Plasma-Induced Decomposition of Copper Complex Ink for the

Feb 23, 2017 - In recent years, there has been a growing interest in low-cost conductive inks and their application in printed electronics.(1-3) To ob...
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Plasma-Induced Decomposition of Copper Complex Ink for the Formation of Highly Conductive Copper Tracks on Heat-Sensitive Substrates Yousef Farraj, Ariel Smooha, Alexander Kamyshny, and Shlomo Magdassi* Casali Center for Applied Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel S Supporting Information *

ABSTRACT: The use of Cu-formate−2-amino-2-methyl-1propanol ink and low-pressure plasma for the formation of highly conductive patterns on heat sensitive plastic substrates was studied. It was found that plasma results in decomposition of copper complex to form metallic copper without heating at high temperatures. Ink composition and plasma parameters (predrying conditions, plasma treatment duration, gas type, and flow rate) were optimized to obtain uniform conductive metallic films. The morphology and electrical characteristics of these films were evaluated. Exposing the printed copper metallo-organic decomposition (MOD) ink to 160 W plasma for 8 min yielded resistivity as low as 7.3 ± 0.2 μΩ cm, which corresponds to 23% bulk copper conductivity. These results demonstrate the applicability of MOD inks and plasma treatment to obtain highly conductive printed patterns on low-cost plastic substrates and 3D printed polymers. KEYWORDS: printed electronics, copper ink, plasma, copper complex, low temperature, high conductivity

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the lowest temperature of 100 °C for pyridine containing complexes with no reported resistivity values.5 The effect of the copper and amine concentrations on the morphology of the obtained copper films were studied by Kim et al. and Choi et al.6,7 Yabuki et al. reported the formation of various copper MOD inks composed of variety amine types followed by thermal decomposition.8−10 Yang et al. studied the effect of chemical treatment of the substrate on the adhesion of the copper complex ink.11,12 Very recently, it was found that by using hybrid inks, containing both copper particles and complexes, a decrease of the decomposition temperature could be achieved.13−17 In addition to conventional heating, two postprinting processes have been reported to date for copper MOD inks: selective laser sintering (SLS)18,19 and intense pulsed light (IPL) illumination.20,21 However, these processes often result in heating the plastic substrates above their Tg, consequently having limited applicability.22 As a result, the required heat treatment prevents the use of heat sensitive substrates that have low glass transition temperature (Tg). This issue is very important and challenging, in view of the recent advances in 3D printed electronics, in which electrical connectors should be embedded within polymeric printed objects. Commercially available polymers typically have a Tg

INTRODUCTION In recent years, there has been a growing interest in low-cost conductive inks and their application in printed electronics.1−3 To obtain high performance from printed devices, it is important to develop inks that enable the formation of conductive features with high uniformity and conductivity. Currently, the most widely used functional materials for attaining conductive features are metals.1,4 Since silver is highly conductive and stable to oxidation, it is the most commonly used material in the production of conductive inks in form of nanoparticles. However, industrial scale fabrication of electronic devices requires low cost conductive inks, in which silver is replaced by lower cost metals with similar electrical conductivity. Copper has electrical conductivity, which is only 6% lower than that of silver, and the current cost of copper is about 100-times lower than that of silver. However, copperbased inks are not yet in use due to their rapid oxidation in air. A possible approach to overcome the oxidation is by using inks composed of metallo-organic decomposition (MOD) inks, which transform into metallic copper by thermal decomposition performed after printing. This decomposition results in intramolecular electron transfer from the ligands to the metal ion leading to its reduction and the formation of metal atoms. The process is followed by nucleation, crystal growth, and eventually leads to the formation of a continuous metallic film. To date, all the reported thermal decomposition MOD inks were usually performed at a temperature above 140 °C, with © 2017 American Chemical Society

Received: November 11, 2016 Accepted: February 23, 2017 Published: February 23, 2017 8766

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

Research Article

ACS Applied Materials & Interfaces

Figure 1. (A) Scheme of the printing and plasma exposure process resulting in formation of continuous copper films; (B) schematic illustration of physicochemical processes in the printed layer.

