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We demonstrate a microwave-frequency, two-track acoustic beam splitter, based on a multistrip coupler design matched to four unidirectional transducers, two on each of the two acoustic tracks that make up the device. We explain the device design and its experimental implementation, showing good agreement between our model and the measured device scattering spectra. The beam splitter regime, dividing an input signal at port 1 into closely equal outputs at ports 2 and 3, is reached over a 94.7 MHz bandwidth centered at 4.79 GHz, with an output power division ratio | S 21 / S 31 | 2 = 1.1 ± 0.2. The measured bandwidth of the device is limited by the bandwidth of the transducers, rather than that of the multistrip coupler. [ABSTRACT FROM AUTHOR]

Directional growth effect on magneto-mechanical properties of Fe81Al19 alloy is studied. The ideal model of heat flux for directional solidification (DS) technique is proposed, and the tuned A/L (the ratio of cross-sectional area and length for the ingot) and ΔT (temperature difference) are adopted to increase heat flux (q). The experimental result shows that the increase of q effectively promotes the degree of (011)[100] Goss texture and therefore helps to form an oriented stripe domain structure. Large λ100 of 93.8 ppm attained for this optimized Fe81Al19 alloy prepared by DS method is very close to that of the Fe81Al19 single crystal (95.0 ppm). For the optimized DS prepared Fe81Al19 alloy, high magnetostriction sensitivity (dλ/dH) of 0.45 ppm/Oe leads to huge ΔEs/E0 of ∼10% and attractive ΔE/E0 of 8.2% at small H = 0.25 kOe. The above remarkable magneto-mechanical properties, low cost of Fe81Al19, and simple process of DS favor for applications. This work proposes an ideal model to emphasize the importance of heat flux in DS, and experimentally attains the remarkable magneto-mechanical properties for Fe81Al19 alloy prepared by DS. [ABSTRACT FROM AUTHOR]

Traditional NdFeB sintered magnets with coercivity larger than 20 kOe, called super-high (SH) level, usually contains considerable amount of high-cost heavy rare earth (HRE), such as Dy or Tb. In this work, high coercivity of 21.4 kOe, which corresponds to SH level, is achieved for HRE-free NdFeB magnet by doping with Ce85Al15 (CeAl) alloy and grain boundary diffusion (GBD) with Pr70Cu15Al15 (PrCuAl) alloy powders, where Ce/RE ratio is about 15% within the magnet. After GBD treatment with PrCuAl on Ce-containing NdFeB magnets, the formation of Pr-containing shell at 2:14:1 grain surface can increase the local magnetic anisotropy filed and therefore enhance the coercivity. Most of Cu and Al, and parts of Ce and Pr appear at grain boundary and triple junction, which can reduce the magnetization of grain boundary phase, strengthen the decoupling effect between grains and thus contribute to high coercivity. This study provides a cost-effective way to obtain high coercivity for HRE-free NdFeB sintered magnet via doping Ce85Al15 and then GBD with Pr70Cu15Al15. [ABSTRACT FROM AUTHOR]

We investigated the structure, ferroelectric, magnetic, and leakage characteristics of Bi0.95H0.05FeO3 (BHFO) polycrystalline films with H = Gd, Tb, Dy, Ho, and Er. Bi0.95H0.05FeO3 films were confirmed to mainly consist of the perovskite phase, and the phase structure belongs to the pseudo-cubic phase. The desired ferroelectric and ferromagnetic properties at the same time, the remanent polarization (2Pr) of 57–81 μC/cm2 and the saturation magnetization (Ms) of 11.6–21.3 emu/cm3, are obtained for Bi0.95H0.05FeO3 films. Lower 2Pr with smaller ionic radius of H is possibly related to limited ion movement because of the reduced volume of the unit cell in BHFO films. Low leakage current characteristics and leakage mechanisms in Bi0.95H0.05FeO3 films are also discussed. In aspect of the magnetic properties, H can significantly improve the magnetic properties of BFO by A-site substitutions due to the suppressed spiral structure and importantly the contribution of high magnetic moment of H ion. The results of this work suggests BHFO films is a good multiferroic material, especially the samples with H = Tb and Dy. [ABSTRACT FROM AUTHOR]

Traditional NdFeB sintered magnets with coercivity larger than 20 kOe, called super-high (SH) level, usually contains considerable amount of high-cost heavy rare earth (HRE), such as Dy or Tb. In this work, high coercivity of 21.4 kOe, which corresponds to SH level, is achieved for HRE-free NdFeB magnet by doping with Ce85Al15 (CeAl) alloy and grain boundary diffusion (GBD) with Pr70Cu15Al15 (PrCuAl) alloy powders, where Ce/RE ratio is about 15% within the magnet. After GBD treatment with PrCuAl on Ce-containing NdFeB magnets, the formation of Pr-containing shell at 2:14:1 grain surface can increase the local magnetic anisotropy filed and therefore enhance the coercivity. Most of Cu and Al, and parts of Ce and Pr appear at grain boundary and triple junction, which can reduce the magnetization of grain boundary phase, strengthen the decoupling effect between grains and thus contribute to high coercivity. This study provides a cost-effective way to obtain high coercivity for HRE-free NdFeB sintered magnet via doping Ce85Al15 and then GBD with Pr70Cu15Al15. [ABSTRACT FROM AUTHOR]

