Fig. 3

Electronic properties of the AuPd nanoalloys measured by XANES spectroscopy. a The XANES spectra of the Au L₃-edge of monometallic Au, AuPd nanoalloys and reference Au foil. b The XANES spectra of the Pd K-edge of monometallic Pd, AuPd nanoalloys and reference Pd foil and PdO. The Pd XANES spectrum at the K-edge of the Pd foil exhibited a pronounced white line due to the unfilled Pd d-band, and the spectrum of PdO exhibited an even more obvious white line that shifted to a higher threshold energy because of the higher oxidation state of Pd in PdO. The hybridization-mediated 1 s → 4d, dp (a) absorption transition in the pre-edge region was unresolved. The near-edge spectrum showed two resonance peaks that are due to the 1 s → 5p (p) and 1 s → 4 f (f) transitions through hybridization. The shape of the second absorption edge reflected the extent of the 4d-5p hybridization. This feature was insignificant in the spectrum of the PdO reference