Room-Temperature Nanowelding of a Silver Nanowire Network

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX

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Room-Temperature Nanowelding of a Silver Nanowire Network Triggered by Hydrogen Chloride Vapor for Flexible Transparent Conductive Films Xianwen Liang,†,‡ Tao Zhao,† Pengli Zhu,*,† Yougen Hu,† Rong Sun,† and Ching-Ping Wong†,§,∥ †

Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen 518055, China § Department of Electronics Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong 999077, China ∥ School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States ‡

S Supporting Information *

ABSTRACT: High contact resistance between silver nanowires (AgNWs) is a key issue in widespread application of AgNW flexible transparent conductive films as a promising candidate to replace the brittle and expensive indium tin oxide. A facile, room-temperature nanowelding method of an AgNW network triggered by hydrogen chloride (HCl) vapor is demonstrated to reduce the sheet resistance of the AgNW network. Under the visible light, O2 and HCl vapor serving as an etching couple induced silver atoms to be transferred from the bottom AgNW at the junction to the top one, and then, these silver atoms epitaxially recrystallized at the contact position with the lattice of the top AgNW as the template, ultimately resulting in the coalescence of the junction between AgNWs. Polydimethylsiloxane (PDMS) was spin-coated onto the HCl-vapor-treated (HVT) AgNW network on the polyethylene terephthalate substrate to fabricate PDMS/HVT AgNW films. The fabricated film with low sheet resistance and high transmittance retained its conductivity after 4000 bending cycles. Furthermore, excellent heating performance, electromagnetic interference shielding effectiveness, and foldability were obtained in the PDMS/HVT AgNW film. Thus, the role of the simple nanowelding process is evident in enhancing the performance of AgNW transparent conductive films for emerging soft optoelectronic applications. KEYWORDS: AgNWs, HCl vapor, nanowelding, epitaxial recrystallization, transparent conductive film

1. INTRODUCTION

(AgNW) transparent electrodes are regarded as the most promising candidate to replace ITO owing to their excellent electrical and optical properties, whereas carbon-based nanomaterials and conductive polymer show much higher sheet resistance (>100 Ω sq−1).15 Moreover, commonly continuous, large-scale solution processes such as spray coating, doctor blade-coating, slot die, and so forth can be conveniently applied to manufacture AgNW films, which are cost-effective and efficient in contrast to ITO. Despite the aforementioned outstanding advantages of the AgNW film, how to achieve a low sheet resistance at the high optical transmittance is still a challenge, which is urgent to be addressed. The electrical conductivity of the AgNW network depends significantly on the junction between AgNWs. The reported contact resistance at the junction even exceeded 1 GΩ

With rapid development in optoelectronics, transparent conductors have served as one of the most essential components for modern optoelectronic devices such as solar cells,1−3 organic light emitting diodes,4−6 liquid crystal displays,7 touch screens,8,9 field effect transistors,10,11 and spectroelectrochemistry investigation.12 As the most commonly used transparent conducting material today, indium tin oxide (ITO) has become a market mainstream thanks to its high transparency. Unfortunately, its brittle ceramic nature, scarcity of supply, and expensive vacuum deposition process remain unsolvable issues, which overshadow its widespread applications in upcoming flexible devices. To overcome these shortcomings, many efforts have been made to develop some alternatives to ITO, including carbon-based nanomaterials such as carbon nanotubes (CNTs),13−15 graphene,7,15−17 highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS),18 as well as metallic nanowires.1−6,8,9,15,19−29 Among these materials, silver nanowire © XXXX American Chemical Society

Received: August 29, 2017 Accepted: November 1, 2017

A

DOI: 10.1021/acsami.7b13048 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 1. Morphological comparison of the pristine AgNW network with the HVT AgNW network. (a) Plane view SEM image of pristine AgNW network. The black arrows show the bright charging exists at the junctions between AgNWs. (b) Enlarged SEM image of (a). (c) Plane view SEM image of the HVT AgNW network. (d) Enlarged SEM image of (c). The white arrows show that the concaves are formed on the edges of HVT AgNWs via O2/HCl etching. (e) Tilted view SEM image of the HVT AgNW network. (f) Enlarged SEM image of (e). The green arrows in (e) show that in situ generated silver nanoparticles selectively grow at the junctions between HVT AgNWs.

when two AgNWs connected naturally.19 For the sake of lowering the sheet resistance, some effective approaches have been proposed to weld the contact position between AgNWs; the examples include thermal heating,30,31 Joule heating,32 mechanical pressing,27 plasmonic welding,25 supersonic spraying,33 capillary-force-induced welding,24 alcohol-based chemical approach,34 and so forth. For thermal heating, it is likely that the AgNWs are oxidized and heat-sensitive substrates degrade, unless the heating temperature and time are controlled accurately.27,35 In the Joule heating process, the morphology of AgNWs may be deteriorated because of electromigration during the electric current flow.32 Mechanical pressing is inappropriate for brittle substrates such as glass; besides, it may damage some useful structures or the active layers of some devices.24 Furthermore, plasmonic welding or supersonic spaying requires specific apparatus. For example, laser or flash lamp is essential for plasmonic welding,25,35 and the supersonic nozzle is indispensable for supersonic spraying to supply a high velocity of impact.33 To reduce sheet resistance more effectively, capillary-force-induced welding requires the re-

peated volatilization of the mist that is repeatedly sprayed on the AgNW network.24 In the alcohol-based chemical welding process, a small amount of silver precursor is applied to weld the AgNW network but the most redundant is removed, resulting in the wastage of expensive silver precursor.34 Hence, it is of great importance to address a convenient and efficacious method to diminish the sheet resistance of the AgNW network. Herein, we introduced room-temperature nanowelding of AgNW networks triggered by HCl vapor to improve the electrical conductivity of AgNW films with a high optical transmittance. Under the illumination of room light, O2 and HCl (O2/HCl) that acted as an etching couple drove Ag atoms to be transferred from the bottom AgNW at the junction to the top one, followed by the epitaxial recrystallization of Ag atoms at the contact position in terms of the lattice of the top AgNW, during which the loose connection between AgNWs evolved into the coalescence. The PDMS/HCl-vapor-treated (HVT) AgNW film with a low sheet resistance of 15 Ω sq−1 at a high transmittance of 85% (@550 nm) was fabricated by spincoating PDMS onto an HVT AgNW network on polyethylene B


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ACS Applied Materials & Interfaces terephthalate (PET). The as-fabricated film showed excellent heating performance, electromagnetic interference (EMI) shielding effectiveness (SE), and foldability. The temperature on the central area of the film exceeded 130 °C under a dc voltage of 9 V. The EMI SE was more than 20 dB (>99%) during the measured frequency range of 8.2 to 12.5 GHz and even reached 47 dB (>99.99%) at 8.8 GHz. Despite hash folding, the PDMS/HVT AgNW film maintained stable electrical performance.

analyzer (E5071C, Keysight), and an electromagnetic wave was guided into the film by means of a waveguide setup.

