Mbe Growth And STM Study Of Silicene, Borophene And Co Molecular Crystal

In the year of 1959,Richard Feynman,the American physicist,hypothesized that what will happen if we can arrange the atoms follow our willing and give full play to the characteristics of each atom? The development of low-dimensional nano-materials and the invention of scanning tunneling microscope(STM)make the hypothesis come true.On one hand,according to Moore’s Law,integration of Chips doubles in every two years.We are going to reach the limitation of chip’s integration soon.Searching new kind of nano materials and new physical effect to develop high speed devices are urgent.Discovering of graphene,open the gate of two-dimensional(2D)materials.Graphene also has some defects even though it has attracted a lot of attention because of it’s excellent properties.To solve these problems,researches were performed on tuning properties of graphene,as well as on searching a series of graphene-like 2D materials.Silicene(belongs to the same main group as C)and borophene(belongs to the same periodic element group as C)come into our life.And their synthesis and electronic properties caused a lot of interests.On the other hand,the invention of STM,let us can detect and manipulate atomic structures in real space.STM is a powerful tool to study low-dimensional nano materials as well as structures and physical or chemical properties of molecules on metal surface,which have a wide potential application in catalyze industry.In the thesis,we have studied structures and properties of silicene,borophene and CO molecular crystal on metal surface by MBE and STM.The thesis contains three main parts as follows:1.We halogenate monolayer silicene on Ag(111)surface by MBE method and studied their structures by STM.We found fully halogenated silicene tend to form several ordered structures.The mechanics of formation of the ordered structures were explained through analysis.Our result may provide a platform to study the new physics based on halogenated silicene.2.Properties of borophene on Ag(111)were studies by STM.We found an 1D charge density ordering at the boundaries of borophene which were may caused by charge density wave.We have successfully synthesized honeycomb borophene on Al(111)surface and broke the previous prediction of unstability of honeycomb borophene.Combined with theoretical calculation,honeycomb borophene stabilized by the near 1 electron charge transformation from the Al(111)substrate to each boron atom.3.We have studied the absorption of CO on Cu(111)by MBE at low temperature and in suit STM characterization.In the issue of little absorption at 77 K,the CO molecules show an abnormal diffusion near point defect on Cu(111)surface.In the issue of full absorption,we have discovered high-density crystal phases of CO molecules and an abnormal phase transition between high density liquid crystal and low density crystalline solid when we cool down the sample from 77 K to 5 K.Combined with theoretical calculation,we found the abnormal phase transition is due to the vibrational entropy of CO molecules which usually neglected in dealing similar problems.Our founding provides a guide to deal with similar gas absorption problem on surface and phase transition phenomena.