Gold deposited on a Ge(0 0 1) surface: DFT calculations | JoVE Visualize

Area of Science:

Surface Science
Materials Science
Condensed Matter Physics

Background:

Understanding the self-organization of metal atoms on semiconductor surfaces is crucial for nanotechnology.
Gold-induced nanowires on Ge(001) surfaces exhibit complex atomic and electronic structures.
Previous studies have explored various aspects, but a comprehensive understanding of atomic geometry, stability, and electronic properties is needed.

Purpose of the Study:

To investigate the atomic geometry, stability, and electronic properties of self-organized gold nanowires on a Ge(001) surface.
To elucidate the role of gold coverage and atomic arrangements in the formation of these nanowires.
To correlate theoretical findings with experimental observations, particularly Scanning Tunneling Microscopy (STM) and angle-resolved photo-emission spectroscopy (ARPES).

Main Methods:

Density-functional theory (DFT) calculations using the generalized gradient approximation (GGA).
Investigation of various gold coverages (e.g., <0.25, 0.50, 0.75 ML) on the Ge(001) surface.
Analysis of formation energies, simulated STM images, and electronic band structures.

Main Results:

Gold substitution of germanium atoms occurs at low gold coverages (<0.25 ML), with evidence of subsurface penetration.
Energetically favorable dimer-row arrayed structures with transition symmetries (4x1, 4x2, c(8x2)) are identified at higher gold coverages (0.50 and 0.75 ML).
The c(8x2) phase exhibits zigzag-shaped protruding chains consistent with STM observations, and a quasi-1D electron-like energy trough is found, aligning with ARPES data.

Conclusions:

The study confirms gold substitution and subsurface penetration at low coverages and identifies specific ordered structures at higher coverages.
The formation of long-range ordered structures requires sufficient energy for germanium atom transport to avoid re-adsorption.
The observed electronic properties, particularly the energy trough in the c(8x2) phase, are well-reproduced by the theoretical model and consistent with experimental findings.