Direct Observation of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>4</mml:mn><mml:mi>f</mml:mi></mml:math>Splitting between (110) Surface and Bulk Atoms of W

Abstract

With large surface-sensitivity enhancement achieved by use of $p$-polarized light, soft-x-ray photoemission spectra of $4f$ core levels from the outermost atoms of the (110) face of tungsten have been observed. High-resolution spectra show two well-separated $4f$ lines split by 0.30 eV, with the low-binding-energy peak being assigned to surface atoms. The ratio of the intensity of the surface peak to the bulk peak as a function of photon energy exhibits striking features which are tentatively explained.