Electrophoretic Deposition of Single Nanoparticles.

The controlled assembly of colloid particles on a solid substrate has always been a major challenge in colloid and surface science. Here we provide an overview of electrophoretic deposition (EPD) of single charge-stabilized nanoparticles. We demonstrate that surface templated EPD (STEPD) assembly, which combines EPD with top-down nanofabrication, allows a wide range of nanoparticles to be built up into arbitrary structures with high speed, scalability, and excellent fidelity. We will also discuss some of the current colloid chemical limitations and challenges in STEPD assembly for sub-10 nm nanoparticles and for the fabrication of densely packed single particle arrays.

Fabrication of Single-Nanocrystal Arrays.

To realize the full potential of nanocrystals in nanotechnology, it is necessary to integrate single nanocrystals into addressable structures; for example, arrays and periodic lattices. The current methods for achieving this are reviewed. It is shown that a combination of top-down lithography techniques with directed assembly offers a platform for attaining this goal. The most promising of these directed assembly methods are reviewed: capillary force assembly, electrostatic assembly, optical printing, DNA-based assembly, and electrophoretic deposition. The last of these appears to offer a generic approach to fabrication of single-nanocrystal arrays.

A Tunable Polymer-Metal Based Anti-Reflective Metasurface.

Anti-reflective surfaces are of great interest for optical devices, sensing, photovoltaics, and photocatalysis. However, most of the anti-reflective surfaces lack in situ tunability of the extinction with respect to wavelength. This communication demonstrates a tunable anti-reflective surface based on colloidal particles comprising a metal core with an electrochromic polymer shell. Random deposition of these particles on a reflective surface results in a decrease in the reflectance of up to 99.8% at the localized surface plasmon resonance frequency. This narrow band feature can be tuned by varying the pH or by application of an electric potential, resulting in wavelength shifts of up to 30 nm. Electrophoretic particle deposition is shown to be an efficient method for controlling the interparticle distance and thereby further optimizing the overall efficiency of the anti-reflective metasurface.

Boosting the Performance of Iron-Phthalocyanine as Cathode Electrocatalyst for Alkaline Polymer Fuel Cells Through Edge-Closed Conjugation.

Recent progress in anion-exchange membranes has evoked increasing interests in alkaline polymer fuel cells (APFCs). A large body of recent research has demonstrated attractive activity of Fe-N macrocycle complexes as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. To be a substitute for Pt in APFCs, however, most of the macrocycle molecules remain largely unsatisfactory in both of the catalytic activity and durability. Herein, we show that a one-pot microwave conjugation results in a polymerized iron-phthalocyanine (pFePc) which exhibits extremely high ORR performance, showing activity much better than that of the FePc monomer and 20 wt % Pt/C, and similar to that of the 60 wt % Pt/C under the same catalyst loading. Furthermore, we proposed an edge-closing strategy to significantly enhance the stability of the pFePc catalyst in alkaline media by eliminating the edge anhydride groups. Using the edge-closed pFePc as the cathode catalyst in APFC, a power density as high as 452 mW·cm-2 is achieved, which is among the best performance of non-noble metal catalyst-based APFCs so far reported.

Direct Assembly of Large Area Nanoparticle Arrays.

A major goal of nanotechnology is the assembly of nanoscale building blocks into functional optical, electrical, or chemical devices. Many of these applications depend on an ability to optically or electrically address single nanoparticles. However, positioning large numbers of single nanocrystals with nanometer precision on a substrate for integration into solid-state devices remains a fundamental roadblock. Here, we report fast, scalable assembly of thousands of single nanoparticles using electrophoretic deposition. We demonstrate that gold nanospheres down to 30 nm in size and gold nanorods <100 nm in length can be assembled into predefined patterns on transparent conductive substrates within a few seconds. We find that rod orientation can be preserved during deposition. As proof of high fidelity scale-up, we have created centimeter scale patterns comprising more than 1 million gold nanorods.

Directed Chemical Assembly of Single and Clustered Nanoparticles with Silanized Templates.

The assembly of nanoscale materials into arbitrary, organized structures remains a major challenge in nanotechnology. Herein, we report a general method for creating 2D structures by combining top-down lithography with bottom-up chemical assembly. Under optimal conditions, the assembly of gold nanoparticles was achieved in less than 30 min. Single gold nanoparticles, from 10 to 100 nm, can be placed in predetermined patterns with high fidelity, and higher-order structures can be generated consisting of dimers or trimers. It is shown that the nanoparticle arrays can be transferred to, and embedded within, polymer films. This provides a new method for the large-scale fabrication of nanoparticle arrays onto diverse substrates using wet chemistry.

Potential-Scanning Localized Plasmon Sensing with Single and Coupled Gold Nanorods.

Single plasmonic nanoparticles can potentially serve as optical sensors for detecting local refractive index changes. However, simultaneous monitoring of the scattering spectra from multiple nanoparticles is not practical. Here we perform potential-scanning localized surface plasmon resonance (LSPR) sensing. Gold nanorods are immobilized on an ITO electrode. Instead of collecting the full spectrum, as is done in conventional LSPR sensing, the electrode potential is scanned while the rod spectra are monitored at a single wavelength. We demonstrate that refractive index changes can be determined from single wavelength experiments and we further find that gold nanorod (NR) dimers exhibit higher refractive index sensitivities than single NRs in both potential-scanning and conventional wavelength-scanning based LSPR sensing.

A virtual instrument to standardise the calibration of atomic force microscope cantilevers.

Atomic force microscope (AFM) users often calibrate the spring constants of cantilevers using functionality built into individual instruments. This calibration is performed without reference to a global standard, hindering the robust comparison of force measurements reported by different laboratories. Here, we describe a virtual instrument (an internet-based initiative) whereby users from all laboratories can instantly and quantitatively compare their calibration measurements to those of others-standardising AFM force measurements-and simultaneously enabling non-invasive calibration of AFM cantilevers of any geometry. This global calibration initiative requires no additional instrumentation or data processing on the part of the user. It utilises a single website where users upload currently available data. A proof-of-principle demonstration of this initiative is presented using measured data from five independent laboratories across three countries, which also allows for an assessment of current calibration.

Fabrication of Hollow Materials by Fast Pyrolysis of Cellulose Composite Fibers with Heterogeneous Structures.

A facile method for the fabrication of inorganic hollow materials from cuprammonium cellulose composite filaments based on fast pyrolysis has been developed. Unlike Ostwald ripening, approaches based on the Kirkendall effect, and other template methods, this process yielded hollow materials within 100 s. The heterogeneous structure of the cellulose composite fibers and the gradient distribution of the metal oxides are the main reasons for the formation of the hollow structure. The diameter, wall thickness, and length of the hollow microfibers could be conveniently controlled. With their perfect morphology, these hollow structural materials have great potential for use in various fields.