EP4669711A2 - Air-stable and printable molecular copper ink materials - Google Patents

Abstract

Provided is a method for making a conductive ink. The conductive ink may be made by reacting copper sulfate with sodium carbonate to obtain copper carbonate; reacting the copper carbonate with formic acid to obtain copper formate particles; and forming an ink. Also provided are inks made by a method described herein.

Description

Attorney Docket No.: 011520.01823 AIR-STABLE AND PRINTABLE MOLECULAR COPPER INK MATERIALS CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/486,027, filed February 20, 2023, the disclosure of which is incorporated herein by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH [0002] This invention was made with government support under contract no. W911NF-20-2-0016 awarded by the U.S. Army Research Office. The government has certain rights in the invention. BACKGROUND OF THE DISCLOSURE [0003] Electronics have advanced rapidly, allowing for the miniaturized sensors, antennas and circuits to be printable, compact, lightweight and flexible. Recent years have seen an increasing emergence of interest in using printable materials, such as graphene, MXenes, metal nanostructures, and conductive polymers. Of these materials, copper show an immense potential due to its abundance, low-cost, and inherently high conductivity. Bulk copper has been extensively used in electronics, but copper itself suffers from oxidation to hinder its conductivity. This is further exacerbated on the nanoscale due to higher surface energies, resulting in greater potential for oxidation. The potential for oxidation overtime greatly limits the stability, reliability and printability of copper nanostructures. Another avenue for printable metal features would be to utilize molecular ink material instead. Unlike the nanostructures, molecular inks do not oxidize as they start as ions (such as Cu²⁺ instead of Cu⁰). However, typical molecular inks suffer from having low concentrations and organic volatile solvents. BRIEF SUMMARY OF THE DISCLOSURE [0004] In an aspect, the present disclosure provides a method for making conductive ink, comprising: reacting copper sulfate with sodium carbonate to obtain copper carbonate; reacting the copper carbonate with formic acid to obtain copper formate particles; and, forming an ink comprising the copper formate particles. [0001] In an aspect, the present disclosure provides compositions. In various examples, a composition is made by a method of the present disclosure. Non-limiting examples of compositions are provided herein (e.g., in the Example, sample claims, and elsewhere). A composition may be referred to as an ink, an ink solution, a conductive ink, or a printable conductive ink. The compositions of the present disclosure do not comprise iodide. [0005] The present disclosure provides printable and air-stable molecular copper ink materials from metal-organic decomposition (MOD) by using copper ions, including both copper formate (CuF-MOD) and aqueous copper formate-amine complex materials (CuA- MOD). [0006] In another aspect, the present disclosure provides a method of printing a conductive film, comprising depositing the ink of the method of the present disclosure on a surface, and heating the ink at 150–200 ºC for 1 to 30 minutes. [0007] In another aspect, the present disclosure provides a method of printing a conductive film, comprising depositing the ink solution of the method of the present disclosure on a surface, and heating the ink solution at 150-350 ºC for 1 to 60 minutes. [0008] In another aspect, the present disclosure provides a method of printing conductive ink. The method includes extruding any of the presently disclosed conductive ink compositions onto a substrate. The extruded ink (on the substrate) is then washed with a solvent (such as, DEGBE, for example, an organic compound) to remove residual undesired materials. [0009] In an aspect, an object (e.g., conductor) may be printed (e.g., 3D printed) from a conductive slurry composition of the present disclosure. The printed object may be passivated with, for example, formate groups, which may be desirable for the printed (e.g., solid) object. BRIEF DESCRIPTION OF THE FIGURES [0010] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures. [0011] Figure 1. Schematic flow of the synthetic process towards copper formate and copper formate-amine complex (top) and printing of ink for printable electronics. The scale bar represents 15 mm.. [0012] Figure 2. (a) The SEM image of prepared CuF particles (top) and sintered conductor (bottom). The scale bar is 5 μm. A TGA curve (b) and FTIR spectra (c) are shown for for CuF- and CuA-MOD ink. [0013] Figure 3. (a) A graph of the conductivity of sintered CuF-MOD prints as a function of DMF wt %. (b) The conductivity (green) and sheet resistance (red) values of sintered CuA-MOD at varying amine ratios. (c) The conductivity values of sintered CuA- MOD at varying sintering temperatures and times. [0014] Figure 4. (a) A schematic of the EMI-SH process