Carbon Nanotube Based Magnetic Tunnel Junctions for Electromagnetic Nondestructive Evaluation
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Carbon Nanotube Based Magnetic Tunnel Junctions for Electromagnetic Nondestructive Evaluation Buzz Wincheski, Min Namkung, 1Sun Mok Paik, and 2Jan Smits NASA LaRC Hampton VA 23681 1 Kangwon University Chunchon, Korea 2 Lockheed Martin Engineering and Sciences Corporation Hampton VA, 23681 ABSTRACT Spin coherent transport in carbon nanotubes enables single-nanotube devices for magnetic field sensing. This unique transport property of single walled carbon nanotubes (SWCNTs) has been studied for development into advanced sensors for nondestructive evaluation (NDE). Coupling of a single walled carbon nanotube to ferromagnetic electrodes is predicted to form a carbon nanotube magnetic tunnel junction. Fabrication of such devices has been performed through scanning probe and electron beam lithography. Purified single walled carbon nanotubes are deposited across electrodes to complete device fabrication. A spincoherent quantum transport theory based on a nonequilibrium Green’s function method has been established to predict conductance and magnetoconductance across junctions. Experimental measurements of the room temperature conductance of Cobalt/SWCNT/Cobalt junctions have been performed. INTRODUCTION Recent advances in nanotechnology have had a direct impact on methods for electromagnetic nondestructive evaluation. Spin valve giant magnetoresisitive (GMR) sensors are now being incorporated into several advanced inspection systems for detection of deeply buried flaws. Research in this area at NASA LaRC includes the development of multi-axis spindependent tunneling sensors for non-destructive evaluation [1], shaped field giant magnetoresistive sensor arrays for materials testing [2], and the GMR based Rotating Probe System for detection of deeply buried flaws under installed fasteners [3]. Future electromagnetic nondestructive evaluation systems are predicted to continue to rely upon advances in nanotechnology. Carbon nanotube based materials in particular are being studied to enable the development of new multifunctional materials with embedded structural health monitoring. Research and development in the area of nanotechnology and carbon nanotubes is one of the latest concepts in materials technology. Carbon nanotubes are arguably the strongest material that will ever be created and have a density a fraction of that of steel. In addition, the electronic properties of carbon nanotubes offer intriguing possibilities for next generation sensors and devices. Future aerospace vehicles are predicted to capitalize on the high strength to mass ratio of carbon nanotube based materials. The goal of this work is to take advantage of the unique transport properties of single walled carbon nanotubes in order to build structural health monitoring capabilities directly into future vehicle systems. In particular, Carbon E6.10.1 Downloaded from https:/www.cambridge.org/core. Cornell University Library, on 15 May 2017 at 18:46:39, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org
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