Method of making durable articles
Optical articles of zinc sulfide and zinc selenide with thick coatings of alumina are disclosed. The alumina coatings are deposited on the zinc sulfide and zinc selenide by a microwave assisted magnetron sputtering. In addition to alumina coatings, the optical articles may also include various polymer coatings.
1. A method comprising:
a) providing a substrate comprising zinc sulfide or zinc selenide on a sputtering drum in a sputtering drum coating chamber;
b) providing a source of alumina, a source of diatomic oxygen and a source of inert gas in the sputtering drum coating chamber, wherein a target distance of the source of alumina to the zinc sulfide or the zinc selenide ranges from 8 cm to 20 cm;
c) rotating the substrate comprising the zinc sulfide or the zinc selenide on the sputtering drum at 0.75 to 3 revolutions per second;
d) introducing diatomic oxygen in the sputtering drum coating chamber at a flow rate of 20 sccm to 80 sccm and introducing inert gas in the sputtering drum coating chamber at a flow rate of 30 sccm to 150 sccm at a total sputtering drum coating chamber pressure of 2×10 −3 Torr to 7×10 −3 Torr;
e) ionizing the diatomic oxygen and inert gas with microwaves at microwave powers of 1 kW to 5 kW and at a frequency of 1 GHz to 5 GHz; and
f) depositing a layer of alumina 30 μm to 60 μm thick by pulsed DC magnetron sputtering or 30 μm to 100 μm thick by AC magnetron sputtering on the zinc sulfide or zinc selenide at a deposition rate of 60 Å/minute to 270 Å/minute at pulsed power ranges of 3 kW to 9 kW and frequency ranges of 20 kHz to 50 kHz, wherein the zinc sulfide or zinc selenide are maintained at temperatures of 40° C. to 200° C.
2. The method of claim 1 , further comprising a step of depositing alternating layers of at least one layer of a composition comprising one or more monomers and at least one layer of the alumina on the zinc sulfide or zinc selenide; and curing the composition.
3. The method of claim 2 , wherein the composition further comprises alumina particles.
4. The method of claim 2 , wherein the one or more monomers is chosen from polyols, polyamines, diisocyanates and diisocyanate derivatives.
5. The method of claim 1 , wherein the deposition rate is 190 Å/minute to 230 Å/minute.
6. The method of claim 1 , wherein diatomic oxygen partial pressure ranges from 1×10 −4 Torr to 20×10 −4 Torr.
7. The method of claim 1 , further comprising pre-cleaning the zinc sulfide or the zinc selenide with microwave plasma prior to deposition.
8. The method of claim 1 , wherein the pulsed power ranges from 5 kW to 7 kW and frequency ranges from 35 kHz to 45 kHz.