Microwave-Resonance Induced Change in Magneto-Resistivity: Hot Surface Electrons on Liquid 3He

Behaviour of the linear magneto-resistivity σ _xx ⁻¹ of the surface-state electrons (SSE) exposed to the microwave radiation is studied in a wide temperature range which covers both vapor-atom and ripplon scattering regimes. The microwaves induce the resonance transitions of SSE between two lowest Rydberg states, and σ _xx ⁻¹ is observed to vary in the vicinity of the resonance. In the vapor-atom scattering regime (T≳0.5 K), magneto-resistivity decreases at the resonance, while in ripplon scattering regime (T≲0.3 K) it rapidly increases with the microwave power in the given range of the pressing electric field. The observed variation of σ _xx ⁻¹, which under the conditions of our experiment is inversely proportional to the scattering rate, is attributed to the strong heating of SSE. The heating results in the increase of electron temperature well above ambient temperature and in significant thermal population of higher excited states. The theoretical predictions are found to be in good agreement with our experimental results in the whole temperature range.      

Investigation of Microwave Absorption of Surface-State Electrons on Liquid 3He

We report on the experimental study of the resonance microwave absorption of surface-state electrons (SSE) on liquid ³He. The absorption is detected as a variation of the microwave power passing through the experimental cell, or as a resonance-induced change in the electron conductivity. In the latter method a decrease of the conductivity is observed, which points out on the possibility of substantial heating of the electrons by the absorbed microwave power. In a vapor-atom scattering regime the temperature dependence of the linewidth agrees well with the theoretical model, and the absolute value of the measured linewidth is about twice larger than the theoretical one. At very high microwave power the side band absorption peaks are observed.     

Anomalous Resonance Phenomena in Two-Dimensional Electrons on the Surface of 3He-4He Liquid Mixtures

No Heading We report on anomalous resonance phenomena observed in a two-dimensional electron system on ³He-⁴He liquid mixtures. The resonance is observed in a Corbino conductivity measurement, in which a magnetic field B is applied prependicular to the electron sheet. We have detected the resonances for ³He concentrations n₂ from 0.475% to 10.20%, and at temperatures below 800 mK. The resonance frequency f_r is inversely proportional to B. In a preliminary study we found that f_r and the resonance amplitude increases when the electron sheet is not parallel to the electrode, and this made the understanding difficult. Here we have made the systematic measurement keeping the parallelism between the electrons and the electrode. We have observed the resonance only at n₃ > 0.475%. This fact finally leads us to conclude that adding ³He atoms to liquid ⁴He induces the nonuniformity in local electron density, and hence the resonance.PACS numbers: 73.20.–r, 67.60.–g     

Static Structure Factor of Two-Dimensional Liquid 3He Adsorbed on Graphite

Liquid ³He is a model system for strongly correlated Fermi liquids. For this reason, many X-ray and neutron scattering experiments have been performed to understand the structure and dynamics of this quantum fluid. We have recently shown that two-dimensional liquid ³He sustains long-lived zero-sound excitations at large wave-vectors (Godfrin et al., Nature, 483:576, 2012). Here we show that its static structure factor can be obtained with reasonable accuracy by integrating the experimental S(Q,ω) over a suitable energy range. A good agreement is found between the static structure factor deduced from the experiment and theoretical models: Quantum Monte Carlo simulations and Dynamical Many Body Theory (DMBT). At high wave-vectors, the experimental values are underestimated because of the limited accessible phase space; nevertheless, even at atomic wave-vectors a semi-quantitative agreement is observed with the theoretical predictions.     

Adiabatic Melting of 4He Crystal in Superfluid 3He at Sub-millikelvin Temperatures

Adiabatic melting of ⁴He crystal to phase separated ³He–⁴He solution (at T< 2 mK) is probably the most promising method to cool the dilute phase down to temperatures substantially below 0.1 mK. When started well below the superfluid transition temperature T _c of pure ³He, this process allows, in principle, to get the final temperature (T _f ) several orders of magnitude less than the initial one (T _i ). This work is the first practical implementation of the method below the T _c of ³He. The observed cooling factor was T _i /T _f =1.4 at 0.9 mK, being mainly limited by the bad performance of the superleak filling line, by incomplete solidification of ⁴He in the cell, and by the improper thermal contact between the cell wall and the liquid.     