We hereby present a simple process, called in situ two-end diffusion (TED), to reach coercivity enhancement with almost unchanged energy product for hot deformed (HD) NdFeB magnets. Coercivity of the HD magnets is increased from 15.1 to 18.7 kOe for the magnet TED with (Nd0.75Pr0.25)70Cu30 (NdPrCu), which is larger than 17.6 kOe for the magnet directly doped with 2 wt. % NdPrCu alloy. Besides, the magnet TED with NdPrCu exhibits good (00L) texture and therefore could support high (BH)max of 43.0 MGOe. In addition, the magnet TED with Ce70Cu30 (CeCu) exhibit superior magnetic properties of Br = 12.8 kG, iHc = 18.0 kOe and (BH)max = 40.7 MGOe to those of traditional doping with CeCu (Br = 11.7 kG, iHc = 16.4 kOe and (BH)max = 34.2 MGOe). For TED process, low-melting CeCu can infiltrate into the center of the magnet, and most Ce distribute at grain boundary. The distribution of Ce and Cu at grain boundary can reduce the magnetization of grain boundary phase, strengthen the decoupling effect between grains and contribute to the coercivity enhancement. This work demonstrates TED with low-melting HRE-free alloys is a simple method to effectively enhance coercivity and keep high Br and (BH)max for HD NdFeB magnets. [ABSTRACT FROM AUTHOR]

We obtain a large in-plane magnetic uniaxial anisotropy in the soft magnetic Fe60Co20B20 (FeCoB) thin films prepared by rotational sputtering. The anisotropy field (Ha) of 75 to 175 Oe was found in the films with wide ranged thickness from 2.5 to 100 nm, which was attributed to the magnetoelastic energy in association with anisotropic tensile stress. This stress-induced anisotropy has outstanding thermal stability that survives up to 350 °C in the annealing process. The similar large uniaxial anisotropy can be realized in other soft magnetic thin films, such as Fe, Co, Ni, FeCo, and NiFe, with the same synthesis technique. The anisotropic FeCoB film was used as a free layer in a synthetic spin valve. A linear resistance change against external field with a range wider than ±100 Oe together with a significantly reduced coercivity of ∼1.1 Oe (∼8.5 Oe in the case with isotropic free layer) was observed in the transfer curve. The results of this work not only confirm the feasibility of films with large stress-induced magnetic anisotropy as a functional layer in spin-valve devices but also demonstrate a simple synthesis route to induce the magnetic anisotropy, which provides an additional control parameter for the spintronic device design. [ABSTRACT FROM AUTHOR]

Ultrafast transmission electron microscopy (UTEM) combines sub-picosecond time-resolution with the versatility of TEM spectroscopies. It allows us to study the ultrafast materials' response using complementary techniques. However, until now, time-resolved cathodoluminescence was unavailable in UTEM. In this paper, we report time-resolved cathodoluminescence measurements in an ultrafast transmission electron microscope. We mapped the spatial variations of the emission dynamics from nano-diamonds with a high density of NV centers with a 12 nm spatial resolution and sub-nanosecond temporal resolution. This development will allow us to study the emission dynamics from quantum emitters with a unique spatiotemporal resolution and benefit from the wealth of complementary signals provided by transmission electron microscopes. It will further expand the possibilities of ultrafast transmission electron microscopes, paving the way to the investigation of the quantum aspects of an electron/sample interaction. [ABSTRACT FROM AUTHOR]

Effect of Ba substitution on the multiferroic properties of non-epitaxially grown polycrystalline Bi1-xBaxFeO3 (BBFO) films on refined Pt(111) electrode buffered glass substrates is studied. The structural analysis shows that a pure perovskite phase is present for BBFofilms (x = 0.05-0.15), and (110) preferred orientation is developed for films with high x = 0.15. The grain size and surface roughness are reduced with increasing x. All studied BBFofilms show desired ferroelectric and ferromagnetic properties. The good ferroelectric properties with the remanent polarization (2Pr) of 36-70 lC/cm2 and electrical coercive field (Ec) of 318-570 kV/cm are attained. On the other hand, the substitution of Ba2+ for Bi3+ in the A site of the BFO crystal structure can effectively enhance the ferromagnetic properties with magnetization (Ms) of 9.4-13.9 emu/cm3 and coercivity (Hc) of 1216-1380 Oe. The ferromagnetic and ferroelectric properties and leakage behavior as functions of Ba content x are discussed. [ABSTRACT FROM AUTHOR]

Structure, ferroelectric, and magnetic properties of BiFeO3 (110) films grown on 20-nm-thick ferromagnetic CoPt(111) buffered glass substrate at 350-550 °C have been studied. (110)-texture of BFO films is developed at the reduced temperature as low as 400-550 °C, but isotropic orientation is found at higher temperature of 600 °C. Low temperature deposition results in dense microstructure, fine grains, and smooth surface morphology, which are favorable for applications. BFO(110) films on CoPt(111) underlayer exhibit desired ferroelectric and magnetic properties. Electrical polarization (2Pr) of 96-137 μC/cm2 and coercive field (Ec) of 495-618 kV/cm for studied BFO (110) films are comparable to those grown on single crystal substrates. Moreover, exchange bias between BFO and CoPt is observed after a field cooling from 370 °C to room temperature (RT) at 2 kOe. Large exchange bias field of 155 Oe at RT and coercivity of 1631 Oe are obtained. The presented results provide useful information for the applications based on electric-magnetic interactions. [ABSTRACT FROM AUTHOR]

Texture control of multiferroic BiFeO3 (BFO) polycrystalline films on glass substrates with various metal electrode underlayers at reduced processing temperature of 450 °C has been demonstrated. The structural results confirm the synthesis of perovskite BFO with (001) texture on the refined Pt(111) and L10-FePt(001) electrode layers and with (110) texture on CoPt(111) one. All studied BFO films exhibit typical ferroelectric properties. Larger remanent electrical polarization 2Pr of 135 μC/cm2 and coercive electric field Ec of 495 kV/cm are obtained for BFO(110) film on CoPt(111) electrode as compared to BFO(001) films on Pt(111) and L10-FePt(001) electrodes (2Pr = 93-98 μC/cm2 and Ec of 304-354 kV/cm), which is consistent with the epitaxial BFO films and theoretical calculations. Besides, the ferroelectric properties of the studied BFO films are comparable to BFO films grown on single crystal substrates. The ferroelectric properties with various metal electrode underlayers are related to the orientation of texture and leakage behavior. [ABSTRACT FROM AUTHOR]

