Supporting On-Line Material for: Revealing Sub-Surface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

Single-walled carbon nanotubes (SWNTs) were synthesized by arc discharge using a non-magnetic catalyst [1] and heated in air at 440◦C for 30 minutes to open their ends. The nanotube diameters were determined by measuring the Radial Breathing Mode (RBM) frequency using Raman spectroscopy. On top a broad distribution of RBM frequencies, we found discrete peaks indicating abundance of nanotubes with diameters 12.6 − 13.0 Å, 14.8− 15.0 Å, 16.2− 16.8 Å, and 18.1− 18.4 Å. Dy@C82 endohedral metallofullerenes were produced by arc vaporization and purified by high-performance liquid chromatography. The Dy@C82 molecules were encapsulated into the SWNTs with different diameters by heating their mixture in a platinum crucible under 10−6 Torr at 440◦C for 5 days [2]. High-resolution transmission electron microscopy (HRTEM) was used to verify the presence of Dy@C82 inside the nanotubes, showing the fullerene cages as circles and the enclosed Dy atoms as dark spots positioned off the center. According to extensive HRTEM observations, the proportion of filled nanotubes was ≈60%. The mixture of SWNTs and (Dy@C82)@SWNT peapods was dispersed in a 1% aqueous SDS solution and deposited onto a highly doped Si substrate covered by a 0.2 μm thick layer of dry SiO2 [2]. The samples were subsequently heated in ultrahigh vacuum at 150◦C for 2 hours to remove the solvent and other adsorbed molecules.