Figure 2. Transformation of copper complex into metallic copper as a function of nitrogen plasma treatment duration (power 200 W). Note that the plasma treatment also causes the transparent substrate to become slightly yellowish.

lower than 80 °C;23,24 therefore, there is an unmet need for conductive inks and new decomposition approaches suitable for heat-sensitive substrates. In this study, we present a new approach to formation of conductive copper films by using plasma treatment for chemical decomposition of the copper complex, which is a functional component of previously reported MOD ink.25 This approach enabled the formation of copper patterns within a few minutes with conductivity only four times lower than that of bulk copper at temperature less than 70 °C. It should be noted that plasma treatment has already been used for sintering silver nanoparticles-based inks, but the mechanism was based on decomposition of the organic stabilizers, which act as an electrical insulator.26,27 This process is demonstrated for screen and inkjet printed copper complex on poly(ethylene naphthalate) (PEN) and on 3D printed objects composed of polymers with Tg as low as 60 °C. We expect that this approach will present new options for low cost 2D and 3D printed electronics. An optimal MOD ink for plastic electronics should meet the following criteria: (i) the complex should undergo intramolecular oxidation−reduction (self-reduction ability); (ii) the complex should have low decomposition temperature (≤140

°C); (iii) the byproducts of ligand decomposition should be volatile to avoid the presence of insulating organic materials; and (iv) the copper complex should be soluble in solvents commonly used in printing processes. We have previously found that inks for thermal decomposition, composed of copper formate and 2-amino-2-methyl-1-propanol (AMP) ligands, meet all of the above criteria.25 As reported, the thermal decomposition of the complex occurs through two main steps, and the minimal temperature for the full decomposition is 140 °C. Therefore, for thermal decomposition approaches, this complex could be used only for polymeric substrates with high Tg.

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RESULTS AND DISCUSSION

Preliminary experiments revealed that the use of plasma instead of heating resulted in the decomposition of the copper complex at lower temperatures, below 70 °C. Figure 1 presents the scheme of overall process, starting from inkjet printing of the MOD ink on the substrate, followed by plasma treatment that causes ligand decomposition accompanied by intramolecular copper reduction, nucleation, crystal growth, and eventually forms a continuous copper metallic film. 8767

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

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ACS Applied Materials & Interfaces

Figure 3. (A) XPS analysis of the temporal tracking of Cu 2p evolution showing three types of characteristic peaks (i) CuII (935 and 955 eV) (ii) CuI (933 and 953 eV), where both exist up to 3 min, (iii) and sharp peaks of Cu0 (933 and 953 eV), which appear after 4 min of the plasma treatment. (B) XPS showing the decay of carbon−hydrogen (285 eV) and carbon−oxygen (286 and 289 eV) bonds with an increase in the duration of the plasma treatment.

The effect of duration of the plasma treatment on the transformation of a copper complex into metallic copper was studied for printed patterns after drying at 100 °C for 2 min. As seen in Figure 2, during the plasma treatment, the blue color of the printed patterns, which is characteristic of the complex, changes to dark green, due to partial decomposition of the copper complex (2−3 min), as similarly occurs in thermal decomposition.25 Then the green color changes into a shiny reddish appearance, characteristic of metallic copper (5 min). The transformation of the copper complex into metallic copper was studied by X-ray photoelectron spectroscopy (XPS) measurements. As seen in Figure 3A, up to 3 min of nitrogen plasma treatment, peaks intensity of 2p3/2 and 2p1/2, which correspond to CuI (933 and 953 eV), gradually increase, whereas the peaks intensity of CuII (935 and 955 eV) decrease, indicating partial reduction of CuII to CuI, without formation of metallic copper. Beyond 4 min of plasma exposure results in total reduction of copper complex into metallic copper, as indicated by the appearance of sharp and intense peaks of Cu0 (933 and 953 eV). X-ray diffraction (XRD) patterns of the obtained copper film are presented in Figure S1, indicating peaks at 43.2°, 50.4°, and 74.1°, corresponding to metallic copper, which is evidence of the complete reduction of the copper ions. Furthermore, Figure 3B shows decrease in carbon content with increase in plasma exposure time, reaching only ∼2 wt % after 5 min. This indicates that the byproducts that formed after decomposition are volatile. The exact wt % of the various species at various plasma durations is presented in Table S1. Although the copper complex was converted to metallic copper after plasma treatment, it was found that the sheet resistance of the printed copper patterns was relatively high, in the range of 3−12 Ω/□, corresponding to only 2−8% of copper bulk conductivity. Figure 4 presents optical microscope images, which were taken for printed copper complex before and after plasma treatment. As seen in Figure 4B, for a sample dried at 100 °C for 30 min, the metallic patterns are composed of many isolated islands, which are probably the reasons for the low conductivity. To improve the homogeneity of the film, we evaluated the drying process prior to plasma treatment, and it was found that excessive drying (100 °C for 30 min) caused crystallization of the copper complex, which led to formation of voids in the printed layer (Figure 4A). These voids become even larger after plasma treatment due to decomposition of the

