Scanning low energy electron loss microscopy (SLEELM)

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Abstract
SUMMARY: High resolution scanning low energy electron loss imaging of a well characterized system of W on Si is demonstrated in reflection geometry at a primary electron energy Ep of 740 eV and spatial resolution of 3 μm. Characteristic losses below 60 eV are chosen to examine contrast between two types of regions (tungsten and silicon dominated, respectively). By differencing between a maximum in loss intensity and an adjacent trough, high quality chemical images are obtained with contrast far superior to Auger electron images produced in comparable times. It should be noted that, in contrast to scanning Auger microscopy, the spatial resolution of SLEELM is limited only by the profile of the incident beam. In addition, the technique is readily capable of chemical analysis at the surface of bulk specimens. A further advantage of low electron loss imaging is that the depth resolution may be varied by altering the primary electron energy, with the possibility of bridging the gap between Auger electron microscopy and X‐ray microprobe analyser. Possible disadvantages of the technique lie in the weakness of the elastic backscattering which is essential to observe the losses in reflection geometry, and the possibility of overlapping low energy characteristic loss peaks, an effect which is, however, less bad than for low energy Auger peaks. It is shown that electron probes with characteristics rather different from those currently used in Auger microscopes are required to optimize the technique, but that SLEELM has the potential to be a very useful form of surface microscopy which will complement other surface imaging techniques.