Laser-based diagnostics for the in situ characterization of non-soot nanoparticles

• Applicant: Professor Dr. Christof Schulz
• Subject Area: Chemical and Thermal Process Engineering ; Energy Process Engineering
• Term: from 2013 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 222540104

Methods that allow an in situ characterization of inorganic nanoparticles during gas-phase synthesis are only little explored - despite the importance to produce defined product qualities. This deficiency is not only due to the poorly known optical properties of such nanomaterials but also because experiments are missing enable direct comparison of optical in situ measurements and conventional (ex situ) particle characterization. The aim of this project is, based on laser-induced incandescence (LII) as a method established for soot diagnostics, to further develop diagnostics for particle size and volume fraction of the inorganic materials systems silicon (Si), germanium (Ge), iron (Fe), and copper (Cu). New insights obtained for Si within the project SCHU 1369/14-1 will be further deepened towards applicability and extended to the other material systems whose optical properties are so far incompletely known in the relevant temperature range. The nanoparticles are generated and optically analyzed in a microwave-plasma reactor at pressures between 30 and 900 mbar. First, the wavelength-dependent absorption function (E(m)) will be determined via line-of-sight absorption (LOSA) investigating the optical properties of the particles both in the absence and the presence of a heating laser pulse that is used for LII. Photodiodes or a combination of a spectrometer and a streak camera will serve as detection units. It is also planned to demonstrate the applicability of a phenomenon that has been discovered for Si in the first proposal period: Liquid-solid phase transitions can be observed via their absorption/emission spectra. This will also be further pursued for the other materials systems. In addition, fluence-dependent incandescence spectra and their temporal development (time-resolved LII) will be recorded for all materials systems and analyzed with respect to their emission properties in the context of particle-size determination. Fluence values will be increased into the range where full particle evaporation is achieved without gas breakdown. This allows to explore the origin of non-thermal emissions that can interfere with the LII signal (Bremsstrahlung, "anomalous cooling" during the LII-process). Particle-based atomic emissions will be investigated (intensity, emission lifetimes) during low-fluence LIBS (laser-induced breakdown) processes in the context of practical applicability. With the optical measurements, particle-size distributions will be determined using inline particle mass spectrometry (PMS) from within the same probe volume. In addition, by thermophoretic sampling and ex situ transmission electron microscopy (TEM) and Raman analysis, particle size and crystallinity will be investigated. All results taken together will strongly increase our knowledge in in particle optical properties and diagnostics and provide valuable input parameters for the underlying models that are required for quantitative analysis of LII and LIBS signals.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Thomas Dreier