Synthesis and Atomic Scale Investigations of Fe-Chalcogenides from Bulk Crystals down to Single Layers

This dissertation reports on investigations of bulk FeTe crystals as well as thin-film heterosystems of the compounds FeTe and FeSe, by means of spin-polarized scanning tunneling microscopy and angle-resolved photoemission spectroscopy. This includes a real space spin-polarized scanning tunneling microscopy investigation of the magneto-structural phase transition of bulk Fe(1+y)Te with different values of excess iron y. These investigations reveal two different low-temperature phases and continuously map the magneto-structural phase transition. The phase transitions in this material are regarded essential for the understanding of the superconducting pairing mechanism in iron-chalcogenide compounds. The growth procedure of bulk Fe(1+y)Te conditionally enforces a finite value of excess iron (y>0) in the compound which has effects on the magnetic and superconducting order in the materials. However, nearly stoichiometric FeTe thin films grown on Bi2Te3 completely lack excess iron at the surface and are therefore ideal for the investigation of nearly pure FeTe. The antiferromagnetic order in such thin films is investigated by temperature dependent spin-polarized scanning tunneling microscopy measurements revealing an enhanced magneto-structural transition temperature T(N) as compared to the bulk compound. Scanning tunneling microscopy measurements show three rotational domains of the FeTe films, enabling to unravel the electronic structure of these thin films as investigated by angle-resolved photoemission spectroscopy of Fe(1+y)Te single crystals. A combined scanning tunneling microscopy and angle-resolved photoemission spectroscopy study further examines the doping effect of the alkali metal rubidium on the Fe(1+y)Te bulk and FeTe thin film system. In addition, the structure and electronic properties of FeSe thin films are studied by scanning tunneling microscopy and spectroscopy showing the reduction of the critical superconducting temperature Tc as compared to the corresponding bulk compound. Finally, the design and construction of a molecular beam epitaxy growth chamber is presented, including a reflection high-energy electron diffraction system, which enables future controlled layer-by-layer growth of iron-chalcogenide thin-film heterostructures.