The effect of substrate temperature on the microstructure and tunnelling magnetoresistance of FeCo–Al2O3 nanogranular films

A series of FeCo–Al₂O₃ granular films were prepared with a magnetron controlled sputtering system. The magnetic–transport properties and microstructure of films sputtered at various substrate temperatures were characterized by conventional four probes method, SQUID magnetometer, analytical electron microscope and transmission electron microscope, respectively. The results indicate that the tunnelling magnetoresistance reaches the peak value of about 6.9% for FeCo (41 vol.%)-Al₂O₃ granular films sputtered at 300 K, while for FeCo granular films sputtered at 473 K, the 6% peak value in tunnelling magnetoresistance vs. volume fraction curve displaces toward the lower FeCo content of about 35 vol.%. Meanwhile, FeCo (30vol.%)-Al₂O₃ granular films sputtered both at room temperature and at 473 K behave as superparamagnetic and the susceptibility of this film increases with increasing substrate temperature. Based on the feature of microstructure of FeCo (41vol.%)-Al₂O₃ granular films sputtered at both room temperature and 823 K, the evolution sequence of two-stage phase separation is suggested. In addition, the effect of the microstructure on tunnelling magnetoresistance has been discussed.     

Investigation of the gas inlet velocity distribution in a fixed granular bed filter

Granular bed filter (GBF) technology can be applied for high-temperature gas cleanup in integrated gasification combined-cycle (IGCC) and pressurized fluidized-bed combustion (PFBC) advanced coal-fired power plants. The design of the gas inlet component of the granular bed filter is important to achieve a uniform gas distribution and higher usage rate of the filter media. Previous studies show that the gas velocity at the inlet is not uniformly distributed. This non-uniformity may lead to a lower usage rate of the filter media. In this study a baffle device is introduced to the inlet system in order to achieve a more uniform gas velocity distribution. A more uniform gas inlet distribution can be obtained by adjustment of the lengths and angles of the baffles. The gas velocities along the inlet and filtration surfaces are measured using a pitot tube. The uniformity of the gas velocity distribution can be characterized by looking at the distributions of the standard deviation of the gas velocity and the differences in the mean velocities between the two filtration surfaces.     

Integrated Circuits Based on Bilayer MoS(2) Transistors

Two-dimensional (2D) materials, such as molybdenum disulfide (MoS(2)), have been shown to exhibit excellent electrical and optical properties. The semiconducting nature of MoS(2) allows it to overcome the shortcomings of zero-bandgap graphene, while still sharing many of graphene's advantages for electronic and optoelectronic applications. Discrete electronic and optoelectronic components, such as field-effect transistors, sensors, and photodetectors made from few-layer MoS(2) show promising performance as potential substitute of Si in conventional electronics and of organic and amorphous Si semiconductors in ubiquitous systems and display applications. An important next step is the fabrication of fully integrated multistage circuits and logic building blocks on MoS(2) to demonstrate its capability for complex digital logic and high-frequency ac applications. This paper demonstrates an inverter, a NAND gate, a static random access memory, and a five-stage ring oscillator based on a direct-coupled transistor logic technology. The circuits comprise between 2 to 12 transistors seamlessly integrated side-by-side on a single sheet of bilayer MoS(2). Both enhancement-mode and depletion-mode transistors were fabricated thanks to the use of gate metals with different work functions.     

Optimization of probe-laser focal offsets for single-particle tracking

In optical tweezers applications, tracking a trapped particle is essential for force measurement. One of the most popular techniques for single-particle tracking is achieved by analyzing the forward and backward light pattern, scattered by the target particle trapped by a trap laser beam, of an additional probe-laser beam with different wavelength whose focus is slightly apart from the trapping center. However, the optimized focal offset has never been discussed. In this paper, we investigate the tracking range and sensitivity as a function of the focal offset between the trapping and the probe-laser beams. As a result, the optimized focal offsets are a 3.3-fold radius ahead and a 2.0-fold radius behind the trapping laser focus in the forward tracking and the backward tracking, respectively. The experimental result agrees well with a theoretical prediction using the Mie scattering theory.     

