BLACK-COLOURED ARTICLE

Abstract

Black-coloured article (1) which is not a photovoltaic device, comprising:—a substantially transparent substrate (3);—a substantially transparent textured layer (5) provided upon a first surface (3a) of said substrate, said textured layer (5) having a textured surface (5a) oriented away from said substrate (3);—an absorption layer (7) comprising silicon-germanium alloy, said absorption layer (7) being situated upon said textured surface (5a) of said textured layer (5).

Claims

1-18. (canceled)

19. A black-colored article which is not a photovoltaic device, comprising: a substantially transparent substrate; a substantially transparent textured layer provided upon a first surface of said substrate, said textured layer having a textured surface oriented away from said substrate; an absorption layer comprising silicon-germanium alloy, said absorption layer being situated upon said textured surface of said textured layer.

20. The black-colored article according to claim 19, wherein said silicon-germanium alloy comprises at least 2% germanium.

21. The black-colored article according to claim 19, further comprising an anti-reflective layer interposed between said substrate and said textured layer, said anti-reflective layer exhibiting an index of refraction greater than an index of refraction of said substrate.

22. The black-colored article according to claim 19, further comprising an anti-reflective coating provided upon a second surface of said substrate, said second surface being opposite to said first surface, said anti-reflective coating exhibiting an index of refraction lower than an index of refraction of said substrate.

23. The black-colored article according to claim 19, wherein said textured layer exhibits an index of refraction lower than an index of refraction of said absorption layer.

24. The black-colored article according to claim 19, wherein said absorption layer has a thickness between 400 and 700 nm.

25. The black-colored article according to claim 19, wherein said textured layer has a thickness of between 0.5 and 5 μm, and has a surface rms roughness on said textured surface of at least 10 nm.

26. The black-colored article according to claim 25, wherein said textured layer comprises zinc oxide and/or tin oxide.

27. The black-colored article according to claim 19, wherein said article is one of: a dial for a timepiece, a timepiece hand, gear, spring or bridge; a decorative element for a watchcase, watch crown, watch bezel, home furniture, interior decoration or automobile decoration; a jewelry element such as a decorative element for a necklace, collar, ring, bracelet, earring, pendant or brooch, a light absorbing element for an optical device such as a light-trapping element, an optical baffle or a beam stopping surface; a decorative cover glass for a phone, tablet or other electronic device.

28. The black-colored article according to claim 19, wherein said absorption layer is substantially undoped.

29. The black-colored article according to claim 19, wherein said absorption layer is substantially homogeneous.

30. A method of manufacturing a black-colored article which is not a photovoltaic device, comprising: providing a substantially transparent substrate; forming a substantially transparent textured layer on a first surface of said substrate, said textured layer having a textured surface oriented away from said substrate; forming an absorption layer comprising silicon-germanium alloy upon said textured surface of said textured layer.

31. The method according to claim 30, wherein said substantially transparent textured layer is formed of a material which automatically develops a surface texture during its deposition.

32. The method according to claim 31, wherein said substantially transparent textured layer comprises zinc oxide or tin oxide deposited by chemical vapor deposition.

33. The method according to claim 30, wherein said substantially transparent textured layer comprises a texture applied by one or more of: mechanical texturing; chemical texturing; ion etching; laser ablation.

34. The method according to claim 30, wherein said substantially transparent substrate has an antireflective layer provided on a second surface thereof.

35. The method according to claim 30, comprising a step of forming an anti-reflective layer on said first surface of said substrate prior to forming said textured layer.

36. The method according to claim 30, wherein said absorption layer is substantially undoped and/or is substantially homogeneous.

37. The black-colored article according to claim 19, wherein said silicon-germanium alloy comprises substantially 30% germanium.

38. The black-colored article according to claim 19, wherein said absorption layer has a thickness between 550 and 675 nm.