3. RESULTS AND DISCUSSION The evidence of room-temperature nanowelding of the AgNW network triggered by HCl vapor is provided by SEM and shown in Figure 1. As shown in Figure 1a,b, pristine AgNWs stack loosely and connect with each other simply, and the junctions exhibit distinct outlines. By contrast, apparent nanosintering takes place at the junctions, and the fused contact positions between AgNWs are observed on the HVT AgNWs network, as depicted in Figure 1c,d. The tilted view SEM images in Figure 1e,f show that the AgNWs are bent over each other and join at the junctions, further confirming the welded junctions between HVT AgNWs. It is noticed that the bright charging appears at the contact positions between pristine AgNWs, as marked by black arrows in Figure 1a, which implies large contact resistance owing to the loose connection of the two crossed AgNWs.21 For HVT AgNWs, the welded junctions reduce contact resistance dramatically, and thus, no charging is observed. Interestingly, some particles selectively appear at the connecting regions between HVT AgNWs, as labeled by green arrows in Figure 1e, which was due to the selective growth of in situ generated silver nanoparticles at the contact positions. These silver nanoparticles serving as the solder can further weld AgNWs and enhance the conductivity of the AgNW network.20 To better understand the underlying mechanism behind the nanowelding of the AgNW network triggered by HCl vapor, the welding process is elaborated as follows: (1) it is wellknown that the as-synthesized or coated AgNWs were exposed to ambient environment and liable to form silver oxide layers on the surface (eq 1). (2) The silver oxide layer was subjected to HCl vapor and would produce silver chloride (AgCl) (eq 2). (3) Under the illumination of visible light, the light-sensitive AgCl was decomposed into Ag atoms and Cl atoms (eq 3).38,39 (4) The as-generated Ag atoms transferred from the bottom AgNW to the top one and epitaxially recrystallized at the junction with the lattice of the top AgNW as the nucleation template, during which the contact position between the AgNWs was welded. 4Ag + O2 → 2Ag 2O (1)

2. MATERIALS AND METHODS 2.1. Materials. AgNWs were synthesized according to previously reported procedure.36,37 The as-synthesized AgNWs were dispersed in absolute ethanol to obtain two solutions (0.92 and 1.84 mg mL−1). Absolute ethanol was provided by Sinopharm Chemical Reagent Co., Ltd. HCl solution (36−38 wt %) was purchased from Dongguan Dongjiang Chemical Reagent Co., Ltd. PDMS elastomer base and curing agent (Sylgard 184) were supplied by Dow Corning. n-Hexane was purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. PET was obtained from Lucky film Co., Ltd. ITO/PET films were provided by Shenzhen Faxinzx Co., Ltd. 2.2. Fabrication of the PDMS/HVT AgNW Flexible Transparent Conductive Film. The obtained AgNW solutions were spincoated on precleaned PET substrates at a speed of 1000 rpm for 20 s. Under the illumination of room light (fluorescent lamp, 16 W, length: 1200 mm), the AgNW network on a PET substrate was attached to a glass slide (100 mm × 100 mm) and then inversely placed 2 cm above the concentrated HCl solution (36−38 wt %, 180 mL concentrated HCl solution in a 200 mL beaker) in an ambient atmosphere (temperature: 25 °C, relative humidity: 65%). PDMS as a protective layer for the HVT AgNW network was obtained via mixing the silicone elastomer base, curing agent, and n-hexane as the solvent (the weight ratio of base, curing agent, and solvent was 10:1:100) and then spincoated onto the HVT AgNW network at a speed of 2000 rpm for 20 s. Finally, the PDMS/HVT AgNW flexible transparent conductive film (size: 50 mm × 50 mm) was fabricated through curing PDMS at 85 °C for 150 min. Two electrodes were painted with silver paste on both edges of the PDMS/HVT AgNW film for testing electrical property. 2.3. Bending Test. Both edges of ITO/PET and the PDMS/HVT AgNW film were firmly fixed to the testing machine for the bending test. The cyclic bending test was carried out using a universal testing machine (Autograph AG-X plus 100N, Shimadzu). The sheet resistance was measured after each bending cycle step from 0 to 4000 cycles with a frequency of 0.1 Hz. 2.4. Measurement of Heating and Defogging Performance. The temperature on the central area of the PDMS/HVT AgNW film was monitored by an infrared scanner under various dc applied voltages. For the defogging test, pristine PET and the PDMS/HVT AgNW film were first placed on a flat artificial ice, and then, the PDMS/HVT AgNW film was tested under an applied voltage of 5 V. 2.5. Folding Test. ITO/PET and the PDMS/HVT AgNW film were cut into 25 mm width and 50 mm length for the folding test. The samples were connected in series with three light-emitting diode (LED) lights (red, green, and blue) and then folded for testing. 2.6. Characterization. The morphology of AgNWs was analyzed using scanning electron microscopy (SEM) (FESEM, Nova NanoSEM 450, FEI) and transmission electron microscopy (TEM) (Tecnai G2 F20 S-Twin, FEI). The elemental and chemical compositions of AgNWs were detected using an X-ray diffractometer with Cu Kα radiation (λ = 1.54178 Å) (D/max-2500v/PC, Rigaku). X-ray photoelectron spectroscopy analysis was performed using PHI 1800 with a monochromatic Al Kα source. The visible light transmittance of the film was characterized through a UV−visible spectrometer (UV3600, Shimadzu). The sheet resistance of the film was measured by a digital multimeter (Agilent 34401A). The temperature of the PDMS/ HVT AgNW film was monitored using an infrared scanner (T335, FLIR). The EMI SE was measured at room temperature in the X-band frequency ranged from 8.2 to 12.5 GHz by an Agilent vector network

