[en] A semi-analytical simulation method is proposed in this paper to assess system reliability of structures. Monte Carlo simulation with variance-reduction techniques, systematic and antithetic sampling, is employed to obtain the samples of the structural resistance in this method. Variance-reduction techniques make it possible to sufficiently simulate the structural resistance with less runs of structural analysis. When resistance samples and its moments determined, exponential polynomial method (EPM) is used to fit the probability density function of the structural resistance. EPM can provide the approximate distribution and statistical characteristic of the structural resistance and then the first-order second-moment method can be carried out to calculate the structural failure probability. Numerical examples are provided for a structural component and two ductile frames, which illustrate the method proposed facilitates the evaluation of system reliability in assessments of structural safety

[en] Nd-Fe-B magnets have outstanding magnetic properties, but their corrosion resistance is poor because the rare-earth-rich phases in them are easily oxidized. In this article, we report an investigation of the corrosion behaviors of sintered Nd-Fe-B magnets with varied compositions in different corrosion conditions. The weight losses of the magnets after corrosion testing were measured after brushing off the corrosion products. The magnetic flux losses of the magnets were measured using a fluxmeter. A scanning electron microscope equipped with an energy dispersive x-ray analysis system was employed to observe the corrosion morphology. It was found that the humid-heat resistance of the magnets was obviously improved by partially substituting Dy for Nd and adding minor Co. The corrosion products and morphologies of Nd-Fe-B magnets for the autoclave test were different from those for the constant humid-heat test. The corrosion rates of the magnets for the former were much slower than for the latter; this is probably because the high-pressure steam led to an oxygen-deficient atmosphere, and the liquid film on the surface of the magnet specimens hindered the diffusion of oxygen into the bulk for the autoclave test.

[en] A nitrogen-loss technique was adopted to fabricate a SiC/SiO₂ luminescent composite. Nitrogen atoms were released from a starting Si–C–N–O film after annealing at high temperature and SiC nanocrystals were produced in the SiO₂ matrix. The density of SiC nanocrystals is as high as 5.2 × 10¹² cm⁻² and the size distribution centralizes at 2.0–2.5 nm. The SiC/SiO₂ composite emits strong ultraviolet light and visible light, which are attributed to intrinsic emission and interface states, respectively, of SiC nanocrytals

[en] The electrical transport properties of nanocontact nanostructures of ferromagnetic metals with different coercive forces have been studied by the I-V measurements at room temperature without applied magnetic field. The result indicates that the nanocontact structure within the critical contact width for NiFe, Fe and Ni can pin a single domain wall at the nanocontact position. A sharp resistance drop will happen when the domain wall is depinned from the contact position by injecting the spin polarized current. Furthermore, we have found that the critical current density for depinning is constant for each ferromagnetic metal. They are 1.8 x 10⁷ A cm^-2 for NiFe, 3.2 x 10⁷ A cm^-2 for Ni and 3.8 x 10⁷ A cm^-2 for Fe, respectively, which increases with the increase of the coercive force of ferromagnetic metal. Micromagnetic simulation results provided a detailed understanding on the magnetic configuration for ferromagnetic metals with different coercive forces

[en] In this article, the direct experimental evidences to determine the effect of grain boundary on local surface conductivity (SC) of diamond films were provided by the measurement using double probe scanning electron microscopy (SEM) technology. Undoped diamond films with (001) orientation were first grown by microwave plasma enhanced chemical vapor deposition and were then hydrogenated at different conditions for SC measurement. In the SEM system, double probes with tiny tip radius severed as two leads were moved along and contacted with the diamond film surface to directly test the local SC of diamond film. The surface electrical property results indicate that for the same distance between the two probes, the local SC of the area across grain boundary is much higher than that of area without grain boundary for the same duration of hydrogenation degrees. In addition, local SC of the area between the two probes increases with the number of grain boundaries in this area, which demonstrates that the grain boundaries play an important role in improving the SC of diamond film. The contribution of the grain boundaries on the local SC of diamond film can be mainly attributed to the defects in grain boundaries that can effectively improve electron transport ability at the diamond film surface

[en] In this paper, we propose a type of interdigitated silver nanoelectrode array fabricated by electron-beam lithography and ion beam etching. Ag nanoelectrode arrays with a width of 90 nm and a period of 150 nm have been successfully fabricated over a large area of 100  ×  100 µm². The Ag interdigitated nanoelectrode arrays have been employed in surface-enhanced Raman scattering (SERS) measurements under different oscillating electric fields, in which the SERS signal of p-thiocresol (C₇H₈S) of 10⁻⁶ M was easily detected. Moreover, the intensity of the Raman modes exhibited distinguishable variations while changing the strengths and frequencies of electric field, which could be attributed to the field-induced stretching and distortion mechanics of molecular bonds. These results demonstrated that the Ag interdigitated nanoelectrode arrays would be a good candidate for sensing devices in the area of analytes detection, by taking advantage of the ability to modulate the orientation of molecules. (paper)

[en] Field electron emission properties of individual diamond cone were investigated using a customized double-probe scanning electron microscope system. The diamond cone was formed by maskless ion sputtering process in bias-assisted hot filament chemical vapor deposition system. The as-formed sharp diamond cone coated with high-sp²-content amorphous carbon exhibited high emission current of about 80 μA at an applied voltage of 100 V. The field emission was stable and well in consistent with the conventional Fowler-Nordheim emission mechanism, due to a stabilization process in surface work function. It has demonstrated the possibility of using individual diamond cone as a point electron emission source, because of its high field electron emission ability and stable surface state after the process of work function stabilization

[en] A uniform diamond nanocone array was formed by plasma etching of diamond film in a hot filament chemical vapor deposition (HFCVD) system. A surface amorphous carbon coating layer, which is formed during CH₄/H₂ plasma-etching process, was removed by Ar plasma in a reactive ion etching system. The hydrogenation of diamond nanocones was performed in H₂ ambience by using the same HFCVD system. The air-diluted NH₃ and NO₂ gases sensing properties of the diamond cone arrays had been studied by using electric current versus measurement time characteristics at room temperature. The repeatable chemical sensing properties of the hydrogenated diamond cone array sensor are enhanced, in comparison with as-formed diamond film. Surface two-dimensional hole gas structure and greatly increased surface-to-volume ratio both play a key role for the excellent detection performance. As-formed diamond nanocone arrays show a promising prospect for applications as chemical sensor for both reducing (NH₃) and oxidizing (NO₂) gases

[en] Tubular carbon cones (TCCs) with a herring-bone-like graphitic structure are synthesized on gold wire via the bias-assisted hot filament chemical vapor deposition (HFCVD) method. The electrical transport properties of an individual TCC are studied in the temperature range from 300 to 500 K by using a double probe scanning electron microscopy (DPSEM) in situ electrical measurement system. The high-resistance I-V characteristics of W-TCC-Au back-to-back double junctions show that electrons tunnel through the W-TCC junction, while thermoionic transport through the Au-TCC junction contributes to low-resistance properties. Temperature dependence of the electrical characteristics indicates that inter-graphitic-plane electrical transport in TCC is metallic.

[en] Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO