In situ studies of particle properties during their formation and growth with optical second-harmonic generation

• Applicant: Professor Dr.-Ing. Wolfgang Peukert
• Subject Area: Mechanical Process Engineering
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260796254

The objective is the development of optical second harmonic generation (second harmonic scattering, SHS) and two-photon fluorescence (2-PF) as methods for in situ investigations of particle formation, growth and surface modifications of nanoparticles < 50 nm. SHS as a non-invasive nonlinear scattering spectroscopy is highly sensitive to changes of particle size, particle shape and of the surface of nanoparticles. The ligand exchange at the surface of nanoparticles < 50 nm can be followed with SHS with high time resolution and allowed for the discrimination of different adsorption steps and surface sites besides gaining thermodynamic information. Alternatively, particle properties of semiconducting quantum dots (down to sizes of 2 -3 nm) can be obtained from 2-PF. In addition, 2-PF enables the investigation of the formation of defects of the particles.Particle formation of metallic and semiconducting nanoparticles will be studied in a T-mixer with SHG and 2-PF, respectively. In combination with in situ UV-Vis spectroscopy and TEM the kinetics of particle growth will be studied. By variation of system parameters the influence of the stabilizer on the particle formation kinetics will be investigated. For ZnO quantum dots a special focus will be put on the formation of defects during particle growth.In the next step, the ligand exchange at the surface of metallic nanoparticles of different sizes will be studied with in situ SHS in order to resolve the dependence of kinetics and thermodynamics of the ligand exchange on differently sized particles. Besides yielding kinetic information the surface coverage of the ligands and thereby the efficiency of the ligand exchange will be determined. For the fast adsorption of catechol on ZnO the T-mixer will be used.In the last step, the simultaneous application of both SHS and 2-PF for particle measurement will be studied. Therefore, 2-PF and SHS of quantum dots will be investigated in dependence of the particle size, excitation wavelength and surface modification.

• DFG Programme: Research Grants