Purchased with a grant from the National Science Foundation

What it does: The Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectrometer (EDS) is used for detailed, high magnification, 3-D imaging and qualitative and semi-quantitative chemical analysis of solids.

How it works: A beam of high energy electrons is produced in the electron gun at the top of the column by applying high voltage to a tungsten filament and nearby anode. This beam is accelerated down past the anode into the column where it is condensed and aligned by a series of electromagnetic lenses and coils within the column. This focused beam continuously rasters back and forth across the sample. Interactions between the electron beam and the sample result in different types of emissions that are measured by a series of detectors located within the sample chamber. The four types of emissions that are measured are: secondary electrons, backscattered electrons, x-rays, and cathode luminescence. X-ray data is sent to the EDS system where it is translated into elemental plots. The other three detectors are connected to a 'TV' screen where the signal produces a clear, black and white (green actually) image of the sample. Secondary electron imaging provides good 3-dimensional topographic views of the sample. Backscattered electron images show less defined topography but clearly display differences in elemental compositions because higher atomic number elements appear brighter. Cathode luminescence imaging highlights chemical variations within individual grains due to trace element variations and zoning.

Instrument Statistics: Our EDS system is run by Spirit software. The detector has a beryllium window. Quantitative analyses are performed at 20 kV using a 25mm working distance, 35% dead time, and are collected for 200 seconds of live time.