New Type of Thermoelectric CdSSe Nanowire Chip.

Facing the increasingly serious problem of environmental pollution and energy waste, the thermoelectric generator has been attracting more and more attention owing to its advantages including low cost, no pollution, and good stability. The family of thermoelectric material is constantly extended with enhanced performance. Note that nanostructuring can enhance thermoelectric performance. However, the most recent excellent material with effective thermoelectric transformation reported from bulk materials has definite benefits to the practical application compared to nanomaterials. In this work, a nanostructure integrated macroscale thermoelectric chip, that is an alloyed band gap gradient macroscale chip (1.0 cm × 2.0 cm) composed of CdSSe nanowires, has been proven as an excellent thermoelectric generator for the first time. A high Seebeck coefficient of -152.4 µV/K and the average output voltage of 10.8 mV are obtained after optimizing the electrode patterns and distance between electrodes. More interestingly, upon illumination by white light from a xenon lamp, a photo-thermoelectric output voltage is greatly elevated to 45 mV due to the high concentration of photogenerated carriers. The CdSSe thermoelectric chip also shows good repeatability and high stability with a relative error of <6%. No study on the thermoelectric performance of such an alloyed band gap gradient macroscale chip is mentioned before. The results illustrate a bright avenue to realize a type of light-modulated macroscale thermoelectric chips by nanostructure, allowing such kinds of CdSSe chips to be used to generate electric energy in the near future.

On-chip programmable optical switch based on CdS multibranched nanowire arrays.

Micro/nano optoelectronic devices are widely studied as basic building blocks for on-chip integrated microsystem and multichannel logic units with excellent optoelectronic properties that are especially important part for interconnection route construction. Here, based on anisotropic waveguides, an optical switch with an on/off ratio of 2.14 is built up in a 2D CdS branched nanowire array. Because the branches are obliquely distributed at the same side of the trunk in a highly ordered form, the guided photoluminescence (PL) intensity from the trunk into the branch tightly relates to its angle. Based on the different intensity of the guided PL emitted from the end of each branch, the position of the incident spot in the backbone area can be identified accurately, making a feasible construction of an on-chip position-sensitive detector to realize an all-optical information process.

Comparative Studies on Two-Dimensional (2D) Rectangular and Hexagonal Molybdenum Dioxide Nanosheets with Different Thickness.

Molybdenum dioxide (MoO2) a kind of semi-metal material shows many unique properties, such as high melting point, good thermal stability, large surface area-to-volume ratio, high-density surface unsaturated atoms, and excellent conductivity. There is a strong connection between structural type and optoelectronic properties of 2D nanosheet. Herein, the rectangular and hexagonal types of thin and thick MoO2 2D nanosheets were successfully prepared from MoO3 powder using two-zone chemical vapor deposition (CVD) with changing the experimental parameters, and these fabricated nanosheets displayed different colors under bright-field microscope, possess margins and smooth surface. The thickness of the blue hexagonal and rectangular MoO2 nanosheets are ~ 25 nm and ~ 30 nm, respectively, while typical thickness of orange-colored nanosheet is around ~ 100 nm. Comparative analysis and investigations were carried out, and mix-crystal phases were indentified in thick MoO2 as main matrix through Raman spectroscopy. For the first time, the emission bands obtained in thick MoO2 nanosheets via a Cathodoluminescence (CL) system exhibiting special properties of semi-metallic and semi-conductors; however, no CL emission detected in case of thin nanosheets. The electrical properties of thin MoO2 nanosheets with different morphologies were compared, and both of them demonstrated varying metallic properties. The resistance of thin rectangular nanosheet was ~ 25 Ω at ± 0.05 V while 64 Ω at ± 0.05 V was reported for hexagonal nanosheet, and observed lesser resistance by rectangular nanosheet than hexagonal nanosheet.

Lithium ion detection in liquid with low detection limit by laser-induced breakdown spectroscopy.

