Hardcoat

Another transparent material for passivation is silicon nitride, Si₃N₄, that also acts as hardcoat.

Such brute-force tactics generally fail for hardcoats on flexible substrates and there seems to be no correlation between scratch resistance and modulus once a certain minimum modulus (~1 GPa) has been reached.

Super Thin Glass: SAIC of McLean, Virginia, and NREL have been developing a front surface mirror concept with a hardcoat protective layer. The material uses an ion-beam-assisted deposition (IBAD) process to deposit the very hard (cleanable), dense (protective) alumina topcoat.