Ag 2O + 2HCl → 2AgCl + H 2O

(2)

visible light

AgCl ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ Ag + Cl

(3)

During the process, O2/HCl was considered as an etching couple, which induced nanowelding of the AgNW network. With a silver oxide layer on the surface of AgNWs consumed by HCl vapor, the fresh AgNW surfaces were exposed to air and oxidized again according to eq 1. The abovementioned photochemical process progressed repeatedly, in which Ag atoms were continually transferred from the bottom AgNW to the top one and epitaxially recrystallized at the contact position. Ultimately, the simple overlap between AgNWs evolved into the coalescence. The O2/HCl etching couple, combined with visible light, played an essential role in welding contact positions between AgNWs. Generally, metal Ag is free from HCl, and the evidence is given by the X-ray diffraction pattern (XRD) of AgNWs immersed into HCl solution, as shown in Figure S1a. Figure S1a exhibits that only four diffraction peaks at 37.49°, 43.72°, 63.83°, and 76.95° are observed and C


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Figure 2. Schematic illustration of room-temperature nanowelding of the pentagonal AgNW junction triggered by HCl vapor under visible light. (a) Loose connection between pristine AgNWs. (b) Welded junction between HVT AgNWs.

respectively derived from the (111), (200), (220), and (311) planes of the face-center-cubic silver crystal (JCPDS no. 030931),33 but there are no peaks from AgCl existing in the pattern. For the AgNWs treated by HCl vapor in ambient atmosphere, as shown in Figure S1b, the peaks at 27.19°, 31.48°, 45.66°, 54.43°, 56.85°, and 66.93°, respectively, correspond to the (111), (200), (220), (311), (222), and (400) planes of cubic-phase AgCl crystal (JCPDS no. 311238),39 suggesting that O2 from the air started the reaction between AgNWs and HCl. Figure S1c,d display SEM images of AgNWs immersed into HCl solution and treated by HCl vapor under ambient atmosphere, respectively. HCl-solution-immersed AgNWs almost maintain the wire shape, which was originated from the lack of O2 in HCl solution. This phenomenon is in good agreement with the XRD pattern in Figure S1a. Actually, it is possible that the weak etching of AgNWs takes place in HCl solution caused by the O2 dissolving into the solution, resulting in the formation of shorter wires and particles.40−43 On the contrary, HVT AgNWs degrade absolutely and are transformed into flakes. Thus, O2 is indispensable for the subsequent etching of AgNWs by HCl, and the existence of O2 is the prerequisite for nanowelding of the AgNW network. Moreover, the role of visible light is essential in the production of Ag atoms. Figure S2 presents the XRD patterns from AgNWs treated by HCl vapor under the illumination and darkness. As shown in Figure S2a, the Ag diffraction peaks are dominant in the XRD pattern from HVT AgNWs under visible light, and only two weak peaks from AgCl are found, which implies that most AgCl has been decomposed into Ag atoms when exposed to visible light. In comparison, obvious AgCl diffraction peaks are observed in the XRD pattern taken from HVT AgNWs without the illumination, as illustrated by Figure S2b, indicating that AgCl could exist stably under darkness. The further evidence is provided by Xray photoelectron spectroscopy of pristine AgNWs and HVT AgNWs under visible light and darkness, as depicted in Figure S3. The detected Cl element from pristine AgNWs in Figure S3a is originated from Cl−-controlled synthesis of AgNWs, and its amount is lower than that of HVT AgNWs, which implies that HVT AgNWs were etched by O2/HCl. In addition, the content of the Cl element from HVT AgNWs under visible light is less than that of HVT AgNWs under darkness, indicating that newly formed AgCl was decomposed under the illumination, as shown in Figure S3b,c. The Ag 3d spectrum of pristine AgNWs in Figure S3d shows Ag 3d5/2 and Ag 3d3/2

peaks at a binding energy of 367.8 and 373.8 eV, respectively. The peaks of Ag 3d5/2 and Ag 3d3/2 can be further divided into four different peaks at about 367.8, 368, 373.8, and 374.2 eV. The peaks at 367.8 and 373.8 eV could be ascribed to the Ag+ from Ag2O on the surface of pristine AgNWs, and the peaks at 368 and 374.2 eV are originated from the metallic Ag0.44−48 Compared with pristine AgNWs, the peaks of Ag 3d5/2 and Ag 3d3/2 from HVT AgNWs, respectively, shift to 368.1 and 374.1 eV as a result of the Ag+ existing in AgCl, suggesting that Ag2O was consumed by HCl and transformed into AgCl.48,49 Figure S3e,f display the Cl 2p and O 1s spectra of pristine AgNWs and HVT AgNWs under illumination and darkness. The peaks of Cl 2p and O 1s from HVT AgNWs present a blue shift in contrast to pristine AgNWs, which further indicates the etching reaction occurred on HVT AgNWs. O2/HCl etching preferentially takes place on the edges of pentagonally twinned AgNWs. It is confirmed by the fact that some concaves formed via O2/HCl etching appear on the edges of AgNWs, as marked by white arrows in Figure 1d (Figure 1b shows that pentagonally twinned AgNWs naturally lie on the substrate with one of the five crystal facets lying flat). It is taken into account that during the growth of AgNWs, a fivefold twinned, decahedral seed could be considered as an assembly of five single crystals, tetrahedral units sharing a common edge and thus included at least one twin defecta single atomic layer in the form of a (111) mirror plane. With Ag atoms added onto ten end facets of the decahedral seed, the fivefold twinned seed eventually evolved into pentagonally twinned nanowire, in which each tetrahedron wire unit had two planes in contact with an adjacent unit through {111} twin planes. For a pentagonally twinned AgNW, the high strain energy existed on the five edges, which was ascribed to five {111} twin planes (five twin defects).50,51 The five twin defects provided active sites for O2/HCl etching, therefore, the edges of AgNWs were inclined to be etched preferentially. In fact, the top edge of the bottom AgNW at the junction suffers from the pressure from the top AgNW, van der Waals’ force and capillary force during solvent evaporating, as illustrated by red dash line in Figure 2a. Compared with other edges of the bottom AgNW or the other region of the top edge, the specific edge region possessed higher stain energy and was most likely to be etched.50,51 Under such circumstances, the Ag atoms were continually transferred from the top edge region of the bottom AgNW and then assembled onto the lattice of the top AgNW, accompanied by epitaxial recrystallization. D


