Spectroscopy of low and intermediate Z elements at extreme conditions: in situ studies of Earth materials at pressure and temperature via X-ray Raman scattering

ABSTRACT

X-ray Raman scattering spectroscopy is an emerging method in the study of low and intermediate Z elements' core-electron excitations at extreme conditions in order to reveal information on local structure and electronic state of matter in situ. We discuss the capabilities of this method to address questions in Earth materials' science and demonstrate its sensitivity to detect changes in the oxidation state, electronic structure, coordination, and spin state. Examples are presented for the study of the oxygen K-, silicon L- and iron M-edges. We assess the application of both temperature and pressure in such investigations exploiting diamond anvil cells in combination with resistive or laser heating which is required to achieve realistic conditions of the Earth's crust, mantle, and core.     

Theoretical design of diamondlike superhard structures at high pressure

Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B–C–N–O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B–C–N–O system,besides the classical example of cubic boron nitride.     

Ultra-low specific on-resistance high-voltage vertical double diffusion metal–oxide–semiconductor field-effect transistor with continuous electron accumulation layer

A new ultra-low specific on-resistance(Ron,sp) vertical double diffusion metal–oxide–semiconductor field-effect transistor(VDMOS) with continuous electron accumulation(CEA) layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration(Nn). In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp.Especially, the two PN junctions within the trench gate support a high gate–drain voltage in the off-state and on-state, respectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS(CSJ-VDMOS)at the same high breakdown voltage(BV).     

基于二元光学设计的高能激光窗口的初步探讨

对非均匀近场强度分布影响强激光远场聚焦效果的原因进行了分析。对高能激光窗口进行了二元光学设计。提高了光束强度分布的均匀性,改善了光束质量。介绍了二元光学设计的基本原理,采用随机并行扰动爬山法对窗口的位相分布、变换后的光束强度分布、衍射效率和光束均匀性进行了计算。计算结果表明,基于二元光学设计的激光窗口能有效地改善光束强度分布的均匀性,提高了发射光束的质量。     

Bimetallic Silver-Gold Film Waveguide Surface Plasmon Resonance Sensor

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver-gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.     

钢铁检测微型光谱仪的研制

针对国内光电直读型钢铁检测微型光谱仪研究的不足,提出基于Czerny-Turner结构的系统设计方法,讨论了优化方法及验证方法,并加工出了光谱仪。光谱仪采用三次多项式拟合标定波长,实测分辨率在436 nm~608 nm全谱段达0.225 nm、中心谱段达0.135 nm,基本满足钢铁检测要求。提出一种基于多帧判断的定性分析方法,7种待测元素检出限优于1.5%,通过建立拟合光谱数据库实现半定量分析,25种样品检测精度达2%,为钢铁牌号识别提供重要参考。     

大功率高温超导滤波器的设计与功率测试

本文在双面YBCO高温超导薄膜上设计并制备了两节大功率超导滤波器,根据滤波器功率承载能力与最大电流密度之间的关系,减小电流密度和分散电流密度的分布是提高功率承载能力的关键.本文采用增加超导谐振器尺寸、优化几何结构及改进馈线耦合方式的方法,设计了两节2 GHz频段梭型谐振器结构的滤波器.设计及测量结果显示了馈线结构及谐振器几何尺寸优化程度对超导滤波器功率承载能力有不同程度的影响,说明了在大功率超导滤波器设计中应选用无结点间隙耦合式馈线以抑制电流密度的聚集.采用优化后的谐振器结构制备的梭型两节超导滤波器经测试功率承载能力为2 W.超导滤波器的尺寸为25×12 mm LaAlO3基片,中心频率2.022 GHz,相对带宽为2.4%.同时给出了超导滤波器功率测试的结构和方法.     

改进的TESLA式高阶模衰减器的实验研究

讨论了TESLA型高阶模耦合器的改进, 对所设计的改进型TESLA式高阶模耦合器进行实验, 对理论计算与实验结果进行详细分析, 结果表明改进的高阶模耦合器理论计算和实验结果符合得较好.     

倾斜直流场下的介质板击穿统计分析

传统分析介质板次级电子倍增问题的粒子追踪算法方法存在运算耗时长、运算量大等缺点,为此采用统计方法实现了倾斜强直流场下介质击穿过程中次级电子倍增效应的数值模拟,给出了击穿过程中电子数量,电子渡越时间等关键参数的时间图像,同时研究了倾斜角、介质表面光滑度和次级电子产生率对次级电子倍增效应的影响。研究结果表明：强直流场下的次级电子倍增效应存在倾斜角的区域,倾斜角太大或者太小,都可能不会发生次级电子倍增效应,如果倾斜角位于区域内,则饱和状态时电子数目随着倾斜角度的变大而变小;选取光滑系数和次级电子产生系数越小的介质材料,抑制次级电子倍增效应的效果越好。     

High-power high-stability Q-switched green laser with intracavity frequency doubling of diode-pumped composite ceramic Nd:YAG laser

We successfully obtain high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight plano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By use of a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.