Bruker AXS Microanalysis has presented solutions for its Quantax microanalysis systems that allow the SEM analyst to obtain elemental information on the nanometre scale.
In recent years, the analysis of increasingly smaller structures in the scanning electron microscope (SEM) has become more important than ever.
While SEMs have been able to resolve nanometre-sized features and produce according images for a long time, the issue is far more difficult for elemental analysis using energy dispersive X-ray analysis systems (EDS) on such microscopes.
A limiting factor for the spatial resolution of classical EDS is the comparatively large interaction volume of high-energy electrons with bulk samples, which is in the range of several cubic microns.
In principle, there are two ways to overcome this limitation.
The first is to reduce the interaction volume by analysing very thin layers that are transmitted by most electrons (100nm), for example, lamella prepared by focused ion beam (FIB).
As only a minority of analysts will have access to such expensive equipment, Bruker has concentrated on the second option to reduce the interaction volume, which is to analyse at lower accelerating voltages - 1-5kV instead of 20-30kV.
The lower-energy electrons penetrate bulk samples not nearly as deep and so resolutions in the nm-range can be obtained.
The prerequisite for this type of analysis is a SEM with field emission gun that can produce sufficient beam current at low accelerating voltages.
This is far more common than FIB.
Due to the physics of EDS a simple reduction of the accelerating voltage is insufficient - far-reaching changes to analysis hardware and software are necessary.
In addition to the good energy resolution of its Xflash silicon drift detectors, Bruker has adapted the detector design and materials to cause minimum interference with the 'soft' low-energy electron beam.
The company also offers a number of geometrical optimisation to maximise the collection angle for X-rays, as far less are produced than at high energies.
The Esprit software of Bruker's Quantax systems has been modified to provide secure identification and deconvolution of the many overlapping element peaks in the low-energy range.
This enables point analyses as well as nano-scale line profiles and 2D maps.
It is also now possible to perform standards-based analysis on low-energy spectra, providing reliable quantitative compositional information.