The Reversible Electrochemical Deposition of Silver onto Transparent Conductive Films and The Effects of Ambient Oxidation on Bismuth Chalcogenide Topological Insulator Surfaces

Abstract

Reversible electrochemical mirrors are a relatively recent field of research wherein an electrochemical reaction, in this case the electrodeposition of silver, is used to control the reflectivity of a transparent conductive window. This can be applied to the infrared spectrum of light as well, however doing so presents unique challenges as most transparent conductive materials are not transparent to infrared light. To address this challenge, graphene can be utilized given its atomic thickness and relatively high conductivity may allow for a window to be transparent while also serving as an electrode for silver electrodeposition.

Further challenges can be raised when these applications are brought into low-pressure or vacuum environments. While most electrolytes used for these applications will evaporate under low-pressure or vacuum conditions, ionic liquids are a unique class of electrolytes capable of tolerating vacuum conditions without undergoing evaporation or mass loss.

In this work, we have addressed both of these challenges to further the goal of a vacuum-compatible reversible electrochemical mirror device that is effective with infrared light. Thus we have investigated the use of various chemical forms of graphene particles and carbon nanotubes, to produce thin conductive films on infrared-transparent sapphire windows. We have also studied the electrodeposition process and long-term reversibility of silver in the ionic liquid 3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) on model electrode systems. Transparent indium-tin oxide and opaque graphene films were used to observe changes in transparency and reflectivity, and to model the deposition onto graphene-like materials, respectively. Additionally, the use of germanium as an infrared-transparent conductive was investigated.

Also presented are results on the oxidation of bismuth chalcogenide topological insulators from ambient conditions. Topological insulators are a recently discovered semiconductor material possessing interesting electronic states allowing them to conduct electricity like a metal along the surfaces. Furthermore, the electrons in this surface conduction possess a spin that is directly influenced by the electron’s momentum. However, these states are very sensitive to chemical effects, such as those brought on by atmospheric exposure. Thus we have studied the systematic exposure of atmospheric reactants on these material surfaces, and monitored the change via photoelectron spectroscopic methods.