[en] Highlights: • The desorption kinetics for LiBH_4 greatly promoted using melt infiltration method. • The LiBH_4 confined in modified MWCNTs shows the best desorption kinetics. • The crystal structure of MWCNTs and SWCNTs is unchanged after ball milling. • Ball milling introduces a great amount of structural defects in the CNTs. • Nano-confinement is dominant on improving the hydrogen desorption of LiBH_4. - Abstract: The dehydrogenation kinetics of LiBH_4 incorporated within various carbon nanotubes has been studied. It is demonstrated that the desorption kinetics of LiBH_4 could be greatly promoted using a simple melt infiltration method and LiBH_4 confined in modified multi-walled carbon nanotubes (MWCNTs) shows the best desorption kinetics. The structural properties of carbon nanotubes and confined samples are demonstrated by means of transmission electron microscopy, powder X-ray diffraction and Raman spectroscopy. The crystal structure of MWCNTs and single-walled carbon nanotubes (SWCNTs) are almost unchanged after ball milling. But high energy ball milling leads to a decrease in the average nanotube length and introduces a great amount of local disorder and structural defects in the CNTs, which may provide a considerable kinetic improvement

[en] Non-polished aluminum sheets were anodized. The nanostructures were investigated in details using an atomic force microscope (AFM). The coexistence of self-assembled stripes and porous arrays on the Al surface was observed. The formation mechanism of the stripes is discussed based on the Brusselator model. We suggest that the self-assembled patterns on the Al surface strongly depend on the competition of the formation and the dissolution rate of alumina film during the reaction process. It is also found that this type of ordered structure can only form in certain conditions

[en] Measurements of dc and ac susceptibility, resistivity, Hall effect, and thermoelectric power (TEP) on pure phase Hg-1223 and mixed phase Hg-1212-1223 cuprates are reported. The mixed phase compounds show the highest critical temperature (magnetic susceptibility onset of 138 K). Both Hall effect and TEP data support an underdoped state with hole-like conduction. Oxygen annealing reduces the Hall coefficient (increasing the concentration of holes) and lowers the TEP (increasing the Fermi energy) features which can be explained by a simple Fermi-gas picture. The Hall coefficient which increases linearly with temperature and the negative temperature coefficient of the TEP, however, cannot be explained by single-band Fermi-gas or -liquid theory, unless one introduces energy dependent carrier scattering. Estimates of the highest critical temperature based on the universality observed in the thermopower data for the cuprates suggest that 138 K is near the maximum one might expect for the Hg cuprates under optimal doping at atmospheric pressure. (orig.)

[en] We have found that substitution of bismuth into the TlBa₂Ca₂Cu₃O₉ system leads to a high temperature superconductor with significantly greater low temperature flux pinning than that of the other copper oxide superconductors. Bi substitutes at the Tl site up to 20 at.%. The superconducting transition temperature T_c increases from 110 K for x=0.0 to 116 K for x=0.2. Scanning electron microscope (SEM) images reveal a platelike morphology which is highly suitable for powder-in-tube processing. The magnetization endash hysteresis loop shows that the Bi-substituted phase has significantly better low temperature flux pinning properties than the pristine Tl cuprate, and exhibits only a weak dependence on temperature and field when compared to that of unsubstituted phase. However, at 77 K the compound has lower J_c, determined magnetically, compared to that of the (Tl,Pb,Bi)Sr_1.6Ba_0.4Ca₂Cu₃O_y and Y-123 systems. The enhancement of superconducting properties is attributed to an increased coupling between the CuO₂ planes along the c axis. Substitution of 20% of Bi in TlBa₂Ca₂Cu₃O₉ makes the compound an excellent choice for magnet wire applications at relatively low temperatures. copyright 1997 American Institute of Physics