Magnetic properties of melt spun Co82-xHf12+xB6 ribbons made with various wheel speeds have been studied. The ribbons with x=0-1 are not easy to crystallize and thus display soft magnetic behavior even at wheel speed of 10m/s. In contrast, the ribbons with x=1.5-4 at optimized wheel speed exhibit good permanent magnetic properties of Br=0.41-0.59T, iHc=120-400kA/m, and (BH)max=10.6-48.1kJ/m³. The optimal magnetic properties of Br=0.59T, iHc=384kA/m, and (BH)max=48.1kJ/m³ are achieved for Co80Hf14B6 ribbons at wheel speed of 30m/s. X-ray diffraction, thermo-magnetic analysis, and transmission electron microscopy results show that good hard magnetic properties of Co82-xHf12+xB6 ribbons (x=2-4) are originated from the Co11Hf2 phase well coupled with the Co phase. The change of magnetic properties for Co82-xHf12+xB6 ribbons spun at various wheel speeds is correlated to microstructure and phase constitution. The strong exchange-coupling effect between magnetic grains for the ribbons with x=2-3 at wheel speed=30m/s leads to remarkable permanent magnetic properties. The presented results suggest that the optimized Co82-xHf12+xB6 (x=2-3) ribbons are much suitable than others (x=0-1.5 and 4) for making rare earth and Pt-free magnets. [ABSTRACT FROM AUTHOR]

A new method to fabricate soft magnetic bulk metallic glasses (BMGs) by an injection casting with applying external magnetic field during solidification has been developed. The effect of applying magnetic fields (Ha) on soft magnetic properties and microstructure of Fe75P8.7B5C7Si4.3 alloy sheets with dimension of t × 4mm × 15mm (t=1-3 mm) have been studied. The microstructure shows that the fully amorphous is attained by the applying magnetic field even at the core region of the thicker sheets with t=3mm. All studied sheets exhibit similar saturation magnetization of 1.23-1.25 T, but the coercivity and resistivity are strongly dependent on the thickness t and the strength of magnetic field Ha, where Hc increases with t, the slope of Hc versus t decreases with the increase of Ha, and the resistivity increases with the increase of Ha. The changes of coercivity and resistivity are strongly related to the fully amorphous induced by Ha. The external magnetic field has significant improvement in glass forming ability, and thus coercivity and resistivity for the studied sheet, especially for larger t=3 mm. This study suggests that applying a magnetic field during the casting process provides a useful way to produce high-performance magnetically soft Fe-based BMGs. [ABSTRACT FROM AUTHOR]

Flip-chip architectures have recently enabled significant scaling-up of multi-qubit circuits and have been used to assemble hybrid quantum systems that combine different substrates, for example, for quantum acoustics experiments. The standard flip-chip method uses superconducting galvanic connections between two substrates, typically implemented using sophisticated indium wafer-bonding systems, which give highly reliable and temperature-cyclable assemblies, but are expensive, somewhat inflexible in design, and require robust substrates that can sustain the large compressive forces required to cold-weld the indium bonds. A much simpler method is to assemble dies using very low-force contacts and air-dried adhesives, although this does not provide a galvanic contact between the dies. Here, we demonstrate that the latter technique can be used to reliably couple superconducting qubit circuits, in which the qubits are on separate dies, without the need for a galvanic connection. We demonstrate full vector qubit control of each qubit on each of the two dies, with high-fidelity single-shot readout, and further demonstrate entanglement-generating excitation swaps as well as benchmark a controlled-Z entangling gate between the two qubits on the two dies. This exemplifies a simple and inexpensive assembly method for two-plus-one-dimensional quantum circuit integration that supports the use of delicate or unusually shaped substrates. [ABSTRACT FROM AUTHOR]

Broadband quantum-limited amplifiers play a critical role in the single-shot readout of superconducting qubits, but a popular implementation, the traveling wave parametric amplifier, involves a complex design and fabrication process. Here, we present a simple design for a Josephson parametric amplifier, using a lumped element resonator comprising a superconducting quantum interference device whose useful bandwidth is enhanced with an on-chip impedance-matching circuit. We demonstrate a flux-coupling geometry that maximizes the coupling to the Josephson loop and minimizes spurious excitation of the amplifier resonant circuit. The amplifier, which operates in a flux-pumped mode, is demonstrated with a power gain of more than 20 dB over a bandwidth of about 300 MHz, where approximate noise measurements indicate quantum-limited performance. A procedure is given for optimizing the bandwidth for this kind of amplifier, using a linearized circuit simulation while minimizing non-linearities. [ABSTRACT FROM AUTHOR]

Significant enhancement in coercivity for hot deformed (HD) NdFeB magnets is achieved by doping R80Al20 (R= La, Ce, Dy, Tb) alloy powders. All studied samples exhibit fine microstructure with good (00L) texture. By doping R80Al20 powders, the coercivity of HD NdFeB magnets is significantly increased from 16.0 kOe to 19.4 kOe, 20.0 kOe, 21.8 kOe, and 23.8 kOe for R = La, Ce, Dy, and Tb, respectively, while (BH)max is decreased from 41.5 MGOe to 39.3-40.8 MGOe slightly. Microstructure analysis shows that Ce or La prefers to distribute mostly at grain boundary, while Dy or Tb and Al locate at grain boundary and surface. The magnetic isolation due to R-rich phase containing Nd, Ce or La, Al at the grain boundary contributes to coercivity enhancement with the samples with R = La and Ce. In additional to magnetic isolation, the strengthened magnetic anisotropy field of 2:14:1 phase due to Tb or Dy, and slight Al substitutions gives rise to the significant enhancement of coercivity for those with R80Al20 (R = Dy and Tb). [ABSTRACT FROM AUTHOR]

