MRI: Development of an Advanced Positron Beam System for Annihilation Spectroscopies of Surfaces, Interfaces and Nanostructures

摘要：这项授予德克萨斯大学阿灵顿分校的重大研究仪器奖支持开发用于材料研究的下一代高通量可变能量自旋极化正电子束仪器。完成后，该系统将成为世界上第一个能够利用自旋极化正电子束进行飞行时间正电子湮灭诱导俄歇电子能谱（PAES）和伽马-伽马能谱的系统。由于注入样品的低能正电子湮灭而发射的俄歇电子和伽马射线的光谱将用于获得有关材料的化学成分和结构的独特信息。由于正电子在湮灭之前被捕获，该仪器将具有高度的表面选择性和对开放体积缺陷的灵敏度。正电子将通过22Na源和高效的Ne慢化剂系统获得，以保持正电子的极化。这将使自旋相关测量成为可能，并且对于研究与非磁性材料相关的不寻常磁性的起源特别有用，这些材料显示出与缺陷相关的大磁矩。先进的正电子束系统提供的关于表面和纳米结构的元素含量、缺陷类型和缺陷浓度的独特信息，有可能在纳米磁性、高能积磁性材料、光催化、纳米粒子光致发光和摩擦学等领域取得突破性发现。本项目将为本科生、研究生和博士后提供开发和应用先进材料表征仪器的培训机会。摘要：该奖项来自主要研究仪器项目，支持德克萨斯大学阿灵顿分校开发下一代仪器，用于利用低能量正电子（反物质电子）束表征材料。完成后，该仪器将是世界上第一个将自旋极化与飞行时间相结合的仪器，正电子湮灭诱导俄歇电子能谱（PAES）和伽马-伽马能谱。从放射源发出的正电子将被植入地表以下的选定深度。对正电子湮灭时发射的伽玛射线和电子的能量分布的分析将提供有关表面和近表面空洞和缺失原子缺陷的元素含量和物理结构的独特信息。先进的光束系统提供的独特信息将在以下领域带来新的发现，包括纳米粒子超磁体的开发，可以吸收光并促进水分解以产生燃料氢的新型催化剂的开发，以及亚微观碳烟引起的摩擦的研究。本项目将为本科生、研究生和博士后提供设计、建造和应用先进材料表征仪器的培训机会。

1338130 WeissTechnical Abstract:This Major Research Instrumentation Award to the University of Texas at Arlington supports the development of a next generation high flux variable energy spin-polarized positron beam instrument for materials research. When completed the system will be the first in the world capable of performing time of flight Positron Annihilation induced Auger Electron Spectroscopy (PAES) and gamma-gamma spectroscopy utilizing a spin polarized positron beam. The spectra of Auger electrons and gamma rays emitted as a result of the annihilation of low energy positrons implanted into the sample will be used to obtain unique information about the chemical composition and structure of materials. The instrument will have a high degree of selectivity for surfaces and sensitivity to open volume defects due to the trapping of positrons prior to annihilation. The positrons will be obtained using a 22Na source and a high efficiency Ne moderator system designed to preserve the polarization of the positrons. This will enable spin dependent measurements and will be particularly useful for the study of the origin of the unusual magnetic properties associated with otherwise non-magnetic materials that show large magnetic moments associated with defects. The unique information provided by the advanced positron beam system regarding the elemental content, defect type and defect concentration of surfaces and nano-structures holds the potential to enable breakthrough discoveries in areas including nano-magnetism, high energy product magnetic materials, photo-catalysis, nano-particle photoluminescence, and tribology. This project will provide training opportunities for undergraduate, graduate, and post-doctoral researchers in the development and application of advanced instruments for the characterization of materials. Non-technical Abstract:This award from the Major Research Instrumentation program supports the University of Texas at Arlington with the development of a next generation instrument for the characterization of materials utilizing a beam of low energy positrons (anti-matter electrons). When completed the instrument will be the first in the world to combine spin polarization with a time of flight Positron Annihilation induced Auger Electron Spectroscopy (PAES) and gamma-gamma spectroscopy. Positrons emitted from a radioactive source will be implanted at a selected depth below the surface. An analysis of the distribution of energies of the gamma-rays and electrons emitted when the positrons annihilate will provide unique information regarding the elemental content and physical structure of surfaces and near surface voids and missing atom defects. The unique information provided by the advanced beam system will enable new discoveries in areas including the development of nano-particle based supermagnets, the development of new catalysts that can absorb light and promote the splitting of water to make hydrogen for fuel, and for the study of friction caused by submicroscopic carbon soot. This project will provide training opportunities for undergraduate, graduate, and post-doctoral researchers in the design, construction, and application of advanced instruments for the characterization of materials.