One-Step Fabrication of Stretchable Copper Nanowire Conductors by

Subscriber access provided by NEW YORK UNIV

Article

One-Step Fabrication of Stretchable Copper Nanowire Conductors by a Fast Photonic Sintering Technique and Its Application in Wearable Devices Su Ding, Jinting Jiu, Yue Gao, Yanhong Tian, Teppei Araki, Tohru Sugahara, Shijo Nagao, Masaya Nogi, Hirotaka Koga, Katsuaki Suganuma, and Hiroshi Uchida ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10802 • Publication Date (Web): 02 Feb 2016 Downloaded from http://pubs.acs.org on February 5, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

One-Step Fabrication of Stretchable Copper Nanowire Conductors by a Fast Photonic Sintering Technique and Its Application in Wearable Devices Su Ding, a, b Jinting Jiu, *b Yue Gao, b Yanhong Tian, *a Teppei Araki, b Tohru Sugahara, b Shijo Nagao, b Masaya Nogi, b Hirotaka Koga, b Katsuaki Suganuma b and Hiroshi Uchida c a

State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, 150001, China. E-mail: [email protected]

b

The Institute of Scientific and Industrial Research (ISIR), Osaka University, Osaka, Japan.

E-mail: [email protected] c

Institute for Polymers and Chemicals Business Development Center, Showa Denko K.K.,

Ichihara, Chiba 290-0067, Japan

Abstract Copper nanowire (CuNW) conductors have been considered to have a promising perspective in the area of stretchable electronics due to the low price and high conductivity. However, the fabrication of CuNW conductors suffers from harsh conditions, such as high temperature, reducing atmosphere, and time-consuming transfer step. Here, a simple and rapid one-step photonic sintering technique was developed to fabricate stretchable CuNW conductors on polyurethane (PU) at room temperature in air environment. It was observed that CuNWs were instantaneously deoxidized, welded and simultaneously embedded into the soft surface of PU through the one-step photonic sintering technique, after which highly conductive network and strong adhesion between CuNWs and PU substrates were achieved. The CuNW/PU

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 35

conductor with sheet resistance of 22.1 Ohm/sq and transmittance of 78%was achieved by the one-step photonic sintering technique within only 20 µs in air. Besides, the CuNW/PU conductor could remain a low sheet resistance even after 1000 cycles of stretching/releasing under 10% strain. Two flexible electronic devices, wearable sensor and glove-shaped heater, were fabricated using the stretchable CuNW/PU conductor, demonstrating that our CuNW/PU conductor could be integrated into various wearable electronic devices for applications in food, clothes, and medical supplies fields.

Keywords: copper nanowires, stretchable conductor, one-step, photonic sintering, wearable device.

1. Introduction Flexible devices provide more functions and convenience compared with traditional rigid ones and have opened new application prospect in our daily life, such as bendable displays electronics

8-9

1-2

, stretchable strain sensors

3-5

, artificial skin

6-7

and wearable

. To realize these applications, developing conductors possessing both

high electrical conductivity and stretchability (40% strain is acceptable for commercialization) is a crucial step. There are two primary strategies in the fabrication of stretchable conductors: one is to design stretchable structures and the other is to use stretchable materials. The former assembles conducting materials into special shapes that can partly withstand the strain during stretching process, e.g. wavy, serpentine, arc shape, or network structures

10-13

nanomaterials including carbon nanotubes (CNTs)

. The later focuses on novel

14-15

, graphene 16, metal nanowires


Page 3 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17-19

and their compounds

20-22

. Recently, integration of the novel nanomaterials and

stretchable structures has also been proven to be a promising way to obtain conductors with high stretchbility and electrical conductivity. Lee et al

19

fabricated

silver nanowire (AgNW) conductors with wavy structure showing negligible resistance increase under a strain up to 460%. Kim et al. demonstrated a corrugated structure with AgNWs on pre-strained elastomeric substrate facilitating effective extension of AgNW network under a high strain of 35%

23

. In both cases, the

unparalleled structure of metal nanowires is essential to achieve high stretchability. AgNWs stretchable conductors have been extensively studied due to the superior conductivity, intrinsic flexibility (good bendability and stretchability with yield strain of 1.55% 24), and simple solution processing

17, 19, 25-26

. The excellent stretchability of

AgNW conductors corresponds to the special structure of percolating network as well as the deformability of nanowires themselves, which perfectly combine the advantage of two strategies mentioned above. However, AgNWs are expensive and easily fail down in 2 days due to electromigration issue even under tiny current, which seriously hinder their practical application

27

. CuNW is much cheaper with a comparable

electrical conductivity as silver, and more stable under electrical current. Thus CuNW film is considered to be an amazing candidate for next generation of flexible, transparent and stretchable conductors. Wiley et al. reported the fabrication of CuNW transparent conductors by annealing method at 175°C in hydrogen atmosphere 28. The annealing process in hydrogen atmosphere, which was used to reduce the oxidations on the surfaces of CuNWs, was dangerous, complex and time-consuming. Also the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 35

high temperature affected the integration of thermal sensitive parts in devices. Won et al. reported an annealing-free process to transfer an acid-chemical treated CuNWs networks onto a pre-strained elastomeric polydimethylsiloxane (PDMS) substrate by a press-method to make stretchable conductors

29

.The CuNW/PDMS electrode was

easily torn off from substrates during stretching process due to the weak adhesion between PDMS and CuNWs. Moreover, the destructive acid-washing process not only caused crystal defects but also induced oxidization onto the fresh surfaces. To enhance the adhesion and achieve highly stretchable conductors, Cheng et al. embedded CuNWs in the surface of elastic poly (acrylate) matrix by firstly annealing CuNWs on a glass plate under hydrogen atmosphere at 300 °C, and then photo polymerizing acrylate monomer into poly matrix with long time

30

. The

partly-embedding structure of CuNW network in poly matrix exhibited good mechanical robustness against bending and stretching up to 10% strain. Hu et al. used a similar annealing method to firstly obtain a highly conductive CuNW network on glass, and then transfer the network into PU matrix by in situ polymerization of PU precursor

