Resumen de Optical manipulation of quantum dots and single magnetic nanostructures
Optical trapping is a technique based on the contactless manipulation of micro and nano-objects by means of a focused laser beam. In the present thesis, experiments were performed in a weakly focused optical trap, which allows the direct measurement of the optical forces exerted on the trapped object. Due to this peculiarity, optical forces exerted on generic individual nanoparticles have been studied and the conditions under which a stable trap is formed have been determined. These conditions have been verified for individual iron oxide nanoparticles encapsulated in silica, and the photoinduced heating resulting from the absorption of light from the laser has been investigated. The theoretical results have been experimentally verified by means of the study of the viscosity in the environment of the trapped nanoparticle, whose decrease when increasing the power of the laser is related to heating. Likewise, it has been shown that the same experimental conditions do not allow the manipulation of individual colloidal quantum dots encapsulated in silica. On the contrary, aggregates of these nanoparticles are easily trapped and show photoluminescence as a result of a two-photon absorption process. The photodynamic processes affecting their emission and limiting their use as remotely controlled sensors have been studied. It has been observed that the isolation of the quantum dots by means of a sulfur intermediate passivating layer and a silica cover delays their degradation in the optical trap. Finally, the manipulation of silver sulfide nanoparticles, which show great interest in fluorescence microscopy in the near-infrared range, is demonstrated.
