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Wide-gap semiconductor SiC is generally considered as a superior candidate for high-radiation applications, due to its higher displacement energy for both Si and C lattice atoms. In this work, we find that the current gain ( $\beta $ ) of 4H-SiC bipolar junction transistors (BJTs) can severely deteriorate after neutron irradiation. Deep-level transient spectroscopy (DLTS) reveals that two major carrier-killer centers, Z1/2 and EH6/7, were produced in neutron-irradiated devices. Surprisingly, we find that the shallow Z1/2 center can play a dominant role over the deep EH6/7 defects in carrier recombination under high-injection conditions, which contributes to the unusual smaller hole capture cross section than that of the electron one, as indicated by the first-principles calculations. Finally, technology computer aided design (TCAD) simulation confirms that the enhanced carrier recombination from the Z1/2 centers is responsible for the degraded performance of SiC BJTs after irradiation. Our findings not only provide a deep insight into the underlying physics for displacement damage in SiC BJTs, but also are of interest for technological applications field related to high-energy particle irradiation or implantation.

Wire rope is a chain structure, and the strength of the weakest link is the strength of the entire wire rope. The axial resolution of loss of metallic cross-sectional area (LMA) detection using the induction coil is related to the length of the detection probe, which is usually greater than or equal to the length of the probe. Improving the axial resolution is an important technical indicator of the LMA. In this article, through theoretical analysis based on the principle of magnetic aggregation and 3-D transient magnetic field simulation, a particular kind of magnetic aggregation structure used for winding coil is proposed and optimized. Simulation and experimental results show that for wire rope LMA detection adding the proposed magnetic aggregation structure, the defect signals’ signal-to-noise ratio (SNR) is improved and the axial resolution of the LMA is increased to 20 mm. At the same time, the cross-sectional area loss can be quantitatively evaluated by the magnetic flux peak-to-peak value. The difference between the maximum and minimum values of the derivative of the magnetic flux signal can be used to evaluate the defect length.

Magnetostrictive guided waves are widely used in nondestructive testing and structural health monitoring of pipes to ensure their integrity. These guided waves are mechanical waves, and if the natural frequencies of the pipe are used as excitation frequencies, the mechanical vibration amplitude can be enhanced, which will then improve the amplitude of the guided waves. Comparison of the various methods to determine the natural frequencies of pipes shows that the white noise signals remain relatively smooth in both time and frequency domains. White noise has a wide bandwidth and uniform energy distribution. It does not require high energy within a short time period, so it is easy to generate. In this article, white noise is used to determine the natural frequencies of pipes. Comparison of the white noise spectra produced by analog and digital circuits shows that the energy spectrum of white noise produced by the analog circuit is high and uniform, so the analog circuit is used as the white noise source and this noise is loaded onto a magnetostrictive sensor. The detected signal spectrum is then analyzed and the frequencies with high power density spectra are determined to be the natural frequencies. The natural frequencies of the pipeline detected using white noise are compared with the results of modal analysis. Simulation results and experimental results demonstrate that the use of white noise allows the natural frequencies of pipes to be determined quickly and accurately. These natural frequencies can be used in magnetostrictive guided-wave nondestructive testing.

Hierarchical arrays of ZnO/Si nanowires were prepared through very convenient two-step solution method on silicon substrates. The tree-like nanowire structures showed high crystal quality, where well aligned Si nanowires were grown vertical to the substrate surface, whereas uniform assembly of branched ZnO nanowires was grown normal to the Si nanowires (backbones). Raman analysis indicated that among all the specimens having identical chemical compositions and dimensions but different forms (thin films or nanowires), Ag-decorated hierarchical arrays of ZnO/Si nanowires possessed the highest intensity peak in surface enhanced Raman scattering spectra. Such arrays demonstrated exceptional ability of detecting Rhodamine 6 G, limiting to a value as low as 1×10−8 mol/L and an enhancement factor up to 1.5 × 104. Both, experimental designing and band structure analysis indicated that electromagnetic effect of the localized surface plasmon resonance of Ag nanoparticles caused eight times enhancement, whereas chemical effect of hierarchical arrays of ZnO/Si nanowires played a more critical role in the high Raman sensitivity. Our results would be helpful to better understand the enhancement mechanisms and meanwhile, could be extended for further potential applications of hierarchical semiconducting nanowires.