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Figure 3. (a) Plane view TEM image of the junction between pristine AgNWs. The inset represents the lattice-resolved TEM image of the junction between pristine AgNWs. (b) Plane view TEM image of the welded junction between HVT AgNWs. The frames represent the approximate positions of the welded junction for the lattice-resolved TEM in (c−f). (c) Lattice-resolved TEM image of the top AgNW away from the junction. The inset presents the power spectrum from the FFT of the top AgNW outside the junction. (d) Lattice-resolved TEM image of the welded junction region. The inset presents a FFT pattern from the welded which is consistent with that of the top AgNW. Lattice-resolved TEM images of the upper (e) and lower (f) interfaces between the bottom AgNW and the junction, respectively. The upper right and lower right insets in (e) present FFT patterns from the bottom AgNW and the junction, respectively, which are different from each other. Lattice orientation of the junction in (f) mismatches that of the bottom AgNW.

Epitaxial recrystallization represents a specific secondary grain growth and can be actuated by a lattice-matched substrate as a result of the gain in interfacial free energy.22 Besides, the diffusion barrier for a single metal atom on the surface of the metal is low (typically less than 1 eV), and thus, separate metal atoms are able to overcome the low barrier to diffuse rapidly via surface diffusion even at room temperature.52,53 Thus, the Ag atoms generated via the decomposition of AgCl on the bottom AgNW possessed dramatic mobility, which enabled epitaxial recrystallization onto the top AgNW. The evidence of epitaxial recrystallization is provided by TEM, high-resolution transmission electron microscopy (HRTEM), and fast Fourier transform (FFT) patterns taken from the representative junctions of pristine AgNWs and HVT AgNWs, as shown in Figures 3 and S4. Figure 3a shows TEM and HRTEM images of the junction between pristine AgNWs. Dark bands elongating along the length are observed in each AgNW owing to the pentagonally twinned nanowire crystal structure, as presented in Figure 3a. These continuous bands along the length of each AgNW suggest two different crystal orientations at the junction (one for each AgNW). The inset in Figure 3a

displays the apparent moiré patterns existing at the junction region, indicating the two pristine AgNWs overlapped loosely. In comparison, for HVT AgNWs, the interrupted dark bands at the junction appear in the bottom AgNW, whereas they match the length of the top AgNW and pass through the junction, as shown in Figure 3b. This implies that only one crystal orientation existed at the welded junction, which was consistent with that of the top AgNW.22 HRTEM images of the welded junction and each individual AgNW in Figure 3c−f indicate that the crystal lattice orientation of the junction is well-coincident with that of the top AgNW but mismatches that of the bottom one. The bottom AgNW outside the junction maintains its original crystal lattice orientation, resulting in two obvious grain boundaries on each side of the junction, as shown in Figure 3e,f. Epitaxial recrystallization is further confirmed by FFT patterns from the representative junctions of pristine AgNWs and HVT AgNWs, as depicted in Figure S4b−d and the insets of Figure 3c−e. For pristine AgNWs, FFT patterns of each AgNW away from the junction run along one direction, forming a series of parallel lines of spots (Figure S4b,c, the white lines denote the orientations of FFT patterns from the E


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Figure 4. Schematic illustration of the fabrication of the PDMS/HVT AgNW flexible transparent conductive film.

Figure 5. (a) Sheet resistance and transmittance (@550 nm) of the PDMS/HVT AgNW films as a function of HCl vapor-treating time. (b) Plot of transmittance (@550 nm) vs sheet resistance of the PDMS/HVT AgNW films, with AgNWs, AgNWs/PEDOT:PSS, copper nanowires (CuNWs), CNTs, graphene, and ITO as references. The inset in (b) shows the digital photograph of the PDMS/HVT AgNW film bent over a flower, indicating excellent transparency and flexibility.

in electrical conductivity of the two films is not found when HCl vapor-treating time is further increased. However, the transmittance at 550 nm of the two films decreases with the HCl vapor-treating time. During the etching of AgNWs by O2/ HCl under visible light, silver nanoparticles would be produced, as shown in Figure 1e. With the treating time increased further, more silver nanoparticles were generated and impaired the transmittance of the PDMS/HVT AgNW film, as presented in Figure 5a. Figure S5 displays that the haze values of the two films rise with the HCl vapor-treating time as a result of increased diffusive transmittance and scattering induced by the increase of in situ generated silver nanoparticles with treating time.54 In comparison to previously reported transparent conductors such as reference AgNWs, 19 AgNWs/PEDOT:PSS,9 CuNWs,55 CNTs,56 graphene,57 and ITO,55 the PDMS/HVT AgNW film shows excellent optoelectronic performance with a low sheet resistance of 15 Ω sq−1 at a high transmittance of 85% at 550 nm, as shown in Figure 5b. Actually, the electrical and optical properties of the PDMS/ HVT AgNW film may be further optimized by tuning the concentration of AgNW solution, the speed and time of spin coating, and HCl vapor-treating time, through which the PDMS/HVT AgNW film with the desired optoelectronic performance can be obtained. Mechanical flexibility of the transparent conductors is crucial for flexible optoelectronics. To evaluate the flexibility of the PDMS/HVT AgNW film, Figure 6 shows sheet resistance of the film as a function of bending radius and bending cycles (two types of bending tests include inner and outer bending). For comparison, a commercial ITO-coated PET (ITO/PET) film is utilized as the reference in sheet resistance versus bending radius. Regardless of the inner or outer bending test, the sheet resistance of the PDMS/HVT AgNW film keeps a flat

