共查询到20条相似文献,搜索用时 171 毫秒
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搭建了一套研究金属和金属氧化物表面的超快激发态电子动力学和光化学动力学的飞秒双光子光电子能谱仪. 该装置将半球形电子能量分析仪和成像技术相结合,同时测量光电子的能量和角度分布.通过Mach-Zehnder干涉仪测量时间分辨的双光子光电子能谱获得超快激发电子态的动力学信息. 这一功能在Cu(111)上得到了证实. 另外还发展了一个通过实时测量双光子光电子能谱来研究表面光化学的方法,并成功应用到CH3CH2OH/TiO2(110)体系. 研究表明,只有将两种方法结合起来才能正确地研究光诱导的表面激发共振的动力学. 相似文献
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本文较详细地评述了高温超导体角分辨光电子能谱研究的所有主要方面的成就及最新进展。所涉及的主题有:角分辨光电子能谱基础知识,费米面的角分辨光电子能谱研究,超导能隙及对称性研究,赝能隙问题的角分辨光电子能谱研究,高温超导体的角分辨光电子能谱谱线形分析,近节点区域准粒子的色散行为,双层能带劈裂。所涉及的材料不仅有最广泛研究的Bi2212,还包括Bi2201,Bi2223,La-214,Y-123乃至电子型掺杂的超导体。所引用的文献特别注意了从新一代高能量、动量分辨的能量分析器得到的系统、深入的工作。 相似文献
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本文较详细地评述了高温超导体角分辨光电子能谱研究的所有主要方面的成就及最新进展。所涉及的主题有:角分辨光电子能谱基础知识,费米面的角分辨光电子能谱研究,超导能隙及对称性研究,赝能隙问题的角分辨光电子能谱研究,高温超导体的角分辨光电子能谱谱线形分析,近节点区域准粒子的色散行为,双层能带劈裂。所涉及的材料不仅有最广泛研究的Bi2212,还包括Bi2201,Bi2223,La_214,Y 123乃至电子型掺杂的超导体。所引用的文献特别注意了从新一代高能量、动量分辨的能量分析器得到的系统、深入的工作。 相似文献
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为获取超快光脉冲信号,提出了一种基于光电子脉冲准线性展宽的高时间分辨二维成像技术。利用高频时变电场的线性工作区加速光电子脉冲信号,通过优化阴极激励源的电参数,选择光电子进入加速区的时刻实现光电子脉冲的准线性展宽。利用曝光时间100ps的门控选通微通道板在脉冲展宽模块的记录面进行选通曝光成像,实现高时间分辨的二维成像。为改善系统的空间分辨和成像畸变,添加轴向聚焦磁场解决电子漂移区中由电子空间电荷效应引起的时间和空间弥散,对于能量4 keV、出射角0.1°的电子束,聚焦磁场的最佳强度为0.057 T,此时阴极中心位置的空间分辨可达5 1p/mm,阴极边缘位置空间分辨稍差。基于光电子脉冲准线性展宽技术,可将漂移距离50 cm,初始脉宽10 ps的电子脉冲展宽10倍,从而可将门控MCP探测器的时间分辨提高1个量级(即10 ps以内)。 相似文献
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《物理》2017,(12)
光电子显微镜是一种基于光电效应的电子显微镜,利用样品不同空间位置光电子产量的差异作为图像衬度进行投影成像。其成像速度快、空间分辨率高、探测无损伤等特点和优势,在表面科学、表面等离激元学、半导体学等学科有着广泛应用。另外,结合超快光泵浦探测技术为光电子显微镜提供了高时间分辨能力,特别适用于高时空分辨的动力学过程研究。时间分辨光电子显微镜是具备多维度直观测量的技术方法,为研究人员开辟了新的道路。文章首先简要回顾电子显微成像技术的发展,然后介绍在表面等离激元学和半导体物理领域中应用光电子显微镜的最新进展,最后介绍北京大学最近建设的超快光电子显微镜系统和相关研究工作及展望。 相似文献
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利用时间分辨的飞秒光电子影像技术结合时间分辨的质谱技术,研究了2,6-二甲基吡啶分子锥形交叉超快动力学过程. 2,6-二甲基吡啶分子吸收266 nm泵浦光从基态跃迁至S2态(π-π*). 母体离子时间变化曲线包含两个指数函数,一个是时间常数为635 fs的快速组分,另一个是时间常数为4.37 ps的慢速组分. 通过时间分辨光电子影像得到的时间依赖的光电子角度分布和能量分辨的光电子谱分布提供了S2态演变的动力学信息. 简言之,快速组分反映了通 相似文献
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采用飞秒时间分辨质谱技术结合飞秒时间分辨光电子影像技术研究了苯乙炔分子电子激发态超快非绝热弛豫动力学.用235 nm光作为泵浦光,将苯乙炔分子激发到第二激发态S2,用400 nm光探测激发态的演化过程.时间分辨的母体离子的变化曲线用指数和高斯函数卷积得到不同的两个组分,一个是超快衰减组分,时间常数为116 fs,一个是慢速组分,时间常数为106 ps.通过分析时间分辨的光电子影像得到光电子动能分布,结合时间分辨光电子能谱数据发现,时间常数为116 fs的快速组分反映了S2态向S1态的内转换过程.实验还表明S1态通过内转换被布局后向T1态的系间窜跃过程为重要的衰减通道.本工作为苯乙炔分子S2态非绝热弛豫动力学提供了较清晰的物理图像. 相似文献
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A. D'Ottavi F. Martelli P. Spano R. Dall'Ara J. Eckner G. Guekos 《Fiber and Integrated Optics》1996,15(3):257-266