starting with the incident wave and resulting in either a reflection, transmission, or absorption of the wave. (b) The EMI-SH efficiencies as a function of conductivity for CuF- and CuA-MOD complex prints. The fit is shown to describe the observed trend of EMI-SH with increasing conductivity. [0015] Figure 5. The SEM images of CuF particles that have been milled for (top) 30 and (bottom) 60 minutes. The SEM images show images which are zoomed in from left to right. The scale bar represents 5 μm. [0016] Figure 6. The TGA for CuF complexed with only TMEDA and only AMP. [0017] Figure 7. The FTIR spectrum of CuF-TMEDA and CuF-AMP. [0018] Figure 8. CuF-amine inks at various amine ratios. The amines ratios here represent the molar ratio of TMEDA:AMP. [0019] Figure 9. The conductivity (bars) and sheet resistance (dots) values of CuA MOD ink after sintering (a) with or without DDA addition, (b) DDA concentration, and (c) HPMC concentration. [0020] Figure 10. The SEM images of CuF-amine inks sintered with (left) or without (right) the addition of DDA. The scale bar represents 5 μm. DETAILED DESCRIPTION OF THE DISCLOSURE [0021] Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. [0022] As used herein, unless otherwise indicated, “about”, “substantially”, or “the like”, when used in connection with a measurable variable (such as, for example, a parameter, an amount, a temporal duration, or the like) or a list of alternatives, is meant to encompass variations of and from the specified value including, but not limited to, those within experimental error (which can be determined by, e.g., a given data set, an art accepted standard, etc. and/or with, e.g., a given confidence interval (e.g.90%, 95%, or more confidence interval from the mean), such as, for example, variations of +/-10% or less, +/-5% or less, +/-1% or less, and +/-0.1% or less of and from the specified value), insofar such variations in a variable and/or variations in the alternatives are appropriate to perform in the instant disclosure. As used herein, the term “about” may mean that the amount or value in question is the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, compositions, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, or the like, or other factors known to those of skill in the art such that equivalent results or effects are obtained. In general, an amount, size, composition, parameter, or other quantity or characteristic, or alternative is “about” or “the like,” whether or not expressly stated to be such. It is understood that where “about,” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise. [0023] Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value) of a range. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “0.1% to 5%” should be interpreted to include not only the explicitly recited values of 0.1% to 5%, but also, unless otherwise stated, include individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5% to 1.1%; 0.5% to 2.4%; 0.5% to 3.2%, and 0.5% to 4.4%, and other possible sub-ranges) within the indicated range. It is also understood (as presented above) that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about, it will be understood that the particular value forms a further disclosure. For example, if the value “about 10” is disclosed, then “10” is also disclosed. [0024] In an aspect, the present disclosure provides a method for making conductive ink, comprising reacting copper sulfate with sodium carbonate to obtain copper carbonate; reacting the copper carbonate with formic acid to obtain copper formate particles; and forming an ink comprising the copper formate particles. [0025] In various embodiments, the method of the present disclosure further includes blending the copper formate particles with one or more solvents. Examples of solvents include, but are not limited to, diethylene glycol butyl ether (DEGBE), di(propylene glycol) methyl ether (DPM), dimethylformamide (DMF), diethylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl ethyl ketone, ethanol, propanol, propylene glycol, ethylene glycol, and the like, and any combinations thereof. In various examples, a single solvent is used during blending. In various embodiments, combinations of solvents are used. [0026] In various embodiments, the method of the present disclosure further comprises dissolving the copper formate particles in an amine solution comprising at least one amine and a solvent, to obtain an ink solution wherein the ink solution has a molar ratio of 2:1 copper formate to total amine (e.g., wherein total amine is a mixture of, for example, 2- methyl propanol (AMP), tetramethyl ethylenediamine (TMEDA)), and wherein the copper formate and amine form a complex. Throughout the disclosure, copper formate may be referred to as CuF. [0027] The amine solution may comprise various amines and combinations of amines. For example, the amine is an aliphatic amine. For example, the aliphatic amine may have 10 to 20 carbon atoms and may be linear or branched and/or have various degrees of unsaturation. The