Using photoelectron emission microscopy with hard-X-rays

We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 μm² for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray. This approach again leads to the unprecedented 0.3 μm lateral resolution, particularly critical for the use of coherence-based phase contrast techniques in real time X-ray radiology.     

铁磁薄膜中圆偏振光感应的瞬态磁光Kerr峰的物理起源

使用飞秒时间分辨抽运-探测磁光Kerr光谱技术,实验研究了圆偏振光抽运面内磁化FePt和垂直磁化GdFeCo薄膜的磁化演化动力学,发现在时间延迟零点处均出现瞬态Kerr峰.分析了此Kerr峰的起源,指出此瞬态Kerr峰与铁磁性无关,可能起源于自由电子的顺磁磁化,而顺磁磁化的外磁场来自圆偏振抽运光的逆Faraday效应.基于顺磁磁化模型的计算结果支持此观点.基于此观点,逆Faraday效应感应的磁场脉冲宽度应该与激光脉冲宽度一致.     

Effects of SiNx on two-dimensional electron gas and current collapse of A1GaN/GaN high electron mobility transistors

SiNx is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiNx films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.     

基于X射线衍射的GaN薄膜厚度的精确测量

结合Williamson-Hall plot方法和线型分析方法的优点,提出了一种有效分离有限晶粒尺寸和非均匀应力等X射线衍射展宽效应的方法,可以用于GaN外延层厚度等参数的快速精确测量.用该方法对一系列在蓝宝石衬底上生长的厚度在0.7—4.2μm的GaN外延膜进行了测量,并与椭圆偏振光谱法测量结果进行了比较,结果表明其差别<4%,反应了这种方法的准确性. 关键词： GaN薄膜 厚度测量 X射线衍射     

非故意掺杂GaN薄膜方块电阻与载气中N2比例关系研究

利用金属有机气相外延方法研究了非故意掺杂GaN薄膜的方块电阻与高温GaN体材料生长时载气中N₂比例的关系.研究发现,随着载气中N₂比例的增加,GaN薄膜方块电阻急剧增加.当载气中N₂比例为50%时,GaN薄膜方块电阻达1.1×10⁸Ω/□,且GaN表面平整,均方根粗糙度为0.233nm.二次离子质谱分析发现,载气中N₂比例不同的样品中碳、氧杂质含量无明显差别.随着载气中N₂比 关键词： 半绝缘GaN薄膜 载气 金属有机气相外延 位错     

On the resolution of 5770-90 Å doublet in Hg-spectrum holographic reconstruction

An exact analysis is given to explain the experimental results of Su et al. The resolving power is shown to vary from extremely good to worse than that based on the Rayleigh criterion, depending upon the location of the illuminated area on the hologram during reconstruction.     

Application of magnetic nanoparticles for the extraction of radium-226 from water samples

Bare (unmodified) and crown ether (CE)-modified Fe₃O₄ magnetic nanoparticles (MNPs) were investigated for the rapid extraction of ²²⁶Ra from water samples. It involved synthesizing the MNPs, introducing them into the sample solutions, ultrasonicating and agitating the suspension, magnetically separating the nanoparticles from solution, and measuring the ²²⁶Ra content in the supernatant. Experimental parameters such as salt choice, salt concentration and pH were optimized to achieve maximum extraction of ²²⁶Ra onto the MNPs. ²²⁶Ra content was determined using a Hidex 300SL liquid scintillation counter with α/β separation capability, or a gamma spectrometric detection system. The bare Fe₃O₄ nanoparticles showed significant pH dependence for the extraction of ²²⁶Ra from an aqueous solution over a pH range of 2–10. They gave an extraction of 95 ± 1 and 98 ± 1 % at pH 9 in 0.1 M NaCl and 0.1 M NaClO₄, respectively, whereas an extraction of 8–24 % was obtained, over the pH ranges from 2 to 5. The CE-modified MNPs yielded extraction efficiencies as high as 99 ± 1 % in the presence of 0.01 M picric acid at pH 4. This study demonstrates that the surface functionalization of Fe₃O₄ MNPs with suitable ligand modification can offer a selective mode of extraction for ²²⁶Ra in the presence of its daughter progenies.     

A Simple Route to Produce Highly Efficient Porous Carbons Recycled from Tea Waste for High-Performance Symmetric Supercapacitor Electrodes

High-performance porous carbons derived from tea waste were prepared by hydrothermal treatment, combined together with KOH activation. The heat-treatment-processed materials possess an abundant hierarchical structure, with a large specific surface of 2235 m² g⁻¹ and wetting-complemental hydrophilicity for electrolytes. In a two-electrode system, the porous carbon electrodes’ built-in supercapacitor exhibited a high specific capacitance of 256 F g⁻¹ at 0.05 A g⁻¹, an excellent capacitance retention of 95.4% after 10,000 cycles, and a low leakage current of 0.014 mA. In our work, the collective results present that the precursor crafted from the tea waste can be a promising strategy to prepare valuable electrodes for high-performance supercapacitors, which offers a practical strategy to recycle biowastes into manufactured materials in energy storage applications.     

Creation of multiquantum coherences from equilibrium spin systems

Recently it has been suggested that zero quantum coherence in scalar coupled spin systems at thermal equilibrium can be created by a single non-selective pulse. In this note, it is shown that the proposed effect will be masked as a consequence of the failure of the conventional high-temperature approximation normally applied to the equilibrium spin density operator. For exacting experiments, its appears that the approximation (eq) ≈ 1-H /kT may not suffice.