Potential use of surface-assisted LIBS for determination of strontium in wines

Solid substrate assisted enhanced laser induced breakdown spectroscopy for metal element analysis in aqueous solution

Due to plasma quenching caused by the dense water medium, laser-induced breakdown spectroscopy (LIBS) faces challenges such as strong continuous background radiation and weak and broadened characteristic spectral lines when directly detecting metal elements in liquids. In this work, we introduced a simple approach to improve underwater LIBS signals with a solid substrate-assisted method, which requires no sample pre-treatment and simple operation and thus has potential for in situ marine applications. In this method, four submerged solid substrates (Zn, Cu, Ni, and Si) were employed to investigate the breakdown characteristics of underwater LIBS and the mechanism of spectral enhancement by using a CaCl2 solution. The results demonstrated a significant improvement in the detection sensitivity of Ca with these substrates even at a short laser pulse with a relatively low laser energy (10 mJ). Among them, the semiconductor Si substrate exhibited the best enhancement effect, with an enhancement factor of over 75 for the Ca ionic lines at 393.4 nm and 396.8 nm and an enhancement factor of 29 for the Ca atomic line at 422.7 nm, respectively. This is mainly because the presence of substrate decreases the breakdown threshold of the liquid sample, and a higher plasma excitation temperature and electron density are obtained, which, in turn, leads to higher signal intensity. Furthermore, significant plasma emission enhancements for a wide range of elements are also achieved from seawater. These findings can contribute to the development of compact underwater in situ LIBS sensors with low power consumption, while ensuring high detection sensitivity.

Heavy Metals Detection in Zeolites Using the LIBS Method

In this study, a possibility of laser-induced breakdown spectroscopy (LIBS) for the analysis of zeolites containing copper, chromium, cobalt, cadmium, and lead in the concentration range of 0.05–0.5 wt.% is discussed. For the LIBS analysis, microporous ammonium form of Y zeolite with the silicon to aluminum molar ratio of 2.49 was selected. Zeolites, in the form of pressed pellets, were prepared by volume impregnation from the water solution using Co(CH3COO)2.4H2O, CuSO4.5H20, K2Cr2O7, PbNO3, and CdCl2 to form a sample with different amounts of heavy metals—Co, Cu, Cr, Pb, and Cd. Several spectral lines of the mentioned elements were selected to be fitted to obtain integral line intensity. To prevent the influence of the self-absorption effect, non-resonant spectral lines were selected for the calibration curves construction in most cases. The calibration curves of all elements are observed to be linear with high regression coefficients. On the other hand, the limits of detection (LOD) were calculated according to the 3σ/S formula using the most intensive spectral lines of individual elements, which are 14.4 ppm for copper, 18.5 ppm for cobalt, 16.4 ppm for chromium, 190.7 ppm for cadmium, and 62.6 ppm for lead.

Tailored Langmuir-Schaefer Deposition of Few-Layer MoS2 Nanosheet Films for Electronic Applications

Few-layer MoS₂ films stay at the forefront of current research of two-dimensional materials. At present, continuous MoS₂ films are prepared by chemical vapor deposition (CVD) techniques. Herein, we present a cost-effective fabrication of the large-area spatially uniform films of few-layer MoS₂ flakes using a modified Langmuir-Schaefer technique. The compression of the liquid-phase exfoliated MoS₂ flakes on the water subphase was used to form a continuous layer, which was subsequently transferred onto a submerged substrate by removing the subphase. After vacuum annealing, the electrical sheet resistance dropped to a level of 10 kΩ/sq, being highly competitive with that of CVD-deposited MoS₂ nanosheet films. In addition, a consistent fabrication protocol of the large-area conductive MoS₂ films was established. The morphology and electrical properties predetermine these films to advanced detecting, sensing, and catalytic applications. A large number of experimental techniques were used to characterize the exfoliated few-layer MoS₂ flakes and to elucidate the formation of the few-layer MoS₂ Langmuir film.

Nano-finishing of the monocrystalline silicon wafer using magnetic abrasive finishing process

The monocrystalline silicon wafer is the key material for micro-electro-mechanical systems. The performance of these wafers depends on their surface and subsurface quality. This research aims to study the effect of process parameters on the reduction ratio rate in surface roughness (%ΔR˙) of monocrystalline silicon wafers during the magnetic abrasive finishing process using response surface methodology. The parameters studied are machining gap, rotational speed, abrasive size, and magnetic abrasive particle (MAP) size. Quadratic models are developed by applying Box-Behnken design. Also, experiments are carried out on the silicon wafer, and the results of surface roughness data are analyzed by using analysis of variance. The most significant factor on each experimental design response is identified. According to our findings, the maximum %ΔR˙ value and the best surface roughness of the silicon wafer achieve 3.70 and 31 nm, respectively. Furthermore, the material removal mechanism in wafers is investigated by using atomic force microscopy. Our observations show that both micro-fracture and micro-cutting mechanisms might happen, and it highly depends on polishing parameters.

Numerical-experimental study on the polishing of silicon wafers using coupled finite element-smoothed particle hydrodynamics

The quality and surface roughness of silicon wafers significantly affects the efficiency and quality of follow-up processing. Smoothed particle hydrodynamics is a robust meshless method with good self-adaptability that can be used in the simulation of the polishing process, which has high speed deformation characteristics. In this study, the coupled algorithm of finite element and surface particle hydrodynamic (SPH) has been used to simulate the surface polishing of monocrystalline silicon wafers with a magnetic abrasive finishing process. The effects of machining gap, abrasive particle size, and rotational speed on surface roughness are comprehensively analyzed. In addition, several experiments are carried out on a 3-in.-diameter circular silicon wafer and the results are compared with the simulation results. Our findings show that the decreases in abrasive particle size and also increases in rotational speed significantly deteriorate the surface roughness of the silicon wafer. The obtained results revealed that the machining gap has an optimum condition in which the minimum surface roughness is achieved. According to our results, the best surface roughness value achieved is 63 nm.

An elevated concentration of MoS2 lowers the efficacy of liquid-phase exfoliation and triggers the production of MoOx nanoparticles

The oxidation of MoS₂ with a simultaneous decrease of MoS₂ content.