Self-assembled Arrays Research Articles

Silk fibroin-based wearable SERS biosensor for simultaneous sweat monitoring of creatinine and uric acid

Sweat biomarkers have the potential to offer valuable clinical insights into an individual's health and disease condition. Current sensors predominantly utilize enzymes and antibodies as biometric components to measure biomarkers present in sweat quantitatively. However, enzymes and antibodies are susceptible to interference by environmental factors, which may affect the performance of the sensor. Herein, we present a wearable microfluidic surface-enhanced Raman scattering (SERS) biosensor that enables the non-invasive and label-free detection of biomarkers in sweat. Concretely, we developed a bimetallic self-assembled anti-opal array structure with uniform hot spots, enhanced the Raman scattering effect, and integrated it into a silk fibroin-based sensing patch. Utilizing a silk fibroin substrate in the wearable SERS sensor imparts desirable properties such as softness, breathability, and biocompatibility, which enables the sensor to establish close contact with the skin without causing chemical or physical irritation. In addition, introducing microfluidic channels enables the controlled and high temporal resolution management of sweat, facilitating more efficient sweat collection. The proposed label-free SERS sensor can offer chemical ‘fingerprint’ information, enabling the identification of sweat analytes. As an illustration of the feasibility, we have effectively monitored the creatinine and uric acid levels in sweat. This study presents a versatile and highly sensitive approach for the simultaneous detection of biomarkers in human sweat, showcasing significant potential for application in point-of-care monitoring.

Interface Engineering Induced Multi-Scale Self-Assembly NiFe-LDH Heterostructures for High-Performance Water Electrolysis.

Confronted with the pressing issue of energy scarcity, the development of an economical and potent bifunctional catalyst is of paramount importance. We adopt an interface engineering strategy to modify the surface of NiFe-LDH nanoplates with O2 plasma treatment. This process enhances the local electric field of NiFe-LDH, resulting in the formation of a self-assembled polycrystalline nanowire array on the nanoplate surface. After O2 plasma treatment for 30 min, the NiFe-LDH-P30 not only formed a heterostructure with rough surface, but also regulated the exposure of crystal surfaces. Due to the strong interface coupling between the self-assembled 3D nanoflowers, 2D nanoplates and 1D nanowires, the NiFe-LDH-P30 exhibits an excellent structural stability. Moreover, it demonstrated exceptional HER and OER activities in alkaline condition, achieving a low overpotentials of 154 mV and 242 mV at 10 mA cm-2, respectively. Furthermore, NiFe-LDH-P30 as the dual-electrode material for the cathode and anode in the process of water splitting results in a low voltage of 1.63 V at a current density of 10 mA cm-2. Through the strategic application of interface engineering, this work has pioneered a novel approach to the creation of transition metal-based electrocatalysts, which is benefit to a range of practical energy applications.

Demonstration of extrinsic chirality in self-assembled asymmetric plasmonic metasurfaces and nanohole arrays

Chirality, the lack of mirror symmetry, can be mimicked in nanophotonics and plasmonics by breaking the symmetry in light-nanostructure interaction. Here we report on versatile use of nanosphere lithography for the fabrication of low-cost metasurfaces, which exhibit broadband handedness- and angle-dependent extinction in the near-infrared range, thus offering extrinsic chiro-optical behavior. We measure wavelength and angle dependence of the extinction for four samples. Two samples are made of polystyrene nanospheres asymmetrically covered by silver and gold in one case and silver only in the other case, with a nanohole array at the bottom. The other two samples are nanohole arrays, obtained after the nanosphere removal from the first two samples. Rich extrinsic chiral features are governed by different chiro-optical mechanisms in the three-dimensional plasmonic semi-shells and planar nanohole arrays. We also measure Stokes parameters in the same wavelength and incidence angle range and show that the transmitted fields follow the extrinsic chirality features of the extinction dissymmetry. We further study the influences of the nanostructured shapes and in-plane orientations on the intrinsic vs extrinsic chirality. The nanoholes are modelled as oval shapes in metal, showing good agreement with the experiments. We thus confirm that nanosphere lithography can provide different geometries for chiral light manipulation at the nanoscale, with the possibility to extend functionalities with optimized oval shapes and combination of constituent metals.

