Introduction

The invention of the scanning tunneling microscope (STM) by Binnig and Rohrer in 1982 revolutionized surface science. Both were awarded with the Nobel Prize in Physics for their technical breakthrough which facilitates the visualization of the atomic structure of surfaces in real space. The nobel lecture can be found in [1]. Since its invention the STM has undergone constant further development. Today, STM studies are no more bound to ultrahigh vacuum conditions as in the early years. Tunneling microscopes have been developed that can be operated at atmospheric pressure to study, e.g., morphological changes at catalyst surfaces under reaction conditions or the atomic structure of electrodes in electrochemical environments. Some of the most impressive insights into have taken place in the field of fundamental surface physics. For example, it has been shown that electron waves (to be precise: the square of the wave function representing the probability density) can directly be imaged: an example is shown in fig. 1, where the waves of conduction electrons from Cu trapped in a circular potential well of adsorbed Fe atoms at a Cu(111) surface can be seen [2].

Figure 1: Standing electron waves observed in a circle of iron atoms