The hollow core inside a carbon nanotube(1) can be used to confine single molecules(2,3) and it is now possible to image the movement of such molecules inside nanotubes(4,5). To date, however, it has not been possible to control this motion, nor to detect the forces moving the molecules, despite experimental and theoretical evidence suggesting that almost friction-free motion might be possible inside the nanotubes(6-13). Here, we report on precise measurements of the mechanical responses of individual metallofullerene molecules (Dy@C-82) confined inside single-walled carbon nanotubes to the atom at the tip of an atomic force microscope operated in dynamic mode(14,15). Using three-dimensional force mapping with atomic resolution(16), we addressed the molecules from the exterior of the nanotube and measured their elastic and inelastic behaviour by simultaneously detecting the attractive forces and energy losses with three-dimensional, atomic-scale resolution.
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