Metallic Nanostructures Research Articles

Universal Click-Chemistry Approach for the DNA Functionalization of Nanoparticles.

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the deoxyribonucleic acid (DNA) conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of nonmetallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate, and provide further functionality to nonmetallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of ∼0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric dimers with a yield of over 50% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell, and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.

Metallic nanostructures arrays by direct nanoimprinting of silver nanoparticles

The direct nanoimprinting of silver nanoparticles (Ag NPs) generated a plasmonic metallic nanostructure. The Ag NPs used in this study have been synthesized by a phase transfer method. The procedure comprised the utilisation of sodium borohydride to reduce silver nitrate in the presence of a stabilizing agent, which facilitated the transfer of the NPs from the aqueous phase to an organic phase, resulting in uniform and stable particles. The size and shape of the Ag NPs were characterized using electron microscopy, revealing spherical particles with an average diameter of 9 nm. The XRD examination revealed that the nanoparticles exhibit a high degree of crystallinity and possess a cubic geometric phase. The UV-visible absorption spectra demonstrate a significant level of homogeneity in the size. The silicon surface imprinted with Ag NPs exhibits hydrophobic behaviour towards water molecules. This approach allows for precise control of Ag NPs on the substrate, resulting in a robust and effective platform for future applications in sensor technology. Furthermore, the hydrophobic nature of the imprinted surface suggests potential applications in water-repellent coatings or self-cleaning materials.

Synthesis of Au@Ag core-shell nanorods with tunable optical properties.

The synthesis of noble metal nanostructures with adjustable optical properties is essential due to their potential applications in various fields such as imaging, (bio) sensors, and catalysis. In this study, Au@Ag core-shell nanorods were synthesized with tunable optical properties. The synthesis process includes a two-stage approach: first, gold nanorods were synthesized through seed-mediated growth, and in the second stage, these gold nanorods were used as seeds to synthesize Au@Ag core-shell nanorods through the silver deposition process. Tunable core-shell nanorods were produced by changing the concentration of silver ions, reducing agent, stabilizing agent, seeds, and buffer as well as pH and the reaction time. Transmission electron microscopy (TEM) images demonstrated the formation of the Au@Ag core-shell nanorod structure. In addition, UV-visible spectroscopy revealed the peak height and its shift towards shorter wavelengths, demonstrating the tunable optical properties of the synthesized nanorods. Overall, in this study, we demonstrated the synthesis of Au@Ag core-shell nanorods with adjustable plasmonic optical properties that could be changed by precisely controlling the thickness of the silver shell on the surface of the gold core.&#xD.

Memristive Control of Plasmon-Mediated Nonlinear Photoluminescence in Au Nanowires.

Nonlinear photoluminescence (N-PL) is a broadband photon emission arising from a nonequilibrium heated electron distribution generated at the surface of metallic nanostructures by ultrafast pulsed laser illumination. N-PL is sensitive to surface morphology, local electromagnetic field strength, and electronic band structure, making it relevant to probe optically excited nanoscale plasmonic systems. It also has been key to accessing the complex multiscale time dynamics ruling electron thermalization. Here, we show that plasmon-mediated N-PL emitted by a gold nanowire can be modified by an electrical architecture featuring a nanogap. Upon voltage activation, we observe that N-PL becomes dependent on the electrical transport dynamics and can thus be locally modulated. This finding brings an electrical leverage to externally control the photoluminescence generated from metal nanostructures and constitutes an asset for the development of emerging nanoscale interface devices managing photons and electrons.

Enhancing oxygen evolution reaction through self-reconstruction of 2D nanoarrays on nickel foam

The synthesis of nanostructured transition metal compounds with adjustable components are often challenging due to the involvement of multiple synthetic procedures or complex manipulations. In this work, a one-step self-regulating acid-etching strategy is employed for nickel iron-layered double hydroxide (NiFe LDH). A two-dimensional (2D) NiFe LDH nanosheet is speedy and efficiently formed. This as-prepared NiFe LDH exhibits electrocatalytic activity for oxygen evolution reaction (OER). This approach avoids numerous structural design challenges and provides highly active sites and a robust interface between catalyst and support. As a result, 2D NiFe LDH electrodes demonstrate highly efficient OER performance with a low overpotential of 300 mV and a Tafel slope of 70.6 mV dec−1 at a current density of 100 mA cm−2.

