Although both a scanning electron microscope (SEM) and a transmission electron microscope (TEM) utilise electrons, their operational principles and resulting images differ significantly. An SEM generates images by using secondary electrons ejected after a sample’s surface is bombarded with primary electrons. In contrast, a TEM resembles an X-ray machine, using a sensor positioned behind the sample to detect primary electrons after they have traversed the sample. Notably, it is feasible to convert an SEM into a TEM with some ingenuity, as demonstrated in a recent project by ProjectsInFlight.
Previously, coverage highlighted how the SEM, initially slated for disposal, was revitalised and is now undergoing a notable enhancement. This transformation from SEM to TEM, termed scanning transmission electron microscopy (STEM), is not a novel phenomenon; it has been achievable for some time using a relatively straightforward reflecting adapter. However, these adapters often carry a hefty price tag that may deter potential buyers, yet they are sufficiently simple that some might opt to construct one independently.
The primary challenge in creating a DIY adapter lies in maintaining appropriate clearance between the sample holder and the delicate internal components of the chamber. This clearance measures just under 14 mm (0.55 inches), which restricts available space, though using a streamlined aluminium sample plate significantly increased the available room for essential elements such as the primary electron mirror.
After completing extensive machining processes, the sample holder was fully assembled. During evaluations, a modification allowed for adjusting the mirror angle within the evacuated vacuum chamber, optimising the adapter’s performance. Initial tests featured gold nanoparticles, which highlighted a deficiency in the secondary electron shield.
Subsequent experiments indicated that the shield required a higher extension for effective blockage of secondary electrons, resulting in a marked improvement in TEM imagery. A mosquito, preserved and no longer viable, provided wings for analysis, revealing intricate structures through TEM imaging.
The next objective involves TEM imaging of biological cells, which necessitates thorough preparation.
Test Your Understanding
How much do you know?