Coercivity enhancement of the sintered NdFeB magnets by grain boundary diffusion (GBD) with Tb70Cu30 powders prepared by different milling methods has been compared. The commercial NdFeB sintered magnets with the magnetic properties of Br=14.0 kG, iHc= 17.5 kOe and (BH)max= 48.4 MGOe are chosen as original magnets. The coercivity increment of the NdFeB magnets is 7.6 kOe and 9.4 kOe after GBD with Tb70Cu30 alloy powders made by high energy ball milling (HEBM) and low-energy ball milling (LEBM), respectively. Higher coercivity increment can be obtained for the magnet GBD treated with Tb70Cu30 powders prepared by LEBM, mainly related to their platelet shape. The platelet shape powders may provide the wider contact area between GBD source and the surface of the magnets. The above effect is helpful in improving diffusion efficiency and enhancing coercivity accordingly. As a result, magnetic properties of Br=13.6 kG, iHc= 25.1 kOe and (BH)max= 46.1 MGOe are achieved. [ABSTRACT FROM AUTHOR]

It has been experimentally found that the carbon surface contamination influences strongly the spectrum signals in reflection electron energy loss spectroscopy (REELS) especially at low primary electron energy. However, there is still little theoretical work dealing with the carbon contamination effect in REELS. Such a work is required to predict REELS spectrum for layered structural sample, providing an understanding of the experimental phenomena observed. In this study, we present a numerical calculation result on the spatially varying differential inelastic mean free path for a sample made of a carbon contamination layer of varied thickness on a SrTiO3 substrate. A Monte Carlo simulation model for electron interaction with a layered structural sample is built by combining this inelastic scattering cross-section with the Mott's cross-section for electron elastic scattering. The simulation results have clearly shown that the contribution of the electron energy loss from carbon surface contamination increases with decreasing primary energy due to increased individual scattering processes along trajectory parts carbon contamination layer. Comparison of the simulated spectra for different thicknesses of the carbon contamination layer and for different primary electron energies with experimental spectra clearly identifies that the carbon contamination in the measured sample was in the form of discontinuous islands other than the uniform film. [ABSTRACT FROM AUTHOR]

Investigations that probe defects one at a time offer a unique opportunity to observe properties and dynamics that are washed out of ensemble measurements. Here, we present confocal fluorescence measurements of individual defects in ZnO nanoparticles and sputtered films that are excited with sub-bandgap energy light. Photon correlation measurements yield both antibunching and bunching, indicative of single-photon emission from isolated defects that possess a metastable shelving state. The single-photon emission is in the range of ~560-720 nm and typically exhibits two broad spectral peaks separated by ~150 meV. The excited state lifetimes range from 1 to 13 ns, consistent with the finite-size and surface effects of nanoparticles and small grains. We also observe discrete jumps in the fluorescence intensity between a bright state and a dark state. The dwell times in each state are exponentially distributed and the average dwell time in the bright (dark) state does (may) depend on the power of the exciting laser. Taken together, our measurements demonstrate the utility of a single-molecule approach to semiconductor defect studies and highlight ZnO as a potential host material for single-defect based applications. [ABSTRACT FROM AUTHOR]

Phonon modes at microwave frequencies can be cooled to their quantum ground state using conventional cryogenic refrigeration, providing a convenient way to study and manipulate quantum states at the single phonon level. Phonons are of particular interest because mechanical deformations can mediate interactions with a wide range of different quantum systems, including solid-state defects, superconducting qubits, and optical photons when using optomechanically active constructs. Phonons, thus, hold promise for quantum-focused applications as diverse as sensing, information processing, and communication. Here, we describe a piezoelectric quantum bulk acoustic resonator (QBAR) with a 4.88 GHz resonant frequency, which, at cryogenic temperatures, displays large electromechanical coupling strength combined with a high intrinsic mechanical quality factor, Q i ≈ 4.3 × 10 4 . Using a recently developed flip-chip technique, we couple this QBAR resonator to a superconducting qubit on a separate die and demonstrate the quantum control of the mechanics in the coupled system. This approach promises a facile and flexible experimental approach to quantum acoustics and hybrid quantum systems. [ABSTRACT FROM AUTHOR]

Variable microwave-frequency couplers are highly useful components in classical communication systems and likely will play an important role in quantum communication applications. Conventional semiconductor-based microwave couplers have been used with superconducting quantum circuits, enabling, for example, the in situ measurements of multiple devices via a common readout chain. However, the semiconducting elements are lossy and furthermore dissipate energy when switched, making them unsuitable for cryogenic applications requiring rapid, repeated switching. Superconducting Josephson junction-based couplers can be designed for dissipation-free operation with fast switching and are easily integrated with superconducting quantum circuits. These enable on-chip, quantum-coherent routing of microwave photons, providing an appealing alternative to semiconductor switches. Here, we present and characterize a chip-based broadband microwave variable coupler, tunable over 4–8 GHz with over 1.5 GHz instantaneous bandwidth, based on the superconducting quantum interference device with two parallel Josephson junctions. The coupler is dissipation-free and features large on-off ratios in excess of 40 dB, and the coupling can be changed in about 10 ns. The simple design presented here can be readily integrated with superconducting qubit circuits and can be easily generalized to realize a four- or more port device. [ABSTRACT FROM AUTHOR]

