Xiangyou Li

Single-Crystalline Rutile TiO2 Hollow Spheres: Room-Temperature Synthesis, Tailored Visible-Light-Extinction, and Effective Scattering Layer for Quantum Dot-Sensitized Solar Cells

A general synthesis of inorganic single-crystalline hollow spheres has been achieved through a mechanism analogous to the Kirkendall effect, based on a simple one-step laser process performed at room temperature. Taking TiO(2) as an example, we describe the laser process by investigating the influence of experimental parameters, for example, laser wavelength, laser fluence/irradiation time, liquid medium, and concentration of starting materials, on the formation of hollow spheres. It was found that the size-tailored TiO(2) hollow spheres demonstrate tunable light scattering over a wide visible-light range. Inspired by the effect of light scattering, we introduced the TiO(2) hollow spheres scattering layer in quantum dot-sensitized solar cells and achieved a current notable 10% improvement of solar-to-electric conversion efficiency, indicating that TiO(2) hollow spheres are potential candidates in optical and optoelectronic devices.

Fabrication of Crystalline Silicon Spheres by Selective Laser Heating in Liquid Medium

Micrometer and submicrometer crystalline silicon spheres were fabricated by selective laser heating of irregular silicon particles in liquid medium. TEM, SEM, XRD, and XPS characterized the structure and morphology of the prepared silicon spheres. The results suggested that they were spherical with a single crystalline structure. In this study, the formation mechanism of the spheres is analyzed, and the process parameters are optimized to obtain high-quality silicon spheres. A theoretical deduction regarding the relationship between critical laser energy density and particle size is also discussed, by which we can predict that larger spheres can be obtained at higher laser energy densities.

Sensitivity improvement in the detection of V and Mn elements in steel using laser-induced breakdown spectroscopy with ring-magnet confinement

To improve the detection sensitivity of vanadium (V) and manganese (Mn) elements in steel using laser-induced breakdown spectroscopy (LIBS), a ring magnet was employed to spatially and magnetically confine plasmas produced from steel samples using an Nd:YAG laser. The results showed that the optical emission and signal-to-noise ratios (SNRs) for both V I 437.92 nm and Mn I 403.08 nm lines were enhanced by the ring-magnet confinement. The enhancements were found to be due to an increase in the plasma temperature and electron density as a result of both spatial and magnetic confinement. The calibration curves of V I 437.92 nm and Mn I 403.08 nm with/without confinement were established. The 3σ-limits of detection (LoDs) for V and Mn in steels were 11 and 30 ppm with the ring magnet, lower than the 18 and 41 ppm with a degaussed magnet and the 41 and 56 ppm in open air, respectively.

Quantitative analysis of phosphorus in steel using laser-induced breakdown spectroscopy in air atmosphere

The quantitative analysis of phosphorus in iron/steel in air atmosphere is considered a challenge for laser-induced breakdown spectroscopy (LIBS) due to strong interference from the matrix. In this study, interference from the iron and copper lines on the P I 214.91 nm line using different gate delays was studied. The interference on the P I 214.91 nm line arises mainly from the ionic lines of iron and copper in the steel. By choosing the gate delays carefully, the interference can be reduced. The spectral resolution and sensitivity of the spectrometer required for the detection of the P I 214.91 nm line in steel plasma were also studied. Based on the results, a Czerny–Turner spectrometer equipped with an intensified charge coupled device camera with a minimum spectral resolution of 0.03 nm is suggested for this application. Finally, the successful quantitative analysis of phosphorus in the UV-vis spectral range was carried out both in pig iron and a low alloy steel. For the pig iron, the R2 calibration factor was 0.9992, the limit-of-detection (LoD) was 12 ppm and the background equivalent concentration (BEC) was 0.11 wt%. For the low alloy steel, the R2 calibration factor was 0.995, the LoD was 9 ppm and the BEC was 0.05 wt%. Interference from copper lines on the P I 214.91 nm line was not observed. It has been shown that a simple LIBS setup can be used for the accurate quantitative analysis of phosphorus in iron/low alloy steel in open air.

Analytical-performance improvement of laser-induced breakdown spectroscopy for steel using multi-spectral-line calibration with an artificial neural network

A multi-spectral-line calibration (MSLC) approach based on an artificial neural network (ANN) was developed to improve the accuracy and precision of steel analysis using laser-induced breakdown spectroscopy (LIBS). The intensity ratios of multiple spectral lines of target and matrix elements were used to train an ANN. The resulting model was able to relate the spectra to the concentrations of target elements more accurately than the conventional internal calibration approach, which led to improvements in the accuracy and precision of the LIBS analysis. This approach was applied to LIBS analysis of steel samples to predict the Cr and Ni concentrations. Compared with a conventional internal calibration approach, the root-mean-square errors of cross-validation for Cr and Ni decreased from 0.018 and 0.067 wt% to 0.010 and 0.023 wt%, respectively, using the proposed MSLC, and the average values of the relative standard deviation for Cr and Ni decreased from 11.3 and 19.5% to 6.4 and 12.9%, respectively.