In this article we report extended measurements of four-wave mixing in bulk-semiconductor amplifiers using continuous wave sources. We demonstrate that four-wave mixing in semiconductor amplifiers permits realizing in the practice frequency conversion in the spectral range of utility for optical telecommunications. Efficiency larger than 1 have been demonstrated up to 1 THz with a low level of background noise. In addition, this technique has allowed us to investigate the carrier dynamics down to an equivalent time resolution of the order of few tens of femtoseconds. 相似文献
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为了实现对更弱、以及物理量跨度更大的信号探测, 满足材料、生物、信息、半导体物理以及能源等重大科学领域对诊断精密化的进一步需求, 需要提高条纹相机的动态范围、空间分辨率和信噪比. 为此, 本文研制了基于电子轰击式CCD(EBCCD)的大动态条纹相机, 条纹变像管采用时间和空间方向分别聚焦的矩形框电极和电四极透镜结构, 可降低空间电荷效应. 并提高电子加速电压, 减小电子渡越时间以降低空间电荷相互作用时间. 采用基于电子轰击读出技术的背照式CCD(BCCD)作为读出器件, 取代传统的像增强CCD(ICCD)以缩短图像转换链, 较大地降低了超快诊断设备转换过程中的图像衰减, 从而提高条纹相机图像的信噪比、空间分辨率和动态范围. 实验得到静态空间分辨率高于35 lp/mm, 动态空间分辨率达到20 lp/mm, 偏转灵敏度为60.76 mm/kV, 动态范围达到2094:1, 扫描速度非线性为5.04%, 条纹相机的电子轰击半导体(EBS)增益达到3000以上. 相似文献
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We present a real-time investigation of ultra-fast carrier dynamics in single-wall carbon nanotube bundles using femtosecond
time-resolved photoelectron spectroscopy. The experiments allow us to study the processes governing the sub-picosecond and
the picosecond dynamics of non-equilibrium charge carriers. On the sub-picosecond time scale the dynamics are dominated by
ultra-fast electron–electron scattering processes, which lead to internal thermalization of the laser-excited electron gas.
We find that quasiparticle lifetimes decrease strongly as a function of their energy up to 2.38 eV above the Fermi level –
the highest energy studied experimentally. The subsequent cooling of the laser-heated electron gas to the lattice temperature
by electron–phonon interaction occurs on the picosecond time scale and allows us to determine the electron–phonon mass-enhancement
parameter λ. The latter is found to be over an order of magnitude smaller if compared, for example, with that of a good conductor
such as copper.
Received: 4 March 2002 / Accepted: 7 March 2002 / Published online: 3 June 2002 相似文献
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The Cu–CdSe–Cu nanowire heterojunctions were fabricated by sequential electrochemical deposition of layers of Cu metal and
CdSe semiconductor within the nano-pores of anodic alumina membrane templates. X-ray diffraction reveals the cubic phase for
Cu and hexagonal phase for CdSe in the electrodeposited Cu–CdSe–Cu nanowire heterojunctions. The composition of the nanowire
heterojunction segments is characterized by energy dispersive X-ray spectroscopy. The morphological study of nanowire heterojunctions
has been made using scanning electron microscope and high resolution transmission microscopy. The nanowire heterojunctions
grown in 100 and 300 nm nano-pore size templates have been found to have optical band gaps of 1.92 and 1.75 eV, respectively.
