Particle-Size-Induced Valence Changes in Samarium Clusters

Samarium clusters exhibit mixed-valence behavior which is sensitive to particle size. X-ray photoemission and ultraviolet photoelectron spectroscopy data show samarium to be primarily divalent ($4f^6$) at small particle size. The trivalent state ($4f^5$) becomes progressively more abundant with increasing size, becoming the dominant state for the bulk metal. These results are interpreted in terms of band narrowing due to reduced surface coordination, which is more dominant than surface tension effects in establishing the valence of small samarium clusters.