Synthese de nanostructures d'oxyde de zinc par procede laser

The main objective of this thesis was to develop a new manufacturing technique allowing the local synthesis of nanostructures on a surface for their eventual integration into nanodevices. The desired process has to be selective, reproducible, versatile, simple, fast and inexpensive for potential industrial utilization. Moreover, the manufacturing process must have a minimal environmental impact for sustainable development. To implement the required specifications, a laser process combining the characteristics of laser-induced chemical liquid deposition (LCLD) and of sol-gel synthesis was proposed. The technique is very simple and consists of three steps. A precursor solution is first prepared. Next, a droplet of a controlled volume is transferred on a substrate by means of a micropipette. The droplet is then irradiated using a laser emitting in the infrared to induce the fast synthesis of nanostructures.;In order to prove the feasibility of the manufacturing concept for the synthesis of nanostructures, the new process was used for the synthesis of zinc oxide (ZnO) nanostructures. ZnO has become one of most studied nanomaterials in the five last years as it presents very interesting properties for optoelectronics and sensing applications, while being synthesizable in a plethora of nanoscale morphologies. Using laser processing, the deposition of coatings of several square millimetres of various nanostructures (nanorods, nanowires, porous films of nanoparticles) was carried out. In particular, nanorods with an average width of 300 nm and a length of two micrometers with hexagonal cross-sections and almost atomically flat surfaces were synthesized. Nanowires with diameters of approximately 50 nm and lengths exceeding four micrometers were also grown. This constituted an innovation among the laser processing techniques, as only laser-induced chemical vapour deposition (LCVD) and pulsed laser deposition (PLD) had been used to produce ZnO, and just in the form of thin films and nanoparticles.;One of the secondary objectives of this thesis was to improve the properties of the deposits for one of the target applications of ZnO, photoluminescent devices. For this reason, a parametric study was carried out during which the influence of the laser-related parameters (irradiation time, intensity) and of the solution-related parameters (precursor, additives, concentration) on morphology and crystallinity was studied. The use of scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that an increase in laser intensity and irradiation time increased nanostructure length and XII crystallite size. Transmission electron microscopy (TEM) demonstrated that the nanorods grew along the c axis of the crystal lattice, at the apex of randomly oriented ZnO crystals forming a seed layer on the substrate. Additionally, an increase in precursor concentration was found to increase the thickness of this seed layer and the introduction of additives in the solution had the effect of promoting the vertically aligned growth of nanorods. Raman and photoluminescence (PL) spectroscopy also showed that the deposits were of high quality with few crystalline defects. In particular, the PL spectroscopy results gave evidence that the ZnO nanostructured deposits produced by the laser process were good for ultraviolet emission applications with the presence of an intense peak at 390 nm. The extensive characterization of the samples also allowed the development of a qualitative growth model for the laser-grown ZnO nanostructures inspired by the growth and nucleation models used for conventional chemical synthesis in a liquid medium. (Abstract shortened by UMI.)...