18

. They also mentioned that pre-treatment of the CuNW network with

6-aminohexanoic acid could enhance the bonding between nanowires and PU matrix, which significantly improved the reversibility of the surface conductance of the CuNW/PU electrode during repeated stretching/releasing process

18

. However, the

inevitable annealing process and the additional transfer step greatly increase the cost. Thus, a simple technique is urgently desired to fabricate highly conductive CuNWs conductors and to simultaneously achieve a strong adhesion between CuNW and


Page 5 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


substrates without any need of high temperature, insert atmosphere or acid corrosion. Recently, photonic sintering technique has been developed to replace traditional thermal sintering due to its high speed, room temperature operation and intelligence to anneal metal nanostructure

31-33

. Our previous study has demonstrated that the

photonic sintering technique was a fast and powerful method to achieve highly conductive CuNWs transparent electrodes on glass substrate at room temperature in air without any protective atmosphere 34. Under the encouragement of these amazing results, stretchable conductors with CuNW percolation network on PU flexible substrate were fabricated using this simple photonic sintering technique at room temperature in air within only one-step. The photonic energy not only welded the CuNWs at contact spots but also deoxidized the oxides on the surfaces of CuNWs at the same time, which together leaded to a highly conductive network. Importantly, the process also induced the softening phenomenon of the PU surface, resulting in a natural evolution that the CuNW network was simultaneously embedded into the surface of PU matrix, which greatly enhance the adhesion between CuNWs and substrates. Furthermore, the stretchability of the CuNW/PU conductors was measured in detail, and the influence of light parameter on the performance of conductors was thoroughly investigated. At last, the robust CuNW/PU conductors were used to produce wearable sensor and heater.

2. Experimental Section 2.1 Synthesis of CuNWs and fabrication of CuNW/PU conductors Anhydrous copper dichloride (CuCl2, 95%), glucose (98%), octadecylamine (ODA),



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

hexane and isopropanol were obtained from Wako Chemicals. CuNWs were synthesized using a green hydrothermal method as reported previously 35-36. Typically, 68 mg CuCl2, 72 mg glucose and 648 mg ODA were sufficiently stirred at room temperature and then transferred to Teflon-lined autoclave to react at 120°C for 24 hours. The product was collected and washed by water, hexane and isopropanol, respectively. The as-prepared CuNWs were dispersed in isopropanol to make Cu ink. Soft PU substrates (TG88-I, Takeda Sangyo Co., Ltd.) were fixed on rigid supporting glasses to avoid being stretched or bended during the fabrication process as shown in Figure 1. Then the Cu ink was sprayed onto the PU substrates using a nozzle powered by an air compressor. The PU substrates were placed on a hot plate with temperature of 60°C to quickly evaporate the solvent and ensure the uniformity of CuNW network. The amount of CuNWs on the film was varied by changing spray times. After that, the CuNWs films were treated with photonic sintering (PulseForge 3300, Novacentrix, Austin, TX, USA) to obtain conductive networks. At last, the CuNW/PU conductors were carefully peeled off from the glass substrate for various evaluations. 2.2 Morphology Characterization and property measurement The morphology of CuNWs on PU was characterized by field-emission scanning electron microscopy (FESEM, Hitachi SU8020, Hitachi High Technologies America, Inc.) and transmission electron microscopy (TEM, JEOL-2100, JEOL Ltd.). Transparency and sheet resistance of CuNW/PU conductors were measured using ultraviolet-visible-near infrared spectrophotometer (V670, JASCO Corp.) and four probe method with a surface resistivity meter (LorestaGP T610, Mitsubishi Chemical


Page 6 of 35

Page 7 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Analytech Co. Ltd.). To test the electrical property during the stretching process, two ends of samples were attached onto a pair of tensile grips in a dynamic mechanical analyzer (EZ Test, Shimadzu) to measure the stretching performance with a constant speed. The electrical resistance of the samples during stretching process was measured using an Agilent Technologies 34410A multimeter and an Agilent Technologies 11059A Kelvin probe set (Agilent Technologies, Santa Clara, USA) through a four-point probe method. The bending property was examined using a home-made machine (Figure S1), which could bend the samples from 0° to 180° and at the same time the resistance changes were real-time recorded using a resistance meter (RM 3544-01, Hioki E.E. Corporation). 2.3 Application of CuNW/PU conductors in sensor and heater The strain sensor is based on the concept of e-skin that can be stretched and bended freely as artificial skin. The CuNW/PU conductors were tightly pasted on the finger joint and connected with the probe set to output corresponding electrical signals using two Ni wires after sputtering platinum (Pt) as electrodes on two ends of the conductor. The bending and relaxing movement of finger caused the resistance vibration in the CuNW/PU conductors, which corresponded to relative movement of finger and can be used in health care and robot. The heaters were fabricated using the CuNW/PU conductors with sputtering Pt at two ends, which were connected with a power source (PMC18-3A, KIKUSUI Electronics Corporation) with two alligator clips to input DC voltage. The temperature of the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

heater was monitored by attaching thermal couples directly onto the conductor surface to record the temperature curve using a multi-type input system (midi logger GL220, Graphtech). An infrared thermometer (Thermo Gear G30, Nippon Avionics Co., Ltd.) was also used to take an infrared photo giving an image of temperature distribution on the heater. A transparent glove-heater was also fabricated to verify the performance. CuNWs were sprayed in a big area of 10×12 cm2 on PU and sintered by the photonic sintering technique, then cut into glove-shape and bound with another piece by staples. Cu tapes were pasted at two ends of the glove and connected with the DC source by two Ni wires. The temperature distribution was recorded by infrared thermometer.

