V 2p core-level spectroscopy of V2+/V3+ mixed valence AV10O15 (A = Ba, Sr) and Ba0.9Sr0.1V13O18

We have studied the surface electronic structure of AV10O15 (A = Ba, Sr) and Ba0.9Sr0.1V13O18 by using x-ray photoemission spectroscopy (XPS). The V 2p XPS shows multiple peaks associated with the charge fluctuation in the system. The relative intensity of each valence component can be extracted by Gaussian and Voigt fittings. The result strongly depends on the number of Gaussians/Voigts. In BaV10O15 and Ba0.9Sr0.1V13O18, the surface state has more V3+ than the bulk. In addition to the presence of surface V3+, the V2.5+ in AV10O15 (A = Ba, Sr) and V2+ in Ba0.9Sr0.1V13O18 systems are observed even in the surface sensitive XPS. The number of Gaussians/Voigts should be as large as four for the V 2p3/2, in order to obtain the results consistent with the bulk sensitive HAXPES study.