The bimetallic Cu@Ag nanoparticle (NP)-based Cu–Cu bonding method is reported to be plausible in electronic packaging, whereas the microstructure and elemental distribution of the joint, which determine the bonding quality, were not well investigated yet. In this work, comprehensive characterization techniques are used to demonstrate the microstructure and elemental information of the joint. Microstructure analysis exhibits a eutectic structure with a low porosity of 2.5%, which is achieved by NP sintering. Twin structures in both the Cu-rich and Ag-rich phases are confirmed, where (111) is the twin mirror plane. Particularly, atom probe tomography analysis accurately demonstrates that the concentration of Cu in the Ag-rich phase is 1.51% and vice versa, 0.45%; this indicates sufficient atom exchange for achieving high-quality bonding. This investigation improves the understanding of the elemental behavior during the core@shell NP bonding process and provides important information for pushing this bonding method toward practical application. [ABSTRACT FROM AUTHOR]

Magnetic properties and phase composition of both MnN/CoFe (MnN at top of bilayer) and CoFe/MnN films (MnN at bottom of bilayer) bilayers through annealing at various temperatures (Ta = 300-450 °C) and then cooling to room temperature under the application of an external magnetic field of 1.5 kOe are compared. The exchange bias field (HE), the magnitude of magnetic hysteresis loop shift, of the studied films is highly related to phase composition of antiferromagnetic (AF) layer. The increase of HE with increasing Ta in the range of 300-375 °C possibly results from the improvement of magnetocrystalline anisotropy of AF related to the promoted crystallinity and stress relaxation of tetragonal face-centered θ-MnN phase. The reduction of HE at higher Ta is due to the decreased volume fraction or disappearance of θ-MnN phase and the formation of impurity phases, such as Mn4N and Mn. The induction of impurity phases is possibly related to the diffusion of part of N out of MnN phase at higher Ta. Higher HE for CoFe/MnN than MnN/CoFe at Ta = 300-375 °C might be attributed to larger amount and higher degree of stress relaxation for θ-MnN phase. For CoFe/MnN film annealed at 375 °C, the highest HE = 562 Oe is attained, and the corresponding interfacial exchange energy of 0.47 mJ/m2 in this study is comparable to that reported by Meinert et al. [Phys. Rev. B 92, 144408 (2015)]. [ABSTRACT FROM AUTHOR]

A significant coercivity enhancement of the commercial NdFeB magnets with the magnetic properties of (BH)max = 48.4 MGOe and iHc = 17.5 kOe through grain boundary diffusion (GBD) with low-melting Tb55R20Cu25 alloys is demonstrated. Adopting Tb55R20Cu25 alloys as GBD sources is effective in increasing coercivity to 29.0 kOe for R = None, 23.8 kOe for R = Y, 25.6 kOe for R = La, 28.0 kOe for R = Ce, respectively. Yet, (BH)max is slightly reduced to 46.2-48.2 MGOe. The preferential appearance of Cu at grain boundary and triple junction of the grains, and the core-shell structure occurred due to Tb at grain surface remarkably enhance the coercivity. Interestingly, higher coercivity enhancement per wt% Tb usage (ΔiHc/wt%Tb) of 7.2 kOe/wt% for the magnet with Tb55Ce25Cu25 than 5.9 kOe/wt% for that with Tb75Cu25 has been found due to the magnetic isolation effect caused by the preferential appearance of Ce at grain boundary, though a slight lower coercivity enhancement was found for the samples with R = Y and La. Lower melting point (637 °C) for Tb55Ce20Cu25 than Tb75Cu25 (743 °C) leads to larger diffusion depth of Tb into the magnet and therefore contributes to higher efficiency of coercivity enhancement for the magnet with R=Ce. [ABSTRACT FROM AUTHOR]

(Fe81-xCoxGa19)80B20 ribbons, with x = 0, 7, 11, 19, and 23, were made by the single-roller quenching method. The x-ray diffraction patterns showed the A2, D019, and L12 diffraction peaks coexisting with the amorphous matrix background. When Fe was replaced by Co, i.e., when x was increased, the first crystallization temperature (TX1) and Curie temperature (TC1) rose greatly. With a sufficiently heavy load (or weight) stretching the ribbon downward, the magnetization MS was pulled along the vertical direction (i.e., the tension-axis). Then, by applying a horizontal field (HE) up to 6 KOe, we determined the sign and magnitude of the saturation magnetostriction (λS). The Young's modulus (ES) at magnetization saturation and ΔE effect was estimated from the stress-strain curve. We discovered that the stress-strain curve of (Fe81Ga19)80B20 exhibits the auxetic (or abnormal) characteristic with ΔE < 0. For the rest of the (Fe81-xCoxGa19)80B20 with x ≠ 0, their stress-strain curves are normal with ΔE > 0. Because the sign of λS of the A2 phase is opposite to that of the D019 and L12 phases, λS of (Fe81-xCoxGa19)80B20 is much reduced. However, ΔE/E0 ≒ 36% is quite large for (Fe58Co23Ga19)80B20. [ABSTRACT FROM AUTHOR]

The pyroelectric coefficient is normally measured under the short circuit condition, while many pyroelectric applications are under the open circuit condition. We present experimental results demonstrating a difference in the pyroelectric coefficient under open and short circuit conditions. We also present results on pyroelectric coefficient enhancement using laminate composites, and show that this technique can enhance the pyroelectric coefficient at open circuit condition, as well as at short circuit condition. [ABSTRACT FROM AUTHOR]