Ultrasensitive refractometric sensing via centimeter-scale metasurfaces with spatially gradient geometry generated by elastomer mechanical stretching.

Plasmonic metasurfaces with gradient geometry are emerging two-dimensional optical elements with unique capabilities, such as manipulating light by imparting local, space-variant phase changes to an incident electromagnetic wave, eliminating the chromatic aberration. However, the costly and time-consuming fabrication process and the requirement of sophisticated optical characterization instruments restrict practical applications of plasmonic metasurfaces. Herein, we present a novel nanofabrication method to generate centimeter-scale metasurface with spatially gradient geometry over the whole metasurface by directional stretching of a trapezoid elastic carrier patterned with regular metallic nanostructures. This strategy eases the requirement of time-consuming and expensive lithographic techniques in conventional methods. The spatially gradient plasmonic metasurface exhibit variable transmittances under monochromatic and polar light illumination, resulting in grayscale patterns with different transmittance intensity distributions. An ultrahigh imaging-based sensitivity of 1495 pixel/refractive index unit (RIU) and a detection limit of 0.00068 RIU can be achieved based on the spatially gradient plasmonic metasurface, which is superior to the performance of the regular metasurface before stretching. This novel strategy is expected to be promising for fabrication of gradient metasurfaces to be employed in many fields of nanophotonics.

Crucial Role of Metal Coordination Number in Optimizing Electrocatalyst Activity of Holey Large-Area 2D Ru Nanosheets.

Low-dimensional metal nanostructures have attracted considerable research attention, owing to their potential as catalysts. A controlled reductive phase transition of monolayer RuO2 nanosheets could provide an effective way to produce holey large-area 2D Ru nanosheets with tailored defect structures and metal coordination number. The locally optimized holey Ru metal nanosheet, with a metal coordination number of ∼10.2, exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) with a reduced overpotential of 38 mV in a 1 M KOH electrolyte. The creation of a highly anisotropic holey nanosheet morphology with optimization of local structure was quite effective in developing efficient catalyst materials. The universal importance of controlling the coordination number was confirmed through a comparative study of Ru nanoparticles, which showed optimized HER activity with an identical metal coordination number. The coordination number plays a pivotal role in governing electrocatalytic activity, which could be ascribed to the formation of the most active structure for HER at most 2 defects near active sites (2,2'), resulting in the stabilization of a dihydrogen Ru-(H2) intermediate and the increased contribution of Volmer-Tafel mechanism.

Supramolecular metallic foams with ultrahigh specific strength and sustainable recyclability

Porous materials with ultrahigh specific strength are highly desirable for aerospace, automotive and construction applications. However, because of the harsh processing of metal foams and intrinsic low strength of polymer foams, both are difficult to meet the demand for scalable development of structural foams. Herein, we present a supramolecular metallic foam (SMF) enabled by core-shell nanostructured liquid metals connected with high-density metal-ligand coordination and hydrogen bonding interactions, which maintain fluid to avoid stress concentration during foam processing at subzero temperatures. The resulted SMFs exhibit ultrahigh specific strength of 489.68 kN m kg−1 (about 5 times and 56 times higher than aluminum foams and polyurethane foams) and specific modulus of 281.23 kN m kg−1 to withstand the repeated loading of a car, overturning the previous understanding of the difficulty to achieve ultrahigh mechanical properties in traditional polymeric or organic foams. More importantly, end-of-life SMFs can be reprocessed into value-added products (e.g., fibers and films) by facile water reprocessing due to the high-density interfacial supramolecular bonding. We envisage this work will not only pave the way for porous structural materials design but also show the sustainable solution to plastic environmental risks.

Direct conversion of CO2 to CH4 on Pd/graphdiyne single-crystalline.

A major impediment to the development of the efficient use of artificial photosynthesis is the lack of highly selective and efficient photocatalysts toward the conversion of CO2 by sunlight energy at room temperature and ambient pressure. After many years of hard work, we finally completed the synthesis of graphdiyne-based palladium quantum dot catalysts containing high-density metal atom steps for selective artificial photosynthesis. The well-designed interface structure of the catalyst is composed of electron-donor and acceptor groups, resulting in the obvious incomplete charge-transfer phenomenon between graphdiyne and plasmonic metal nanostructures on the interface. These intrinsic characteristics are the origin of the high performance of the catalyst. Studies on its mechanism reveal that the synergism between 'hot electron' from local surface plasmon resonance and rapid photogenerated carrier separation at the ohmic contact interface accelerates the multi-electron reaction kinetics. The catalyst can selectively synthesize CH4 directly from CO2 and H2O with selectivity of near 100% at room temperature and pressure, and exhibits transformative performance, with an average CH4 yield of 26.2 μmol g-1 h-1 and remarkable long-term stability.