Lithium (Li), as the lightest metal and the most important powerful material in battery fabrication, is widely used in many fields. The fast detection of Li is necessary for industrial application. The slow-speed detection methods, including atomic absorption spectroscopy and inductively coupled plasma mass spectroscopy with high accuracy and low limit of detection, are hard to utilize in in situ industrial control due to complex prepreparation of samples. Here, through the analysis of the typical spectrum line at Li I 670.79 nm, Li ions in water were detected quantitatively in 1 min, including sample preparation by laser-induced breakdown spectroscopy (LIBS) with filter paper as the adsorption substrate. The calibration curve by polynomial function fitting is used to predict the Li+ concentration. The limit of detection (LOD) as low as 18.4 ppb is obtained, which is much lower than the results ever reported by using filter paper. The related factor R2 reaches 99%, and the prediction error is lower than 2%, proving the fast and online monitor for Li+ by LIBS is feasible. Furthermore, by comparison with the results with filter paper enrichment, the Li+ detection from water directly shows higher LOD to 10.5 ppm. Moreover, the plasma images, by gate-controlled intensified charge-coupled device, illustrate a different morphology and evolution between that on water surface and filter paper surface through visual observation. This study provides experimental and theoretical experience in a fast way for the quantitative detection of the lightest metal ion (Li+) in liquid.

Accuracy enhancement of laser induced breakdown spectroscopy by safely low-power discharge.

Improvement in detection accuracy is an important and hot topic for laser induced breakdown spectroscopy (LIBS). Discharged-pulse assisted (DPA) plasma has been investigated as an effective way to enhance analytical capabilities and accuracy of LIBS. Most of reported DPA experiments have been performed using high voltage and power to comprehend spectrum enhancement. For safety concerns and maneuverability of LIBS equipment; low power and small current discharge are viable for industrial application. In this paper, the enhanced spectra with many extra peaks and higher line intensities were also detected, realized by a low-power discharge assisted LIBS (Max. 2.8 kV and ~1 mA), which are much lower than reported in literature ~MW discharge. The number of atomic peaks of the sample increases, on the other hand, and gradual peaks become stronger with the increase of discharged HV from 1 kV to 1.5 kV, 1.75 kV, 2 kV, 2.5 kV and 2.8 kV. The discharge current increases from 0.2 mA to 1.5 mA, which is almost threshold discharge voltage. After processing, the original spectra, including the peak shift and peak correction by statistics and physics, resulted in achievement of better line stability in terms of relative standard deviation (RSD) of ash, carbon, and volatile coal samples with root mean square error prediction (RMSEP) of 0.4864, 0.3682, 0.3374 and the linear regression coefficient R2 = 0.99, 0.99,0.98, respectively. The result proposes a promising method to improve detection accuracy of LIBS with simple setup, high safety and low-cost.

Accuracy enhancement of laser induced breakdown spectra using permittivity and size optimized plasma confinement rings.

The inevitable problems in laser induced breakdown spectroscopy are matrix effect and statistical fluctuation of the spectral signal, which can be partly avoided by utilizing a proper confined unit. The dependences of spectral signal enhancement on relative permittivity were studied by varying materials to confine the plasma, which include polytetrafluoroethylene(PTFE), nylon/dacron, silicagel, and nitrile-butadiene rubber (NBR) with the relative permittivity 2.2, ~3.3, 3.6, 8~13, 15~22. We found that higher relative permittivity rings induce stronger enhancement ability, which restricts the energy dissipation of plasma better and due to the reflected electromagnetic wave from the wall of different materials, the electromagnetic field of plasma can be well confined and makes the distribution of plasma more orderly. The spectral intensities of the characteristic lines Si I 243.5 nm and Si I 263.1 nm increased approximately 2 times with relative permittivity values from 2.2 to ~20. The size dependent enhancement of PTFE was further checked and the maximum gain was realized by using a confinement ring with a diameter size of 5 mm and a height of 3 mm (D5mmH3mm), and the rings with D2mmH1mm and D3mmH2mm also show higher enhancement factor. In view of peak shift, peak lost and accidental peaks in the obtained spectra were properly treated in data progressing; the spectral fluctuation decreased drastically for various materials with different relative permittivities as confined units, which means the core of plasma is stabilized, attributing to the confinement effect. Furthermore, the quantitative analysis in coal shows wonderful results-the prediction fitting coefficient R2 reaches 0.98 for ash and 0.99 for both volatile and carbon.