| AVS 65th International Symposium & Exhibition | |
| Processing and Characterization of Air-Liquid, Solid-Liquid and Air-Solid Interfaces Focus Topic | Tuesday Sessions |
| Session PC+AS+BI+EM+NS+PB+SS-TuP |
| Session: | Processing and Characterization of Gas-Liquid, Solid-Liquid, and Gas-Solid Interfaces |
| Presenter: | Jordi Fraxedas, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain |
| Authors: | J. Fraxedas, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain K. Zhang, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain B. Sepulveda, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain M.J. Esplandiu, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain X. Garcia, Institute of Energy Technologies, Department of Chemical Engineering and Barcelona Research Center in Multiscale Science and Engineering. Universitat Politècnica de Catalunya, Spain J. Llorca, Institute of Energy Technologies, Department of Chemical Engineering and Barcelona Research Center in Multiscale Science and Engineering. Universitat Politècnica de Catalunya, Spain V. Perez-Dieste, Alba Synchrotron Light Source, Spain C. Escudero, Alba Synchrotron Light Source, Spain |
| Correspondent: | Click to Email |
Self-propelled motors that can harvest chemical energy from their surroundings to convert it in mechanical energy are at the cutting edge of nanotechnology for their appealing applications in e.g., environmental remediation and nanobiomedicine. A full understanding of the propulsion mechanism is crucial to improve their performance and controllability. Recently, a simple motor made of silicon and a noble metal that can operate with visible light has been developed [1]. The photoactivation mechanism and consequent motion is essentially based on the formation of electron/hole pairs. The holes are strong oxidizing agents for the species in the fluid producing protons and the electrons can diffuse towards the metal surface and participate in the counterpart reduction reaction. As a result, a gradient of proton concentration is formed in the fluid which builds-up an electric field driving the motion of the fluid through electro-osmosis. A mechanism that competes with the electro-osmotic process is based on diffusion-osmosis and is triggered by the redox decomposition exclusively at the metal surface and is not light responsive. We have recently shown that it is possible to enhance/suppress one mechanism over the other by tuning the surface roughness of the micromotor metal. Thus, the actuation mechanism can be switched from light-controlled electrokinetics to light-insensitive diffusio-osmosis by only increasing the metal surface roughness [2].
We have recently performed near ambient pressure photoemission studies of Pt/Si micromotor surfaces activated by oxygen plasma in water atmosphere at the NAPP endstation of the CIRCE beamline at the ALBA synchrotron near Barcelona. We have used p-type silicon substrates with one half covered with a Pt film with a thickness of about 50 nm grown by both e-beam and sputtering deposition. The results reveal a chemical gradient at the Si/Pt edge with a reduction of the Pt species. The analysis has to carefully consider the photochemical reactions induced by the combined action of the impinging beam and the water condensed at the surfaces. The beam induced damage evolves in two regimes: an initial preferential reduction of Pt4+ species and then the reduction of Pt2+ species, which increases the metallic character of the surface.
[1] M.J. Esplandiu, A. Afshar Farniya, A. Bachtold, ACS Nano, 9, 11234 (2015).
[2] K. Zhang, J. Fraxedas, B. Sepulveda, M. J. Esplandiu, ACS Appl. Mater. Interfaces 9, 44948 (2017).