Radial elasticity of multi-walled carbon nanotubes
  We report an experimental and a theoretical study of the radial elasticity of multi-walled carbon nanotubes as a function of external radius. We use atomic force microscopy and apply small indentation amplitudes in order to stay in the linear elasticity regime. The number of layers for a given tube radius is inferred from transmission electron microscopy, revealing constant ratios of external to internal radii. This enables a comparison with molecular dynamics results, which also shed some light onto the applicability of Hertz theory in this context. Using this theory, we find a radial Young modulus strongly decreasing with increasing radius and reaching an asymptotic value of 30 +/- 10 GPa. 
Ismael Palaci, Stephan Fedrigo, Harald Brune, Christian Klinke,   Michael Chen, Elisa Riedo
cond-mat.mtrl-sci