掺杂纳米硅薄膜中电子自旋共振研究

研究了掺杂纳米硅薄膜(nc∶Si∶H)中的电子自旋共振(ESR)及与之相关的缺陷态.样品是用等离子体增强化学气相沉积方法制成,为两相结构,即纳米晶粒镶嵌于非晶本体之中.对掺磷的nc-Si∶H样品,测量出其ESR信号的g值为1.9990—1.9991,线宽ΔH_pp为(40—42)×10^-4T,ESR密度Nss为10¹⁷cm^-3数量级.对掺硼的nc-Si∶H样品,其ESR信号的g值为2.0076—2.0078,ΔH_{关键词： 纳米硅薄膜 微结构 电子自旋共振}     

TE011腔使用扁平样品管提高水溶液样品ESR波谱灵敏度的研究

实验表明,在TE₀₁₁模式园柱形腔中,不但可以使用扁平样品管测量水溶液样品的ESR波谱,而且获得好的腔品质因子Q和高品质的ESR信号。所观察到的信号高度,是使用最佳尺寸毛细管样品时最大信号高度的3.2倍;又是在具有波导尺寸的TE₁₀₂腔中使用扁平样品管时所获得信号高度的3倍。本文对此作了定性的理论分析。     

(Ga,Mn)As光调制反射光谱

室温下我们研究了稀磁半导体(Ga,Mn)As的光调制反射(PR)光谱,观测到来自样品的Franz-Keldysh振荡(FKO)信号。随着Mn原子浓度的增加,PR线形展宽,但是临界点E₀和E₀+Δ₀没有明显的移动。根据FKO振荡数据,计算得到样品表面电场强度随Mn原子掺杂浓度的增加而增强。测量到与Mn原子掺杂相关的杂质带,其能量位置离GaAs价带边~100 meV。根据样品的表面电场强度和表面耗尽层模型,估算样品的空穴浓度为~10¹⁷cm^-3,较低的空穴浓度可能与样品具有较低的居里温度有关,或测量的PR信号来自于样品中外延层的部分耗尽区域。     

纳米NiAl的电子自旋共振研究

对纳米NiAl样品进行电子自旋共振(ESR)研究时发现晶粒尺寸效应产生的非磁-磁性转变.大块多晶NiAl合金的没有ESR信号,只有很弱的Pauli顺磁性.而粒径为8.6nm的纳米NiAl样品的ESR信号,随温度的增高而显著下降,其居里温度T_C为124K,在室温下ESR信号很弱.8.6nm的纳米NiAl样品经550℃和707℃退火处理后得到粒径分别为12nm和21nm的两个样品,它们在室温下都有较强的ESR信号,并能够被永磁体吸起。多晶NiAl合金与纳米NiAl之间存在非磁-磁性转变,     

单轴压缩条件下岩石样品声发射信号的频谱分析

本文对单轴压缩条件下大理岩和辉长岩样品变形过程中的声发射信号进行了频谱分析,分析的范围从25—387kHz。应用高速数字化数据采集系统记录了岩石变形各阶段产生的声发射波形。对32个声发射信号进行了快速傅里叶变换处理（FFT）,得到它们的振幅谱。比较了不同种类岩石的频谱以及频谱随应力的变化,找出了声发射信号的频谱分布范围。
本文选取声发射信号振幅谱的主频f_Amax,峰个数n和单个声发射释放的能量IE三个参量对岩石声发射振幅谱作了统计分析,主要结果如下:
（1）在岩石样品表面探测到的声发射信号包含多种频谱成份,并且频谱具有谐波特性。对本实验所使用的岩石样品尺度（直径2.5—5cm;长度5—10cm的圆柱形）,声发射的主要能量分布在40—110kHz的频率范围内。
（2）大理岩和辉长岩的主频分布没有明显的差异,但与样品大小有关。
（3）岩石样品声发射频谱随压力的变化具有随机性质,没有显著的随应力增加而增大或减小的现象。     

