Polarized Electron Physics

极化电子物理

• 批准号: 1806771
• 负责人: Timothy Gay
• 金额: $ 57万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1806771&HistoricalAwards=false
• 关键词: Polarized; Electron; Physics

Electrons have the fundamental property of "spin," which is analogous to that of a spinning toy top, and is associated with their angular momentum. This project studies collisions between polarized electrons, which have their spins aligned in one direction, and chiral, or "handed" molecules. Such molecules, of which DNA is an example, are characterized by a spiral, or helical geometry. These experiments address physics questions about the dynamics of electron-chiral molecule scattering, particularly with regard to the role played by the electron spins. They will also provide important clues about the origins of biological homochirality - the fact that all naturally-occurring DNA spirals in the same direction. Atoms of zinc are also being used as targets, to check the results of an experiment done recently by another group in which zinc atoms excited by polarized electrons emitted light in a way that is forbidden by all known theories of atomic collisions. If that result is reproduced, much of the basic theoretical knowledge about spin-polarized electron-impact-excitation physics would need to be revised. Improved sources of polarized electrons are also being developed in this project, with the goal of making "turnkey" components that will be easily integrated into other experimental systems. Two particular ways to make polarized electrons are being investigated in this project. The first involves electron collisions with rubidium atoms in which spin is transferred from the rubidium to the free electrons. The second uses multiphoton ionization of semiconductors such as gallium arsenide (GaAs) to give the electrons a preferential spin direction. This research to develop polarized electron technology holds the promise of providing new analytical tools that can be used for biological and materials research, and for industry. Experiments involving collisions between polarized electrons and chiral molecules will extend previous work that showed chiral sensitivity in both quasi-elastic and reactive scattering with halocamphor targets. Now that such sensitivity has been observed, the goal is to demonstrate such effects in molecules that have biological significance, such as cysteine, and to study the effect of the maximum target nuclear charge and location of the target's chiral center on the chiral asymmetries we observe. The goal in the Zn experiments is to check whether the rather large value of canted linear polarization (polarization fraction P2) observed in fluorescence from excited Zn atoms is reproducible. No extant theory of electron-atom scattering, including the state-of-the-art "R-matrix with pseudostates" approach, has been able to confirm this result, even though they make quantitatively accurate predictions of other collision parameters for this system. Source development work will be based on the successfully demonstrated "Rb spin-filter" design by the group, in which optically-pumped Rb undergoes spin-exchange collisions with an incident unpolarized beam of electrons. This project will focus on improving the vacuum system, the Rb target reliability, and the optical pumping protocol. It will also study a variety of buffer gases to understand the complex physics of the interaction between the electron beam and the Rb vapor. In the GaAs experiment, unamplified pulses from a femtosecond Ti:Saph oscillator are used to photo-emit electrons. First experiments will investigate the intensity and polarization of the electrons emitted from bulk GaAs and tip-like GaAs shards. Then targets of GaAs cusp arrays will be considered.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

电子具有“自旋”的基本性质，这类似于旋转的玩具顶部，并与它们的角动量有关。这个项目研究极化电子与手性分子之间的碰撞，极化电子的自旋方向是一个方向。以DNA为例的这类分子具有螺旋或螺旋几何结构的特征。这些实验解决了有关电子-手性分子散射动力学的物理问题，特别是关于电子自旋所起的作用。它们还将提供关于生物同性起源的重要线索--所有自然发生的DNA都朝着同一方向螺旋的事实。锌原子也被用作靶子，以检查另一个小组最近进行的一项实验的结果。在该实验中，被极化电子激发的锌原子以一种所有已知的原子碰撞理论都禁止的方式发光。如果这一结果重现，许多关于自旋极化电子碰撞激发物理的基本理论知识将需要修改。在这个项目中，还在开发改进的极化电子源，目标是制造易于集成到其他实验系统中的“交钥匙”组件。在这个项目中，人们正在研究两种制造极化电子的特殊方法。第一个涉及电子与Rb原子的碰撞，其中自旋从Rb原子转移到自由电子。第二种是利用半导体的多光子电离，如砷化镓(GaAs)，使电子有一个优先的自旋方向。这项旨在开发极化电子技术的研究有望提供可用于生物和材料研究以及工业的新分析工具。涉及极化电子和手性分子之间碰撞的实验将扩展先前的工作，即在与卤素目标的准弹性和反应散射中显示手性敏感性。既然已经观察到了这种敏感性，我们的目标是在具有生物学意义的分子中展示这种效应，例如半胱氨酸，并研究最大靶核电荷和靶手性中心位置对我们观察到的手性不对称性的影响。锌实验的目的是检查在被激发的锌原子的荧光中观察到的相当大的斜线性极化(极化分数P2)是否可重现。现有的电子-原子散射理论，包括最先进的“具有赝态的R矩阵”方法，都不能证实这一结果，尽管它们对该系统的其他碰撞参数进行了准确的定量预测。光源的开发工作将基于该小组成功演示的“RB自旋过滤器”设计，在该设计中，光泵浦的RB与入射的未极化电子束进行自旋交换碰撞。该项目将重点改进真空系统、RB靶标可靠性和光泵浦方案。它还将研究各种缓冲气体，以了解电子束和Rb蒸气之间相互作用的复杂物理。在砷化镓实验中，利用飞秒Ti：SAPH振荡器产生的未放大脉冲发射电子。首先，实验将研究从块状和尖端状的砷化镓碎片发射的电子的强度和极化。这项裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Helmholtz spacing of thin rectangular magnetic field coils

薄矩形磁场线圈的亥姆霍兹间距

• DOI: 10.1063/5.0023024
• 发表时间: 2020
• 期刊: Review of Scientific Instruments
• 影响因子: 1.6
• 作者: Ahrendsen, K. J.;Reyes, S.;Gay, T. J.
• 通讯作者: Gay, T. J.

High precision 5 MeV Mott polarimeter

高精度5 MeV莫特旋光计

• DOI: 10.1103/physrevc.102.015501
• 发表时间: 2020
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Grames, J. M.;Sinclair, C. K.;Poelker, M.;Roca-Maza, X.;Stutzman, M. L.;Suleiman, R.;Mamun, Md. A.;McHugh, M.;Moser, D.;Hansknecht, J.
• 通讯作者: Hansknecht, J.

Femtosecond-laser-induced spin-polarized electron emission from a GaAs tip

GaAs 尖端的飞秒激光诱导自旋极化电子发射

• DOI: 10.1063/1.5070059
• 发表时间: 2019
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Brunkow, Evan;Jones, Eric R.;Batelaan, Herman;Gay, T. J.
• 通讯作者: Gay, T. J.

Spin-polarized electron transmission through chiral halocamphor molecules

通过手性卤樟脑分子的自旋极化电子传输

• DOI: 10.1088/1361-6455/aae1bd
• 发表时间: 2018
• 期刊: Molecular and Optical Physics
• 作者: Dreiling, J M;Lewis, F W;Gay, T J
• 通讯作者: Gay, T J

Spin- and angle-resolved photoemission studies of the electronic structure of Si(110)“ 16×2 ” surfaces

Si(110)—16—2—表面电子结构的自旋和角度分辨光发射研究

• DOI: 10.1103/physrevb.100.075302
• 发表时间: 2019
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Lewis, N. K.;Lassailly, Y.;Martinelli, L.;Vobornik, I.;Fujii, J.;Bigi, C.;Brunkow, E.;Clayburn, N. B.;Gay, T. J.;Flavell, W. R.
• 通讯作者: Flavell, W. R.