Combined particle- and time-of-flight mass spectrometry in flame-based nanoparticle synthesis

基于火焰的纳米颗粒合成是由均相气相反应、颗粒初始、生长、动力学和表面化学之间的复杂相互作用控制的。为了更深入地了解在层流、预混、低压、平焰反应器中合成纳米颗粒的过程，将使用分子束质谱仪研究反应时间和火焰成分(当量比、燃料、前体)的函数。在该项目的第一阶段，出现了利用飞行时间质谱仪(TOF-MS)分析气相化学并结合粒子质谱仪(PMS)测量颗粒尺寸分布的有希望的实验。我们首次能够测量金属氧化物团簇的浓度分布，这与第一批稳定的纳米颗粒在气相合成过程中的生长情况非常一致。这项提议的目的是继续在第一个资助期的提议中描述的研究战略。一项重要的改进将是在飞行时间质谱仪中使用带有VUV光子(9.8 eV)的单光子光电离，以减少多电荷团簇和分子碎片的形成。应该通过将详细的TOF-MS测量与非原位光电子能谱(XPS)和俄歇能谱(SAM)进行比较来验证研究在线粒子化学计量比的可能性。该项目的结果一方面将用于验证现有的用于火焰合成定制纳米材料的化学动力学机制，另一方面将用于在需要时建立新的反应机制。

Flame-based nanoparticle synthesis is governed by a complex interplay between homogeneous gas-phase reactions, particle inception, growth, and dynamics as well as surface chemistry. To establish a deeper understanding of the processes involved the synthesis of nanoparticles in a laminar, premixed, low-pressure, flat-flame reactor will be studied as a function of reaction time and flame composition (equivalence ratio, fuel, precursor) using molecular-beam mass spectrometry. Within the first period of the project, promising experiments utilizing analysis of gas-phase chemistry via time-of-flight mass-spectrometry (TOF-MS) in combination with particle-size distributions measured by particle mass spectrometry (PMS) emerged. For the first time we were able to measure concentration profiles of metal oxide clusters in good agreement with the growth of the first stable nanoparticles during gas-phase synthesis.The aim of this proposal is to continue the research strategy described in the proposal for the first funding period. One important improvement will be to use single-photon photoionization with VUV photons (9.8 eV) for the time-of-flight mass spectrometer to reduce the formation of multiply-charged clusters and molecular fragments. The possibility to study the stoichiometry of the particle inline should be validated by comparing detailed TOF-MS measurements with ex situ photo electron spectroscopy (XPS) and Auger spectroscopy (SAM). The results of the project will be used on the one hand to validate existing chemical kinetics mechanisms for the flame synthesis of tailored nanomaterials and on the other hand to establish new reaction mechanisms if needed.