Gold Nanostructure Arrays Research Articles

Multi-wavelength and broadband plasmonic switching with V-shaped plasmonic nanostructures on a VO2 coated plasmonic substrate

In this paper, periodic arrays of identical V-shaped gold nanostructures and variable V-shaped gold nanostructures are designed on top of a gold-coated silicon dioxide (SiO2) substrate with a thin spacer layer of vanadium dioxide (VO2) to realize multi-wavelength and broadband plasmonic switches, respectively. The periodic array of identical V-shaped nanostructures (IVNSs) with small inter-particle separation leads to coupled interactions of the elementary plasmons of a V-shaped nanostructure (VNS), resulting in a hybridized plasmon response with two longitudinal plasmonic modes in the reflectance spectra of the proposed switches when the incident light is polarized in the x-direction. The x-direction is oriented along the axis that joins the V-junctions of all VNSs in one unit cell of the periodic array. On exposure to temperature, electric field, or optical stimulus, the VO2 layer transforms from its monoclinic semiconducting state to its rutile metallic state, leading to an overall change in the reflectance spectra obtained from the proposed nanostructures and resulting in an efficient multi-wavelength switching action. Finite difference time domain modelling is employed to demonstrate that an extinction ratio (ER) >12 dB at two wavelengths can be achieved by employing the proposed switches based on periodic arrays of IVNSs. Further, plasmonic switches based on variable V-shaped nanostructures—i.e. multiple VNSs with variable arm lengths in one unit cell of a periodic array—are proposed for broadband switching. In the broadband operation mode, we report an ER >5 dB over an operational wavelength range >1400 nm in the near-IR spectral range spanning over all optical communication bands, i.e. the O, E, S, C, L and U bands. Further, it is also demonstrated that the wavelength of operation for these switches can be tuned by varying the geometrical parameters of the proposed switches. These switches have the potential to be employed in communication networks where ultrasmall and ultrafast switches with multi-wavelength operation or switching over a wide operational bandwidth are inevitably required.

Bowl Shaped Oxide‐Templated Gold Nanostructured Arrays and Structure‐Induced Hydrophilic–Hydrophobic Transition and Molecular Trapping Effect (Adv. Mater. Technol. 13/2024)

Bowl Shaped Oxide‐Templated Gold Nanostructured Arrays and Structure‐Induced Hydrophilic–Hydrophobic Transition and Molecular Trapping Effect (Adv. Mater. Technol. 13/2024)

Bowl Shaped Oxide‐Templated Gold Nanostructured Arrays and Structure‐Induced Hydrophilic–Hydrophobic Transition and Molecular Trapping Effect

AbstractA facile and versatile methodology is developed for the synthesis of diverse gold nanostructured arrays employing an oxide secondary template combined with sputtering deposition. A bowl‐shaped tin oxide‐built array, with fine structure on its bowl edges, is first designed and prepared by solution‐dipping of an organic colloidal monolayer, drying, and heating treatment. This array is then used as a secondary template for a gold nanostructured array by sputtering deposition on it. By controlling the solution's concentration and drying rate to adjust the fine structure of the secondary template, various new gold nanostructured arrays with hexagonal arrangement are fabricated, including “graphene‐structured” gold nanoarray, non‐contact nanoparticle's ring array, closely contacted nanoring array, and bowl/nanoparticle binary composite nanoarray, achieving the structural diversity and morphological tunability of nanoarrays. Additionally, these gold nanostructured arrays can transition from hydrophilic to hydrophobic properties solely by adjusting their surface architecture. Importantly, the bowl‐shaped structural units within these gold nanoarrays demonstrate a marked capability for capturing target molecules that can only very weakly interact with plasmonic metals. This work offers an efficient route to achieve the structural diversity of nanoarrays, which is of significance in designing and fabricating foundational materials for the next generation of multifunctional nanodevices.

Abrasive-free chemical-mechanical planarization (CMP) of gold for thin film nano-patterning.

