Scanning Tunneling Spectroscopy of Magnetic Bulk Impurities

Magnetic impurities in a non-magnetic host metal have beenactively explored in condensed matter physicsin recentlast decades. Fromboth fundamental and appliedviewpoints these systems are very interesting because they can exhibit strong electronic correlations that give rise to various fascinating phenomena beyond the single particle picture. Up to now our understanding of the underlying processes remains limited due to difficulties involved in measuring these systems on a microscopic scale. Withtheir unique control, scanning tunneling microscopy (STM) and spectroscopy (STS) allow for the first time investigations ofphenomena occurring on very small length and energy scales. Here, single magnetic iron and cobalt atoms embedded beneath a metal surface are investigated using these techniques. In particular, the transition from single impurity Kondo physics to two interacting impurities is studied in real space. This thesis contains a comprehensive description of the STM /STS technique, sub-surface impurities, as well as single- and two-impurity Kondo physics - and as such offers avaluable introduction to newcomers to the field.