Matts, Olga

The chemical interface damping (CID) effect increases the collision frequency of free electrons in metals by changes to the metal surface. We have now experimentally disentangled the two contributions to CID: induced roughness and direct charge transfer. The latter is an important area of research in photoelectrochemistry with potential applications in light-induced chemical reactions. We present a broadband investigation of the CID effect on Au(111) covered by a self-assembled monolayer of decanethiol. Spectroscopic ellipsometry measurements show a photon-energy-dependent increase of the collision frequency. We observe a constant, photon energy-independent contribution, which is attributed to induced roughness, and a contribution that linearly increases with photon energy from about 1 eV upward, which we attribute to direct charge transfer. The onset of the charge transfer mechanism corresponds to the occupied orbitals of thiols bound to the Au surface, as confirmed by density functional theory calculations.

This thesis investigates functional mechanical properties of smart stimuli-sensitive hybrids based on nanoporous gold and organic layers. As a metal skeleton, unimodal and hierarchical nanoporous nested networks fabricated via an electrochemical dealloying were employed. Three electrochemistry-inspired approaches are integrated to surface modification of nanoporous gold – reversible capacitive assembly of ionic charges in the electric double layer, electrosorption of oxygen-species, and chemisorption of electroactive ferrocene-terminated alkanethiol self-assembled monolayers. To probe functionalities such as actuation and tunable stiffness, in situ experiments are carried out in electrochemical environment. In situ dilatometry is employed to investigate the impact of the electrochemicallycontrolled interface on the actuation behavior of the hybrids. The findings demonstrate remarkable differences in the strain responses of the materials with respect to the pore morphology and surface state. The contribution of the surface stress to the reproducible macroscopic actuation is experimentally confirmed for all hybrids under study. The negative values of the electrocapillary coupling parameters are determined pointing to the compressive surface stress in the metal surface upon the capacitive charging and electrosorption of oxygen-species. In nanoporous gold modified with the ferrocene-bearing self-assembled molecules, the actuation strain non-linearly scales with the ferrocene surface fraction testifying to the impact of the redox-events in the monolayer on the macroscopic actuation of the nanoporous network. The estimation of the mean actuation coefficient in the hybrids with the electroactive self-assembled monolayers pointed out to an enhanced strain response compared to those induced by conductive polymers. Along with actuation, the thesis explores the size-dependence of the effective elastic modulus of the hybrids via in situ dynamic mechanical analysis. Experimental observations in this study at a structural size below 100 nm support a hypothesis that the effective elastic behavior is dominated by the surface excess elasticity at this scale when specific adsorption is involved. Subsequently, the electro-elastic coupling parameters have been estimated for bulk nanoporous networks. Overall, this thesis discusses the electro-chemo-mechanical coupling in the nanoporous hybrids. It demonstrates that hierarchical nanoporous gold serves as a robust platform for enhancing the functional properties of nanoporous materials. Incorporating organic films allows nanoporous gold to convert chemical processes into mechanical motion, paving the way for further research and practical applications of nanoscale materials with tunable properties.

Filters

Settings

Sort By

Results per page