Vertically-aligned carbon nanotube (CNT) arrays are grown on a moving substrate, demonstrating continuous growth of nanoscale materials with long-range order. A cold-wall chamber with an oscillating moving platform (Figure 1) is used to locally heat a silicon growth substrate coated with a Fe/Al₂O₃ catalyst film for CNT growth via chemical vapor deposition.  The reactant gases are introduced over the substrate through a directed nozzle to attain high-yield CNT growth.  Aligned multi-wall carbon nanotube (MWNT) arrays (or “forests”) with heights of »1 mm are achieved at substrate speeds up to 2.4 mm/s. Arrays grown on moving substrates at different velocities are studied to identify potential physical limitations of repeatable and fast growth on a continuous basis. No significant differences are noted between static and moving growth as characterized by SEM (Figure 2) and Raman spectroscopy, although overall growth height is marginally reduced at the highest substrate velocity. CNT arrays produced on moving substrates are also found to be comparable to those produced through well-characterized batch processes consistent with a base-growth mechanism. Growth parameters required for the moving furnace are found to differ only slightly from those used in a comparable batch process; thermal uniformity appears to be the critical parameter for achieving large-area uniform array growth.

Once the parameters have been optimized, a desktop continuous growth apparatus has been designed and implemented to grow VACNTs on silicon wafers (Figure 2), flexible sheets, and alumina fibers continuously. We have demonstrated and reported the ability to manufacture VACNT arrays in a continuous manner, significantly reducing the time spent, energy consumed, and reaction products created as compared to batch processing of these technologically valuable assemblies of nanoscale materials.

1. R. Guzman de Villoria, S. L. Figueredo, A. J. Hart. S. A. Steiner III, A. H. Slocum, and B. L. Wardle, “High-yield growth of vertically aligned carbon nanotubes on a continuously moving substrate,” Nanotechnology, vol. 20, no. 40, pp. 405611-405618, 2009.

Catastrophic structural failures are the cause of many physical and personal losses, with prevention estimated at billions of dollars in savings each year. Non-destructive evaluation (NDE) techniques have been pursued and employed for damage detection of such structures to detect cracks and other damage at pre-critical levels for remediation ^{[1] [2]} . Here, a novel multi-physics approach is reported that addresses drawbacks in existing techniques by taking advantage of the effects that damage, such as a crack, has on the electric and thermal transport in a material containing a CNT network distributed in the bulk material. When a potential is applied to a nano-engineered structure (Figure 1), electric field lines concentrate in the vicinity of cracks as electrons flow around damage, causing field concentrations and “hot spots” via Joule heating, an effect which is amplified because the heat flow is also impeded in areas of damage (e.g., across a crackface). These changes of temperature can be localized through a conventional infrared thermal camera. Low power operation (a 9-V standard battery is exemplary, providing a 15C rise at 1 Watt as in Figure 2), and high spatial resolution is demonstrated that is beyond state-of-the-art in non-destructive evaluation.

Using this technique, multiple applications have been identified such as crack detection in composite components that are joined by metallic fasteners, structures having internal nonvisible damage due to impact, and in situ progressive damage monitoring during a tensile strength test.  The thermal nano-engineered NDE technique demonstrated here can provide a new and effective inspection route for monitoring next-generations of safer infrastructure ^{[3] [4]} .

1. D. Barber, S. Wicks, A. Raghavan, C. T. Dunn, ,S. S. Kessler, and B. L. Wardle, “Health monitoring of aligned carbon nanotube (CNT) enhanced composites,” presented at 2009 SAMPE Fall Technical Conference, Wichita, KS, Oct. 2009.
2. S. Wicks, A. Raghavan,, R. Guzmán de Villoria, S. S. Kessler, and B. L. Wardle, “Tomographic electrical resistance-based damage sensing in nano-engineered composite structures,” in AIAA-2010-2871, presented at 51st AIAA Structures, Structural Dynamics, and Materials (SDM) Conference, Orlando, FL, April 12-15, 2010.
3. R. Guzman de Villoria, N. Yamamoto, A. Miravete, and B. L. Wardle, “Multi-physics damage sensing in nano-engineered structural composites,” Nanotechnology, vol. 22,  pp. 185502-185508, 2011.
4. R. Guzmán de Villoria, A. Miravete, N.Yamamoto, and B. L. Wardle, “Enhanced thermographic damage detection enabled by multifunctional nano-engineered composite laminates,” in AIAA-2011-1798, presented at 52^nd AIAA Structures, Structural Dynamics, and Materials (SDM) Conference, Denver, CO, April 4-7, 2011.