Controlled AFM detachments and movement of nanoparticles: gold clusters on HOPG at different temperatures

The effect of temperature on the onset of movement of gold nanoclusters (diameter 27 nm)deposited on highly oriented pyrolytic graphite (HOPG) has been studied by atomic forcemicroscopy (AFM) techniques. Using the AFM with amplitude modulation (tapping modeAFM) we have stimulated and controlled the movement of individual clusters. We show how,at room temperature, controlled detachments and smooth movements can be obtained forclusters having dimensions comparable to or smaller than the tip radius. Displacement ispractically visible in real time and it can be started and stopped easily by adjusting only oneparameter, the tip amplitude oscillation. Analysing the energy dissipation signal at the onset ofnanocluster sliding we evaluated a detachment threshold energy as a function of temperaturein the range 300–413 K. We also analysed single cluster thermal induced displacement andcombining this delicate procedure with AFM forced movement behaviour we conclude thatdetachment threshold energy is directly related to the activation energy of nanoclusterdiffusion and it scales linearly with temperature as expected for a single-particle thermallyactivated process.