Colossal Barocaloric Effect by Large Latent Heat Produced by First-Order Intersite-Charge-Transfer Transition

Materials which show novel thermal properties can be used to make highly efficient and environmentally friendly energy systems for thermal energy storage and refrigeration through caloric effects. An A-site-ordered quadruple perovskite-structure oxide, NdCu₃Fe₄O₁₂, is found to release significant latent heat, 25.5 kJ kg⁻¹ (157 J cc⁻¹), at the intersite-charge-transfer transition temperature near room temperature. The transition is first-order and accompanied by an unusual magnetic ordering and a large negative-thermal-expansion-like volume change, and thus, it causes a large entropy change (84.2 J K⁻¹ kg⁻¹). The observed entropy change is comparable to the largest changes reported in inorganic solid materials, and more importantly, it is utilized through a colossal barocaloric effect. The adiabatic temperature change by applying 5.1 kbar pressure is estimated to reach 13.7 K, which means efficient refrigeration can be realized through this effect.     

Metal Single-Atom Cocatalyst on Carbon Nitride for the Photocatalytic Hydrogen Evolution Reaction: Effects of Metal Species

Single-atom (SA) catalysts exhibit high activity in various reactions because there are no inactive internal atoms. Accordingly, SA cocatalysts are also an active research fields regarding photocatalytic hydrogen (H₂) evolution which can be generated by abundant water and sunlight. Herein, it is investigated whether 10 transition metal elements can work as an SA on graphitic carbon nitride (g-C₃N₄; i.e., gCN), a promising visible-light-driven photocatalyst. A method is established to prepare SA-loaded gCN at high loadings (weight of ≈3 wt.% for Cu, Ni, Pd, Pt, Rh, and Ru) by modulating the photoreduction power. Regarding Au and Ag, SAs are formed with difficulty without aggregation because of the low binding energy between gCN and the SA. An evaluation of the photocatalytic H₂-evolution activity of the prepared metal SA-loaded gCN reveals that Pd, Pt, and Rh SA-loaded gCN exhibits relatively high H₂-evolution efficiency per SA. Transient absorption spectroscopy and electrochemical measurements reveal the following: i) Pd SA-loaded gCN exhibits a particularly suitable electronic structure for proton adsorption and ii) therefore they exhibit the highest H₂-evolution efficiency per SA than other metal SA-loaded gCN. Finally, the 8.6 times higher H₂-evolution rate per active site of Pd SA is achieved than that of Pd-nanoparticles cocatalyst.     

Nanoimprinting using release-agent-coated resins

A fluorinated self-assembled monolayer (F-SAM) is mainly used as the antisticking layer. To prevent the F-SAM coated on the nanoimprint lithography (NIL) mold from deteriorating, we propose a new form of nanoimprinting using a release-agent-coated resin. The results from measuring the surface free energy and observations by scanning probe microscopy (SPM) confirmed that the surface free energy, frictional force, and adhesion force of the release-agent spray-coated polymethylmethacrylate (PMMA) were lower than those of PMMA. To prove the release-agent spray-coated PMMA had a releasing effect, we tried to undertake thermal nanoimprinting on it using a mold without F-SAM. The pattern was clearly imprinted on the resin without any signs of adhesion.     

Grain boundary atomic structures and light-element visualization in ceramics: combination of Cs-corrected scanning transmission electron microscopy and first-principles calculations

Grain boundaries and interfaces of crystals have peculiar electronic structures, caused by the disorder in periodicity, providing the functional properties, which cannot be observed in a perfect crystal. In the vicinity of the grain boundaries and interfaces, dopants or impurities are often segregated, and they play a crucial role in deciding the properties of a material. Spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM), allowing the formation of sub-angstrom-sized electron probes, can directly observe grain boundary-segregated dopants. On the other hand, ceramic materials are composed of light elements, and these light elements also play an important role in the properties of ceramic materials. Recently, annular bright-field (ABF)-STEM imaging has been proposed, which is now known to be a very powerful technique in producing images showing both light- and heavy-element columns simultaneously. In this review, the atomic structure determination of ceramic grain boundaries and direct observation of grain boundary-segregated dopants and light elements in ceramics were shown to combine with the theoretical calculations. Examples are demonstrated for well-defined grain boundaries in rare earth-doped Al(2)O(3) and ZnO ceramics, CeO(2) and SrTiO(3) grain boundary, lithium battery materials and metal hydride, which were characterized by Cs-corrected high-angle annular dark-field and ABF-STEM. It is concluded that the combination of STEM characterization and first-principles calculation is very useful in interpreting the structural information and in understanding the origin of the properties in various ceramics.     

