materials and surface morphologies, this technology allows the fabrication of freestanding, 3D architectures with feature sizes down to the sub-20 nm range. While indispensably needed for some concepts (e.g., 3D nano-plasmonics), the final applications can also be limited due to low mechanical rigidity, and thermal- or electric conductivities. To optimize these properties, without changing the overall 3D architecture, a controlled method for tuning individual branch diameters is desirable. Following this motivation, here, we introduce on-purpose beam blurring for controlled upward scaling and study the behavior at different inclination angles. The study reveals a massive boost in growth efficiencies up to a factor of five and the strong delay of unwanted proximal growth. In doing so, this work expands the design flexibility of this technology.

Metal-enhanced fluorescence (MEF) is a unique phenomenon of surface plasmons, where light interacts with the metallic nanostructures and produces electromagnetic fields to enhance the sensitivity of fluorescence-based detection. In particular, this enhancement in sensing capacity is of importance to many research areas, including medical diagnostics, forensic science, and biotechnology. The article covers the basic mechanism of MEF and recent developments in plasmonic nanostructures fabrication for efficient fluorescence signal enhancement that are critically reviewed. The implications of current fluorescence-based technologies for biosensors are summarized, which are in practice to detect different analytes relevant to food control, medical diagnostics, and forensic science. Furthermore, characteristics of existing fabrication methods have been compared on the basis of their resolution, design flexibility, and throughput. The future projections emphasize exploring the potential of non-conventional materials and hybrid fabrication techniques to further enhance the sensitivity of MEF-based biosensors.

Surface-enhanced Raman scattering (SERS) enables the highly sensitive detection of (bio)chemical analytes in fluid samples; however, its application requires nanostructured gold/silver substrates, which presents a significant technical challenge. Here, we develop and apply a novel method for producing gold nanostructures for SERS application via the alternating current (AC) electrokinetic assembly of gold nanoparticles into two intricate and frequency-dependent structures: (1) nanowires, and (2) branched “nanotrees”, that create extended sensing surfaces. We find that the growth of these nanostructures depends strongly on the parameters of the applied AC electric field (frequency and voltage) and ionic composition, specifically the electrical conductivity of the fluid. We demonstrate the sensing capabilities of these gold nanostructures via the chemical detection of rhodamine 6G, a Raman dye, and thiram, a toxic pesticide. Finally, we demonstrate how these SERS-active nanostructures can also be used as a concentration amplification device that can electrokinetically attract and specifically capture an analyte (here, streptavidin) onto the detection site.

Cathodoluminescence (CL) as a radiative light produced by an electron beam exciting a luminescent material, has been widely used in imaging and spectroscopic detection of semiconductor, mineral and biological samples with an ultrahigh spatial resolution. Conventional CL spectroscopy shows an excellent performance in characterization of traditional material luminescence, such as spatial composition variations and fluorescent displays. With the development of nanotechnology, advances of modern microscopy enable CL technique to obtain deep valuable insight of the testing sample, and further extend its applications in the material science, especially for opto-electronic investigations at nanoscale. In this article, we review the study of CL microscopy applied in semiconductor nanostructures for the dislocation, carrier diffusion, band structure, doping level and exciton recombination. Then advantages of CL in revealing and manipulating surface plasmon resonances of metallic nanoantennas are discussed. Finally, the challenge of CL technology is summarized, and potential CL applications for the future opto-electronic study are proposed.