Figure 4. Backlight micrographs of samples dried at 100 °C for 30 min (A) before plasma treatment and (B) after plasma treatment (200 W, 10 min), and samples dried at 100 °C for 4 min (C) before plasma treatment and (D) after plasma treatment (200 W, 10 min).

complex and release of gas (Figure 4B). It should be noted that the complex melting point is 110 °C, which is higher than the temperature used for the drying process. The results revealed that drying the samples for 2−4 min at 100 °C resulted in the formation of continuous copper films (Figure 4C,D) with improved conductivity. Additional experiments performed by drying at 70 and 50 °C yielded similar resistivities as for samples dried at 100 °C; however, they had longer drying time (7 and 10 min correspondingly compared to 2−4 min at 100 °C). Accordingly, the samples that were screen printed on PEN were dried for 4 min at 100 °C prior to the plasma treatment, and in case of inkjet printing, the printing plate was maintained at fixed temperature of 60 °C so that the post printing drying process was not required. Therefore, the use of the copper complex ink with plasma treatment is suitable for 3D objects made of polymers with a Tg of 80 °C, which are common in industrial 3D printers. We performed inkjet printing of Cucomplex ink on PEN and on 3D printed substrate, and we found that there are no formation of “islands” within the patterns. The conversion of the copper complex into copper comprises two main stages that are significantly affected by the plasma parameters. The first stage is the decomposition of the 8768

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

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ACS Applied Materials & Interfaces

atmosphere of nitrogen or argon and were aimed at minimizing the cracks through changing the ink composition. To completely prevent cracks, even at low gas flow rate, we added a polymeric binder, poly(N-vinyl-2-pyrrolidone) (PVP), to the copper complex ink. Figure 7A−D show optical microscope images of films obtained with inks with PVP at various concentrations. It is clear that the PVP indeed led to the prevention of cracks, and at 3 wt %, a homogeneous film was formed without any cracks after the plasma treatment. It is important to note that although the cracks were prevented, the addition of PVP did not result in improving the electrical conductivity (Figure 7E). This may be attributed to the tradeoff between the two opposite effects of PVP: cracks prevention versus an increase in the amount of organic residues in the films. According to these findings, the following experiments were performed with inks containing 3 wt % PVP and plasma exposure under nitrogen flow rate of 9 cm3/min. To improve the conductivity, further investigations were carried by varying the plasma duration and applied power. As seen in Figure 8A, the sheet resistance drastically decreases as the plasma duration increases. After 8 min, the sheet resistance value remains constant for both 140 and 200 W. Figure 8B shows the dependence of the sheet resistance as a function of the applied power during a fixed plasma treatment time of 10 min. While the plasma power increased, the value of sheet resistance decreased until it reached the lowest value at 160 W. To estimate the resistivity (a product of multiplication of the sheet resistance and thickness of printed layer2) of the obtained copper films, their thicknesses were evaluated. Figure 9 shows SEM micrographs of the printed patterns (with a tilt of 52°), which indicated a wavy structure. Using focused ion beam system coupled with a scanning electron microscope (FIBSEM), the gallium ion milling enables imaging of the crosssection of the copper layer (Figure 9C, region I). As seen, the thickness of the copper layer is in the range of 50−70 (regions II and III belong to the deposited protective layers (Pt)). In addition, it can be observed that the wavy part of the structure is detached from the PEN substrate. Energy-dispersive X-ray (EDX) mapping of the film cross-section also proves that the thin film is composed of copper, as presented in Figure S2. Assuming that the copper layer is completely dense, we further

