An X-ray Photoelectron Study of Valence Charge in Transition Metal Aluminides

In an earlier paper we proposed a new method for interpretation of background structure in X-ray photoelectron (XP) spectra and showed that this could be used to study bonding states in intermetallic compounds using, as an example, a particular Ti—Al alloy. In this paper we have applied this method to study a set of aluminides: Me—Al alloys, where Me represents a transition metal: Ti, V, Fe, Ni or Nb. The method for background interpretation is based on a peak-shape parameter k, which links the intrinsic energy loss structure, associated with a given line in the XP spectrum, to the atomic number. This parameter is thus related to the number of final state configurations available to the photoexcited atom or ion and we show, now, how the value for aluminium varies across a series of compounds with the transition metals. The results for k are accompanied by measurement of the Auger parameters which may be indicative of the charge transfer occurring between Al and Me and thus are also influenced by the final state configuration. The approximate proportionality found between these two parameters gives confirmation that k may be a sensitive probe of the final state and bonding effects and confirms the extent to which aluminium orbitals interact with the 3d transition metal structure of vanadium, iron and nickel, and the 4d of Nb. This is in full accord with the results obtained from the TiAl alloy. Complementary information was obtained by comparing the values of k for the pure metals with those for the vanadium, iron, nickel, niobium and aluminium peaks in the intermetallic compound. XP spectra have been obtained from the alloys and these are also presented in the paper. As a result of this work it is concluded that the final state features of the spectra result from charge transfer between sp and sd valence bands.