Metallic Nanostructures Research Articles

Ultrafast micro/nano-manufacturing of metastable materials for energy.

The structural engineering of metastable nanomaterials with abundant defects has attracted much attention in energy-related fields. The high-temperature shock (HTS) technique, as a rapidly developing and advanced synthesis strategy, offers significant potential for the rational design and fabrication of high-quality nanocatalysts in an ultrafast, scalable, controllable and eco-friendly way. In this review, we provide an overview of various metastable micro- and nanomaterials synthesized via HTS, including single metallic and bimetallic nanostructures, high entropy alloys, metal compounds (e.g. metal oxides) and carbon nanomaterials. Note that HTS provides a new research dimension for nanostructures, i.e. kinetic modulation. Furthermore, we summarize the application of HTS-as supporting films for transmission electron microscopy grids-in the structural engineering of 2D materials, which is vital for the direct imaging of metastable materials. Finally, we discuss the potential future applications of high-throughput and liquid-phase HTS strategies for non-equilibrium micro/nano-manufacturing beyond energy-related fields. It is believed that this emerging research field will bring new opportunities to the development of nanoscience and nanotechnology in both fundamental and practical aspects.

Microstructure Evolution during High-Pressure Torsion in a 7xxx AlZnMgZr Alloy.

A homogenized, supersaturated AlZnMgZr alloy was processed via severe plastic deformation (SPD) using a high-pressure torsion (HPT) technique for different revolutions at room temperature to obtain an ultrafine-grained (UFG) microstructure. The microstructure and mechanical properties of the UFG samples were then studied using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile and hardness measurements. The main purpose was to study the effect of shear strain on the evolution of the microstructure of the investigated alloy. We found a very interesting evolution of the decomposed microstructure in a wide range of shear strains imposed by HPT. While the global properties, such as the average grain size (~200 nm) and hardness (~2200 MPa) appeared unchanged, the local microstructure was continuously transformed. After 1 turn of HPT, the decomposed UFG structure contained relatively large precipitates inside grains. In the sample processed by five turns in HPT, the segregation of Zn atoms into grain boundaries (GBs) was also observed. After 10 turns, more Zn atoms were segregated into GBs and only smaller-sized precipitates were observed inside grains. The intensive solute segregations into GBs may significantly affect the ductility of the material, leading to its ultralow-temperature superplasticity. Our findings pave the way for achieving advanced microstructural and mechanical properties in nanostructured metals and alloys by engineering their precipitation and segregation by means of applying different HPT regimes.

Fabrication of silver nanostructure array patterns (SNAPs) on silicon wafer for highly sensitive and reliable SERS substrates

Metal nanostructure arrays with large amounts of nano-gaps are important for surface enhanced Raman scattering applications, though the fabrications of such nanostructures are difficult due to the complex and multiple synthetic steps. In this research, we report silver nanostructure array patterns (SNAPs) on silicon wafer, which is fabricated with semiconductor manufacturing technology, Cu2O electrochemistry deposition, and Ag In-situ oxidation–reduction growth. Benefiting from the dense and uniform distribution of Ag nanowires, the fabricated SNAPs demonstrate a very strong and uniform surface-enhanced Raman scattering (SERS) effect. The efficiency of SNAPs was investigated by using rhodamine 6G (R6G) dye as an analyte molecule. The results show that the minimum detectable concentration of R6G can reach as low as 10−11 M, and the Raman signals in the random region show good signal homogeneity with a low relative standard deviation (RSD) of 4.77 %. These results indicate that the SNAPs perform a great sensitivity and uniformity as a SERS substrate. Furthermore, we used the SNAPs substrate to detect antibiotic sulfadiazine. The main peaks in sulfadiazine Raman and vibration modes assignments were obtained and the quantitative analysis model was established by principal component analysis (PCA). The detection and application results of sulfadiazine indicate that the SNAPs substrate can be applied for trace detection of antibiotics. In addition, we have cited the application of the SNAPs substrate in anti-counterfeiting labels. These practical applications demonstrate that the fabricated SNAPs can potentially provide a way to develop low-cost SERS platforms for environmental detections, biomedicine analysis, and commodities anti-counterfeiting.