Molecular insights into strengthening of biomineral apatite with carbon nanofillers: A simulation study

Biomineral apatite (Ap) has been widely utilized in clinical bone graft procedures for over 25 years. However, its lower tensile strength and fracture toughness compared to natural bone limit its application in large load-bearing systems. This approach aims to enhance the mechanical performance of Ap while preserving its bioactivity, thereby expanding its potential clinical applications. In this study, the creation and processing of carbon nanofiller-based Ap nanocomposites, including pristine and vacancy-defective carbon nanofillers, are investigated using molecular dynamics simulations. The mechanical behaviour of Ap nanocomposites reinforced with three types of carbon nanofillers (CNF) is examined: (i) three-dimensional metallic carbon nanostructure with interlocking hexagons T6B (beam-like), (ii) carbon nanotubes (CNT), and (iii) three-dimensional metallic carbon nanostructure with interlocking hexagons T6P (plate-like). The analysis encompasses detailing the methodology utilized for modelling the equilibrated structures of CNF/Ap nanocomposites, along with the characterization of their elastic parameters. Computational findings reveal the significant impact of CNT chirality, Aspect Ratio (AR) of T6B and orientation of T6P on the mechanical properties of the nanocomposites and observed inclusion of CNF enhances the mechanical properties compared with those of pure Ap. The findings indicate that the lower diameter CNT and smaller cross-sectional area of T6B exhibit higher tensile strength compared to the larger CNT diameter and larger cross-sectional area of T6B of the same length. Further, the analysis highlights the substantial influence of vacancy defects concentration on CNF on the mechanical behaviour of nanocomposites, with an increase in defects correlating to a decrease in the mechanical strength of both CNF and CNF-based nanocomposites.

Reduced-Dimensionality Al Nanocrystals: Nanowires, Nanobars, and Nanomoustaches.

Aluminum nanocrystals created by catalyst-driven colloidal synthesis support excellent plasmonic properties, due to their high level of elemental purity, monocrystallinity, and controlled size and shape. Reduction in the rate of nanocrystal growth enables the synthesis of highly anisotropic Al nanowires, nanobars, and singly twinned "nanomoustaches". Electron energy loss spectroscopy was used to study the plasmonic properties of these nanocrystals, spanning the broad energy range needed to map their plasmonic modes. The coupling between these nanocrystals and other plasmonic metal nanostructures, specifically Ag nanocubes and Au films of controlled nanoscale thickness, was investigated. Al nanocrystals show excellent long-term stability under atmospheric conditions, providing a practical alternative to coinage metal-based nanowires in assembled nanoscale devices.

Helium plasma irradiation on Nickel: Nanostructure formation and electrochemical characteristics

Nanotechnology offers new avenues for the design, fabrication, and application of novel materials. Helium plasma exposure is a technique that can be used to fabricate self-supported metallic nanostructures. In this work, we explore the plasma irradiation conditions for fabricating various morphologies on planar nickel surfaces, and evaluate the electrochemical performance of these surfaces for oxygen evolution reaction (OER) in alkaline media. The preferential growth towards certain morphologies such as nano-pillars, nano-blocks, and micro-structures, is found to be primarily influenced by the applied plasma conditions and two counteracting processes of sputtering and annealing. The plasma treatment increased the electrochemical surface area of the modified samples by approximately 3 to 4 times as compared to the planar/unmodified surfaces, along with an increase in the OER performance for all morphologies. However, in addition to the increased surface area, the electrochemical performance was found to be dependent on the shape, size and thickness of the nano/micro-features. Moving ahead, the ability of this technique to achieve control over the feature size along with its effectiveness for a broad range of metals offers new routes for nanostructuring and functionalization of emerging materials.

Copper/Polyaniline Interfaces Confined CO2 Electroreduction for Selective Hydrocarbon Production.

