Patent Application
20240133038
The present disclosure relates to additive solution-processed methods of forming structural color components, such as metal-dielectric-metal structural color components.
This section provides background information related to the present disclosure which is not necessarily prior art.
Colored pigments are used extensively. Many existing color pigments, filters or coatings are based on conventional organic dyes or pigments, which may be vulnerable to damage from various factors, for example, exposure to ultraviolet (UV) radiation and high temperatures. Further, components based on dyes usually require micrometer-scale thicknesses to produce distinctive colors.
While the dye pigments usually suffer from long-term stability, structural color pigments are much more durable, robust and environmental-friendly. However, conventional fabrication of structural color pigments either heavily relies on vacuum-based deposition techniques or involves very complicated patterning procedures, which greatly limits their applications for large scale cost-effective production. Therefore, much effort has been devoted into the solution-based processes.
It would be desirable to have a new process for forming structural colors, like color pigments, formed via such mass manufacturing processes having reduced complexity, but that are robust, have long-term stability with color performance and capable of use on various substrates.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure provides methods of forming a structural color component. In certain aspects, a method of forming a structural color comprising a multilayer stack comprising at least one first metal layer and one or more dielectric layers is provided, where all materials layers are deposited sequentially via a solution process. For example, such layers may be deposited in the absence of an applied electric field. The at least one metal layer may be deposited via electroless deposition, while the dielectric layer(s) may be deposited by one or more sol-gel processes.
The present disclosure also provides methods of forming a structural color metal-dielectric-metal (MDM) component. The method may comprise forming a first metal layer over a treated surface of a substrate by a first electroless deposition process by contacting a surface of the treated substrate with a first plating bath, wherein the first metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, alloys, and combinations thereof. The method may further comprise depositing a dielectric layer over the first metal layer by a sol-gel process. In certain variations, the methods may further comprise forming a second metal layer over the dielectric layer by a second electroless deposition process by contacting the dielectric layer with a second plating bath having a pH of greater than or equal to about 6.5 to less than or equal to about 7.5, wherein the second metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, alloys, and combinations thereof.
In certain aspects, the methods comprise forming a first metal layer over a treated surface of a substrate by a first electroless deposition process by contacting a surface of the treated substrate with a first plating bath. The first metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, alloys, and combinations thereof. The method also comprises depositing a dielectric layer over the first metal layer by a sol-gel process. The method further comprises forming a second metal layer over the dielectric layer by a second electroless deposition process by contacting the dielectric layer with a second plating bath having a pH of greater than or equal to about 6.5 to less than or equal to about 7.5. The second metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, alloys, and combinations thereof.
In one aspect, the first metal layer and the second metal layer independently have a thickness of greater than or equal to about 20 nm to less than or equal to about 200 nm.
In one aspect, the first metal layer has a first thickness of greater than or equal to about 20 nm to less than or equal to about 150 nm and the second metal layer has a second thickness of less than or equal to about 50 nm.
In one aspect, the first metal layer has a first morphology and the second metal layer has a second morphology that is distinct from the first morphology.
In one aspect, the dielectric layer has a thickness of greater than or equal to about 40 nm to less than or equal to about 150 nm.
In one aspect, the dielectric layer comprises a dielectric material selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), or other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof.
In one aspect, the first metal layer and the second metal layer comprise copper and the dielectric layer comprises silicon dioxide (SiO2).
In one aspect, the first metal layer and the second metal layer comprise copper and the dielectric layer comprises titanium dioxide (TiO2).
In one aspect, the method further comprises treating the surface of the substrate to form the treated substrate by a first silanizing process to form a first silanized surface followed by applying palladium nanocolloids over the first silanized surface.
In one further aspect, the first silanizing process comprises exposing a surface of the substrate to 3-aminopropyltrimethoxysilane (APTMS).
In one further aspect, the substrate is a plastic or polymeric material and prior to the first silanizing process, treating the surface of the substrate with stearylmethylammonium chloride (SC).
In one aspect, the dielectric layer is a first dielectric layer and the method further comprises depositing a second dielectric layer over the second metal layer to form a metal-dielectric-metal-dielectric (MDMD) structure. The second dielectric layer optionally comprises a dielectric material selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), or other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof.
