sentences:  This may lead to deposition of residual charge on the screen, effectively decreasing the energy of the impacting electrons due to electrostatic repulsion (an effect known as "sticking").To eliminate this, a thin layer of aluminium (about 100 nm) is deposited over the phosphors, usually by vacuum evaporation, and connected to the conductive layer inside the tube.This layer also reflects the phosphor light to the desired direction, and protects the phosphor from ion bombardment resulting from an imperfect vacuum.