39. The black-colored article according to claim 19, wherein said textured layer has a thickness of between 2.5 and 3 μm, and has a surface rms roughness on said textured surface of at least 10 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further details of the invention will appear more clearly upon reading the description below, in connection with the following figures which illustrate:

[0033] FIG. 1 is a schematic cross-sectional view of the simplest form of an article according to the invention;

[0034] FIG. 2 is a schematic cross-sectional view of a further variant of an article according to the invention;

[0035] FIGS. 3a and 3b are graphs of total and diffuse reflection of various different samples of articles according to the invention;

[0036] FIG. 4 is a schematic cross-sectional view of a yet further variant of an article according to the invention;

[0037] FIG. 5 is a schematic representation of three advantageous uses of an article according to the invention; and

[0038] FIG. 6 is a schematic representation of a method of manufacturing an article according to the invention.

EMBODIMENTS OF THE INVENTION

[0039] FIG. 1 illustrates a schematic cross section of the simplest form of a black-coloured article 1 according to the invention. As mentioned above, this article 1 can be a watch dial, a jewellery element, a light absorbing element for an optical instrument, or any other article desired to be very light-absorbent. The article 1 is not a photovoltaic device, i.e. is not a solar cell. In other words, it is substantially photovoltaically inert, and is not adapted to produce or deliver an electric current when exposed to light. Article 1 comprises a substantially-transparent substrate 3 of any desired thickness, which may be made of glass, polymer, a transparent ceramic such as sapphire or alumina, a glass-ceramic or any other convenient material. In the present text, “substantially transparent” should be understood as exhibiting a transmissivity of at least 95% of visible light (350-750 nm wavelength), and all indexes of refraction mentioned are in respect of visible light wavelengths. Although the substrate 3, and the resulting article, are illustrated as being planar, they can also be curved or formed to any desired shape.

[0040] Upon a first surface 3a of the substrate 3, which faces away from an intended viewing direction (indicated schematically by means of the eye symbol representing the point of view of an observer), is provided a substantially transparent textured layer 5. This textured layer 5 may be directly situated upon said first face 3a as illustrated in FIG. 1, or may be indirectly situated thereupon, with one or more supplemental layers interposed between the substrate 3 and the textured layer 5, as will be discussed in more detail in the context of FIG. 2 below.

[0041] Textured layer 5 may be for instance a layer of zinc oxide formed upon the first surface 3a by means of chemical vapour deposition (CVD) or similar, which will cause the surface 5a of the textured layer 5 which faces away from the substrate 3a to exhibit a plurality of pyramidal forms, as represented schematically by means of an irregular zigzag line. Another particularly suitable material for this layer is CVD-deposited tin oxide, which is transparent and exhibits a more rounded surface morphology than the sharply-defined pyramidal forms of zinc oxide. Other substances exhibiting similar properties are also possible.

[0042] It is also possible to texture said surface 5a in a separate step after depositing a different material that does not inherently form a textured surface, such as a transparent polymer, alumina, or similar. This texturing can be carried out mechanically (e.g. by machining, grinding, abrasive brushes, sand or bead blasting, or similar), by means of ion etching, laser etching or ablation, or by chemical etching.

[0043] Alternatively, the surface 3a of the substrate may itself be textured; this texture being transferred to surface 5a of the textured layer 5 even if it is made of a material that does not inherently form a textured surface.

[0044] It is unimportant how the texture is formed, but ideally the texture should have a minimum rms value of 10 nm, and may be stochastic or non-stochastic. In particular, values of 15 nm to 500 nm rms are the most useful. RMS roughness is described in the standard ASME B46.1, and is hence well-known to the skilled person.

[0045] Irrespective of how the textured layer 5 is formed, its thickness is ideally between 0.5 and 5 μm thick, preferably between 2.5 and 3.0 μm thick.

[0046] Upon said surface 5a of the textured layer 5 is formed an absorption layer 7 of silicon-germanium alloy comprising at least 2% germanium, preferably at least 10% or 20% germanium, further preferably 20% to 40% germanium, further preferably substantially 30% germanium, the balance being substantially all silicon and hydrogen in the case in which the layer is hydrogenated (SiGe:H). This layer typically has a thickness of between 400 and 700 nm, more particularly between 550 and 675 nm, and is typically deposited directly upon the textured layer 5 although intervening layers are also possible.

