INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Corridor 22-23 - 3rd étage, salle 307

Laurent Pelliser, team Chemical Physics and Dynamics of Surfaces

« Organization and assembly of semi-conducting nanoparticles in networks of smectic topological defects »

Abstract This thesis discusses the use of a liquid crystal structure, called oily streaks, formed by the competition of two antagonist anchorings on each side of a submicrometric liquid crystal layer in smectic A phase. This structure is used to achieve the self-alignment and the organization, of single photon emitters on an individual scale with the possibility of a controlled modification of their optical properties for higher concentrations.

We present the internal layout of these oily streaks through measurements done in polarized optical microscopy, ellipsometry and X-ray diffraction analysis. These data sets are correlated in into a description of the internal structure of the oily streaks, characterized by the formation of a pattern of oriented topological defects. These streaks are then used as a template to align single photon emitters, CdSe:CdS dot-in-rods, on an individual scale alongside the main axis of the defects. The measurement of the alignment of their dipoles as well as their degree of polarization allows us to discuss the behaviour of the particles in the topological defects of the oily streaks. Finally is discussed a statistical analysis of the behaviour of nanoparticles in oily streaks once their concentration is increased, depending on their size in number of particles as well as the structure of the defects in which the single particles or the clusters are trapped. We observe an alignement of the particles both on the individual and cluster levels as well as a conservation or a reinforcement of their degree of polarization. This last element could be caused by dipolar interactions orginating in the auto-organisation of these particles, itself controlled by the thickness of the liquid crystal film.

Composition of jury

• Emmanuelle LACAZE – Thesis director
• Doru CONSTANTIN – Protractor
• Thierry GACOIN – Protractor
• Teresa LOPEZ-LEON – Examinator
• Régine PERZYNSKI – Examinator
• Charles ROSENBLATT – Examinator