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In present work, the effects of hydrogen charging on Ln-based (Ln=La,Ce) bulk-metallic glasses (BMG) are studied. The (La0.5Ce0.5)65Al10Co25 were charged with hydrogen by an electrochemical method in an alkali solution. The hydrogen concentration in the sample after a 36 h charge can reach as high as 1286 w-ppm. With the presence of hydrogen atoms, the hardness of specimen increased by 80% compared to the as-cast samples. The structural evolution of the amorphous matrix due to the hydrogen-uptake process was investigated by the high-energy x-ray scattering technique. The sample surface was crystallized after hydrogen charging. X-ray diffraction measurements revealed broad crystalline peaks superimposed on an amorphous-scattering pattern. The crystalline phase grew from the surface to at least one hundred microns deep into the amorphous matrix. The atomic arrangements of both amorphous and crystalline phases were characterized by the atomic pair-distribution function. [ABSTRACT FROM AUTHOR]

Self-assembled In1-xMnxAs quantum dots (0.19≤=x≤=0.45) have been grown on GaAs (100) substrates by low-temperature molecular beam epitaxy. The microstructure analysis revealed that the uniformly distributed In1-xMnxAs dots have a zinc blende structure as x≤=0.38. Furthermore, all samples exhibit ferromagnetic state at 5 K, and their Curie temperatures range from 260 to 340 K varying with x. These (In, Mn)As quantum dots are promising for room-temperature spintronic devices [ABSTRACT FROM AUTHOR]

The precipitation of arsenic in annealed Be delta-doped GaAs grown by low-temperature molecular-beam epitaxy has been studied using transmission electron microscopy. It was found that the planes doped with [Be] = 1.0 10[sup 14] cm[sup -2] always accumulate As precipitates, while the planes doped with [Be] = 1 × 10[sup 13] cm[sup -2] tend to deplete As precipitates. In contrast, the planes doped with [Be] = 3 and 2 × 10[sup 13] cm[sup -2] exhibit a weak accumulation property when annealed at 700 °C, but a depletion property when annealed 800 °C. The existence of twins and/or precipitates around the [Be]= 1.0 × 10[sup 14] cm[sup -2] doped planes found in the as-grown sample suggests a strain-induced mechanism to account for the As precipitates accumulation on these planes. [ABSTRACT FROM AUTHOR]

Investigates the measurement of the conduction-band discontinuity in pseudomorphic In[sub x]Ga[1-x]As/In[sub 0.52]Al[sub 0.48]As heterostructures. Use of strained quantum wells; Effects of the conduction-band nonparabolicity on the Fermi potential; Ways to obtain the conduction-band discontinuity at the spacer-barrier interface.

We fabricated lateral junctions by crossing superconducting Nb strips in metallic contact with a ferromagnetic NiFe strip. Transport measurements on the Nb lateral junctions exhibit modulations of the critical current with a varying perpendicular magnetic field similar to a Fraunhofer interference pattern, which demonstrates the dc Josephson effect. The modulations of the critical current could be attributed to an effective weak link embedded in the Nb strip and formed a Josephson junction. Appearance of Shapiro steps on the current-voltage curves of these junctions when microwaves irradiation is applied proves the ac Josephson effect. The underlying physics of the effective weak link induced by the NiFe strip is discussed. [ABSTRACT FROM AUTHOR]

The precipitation of arsenic in superlattice structures of alternately undoped and [Be]=2.4×10[sup 19] cm[sup -3] doped GaAs grown at low temperatures has been studied using transmission electron microscopy. Novel precipitate microstructures were observed in annealed samples, including preferential accumulation of precipitates toward each interface of Be-doped GaAs and the following grown undoped GaAs. Specifically, after 800 °C annealing, the precipitates are totally confined in Be-doped regions, forming two-dimensional dot arrays near the aforementioned interfaces. Data are also presented to show that the heavily Be-doped GaAs has a smaller lattice constant than the undoped GaAs. A strain-induced mechanism was proposed to account for the segregation of As clusters. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

La(Fe, Si)13 hydride is regarded as one of the most promising room-temperature refrigerants. However, to use the alloys in an active magnetic regenerator machine, it is vital to prepare thin refrigerants. In this work, a high H2 gas pressure of 50 MPa was employed to suppress the desorption of hydrogen atoms during the sintering process of plate-shaped La0.5Pr0.5Fe11.4Si1.6 hydrides. At 330K, a high-density sintered thin plate shows a large magnetic-entropy change ΔSm of 15.5 J/kgK (106mJ/cm³K) for a field change of 2T. The volumetric DSm is almost twice as large as that of bonded La(Fe,Si)13 hydrides. Favorably, hysteresis is almost absent due to the existence of micropores with a porosity of 0.69% which has been analyzed with high-resolution X-ray microtomography. [ABSTRACT FROM AUTHOR]