SiO2-GeO2薄膜电场极化后倍频效率与极化电压的超平方关系

采用溶胶-凝胶方法制备了SiO₂-GeO₂薄膜.通过对薄膜样品平板电极极化和电晕极化后二次谐波产生信号的研究,发现样品中有效偶极子数目随平板电极极化电压的增加而逐渐增大.提出了有效偶极子释放模型,解释了样品倍频效率与极化电压之间的超平方关系. 关键词：     

锁相热像方法实验测量Nb2O5薄膜吸收率

利用锁相热像方法定量测量了光学镀膜的吸收率。待测薄膜吸收周期调制的激光能量,在表面形成热波,将红外相机记录的热分布信号进行锁相相关处理,获得信噪比提高的热图像。采用标准吸收样品对系统进行定标,可获得光热信号幅度与样品吸收率之间的定量联系,进而在相同实验条件下测量待测样品,可通过光热信号直接计算获得其绝对吸收率。在1 060 nm波长处开展了实验研究,测量获得了不同厚度Nb₂O₅镀膜的吸收率数值,实测的吸收可达80 ppm。     

利用相位步进脉冲消除探头13C NMR背景信号

由静态探头线圈外有机材料产生的¹³C NMR背景信号强度大，化学位移范围广（δ_C 20~250），此背景信号在交叉极化实验中还可被增强，并随着样品信号的累积而累积，严重影响谱图分析.将相位步进脉冲引入交叉极化实验（称为PIPCP）中可以有效去除经交叉极化增强的¹³C NMR背景信号，但样品信号不受影响.这是由于经过相位步进脉冲后，线圈外相位严重畸变，而且线圈外锁定场强度急剧降低，来自探头材料的¹³C NMR背景信号无法有效地进行交叉极化.而对于被测样品甘氨酸来说，由于I核和S核之间强烈的偶极耦合作用，所加相位步进脉冲对锁定场强度的影响只有1.4%.     

二维WTe2晶格对称性的光学研究

二维WTe₂由于特殊的晶格对称性而衍生出量子自旋霍尔效应、非线性霍尔效应等奇异性质.确定其晶体结构的细节,是理解这些性质的重要出发点.本文利用温度、偏振依赖的拉曼光谱与光学二次谐波产生,详细研究了一至三层WTe₂的晶格对称性.实验发现,单层样品具有可观的二次谐波产生信号,表明其晶格中心对称性破缺,且偏振依赖符合C_s点群,与此前普遍认为的中心对称的1T’结构不同.双层样品具有更为显著的二次谐波产生信号,且信号强度的温度依赖与铁电相变一致,表明层间堆叠产生了更强的中心对称性破缺,提供了该体系中存在层间滑移铁电的证据.三层样品的二次谐波产生信号约为单层样品的五倍,但比双层样品弱一个数量级,表明层间堆叠导致其具有较弱的中心对称性破缺.仅单层与双层样品中出现了多个显著的二阶拉曼散射峰,其温度依赖反映出电子结构对层间耦合高度敏感.这些结果将有助于完善对原子级厚度WTe₂物理性质的理解.     

三维自组装Eu3+-石墨烯复合材料的制备及其磁性研究

采用一锅水热法在180 ℃ 下制备三维Eu³⁺-石墨烯自组装复合材料. 通过X射线衍射、 扫描电子显微镜、透射电子显微镜表征了合成样品的物相及形貌特征. 结果表明: 合成的样品具有多孔性结构, 层与层之间堆叠成三维结构, 并且结果显示产物中没有Eu³⁺的团聚体. 经过拉曼光谱, 傅里叶红外光谱分析表明, Eu³⁺通过含氧官能团与石墨烯复合. 通过振动样品磁强计测定样品的磁滞回线, 对其磁学性能进行研究, 剥离顺磁信号后, 测得相应的矫顽力H_c ≈ 39.61 Oe(1 Oe=79.5775 A/m), 饱和磁化强度M_s ≈ 0.08 emu/g, 发现该产物具有弱的铁磁性, 与石墨烯相比, Eu³⁺的加入使得产物的铁磁性有较大提高. 关键词： 三维石墨烯 3+')" href="#">Eu³⁺ 水热法 磁性     