Polyaniline (PANI) provides an attractive organic platform for CO2 electrochemical reduction due to the ability to adsorb CO2 molecules and in providing means to interact with metal nanostructures. In this work, a novel PANI supported copper catalyst has been developed by coupling the interfacial polymerization of PANI and Cu. The hybrid catalyst demonstrates excellent activity towards production of hydrocarbon products including CH4 and C2H4, compared with the use of bare Cu. A Faradaic efficiency of 71.8 % and a current density of 16.9 mA/cm2 were achieved at -0.86 V vs. RHE, in contrast to only 22.2 % and 1.0 mA/cm2 from the counterpart Cu catalysts. The remarkably enhanced catalytic performance of the hybrid PANI/Cu catalyst can be attributed to the synergistic interaction between the PANI underlayer and copper. The PANI favours the adsorption and binding of CO2 molecules via its nitrogen sites to form *CO intermediates, while the Cu/PANI interfaces confine the diffusion or desorption of the *CO intermediates favouring their further hydrogenation or carbon-carbon coupling to form hydrocarbon products. This work provides insights into the formation of hydrocarbon products on PANI-modified Cu catalysts, which may guide the development of conducting polymer-metal catalysts for CO2 electroreduction.

Crystal plane orientation-dependent surface atom diffusion in sub-10-nm Au nanocrystals.

Surface atom diffusion is a ubiquitous phenomenon in nanostructured metals with ultrahigh surface-to-volume ratios. However, the fundamental atomic mechanism of surface atom diffusion remains elusive. Here, we report in situ atomic-scale observations of surface pressure-driven atom diffusion in gold nanocrystals at room temperature using high-resolution transmission electron microscopy with a high-speed detection camera. The topmost layer of atoms on (001) plane initially diffuse in a column-by-column manner. As diffusion proceeds, the remaining atomic columns collectively inject into adjacent underlayer, accompanied by nucleation of a surface dislocation. In comparison, atoms on (111) plane directly diffuse to the base without collective injection. Quantitative calculations indicate that these crystal plane orientation-dependent atom diffusion behaviors contribute to the larger diffusion coefficient of (111) plane compared to (001) plane in addition to the effect of diffusion activation energy. Our findings provide valuable insights into atomic mechanisms of diffusion-dominant morphology evolution of nanostructured metals and guide the design of nanostructured materials with enhanced structural stability.

Localization of hot carriers in Au144(SCH3)60 clusters doped with copper

Hot carriers (HCs) generated by visible light in metal nanostructures present significant potential for various applications. Nevertheless, comprehending HCs at a microscopic level has been a formidable challenge. This research delves into the spatial distribution of HCs within thiolate-protected Au144(SCH3)60 cluster doped with copper through real-time time-dependent density functional theory (rt-TDDFT). By accurately adjusting a Gaussian laser pulse to correspond to the dominant photoabsorption frequencies, we reveal the formation of hot electrons and hot holes. Throughout all the examined configurations, it was noted that copper doping creates a more pronounced influence on the distribution of hot holes compared to hot electrons, indicating the potential for precise control over HC generation in nanoscale systems with well-defined electronic structures.

Toward Optimum Coupling between Free Electrons and Confined Optical Modes.

Free electrons are excellent tools to probe and manipulate nanoscale optical fields with emerging applications in ultrafast spectromicroscopy and quantum metrology. However, advances in this field are hindered by the small probability associated with the excitation of single optical modes by individual free electrons. Here, we theoretically investigate the scaling properties of the electron-driven excitation probability for a wide variety of optical modes including plasmons in metallic nanostructures and Mie resonances in dielectric cavities, spanning a broad spectral range that extends from the ultraviolet to the infrared region. The highest probabilities for the direct generation of three-dimensionally confined modes are observed at low electron and mode energies in small structures, with order-unity (∼100%) coupling demanding the use of <100 eV electrons interacting with eV polaritons confined down to tens of nanometers in space. Electronic transitions in artificial atoms also emerge as practical systems to realize strong coupling to few-eV free electrons. In contrast, conventional dielectric cavities reach a maximum probability in the few-percent range. In addition, we show that waveguide modes can be generated with higher-than-unity efficiency by phase-matched interaction with grazing electrons, suggesting a practical method to create multiple excitations of a localized optical mode by an individual electron through funneling the so-generated propagating photons into a confining cavity─an alternative approach to direct electron-cavity interaction. Our work provides a roadmap to optimize electron-photon coupling with potential applications in electron spectromicroscopy as well as nonlinear and quantum optics at the nanoscale.

Customized Self-Assembled Gold Nanoparticle-DNA Origami Composite Templates for Shape-Directed Growth of Plasmonic Structures.

