Quality Control Measures for Enhancing Confidence in Nanoscale IR Spectroscopy

Photo-induced Force Microscopy (PiFM) is a nanoanalytical, surface-sensitive new-frontier technique that provides in situ infrared spectroscopy at a spatial resolution of ~ 5 nm², which is approximately one billion times higher than traditional FTIR. These advantages led to significant discoveries in Earth and environmental sciences, as well as related disciplines. However, the high resolution and surface sensitivity of PiFM makes it highly susceptible to surface contamination. Factors such as sample preparation, handling and storage can introduce particulate and/or molecular layer contaminants, which may interfere with data analysis and lead to misinterpretation of results. In this study, we systematically investigated common laboratory materials, including gloves, mounting materials, polishing agents and storage solutions as potential sources of particulate and molecular contaminants and compiled a library of reference spectra available to all users of nano-scale molecular analyses. Further, we determined the contaminant signatures of human skin and gloves on AFM substrates and provided recommendations for sample preparation, handling and storage as well as strategies for contamination mitigation to ensure better-informed analysis of structurally and compositionally complex geological materials. We identified molecular and particulate contaminants through their specific IR absorption bands, and provide recommendations to selectively avoid or remove them, thereby improving the reliability of nanoscale molecular analyses by PiFM, ultimately increasing confidence in new discoveries.