copper complex followed by copper reduction: in this step, the higher plasma energy (high flow rate and high power) causes massive ion bombardments and thus enables faster copper complex decomposition. However, in the next stage (nucleation, growth, and sintering), such high energy can cause cracks formation, which result in defects within the copper pattern and consequently low conductivities (Figure 5). Therefore,

Figure 5. (left) Copper tracks obtained after plasma decomposition. (right) Optical microscope image of printed tracks after plasma treatment at 200 W for 10 min.

opposite effects are expected, and therefore, there should be a set of optimal parameters that lead to sufficiently high energy to induce fast decomposition but not too high to prevent the cracks in the copper pattern. Figure 6A shows the sheet resistances of the printed copper tracks as a function of flow rates of the inlet gases (N2 and Ar). As seen, increasing the flow rate up to 45 cm3/min resulted in an increase in sheet resistance, whereas for higher flow rates, there was no conductivity at all. As shown in Figure 6B−E, the cracks in the printed films become more severe with the increase in flow rate. The possible reason may be enhancement in removal of some evolving species from the film at larger flow rate or due to increase in plasma density, thus leading to stronger ion bombardment,28 resulting in damage to the copper tracks and copper ablation. It should be noted that the lowest sheet resistance was obtained while the plasma chamber was operated at a pressure of 0.2−0.3 mbar, without nitrogen or argon, so there could be traces of air. However, since this experiment is not conducted under fully controlled conditions, all further experiments were performed only under controlled

Figure 6. (A) Sheet resistance as a function of nitrogen/argon inlet flow rate at 200 W, for 10 min. (B−E) Backlight optical microscope images of samples that have undergone plasma treatment with nitrogen flow rate of 0 (no gas flow), 18, 36, and 54 cm3/min, respectively, at 200 W for 10 min. 8769

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

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ACS Applied Materials & Interfaces

Figure 7. (A−D) Backlight optical microscope images of copper tracks with PVP concentrations of 0%, 1%, 2%, and 3%, respectively, obtained after plasma treatment with nitrogen purging of 9 cm3/min (power of 200 W for 6 min). (E) Sheet resistance as a function of PVP concentration.

Figure 8. (A) Sheet resistance as a function of plasma exposure time at 140 and 200 W of applied power with nitrogen flow rate of 9 cm3/min. (B) Sheet resistance as a function of applied power for 10 min process duration with nitrogen flow rate of 9 cm3/min.

Figure 9. (A) SEM micrographs of tilted sample (52°) showing (B) a wave-like morphology. (C) Cross-section of the copper sample composed of (I) highly sintered copper film, (II) first Pt protective layer, and (III) second Pt protective layer.

5% organic residues. The actual result of 7% can be due to the effect of PVP in preventing cracks formation, and therefore, more organic residues, as a result of the decomposition, were trapped within the copper layer. It may be argued that the decomposition of the copper complex into copper is due to thermal effects. To rule out this possibility, we performed the plasma sintering experiment while a piece of PEN film was placed as a bridge over part of the printed pattern. As shown in Figure S3, copper was obtained only outside of the protected zone, even though the whole pattern was subjective to the same temperature in the plasma chamber. Figure S4 shows the measured temperature of the PEN substrate during plasma treatment at different powers up to 15 min, indicating that under optimal decomposition and sintering conditions (160 W for 8 min) the temperature is less

calculated the thickness of the copper layer by measuring the copper content with inductively coupled plasma analysis (ICP). The calculated thickness was 60 ± 2 nm, in agreement with the SEM observations. In conclusion, the calculated resistivity for the best samples (160 W for 8 min) was as low as 7.3 ± 0.2 μΩ cm, which is only four-times higher compared to the resistivity of bulk copper. XPS analysis for copper patterns formed using ink containing 3 wt % PVP revealed the existence of ∼7 wt % organic residues, compared to ∼1.9 wt % in copper patterns formed without PVP in the ink (Table S1). The organic residues interfere with the conductivity by acting as an insulator. On the basis of XPS analysis (Table S1), the amount of organic residues after decomposition of the copper complex without PVP is 1.9 wt %. Therefore, we would expect that after the addition of 3% PVP, the XPS analysis will result in about 8770

