电子器件散粒噪声测试方法研究

本文分析了超导量子干涉器(SQUID)和超导-绝缘-超导(SIS)约瑟夫森结散粒噪声测试方法的应用局限性,提出了常规器件的散粒噪声测试方案.针对常规电子器件散粒噪声特性,研究了噪声测试基本条件,并建立了低温测试系统.通过采用双层屏蔽结构和超低噪声前置放大器,实现了较好的电磁干扰屏蔽和极低的背景噪声.在10 K温度下对常规二极管散粒噪声进行了测试,通过理论和测试结果对比分析,验证了测试系统的准确和可信性. 关键词： 散粒噪声 电子器件 噪声测试     

压电振子阵列型超声喷丸强化*

为了提高超声喷丸强化加工的面积、效率及加工质量,对传统单振子超声喷丸强化技术进行了改进,提出了压电振子阵列型超声喷丸强化加工方法。分析了超声喷丸强化的机理,进行了压电振子的优化设计,分析了激振片的谐振响应,实验测试了系统样机在不同超声电源功率下弹丸撞击工件的区域分布;探究了超声电源功率、喷丸距离、弹丸直径和喷丸时间对加工样件显微硬度的影响,结果表明：以超声电源功率作为唯一变量,弹丸冲击工件表面的区域面积随超声电源功率增大而增大;7075铝合金样件的表面显微硬度及其提高率,随超声电源功率的增大、喷丸时间的增加、喷丸距离的减小及弹丸直径的增大而增大;超声电源功率为50W、喷丸时间为20min、喷丸距离为5mm、弹丸直径为1.5mm时喷丸效果最好,此时工件表面显微硬度增加量为65.1HV,表面显微硬度提高率为36.7%。压电振子阵列型超声喷丸强化技术可以有效增加喷丸冲击工件的面积,提高工件的表面显微硬度和加工效率。     

High frequency noise of epitaxial graphene grown on sapphire

Microwave noise technique is applied to study in‐plane electronic properties of epitaxial graphene grown on sapphire by chemical vapor deposition and subjected to high electric field applied in the plane. The noise spectrum is measured in the field direction at room temperature. While a 1/f^1.25‐type dependence is observed in the 200 MHz–2.5 GHz band, a shot noise contribution is resolved at 10 GHz. The shot noise is possibly associated with hole jumps across the potential barriers located in the graphene layer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonequilibrium Shot Noise Spectrum Through a Quantum Dot in the Kondo Regime:A Master Equation Approach under Self-Consistent Born Approximation

We construct a number(n)-resolved master equation(ME)approach under self-consistent Born approximation(SCBA)for noise spectrum calculation.The formulation is essentially non-Markovian and incorporates properly the interlay of the multi-tunneling processes and many-body correlations.We apply this approach to the challenging nonequilibrium Kondo system and predict a profound nonequilibrium Kondo signature in the shot noise spectrum.The proposed n-SCBA-ME scheme goes completely beyond the scope of the Born-Markovian master equation approach,in the sense of being applicable to the shot noise of transport under small bias voltage,in non-Markovian regime,and with strong Coulomb correlations as favorably demonstrated in the nonequilibrium Kondo system.     

A guide for proper utilisation of stable isotope reference materials*

Many scientific publications about stable isotope ratios suffer from flawed practices regarding calibration and normalisation of raw δ values in conjunction with prescribed δ values of reference materials. Violations of the identical treatment principle with regards to samples and standards (i.e. reference materials) and lack of adherence to SI-mandated and IUPAC-recommended nomenclature exacerbate the widespread problem of lackadaisical analytical practice and reporting. Science is supposed to strive for exactness, whereas ambiguity and jargon confound interdisciplinary communication. This contribution aims to expose typical misconceptions and avoidable errors and offers guidance toward the reproducible generation of isotope data, isotopic scale normalisation, and proper data reporting. We offer a comprehensive overview of sources of light stable isotope reference materials to best match sample matrices encountered by stable isotope practitioners with chemically similar reference materials.     

Auto- versus Cross-Correlation Noise in Periodically Driven Quantum Coherent Conductors

Expressing currents and their fluctuations at the terminals of a multi-probe conductor in terms of the wave functions of carriers injected into the Fermi sea provides new insight into the physics of electric currents. This approach helps us to identify two physically different contributions to shot noise. In the quantum coherent regime, when current is carried by non-overlapping wave packets, the product of current fluctuations in different leads, the cross-correlation noise, is determined solely by the duration of the wave packet. In contrast, the square of the current fluctuations in one lead, the autocorrelation noise, is additionally determined by the coherence of the wave packet, which is associated with the spread of the wave packet in energy. The two contributions can be addressed separately in the weak back-scattering regime, when the autocorrelation noise depends only on the coherence. Analysis of shot noise in terms of these contributions allows us, in particular, to predict that no individual traveling particles with a real wave function, such as Majorana fermions, can be created in the Fermi sea in a clean manner, that is, without accompanying electron–hole pairs.     

航空薄壁弧形结构件喷丸强化变形预测

喷丸强化是一种有效提高工件抗疲劳性能的表面处理工艺，经喷丸强化处理后的航空薄壁弧形结构件发生变形是航空制造领域的共性难题．本文基于变截面曲梁平面弯曲理论，建立了弧形件喷丸诱导应力与变形方程，将得到的构件最大变形与有限元方法计算结果进行对比，所建立理论模型能有效预测弧形件喷丸强化后的变形．讨论了喷丸压力和喷丸区域对喷丸变形的影响，结果表明：喷丸强化工艺仅作用于弧形件腹板表面时，弧形件变形以径向收缩为主；喷丸强化工艺仅作用于弧形件筋板表面时，弧形件变形以径向扩张为主；与局部喷丸相比，对弧形件所有表面喷丸强化时，弧形件弯曲变形减小，轴向伸长增大．     

The study on vulcanization fouling behavior of nanocrystalline layer

Mold fouling can degrade the physical properties and reduce the aesthetic value of the molded product. A plethora of research efforts have tried addressing these drawbacks, however, an effective method to prevent the foregoing adverse effects of mold fouling is still a challenge. Here, the fouling performance of aluminum alloy with a nanocrystalline surface layer fabricated by High Pressure Shot Peening (HPSP) during vulcanization has been investigated. Results indicate that an HPSP‐treated sample shows excellent resistance of mold fouling with only 1/8 weight gain after 25 cycles, compared to its HPSP‐free counterpart. The improved release performance can be attributed to the compact passivation layer with a larger thickness and low‐energy surface obtained after HPSP treatment, as well as the strengthened surface with a lower friction coefficient. Copyright © 2011 John Wiley & Sons, Ltd.     

激光脉冲重复频率对等离子体辐射特性的影响

为了提高激光诱导击穿光谱质量,采用Nd∶YAG激光器输出的纳秒脉冲激光激发产生土壤等离子体,采用光栅光谱仪和光电检测系统记录了元素谱线AlⅠ394.401 nm,BaⅠ455.403 nm,FeⅠ430.791 nm和TiⅠ498.173 nm的辐射强度和信背比,研究了激光脉冲重复频率(5,10和15 Hz)对等离子体辐射特性的影响。实验结果表明,在相同的激光输出能量条件下,当采用15 Hz的激光脉冲重复频率时,元素Al,Ba,Fe和Ti的谱线强度要比5 Hz时的分别提高50.94%,112.7%,107.46%和99.38%,光谱信背比分别提高15.16%,24.08%,40.26%和72.06%。通过测量等离子体参数,解释了激光脉冲重复频率对等离子体辐射特性的影响机理。     

Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet

We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F >> 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously.