Atomic structure and peculiarities of the electronic properties of Br layers on Ag(111) at different coverages

The structure and electronic properties of Br layers on Ag(111) at different coverage were studied by low-temperature scanning tunnelling microscopy, scanning tunnelling spectroscopy (STS) and density functional theory (DFT) calculations. The Br layers are found to form a hexagonal (root 3 x root 3)R30 degrees structure for coverage similar to 0.3 monolayer (ML) and a striped ((6)(-1) (1)(2)) structure for coverage similar to 0.4ML. STS measurements reveal suppressed differential conductance for both structures at voltages ranging between -1.2 and 1.4V, and surprisingly intense peaks at 1.5V and 2.0V. The position of the high-intensity peak in the spectra for the striped structure shows lateral variations within the unit cell and is determined by the Br coverage. In our structural model for the striped structure, supported by DFT calculations, the hexagonal (root 3 x root 3)R30 degrees structure transforms to the 3 striped structure due to uniaxial inhomogeneous compression of Br atomic rows. The local work function for the Br/Ag(111) surface, estimated from dz/dV(V) measurements, is 5.0 +/- 0.2eV, which is higher than for the Ag(111) surface (4.4 +/- 0.1eV). This suggests an increase in the electrostatic dipole barrier on Ag(111) due to Br adsorption. Combined with the suppressed local density of states around the Fermi level observed by STS, these results clarify the usefulness of Br layers in reducing the coupling between Ag(111) electrons and adsorbates.

Automated summary

The structure and electronic properties of Br layers on Ag(111) at different coverage were investigated using low-temperature scanning tunnelling microscopy, scanning tunnelling spectroscopy, and density functional theory calculations. It was found that the Br layers form a hexagonal (√3×√3)R30° structure with a coverage of around 0.3 monolayer, and a striped (6)(-1)(1)(2) structure with a coverage of around 0.4 monolayer. The study also revealed suppressed differential conductance for both structures at certain voltages, indicating the usefulness of Br layers in reducing the coupling between Ag(111) electrons and adsorbates.