[en] The structural evolution and temperature dependence of the Schottky barrier heights of Pt contacts on n-GaN epilayer at various annealing temperatures were investigated extensively by Rutherford backscattering spectrometry, x-ray diffraction measurements, Auger electron spectroscopy, scanning electron microscopy and current-voltage measurements. The temperature dependence of the Schottky barrier heights may be attributed to changes of surface morphology of Pt films on the surface and variation of nonstoichiometric defects at the interface vicinity. Experimental results indicated the degradation of Pt contacts on n-GaN above 600 deg. C

[en] The interface states of [NiFe/Mo]₃₀ and [Fe/Mo]₃₀ multilayers have been investigated by x-ray small angle reflection and diffuse scattering. Significant interface roughness correlation was observed in both ultrathin [NiFe/Mo]₃₀ and [Fe/Mo]₃₀ multilayers. An uncorrelated roughness of about 2.7-3.1 A was revealed in the [NiFe/Mo]₃₀ multilayers, which is explained as originating from a transition layer between the NiFe and the Mo layers. By the technique of diffuse scattering, it is clearly indicated that the interfacial roughness of NiFe/Mo is much smaller than that of Fe/Mo although the lattice mismatch is the same in both multilayers. (author)

[en] In this paper, we report transport and transmission electron microscopy (TEM) measurements on Tl-based superconducting films prepared by two non-vacuum techniques: electrodeposition and spray pyrolysis. For electrodeposition, a conducting Ag layer was used on insulating substrates such as (LaAlO₃) LAO to enable electroplating the Tl-oxide precursor films. The behaviour of the Ag layer after processing the precursor films has never been understood. We resolved this issue by performing TEM analysis of several processed electroplated Tl-oxide films. In this paper, we also report on the TEM analysis of MgO nanoparticle-incorporated spray pyrolysis films. Spray pyrolysis films were prepared with and without MgO nanoparticles. MgO nanoparticles were included in the spray pyrolysis films to improve the flux pinning and critical current densities of the Tl-1223 films. (author)

[en] A two-dimensional (2D) thin film composed of Tb nanocrystals with uniform orientations is fabricated directly from Tb₆₅Fe₂₅Al₁₀ alloy melt upon quenching. The Tb nanocrystals with vertical height of 15-30 nm and lateral width of 10-20 nm are assembled in the nanocrystalline array on an amorphous substrate. The formation mechanism for the aligned Tb nanocrystals is discussed. The single-step formation method may provide a new and flexible alternative to fabricate nanostructured films or arrays used for submicron devices

[en] The effects of growth time on the structure and morphology of cubic GaN nucleation layers on GaAs(001) substrates by metalorganic chemical vapor deposition (MOCVD) have been investigated using a synchrotron X-ray diffraction (XRD). The XRD results show that the GaN 111 reflections at 54.74 degree in x are a measurable component, however the 002 reflections parallel to GaAs(001) surface are not detected. The XRD Φ scans and pole figures give a convincing proof that the GaN nucleation layers show exactly the cubic symmetrical structure. The coherence lengths along the close-packed <111> direction estimated from the 111 peak are nanometer order of magnitude. The optimal photoluminescence (PL) spectrum was obtained from the cubic GaN layer deposited on the nucleation layer for 60 sec

[en] Coupling agents have been widely used to retard the sintering of silver paste and minimize co-firing defects due to densification mismatch between silver and dielectrics. The thermal-decomposition and crystallization behavior of the coupling agent is a subject of great concern. To elucidate what is responsible for the oxidation, Ti organometallic compounds were calcined at different temperatures (350, 400, 500, 600 ^oC) for 2 h and the crystallization behavior was determined by X-ray diffraction (XRD). The activation energy for crystallization of coupling agents was studied by using isothermal methods. According to the quantitative XRD method, the values calculated by the Johnson-Mehi-Avrami equation are 134.9 kJ mol^-1. The growth morphology parameters are 1.061, 0.915, 1.016 respectively. Combining the results of DTA, XRD and TEM, it is found that formation of nanocrystallized titania accompanies the combustion of organometallic compounds.