In one aspect, the first plating bath comprises copper and formaldehyde (HCHO) and the first metal layer is formed by submerging the treated substrate in the first plating bath.
In one aspect, the dielectric layer comprises silicon dioxide (SiO2) and the depositing of the dielectric layer comprises contacting the first metal layer on the treated substrate with a tetraethyl orthosilicate (TEOS) solution for the sol-gel process.
In one aspect, the contacting comprises submerging the first metal layer on the treated substrate in the TEOS solution and withdrawing the treated substrate from the TEOS solution at a constant rate equal or greater than 250 micrometers/second.
In one aspect, the method further comprises drying the dielectric layer at a temperature of greater than or equal to about 70° C.
In one aspect, the dielectric layer comprises titanium dioxide (TiO2) and the depositing of the dielectric layer comprises contacting the first metal layer on the treated substrate with a titanium tetraisopropoxide (TTIP) solution for the sol-gel process.
In one aspect, the contacting comprises submerging the first metal layer on the treated substrate in the TTIP solution and withdrawing the treated substrate from the TTIP solution at a constant rate equal or greater than 250 micrometers/second.
In one aspect, the method further comprises drying the dielectric layer at a temperature of greater than or equal to about 70° C.
In one aspect, the method further comprises treating the dielectric layer prior to the forming the second metal layer by conducting a second silanizing process of the dielectric layer to form a second silanized surface followed by applying palladium nanocolloids over the second silanized surface.
In one aspect, the second silanizing process comprises exposing the dielectric layer to 3-aminopropyltrimethoxysilane (APTMS).
In one aspect, the second plating bath comprises copper and dimethylamine-borane complex (DMAB) and the second metal layer is formed by submerging the treated substrate in the second plating bath.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.
Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.
In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.
Example embodiments will now be described more fully with reference to the accompanying drawings.
In contrast to conventional vacuum-based deposition techniques, the present disclosure provides a cost-effective solution-based process for metal-dielectric-metal (MDM) structural color. Further, in certain aspects, the present technology provides a simpler structure of a very thin metal layer formed over a colored substrate.
The present disclosure contemplates methods of forming a structural color component. In certain aspects, a method of forming a structural color comprising a multilayer stack comprising at least one first metal layer and one or more dielectric layers is provided, where all materials layers are deposited sequentially via a solution process. For example, such layers may be deposited in the absence of an applied electric field. The at least one metal layer may be deposited via electroless deposition, while the dielectric layer(s) may be deposited by one or more sol-gel processes. Such a process may form a metal-dielectric-metal (MDM) as further described herein.
Conformal coating of the MDM structures with different colors is achieved on various types of substrates regardless of their electrical conductivity. Appropriate deposition conditions for each layer are successfully determined to provide not only good thickness control, but also chemical compatibility with all previous layers. All depositions are driven with the inherent chemical potentials of the solution, without any external power or fields (e.g., electric, photonic, mechanical, etc.) applied.
In various aspects, a general solution-based process for a metal-dielectric-metal (MDM) structure fabrication on different substrates, both conductive and non-conductive, is provided. In certain aspects, electroless deposition of metal is employed in the process. By “electroless surface coating,” it is meant that the coating is applied to a surface of the substrate in an electroless process without use of an applied voltage or potential during the deposition. Electroless plating typically refers to a chemically applied metal coating, where the depositing of the metal is accomplished via autocatalytic reaction, rather than by presence of electrical current or potential.
In various aspects, the present disclosure provides methods of forming a structural color metal-dielectric-metal (MDM) component. The method comprises forming a first metal layer over a treated surface of a substrate by a first electroless deposition process. The first electroless deposition process can be conducted by contacting a surface of the treated substrate with a first plating bath, wherein the first metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, alloys, and combinations thereof. In certain variation, the metal comprises copper.
Copper may be used as a top metal and a bottom metal in the MDM, which can serve to reduce costs.
Next, a dielectric layer is formed over the first metal layer by a sol-gel process via dip coating. The withdrawal rate of the dip coating method may vary between greater than or equal to about 100 micrometers/s to less than or equal to about 500 micrometers/s. The dielectric material may be selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof. In certain variations, the dielectric material is silicon dioxide (SiO2). When the dielectric material comprises silicon dioxide (SiO2) formed from a sol-gel process and is used as the middle dielectric layer, it enables an iridescent color performance. In other variations, the dielectric material comprises titanium dioxide (TiO2).
