Quantitative Analysis - Quantitative results can be obtained from the relative x-ray counts at the characteristic energy levels for the sample constituents. The minimum detection limits vary from approximately 0.1 to a few atom percent, depending on the element and the sample matrix. Elements with atomic numbers ranging from that of beryllium to uranium can be detected. Qualitative Analysis - The sample x-ray energy values from the EDS spectrum are compared with known characteristic x-ray energy values to determine the presence of an element in the sample.
The spectrum of x-ray energy versus counts is evaluated to determine the elemental composition of the sampled volume. The energy, as determined from the voltage measurement, for each incident x-ray is sent to a computer for display and further data evaluation. The signal is then sent to a multichannel analyzer where the pulses are sorted by voltage. The charge pulse is converted to a voltage pulse (which remains proportional to the x-ray energy) by a charge-sensitive preamplifier. When an incident x-ray strikes the detector, it creates a charge pulse that is proportional to the energy of the x-ray. The detector is typically a lithium-drifted silicon, solid-state device. The EDS x-ray detector measures the relative abundance of emitted x-rays versus their energy. The x-ray energy is characteristic of the element from which it was emitted. The resulting electron vacancies are filled by electrons from a higher state, and an x-ray is emitted to balance the energy difference between the two electrons' states. When the sample is bombarded by the SEM's electron beam, electrons are ejected from the atoms comprising the sample's surface. Features or phases as small as 1 µm or less can be analyzed. (See Handbook section on SEM.) The EDS technique detects x-rays emitted from the sample during bombardment by an electron beam to characterize the elemental composition of the analyzed volume.
Energy Dispersive X-Ray Spectroscopy (EDS or EDX) is a chemical microanalysis technique used in conjunction with scanning electron microscopy (SEM).
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