STM in the presence of fast current-induced structural fluctuations

Abstract

Dangling bond (DB) arrays on Si(001):H and Ge(001):H surfaces can be patterned with atomic precision and they exhibit complex and rich physics making them interesting from both technological and fundamental perspectives. But their complex behavior often makes scanning tunneling microscopy (STM) images difficult to interpret and simulate. Recently it was shown that low-temperature imaging of unoccupied states of an unpassivated dimer on Ge(001):H results in asymmetric butterfly-like STM pattern, despite that the equilibrium dimer configuration is expected to be a bistable, buckled geometry. Based on a thorough characterization of the low-bias switching events on Ge(001):H, we propose a new imaging model featuring a dynamical two-state rate equation. In our recent paper, we show that on both Si(001):H and Ge(001):H, this model allows us to reproduce the features of the observed symmetric empty-state images. This strongly enforces the idea that the patterns arise due to fast switching events and provides insight into the relation between the tunneling current and switching rates. Our new imaging model can be applied to simulate other bistable systems where fluctuations arise from transiently charged electronic states – such as the four atom Si cluster considered by Yamazaki et al. And the insight we have gained could be used to presicely control the microscopic state.