lokki

nit-pick alert

Basic SEM work requires a conductive surface (carbon coatings also work), and in some cases you can skip that if you have a good carrier gas. The real limitation here is that most SEMs require you to pump down to vacuum, which would eliminate the water. Even variable-pressure SEMs that operate close to atmosphere require a purge, first.

So the limit is the vacuum, not the metal coating.

Inches are a defined construct, not an absolute. They are convenient chunks so we dumb humans and communicate with some level of accuracy.

Dollars are exactly the same - assigning value lets us communicate and relate otherwise abstract concepts in a meaningful way. While we can't eat gold, we can imagine how much food gold can buy, with all the caveats about exchanges and locations in place. The important bit to take away is providing a framework for common understanding.