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

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Figure 10. Inkjet printed copper patterns obtained after plasma treatment. (A) Printed on PEN substrate; (B) printed on a 3D object fabricated by Objet303D printer (VeroBlue, Tg = 60 °C).

than 60 °C, much below the temperature required for decomposition of the copper complex by heat treatment. It should be noted that 8 min plasma exposure is much shorter than typical heat sintering times for conductive inks (30 min),29−31 and therefore, the plasma decomposition is expected to be applicable to industrial processes. To examine the effect of oxidation of the copper patterns on the conductivity, we measured the change in sheet resistance of printed patterns at ambient conditions and while stored in a Petri dish sealed with parafilm. As shown in Figure S5, there is an increase of only about 17% after 45 days while exposed to air and only 3% increase while stored in a sealed Petri dish. Finally, after the optimal sintering conditions were reached, we evaluated the possibility of forming an electrical circuit while sintering printed patterns on plastic 2D substrates and 3D objects. Figure 10 demonstrates inkjet printed copper complex ink followed by plasma treatment onto PEN film and onto a 3D object (having a Tg = 60 °C) fabricated by 3D printing.

washed with ethanol prior to printing. For wetting improvement, 0.06% TEGO Dispers 652 (Evonik Industries) was used. Printing. Inkjet. Printing experiments were performed with Dimatix DMP-2800 printer (Dimatix-Fujifilm Inc., USA), equipped with 10 pL cartridge (DMC-11610). The printhead contained 16 nozzles, and the diameter of each nozzle was 21 μm. The printing height was set to 1 mm, and the jetting frequency was set to 1 kHz, using dot spacing of 42 μm (equivalent to 600 dpi). The printer plate was set to 60 °C. Screen Printing. A polyester mesh (180 threads per centimeter, NBC, Ponger 2000, Israel) was patterned by a conventional screen printing process. Both screen-printed and inkjet-printed patterns were composed of three lines, 24 mm in length and 1.3 mm in width. The screen printed films were dried at 100 °C prior to plasma treatment. 3D Printing. The 3D printed objects were inkjet printed using Objet 30 printer, Stratasys using VeroBlue RGD840 material (Tg < 60 °C). Plasma Process. The plasma treatment (argon or nitrogen) was performed for various durations by low-pressure plasma chamber (Diener PICO UHP,40 kHz/200 W/0.2 mbar) under various operation conditions. Characterization Methods. A two-point probe method was used to measure the resistance of the printed copper lines using a multimeter. The electrical resistivity ρ of the lines was calculated from the resistance R, line length L, line width W, and line thickness T, as ρ = R × T × W/L. The line thickness was determined as described below. The top-view and cross-section micrographs were taken using a FIB-SEM (Helios 460F1, FEI). The specimen surface milling for the cross-section analysis was performed after selective coating of the surface-of-interest with two layers of platinum to prevent damaging the sample. Elemental analysis of the cross-section was performed using a SEM (XHR Magellan 400L) equipped with an EDX probe (Oxford XMAX, Oxford Instruments). The patterns thickness for the electrical resistivity measurements were evaluated by both the dimensions of the cross-section and by the amount of copper in the printed lines. The latter was determined by using ICP (OES model Optima 3000, PerkinElmer). Sample preparation was done by dissolving the copper tracks with 70% nitric acid, followed by diluting the solution with 1% nitric acid in TDW. This method enabled to calculate the patterns with known length and width, while the copper density was considered to be 8.96 gr/cm3. XPS analysis was performed using an Axis Ultra Spectrometer (XPS/ESCA) of Kratos Analytical. Optical imaging was done with an Olympus CX41 microscope. XRD measurements where made using Xray diffractometer D8 Advance of Bruker AXS.

