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Double-layered nanoporous silver is fabricated by dealloying an electrodeposited AgCu double layer with different compositions in each layer. The pore/ligament size and porosity of each layer can be conveniently tailored by controlling the applied voltage profile when electrodepositing the AgCu double-layer precursors. Therefore, nanoporous Ag double layers with a tailor-made porous profile along the film thickness can be easily fabricated. The Ag structures thus obtained are particularly attractive as novel multifunctional enhancement substrates for surface-enhanced Raman spectroscopy (SERS) applications. When a higher porosity is created in the top layer, the double layer can trap more light because of the antireflection effect, enabling stronger SERS enhancement. On the other hand, with smaller pores formed in the top layer, the double layer readily works as a size-screening SERS substrate that can help distinguish SERS signals from a mixture of reagents with different sizes. The theoretical simulation shows good agreement with the experimental observation.

Dealloying is an important industrial technique for generating nanoporous metallic structures by selectively leaching out the more reactive metal component from an alloy material. A constant voltage is often applied to facilitate the dealloying process. Here we report the first study on dealloying with the application of a voltage waveform—specifically, pulsed voltage waveforms are applied for dealloying Ni–Cu alloys. It is found that pulsed dealloying voltage waveforms can exert a strong impact on the dealloying process by 1) significantly lowering the compositional threshold of the more reactive metal component for the dealloying reaction to take place, 2) more thoroughly removing the more reactive metal component and thus producing a porous metal of higher purity and higher porosity (volume fraction of voids), and 3) greatly affecting the morphology of the generated porous metal structure (e.g., leading to significantly thinner ligaments). The nanoporous metallic materials obtained by the pulsed voltage waveform enable supercapacitor electrodes of significantly better performance than the counterpart dealloyed with a constant voltage.

A novel porous Si (PSi) films with interconnected channels and periodic nanostructures are fabricated by a facile electrochemical etching method. The films thus obtained feature highly porous structures with nano-branches connecting pores, possessing periodically varying porosity profiles along the film thickness direction. These periodic porous Si films are found to be promising anode materials for rechargeable lithium ion batteries with a high reversible specific capacity over 2500 mAh g−1 and capacity retention over 83% after 60 cycles, which compares favorably with the conventional Si-based electrodes, including the commercially available Si nanoparticles, sputtered Si thin films, and the normal porous Si films with homogenous porosities. The improved cycling stability achieved on the periodic porous Si film is ascribed to its special nanoporous morphology featuring high surface area, interconnecting nano-branches, and structural periodicity, which helps efficiently accommodate the volume expansion and contraction along both the vertical and the planner directions during lithiation and delithiation.

In this article, we report a facile electrochemical method to modify anatase TiO2 by cathodically biasing TiO2 in an ethylene glycol electrolyte. The resulting black TiO2 is highly stable with a significantly narrower bandgap and higher electrical conductivity. Furthermore, largely improved photoconversion efficiency (increased from 48% to 72% in the visible region, and from nearly 0% to 7% in the UV region), photocatalytic efficiency, and charge-storage capability (∼42 fold increase) are achieved for the treated TiO2.

We report a scalable strategy to synthesize Fe3O4/graphene nanocomposites as a high-performance anode material for lithium ion batteries. In this study, ferric citrate is used as precursor to prepare Fe3O4 nanoparticles without introducing additional reducing agent; furthermore and show that such Fe3O4 nanoparticles can be anchored on graphene sheets which attributed to multifunctional group effect of citrate. Electrochemical characterization of the Fe3O4/graphene nanocomposites exhibit large reversible capacity (∼1347 mA h g−1 at a current density of 0.2 C up to 100 cycles, and subsequent capacity of ∼619 mA h g−1 at a current density of 2 C up to 200 cycles), as well as high coulombic efficiency (∼97%), excellent rate capability, and good cyclic stability. High resolution transmission electron microscopy confirms that Fe3O4 nanoparticles, with a size of ∼4–16 nm are densely anchored on thin graphene sheets, resulting in large synergetic effects between Fe3O4 nanoparticles and graphene sheets with high electrochemical performance.

We report on Ni-modified TiO2 nanotubes with improved photocatalytic properties. Using the as-anodized TiO2 nanotubes as templates, Ni was electrodeposited using pulsed current waveforms. It was found that the Ni deposition was first initiated at the bottoms of the intertubular voids and then grew upward, resulting in a Ni/TiO2 coaxial nanostructure with Ni wrapping around the TiO2 nanotubes. Moreover, the tube inside was kept empty and tube openings unclogged for the fabricated Ni/TiO2 nanocomposites. Further photodegradation tests using methyl red revealed that the fabricated Ni/TiO2 nanocomposites possess higher photocatalytic efficiency than the counterparts of pristine TiO2 nanotubes. The observed improved photocatalytic efficiency is ascribed to the Schottky barriers formed between Ni and TiO2.

