Raster tunnel spectroscopy – Wikipedia

The Raster tunnel spectroscopy ( English scanning tunneling spectroscopy , STS ) is a method of raster tunnel microscope. With it the local (sideline -close) state densities (LDOS) of electrons (or holes
, so missing electrons).

The scanning tunnel spectroscopy is carried out with a scanning tunnel microscope. When creating a DC voltage

${displaystyle V}$

A small current flows between a fine tip and surface at a sufficiently small distance. This is created by tunnels of electrons from occupied conditions through a barrier that arises from the distance of the tip and the surface. The tip is now racing over the surface, a height topography of constant electron density can be recorded. The tunnel current therefore depends in the first approximation from the distance of the tip to the surface and from the electron density of the surface below the top. Because the topography is primarily interested in the raster tunnel microscopy, a DC voltage is used to record an image, which promises a good images. With the raster tunnel spectroscopy

${displaystyle V_{T}}$

On the other hand, altered in a targeted manner, while the tip rests on one place with a constant height. The measured electricity response

${displaystyle I_{T}}$

is a function of electron energy, which provides information about the state density.

${displaystyle Ipropto LDOS_{text{Spitze}}int _{0}^{eV}LDOS_{text{Probe}}(E)mathrm {d} E}$

^[first]

Variation of the tunnel voltage when mapping [ Edit | Edit the source text ]

If you want to measure an influence of the tunnel voltage on the tunnel current, you can measure the same surface several times with different tunnel voltage. Alternatively, you can change the voltage even after each line if you can assume that there is a periodic structure (e.g. single -crystal).

Point [ Edit | Edit the source text ]

However, if individual points are of interest on the surface, the tip can be placed in a targeted manner and a point spectroscopy can then be carried out. For this purpose, an alternating voltage is created to the top and systematically moved it with a DC-offset. You are now wearing

${displaystyle mathrm {d} I/mathrm {d} V}$

you get the condition density of the electrons at this point. It is often difficult to check whether the tip is exactly above the desired place.

Image spectroscopy [ Edit | Edit the source text ]

Another approach is to record pictures and

${displaystyle mathrm {d} I/mathrm {d} V}$

– Curves with different tunnels. It should be ensured that despite changing the tunnel voltage, the top distance is constant. Otherwise a data analysis is difficult due to the overlay of electronic and geometric effects.

• D. P. Woodruff, T. A. Delchar: Modern Techniques of Surface Science . 2nd Edition. Cambridge University Press, Cambridge, GbR 1994, ISBN 978-0-511-62317-2 ( EBLIB.com [accessed on October 26, 2018]).
• J. Tersoff, D. R. Hamann: Theory of the scanning tunneling microscope . In: Phys. Rev. B . Band thirty first , No. 2 , 1985, S. 805–813 , doi: 10.1103/PhysRevB.31.805 .

1. ↑ Christian Hess: Introduction to Scanning Tunneling Microscopy and Spectroscopy. In: Superconductivity II. Ifw dresden, Retrieved on October 26, 2018 (English).