Abstract
Alloys are mixtures of two or more metals. Alloys in which the positionsof the atoms form an approximate crystal structure, but where the patternformed by considering the chemical elements to which the atoms belong isnot periodic, are of fundamental importance to metallurgy andnanotechnology. Atoms belonging to the same element in such ‘disorderedalloys’ will exhibit a variety of environments. For example, in an alloyconsisting of two elements A and B, the environment of an A atom couldconsist entirely of A atoms, entirely of B atoms, or a mixture of both.Differences in the environments of A atoms leads to differences in theelectronic structures ‘within’ these atoms, which can be detectedexperimentally using core-level X-ray photoelectron spectroscopy(CL-XPS). Therefore the prospect exists of using CL-XPS to probe specificatomic environments in alloys. One possible application of this is tonon-destructively characterise alloy-based nanomaterials and nanodeviceson the atomic scale. However, to make this a reality one must understandthe relationship between an atom’s environment, its electronic structure,and the binding energies of its core levels. I will describe a simple model for the distribution of core level bindingenergies in alloys, and apply it to a variety of disordered alloys, withthe aim of elucidating the relationship between atomic environment andcore level binding energies in alloys. The model reveals a number ofinteresting phenomena which must be taken into account when interpretingthe CL-XPS spectra of these systems. These include anomalously large’disorder broadenings’ of spectra in alloys exhibiting inhomogeneousconcentration profiles; and a counterintuitive relationship between anatom’s core level binding energies, and its local and globalconcentration of ‘unlike’ atoms: increasing the local concentrationalters the core level binding energies in the opposite direction toincreasing the global concentration.
