I don't know about you, but when I think about a "scanning electron microscope" my brain tends to categorize it into a "not possible to build at home" bin. I'm not sure why - maybe because I have never seen an SEM in someone's home. Every time I've ever seen or used an SEM, it has been a hugely expensive device in a corporate or university lab.
And yet... there is nothing to stop someone from trying to build one at home... and here is a genius-type person who has done exactly that. Even better, he has taken the time to explain how it works by showing us his stuff of genius:
Here is what a lab-quality SEM looks like:
To learn more about a scanning electron microscope see How Scanning Electron Microscopes Work.