Detection and Imaging of Nanoscale Defects

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9732804GidleyWe propose an interdisciplinary research program that combines the well known defect sensitivity of positron techniques with state-of-the-art positron beam technology in order to detect and image the early stages of microstructural damage in a wide range of engineering materials where traditional techniques are not adequate. The inability to characterize defect evolution on the manometer size scale represents a major missing link in our fundamental knowledge of the synthesis-to-failure life cycle of many engineering materials. If materials scientists can measure the microstructural evolution of damage from synthesis to failure they will be greatly aided in improving such material properties as strength and durability, wear and corrosion resistance, environmental compatibility, and fabrication cost effectiveness.The major goal of this research is to demonstrate new measurement technology which addresses the initial stages of the nucleation and growth of defects to form larger voids that eventually lead to sample failure. Such defect accumulation (which can be highly localized) may be induced by mechanical means (e.g., fatigue, thermal stress), by chemical means (e.g., corrosion), by radiation, or by other agents such as electromigration. Sample systems range from crystalline metals to amorphous polymers to heterogeneous composites, and include such diverse items as microelectronic devices, passivation layers on reactive metal surfaces, and pipes in nuclear power reactors. The primary new technique to be used in this research is the positron microscope/microprobe. This advancement in positron beam technology will extend the known defect sensitivity of Doppler broadening spectroscopy, positron emission, and positron lifetime spectroscopy by incorporating depth profiled, microscopic lateral resolution. This will pen-nit non-destructive, three dimensional, nanoscale, defect imaging. A more traditional non-microscopic beam will continue to be used in a depth profiled mode when studying particular surfaces and films that do not require lateral resolution.The proposed research is a broad-based exploratory program that builds upon a strong existing collaboration between the University of Michigan Physics Department and the Materials Science and Engineering Department. To provide critical guidance in such an interdisciplinary program we have sought out expert collaborators working at universities, national laboratories and in industry.***