bottom and top AgNWs outside the junction). At the junction shown in Figure S4d, double FFT spots with a certain included angle form a grid pattern and elongate along two directions, which are in good correspondence with that of the top and bottom AgNWs, respectively. However, the insets of Figure 3c−e show that FFT spots of the junction between HVT AgNWs only run along a single direction and agree with that of the top AgNW, but there are no FFT spots associated with the bottom AgNW appearing at the junction. The upper right inset in Figure 3e suggests the bottom AgNW retains its original crystal lattice orientation outside the junction area. Taken together, it can be concluded that at the junction of HVT AgNWs, epitaxial recrystallization did not perform only at the interface between the AgNWs, but absolutely throughout the bottom AgNW, in which the top AgNW served as a nucleation template to locally redirect the bottom AgNW.22 Figure 4 presents the fabricating process of the PDMS/HVT AgNW flexible transparent conductive film. The detailed procedure is depicted as follows: first, an AgNW network was fabricated via spin-coating of AgNW solution onto a precleaned PET substrate. Second, the obtained AgNW network was subject to HCl vapor for some time under the illumination of room light. Finally, PDMS as a protective layer was spin-coated onto the HVT AgNW network to obtain the PDMS/HVT AgNW film. Figure 5a presents that the variation of sheet resistance and transmittance of the PDMS/HVT AgNW films with HCl vapor-treating time. For the two PDMS/HVT AgNW films coated with 0.92 and 1.84 mg mL−1 AgNW solutions, the decrement in the sheet resistance is, respectively, achieved to 55.7% (from 122 to 54 Ω sq−1) at 100 s and 48.3% (from 29 to 15 Ω sq−1) at 60 s, and the corresponding transmittance at 550 nm retains the high values of 93 and 85%. Extra enhancement F


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Figure 6. Plot of sheet resistance of ITO/PET and the PDMS/HVT AgNW films vs bending radius. (a) Inner and (b) outer bending. Bending fatigue test of (c,d) PDMS/AgNW and (e,f) PDMS/HVT AgNW films under the bending radius of 3, 5, 7, and 10 mm, respectively. (c,e) Inner and (d,f) outer bending. The inset in (e) shows the digital photograph of the bending fatigue test.

trend with the bending radius decreased from 10 to 3 mm, whereas the electrical performance of the ITO/PET film extremely degrades especially under outer bending because of the brittle ceramic nature of ITO, as shown in Figure 6a,b. The bending durability of the PDMS/AgNW and PDMS/HVT AgNW films is demonstrated in Figure 6c−f. The sheet resistance of the PDMS/AgNW film can retain a constant value during the inner and outer bending cycle test under the bending radius above 7 mm, whereas it increases obviously under the bending radius below 5 mm, as depicted in Figure 6c,d. By contrast, the PDMS/HVT AgNW film maintains its original electrical performance after 4000 inner and outer bending cycles, as presented in Figure 6e,f, which is due to the nanowelding-induced tight connection between AgNWs. To evaluate the practical applications of the PDMS/HVT AgNW film, the heating performance and EMI shielding effectiveness were measured under the applied voltages from 3 to 9 V and at the measured frequency range of 8.2−12.5 GHz,

respectively, as well as the resistance to folding was demonstrated. Figure 7a shows that the higher the dc voltage is applied on the film, the higher a temperature can be achieved. The temperature on the central area of the PDMS/HVT AgNW film is above 130 °C when the applied voltage is increased to 9 V. Meanwhile, Figure 7a implies that accurate control over the film temperature can be achieved via adjusting the applied voltage. On the basis of excellent heating performance and transparency, the PDMS/HVT AgNW film can be employed as the transparent heater for defogging. Figure 7b displays that the PDMS/HVT AgNW film placed onto an ice keeps transparent all the time under an applied voltage of 5 V in contrast to the misted PET (Movies S1 and S2 demonstrate the comparison of defogging performances of the PDMS/HVT AgNW film and PET). Figure 7c demonstrates the PDMS/HVT AgNW film is sandwiched between the waveguide sample holders for EMI shielding measurement. G


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Figure 7. (a) Plot of the temperature of the PDMS/HVT AgNW film vs time at various applied voltages. The inset presents the temperature on the central area of the film under an applied voltage of 9 V. (b) Digital photograph of the defogging performance of the PDMS/HVT AgNW film placed onto an ice, with pristine PET as the reference. (c) Experimental setup for EMI shielding measurement. (d) Plot of EMI SE of the PDMS/HVT AgNW film vs measured frequency. Digital photographs of foldability testing of (e) PDMS/HVT AgNW film and (f) ITO/PET film connected in series with three LED lights.

than 21 dB (>99%), whereas both PET and PDMS-coated PET keep low values less than 0.5 dB, as presented in Figure 7d. As the frequency is increased to 8.8 GHz, the highest SE value of 47 dB (>99.99%) is achieved in the PDMS/HVT AgNW film.59 The commercial applications require the EMI SE value larger than 20 dB.60 This suggests that the PDMS/HVT AgNW film has a significant potential applied in flexible transparent EMI shielding as a protective cover for displays, keyboards, observation windows, and so forth to shield the EMI from outside or within.60 To demonstrate the foldability of the PDMS/HVT AgNW film, the film connected with three LED lights (red, green, and blue) experiences severe folding, and the LED lights maintain their original brightness, indicating the outstanding foldability of the PDMS/HVT AgNW film, as depicted in Figure 7e (Movie S3). By contrast, the LED lights connected with the ITO/PET film become dim after the film is folded once (Movie S4), as shown in Figure 7f.

Also, the total SE, SE absorption, and SE reflection can be calculated in terms of the measured S parameters as follows58 R = |S11|2 ,

T = |S21|2 ,

A=1−R−T (4)

SEref (dB) = −10 log(1 − R ), SEabs (dB) = −10 log(T /(1 − R ))

⎛P ⎞ SEtotal (dB) = 10 log⎜ I ⎟ = SEref + SEabs ⎝ PT ⎠

(5)

(6)

where R, T, A, PI, and PT are reflection coefficient, transmission coefficient, absorption coefficient, the incident power, and the transmitted power, respectively. Eventually, the EMI shielding effectiveness SEtotal is obtained according to the abovementioned equations. Within the whole measured frequency range, the EMI SE of the PDMS/HVT AgNW film is higher H


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4. CONCLUSIONS To sum up, we reported HCl-vapor-triggered room-temperature nanowelding of the AgNW network. The nanowelded AgNW network on the PET substrate was coated with PDMS to fabricate the PDMS/HVT AgNW flexible transparent conductive film. The as-fabricated film displayed a low sheet resistance of 15 Ω sq−1 at a high transmittance of 85% due to the welded junctions between HVT AgNWs and excellent bending stability after 4000 inner and outer bending cycles at a curvature radius of 3 mm. Simultaneously, the PDMS/HVT AgNW film was employed for defogging, EMI shielding, and folding test. The temperature on the central area of the film exceeded 130 °C under an applied voltage of 9 V, which contributed to the defogging performance. Within the whole measured frequency range of 8.2−12.5 GHz, the EMI SE of the film was above 21 dB, and it was achieved to the highest value 47 dB at 8.8 GHz. In spite of a harsh folding process, the PDMS/HVT AgNW film retained its original electrical properties. These results reveal that the HCl vapor-treating process provides a facile and efficacious method toward welding AgNWs that has been widely regarded as the next-generation transparent electrode for various flexible optoelectronics such as touch screens, displays, and smart windows.

