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For smooth surfaces, chemical composition can be readily analyzed using various spectroscopic techniques, a prominent example is X-ray photoelectron spectroscopy (XPS), where the relative proportions of the elements are mainly determined by the intensity ratio of the element-specific photoelectrons. However, this analysis becomes more complex for nanorough surfaces like black silicon (b-Si) due to the geometry's steep slopes, which mimic local variations in emission angles. In this study, we explicitly quantify this effect through an integral geometric analysis using Minkowski tensors, correlating XPS chemical data with topographical information from Atomic Force Microscopy (AFM). This approach yields reliable estimates of layer thicknesses for nanorough surfaces. For b-Si, we found that the oxide layer is approximately 50% thicker than the native oxide layer on a standard Si wafer. This study underscores the significant impact of nanoscale geometries on chemical property analysis.

Streptococcus mutans cells form robust biofilms on human teeth and are strongly related to caries incidents. Hence, understanding the adhesion of S. mutans in the human oral cavity is of major interest for preventive dentistry. In this study, we report on AFM-based single cell force spectroscopy measurements of S. mutans cells to hydroxyapatite surfaces. We observe a significant increase of adhesion strength if S. mutans cells were exposed to human saliva before adhesion. In contrast, Staphylococcus carnosus cells are almost unaffected by the pre-treatment. Our results demonstrate that S. mutans cells are well-adapted to their natural environment, the oral cavity. This ability promotes the biofilm-forming capability of that species and hence the production of caries-provoking acids. In consequence, understanding the fundamentals of this mechanism may pave a way towards more effective caries-reducing techniques., Comment: 14 pages, 6 figures