IRTG 2022 "ATUMS" - Project 6.

Project 6. Tuning electronic and chiroptical properties of Si-nanoparticles by size and chemical environment


TUM: Heiz, Rieger
UofA: Meldrum, Veinot
Students: Lorenzo Chille


Abstract:

Results of the first ATUMS phase demonstrate photoluminescence (PL) to be strongly size dependent for SiNCs with sizes as large as ∼10 nm. Whereas down to sizes of ∼2 nm we expect a monotonous and scalable blue-shift of PL, nothing is known about the PL when going to sizes as small as a couple of atoms, i.e. Si clusters. One of the main questions to be answered here is, at what size the band structure of the particles collapse and their optical response is dominated by molecular transitions. Another aspect will be the functionalization of SiNCs with chiral ligands. We will develop recipes for nanoparticles preparation to achieve an efficient chirality transfer and expect the influence of chiral ligands to be much stronger for smaller Si particles and clusters. To prepare truly monodispersed cluster samples, we will use the established methodology to generate Si clusters in the gas phase by using laser vaporization techniques coupled with supersonic expansion and mass selection. These will be compared with the wet chemically prepared SiNCs. The intrinsic properties of the clusters and nanoparticles can be characterized by a large portfolio of spectroscopic tools including surface second harmonic generation (s-SHG) and cavity ring-down (CRD) spectroscopies. Induced chiroptical properties of the particles will be routinely probed by commercial CD (circular dichroism) spectroscopy or by a more sensitive nonlinear method of second harmonic generation circular dichroism (SHG-CD). Other methods that are available or will be established for (in-situ) characterisation and comparison of Si clusters and nanoparticles include XPS, XRD, TEM, MIES, UPS, PL, FTIR, Auger spectroscopy, etc. With our studies, we aim at the fundamental understanding of the band gap evolution and the related optical properties of SiNCs with size and changing chemical environment including the mechanism of chirality transfer.