Hierarchical Structured Ni Nanoring and Hollow Sphere Arrays by Morphology Inheritance Based on Ordered Through-Pore Template and Electrodeposition

Silver nanoparticle-assembled micro-bowl arrays for sensitive SERS detection of pesticide residue

It is of great significance to develop a simple and effective method for constructing large-scale high-quality surface-enhanced Raman scattering (SERS) substrate. Here, an Ag nanoparticle-assembled micro-bowl array was prepared by a close-packed polystyrene (PS) sphere monolayer templated electrodeposition approach. The fabricated Ag nanoparticle-assembled micro-bowl array shows high SERS sensitivity to rhodamine 6G (R6G) under an ultra-low concentration of 1 fM, and exhibits excellent SERS spectral uniformity with a small relative standard deviation (RSD) of 7.6% and good reproducibility (a RSD ∼8.2% for the average peak intensities from different batches of SERS substrates). The fabricated micro-bowl array SERS substrate was employed to detect pesticide residue (thiram and methyl parathion) on vegetables. The limit of detections (LODs) for the two pesticides are lower than the maximum residue limits (MRLs) set by the European Union respectively, showing promising application in rapid inspection of food safety.

Colloidal lead iodide nanorings

Colloidal chemistry of nanomaterials experienced a tremendous development in the last decades. In the course of the journey 0D nanoparticles, 1D nanowires, and 2D nanosheets have been synthesized. They have in common to possess a simple topology. We present a colloidal synthesis strategy for lead iodide nanorings, with a non-trivial topology. First, two-dimensional structures were synthesized in nonanoic acid as the sole solvent. Subsequently, they underwent an etching process in the presence of trioctylphosphine, which determines the size of the hole in the ring structure. We propose a mechanism for the formation of lead iodide nanosheets which also explains the etching of the two-dimensional structures starting from the inside, leading to nanorings. In addition, we demonstrate a possible application of the as-prepared nanorings in photodetectors. These devices are characterized by a fast response, high gain values, and a linear relation between photocurrent and incident light power intensity over a large range. The synthesis approach allows for inexpensive large-scale production of nanorings with tunable properties.

Surface-enhanced Raman scattering on organic–inorganic hybrid perovskites

For the first time SERS on organic–inorganic hybrid perovskites is explored. The enhancement mechanism is discussed according to charge transfer.

Facile fabrication of pH-sensitive peptide–inorganic hollow spheres using a template-free method

The self-assembly of a heptapeptide and phosphotungstic acid into hollow spheres with pH-responsive properties was achieved using a template-free method.

Templated fabrication of periodic arrays of metallic and silicon nanorings with complex nanostructures

Here we report a scalable colloidal templating approach for fabricating periodic arrays of metallic and silicon nanorings with complex nanostructures. Non-close-packed monolayer silica colloidal crystal prepared by a simple spin-coating technology is first used as template for making periodic arrays of mushroom-like composite nanostructures consisting of silica spherical caps and polymer stems. Subsequent metal sputtering and reactive ion etching lead to the formation of ordered asymmetric nickel nanorings which can be further utilized as etching masks for patterning periodic arrays of symmetric silicon nanorings. Moreover, periodic arrays of metallic and silicon concentric double nanorings can be fabricated by using the asymmetric nickel nanorings as templates. We have also demonstrated that gold concentric double nanorings show strong surface-enhanced Raman scattering (SERS) with a SERS enhancement factor of ∼9.5 × 10(7) from adsorbed benzenethiol molecules. The SERS enhancement and the electric field amplitude distribution surrounding gold concentric double nanorings have been calculated by using finite element electromagnetic modeling. This new colloidal templating technique is compatible with standard microfabrication and enables wafer-scale production of a variety of periodic nanorings with hierarchical structures that could find important technological applications in plasmonic and magnetic devices.

Layer-controlled synthesis of WO₃ ordered nanoporous films for optimum electrochromic application

We report on a layer-controlled fabrication of two-dimensional (2D) WO3 ordered nanoporous films via a step-by-step template-assisted strategy. For this purpose, a polystyrene sphere monolayer colloidal crystal (MCC), capable of intact transfer, is adopted as the fabrication template. WO3 nanoporous films with a monolayer (L1), bilayer (L2) and trilayer (L3) were typically constructed and technical analysis illustrates that each layer is composed of fully crystalline monoclinic WO3 nanoparticles and aggregated skeletons possessing hexagonally ordered arrangements at long range. Electrochromic characterization reveals that the ITO-based WO3 nanoporous films have long cycling stability over time and improved cation insertion/extraction capacities with increasing film layer. The inserted/extracted cations of the L2 film are nearly twice that of L1, while slightly inferior to that of L3. For the L3 film, the excessive layer thickness results in longer cation diffusion path lengths, leading to relatively poor charge reversibility. Therefore, the WO3 nanoporous bilayer films prepared in our work show optimum electrochromic properties after comprehensive characterization. Additionally, the uniform nanoporous film prepared by the proposed strategy can be successfully constructed onto a curved ceramic substrate with rough surfaces, which is still a challenge for traditional spin- or dip-coating methods. This substrate-compatible feature will facilitate construction of specific functional devices and layer-controlled fabrication by a low-cost strategy could find promising applications in chemical sensors, electrochromic windows, and so on.

