Physical Deposition Improved SERS Stability of Morphology Controlled Periodic Micro/Nanostructured Arrays Based on Colloidal Templates

An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal template induced precursor solution dipping strategy, different periodic arrays of semi‐hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb‐shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template‐induced chemical deposition. Additionally, a honeycomb‐shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb‐shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10^?11 M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.     

Ag Nanoparticle‐Grafted PAN‐Nanohump Array Films with 3D High‐Density Hot Spots as Flexible and Reliable SERS Substrates

A facile fabrication approach of large‐scale flexible films is reported, with one surface side consisting of Ag‐nanoparticle (Ag‐NP) decorated polyacrylonitrile (PAN) nanohump (denoted as Ag‐NPs@PAN‐nanohump) arrays. This is achieved via molding PAN films with ordered nanohump arrays on one side and then sputtering much smaller Ag‐NPs onto each of the PAN‐nanohumps. Surface‐enhanced Raman scattering (SERS) activity of the Ag‐NPs@PAN‐nanohump array films can be improved by curving the flexible PAN film with ordered nanohump arrays during the Ag‐sputtering process to increase the density of the Ag‐NPs on the sidewalls of the PAN‐nanohumps. More 3D hot spots are thus achieved on a large‐scale. The Ag‐NPs@PAN‐nanohump array films show high SERS activity with good Raman signal reproducibility for Rhodamine 6G probe molecules. To trial their practical application, the Ag‐NPs@PAN‐nanohump array films are employed as SERS substrates for trace detection of trinitrotoluene and a congener of polychlorinated biphenyls. A lower detection limit of 10⁻¹²m and 10⁻⁵m can be achieved, respectively. Furthermore, the flexible Ag‐NPs@PAN‐nanohump array films can also be utilized as swabs to probe traces of methyl parathion on the surface of fruits such as apples. The as‐fabricated SERS substrates therefore have promising potential for applications in rapid safety inspection and environmental protection.     

Environmental Hazard Potential of Nano‐Photocatalysts Determined by Nano‐Bio Interactions and Exposure Conditions

Nano‐photocatalysts are known for their ability to degrade pollutants or perform water splitting catalyzed by light. Being the key functional ingredients of current and future products, the potential of nano‐photocatalysts releasing into the environment and causing unintended harm to living organisms warrants investigation. Risk assessment of these materials serves as an important step to allow safe implementation and to avoid irrational fear. Using TiO₂ and g‐C₃N₄ as representative nano‐photocatalysts, this study evaluates their hazard potential in zebrafish. Under simulated solar light, nano‐photocatalysts up to 100 mg L^?1 show no acute toxicity to zebrafish embryos due to the protection of chorions. The short‐lived reactive oxygen species generated by nano‐photocatalysts only exert injury to the hatched larvae at and above 50 mg L^?1. The input of solar energy, determined by the depth of water, irradiation time, and light intensity, greatly influences the toxicity outcome. Increasing concentrations of natural organic matters contribute positively to the hazard potential at 0–10 mg L^?1 while gradually diminishing the hazardous effect above 10 mg L^?1. This study demonstrates the importance of nano‐bio interactions and environmental exposure conditions in determining the safety profile of nano‐photocatalysts.     

Cobalt Nanoparticle Arrays made by Templated Solid‐State Dewetting

Self‐assembled cobalt particle arrays are formed by annealing, which cause agglomeration (dewetting) of thin Co films on oxidized silicon substrates that are topographically prepatterned with an array of 200‐nm‐period pits. The Co nanoparticle size and uniformity are related to the initial film thickness, annealing temperature, and template geometry. One particle per 200‐nm‐period pit is formed from a 15‐nm film annealed at 850 °C; on a smooth substrate, the same annealing process forms particles with an average interparticle distance of 200 nm. Laser annealing enables templated dewetting of 5‐nm‐thick films to give one particle per pit. Although the as‐deposited films exhibit a mixture of hexagonal close‐packed and face‐centered cubic (fcc) phases, the ordered cobalt particles are predominantly twinned fcc crystals with weak magnetic anisotropy. Templated dewetting is shown to provide a method for forming arrays of nanoparticles with well‐controlled sizes and positions.     

