Optimization of Carbon Nanotube Based Chemical Sensors Through Micro-Raman Enabled Defect Analysis

Overview: This project is aimed at developing highly efficient carbon nanotube (CNT) based chemical sensors through in-situ identification and manipulation of defects in the CNT conduction channel. These defects have been shown to play a central role in CNT electrochemical sensitivity but there has been no rigorous study of how specific defect types and/or distributions affect actual CNT-based devices. To achieve this goal a unique and highly integrated process involving micro-Raman spectroscopy, electron microscopy, numeric modeling and microenvironment electrical characterization will be applied for the first time. This will be carried out by the following efforts:

• Fabrication of large arrays of CNT field effect transistors with exposed conduction channels that will serve as chemFETs for analyte detection.
• Micro-Raman spectroscopy of each CNT channel to assemble a detailed two-dimensional map of defect locations.
• Defect identification by comparing the spectra in the map against theoretical predictions of Raman lines for mono-vacancy, double-vacancy and Stone-Wales defects.
• Highly controlled testing of these defect manipulation schemes in a specially designed microenvironment probe station capable of handling a wide variety of analyte gas species.
• Development of a numeric model, based on actual fabricated device morphology, to predict baseline electrical performance given the existing defects. The effect on chemFET performance of adding or removing specific defect types will also be simulated to guide optimization schemes involving defect manipulation in existing devices.

This investigation represents a multi-disciplinary approach in which CNT growth, nanodevice fabrication and simulation, Raman spectroscopy and standardized electrical testing of the chemFET in relation to the gas analytes must all be utilized. These efforts take advantage of the PIs expertise in nanoscale material synthesis, device fabrication, and their structural, electrical and optical property characterization, as well as the co-PIs demonstrated ability with complex numeric modeling and device architecture.

Intellectual Merit: The proposed research directly tackles one of the principle roadblocks to the enormous potential of CNT-based chemical sensors. For the first time, an effort is made to verify how a specific set of graphitic defect types (mono-vacancy, Stone-Wales, etc.) impact actual chemFET performance. The intellectual merit is therefore twofold: 1) Development of low-cost CNT-based chemical sensors with improved analyte sensitivity, efficiency and selectivity through defect analysis and manipulation, and 2) Advancement of next-generation in-situ nanometrology by integrating electron microscopy, micro-Raman spectroscopy, and microenvironmental-controlled electrical characterization into one comprehensive process and applying them to exam CNT conduction channels in actual working devices, that have traditionally not been systematically addressed by the combination of these methods. If the proposed research is successful, it will not only allow us to gain an in-depth understanding of how these defects affect the performance of working nanodevices, but will also change our way of characterizing nanostructure-based nanoelectronics.

Broader Impact: The proposed research will be integrated with the Physics, Mathematics and Electron Microscopy courses currently taught by the PIs. The various research activities will involve minority undergraduate students and girls from local K-12 schools through NSF-sponsored LSAMP/REU programs and Oregon Saturday Academys Apprenticeship in Science and Engineering programs to enable them to join a competitive workforce in the near future. The research program will advance the research infrastructure at PSU and beyond by continuing the development of next generation nanometrology tools and techniques. The research findings will be disseminated broadly through journal publications, conference presentations, seminars, and the PIswebsite (http://www.physics.pdx.edu/~jiaoj/ and http://www.mth.pdx.edu/~bjiang/).