Nanosphere Arrays Research Articles

Ultra 40 % optical and electrical performance enhancement of silver nanosphere array-structured radioluminescent nuclear batteries

Weak performance output is currently the major factor limiting the further development of radioluminescent nuclear batteries for sustainable and stable applications. This work proposed a method for enhancing the radiofluorescence absorption to boost the electrical output of these batteries with metal nanosphere array structures for photovoltaic modules. The radiofluorescence absorption enhancement of photovoltaic modules, the electrical output enhancement of batteries, and the fundamental enhancement mechanism of metal nanosphere array structures were investigated from multiple perspectives. Silver nanosphere array structure on the surface of the photovoltaic module could enhance the forward scattering probability of radiofluorescence generated by the radioluminescent material inside the photovoltaic module, thereby achieving a radiofluorescence absorption gain of up to 43.66 % for the photovoltaic module and an electrical output gain of up to 44.91 % for the radioluminescent nuclear battery.

Valence Band-Tunable NiFe Electrocatalyst Triggered by the Dynamic Mo Exudation and Re-Deposition for Superior High Current Density Oxygen Evolution Reaction.

Developing energy- and time-efficient strategies to derive high-performance non-precious electrocatalysts for anodic oxygen evolution reaction (OER), especially stably working at industrial-demanding current density, is still a big challenge. In this work, a concise molten salt erosion scenario was devised to rapidly modulate the smooth surface of the commercial NiMo foam substrate into the rough, electronically coupled, and hierarchically porous Ni/Fe/Mo(oxy)hydroxide catalyst layer assembled by the nanosphere array. This self-supported catalyst is super-hydrophilic for the alkaline electrolyte and distinguished by a balanced Mo leaching/surface-readsorption process to tune the metal d band center and electronic perturbation. The altered electronic environment with the favored OER intermediate adsorption behavior attains the outstanding OER activity in terms of a very small overpotential of 230.21 mV at 10 mA cm-2 and an ultra-long stability for 1179.45 h to sustain the initial commercial-level current density of ca. 1000 mA cm-2. This superb performance transcends most of the edge-cutting transition metal peers reported recently and can satisfy the standards of industrial applications. This industrial-compatible synthesis technology holds profound implications for hydrogen production via water splitting and other electrochemical applications.

Flexible/Regenerative Nanosensor with Automatic Sweat Collection for Cytokine Storm Biomarker Detection.

The real-time monitoring of low-concentration cytokines such as TNF-α in sweat can aid clinical physicians in assessing the severity of inflammation. The challenges associated with the collection and the presence of impurities can significantly impede the detection of proteins in sweat. This issue is addressed by incorporating a nanosphere array designed for automatic sweat transportation, coupled with a reusable sensor that employs a Nafion/aptamer-modified MoS2 field-effect transistor. The nanosphere array with stepwise wettability enables automatic collection of sweat and blocks impurities from contaminating the detection zone. This device enables direct detection of TNF-α proteins in undiluted sweat, within a detection range of 10 fM to 1 nM. The use of an ultrathin, ultraflexible substrate ensures stable electrical performance, even after up to 30 extreme deformations. The findings indicate that in clinical scenarios, this device could potentially provide real-time evaluation and management of patients' immune status via sweat testing.

Simulations of Femtosecond-Laser Near-Field Ablation Using Nanosphere under Dynamic Excitation.

Femtosecond lasers have garnered widespread attention owing to their subdiffraction processing capabilities. However, their intricate natures, involving intrapulse feedbacks between transient material excitation and laser propagation, often present significant challenges for near-field ablation predictions and simulations. To address these challenges, the current study introduces an improved finite-difference time-domain method (FDTD)-plasma model (plasma)-two-temperature model (TTM) framework for simulating the ablation processes of various nanospheres on diverse substrates, particularly in scenarios wherein dynamic and heterogeneous excitations significantly influence optical-field distributions. Initially, FDTD simulations of a single Au nanosphere on a Si substrate reveal that, with transitions in the excitation states of the substrate, the field-intensity distribution transforms from a profile with a single central peak to a bimodal structure, consistent with experimental reports. Subsequently, simulations of a polystyrene nanosphere array on a SiO2 substrate reveal that different excitation states of the nanospheres yield two distinct modes, namely near-field enhancement and masking. These modes cannot be adequately modeled in the FDTD simulations. Our combined model also considers the intrapulse feedback between the electromagnetic-field distribution resulting from near-field effects and material excitations. Furthermore, the model can quantitatively analyze subsequent electron-phonon coupling and material removal processes resulting from thermal-phase transitions. Consequently, our model facilitates predictions of the femtosecond-laser ablation of single nanospheres or nanosphere arrays with varying sizes and materials placed on substrates subjected to near-field effects.