The diameter of fine steel wire rope (FSWR) is generally a few millimeters. Its magnetic flux leakage (MFL) signal is weak, and the number of magnetic sensors installed for defect detection is limited because of the small diameter. In FSWR production workshops, different kinds of machinery work together, deteriorating the power quality and making the spatial electromagnetic environment complex; the weak MFL is thus interfered with further. It is difficult to carry out online nondestructive testing (NDT) of FSWR in the process of manufacturing. In this paper we present a novel MFL method for FSWR NDT in a strong electromagnetic interference environment. We use a three-dimensional finite element method (FEM) to analyze the MFL signals. A simplified magnetic circuit is presented to excite the FSWR; the circuit comprises two half-sized radial magnetizing ring NdFeB magnets, and because there is no need for a magnetic yoke, the device is simple and light. A single Hall sensor is used to measure the flux leakage field. A stable performance power system is designed for the NDT power supply, which is not only resistant to voltage sags, but also has very low output noise. To enhance the signal-to-noise ratio (SNR) of the MFL defects signal, a signal conditioning and processing circuit are designed to enhance the detectability of signals in MFL data. The novel and small FSWR NDT system realizes on-line testing in an environment of strong electromagnetic interference, and for the experiment with a 1.5-mm-diameter wire rope twisted by 19 wires, the minimum damage of a pit on half of a wire can be identified.

Inductive coil is used as the nondestructive testing sensor of a wire rope or a pipe, because of its low cost and high durability. However, the winding structure is complex and difficult to design during the field test. Hundreds or even thousands of turns are needed to improve the signal to noise ratio (SNR) and the data processing is cumbersome. In this paper, based on the theoretical analysis and 3D transient magnetic field simulation, a kind of iron core is presented as coil winding skeleton for the wire rope nondestructive testing. Additional iron core plays a role of magnetism concentration, where the magnetic flux leakage (MFL) path is changed and the MFL of the defect is converged to the core. Therefore, the SNR of the coil which is wound on the iron core is improved, and the coil winding skeleton is simplified with the iron core structure optimization. Meanwhile, the influence of the coil cross-section area on the test result analysis is eliminated, and the influence of the lift-off distance between coil and wire rope on the detection result is also reduced. Finally, it is proved by experiment that the SNR of coil with the iron core proposed in this paper is increased almost six times, which makes it easier for defect analysis.

Enhancing the dopability of semiconductors via strain engineering is critical to improving their functionalities, which is, however, largely hindered by the lack of basic rules. In this study, for the first time, we develop a universal theory to understand the total energy changes of point defects (or dopants) with different charge states under strains, which can exhibit either parabolic or superlinear behaviors, determined by the size of defect-induced local volume change (Δ V). In general, Δ V increases (decreases) when an electron is added (removed) to (from) the defect site. Consequently, in terms of this universal theory, three basic rules can be obtained to further understand or predict the diverse strain-dependent doping behaviors, i.e., defect formation energies, charge-state transition levels, and Fermi pinning levels, in semiconductors. These three basic rules could be generally applied to improve the doping performance or overcome the doping bottlenecks in various semiconductors.

Silicon carbide (SiC) has been considered one of the most important wide bandgap semiconductors for both scientific interest and technological applications. The existence of stacking faults induced inclusions, originated from the “wrong” stacking sequences of Si–C bilayers, is a general feature in SiC. Until now, however, a systematical understanding of the role of cubic inclusions (CIs) in the electronic and doping properties of hexagonal SiC is still lacking, which may prevent further improvement of its electronic performance. In this article, using advanced first-principles calculations, we have systematically studied the stability, electronic structures, and doping properties of hexagonal SiC with CIs. First, we find that the CIs in SiC have rather low formation energies but high kinetic stability. Second, we find that the electronic structures of SiC can be dramatically tuned by the ratio of CIs in SiC. Third, we demonstrate that the CI-induced band offset and the dipole-discontinuity-induced dipole field in the system can give rise to different ground-state doping sites for dopants at their different charge-states, which can consequently result in novel doping-site-dependent charge-state transition levels (CTLs). Meanwhile, the intrinsic dipole field can dramatically enhance the structural relaxation effects during the ionization of the dopants, which can push the CTLs deeper inside the bandgap compared to the case without CIs. Our findings suggest that CIs could play unusual roles in determining the overall electronic and doping properties of SiC and other similar semiconductors.

The traditional electromagnetic nondestructive testing probe structure includes magnets and yokes, and forms an excitation circuit with the wire rope. The wire rope is excited to a near-saturation state. The magnetic sensor is used for qualitative or quantitative detection of leakage flux from defects. The yoke is essential in the traditional excitation circuit. However, the use of a yoke in a detection probe of such an excitation mechanism has a large volume and is heavy. Through simulation, we improved the magnetization direction and installation position of the permanent magnets. Without a yoke, the permanent magnets were placed in the direction of co-extrusion. The wire rope was excited to near saturation in the permanent-magnet part. However, there was no excitation in the center of the two permanent magnets. The magnetic sensor was placed in the center of two permanent magnets to pick up the magnetic-flux-leakage signal for nondestructive testing of the steel wire rope. This method simplifies the permanent-magnet magnetization. The excitation probe with the yoke removed was also reduced in volume and weight. Through experimental testing, it was proven that the proposed shoving-magnetic-field structure and the traditional detection structure have the same detection effect.