High-Power Impulse Magnetron Sputter Deposition of Ag on Self-Assembled Au Nanoparticle Arrays at Low-Temperature Dewetting Conditions.

Plasmons have facilitated diverse analytical applications due to the boosting signal detectability by hot spots. In practical applications, it is crucial to fabricate straightforward, large-scale, and reproducible plasmonic substrates. Dewetting treatment, via applying direct thermal annealing of metal films, has been used as a straightforward method in the fabrication of such plasmonic nanostructures. However, tailoring the evolution of the dewetting process of metal films poses considerable experimental complexities, mainly due to nanoscale structure formation. Here, we use grazing-incidence small- and wide-angle X-ray scattering for the in situ investigation of the high-power impulse magnetron sputter deposition of Ag on self-assembled Au nanoparticle arrays at low-temperature dewetting conditions. This approach allows us to examine both the direct formation of binary Au/Ag nanostructure and the consequential impact of the dewetting process on the spatial arrangement of the bimetallic nanoparticles. It is observed that the dewetting at 100 °C is sufficient to favor the establishment of a homogenized structural configuration of bimetallic nanostructures, which is beneficial for localized surface plasmon resonances (LSPRs). The fabricated metal nanostructures show potential application for the surface-enhanced Raman scattering (SERS) detection of rhodamine 6G molecules. As SERS platform, bimetallic nanostructures formed with dewetting conditions turn out to be superior to those without dewetting conditions. The method in this work is envisioned as a facile strategy for the fabrication of plasmonic nanostructures.

Enhancing Methane Gas Sensing through Defect Engineering in Ag-Ru Co-doped ZnO Nanorods.

Detection of leaks of flammable methane (CH4) gas in a timely manner can mitigate health, safety, and environmental risks. Zinc oxide (ZnO), a polar semiconductor with controllable surface defects, is a promising material for gas sensing. In this study, Ag-Ru co-doped into self-assembled ZnO nanorod arrays (ZnO NRs) was prepared by a one-step hydrothermal method. The Ag-Ru co-doped sample shows a good hydrophobic property as a result of its particular microstructure, which results in high humidity resistance. In addition, oxygen vacancy density significantly increased after Ag-Ru co-doping. Density functional theory (DFT) calculations revealed an exceptionally high charge density accumulated at the Ru sites and the formation of a localized strong electric field, which provides additional energy for the CH4 reaction with •O2- at the surface at room temperature. Optimized AgRu0.025-ZnO demonstrated an outstanding CH4 sensing performance, with a limit of detection (LOD) as low as 2.24 ppm under free-heat and free-light conditions. These findings suggest that introducing defects into the ZnO lattice, such as oxygen vacancies and localized ions, offers a promising approach to improving the gas sensing performance.

Transformative Dynamics: Self-Assembly of Iron Oxide Hydroxide Nanorods into Iron Oxide Microcubes for Enhanced Perfluoroalkyl Substance Remediation.

We report the controlled synthesis of iron oxide microcubes (IOMCs) through the self-assembly arrays of ferric oxide hydroxide nanorods (NRs). The formation of IOMCs involves a complex interplay of nucleation, self-assembly, and growth mechanisms influenced by time, thermal treatment, and surfactant dynamics. The self-assembly of vertically aligned NRs into IOMCs is controlled by dynamic magnetism properties and capping agents like cetyltrimethylammonium bromide (CTAB), whose concentration and temperature modulation dictate growth kinetics and structural uniformity. These controlled structural growths were obtained via a hydrothermal process at 120 °C at various intervals of 8, 16, 24, and 32 h in the presence of CTAB as the capping agent. In this hydrothermal method, the formation of vertically oriented NR arrays was observed without the presence of ligands, binders, harsh drying techniques, and solvent evaporation. The formation of the self-assembly of NRs to IOMCs is obtained with an increase in saturated magnetization to attain the most stable state. The synthesized IOMCs have a uniform size, quasi-shape, and excellent dispersion. Due to its excellent magnetic and catalytic properties, IOMCs were employed to remove the various emerging pollutants known as per- and polyfluorinated substances (PFAS). Various microscopic and spectroscopic techniques were employed for the characterization and interaction studies of IOMCs with various PFAS. The interaction between IOMCs and perfluoroalkyl substances (PFAS) was investigated, revealing strong adsorption tendencies facilitated by electrostatic interactions, as evidenced by UV-vis and FT-IR spectroscopic studies. Furthermore, the higher magnetic and positive surface charge of IOMCs is responsible for an effective remediation eliminating any secondary pollution with ease of recovery after the sorption interaction studies, thereby making it practically worthwhile.

Design and synthesis of new water-soluble dinuclear manganese(II) complexes as monosaccharide binding models

The present article describes the design, synthesis, physicochemical characterization and monosaccharide binding events of two new water-soluble dinuclear manganese(II) complexes [Mn2(phpda)(µ-Cl)]·2H2O (1) and [Mn2(phpda)(µ-OAc)]·2H2O (2) of carboxylate and pyridyl-functionalized multidentate ligand, H3phpda (H3phpda = N,N′-bis[2-pyridylmethyl]-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid). FTIR, UV–Vis, ESI-MS, microanalysis, molar conductivity, cyclic voltammetry and room-temperature magnetic data establish their compositions. Structural features of 1 and 2 obtained from theoretical calculations indicate a self-assembled and well-packed array with average Mn···Mn separation of 2.952 Å. Both 1 and 2 have been studied towards 1:1 binding interactions with biologically important monosaccharides, such as d-glucose, d-xylose and d-glucosamine by employing UV–Vis spectroscopy and DFT computation. The binding constant values of monosaccharide-bound manganese(II) complexes evaluated from UV–Vis titration data are 2.145 x 103 M−1, 2.156 x 103 M−1, 2.652 x 103 M−1, 1.388 x 103 M−1, 1.793 x 103 M−1 and 2.146 x 103 M−1 for 1/d-glucose, 1/d-xylose, 1/d-glucosamine, 2/d-glucose, 2/d-xylose and 2/d-glucosamine assemblies, respectively. The possible metal centers engaged in the binding events have been ascertained by calculating the Fukui functions (fk+) on the manganese sites, including HOMOs and LUMOs. A comparative assessment of sugar-binding properties, in particular, suggests that the order of binding ability of monosaccharides with 1 and 2 is found to be d-glucosamine > d-xylose > d-glucose.

Tunable polarization control with self-assembled arrays of anisotropic plasmonic coaxial nanocavities

Polarization control with nanostructures having a tunable design and allowing inexpensive large-scale fabrication is important for many nanophotonic applications. For this purpose, we developed and experimentally demonstrated nanostructured plasmonic surfaces based on hexagonal arrays of anisotropic coaxial nanocavities, which can be fabricated by a low-cost self-assembled nanosphere lithography method. Their high polarization sensitivity is achieved by engineering anisotropy of the coaxial nanocavities, while the optical response is enhanced by the excitation of surface plasmon resonances. Particularly, varying the geometrical parameters of the coaxial nanocavities, namely the height and tilt angle of their central core nanoellipsoids, the plasmonic resonance wavelengths as well as the polarization-selective behavior can be individually tuned in the entire visible and near-infrared spectral regions, which makes such nanostructures good candidates for the implementation of polarization-controlled optical switches and polarization-tunable filters. Moreover, the developed nanostructures demonstrate sensitivity up to 1335 nm/RIU in refractive index sensing.