Synergistic Modulation of Surface Interaction to Assemble Metal Nanoparticles into Two‐Dimensional Arrays with Tunable Plasmonic Properties

A simple strategy based on the synergistic modulation of inter‐particle and substrate‐particle interaction is applied for the large‐scale fabrication of two‐dimensional (2D) Au and Ag nanoparticle arrays. The surface charge of the substrate is used to redistribute the double layer electric charges on the particles and to modulate the inter‐particle distance within the 2D nanoparticle arrays on the substrate. The resultant arrays, with a wide range of inter‐particle distances, display tunable plasmonic properties. It can be foreseen that such 2D nanoparticle arrays possess potential applications as multiplexed colorimetric sensors, integrated devices and antennas. Herein, it is demonstrated that these arrays can be employed as wavelength‐selective substrates for multiplexed acquisition of surface‐enhanced Raman scattering (SERS) spectra. This simple one step process provides an attractive and low cost strategy to produce high quality and large area 2D ordered arrays with tunable properties.     

Ordered Arrays of Nanostructures and Applications in High‐Efficient Nano‐Generators

Large‐scale ordered nanostructure arrays on substrates, including nanowires, nanotubes, nanodots, and nano‐holes, can be fabricated using template fabrication processes. The controllable structural parameters and properties of the ordered nanostructure arrays make them quite suitable to be used in many device‐related application areas. It is shown that large‐scale nanowire arrays are good candidates for the realization of a nano‐generator based on the piezoelectric effect of ZnO nanowires. The mechanism of a proposed high‐efficient nano‐generator based on an assembled nanowire/nanohole embedded structure shows high application potentials for biological and nanometer‐sized devices.     

Towards Perfectly Ordered Novel ZnO/Si Nano‐Heterojunction Arrays

The fabrication of a highly ordered novel ZnO/Si nano‐heterojuntion array is introduced. ZnO seed layer is first deposited on the Si (P<111>) surface. The nucleation sites are then defined by patterning the surface through focused ion beam (FIB) system. The ZnO nanorods are grown on the nucleation sites through hydrothermal process. The whole fabrication process is simple, facile and offers direct control of the space, length and aspect ratio of the array. It is found that ZnO/Si nanojunctions show an improved interface when subjected to heat treatment. The recrystallization of ZnO and the tensile lattice strain of Si developed during the heating process contribute the enhancement of their photoresponses to white light. The photoluminescence (PL) measurement result of nano‐heterojunction arrays with different parameters is discussed.     

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Periodic hexagonal spherical nanoparticle arrays are fabricated by a sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. The regular network‐structured arrays are first templated by colloidal monolayers and then they are changed to novel periodic spherical nanoparticle arrays by further sputtering deposition due to multiple direction deposition and shadow effect between adjacent nanoparticles. The nanogaps between two adjacent spherical nanoparticles can be well tuned by controlling deposition time. Such periodic nanoparticle arrays with gold coatings demonstrate a very stable and high sensitive surface‐enhanced Raman scattering spectroscopy (SERS) performance. The periodic nanoparticle arrays with 10 nm gaps display much stronger SERS enhancement due to electromagnetic coupling. The chemically modified nanoparticle arrays show good hydrophobicity, which shorten process of detecting probe molecules using them as SERS‐active substrates by localized concentration of droplet evaporation and a low detection limit of 10⁻¹² m R6G can be achieved without solution wasting in a short time. The hydrophobic substrate offers a simple, convenient, and economical method to examine SERS performance by rapid concentration of solution on it and it is highly helpful to improve its practical applications in portable Raman detecting devices to detect organic molecules.     

Reinforcement in Al Matrix Composites: A Review of Strengthening Behavior of Nano‐Sized Particles

Aluminum matrix composites (AMCs) reinforced with the nano‐sized particles are very important materials for the applications in industrial fields. These aluminum matrix composites consist of an aluminum matrix and nano‐sized particles, which own very different physical and mechanical properties from those of the matrix. Nano‐sized particles show a more obvious strengthening effect on the matrix than the micro‐sized particles do, because of the high specific surface area which is positive for the pinning effect during the deformation process. Thus, the nano‐sized particle‐reinforced AMCs usually exhibit a good ductility. The main issues of the fabrication methods are the low wettability between the nano‐sized particles and the molten aluminum alloys, which is fatal to the conventional casting methods, and the agglomeration of nano‐sized particles which happened easier than the larger particles. Several alternative processes have been presented in literature for the production of the nano‐sized particle‐reinforced aluminum composites. This paper is aimed at reviewing the feasible manufacturing techniques used for the fabrication of nano‐sized particle‐reinforced aluminum composites. More importantly, the strengthening mechanisms and models which are responsible for the improvement of mechanical properties of the nano‐sized particle‐reinforced aluminum composites have been reviewed.