The pyroelectric coefficients of laminate composites under short circuit condition have been investigated by analytical modeling and numerical simulations. Indicators for various pyroelectric/non-pyroelectric material pairs that can be utilized to determine their pyroelectric coefficient enhancement credentials have been identified. Six pyroelectric materials were paired with six non-pyroelectric/elastic materials and their pyroelectric coefficient enhancement potential and figure of merit for efficiency were investigated. The best performing partnership out of the 36 pairs was lead zirconate titanate (PZT5H)-chlorinated polyvinyl chloride thermoplastic (CPVC) for thickness ratios (R) below 0.09 and PZT5H-zinc for R larger than 0.09 with both demonstrating total pyroelectric coefficient of approximately -20×10-4 C m-2 K-1 at R=0.09, which corresponds to approximately 300% increase in the coefficient. PZT5H-CPVC also showed maximum of 800% rise in the pyroelectric coefficient while figure of merit for efficiency indicated up to twentyfold increase in its electrical response output per given thermal stimuli when compared to that of PZT5H by itself. [ABSTRACT FROM AUTHOR]

An analytical model for the pyroelectric (PY) effect under open circuit condition and 2-2 connectivity laminates of various pairs of PY and nonpyroelectric (NP)/elastic materials has been developed. It is evident from our analysis that there indeed is a substantial dissimilarity between the PY coefficients and figure of merit for efficiency for various PY-NP pairs under short circuit and open circuit conditions. We believe this implies that there should be a greater distinction made between the PY coefficients under these two electrical conditions than previously thought. The indicators for various PY-NP material pairs that can be utilized to determine their PY coefficient enhancement potential under open circuit condition have been identified. The investigated PY materials are lead zirconate titanate (PZT-5H and PZT-5A), barium titanate, lithium tantalate, lithium niobate, and polyvinylidene fluoride (PVDF), while the NP materials are stainless steel, polytetrafluoroethylene (PTFE or Teflon), chlorinated polyvinyl chloride thermoplastic (CPVC), aluminum, zinc, and Invar 36. Extraordinarily large PY coefficient of 97×10-4 C m-2 K-1 at minimum thickness ratio Rmin is expected for PZT-5H-CPVC pair while PVDF-CPVC could show increase in the secondary PY coefficient of up to 350%. In addition, where the figure of merit for efficiency is concerned, for the same volume of the composite PZT-5A-PTFE pair it reaches 24, a 24-fold increase in efficiency at Rmin. Our analysis techniques should provide a methodological way for appraising the potentials of particular PY material and its 2-2 laminates for applications under open circuit condition such as PY X-ray generation, electron accelerator, and nuclear fusion. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) ultraviolet metal-semiconductor-metal photodetectors (PDs) grown on Si substrates were demonstrated. The dark current of PDs fabricated on Si substrates was substantially smaller in magnitude compared to identical devices prepared on sapphire substrates. With an incident wavelength of 359 nm, the maximum responsivities of the n--GaN MSM photodetectors with TiW and Ni/Au contact electrodes were 0.187 and 0.0792 A/W, corresponding to quantum efficiencies of 64.7% and 27.4%, respectively. For a given bandwidth of 1 kHz and a given bias of 5 V, the corresponding noise equivalent powers of our n--GaN MSM photodetectors with TiW and Ni/Au electrodes were 1.525×10-12 and 5.119×10-12 W, respectively. Consequently, the values of detectivity (D*) determined for devices with TiW and Ni/Au electrodes were then calculated to be 1.313×1012 and 3.914×1011 cm Hz0.5 W-1, respectively. [ABSTRACT FROM AUTHOR]

InGaN quantum dots (QDs) deposited on SiNx nanomasks have been investigated by atomic force microscopy, photoluminescence (PL), and photoluminescence excitation (PLE) measurements. It was found that the size of QDs can be well controlled by SiNx nanomasks, enabling the manipulation of quantum confinement effect. The PL spectra of InGaN QDs contain several fine structures, and the main peaks can be attributed to families of QDs with different sizes. The emission arising from InGaN QDs and GaN buffer layer can be clearly distinguished based on PLE measurement, which can be used to improve the interpretation in the previous reports. Our study indicates that the quantum confined Stark effect due to piezoelectric field plays a very important role in the optical properties of InGaN QDs, which is very useful for the application of optoelectronic devices. [ABSTRACT FROM AUTHOR]

We have controlled and investigated the ion density ratio ([O+]/[O2+]) in oxidation plasma by He and Xe mixing. The ion density ratio increases from 0.26 to 0.97 by He mixing, and decreases to 0.015 by Xe mixing. The ratio is a strong function of the electron density and electron temperature. When the other conditions are fixed, the ion density ratio is proportional to the electron density in all the cases: the He/O2 and Xe/O2 mixtures as well as pure O2 plasma. This may be due to the increase in the dissociation rate and the process of ionization from O to O+. The rate of increase in the ion density ratio with the electron density is different in the two cases: In the He/O2 mixture, the rate of increase is slightly higher than that in the pure O2 plasma. However, the rate is very low in the Xe/O2 mixture. In the Xe/O2 mixture, the ion density ratio is actually a strong function of the electron temperature rather than the electron density. [ABSTRACT FROM AUTHOR]

Step edge growth of Co nanoislands on Cu(111) surface have been investigated by scanning tunneling microscopy (STM). The cobalt atoms cluster at the upper step edges and form bilayer islands of 2 nm in diameter (about nine Co atoms in width) initially during the initial stage of Co deposition. This result is in accordance with the total energy calculations within density functional theory. Besides, the size and amount of nanoislands increase with increasing coverage. The average number of Co atoms contained in one island increases with a rate of 375 atoms per monolayer (ML). The statistics data on the STM images indicate that the cobalt nanoislands preferentially grow at the upper step edge during the first stage of Co deposition, then toward terrace, and finally, the growth rate of islands in edge is almost the same as that in terrace for Co thickness above 0.78–1.42 ML. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of Pr9+xFe73-x-yTiyCo10B4C4 (x=0,0.5,1,1.5; y=0,2) melt-spun ribbons have been investigated. All these ribbons consist mainly of three phases, namely, 2:14:1, α-(Fe,Co), and 2:17 phases. It was found that the grain size of these phases decreases with increasing Pr content. A small substitution of Ti for Fe suppresses the grain growth of α-(Fe,Co) phase. The intergranular exchange coupling remarkably increases with increasing Pr and Ti substitution. For Ti-free Pr9+xFe73-xCo10B4C4 ribbons, the iHc increases, and Br decreases, but (BH)max nearly keeps invariable up to x=1.0, then slightly increases, with increasing x. A Br of 9.1 kG, iHc of 10.0 kOe, and (BH)max of 12.5 MG Oe were obtained in Pr10.5Fe71.5Co10B4C4. The coercivity and demagnetization-curve shape are substantially improved with Ti substitution, without a sacrifice of remanence (except for x=0). The (BH)max increases by a large amount (∼5 MG Oe) with a small substitution (2 at. %) of titanium. A Br of 9.6 kG, iHc of 10.2 kOe, and (BH)max of 17.4 MG Oe have been achieved in Pr10.5Fe69.5Ti2Co10B4C4 ribbon. [ABSTRACT FROM AUTHOR]