Finally, the method comprises forming a second metal layer over the dielectric layer by a second electroless deposition process. The second electroless process may be conducted by contacting the dielectric layer with a second plating bath having a neutral pH, for example, from greater than or equal to about 6.5 to less than or equal to about 7.5, optionally about 7. The second metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, alloys, and combinations thereof.
Appropriate deposition conditions for each layer are described herein and achieve not only good control over thickness of the deposited layer, but also compatibility with all previous layers. As noted above, in the fabrication processes, all depositions are driven with the inherent chemical potentials of the solution, without any external power being applied (e.g., electric, photonic, mechanic, etc.).
In certain aspects, the first metal layer and the second metal layer formed by the first and second electroless deposition processes each independently have a thickness of less than or equal to about 200 nm. In certain aspects, the first metal layer has a first thickness of less than or equal to about 150 nm, for example, greater than or equal to about 20 nm to less than or equal to about 150 nm. When the bottom or first metal layer serves to block any transmitted light, it can be thicker than 50 nm. The second metal layer may have a thickness of less than or equal to about 50 nm. In other variations, the first metal layer has a first thickness and the second metal layer independently has a second thickness of less than or equal to about 50 nm.
In certain aspects, the first metal layer may have a first morphology and the second layer may have a second morphology, where the second morphology is different than the first morphology. For example, the second morphology of the second layer may be a discontinuous island-like morphology giving rise to optical properties different from that of thin, smooth metal first layer/film, which leads to colors that cannot be produced by smooth metal films alone.
The dielectric layer optionally has a thickness of greater than or equal to about 40 nm to less than or equal to about 200 nm. For example, where the dielectric layer comprises a lower refractive index dielectric material, such as silicon dioxide (SiO2), a thickness may be greater than or equal to about 50 nm to less than or equal to about 150 nm. For a higher refractive index dielectric material, like titanium dioxide (TiO2), a thickness of the dielectric layer may be greater than or equal to about 40 nm to less than or equal to about 200 nm. When higher order optical resonance is used, the dielectric layer can be much thicker than the above numbers, for example, doubling the thicknesses specified. In certain variations, the dielectric layer has a thickness of greater than or equal to about 40 nm to less than or equal to about 150 nm, optionally at greater than or equal to about 100 nm for higher order resonance.
In certain alternative variations, the structure may include both a first dielectric layer and a second dielectric layer. The second dielectric layer may be disposed atop the second metal layer and serves to produce a peak in the reflection spectra. The second dielectric layer may have any of the compositions or properties of the first dielectric layer as specified above. Further, the second dielectric layer may be formed by the sol-gel methods described in the context of forming the first dielectric layer.
In certain variations, the first metal layer and the second metal layer comprise copper and the dielectric layer comprises silicon dioxide (SiO2).
In certain other variations, the first metal layer and the second metal layer comprise copper and the dielectric layer comprises titanium dioxide (TiO2).
The method may further comprise treating the surface of the substrate to form the treated substrate by a first silanizing process to form a first silanized surface. This may be followed by applying palladium nanocolloids over the first silanized surface, so that palladium (Pd) metal is associated with the treated first silanized surface for catalysis and formation of the first metal layer in the first electroless deposition process. In one variation, the first silanizing process comprises exposing a surface of the substrate to 3-aminopropyltrimethoxysilane (APTMS).
In certain aspects, the substrate is a plastic material and prior to the first silanizing process, treating the surface of the substrate with stearylmethylammonium chloride (SC).
In certain variations, the first plating bath comprises copper and formaldehyde (HCHO) and the first metal layer is formed by submerging the treated substrate in the first plating bath.
In certain variations, the dielectric layer comprises silicon dioxide (SiO2) and the depositing of the dielectric layer comprises contacting the first metal layer on the treated substrate with a tetraethyl orthosilicate (TEOS) solution for the sol-gel process. The contacting may comprise submerging the first metal layer on the treated substrate in the TEOS solution and withdrawing the treated substrate from the TEOS solution at a constant rate of greater than about 200 micrometers/second, for example, about 250 micrometers/second or any of the withdrawal rates specified above.
