In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.

Multiferroics: progress and prospects in thin films.

In this review, the technologies and working principles of different materials used in supercapacitors are explained. The most important supercapacitor active materials are discussed from both research and application perspectives, together with brief explanations of their properties, such as specific surface area and capacitance values. A review of different supercapacitor electrolytes is given and their positive and negative features are discussed. Finally, cell configurations are considered, pointing out the advantages and drawbacks of each configuration.

Review on supercapacitors: Technologies and materials

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

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Ferroelectric thin films: Review of materials, properties, and applications

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

High J/sub c/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films have been fabricated on LaMnO/sub 3/ buffered ion-beam assisted deposition (IBAD) MgO template layers. A LaMnO/sub 3/ buffer layer is compatible with MgO surfaces and also provides a good template for growing high current density YBCO films. LaMnO/sub 3/ buffer layers were deposited using rf magnetron sputtering. On LaMnO/sub 3/-buffered-MgO [100] single crystal substrates, YBCO films with a J/sub c/ of over 4 M/cm/sup 2/ were grown using both pulsed laser deposition (PLD) and ex-situ BaF/sub 2/ process. Using PLD, J/sub c/ of 1.8 MA/cm/sup 2/ at 77 K was obtained on 200-nm-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates. In addition, an I/sub c/ of 230 A/cm-width was obtained for 1.65-/spl mu/m-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates using PLD at Los Alamos National Laboratory. This performance is comparable to the best single-layer results achieved on IBAD-MgO substrates.

Fabrication of high J/sub c/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// tapes using the newly developed lanthanum manganate single buffer layers

We report temperature and magnetic field dependences of the longitudinal and transverse magnetoresistances of high-quality epitaxial ${\mathrm{SrRuO}}_{3}$ thin films. We also report Hall effect measurements in the paramagnetic and ferromagnetic states. The magnetic field dependence of the longitudinal magnetoresistivity shows a simple scaling \ensuremath{\sim}${\mathit{H}}^{2}$/(T-${\mathit{T}}_{\mathit{c}}$${)}^{2}$ far above the ferromagnetic transition temperature ${\mathit{T}}_{\mathit{c}}$. This observation supports a presence of localized magnetic moments above ${\mathit{T}}_{\mathit{c}}$. \textcopyright{} 1996 The American Physical Society.

Magnetotransport properties of SrRuO3 epitaxial thin films on (100) LaAlO3: Presence of localized magnetic moments.

The critical current density (Jc) of very thin YBa2Cu3O7?? (YBCO) films can approach 10?MA?cm?2 at 77?K in self-field, but for such films Jc drops sharply as the film thickness is increased. We have shown previously that this strong thickness dependence results from an enhancement of Jc near the film?substrate interface. In the present paper we investigate interfacial enhancement using laser-deposited YBCO films on NdGaO3 substrates, and find that we can adjust deposition conditions to switch the enhancement on and off. We find that the 'on' state is accompanied by a dense array of interfacial misfit dislocations, while we do not observe dislocations in films prepared in the 'off' state. This result appears to be but one of many examples in which interfacial properties of electronic film materials are profoundly affected by stress-induced defects at the film?substrate interface; however, to our knowledge the present work is the only case in which electronic properties are shown to be enhanced by such defects.

The role of interfacial defects in enhancing the critical current density of YBa2Cu3O7−δ coatings

Local atomic structure in cubic stabilized zirconia

Misfit dislocations at YBa 2 Cu 3 O 7− δ (YBCO)/SrTiO 3 (STO) interfaces were studied to understand effects which could be responsible for the high interfacial J c in YBCO thin films. In YBCO films with thickness ranging from 5 to 100 nm, the interfacial structures (e.g. misfit dislocations) of YBCO/STO were investigated using moire fringe contrast in plan-view transmission electron microscopy (TEM). The observed moire pattern has a spacing of 17 nm which corresponds to the lattice mismatch between the YBCO a lattice spacing and the cubic STO lattice constant. As the YBCO thickness reaches 100 nm, twin structures dominate the image contrast. Our observations indicate that the moire pattern originates from the lattice mismatch between the substrate and the orthorhombic phase of YBCO.

S. R. Foltyn

Papers

Fabrication of high J/sub c/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// tapes using the newly developed lanthanum manganate single buffer layers

Magnetotransport properties of SrRuO3 epitaxial thin films on (100) LaAlO3: Presence of localized magnetic moments.

The role of interfacial defects in enhancing the critical current density of YBa2Cu3O7−δ coatings

Local atomic structure in cubic stabilized zirconia

Identification of the misfit dislocations at YBa2Cu3O7−δ/SrTiO3 interface using moiré fringe contrast