Carbon-based Nano-thin Film for Enhancing Surface Abrasion Resistance on Sapphire Thin Film

Abstract

The present disclosure relates to display, windows, camera cover, lens and lens cover, optical/infra-red sensors, glasses and spectacles.

Claims

1. A method of enhancing surface abrasion resistance on a substrate comprising depositing a carbon-based film with a thickness of no more than 100 nm on to said substrate such that the carbon-based film deposited substrate has an optical transmittance of at least 70%.

2. The method of claim 1, wherein the substrate comprises glass, quartz, fused silica, metals and sapphire.

3. The method of claim 1, wherein said depositing comprises physical vapor deposition and/or chemical vapor deposition.

4. The method of claim 3, wherein the physical vapor deposition comprises DC sputtering, RF sputtering, thermal evaporation, and e-beam evaporation.

5. The method of claim 3, wherein said chemical vapor deposition is plasma enhanced chemical vapor deposition.

6. The method of claim 1, wherein said deposition is carried out in a temperature from about room temperature to about 800 C.

7. The method of claim 1, wherein said carbon-based film comprises one or more of C60, carbon nano-tube, graphene, graphite, diamond-like carbon, and/or metal.

8. The method of claim 7, wherein the carbon-based film comprises graphite and metal in which the metal is deposited as a precursor to enhance adhesion between the substrate and the carbon-based film, and wherein the thickness ratio between the metal layer and the carbon-based film is no more than 1:10.

9. The method of claim 7, wherein the metal is deposited by physical vapor deposition comprising DC sputtering, RF sputtering and e-beam evaporation.

10. The method of claim 7 wherein said metal comprises aluminium, silver, chromium, titanium, and magnesium.

11. The method of claim 7, wherein said metal is deposited at a temperature from about room temperature to 900 C.

12. The method of claim 2, wherein the carbon-based film deposited sapphire has a hardness of up to 9.5 mohs.

13. The method of claim 1, wherein the carbon-based film deposited substrate has an optical transmittance of 70-99%.

14. The method of claim 1, wherein the thickness of the carbon-based film is less than 30 nm.

15. A sapphire film coated substrate prepared by the method of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and other objects and features of the present invention will become apparent from the following description of the present invention, when taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 shows the transmittance of carbon film as a function of film thickness.

[0025] FIG. 2 shows the optical transmission properties of DLC.

[0026] FIG. 3 shows the DLF film hardness

[0027] FIG. 4 shows the nanoindentation results of graphite film on sapphire film comparing it with other films/materials.

DETAILED DESCRIPTION OF THE INVENTION

[0028] This invention is to deposit a sub-100 nm thick carbon-based film on to patented sapphire film (U.S. Pat. No. 9,695,501 B2; U.S. Pat. No. 10,072,329B2, U.S. Pat. No. 9,932,663B2) to enhance the surface smoothness. This invention can also be deposited onto other thin film surfaces. The carbon film is to act as a layer of lubricant on the sapphire film that is sufficiently hard to resist direct scratching. However, its hardness and surface roughness can cause marks being made on the surface, giving an impression of being scratched. The carbon film will reduce the scratching friction thus eliminate any markings. The carbon-based film has an added advantage of further enhancing the sapphire film hardness.

[0029] The following is an example of the present method, including the steps of: [0030] 1. A layer of 1-100 nm thick carbon-based film is deposited onto a sapphire film using PVD methods. The sapphire film is prepared according to US patents: U.S. Pat. No. 9,695,501 B2; U.S. Pat. No. 10,072,329 B2, U.S. Pat. No. 9,932,663 B2. [0031] 2. The deposition methods can be one of the PVD methods such as DC sputtering, RF sputtering thermal evaporation, and e-beam evaporation. [0032] 3. The deposition of carbon-based film can be done at room temperature (or 25 C.) and up to 800 C. [0033] 4. The material(s) of carbon-based film can be graphite, metal plus graphite in which metal is deposited as a precursor that can enhance adhesion between the sapphire film and the carbon-based film. [0034] 5. The metals can be deposited by one of the PVD methods such as DC sputtering, RF sputtering and e-beam. [0035] 6. Metals can be Al, Ag, Cr, Ti and Mg but exclusive these. [0036] 7. The metal layer thickness is ranged from 1 to 30 nm. The ratio of thickness of the metal layer to the carbon-based film is no more than 1:10. [0037] 8. The deposition of metal can be done at room temperature and up to 900 C. [0038] 9. The deposited carbon-based film together with the sapphire film can have hardness up to 9.5 mohs. [0039] 10. The optical transmission of the deposited carbon-based film together with the sapphire film is in the range of 70-99%.

[0040] Graphite film was deposited onto sapphire film and the hardness of the bilayer was measured. Its hardness is compared to other materials as well as the sapphire film itself. No obvious enhancement in hardness was observed but there is also no degradation of the hardness of the sapphire film (Table 1).

[0041] Table 1 Hardness of graphite film on sapphire film comparing it to the hardness of other materials/films.

TABLE-US-00001 Hardness GPa at 50 nm Mohs Sapphire 37.15 8.9 Al2O3 film 10.74 6.3 Carbon film on Al2O3 film 9.47 6 Quartz 15.36 7 Bare Soda-lime Glass 6.37 5.2
Deposition of DLC onto Sapphire Film

[0042] The base material, or substrate, can be a sapphire film coated glass/plastic/metal (U.S. Pat. No. 9,695,501 B2; U.S. Pat. No. 10,072,329 B2, U.S. Pat. No. 9,932,663 B2). Deposition methods are CVD and PVD, the latter is more environmentally friendly.

[0043] For PVD, RF sputtering is preferred method, although other methods such as thermal evaporation, e-beam and CVD, these methods can deposit a range of carbon-based films, including graphite, DLC, carbon nanotube and graphene. Each of these methods has its specific advantage in depositing one or two types of carbon-based films and thus they can be selectively used to deposit the desired type. For examples, graphite film can be deposited by thermal deposition, sputtering and CVD are used more for DLC deposition etc.

[0044] Carbon-based films are not optically transparent when they are too thick. FIG. 1 shows optical transmission as a function of graphite film thickness. The result show that film thickness greater than 30 nm has low optical transmission and is not desirable for certain applications such as anti-scratch film for display. Different types of carbon-based film have different transmission characteristics.

[0045] For example, in FIG. 2, DLC film deposited by using PECVD (plasma enhanced chemical vapour deposition) shows a clear transmission variation with respect to film thickness. In DLC structure, the transmission has improved; for a @35 nm thick film at 400 nm, the transmission of DLC is about 60% whereas for a graphite film the transmission is only about 28%. Therefore, in terms of optical applications DLC is preferred.

[0046] DLC also has better mechanical property than graphite film; it is harder; in fact its hardness is getting close to that of sapphire single crystal. At about 200 nm DLC has a hardness of about 22 GPa viz 8 mho. This hardness will increase further when DLC is deposited onto a sapphire film bringing the total hardness close to 9 mho. It would mean that hardness of the DLC/sapphire film prepared at room temperature will have an enhanced hardness (FIG. 3).

[0047] The hardness of graphite film deposited onto sapphire film was measured and is shown in FIG. 4. The enhancement is not as obvious as that of DLC on sapphire film but it does show that overall there is no degradation of hardness.