Colm O'Dwyer

Light‐Emitting Diodes with Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals are promising luminophores for creating a new generation of electroluminescence devices. Research on semiconductor nanocrystal based light-emitting diodes (LEDs) has made remarkable advances in just one decade: the external quantum efficiency has improved by over two orders of magnitude and highly saturated color emission is now the norm. Although the device efficiencies are still more than an order of magnitude lower than those of the purely organic LEDs there are potential advantages associated with nanocrystal-based devices, such as a spectrally pure emission color, which will certainly merit future research. Further developments of nanocrystal-based LEDs will be improving material stability, understanding and controlling chemical and physical phenomena at the interfaces, and optimizing charge injection and charge transport.

Bottom-up growth of fully transparent contact layers of indium tin oxide nanowires for light-emitting devices

Thin layers of indium tin oxide are widely used as transparent coatings and electrodes in solar energy cells, flat-panel displays, antireflection coatings, radiation protection and lithium-ion battery materials, because they have the characteristics of low resistivity, strong absorption at ultraviolet wavelengths, high transmission in the visible, high reflectivity in the far-infrared and strong attenuation in the microwave region. However, there is often a trade-off between electrical conductivity and transparency at visible wavelengths for indium tin oxide and other transparent conducting oxides. Here, we report the growth of layers of indium tin oxide nanowires that show optimum electronic and photonic properties and demonstrate their use as fully transparent top contacts in the visible to near-infrared region for light-emitting devices.

Structuring materials for lithium-ion batteries: advancements in nanomaterial structure, composition, and defined assembly on cell performance

This review outlines the developments in the structure, composition, size, and shape control of many important and emerging Li-ion battery materials on many length scales, and details very recent investigations on how the assembly and programmable order in energy storage materials have not only influenced and dramatically improved the performance of some Li-ion batteries, but offered new routes toward improved power densities. This review also describes and discusses material aspects of hybrid and multiphasic materials including silicon, germanium, a wide range of metal oxides, alloys and crystal structures, carbons and other important materials. Methods including engineered porosity that offer the energy density of Li-ion batteries and the power density of pseudocapacitors are also highlighted. Recent developments in the analytical methods, electrochemical response, and the structure, composition, size, shape and defined assembly of active materials for a wide range of Li-ion cathodes and anodes are compared and assessed with respect to cell performance. Perspectives on the future development of energy storage materials based on structure as well as chemistry are also outlined.

Artificial opal photonic crystals and inverse opal structures – fundamentals and applications from optics to energy storage

Photonic crystals (PhCs) influence the propagation of light by their periodic variation in dielectric contrast or refractive index. This review outlines the attractive optical qualities inherent to most PhCs namely the presence of full or partial photonic band gaps and the possibilities they present towards the inhibition of spontaneous emission and the localization of light. Colloidal self-assembly of polymer or silica spheres is one of the most favoured and low cost methods for the formation of PhCs as artificial opals. The state of the art in growth methods currently used for colloidal self-assembly are discussed and the use of these structures for the formation of inverse opal architectures is then presented. Inverse opal structures with their porous and interconnected architecture span several technological arenas – optics and optoelectronics, energy storage, communications, sensor and biological applications. This review presents several of these applications and an accessible overview of the physics of photonic crystal optics that may be useful for opal and inverse opal researchers in general, with a particular emphasis on the recent use of these three-dimensional porous structures in electrochemical energy storage technology. Progress towards all-optical integrated circuits may lie with the concepts of the photonic crystal, but the unique optical and structural properties of these materials and the convergence of PhC and energy storage disciplines may facilitate further developments and non-destructive optical analysis capabilities for (electro)chemical processes that occur within a wide variety of materials in energy storage research.

The origin of shape sensitivity in palladium-catalyzed Suzuki–Miyaura cross coupling reactions

The shape sensitivity of Pd catalysts in Suzuki-Miyaura coupling reactions is studied using nanocrystals enclosed by well-defined surface facets. The catalytic performance of Pd nanocrystals with cubic, cuboctahedral and octahedral morphologies are compared. Superior catalytic reactivity is observed for Pd NCs with {100} surface facets compared to {111} facets. The origin of the enhanced reactivity associated with a cubic morphology is related to the leaching susceptibility of the nanocrystals. Molecular oxygen plays a key role in facilitating the leaching of Pd atoms from the surface of the nanocrystals. The interaction of O2 with Pd is itself facet-dependent, which in turn gives rise to more efficient leaching from {100} facets, compared to {111} facets under the reaction conditions.