Game theory-based Cooperation of Process Planning and Scheduling

One of the significant trends in manufacturing planning is to make computer automated process planning and scheduling to work more cooperatively. To build up cooperative process planning and scheduling (CPPS), in this research, three game theory- based strategies, i.e., Pareto strategy, Nash strategy and Stackelberg strategy, have been introduced to analyze the cooperation of the two functions in a systematic way. Modern heuristic algorithms, including particle swarm optimization (PSO), simulated annealing (SA) and genetic algorithm (GA), have been developed and applied to the CPPS problem to identify targeted solutions efficiently from the vast search space caused by the complexity of the problem. Meanwhile, adaptive strategies have been developed to accommodate dynamic changes in job shops.

Determination of cobalt in low-alloy steels using laser-induced breakdown spectroscopy combined with laser-induced fluorescence

Cobalt element plays an important role for the properties of magnetism and thermology in steels. In this work, laser-induced breakdown spectroscopy combined with laser-induced fluorescence (LIBS-LIF) was studied to selectively enhance the intensities of Co lines. Two states of Co atoms were resonantly excited by a wavelength-tunable laser. LIBS-LIF with ground-state atom excitation (LIBS-LIFG) and LIBS-LIF with excited-state atom excitation (LIBS-LIFE) were compared. The results show that LIBS-LIFG has analytical performance with LoD of 0.82μg/g, R(2) of 0.982, RMSECV of 86μg/g, and RE of 9.27%, which are much better than conventional LIBS and LIBS-LIFE. This work provided LIBS-LIFG as a capable approach for determining trace Co element in the steel industry.

Direct fabrication of electric components on insulated boards by laser microcladding electronic pastes

In this paper, a novel method to fabricate the electronic components directly on insulating boards such as glass, ceramics, and organic laminated boards by laser microcladding electronic pastes was reported. With computer-aided design/computer-aided manufacturing (CAD/CAM) capability, the conductive metal lines and resistors with different patterns were fabricated successfully by this technique without mask. The experimental results demonstrated that the fabricated conductive lines and resistors have the same properties as those made by conventional thick-film methods and were bonded very well with the substrate. The minimum widths of the conductive lines on ceramic board, glass board, and printed circuit board can reach 20, 40, and 80 /spl mu/m, correspondingly. The maximum rates for laser microcladding can be beyond 50 mm/s. Some typical examples of circuit boards fabricated by this method were illustrated.

Determinations of trace boron in superalloys and steels using laser-induced breakdown spectroscopy assisted with laser-induced fluorescence.

Boron (B) is widely applied in microalloying of metals. As a typical light element, however, determination of boron in alloys with complex matrix spectra is still a challenge for laser-induced breakdown spectroscopy (LIBS) due to its weak line intensities in the UV-visible-NIR range and strong spectral interference from the matrix spectra. In this study, a wavelength-tunable laser was used to enhance the intensities of boron lines selectively. The intensities of B I 208.96 nm from boron plasmas were enhanced approximately 3 and 5.8 times while the wavelength-tunable laser was tuned to 249.68 and 249.77 nm, respectively. Utilizing the selective enhancement effect, accurate determinations of trace boron in nickel-based superalloys and steels were achieved by laser-induced breakdown spectroscopy assisted by laser-induced fluorescence (LIBS-LIF), with limits of detection (LoDs) of 0.9 and 0.5 ppm, respectively. The results demonstrated that LIBS-LIF can hopefully be used in boron determinations and has great potential for improving the ability of LIBS to determine light elements in alloys with a complex matrix.

Self-absorption reduction in laser-induced breakdown spectroscopy using laser-stimulated absorption

The self-absorption effect is one of the main bottlenecks for the laser-induced breakdown spectroscopy (LIBS) technique. In this Letter, LIBS assisted by laser-stimulated absorption (LSA-LIBS) is proposed to solve this problem. The process of LSA in self-absorption reduction is discussed and confirmed. The serious self-absorption phenomena of spectral lines (K, Mn, and Al) were not observed in LSA-LIBS. The full width at half-maximum (FWHM) of K, Mn, and Al was reduced by about 58%, 25%, and 52%, respectively. The results demonstrate the capability of this approach to self-absorption reduction in the LIBS technique.