Collective and individual emissions from In0.5Ga0.5As quantum dots (QDs) in single-defect photonic crystal nanocavities are investigated. When the cavity mode is collectively excited by the QD ensemble, a pair of dipolelike modes with definite linear polarizations is shown. Under low excitations, single-exciton emission lines are resolved. The power dependence of individual QD emissions reveals a nearly tenfold light enhancement for on-resonance QDs. The polarization state of each individual QD is also investigated. It is found that an individual dot could excite either a pure dipole mode or a mixture of both dipole modes. This behavior can be attributed to the random distribution of QDs in the nanocavity. [ABSTRACT FROM AUTHOR]

We measured electrical characteristics of capacitively coupled plasma at low pressure (2.67 Pa) with different driving frequencies. From these measurements, we observed a significant change in discharge power characteristics during the frequency increase. While increasing the frequency, a square dependence of power characteristics (P∼I[sup 2]) changes to a linear dependence (P∼I). This observed result reflects that a power dissipation mode transition from an ion-dominated dissipation mode to an electron-dominated dissipation mode takes place during the driving frequency increase. Both the results calculated from a simple sheath model and a particle-in-cell simulation are in a good agreement with the experimental data. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Surface CH stretching features on diamond nanocrystals of different origins and sizes have been characterized by Fourier transform infrared spectroscopy and density functional calculations. Independent of the origins of the samples, a single sharp transition, corresponding to the CH stretch on C(111)-1×1, is observed at 2834 cm[sup -1] for particles of sizes (d) larger than 100 nm. The feature, however, gradually diminishes as the particle size decreases and disappears nearly completely at d=5 nm. We interpreted the observation in terms of a domain size effect, namely, the domains of the {111}-type facets on the 5 nm diamonds are too small to yield the characteristic CH stretching feature [Chen et al., J. Chem. Phys. 116, 1211 (2002)]. The interpretation is supported by the present density functional calculations performed at the B3LYP/6-31G[sup *] level for three H-truncated diamond model clusters, C[sub 22]H[sub 28], C[sub 38]H[sub 42], and C[sub 58]H[sub 58]. Both “isolated” and “coupled” frequencies of the C–H stretching features on the {111}-type facets of these clusters are calculated and the results agree satisfactorily with the values obtained from the mixed isotope measurements conducted on diamond C(111)-1×1 single crystal surfaces [Cheng et al., J. Chem. Phys. 106, 7411 (1997)]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic properties, phase evolution and aftereffect of melt-spun Pr[sub 10]Fe[sub 90-x]B[sub x] (x = 5.88-11.5) nanocomposite ribbons have been studied. Summarizing the results of thermal magnetic analysis and Mössbauer spectroscopy, two phases, namely Pr[sub 2]Fe[sub 14]B and α-Fe, were found for ribbons with x = 5.88 and 7.5, while additional two metastable phases, Pr[sub 2]Fe[sub 23]B[sub 3] and Fe[sub 3]B, prevailed for x = 9. For x = 10 and 11.5, only three of these phases: Pr[sub 2]Fe[sub 14]B, Pr[sub 2]Fe[sub 23]B[sub 3], and Fe[sub 3]B, but not α-Fe were present. The optimal magnetic properties of B[sub r] = 10.1 kG, [sub i]H[sub c] = 6.4 kOe, and (BH)[sub max] = 16.1 MGOe were achieved in the Pr[sub 10]Fe[sub 84.12]B[sub 5.88] ribbon, while [sub i]H[sub c] 8.71 kOe and (BH)[sub max] 14.7 MGOe were obtained in Pr[sub 10]Fe[sub 80]B[sub 10]. Furthermore, Pr[sub 10]Fe[sub 78.5]B[sub 11.5] having the optimal [sub i]H[sub c] (9.33 kOe) exhibited minimum values in activation volume V = 5.03 × 10[sup -19] cm³, because it possessed the least volume fraction of the magnetically soft phases. Finally, confirmation of the absence of spin reorientation in Pr[sub 2]Fe[sub 14]B down to 5 K assures its advantage over Nd[sub 2]Fe[sub 14]B for low-temperature applications. [ABSTRACT FROM AUTHOR]