Despite high demand for gold film nanostructuring, patterning gold at the nanoscale still presents considerable challenges for current foundry-compatible processes. Here, we present a method based on abrasive-free chemical mechanical planarization (CMP) to planarize nanostructured gold surfaces with high selectivity against SiO2. The method is efficient in a damascene process and industry-compatible. Investigations into the material removal mechanism explore the effects of CMP parameters and show that the material removal rate is highly tunable with changes in slurry composition. Millimeter-scale arrays of gold nanostructures embedded in SiO2 were fabricated and the planarization dynamics were monitored over time, leading to the identification of distinct planarization phases and their correlation with the material removal mechanism. Finally, plasmonic cavities of gold nanostructure arrays over a gold mirror were fabricated. The cavities exhibited efficient plasmonic resonance in the visible range, aligning well with simulation results.

Chromatic limits of color filters based on gold nanostructure arrays: The role of surface plasmon and bulk contributions

Chromatic limits of color filters based on gold nanostructure arrays: The role of surface plasmon and bulk contributions

Model of Chronoamperometric Response towards Glucose Sensing by Arrays of Gold Nanostructures Obtained by Laser, Thermal and Wet Processes.

Non-enzymatic electrochemical glucose sensors are of great importance in biomedical applications, for the realization of portable diabetic testing kits and continuous glucose monitoring systems. Nanostructured materials show a number of advantages in the applications of analytical electrochemistry, compared to macroscopic electrodes, such as great sensitivity and little dependence on analyte diffusion close to the electrode-solution interface. Obtaining electrodes based on nanomaterials without using expensive lithographic techniques represents a great added value. In this paper, we modeled the chronoamperometric response towards glucose determination by four electrodes consisting of nanostructured gold onto graphene paper (GP). The nanostructures were obtained by electrochemical etch, thermal and laser processes of thin gold layer. We addressed experiments obtaining different size and shape of gold nanostructures. Electrodes have been characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, and chronoamperometry. We modeled the current-time response at the potential corresponding to two-electrons oxidation process of glucose by the different nanostructured gold systems. The finest nanostructures of 10-200 nm were obtained by laser dewetting of 17 nm thin and 300 °C thermal dewetting of 8 nm thin gold layers, and they show that semi-infinite linear diffusion mechanism predominates over radial diffusion. Electrochemical etching and 17 nm thin gold layer dewetted at 400 °C consist of larger gold islands up to 1 μm. In the latter case, the current-time curves can be fitted by a two-phase exponential decay function that relies on the mixed second-order formation of adsorbed glucose intermediate followed by its first-order decay to gluconolactone.

Amplified EQCM-D detection of extracellular vesicles using 2D gold nanostructured arrays fabricated by block copolymer self-assembly.

Extracellular vesicles (EVs) are routinely released from nearly all cell types as transport vehicles and for cell communication. Crucially, they contain biomolecular content for the identification of health and disease states that can be detected from readily accessible physiological fluids, including urine, plasma, or saliva. Despite their clinical utility within noninvasive diagnostic platforms such as liquid biopsies, the currently available portfolio of analytical approaches are challenged by EV heterogeneity in size and composition, as well as the complexity of native biofluids. Quartz crystal microbalance with dissipation monitoring (QCM-D) has recently emerged as a powerful alternative for the phenotypic detection of EVs, offering multiple modes of analyte discrimination by frequency and dissipation. While providing rich data for sensor development, further progress is required to reduce detection limits and fully exploit the technique's potential within biosensing. Herein, we investigate the impact of nanostructuring the sensor electrode surface for enhancing its detection capabilities. We employ self-assembly of the block copolymer polystyrene-block-poly(4-vinylpyridine) to create well defined 2D gold islands via selective impregnation of the pyridine domain with gold precursors and subsequent removal of the template. When matched to the EV length scale, we find a 4-fold improvement in sensitivity despite a 4-fold reduction in area for analyte and ligand anchoring in comparison to a flat sensor surface. Creation of tailored and confined sensing regions interspersed by non-binding silica provides optimal spatial orientation for EV capture with reduced steric effects and negative cooperativity of grafted antibodies, offering a promising route for facilitated binding and enhanced performance of sensor platforms.

Nanoparticle manipulation using plasmonic optical tweezers based on particle sizes and refractive indices.