Atomic-scale observation of nucleation- and growth-controlled deformation twinning in body-centered cubic nanocrystals

Twinning is an essential mode of plastic deformation for achieving superior strength and ductility in metallic nanostructures. It has been generally believed that twinning-induced plasticity in body-centered cubic (BCC) metals is controlled by twin nucleation, but facilitated by rapid twin growth once the nucleation energy barrier is overcome. By performing in situ atomic-scale transmission electron microscopy straining experiments and atomistic simulations, we find that deformation twinning in BCC Ta nanocrystals larger than 15 nm in diameter proceeds by reluctant twin growth, resulting from slow advancement of twinning partials along the boundaries of finite-sized twin structures. In contrast, reluctant twin growth can be obviated by reducing the nanocrystal diameter to below 15 nm. As a result, the nucleated twin structure penetrates quickly through the cross section of nanocrystals, enabling fast twin growth via facile migration of twin boundaries leading to large uniform plastic deformation. The present work reveals a size-dependent transition in the nucleation- and growth-controlled twinning mechanism in BCC metals, and provides insights for exploiting twinning-induced plasticity and breaking strength-ductility limits in nanostructured BCC metals.

Squeezed Protons and Infrared Plasmonic Resonance Energy Transfer.

Unusual nuclear quantum effects may emerge near noble metal nanostructures such as squeezed vibrational states in molecular junctions and plasmonic resonance energy transfer in the infrared domain. Herein, nuclear quantum effects near heavy metals are studied by nuclear-electronic orbital density functional theory (NEO-DFT) with an effective core potential. For a quantum proton sandwiched between a pair of gold tips modeled by two Au6 clusters, NEO-DFT calculations suggest that the quantum proton density can be squeezed as the tip distance decreases. For an HF molecule placed near a one-dimensional Au nanowire composed of up to 34 Au atoms, real-time NEO time-dependent density functional theory (RT-NEO-TDDFT) shows that the infrared plasmonic motion within the Au nanowire may resonantly transfer electronic energy to the HF proton vibrational stretch mode. Overall, these calculations illustrate the advantages of the NEO approach for probing nuclear quantum effects, such as squeezed proton vibrational states and infrared plasmonic resonance energy transfer.

Electronic transparency of internal interfaces in metallic nanostructures comprising light, heavy and ferromagnetic metals measured by terahertz spectroscopy

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

Highly sensitive SERS platform using sub-10-nm Ag nanoparticles on GaN distributed Bragg reflector for detecting organic pollutants

Surface-enhanced Raman scattering (SERS) is crucial for the development of advanced detection technology and achieving high-sensitivity optical signals. Sub-10 nm noble metal nanostructures with high specific surface area and good catalytic activity are suitable for in-situ SERS analysis, while their SERS performance is inferior compared to larger noble metal nanoparticles with sizes of tens of nm. In this study, the weak SERS signals from sub-10 nm Ag nanoparticles (NPs) are greatly enhanced by developing a highly reflective multi-component system, in which monodisperse sub-10 nm Ag NPs are deposited onto a GaN-based distributed Bragg reflector (DBR). This Ag-NP/GaN DBR system exhibits remarkable SERS enhancement, approximately two orders of magnitude. This enhancement effect is further confirmed by SERS mapping over an area of 50 × 50 µm2. Moreover, the Ag-NP/GaN DBR system enables the in-situ monitoring of catalytic reaction processes of R6G and 4-NBT molecules, indicating high analytical sensitivity. To demonstrate practical applications, this Ag-NP/GaN DBR system is exploited to detect the toxic malachite green molecules and polyethylene microplastics, which show strong fingerprint signals. This work provides an effective solution to boost the weak SERS signals of sub-10 nm Ag NPs and paves the way towards practical applications.

Enhancing SERS Sensitivity in N‐Graphene Hydrangea by Synergistic Charge‐Transfer and Excitation Light Absorption

Surface‐enhanced Raman scattering (SERS) is a versatile spectroscopic technique, which plays a crucial role in enhancing analytical sensitivity, investigating interfacial reaction mechanisms, enabling biosensing, and fostering efficient catalysis. Currently, the common SERS substrates are primarily metal nanostructures, which entail high manufacturing costs, complex processes, and the metal surface undergo change over time and with environmental conditions. These issues limit the development of SERS technology. In this work, a nitrogen‐doped graphene (N‐graphene) hydrangea was synthesized on a silicon (Si) substrate using plasma‐assisted chemical vapor deposition (PACVD), forming an N‐graphene hydrangea/Si hybrid structure as a SERS substrate. This substrate offers the advantages of high stability, ultra‐sensitivity, and reusability. The three‐dimensional nano‐cavity structure of graphene can increase the interaction between light and graphene, resulting in an increased localized electric field. Combining theoretical simulation analysis, the introduction of nitrogen (N) elements adjusts the Fermi level of graphene, promoting efficient charge transfer. In practical scenarios, Di(2‐ethylhexyl) phthalate (DEHP), a commonly used plasticizer, has raised concerns due to its potential as an endocrine disruptor and carcinogen. The as‐prepared SERS substrate achieves a remarkable detection limit of as low as 10−8 m for DEHP, providing significant support for environmental conservation and human health.