The metal plasmonic nanostructure has the optical property of plasmon resonance, which holds great potential for development in nanophotonics, bioelectronics, and molecular detection. However, developing a general and straightforward method to prepare metal plasmonic nanostructures with a controllable size and morphology still poses a challenge. Herein, we proposed a synthesis strategy that utilized a customizable self-assembly template for shape-directed growth of metal structures. We employed gold nanoparticles (AuNPs) as connectors and DNA nanotubes as branches, customizing gold nanoparticle-DNA origami composite nanostructures with different branches by adjusting the assembly ratio between the connectors and branches. Subsequently, various morphologies of plasmonic metal nanostructures were created using this template shape guided strategy, which exhibited enhancement of surface-enhanced Raman scattering (SERS) signals. This strategy provides a new approach for synthesizing metallic nanostructures with multiple morphologies and opens up another possibility for the development of customizable metallic plasmonic structures with broader applications.

High-Q plasmonic surface lattice resonance in the ultraviolet region

Surface lattice resonances (SLRs) arise from the long-range dipolar interaction in periodic plasmonic metallic nanostructures and exhibit higher quality factors (Q-factors) compared to plasmon resonances supported in isolated metallic nanostructures. In this Letter, we report a significant improvement in the Q-factor of SLR by a factor of three via modulating the efficiency of a long-range dipolar interaction, which can be achieved by varying the thickness or refractive index of the coating layer on the top of the metallic nanostructures. Under the condition of a weak long-range dipolar interaction, we observe a nascent state of SLR located directly at the Rayleigh cutoff wavelength. Due to the absence of an in-plane diffraction mode at shorter wavelengths, the nascent-SLR dip exhibits an asymmetric shape with a high Q-factor. We experimentally monitor the evolution trend at the onset of the SLR and demonstrate a plasmonic resonance reaching an experimental Q-factor exceeding 100 in the ultraviolet region, outperforming other resonance modes in metallic nanostructures. The reported nascent SLR holds promise for boosting the performance of nano-optic devices.

Exploring Metal Electroplating for Energy Storage by Quartz Crystal Microbalance: A Review

AbstractThe development and application of Electrochemical Quartz Crystal Microbalance (EQCM) sensing to study metal electroplating, especially for energy storage purposes, are reviewed. The roles of EQCM in describing electrode/electrolyte interface dynamics, such as the electric double‐layer build‐up, ionic/molecular adsorption, metal nucleation, and growth, are addressed. Modeling of the QCM sensor is introduced and its importance is emphasized. Challenges of metal electrode use, including side reactions and dendrite formation, along with their mitigation strategies are reviewed. Numerous factors affecting the electroplating processes, such as electrolyte composition, additives, temperature, and current density, and their influence on the electroplated metals’ mass, structural, and mechanical characteristics are discussed. Looking forward, the need for deeper fundamental understanding and advancing simulations of the QCM signal response as a result of electroplating metal nanostructures is stressed. Further development and integration of innovative EQCM‐strategies will provide unique future means to fundamentally understand and optimize metal electroplating for energy storage and application alike.

Design, synthesis, and pharmacological efficacy of sonication-irradiated nanostructured transition metal (II) designed macrocyclic complexes

The synthesis of transition metal (II) complexes from aspartic acid was accomplished by using sonication irradiation in this work. Sonication irradiation is a straightforward and efficient technique for synthesis. Physiological and spectroscopic studies were carried out to investigate the process of assembling nanostructured complexes. Using the serial dilution (2-fold) and free radical scavenging (DPPH) procedures, the antioxidant and antibacterial activity were assessed, respectively. Various bacteria, including Gram-positive and Gram-negative strains and fungi, were tested to determine the antimicrobial efficacies of the macrocyclic ligand and its accompanying metal complexes. The inhibitory results on microbes showed that metal complexes had more potent antibacterial effects than their Schiff base ligands. The findings demonstrated that the biological activity had a positive impact. Sonication irradiation of some complexes increased the movement of those complexes at concentrations ranging from 3.125 to 6.250 μg/ml (MIC). The Gaussian 09 software was utilized to simulate the three-dimensional structure of the complexes, the chemical reactivity of the produced macrocyclic ligand, and the binding energy of its complexes’ EHOMO and ELUMO energies using the B3LYP Density Functional Theory (DFT) method. This method is well-suited for pharmaceutical applications in the real world since it requires little effort to set up, produces a high yield, and requires a relatively small amount of solvent.