3. Results and Discussion Figure 1a illustrates the fabrication process of CuNW/PU conductors. The well dispersed CuNWs suspension was sprayed onto PU substrate (supported by a rigid supporting glass) to form CuNW network. Then the network was treated by photonic sintering under ambient condition. Flexible CuNW/PU conductors were achieved by carefully peeling off the film from the supporting glass. The as-prepared CuNWs have diameters of 30-40 nm and lengths around 10-30 µm, as shown in Figure 1b. The tilted image of CuNWs on PU before photonic sintering indicates the CuNWs were gently contacted with each other with clear gaps and the junctions were weak (Figure 1c). Normally, the conductivity of the CuNW film was determined by the junctions between nanowires in the network structure. Thus, the freshly-prepared CuNW films showed poor electrical conductivity over 105 ohm/sq because of the huge contact resistance resulted from the weak interconnection


Page 8 of 35

Page 9 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


between nanowires and easy oxidation of fine copper

37-38

. To improve the

conductivity of CuNW network, the samples were generally annealed at high temperature (over 175°C) in reducing atmosphere, such as hydrogen. However, PU could not endure such high temperature for long term. In this study, we utilized the fast photonic sintering process to enhance the electrical conductivity instead of long-time heating treatment. It is clear that CuNWs were almost completely embedded in PU after the photonic sintering with light energy of 272 mJ/cm2 for only 20 µs in air (Figure 1d). At the same time, the vertical distances of nanowires were greatly shortened compared with pristine ones (Figure 1c). The resistance of CuNWs films was largely decreased from 105 to several ohm/sq within only 20 µs, indicating the contact resistance between nanowires was drastically decreased due to the welding of CuNWs at the crossing points. The sole blemish is that the transmittance of CuNW/PU conductor was slightly decreased about 2-4% after the photonic sintering (Figure S2), which might be related to the surface deterioration of PU during photonic sintering. A series of CuNW/PU conductors were fabricated by the one-step photonic sintering to investigate the relationship between transmittance and sheet resistance of CuNW/PU conductors (Figure 1e). In general, the resistance was quickly decreased as the transmittance was decreased. CuNW/PU conductors with sheet resistance of 22.1, 4.54, 2.54 Ohm/sq and transmittance of 78%, 41%, 21% were achieved within only 20 µs in air using this photonic sintering method, which was superior to those complicated high temperature sintering processes. The rapid photonic sintering technique is powerful, feasible and convenient to obtain high performance conductors



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

for the easily oxidized CuNWs in air condition. Excitingly, the photonic sintering process buried CuNWs into the surface of PU substrate to form a strong-adhesion and percolation network even without any additional transfer process or coating layer

25-26, 29, 39-40

. To confirm the adhesion, a

Scotch tape test was carried out with cover-tear-cover-tear process to check the resistance evolution. The sheet resistance almost remained unchanged even after several cycles, indicating the strong physical adhesion between CuNWs and PU (Figure S3). This percolation network with strong adhesion to substrate was expected to be beneficial to hold nanowires under mechanical deformation, which have been realized by transfer method 18, 29. Present photonic sintering process leaded to the high conductivity and strong adhesion between Cu NWs and PU substrate just by one-step within only 20 µs, showing superiority of the photonic sintering process, which greatly simplified the operation and significantly decreased the processing cost.


Page 10 of 35

Page 11 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure1 (a) Schematic illustration of the fabrication process of CuNW/PU conductors. (b) SEM image of as prepared CuNWs. Tilted SEM images of CuNW networks on PU matrix (c) before and (d) after photonic sintering. (e) Plot f transmittance (λ = 550 nm) verse sheet resistance for photonic sintering CuNW conductors.

The mechanical properties of CuNW/PU conductors fabricated using the photonic sintering technique were investigated, as shown in Figure 2. The size of CuNW/PU conductors were 15×15 mm2. Figure 2a shows the resistance change of a CuNW/PU conductor with original resistance of 8.5 Ohm during stretching/releasing process at a constant strain rate of 0.5 mm/min. The resistance was firstly slowly risen when the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

strain was less than 30% and then quickly gone up when the strain was further increased, which was caused by the quickly reduction in concentration of CuNWs in a certain area with the increasing strain 40. After that, the conductor was released and the resistance partly recovered. When the strain was loaded on the CuNW/PU conductor, the film was elongated which compelled the nanowires to slide along the stretching direction especially under large strain at 50% (Figure S4). Part of the contact spots among CuNWs became loose due to the sliding of nanowires under the stretching strain, which led to the increase in resistance. After the strain was removed, these nanowires were slid back to decrease the resistance owing to the strong adhesion between CuNWs and PU. However, the strain also broke some nanowires during the movement process (Figure S4), which might be the main reason for the irreversible increase in resistance. Thus, after stretched/released at 50% strain, the resistance was partly recovered to 36 Ohm, about 4 times higher than original value, when the strain was 0%. On the other hand, the length of PU substrate has been slightly elongated about 9% after strain, which could partly be attributed to the increased resistance of Cu NWs/PU conductors. Moreover, the first stretching always caused a large degeneration of conductivity, which could be indicated by the data in Figure 2b. Figure 2b demonstrates the relative resistance change after 10 cycles of stretching-releasing under 10% strain for three groups of CuNW/PU conductor with various transmittances. T20, T40, T60 represented conductors with transmittance of 20%, 40% and 60% and the corresponding original sheet resistance was7.8, 17.9, 91.9 Ohm, respectively. It is clear that the increase of resistance in first cycle was larger


Page 12 of 35

Page 13 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


than that in other cycles (Figure 2b). In some reports, the stretchability was always improved by pre-stretching the conductors for several cycles

