Surface coatings and thin films are of great commercial importance in many industries and are used to enhance or provide required properties to bulk materials specific to their applications. Thin films can range from tens of Angstroms to several microns in thickness and find application in areas as diverse as optical anti-reflective coatings, architectural glazing and drug eluting thin films in the pharmaceutical industry. XPS is ideally suited to characterising the surface chemistry of these thin films and when combined with sputter depth profiling can be used to determine the elemental and chemical composition as a function of depth through the film.
Here we detail a sputter depth profile through a laser mirror sample consisting of multiple, alternating layers of GaAs and AlAs on a GaAs single crystal. The samlple is shown in the schematic diagram below.
Figure 1: Schematic diagram of multilayer GaAs/AlAs laser mirror.
The sample was sputter depth profiled using 500 eV monatomic Ar+ ions rastered across the sample to create a flat bottomed sputter crater. The sample was analysed between sputter cycles using a 110 um diameter analysis area at the centre of the sputter crater. The low Ar+ ion energy was chosen to minimise the damage and mixing of the layers during the sputter process. Spectra for the core levels were acquired in snapshot mode which can reduce the total experimental duration by up to 40% compared to traditional scanned acquisition modes as snapshot mode does not require the lens/analyser to be scanned during data acquisition and therefore eliminates the 'over scanning'.
Figure 2: Concentration depth profile through laser mirror.