electronic structure of beta'-nickel-aluminum and its low-index, high-symmetry surfaces

The electronic structure of beta'-NiAl alloy and its low-index high-symmetry surfaces has been studied with a combination of photocurrent and first-principles electronic structure calculations. Bulk calculations have been performed with both the LMTO and LSMS computational codes, and the core level shifts upon alloying are discussed in detail. Defect formation and bonding mechanisms in off-stoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces are investigated using the LMTO and LSMS, and electronic potentials for input to the photocurrent code are evaluated in the surface geometry. Photocurrent calculations for the (110), (100) and (111) surface are presented and compared with high quality experimental measurements. The (100) surface is found to have a double Ni termination. This defect layer is predicted to sustain a magnetic moment. The rippling of the (110) surface is modelled in the photocurrent calculations, and is found to effect the spectral profile in significant ways. The calculated photocurrent spectra are used to predict the surface composition for the (100), (111) and (110) surfaces, and the rippling value of the (110) surface. Agreement with experiment is good. A method for utilizing computational photoemission spectra to predict the structure and composition of metallic surfaces is presented, and its strengths and weaknesses are discussed.