R. Dombrowski

A low-temperature ultrahigh-vacuum scanning tunneling microscope with rotatable magnetic field

We present a new design of a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope setup with a combination of a solenoid and a split-pair magnet. The scanning tunneling microscope can be operated at temperatures down to 8 K and in a rotatable magnetic field of up to 1 T. Magnetic fields of up to 7 T perpendicular and 2 T parallel to the sample surface can be applied. The UHV part of the system allows in situ preparation and low energy electron diffraction/Auger analysis of samples. First topographic and spectroscopic measurements on p-InAs(110) are presented.

Low temperature scanning tunneling spectroscopy on InAs(110)

Abstract We review our recent work on low temperature scanning tunneling spectroscopy (STS) in magnetic field on InAs(110). First, we describe the influence of the tip on the sample. It results in band bending at the InAs-surface, more precisely in a so called tip induced quantum dot. STS of the quantum dot states is used to reconstruct the quantum dot potential, a major requirement for all further measurements. Second, we analyze the appearance of ionized dopants in constant current images within a simple model based on the local band bending approach. Third, we show scattering states of ionized dopants at different energies appearing in normalized d I /d U -images. Comparison with calculated scattering states in the Wentzel–Kramers–Brillouin (WKB)-approximation gives good correspondance and a good estimate of the depth of individual dopants beneath the surface. Finally, we discuss the energy quantization of the unoccupied states of the tip induced quantum dot in magnetic field. The corresponding d I /d U -curves exhibit peaks attributed to the Landau quantization and the spin splitting of the quantum dot.

Landau Level Quantization Measured by Scanning Tunneling Spectroscopy on n-InAs(110)

The in-situ cleaved n-InAs(110) surface is studied by low temperature scanning tunneling spectroscopy and microscopy in magnetic fields up to 6 T perpendicular to the surface. The dI/dV(V) curves exhibit characteristic oscillations in magnetic field, which are attributed to Landau levels in the conduction band. The energy dependence of the effective electron mass is determined. Dopants reduce the Landau level energy. As expected, the energy reduction decreases with increasing Landau level number.