微波ECR等离子体特性及其对DLC膜性能的影响

为了解并优化在微波ECR等离子体增强化学气相沉积制备类金刚石膜工艺研究中的等离子体特性，利用朗缪尔探针法系统地测量了等离子体密度(Ne)、电子温度(Te)随工作气压(p)变化的关系。DLC膜的结构和性能依赖于沉积条件，提高等离子体密度有利于DLC膜的生长。本文示出了不同的CH4流量时，DLC膜的拉曼光谱和表面均方根粗糙度Rmax变化曲线，阐述了等离子体密度Ne、电子温度Te对DLC膜结构和性能的影响。     

微波消解——石墨炉原子吸收光谱法测定紫菜中的铅

应用石墨炉原子吸收光谱法测定紫菜中铅含量,以HNO3-H2O2为氧化剂,微波消解处理样品,磷酸二氢铵作测铅基体改进剂,考察了基体改进剂浓度、灰化温度、原子化温度对吸光值的影响。在最优条件下,低浓度的铅与吸光值具有良好的线性关系,线性方程为：A=0．0058C＋0．0052,r=0．9994,检出限为1．0μg／L。运用该方法测定10次加标样的RSD为1．512％～2．469％,加标回收率为98．4％～101．1％。该方法简单、快速、重现性好,适合日常批量检测。     

Surface Electron Spin Resonance Study on Ruby Crystal Using Evanescent Microwave Microscopy Techniques

As the silicon technology approaches to its physical limit, the future electronic devices will depend on behaviors of a few electrons. This study is to explore the possibility of detecting a single electron spin transition by using nondestructive evanescent microwave microscopy (EMM) techniques. To enhance the RF magnetic field and minimize the dielectric losses, the sample is placed at the center of the conventional electron spin resonance (ESR) microwave cavity that does not have scanning image capabilities. In this paper, a magnetic dipole probe (MDP) is presented that not only has the advantages of the microwave cavity, but is also capable of surface scanning at high speeds. At present, the minimum detectable electron spin transitions are 20 000 on the ruby crystal (Cr³⁺ doped in Al₂O₃) surface, whereas the commercially available ESR microwave cavity has a resolution of 10⁶ minimum detectable spins limit. Three ESR energy absorption spikes were detected at 3.77 and 3.73 GHz with the ruby crystal placed inside and outside of the MDP conductor loop, respectively. The measured ESR energy absorption spectra are consistent with theoretical analysis and the conventional ESR experimental results. The current MDP sensor has a 500-mum spatial resolution with a 1-mm radius conductor loop made by 150-mum copper wires. The nondestructive and noninvasive natures of the EMM microscopy are suitable for many biomedical applications, such as DNA sequencing, Alzheimer, and other biological tissue studies. Future efforts will be focused on integration of the MDP on the atomic force microscopy with carbon-nanotube bridges     

Induced Crystallization-Controllable Nanoarchitectonics of 3D-Ordered Hierarchical Macroporous Co@N-Doped Carbon Frameworks for Enhanced Microwave Absorption

The construction of ordered hierarchical porous structures in metal–organic frameworks (MOFs) and their derivatives is highly promising to meet the low-density and high-performance demands of microwave absorption materials. However, traditional methods based on sacrificial templates or corrosive agents inevitably suffer from the collapse of the microporous framework and the accumulation of nanoparticles during the carbonization transformation, resulting in the deteriorating impedance match, which greatly limits the incident and attenuation of microwaves. Herein, an induced crystallization and controllable nanoarchitectonics strategy is employed to replace traditional growing-etching methods and successfully synthesize carbonized 3D-ordered macroporous Co@N-doped carbon (3DOM Co@NDC) based on the 3D-ordered template. The obtained 3D-ordered macroporous structure ensures the stable growth of hybrid carbon frameworks and Co C nanoparticles without collapse, preserves abundant interfaces for both the incident and attenuation performance, so as to significantly improve the impedance matching and absorption properties compared to conventional MOFs derivatives. The minimum reflection loss of 3DOM Co@NDC is −57.36 dB at the thickness of 1.9 mm, and the effective bandwidth is 7.36 GHz at 1.6 mm. Moreover, the innovative strategy to prepare 3D-ordered hierarchical macroporous structures opens up a new avenue for advanced MOFs-derived absorbers with excellent performance.     

环氧树脂/填料功能梯度材料的微波固化及其水声性能研究

以环氧树脂和蛭石粉为原料,采用微波固化制备了环氧树脂/蛭石粉水声功能梯度材料,研究了微波固化对试样的玻璃化转变温度、动态力学性能的影响,并着重对功能梯度材料的水下吸声性能进行了研究。研究表明,用微波固化制备功能梯度材料是可行的,微波固化对固化试样的玻璃化转变温度、动态力学性能影响不大,但能明显提高试样在低频区域的吸声性能。     

Nonresonant Microwave Absorption in Bi2212 Single Crystal: Second Peak and Microwave Power Dependence

Nonresonant microwave absorption (NMA) measurements were carried out at liquid-nitrogen temperature on a high quality Bi2212 single crystal, as a function of microwave power in three mutual orientations of crystal ab plane, dc field (H_dc), and microwave magnetic field (H_w). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (P₁ peak) located near zero field, followed by a much broader second peak (P₂ peak) in the particular orientations. More excitingly, we show that the P₂ peak qualitatively evolves as a function of microwave power in the orientation of H_dc ab plane, plane, and H_dc H_w. In this configuration, as the microwave power is progressively increased, the broad P₂ peak first gets smeared off and then a multiple peak structure appears, which develops into another narrower second peak (P_s-peak) at high enough microwave powers. In the orientation of plane, H_w ab plane, and H_dc H_w, we report for the first time the appearance and disappearance of a new second peak (P₂-like peak) as a function of microwave power.     

