Abstract
This thesis contains two research subjects. In the first part, we constructed a scanning tunneling microscope (STM) and used this STM system to study the superconductivity of FeSe0.3Te0.7 thin films. The FeSe0.3Te0.7 sample, fabricated using pulse laser deposition, was designed to have two orientations of grains on the same MgO substrate with an angle between these two grains at about 45 degree. Significant enhancement of superconducting energy gap from 1.78 meV to 18.6 meV near the grain boundary region was observed. Since the grains of these two orientations squeeze each other in the boundary region to generate substantial strain force, we suggest that the superconductivity of FeSeTe can be enhanced in the strained region. In the second part, we developed an instrument that can probe the distribution of magnetic fields and surface topography simultaneously by integrating scanning SQUID and STM into one, which is named as Scanning Squid Tunneling Microscope (SSTM). It is well known that scanning SQUID has a high sensitivity in detecting magnetic flux, and STM can resolve surface topography and probe electric properties at atomic scale. This newly designed SSTM system is therefore a powerful tool to analyze the correlations between magnetic and electric properties of intended sample surfaces. We demonstrated the capabilities of this SSTM system by measuring the superconducting Nb films and the colossal magnetoresistive La0.67Ca0.33MnO3 films. We have found an interesting evolution of superconducting energy gap of Nb varying symmetrically in a trapped magnetic flux region, and some periodic magnetic field ripples of the La0.67Ca0.33MnO3 films in the presence of a uniform external magnetic field. Although the physical origins of these observations are still unclear, our SSTM is undoubtedly proven a powerful instrument to explore new physics and new materials.