In a new YouTube video, maker [ProjectsInFlight](https://www.youtube.com/channel/UCDP6MKXqZB1C72QJ8 HO7g) revealed how he created a high-contrast resolution target for his recently repaired scanning electron microscope (SEM).
The target is crucial for calibrating the SEM, especially the focus, astigmatism and beam centring, and it also allows him to test the maximum magnification the SEM can currently achieve.
He created the high-density portion of the target by depositing gold nanoparticles of various sizes onto slices of silicon, using a homemade quartz crystal microbalance.
This involved dissolving gold in aqua regia to make chloroauric acid, then adding sodium citrate to reduce the acid back to gold nanoparticles – a reaction that gave him particles in the 50-100nm range.
He finally managed to create larger particles by cooling the reaction solution to near freezing.
