STM study of the preparation of superconducting Ta(110) surfaces

Exciting physics is expected on superconductor-ferromagnet interfaces. Scanning tunneling microscopy/spectroscopy (STM/STS) has an great potential to study such systems due to it's lateral, energy and spin resolution capabilities. However, extreme sensitivity of STM/STS to surface contaminations requires a clean sample for reliable experiments. We explore possibilities to obtain clean and homogeneous Ta(110) surfaces which are characterized by STM/STS, by low-energy electron diffraction, and by Auger spectroscopy. In an early stage of the preparation we identify a surface reconstruction which is attributed to oxygen contaminants, favored by oxygen's high solubility and diffusivity within the Ta bulk crystal. We remove the oxygen from the surface by repeated cycles of high-temperature annealing in ultrahigh vacuum and Ar ion sputtering. Using this approach we succeeded in the preparation of surfaces with an effective contaminant-coverage of less than 5%.