A rolled sheet of hexagonal carbon forming a seamless tube 
Can be capped by fullerene hemispheres 
Can be single- or multi-walled 
Diameter and orientation can defined :
 B. Bhushan, Springer handbook of nanotechnology , 2 nd ed. (Springer, 2006), pp. 44-47.  D. Qian, G.J. Wagner, W.K. Liu, M.F. Yu, R.S. Ruoff, “Mechanics of carbon nanotubes,” Appl. Mech. Rev. 55 (6), 495 (2002).
CNT variations  D. Qian, G.J. Wagner, W.K. Liu, M.F. Yu, R.S. Ruoff, “Mechanics of carbon nanotubes,” Appl. Mech. Rev. 55 (6), 495 (2002).  R. Andrews, D. Jacques, A.M. Rao, F. Derbyshire, D. Qian, X. Fan, E.C. Dickey, J. Chen, “Continuous production of aligned carbon nanotubes: a step closer to commercial realization,” Chem. Phys. Let. 303 , 467-474 (1999).  
Curvature creates cavities of molecular dimension 
Superposition of potential fields in cavities 
Larger attractive force on hydrogen molecules
Theoretical RT storage capacity 
7.7 wt% by chemisorption
 P. Barbaro, C. Bianchini, Catalysis for Sustainable Energy Production (Wiley-VCH, 2009) pp. 123-124.  J. Li, T. Furuta, H. Goto, T. Ohashi, Y. Fujiwara, S. Yip, “Theoretical evaluation of hydrogen storage capacity in pure carbon nanostructures,” Journ. Of Chem. Phys. 119 (4), 2376-2385 (2003).
Hydrogenation causes formation of “shoulder” in spectrum, which is attributed to hydrogenated Carbon atoms. Based on intensity ratio of the two peaks and theoretical calculations, the amount of hydrogenated Carbon atoms was estimated to be 5.1 +/- 1.2 wt. % of SWNT. (close to 6.5%!) Found to be stable at ambient; breaks up completely by 600º C reverseable process. Theoretical values of the carbon 1s core-level chemical shifts between sp-2 and sp-3 due to C-H bond formation for SWNTs. Measured results correspond well with calculations!
widely-used technique for determining the local geometric and/or electronic structure of matter
XAS data are obtained by tuning the photon energy using a crystalline monochromator to a range where core electrons can be excited (0.1-100 keV photon energy). The "name" of the edge depends upon the core electron which is excited: the principal quantum numbers n=1, 2, and 3, correspond to the K-, L-, and M-edges, respectively. For instance, excitation of a 1s electron occurs at the K-edge, while excitation of a 2p electron occurs at an L-edge (Figure 1).
X-ray photoelectron spectroscopy (XPS) is a quantitative spectroscopic technique that measures the elemental composition, empirical formula , chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy (KE) and number of electrons that escape from the top 1 to 10 nm of the material being analyzed. XPS requires ultra high vacuum (UHV) conditions.