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The interaction of H atoms with the curved concentric graphene walls of a multiwall carbon nanotube and the stacked planar graphene sheets of graphite was investigated using a combination of high resolution transmission electron microscopy (HRTEM) in conjunction with electron energy-loss and Raman spectroscopies. Continuous cylindrical graphene walls of a nanotube are etched and amorphized by the H atoms. Etching is not uniform across the length of the CNT but rather, small etch pits form at defective sites on the CNT walls along the entire nanotube length. Once an etch pit is formed, etching proceeds rapidly, and the remainder of the CNT is quickly etched away. The carbon K core-loss edge spectra collected from etch pits do not differ from the spectra collected from pristine CNT walls, indicating that reactions occur exclusively at the exposed graphene edges. Similar observations were made when sheets of planar graphite were exposed to H atoms. Confocal Raman spectroscopic measurements revealed that H etching occurs preferentially at the graphite edges. Eventually, large holes appear in the graphite, as observed under HRTEM. Etched holes in planar graphite are similar to the etch pits that form when a graphene layer is rolled up to form the cylindrical walls of a CNT. Once a hole or an etch pit is formed, the edges of the planar graphene sheets or cylindrical CNT walls become exposed, and H etching proceeds quickly from these edges.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures (Volume:28 , Issue: 6 )
Date of Publication: Nov 2010