Valence-band structure of silver alongΛfrom angle-resolved photoemission

Abstract

Angle-resolved normal photoemission spectra of Ag(111) are reported for photon energies $h\nu =6-32\mathrm{}$ eV, obtained by the use of synchrotron radiation. Very good agreement was found with the theoretical relativistic-augmented-plane-wave band structure of Christensen. Experimental dispersion relations along $\Lambda$ were derived and tabulated. The $d$-band spacings at $\Gamma$ were determined for the first time and were interpreted to yield the "ligand field" parameters $10Dq=0.865\pm 0.027$ eV, $\xi \mathrm{}\left(4d\right)=0.232\mathrm{}\pm 0.011$ eV. These parameters, which are meaningful only at $\Gamma$, are in excellent agreement with Christensen's band structure. The spin-orbit parameter is very close to the free-atom value, and the positive sign of $10Dq$ indicates attractive interaction of the electrons with neighbor ion cores. Two pieces of evidence for indirect transitions via thermal broadening were noted. A resonance at $h\nu =22\mathrm{}$ eV in the band-4 (${\Gamma }_7$) intensity was attributed to a flat region in band $7 \left({\Gamma }_6\right)$. The flatness in band 7 (and pershaps band 8) also yields an effect equivalent to the angle-resolved secondary electron emission phenomenon of Willis and co-workers. In this case electrons moving in the [111] direction are scattered down into band 7 and trapped, yielding a peak at 17-eV kinetic energy.