Instrument: Oxford Instruments EDX
Energy dispersive X-ray spectroscopy (EDX) is a spectroscopic technique which enables the elemental composition of a sample to be determined.
By linking the technique to scanning electron microscopy (SEM-EDX), sites of interest can be identified based on sample morphology and then the associated chemical composition determined to create an elemental map of the sample.
Following bombardment of a sample by an electron beam ionisation can occur. The emitted electrons can be replaced by electrons from higher energy states as the material settles towards its ground state.
As the electron moves to a lower energy state, energy is released in the form of X-ray radiation. Since the energy difference between electron energy levels is specific to each element, so too will the energy of the emitted X-ray be unique to the element releasing it. Thus by measuring the energy of the X-rays being emitted from a sample the elemental composition may be determined.
EDX provides compositional analysis for a wide range of solid samples and is thus useful for identification of unknown samples or to confirm suspected samples. The technique is widely used in conjunction with SEM to identify the mineralogy of geological samples based on both the sample morphology and the elemental composition.
Due to the spatial scale at which measurements can be taken EDX lends itself to looking at the distribution of elements through coatings and along surfaces generally. Failure/ corrosion mechanisms can be readily evaluated using EDX in combination with SEM.
EDX also offers a quick way to assess the metallurgical composition of a sample when compared to ICP techniques and is non-destructive if handling precious samples.
EDX is readily semi-quantitative and can be fully quantitative if appropriate standards are used.
EDX is performed in conjunction with SEM thus the sample requirements for EDX are largely dependent on those for SEM. That is, samples should be in a solid form and conductive to prevent build up of electric charge on the sample.
If subsampling is required to obtain a sample small enough care should be taken to ensure that either the sample is representative of the bulk or that enough subsamples are taken to overcome heterogeneity within the sample.
Note that EDX spectra are possible for elements ranging from beryllium to uranium. Detection limits are somewhat dependent on the matrix but typical detection limits are of the order of ppt.