Expanded austenite γN formed after nitrogen insertion into austenitic stainless steel and CoCr alloys is known as a hard and very wear resistant phase. Nevertheless, no single composition and lattice expansion can describe this phase with nitrogen in solid solution. Using in situ X-ray diffraction (XRD) during ion beam sputtering of expanded austenite allows a detailed depth-dependent phase analysis, correlated with the nitrogen depth profiles obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) or glow discharge optical emission spectroscopy (GDOES). Additionally, in-plane XRD measurements at selected depths were performed for strain analysis. Surprisingly, an anomalous peak splitting for the (200) expanded peak was observed for some samples during nitriding and sputter etching, indicating a layered structure only for {200} oriented grains. The strain analysis as a function of depth and orientation of scattering vector (parallel/perpendicular to the surface) is inconclusive.

In situ x-ray diffraction (XRD) during ion implantation or thin film deposition is a powerful method to follow the time evolution of diffusion and phase transition processes in thin films, even as the depth resolution is still dominated by the information depth of the x rays. However, in the case of sputter etching with energetic ions at moderate temperatures, where no diffusion or phase transformation processes are active, this limitation is no longer of concern. Here, thin surface layers which are removed by sputtering can be identified with a depth resolution of 25 nm or better—while information from the substrate—despite overlayers of several micrometers—is accessible. However, considerable mathematical operations are necessary to convert the time series of diffractograms measured by XRD into a depth series. In this paper, a method is highlighted describing which depth-resolved properties of thin films can be accessed using such in situ measurements during ion beam sputtering in the model system austenitic stainless steel + nitrogen: (i) the influence of concentration gradients on the peak shape and peak width for conventional XRD scans in Bragg–Brentano geometry is determined; (ii) correlations between the local nitrogen concentration and the local lattice expansion can be established; and (iii) the evolution of the scattering intensity with depth becomes accessible, thus depth-resolved information on defect densities or grain size (normal to the surface) can be extracted without resorting to transmission or scanning electron microscopy.

Large area manufacturing processes of thin films such as large-area vacuum roll-to-roll coating of dielectric and gas permeation barrier layers in manufacturing industry require a precise control of e.g. film thickness, homogeneity, chemical compositions, crystallinity and surface roughness. In order to determine these properties in real time, hyperspectral imaging is a novel, cost-efficient, and fast tool as in-line technology for large-area quality control. We demonstrate the application of hyperspectral imaging to characterize the thickness of thin films of the multilayer system ZTO/Ag/ITO produced by roll-to-roll magnetron sputtering on 220 mm wide PET substrate. X-ray reflectivity measurements are used to determine the thickness gradients of roll-to-roll produced foils with sub nanometer accuracy that serve as ground truth data to train a machine learning model for the interpretation of the hyperspectral imaging spectra. Based on the model, the sub-layer thicknesses on the complete substrate foil area were predicted which demonstrates the capabilities of this approach for large-scale in-line real-time quality control for industrial applications.