aliphatic amines may have various substituents, such as, for example, additional alkyl groups (e.g., methyl groups) or hydroxy groups. Non-limiting examples of amines in include, 2-amino-2-methyl propanol (AMP), tetramethyl ethylenediamine (TMEDA), and combinations thereof. [0028] In embodiments the amine solution of the method comprises a 1:1 molar ratio of 2-amino-2-methyl propanol (AMP) to tetramethyl ethylenediamine (TMEDA) and a solvent. [0029] The amine solution may comprise various solvents. Examples of solvents include, but are not limited to, ethanol, H2O (e.g., DI H2O), methanol, and the like, and combinations thereof. Other examples of solvents include, but are not limited to, glycols and polar protic solvents. Examples of glycols include, but are not limited to, ethylene glycol, propylene glycol, and the like. Combinations of solvents may be used. In various embodiments, a single solvent is used (e.g., one solvent and the combination of AMP and TMEDA). [0030] In various embodiments of the present disclosure, the method further comprises adding a hydroxypropyl methylcellulose (HPMC) solution, comprising 2 wt% of HPMC in a solvent (e.g., H2O), to the ink solution, wherein the ink solution has a weight ratio of 1:1:2 copper formate-amine complex to HPMC solution to solvent (e.g., H₂O). In this way, the viscosity of the composition may be controlled according to the amount of HPMC (e.g., concentration). For example, the concentration of the HPMC solution may be in the range of 1 wt% – 5 wt%, inclusive and values in between, or the concentration may be higher or lower. In some embodiments, the concentration is between 1 wt%-5 wt%, inclusive, and values in between. In various embodiments, acrylics and acrylic hybrid solutions such as acrylic latexes, as well as polyurethanes, may be added with the HPMC solution. The volume of HPMC solution and the volume of acrylic and/or polyurethane additive may be between 10:90 up to 90:10, respectively. [0031] In embodiments, the solvent of the amine solution, the solvent of the HPMC solution, and the solvent of the ink solution may be independently chosen from ethanol, DI H₂O, and methanol. In some embodiments, the solvent of the present disclosure may be any combination of ethanol, DI H2O, and methanol. [0032] In various embodiments, the method further comprises adding 0.1 wt% – 0.5 wt% (e.g., 0.1, 0.2, 0.3, 0.4, or 0.5) dodecanoic acid (DDA) to the composition. The DDA may be added in the final step of the method. The DDA may be added as a solution comprising DDA and a polar protic solvent. [0033] In various embodiments of the present disclosure, the ink has a molar ratio of about 4.5 parts copper formate to about 4.75 parts DEGBE to about 0.75 parts DMF. In various embodiments of the present disclosure, the ink has a molar ratio of 4.5 parts copper formate to 4.75 parts DEGBE to 0.75 parts DMF. [0034] In an aspect, the present disclosure provides compositions. In various examples, a composition is made by a method of the present disclosure. Non-limiting examples of compositions are provided herein. A composition may be referred to as an ink, an ink solution, a conductive ink, or a printable conductive ink. The compositions of the present disclosure do not comprise iodide. [0035] In various embodiments, a composition of the present disclosure comprises copper, wherein the total molar copper of the composition is less than or equal to 30 percent by mole Cu⁰. In various embodiments, the total molar copper of the composition of the present disclosure is at least 70 percent by mole Cu²⁺. In various embodiments, the compositions comprise 30 to 70 percent by mole Cu²⁺, including all 0.1% values and ranges therebetween. [0036] The present disclosure provides printable and air-stable molecular copper ink materials from metal-organic decomposition (MOD) by using copper ions, including both copper formate (CuF-MOD) and aqueous copper formate-amine complex materials (CuA- MOD). [0037] Heating the inks (e.g., sintering the inks) facilitates the decomposition of the non-conductive organics while annealing the Cu for increased contact and density. The decomposition temperature (i.e., the temperature at which the non-conductive organics decompose) for CuF is observed at 200 °C. The decomposition temperature for CuA is observed at 150 °C. The amine complex allows for lower temperature sintering, which is desirable for paper and polyester-based flexible electronics. Without intending to be bound by any particular theory, it is considered that the CuF-MOD ink allows for significantly higher loading due to lower solvent content, while exhibiting high electric conductivity (35 MS/m) of printed features. Additionally, the CuF-MOD ink shows high electromagnetic interference shielding (EMI-SH) efficiency of 65 dB. The CuA-MOD ink is water soluble to achieve electric conductivities of 4 MS/m and EMI-SH capabilities of 50 dB. [0038] In embodiments, the CuA-MOD ink has copper formate and an amine in a metal-ion complex. In some embodiments, there may be a mixture