     

A Droplet‐Based High‐Throughput SERS Platform on a Droplet‐Guiding‐Track‐Engraved Superhydrophobic Substrate

A novel droplet‐based surface‐enhanced Raman scattering (SERS) sensor for high‐throughput real‐time SERS monitoring is presented. The developed sensors are based on a droplet‐guiding‐track‐engraved superhydrophobic substrate covered with hierarchical SERS‐active Ag dendrites. The droplet‐guiding track with a droplet stopper is designed to manipulate the movement of a droplet on the superhydrophobic substrate. The superhydrophobic Ag dendritic substrates are fabricated through a galvanic displacement reaction and subsequent self‐assembled monolayer coating. The optimal galvanic reaction time to fabricate a SERS‐active Ag dendritic substrate for effective SERS detection is determined, with the optimized substrate exhibiting an enhancement factor of 6.3 × 10⁵. The height of the droplet stopper is optimized to control droplet motion, including moving and stopping. Based on the manipulation of individual droplets, the optimized droplet‐based real‐time SERS sensor shows high resistance to surface contaminants, and droplets containing rhodamine 6G, Nile blue A, and malachite green are successively controlled and detected without spectral interference. This noble droplet‐based SERS sensor reduces sample preparation time to a few seconds and increased detection rate to 0.5 µ L s^?1 through the simple operation mechanism of the sensor. Accordingly, our sensor enables high‐throughput real‐time molecular detection of various target analytes for real‐time chemical and biological monitoring.     

One‐Step Synthesis of Monodispersed Mesoporous Carbon Nanospheres for High‐Performance Flexible Quasi‐Solid‐State Micro‐Supercapacitors

Cost‐effective synthesis of carbon nanospheres with a desirable mesoporous network for diversified energy storage applications remains a challenge. Herein, a direct templating strategy is developed to fabricate monodispersed N‐doped mesoporous carbon nanospheres (NMCSs) with an average particle size of 100 nm, a pore diameter of 4 nm, and a specific area of 1093 m² g^?1. Hexadecyl trimethyl ammonium bromide and tetraethyl orthosilicate not only play key roles in the evolution of mesopores but also guide the assembly of phenolic resins to generate carbon nanospheres. Benefiting from the high surface area and optimum mesopore structure, NMCSs deliver a large specific capacitance up to 433 F g^?1 in 1 m H₂SO₄. The NMCS electrodes–based symmetric sandwich supercapacitor has an output voltage of 1.4 V in polyvinyl alcohol/H₂SO₄ gel electrolyte and delivers an energy density of 10.9 Wh kg^?1 at a power density of 14014.5 W kg^?1. Notably, NMCSs can be directly applied through the mask‐assisted casting technique by a doctor blade to fabricate micro‐supercapacitors. The micro‐supercapacitors exhibit excellent mechanical flexibility, long‐term stability, and reliable power output.     

High‐Yield Synthesis of Hollow Octahedral Silver Nanocages with Controllable Pack Density and Their High‐Performance Sers Application

Nanoparticle‐assembled octahedral Ag nanocages with sharp edges have been successfully synthesized through a Cu₂O‐based template‐assisted strategy. In the reaction system, Ag nanoparticles can be self‐assembled on the surface of Cu₂O octahedrons, which is accomplished by the reduction of Ag⁺ by NaBH₄ in the presence of sodium citrate as a capping agent. The hollow octahedral Ag nanocages are obtained after removing the inner Cu₂O cores with acetic acid. According to the scanning electron microscopy (SEM) and transmission electron microscopy characterization, the Ag nanocages are weaved by small nanoparticles, the rough surfaces are bestrewed with pores and sharp edges. It is found that the pack density of Ag nanoparticles strongly affects the surface enhanced Raman scattering (SERS) activities. The as‐prepared 1.05‐Ag cages with optimal pack density have suitable interparticle distance and suitable size of pores, which significantly enhance SERS signals. The SERS signals of rhodamine 6G (R6G) molecules can be detected at an ultralow concentration of 10^?14 m when 1.05‐Ag cages are used as substrates. In addition to sensitivity, 1.05‐Ag cages also exhibit good reproducibility. It is expected that the ultrahigh sensitivity will endow the Ag nanocages to become a promising candidate as high‐performance SERS‐based chemical sensor.     