Fabrication and characterization of porous Ti–7.5Mo alloy scaffolds for biomedical applications

Porous titanium and titanium alloys are promising scaffolds for bone tissue engineering, since they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of natural bone. In the present study, porous Ti–7.5Mo alloy scaffolds with various porosities from 30 to 75 % were successfully prepared through a space-holder sintering method. The yield strength and elastic modulus of a Ti–7.5Mo scaffold with a porosity of 50 % are 127 MPa and 4.2 GPa, respectively, being relatively comparable to the reported mechanical properties of natural bone. In addition, the porous Ti–7.5Mo alloy exhibited improved apatite-forming abilities after pretreatment (with NaOH or NaOH + water) and subsequent immersion in simulated body fluid (SBF) at 37 °C. After soaking in an SBF solution for 21 days, a dense apatite layer covered the inner and outer surfaces of the pretreated porous Ti–7.5Mo substrates, thereby providing favorable bioactive conditions for bone bonding and growth. The preliminary cell culturing result revealed that the porous Ti–7.5Mo alloy supported cell attachment.     

Metal-Insulator Transition and Cu K-Edge XANES Studies for Pr1.85Ce0.15CuO4+δ High-Tc Superconductors

Metal-insulator transition near oxygen content parameter –0.018 was observed for electron-doped Pr_1.85Ce_0.15CuO₄₊ (–0.0030.03) cuprates. Cu K-edge X-ray absorption near-edge structure (XANES) studies with nearly identical threshold edge energy E₀ of 8980.8 eV indicate a Cu formal valence smaller than 2 for all samples, which is consistent with the estimated Cu valence of 1.84 for 20.5 K superconductor Pr_1.85Ce_0.15CuO_3.997 and 1.91 for Pr_1.85Ce_0.15CuO_4.03 insulator. The XANES spectrum reflects the Cu 3d ⁿ character where low energy peak A ₁ reflects the 3d ¹⁰ configuration of Cu(I) oxidation state and A ₂ peak reflects the 3d¹⁰ ( for a oxygen ligand hole) configuration for Cu(II) oxidation state. The variation of energy separation E(A ₂–A ₁) is consistent with the observed metal-insulator transition, increases sharply from 2.42 eV for Pr_1.85Ce_0.15CuO_4.018 insulator to 2.74 eV for 15 K underdoped superconductor Pr_1.85Ce_0.15CuO_4.015.     

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al₂O₃) films have been deposited on lithium niobate (LiNbO₃) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al₂O₃ films to LiNbO₃ substrates. As Al₂O₃ thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al₂O₃/LiNbO₃ structure was found to increase with the insertion of an Al₂O₃ film, which can be attributed to the stiffening effect of the Al₂O₃ layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al₂O₃ (9.7 μm)/LiNbO₃ sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO₃ structure, whose the velocity change ratio is 2%.     

pH-insensitive fabrication of gold nanoparticles with high concentration by ultrasound-assisted electrochemical process via aid of chitosan

In this work, we report a new pathway to prepare pure gold nanoparticles with high concentrations in acid solutions via the aid of chitosan without the addition of other stabilizers and reductants based on electrochemical methods. Interestingly, this fabrication of gold nanoparticles with high concentrations in solutions is pH-insensitive. The characteristics of prepared gold nanoparticles were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (HRXPS) measurements. Experimental results indicate the concentration and the particle size of Au nanoparticles prepared in 0.1N HCl are ca. 50 ppm and 12 nm in diameter, respectively. Similar experiment performed in 0.1N NaCl with the aid of chitosan shows that the corresponding concentration of prepared Au nanoparticles is ca. 100 ppm. Further similar experiments performed in 0.1N HCl and 0.1N NaCl without the aid of chitosan show that the corresponding concentrations of prepared Au nanoparticles are ca. 1 and 60 ppm, respectively.     

ZrO2/hydroxyapatite coating on titanium by electrolytic deposition

In this study, hydroxyapatite (HA) was coated on a titanium (Ti) substrate over a ZrO(2) layer by the electrolytic deposition method, this double layer coating was then compared with a single layer coating of HA. The HA layer was used to increase the bioactivity and osteoconductivity of the Ti substrate, and the ZrO(2) layer was intended to improve the bonding strength between the HA layer and Ti substrate, and to prevent the corrosion of the Ti substrate. The electrolytic deposition formed an HA layer with a thicknesses of approximately 20 mum, which adhered tightly to the Ti substrate. The bonding strength of the HA/ZrO(2) double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The improvement in bonding strength with the use of a ZrO(2) base layer was attributed to the resulting increase in chemical affinity of the ZrO(2) to the HA layer and to the Ti substrate. The osteoblast-like cells cultured on the HA/ZrO(2) coating surface, proliferated in a similar manner to those on the HA single coating and on the pure Ti surfaces. At the same time, the corrosion resistance of Ti was improved by the presence of the ZrO(2) coating, as shown by a potentiodynamic polarization test.