[0047] Silicon-germanium alloy absorbs visible light wavelengths particularly strongly, and also has a high index of refraction of the order of 3-4, which is typically significantly in excess of the index of refraction of the textured layer 5. In the case of zinc oxide, this refractive index is around 2. As a result, visible light leaving the textured layer 5 at its textured surface 5a is recycled into the absorbing layer 7 by multiple reflections and thus resulting in the absorption a maximum of light.

[0048] As a result, it is possible to arrange the various layers such that the index of refraction increases from the substrate 3 (or from the anti-reflective coating 9, if present) to the Si—Ge layer 7, which minimises specular reflections.

[0049] It should be noted that in this construction, and in all the constructions disclosed herein, that absorbing layer 7 is the only layer present which is formed from a semiconductor material. Since the article 1 is not a photovoltaic device, i.e. is substantially photovoltaically inert, absorbing layer 7 is typically undoped (i.e. intrinsic-type), although it is not excluded that P-type or N-type dopants may be present. Furthermore, the article is free of any P-N, N-P, PIN, NIP or other type of photovoltaically-active junction formed by different dopings or similar. In essence, it is coincidental that the Si—Ge of layer 7 is a semiconductor, since it has been chosen for its light-absorbing properties. It should also be noted that layer 7 is typically a single, substantially homogeneous layer, and is not a layer stack or other more complicated arrangement, since this ensures that its deposition can be carried out rapidly and efficiently, in a single process step, leading to very economic production.

[0050] FIG. 2 illustrates a further variant of a black-coloured article 1, in which two further measures to improve the blackness have been implemented. However, it is entirely possible to apply one or other of them individually.

[0051] Layers 3, 5 and 7 are as described above, and need not be discussed again.

[0052] The first measure to further deepen the colour is the presence of an anti-reflective coating 9 comprising one or more layers applied on the surface of the substrate 3 facing towards the intended viewing direction, i.e. facing away from the Si—Ge alloy layer 7. This surface is defined as the “second surface” 3b.

[0053] This anti-reflective coating 9 may also have anti-scratch and anti-abrasion properties, such coatings being well-known in and of themselves, particularly in the field of eye glasses to reduce specular reflections and hence reduce shine. Examples thereof are disclosed in e.g. U.S. Pat. No. 9,726,786, WO2008112047, DE102015114877, U.S. Pat. No. 9,817,155 and innumerable other documents. Alternatively, an additional anti-scratch coating (not illustrated) may be provided upon the anti-reflective coating 9 if this latter has poor resistance to scratches etc.

[0054] In the context of the present invention, the anti-reflective coating advantageously has a refractive index lower than that of the substrate 3, which helps to reduce back-reflections and hence to deepen the colour.

[0055] The second measure to deepen the colour is a further anti-reflective layer 11, interposed between the substrate 3 and the textured layer 5. This layer typically has a refractive index with a value situated between that of the substrate 3 and the textured layer 5, and may for instance be a layer of silicon oxynitride with a thickness of between 10 and 200nm, and more preferably between 70 and 90 nm. This layer may also be a multilayer exhibiting a graded index of refraction, increasing towards the Si—Ge layer 7.

[0056] FIGS. 3a and 3b show a pair of graphs representing the effect of the invention, illustrating the percentage of reflected light for both total reflection and for diffuse reflection as a function of the wavelength of incident light, with five different samples. The average results for the 450-740 nm wavelength ranges for five different samples are as follows, listed from left to right, top to bottom of the legend of each graph of FIGS. 3a and 3b:

TABLE-US-00001 Total Diffuse reflection (%) reflection (%) Sample layers (FIG. 3a) (FIG. 3b) a) glass substrate 3; ZnO 6.50 0.50 textured layer 5; Si—Ge absorption layer 7 b) anti-reflective coating 9; 2.60 0.60 glass substrate 3; ZnO textured layer 5; Si—Ge absorption layer 7 c) glass substrate 3; anti- 4.75 0.65 reflective layer 11; ZnO textured layer 5; Si—Ge absorption layer 7 d) anti-reflective coating 9; 1.30 0.70 glass substrate 3; anti- reflective layer 11; ZnO textured layer 5; Si—Ge absorption layer 7 e) Carbon nanotubes 1.0 1.0

[0057] In each case, the thickness of the anti-reflective coating 9 is approximately 70-90 nm ; that of the glass substrate 3 is approximately 0.5 mm; that of the anti-reflective layer 11 is approximately 80 nm; that of the ZnO layer 5 is approximately 2.5 μm; and that of the SiGe absorption layer 7 is approximately 625 nm.

