Resumen de Electrodeposició de capes metàl.liques per a la seva incorporació en sensors i actuadors / Metallic films deposition for their incorporation in sensors and actuators
Meritxell Cortés Francisco
Electrodeposition involves chemical phenomena associated with charge separation and transfer that can occur homogeneously in solution, or heterogeneously over electrode surfaces. In order to assure electroneutrality at least two charge transfer half-reactions should take place. In the case of heterogeneous redox reactions, these half-reactions occur over two different electrodes immersed in a solution. It presents several advantatges over other methods commonly used to prepare films and structures which require vacuum conditions, physical or chemical vapor deposition (PVD or CVD), plasma enhanced deposition (PLD), sputtering. One of these advantages is its low cost and high simplicity of the experimental setup. The equipment used is cheap and maintenance is hardly required. On the other hand, room temperature is commonly used to grow the material or, at least, temperatures lower than 100°C. Nowadays electrodeposition is used in a wide range of applications as metal processing and finishing. Electroplating is a process widely used in industry for coating metal objects with a thin layer of a different metal. It is one of the most important in terms of volume of production, and it also has one of the greatest economic impacts. The purpose of these coatings is to provide the metal object with some desired property that the metal object does not have. Electrodeposition has come a long way since its inception; developing new techniques that have increased the range of applications of the same. This thesis mainly focuses on the new applications and uses of electrodeposition as a tool of fabricating some materials that can be integrated in different kind of devices such as sensors and actuators. Electrodeposition has a high materials and structures versatility that can be obtained which permits its integration in lots of processes. In this tesis different applications for electrodeposition have been studied: First of all, the design, preparation and characterisation of planar coils to be implemented in inductive biosensors has been performed. It was necessary to perform the study of the optimum bath, electrodeposition conditions and fabrication processes to prepare robust, low resistant and adherent planar copper coils of different aspect ratios, which allow detecting magnetic particles. In order to do that, simulations of the main parameters based in previous designs to improve the sensitivity of the coils have been executed. The final objectives were the fabrication of the new designed coils and to perform the first tests of their sensing ability. Then, the deposition of a hard magnetic alloy for MEMS application has been tested. A basic study of the electrodeposition process of the CoPt alloy to find the optimum bath has been performed. Structures with different shapes and geometries (films, thin films, photolitographied microstructures, nanoparticles, nanowires...) over different substrates have been obtained applying the conditions based on the previous electrochemical results. The influence of the electrodeposition and preparation conditions on the properties of the CoPt alloy (morphology, composition, crystalline structure, magnetic properties,) and analysis of the relationship among those properties has been studied. Finally, the organic monolayer formation on top of several electrodeposited magnetic substrates (magnetic/non-magnetic assembly) as the first step to fabricate a molecular spintronic device has been performed. The preparation of smooth thin films of magnetite and CoP by means of electrodeposition and the formation and study of octanethiol and acid oleic monolayers on top have been achieved as the first step to obtain a molecular spintronic device. Electrodeposition has been demonstrated to be a useful technique for the design and fabrication of micro/nanomaterials with specific properties that allow them to be implemented in biosensors, MEMS and molecular spintronic devices.
