Spontaneous translation symmetry breakdown for quantum lattice systems

We study the set of equilibrium states for quantum lattice states in the presence of a translation symmetry of the model. We derive a characterization of the spontaneous breaking of this symmetry, i.e., the decomposition of an invariant equilibrium state into a mixture of noninvariant equilibrium states, in terms of the separability in mean energy of these states for a class of perturbed dynamics.     

具有部分超结的新型SiC SBD特性分析

提出了一种具有部分超结（super junction, SJ）结构的新型SiC肖特基二极管,命名为SiC Semi-SJ-SBD结构,通过将常规SBD耐压区分为常规耐压区和超结耐压区来减小导通电阻,改善正向特性.利用二维器件模拟软件MEDICI仿真分析,研究了不同超结深度和厚度时击穿电压(V_B)和比导通电阻(R_on-sp),与常规结构的SBD比较得出,半超结结构可以明显改善SiC肖特基二极管特性,并得到优化的设计方案,选择超结宽度2< 关键词： SiC肖特基二极管 super junction 导通电阻 击穿电压     

针板型电晕稳定开关的电晕稳定性

设计了一款可用于触发和自触发的针板型电晕稳定开关,其中针电极直径为2 mm,主间隙距离为10 mm,触发间隙为5 mm。通过静电场的模拟得知其场强的不均匀系数大于7,并且通过大量实验数据得出:开关起晕电压和击穿电压分别为6.8 kV和19.3 kV,由此得知电晕稳定开关的电晕稳定因子为0.55,这说明开关具有较好的电晕稳定性。     

多脉冲加载下材料的绝缘特性

利用多脉冲实验平台分别对尼龙与交联聚苯乙烯两种绝缘材料在单脉冲与三脉冲两种不同加载条件下的绝缘特性差异进行初步研究,得到了两种绝缘材料在不同加载条件下沿面闪络场强的统计平均值,结合实验现象对所得实验结果做出了初步分析。通过进行单脉冲与三脉冲加载条件下材料沿面闪络场强的对比实验,为新型绝缘器件设计中相关参数的确定提供了实验依据。     

高超声速飞行器高温流场对激光武器毁伤效应的影响

以美国ABL系统激光武器为例,分析了高超声速飞行器高温流场气体影响激光武器毁伤效应的一些主要因素,包括气体击穿、等离子体屏蔽效应、烧蚀产物颗粒的影响。结果表明:通常情况下,流场电子数密度小于1017cm-3,流场本身等离子体特性不会引起对激光的等离子体屏蔽效应;只有在0.5 km射程以内和宽脉冲激光引起的高压流场(约10 MPa以上)气体击穿,才会导致明显的等离子体屏蔽效应,但在实际战场条件下这种情况一般不会发生;对采用烧蚀手段进行防热的飞行器而言,飞行高度大于10 km,并且基于自由来流流量的无量纲化烧蚀流量小于10-2左右时,烧蚀产物颗粒不会引起激光的衰减。     

溶液中金属元素的激光诱导击穿光谱

利用激光击穿光谱的方法对水溶液样品中的金属元素进行定性和定量分析。分别采用竖直喷流(口径0.5 mm)和静止液面两种样品采样模式,针对不同质量浓度的Cd,Fe,Al和Pb元素进行了检测分析并得到了其定标曲线(线性拟合相关度基本在0.99以上),初步确定了4种元素在喷流模式下的检测限为0.206 5(Cd),0.147 6(Fe),0.061 9(Al)和0.200 9(Pb)g/L;静止液面模式下的检测限为0.050 1(Cd),0.0239(Fe),0.014 8(Al)和0.006 9(Pb)g/L。实验所得的结果为检测工业废水中金属元素的含量提供了依据。     

RECENT DEVELOPMENTS IN INSTRUMENTATION FOR LASER INDUCED BREAKDOWN SPECTROSCOPY

ABSTRACT

This review describes, in detail, the most recent developments in instrumentation for laser induced breakdown spectroscopy (LIBS). The paper focuses on various laser systems, including excimer, CO₂, and Nd: YAG and their performance in LIBS. The coupling of fiber-optics to LIBS and development of portable LIBS systems and their performance is presented. New approaches such as dual pulse operation, multi-fiber, resonant ablation, and combination with laser induced fluorescence are further described. Finally the use of the Echelle spectrometer in which it has been combined with various charge coupled devices.     

Spectroscopy of Laser Plumes for Atto‐Mole and ng/g Elemental Analysis

Abstract

Two all‐optical analytical techniques are reviewed. Both are capable of highly sensitive multi‐element analysis. One is by means of resonance‐enhanced plasma spectroscopy. It minimizes the continuum background associated with laser‐induced plasmas. Relative to laser‐induced breakdown spectroscopy, the signal‐to‐noise ratio is improved by orders of magnitude, thus allowing the quantitation of sodium and potassium at the single blood cell level. The other technique utilizes laser‐excited atomic fluorescence. It has been traditionally handicapped by its one wavelength–one transition specificity. We showed, however, that numerous elements could be induced to fluoresce at a single excitation wavelength of 193 nm provided that the analytes were imbedded in dense plumes, such as those produced by pulsed laser ablation. This method eliminates the continuum plasma background and sub‐ppb sensitivity was demonstrated in the analysis of aqueous lead colloids.     

Pre- and post-breakdown electrical studies in ultrathin Al2O3 films by conductive atomic force microscopy

The loss of local dielectric integrity in ultrathin Al₂O₃ films grown by atomic layer deposition is investigated using conducting atomic force microscopy. I–V spectra acquired at different regions of the samples by constant and ramping voltage stress are analyzed for their pre- and post-breakdown signatures. Based on these observations, the thickness dependent dielectric reliability and failure mechanism are discussed. Our results show that remarkable enhancement in breakdown electric field as high as 130 MV/cm is observed for ultrathin films of thickness less than 1 nm.     

A low specific on-resistance SOI MOSFET with dual gates and a recessed drain

A low specific on-resistance(Ron,sp) integrable silicon-on-insulator(SOI) metal-oxide semiconductor field-effect transistor(MOSFET) is proposed and investigated by simulation.The MOSFET features a recessed drain as well as dual gates,which consist of a planar gate and a trench gate extended to the buried oxide layer(BOX)(DGRD MOSFET).First,the dual gates form dual conduction channels,and the extended trench gate also acts as a field plate to improve the electric field distribution.Second,the combination of the trench gate and the recessed drain widens the vertical conduction area and shortens the current path.Third,the P-type top layer not only enhances the drift doping concentration but also modulates the surface electric field distributions.All of these sharply reduce Ron,sp and maintain a high breakdown voltage(BV).The BV of 233 V and Ron,sp of 4.151 mΩ·cm2(VGS = 15 V) are obtained for the DGRD MOSFET with 15-μm half-cell pitch.Compared with the trench gate SOI MOSFET and the conventional MOSFET,Ron,sp of the DGRD MOSFET decreases by 36% and 33% with the same BV,respectively.The trench gate extended to the BOX synchronously acts as a dielectric isolation trench,simplifying the fabrication processes.