Jury :

Supervisors:
Dr. Louis BIADALA (IEMN - CNRS) - Director of thesis
Prof. Iwan MOREELS (PCN group, Ghent University) - Co-supervisor

The committee consists of:
Dr. Bruno GRANDIDIER (IEMN-CNRS) - Committee President
Dr. Amandine BELLEC (MPQ - CNRS, Paris Cité University) - Reviewer
Prof. Sandrine ITHURRIA (ESPCI-Paris, PSL Research University, Sorbonne)
University) - Reviewer
Dr. Benoit MAHLER (ILM - Claude Bernard Lyon 1 University) - Examiner
Prof. Jean-Pierre HERMIER (University of Versailles St-Quentin-en-Yvelines) - Examiner
Prof. Jolien DENDOOVEN (Ghent University) - Examiner

Summary:

Colloidal nanoplatelets (NPLs) (e.g. CdSe, PbSe) are an interesting class of nanomaterials, which have attracted considerable attention due to the combination of their specific shape with unique electronic properties. For example, CdSe LNPs exhibit a strong quantum confinement effect along the thickness, resulting in tunable optoelectronic properties. However, colloidal NPLs contain numerous surface defects caused by structural flaws and unpassivated dangling bonds (DBs), which greatly reduce the quantum efficiency of PL. Not all dangling links are detrimental to potential NPL applications. Surface DB spins have been shown to modify the optical and magnetic properties of CdSe NPLs, via their interactions with a localised electron spin in the NPLs. These spin interactions give rise to interesting magneto-optical effects in CdSe NPLs. To exploit NPLs in optoelectronic applications, an in-depth understanding of their fundamental properties, at the scale of an individual nanocrystal, is required. In this thesis, we used low-temperature scanning tunneling microscopy (LT-STM) and spectroscopy (STS) to study the structural and electronic properties of individual NPLs at the nanoscale. In addition, we used magneto-photoluminescence (PL) spectroscopy to study the optical properties of CdSe and CdSe/CdS core/crown. The results obtained provide an insight into the structure of electronic bands (e.g. band gap, defect states, etc.) and the optical properties of NPLs, in particular quantum confinement and magneto-optical effects.

Abstract:

Colloidal nanoplatelets (NPLs) (e.g. CdSe, PbSe) are an interesting class of nanomaterials, that have attracted considerable attention due to the combination of their specific shape with unique electronic properties. For example, CdSe NPLs exhibit a strong quantum confinement effect along the thickness, resulting in tunable optoelectronic properties. However, colloidal NPLs contain many surface defects caused by structural defects and unpassivated dangling bonds (DBs), which strongly reduces the PL quantum efficiency. Not all dangling bonds are harmful to the potential applications of NPLs. Surface DB spins have been shown to alter the optical and magnetic properties of CdSe NPLs, via their interactions with an electron spin localized in NPLs. These spin interactions cause interesting magneto-optical effects in CdSe NPLs. To exploit NPLs in optoelectronic applications, a deep understanding of their fundamental properties, at the scale of an individual nanocrystal, is necessary. In this thesis, we used low-temperature scanning tunneling microscopy (LT-STM) and spectroscopy (STS) to investigate the structural and electronic properties of individual NPLs at the nanoscale. In addition, we used magneto-photoluminescence (PL) spectroscopy to investigate the optical properties of CdSe and CdSe/CdS core/crown NPLs. The obtained results provide insight into the electronic band structure (e.g. band gap, defect states...) and optical properties of NPLs, in particular quantum confinement and magneto-optical effects.