of copper-amine complex and copper formate-amine complex in the ink. [0039] In various embodiments, the CuF ink is a suspension of copper formate particles (i.e., a slurry). The particles may have dimensions ranging from 500 nm to 2000 nm in size, including sphere, plate, or needle-geometry particles. [0040] In various embodiments, the CuA ink is a solution where all components are dissolved by the solvent. [0041] In another aspect, the present disclosure provides a method of printing a conductive film, comprising depositing the ink of the method of the present disclosure on a surface, and heating the ink at 150–200 ºC (including all 0.1 ºC values and ranges therebetween) for 1 to 30 minutes (including all integer second values and ranges therebetween). [0042] In another aspect, the present disclosure provides a method of printing a conductive film, comprising depositing the ink solution of the method of the present disclosure on a surface, and heating the ink solution at 150-350 ºC (including all 0.1 ºC values and ranges therebetween) for 1 to 60 minutes (including all integer second values and ranges therebetween). [0043] In another aspect, the present disclosure provides a method of printing conductive ink. The method includes extruding any of the presently disclosed conductive ink compositions onto a substrate. The extruded ink (on the substrate) is then washed with a solvent (such as, DEGBE, for example, an organic compound) to remove residual undesired materials. [0044] In an aspect, an object (e.g., conductor) may be printed (e.g., 3D printed) from a conductive slurry composition of the present disclosure. The printed object may be passivated with, for example, formate groups, which may be desirable for the printed (e.g., solid) object. [0045] In various examples, an article of manufacture is printed from the conductive slurry of the present disclosure. The article of manufacture may comprise one or more component, which may be a passive component or components (e.g., conductor(s), wire(s), and the like, and combinations thereof) and/or an active component or components (e.g., antennas, relays, switch leads, RF shields, and the like, and combinations thereof), comprising the nanoplates of the present disclosure. The nanoplates may be useful for producing electrodes. [0046] The article of manufacture may be an electrical device. Non-limiting examples of electrical devices include electrical motors, electrical generators, transformers, switching regulators, converters, inverters, charging circuits, discharge circuits, PCL control devices, transmission and distribution units (which may be high-voltage transmission or distribution units), circuit breakers, and the like. Additional non-limiting examples include consumer electronic devices (e.g., computer, cellular phone, and the like), home appliance devices (e.g., television, washers, dryers, and the like), solar cells, sensor devices (e.g., wireless sensor devices), control devices, amplifiers, attenuators, Internet of Things (IOT) devices, audio devices, RFID devices, illuminating devices, and the like. [0047] An electrical device or electronic devices may comprise one or more component that comprises one or more nanocomposite. Non-limiting examples of components include antennas, contacts, conductors, relays, switch leads, RF shields, and the like. [0048] The electronic device may be flexible. For example, the conductive slurry composition may be used to print a conductor onto a substrate. The substrate may have various thicknesses. For example, the substrate may have a thickness of 10 nm to 1000 nm, including all 0.1 nm values and ranges therebetween. [0049] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present invention. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps. [0050] The following Statements provide various embodiments of the present disclosure. Statement 1. A method for making a conductive ink, comprising: reacting copper sulfate with sodium carbonate to obtain copper carbonate; reacting the copper carbonate with formic acid to obtain copper formate particles; and forming an ink comprising the copper formate particles. Statement 2. A method according to Statement 1, wherein the forming further comprises: blending the copper formate particles with diethylene glycol butyl ether (DEGBE), di (propylene glycol) methyl ether (DPM), dimethylformamide (DMF), diethylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl ethyl ketone, ethanol, propanol, propylene glycol, ethylene glycol, or the like, or any combination thereof. Statement 3. A method according to Statement 1, wherein the forming further comprises: dissolving the copper formate particles in an amine solution comprising at least one amine and a solvent to obtain an ink solution, wherein the ink solution has a molar ratio of copper formate to amine of 3:1 – 1:2 (e.g., 3:1, 2.5:1, 2:1, 1.5:1, 1:1, 1:1.5, 1:2, or any ratio value in between), and wherein the copper formate and amine form a complex. Statement 4. A method according to Statement 3, wherein