EXC 3120 BlueMat - Research Topic C2: Tunable MIR and NIR Permittivity by Electrochemical Oxidation and Hydrogen Insertion

In this RT, we will electrochemically modify the optical properties of materials interacting with water. Specifically, the reversible partial oxidation of Cu photonic structures in aqueous electrolytes will be studied. Cu has IR reflectivity comparable to gold and can be reversibly oxidized. In this case, the complex effective permittivity of porous Cu will be tuned via changes in the metal filling fraction and metal electron collision frequency, known as chemical interface damping (CID). Furthermore, we will investigate the reversible and controlled hydrogen insertion from water into porous photonic hybrid structures. We will induce the formation of hydrogen bronzes within vanadium dioxide, changing it from a dielectric to metallic state. Later, hydrogen-induced reduction will be also explored to tune the optical properties of titanium dioxide. The hydrogen insertion will be driven by water-based electrochemistry and by thermal treatments in water-containing vapor. The structures considered will be much smaller than the wavelength and, thus, will work in an effective medium regime. The change of the effective permittivity from a metallic to dielectric state in both cases will allow the control of NIR and MIR absorption. The key scientific questions are: How can we strongly and reversibly tune IR absorption of porous Cu via electrochemical oxidation? How can we induce a reversible phase transition in VO2 and TiO2 via hydrogen insertion? How can we utilize nanoscale structures to increase the tuning rate and amplitude?

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