17, 40-41

. The photonic

sintering might induce stress in the CuNW/PU conductors, which was released with the first cycle. However, it is still unclear. On the other hand, the resistance peak under stretching status of these CuNW/PU conductors was also given in Figure S5. It is clear that peak value depended on the original resistance and transmittance. Higher resistance with higher transmittance gave larger resistance peak value, and vice versa. CuNW/PU conductors with higher density of nanowires were more robust to the mechanical stretching with a small resistance amplitude. Conversely, CuNW/PU conductors with low density of nanowires were more sensitive to external mechanical deformation. CuNW/PU conductors at lower transmittance loaded lager amount of CuNWs which included lots of contact spots among nanowires. When the CuNW/PU conductors were stretched, the network structure was deformed and the contact spots between nanowires were weakened even interrupted leading to the increase in relative resistance. At high transmittance, the contact spots between nanowires were scarce and crucial for electron transfer. If stretching strain caused the broken of contact spots, the resistance will be largely increased due to the loss of key tunnel for electronic transfer. Conversely, CuNW/PU conductors with low transmittance included a lot of nanowires to make excessive contact spots. When some contact spots were broken during stretching process, other spots still transferred the electron and kept the low resistance. It should be mentioned that the resistance was always recovered except the first-cycle for all the samples when the strain was released (Figure 2b), which was



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

possibly attributed to the strongly adhesive structure. Figure 2c shows the resistance evolution of a CuNW/PU conductor with transmittance of 20%, which was firstly stretched for one time to release the stress, and then was repeatedly stretched/released under 10% strain. The resistance increased less than 3 times even after 1000 cycles exhibiting an excellent reversible stretching property compared with other reports30, which indicated that the CuNW/PU conductors prepared by the fast one-step photonic sintering were excellent and could be used in many stretchable devices. The bending performance was also investigated by curving the CuNW/PU conductors along a cylinder with diameter of 20 mm from 0 to 180 degree (Figure 2d). The resistance of CuNW/PU conductors kept superior stability against deformation even after 100 bending cycles. No clear difference was observed for these three samples with different transmittance. The excellent mechanical properties were corresponding to the strong adhesion between CuNWs and PU substrates, which was mentioned in many references14, 18, 30, 31.


Page 14 of 35

Page 15 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2 (a) Resistance change with strain up to 50% at a constant stretching speed of 0.5 mm per minute and the initial sheet resistance was 8.4 Ohm/sq. (b) Relative resistance change of three types of CuNW/PU conductors stretched/released repeatedly for 10 times at 10% strain. (c) Relative

resistance

of

pre-stretched

CuNW/PU

conductor

(T

=

20%)

during

the

stretching/releasing process with the peak value of 10% strain. Inset graph shows the last several cycles. (d) Change of relative resistance of CuNW/PU conductors during bending for 100 cycles. Inset graph shows the schematic diagram that the CuNW/PU conductors were bended along a rod with a diameter of 20 mm.

The photonic sintering technique was considered to be a promising method for practical production due to its fast speed, ambient conditions, cost effective, and reactivity of light

33, 42-44.

For fabrication of CuNW/PU conductors, the photonic

sintering technique has three advantages. (1) Highly conductive CuNW network could



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 35

be obtained in an extremely fast speed at room temperature without any protection atmosphere. When CuNWs were exposed under the flash lamp, the irradiation energy was mostly adsorbed by the CuNW network and transformed into thermal energy to weld these nanowires at contact spots due to the surface diffusion of Cu atoms

33-34

.

The welding of nanowires greatly contributed to the high conductivity of CuNW film. This process happened within only tens of microseconds, while conventional sintering technique needed more than 30 minutes under protection atmosphere. (2) The surface oxides and organic residuals were removed by the intense light. It is known that CuNWs are highly sensitive to oxidation even at room temperature during the post washing and short-term storage process, which would greatly increase the contact resistance of CuNW network

34-35

. Figure 3 compares the surface of a single CuNW

before and after the photonic sintering using the high resolution TEM (HRTEM) images. The lattice spaces perpendicular to the long axis were 0.25 and 0.30 nm, corresponding to the {110} planes of Cu andCu2O, respectively (Figure 3a). It suggested the existence of Cu oxides even in fresh-prepared CuNWs. The result was well agreed with those reports that the surfaces of CuNWs were always covered by oxides layer once exposing in air even at room temperature

45-46

.It is also the reason

that the resistance of CuNW films without post treatment was unusually much higher than that of AgNW films. Thus, lots of methods were developed to remove the surface oxides, such as hydrogen reducing at high temperature 18, 28-29, 31, acid washing 30, 36-38 and solvent-dipped reducing method

47

. In our work, the facile photonic sintering

technique was attempted to remove the oxides. The high magnification TEM image


Page 17 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


indicates that the distance of lattice spaces became 0.21 and 0.25 nm (Figure 3b), which could be indexed to the {111} and {110} planes of metal Cu. It implied that the oxides on the surface of CuNWs were removed by the photonic sintering process even though the entire process was operated in air atmosphere. The removal of the oxides might be related to a photothermochemical reduction process in the presence of organics on the surface of these CuNWs 32, 34. It has been confirmed the PVP could be photodegraded into alcohol and acid under the function of high intensity pulsed light and CuO was reduced to be Cu at the same time

44

. As organic, ODA might play a

same role and was decomposed under the irradiation of high intensity light to accelerate the removal of Cu oxides. Moreover, after photonic sintering, the surface of nanowires was changed from rough and messy to smooth and regular indicating the degradation of organics and re-assemble of surface state (Figure S6). (3) CuNWs networks were embedded into PU substrates during the one-step photonic sintering process. Apart from sintering of CuNW networks, the heat might be instantaneously transmitted to PU substrates due to the high thermal conductivity of CuNWs (401 Wm-1K-1). Although most of the heat was immediately emitted to surrounding atmosphere, a part of heat was maintained at the interface between CuNWs and PU due to small heat conduction coefficient of PU (0.02 Wm-1K-1). The thermal energy easily softened the surface of the polymer PU, and the CuNWs were naturally immersed into the substrates. All these three advantages were successfully realized with one step in only 20 µs by the photonic sintering technique, which is much superior to any other existing methods for CuNWs.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3 High resolution TEM images of CuNW before (a) and after (b) photonic sintering. The marked lattice spaces of 0.21 and 0.25 nm are corresponding to {111} and {110} planes of Cu, while, 0.30 nm is corresponding to {110} planes of Cu2O.