Well-ordered Au@Ag NBPs/SiO2 nanoarray for sensitive detection of chloramphenicol via DNAzyme-assisted SERS sensing

Misuse of chloramphenicol (CAP) can lead to severe food safety issues. Therefore, the accurate and sensitive detection of CAP residues is important for public health. Herein, a convenient and reliable interfacial self-assembly technique was used to form a uniform Au@Ag nanobipyramids (NBPs) film on an ordered SiO2 nanosphere array (SiO2 NS), which served as a Raman-enhanced substrate. In conjunction with a deoxyribonucleic acid enzyme–induced signal amplification strategy, we developed a novel surface-enhanced Raman scattering (SERS) biosensor for the selective and sensitive detection of CAP. The biosensor exhibited a detection limit of 6.42 × 10−13 mol·L−1 and a detection range of 1.0 × 10−12–1.0 × 10−6 mol·L−1. The biosensor could detect CAP in spiked milk samples with a high accuracy, and its recovery rates ranged from 97.88% to 107.86%. The as-developed biosensor with the advantages of high sensitivity and high selectivity offers a new strategy for the rapid, reliable and sensitive detection of CAP, rendering it applicable to food safety control.

Self‐Assembled Hierarchical Nanostructures: Toward Engineered SERS‐Active Platforms

AbstractThe creation of SERS‐active substrates is investigated by self‐assembling hierarchical structures of plasmonic‐assisted nanospheres (HSNs). The hierarchical architecture exploits the advantages of the well‐known ordered configuration of a hexagonally closed‐packed array (CPA) of nanospheres. A further layer of upper nanospheres is used to provide regular and intense surface hotspots, located at the nanogaps between neighboring nanospheres. Numerical analysis is carried out to predict the SERS performances and to identify the more promising configurations, by offering design criteria and a physical insight on the conditions affecting the SERS response of the self‐assembled substrates. Two alternative self‐assembly fabrication methods have been pursued to realize HSNs, namely co‐deposition and sequential deposition. Morphological analysis revealed the formation of well‐ordered hierarchical structures with different ratios between the diameters of the bottom and upper nanospheres. Experimental analysis of the SERS response demonstrates that HSNs can work as cost‐effective SERS substrates with superior performances with respect to the simpler single‐layer CPA configurations.

High-density, highly sensitive sensor array of spiky carbon nanospheres for strain field mapping

While accurate mapping of strain distribution is crucial for assessing stress concentration and estimating fatigue life in engineering applications, conventional strain sensor arrays face a great challenge in balancing sensitivity and sensing density for effective strain mapping. In this study, we present a Fowler-Nordheim tunneling effect of monodispersed spiky carbon nanosphere array on polydimethylsiloxane as strain sensor arrays to achieve a sensitivity up to 70,000, a sensing density of 100 pixel cm−2, and logarithmic linearity over 99% within a wide strain range of 0% to 60%. The highly ordered assembly of spiky carbon nanospheres in each unit also ensures high inter-unit consistency (standard deviation ≤3.82%). Furthermore, this sensor array can conformally cover diverse surfaces, enabling accurate acquisition of strain distributions. The sensing array offers a convenient approach for mapping strain fields in various applications such as flexible electronics, soft robotics, biomechanics, and structure health monitoring.

Manipulation of plasmon dephasing time via the coupling between localized surface plasmon resonance and waveguide modes

Manipulation of plasmon dephasing time of the hybrid modes has gained much attention in recent years, which plays critical roles in many important applications of plasmonics. Here, we manipulate the dephasing time of plasmonic field resulting from coupling of the localized surface plasmon (LSP) of the nanosphere array and the waveguide mode supported by the indium tin oxide film with quasi-normal mode-assisted harmonic oscillator model method. It results in the formation of two distinct modes, transverse electric (TE) and transverse magnetic (TM) modes. Such coupling can significantly modify the dynamics of the original plasmonic modes. The dephasing time of the hybrid plasmon modes, encompassing both TE and TM modes, can be extended from 1.25fs to 4.95fs, which is about 2–7 times compared to that of a single localized surface plasmon resonant mode. More importantly, by changing the structural parameters, we can flexibly manipulate either the dephasing time with a fixed wavelength or the resonant wavelength with a fixed dephasing time.