As an effective tool for micro/nano-scale particle manipulation, plasmonic optical tweezers can be used to manipulate cells, DNA, and macromolecules. Related research is of great significance to the development of nanoscience. In this work, we investigated a sub-wavelength particle manipulation technique based on plasmonic optical tweezers. When the local plasmonic resonance is excited on the gold nanostructure arrays, the local electromagnetic field will be enhanced to generate a strong gradient force acting on nanoparticles, which could achieve particle sorting in sub-wavelength scale. On this basis, we explored the plasmonic enhancement effect of the sorting device and the corresponding optical force and optical potential well distributions. Additionally, the sorting effect of the sorting device was investigated in statistical methods, which showed that the sorting device could effectively sort particles of different diameters and refractive indices.

Dielectric nanocavity-coupled surface lattice resonances for high-efficiency plasmonic sensing

Surface lattice resonances (SLRs) arising in metal nanostructure arrays have shown tremendous application prospects in the field of plasmonic biosensing. However, these SLRs still suffer from poor optical properties, such as broad linewidth or weak resonance intensity that is especially excited under normal incidence and asymmetric environments, which hinder further practical applications. Herein, we theoretically propose an effective strategy to tailor the SLRs performance of metal nanostructure arrays by introducing a dielectric nanocavity. Originating from the strong interference between the in-plane lattice resonance mode and plasmonic gap cavity modes, the dielectric nanocavity-mediated gold nanostructure arrays exhibit both narrow spectral features with a linewidth of ∼8.2 nm and strong resonance intensity with absorbance amplitude exceeding 95%, even though under normal incidence and asymmetric environment excitation. The simulation results then show that the sensitivity and the figure of merit can reach up to 527.5 nm RIU−1 and 64.3, respectively, as for plasmonic refractive index sensing. This work not only paves the way toward the achievement of effective control of in-plane SLRs, but also provides a potentially attractive candidate for the development of high-efficiency plasmonic sensors.

Purcell-enhanced photoluminescence of few-layer MoS2 transferred on gold nanostructure arrays with plasmonic resonance at the conduction band edge.

Plasmonic coupling of metallic nanostructures with two-dimensional molybdenum disulfide (MoS2) atomic layers is an important topic because it provides a pathway to manipulate the optoelectronic properties and to overcome the limited optical cross-section of the materials. Plasmonic enhanced light-matter interaction of a MoS2 layer is known to be mainly governed by optical field enhancement and the Purcell effect, while the discrimination of the contribution from each mechanism to the plasmonic enhancement is challenging. Here, we investigate photoluminescence (PL) enhancement from few-layer MoS2 transferred on Au nanostructure arrays with controlled localized surface plasmon resonance (LSPR) spectral positions that were detuned from the excitation wavelengths. Two distinctive regimes in LSPR mode-dependent PL enhancement were revealed showing a maximum enhancement (∼40-fold) with zero detuning and a modest enhancement (∼10-fold) with the red-shift detuned LSPR from the excitation wavelength, which were attributed to LSPR-induced optical field enhancement and the Purcell effect, respectively. By applying the experimental parameters into the Purcell effect formalism, an effective mode volume of ∼0.016λ03 was estimated. Our work provides an insight into how to utilize few-layer MoS2 as a base material for optoelectronics by harnessing Purcell-enhanced optical responsivity.

Simultaneous Evaluation of Electrochemical Impedance and Cell Membrane Damage to Understand Antibacterial Mechanism on Nanostructured Surface