The absorption spectra of 100 nm nanowire heterojunctions show a blue shift of 0.18 eV. The collective nonlinear current–voltage
(I–V) characteristics of the 300 and 100 nm nanowire heterojunctions show their rectifying and asymmetric behaviour, respectively. 相似文献
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We present a time-resolved technique to measure optical excitation processes with a time resolution shorter than the oscillation period of the exciting light. Our terahertz (THz) experiments fully resolve the polarization dynamics of electrons in semiconductor heterostructures when they are excited by a THz pulse. The time resolution of the polarization enables us to deduce the population dynamics of the excited state, which includes the dynamics of a virtual population in the case of off-resonant excitation. 相似文献
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Novel applications of the technique of optically detected cyclotron resonance (ODCR) are discussed. This method is an extension of the conventional cyclotron resonance investigations and shows important advantages when applied to characterization of semiconductor materials. These advantages are due to a higher sensitivity and a longer momentum relaxation time caused by photoneutralization of ionized impurities. This in turn enables experiments at lower magnetic fields and lower microwave radiation frequency. Photoexcitation used in ODCR often results in a simultaneous observation of electron and hole cyclotron resonances in the same sample, which is a rare case in a conventional CR study. High magnetic field far infrared ODCR experiments utilize all these advantages of the method. For the most common X-band (10 GHz) microwave setups, the ODCR resolution often is too low to allow accurate CR determination of the band structure parameters of the material studied. In that case, ODCR may be used for high-resolution photoluminescence experiments and for identification of carrier capture and recombination paths at impurities, as was proposed recently. These new and important applications of the ODCR technique are described here, and documented by recent experimental results. The mechanism of ODCR detection for pure and doped semiconductors is discussed, and a prominent role of the impact ionization mechanism is demonstrated. This is followed by a discussion of recent applications of ODCR for identification of recombination mechanisms. Then high spectral resolution ODCR experiments are described, with the example of overlapping free-to-bound and donor-acceptor pair transitions. Some special applications of ODCR are demonstrated. ODCR also can be applied to analyze quantum confinement of carriers in two-dimensional (2D) structures such as heterojunctions and quantum wells. It is shown that useful information can be obtained on the electronic properties of the 2D electron (or hole) gas and the interlayer carrier transfer enhanced by carrier heating at CR absorption in such structures. 相似文献
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This paper reports some recent results of time-resolved studies of the carrier dynamics in GaAs/GaAlAs quantum well structures with picosecond and subpicosecond time resolution. These experiments have provided insight into carrier trapping, energy relaxation, and carrier recombination processes. Carrier trapping into the quantum well layers is very efficient and determines the decay of the GaAlAs luminescence even for 1 μm thick cladding layers. Carrier recombination is enhanced particularly at low temperatures. This effect has been attributed to the increased overlap of electron and hole (exciton) wavefunctions in the quasi-two-dimensional carrier system. 相似文献
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Magnetic soft X-ray microscopy images magnetism in nanoscale systems with a spatial resolution down to 15 nm provided by state-of-the-art Fresnel zone plate optics. X-ray magnetic circular dichroism (X-MCD) is used as the element-specific magnetic contrast mechanism similar to photoemission electron microscopy (PEEM), however, with volume sensitivity and the ability to record the images in varying applied magnetic fields which allows study of magnetization reversal processes at fundamental length scales. Utilizing a stroboscopic pump-probe scheme one can investigate fast spin dynamics with a time resolution down to 70 ps which gives access to precessional and relaxation phenomena as well as spin torque driven domain wall dynamics in nanoscale systems. Current developments in zone plate optics aim for a spatial resolution towards 10 nm and at next generation X-ray sources a time resolution in the fs regime can be envisioned. 相似文献
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Masashi Usami Kohsuke Nishimura 《Journal of Optical and Fiber Communications Reports》2005,2(6):497-529
Semiconductors have large optical nonlinearity with response speed in the several tens of picosecond range, making them ideal
use as all-optical regenerators and wavelength converters. We theoretically and experimentally investigated optical nonlinearities
induced by carrier dynamics both in forward biased semiconductor waveguide (SOA) and in reverse biased semiconductor waveguide
(EAM). We made a detailed theoretical study of carrier dynamics in semiconductor waveguides by using the newly developed time-dependent
transfer matrix method. To confirm the simulation results, we propose utilizing a polarization discriminating delayed interferometer
(PD-DI) configuration as a simple technique for measuring optical nonlinearities such as cross gain modulation (XGM), cross
absorption modulation (XAM), and cross phase modulation (XPM). In the first part of the paper, we reviewed SOA-based regenerators.
As expected from the simulation results, we confirmed that injection of the transparent assist light was very effective in
reducing of the SOA gain recovery time of down to a few tens of picoseconds. We further demonstrated 40 Gbit/s regeneration
using an SOA-one-arm MZI (so-called UNI) configuration. The superior regeneration capability of two-stage UNI was successfully
confirmed by a recirculating loop experiment up to 30,000 km with 150 regenerations. In the latter part of the paper, we reviewed
all-optical regenerators using EAM. A bit-synchronized rf-driven XAM 3R regenerator consisting of only one EAM for both gating
and timing correction was demonstrated at 20 Gbit/s. An EAM in conjunction with delayed interferometer configuration, which
utilizes XPM as well as XAM in the EAM, has structurral simplicity and fast regeneration operability up to 100 Gbit/s. The
fast response of EAM allows the optical regeneration with a small pattern word effect. 相似文献
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Knorr A. Steininger F. Girndt A. Stroucken T. Haas S. Thomas P. Koch S. W. 《Il Nuovo Cimento D》1995,17(11):1265-1276
Il Nuovo Cimento D - The transport of radiative and electronic excitations in coherently driven semiconductor quantum wells is analysed. On ultrashort time scales the spatial dynamics is determined... 相似文献