It has been well documented that the surfaces of solids may differ from their bulk counterpart. The symmetry that a bulk possesses is broken at the surface. Due to this broken symmetry in the reduced dimension of the surface, the energetic of the surface also differs from the bulk counterpart. Reconstruction, charge redistribution, and surface alloying are phenomena that minimize the surface free energy.
Surface properties of scientifically and technologically important bimetallic systems are the main focus of this dissertation. Specifically, surfaces of bulk alloy or heteroepitaxially grown metal-on-metal systems have been investigated primarily with two indispensable surface techniques, scanning tunneling microscopy and angle-resolved photoemission spectroscopy, which reveal the atomic and electronic structure of bimetallic systems, respectively.
In the first system detailed herein, the surfaces of the ordered intermetallic alloy FeAl(110) exhibit surface segregation , which changes the Al concentration in the near surface region. The segregation and corresponding concentration change of Al induces a reconstruction on the surface as a function of annealing temperatures. The increased Al concentration gives rise to stronger Al and Fe interaction and results in hybridization of the Al-sp and Fe-d. Moreover, the oxide that forms on this surface is a homogeneous ultrathin alumina film. Because of the nanometer thickness, this thin film displays a two dimensional electronic structure. It is concluded that an even mix of octahedrally and tetrahedrally coordinated Al ions in the zigzag-stripe thin-film alumina structure is formed, which has been under scientific debate for many years.
The atomic and electronic structure of Ag on Cu(110) and on Cu(100) systems has also been studied. These bimetallic systems form a surface confined alloying at the initial stages of growth and an overlayer phase as the Ag concentration increases in order to relieve the strain caused by Ag atoms, which have larger atomic size than Cu atoms. Electronically, bulk like energy distribution of the states indicates stronger interaction of Ag and Cu in the surface alloy phases than the overlayer phase, which displays only a two dimensional structure.