Self-Assembly of Organic Semiconductors on Strained Graphene under Strain-Induced Pseudo-Electric Fields.

Graphene is used as a growth template for van der Waals epitaxy of organic semiconductor (OSC) thin films. During the synthesis and transfer of chemical-vapor-deposited graphene on a target substrate, local inhomogeneities in the graphene-in particular, a nonuniform strain field in the graphene template-can easily form, causing poor morphology and crystallinity of the OSC thin films. Moreover, a strain field in graphene introduces a pseudo-electric field in the graphene. Here, the study investigates how the strain and strain-induced pseudo-electric field of a graphene template affect the self-assembly of π-conjugated organic molecules on it. Periodically strained graphene templates are fabricated by transferring graphene onto an array of nanospheres and then analyzed the growth and nucleation behavior of C60 thin films on the strained graphene templates. Both experiments and a numerical simulation demonstrated that strained graphene reduced the desorption energy between the graphene and the C60 molecules and thereby suppressed both nucleation and growth of the C60. A mechanism is proposed in which the strain-induced pseudo-electric field in graphene modulates the binding energy of organic molecules on the graphene.

Improved optical performance of CH3NH3PbI3 perovskite-germanium heterostructure photodetectors assisted by a periodic nanosphere array

The methylammonium lead iodide (CH3NH3PbI3)-germanium (Ge) heterojunction with a layer of periodic nanospheres was numerically studied to achieve improved performance over broadband from 300 nm to 1600 nm by the 3D finite element method (FEM). Under AM 1.5 g illumination, the total absorbed power increased 14% in heterojunction photodetectors assisted by an Al2O3 antireflection (AR) array, after optimizing the thickness of perovskite and Ge, as well as the radius, period and material type (metal or dielectric permittivity) of nanosphere array by genetic algorithm, with reference to a corresponding device without nanospheres. The enhanced optical properties were further elaborated and demonstrated by comparatively analyzing broadband absorptance, electric field distributions, absorbed power distributions and the optical generation rate of charge carriers in the two photodetector models. The proposed perovskite-Ge heterojunction with spheres shows great promise for optoelectronic devices.

Contractible Plasmonic Nanospheres Array with Dynamically Tailorable Gap Size for Molecule Trapping and Sensitive SERS Detection

AbstractSurface‐enhanced Raman spectroscopy (SERS) is a powerful analysis technique, and the SERS sensitivity is strongly dependent on metallic nanogaps with a greatly enhanced local electromagnetic field (i.e., hot spots). Once the analytes are located in the hot spot region, their Raman signals are enormously amplified. However, delivering analytes into such tiny hot spots remains a great challenge, particularly for molecules with small Raman scattering cross‐sections and no metal affinity. Here, by employing the isotropic contraction characteristics of polyvinyl chloride (PVC) when heated, a molecule trapping and SERS sensing strategy is demonstrated based on a large‐area ordered gold‐coated polystyrene nanospheres (PS@Au NSs) array with well‐controlled gap size assembled on PVC sheet. Compared with the traditional contraction‐adsorption mode, the developed adsorption‐contraction mode enables efficient delivery of analytes with or without metal affinity into the hot spots between the PS@Au NSs, leading to a significantly improved SERS performance with a large SERS enhancement factor of ≈3.57 × 107. The contractible SERS substrate exhibits a high sensitivity of 10−12 m for rhodamine 6G (R6G), 10−10 m for thiram, and 5 × 10−6 m for 2,3,4‐trichlorobiphenyl, as well as good signal reproducibility with relative standard deviations of 2.81% and 4.25% for R6G and thiram, respectively.

Inverse design of a light nanorouter for a spatially multiplexed optical filter.

It is attractive to use an optical nanorouter by artificial nanostructures to substitute the traditional Bayer filter for an image array sensor, which, however, poses great challenges in balancing the design strategy and the ease of fabrication. Here, we implement and compare two inverse design schemes for rapid optimization of RGGB Bayer-type optical nanorouter. One is based on the multiple Mie scattering theory and the adjoint gradient that is applicable to arrays of nanospheres with varying sizes, and the other is based on the rigorous coupled wave analysis and the genetic algorithm. In both cases, we study layered nanostructures that can be efficiently modeled respectively which greatly accelerates the inverse design. It is shown that the color-dependent peak collection efficiencies of nanorouters designed in the two methods for red, green, and blue wavelengths reach 37%, 44%, and 45% and 52%, 50%, and 66%, respectively. We further demonstrate color nanorouters that provide light focusing to four quadrants working in both the visible and infrared bands, which promises multispectral imaging applications.

