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、颗粒起始、生长和动力学以及表面化学之间复杂的相互作用所控制的。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，将使用分子束质谱法研究反应时间和火焰组成（等效比、燃料、前驱体）的函数。在项目的第一阶段，利用飞行时间质谱法（TOF-MS）分析气相化学，结合粒子质谱法（PMS）测量颗粒大小分布的有希望的实验出现了。我们第一次能够测量出与气相合成过程中第一个稳定纳米颗粒生长良好一致的金属氧化物簇的浓度分布。本提案的目的是在第一个资助期继续执行提案中所述的研究策略。一个重要的改进将是在飞行时间质谱仪中使用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。通过将详细的TOF-MS测量结果与非原位光电子能谱（XPS）和俄歇能谱（SAM）进行比较，验证了研究颗粒在线化学计量学的可能性。该项目的结果一方面将用于验证火焰合成定制纳米材料的现有化学动力学机制，另一方面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.