MBE Growth Of Pb And Pb_1-xBi_x Ultra-thin Films And Scanning Tunneling Microscopy Study

Bulk Pb is a type I conventional s-wave superconductor whose critical temperature(Tc)is 7.2K.Elemental Pb is the simplest superconducting system among those with strong spin-orbit coupling.Due to the strong Quantum Size Effect(QSE)and superconductivity,Pb films have been extensively studied both theoretically and experimentally.Besides,both Pb and PbxBi1-x films are proper systems to study the topological superconductor.We used molecular beam epitaxy(MBE)chamber to grow such two kinds of films on the Si(111)substrate.And then we used Scanning Tunneling Microscope(STM)system to characterize the topography and electronic properties of the films.The first chapter shows the Josephson Effect,Josephson junction and three growth modes of films.In the second chapter,correspond experimental instruments and techniques are introduced.In the third chapter,the history of research in QSE of Pb film and recent progress of Pb film are introduced.The fourth chapter shows the Pb films on the Si(111)substrate with high quality.We determined the thickness of the different Pb films by measuring the positions of the quantum well states(QWS).By measuring tunneling spectroscopy of the SIS junction(using Pb tips)and compared with NIS junction(using W tips),we show the improved dI/dV spectra resolution with Pb tips.We used the Pb tip,tunnel together with Pb films to make up the SIS junction,and observed the Josephson Effect in the junction.Furthermore,we estimated that the temperature of Pb tips is 3.6K-4.2K lower than the sample in such low STM system.In the last chapter,we display the SIC phase with high quality of Pb on the Si(111)substrate,and then the method to grow PbxBi1-x films on the SIC phase is introduced.We also show the topography of PbxBi1-x films by STM.