Dielectric light-trapping nanostructure for enhanced light absorption in organic solar cells

Dielectric scatterers where Mie resonances can be excited in both electric and magnetic modes have emerged as a promising candidate for efficient light trapping (LT) in thin-film solar cells. We present that light absorption in organic solar cells (OSCs) can be significantly enhanced by a front-sided incorporation of a core–shell nanostructure consisting of a high-refractive-index dielectric nanosphere array conformally coated with a low-refractive-index dielectric layer. Strong forward light scattering of the all-dielectric LT structure enables the absorption in an organic semiconductor to be remarkably boosted over a broad range of wavelengths, which is attributed to interference of a simultaneous excitation of the electric and magnetic dipole resonant modes. The OSC with the LT structure shows the short-circuit current density (Jsc) of 28.23 mA/cm2, which is 10% higher than that of a flat OSC. We also explore how the LT structure affects scattering cross-sections, spectral multipole resonances, and far-field radiation patterns. The approach described in this work could offer the possibility for the improvement of characteristic performances of various applications, such as other thin-film solar cells, photodiodes, light-emitting diodes, and absorbers.

Silver nanosphere array substrates fabricated by glancing angle deposition: Morphology, hot spots and SERS properties

The generation and exploitation of hot spots play a crucial role in the fabrication of highly sensitive surface-enhanced Raman scattering (SERS) substrates. In this work, silver nanosphere (AgNS) array substrates with various morphologies of polystyrene (PS) core/Ag shell were fabricated by reactive ion etching and glancing angle deposition technique on PS sphere templates. The electromagnetic field distribution (hot spots) of AgNS array was calculated by the finite difference time domain method. R6G and MB were used as probe molecules to investigate the effect of structure spacing on electric field enhancement. Under 785 nm excitation, an AgNS substrate with a gap of approximately 20 nm exhibited the best SERS enhancement, and the limit of detection reached 5 × 10−8 M for both analytes. For R6G and MB, the relative standard deviations (RSDs) were 2.39 % and 7.22 %, and the enhancement factors (EFs) were 7.25 × 108 and 7.68 × 107, respectively. These results serve as a reference for the development of new highly sensitive SERS sensors.

Multiple surface lattice resonances of overlapping nanoparticle arrays with different lattice spacing.

Multiple surface lattice resonances generated with nanoparticle arrays are promising to enhance light-matter interactions at different spectral positions simultaneously, and it is important to tailor these resonances to desired frequencies for practical applications such as multi-modal nanolasing. To this end, this study proposes to generate multiple surface lattice resonances using overlapping nanoparticle arrays with different lattice spacing. Both full-wave numerical simulations and analytical coupled dipole approximation calculations reveal that for the overlapping structures composed with two different gold nanosphere arrays, both surface lattice resonances for the element structures are effectively excited. Considering that the optical responses are governed by the dipole-dipole interactions between the nanoparticles, it is interesting to find that the multiple surface lattice resonances are almost invariant by adjusting the relative shifts between the two arrays, which can be useful to tailor the high-quality factor resonances to desired spectral positions. In addition, due to the same reason, it is also shown that the multiple surface lattice resonances can be further finely tuned by selectively removing specific nanoparticles in the array. We anticipate that the tolerance to generate multiple surface lattice resonances and the flexible tunability make the overlapping nanoparticle arrays useful to design high performance linear and nonlinear nanophotonic devices.

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

Bloch point nanospheres for the design of magnetic traps

Through micromagnetic simulations, this work analyzes the possibility of using an array of magnetic nanospheres hosting Bloch points (BPs) to compose a system with the features of a magnetic trap (MT). We show that a BP can be nucleated as a metastable configuration in a wide range of the nanosphere radius compared to a quasi-uniform and vortex state. We also show that the stabilized BP generates a quadrupolar magnetic field outside the nanosphere. Based on this fact, we analyze the field profile of different arrays of these nanospheres, showing that the obtained magnetic field profiles share the needed features to compose MTs. Some highlights of using an array of Bloch point nanospheres in MTs rely on the magnetic field gradients achieved, which are orders of magnitude higher than similar standard systems, and allow three-dimensional trapping. Our results could be useful in trapping particles through the intrinsic magnetization of ferromagnetic nanoparticles while avoiding the commonly used mechanisms associated with Joule heating.