[0058] As can clearly be seen, the results are extremely similar for diffuse reflection, at well under 1% reflection, and both the anti-reflective coating 9 and anti-reflective layer 11 contribute to bring total reflection down to just over 1% when used in combination (sample e). This represents a very deep black colour.

[0059] Furthermore, measurements of colour of the four samples were taken, the colour parameters being measured in the L*a*b* system, which is perceptually uniform and correlates with the human eye perception. In this model, L* represents the luminance (from L*=0, black to L*=100, white), a* is the green-red scale (from a*=−128, green to a*=+127, red) and b* is the blue-yellow scale (from b*=−128, blue to b*=+127, yellow). Thus, a perfect black is defined by L*=a*=b*=0. The samples are measured simultaneously in SCI (“Specular Component Included”) mode, where the specular component of the reflection is included (i.e. total reflection), and in SCE (“Specular Component Excluded”) mode, where only the diffuse component of the reflection is included. In each case, a standard D65 illuminant was used, with a 10° observer.

[0060] The approximate results were as follows:

TABLE-US-00002 L* (total a* (total b* (total L* a* b* re- re- re- (diffuse (diffuse (diffuse Sample flection) flection) flection) reflection) reflection) reflection) a 30 0.0 −2.4 4.2 −0.6 0.0 b 19 −0.6 −2.0 5.0 0.0 0.0 c 26 0.6 −2.8 6.0 −0.5 0.0 d 11 1.7 −3.9 6.2 0.0 −1.2 e 8.6 −0.6 −1.7 8.6 −0.6 −1.7

[0061] As can be seen from these figures, the blackness of the samples is extremely deep, and that the anti-reflective coating 9 and layer 11 reduce the specular component of reflection without substantially changing the colour values. This result is all the more surprising due to the fact that the absorption layer 7 is situated away from the direction of incident light, whereas in conventional black-coloured articles, the black colour is provided on the surface facing the viewer as a lacquer or coating.

[0062] As a result, the absorption layer 7 is not situated on an observer-facing surface of the article 1 and is hence protected from damage in handling. Indeed, this layer 7 can even sustain superficial damage without this being visible to the user, since it is on a rear face thereof facing away from him. Since the substrate 3, and any coatings thereupon such as anti-reflective and/or anti-scratch coatings 9, are on the user-facing side of the article 1, they can be easily handled and cleaned with conventional mechanical and chemical products, without risking damaging the light-absorbing layer 7 or affecting the optical properties of the article. To maximise the cleanability (and resistance to scratches), the second surface 3b of the substrate 3 and/or the outermost surface of any coating 9 provided thereupon ideally exhibits a maximum surface roughness of 5 nm rms, more particularly 1 nm rms or less.

[0063] FIG. 4 illustrates an embodiment of an article 1 corresponding to that illustrated in FIG. 2, in which several further optional measures have been taken. These measures can be applied individually or in combination, and it is equally possible to leave out the anti-reflective coating 9 and/or the anti-reflective layer 11.

[0064] Firstly, the absorber layer 7 can be protected on the underside of the article 1 by means of further protective layer 13, e.g. of an encapsulant, deposited thereupon to protect it.

[0065] In addition, it is also possible to provide a deliberately-formed relief motif 3c, on one, other or both of the faces of the substrate. This motif may e.g. be a regular pattern, lettering, an image or similar, and may extend above the main surface of the substrate 3, or may be recessed into said surface, the height and/or depth of the relief being at least 1 μm above and/or below the main surface of the substrate 3 as appropriate.

[0066] Also, it should be noted that further layers can be incorporated as required, such as diffusion layers and similar. In the case in which such a layer is disposed between the textured layer 5 and the Si—Ge alloy layer 7, it should be noted that the texture will be transposed through this extra layer such that the surface of the Si—Ge alloy layer 7 facing towards the substrate 3 will still be textured.

