Understanding the Mechanism of RO Foulant Deposition Using STEM-EDS

In this paper we present the first results of the characterization of fouled desalination RO membranes with STEM-EDS. This technique permits to visualize the cross-section of the fouled membrane with taking advantage of the very high resolution of transmission electron microscope (TEM) and getting its chemical composition with the energy dispersive X-ray spectroscopy (EDS). A focused ion beam (FIB) and a micromanipulator are used to cut, lift out and placed on a TEM grid a very thin slide of cross-section (150 nm wide) isolated from the membrane specimen. EDS line profiles were performed by scanning successive square areas and by dwelling the beam during enough time to have significant signal. Electron collision simulations indicate that the area of X-ray production extends to 20 nm beyond the electron beam (assuming to have a 5 nm size). So the real analyzed surface is a square having a side equal to the square side of the scanned area plus 20 nm.