Ultra-narrowband, electrically switchable, and high-efficiency absorption in monolayer graphene resulting from lattice plasmon resonance

We propose a novel approach to obtain the ultra-narrowband, electrically switchable, and high-efficiency absorption in the monolayer graphene. The monolayer graphene is sandwiched between the silica substrate and a square array of silver nanospheres, which is covered by a very thick silica layer. The fundamental role of the thick silica cover layer is to homogenize the surrounding medium of the silver nanospheres, and thus efficiently exciting the lattice plasmon resonance. The lattice plasmon resonance arising from the coupling between the dipolar plasmon resonance of silver nanospheres and the zero-order diffraction wave at Wood anomaly can enhance the electromagnetic fields at the graphene surface, and thus greatly improve the near-infrared light absorption of the monolayer graphene with the maximum absorption efficiency up to 45%. Owing to the low radiation loss of the lattice plasmon resonance, the absorption linewidth of the monolayer graphene can be largely compressed to only several nanometers (3.2 nm ∼ 7.4 nm). Moreover, the absorption of the monolayer graphene in our proposed nanostructures has a nearly 100% modulation depth to exhibit an excellent switching property. Our work will be helpful for some graphene-based photoelectric devices.

Arrays of TiO2 Nanosphere Monolayers on GaN-Based LEDs for the Improvement of Light Extraction

We report on the fabrication of TiO2 nanosphere (NS) monolayer arrays for the enhancement of light extraction quantum efficiency of GaN-based light-emitting diodes (LEDs). The fabricated TiO2 NSs monolayer arrays were composed of different phases of anatase (An-) and amorphous (Am-) TiO2. The arrays were transferred onto the topmost layer of LED chips via the facile icing transfer method. The LED chips covered with Am-TiO2 NS monolayer arrays showed 3.0- times enhanced light output power intensity compared with reference LED chips at a fixed injection current of 100 mA. The enhanced light extraction of LED chips by an Am-TiO2 NS monolayer can be attributed to a high transmittance (91.1%) in visible and increased light extraction probability of photons generated in LEDs, resulting from the enhanced light coupling efficiency by reduced total internal reflection (TIR). Finite-difference time-domain (FDTD) simulation results also agreed well with the experimentally observed results. Based on the experimental and theoretical results, our suggested Am- and An-TiO2 NS arrays can be considered a very facile and effective method to improve the device performance of various visible LED chips.

Promoted photocatalytic hydrogen evolution via double-electron migration in Ag@g-C3N4 heterojunction

The unsaturated edge Ag introduced on the surface of photocatalysts plays an important role in boosting photo-excited electrons for the photoreduction H2O reaction. However, a moderate and tractable strategy to efficiently expose edge Ag remains an enormous challenge. For this purpose, a core skeleton with ‘Ag conductive nanosphere array’ inside and a two-dimensional sheet structure with g-C3N4 layer outside are formed. The introduction of Ag nanospheres into g-C3N4 not only enlarges the distance between g-C3N4 nanolayers, but also increases the exposure of Ag nanospheres. When Ag intimately contacts with g-C3N4, the electrons of g-C3N4 voluntarily flow to the Ag. Consequently, a built-in electric field (IEF) has been formed at interface of Ag@g-C3N4 heterojunction, which prevents the continuous flow of electrons from g-C3N4 to Ag. Under irradiation, the e− accumulated in Ag tend to recombine with the h+ in the valence band of g-C3N4 which is driven by Coulomb interaction and IEF. Ag nanospheres are fabricated as a co-catalyst to decorate the g-C3N4 nanolayer, which hinder the conglomeration of g-C3N4 nanolayers. Moreover, Ag@g-C3N4 heterojunction provides polyunsaturated edge Ag as active sites, inducing prolonged lifetime of photogenerated electrons and formed the unique charge transfer channels. In addition, abundant nitrogen vacancies are formed, which strengthens the chemisorption of H2O. As a result, supreme Ag@g-C3N4 realizes a high H2 evolution of 312.5 μmol and preserves a good sustainability. This paper emphasizes the importance of unique electron transfer pathway and chemisorption of water for photoreduction H2O.