Determination of the path of a sound source moving in an inhomogeneous medium

The possibility of determining the actual paths of moving sound sources from the signals received by a linear horizontal array whose size is large compared to the wavelength is investigated with the use of procedures suggested earlier for the imaging of dynamic objects moving below an inhomogeneous layer. Two cases of signal reception are considered: when the signals propagate in the oceanic waveguide and when the signals propagate through an inhomogeneous layer located near the array. It is shown that, unlike the standard spatial processing procedures, the proposed methods allow one to measure the absolute angular displacements to within the diffraction resolution of the array and to eliminate the ambiguity in angular measurements. An important point is that the proposed methods require no prior data on the parameters of the inhomogeneous layer or the multimode waveguide.     

Co膜中多次超快瞬态反射突变现象研究

飞秒激光泵浦瞬态热反射技术是研究金属薄膜超快动力学的有效手段,这种技术具有两大突出特点：首先,可以揭示飞秒激光激发的微观电、声子的传输过程是一个非平衡热输运过程。其次,反射率瞬态变化实验中电子运动的超短时间分辨可以用来研究热过程中电子的非平衡相互作用情况。利用磁控溅射真空镀膜技术,在玻璃衬底和硅衬底上蒸镀了不同厚度的Co单层膜,Cr,Co双层膜以及Ag,Co双层膜。利用飞秒激光瞬态反射技术研究了Co膜及其双层膜的瞬态反射率响应。结果表明,在同一厚度的Co膜样品上,施加不同的泵浦光功率时,Co膜内电子的加热时间与泵浦光功率的大小无关,均为0.1344 ps。而对于不同厚度的Co膜,电子的热化时间与薄膜厚度直接相关。此外,发现与以往研究结果不同的是,在泵浦光功率足够大时,玻璃衬底上的Co膜在飞秒激光脉冲泵浦下会出现两次或三次瞬态反射率下降现象,Co膜厚度决定了Co膜内瞬态反射率突变的次数,即Co膜内电子的超快动力学变化次数。     

Multilayer optical disc system using homodyne detection

A write/read system using high-productivity multilayer optical discs was developed. The recording medium used in the system consists of planar recording layers and a separated guide layer, and is fabricated by web coating and lamination process. The recording layers in the medium are made of one-photon-absorption material, on which data can be recorded with a normal laser diode. The developed system is capable of focusing and tracking on the medium and amplifying readout signals by using phase-diversity homodyne detection. A highly layer-selective focusing method using homodyne detection was also proposed. This method obtains stable focus-error signals with clearly separated S-shaped curves even when layer spacing is quite narrow, causing large interlayer crosstalk. Writing on the medium and reading with the signal amplification effect of homodyne detection was demonstrated. In addition, the effectiveness of the method was experimentally evaluated.     

PIN限幅器微波脉冲热损伤温度特性

分析了微波对PIN限幅器的热损伤机理,基于器件物理模拟分析法,利用Sentaurus-TCAD仿真器建立了器件微波热效应模型,研究了频率为5.3,7.5,9.4 GHz的微波信号作用下,器件损伤过程中温度瞬态变化规律和瞬态温度分布规律。结果表明：PIN限幅器尖峰泄露阶段器件温度上升较快;稳态限幅后温度上升缓慢;临近热击穿状态,器件进入热电失控状态,峰值温度快速上升,最终器件因温度过高烧毁;PIN二极管中的I区或P区与I区之间的结边缘处,较容易烧毁。对PIN限幅器进行大功率微波注入实验,器件损伤实验结果与数值模拟结果吻合较好。     

