Density of States of Ni: Soft-X-Ray Spectrum and Comparison with Photoemission and Ion Neutralization Studies

Abstract

Soft-x-ray studies have been made on paramagnetic Ni and interpreted in terms of the single-particle density of states. In particular, the Af 2 ,3 emission spectrum has been investigated, using improved experimental techniques. Measurements were made at 960°C, at an average pressure of 5X10~8 Torr, using an oxide-free surface. Fine structure was observed in the spectrum. Although first-principles correction of self-absorption effects and satellite and subband overlap is not yet possible, careful consideration is given them, with the result that the Ms band can be resolved from the accompanying structure in a plausible way. Most of its features can be taken with reasonable confidence to be characteristic of the true M% emission band. Comparison is made with earlier soft-x-ray results, with band calculations for paramagnetic Ni, and with ion neutralization and photoemission measurements on ferromagnetic Ni. Systematic variations in transition matrix elements and lifetime broadening appear important when relating any experiment with theory, and an aspect of each of these problems has been considered quantitatively. The variation obtained is more severe for the photoemission than for the soft-x-ray analysis. The ion-neutralization and soft-x-ray results appear closer to the single-particle density of states.

Electronic densities of states from x-ray photoelectron spectroscopy

“…The SXS results in figure 8a were obtained from measurements of L x rays [3]. Similar work on M x rays (for whi ch tran sition probability modulation may be a smaller effect [2]) shows somewhat more fine structure and a FWHM of -3 eV [2] , agreeing rather well with XPS. Nickel has also been investigated by INS [4] and a smooth peak of roughly the same position and width as the XPS peak is observed.…”

“…Th e various theoretical prE) es timates for Ni have been dis cussed previously [2,12]. The FWHM of these estimates vary from -3 to 4.5 eV, with the smallest width co ming from an un hybridized calculation [14J.…”

“…The principal tec hniques presently being appli ed to metals are soft xray s pectroscopy (SXS) [2,3] ion-neutralization spectroscopy (INS) [4], and photoele ctron spectroscopy (by me ans of ultraviolet [5] or x-ray [6 ,7] excitation)_ In each of these methods, either the initial or the final state involves a hole in the bands under study_ Thus the measuring process is inherently disruptiv e_ The actual initial and final states may n ot be simply related to th e undi sturbe d ground s tat e [8] , a nd onl y for this ground state does prE) have precise meanin g. Eve n if the deviation s from a ground state descri pti on ca n be neglected , th ere are co mpli cati ons for eac h of the above techniques in r elatin g meas ured qu a nti ties to prE) [2 ,3 ,4 ,5]. Ne ve rth eless, all fo ur have bee n a pplied with some success, and , wh ere possibl e, expe rim e ntal res ults have been compared to the theoretical predictions of one-electron band theory.…”

Photoemission from Clean and Cesium-Covered Nickel Surfaces

“…to the photoemission peak at -4.5 eV. 8,9 Densities of states calculated from theoretical band structures show a similar structure with a high density of d electrons extending to about 4 eV below the Fermi level and a much smaller density of electrons extending to lower energies. 10 Various experimental results that are interpreted as showing the density of filled states in Ni are exhibited in Fig.…”

“…8 The resolution of the PED's is about 0.2 eV, so that energy losses smaller than this, including specifically single-phonon losses, are negligible for this work. 178 tion and hv is the photon energy.…”