Exchange-coupled R2Fe14B/α-Fe (R=Nd or Pr) nanocomposite bulk magnets with nearly full density have been successfully produced by shock compaction of melt-spun powders. X-ray diffraction and transmission electronic microscopy analyses of the shock-consolidated compacts showed no grain growth upon compaction, in fact, a decrease in the crystallite size of both the hard and soft phases was observed. As a consequence, magnetic properties were retained and even improved after compaction. Hysteresis loops of the shock-consolidated powder compacts showed a smooth single-phaselike behavior, indicating effective exchange coupling between hard and soft magnetic phases.
Electron energy-loss spectroscopy (EELS) is one of the most important analytical tools that modern transmission electron microscopy (TEM) possesses. EELS is powerful not only in quantitative chemical microanalysis but also in probing local chemical-bonding information. Using a ultrafine electron probe, EELS analysis can be carried out from a region smaller than 1 nm. The analytical information from EELS can be combined with the image and diffraction data provided by TEM, providing a comprehensive characterization on the local atomic, chemical, and electronic structures (1–3). As an extensive development of EELS, energy-filtered electron imaging has been implemented in recent years, which allows high-spatial-resolution chemical imaging as well as imaging using fine structures provided by EELS (4). The most recent advances in developing a fine electron probe, as small as 0.1–0.2 nm, allows chemical analysis atomic column-by-column (5,6). These powerful techniques are undoubtedly the most effective tools that can be used in complementary with high-resolution TEM for quantitative structure determination of materials that are of importance to industry applications. The objective of this chapter is to outline the fundamentals of EELS, energy-filtered electron imaging, and their applications in analysis of chemical and electronic structures of inorganic materials. This chapter serves as an introduction to these techniques and our emphasis is on their applications in problems of interesting to industry.
The phase transformation, coalescence, and twin structure of thermally annealed 6 nm FePt nanocrystals under high vacuum on an amorphous carbon surface have been investigated. A1-FePt phase to L10−FePt phase transformation occurs at 530 °C. The multilayered nanocrystal assemblies coalesce to form larger grains at 600 °C. These coalesced nanocrystals do not form a single grained structure; instead, twinning becomes a characteristic structure feature. The surface of the coalescent grains consists of {111} and (001) facets.
Conversion cells for harvesting solar energy and mechanical energy are usually separate and independent entities that are designed and built following different physical principles. Developing a technology that harvests multiple-type energies in forms such as sun light and mechanical around the clock is desperately desired for fully utilizing the energies available in our living environment. We report a hybrid cell that is intended for simultaneously harvesting solar and mechanical energies. Using aligned ZnO nanowire arrays grown on surfaces of a flat substrate, a dye-sensitized solar cell is integrated with a piezoelectric nanogenerator. The former harvests solar energy irradiating on the top, and the latter harvests ultrasonic wave energy from the surrounding. The two energy harvesting approaches can work simultaneously or individually, and they can be integrated in parallel and serial for raising the output current and voltage, respectively, as well as power. It is found that the voltage output from the solar cell can be used to raise the output voltage of the nanogenerator, providing an effective approach for effectively storing and utilizing the power generated by the nanogenerator. Our study demonstrates a new approach for concurrently harvesting multiple types of energies using an integrated hybrid cell so that the energy resources can be effectively and complementary utilized whenever and wherever one or all of them is available.
Abstract Water covers ≈70% of the Earth's surface and it contains a tremendous amount of energy that remains unexploited. With the advance of nanotechnology, new strategies toward harnessing water energy based on new mechanisms are proposed. Here, the interaction mechanisms between a water droplet and a solid surface for harvesting energy, including water–solid contact electrification in the four basic working modes of a triboelectric nanogenerator and streaming current, are reviewed. Among them, nanogenerators based on the contact electrification show the highest output. Practical applications are also presented, such as sensing application, wearable power generation, all‐weather power generation, and blue energy solutions. At last, perspectives and opportunities for using water/liquid‐based energy are discussed.
The work function at the tips of individual multiwalled carbon nanotubes has been measured by an in situ transmission electron microscopy technique. The tip work function shows no significant dependence on the diameter of the nanotubes in the range of 14–55 nm. Majority of the nanotubes have a work function of 4.6–4.8 eV at the tips, which is 0.2–0.4 eV lower than that of carbon. A small fraction of the nanotubes have a work function of ∼5.6 eV, about 0.6 eV higher than that of carbon. This discrepancy is suggested due to the metallic and semiconductive characteristics of the nanotube.
