HIM Applications in Combustion Science: Imaging of Catalyst Surfaces and Nascent Soot

In this chapter, selected applications of helium ion microscopy are presented which demonstrate the strength of this method in characterizing systems relevant for the field of combustion science: nascent soot and transition metal oxide catalysts. Soot consists of carbon-based nanoparticles which were generated in flames. The knowledge about soot growth at very early stages is of high interest in combustion science, where HIM yields a new lower size limit for imaging such particles with high contrast. In fact, the contrast on samples composed of light elements, in combination with the high lateral resolution, are key advantages of HIM which are relevant for studying soot. HIM allowed time efficient probing of a high number of particles with sizes and shapes down to 2 nm. In the first part of this chapter, this is demonstrated for soot from different flames. Their sizes and shapes were simultaneously analyzed for typically 1000 particles per sample. Due to the high resolution and high depth of focus, HIM is also well suited to investigate the surface morphology of highly corrugated catalysts, which is shown here for transition metal oxide films grown by pulse spray evaporation CVD. In the second part of this chapter, examples of such catalyst surfaces are presented. In particular, the morphologie of oxides of iron, iron-cobalt and iron-copper films are characterized by HIM with high resolution.