The fabrication of transient electronic devices based on non-toxic materials is an emerging field, in which the key characteristic is the complete dissolution of the devices within a settled period of time. Usually, these devices are built in polymeric substrates or pure metals; however they show some disadvantages such as low degradation rate. The aim of this work was to investigate the feasibility of electrodeposition of FeMn-based films from green sulfate-based aqueous electrolytes without and with the use of additives toward the possible replacement of the aforementioned materials. The results obtained from the first experiments regarding the electrodeposition of Fe and Mn as single metals allowed the design of the experiment to synthesize FeMn layers. Potentiostatic deposition of metallic Mn layers from environmentally friendly aqueous manganese sulphate electrolytes with a pH value of 3 was successfully demonstrated. A continuous flow in the cathodic compartment of the electrochemical cell to control the pH value during the electrodeposition experiments was found to be essential for achieving good layer qualities. It also allowed the co-electrodeposition with a second element, Fe, which also needs an acidic pH value to be electrodeposited from aqueous electrolytes. Cyclic voltammetry analyses were performed in combination with electrochemical quartz microbalance measurements in the MnSO4 containing electrolytes and a suitable deposition potential range was identified. The electrolyte composition played an important. The addition of H3BO3 provided mechanical stability to the Mn films and avoided their disintegration. An increase of the (NH4)2SO4 concentration increases the deposit roughness but also the layer quality, without impurities and a better crystalline α-Mn structure. An increase of the deposition potential led to an increase of the film thickness. Mn-oxides/-hydroxides were identified only in a thin surface region of the films. The Mn electrodeposited films were deeply characterized by means of SEM, XRD, GD-OES and XPS. The results related to the Mn electrodeposition allowed further design of the electrolytes and experiments to electrochemically synthesize FeMn layers. The assessment of the impact of the electrodeposition parameters on the structural, morphological and magnetic properties of the obtained films was also aimed in this work. With view to possible application of FeMn-based films in transient devices, their corrosion behavior in chloride-containing solution and their cytotoxicity were also evaluated. The electrolytes were characterized by means of CV and EQCM analyses. The ratio of the metal ions Mn2+:Fe2+ and the presence of glycine as complexing agent in the electrolyte determined the layer composition. The formation of the complexes Fe(gly)+ and Mn(gly)+ established a new reduction step modifying the Fe and Mn reduction/deposition. Glycine also leaded to a better film quality. A set of magnetron co-sputtered FeMn thin films was deposited as reference in order to compare the two synthesis methods with a broader range of Mn content between 10 and 70 wt.%. Metallic electrodeposited FeMn films presented a bcc structure with a Im-3m symmetry as well as the sputtered samples with a low Mn content up to 25 wt.%. An increase of the Mn content in the electrodeposited layers yielded to the formation of oxidized compounds with a fcc structure and Fm-3m symmetry. An increase in the Mn content for the sputtered films maintained the bcc structure but the symmetry was lowered to I-43m. With view to possible application of FeMn-based films in transient devices, their corrosion behavior in chloride-containing solution and their cytotoxicity were also evaluated. Regarding their corrosion behaviour, both techniques produced FeMn films with an active dissolution behaviour in chloride containing solutions. In vitro cytotoxicity tests revealed significant biocompatible characteristics of the sputtered films regardless of their Mn content. However, electrodeposited FeMn based layers did not presented optimal biocompatible characteristics. Furthermore, template-assited electrodeposition to obtain microrobots was studied in this work. Observed confinement effect was exploited, which results in compositional gradients with Mn-rich and Fe-rich regions and tubular or mushroom-like shapes. The propulsion performance of these electrochemically prepared hybrid micromotors was studied in the presence of H2O2 fuel with Triton-X as a surfactant and a magnetic field of 23.5 mT was applied. Bubbles produced by the catalytic decomposition of the H2O2 by the MnO2 and MnFe2O4 compounds was clearly the motion mechanism. Wireless modulated trajectory by the application of an external magnetic field was possible thanks to the magnetic phases, Fe3O4 and MnFe2O4.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:38639 |
| Date | 04 March 2020 |
| Creators | Fernandez Barcia, Monica |
| Contributors | Nielsch, Kornelius, Zabinski, Piotr, Cuniberti, Gianaurelio, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | info:eu-repo/grantAgreement/Europäische Komission/Horizon2020/642642//Smart ELECTrodeposited Alloys for environmentally sustainable applications: from advanced protective coatings to micro/nano-robotic platforms/SELECTA |
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