Correlation between charge-transfer and rotation of C₆₀ on WO₂/W(110)

Understanding molecular switching between different charge states is crucial to further progress in molecule-based nano-electronic devices. Herein we have employed scanning tunnelling microscopy to visualize different charge states of a single C₆₀ molecule within a molecular layer grown on the WO₂/W(110) surface. The results obtained demonstrate that individual C₆₀ molecules within the layer switch between neutral and negatively charged states in the temperature range of 220-260 K over the time scale of the experiment. The charging of the C₆₀ causes changes in the local density of electron states and consequently a variation in tunnelling current. Using density functional theory calculations, it was found that the charged state corresponds to the negatively charged C₆₀^-, which has accepted an electron. The switching of the molecule into the charged state is triggered continuously by tunnelling electrons when the STM tip is static above an individual C₆₀ molecule with a bias applied. Molecular movement accompanies the molecule's switching between these states.