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In this work, thermal chemical vapor deposition with gravity effect and water-assisted selective etching have been employed to synthesize vertically aligned carbon nanotubes (CNTs) with high aspect ratio and low defect density. CNTs were grown by placing the substrate upside down along gravitational field and the periodic introduction of acetylene and low concentration water vapor through argon. The water vapor concentration and its introduction time are optimized for stackless growth of catalyst-removed CNTs. The water vapor concentration of 300 ppm and introduction time of 3 minutes was found to be an optimum condition. Vertically aligned CNTs of 8-15 nm in diameter and nearly 90 mum long are achieved. Characterization of CNTs by transmission electron microscope (TEM) confirms that the CNTs are of good quality with low defects and almost catalyst-free. Moreover, the fabricated CNTs have been characterized for electron field emission applications. The high aspect ratio CNTs exhibits reproducible low field emission with turn-on electric field of ~3 V/mum.