Correlative optical and scanning probe microscopy of silicon quantum dots

In this work, we tackle some of the interesting and unresolved questions of the microscopic origin of emission from silicon quantum dots (Si-QDs). In particular, our interest is mainly in Si-QDs that exhibit a fast radiative rate, which is interesting for the applications in lighting and photovoltaics, suggesting a high oscillator strength. This is in literature mostly reported from the organically capped Si-QDs, which are the central material of this thesis. In chapter 2 we critically assess a main synthesis route for organically capped Si-QDs, arguing that there is an important need to separate the contribution of Si-QD emission from that of carbon quantum dots that may also be formed. In chapter 3 and 4 we address the dependence of quantum dot emission on ligand choice, examining the dependence of emission on pH, and examining physics of the transition dipole moment through a study of photoluminescence polarization anisotropy. Finally, to better understand the size-effect in such QDs, we assembled a correlative system that allows us to perform a single dot optical microscopy and atomic force microscopy (AFM) for a single QD at the same time (or in a fast sequence). We demonstrate its importance for analysis of emission origin in Si-QDs in Chapter 5, while leveraging it to study a new type of mesoscopic quantum dot assemblies in Chapter 6. These assemblies may have applications as countermeasure against counterfeiting.