Heiner Jaksch

Compositional contrast of uncoated fungal spores and stained section-face by low-loss backscattered electron imaging

Comparative surface imaging was performed on uncoated fungal spores and stained section-face by field emission scanning electron microscopy with an in-column energy-selective backscattered electron detector. Epoxy resin thin sections (ca. 200 and 500 nm thick) of the osmicated and uranyl acetate/lead citrate-stained fungus were examined with the microscope. Topographical contrast was evident in secondary electron imaging by either a below-lens or an in-lens detector. Meanwhile, low-loss backscattered electron images showed mainly compositional contrast at low accelerating voltages (mostly below 1 kV). With attenuated topographical contrast, several different electron densities could be detected, exhibiting several levels of electron density even on a flat plane of spines. Minute differences in topography on epoxy resin sections as seen by secondary electron imaging represented the periphery of the fungal spores and hyphae. On the other hand, the compositional contrast could be retrieved from stained section-face in low-loss BSE imaging, revealing subcellular entities after contrast inversion. The resolution of low-loss BSE imaging was sufficient to resolve plasma membrane, and various types of vacuoles and vesicles. These results suggest that low-loss backscattered electron imaging could potentially provide compositional information to resolve surface chemical features of uncoated microbial cells and stained section-face with heterogeneous surface compositions.

Strain related Contrast mechanisms in crystalline materials imaged with AsB detection

At high landing energies the conventional BSE images are showing a contrast mechanism, dominated by multiple elastic scattering processes in the sample. These processes are described in the Rutherford scattering equation. To see crystallographic information we have to “remove” this blurring multiple elastic scattering contrast — known as Z-contrast - and optimize the image formation by “selecting” more single elastic scattered electrons. These electrons carry mainly crystallographic contrast, also known as channelling contrast coming from Mott scattering. This contrast is one of the oldest contrast mechanisms described in the literature of electron microscopy.

Low Loss BSE imaging with the EsB Detection system on the Gemini Ultra FE-SEM

The sensitivity of the GEMINI Inlens detection systems is worldwide known. Especially the EsB detection provides compositional contrast down to the ppm level of concentration. Due to direct detection of the boosted low voltage BSE electrons, a very strong signal is generated on the on axis Inlens BSE detector. Additional a filtering of the BSE electrons can be applied. The filtered information can be reduced down to the low loss BSE region where only a few 10eV to 100eV of