Ni-PI-Ni based nanoarchitectonics near-perfect metamaterial absorber with incident angle stability for visible and near-infrared applications

This article presents a wideband metamaterial absorber (WMMA) for the visible and near-infrared (NIR) region application. The proposed metamaterial absorber comprises three layers of sandwiched (metal-dielectric-metal) model based on Nickel-Polyamide-Nickel. The multiple resonators on top layers achieve an average absorption of 98.16% over a range from 380 to 2300 nm with a compact unit cell size of 100 × 100 × 42 nm3. The designed WMMA shows 99% perfect absorption for a large bandwidth of 685 nm. Considering its wideband absorption, the physical absorption phenomenon was also explained in terms of the proposed WMMA's surface electric field, magnetic field, and current distribution. Also, the effects of materials and structural parameters on absorption performance with a FOM have been studied. The absorption performance is analysed with various polarization angles to demonstrate polarization insensitivity. The designed WMMA shows the absorption of >70% at large incident angles of 70°. The perceptible contribution of this WMMA is large unity absorption bandwidth at visible to NIR region with high incident angle stability, polarisation insensitivity, thermal robustness of the constituting metal and simple nanostructure geometry. Therefore, the proposed WMMA has good potential in sensors, thermal emitters, photodetectors, and absorber applications.

Synthesis of Metallic Nanostructures Using Ionizing Radiation and Their Applications.

This paper reviews the radiation-induced synthesis of metallic nanostructures and their applications. Radiolysis is a powerful method for synthesizing metallic nanoparticles in solution and heterogeneous media, and it is a clean alternative to other existing physical, chemical, and physicochemical methods. By varying parameters such as the absorbed dose, dose rate, concentrations of metallic precursors, and nature of stabilizing agents, it is possible to control the size, shape, and morphology (alloy, core-shell, etc.) of the nanostructures and, consequently, their properties. Therefore, the as-synthesized nanoparticles have many potential applications in biology, medicine, (photo)catalysis, or energy conversion.

Structural control of nanoporous frameworks consisting of minimally stacked graphene walls

This mini-review provides an in-depth analysis of the formation and post-processing of nanoporous graphene materials via methane chemical vapor deposition (CH4-CVD) using nanostructured metal oxide templates, including Al2O3, MgO, and SiO2. Initially, the formation of graphene sheets is discussed in terms of the role of CH4-CVD, the influence of templates, and the underlying mechanism for tailoring the structures of the graphene-based materials. Following this, the discussion extends to the post-graphene formation process. We focus on key steps, including template removal and graphene repair via zipping reactions at high temperatures. Additionally, we evaluate the conditions to prevent undesired structural transformations. The correlation between the structural features and transformations occurring during post-processing is also examined. The materials fabricated through these methods exhibit impressive properties of high porosity, minimal edge sites, superior oxidation resistance, and elasticity, positioning them as promising materials in various applications.

Candle soot carbon-Co3O4 nanofibers composite as a binder-free electrode for high-performance supercapacitor application: An experimental and theoretical investigation