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(2014B030301014), Youth Innovation Promotion Association (2017411), Guangdong TeZhi plan youth talent of science and technology (2014TQ01C102), Shenzhen basic research plan (JSGG20150512145714246), and Shenzhen Science & Technology Program (JSGG20160229155249762).

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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.7b13048. XRD patterns and SEM images of AgNWs immersed into HCl solution and treated by HCl vapor for 24 h under darkness; XRD patterns of AgNWs treated by HCl vapor for 5 min under visible light and darkness; XPS spectra of pristine AgNWs, AgNWs treated by HCl vapor for 5 min under visible light and darkness; plane view TEM image of the junction between pristine AgNWs, and FFT patterns from each individual AgNW and the pristine AgNW junction; haze of the PDMS/HVT AgNW films (PDF) Defogging performance of the PDMS/HVT AgNW film (AVI) Defogging performance of the PET film (AVI) Electrical performance of the PDMS/HVT AgNW film suffering from severe folding (AVI) Electrical performance of the ITO/PET film suffering from severe folding (AVI)

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REFERENCES

(1) Krantz, J.; Richter, M.; Spallek, S.; Spiecker, E.; Brabec, C. J. Solution-Processed Metallic Nanowire Electrodes as Indium Tin Oxide Replacement for Thin-Film Solar Cells. Adv. Funct. Mater. 2011, 21, 4784−4787. (2) Krantz, J.; Stubhan, T.; Richter, M.; Spallek, S.; Litzov, I.; Matt, G. J.; Spiecker, E.; Brabec, C. J. Spray-Coated Silver Nanowires as Top Electrode Layer in Semitransparent P3HT:PCBM-Based Organic Solar Cell Devices. Adv. Funct. Mater. 2013, 23, 1711−1717. (3) Yu, Z.; Li, L.; Zhang, Q.; Hu, W.; Pei, Q. Silver NanowirePolymer Composite Electrodes for Efficient Polymer Solar Cells. Adv. Mater. 2011, 23, 4453−4457. (4) Chen, D.; Liang, J.; Liu, C.; Saldanha, G.; Zhao, F.; Tong, K.; Liu, J.; Pei, Q. Thermally Stable Silver Nanowire-Polyimide Transparent Electrode Based on Atomic Layer Deposition of Zinc Oxide on Silver Nanowires. Adv. Funct. Mater. 2015, 25, 7512−7520. (5) Li, L.; Yu, Z.; Hu, W.; Chang, C.-h.; Chen, Q.; Pei, Q. Efficient Flexible Phosphorescent Polymer Light-Emitting Diodes Based on Silver Nanowire-Polymer Composite Electrode. Adv. Mater. 2011, 23, 5563−5567. (6) Spechler, J. A.; Koh, T.-W.; Herb, J. T.; Rand, B. P.; Arnold, C. B. A Transparent, Smooth, Thermally Robust, Conductive Polyimide for Flexible Electronics. Adv. Funct. Mater. 2015, 25, 7428−7434. (7) Blake, P.; Brimicombe, P. D.; Nair, R. R.; Booth, T. J.; Jiang, D.; Schedin, F.; Ponomarenko, L. A.; Morozov, S. V.; Gleeson, H. F.; Hill, E. W.; et al. Graphene-based Liquid Crystal Device. Nano Lett. 2008, 8, 1704−1708. (8) Jang, J.; Im, H.-G.; Jin, J.; Lee, J.; Lee, J.-Y.; Bae, B.-S. A Flexible and Robust Transparent Conducting Electrode Platform Using an Electroplated Silver Grid/Surface-Embedded Silver Nanowire Hybrid Structure. ACS Appl. Mater. Interfaces 2016, 8, 27035−27043. (9) Lee, J.; Lee, P.; Lee, H. B.; Hong, S.; Lee, I.; Yeo, J.; Lee, S. S.; Kim, T.-S.; Lee, D.; Ko, S. H. Room-Temperature Nanosoldering of a Very Long Metal Nanowire Network by Conducting-Polymer-Assisted Joining for a Flexible Touch-Panel Application. Adv. Funct. Mater. 2013, 23, 4171−4176. (10) Di, C.-a.; Wei, D.; Yu, G.; Liu, Y.; Guo, Y.; Zhu, D. Patterned Graphene as Source/drain Electrodes for Bottom-Contact Organic Field-Effect Transistors. Adv. Mater. 2008, 20, 3289−3293. (11) Pang, S.; Tsao, H. N.; Feng, X.; Müllen, K. Patterned Graphene Electrodes from Solution-Processed Graphite Oxide Films for Organic Field-Effect Transistors. Adv. Mater. 2009, 21, 3488−3491. (12) Weber, C. M.; Eisele, D. M.; Rabe, J. P.; Liang, Y.; Feng, X.; Zhi, L.; Müllen, K.; Lyon, J. L.; Williams, R.; Vanden Bout, D. A.; et al. Graphene-Based Optically Transparent Electrodes for Spectroelectrochemistry in the UV-Vis Region. Small 2010, 6, 184−189. (13) Zhang, M.; Fang, S.; Zakhidov, A. A.; Lee, S. B.; Aliev, A. E.; Williams, C. D.; Atkinson, K. R.; Baughman, R. H. Strong, Transparent, Multifunctional, Carbon Nanotube Sheets. Science 2005, 309, 1215−1219. (14) Wu, Z.; Chen, Z.; Du, X.; Logan, J. M.; Sippel, J.; Nikolou, M.; Kamaras, K.; Reynolds, J. R.; Tanner, D. B.; Hebard, A. F.; et al. Transparent, Conductive Carbon Nanotube Films. Science 2004, 305, 1273−1276. (15) Hecht, D. S.; Hu, L.; Irvin, G. Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures. Adv. Mater. 2011, 23, 1482−1513. (16) Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.-H.; Kim, P.; Choi, J.-Y.; Hong, B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Nature 2009, 457, 706−710.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Pengli Zhu: 0000-0001-6830-7760 Rong Sun: 0000-0001-9719-3563 Ching-Ping Wong: 0000-0003-3556-8053 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (21571186), Chinese Academy of Sciences Key Research Projects of Frontier Science (QYZDYSSW-JSC010), Guangdong Provincial Key Laboratory I


