Scanning Tunneling Microscope


VT STM by Scienta Omicron


Analysis:

  • Scanning Tunneling Microscopy (STM)
  • Scanning Tunneling Spectroscopy (STS)


Sample specification

  • Area typically ~ 10 mm x 10 mm, thickness 1-2 mm

In Scanning Tunneling Microscopy (STM) the tunneling current between a sharp tip and the surface of a (conductive) sample is probed upon scanning the tip above the surface of the sample. Depending of the shape of the tip it is possible to probe the topography of the surface as well as its electronic properties with atomic resolution. Since the tunneling current strongly depends on the distance between tip and the surfaceSTM excels by its very high surface sensitivity.

Fig. 2a shows a 2 nm x 2 nm area of graphene (as epitaxially grown on a Cu(111) wafer) with atomic resolution. The cross section in Fig. 2b displays exactly the lattice parameter of graphene. Due to the lattice mismatch between graphene and the Cu(111) surface, the overall topography forms a Moiré pattern (with a period of 5.23 nm ) as displayed by the extended 12 nm x 8 nm area in Fig. 2c.

In Scanning Tunneling Spectroscopy (STS) the tunneling current is recorded upon varying the bias voltage between the tip and the sample. STS spectra (i.e. dI/dV is plotted versus the bias voltage V) provide a measure for the local electronic density of states.

The VT STM is mounted to the preparation chamber of the VG ESCA-MkII Photoelectron Spectrometer (see Ultra High Vacuum Lab).



Figure 1: Inside view of the Scienta Omicron VT STM scan head.



Figure 2: STM data of epitaxial graphene on Cu(111). (a) 2 nm x 2nm scan with atomic resolution displaying the hexagonal graphen lattice. (b) Cross section along XY in (a) displaying the lattice parameter of graphene. (c) 12 nm x 8 nm scan with atomic resolution displaying a 5.2 nm Moiré pattern. (graphics taken from F. Müller, J.U. Neurohr, S. Grandthyll, A. Holtsch, B. Uder, K. Jacobs, M. Weinl, M. Schreck, Epitaxial Growth of Graphene on Single-Crystal Cu(111) Wafers, Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry (2018), doi.org/10.1016/B978-0-12-409547-2.14167-8)