Lithographically patterned electrodeposition of gold, silver, and nickel nanoring arrays with widely tunable near-infrared plasmonic resonances

A novel low-cost nanoring array fabrication method that combines the process of lithographically patterned nanoscale electrodeposition (LPNE) with colloidal lithography is described. Nanoring array fabrication was accomplished in three steps: (i) a thin (70 nm) sacrificial nickel or silver film was first vapor-deposited onto a plasma-etched packed colloidal monolayer; (ii) the polymer colloids were removed from the surface, a thin film of positive photoresist was applied, and a backside exposure of the photoresist was used to create a nanohole electrode array; (iii) this array of nanoscale cylindrical electrodes was then used for the electrodeposition of gold, silver, or nickel nanorings. Removal of the photoresist and sacrificial metal film yielded a nanoring array in which all of the nanoring dimensions were set independently: the inter-ring spacing was fixed by the colloidal radius, the radius of the nanorings was controlled by the plasma etching process, and the width of the nanorings was controlled by the electrodeposition process. A combination of scanning electron microscopy (SEM) measurements and Fourier transform near-infrared (FT-NIR) absorption spectroscopy were used to characterize the nanoring arrays. Nanoring arrays with radii from 200 to 400 nm exhibited a single strong NIR plasmonic resonance with an absorption maximum wavelength that varied linearly from 1.25 to 3.33 μm as predicted by a simple standing wave model linear antenna theory. This simple yet versatile nanoring array fabrication method was also used to electrodeposit concentric double gold nanoring arrays that exhibited multiple NIR plasmonic resonances.

Fabrication of size-controllable Fe2O3 nanoring array via colloidal lithography

Tailed-Fe(2)O(3) ring arrays are fabricated by solution-dipping on a colloidal monolayer template. The influence of synthesis parameters on the quality of nanostructures has been investigated. The ring size can be controlled by changing the precursor concentration and varying the annealing time of the polystyrene sphere colloidal monolayer. In addition, the edge of the rings is sensitive to the surface tension of precursor solution, and high quality ordered ring arrays can be obtained by tuning the surface tension. This strategy allows the fabrication of specific metal oxides ring arrays with high quality and uniform morphology.

Semiconducting two-dimensional graphene nanoconstriction arrays

The fabrication and characterization of two-dimensional nanoconstriction arrays consisting of sub-20-nm graphene constrictions and interconnecting graphene islands are reported. The arrays are fabricated in a scalable top-down fashion using self-assembled close-packed polystyrene nanospheres as lithographic templates and characterized using electron microscopy, Raman spectroscopy, and charge transport measurements. At room temperature, the arrays behave as semiconductors with a field-effect conductance modulation of up to 450 and charge mobilities of ~1 cm(2) V(-1) s(-1) . The effective bandgap of the arrays scales inversely with the nanoconstriction width, indicating that its magnitude is determined by quantum confinement in the constrictions. At low temperatures, the arrays act as semiconductors, with increasing ON/OFF conductance modulation up to ∼1000, and simultaneously act as 2D arrays of coupled Coulomb islands affected by single-electron charging events. The high conductance modulation of these nanopatterned graphene materials, combined with the scalability of the patterning approach is expected to impact thin film, flexible, and transparent semiconductor electronics.

Colloidal self-assembly meets nanofabrication: from two-dimensional colloidal crystals to nanostructure arrays

Self-assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self-assembly with nanofabrication techniques, two-dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as "colloidal lithography", which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self-assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal-crystal-assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.

Strings of metal half-shells fabricated using colloidal particle monolayer as a template

A two-dimensional (2-D) polystyrene (PS) particle monolayer is demonstrated as a template for the fabrication of one-dimensional (1-D) strings of metal shells. Metal is deposited by vacuum evaporation onto the PS particle monolayer, which is tilted at an angle (theta) between the normal of the monolayer plane and the direction of metal deposition. The effects of the metal deposition thickness, the tilt angle (theta) of the particle monolayer, and the type of metal on the formation of 1-D strings of metal shells are investigated. Strings of fan-shaped Au shells are obtained at a given tilt angle and deposition thickness. On the other hand, 1-D strings of Cr and Ag cannot be obtained, and they tend to form 2-D films and half-shell dots of the metal, respectively.