Research Article


Transparent Conductors and Stretchable Electronics. Adv. Mater. 2014, 26, 5808−5814. (36) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. One-Dimensional Nanostructures: Synthesis, Characterization, and Applications. Adv. Mater. 2003, 15, 353−389. (37) Korte, K. E.; Skrabalak, S. E.; Xia, Y. Rapid Synthesis of Silver Nanowires Through a CuCl- or CuCl2-Mediated Polyol Process. J. Mater. Chem. 2008, 18, 437−441. (38) Yu, J.; Dai, G.; Huang, B. Fabrication and Characterization of Visible-Light-Driven Plasmonic Photocatalyst Ag/AgCl/TiO2 Nanotube Arrays. J. Phys. Chem. C 2009, 113, 16394−16401. (39) Zhu, Y.; Liu, H.; Yang, L.; Liu, J. Study on the Synthesis of Ag/ AgCl Nanoparticles and Their Photocatalytic Properties. Mater. Res. Bull. 2012, 47, 3452−3458. (40) Liang, X.; Zhao, T.; Hu, Y.; Zhu, P.; Sun, R.; Lu, D. q.; Wong, C. CuCl2 and Stainless Steel Synergistically Assisted Synthesis of Highpurity Silver Nanowires on a Large Scale. RSC Adv. 2014, 4, 47536− 47539. (41) Campbell, C. T. Atomic and Molecular Oxygen Adsorption on Ag(111). Surf. Sci. 1985, 157, 43−60. (42) Sexton, B. A.; Madix, R. J. Vibrational Spectra of Molecular and Atomic Oxygen on Ag(110). Chem. Phys. Lett. 1980, 76, 294−297. (43) de Mongeot, F. B.; Cupolillo, A.; Valbusa, U.; Rocca, M. O2 Dissociation on Ag(001): The Role of Kink Sites. Chem. Phys. Lett. 1997, 270, 345−350. (44) Tjeng, L. H.; Meinders, M. B. J.; van Elp, J.; Ghijsen, J.; Sawatzky, G. A.; Johnson, R. L. Electronic Structure of Ag2O. Phys. Rev. B: Condens. Matter Mater. Phys. 1990, 41, 3190−3199. (45) Zhu, M.; Chen, P.; Liu, M. Sunlight-Driven Plasmonic Photocatalysts Based on Ag/AgCl Nanostructures Synthesized via An Oil-In-Water Medium: Enhanced Catalytic Performance by Morphology Selection. J. Mater. Chem. 2011, 21, 16413−16419. (46) Zhu, M.; Chen, P.; Liu, M. Graphene Oxide Enwrapped Ag/ AgX (X = Br, Cl) Nanocomposite as A Highly Efficient Visible-Light Plasmonic Photocatalyst. ACS Nano 2011, 5, 4529−4536. (47) Zhu, M.; Chen, P.; Liu, M. Highly Efficient Visible-Light-Driven Plasmonic Photocatalysts Based on Graphene Oxide-Hybridized OneDimensional Ag/AgCl Heteroarchitectures. J. Mater. Chem. 2012, 22, 21487−21494. (48) He, H.; Li, Y.; Zhang, X.; Yu, Y.; Zhang, C. Precipitable Silver Compound Catalysts for The Selective Catalytic Reduction of NOx by Ethanol. Appl. Catal., A 2010, 375, 258−264. (49) Kaushik, V. K. XPS Core Level Spectra and Auger Parameters for Some Silver Compounds. J. Electron Spectrosc. Relat. Phenom. 1991, 56, 273−277. (50) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics. Angew. Chem., Int. Ed. 2008, 48, 60−103. (51) Xiong, Y.; Chen, J.; Wiley, B.; Xia, Y.; Aloni, S.; Yin, Y. Understanding The Role of Oxidative Etching in The Polyol Synthesis of Pd Nanoparticles With Uniform Shape and Size. J. Am. Chem. Soc. 2005, 127, 7332−7333. (52) Lu, Y.; Huang, J. Y.; Wang, C.; Sun, S.; Lou, J. Cold Welding of Ultrathin Gold Nanowires. Nat. Nanotechnol. 2010, 5, 218−224. (53) Sanders, D. E.; DePristo, A. E. Predicted Diffusion Rates on fcc (001) Metal Surfaces for Adsorbate/Substrate Combinations of Ni, Cu, Rh, Pd, Ag, Pt, Au. Surf. Sci. 1992, 260, 116−128. (54) Moon, H.; Won, P.; Lee, J.; Ko, S. H. Low-haze, Annealing-Free, Very Long Ag Nanowire Synthesis and Its Application in A Flexible Transparent Touch Panel. Nanotechnology 2016, 27, 295201. (55) Rathmell, A. R.; Wiley, B. J. The Synthesis and Coating of Long, Thin Copper Nanowires to Make Flexible, Transparent Conducting Films on Plastic Substrates. Adv. Mater. 2011, 23, 4798−4803. (56) Salvatierra, R. V.; Cava, C. E.; Roman, L. S.; Zarbin, A. J. G. ITO-Free and Flexible Organic Photovoltaic Device Based on High Transparent and Conductive Polyaniline/Carbon Nanotube Thin Films. Adv. Funct. Mater. 2013, 23, 1490−1499. (57) Yang, Y.; Dai, J.; Li, Y.; Jia, M.; Huang, X. Less Defective Fluorine-Containing Graphene With Good Dispersity: Preparation,