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CONCLUSIONS A new approach to obtain highly conductive copper patterns on heat-sensitive substrates is presented. The approach is based on using a nonthermal plasma-induced decomposition of MOD inks. By applying plasma treatment to printed films of Cu formate−AMP complex on plastic substrates, metallic conductors with conductivity as high as 23% of bulk copper were obtained. The results pave the way to the use MOD inks for the fabrication of various electronic devices on heat-sensitive substrates, such as low-cost polymers and paper, by printing processes that include R2R processing and 3D manufacturing. It should be noted that the minimum width depends on the printing technology, which requires tailoring the physicochemical properties of the ink such as viscosity, surface tension, and evaporation rate. For example, typical inkjet printing enables printing of 30−80 μm lines,1 aerosol jet printing enables obtaining 10−20 μm,32 and fountain pen yields line width of less than a micron as we recently reported.33

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EXPERIMENTAL PROCEDURES

Materials. Copper MOD ink for screen printing (13.5 wt % Cu loading) was formed by mixing 20 mmol of anhydrous copper formate (45 wt % Cu, Wuhan Kemi-works) with a mixture of 35 mmol 2amino-2-methyl-1-propanol (AMP) and 25 mmol diethylene glycol methyl ether (DM) at 60 °C. A clear, blue solution was formed within 15 min. Copper MOD ink for inkjet printing (7 wt % Cu loading) was formed by adding 50 mmol of anhydrous copper formate to a mixture of 90 mmol AMP, 200 mmol DM, and 40 mmol n-pentanol at 60 °C. PVP powder (MW ≈ 9000) from BASF, Luvitec K17 was used to improve film morphology. PEN that was used as a substrate was

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b14462. Table of copper complex ink composition during plasma treatment; figures of XRD, SEM and EDX mapping, 8771

DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

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(12) Yang, W.-d.; Liu, C.-y.; Zhang, Z.-y.; Liu, Y.; Nie, S.-d. Copper Inks Formed Using Short Carbon Chain Organic Cu-Precursors. RSC Adv. 2014, 4, 60144−60147. (13) Yonezawa, T.; Tsukamoto, H.; Yong, Y.; Nguyen, M. T.; Matsubara, M. Low Temperature Sintering Process of Copper Fine Particles Under Nitrogen Gas Flow With Cu 2+-Alkanolamine Metallacycle Compounds for Electrically Conductive Layer Formation. RSC Adv. 2016, 6, 12048. (14) Yong, Y.; Nguyen, M. T.; Yonezawa, T.; Asano, T.; Matsubara, M.; Tsukamoto, H.; Liao, Y.-C.; Zhang, T.; Isobe, S.; Nakagawa, Y. Use of Decomposable Polymer-Coated Submicron Cu Particles With Effective Additive for Production of Highly Conductive Cu Films at Low Sintering Temperature. J. Mater. Chem. C 2017, 5, 1033. (15) Matsubara, M.; Yonezawa, T.; Minoshima, T.; Tsukamoto, H.; Yong, Y.; Ishida, Y.; Nguyen, M. T.; Tanaka, H.; Okamoto, K.; Osaka, T. Proton-Assisted Low-Temperature Sintering of Cu Fine Particles Stabilized by a Proton-Initiating Degradable Polymer. RSC Adv. 2015, 5, 102904−102910. (16) Li, W.; Cong, S.; Jiu, J.; Nagao, S.; Suganuma, K. Self-Reducible Copper Inks Composed of Copper−Amino Complexes and Preset Submicron Copper Seeds for Thick Conductive Patterns on a Flexible Substrate. J. Mater. Chem. C 2016, 4, 8802−8809. (17) Yong, Y.; Yonezawa, T.; Matsubara, M.; Tsukamoto, H. The Mechanism of Alkylamine-Stabilized Copper Fine Particles Towards Improving the Electrical Conductivity of Copper Films at Low Sintering Temperature. J. Mater. Chem. C 2015, 3, 5890−5895. (18) Yu, J. H.; Rho, Y.; Kang, H.; Jung, H. S.; Kang, K.-T. Electrical Behavior of Laser-Sintered Cu Based Metal-Organic Decomposition Ink in Air Environment and Application as Current Collectors in Supercapacitor. International Journal of Precision Engineering and Manufacturing-Green Technology 2015, 2, 333−337. (19) Lee, J.; Lee, B.; Jeong, S.; Kim, Y.; Lee, M. Microstructure and Electrical Property of Laser-Sintered Cu Complex Ink. Appl. Surf. Sci. 2014, 307, 42−45. (20) Wang, B.-Y.; Yoo, T.-H.; Song, Y.-W.; Lim, D.-S.; Oh, Y.-J. Cu Ion Ink for a Flexible Substrate and Highly Conductive Patterning by Intensive Pulsed Light Sintering. ACS Appl. Mater. Interfaces 2013, 5, 4113−4119. (21) Araki, T.; Sugahara, T.; Jiu, J.; Nagao, S.; Nogi, M.; Koga, H.; Uchida, H.; Shinozaki, K.; Suganuma, K. Cu Salt Ink Formulation for Printed Electronics Using Photonic Sintering. Langmuir 2013, 29, 11192−11197. (22) Schroder, K. Mechanisms of Photonic Curing: Processing High Temperature Films on Low Temperatures Substrates. Nanotechnology 2011, 2, 220−223. (23) Materials word. High performance materials. Asiga, 2017. https://www.asiga.com/products/materials/. (24) 3D Printing with high temperature material. Stratasys Ltd., 2017. http://www.stratasys.com/materials/polyjet/high-temperature. (25) Farraj, Y.; Grouchko, M.; Magdassi, S. Self-Reduction of a Copper Complex MOD Ink for Inkjet Printing Conductive Patterns on Plastics. Chem. Commun. 2015, 51, 1587−1590. (26) Reinhold, I.; Hendriks, C. E.; Eckardt, R.; Kranenburg, J. M.; Perelaer, J.; Baumann, R. R.; Schubert, U. S. Argon Plasma Sintering of Inkjet Printed Silver Tracks on Polymer Substrates. J. Mater. Chem. 2009, 19, 3384−3388. (27) Perelaer, J.; Jani, R.; Grouchko, M.; Kamyshny, A.; Magdassi, S.; Schubert, U. S. Plasma and Microwave Flash Sintering of a Tailored Silver Nanoparticle Ink, Yielding 60% Bulk Conductivity on CostEffective Polymer Foils. Adv. Mater. 2012, 24, 3993−3998. (28) Cardinaud, C.; Peignon, M.-C.; Tessier, P.-Y. Plasma Etching: Principles, Mechanisms, Application to Micro-and Nano-Technologies. Appl. Surf. Sci. 2000, 164, 72−83. (29) Abbel, R.; Teunissen, P.; Rubingh, E.; van Lammeren, T.; Cauchois, R.; Everaars, M.; Valeton, J.; van de Geijn, S.; Groen, P. Industrial-Scale Inkjet Printed Electronics ManufacturingProduction Up-scaling from Concept Tools to a Roll-to-Roll Pilot Line. Transl. Mater. Res. 2014, 1, 015002.

sample showing effect of plasma on partially covered copper complex pattern, monitoring of PEN temperature during plasma, and sheet resistance of copper patterns versus time of storing (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Shlomo Magdassi: 0000-0002-6794-0553 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was partially supported by the Israel Ministry of Science, Technology & Space, the FTA program of the Israel National Nanotechnology Initiative, and the National Research Foundation, Prime Minister’s Office, Singapore under the CREATE program: Nanomaterials for Energy and EnergyWater nexus. We would like to thank Ofir Tirosh from the HUJI for the ICP measurements, and Atzmon Vakahi from the Nano-Center at HUJI for assistance with FIB-SEM.

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REFERENCES

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DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773

Research Article

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DOI: 10.1021/acsami.6b14462 ACS Appl. Mater. Interfaces 2017, 9, 8766−8773