The success of high conductivity and strong adhesion of CuNWs/PU conductor are based on the strong adsorption of light，which was determined by both the density of CuNWs and the parameters of the light. When the loading of CuNWs was fixed, the parameters should be adjusted to perfectly embed the nanowires into PU. The effect of the light energy on the electromechanical property was investigated on CuNW/PU conductors with transmittance around 20%. E1, E2, E3 and E4 represented the samples were treated with light energy of 181, 272, 344 and 399 mJ/cm2, respectively. When the energy was as low as 181 mJ/cm2, the resistance of the CuNW/PU conductor after photonic sintering was around 500 Ohm. The resistance was dramatically decreased to 7.8 Ohm when the energy was increased to 272 mJ/cm2 as mentioned in Figure 2(b). Unfortunately, higher energy at 344 mJ/cm2 caused a higher resistance at 18 Ohm. Further improving the energy to 399 mJ/cm2, a worse conductivity of 60 Ohm was obtained. It was found that some CuNWs were “blown”


Page 18 of 35

Page 19 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


away from PU because the transmittance has been increased from original 20% to around 60%. Thus, it was essential to select proper parameters to achieve high performance CuNW/PU conductors. The stretching-releasing process of these three samples was also carried out as shown in Figure 4a. The resistance quickly increased to 2558 Ohm after the first stretching and climbed to 10 times of original value after 10 cycles for the CuNW/PU conductor treated with E1. The robustness against stretching was greatly improved in the case of E2, the final resistance was increased only twice (18 Ohm). Surprisingly, even the CuNW network was damaged to some extent under light energy of E3 and E4, the resistance was only also increased to twice of original resistance (36.6 and 115.8 Ohm) after 10 cycles. The SEM images were given to show the detailed microstructure of CuNW/PU conductors (Figure 4b-e). After the light treatment with energy of E1, the CuNWs were connected with each other and the distance between wires was reduced compared with Figure 1b demonstrating the welding was formed between nanowires. However, the CuNWs only covered on top of PU instead of being embedded into PU. When the CuNW/PU conductor was stretched, CuNWs hanging on the surface of PU were shaken off leading to unrecoverable resistance growth. Thus, the resistance increased quickly to 10 times.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 35

Figure 4 (a) Resistance change of CuNW/PU conductors treated with light energy of 181 (E1), 272 (E2), 344 (E3) and 399 (E4) mJ/cm2 during the stretching/releasing process. SEM images of CuNW networks on PU treated with light energy of (b) E1, (c) E2, (d) E3 and (e) E4.

With higher light energy, the CuNWs were merged into PU, and the boundaries of nanowires and soft PU was fused together to achieve good stretchability (Figure 4c, 4d and 4f). The results agreed with those reports that in situ polymerization always was used to embed AgNW or CuNW into substrates to improve the stretchability 25-26, 29

18,

. The embedding structure is crucial for high stretchability for nanowire


Page 21 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


conductors. Additionally, from the SEM images samples treated with light energy of E2 and E3, the difference was unclear, which agreed with the same performance of stretchablilty (Figure 4a). However, the density of CuNWs for E4 was clearly smaller than E2 and E3, which confirmed the removal of CuNWs mentioned above with excessive light energy. Although parts of the CuNWs were removed, the strong adhesion between the residual nanowires and PU contributed to the good performance under deformation (Figure 4a). It confirmed again that the embedding structure was prerequisite for high performance stretchable conductor. Combined with the stretching property and the microstructure of these CuNW/PU films, it can be concluded that strong adhesion between nanowires and substrate significantly affects the mechanical robustness of CuNW/PU conductors. Also, selecting proper sintering parameters of the light offered not only high electrical property but also good performance for stretching. Considering the excellent mechanical performance of the CuNW/PU conductor, it was used to fabricate flexible devices. A CuNW/PU conductor was attached onto the joint of index finger and the relative resistance change of conductor was recorded (Figure 5a, inset is the optical image). The resistance evolution depended on the movement of finger. It was correspondingly increased when the finger was slowly bended to stretch the CuNW/PU conductor, while the resistance was decreased when the finger was slowly straightened to release the CuNW/PU conductor. During the bending process of finger, some small bending-vibration induced relative resistance change with some small peaks, suggesting the sensitivity of CuNW/PU conductor. Excellent peak-valley



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

curve of resistance change was also obtained corresponding to the big movement of finger. The results implied that the CuNW/PU conductor could be used as e-skin to detect the gesture of finger or articular.

Figure 5 Application of CuNW/PU conductors on strain sensor. (a) Relative resistance response of CuNW/PU conductor to the bending and releasing of finger. Inset shows the photo of CuNW/PU conductor attached onto the joint of index finger. (b) Relative resistance signal recording Morse code of “c” and “u”.

To further discover the possibility of application as e-skin, two CuNW/PU conductors with different sheet resistant of 5.8 and 6.7 Ohm/sq were fixed on index finger and middle finger to generate distinguishable signals. Here, assume the large and small change of resistance to be “dash” and “dot” in Morse code, respectively. The character of “c” (Morse code was dash-dot-dash-dot) was described with electrical signals by bending-releasing finger with the order of middle-index-middle-index (Figure 5b upper panel and Video S1). Also, the character of “u” (Morse code was dot-dot-dash) was also output by bending-releasing movement of fingers with order of index-index-middle (Figure 5b lower panel and Video S2). The results indicate that


Page 22 of 35

Page 23 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


these stretchable CuNW/PU conductors can be easily used in the Robert, health-care, or communication fields. Metal nanowires have been used as heater and gave good performance with small applying voltage