3D sodiophilic mixed-ion-electron-conducting framework of hierarchical nanowire arrays for ultra-stable sodium-metal batteries

Sodium metal batteries (SMBs) have attracted increasing attentions as next-generation energy storage systems, regarding its high energy density and raw materials abundance. However, its practical application is impeded by the inferior reversibility of Na anode, stemmed from the non-uniform Na plating/stripping process and formation of “dead Na”. Herein, a three-dimensional (3D) mixed-ion-electron-conducting scaffold (MIECS) is in-situ established by self-assembled hierarchical Cu2S nanowire arrays, which renders enhanced sodiophilicity, high surface area, and robust architecture to the current collector, thereby promoting interfacial kinetics, homogenizing Na deposition, and ensuring “top-down” dissolution. As a result, Cu2S NWs@Cu MIECS enabled Na metal anode with exceptional Coulombic efficiency as high as 99.94 % over 1600 cycles at 4 mA cm−2, as well as steady plating/stripping profile for at least 2000 h at depth of discharge of 75 %. Impressively, full-cell SMB achieves ultra-stable cycling of 2000 cycles, exhibiting capacity retention as high as 96.3 % at high cathode loading of 14.7 mg cm−2, or that of 87.8 % at 5 C, with limited Na excess (N/P = 3). The 3D sodiophilic Cu2S NWs@Cu MIECS provides a promising route to highly reversible Na metal anode for developing high-energy-density SMBs.

Ultra-low detection limit self-sensing nanocomposites with self-assembled conductive microsphere arrays for asphalt pavement health monitoring

Accurately monitoring micro-level strain within pavements poses a significant challenge in contemporary road engineering, limiting the effectiveness of early-stage pavement health diagnostics. Addressing this critical gap, this study introduces an innovative ultra-low detection limit sensor, specifically designed for intricate pavement health monitoring. It pivots on the unique structural design of a well-ordered 3D conductive network, where the self-assembly effect of microsphere arrays ingeniously mitigates the prevalent issue of nanofiller agglomeration within polymer matrices. The study highlights the significant role of carbon nanotubes (CNTs) length in shaping the structure of conductive networks, revealing that while longer CNTs lead to less uniform microsphere assemblies, they significantly enhance the bridging effect crucial for conductive pathways. To balance these traits, surface chemical modifications were strategically applied, effectively enhancing microsphere organization and dispersion, thereby elevating the conductive and sensing performance. The optimized sensor stands out for the ultra-low detection limit of 0.0005% (5 uε), significantly surpassing those of current strain sensors. Moreover, it exhibits remarkable sensitivity, evidenced by a gauge factor of 13.2, along with swift response and recovery times of 19 ms and 26 ms respectively, and impressive durability, enduring over 100,000 loading-unloading cycles. Field tests under diverse vehicular loads and speeds further validate the sensor's accuracy in capturing dynamic responses within pavement structures, a key factor in proactive pavement maintenance and management. Hence, this advancement shows promise in contributing to the development of safer and more resilient road networks, playing a beneficial role in the significant progress of intelligent transportation and sustainable infrastructure management.

Lead-free perovskite Cs2AgBiBr6 photodetector detecting NIR light driven by titanium nitride plasmonic hot holes