Extensive research has been conducted on nanostructured metal oxide electrodes for energy storage applications, particularly in supercapacitors, owing to their high specific capacitance. However, a major hindrance to their commercialization is their limited life cycles. To address this issue, incorporating carbon allotropes as a conductive support to enhance the electrode's stability has been explored. In the current work, a novel composite material was synthesized by combining candle soot carbon with cobalt oxide (Co3O4) to create a highly efficient electrode. The optimal composite, with a 2 wt% of candle soot carbon to Co3O4, exhibited utmost specific capacitance (997.5 Fg−1) at 1 Ag−1. After subjecting both electrodes to 10,000 cycles of repetitive charge and discharge, the composite demonstrated a capacitance retention of 83.3 %, while the Co3O4 electrode only achieved 75 % under identical conditions. Additionally, Density Functional Theory (DFT) investigations were performed to elucidate the improved charge-storing capacities of the composite electrode. The computed density of states indicates enrichment of energy states near the Fermi level in the composite when seen to pristine Co3O4. The Partial Density of States (PDOS) analysis illustrates the transportation of charge from the carbon p orbital (candle soot carbon) to the Co d orbital (Co3O4), validating the conductivity improvement in the hybrid configuration, which benefits from enhanced charge storage performance. Overall, the composite material is promising for hybrid supercapacitors, especially due to the incorporation of candle soot carbon as one of its components. It not only enhances the performance of the supercapacitor but also offers the advantage of being a renewable material derived from waste materials. This combination makes the composite an appealing and sustainable choice for next-generation energy storage devices.

Surface-Enhanced Raman Spectroscopy Using a Silver Nanostar Substrate for Neonicotinoid Pesticides Detection.

Surface-enhanced Raman spectroscopy (SERS) has been introduced to detect pesticides at low concentrations and in complex matrices to help developing countries monitor pesticides to keep their concentrations at safe levels in food and the environment. SERS is a surface-sensitive technique that enhances the Raman signal of molecules absorbed on metal nanostructure surfaces and provides vibrational information for sample identification and quantitation. In this work, we report the use of silver nanostars (AgNs) as SERS-active elements to detect four neonicotinoid pesticides (thiacloprid, imidacloprid, thiamethoxam and nitenpyram). The SERS substrates were prepared with multiple depositions of the nanostars using a self-assembly approach to give a dense coverage of the AgNs on a glass surface, which ultimately increased the availability of the spikes needed for SERS activity. The SERS substrates developed in this work show very high sensitivity and excellent reproducibility. Our research opens an avenue for the development of portable, field-based pesticide sensors, which will be critical for the effective monitoring of these important but potentially dangerous chemicals.

Enhanced charge transport and broadband photoresponse of MoS2 photodetectors with sparsely distributed Ag@SiO2 core–shell nanostructures

Integrating metal nanostructures with two-dimensional (2D) material photodetectors has been demonstrated that can greatly improve device performance owning to various extraordinary optoelectronic phenomena. For example, metal nanostructures are served as ideal plasmonic materials to maximize local electromagnetic fields leading to light absorption of 2D materials. In this work, other than the widely reported plasmonic effects, we discover the contribution of metal nanostructures in charge transport engineering in 2D material photodetectors, which is important but always ignored in previous studies by others. Notable improvements of carrier mobility and carrier concentration attributing to the integration of sparsely distributed Ag@SiO2 core–shell nanoparticles on the MoS2 detector were experimentally established, originating from reduced carrier scattering and interfacial gating. Consequently, a 1.5-fold broadband (400–1100 nm) uniform photocurrent enhancement was observed, which was entirely derived from the improved charge transport. These findings open up a new research perspective for the precise identification and objective evaluation of different effects of metal nanostructures on optoelectronic devices.

Nanosecond Laser Fabrication of Novel Micro-/Nanostructured Metal Surfaces: A Dual-Functional Supersurface Combining Antireflectivity and Superhydrophobic Properties.

The research and applications in the field of micro/nano surface manufacturing are progressively shifting their focus toward multifunctional surfaces. In practical applications, objects often need to operate under demanding environmental conditions, and single-function surfaces have inherent limitations in terms of performance, adaptability, and longevity. In this paper, a micro-/nanolayered structural strategy with dual functions of ultrahigh antireflective properties and superhydrophobicity was created on the surface of titanium alloy by using nanosecond pulsed laser processing, and two structural modes of periodic honeycomb and lattice with controllable shapes were designed. In addition, the morphology and formation mechanism of multilevel micro-/nanostructures were investigated in depth, combining laser texturization and silanization of substrate microstructures. The effects of the micro-/nanostructured morphology on the reflection and wettability properties were evaluated with different pulse widths and lateral overlap index. This study also demonstrated that water droplets exhibit excellent bouncing and rolling behavior on superhydrophobic surfaces, further verifying the excellent hydrophobic properties of the prepared samples. Furthermore, in addressing the challenges of susceptibility to dust contamination and performance degradation in extreme environments associated with antireflective surfaces, a series of durability and mechanical stability tests were conducted on controllability periodic micro-/nanostructured surfaces. Successfully meeting this challenge will open up great potential and opportunities for significant improvements in equipment performance and stable operation under extreme operating conditions.

