Interfacial Doping at Surfaces and in Low-Dimensional Materials

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The word to dope' derives from the Dutch word doop' meaning thick dipping sauce', so doopen' means to dip'. In the context of electronic materials, it refers to introducing impurities (dopants) into or onto a material that lead to a change in its electronic properties. Such a change is easily detected, e.g. by measuring the change in resistance of a thin film or low-dimensional structure. So the absence or presence of the dipping sauce', or dopant, can be determined quantitatively with great accuracy, e.g. for use in gas or liquid sensors. A challenge for such a sensor is how to remove the dipping sauce' afterwards in order to reuse the device. We introduce the concept of molecular switches as chemical dopants for thin nanocarbon (or other two-dimensional material) films. These molecules can be switched between doping and non-doping states in the presence or absence of a particular analyte. They impart selectivity not only due to their change in doping behavior, but also by physically blocking other potential dopants in the analyte solution from interacting with the conductive film. In effect, they form a dipping sauce' that can stay on, because it can be made to change flavor. Based on this concept, we have demonstrated disinfectant sensors for drinking water fabricated from carbon nanotube networks or pencil-drawn films coated in redox-switchable oligoanilines. The concept can also be applied to other analytes (pH, anions, cations, etc. in drinking water), but it becomes necessary to better understand these switchable dopants, and how they work. ******This proposal aims to build an understanding of the interactions of switchable dopant molecules with 2-dimensional materials such as graphene, molybdenum disulfide or percolation networks made of different grades of carbon nanotubes. In particular, there are five aspects of the molecule-substrate interaction that we will elucidate: (1) The role of the chemical identity of the substrate; (2) The role of substrate film topology (e.g. network vs. single crystal); (3) Application of an external electric field to balance out and quantify the molecular doping effect; (4) Electronic structure of the molecules, also considering steric aspects; (5) Nature of the tether of the molecules to the substrate film (non-covalent vs. covalent) and relation to chemical defects in the substrate. ******Our sensors have the potential to be more robust, simple and reliable than any other available technology. The disinfectant sensors are already on their way to commercialization for drinking water quality control, but we aim to develop and deploy anion, cation, pH, and disinfectant sensors for water quality control in municipal water supplies, on first nations reserves, surface waters near mines or agricultural land, etc., thus benefitting the health of all Canadians, and their environment. Our sensors can also find applications in healthcare, research, or process control.