Strong resonant intersubband magnetopolaron effect in heavily modulation-doped GaAs/AlGaAs single quantum wells at high magnetic fields

Electron cyclotron resonance (CR) has been studied in magnetic fields up to 32 T in two heavily modulation-delta-doped GaAs/Al0.3Ga0.7As single quantum well samples. Little effect on electron CR is observed in either sample in the region of resonance with the GaAs LO phonons. However, above the LO-phonon frequency energy E-LO at B > 27 T, electron CR exhibits a strong avoided-level-crossing splitting for both samples at energies close to E-LO + (E-2 - E-1), where E-2, and E-1 are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large, reaching a minimum of about 40 cm(-1) around 30.5 T for both samples. This splitting is due to a three-level resonance between the second LI, of the first electron subband and the lowest LL of the second subband plus an LO phonon. The large splitting in the presence: of high electron densities is due to the absence of occupation (Pauli-principle) effects in the final states and weak screening for this three-level process. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. (C) 1998 Elsevier Science B.V. All rights reserved.

傅立叶变换离子回旋共振质谱在含糖小分子分析中的应用

傅立叶变换离子回旋共振质谱是一种近些年来逐渐发展起来的新型质谱仪器，由于该类质谱检测器的设计和检测原理与传统质谱有着根本的区别，通过它获取的数据具有高分辨和高质量测量精度的特点。通常，超过100000以上的分辨本领能够对质谱中非常临近的质谱峰进行区分，并结合串联质谱中的高质谱测量精度数据，可以给出明确的串联质谱碎裂途径。 本论文选择4对具有同分异构特点的二糖黄酮进行了系统研究，实验采取负离子模式的电喷雾傅立叶变换离子回旋共振质谱，结合持续非共振辐照碰撞诱导解离模式，对同分异构体的区分进行了研究。在实验过程中，建立了一种全新的质量校正方法，使得质谱测量平均误差小于1.00 ppm1。首次直接利用子离子的结构信息，确定了负离子模式下二糖黄酮的去质子化位点。实验中还发现，RDA解离途径仅仅当二糖黄酮的苷元是黄烷酮并且B环上没有过多的富电子基团的情况下才能发生，同时，具有α1→2糖连接的二糖黄酮在串联质谱中能够发生多键解离，并采用Gaussian 03 程序利用 B3LYP/6-31G方法对其进行了理论计算。为了进一步讨论α1→2糖连接二糖黄酮的串联质谱特点，在温和实验条件下，对上述化合物进行了氢氘交换实验。实验中首次发现温和条件下，黄酮的氢氘交换位点依赖于苷元结构，除了糖链上羟基和苷元上的酚羟基能够发生氢氘交换外，苷元为黄烷酮的二糖黄酮中，C（3）、C（6）和C（8）上的氢能够被直接交换掉，而苷元为黄酮骨架的二糖黄酮则在此位点不发生氢氘交换反应，并依据高质量测量精度数据对其子离子产生途径进行研究。 论文还系统研究了由葡萄糖缩合而成的二糖，4对二糖异构体负离子模式电喷雾傅立叶变换离子回旋共振质谱研究表明，其离子化过程中，生成的去质子化的二聚体是主要气相离子，依据单糖的实验和计算化学结果，论文中提出二糖化合物的离子化模型。计算化学的结果还证实，构成二聚体的单体直接具有强烈的相互作用，能够在串联质谱中产生共价键解离的子离子，而不是简单的单体解离。利用SORI CID还对二糖化合物的糖连接位点和糖苷键构型进行了区分研究。 论文的最后一部分研究了人工合成类肝素类化合物DHα、THα 和 THβ的结构表征，在极其温和的负离子模式电喷雾质谱条件下，类肝素化合物仍然容易发生多个SO3中性丢失。串联质谱中的子离子通过傅立叶变换离子回旋共振质谱高质量精度测量数据进行了确认。实验对研究类肝素类化合物的质谱表征提供了借鉴。

Resonant subband Landau level coupling in symmetric quantum well

Subband structure and depolarization shifts in an ultrahigh mobility GaAs/Al0.24Ga0.76As quantum well are studied using magnetoinfrared spectroscopy via resonant subband Landau level coupling. Resonant couplings between the first and up to the fourth subbands are identified by well-separated antilevel-crossing split resonance, while the hy-lying subbands were identified by the cyclotron resonance linewidth broadening in the literature. In addition, a forbidden intersubband transition (first to third) has been observed. With the precise determination of the subband structure, we find that the depolarization shift can be well described by the semiclassical slab plasma model and the possible origins for the forbidden transition are discussed.

Resonant magnetopolaron effects due to interface phonons in GaAs/AlGaAs multiple quantum well structures

Polaron cyclotron resonance (CR) has been studied in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well structures in magnetic field up to 30 T. Large avoided-level-crossing splittings of the CR near the GaAs reststrahlen region, and smaller splittings in the region of the AlAs-like optical phonons of th AlGaAs barriers, are observed. Based on a comparison with a detailed theoretical calculation, the high frequency splitting, the magnitude of which increases with decreasing well width, is assigned to resonant polaron interactions with AlAs-like interface phonons.

Magnetospectroscopy of bound phonons in high purity GaAs

Far infrared magnetophotoconductivity performed on high purity GaAs reveals the existence of fine structures in the resonant magnetopolaron regions. The fine structures are attributed to the presence of bound phonons due to multiphonon processes. We demonstrate that the magnetopolaron energy spectrum consists of bound phonon branches and magnetopolaron branches. Our results also indicate that different phonons are bound to a single impurity, and that the bound phonon in Si-doped GaAs is a quasilocalized mode.