32, 48-49

. Here, a stretchable CuNW/PU conductor with sheet

resistance of 4.7 Ohm/sq was tested as heater under different input voltages (Fig 6a). The size of the CuNW/PU conductors was 15×15 mm2. It is clear the temperature depended on the voltage. It was about 46oC at voltage of 3V, then increased to 78.7 and 102oC when the voltage was went up to 5V and 7V. The CuNW/PU conductor generated thermal energy following the formula Q = U2t/R, where Q, U, t and R represents thermal energy, voltage, time and resistance. In this condition, when the voltage was fixed, smaller resistance would give better performance. Because of the high conductivity of CuNW/PU conductors, the electrical energy was efficiently and rapidly transformed into Joule heat even under small voltage. The inserted infrared images under different voltages clearly showed the temperature evolution (Figure 6a).The stability of the heater was also confirmed by repeated on-off cycles under an applied voltage of 3V (Figure 6b). The peak temperature almost kept at 46 oC after 10 cycles, indicating a good reliability even under current and high temperature. The temperature of 46oC was high enough to be used as articular hyperthermia instrument. High temperature was also useful in the fields of disinfection and sterilization. A patterned heater with the logo of Osaka University was also fabricated on PU substrates (Figure 6c). Without the application of voltage, the temperature on the ginkgo leaf was kept at room temperature. After applying voltage through the Cu



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

electrodes, the temperature only increased along the shape of ginkgo leaf and went up to around 50 oC at the bottom of ginkgo leaf due to the narrow conduction path. The patterned heater saves the waste of CuNWs and enables itself to heat designated area, which can be integrated into various devices and applied into food, clothes, construction materials, medical supplies and so on. Here, a simple and transparent heater glove was realized to warm hands especially at the finger area as shown in Figure6d. When voltage was applied, the glove gave a warm image, which warmed the finger and articular. It is an amazing and desirable glove for those people who need heater to massage the rheumatism, numbness and swelling of hand in the cold winter.

Fig. 6 Application of CuNW/PU conductors as heater. (a) Temperature profiles under applied voltages of 3, 5, and 7V on the heater. Inset shows the infrared images of the heater under different


Page 24 of 35

Page 25 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


voltages. (b) Cycled responses of temperature by switching on/off voltage of 3V. (c) Schematic illustration of the ginkgo leaf shaped heater (top left), the actual photo of the patterned CuNW/PU heater (bottom left), infrared images of the heater when the voltage was off (above right) and on (bottom right). (d) Photo of heater glove wearing on hands (left), infrared images of the glove when the voltage was off (above right) and on (bottom right).

4. Conclusion In summary, we developed a one-step photonic sintering technique to fabricate highly conductive and stretchable CuNW/PU conductors at room temperature in air atmosphere within only 20 µs. The light energy adsorbed by the CuNWs induced the welding between nanowires, removed those oxides and organics on the surface of nanowires, and simultaneously affected the surface state of PU substrate to embed these CuNWs into the PU matrix. The one-step process resulted in high conductivity and strong adhesion CuNW/PU conductors with sheet resistance of 22.1, 4.54 and 2.54 Ohm/sq with transmittance of 78%, 41% and 21%, respectively. The stretchability of CuNW/PU conductors closely depended on the embedding structure, which was affected by the light energy. A CuNW/PU conductor enduring 1000 cycles of stretching/releasing under 10% strain was obtained with slightly increase in resistance. The wearable and stretchable CuNW/PU conductors were used to detect the movement of finger and articular, fine signal output, and made as heater to integrate into various devices applied into food, clothes and medical supplies fields.

Supporting Information Photo of the home-made bending machine, transmittance spectrum of CuNW/PU



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

conductors with various transmittance before and after the photonic sintering, sheet resistance change during the peeling test, SEM images of CuNW network on PU substrate under various strains, relative resistance variation for three samples under stretching statue at 10% strain for 10 cycles, TEM images of fresh prepared CuNWs before and after photonic sintering process.

Acknowledgements Su Ding thanks the financial support from China Scholarship Council for her PhD research in Osaka University. This work was partly supported by the COI Stream Project, Showa Denko K. K. and Grant-in-Aid for Scientific Research (Kaken S, 24226017). The authors are also grateful for financial support from the National Science Foundation of China (Grant No. 51522503) and support from Program for New Century Excellent Talents in University (NCET-13-0175).


Page 26 of 35

Page 27 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References 1.

Bae S,; Kim H.; Lee Y.; Xu X.; Park J.; Zheng Y.; Balakrishnan J.; Lei T.; Kim H. R.; Song Y.; Kim Y.; Kim K. S.; özyilmaz B.; Ahn J.; Hong B. H.; Iijima S. Roll-to-roll Production of 30-inch Graphene Flms for Transparent Electrodes.

Nat. Nanotechnol. 2010, 5, 574-578. 2.

Lee J.; Lee P.; Lee H.; Lee D.; Lee S. S.; Ko S. H. Very Long Ag nanowire Synthesis and Its Application in a Highly Transparent, Conductive and Flexible Metal Electrode Touch Panel. Nanoscale, 2012, 4, 6408-6414.

3.

Amjadi M.; Pichitpajongkit A.; Lee S.; Ryu S.; Park I. Highly Stretchable and Sensitive Strain Sensor Based on Silver Nanowire Elastomer Nanocomposite.

ACS nano, 2014, 8, 5154–5163. 4.

Wang J.; Jiu J.; Nogi M.; Sugahara T.; Nagao S.; Koga H.; He P.; Suganuma K. A Highly Sensitive and Flexible Pressure Sensor with Electrodes and Elastomeric Interlayer Containing Silver Nanowires. Nanoscale, 2015, 7, 2926-2932.

5.

Yao S.; Zhu Y. Wearable Multifunctional Sensors Using Printed Stretchable Conductors Made of Silver Nanowires. Nanoscale, 2014, 6, 2345-2352.

6.

Someya T.; Sekitani T.; Iba S.; Kato Y.; Kawaguchi H.; Sakurai T. A large-area, Flexible Pressure Sensor Matrix with Organic Field-Effect Transistors for Artificial Skin Applications. PNAS, 2004, 101, 9966-9970.

7.