Single-crystal silver nanowires: Preparation and Surface-enhanced Raman Scattering (SERS) property

Ordered Ag nanowire arrays with high aspect ratio and high density self-supporting Ag nanowire patterns were successfully prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide (AAO) template. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation. Transmission electron microscopy and scanning electron microscopy investigation reveal that large-area and ordered Ag nanowire arrays with smooth surface and uniform diameter were synthesized. Surface-enhanced Raman Scattering (SERS) spectra show that the Ag nanowire arrays as substrates have high SERS activity.     

A Hierarchically Ordered TiO2 Hemispherical Particle Array with Hexagonal‐Non‐Close‐Packed Tops: Synthesis and Stable Superhydrophilicity Without UV Irradiation

A hierarchical TiO₂ ordered hemispherical particle array with hexagonal‐non‐close‐packed (hncp) tops is prepared by pulsed laser deposition (PLD) using a polystyrene colloidal monolayer as a template. Compared with conventional lithography, the route presented has the advantage of low cost for producing hncp nanostructured arrays. This hierarchical particle array exhibits excellent superhydrophilicity with a water contact angle of 0° without further UV irradiation. The superhydrophilic property originates from oxygen defects or vacancies on the surface of the TiO₂ nanoparticles produced by PLD and the increased roughness of the hierarchical particle arrays. More importantly, this property is very stable for half a year and could be used in self‐cleaning surfaces and microfluidic devices.     

Nano‐Composites for Water Remediation: A Review

As global populations continue to increase, the pressure on water supplies will inevitably intensify. Consequently the international need for more efficient and cost effective water remediation technologies will also rise. The introduction of nano‐technology into the industry may represent a significant advancement and zero‐valent iron nano‐particles (INPs) have been thoroughly studied for potential remediation applications. However, the application of water dispersed INP suspensions is limited and somewhat contentious on the grounds of safety, whilst INP reaction mechanisms, transport properties and ecotoxicity are areas still under investigation. Theoretically, the development of nano‐composites containing INPs to overcome these issues provides the logical next step for developing nano‐materials that are better suited to wide application across the water industry. This review provides an overview of the range of static, bulk nano‐composites containing INPs being developed, whilst highlighting the limitations of individual solutions, overall classes of technology, and lack of comparative testing for nano‐composites. The review discusses what further developments are needed to optimize nano‐composite water remediation systems to subsequently achieve commercial maturity.     

High‐Density Sb2Te3 Nanopillars Arrays by Templated,Bottom‐Up MOCVD Growth

Sb₂Te₃ exhibits several technologically relevant properties, such as high thermoelectric efficiency, topological insulator character, and phase change memory behavior. Improved performances are observed and novel effects are predicted for this and other chalcogenide alloys when synthetized in the form of high‐aspect‐ratio nanostructures. The ability to grow chalcogenide nanowires and nanopillars (NPs) with high crystal quality in a controlled fashion, in terms of their size and position, can boost the realization of novel thermoelectric, spintronic, and memory devices. Here, it is shown that highly dense arrays of ultrascaled Sb₂Te₃ NPs can be grown by metal organic chemical vapor deposition (MOCVD) on patterned substrates. In particular, crystalline Sb₂Te₃ NPs with a diameter of 20 nm and a height of 200 nm are obtained in Au‐functionalized, anodized aluminum oxide (AAO) templates with a pore density of ≈5 × 10¹⁰ cm^?2. Also, MOCVD growth of Sb₂Te₃ can be followed either by mechanical polishing and chemical etching to produce Sb₂Te₃ NPs arrays with planar surfaces or by chemical dissolution of the AAO templates to obtain freestanding Sb₂Te₃ NPs forests. The illustrated growth method can be further scaled to smaller pore sizes and employed for other MOCVD‐grown chalcogenide alloys and patterned substrates.     

