Speaker
Description
The magnitude of the tunneling current at a fixed bias in scanning tunneling microscopy (STM) is exponentially dependent on the distance between the tip and the sample as observed by recording IZ spectra. Here we report reproducible IZ spectra recorded over Si(100), with and without H-termination. While spectra taken over a dangling bond display an initial rise in current with decreasing tip-sample separation, current reaches a peak and then decreases in the regime of tip-sample contact. Jelinek et al previously reported similar behavior in a study of Si(111)-7x7 [PRL 101, 176101 (2008)].
In an effort to better understand the nature of the phenomenon we expand the scope to include study of single dangling bonds (DBs), contiguous patches of many DBs, and fully hydrogen terminated Si on n-type H-Si(100)-2⨉1. Our results show that while DBs and DB patches show current reduction in the contact regime, current recorded over H-Si continues to increase with reduced separation.
Two distinct theoretical models accounting for the observed peaked IZ curves are discussed. In the first model, the onset of covalent bonding with reduced separation between tip and sample is seen to initially lead to increasing current; but as a repulsive regime is entered, strained bonds and less favourable electronic interactions among multiple atoms in the contact area result in reduced current. In the second model, the broadening of a discrete state (dangling bond) in the presence of a continuum (metal tip states) is seen to lead to decreased transmission on close tip approach.
We will discuss the merits of the two models.
| Keyword-1 | STM |
|---|---|
| Keyword-2 | Silicon |
| Keyword-3 | Nanoscale Contact |