Dispersion of laser generated surface waves in an epoxy-bonded layered medium

In this paper, the dispersion of laser generated surface wave in an epoxy bonded copper-aluminum layered specimen is studied. A laser ultrasonic experiment based on the point-source/point-receiver (PS/PR) technique was conducted to measure the surface wave signals in the layered specimen. The received wave signals were then processed in the frequency domain to obtain the dispersion relation of the fundamental surface wave mode. Theoretical calculations of the dispersion relations of the fundamental surface wave modes in two-layered and three-layered specimens were conducted to explore the influence of the bonding layer thickness on the dispersion relation. The experimental dispersion relation for the epoxy bonded copper-aluminum layered specimen is in good agreement with the calculated dispersion relation. The influence of the bonding layer thickness on the dispersion relation is studied and the potential application of the present results to the NDE of bonded layered media based on laser ultrasonics is also addressed.     

Real-time optodynamic monitoring of pulsed laser decoating rate

This paper deals with a laser-cleaning process for removing a layer of paint. The effects of each individual laser pulse were monitored by a three-probe system. Ultrasonic signals from the rear surface of the substrate were obtained using an arm compensated Michelson interferometer, the optoacoustic waves in the surrounding air were detected using a laser beam deflection probe and the shape of the growing crater was measured using a laser anamorph profilometer. Two different cleaning lasers were used: an Excimer and a Nd:YAG laser. Typical parameters of the optodynamic signals versus the laser-pulse number are presented. A linear correlation between the quantity of ablated material and the integral of the ultrasonic signals was found together with an exponential relationship between the time-of-flight of the optoacoustic signals and the decoating rate.     

PIN限幅器微波脉冲热损伤温度特性

分析了微波对PIN限幅器的热损伤机理,基于器件物理模拟分析法,利用Sentaurus-TCAD仿真器建立了器件微波热效应模型,研究了频率为5.3,7.5,9.4 GHz的微波信号作用下,器件损伤过程中温度瞬态变化规律和瞬态温度分布规律。结果表明:PIN限幅器尖峰泄露阶段器件温度上升较快;稳态限幅后温度上升缓慢;临近热击穿状态,器件进入热电失控状态,峰值温度快速上升,最终器件因温度过高烧毁;PIN二极管中的I区或P区与I区之间的结边缘处,较容易烧毁。对PIN限幅器进行大功率微波注入实验,器件损伤实验结果与数值模拟结果吻合较好。     

基于AR模型与神经网络的核爆与闪电电磁脉冲信号识别

对平稳随机信号功率谱估计的AR模型,分别利用自相关函数法和Burg算法求该模型系数,作为核爆炸和闪电电磁脉冲信号的特征值;采用BP神经网络作为分类器以及不同的隐含层数和隐含层节点数,对核爆和闪电电磁脉冲实测数据进行识别研究。结果表明：AR参数模型法对两类信号特征值提取是非常有效的,采用Burg算法来求AR模型参数,其特征值提取效果优于自相关函数法。     

Frequency correlation of fluctuations of short-wave signals in the theory of refractive scattering of radiowaves in the ionosphere

We consider the problem of frequency correlation of phase fluctuations of HF signals reflecte from a turbulent ionospheric layer with an arbitrary profile of electron density in vertical and oblique sounding of the ionosphere. Expressions for evaluation of the coherence band of HF signals reflected from a randomly inhomogeneous ionosphere are obtained. Calculation results are compared with corresponding calculations of frequency correlation of fluctuations of HF radiowaves in Buker's theory of refractive scattering of radiowaves. It is shown, in particular, that the influence of splitting of rays for waves with different frequencies in an inhomogeneous ionosphere on the frequency distortions of HF signals prevails compared with the phenomenon of frequency decorrelation of fluctuating HF signals propagating in a free space beyond a turbulent ionospheric layer.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 9, pp. 893–900, September, 1995.     

Nonlinear scattering of acoustic waves by natural and artificially generated subsurface bubble layers in sea

The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31-37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.