General synthesis of 2D ordered hollow sphere arrays based on nonshadow deposition dominated colloidal lithography

A general strategy, nonshadow deposition dominated colloidal lithography (NSCL), was proposed for the synthesis of two-dimensional (2D) ordered hollow sphere arrays of conductive materials. Gold, polypyrrole, CdS, and ZnO were taken as model materials to demonstrate the NSCL strategy, and built as 2D hollow sphere arrays successfully. In this strategy, a thin gold coating is first introduced on a polystyrene sphere (PS) colloidal monolayer via ion-sputtering deposition, and a hollow sphere array can thus be obtained by further electrochemical deposition on such a monolayer and by subsequent removal of PSs. The proposed strategy is flexible and facile to control the microstructure and size of the hollow sphere array, and the features are as follows: (i) controllable shell of the hollow sphere from single-layer to multilayer with single or multiple compositions, (ii) tunable morphology from simple structure to hierarchical micro/nanostructure, and (iii) changeable arrangement of hollow spheres from close-packing to non-close-packing. Besides these, the hollow sphere size and the shell thickness can also be controlled by changing the colloidal sphere and deposition time, respectively. Further investigation indicates that the success of NSCL should be owed to a key step, that is, an ion-sputtering induced nonshadow deposition surrounding the whole surfaces of colloidal spheres. This allows an equipotential face and thus homogeneous deposition surrounding the surfaces of PSs in an electrochemical deposition process, and final formation of hollow sphere structure. The 2D ordered hollow sphere arrays with controllable microstructure and size could exhibit importance both in fundamental research and in practical applications.

Controllable growth and magnetic properties of nickel nanoclusters electrodeposited on the ZnO nanorod template

The ZnO nanorods were used as a template to fabricate nickel nanoclusters by electrodeposition. The ZnO nanorod arrays act as a nano-semiconductor electrode for depositing metallic and magnetic nickel nanoclusters. The growth sites of Ni nanoclusters could be controlled by adjusting the applied potential. Under -1.15 V the Ni nanoclusters could be grown on the tips of ZnO nanorods. On increasing the potential to be more negative the ZnO nanorods were covered by Ni nanoclusters. The magnetic properties of the electrodeposited Ni nanoclusters also evolved with the applied potentials.

General and simple route to micro/nanostructured hollow-sphere arrays based on electrophoresis of colloids induced by laser ablation in liquid

A general and simple route was presented to fabricate hollow sphere arrays (HSAs) with hierarchical micro/nanostructure based on electrophoresis on a polystyrene colloidal monolayer in a corresponding colloidal solution prepared by laser ablation in liquid. Si was chosen as a model material to demonstrate the validity of the route. The size and structure of such-prepared hollow spheres can be easily controlled by the size of the polystyrene spheres, the electrophoresis parameters, and the morphology of the colloidal nanoparticles. Further experiments have revealed that this strategy can be extended to produce other semiconductors' and metals' compact or noncompact HSAs, and even multicomponent HSAs with controllable spacings between adjacent spheres and tunable size of nanoparticles in the shell layers. This study could be important to synthesize some key materials in the fields of ion batteries, surface enhanced Raman scattering, new micro/nanostructured devices, and so on.

Design and electrochemical fabrication of gold binary ordered micro/nanostructured porous arrays via step-by-step colloidal lithography

Colloidal lithography is a low-cost, high-throughput, facile nanofabrication technique capable of producing a large variety of nanostructured arrays. In this letter, we report a methodology, named step-by-step colloidal lithography, using electrochemical deposition as a fabrication technique to sculpture various hexagonally packed 2D-ordered gold binary micro/nanostructured porous arrays. By the designed fabrication routes, the structures of arrays and the morphology of the building blocks in the arrays can be easily controlled. Because of the feature of step-by-step fabrication, such a strategy will provide a versatile methodology not only for unitary components but also for binary and even multiplex materials, leading to heterostructured arrays with controlled compositions and block sizes. Such morphology and structure-controlled 2D binary porous arrays will exhibit the importance in building micro/nanostructured devices.

High sensitivity and large field enhancement of symmetry broken Au nanorings: effect of multipolar plasmon resonance and propagation

The multipolar plasmon resonance and propagation of Au nanorings with symmetry broken were analyzed by using DDA and FDTD methods. Based on the multipolar plasmon resonance and propagation, we proposed ring-nanosensors with high sensitivities and optical ringnanoantennas with large local field enhancements. We revealed that the refractive index sensitivities of split nanorings are about 100% larger than those of perfect nanorings with same size; the local field intensity enhancement of split nanoring with three gaps has increased by 37% than that of dipole antennas.