In recent years, biomimetics or biomimicry have been paid attention which focus on biotic micro and nano structures. These structures show excellent and multiple functions. It is reported that the wings of cicada and dragonfly have countless nanostructures which exhibit antibacterial and bactericidal activities. These structures kill bacteria physically1-3). One of acceptable mechanism of bactericidal effect is proposed as below: the cell membrane is stretched by the interaction between the structure and bacteria, which induce the cell membrane to be deformed. Then the intracellular fluid leaks which make the cell death4). However, the detailed mechanism has not been cleared. In this study, electrochemical impedance spectroscopy (EIS) measurement and fluorescence microscopy were performed simultaneously to analyze the mechanism of cell adhesion and deformation on the nanostructure surface. The experimental method is described as below. A working electrode (WE) with the diameter of 100 µm was fabricated on a Si substrate. The WE had gold nanostructure arrays which were fabricated by using electron beam lithography and pulse deposition. In order to observe the surface of the WE by a fluorescent microscope, a counter electrode (CE) composed of Au thin film and a reference electrode (RE) were formed on a glass substrate by using photolithography and sputtering. Here, Ag/AgCl paste was solidified and used for the RE. These substrates were opposed to each other as shown in Fig. 1-a, and silicon rubber with a sample chamber with a thickness of 500 µm was sandwiched between these substrates and fixed with screws. An electrolyte solution (PBS (pH = 7.4) containing NaCl (0.15 M) and Fe(CN)6 3- / 4- (1 mM)) was injected through a hole provided on the glass substrate. Escherichia coli (E. coli) was used as a model bacteria and concentration of E. coli was adjusted to OD600 = 0.2. We used DNA staining reagent of SYTO 9 and PI. SYTO 9 diffuses into the cell cytoplasm through the cell membrane and stains DNA green. In contrast, PI enters the cell cytoplasm and stains DNA red when the cell membrane is damaged. Therefore, adhered cells without membrane damage were colored green. After mixing the bacterial broth and the electrolyte solution, the mixture was injected through a hole Then, AC impedance measurement and time-lapse observation using the fluorescence microscope were simultaneously performed every 5 minutes to evaluate changes over time. The obtained fluorescence images are summarized in Table 1, and Fig. 1-b shows the change rate of Rct over time. From Table 1, the number of E. coli stained red increased with the lapse of time on the pillared electrode. E. coli stained green was hardly observed. On the other hand, microscopic observation showed adsorption and desorption of E. coli which stained green on the flat electrode, Here, E. coli stained red could not be observed. According to Fig. 1-b, it was found that the change rate of Rct on the pillared electrode increased gradually and was much larger comparing with that on the flat electrode. In the case of the flat electrode, it is considered that the increase and decrease of impedance was due to adsorption and desorption of E. coli, respectively. In the case of the pillared electrode, the cell membrane was damaged and died after E. coli attached on the WE. The impedance continued to rise because E. coli died and remained on the electrode. At this time, only the attachment process of E. coli could be analyzed. In the future, we will aim for single-cell level analysis by reducing the electrode diameter. We plan to make measurements closer to real time and report more detailed analysis results. 【 References】1) E. P. Ivanova, et al.：Small 8, p. 2489-2494 (2012)2) E. P. Ivanova, et al.：Nature Communications 4, p. 1-7 (2013)3) A. Tripathy, et al.：Advances in Colloid and Interface Science, 248, p. 85-104 (2017)4) K. Nakade, et al.：ACS Applied Nano Materials, p. 5736-5741 (2018) Figure 1

Surface Enhanced Raman Scattering on Regular Arrays of Gold Nanostructures: Impact of Long-Range Interactions and the Surrounding Medium.

Long-range interaction in regular metallic nanostructure arrays can provide the possibility to manipulate their optical properties, governed by the excitation of localized surface plasmon (LSP) resonances. When assembling the nanoparticles in an array, interactions between nanoparticles can result in a strong electromagnetic coupling for specific grating constants. Such a grating effect leads to narrow LSP peaks due to the emergence of new radiative orders in the plane of the substrate, and thus, an important improvement of the intensity of the local electric field. In this work, we report on the optical study of LSP modes supported by square arrays of gold nanodiscs deposited on an indium tin oxyde (ITO) coated glass substrate, and its impact on the surface enhanced Raman scattering (SERS) of a molecular adsorbate, the mercapto benzoic acid (4-MBA). We estimated the Raman gain of these molecules, by varying the grating constant and the refractive index of the surrounding medium of the superstrate, from an asymmetric medium (air) to a symmetric one (oil). We show that the Raman gain can be improved with one order of magnitude in a symmetric medium compared to SERS experiments in air, by considering the appropriate grating constant. Our experimental results are supported by FDTD calculations, and confirm the importance of the grating effect in the design of SERS substrates.