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix(FMCA)was synthesized successfully with a novel confinement strategy.The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz.The addition of MnO2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon.The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties.Meanwhile,adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network.The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption.The optimal reflection loss(RL)is up to−45 dB,and the effective bandwidth(RL<−10 dB)is 5.0 GHz with 2.0 mm thickness.The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber,but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields.     

微波电子回旋共振等离子体的阻抗特性分析

基于微波电子回旋共振（ECR）等离子体中的物理和化学性质变化会引起微波传输线阻抗的变化，采用微波三探针研究了ECR等离子体的微波阻抗随装置运行参数的变化情况，并通过一个简单的放电等效电路将阻抗的变化和等离子体性质的变化联系起来。实验结果表明，通过对ECR等离子体进行阻抗特性分析，可以在不对其产生干扰的情况下了解其性质的变化。阻抗特性分析为ECR等离子体的机理研究提供了一种新的诊断途径，有利于ECR等离子体工艺的推广和应用。     

微波消解-石墨炉原子吸收法测定纸巾纸中砷含量

建立了石墨炉原子吸收光谱法测定纸巾纸中砷含量的方法。采用微波消解技术处理样品,加入基体改进剂硝酸镍,应用石墨炉原子吸收光谱法测定砷。结果表明,测定一次回归方程为Y=0.0025X+0.0004,相关系数r=0.9996。检出限为0.12 ug/L,回收率为95.8%～100.3%,相对标准偏差为2.37%。该方法具有快速、准确、灵敏度高等优点,适用于纸巾纸中砷含量的检测。     

掺杂对锶铁氧体基复合材料吸波特性的影响

将锶铁氧体、铁砂、混合稀土加工成基础材料,通过掺入一系列的不同类型的吸收介质制成复合电波吸收材料,在8-18GHz频段内测其吸波特性.实验结果表明,在基础材料中掺入Cu粉,使吸收峰移向低频,匹配厚度变大.在基础材料中同时加入MnZn铁氧体,最大衰减量明显增加,-10dB带宽无明显变化.同时掺入几种不同类型的吸收介质,产生了部分的累积效果.     

Spin Polarized Liquid 3He Obtained by Rapid Melting : Towards Lower Temperatures and Larger Pressures?

Our variant of the rapid melting technique enables us to study strongly polarized liquid ³ He around 80 mK below 29 bars, the minimum of the melting curve. Analysis of our results suggests that lower temperatures or larger pressures could only be obtained using a Pomeranchuk cell to control the pressure during melting. This paper describes an attempt in this direction. Now at     

W型钡铁氧体的溶胶-凝胶法制备及吸波性能研究

利用溶胶-凝胶法制备了W型BaZn1.5Co0.5Fe16O27钡铁氧体.在1000℃得到了单一W相纳米晶,晶粒大小为38nm,在1100℃完全形成了大小均匀的平面六角片状结构,其长度为1～3μm,横向尺寸为143～286nm.对其吸波性能进行了测量,发现有2个强吸收峰:0.9GHz和2.4GHz.吸收性能随烧结温度的升高而下降,在0.9GHz的能量吸收率:1000℃为68%,1100℃为48%;在2.4GHz的能量吸收率:1000℃为94%,1100℃为88%.     

轻质核壳结构吸波材料的研究进展

随着现代科技的发展,电磁波辐射对人类的影响越来越大,在电子电路中释放的电磁波会破坏其他设备的性能并且损害人体健康,因此吸波材料的研究显得尤为重要。此外,具有优良电磁性能的复合吸波材料还可以用于制备飞行器隐身材料。这是因为高强度的微波吸收材料具有良好的介电损耗和磁性损耗,同时具有优越的阻抗匹配,而核壳结构的吸波材料是复合吸波材料中较为理想的材料。本文详细介绍了核壳结构吸波材料的合成方法,并根据核壳结构材料的分类及具体应用,阐述了近年来国内外核壳结构吸波材料的最新研究进展。     

铈掺杂钛酸钡微粉制备与微波吸收特性研究

采用溶胶一凝胶法制备了稀土铈掺杂钛酸钡纳米晶粉体,借助XRD、Raman、SEM以及矢量网络分析仪等分析测试手段对样品晶相、晶格常数、粒径、表面形貌及微波吸收特性进行了研究.结果表明:铈掺杂样品均形成四方相钛酸钡微晶,晶粒发育良好.随着铈掺杂量增大,晶粒逐渐细化,晶格常数a变大,晶格常数c减小;与未掺杂钛酸钡相比,在2-18GHz频率范围内,稀土铈掺杂材料(掺杂量0.2%)的反射损耗明显地提高,反射峰发生蓝移,尤其5.8GHz和7GHz处反射损耗分别提高了15dB和30dB,频带拓宽近2倍.由此可见铈掺杂有利于改善钛酸钡材料的微波吸收特性.