Measurements of white line intensities in 4d transition metals using Electron Energy Loss Spectrometry (EELS)

Abstract

A feature of considerable interest in the electron energy loss spectra of transition metals is the L23 edge which is composed of two sharp “white lines” superimposed on a broad edge that makes up the trailing background. The white lines are due to the excitations of electrons from filled 2p1/2 and 2p3/2 states to unoccupied 3d or 4d states, and the background intensity is due to continuum excitations. Recent work on the white lines of the 3d transition metals has shown that when normalized to the continuum excitations, the total white line intensity decreases nearly linearly with atomic number (or d band occupancy) across the 3d series. Furthermore, this linear relationship may be used to measure the changes in 3d state occupancy local to specific atoms during alloying and during solid state phase transformations. In the present paper the experimental analysis of the white lines is extended to the 4d transition metals and is then compared to experimental results from the 3d metals.Electron-transparent specimens of the pure 4d metals were prepared by standard electropolishing and evaporation techniques. To prevent oxidation of the Yttrium specimen, however, a 40 nm film of Yttrium was deposited between 15 nm films of Vanadium by direct current ion sputtering in a chamber with a base pressure of < 1.0 × 10−7 Torr. Energy loss spectra were obtained using a Gatan 607 electron energy loss spectrometer attached to a Philips EM 430 electron microscope operating in image mode at 200 kV.