In certain variations, the dielectric layer comprises titanium dioxide (TiO2) and the depositing of the dielectric layer comprises contacting the first metal layer on the treated substrate with a titanium tetraisopropoxide (TTIP) solution for the sol-gel process. The contacting may comprise submerging the first metal layer on the treated substrate in the TTIP solution and withdrawing the treated substrate from the TTIP solution at a constant rate of greater than about 200 micrometers/second, for example, about 250 micrometers/second or any of the withdrawal rates specified above.
The method may also comprise drying the dielectric layer to remove residual solvent, for example, at a temperature of greater than or equal to about 70° C.
In various aspects, the dielectric layer thus formed may be treated prior to the forming the second metal layer by conducting a second silanizing process of the dielectric layer to form a second silanized surface. After the second silanizing process, this may be followed by applying palladium nanocolloids over the second silanized surface. In certain aspects, the second silanizing process comprises exposing the dielectric layer to 3-aminopropyltrimethoxysilane (APTMS).
In yet other aspects, the neutral pH second plating bath comprises copper and dimethylamine-borane complex (DMAB) and the second metal layer is formed by submerging the treated substrate in the second plating bath.
One variation of a solution-based layer-by-layer fabrication process according to certain aspects of the present disclosure is shown in
Next, silanization can be performed on the surface. For example, silanizing may include exposing the surface to 3-aminopropyltrimethoxysilane (APTMS). For example, a silicon (e.g., silicon wafer) or glass (e.g., silicon dioxide containing) substrate can undergo a silanization step with 3-aminopropyltrimethoxysilane (APTMS) to ensure an amine terminated surface, which can subsequently serve to anchor the catalyst particles. As noted above, for plastic substrates such as ABS, PET, etc., where silanization is not possible, pretreatment with stearyltrimethylammonium chloride (SC) on the surface helps with palladium (Pd) nanocolloids adsorption due to the positively-charged amine group.
Next, the silanized surface may be followed by absorption of palladium (Pd) nanocolloids. Thus, the treated substrate can then be immersed in a pre-synthesized Pd nanocolloidal solution for Pd absorption.
An electroless metal deposition process then occurs. As noted above, the first metal layer comprises a metal selected from the group consisting of: copper, aluminum, silver, titanium, manganese, iron, cobalt, gold, nickel, zinc, and alloys thereof. In certain variations, the metal comprises copper. This may include immersing the modified substrate in a copper plating bath with formaldehyde (HCHO), for example, for 2 minutes, resulting in a shiny copper film (having a thickness of approximately 40 nm) disposed on the surface of the substrate. The autocatalytic Cu electroless deposition process can thus be carried out on the silicon surface, where Cu complex is reduced by formaldehyde as follows:
[Cu(II)-Tar]+2HCHO+2OH−→2HCOOH+H2+H2O+Tar2-+Cu(0),
where Tar2- is the tartrate anion. A strong basic solution (pH>11.5) would typically be present because the formation of methylene glycolate anion is favored at high pH. The Cu color gradually appears on the top of the silicon substrate, indicating an increasing Cu layer thickness with immersing time. For example, in one process the Cu layer grows at the rate of 0.27 nm/s, following a nucleation and growth mechanism. The Pd nanocolloids serve as an autocatalytic center as well as a nucleation center, where Cu nanoparticles start to form and merge as the deposition goes on. Such mechanism can be seen from the scanning electron microscopy (SEM) images, as well as observed refractive index changes with increasing Cu thickness. In one variation, a plating time of 2 minutes/120 seconds for the bottom Cu layer having an approximate 40 nm thickness is selected, as the reflection spectra hardly changes thereafter. The resulted shiny Cu film has a root-mean-square (RMS) surface roughness of 5.8 nm, which ensures the smoothness and uniformity for the bottom reflector in the MDM structure.
Next, a dielectric layer is applied. The dielectric material may be selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof. Dielectrics with different refractive indices, such as silicon dioxide (SiO2) or titanium dioxide (TiO2)) from sol-gel process may be used as the middle dielectric layer to tune different colors. Thus, the dielectric layer comprises a dielectric material selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof.
