Epitaxial Growth of Ba(Fe_1-xCo_x)_2As_2 and LiFeAs Pnictide Layers using Pulsed Laser Deposition

Abstract

Most scanning tunneling microscopy (STM) investigations of high-Tc superconductors have been performed on the cleaved surface of single crystal samples. However, the combination of STM with well-controlled growth, such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD), overcomes problems due to various imperfections in materials and ambient contamination, and therefore enables researchers to reveal the intrinsic properties. In this thesis, I will present STM investigation of superconducting iron pnictide thin films grown by PLD. Epitaxial thin films of Ba(Fe1-xCox)2As2 and LiFeAs were grown on SrTiO3(001) substrates and examined in a STM chamber directly connected to the growth chamber. The crystallinity of the epitaxial thin films was monitored using reflection high-energy electron diffraction (RHEED) and low energy electron diffraction (LEED) during and after deposition. A (2×2) structure was observed in the Ba(Fe1-xCox)2As2 surface. A (1×1) structure was revealed in the LiFeAs surface. These films exhibited superconducting behavior in four probe transport measurements.