Plasmon-enhanced second harmonic generation of metal nanostructures.

As the most common nonlinear optical process, second harmonic generation (SHG) has important application value in the field of nanophotonics. With the rapid development of metal nanomaterial processing and chemical preparation technology, various structures based on metal nanoparticles have been used to achieve the enhancement and modulation of SHG. In the field of nonlinear optics, plasmonic metal nanostructures have become potential candidates for nonlinear optoelectronic devices because of their highly adjustable physical characteristics. In this article, first, the basic optical principles of SHG and the source of surface symmetry breaking in metal nanoparticles are briefly introduced. Next, the related reports on SHG in metal nanostructures are reviewed from three aspects: the enhancement of SHG efficiency by double resonance structures, the SHG effect based on magnetic resonance and the harmonic energy transfer. Then, the applications of SHG in the sensing, imaging and in situ monitoring of metal nanostructures are summarized. Future opportunities for SHG in composite systems composed of metal nanostructures and two-dimensional materials are also proposed.

Preparation and photocatalytic activity of TiO2 photonic crystals modified by bimetallic Ag–Pt nanostructures

To better understand the interactions between TiO2 photonic crystals (PC) and metallic nanostructures (MNSs), we studied the slow photon effects in PC and electron trapping taking place in MNSs on the photocatalytic decomposition of rhodamine B.

Plasmonic optoelectronic devices and metasurfaces

We report recent progress on optoelectronic devices and metasurfaces involving surface plasmons, enabled by metal-oxide-semiconductor (MOS) structures on Si and on epsilon-near-zero materials. We discuss electrically tuneable metasurfaces, high-speed electro-absorption modulators, and reflection modulators. Hot carriers created by the absorption of plasmons in metallic nanostructures on MOS structures are also discussed as they lead to novel device physics that open the door to new device concepts.

Thermal-effect dominated plasmonic catalysis on silver nanoislands.

Plasmonic metal nanostructures with the intrinsic property of localized surface plasmon resonance can effectively promote energy conversion in many applications such as photocatalysis, photothermal therapy, seawater desalinization, etc. It is known that not only are plasmonically excited hot electrons generated from metal nanostructures under light irradiation, which can effectively trigger chemical reactions, but also plasmonically induced heating simultaneously occurs. Although plasmonic catalysis has been widely explored in recent years, the underlying mechanisms for distinguishing the contribution of hot electrons from thermal effects are not fully understood. Here, a simple and efficient self-assembly system using silver nanoislands as plasmonic substrates is designed to investigate the photo-induced azo coupling reaction of nitro- and amino-groups at various temperatures. In the experiments, surface-enhanced Raman spectroscopy is employed to monitor the time and temperature dependence of plasmon-induced catalytic reactions. It was found that a combination of hot electrons and thermal effects contribute to the reactivity. The thermal effects play the dominant role in the plasmon-induced azo coupling reaction of nitro-groups, which suggests that the localized temperature must be considered in the development of photonic applications based on plasmonic nanomaterials.

Advancements in the Improvement of Optical Outcoupling Efficiency for Perovskite LEDs

In the past 10 years, the development of perovskite light-emitting diodes (PeLEDs) was fast. Due to the excellent properties of high brightness and color purity, multiple color emission, and cost-effective fabrication technology, PeLEDs have been very promising in semiconductor lighting and display applications. In an effort to achieve high-efficient PeLED devices, researchers have devoted themselves to explore and optimize the emitted materials and device structures. Among various research approaches, raising the optical outcoupling efficiency ( η out ) of PeLED through light management strategies is very important for further promoting device performances, which is due to that approximately 80% of the photons generated internally are captured or worn out in different optical modes in the device. In this review, the latest researches on optical outcoupling regulations in PeLED are outlined, which mainly focus on photophysical properties and implementation methods. As the key part of this review, implementation strategies are classified into the optimization of characteristics of functional materials (refractive index, film thickness, anisotropy, and photon recovery) and adjustment of device architecture (patterned nanostructures, photonic crystals, metal nanostructures, and external couplers). Additionally, a prospect of the future directions and development trend for this research field is presented in order to achieve ultra-efficient PeLED and future commercial applications.