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Demixing in a solid-soluted Co–40 at. % Pd alloy has been induced by microwave plasma hydrogen irradiation on mixture of Pd–Co island grains on Si substrate. The microstructure observation and X-ray microanalysis by a transmission electron microscope before and after the microwave plasma hydrogen irradiation provide a clear evidence of demixing in metallic Co–Pd alloys, that may indicate a possibility of the decomposition into Pd hydride and Co under a hydrogen irradiation at high temperatures.

A technique for measuring micromechanical displacement is proposed using a liquid-delay-line oscillator, which consists of two pairs of arch-shaped interdigital transducers (IDTs) on a double-layered substrate composed of an acrylic plate and a piezoelectric ceramic plate, a reflecting plate and a water layer. In the use of the double-layered substrate, the seventh higher-order mode of leaky Lamb wave is favorable for the oscillator construction, because of high phase velocity and large transducer efficiency, while retaining sufficient mechanical strength, compared with the use of an only piezoelectric ceramic plate. The mechanical displacement is evaluated as a function of oscillation frequency, on the basis of the acoustical delay length, linearly dependent on the thickness of the water layer. The present technique is promising for sensing microdisplacement as a precise and convenient method.

A technique for measuring the moving target speed is described using an ultrasound device, composed of two leaky Lamb wave interdigital transducers (IDTs) and a thickness-mode transducer on a thin piezoelectric ceramic plate. The thickness-mode transducer located between the two IDTs radiates an ultrasound beam into a liquid in the thickness direction of the piezoelectric substrate. The IDT functions as a detector of the ultrasound signal reflected in an oblique direction from a moving medium in the liquid. The reflected delayed-output has a frequency shift via a Doppler effect, corresponding to the moving speed of the reflection object. Basic performances of the device with two IDTs and the central thickness-mode transducer and the measured results of the moving speed of a metal disk are presented for the first antisymmetrical Lamb wave mode with the highly dispersive property.

A technique for measuring mechanical vibration is proposed using a thickness-mode piezoelectric transducer. The transducer has three electrode groups, which are an interdigital arrangement of two comb-shaped electrodes mounted on one surface of a piezoelectric ceramic plate and a counter electrode on the other surface of the ceramic plate. A combination of one of the two comb-shaped electrodes and the counter electrode operates as a thickness-mode vibrator for radiating a longitudinal wave into a water layer. The other comb-shaped electrode is used to detect a reflected ultrasound beam from the vibrating diaphragm, and is also applicable for receiving an electromagnetically coupled signal from an electric signal applied to the input comb-shaped electrode. Interference between the reflected signal and the coupled signal results in a change of the amplitude of the output signal, corresponding to the mechanical displacement of the diaphragm. This technique has the advantages of excellent transducer performance and concise signal processing.

Si-based epitaxial β-FeSi2 thin films are attractive as materials for on-chip thermoelectric power generators. We investigated the structure, crystallinity, and thermoelectric properties of β-FeSi2 thin films epitaxially grown on Si(111) substrates by using three different techniques: conventional reactive deposition epitaxy followed by molecular beam epitaxy (RDE+MBE), solid phase epitaxy (SPE) based on codeposition of Fe and Si presented previously, and SPE followed by MBE (SPE+MBE) presented newly by this work. Their epitaxial growth temperatures were fixed at 530 °C for comparison. RDE+MBE thin films exhibited high crystalline quality, but rough surfaces and rugged β-FeSi2/Si(111) interfaces. On the other hand, SPE thin films showed flat surfaces and abrupt β-FeSi2/Si(111) interfaces but low crystallinity. We found that SPE+MBE thin films realized crystallinity higher than SPE thin films, and also had flatter surfaces and sharper interfaces than RDE+MBE thin films. In SPE+MBE thin film growth, due to the initial SPE process with low temperature codeposition, thermal interdiffusion of Fe and Si was suppressed, resulting in the surface flatness and abrupt interface. Second high temperature MBE process improved the crystallinity. We also investigated thermoelectric properties of these β-FeSi2 thin films. Structural factors affecting the thermoelectric properties of RDE+MBE, SPE, and SPE+MBE thin films were investigated.

We propose a method derived from fast Fourier transform (FFT) process to measure the characteristic length scale of bicontinuous nanoporous structures. By rotationally averaging the FFT power spectrum of a nanoporous micrograph from scanning electron microscope (SEM) or transmission electron microscope (TEM), a significant peak in the power spectrum can be obtained, which reflects the characteristic length scale of the quasi-periodic structure. This method is demonstrated for the bicontinuous morphology that is frequently observed in nanoporous metals prepared by chemical or electrochemical dealloying.