Infrared spectra of CH stretches have been investigated on the surfaces of synthetic diamond crystallites (5, 100, and 700 nm in diameter) to provide insights into the mid-infrared emission bands of stardusts in interstellar media. While the spectrum of 5-nm diamonds fails to display the distinct 2835 cm-1 (or 3.53 μm) band, a remarkably good match of the absorption bands of larger diamond grains with the emission observed for the stars Elias 1 and HD 97048 is obtained. Suggested by this study, the nanodiamonds that can display such characteristic emission bands at 3.53 μm in these two interstellar systems have a size significantly larger than 5 nm. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent significant advances in coupling superconducting qubits to acoustic wave resonators have led to demonstrations of quantum control of surface and bulk acoustic resonant modes as well as Wigner tomography of quantum states in these modes. These advances were achieved through the efficient coupling afforded by piezoelectric materials combined with GHz-frequency acoustic Fabry-Perot cavities. Quantum control of "itinerant" surface acoustic waves appears in reach but is challenging due to the limitations of conventional transducers in the appropriate gigahertz-frequency band. In particular, gigahertz-frequency unidirectional transducers would provide an important addition to the desired quantum toolbox, promising unit efficiency with directional control over the surface acoustic wave emission pattern. Here, we report the design, fabrication, and experimental characterization of unidirectional distributed acoustic reflection transducers demonstrating a high transduction frequency of 4.8 GHz with a peak directivity larger than 25 dB and a directivity greater than 15 dB over a bandwidth of 17 MHz. A numerical model reproduces the main features of the transducer response quite well, with ten adjustable parameters (most of which are constrained by geometric and physical considerations). This represents a significant step toward quantum control of itinerant quantum acoustic waves. [ABSTRACT FROM AUTHOR]

A challenge faced by experimenters exploring hybrid quantum systems is how to integrate and interconnect different materials and different substrates in a quantum-coherent fashion. Here, we present a simple and inexpensive flip-chip bonding process, suitable for integrating hybrid quantum devices on chips from different substrates. The process only requires equipment and materials used routinely for contact photolithography, and it is possible to undo the bonding and reuse the chips. The technique requires minimal compressive force, so it is compatible with a wide range of different substrates. Unlike indium-based bonding, this process does not establish a galvanic connection between the two chips, but as we show, in some situations this is not necessary. We demonstrate the technique using lithographically patterned quarter-wave coplanar waveguide resonators, fabricated on one chip, and couple these inductively to a transmission line patterned lithographically on a separate chip. The two chips have a vertical interchip gap of about 7 μm, and we can repeatedly achieve lateral alignments of better than 2 μm. We measure electromagnetic resonances with low-power (∼1 photon) internal quality factors Qi around 5 × 105, comparable to single-chip performances, with as-designed coupling quality factors Qc ranging from 2 × 102 to 5 × 105. [ABSTRACT FROM AUTHOR]

Structure and magnetic properties of sputter-prepared Co(5 nm)/MnPt(20 nm) and MnPt/Co polycrystalline films with various annealing temperatures (T) have been compared. XRD and TEM analysis show that MnPt is more compressive in film plane for Co/MnPt than MnPt/Co at as-deposited state. Large HE of 464-560 Oe are attained in two series films through proper thermal process of post annealing and cooling in external magnetic field. The increase of HE with T is mainly dominated by the ordering degree of MnPt layer and the roughness of the interface. As compared to MnPt/Co film (T = 250 °C), Co/MnPt film with more compressive in film plane exhibits L10-ordering, the onset of stress release, and the optimized HE at lower T = 200 °C. Higher HE for MnPt/Co film at T = 250 °C (560 Oe) than Co/MnPt film T = 200 °C (464 Oe) might be related to grain growth for L10 phase. Nevertheless, higher annealing temperature leads to the interdiffusion, the roughened surface and therefore the decrease of HE and Hc. This study provides useful information to fabricate exchange-bias system with L10-MnPt as an antiferromagnetic layer. [ABSTRACT FROM AUTHOR]

We present a phenomenological model to account for the observations of the hydrogen interchange tunneling at N=v1+v2=1–3 of the free (v1) and the bound (v2) HF stretches of (HF)2. Good agreement is obtained between calculations and observations at the levels (v1,v2) of v1-v2=±1 for both N=1 and 3, suggesting that the observed hydrogen tunneling splittings in these levels are direct rather than the results of many extraneous perturbations. The model also predicts well the ratios of the rates of vibrational predissociation at these states, in addition to the splittings. We attribute the unusually large vibrational dependence of the splittings upon valence bond excitation to the result of interbond coupling between the two HF local oscillators. Significant differences in the vibrational energy of the level (1,2) as well as the tunneling splitting at (2,0) between observation and prediction are, however, noted. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study that observed giant magnetoresistance effect in Fe-XCr-Co (W[subFe]/W[subCo]=1) ternary heterogeneous alloy films. Methodology of the study; Results and discussion on the study; Conclusions.

Provides information on a study that observed large negative magnetoresistace in Fe-xCr-10Co alloy thin films prepared by ion beam sputter. Experimental procedure; Results and discussion; Conclusions.

Focuses on a study which investigated the effect of deep levels in semi-insulating indium phosphide substrate material on the electrical properties of accumulation-type metal-insulator-semiconductor field-effect transistors (MISFET). Description of MISFET fabrication; Determination of iron content; Measurements and discussion.

Presents a study which highlights the near-band-edge properties of the epilayers of the ZnSe. Comparison of the contactless electroreflectance (CER) and piezoreflectance spectra; Calculation of the energy splitting between heavy-hole related transition energies; Reference to the degradation of these devices.

Examines the optical and electrical properties of nitrogen ion implanted p-type ZnSSE/p+GaAs. Achievement of dopant activation and annealing out the implant damage; Employment of Schottky structures; Examination by photoluminescence spectroscopy, current-voltage, current-voltage temperature and high frequency capacitance-voltage measurements.

Presents a study that examined the recombination properties of quantum wires using photoluminescence spectroscopy. Methodology; Analysis of the spectral shifts in the quantum wires; Correlation between photoluminescence efficiency and wire width.

Presents a study which determined the optical waveguiding in single-crystal, epitaxial oriented rutile thin films grown on sapphire substrates using the metal-organic chemical vapor deposition technique. Waveguide modes of the anisotrophic film; Methodology; Results and discussion; Conclusions.