Caesium hydroxide
[8] Caesium hydroxide fusion at 750°C produces complete dissolution of glass pellets.[8] Due to its high reactivity, caesium hydroxide is extremely hygroscopic.This technique can form pyramids and regularly shaped etch pits for uses such as Microelectromechanical systems.It is known to have a higher selectivity to etch highly p-doped silicon than the more commonly used potassium hydroxide.This compound is not commonly used in experiments due to the high extraction cost of caesium and its reactive behaviour.