A potential energy landscape (PEL) gives rise to diverse non-equilibrium dynamics in complex systems. In this study, we visualize the topological landscape of a steady-state flow under shear deformation in a model metallic glass. We use the “state space network” as the best predictor of state transitions in terms of statistical model selection. The proposed scheme visualizes the underlying PEL regarding α transitions associated with irreversible cage-breaking events as the cooperative motion of clusters. By characterizing the topological property of the state space network, we observe characteristics of a small-world network. The proposed scheme has a significant potential to enable the understanding of the underlying mechanisms of glass physics, and is analogous to biological networks.

We investigate the direct d–d interactions among substitutional 3d transition metal impurities in various III–V semiconductor hosts by first-principles calculations. We find that for nearest neighbor impurity pairs, such d–d interactions, to some extent, always appear. These d–d interactions become particularly important for light 3d transition metal impurities in nitride semiconductors, which may lead to dramatic effects in the magnetic and chemical interactions.

Heterostructure based interface engineering has been proved an effective method for finding new superconducting systems and raising superconductivity transition temperature (TC). In previous work on one unit-cell (UC) thick FeSe films on SrTiO3 (STO) substrate, a superconducting-like energy gap as large as 20 meV, was revealed by in situ scanning tunneling microscopy/spectroscopy (STM/STS). Angle resolved photoemission spectroscopy (ARPES) further revealed a nearly isotropic gap of above 15 meV, which closes at a temperature of ~ 65 K. If this transition is indeed the superconducting transition, then the 1-UC FeSe represents the thinnest high TC superconductor discovered so far. However, up to date direct transport measurement of the 1-UC FeSe films has not been reported, mainly because growth of large scale 1-UC FeSe films is challenging and the 1-UC FeSe films are too thin to survive in atmosphere. In this work, we successfully prepared 1-UC FeSe films on insulating STO substrates with non-superconducting FeTe protection layers. By direct transport and magnetic measurements, we provide definitive evidence for high temperature superconductivity in the 1-UC FeSe films with an onset TC above 40 K and a extremely large critical current density JC ~ 1.7*106 A/cm2 at 2 K. Our work may pave the way to enhancing and tailoring superconductivity by interface engineering.

The controlled formation of quasi-one-dimensional (1D) chainlike structures of transition metal impurities in diluted magnetic semiconductors has been proposed to increase their Curie temperatures. We investigate the stability and magnetism of several quasi-1D Cr chains embedded in the prototype system (Zn,Cr)Te by first-principles calculations. We find that the quasi-1D Cr chains indeed are stable, and the binding energy driving this phase separation is enhanced as the wires become thicker. However, the ferromagnetic stabilization energy weakens as the quasi-1D Cr chains become thicker, which will decrease Curie temperatures.

The operational performance of an A0-mode Lamb wave interdigital transducer is described in a delay line structure. The delay line is composed of two interdigital transducers (IDTs) on a thin piezoelectric ceramic plate, under the air- or water-loaded condition. The A0-mode Lamb wave device has two frequency ranges in the forms of nonleaky and leaky Lamb waves. The boundary frequency is related to the longitudinal wave velocity in water. The basic performance of the A0-mode delay line is presented with measured results in the vicinity of the transition region, where the A0-mode Lamb wave velocity is near the longitudinal wave velocity in water. The A0-mode IDT operates efficiently as an underwater transducer with a shallow radiation angle in the operation region as the leaky wave.

A measurement technique for mechanical displacement using a liquid delay line oscillator is described. The delay line is composed of a leaky Lamb wave device with two interdigital transducers (IDTs), a liquid cavity as the propagation medium for an ultrasound beam and an amplifier connected between two IDTs. The IDT for leaky Lamb waves functions as a longitudinal wave radiator or a detector of a reflected ultrasound beam from the surface of a wall in the liquid cavity. The two lowest modes, S0 and A0, propagating in a thin piezoelectric ceramic plate are useful for constructing the leaky wave transducer because of high transducer efficiency. The acoustic delay length changes with mechanical displacement, which results in a change of oscillation frequency. The basic performance of the delay line oscillator is presented with the results of measurements in two operating modes, S0 and A0.