the amine solution comprises a 1:1 molar ratio of 2-amino-2-methyl propanol (AMP) to tetramethyl ethylenediamine (TMEDA), and a solvent. Statement 5. A method according to Statement 3, wherein the solvent is chosen from glycols (e.g., ethylene glycol, propylene glycol, and the like), polar protic solvents (e.g., ethanol, DI H2O, methanol, and the like), and combinations thereof. Statement 6. A method according to any one of Statements 3–5, further comprising adding a hydroxypropyl methylcellulose (HPMC) solution, wherein the HPMC solution comprises 1–5 wt% of HPMC in the solvent (e.g., 2 wt% HPMC in the solvent), to the ink solution whereby the ink solution has a molar ratio of 1:1:2 copper formate-amine complex to HPMC solution to the solvent. In some embodiments, acrylics and acrylic hybrid solutions such as acrylic latexes, as well as polyurethanes may be added with the HPMC solution. The volume of HPMC solution and the volume of acrylic and/or polyurethane additive may be between 10:90 up to 90:10, respectively. Statement 7. A method according to any one of Statements 3–6, further comprising adding 0.1 wt%–0.5 wt% dodecanoic acid (DDA), where the wt% is relative to the weight of the entire solution. Statement 8. A method according to Statement 2, wherein the ink has a molar ratio of 4.5 to 4.75 to 0.75 copper formate to DEGBE to DMF. Statement 9. A composition comprising the ink according to Statement 2. Statement 10. A composition comprising the ink solution according to Statement 3. Statement 11. A method of printing a conductive film, comprising: depositing the ink according to Statement 2 on a surface; and heating the ink at a temperature in the range of 150–200 ºC (including all 0.1 ºC values and ranges therebetween) for 1–30 minutes (including all 0.1 s values and ranges therebetween). Statement 12. A method of printing a conductive film, comprising: depositing the ink solution according to Statement 3 on a surface; and, heating the ink solution at 150–350 ºC (including all 0.1 ºC values and ranges therebetween)for 1–60 minutes (including all 0.1 s values and ranges therebetween). Statement 13. A composition according to Statements 9 or 10 comprising copper, wherein the total molar copper is less than or equal to 30 percent by mole Cu⁰. Statement 14. A composition according to Statement 13, wherein the total molar copper is at least 70 percent by mole Cu²⁺. In various embodiments, the compositions comprise 30 to 70 percent by mole Cu²⁺, including all 0.1% values and ranges therebetween. Statement 15. A method for producing a conductive ink from copper formate particles, comprising: blending the copper formate particles with diethylene glycol butyl ether (DEGBE), di (propylene glycol) methyl ether (DPM), and dimethylformamide (DMF). Statement 16. A method for producing a conductive ink from copper formate particles, comprising: dissolving the copper formate particles in an amine solution comprising at least one amine and a solvent to obtain an ink solution, wherein the ink solution has a molar ratio of 3:1 – 1:2 (e.g., 3:1, 2.5:1, 2:1, 1.5:1, 1:1, 1:1.5, 1:2, or any ratio value in between) copper formate to amine, and wherein the copper formate and amine form a complex. [0051] The following example is presented to illustrate the present disclosure. It is not intended to be limiting in any matter. EXAMPLE [0052] This example provides a description of ink materials of the present disclosure and methods of making and using same. [0053] Nanostructured metal materials promise printable and flexible electronics are known to have oxidation and stability drawbacks due to their high surface energies. Described herein are printable ink materials which can be used to print flexible electronics, and exhibit desirable air stability and resistance to oxidation. Air-stable molecular metal ink materials described herein can be printed to flexible electronics through metal-organic decomposition. The desirable air stability and resistance to oxidation is facilitated by copper ions, which are present in copper formate and aqueous copper formate-amine complex. By complexing copper formate with amines, the decomposition temperature of printed molecular copper ink is observed to decrease 50 °C (i.e., the decomposition temperature of the ink containing a copper formate-amine complex is observed to be 50 ºC lower than the decomposition temperature of ink containing copper formate without amines or an amine complex) while maintaining its electric conductivity. The printed copper conductors exhibit high electric conductivity of 35 MS/m (>50% of bulk copper’s electric conductivity at room temperature) and electromagnetic interferences shielding effectiveness of 65 dB. The findings shown here of molecular decomposition ink promise its applications in printable electronics. [0054] Figure 1 shows the schematic diagram from the MOD ink preparation to the printed copper conductor. The preparation of copper formate (CuF) can be made through a two-step reaction by first reacting copper sulfate with