The focal point of my thesis lay on the construction of an ultrahigh-vacuum, low-temperature STM (scanning tunnelling microscope). On the basis of already existing instruments, a highly stable STM has been developed, which is capable to image and manipulate surfaces and adparticles on the atomic scale between 4.9 K and 300 K. As compared to the predecessors, the stability of the STM has been enhanced by an optimisation of the scanner and by improved thermal resistances the minimal temperature has been lowered from 15 K to 4.9 K. These measures led to a vertical resolution better than 0.2 pm and allow furthermore the manipulation of single atoms. The simultaneous optical access during the measurements permit the combination of the low-temperature STM with optical methods.
The lowest actually attainable temperature at the sample was determined by dI/dV-spectroscopy of the LDOS of superconductive Pb-films on a Ag(111)-substrate. By this an energy resolution of only 2 meV has been demonstrated and a minimal sample temperature of T=4.9 K has been verified.
With the system LiF/Ag(111) the fractal growth of an ionic insulator on a metal substrate has been observed for the first time. The data are consistent with the scaling law for island densities and the island density distribution for the critical clustersize corresponding to i = 1. The data yielded an estimation for the diffusion barrier of LiF-monomers on Ag(111) of 30 - 47 meV and the fractal dimension has been determined to be d=1.75±
0.01. The local cubic symmetry show a (100)-termination of the LiF-islands. At the step edges an unusual symmetrical growth to both sides has finally been found which can be explained by the charge redistribution at the step edges.
The Cr(110)-surface has been investigated at temperatures between 6 K and 145 K with STM and it was shown for the first time that the charge density wave which accompanies the spindensity wave in Cr produces a modulation of the charge density at the surface. For tunnelling voltages in the range of ±
150 meV a charge density wave with a wave length of 42 ? was observed. The observed wave pattern could be explained as the projection of the volume charge density wave. Through the coupling of the spin density wave with the charge density wave the antiferromagnetic domain structure can thus be imaged indirectly on a nm-scale.
Atomic manipulation with the STM was used for the determination of the lifetime of surface electrons. For this experiment a triangular scattering geometry has been constructed consisting of 51 Ag atoms on a Ag(111)-surface. The electrons of the surface state are scattered by the adatoms, resulting in a standing wave pattern which has been measured in the dI/dV-mode. Based on a multiple scattering approach, calculations of the wave pattern have been performed. Adjustment of the calculations to the data yields the absorption and the phase of the scatterers and the electron lifetimes. With this experiment the lifetime of surface electrons inside a artificial atomic structure has been measured for the first time.