Takei K.; Takahashi T.; Ho J. C.; Ko H.; Gillies A. G.; Leu P. W.; Fearing R. S.; Javey A. Nanowire Active-Matrix Circuitry for Low-Voltage Macroscale



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Artiﬁcial Skin. Nat. mater. 2010, 9, 821-826. 8.

Lee M.; Lee K.; Kim S.; Lee H.; Park J.; Choi K.; Kim H.; Kim D.; Lee D.; Nam S.; Park J. High-Performance, Transparent, and Stretchable Electrodes Using Graphene-Metal Nanowire Hybrid Structures. Nano Lett. 2013, 13, 2814-2821.

9.

Rogers J. A.; Someya T.; Huang Y. Materials and Mechanics for Stretchable Electronics. Science, 2010, 327, 1603-1607.

10. Xu F.; Wang X.; Zhu Y.; Zhu Y. Wavy Ribbons of Carbon Nanotubes for Stretchable Conductors. Adv. Funct. Mater. 2012, 22, 1279-1283. 11. Lim S.; Son D.; Kim J.; Lee Y. B.; Song J.; Choi S.; Lee D. J.; Kim J. H.; Lee M.; Hyeon T.; Kim D. Transparent and Stretchable Interactive Human Machine Interface Based on Patterned Graphene Heterostructures. Adv. Funct. Mater.

2015, 25, 375-383. 12. Kim D.; Xiao J.; Song J.; Huang Y.; Rogers J. A. Stretchable, Curvilinear Electronics Based on Inorganic Materials. Adv. Mater. 2010, 22, 2108-2124. 13. Hu W.; Niu X.; Zhao R.; Pei Q. Elastomeric Transparent Capacitive Sensors based on An Interpenetrating Composite of Silver Nanowires and Polyurethane.

Appl. Phys. Lett. 2013, 102, 083303. 14. Zhang Y.; Sheehan C. J.; Zhai J.; Zou G.; Luo H.; Xiong J.; Zhu Y. T.; Jia Q. X. Polymer-Embedded Carbon Nanotube Ribbons for Stretchable Conductors. Adv.

Mater. 2010, 22, 3027-3031. 15. Cai L.; Song L.; Luan P.; Zhang Q.; Zhang N.; Gao Q.; Zhao D.; Zhang X.; Tu


Page 28 of 35

Page 29 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


M.; Yang F.; Zhou W.; Fan Q.; Luo J.; Zhou W.; Ajayan P. M.; Xie S. Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection. Sci. Rep. 2013, 3, 3048. 16. Kim K. S.; Zhao Y.; Jang H.; Lee S. Y.; Kim J. M.; Kim K. S.; Ahn J.; Kim P.; Choi J.; Hong B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Nature 2009, 457, 706-710. 17. Xu F.; Zhu Y. Highly Conductive and Stretchable Silver Nanowire Conductors.

Adv. Mater. 2012, 24, 5117-5122. 18. Hu W.; Wang R.; Lu Y.; Pei Q. An Elastomeric Transparent Composite Electrode Based on Copper Nanowires and Polyurethane. J. Mater. Chem. C

2014, 2, 1298-1305. 19. Lee P.; Lee J.; Lee H.; Yeo J.; Hong S.; N. K. Hyun.; Lee D.; Lee S. S.; Ko S. H. Highly Stretchable and Highly Conductive Metal Electrode by Very Long Metal Nanowire Percolation Network. Adv. Mater. 2012, 24, 3326–3332. 20. Lee M.; Lee K.; Kim S.; Lee H.; Park J.; Choi K.; Kim H.; Kim D.; Lee D.; Nam S.; Park J. High-Performance, Transparent, and Stretchable Electrodes Using Graphene-Metal Nanowire Hybrid Structures. Nano Lett. 2013, 13, 2814-2821. 21. Chen R.; Das S. R.; Jeong C.; Khan M. R.; Janes D. B.; Alam M. A. Co-percolating Graphene-Wrapped Silver Nanowire Network for High Performance, Highly Stable, Transparent Conducting Electrodes. Adv. Funct.

Mater. 2013, 23, 5150-5158.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22. Kholmanov I. N.; Domingues S. H.; Chou H.; Wang X.; Tan C.; Kim J.; Li H.; Piner R.; Zarbin A. J. G.; Ruoff R. S. Reduced Graphene Oxide/Copper Nanowire Hybrid Films as High-Performance Transparent Electrodes. ACS

nano 2013, 7, 1181-1186. 23. Kim K. K.; Hong S.; Cho H. M.; Lee J.; Suh Y. D.; Ham J.; Ko S. H. Highly Sensitive and Stretchable Multidimensional Strain Sensor with Prestrained Anisotropic Metal Nanowire Percolation Networks. Nano Lett. 2015, 15, 5240-5247. 24. Zhu Y.; Qin Q.; Xu F.; Fan F.; Ding Y.; Zhang T.; Wiley B. J.; Wang Z. L. Size Effects on Elasticity, Yielding, and Fracture of Silver Nanowires: In Situ Experiments. Phys. Rev. B 2012, 85, 045443. 25. Chen S.; Liao Y. Highly Stretchable and Conductive Silver Nanowire Thin Films Formed by Soldering Nano mesh Junctions. Phys. Chem. Chem. Phys.

2014, 16, 19856-19860. 26. Liang J.; Li L.; Niu X.; Yu Z.; Pei Q. Elastomeric Polymer Light-Emitting Devices and Displays. Nat. Photonics 2013, 7, 817-824. 27. Khaligh H. H.; Goldthorpe I. A. Failure of Silver Nanowire Transparent Electrodes under Current Flow. Nanoscale Res. Lett. 2013, 8, 235. 28. 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. 29. Won Y.; Kim A.; Yang W.; Jeong S.; Moon J. A Highly Stretchable, Helical


Page 30 of 35

Page 31 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Copper Nanowire Conductor Exhibiting a Stretchability of 700%. NPG Asia

Mater. 2014, 6, e132. 30. Cheng Y.; Wang S.; Wang R.; Sun J.; Gao L. Copper Nanowire Based Transparent Conductive Films with High Stability and Superior Stretchability. J.