Thermal tracing of a highly reconfigurable and wideband infrared heat sensor based on vanadium dioxide

In this paper, we investigate the thermodynamic properties of a highly reconfigurable and broadband perfect metamaterial absorber in the near-infrared region. Our model is a periodic nanostructure composed of an array of L-shaped hybrid gold and vanadium dioxide nanostructures on gold and glass substrates. The reconfigurability of the nanostructure is based on the metal–insulator transition of vanadium dioxide. The degree of reconfigurability depends on the temperature of the vanadium dioxide nanostructure. In order to study the photo-thermal effect on the reconfigurability of the nanostructure, we irradiate it with a time-dependent Gaussian pulse laser with a 1.5 ns pulse width. Our main purpose is twofold. On the one hand, we aim to investigate how the laser increases the temperature of the nanostructure, and on the other hand, we intend to explore whether the temperature modifies the absorption and reflection of the array. Our results reveal that the VO2 fully transitions to its metallic phase when the fluence of the incident laser is adjusted to 17.8 mJ/cm2.

Effect of deposition angle on fabrication of plasmonic gold nanocones and nanodiscs

Metal nanocones can exhibit several strong plasmonic resonances, which are associated with intense and accessible electromagnetic hot spots. They can thus be used to enhance light–matter interactions or to facilitate location-specific sensing while enabling separation of some non-specific contributions towards the sensing signal. Nanocones and similar 3D structures are often fabricated with the use of the so-called self-shading effect, which occurs during the evaporation of a metal film into circular nanowells. Unfortunately, a full description of a successful deposition process with all the essential details is currently missing in literature. Here we present a detailed view of the fabrication of ordered arrays of conical gold nanostructures using electron beam lithography and gold electron beam evaporation. We show that the symmetry of the fabricated nanostructures is influenced by the lateral position of the substrate on the sample holder during the deposition. Off-axis deposition or tilt of the sample leads to asymmetric nanostructures. When the deposited film is thick enough, or the nanowells narrow enough, the entrance aperture is clogged, and nanocones with sharp tips are formed. In contrast, flat-top truncated cones are produced for thinner films or wider nanowells. All these findings help to identify inherent limits for the production of wafer-scale arrays of such non-planar nanostructures. On the other hand, they also suggest new fabrication possibilities for more complicated structures such as mutually connected nanocones for electrically addressable chips.

Tunable Plasmonic Resonances in Hexagonally Ordered Gold Nanostructure Arrays with Increasing Interstice Size

Gold nanostructure arrays were fabricated by combining colloidal lithography with inclined reactive ion etching and inclinded sputtering. Field emission scanning electron microscopy studies of this substrate show uniaxial hexagonally ordered graded nanostructure arrays with increasing interstice at different positions. Optical spectroscopy studies in visible range reveal that these structures support localized surface plasmon resonance, surface plasmon polaritons, and hybridized modes. Optical spectra were found at each position along the direction of increasing interstice size, and the resonances tend to redshift with position. Different morphologies lead to 50 nm spectral tunability across 10 mm length of the substrate. Based on spectral resolution, optimum peak arising due to localized surface plasmon resonance in reflectance was selected for refractive index sensing application. The sensitivity and figure of merit were evaluated at each position. The sensitivity was found to increase accompanied by decrease in figure of merit with position. The highest sensitivity of 621.6 nm/RIU is obtained for the structure in which interstice size is maximum.

Polarization dependent, plasmon-enhanced infrared transmission through gold nanoslits on monolayer black phosphorus

Enhanced transmission is essential in many application cases. However, as an ordinary method to enhance wave transmission, traditional extraordinary transmission based on nanohole array structures has no capability to widen its operation bandwidth. Here, we use a continuous monolayer black phosphorus film to enhance transmission through gold nanostructure arrays at the mid-infrared region. By exciting surface plasmon polaritons at the BP/gold nanostructure arrays interface, enhanced transmission over a broad range of wavelengths was theoretically demonstrated. Using finite-difference time-domain simulations, we analyzed the effects of geometric parameters on the transmission spectra and demonstrated unique polarization-dependent transmission enhancement in BP/gold silt arrays and BP/gold patch arrays, which originates from the anisotropic properties of BP. Our work provides new guidance to the design of broadband, polarization-dependent extraordinary transmission enhancement.