[0067] FIG. 5 represents schematically three potential non-limitative application of the article 1 according to the invention. On the left of this figure is represented a timepiece 21, in which the article 1 is used as a dial 22, the substrate 3 thereof facing towards the user when he reads the time.

[0068] In the middle of FIG. 5, the article 1 is incorporated as a decorative element into a piece of jewellery, such as a bracelet, pendant, brooch, earring or similar.

[0069] On the right of FIG. 5, the article 1 is incorporated into an optical sensor 25, comprising a housing 26 defining an enclosed space 27 containing a photosensor 29. This latter faces a shutter or opening 31, and the article 1 is arranged to absorb undesired light other than that passing directly from the shutter 31 to the sensor 29, the substrate 3 being arranged in each section of the article 1 facing the interior of the housing and/or towards the shutter 31.

[0070] Other applications are, of course, possible.

[0071] In terms of manufacturing steps, FIG. 6 illustrates schematically the manufacture of an article 1 corresponding to that of FIG. 2. In the case of an article 1 according to FIG. 1, or an article in which one or other of the anti-reflective coating 9 or the anti-reflective layer 11 is omitted, the corresponding method steps are simply omitted.

[0072] Firstly, the substrate 3 is provided, and serves as the basis upon which all other layers are formed. Since appropriate materials for the substrate 3 have been discussed in detail above, they will not be repeated here.

[0073] If present, the anti-reflective coating 9 is provided on the second surface 3b of the substrate 3, for instance as described in U.S. Pat. No. 9,726,786, WO2008112047, DE102015114877, U.S. Pat. No. 9,817,155 or in innumerable other documents, at any convenient moment in the method, and does not need to be the first layer deposited. However, since commercially-available glass and plastic substrates already provided with anti-reflective coatings are available off-the-shelf, it will often be the case that this layer is indeed deposited first, and will hence already be present on the substrate 3 when the other layers are deposited.

[0074] If present, the anti-reflective layer 11 is subsequently deposited on the first surface 3a of the substrate 3. As a non-limiting example, this may be a layer of silicon oxynitride, deposited by plasma-assisted chemical vapour deposition under the following conditions in a reactor with 13.56 MHz plasma excitation frequency, 15 mm inter-electrode distance, 45×55 cm electrode surface dimensions, to give the thickness indicated:

TABLE-US-00003 [SiH.sub.4] Plasma thick- Layer flow rate [NH.sub.3] flow [CO.sub.2] flow pressure power ness type (sccm) rate (sccm) rate (sccm) (mbar) (W) (nm) SiNxOy 15-20 60-100 10-40 1.5 50 70-90

[0075] Subsequently, the textured layer 5 is deposited directly or indirectly upon said first surface 3a. In the case in which this layer is made of zinc oxide, it may be deposited by low-pressure chemical vapour deposition under the following conditions in the above-mentioned reactor, to give the thickness indicated:

TABLE-US-00004 [H.sub.2O] [Diethyl zinc] Layer flow rate flow rate pressure T thickness type (sccm) (sccm) (mbar) (° C.) (um) ZnO 255 160 0.5 190 1.5 to 5

[0076] In the case in which the textured layer 5 is made of a material which, unlike ZnO, does not have a suitable surface texture as a result of its deposition, it may be mechanically, chemically, optically or ionically structured as described above.

[0077] Subsequently, the absorption layer 7 of Si—Ge alloy is deposited directly or indirectly upon the free surface of the textured layer 5, for instance by plasma assisted chemical vapour deposition under the following conditions in the above-mentioned reactor, to give the thickness indicated:

TABLE-US-00005 [SiH.sub.4] [GeH.sub.4] [H.sub.2] flow Thick- Layer flow rate flow rate rate Pressure Plasma ness type (sccm) (sccm) (sccm) (mbar) power (W) (nm) (i) SiGe 40 12 1300 3.3 110 625 ± 35

[0078] Other intermediate or exterior layers can of course be deposited as required.

[0079] Although the invention has been described with reference to specific embodiments, variations thereto are possible without departing from the scope of the invention as defined in the appended claims.