A stable, label-free optical biosensor based on a porous silicon-carbon (pSi-C) composite is demonstrated. The material is prepared by electrochemical anodization of crystalline Si in an HF-containing electrolyte to generate a porous Si template, followed by infiltration of poly(furfuryl) alcohol (PFA) and subsequent carbonization to generate the pSi-C composite as an optically smooth thin film. The pSi-C sensor is significantly more stable toward aqueous buffer solutions (pH 7.4 or 12) compared to thermally oxidized (in air, 800 °C), hydrosilylated (with undecylenic acid), or hydrocarbonized (with acetylene, 700 °C) porous Si samples prepared and tested under similar conditions. Aqueous stability of the pSi-C sensor is comparable to related optical biosensors based on porous TiO(2) or porous Al(2)O(3). Label-free optical interferometric biosensing with the pSi-C composite is demonstrated by detection of rabbit IgG on a protein-A-modified chip and confirmed with control experiments using chicken IgG (which shows no affinity for protein A). The pSi-C sensor binds significantly more of the protein A capture probe than porous TiO(2) or porous Al(2)O(3), and the sensitivity of the protein-A-modified pSi-C sensor to rabbit IgG is found to be ~2× greater than label-free optical biosensors constructed from these other two materials.

Periodically structured Fe2O3 films are successfully fabricated by anodizing Fe foils using sinusoidally modulated current waveforms. The fabricated Fe2O3 films possess nanopores and long-range structural periodicities which can be conveniently adjusted by tuning the anodization parameters. Strong optical response and vivid film color were readily observed on the fabricated Fe2O3 films. Keywords: Fe2O3, Periodic structure, Anodization, Optical sensing

Metallic rugate filters are theoretically investigated for the first time. Our model builds on randomly dispersed metallic nanorod arrays with sinusoidally varying porosities along the film thickness. It was found that metallic rugate filters can display strong optical response in the visible and near-infrared regions for both TE and TM polarizations and for a wide range of incident angles. Moreover, the optical features of a metallic rugate filter can be fine tuned by adjusting its structural features. Interestingly, multiple-peak rugate filters can be conveniently achieved by combining different periodicities in one rugate structure. The interesting optical behaviors of the novel metal-based reflectors, combined with the many desirable properties of metals (e.g. electric, thermal, magnetic, mechanical, and chemical properties) are bound to lead to various multi-functional optical devices.

Self-organized TiO2 nanomaterials grown by anodic oxidation of Ti foils have attracted broad scientific interest due to their wide potential applications. The majority of anodic TiO2 nanostructures studied to date are in the form of self-ordered nanotube arrays. Here we report an exotic type of multilayered nanoporous TiO2 films that are conveniently fabricated by anodizing Ti foils of high imperfection levels using a novel multipulse anodization method. The fabricated TiO2 films feature tens of well-defined layers whose long-range structural periodicity leads to photonic band gaps in the visible wavelengths and vivid film colors. Moreover, the optical responses (or the film color) of the fabricated TiO2 multilayers not only are sensitive to environmental chemicals but also can be electrically switched on and off repeatedly, demonstrating their novel potential applications for, e.g., colored smart windows or electric display boards.

Gradient self-organized TiO2 nanotube arrays with the tube diameters and length gradually changing along the sample plane are conveniently fabricated. The fabrication method is based on asymmetric anodization with the point cathode placed close to the edge of the titanium foil anode. Mechanism study reveals that the drastic variance in the voltage drop over the tube bottom at different locations along the film is responsible for the formation of the gradient morphology. Experimentally, moderate electrolyte conductivitiesandsufficientlyhighanodizationvoltagesarenecessarytoenablethedesiredgradientTiO2 nanotubearrays.Moreover, the structural features of the fabricated gradient TiO2 nanotube arrays can be further adjusted by controlling the imperfection level of the titanium substrate.

Here we present a simple and effective method to fabricate porous silicon photonic crystal-based hybrid particles by soft lithography. These fabricated hybrid particles are composed of pristine porous silicon structures strengthened by a polymer infused nanocomposite framework. The pristine porous silicon moiety serves as a sensor because of its environmentally sensitive optical features, while the polymer-infused moiety provides a mechanically resilient scaffold and its invariant optical features can be used as an optical barcode and a built-in self-reference for optical sensing. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

From searching the Cambridge Structural Database (CSD), we noticed an exceptionally widespread distribution of the interatomic distances (from 2.39 to 3.52 A) between thioether S atoms and Ag(I) ions, in comparison with the cases in other common ligands such as nitriles and pyridyls. The variable bonding distances point to a highly flexible and reversible nature of thioether−Ag(I) interaction, which might help crystallize large and complex organic molecules into ordered coordination networks under mild conditions. We provide a number of new structures for illustration. In 1, two Ag(I) ions are coordinated by three 1,2,3-tris(methylthio)phenyl groups (i.e., 9 S atoms) to form a three-bladed paddlewheel block as a node for an enlarged honeycomb sheet. In 2, a porphyrin molecule with four 1,2,3-tris(phenylthio)phenyl groups coordinates to Ag(I) atoms to form a parallelogram net, featuring free-standing phenylthio groups in the channel. In 3, a starburst molecule with six 4-methylthiophenyl groups attached to...

