Detection of Nitrogen in Layer-by-Layer Polymeric Films by Energy Dispersive X-Ray Spectroscopy

Scanning electron microscopy - energy dispersive X-ray spectrometry (SEM-EDS) is an elemental analysis technique widely used in various fields to identify any element in the periodic table except H, He and Li. It can be a quick way to assess the response of sensing films before deposition on sensing devices. Sensing films are usually organic thin films, but quantitative analysis of light elements and thin films is not recommended for SEM-EDS due to its limitations. In this study, SEM-EDS analysis of nitrogen in layer-by-layer polymeric thin film was optimized. The films were analyzed containing nitrogen in the form of nitrate counterions or as part of the repeat unit of the polymer. The build-up of the layer was verified by thickness measurement using atomic force microscopy. The results show that the limit for nitrogen concentration detection using nitrates was 2% by mass. Below this concentration, nitrogen content had no quantifiable response in either calculated nitrogen concentration by standardless correction methods or intensity of N Kα X-ray line. However, by adding nitrate ions to a film that already contains nitrogen in its structure the concentration was raised to 13.75%. In the range of 9.63 to 13.75%, a nonlinear response was observed using calculated nitrogen concentration while the response was linear with intensity of N Kα.