For example, silicon dioxide may be deposited on top of the copper (Cu) film with a dip-coating method. Tetraethyl orthosilicate (TEOS) solution may be prepared by mixing 35.5 ml ethanol, 5 ml water, TEOS and methyltriethoxysilane (MTES, 99%, Sigma-Aldrich) in order. 0.1 M HCl is used in the solution having a pH to 3 for hydrolysis. The amount of TEOS added increases gradually from 6.4 ml to 22.4 ml with 3.2 ml interval. The MTES may be added in proportion to TEOS, for example, with a volume ratio of 4:1 (TEOS:MTES). The Cu coated substrate may then be immersed into the TEOS solution for several minutes and withdrawn at a constant rate.
The metal (e.g., copper) coated substrate is withdrawn slowly from a tetraethyl orthosilicate (TEOS) solution, which may be done at constant rate ranging from greater than or equal to about 100 micrometers (μm)/s to less than or equal to about 500 micrometers/s, for example, at about 200 μm/s to about 250 μm/s using a linear actuator (Z6254B 25 mm motorized actuator, Thorlabs Inc.). In this manner, a dielectric SiO2 layer is formed having a thickness of greater than or equal to about 50 nm to less than or equal to about 150 nm that can be obtained by varying the TEOS concentration. The as-deposited SiO2 may be dried on a hot plate, for example having a temperature of about 70° C. to remove any residue solvent. After drying the SiO2 material, another silanization process is conducted by first treating with 3-aminopropyltrimethoxysilane (APTMS). The silanized surface is then immersed in Pd nanocolloidal solution and is ready for another metal layer formed by an electroless process.
Alternatively, titanium dioxide (TiO2) may be deposited on top of the copper (Cu) film with a dip-coating method. A TiO2 deposition solution comprising titanium tetraisopropoxide (TTIP, 97%, Sigma-Aldrich) may be first obtained by mixing 30 ml ethanol, acetylacetonate (AcAc) and TTIP for 30 minutes. The amount of TTIP may be increased, for example, from about 4.44 ml to about 17.76 ml. The AcAc was added in proportion to TEOS with a volume ratio of 2.9:1 (TTIP:AcAc). Then, 1.2, 2.4, 3.6, and 4.8 ml water may be added dropwise to the TTIP solutions. The final solution may be stirred for another hour to ensure hydrolysis. The Cu coated substrate may then be immersed into the TTIP solution for several minutes and withdrawn at a constant rate, as specified above in the context of the silicon dioxide layer.
Next, a thin copper (Cu) deposition layer may be formed over the silanized treated surface of the dielectric material layer, such as the SiO2 or TiO2 layers. Typical copper plating solution requires a basic environment where pH is greater than 10. However, the remaining hydroxyl groups inside the TEOS-derived SiO2 tend to undergo a further condensation reaction and give rise to a significant amount of internal stress inside the thin film. This potentially leads to a catastrophic cracking of the dielectric (e.g., SiO2) layer with no copper being plated on top. Therefore, a neutral pH plating composition is instead selected having dimethylamine-borane complex (DMAB) that may be at 50° C. A thin copper layer having a thickness of less than or equal to about 30 nm can be obtained, for example, within about 3 minutes. An SEM image reveals a typical nucleation and growth mechanism of the Cu plating, where discontinuous copper islands grow into a continuous thin film. As noted above, for non-conductive plastic substrates, surface treatment with stearyltrimethylammonium chloride is carried out before Pd nanocolloids absorption to facilitate a uniform distribution of Pd across the substrate surface. Similar deposition procedures are implemented once Pd nanocolloids are deposited.
The resultant MDM structural color varies from orange to cyan with increasing SiO2 layer thickness (
It was observed that because the copper deposition follows a nucleation and growth mechanism, nontrivial optical properties than bulk copper could be obtained with very short deposition time. In
Another embodiment of solution processed color processes according to certain variations of the present application is to deposit a thin metallic layer (such as Cu) over a colored substrate, which significantly modifies the color appearance, and special visual or artistic effects. This is the result of the interference of light reflecting from multiple interfaces, where light absorption by the colored substrates plays an important role. Experiments were carried by using colored Lego pieces made of ABS plastics. As such, the process is applicable to a wide range of materials.
