  We examine the effect of van der Waals (vdW) interactions between atomic
force microscope (AFM) tips and individual carbon nanotubes (CNTs) supported on
SiO2. Molecular dynamics (MD) simulations reveal how CNTs deform during AFM
measurement, irrespective of the AFM tip material. The apparent height of a
single- (double-) walled CNT can be used to estimate its diameter up to ~2 nm
(~3 nm), but for larger diameters the CNT cross-section is no longer circular.
Our simulations were compared against CNT dimensions obtained from AFM
measurements and resonant Raman spectroscopy, with good agreement for the
smaller CNT di-ameters. In general, AFM measurements of large-diameter CNTs
must be interpreted with care, but the reliability of the approach is improved
if knowledge of the number of CNT walls is avail-able, or if additional
verification (e.g. by optical techniques) can be obtained.