(17) Pang, S.; Hernandez, Y.; Feng, X.; Müllen, K. Graphene as Transparent Electrode Material for Organic Electronics. Adv. Mater. 2011, 23, 2779−2795. (18) Vosgueritchian, M.; Lipomi, D. J.; Bao, Z. Highly Conductive and Transparent PEDOT:PSS Films with a Fluorosurfactant for Stretchable and Flexible Transparent Electrodes. Adv. Funct. Mater. 2012, 22, 421−428. (19) Hu, L.; Kim, H. S.; Lee, J.-Y.; Peumans, P.; Cui, Y. Scalable Coating and Properties of Transparent, Flexible, Silver Nanowire Electrodes. ACS Nano 2010, 4, 2955−2963. (20) Lu, H.; Zhang, D.; Ren, X.; Liu, J.; Choy, W. C. H. Selective Growth and Integration of Silver Nanoparticles on Silver Nanowires at Room Conditions for Transparent Nano-Network Electrode. ACS Nano 2014, 8, 10980−10987. (21) Zhu, R.; Chung, C.-H.; Cha, K. C.; Yang, W.; Zheng, Y. B.; Zhou, H.; Song, T.-B.; Chen, C.-C.; Weiss, P. S.; Li, G.; et al. Fused Silver Nanowires with Metal Oxide Nanoparticles and Organic Polymers for Highly Transparent Conductors. ACS Nano 2011, 5, 9877−9882. (22) Garnett, E. C.; Cai, W.; Cha, J. J.; Mahmood, F.; Connor, S. T.; Christoforo, M. G.; Cui, Y.; McGehee, M. D.; Brongersma, M. L. SelfLimited Plasmonic Welding of Silver Nanowire Junctions. Nat. Mater. 2012, 11, 241−249. (23) Kim, J.; Nam, Y. S.; Song, M. H.; Park, H. W. Large Pulsed Electron Beam Welded Percolation Networks of Silver Nanowires for Transparent and Flexible Electrodes. ACS Appl. Mater. Interfaces 2016, 8, 20938−20945. (24) Liu, Y.; Zhang, J.; Gao, H.; Wang, Y.; Liu, Q.; Huang, S.; Guo, C. F.; Ren, Z. Capillary-Force-Induced Cold Welding in SilverNanowire-Based Flexible Transparent Electrodes. Nano Lett. 2017, 17, 1090−1096. (25) Park, J. H.; Hwang, G.-T.; Kim, S.; Seo, J.; Park, H.-J.; Yu, K.; Kim, T.-S.; Lee, K. J. Flash-Induced Self-Limited Plasmonic Welding of Silver Nanowire Network for Transparent Flexible Energy Harvester. Adv. Mater. 2016, 29, 1603473. (26) Seong, B.; Chae, I.; Lee, H.; Nguyen, V. D.; Byun, D. Spontaneous Self-Welding of Silver Nanowire Networks. Phys. Chem. Chem. Phys. 2015, 17, 7629−7633. (27) Tokuno, T.; Nogi, M.; Karakawa, M.; Jiu, J.; Nge, T. T.; Aso, Y.; Suganuma, K. Fabrication of Silver Nanowire Transparent Electrodes at Room Temperature. Nano Res. 2011, 4, 1215−1222. (28) Xue, J.; Song, J.; Dong, Y.; Xu, L.; Li, J.; Zeng, H. Nanowirebased Transparent Conductors for Flexible Electronics and Optoelectronics. Sci. Bull. 2017, 62, 143−156. (29) Xue, J.; Song, J. Z.; Zou, Y. S.; Huo, C. X.; Dong, Y. H.; Xu, L. M.; Li, J. H.; Zeng, H. B. Nickel Concentration-Dependent Optoelectrical Performances and Stability of Cu@CuNi Nanowire Transparent Conductors. RSC Adv. 2016, 6, 91394−91400. (30) Lee, J.-Y.; Connor, S. T.; Cui, Y.; Peumans, P. SolutionProcessed Metal Nanowire Mesh Transparent Electrodes. Nano Lett. 2008, 8, 689−692. (31) Madaria, A. R.; Kumar, A.; Ishikawa, F. N.; Zhou, C. Uniform, Highly Conductive, and Patterned Transparent Films of a Percolating Silver Nanowire Network on Rigid and Flexible Substrates Using a Dry Transfer Technique. Nano Res. 2010, 3, 564−573. (32) Guo, S. The Creation of Nanojunctions. Nanoscale 2010, 2, 2521−2529. (33) Lee, J.-G.; Kim, D.-Y.; Lee, J.-H.; Sinha-Ray, S.; Yarin, A. L.; Swihart, M. T.; Kim, D.; Yoon, S. S. Production of Flexible Transparent Conducting Films of Self-Fused Nanowires via OneStep Supersonic Spraying. Adv. Funct. Mater. 2017, 27, 1602548. (34) Xiong, W.; Liu, H.; Chen, Y.; Zheng, M.; Zhao, Y.; Kong, X.; Wang, Y.; Zhang, X.; Kong, X.; Wang, P.; et al. Highly Conductive, Air-Stable Silver Nanowire@Iongel Composite Films toward Flexible Transparent Electrodes. Adv. Mater. 2016, 28, 7167−7172. (35) Han, S.; Hong, S.; Ham, J.; Yeo, J.; Lee, J.; Kang, B.; Lee, P.; Kwon, J.; Lee, S. S.; Yang, M.-Y.; et al. Fast Plasmonic Laser Nanowelding for a Cu-Nanowire Percolation Network for Flexible J


Research Article

ACS Applied Materials & Interfaces Characterization, and Application in Transparent Conductive Thin Film. Carbon 2017, 115, 285−292. (58) Shen, B.; Li, Y.; Yi, D.; Zhai, W.; Wei, X.; Zheng, W. Microcellular Graphene Foam for Improved Broadband Electromagnetic Interference Shielding. Carbon 2016, 102, 154−160. (59) Yu, Y.-H.; Ma, C.-C. M.; Teng, C.-C.; Huang, Y.-L.; Lee, S.-H.; Wang, I.; Wei, M.-H. Electrical, Morphological, and Electromagnetic Interference Shielding Properties of Silver Nanowires and Nanoparticles Conductive Composites. Mater. Chem. Phys. 2012, 136, 334− 340. (60) Hu, M.; Gao, J.; Dong, Y.; Li, K.; Shan, G.; Yang, S.; Li, R. K.-Y. Flexible Transparent PES/Silver Nanowires/PET Sandwich-Structured Film for High-Efficiency Electromagnetic Interference Shielding. Langmuir 2012, 28, 7101−7106.

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Room-Temperature Nanowelding of a Silver Nanowire Network

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