Magnetophonon resonance in the energy relaxation of electrons in a quantum well

The magnetophonon resonance effect in the energy relaxation rate is studied theoretically for a quasi-two-dimensional electron gas in a semiconductor quantum well. An electron-temperature model is adopted to describe the coupled electron-phonon system. The energy relaxation time, derived from the energy relaxation rate, is found to display an oscillatory behavior as the magnetic-field strength changes, and reaches minima when the optical phonon frequency equals integer multiples of the electron cyclotron frequency. The theoretical results are compared with a recent experiment, and a qualitative agreement is found.

Electron effective mass and resonant polaron effect in CdTe/CdMgTe quantum wells

Cyclotron resonance in CdTe/CdMgTe quantum wells (QWs) was studied. Due to the polaron effect the zero-field effective mass is strongly influenced by the QW width. The experimental data have been described theoretically by taking into account electron-phonon coupling and the nonparabolicity of the conduction band. The subband structure was calculated self-consistently. The best fit was obtained for an electron-phonon coupling constant alpha = 0.3 and bare electron mass of m(b) = 0.092m(0).

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. (C) 1998 Elsevier Science B.V. All rights reserved.

Speed of the internal pellet target in CSRm

Pellet target is one of the main candidate targets in CSRm (cooler storage ring’s main ring) for hadron physics studies. Pellet speed is an important physical parameter for the target. Larger pellet speed could shorten the interacting time interval between the pellet and the cyclotron beam, and thus results in a small temperature variation for the pellet. This could make the pellet facility work in a stable condition. A fluid dynamic simulation was carried out for the pellet speed, and it was found that the maximum speed for the target pellet may be restricted to about 100 m/s even if all working parameters were set to their optimal values.

Research for HIRFL new improvement project

According to the newest matching mode between the two cyclotrons at HIRFL, the beam obit properties were researched, especially for the harm of existing ‘over-magnetic shim’ in SSC as well as the trajectory in the new mode. The results obtained are encouraging.

全永磁ECR离子源研究进展

Electron Cyclotron Resonance (ECR) ion source is regarded as the most efficient machine to produce stable multiple charge state ion beams. Because of the special characteristics, all-permanent magnet ECR ion sources have been widely adopted around the world to produce stable ion beams of multiple charge state with good repetition have been widely adopted around the world to produce stable ion beams of multiple charge state with good repetition and high duty factor for compact research platforms and ion beam implanters. In this paper, all-permanent magnet ECR ion sources developed at IMP are presented, and typical parameters and performances are discussed. The high charge state source, LAPECR2, is mainly used to produce intense high charge state ion beams, and the LAPECR1 source is designed to produce intense ion beams of medium and low charge state. An improved LAPECR1-M is specially designed to produce heavy metal ion beams of low charge state. These ECR ion sources have been adopted by different experimental terminals at IMP and, with their nice performance, many experimental studies could be possible. 中文文摘：ECR(电子回旋共振)离子源是产生稳定的强流多电荷态离子束流最有效装置。全永磁ECR 离子源因其独特的特点为很多中小型多电荷态离子束流实验平台与离子注入机等系统所采用，为后者产生重复性好、稳定性强的多电荷态离子束流。本文着重论述了中国科学院近代物理研究所研制的几台全永磁多电荷态ECR 离子源及其特性与典型性能，如能产生强流高电荷态离子束流的高性能全永磁离子源LAPECR2，能产生强流中 低电荷态离子束流的LAPECR1，能产生多电荷态重金属离子束流的LAPECR1-M 等。这些性能稳定的离子源为提高近代物理研究所相关试验平台的性能提供了关键的束流品质保障。

Effects of magnetic configuration on hot electrons in highly charged ECR plasma

To investigate the hot electrons in highly charged electron cyclotron resonance (ECR) plasma, Bremsstrahlung radiations were measured on two ECR ion sources at the Institute of Modern Physics. Used as a comparative index of the mean energy of the hot electrons, a spectral temperature, Tspe, is derived through a linear fitting of the spectra in a semi-logarithmic representation. The influences of the external source parameters, especially the magnetic configuration, on the hot electrons are studied systematically. This study has experimentally demonstrated the importance of high microwave frequency and high magnetic field in the electron resonance heating to produce a high density of hot electrons, which is consistent with the empirical ECR scaling laws. The experimental results have again shown that a good compromise is needed between the ion extraction and the plasma confinement for an efficient production of highly charged ion beams. In addition, this investigation has shown that the correlation between the mean energy of the hot electrons and the magnetic field gradient at the ECR is well in agreement with the theoretical models.中文摘要：ECR(电子回旋共振)离子源是产生稳定的强流多电荷态离子束流最有效装置。全永磁 ECR 离子源因其独特的特点为很多中小型多电荷态离子束流实验平台与离子注入机等系统所采用，为后者产生重复性好、稳定性强的多电荷态离子束流。本文着重论述了中国科学院近代物理研究所研制的几台全永磁多电荷态ECR离子源及其特性与典型性能，如能产生强流高电荷态离子束流的高性能全永磁离子源LAPECR2，能产生强流中低电荷态离子束流的LAPECR1，能产生多电荷态重金属离子束流的LAPECR1-M等。这些性能稳定的离子源为提高近代物理研究所相关试验平台的性能提供了关键的束流品质保障。