sodium carbonate to form copper carbonate, then reacting with formic acid to produce copper formate. The molecular MOD inks can be prepared in two different ways by using CuF to either yield CuF-MOD or complexing with amines to form CuA-MOD. The formation of CuF-MOD particles increases the amount of Cu content loading in the ink, whilst resulting in a slurry paste. Complexing CuF with amines can alter its printability characteristics, such as improving solubility in different solvents or decreasing the decomposition temperature of CuF. The two amines used in this embodiment are tetramethylethylene diamine (TMEDA) and 1-amino-2-methyl propanol (AMP). The addition of TMEDA improves the CuA-MOD complex’s solubility in water. [0055] Figure 2.2A shows the scanning electron microscopy (SEM) image for the printed CuF-MOD features before (top) and after (bottom) sintering. The as-prepared CuF- MOD materials are observed to be sheet-like features, and once sintered the conductor formed a uniform and dense film (further SEM images are shown in the Figure 5). The thermogravimetric curves (TGA) are shown in 2B for the CuF-MOD and CuA-MOD complex. A significant decrease in weight around 200-220 °C for CuF indicates the decomposition of CuF into the metallic Cu. On the other hand, CuA-MOD complex shows a significant change in weight around 100-150 °C, a decrease in decomposition temperature by 50 °C as compared to CuF-MOD. The TGA of CuF with a single amine shows a significant change in weight at 150 °C and 175 °C for TMEDA and AMP, respectively, corresponding to the decomposition of CuA-MOD with these amines (Figure 6). This decrease in decomposition temperature is attributed to the effect of amine complexation with the Cu ion. To further confirm the formation of CuA-MOD complex, Fourier transform infrared (FTIR) spectra for CuF- and CuA-MOD are shown in Figure 2c. The spectrum of CuF has a broad peak around 3000-3500 cm^-1, which is indicative of O-H stretching bands, suggesting the presence of water. CuA spectra have defined and sharper peaks at this region which corresponds to both C-H (below 3000 cm^-1) and N-H stretching bands (3000 to 3300 cm^-1), the latter suggesting the presence of amines. Additionally, the C-H and N-H spectral features of CuF-TMEDA and CuF-AMP are also shown in CuA (Figure 7). The clear difference of bands in the FTIR between CuA and CuF further indicates CuF complexation. [0056] Figure 3.3A shows electric conductivity of the printed samples made from CuF-MOD are investigated as a function of solvent dimethylformamide (DMF) concentration (wt. %). At lower concentrations of DMF, it is observed that its electric conductivity can reach 35 MS/m (above 50% of bulk copper’s conductivity). As the concentration of DMF increases, the conductivity decreases to 10 MS/m at 5 wt. %, confirming the role of copper content on its electric conductivity. For CuA-MOD ink, the amine ratio and sintering profiles play an important role in its electric conductivity.3B explores the amine molar ratios of TMEDA to AMP, where an amine ratio of 1:0 and 0:1 represents only TMEDA and only AMP, respectively (e.g., an amine ratio of 1:0 is 1 part TMEDA to 0 parts AMP, or only TMEDA; and an amine ratio of 0:1 is 0 parts TMEDA to 1 part AMP, or only AMP). It is observed that increasing the proportion of TMEDA results in a complex which is water soluble, whereas increasing the proportion of AMP decreases its solubility in water (Figure 8). A molar ratio of 1:1 of TMEDA to AMP produced a printed copper feature with electric conductivity of 2 MS/m, while other amine ratios show decreased conductivities from 250 kS/m to 750 kS/m. Further printability studies of CuA-MOD ink materials investigated the addition of dodecanoic acid (DDA, Figure 9a-9b), and hydroxypropyl methylcellulose (HPMC) concentration (Figure 9c). It is observed that the additive of DDA affects the percolation of the copper prints (the SEM images are shown in Figure 10). DDA is a sintering agent, and provides a control on the growth of the copper particle networks. However, having higher content of DDA decreased conductivity due to the formation of small copper particles. Additionally, an increase in the HPMC concentration leads to decreased electric conductivity of printed copper features. Therefore, a desired sintering temperature and time for CuA-MOD ink is shown in Figure 3c. For sintering temperature, it is observed that sintering at 150 °C for 30 minutes produces a conductive copper feature (~30 kS/m). Increasing the sintering temperature to 250 °C increases the electric conductivity to 3 MS/m. When evaluating the sintering time at 250 °C, an increase in electric conductivity is observed with increased sintering duration, from 5 minutes (~2 MS/m) to 30 minutes (around 4 MS/m). [0057] Figure 4. Electromagnetic interference shielding of metallic materials is necessary to reflect or absorb the incident electromagnetic (EM) waves in electronic devices. The materials tend to be utilized in the bulk form. However, while effective, the bulk