MRI: Development of a Secondary Ion Mass Spectrometer Using a Laser Multicharged Ion Source

这项主要研究仪器（MRI）奖将开发一种二次离子质谱仪，该质谱仪比目前的商用仪器灵敏度更高，深度分辨率也更好。二次离子质谱法用于固体表层的化学分析，具有高达百万分之一的灵敏度和纳米深度分辨率。在这种化学分析方法中，使用离子束从样品的最外表面去除物质。这种光束被称为主离子束。一些被移除的材料失去电子，形成二次离子，与中性离子一起逃离研究材料的表面。然后对这些次级离子进行分析，找出它们的质量，从而得出材料成分。二次离子与中性离子之比的增加增加了检测灵敏度和分辨率。目前的商用二次离子质谱仪使用单电荷离子从样品表面去除分子。在本项目中，将使用激光烧蚀产生的多电荷离子作为一次离子，这可以提高研究样品中二次离子与中性离子的比例，从而提高化学检测的灵敏度和分辨率。开发的仪器将使超薄层的化学分析用于纳米电子学的高速计算机，先进的电子设备和传感器。该仪器还将使基础研究能够更好地理解多电荷离子与材料的相互作用，从而推进多电荷离子在纳米制造中的应用。至少有三名博士生将参与仪器的开发，而许多教师、研究生和本科生将在仪器投入使用后使用。此外，在项目期间，20-24名老道明大学的本科生将参与该项目，作为其工程和物理高级项目的一部分，2-4名加州大学伯克利分校的本科生将参与仪器离子束组件的模拟。该项目将开发一种二次离子质谱仪（SIMS），其灵敏度比目前的商用SIMS高，深度分辨率也更好。关键的技术改进是利用紧凑激光离子源产生的多电荷离子（MCI）脉冲作为主光束。目前的商业SIMS使用单电荷离子或簇作为主光束，通过从样品表面碰撞溅射引起二次离子喷射。除了碰撞溅射外，具有高势能的多电荷一次离子还会引起势能溅射，其中二次光束的电离分数可能比单电荷离子或簇高出两到三个数量级。较高的电离分数导致SIMS的灵敏度和深度分辨率相应提高。脉冲激光将用于烧蚀铋或金目标，产生强烈的MCIs源。这些离子脉冲将被加速并缩短到几纳秒。然后，将选择特定的电荷并将其入射到待分析的样品上。将建立一个飞行时间离子光谱仪来确定次级离子的质量。仪器的灵敏度、质量分辨率、深度和横向分辨率将在静态和动态SIMS下进行测试。MCI-SIMS将实现浅层注入掺杂剂的元素深度分析，识别薄膜和超薄层表面区域的组成，大大减少了预平衡区域和混合效应，并为基于注入的量子器件提供纳米级离子注入。该仪器将为进一步研究MCI与表面的相互作用以及MCI-表面相互作用与激光表面激发之间的协同作用提供基础。至少有三名博士生将参与MCI-SIMS的开发，而许多教师、研究生和本科生将在投入使用后使用该仪器。此外，在四年的时间里，20-24名老道明大学的本科生将参与该项目，作为他们工程毕业设计和物理毕业论文的一部分，2-4名加州大学伯克利分校的本科生将被介绍到细胞内粒子模拟作为本科研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThis Major Research Instrumentation (MRI) award will develop a secondary ion mass spectrometer with higher sensitivity than current commercial instruments and also with better depth resolution. Secondary ion mass spectrometry is used for chemical analysis of the surface layer of solids with up to part per million sensitivity and nanometer depth resolution. In this chemical analysis method, an ion beam is used to remove material from the outermost surface of the sample. This beam is referred to as the primary ion beam. Some of the removed materials lose electrons forming secondary ions that escape the surface of the studied material along with neutrals. These secondary ions are then analyzed to find their mass which yields the material composition. An increase in the ratio of secondary ions to neutrals increases the detection sensitivity and resolution. Current commercial secondary ion mass spectrometers use singly-charged ions to remove molecules from the surface of the sample. In this project, multicharged ions from laser ablation will be used as the primary ions, which can enhance the ratio of secondary ions to neutrals from the studied sample and, correspondingly, increase chemical detection sensitivity and resolution. The developed instrument will enable the chemical analysis of ultrathin layers used in nanoelectronics for high-speed computers, advanced electronic devices, and sensors. The instrument will also enable fundamental studies to better understand the interaction of multicharged ions with materials, therefore, advancing the use of multicharged ions in nanofabrication. At least three Ph.D. students will be involved in the development of the instrument, while many faculty and graduate and undergraduate students will utilize the instrument once it is commissioned. Also, over the duration of the project, 20‒24 Old Dominion University undergraduate students will participate in the project as part of their engineering and physics senior projects, and 2‒4 University of California-Berkeley undergraduate students will participate in the simulation of the ion beam components of the instruments. TECHNICAL SUMMARYThis project will develop a secondary ion mass spectrometer (SIMS) with higher sensitivity than current commercial SIMS and also with better depth resolution. The key technological improvement is the use of multicharged ion (MCI) pulses generated from a compact laser ion source as the primary beam. Current commercial SIMS uses singly-charged ions or clusters for the primary beam, which causes secondary ion ejection by collisional sputtering from the surface of a sample. Multicharged primary ions with high potential energy cause potential energy sputtering in addition to collisional sputtering, in which the ionization fraction for the secondary beam can be two-to-three orders of magnitude higher than for singly-charged ions or clusters. The higher ionization fraction results in a corresponding increase in SIMS sensitivity and depth resolution. A pulsed laser will be used to ablate bismuth or gold targets, producing an intense source of MCIs. These ion pulses will be accelerated and shortened to a few nanoseconds. Then, a specific charge will be selected and incident on the sample to be analyzed. A time-of-flight ion spectrometer will be built to identify the mass of the secondary ions. The instrument sensitivity, mass resolution, and depth and lateral resolutions will be tested under static and dynamic SIMS. The MCI-SIMS will enable elemental depth profiling of shallow-implanted dopants, identification of the composition of the surface region of thin films and ultrathin layers with much reduced pre-equilibrium region and mixing effects, and nanoscale ion implantation for implantation-based quantum devices. The instrument will enable further research on MCI interaction with surfaces and the study of synergy between MCI-surface interaction and laser surface excitation. At least three Ph.D. students will be involved in the development of the MCI-SIMS, while many faculty and graduate and undergraduate students will utilize the instrument once it is commissioned. Also, over the four years, 20‒24 Old Dominion University undergraduate students will participate in the project as part of their engineering capstone senior design and physics senior thesis, and 2‒4 University of California-Berkeley undergraduate students will be introduced to particle-in-cell simulation as undergraduate research.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.