Barrier crossing in a dissipative environment: a reduced density matrix treatment of STM-induced atom transfer dynamics

The fate of many surface processes is determined by the competition between externally driven dynamics and intrinsic substrate-induced relaxation. In this work, we use the reduced density matrix theory to simulate the dynamic s of STM-induced atom transfer between a metal surface and the STM tip, whi ch can be considered as an activated barrier crossing process. Our model de scribes the vibrational excitation as a result of temporary occupation of a negative ion resonance by a tunnelling electron. The vibrational relaxatio n due to substrate phonons or electron-hole pairs is characterized in the f ramework of the Redfield theory. The results are consistent with experiment al observations. (C) 2000 Elsevier Science B.V. All rights reserved.