Atomically resolved mechanical response of individual metallofullerene molecules confined inside carbon nanotubes

Abstract

The hollow core inside a carbon nanotube can be used to confine single molecules and it is now possible to image the movement of such molecules inside nanotubes. 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. Here, we report on precise measurements of the mechanical responses of individual metallofullerene molecules (Dy@C82) confined inside single-walled carbon nanotubes to the atom at the tip of an atomic force microscope operated in dynamic mode. Using three-dimensional force mapping with atomic resolution, 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.

Revealing Subsurface Vibrational Modes by Atomic-Resolution Damping Force Spectroscopy

“…and consistent with lattice parameters of graphitic carbon, as show in Fig. 8.7 [28]. In that case the AFM tip was reported to have an "atomically sharp" apex, whose radius R was estimated to be less than 0.5 nm [5].…”

“…8.9D, is smaller than optimum. In this case, the enclosed molecules distort elastically the nanotube wall, causing an undulation along the nanotube axis, as reported in [28] and as seen in Fig. 8.9D.…”

“…8.7B, C) were obtained in both forward and backward scan directions. Thereby the significant enhancement of the damping signals might be assigned to the instability originating unlikely from atomic conformation changes in the tip apex side but more likely from the existence of encapsulated molecules in the peapod sample [5,28]. As mentioned furthermore below, the presence of significant damping shown in Fig.…”

“…8.13A) and damping signals (Fig. 8.13a) obtained over the narrowest peapod show an axial undulation with the axial periodicity of 1.15 ± 0.05 nm and amplitudes of 56 ± 5 pm in topographic height and 70 ± 5 meV in damping energy [28]. The profiles in the bottom panels, where the vertical scales are normalized, show that the atomic-scale contrast in damping (right panels) is generally larger than in topography (left panels).…”

Atomic-Scale Spintronics

“…This new type of scanning probe microscopy, called magnetic exchange force microscopy (MExFM), offers a powerful tool to investigate different types of spin-spin interactions based on direct indirect, or superexchange down to the atomic level [20,21], in contrast to magnetic force microscopy (MFM), which probes magnetic dipole forces with a ferromagnetic tip at a typical tip-to-surface distance of 10-20 nm [22][23][24]. By combining MExFM with high-precision measurements of damping forces [25], localized or confined spin excitations in magnetic systems of reduced dimensions become experimentally accessible.…”