Article having optimised thermomechanical properties, comprising a layer of titano-organic nature
The invention relates to an article comprising a substrate having at least one major surface coated with a layer A of a material obtained by ion beam assisted vacuum deposition of at least one titanium oxide and of at least one organosilicate compound B, said material having a refractive index at 550 nm higher than or equal to 1.8, an extinction coefficient k at 550 nm lower than or equal to 0.02, and an H:E ratio higher than or equal to 0.046, where H and E designate the hardness of the material and the elastic coefficient of the material, respectively.
1. An article comprising a substrate having at least one main surface coated with a layer A of a material obtained by ion beam deposition under vacuum of at least one titanium oxide and at least one organosilicon compound wherein said material exhibits:
a refractive index at 550 nm of greater than or equal to 1.8,
an extinction coefficient k at 550 nm of less than or equal to 0.02,
an H/E ratio of greater than or equal to 0.046, where H and E respectively denote the hardness of the material and the modulus of elasticity of the material, wherein the hardness H and the modulus of elasticity E are evaluated by nano-indentation measurement on a 500 nm thick coating of layer A on a silicon wafer support, wherein the nano-indentation measurement comprises causing a Berkovich diamond tip to penetrate the layer A under a force varying from 100 μN to 10,000 μN and continuously recording the force, F, applied as a function of the depth of penetration, h, of the tip to obtain a force-penetration curve and applying the force-penetration curve to the following formulae:
A c =24.56× h c 2
H
=
F
max
A
c
h
c
=
h
max
-
ɛ
·
F
max
S
S
=
∂
F
∂
h
=
2
π
·
E
r
·
A
c
1
E
r
=
1
-
υ
i
2
E
i
+
1
-
υ
2
E
wherein h max is the maximum depth of penetration, F max is the maximum force, ε is the indenter geometry constant, E r is the reduced modulus, E i is the modulus of the indenter and ν is the Poisson coefficient,
wherein the atomic percentage of titanium atoms in layer A ranges from 10 to 30%, the atomic percentage of carbon atoms in layer A ranges from 10 to 20%, the atomic percentage of silicon atoms in layer A ranges from 10 to 20%, the atomic percentage of oxygen atoms in layer A ranges from 20 to 40%, and the atomic percentage of hydrogen atoms in layer A ranges from 10 to 30%.
2. The article of claim 1 , wherein the deposition comprises ion bombardment.
3. The article of claim 1 , wherein the organosilicon compound comprises at least one Si—C bond.
4. The article of claim 1 , wherein the organosilicon compound comprises at least one divalent group of formula:
where R′ 1 to R′ 4 independently denote alkyl, vinyl, aryl or hydroxyl groups or hydrolysable groups, or in that the organosilicon compound corresponds to the formula:
in which R′ 5 , R′ 6 , R′ 7 and R′ 8 independently denote hydroxyl groups or hydrolysable groups.
5. The article of claim 1 , wherein the organosilicon compound is chosen from octamethylcyclotetrasiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, decamethyltetrasiloxane, decamethylcyclopentasiloxane, dodecamethylpentasiloxane or hexamethyldisiloxane.
6. The article of claim 1 , wherein the silicon atom or atoms of the organosilicon compound do not comprise any hydrolysable group or hydroxyl group.
7. The article of claim 1 , wherein the titanium oxide is a substoichiometric titanium oxide of formula TiO x with x<2.
8. The article of claim 1 , wherein the layer A has a thickness ranging from 20 to 150 nm.
9. The article of claim 1 , wherein the layer A constitutes a layer of a multilayer interference coating.
10. The article of claim 9 , wherein the interference coating is an antireflective coating.
11. The article of claim 1 , further defined as an ophthalmic lens.
12. The article of claim 1 , further defined as possessing a critical temperature of greater than or equal to 70° C.
13. The article of claim 4 , wherein the hydrolysable groups are OR groups, in which R is an alkyl group.
14. A process for the manufacture of an article according to claim 1 , comprising:
providing an article comprising the substrate having at least one main surface;
depositing, on said main surface of the substrate, the layer A of the material having the refractive index of greater than or equal to 1.8, the extinction coefficient k at 550 nm of less than or equal to 0.02 and the H/E ratio of greater than or equal to 0.046, where H and E respectively denote the hardness of the material and the modulus of elasticity of the material,
recovering the article comprising the substrate having the at least one main surface coated with the layer A,
the layer A having been obtained by ion beam deposition under vacuum of at least one titanium oxide and at least one organosilicon compound.