Facile growth of horizontally suspended carbon nanotubes

This paper reports a facile method to grow horizontally suspended carbon nanotubes (CNTs) spanning across wide trenches. The vertical thickness of resultant CNT mats was controlled by adjusting the deposition direction of catalysts relative to the top surface of the substrate. The Raman spectroscopy reveals that the structural quality of CNTs gradually improves from CNT roots to tips, which is mainly attributed to the decay of catalyst activity during the CNT growth. The uneven longitudinal quality distribution may also exist in many other low-dimensional nanomaterials obtained via catalyst, thus it could shed light on the growth mechanism and quality control of these nanostructures.