La(Fe, Si)13 hydride is regarded as one of the most promising room-temperature refrigerants. However, to use the alloys in an active magnetic regenerator machine, it is vital to prepare thin refrigerants. In this work, a high H2 gas pressure of 50 MPa was employed to suppress the desorption of hydrogen atoms during the sintering process of plate-shaped La0.5Pr0.5Fe11.4Si1.6 hydrides. At 330 K, a high-density sintered thin plate shows a large magnetic-entropy change ΔSm of 15.5 J/kg K (106 mJ/cm3 K) for a field change of 2 T. The volumetric ΔSm is almost twice as large as that of bonded La(Fe,Si)13 hydrides. Favorably, hysteresis is almost absent due to the existence of micropores with a porosity of 0.69% which has been analyzed with high-resolution X-ray microtomography. [ABSTRACT FROM AUTHOR]

A three-electrode nanodiamond vacuum field emission (VFE) device with gate modulated triode characteristics is developed by integrating nanodiamond emitter with self-aligned silicon gate and anode, employing a mold transfer technique in conjunction with chemical vapor deposition of nanodiamond. Triode behavior showing emission current modulation with high current density at low operating voltages is achieved. A systematic analysis based on modified Fowler-Nordheim theory is used to analyze gate modulated VFE characteristics, confirming the triode field emission mechanism and operating principle. The realization of an efficient VFE microtriode has achieved the fundamental step for further development of vacuum integrated microelectronics. [ABSTRACT FROM AUTHOR]

Using measurements of resonant x-ray scattering from a LaMnO3/SrMnO3 superlattice grown on SrTiO3(001), we present experimental evidence for the enhancement of the Jahn-Teller distortion by magnetic ordering in manganites. With a specially tuned periodicity of the superlattice, scattering due to the Jahn-Teller (JT) distortion is separated from charge and magnetic scattering. The measured JT distortion is markedly enhanced upon the emergence of magnetization and strongly correlated with the spin ordering in the superlattice. Such strong correlation reveals the nature of electron-electron interaction for orbital ordering in manganites. [ABSTRACT FROM AUTHOR]

We investigated the electronic reconstruction at the n-type LaAlO3/SrTiO3 interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 Å (∼12 unit cells) and an estimated total charge transfer of ∼0.24 electrons per two-dimensional unit cell. [ABSTRACT FROM AUTHOR]

We examine the effects of modifying the Co hard layer thickness of Co/Cu/Co spin valve submicron pillars with current flowing perpendicular to the plane. The magnetoresistance (MR) ratios and switching currents show complementary behaviors. As the Co hard layer thickness is increased, the MR ratio shows an initial increase with a peak around 21 nm. The critical switching current shows a dip around the same thickness, which is close to the spin diffusion length. The product of the MR ratio and critical current density is about a constant independent of the Co hard layer thickness. Thus, we provide an approach to achieving maximum efficiency (MR ratio) and minimum consumption (critical current) for a practical device. [ABSTRACT FROM AUTHOR]

In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO2/OA-CdSe photoanode in a two-electrode device exhibited a photon-to-current conversion efficiency of 17.5% at 400 nm. At AM1.5G irradiation with 100 mW/cm2 light intensity, the QDSSCs based on OA-capped CdSe showed a power conversion efficiency of about 1%. The function of OA was to increase QD loading, extend the absorption range and possibly suppress the surface recombination. [ABSTRACT FROM AUTHOR]

An atomically flat and uniform reaction layer of Mn(Ga)As was found to self-organize at the (Ga,Mn)As/IrMn interface by postannealing. The Mn(Ga)As layer exhibits strong ferromagnetic characteristics up to the measured 300 K. In particular, the manifested horizontal shift of field-cooled hysteresis loops shows a clear signature of exchange bias attributable to the exchange coupling between IrMn and Mn(Ga)As. Implication from composition analyses, exchange-bias effect, and thickness dependence of the Mn(Ga)As layer versus annealing conditions is also discussed. [ABSTRACT FROM AUTHOR]

A spin transistor which consists of a metallic giant magnetoresistance emitter, a copper base, and a p-n junction was prepared on a Si(100) wafer. The emitter current changes from 1 mA at a magnetically parallel state to 0.968 mA at a magnetically antiparallel state. At the same states the base currents were 29.3 μA and 333 nA, respectively, which gave a magnetocurrent ratio of ∼8600% and a transfer ratio of 3×10-2 at room temperature for a common collector configuration. The sensitivity of this spin device is higher than 4000%/Oe. The memory effect and the high performance make it possible for practical usage. The working principle of this kind of three-terminal spin device can be simply described by circuit theory. [ABSTRACT FROM AUTHOR]

Al[sub 0.35-δ]In[sub δ]Ga[sub 0.65]N/GaN heterostructures have been studied by using transmission electron microscopy, photoluminescence, and Shubnikov–de Haas (SdH) measurements. In the sample of δ<0.01%, two SdH oscillations beat each other due to the population of the lowest two subbands. The carrier concentrations of these two subbands are 1.398 and 1.248×10[sup 13] cm[sup -2] and the electric field at the interface is reduced to 2.19×10[sup 4] V/cm, which is one order of magnitude smaller than that of Al[sub 0.35]Ga[sub 0.65]N/GaN heterostructure. We suggest that a small fraction of In atoms in the Al[sub 0.35-δ]In[sub δ]Ga[sub 0.65]N can be used as a tuning parameter to control the strain and the piezoelectric field at the interface. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]