For a set of fcc metals our total energy calculations, based on many bodypotentials, show that activation barriers for lateral manipulation of an adatomat a step edge depend on the tip/substrate composition. Of the six homogeneoussystems studied, manipulation on stepped Ag(111) showed the lowest energybarrier for adatom hopping towards the tip, although the relative probabilityfor this process was largest on Cu(111). For a representative Cu/Ptheterogeneous system we find lateral manipulation of a Pt adatom along a stepon Pt(111) by a Cu(100) tip to be energetically much less favourable than thereverse case of a Cu adatom manipulated by a Pt(100) tip. In the case ofvertical manipulation, atomic relaxations of the tip and its neighbouring atomsare found to be prominent and tip induced changes in the bonding of the adatomto its low coordinated surroundings help explain the relative ease with whichan adatom next to a step edge or a kink site, may be pulled, as compared tothat on a flat surface.
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