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Synthesis and Application of Magnetic/Plasmonic Anisotropic Nanostructures

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Anisotropic properties of both magnetic and plasmonic nanostructures make them interesting research topics, as the shape anisotropy of the magnetic nanorods could be used to control their orientation and that of the plasmonic nanostructures attached to them. Thus, by applying an external magnetic field, instantaneous and reversible tuning of the plasmonic property of anisotropic metal nanostructures could be achieved. This holds great promises for developing novel optoelectronic devices and effective chemical and biomedical sensors. This dissertation discusses our efforts in the synthesis and application of magnetic/plasmonic anisotropic nanostructures.

Firstly, uniform nonmagnetic β-FeOOH nanorods with different sizes and aspect ratios were synthesized by the hydrolysis of FeCl3. Parameters influencing the synthesis, such as the concentration of reagents, different ligands, and temperature, were systematically studied. The indirect synthesis of magnetic iron oxide nanorods was achieved by a post-reduction method.

Then we successfully synthesized the anisotropic magnetic/plasmonic Fe3O4 NRs@SiO2@Au core-shell nanocomposites by combining a post-reduction and a seeded growth method. The nanocomposites exhibited angle-dependent plasmonic property. Furthermore, we demonstrated the nanocomposites array, when fixed inside a polymer film, could find unique applications for information encryption. In particular, we have fabricated a six-column nanocomposite array film and demonstrate that it could realize multi-level information encryption. Taking advantage of the instantaneous tuning over the orientation of the nanocomposites in solution, we extended the working principle and fabricated a new type of magnetic field direction sensor. An actuator system which consists of the sensor and a MeArm base servo motor vividly showed the performance of the sensing ability.

Finally, we demonstrated that the confined growth of gold and silver nanorods within resorcinol-formaldehyde (RF) resin could be realized by using β-FeOOH nanorods as sacrificial templates through a seeded growth method. The RF shell is flexible and stretchable, due to its polymer nature, which offers more size tunability within one Au seed@RF template. At the same time, partially reduced FexOy@RF could serve as the reducing agent, and facilitate the gold shell formation between FexOy nanorod and RF layer. More efforts will be put into the investigation of formation mechanism and optimization of the shell quality.

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