On-substrate porous-anodic-alumina-assisted gold nanostructure arrays: Meeting the challenges of various sizes and interfaces

Arrays of 0- and 1-dimensional noble-metal nanostructures aligned on solid substrates are in demand for nanocatalysis, bio- and optical sensing, or biomolecular analysis. Here we introduce a range of advances based on a systematic research towards the porous-anodic-alumina (PAA)-assisted on-substrate arrays of gold nanostructures, such as rods and spheres, spatially-separated and highly aligned on a metal or semiconductor supporting layer via a blend of the anodizing, re-anodizing, and post-anodizing treatments applied to a thin layer of Al superimposed on selected valve metals (W, Ti, Hf), metal bilayers (W/Ti), or binary metal alloy layers (W-Ti). The achievements are due to (1) the improved self-organization in the PAA thin films during the self-localizing high-current anodization of the upper Al layer at challenging potentials ranging 100–250 V and 20 to 5 V, and (2) the enhanced penetration of the alumina barrier layer by the undergrowing metal oxide due to the increasing polarization (re-anodizing). The protrusions of the undergrown metal oxide can be either selectively dissolved away providing perfect nanoholes in the alumina barrier layer or left as formed in the barrier layer and annealed in vacuum to increase their electron conductance and serve as the supports for subsequent metal electrodeposition. Additionally, the in-situ amplitude-modulated constant-current pulse deposition mode combined with the original surface-wiping technique to remove the overdeposited gold allow for smooth nucleation and uniform finishing of perfect arrays of on-substrate gold nanospheres and nanorods, having diameters from 10 to over 250 nm and length up to 2.5 μm.

Experimental and numerical investigation of biosensors plasmonic substrates induced differences by e-beam, soft and hard UV-NIL fabrication techniques

This paper compares plasmonic substrates manufactured by three lithography methods: E-beam, soft and hard UV NanoImprint Lithography. The different plasmonic modes existing in samples made of an array of gold nanostructures on gold film are investigated for biochemical detections taking advantage of Surface Plasmon Resonance Imaging (SPRI) and Surface-Enhanced Raman Scattering (SERS). Recently, it has been shown that this geometry of substrate is of great interest for both SPRI and SERS measurements. A comparison of their performances obtained by the different lithographic methods is provided. In particular, due to limitations in NanoImprint Lithographic techniques, the impact of sidewall geometry of nanostructures is investigated in regard to plasmonic properties. Thus, experimental optical characterization analyses have been carried out on samples and compared with the numerical simulations.

Polarization-controlled coherent phonon generation in acoustoplasmonic metasurfaces

Acoustic vibrations at the nanoscale (GHz-THz frequencies) and their interactions with electrons, photons and other excitations are the heart of an emerging field in physics: nanophononics. The design of ultrahigh frequency acoustic-phonon transducers, with tunable frequency, and easy to integrate in complex systems is still an open and challenging problem for the development of acoustic nanoscopies and phonon lasers. Here we show how an optimized plasmonic metasurface can act as a high-frequency phonon transducer. We report pump-probe experiments in metasurfaces composed of an array of gold nanostructures, revealing that such arrays can act as efficient and tunable photon-phonon transducers, with a strong spectral dependence on the excitation rate and laser polarization. We anticipate our work to be the starting point for the engineering of phononic metasurfaces based on plasmonic nanostructures.

Nanostructured substrates for multi-cue investigations of single cells

Cellular adhesion depends on the integration of numerous signaling inputs generated by the chemical and physical properties of the substrate. The complex coupling among inputs makes it challenging experimentally to deconvolve their individual contributions to the adhesion process. To address this roadblock, we have employed a combination of electron beam and optical lithographic techniques to fabricate substrates with independently tunable topographical and chemical signaling cues. Arrays of gold nanostructures were patterned atop quartz substrates, half of which were etched into gold-capped nanopillars. Individual A549 cells exposed simultaneously to Arg-Gly-Asp-functionalized etched and nonetched arrays exhibited strongly preferential adherence to the nanopillars.