Mater. Chem. C 2014, 2, 5309-5316. 31. Yang Y.; Ding S.; Araki T.; Jiu J.; Sugahara T.; Wang J.; Vanfleteren J.; Sekitani T.; Suganuma K. Facile Fabrication of Stretchable Ag Nanowire/Polyurethane Electrodes Using High Intensity Pulsed Light. Nano Res. 2015, DOI: 10.1007/s12274-015-0921-9. 32. Han S.; Hong S.; Yeo J.; Kim D.; Kang B.; Yang M.; Ko S. H. Nanorecycling: Monolithic Integration of Copper and Copper Oxide Nanowire Network Electrode through Selective Reversible Photothermochemical Reduction. Adv.

Mater. 2015, DOI: 10.1002/adma.201503244. 33. Jiu J.; Nogi M.; Sugahara T.; Tokuno T.; Araki T.; Komoda N.; Suganuma K.; Uchida H.; Shinozaki K. Strongly Adhesive and Flexible Transparent Silver Nanowire Conductive Films Fabricated with A High-Intensity Pulsed Light Technique. J. Mater. Chem. 2012, 22, 23561-23567. 34. Ding S.; Jiu J.; Tian Y.; Sugahara T.; Nagao S.; Suganuma K. Fast Fabrication of Copper Nanowire Transparent Electrodes by A High Intensity Pulsed Light Sintering Technique in Air. Phys. Chem. Chem. Phys. 2015, 17, 31110-31116. 35. Jiang Z.; Tian Y.; Ding S. Synthesis and Characterization of Ultra-Long and Pencil-Like

Copper

Nanowires

with

a

Penta-Twinned


Structure

by


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 35

Hydrothermal Method. Mater. Lett. 2014,136, 310-313. 36. Chang Y.; Lye M. L.; Zeng H. C. Large-Scale Synthesis of High-Quality Ultralong Copper Nanowires. Langmuir 2005, 21, 3746-3748. 37. Won Y.; Kim A.; Lee D.; Yang W.; Woo K.; Jeong S.; Moon J. Annealing-Free Fabrication of Highly Oxidation-Resistive Copper Nanowire Composite Conductors for Photovoltaics. NPG Asia Mater. 2014, 6, e105. 38. Kevin M.; Lim G. Y. R.; Ho G. W. Facile Control of Copper Nanowire Dimensions via the Maillard Reaction: Using Food Chemistry for Fabricating Large-Scale

Transparent

Flexible

Conductors.

Green

Chem. 2015, 17,

1120-1126. 39. Choi S.; Park J.; Hyun W.; Kim J.; Kim J.; Lee Y. B.; Song C.; Hwang H. J.; Kim J. H.; Hyeon T.; Kim D. Stretchable Heater Using Ligand-Exchanged Silver Nanowire Nanocomposite for Wearable Articular Thermotherapy. ACS

Nano 2015, 9, 6626-6633. 40. Huang

G.;

Xiao

H.;

Fu

S.

Wearable

Electronics

of

Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing.

Sci. Rep. 2015, 5, 13971. 41. Tang Y.; Gong S.; Chen Y.; Yap L. W.; Cheng W. Manufacturable Conducting Rubber Ambers and Stretchable Conductors from Copper Nanowire Aerogel Monoliths. ACS nano 2014, 8, 5707-5714. 42. Song C.; Ok K.; Lee C.; Kim Y.; Kwak M.; Han C. J.; Kim N.; Ju B.; Kim J. Intense-Pulsed-Light Irradiation of Ag Nanowire-Based Transparent Electrodes


Page 33 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for Use in Flexible Organic Light Emitting Diodes. Org. Electron. 2015, 17, 208-215. 43. Jiu J.; Sugahara T.; Nogi M.; Araki T.; Suganuma K.; Uchida H.; Shinozaki K. High-Intensity Pulse Light Sintering of Silver Nanowire Transparent Films on Polymer Substrates: the Eﬀect of the Thermal Properties of Substrates on the Performance of Silver Films. Nanoscale, 2013, 5, 11820-11828. 44. Ryu J.; Kim H.; Hahn H. T. Reactive Sintering of Copper Nanoparticles Using Intense Pulsed Light for Printed Electronics. J. Electron. Mater. 2011, 40, 42-50. 45. Liu Z.; Yang Y.; Liang J.; Hu Z.; Li S.; Peng S.; Qian Y. Synthesis of Copper Nanowires via A Complex-Surfactant-Assisted Hydrothermal Reduction Process. J. Phys. Chem. B 2003, 107, 12658-12661. 46. Ye E.; Zhang S.; Liu S.; Han M. Disproportionation for Growing Copper Nanowires and their Controlled Self-Assembly Facilitated by Ligand Exchange.

Chem. Eur. J. 2011, 17, 3074-3077. 47. Yin Z.; Song S. K.; You D.; Ko Y.; Cho S.; Yoo J.; Park S. Y.; Piao Y.; Chang S. T.;

Kim Y. S. Novel Synthesis, Coating, and Networking of Curved Copper

Nanowires for Flexible Transparent Conductive Electrodes. Small 2015, 11, 4576-4583. 48. Choi S.; Park J.; Hyun W.; Kim J.; Kim J.; Lee Y. B.; Song C.; Hwang H. J.; Kim J. H.;

Hyeon T.; Kim D. Stretchable Heater Using Ligand-Exchanged

Silver Nanowire Nanocomposite for Wearable Articular Thermotherapy. ACS

nano 2015, 9, 6626-6633.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

49. Huang Q.; Shen W.; Fang X.; Chen G.; Guo J.; Xu W.; Tan R.; Song W. Highly Flexible and Transparent Film Heaters Based on Polyimide Films Embedded with Silver Nanowires. RSC Adv. 2015, 5, 45836-45842.


Page 34 of 35

Page 35 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents graphic


One-Step Fabrication of Stretchable Copper Nanowire Conductors by

Recommend Documents