Lead-free perovskite Cs2AgBiBr6 manifests great potential in developing high-performance, environmentally friendly, solution-processable photodetectors (PDs). However, due to the relatively large energy bandgap, the spectrum responses of Cs2AgBiBr6 PDs are limited to the ultraviolet and visible region with wavelengths shorter than 560 nm. In this work, a broadband Cs2AgBiBr6 PD covering the ultraviolet, visible, and near infrared (NIR) range is demonstrated by incorporating titanium nitride (TiN) nanoparticles that are prepared with the assistance of self-assembled polystyrene sphere array. In addition, an atomically thick Al2O3 layer is introduced at the interface between the Cs2AgBiBr6 film and TiN nanoparticles to alleviate the dark current deterioration caused by nanoparticle incorporation. As a result, beyond the spectrum range where Cs2AgBiBr6 absorbs light, the external quantum efficiency (EQE) of the TiN nanoparticle incorporated Cs2AgBiBr6 PD is enhanced significantly compared with that of the control, displaying enhancement factors as high as 2000 over a broadband NIR wavelength range. The demonstrated enhancement in EQE arises from the photocurrent contribution of plasmonic hot holes injected from TiN nanoparticles into Cs2AgBiBr6. This work promotes the development of broadband solution-processable perovskite PDs, providing a promising strategy for realizing photodetection in the NIR region.

Rational construction of MOF-on-MOF heterojunction with an array of flexible two-dimensional microsheets for efficient CO2 photoreduction

MOF-on-MOF composites are deemed promising candidates to accomplish synergistic CO2 capture and photoreduction thanks to their plentiful active sites, extended light response range, timely separation of photoexcited electron-hole pairs, and large CO2 adsorption capacities. Unfortunately, the controllable growth of the designed MOF-on-MOF heterostructure is challenging. Deficient interphase contact and the consequent mass transfer deprivation is one of the primary obstacles severely impairing the catalytic efficiency. Herein, the contact between two widely-employed MOFs of Ni-BDC and NH2-MIL-125 was significantly strengthened by exploiting a self-assembled array of Ni-BDC microsheets. In contrast to the spontaneously formed spheroidal aggregate, the loosely-packed array exhibits amplified accessible surfaces to interact with NH2-MIL-125, contributing to a radically improved interfacial built-in electric field and 7∼9 times rises in the product yields. Moreover, the preferably thin thickness of Ni-BDC microsheets prompts its macroscopic flexibility, permitting intensified deformation for enhanced interphase contact. Coupled with the additional contribution from its copious Lewis acid sites, the developed NH2-MIL-125@Ni-BDC array simultaneously converted CO2 into CO and CH4 at rates that cannot be matched by its isostructural Co counterpart with declined acidity and flexibility. This work innovatively reveals the immense importance of morphology tailoring and assembly tactic to interphase contact modulation and the upgrade of catalyst performances.

Self-Assembled Nanostructures Presenting Repetitive Arrays of Subunit Antigens for Enhanced Immune Response.

Infectious diseases pose persistent threats to public health, demanding advanced vaccine technologies. Nanomaterial-based delivery systems offer promising solutions to enhance immunogenicity while minimizing reactogenicity. We introduce a self-assembled vaccine (SAV) platform employing antigen-polymer conjugates designed to facilitate robust immune responses. The SAVs exhibit efficient cellular uptake by dendritic cells (DCs) and macrophages, which are crucial players in the innate immune system. The high-density antigen presentation of this SAV platform enhances the affinity for DCs through multivalent recognition, significantly augmenting humoral immunity. SAV induced high levels of immunoglobulin G (IgG), IgG1, and IgG2a, suggesting that mature DCs efficiently induced B cell activation through multivalent antigen recognition. Universality was confirmed by applying it to respiratory viruses, showcasing its potential as a versatile vaccine platform. Furthermore, we have also demonstrated strong protection against influenza A virus infection with SAV containing hemagglutinin, which is used in influenza A virus subunit vaccines. The efficacy and adaptability of this nanostructured vaccine present potential utility in combating infectious diseases.

Designing 2D stripe winding network through crown-ether intermediate Ullmann coupling on Cu(111) surface.

