Figure 2: Characterization of CNT carpet grown from graphene.

(a–h) SEM images of nanotube carpet grown from a graphene-covered copper foil. (a,b) The samples grown by using 0.3 nm of iron and 3 nm of alumina. The dark regions in a are gaps in the broken alumina layer and the brighter regions are alumina-covered areas. Scale bar in a, 50 μm. (b) An enlarged image for one of the lifted areas where the CNTs were grown. Scale bar in b, 10 μm. (c,d) The samples grown by using 0.5 nm of iron and 3 nm of alumina. Scale bar in c and d, 10 μm. (c) The top alumina layer is partially broken. (d) The top alumina layer is fully removed during growth. (e–h) The samples grown by using 1 nm of iron and 3 nm of alumina. (e,f) Top view of the CNT carpet on the graphene-covered copper foil. Scale bar in e, 50 μm. Scale bar in f, 10 μm. (g) The side view of the CNT carpet grown on the graphene; the height of the CNT is ~120 μm. Scale bar in g, 10 μm. (h) The close-up view on the upper portion of the CNT carpet. Scale bar in h, 1 μm. (i,j) Raman spectra of the CNT carpet and graphene. (i) Raman spectrum of the CNT carpet (excitation wavelength 633 nm). Inset: the spectrum of the radial breathing modes (RBMs). (j) Raman spectra of graphene before (black) and after (red) CNT growth (excitation wavelength 514 nm). (k) The diffraction pattern of the graphene after CNT growth. (l–n) TEM images of CNTs grown in this work. Scale bar in l, m and n, 5 nm. (l) Single-walled nanotube. (m) Double-walled nanotube. (n) Triple-walled nanotube.