The traction technology used for elevators in the current market has gradually changed from wire rope-type to steel strip technology. The traditional nondestructive testing of elevator wire ropes mainly involves manual observation. The steel strip is composed of both rubber and multiple wire ropes. Therefore, manual observation can only detect wear of the rubber surface or wire leakage and cannot detect internal defects in the wire ropes. The wire ropes in the steel strip are thus generally electrified to determine whether or not any of these wire ropes have broken. This approach cannot detect whether the wire ropes contain small defects. In this paper, different modes are designed for magnetostrictive guided wave sensors according to the structural characteristics of elevator steel strips. The different sensor modes are determined by comparing the detection effects of the various sensors. Finally, the magnetostrictive guided wave sensors are used to detect defects in the steel strip. The experiments show that the sensor designed in this paper can detect defects within the steel strip effectively.

The detection of internal and external defects in steel wire rope is a very important task. Current nondestructive testing methods cannot distinguish between internal and surface defects, and cannot determine the quantitative characteristics of internal defects. This paper first analyzes the advantages and disadvantages of induction coil magnetic flux detection and Hall sensor-based magnetic flux leakage detection. The problem of simultaneous detection using these two methods is then solved, and a new quantitative detection method is proposed for internal and surface defects in wire rope. Finally, a calculation method that uses a two-step training algorithm to establish two sets of neural networks is proposed. Results from simulations and experiments verify that the proposed method can accurately distinguish between internal and surface defects in wire rope, and can also quantitatively detect the width, cross-sectional loss rate, and depth of the defects.

As a wide bandgap semiconductor, SiC holds great importance for high temperature and high power devices. It is known that the intrinsic defects play key roles in determining the overall electronic properties of semiconductors; however, a comprehensive understanding of the intrinsic defect properties in the prototype 4H-SiC is still lacking. In this study, we have systematically investigated the electronic properties and kinetic behaviors of intrinsic point defects and defect complexes in 4H-SiC using advanced hybrid functional calculations. Our results show that all the point defects in 4H-SiC have relatively high formation energies, i.e., low defect concentrations even at high growth temperatures. Interestingly, it is found that the migration barriers are very high for vacancies (>3 eV) but relatively low for interstitial defects (∼1 eV) in SiC. Meanwhile, the diffusion energy barriers of defects strongly depend on their charge states due to the charge-state-dependent local environments. Furthermore, we find that VSi in SiC, a key defect for quantum spin manipulation, is unstable compared to the spin-unpolarized VC–CSi complex in terms of the total energy (under p-type conditions). Fortunately, the transformation barrier from VSi to VC–CSi is as high as 4 eV, which indicates that VSi could be stable at room (or not very high) temperature.

Devices used for nondestructive testing of wire rope often include a guide wheel, which is connected to an encoder to measure the running distance of the wire rope and to provide information about defect positions. However, in use, problems with the guide wheel such as contact jittering, slipping, idling, and bouncing cause encoder pulse loss, which affects the location measurements and quantitative analysis of the defects. Also, the wire rope running at high speed is a safety problem. However, these issues can be avoided by using the unique winding of the wire rope to provide a strand wave signal. Using wave signal processing, the distance traveled by the wire rope can be measured. Then, a phase-locked loop locks and multiplies the frequency of the strand wave signal. The multiple-frequency signal is used as a trigger signal for equal distance sampling of the wire rope. This method not only replaces the use of guide wheels and encoders when the wire rope is running at uniform velocity, but also improves the precision of the positioning and quantitative analysis of defects.

ZnO/Si nanowire arrays with hierarchical architecture were synthesized by solution method with ZnO seed layer grown by atomic layer deposition and magnetron sputtering, respectively. The photocatalytic activity of the as-grown tree-like arrays was evaluated by the degradation of methylene blue under ultraviolet light at ambient temperature. The comparison of morphology, crystal structure, optical properties, and photocatalysis efficiency of the two samples in different seeding processes was conducted. It was found that the ZnO/Si nanowire arrays presented a larger surface area with better crystalline and more uniform ZnO branches on the whole sidewall of Si backbones for the seed layer by atomic layer deposition, which gained a strong light absorption as high as 98% in the ultraviolet and visible range. The samples were proven to have a potential use in photocatalyst, but suffered from photodissolution and memory effect. The mechanism of the photocatalysis was analyzed, and the stability and recycling ability were also evaluated and enhanced. Electronic supplementary material The online version of this article (doi:10.1186/s11671-016-1803-0) contains supplementary material, which is available to authorized users.