Evaluation of TEM samples of an Mg-Al alloy prepared using FIB milling at the operating voltages of 10 kV and 40 kV

Transmission electron microscopy (TEM) samples of an Mg-Al alloy has been prepared using a Ga-focused ion beam (FIB) milling at two different operating voltages of 10 kV and 40 kV to investigate the influence of the FIB energy on the sample quality. The fine structures of the samples have been studied using a high resolution TEM, and the concentration of the implanted Ga was analysed using an energy dispersive X-ray (EDX) analysis. The result of the TEM observation revealed that point defects were introduced to the sample finally milled at 40 kV but not at 10 kV. However, crystal lattice images and electron diffraction patterns were clearly observed on both the samples. The typical influence of the FIB energy was indicated in the elemental analysis. The relative Ga concentration in the thin sample finally milled at 10 kV was 1.0-2.0 at% that is less than half of 4.0-6.0 at% of the Ga concentration in the sample finally milled at 40 kV. A comparison between the experimental results of the Ga concentration measurement with simulation was also discussed.     

A high fill factor and progressive scan PtSi Schottky-barrier IR-CCD image sensor using new wiring technology

A back surface illuminated 130/spl times/130 pixel PtSi Schottky-barrier (SB) IR-CCD image sensor has been developed by using new wiring technology, referred to as CLOSE Wiring, CLOSE Wiring, designed to effectively utilize the space over the SB photodiodes, brings about flexibility in clock line designing, high fill factor, and large charge handling capability in a vertical CCD (VCCD). This image sensor uses a progressive scanned interline-scheme, and has a 64.4% fill factor in a 30 /spl mu/m/spl times/30 /spl mu/m pixel, a 3.9 mm/spl times/3.9 mm image area, and a 5.5 mm/spl times/5.5 mm chip size. The charge handling capability for the 3.3 /spl mu/m wide VCCD achieves 9.8/spl times/10/sup 5/ electrons, The noise equivalent temperature difference obtained was 0.099 K for operation at 120 frames/sec with a 50 mm f/1.3 lens.<>     

Effects of Heavy Element Substitution on Electronic Structure and Lattice Thermal Conductivity of Fe2VAl Thermoelectric Material

By using first-principles cluster calculations, we identified that Ta or W substitution for V is useful for decreasing the lattice thermal conductivity of the Fe₂VAl Heusler alloy without greatly affecting the electron transport properties. It was clearly confirmed that the Fe₂(V_1?x Ta _x )Al_0.95Si_0.05 (x?=?0, 0.025, 0.05), Fe₂(V_0.9?x Ta _x Ti_0.1)Al (x?=?0, 0.10, 0.20), and Fe₂(V_0.9?2x W _x Ti_0.1+x )Al (x?=?0, 0.05, 0.10) alloys indeed possessed large Seebeck coefficient regardless of the amounts of substituted elements, while their lattice thermal conductivity was effectively reduced. As a result of partial substitution of Ta for V, we succeeded in increasing the magnitude of the dimensionless figure of merit of the Heusler phase up to 0.2, which is five times as large as the Ta-free compound.     

Vacuum microelectronics: what's new and exciting

It is argued that the key factor required to make vacuum microelectronics successful is closely related to an understanding and control of the physics, materials and microfabrication technology for field emitter arrays (FEAs). The topics discussed are the optimization and theoretical limit of the FEA; thermal stability of the FEA and the mesoscopic FEA; fabrication and materials of FEAs; and characteristics of FEAs. The author examines basic characteristics, limits and capabilities of FEAs from the viewpoint of optimizing the concept of the most current for the least voltage     

Extraction of a plasma time-activity curve from dynamic brain PET images based on independent component analysis

A compartment model has been used for kinetic analysis of dynamic positron emission tomography (PET) data [e.g., 2-deoxy-2-18F-fluoro-D-glucose (FDG)]. The input function of the model [the plasma time-activity curve (pTAC)] was obtained by serial arterial blood sampling. It is of clinical interest to develop a method for PET studies that estimates the pTAC without needing serial arterial blood sampling. For this purpose, we propose a new method to extract the pTAC from the dynamic brain PET images using a modified independent component analysis [extraction of the pTAC using independent component analysis (EPICA). Source codes of EPICA are freely available at http://www5f.biglobe.ne.jp/?kimura/Software/top.html]. EPICA performs the appropriate preprocessing and independent component analysis (ICA) using an objective function that takes the various properties of the pTAC into account. After validation of EPICA by computer simulation, EPICA was applied to human brain FDG-PET studies. The results imply that the EPICA-estimated pTAC was similar to the actual measured pTAC, and that the estimated blood volume image was highly correlated with the blood volume image measured using 15O-CO inhalation. These results demonstrated that EPICA is useful for extracting the pTAC from dynamic PET images without the necessity of serial arterial blood sampling.