XPS allows the identification and quantification of elements present on the surface of thin films & coatings. By analysing the binding energies of the photoelectrons, it is possible to determine the elemental composition, providing critical information for quality control and material characterisation. Furthermore, the quantitative nature of XPS makes it an indispensable tool for determining the concentration of elements within a thin film or coating. This information is vital for tailoring material properties to specific requirements. It is also important to note that XPS is sensitive to the chemical state of elements, providing information about their oxidation states and bonding environments. This is particularly valuable when assessing the stability and reactivity of thin films, as changes in chemical states can impact the material’s performance over time. An example of the value of XPS applied to thin-film characterisation is the chemical state determination of chromate passivation chemistries. Where a thin film thickness is less than the sampling depth of XPS, chemical depth distribution may be determined using angle-resolved XPS (ARXPS). ARXPS involves varying the collection angle of the ejected photoelectrons relative to the surface normal. By tilting the sample relative to the AXIS of the electrostatic lens column of the spectrometer, the sampling depth is decreased. With photoelectrons collected at an angle of 75 degrees from the surface normal, the sampling depth is decreased from 10 nm to 2-3 nm. Spectra acquired over a range of collection angles can be used to reconstruct a concentration depth profile using algorithms available in our ESCApe software. Depth information can also be derived by using different excitation photon energies. By using the Ag Lα excitation HAXPES source, the sampling depth can be increased to almost double that of the conventional Al K α excitation. Comparing spectra excited with the two different excitation energies, depth distribution can be inferred. A sputter depth profile involves removing material using an ion source and repeating this in a sequence with XPS analysis. Energetic ions are used to remove material from the sample. Over the last decade, significant advances have been made by using cluster ions for depth profiling. The cluster size and energy can be controlled to optimise sample sputtering and minimise ion induced chemical changes. The use of cluster ions generated by the Minibeam 6 Gas Cluster Ion Source (GCIS) has allowed successful depth profiling of organic polymer thin films and multilayer materials.
