Vorschau

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Abstract

Sample surface charging and electron beam damage are common problems in scanning electron microscopy. In the case of serial block‐face electron microscopy (SBEM), sample charging prevents or restricts stack acquisition of non-conducting samples in high vacuum; beam damage imposes a lower limit on the cutting thickness (z-resolution). In this dissertation, I present three approaches that aim to overcome these limitations. To solve the charging problem, I implemented and evaluated two charge elimination techniques for SBEM: surface charge neutralization with an ion gun and automated in-chamber specimen coating with an electron beam evaporator. The ion gun method provides only partial charge neutralization in many cases, although high positive ion current densities are achieved. The automated in-chamber coating method, on the other hand, provides reliable charge elimination in all cases and allows the acquisition of SBEM stacks of non-conducting samples in high vacuum. Thin metallic films provide charge elimination for large sample surfaces and high beam currents, and reduce the signal-to-noise ratio less than the widely-used low-vacuum method. To reduce the effects of beam damage – with the aim of allowing thin cutting at higher electron doses – I have explored imaging and cutting at low temperatures (~100 K) using a closed-loop cooling system and a custom-built cryo-microtome. Further experiments will be necessary to quantify potential improvements of 'Cryo-SBEM' over room-temperature SBEM operation.