materials tend to be heavy, rigid, and are also energetically expensive to produce. Here, the copper molecular inks were printed and evaluated for EMI-SH capabilities. A schematic image of the interaction between the printed Cu and the EM wave is described in Figure 4A. While the two mechanisms of EMI-SH are to reflect or to absorb the incident wave, due to high electric conductivities of copper conductors. As such, these printed materials have high EMI-SH efficiencies and have great potentials while decreasing the amount of material, resulting in a lighter and flexible film relative to bulk. Figure 4B shows the EMI-SH efficiency as a function of electric conductivity for both printed and sintered CuF- and CuA- MOD features. The EMI-SH coefficients for CuA-MOD and CuF-MOD show an optimum value of 50 dB and 65 dB, respectively. An increase in electric conductivity increases the EMI-SH efficiency of the printed copper features up to 3 MS/m before plateauing. [0058] Described are copper-based MOD inks by using the copper ions as the material feedstock. The CuF-MOD ink produced a dense and continuous film, yielding high electric conductivity of 35 MS/m (greater than 50% of bulk copper’s conductivity) along with high EMI-SH efficiencies (65 dB). Once complexed with an anime, a 50 °C decrease in decomposition temperature is observed, allowing for a lower temperature sintering. Comparatively, the aqueous CuA-MOD complex exhibits an electric conductivity of 4 MS/m and EMI-SH effectiveness of 50 dB. Utilizing copper-based MOD inks simplifies and shortens the processability of the materials for printable ready inks. In addition, exploring the potential for greener solvents or decreasing the temperature needed for sintering opens the potential towards printable inks that are more environmentally friendly. [0059] Materials. Copper(II) formate tetrahydrate (CuF), Diethylene glycol butyl ether (DEGBE), Dimethylformamide (DMF), Di (propylene glycol) methyl ether (DPM), tetramethyl ethylenediamine (TMEDA), 2-amino-2-methyl propanol (AMP), ethylenediamine (EDA), butylamine (BA), octylamine (OA), triethylamine (TEA), aniline, hexadecylamine (HDA), dodecanoic acid (DDA), isopropanol (IPA) [0060] Preparation of CuF-MOD particles. The MOD complex was formed by complexing the respective ratios of CuF, DPM, DEGBE, and DMF within a ball milling grinding jar. The slurry was ball milled at 300 rpm for 1 hour after which the resulting ink was washed with DEGBE. The ink was washed by re-dispersing the solution within 2 mL of DEGBE with a vortex mixer. Excess solution was then poured off after centrifugation at 5000 rpm for 5 min. The ink was directly screen printed on Kapton with a 200 stainless steel mesh. [0061] After drying in open atmosphere, the prints were placed within a glass slide (Figure 1). The end that faces the entrance of the nitrogen flow was also taped as were the sides to prevent reduced decomposition due to high flow rates. Note that prints without a cover and under an open flow of gas produce a near nonconductive film. Inclusion of additives were done after ball milling and washing of the original ink. [0062] The ultra-sonicated trials involved the optimal ink concentration with a ratio of 4.5/4.75/.75 CuF/DEGBE/DMF doubled in order to produce approximately 20 mL of solution. The ink was placed in a centrifuge tube submerged in an ice bath and sonicated at 25 kHz for 2 mins. Washing, printing and sintering methods were identical. [0063] Preparation of CuA-MOD Ink. The amines were first dissolved into an appropriate solvent to create an amine solution. CuF was then added into the amine solution changing the color to dark-blue or purple, indicating the CuF-amine complex. This solution was then mixed until all the CuF was fully dissolved. The molar ratio of CuF to amines is 1:2. Initially, the solvent used was ethanol, then was changed to DI H2O. Once dissolved, HPMC solution (2 wt.% HPMC in H₂O) was added to increase the viscosity of the ink. The final weight ratios are 1:1:2 (CuF-amine complex: HPMC solution: H2O). To assist with sintering, various amount of DDA (dissolved in IPA) were added. [0064] First, the ink was applied through drop casting and allowing to dry. Later, direct writing was utilized through Voltera V-One for printing the MOD solutions onto plastics (Kapton^®) and allowed to dry. Once dried, the prints were sintered under low nitrogen flow to remove any residuals while also decomposing the MOD into pure copper. [0065] Characterization. Pre-sintered CuF inks and sintered films were studied with the use of a scanning electron microscope (SEM). The crystal structures of the CuF inks were characterized with a powder x-ray diffraction (pXRD) instrument. A thermogravimetric analysis was used to identify the decomposition of chemicals in solution. [0066] Although the present disclosure has been described with respect to one or more particular embodiments and/or examples, it will be understood that other embodiments and/or examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

