Experimental Study of the Photoelectron Spectra of Magnesium–Barium Alloy

Magnesium crystals and their alloys with barium are studied in a multifunctional ultra-high vacuum installation using Auger and photoelectron spectroscopy. Krypton and xenon resonance lamps are used as radiation sources in the vacuum-ultraviolet region. The energy distributions of photoelectrons N(E) and spectral dependences of the quantum yield of photoelectron emission before and after heating magnesium and magnesium–barium alloy are studied. The contribution of surface states and bands formed by magnesium and barium atoms is analyzed. As a result of comparing the photoelectron spectra of magnesium and magnesium–barium alloy obtained at hν = 8.4 and 10 eV, it is found that the electronic structure contains maxima at 0.6–0.7, 1.1–1.2, and 1.5–1.6 eV below the Fermi level caused by the density of electronic states of magnesium and barium. After annealing the magnesium–barium alloy with a volume concentration of barium atoms of 1% at a temperature of 350–400°C, the segregation and thermal diffusion of barium atoms in the alloy surface layers are observed. For the first time, the chemical shifts of the magnesium Auger peaks are established as the concentration of barium atoms in the alloy surface region increases. They are related to the formation of intermetallic compounds with different stoichiometric compositions. It is shown that in the photon-energy range of 5 eV, the quantum yield of photoelectron emission of the alloy is almost an order of magnitude greater than that of pure magnesium. The results are discussed on the basis of published theoretical calculations, in which the magnesium densities of states of magnesium–barium model structures are used.