Gold on Mica

Gold, as an inert metal, is a good sample to test the functionality of a STM. A simple way to obtain a gold (111) surface is epitaxially growth on a mica substrate. These samples are commercially available and can be flame annealed in air and then inserted into the UHV system to give a clean (111) surface. The surface typically reconstructs exhibiting lines of HCP stacking among the usual FCC stacking order.

Herringbone reconstruction on Au (111) (30x30 nm2)

Standing Waves

Gold (111) exhibits a surface state. The electrons confined in this state form a 2D electron gas. The electrons scatter of steps and impurities leading to a energy dependent interference pattern. The pattern can be observed by STM at low temperature and used to determine the energy dispersion and thereby the effective mass of the electrons involved.

Topography, dI/dV spectrum and fourier transform thereof showing the standing wave pattern. (38x38 nm2, 160 mV)

Comparison of the dispersion relation to STM and photo emission data.
  • Y. Hasegawa and Ph Avouris, Phys. Rev. Lett. 71, 1071 (1993).
  • S.D. Kevan and R.H. Gaylord, Phys. Rev. B. 36, 5809 (1987).

Moving Steps

The surface atoms of gold are relatively mobile. At elevated temperature as well as room temperature the motion of steps including erosion of islands and filling in of voids. However, at low temperature this motion should be suppressed. In our case we observed tip induced motion of the gold steps as well as a reconfiguration of the herring bone structure.

Tip induces transport of gold atoms. (50 pA, 100 mV, 1.5 μm/s, 10 min/image)

Tip induced changes of the herringbone reconstruction. (50 pA, 800 mV, 1.5 μm/s, 10 min/image)