A carbon nanotube-based device includes a substrate (10); a catalyst layer (13) disposed on the substrate, the catalyst layer comprising a number of nano-sized catalyst particles (131), a size of the catalyst particles decreasing along a given direction; and an array of aligned carbon nanotubes (14) extending from the catalyst layer in an arc toward the given direction. A method for making the carbon nanotube based device includes the steps of: (1) providing a substrate; (2) forming a catalyst layer on the substrate, a thickness of the catalyst layer decreasing along a given direction; (3) annealing the treated substrate in air to form nano-sized catalyst particles; (4) introducing a carbon source gas; and (5) forming an array of carbon nanotubes extending from the catalyst particles using a chemical vapor deposition method.