Search

To study anisotropic hydrogen segregation and diffusion in nickel polycrystalline, Secondary Ion Mass Spectrometry (SIMS) and Electron Back Scattered Diffraction (EBSD) are integrated to investigate hydrogen distribution around grain boundaries. Hydrogen distribution in pre-charged samples were correlated with grain boundary character by integrating high-resolution grain microstructure from EBSD inverse pole figure map and low-resolution hydrogen concentration profile map from SIMS. This multimodal imaging instrumentation shows that grain boundaries in nickel can be categorized into two families based on behavior of hydrogen distribution crossing grain boundary: the first one includes random grain boundaries with fast hydrogen diffusivity, showing a sharp gap for hydrogen concentration profile cross the grain boundaries The second family are special Σ3n grain boundaries with low hydrogen diffusivity, showing a smooth gradient of hydrogen concentration cross the grain boundary. Heterogeneous hydrogen distributions due to grain boundary family revealed by SIMS/EBSD on mesoscale further validate the recent hydrogen permeation data and anisotropic ab-initio calculations in nanoscale. The results highlight the fact that grain boundaries character impacts hydrogen distribution significantly.

The possibility of a spectrally tunable solar-like light source is drawing attention with the development of LEDs. We researched the market of high-power, monochromatic LEDs and established a database with 103 kinds of LED by a new model. We used the database to match the solar spectrum in the wavelength range 380–780 nm. The optimal combination maximising the fit to the solar spectral curve was obtained. The trade-off relationship between the selection of LEDs and the fit was investigated in detail. The results show that the optimal combination contains 34 types of LED with a maximum correlation index R2 of 88.67%. The value of R2 reduces to 85.06% when the number of LED types is reduced to 20, but the R2 value decreases sharply if the number of LED types is decreased to 16, with a R2 of 79.97%.

The effects of high magnetic field annealing on the preferred orientation distribution (texture) and magnetic anisotropy of arc-melted FePd alloy were studied by recalculated pole figure method and vibrating sample magnetometry. A rigorous texture characterization method was used to analyze the crystal orientation distribution of the annealed FePd. As compared with annealing without magnetic field, the high magnetic field annealing increases the volume fraction of crystal grains with c-axis aligned along the annealing magnetic field direction. A corresponding uniaxial magnetic anisotropy was also observed in the magnetically annealed FePd alloy.

We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50K for the sample with the shorter deposition time, and above 100K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination c...

The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.

Magnetically soft/hard exchange-coupled Ni80Fe20/Si3N4/Sm40Fe60 and Ni80Fe20/mixture/Sm40Fe60 layered structures with induced in-plane uniaxial anisotropy were deposited by sputtering on Si (100) substrates. The interfacial exchange coupling strength between the soft and hard layers was tailored by inserting a thin nonmagnetic insulating Si3N4 layer or by varying interfacial mixture of NiFe and SmFe. It was found that the reduction in the exchange coupling greatly reduces the nucleation field HN of the soft layer and increases the irreversible switching field Hirr of the hard layer. The simple formula used before to describe the nucleation field of the soft layer does not work in the case of the reduced interfacial exchange coupling.

Longitudinal tensile tests have been conducted on unidirectional SiC fibre reinforced 6061 aluminium matrix composites in the annealed and as-manufactured conditions. The results are presented in terms of stress-strain curves and tangent modulus-strain relations, which show considerable non-linearity. Corresponding micromechanical finite element modelling is performed including the effects of the manufacturing process on the matrix in-situ properties. The analysis shows that the non-linear behaviour of the composite is caused by the elastic-plastic deformation of the matrix alloy. The matrix fully yields during the cooldown from manufacturing. Residual stress relaxation plays an important role in the stress-strain characteristics of the annealed aluminium matrix composite by introducing some initial elastic deformation. The amount of elastic deformation for the as-manufactured condition is greater because of subsequent age hardening. However, more linear elastic deformation was observed than predicted in the as-manufactured specimens, which is believed to be due to higher precipitation hardening caused by metallurgical effects induced in the manufacturing process.

Superparamagnetic iron oxide nanoparticles (SPIONs) have been produced and used as contrast-enhancing agents in magnetic resonance imaging (MRI) for diagnostic use in a wide range of maladies including cardiovascular, neurological disorders, and cancer. The reasons why these SPIONs are attractive for medical purposes are based on their important and unique features. The large surface area of the nanoparticles and their manipulation through an external magnetic field are features that allow their use for carrying a large number of molecules such as biomolecules or drugs. In this scenario, the present work reports on the synthesis and characterization of SPIONs and in vitro MRI experiments to increase their capacity as probes for MRI applications on stem cells therapy. Initially, the SPIONs were prepared through the co-precipitation method using ferrous and ferric chlorides in acidic solution. The SPIONs were coated with two thiolmolecules such as mercaptosuccinic acid (MSA) and cysteine (Cys) (molar ratio SPIONs:ligand = 1:20), leading to the formation of a stable aqueous dispersion of thiolated nanoparticles (SH-SPIONs). The SH-SPIONs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results showed that the SH-SPIONs have a mean diameter of 14 nm and display superparamagnetic behavior at room temperature. Preliminary tests of incorporation of SH-SPIONs were evaluated stem cells. The results showed that the thiolated nanoparticles have no toxic effects for stem cells and successfully internalized and enhance the contrast in MRI.

In the present study, the enhanced magnetic properties of Nd-Fe-B sintered magnet pieces treated with the Dy or Tb metal as reduced by heating their oxides or fluorides with CaH2 are reported together with the results obtained on the samples simply coated and heated with the oxide or fluoride of Dy and Tb elements and the mechanism for enhancing the coercivity is disscussed to produced much powerful Nd-Fe-B sintered magnets.

Enhanced magnetic properties of Nd-Fe-B sintered magnet pieces treated and high-performance characteristics of small motors mounting them are reported. A well-defined treatment to enhance the coercivity of Nd-Fe-B sintered magnet pieces is developed and is showing great potential for producing high-performance magnets in higher temperatures.

The interface between the Nd2Fe14B particles and the grain boundary surrounding them in Nd-Fe-B sintered magnets was modified by diffusion Dy metal selectively through the grain boundary involving the reduction of Dy2O3 or DyF3 with CaH2 and the coercivity of them was effectively enhanced from 0.98 MA/m to 1.42 MA/m with keeping the high value of remanence. The resultant coercivity was higher than that of the magnets modified with Dy2O3 (HcJ = 1.10 MA/m) and DyF3 (HcJ = 1.24 MA/m) without using any reductant such as CaH2, respectively.

The magnetic properties of NdFeB/Tb multilayered films annealed at 773-1273K were investigated by evaluating the effect of Tb spacer layer and comparing them with those of NdFeB single layered films. The as-deposited NdFeB/Tb film with a amorphous structure was crystallized at the higher annealing temperature than 923K and Nd-rich phases were formed at 1073 K, meanwhile the coercivity increased substantially. By observations of the microstructure, Tb element was found to diffuse into the Nd-rich phases to form a Tb-enriched phase around the Nd2Fe14B primary phase particles in the multilayered films.