Gradient TiO2 nanotube arrays were fabricated by anodization using an asymmetric electrode configuration. The nanotube arrays thus obtained display a gradually changing distribution of tube diameters and length across the sample plane. The application of the fabricated gradient TiO2 nanotube arrays as optical sensors is also demonstrated. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Four cubane-like Cu4I4 units are assembled around an iodine atom to form the giant, mixed-valent Cu(II)Cu(I)15I17 cluster. The Cu(II)Cu(I)15I17 cluster and a bipyrazole linker form a 3D open framework with paramagnetic and thermochromic properties. This paper also touches on the resemblance of this cluster to the self-similar object of a Sierpinski tetrahedron.

The large aromatic ligand 9,10-bis{[3,4-bis(methylthio)phenyl]ethynyl}anthracene (L) interacts with CuCN to form a 2D, fluorescent hybrid network, L·2CuCN. Although the edge-to-face stacking between the organic π-electron systems prevails in the molecular crystal structure of L, the face-to-face stacking becomes more distinct in L·2CuCN. A preliminary survey on similar hybrid networks in the Cambridge Structural Database (CSD) suggests that 1D inorganic moieties may help maintain and induce cofacial stacking of the associated aromatic ligands.

We report the numerical study of a selective thermal emitter based on a metallic multilayered structure consisting of a graded antireflection top layer, a middle layer with uniform porosity (i.e., volume fraction of voids), and a nonporous substrate layer. Simulation results show that the proposed emitters feature an emission edge in near-IR where the emissivity drops from over 0.9 to below 0.1, for both the TE and TM polarizations. Moreover, these desired emission characteristics persist for a wide range of emission angles with the emission edge nearly nonshifted, making the proposed emitters promising for achieving isotropic thermal emission. The designed emitters are particularly attractive for the thermal-photovoltaic applications by suppressing emission below the photovoltaic material bandgap, which is normally in near-IR.

A facile electrochemical method to selectively remove the outer walls of anodic TiO(2) nanotubes by leaving the as-anodized nanotubes in the same electrolyte and applying an electric field parallel to the anodic film for several minutes is reported. The better-separated single-walled TiO(2) nanotubes thus obtained show significantly improved photocatalytic efficiency compared with their non-etched counterparts.

Plasmonic materials offer the remarkable ability to manipulate light by metal-dielectric features significantly smaller than the wavelengths of free space photons. The fabrication of such miniscule features for the desired plasmonic properties, however, remains challenging. Here we report an economical and versatile bottom-up approach that combines electrodeposition and dealloying techniques for fabricating elaborate metal-based structures, achieving structural resolutions comparable to current lithography techniques. We present our studies on the metal-based counterpart of the rugate filter. These metal-based photonic films are porous, magnetic, and feature strong optical responses in visible wavelengths, while their structural periodicities are an order of magnitude smaller than the light's free space wavelength.

Rugated porous Fe3O4 thin films were synthesized by a facile multi-pulse electrochemical anodization method. The fabricated Fe3O4 films are directly grown on Fe, featuring nano-channels with periodically rugated channel walls running throughout the film thickness direction. Electrochemical measurements show that the as-prepared Fe3O4 films readily serve as high-performance anode materials for lithium ion batteries with a specific capacity of 1100, 880 and 660 mA h g−1 at 0.1, 0.2, and 0.5 C, respectively, which compared favorably with the conventional straight-channel counterparts fabricated by DC anodization. Moreover, the cycling capability test of the novel electrode at 0.1 C for 100 cycles shows a steady charge/discharge platform, indicating a high cycling stability and structural robustness. The observed improvements of the rugated Fe3O4 films as lithium ion battery anode materials are attributed to their special periodic rugated nanostructures.

Plasmonic materials offer the remarkable ability to manipulate light by metal―dielectric features significantly smaller than the wavelengths of free space photons. The fabrication of such minuscule features for the desired plasmonic properties, however, remains challenging. Here, we report an economical and versatile bottom-up approach that combines electrodeposition and de-alloying techniques for fabricating elaborate metal-based structures, achieving structural resolutions comparable to the present lithography techniques. We present our studies on the metal-based counterpart of the rugate filter. These metal-based photonic films are porous, magnetic, and feature strong optical responses in visible wavelengths, while their structural periodicities are an order of magnitude smaller than the light's free space wavelength.