Vanadate Conformation Variations in Vanadium Pentoxide Nanostructures

We report the comparative structural-vibrational study of nanostructures of nanourchins, nanotubes, and nanorods of vanadium oxide. The tube walls comprise layers of vanadium oxide with the organic surfactant intercalated between atomic layers. Both Raman scattering and infrared spectroscopies showed that the structure of nanourchins, nanotubes, and nanorods of vanadium oxide nanocomposite are strongly dependent on the valency of the vanadium, its associated interactions with the organic surfactant template, and on the packing mechanism and arrangement of the surfactant between vanadate layers. Accurate assignment of the vibrational modes to the V–O coordinations has allowed their comparative classification and relation to atomic layer structure. Although all structures are formed from the same precursor, differences in vanadate conformations due to the hydrothermal treatment and surfactant type result in variable degrees of crystalline order in the final nanostructure. The nanotube-containing nanourchins contain vanadate layers in the nanotubes that are in a distorted –V 5+ conformation, whereas the the nanorods, by comparison, show evidence for V 5+ and V 4+

Hierarchical NiO–In2O3 microflower (3D)/ nanorod (1D) hetero-architecture as a supercapattery electrode with excellent cyclic stability

Three-dimensional (3D) hybrid nanostructured electrodes based on one-dimensional (1D) nanorod arrays have recently attracted great attention owing to their synergistic effect of three-dimensional nanostructures and application in energy storage and conversion devices. Here, we designed a heterostructured supercapattery electrode from a combination of NiO and In2O3 with a hierarchical hybrid microstructure on nickel foam (NF). Simultaneous heterogeneous growth of 1D nanorod-supported 3D microflower structures on nickel foam enhanced the non-capacitive faradaic energy storage performance due to the synergistic contribution from hierarchical hybrid nanostructure. The heterostructured electrode exhibits a high specific capacity of 766.65 C g−1 at 5 A g−1 and remains as high as 285.12 C g−1 at 30 A g−1. The composite electrode shows an excellent rate performance as a sandwich type symmetric device, offering a high specific energy of 26.24 W h kg−1 at a high power of 1752.8 W kg−1. The device shows a long term cyclic stability with 79% retention after 50 000 cycles, which is remarkable for an oxide based pseudocapacitor. These results suggest that NiO–In2O3 with hybrid micro/nano architecture could be a promising electrode for next generation supercapatteries.

Pattern formation induced by an electric field in a polymer-air-polymer thin film system†

Strong electric fields produce forces that can overcome the surface tension in thin liquid polymer films and in this way induce an instability of the free surface of the film, that triggers the formation of structures on a micrometer length scale. Here, we study experimentally a polymer–air–polymer system for several combinations of polymer films. These results are accompanied by theoretical considerations based on coupled long-wave time evolution equations for the two free surface profiles. The linear stability and nonlinear time evolution are investigated and compared to the experimental findings. The prediction that the instability always evolves through a mirror mode that couples the two surfaces in an anti-phase manner agrees well with the experimental results. The model describes well the linear (early stage) evolution of the instability. In the non-linear (later stage) evolution, topographical differences in the instability pattern occur if the mobilities of the two layers significantly differ and an unpredicted acceleration of growth is seen in thinner less mobile films. Possible reasons for the mismatch are discussed.

Atomic Layer Structure of Vanadium Oxide Nanotubes Grown on Nanourchin Structures

Science Foundation Ireland (SFI grant no. 02/IN.1/172); Fondo Nacional de Desarrollo Cientifico y Tecnologico, Chile ( FONDECyT grants 1050344, 1030102, 7050081); University of Chile; Universidad Tecnologica Metropolitana, Chile

Supercapattery Based on Binder-Free Co3(PO4)2·8H2O Multilayer Nano/Microflakes on Nickel Foam

A binder-free cobalt phosphate hydrate (Co3(PO4)2·8H2O) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co2+ and PO4-3 were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co3(PO4)2·8H2O modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g-1 (capacitance of 1578.7 F g-1) at a current density of 5 mA cm-2 and remains as high as 566.3 C g-1 (1029.5 F g-1) at 50 mA cm-2 in 1 M NaOH. A supercapattery assembled using Co3(PO4)2·8H2O/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g-1 (volumetric capacitance of 4.44 F cm-3). Furthermore, the device offers a high specific energy of 29.29 Wh kg-1 (energy density of 1.17 mWh cm-3) and a specific power of 4687 W kg-1 (power density of 187.5 mW cm-3).