Research in Secondary Ion and Neutral Mass Spectrometry

在分析和表面化学计划的支持下，德克萨斯A&M大学的Emile Schweikert教授和他的同事们正在开发表面质谱学的新方法。研究重点是从KeV单原子和多原子弹丸轰击表面时产生的抛射物中提取更多信息。一个目标是通过检测巧合发射的二次离子来实现纳米相表征。该方法依赖于“质量分离飞行时间质谱学”的新概念。第二个目标是提高检测灵敏度，这转化为检测中性物质的要求。该方法是在常压下碰撞冷却解吸的中性分子，将它们收集到超音速分子束中，并对它们进行有效的高温电离，以便随后通过飞行时间质谱仪进行鉴定。除了增强检测灵敏度外，该程序对不易在真空中进行检测的表面也很有用。本项目致力于提高检测表面的化学分析专业知识。以纳米结构为重点的表面科学和技术的进步要求检测到数量极少的分子。这项研究旨在提高我们识别纳米结构的化学组成和检测分散在表面上的少量分子的能力。这项工作将集中在两种新的质谱学方法上。一种基于“质量分离飞行时间质谱学”的方法有望实现对小到30 nm的纳米结构域的化学分析。另一种是“常压二次中性质谱学”，其目标是检测分子随机分布在表面(而不是组装在纳米结构中)时，以及它们以目前技术无法检测到的数量存在时的情况。

In research supported by the Analytical and Surface Chemistry Program, Professor Emile Schweikert and his coworkers at Texas A&M University are developing new methods for mass spectrometry of surfaces.The research focuses on extracting more information from the ejecta generated when bombarding surfaces with keV mono and polyatomic projectiles. One objective is to achieve nanophase characterization via the detection of coincidentally emitted secondary ions. The approach relies on the novel concept of "mass separated time-of-flight mass spectrometry". A second objective is to advance detection sensitivity, which translates into the requirement of detecting neutrals. The approach is to collisionally cool the desorbed neutrals at ambient pressure, collect them into a supersonic molecular beam and subject them to efficient hyperthermal ionization for subsequent identification by time-of-flight mass spectrometry. In addition to enhanced detection sensitivity, the procedure should be useful for surfaces not readily amenable to examination in vacuum.This project deals with advancing chemical analysis expertise for examining surfaces. Progress in surface science and technology with emphasis on nanostructures requires the detection of vanishingly small amounts of molecules. The research aims to enhance our capabilities for identifying the chemical makeup of nanostructures and for detecting small numbers of molecules dispersed on a surface. The work will focus on two novel methods of mass spectrometry. One based on "mass-separated time-of-flight mass spectrometry" is expected to enable chemical analysis of nanodomains as small as ~ 30 nm. The other involves "ambient pressure secondary neutral mass spectrometry" with the goal of detecting molecules when they are randomly distributed on a surface (rather than assembled in a nanostructure) and when they are present in amounts which cannot be detected with current techniques.