Chemical synthesis typically yields the most thermodynamically stable ordered arrangement, a principle also governing surface synthesis on an atomically level two-dimensional (2D) surface, fostering the creation of structured 2D formations. The linear connection arising from energetically stable chemical bonding precludes the generation of a 2D random network comprised of one-dimensional (1D) convoluted stripes through on-surface synthesis. Nonetheless, we underscored that on-surface synthesis possesses the capability not solely to fashion a 2D ordered linear network but also to fabricate a winding 2D network employing a precursor with a soft ring and intermediate state bonding within the Ullmann reaction. Here, on-surface synthesis was exhibited on Cu(111) employing a 2D self-assembled monolayer array of 4,4',5,5'-tetrabromodibenzo[18]crown-6 ether (BrCR) precursors. These precursors were purposefully structured, with a crown ether ring at the core and Br atoms positioned at the head and tail ends, facilitating preferential connections along the elongated axis to foster a 1D stripe configuration. We illustrate how adjustments in the quantities of the intermediate state, serving as a primary linkage, can yield a labyrinthine, convoluted winding 2D network of stripes. The progression of growth, underlying mechanisms, and electronic structures were scrutinized using an ultrahigh vacuum low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) setup combined with density functional theory (DFT) calculations. This experimental evidence opens a novel functionality in leveraging on-surface synthesis for the formation of a 2D random network. This discovery holds promise as a pioneering constituent in the construction of a ring host supramolecule, augmenting its capability to ensnare guest atoms, molecules, or ions.

Fabrication strategies and microscale sensing functionalities of mechanochromic colloidal photonic crystals for underwater applications

Mechanochromic colloidal photonic crystals (PCs), which typically integrate a self-assembled PC array with highly elastic medium, exhibit the ability to reversibly respond to external mechanical stimuli by altering the periodicity of PC structures. Nowadays, leveraging visible indications and optical signals for mechanical forces, mechanochromic colloidal PCs have been widely used in reflecting body motion, health monitoring, and communications in daily life. However, despite their extensive applications on land, it is vital to explore the potential of mechanochromic sensing applications under water, where message transmission mainly relies on body gestures and motions. This review comprehensively examines recent advancements in mechanochromic colloidal PCs and their underwater applications. The first part introduces the response mechanism of mechanochromic colloidal PCs, emphasizing the main principles that facilitate sensing on the micro scale. The second part describes the fabrication strategies for constructing mechanochromic colloidal PCs, demonstrating various approaches to establish optical sensors with specific functionalities. The final section discusses the confronted challenges and summarizes the potential opportunities in developing mechanochromic colloidal PCs for underwater sensing applications.

Liquid Interfacial Coassembly of Plasmonic Arrays and Trace Hydrophobic Nanoplastics in Edible Oils for Robust Identification and Classification by Surface-Enhanced Raman Spectroscopy.

The ubiquity of micro-/nanoplastics poses a visible threat to the environment, aquatic organisms, and human beings and has become a global concern. Here, we proposed a liquid interface-based strategy using surface-enhanced Raman spectroscopy to coassemble nanoplastics and gold nanoparticles into a dense and homogeneous plasmonic array, thereby enabling the rapid and sensitive detection of trace nanoplastics. In addition, due to the uniqueness of the oil-water immiscible two-phase interface, we achieved ideal results for the detection of nanoplastics in a complex matrix (e.g., aqueous environment and edible oil) with a detection limit of μg/mL. With the aid of the principal component analysis algorithm, the differentiation and identification of multiple nanoplastic components (e.g., polystyrene, polyethylene, and polyethylene terephthalate) in aqueous environments and common hazards (e.g., Bap and Phe) in edible oil were achieved. Therefore, our self-assembled plasmonic arrays are expected to be used for monitoring environmental pollution and food safety.

