Depth selective local coordination in CoFeB thin films probed by XAFS and ToF-SIMS

Abstract

The compositional profile and local atomic structure in a Co40Fe40B20 thin film sandwiched between two W layers, have been probed combining time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray absorption fine structure spectroscopy techniques in standing wave geometry (SW-XAFS). The data analysis demonstrated inhomogeneities in the composition profile as well as in the local atomic structure around transition metals, along the film thickness. Boron concentration shows a gradual increase from the bottom to the surface of the film The quantitative analysis of the Fe and Co K edges SW-XAFS spectra reveals distinct differences in the local coordination geometry along the film thickness and between the two metals. Specifically, the local structure around Fe appeared to be more disordered on average compared to Co and the bond lengths exhibited significant variation as a function of depth,