Nano‐Dissection and Sequencing of DNA at Single Sub‐Nuclear Structures

The relative positioning of gene loci within a mammalian nucleus is non‐random and plays a role in gene regulation. Some sub‐nuclear structures may represent “hubs” that bring specific genetic loci into close proximity where co‐regulatory mechanisms can operate. The identification of loci in proximity to a shared sub‐nuclear structure can provide insights into the function of the associated structure, and reveal relationships between the loci sharing a common association. A technique is introduced based on the nano‐dissection of DNA from thin sections of cells by high‐precision nano‐tools operated inside a scanning electron microscope. The ability to dissect and identify gene loci occupying a shared site at a single sub‐nuclear structure is demonstrated here for the first time. The technique is applied to the nano‐dissection of DNA in vicinity of a single promyelocytic leukemia nuclear body (PML NB), and reveals novel loci from several chromosomes that are confirmed to associate at PML NBs with statistical significance in a cell population. Furthermore, it is demonstrated that pairs of loci from different chromosomes congregate at the same nuclear body. It is proposed that this technique is the first that allows the de novo determination of gene loci associations with single nuclear sub‐structures.     

A contact detection algorithm for multi‐sphere particles by means of two‐level‐grid‐searching in DEM simulations

In discrete element method simulations, multi‐sphere particle is extensively employed for modeling the geometry shape of non‐spherical particle. A contact detection algorithm for multi‐sphere particles has been developed through two‐level‐grid‐searching. In the first‐level‐grid‐searching, each multi‐sphere particle is represented by a bounding sphere, and global space is partitioned into identical square or cubic cells of size D, the diameter of the greatest bounding sphere. The bounding spheres are mapped into the cells in global space. The candidate particles can be picked out by searching the bounding spheres in the neighbor cells of the bounding sphere for the target particle. In the second‐level‐grid‐searching, a square or cubic local space of size (D + d) is partitioned into identical cells of size d, the diameter of the greatest element sphere. If two bounding spheres of two multi‐sphere particles are overlapped, the contacts occurring between the element spheres in the target multi‐sphere particle and in the candidate multi‐sphere particle are checked. Theoretical analysis and numerical tests on the memory requirement and contact detection time of this algorithm have been performed to verify the efficiency of this algorithm. The results showed that this algorithm can effectively deal with the contact problem for multi‐sphere particles. Copyright © 2015 John Wiley & Sons, Ltd.     

A rapid simulation of nano‐particle transport in a two‐dimensional human airway using POD/Galerkin reduced‐order models

An approach is proposed for the rapid prediction of nano‐particle transport and deposition in the human airway, which requires the solution of both the Navier–Stokes and advection–diffusion equations and for which computational efficiency is a challenge. The proposed method builds low‐order models that are representative of the fully coupled equations by means of the Galerkin projection and proper orthogonal decomposition technique. The obtained reduced‐order models (ROMs) are a set of ordinary differential equations for the temporal coefficients of the basis functions. The numerical results indicate that the ROMs are highly efficient for the computation (the speedup factor is approximately 3 × 10³) and have reasonable accuracy compared with the full model (relative error of ≈7 × 10^?3). Using ROMs, the deposition of particles is studied for 1≤d_n≤100 nm, where d_n is the diameter of a nano‐particle. The effectiveness of this approach is promising for applications of health risk assessment. Copyright © 2015 John Wiley & Sons, Ltd.     

In Situ Electrochemical Synthesis and Deposition of Discotic Hexa‐peri‐hexabenzocoronene Molecules on Electrodes: Self‐Assembled Structure,Redox Properties,and Application for Supercapacitor

Discotic hexa‐peri‐hexabenzocoronene (HBC) molecules are synthesized by electrochemical cyclodehydrogenation reaction and in situ self‐assembled to π‐electronic, discrete nanofibular objects with an average diameter about 70 nm, which are deposited directly onto the electrode. The nanofibers consist of columnar arrays of the π‐stacked HBC molecules and the intercolumnar distance is determined to be 1.19 nm by X‐ray diffraction, which corresponds well to the distance of 1.1 nm observed by high‐resolution transmitting electron microscopy. The diameter of the molecular columns matches the size of the discotic HBC molecule indicating face‐to‐face π‐stacking of HBC units in the column. The HBC nanofibers on electrode are redox active, and the nanosized columnar structures provide a huge surface area, which is a great benefit for the charging/discharging process, delivering excellent capacitance of 155 F g^?1. The described electrochemical deposition method shows great advantage for self‐assembling the family of insoluble and structurally designable graphene‐like nano materials, which constitutes an important step toward molecular electronics.