As noted above, in certain variations, the dielectric layer may be a first dielectric layer. Thus, the method may further comprise depositing a second dielectric layer over the second metal layer to form a metal-dielectric-metal-dielectric (MDMD) structure, in a process step like those described above in the context of the first dielectric layer, for example, a sol-gel process. The second dielectric layer comprises a dielectric material selected from the group consisting of: silicon dioxide (SiO2), silicon nitride (Si3N4), other metal oxides and sulfides, including zinc oxide (ZnO), hafnium oxide (HfO2), molybdenum trioxide (MoO3), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), oxide tungsten trioxide (WO3), zinc selenide (ZnSe), zinc sulfide (ZnS), aluminum oxide (Al2O3), magnesium fluoride (MgF2), and combinations thereof. In this manner, a metal-dielectric-metal-dielectric (MDMD) structural color device may be formed.
In summary, the present disclosure provides a series of solution-based methods for thin layer deposition of metal-dielectric-metal (MDM) structural color aiming at similar quality to the costly vacuum processes. In contrast to conventional vacuum-based deposition techniques, the present disclosure thus contemplates a cost-effective solution-based process for metal-dielectric-metal (MDM) structural color, and a simpler structure of a very thin metal layer over a colored substrates. Conformal coating of the MDM structures with different colors are achieved on various types of substrates regardless of their conductivity.
As noted above, advantageously all depositions were driven with the inherent chemical potentials of the solution, without any external power (i.e., electric, photonic, mechanic, etc.) input. The entire process may be carried out on various substrates near ambient pressure and temperature with minimal heating (e.g., about 50° C.) including during the top metal (Cu) layer deposition. The minimal heating was used to achieve a faster deposition rate. The full-solution color methods of the present disclosure are versatile and can be used with a variety of different substrates, including silicon wafer, glass, polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), and the like. Color coatings from orange to cyan may be produced by varying the thickness of the dielectric layer. The trilayer MDM structure gives vivid colors from orange to cyan with a good control of the dielectric layer thickness. Angle-dependent spectra responses are also observed for SiO2 based samples and gave the sample an iridescent appearance due to the low refractive index of SiO2. The color angle-sensitivity can also be easily tuned by switching the dielectric between SiO2 and TiO2 under an almost identical fabrication process. Due to the nucleation and 3D growth, the top thin Cu layer presented new optical properties at different electroless deposition times, which gave the Cu/SiO2/Cu structure a new color appearance beyond the color gamut obtained by the conventional MDM resonator. Thus, colors beyond the conventional MDM color gamut are also achievable by carefully tuning the top Cu layer morphology, where an effective layer plays an important role in modifying the imaginary part of the refractive index. This fabrication strategy can be extended to the deposition of other metals (e.g., nickel (Ni), silver (Ag), and the like) and dielectrics (e.g., zirconium dioxide (ZrO2), and the like). Further pigmentation and packaging strategies (including anti-scratching coating) are contemplated. The electroless deposition and dip-coating techniques can be readily scaled up and made into a continuous fabrication process. All these aspects help to reduce the cost and accelerate the implementation of MDM structural colors. Thus, such facile and cost-effective fabrication methods can be easily scaled up for mass production and lead to an extensive usage of structural color in diverse fields such as color displays, cosmetics, solar cells, aesthetic decorations, and the like.
One example embodiment of a first metal layer of copper, dielectric of silicon dioxide, and second metal layer of copper (Cu/SiO2/Cu) is used as a model system due to its easy accessibility and low cost. Another example is a first metal layer of copper, dielectric of titanium dioxide, and second metal layer of copper (Cu/TiO2/Cu). Electroless plating of copper is implemented for the top and bottom metal, while a sol-gel process is employed for depositing the middle layer comprising silica or titania. A systematic investigation was carried out for each deposition layer to ensure good film quality as well as its compatibility with all previous layers. The present technology can thus enable large scale, full solution-processed production of structural color coatings and pigments and could potentially lead to an extensive usage of in diverse fields such as color displays, cosmetics, aesthetic decorations, and the like.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
This application claims the benefit of U.S. Provisional Application No. 63/417,734, filed on Oct. 20, 2022. The entire disclosure of the above application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63417734 | Oct 2022 | US |