CLAIMS: 1. A method for making a conductive ink, comprising the steps of: reacting copper sulfate with sodium carbonate to obtain copper carbonate; reacting the copper carbonate with formic acid to obtain copper formate particles; and, forming an ink comprising the copper formate particles.

2. The method of claim 1, wherein the forming further comprises: blending the copper formate particles with diethylene glycol butyl ether (DEGBE), di (propylene glycol) methyl ether (DPM), dimethylformamide (DMF), diethylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl ethyl ketone, ethanol, propanol, propylene glycol, ethylene glycol, or any combination thereof.

3. The method of claim 1, wherein the forming further comprises: dissolving the copper formate particles in an amine solution comprising at least one amine and a solvent to obtain an ink solution, wherein the ink solution has a molar ratio of copper formate to amine of 3:1 – 1:2, and wherein the copper formate and amine form a complex.

4. The method of claim 3, wherein the amine solution comprises a 1:1 molar ratio of 2- amino-2-methyl propanol (AMP) to tetramethyl ethylenediamine (TMEDA), and a solvent.

5. The method of claim 3, wherein the solvent is chosen from glycols, polar protic solvents, and combinations thereof.

6. The method of claim 5, wherein the solvent is chosen from ethanol, H2O, ethylene glycol, propylene glycol, methanol, and any combination thereof.

7. The method of claim 3, further comprising adding a hydroxypropyl methylcellulose (HPMC) solution, wherein the HPMC solution comprises 1–5 wt% of HPMC in the solvent, to the ink solution whereby the ink solution has a molar ratio of 1:1:2 copper formate-amine complex to HPMC solution to the solvent.

8. The method of claim 3, further comprising adding 0.1 wt%–0.5 wt% dodecanoic acid (DDA), wherein the wt% is relative to the entire solution.

9. The method of claim 2, wherein the ink has a molar ratio of 4.5 to 4.75 to 0.75 copper formate to DEGBE to DMF.

10. A composition comprising the ink of claim 2.

11. The composition of claim 10 comprising copper, wherein the total molar copper is less than or equal to 30 percent by mole Cu⁰.

12. The composition of claim 11, wherein the total molar copper is 30 to 70 percent by mole Cu²⁺.

13. A composition comprising the ink solution of claim 3.

14. The composition of claim 13 comprising copper, wherein the total molar copper is less than or equal to 30 percent by mole Cu⁰.

15. The composition of claim 14, wherein the total molar copper is at least 30 to 70 percent by mole Cu²⁺.

16. A method of printing a conductive film, comprising: depositing the ink of claim 2 on a surface; and, heating the ink at 150–200 ºC for 1–30 minutes.

17. A method of printing a conductive film, comprising: depositing the ink solution of claim 3 on a surface; and, heating the ink solution at 150–350 ºC for 1–60 minutes.

18. A method for producing a conductive ink from copper formate particles, comprising: blending the copper formate particles with diethylene glycol butyl ether (DEGBE), di (propylene glycol) methyl ether (DPM), dimethylformamide (DMF), diethylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl ethyl ketone, ethanol, propanol, propylene glycol, ethylene glycol, or any combination thereof.

19. A method for producing a conductive ink from copper formate particles, comprising: dissolving the copper formate particles in an amine solution comprising at least one amine and a solvent to obtain an ink solution, wherein the ink solution has a molar ratio of 3:1 – 1:2 copper formate to amine, and wherein the copper formate and amine form a complex.