Nanoscale Electron Beam Induced Processing using Liquid Reactants

The major goal of this project is to fabricate nanoporous Titanium Dioxide (Ti02), Tin Oxide (Sn02) films with reproducible sensing properties that can be understood in terms of the underlying structureproperty correlations. Ti02, Sn02 films have been widely used as gas and humidity sensors. The sensor response to variations in microstructure focuses attention on ways of obtaining controlled, reproducible and regular microstructures with critical dimensions commensurate with the Debye length of the oxide (typically Ti02 and 5n02 in our case). Nanoporous films with large surface area are expected to improve the gas sensing characteristics. Although a variety of preparation methods have been developed, the creation of high quality, uniform porous structures over large areas, at low cost, is still a challenging problem. Sol-gel fabrication and electrochemical anodization are ideally suited to address this problem. Our expertise is in the fabrication of nanoporous metal oxide films by using (1) a template free method (self assembly) by carefully controlling the deposition conditions and (2) electrochemical anodization process. Combining our expertise in fabricating nanoporous films with design and application of sensor platforms, we propose to fabricate nano-porous Ti02, Sn02 films and evaluate their gas sensing characteristics. The intellectual merit of this proposal lies in the fact that, it addresses the growing demand for highly sensitive nanostructured gas sensors with reproducible sensing properties that can be understood in terms of the underlying structure-property correlations. Specifically the proposal aims to investigate the nanostructured (nanocrystalline and nanoporous) films of reproducible and regular microstructures with critical dimensions commensurate to the Debye length of the oxide (typically Ti02 and Sn02 in our case). Through this proposal, we will investigate the (1) effect of size, (2) effect of crystalline phase, (3) effect of surface area on sensor response in addition to the formation mechanism and evaluation of nanoporous morphology in anodized metal oxide films. Innovative aspects of the Proposal are (1) Self-assembly based approach for fabricating nanoporous/nanocrystalline films scalable to large areas with excellent process control over morphology, (2) Electrochemical process for creating nanoporous films of titania and tin oxide with tunable pore size, morphology and inter-pore distance for correlation with sensor response, (3) Investigation of structureproperty correlations in nanoporous metal oxide films, (4) Creation of model parameters for the nanoporous films with respect to their structure and morphology, (5) Derive analytical models for the response of sensors based on nanocrystalline and nanoporous films, (6) High sensitivity at room temperature to ammonia as evidenced from preliminary experiments, (7) Integration of nanoporous structures into a sensor platform and (8) complete evaluation of sensor stability, aging effects and performance in changing background conditions (e.g. humidity, presence of interfering gases, temperature ). Broad impacts of proposed research includes, 1. Advancement of robust sensor platform for room temperature sensing of gases like NH3. 2. Technology for fabricating large area ordered pore arrays. 3. A nano template platform for a multitude of technologies including sensor and photovoltaic devices. 4. Training of scientists and engineers for the sensor and nanotechnology industries. 5. Simulation platform for use in evaluating current and next generation sensor technologies. Completion of this project would lead to, 1. Sensor platform based on nanoporous films with reproducible sensing properties that can be understood in terms of the underlying microstructure of the material. 2. Training of future talent for research in nanotechnology.