Dissipation imaging with low amplitude off-resonance atomic force microscopy

A small amplitude non-contact atomic force microscope/scanning tunnelling microscope (nc-AFM/STM) is used to study dissipative interactions at atomic resolution on Cu(100) and Si(111) surfaces. For Cu(100) atomic resolution images of phase contrast are obtained, showing energy dissipation as high as 100meV/cycle at each atomic site during constant tunnel current scans. In contrast, the Si(111) 7 × 7 surface usually did not exhibit significant phase contrast during normal STM operating conditions. However, when the driving oscillation frequency was set to a sub-harmonic of the lever resonant frequency, atomic contrast in phase could be readily observed. We believe this harmonic coupling is due to the nonlinearity of the tipsample interaction, and at these frequencies part of the energy is dissipated via the lever Q.