Shrinking gap between nanoparticles in gold nanofilms to enhance Surface-Enhanced Raman Spectroscopy performance investigated by both experimental and theoretical methods

Sensitive and reliable interfacial self-assembled nanomembranes are widely used for the detection of chemical contaminants in food and environment. This study developed a high-performance Surface-Enhanced Raman Spectroscopy (SERS) analytical platform by self-assembling Au nanoparticles (AuNPs) at the three-phase liquid–liquid interface. The assembled nanoparticles arrays were immersed in halogen ions solution and the nanoparticle gaps were further shrunk through electrostatic interactions, resulting in a large-scale array of closely packed nanoparticles. The average gap between adjacent nanoparticles was less than 3 nm, where dense SERS ‘hot spots’ were generated and used for highly sensitive detection. The homogeneity of the self-assembled nanoparticle arrays under different conditions was still guaranteed despite the reduced integration time and the number of times in the mapping face sweep of the Au arrays. The improved high-throughput fabrication of self-assembled nanoparticle arrays in this way holds great promise for the development of a sensitive and reliable SERS platform for chemical contaminant monitoring.

Mold-free self-assembled scalable microlens arrays with ultrasmooth surface and record-high resolution

Microlens arrays (MLAs) based on the selective wetting have opened new avenues for developing compact and miniaturized imaging and display techniques with ultrahigh resolution beyond the traditional bulky and volumetric optics. However, the selective wetting lenses explored so far have been constrained by the lack of precisely defined pattern for highly controllable wettability contrast, thus limiting the available droplet curvature and numerical aperture, which is a major challenge towards the practical high-performance MLAs. Here we report a mold-free and self-assembly approach of mass-production of scalable MLAs, which can also have ultrasmooth surface, ultrahigh resolution, and the large tuning range of the curvatures. The selective surface modification based on tunable oxygen plasma can facilitate the precise pattern with adjusted chemical contrast, thus creating large-scale microdroplets array with controlled curvature. The numerical aperture of the MLAs can be up to 0.26 and precisely tuned by adjusting the modification intensity or the droplet dose. The fabricated MLAs have high-quality surface with subnanometer roughness and allow for record-high resolution imaging up to equivalently 10,328 ppi, as we demonstrated. This study shows a cost-effective roadmap for mass-production of high-performance MLAs, which may find applications in the rapid proliferating integral imaging industry and high-resolution display.

V6O13 Micro-Flower Arrays Grown In Situ on Ni Foam as Efficient Electrocatalysts for Hydrogen Evolution at Large Current Densities

Developing a high-activity, robust and economic electrocatalyst for large-scale green hydrogen production is still of great significance. Herein, a novel V6O13 nanosheets self-assembled micro-flower array self-supporting electrode is synthesized using a facile one-pot hydrothermal route. Owing to the large electrochemically active surface area of a unique hierarchical micro-flower and the stable all-in-one structure, the as-prepared V6O13/NF electrode delivers impressive HER activity with extremely low overpotentials of 125 and 298 mV at large current densities of 100 and 1000 mA cm−2, respectively, and a long-term durability for at least 90 h in an alkaline condition. This work extends the application of vanadium oxides to the realm of electrocatalytic hydrogen fuel production.

Broadband, angle-dependent optical characterization of asymmetric self-assembled nanohole arrays in silver

Plasmonic nanostructured materials made of nanohole arrays in metal are significant plasmonic devices exhibiting resonances and strong electromagnetic confinement in the visible and near-infrared range. As such, they have been proposed for use in many applications such as biosensing and communications. In this work, we introduce the asymmetry in nanoholes, and investigate its influence on the electromagnetic response by means of broadband experimental characterization and numerical simulations. As a low-cost fabrication process, we use nanosphere lithography, combined with tilted silver evaporation, to obtain a 2D hexagonal array of asymmetric nanoholes in Ag. Our experimental set-up is based on a laser, widely tunable in the near-infrared range, with precise polarization control in the input and in the output. We next resolve the circular polarization degree of the transmitted light when the nanohole array is excited with linear polarization. We attribute the disbalance of left and right transmitted light to the asymmetry of the nanohole, which we support by numerical simulations. We believe that the optimization of such simple plasmonic geometry could lead to multifunctional flat-optic devices.