Carbon nanotubes (mono/multi-layers of carbon atoms rolled into seamless tubes) are known to have superior electrical, mechanical, thermal and chemical properties. Interestingly, the same reasons behind their superiority also make them very sensitive to electrical, mechanical, thermal and chemical fields. Practical applications, as in electronics, sensors and actuators, composites and bio-medical, are likely to involve nanotubes that are mechanically strained and chemically treated during fabrication - and not the pristine ones. The very high power density of such ultraminiaturized devices will cause higher operating temperatures (observed even in the existing computer chips), which will drastically alter the transport properties of the highly confined nanotube electrons. Studies involving the sensitivity of electrical properties under mechanical or thermal fields (such as tuning electrical properties with mechanical displacement or vice versa) have been mostly theoretical. Experimental studies focusing on the simultaneous effects of temperature (>300 K) and mechanical force-displacement on the electrical properties of the nanotubes are rare in the literature, an observation that motivates this research proposal.
Proposed Activities and their Intellectual Merits: The specific aims of this research are, (i) Development of a micro-electro-mechanical characterization instrument with co-fabricated freestanding single carbon nanotube specimens. The 1mm x 1mm size device will be compatible with any type of microscopy (Optical/SEM/TEM/STM). It will measure force and displacement with 20 pico-Newton and 5 nm resolutions respectively, using an optical microscope. The mechanical sensors (electrically isolated and metallized silicon microbeams) will also work as electrical connectors to measure current-voltage signals. (ii) Study the effects of elevated temperature on the mechanical properties (Young's modulus, fracture stress and strain) of individual carbon nanotubes, in-situ inside the transmission electron microscope. (iii)Study the electrical properties of carbon nanotubes for a wide range of temperature (300-500K) and mechanical strain (up to 30%), for which data is not yet available in the literature. The instrument will allow in-situ atomic resolution experiments on individual carbon nanotubes for simultaneous qualitative (direct visual information on deformation, defect generation and failure of the nanotubes) and quantitative information. The wealth of data on the separate and coupled effects of thermal, mechanical and chemical environmental factors will help researchers gaining insight to the coupling of these fields.
Broader Impacts of the Proposed Activities: The experimental data and the fundamental understanding in the coupling of thermal, electrical and mechanical fields will provide better design guidelines for future nanoscale electronics, sensors and novel materials applications. The proposed novel experimental tool will bridge the existing wide gap between theoretical andexperimental studies on nanostructures. Technology transfer of the low cost tool ($25/unit) will promote multi-disciplinary research (such as mechano-biology), wherever high-resolution force and displacement sensing are required. We will train one graduate and one under-represented category undergraduate student (employed through Minority in Engineering program at Penn State) in this cutting-edge research. The research results will be used as a case study in a new technical elective course, which the PI developed to bring nanoscale sensors and actuators, materials science, electronics and electron microscopy in the classroom. We will also train high school teachers in the fundamental aspects of micro and nanotechnology and give their students 'virtual' experience on electron microscopy (web-based remote operation of a scanning electron microscope) to reach out to our future workforce in the each years of this research project.
