Continuous Draw Spinning of Extra-Long Silver Submicron Fibers with

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Continuous dry spinning of extra-long silver submicron fibers with micrometer patterning capability Xiaopeng Bai, Suiyang Liao, Ya Huang, Jianan Song, Zhenglian Liu, Minghao Fang, Chencheng Xu, Yi Cui, and Hui Wu Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b05205 • Publication Date (Web): 06 Feb 2017 Downloaded from http://pubs.acs.org on February 7, 2017

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Continuous dry spinning of extra-long silver submicron fibers with micrometer patterning capability Xiaopeng Bai,1 Suiyang Liao,1 Ya Huang,1 Jianan Song,1 Zhenglian Liu,2 Minghao Fang,2 Chencheng Xu,1 Yi Cui,3 and Hui Wu1,* 1

State Key Laboratory of New Ceramics and Fine Processing, School of Materials

Science and Engineering, Tsinghua University, Beijing 100084, China. 2

School of Materials Science and Technology, China University of Geosciences,

Beijing, 100083 China. 3

Department of Materials Science and Engineering, Stanford University, Stanford,

California 94305, USA. * Email: [email protected] ABSTRACT: Ultrathin metal fibers can serve as highly conducting and flexible current and heat transport channels, which are essential for numerous applications ranging from flexible electronics to energy conversion. Although industrial production of metal fibers with diameters of down to 2 µm is feasible, continuous production of high-quality and low-cost nanoscale metal wires is still challenging. Herein, we report the continuous dry spinning of highly conductive silver submicron fibers with the minimum diameter of ~200 nm and length of more than kilometers. We obtained individual AgNO3/polymer fibers by continuous drawing from an aqueous solution at a speed of up to 8 m/s. With subsequent heat treatment, freestanding Ag submicron fibers with high mechanical flexibility and electric conductivity have been obtained. Woven mats of aligned Ag submicron fibers were used as transparent electrodes with high flexibility and high performance, with sheet resistance of 7 Ω sq−1 at a transparency of 96 %. Continuous dry spinning opened new avenues for scalable, flexible, and ultralow-cost fabrication of extra-long conductive ultrathin metal fibers. KEYWORDS: Silver submicron fibers, Continuous dry spinning, flexible electronics, micrometer patterning Ultrathin metal wires have been intensely studied according to their unique mechanical1, electrical2, magnetic3 and optical properties4, and have been further

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developed for applications in numerous fields, for instance, transparent electrodes5, nanoelectronic circuits6, artificial electronic skin7, sensitive strain sensor8, flexible energy storage and conversion9,10. For these practical applications and fundamental studies, the ability of controllable and facile fabrication of ultrathin metal wires are crucial. Particularly, small diameters, controllable orientation and patterning, as well as high aspect ratios of metal wires are highly desired. Multiple techniques have been developed to produce ultra-thin metal and other conducting wires/fibers, for examples, electrospinning11-14, melt spinning15, wet spinning16, The electrospinning method has been widely used for the fabrication of ultra-thin fibers of polymer, ceramic, metal and carbon17-19. However, producing the delicate and precise alignment of the electrospun fibers remains to be an important challenge. Melt spinning and traditional wet spinning can obtain polymer wires at high speed and efficiency, however, the diameter of the fibers are usually more than 10 µm20. More recently, new techniques have been developed to achieve ultrathin conductive wires with uniform alignments, such as lithography21, ink-jet printing22, robocasting23, template synthesis24, and spray-printing25. While these strategies can produce aligned conductive nanowires with high quality and high density, these methods are usually time-consuming, expensive, and relies on complex process of coating and surface treatments. Direct writing of metallic fibers also attracted considerable attention, various maneuverable and low-cost writing instruments, such as pencil26,27, fountain pen28,29, brush pen30, and ball pen31, have been used to form uniform fiber arrays with low-cost, and enabled facile and precise deposition of conductive wires on different substrates, including paper and plastics. However, the pitch between wires is commonly more than 100 µm, and the writing speed is slow and usually within the range of ~1 cm/s to 2 cm/s32-34. Another problem for these lithography, printing or writing technology to fabricate nano-patterns is that a solid substrate is required to support the materials, the generation of freestanding, suspended ultrathin fibers and patterns are still very challenging. Herein, we report the fabrication of kilometers long ultrathin silver fibers and patterns by continuous dry spinning process. Dry spinning has been used for the


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preparation of submicron scale polymer fiber, for instance PMMA fiber35, PLLA fiber36, PS fiber37, however, the extra-long metal submicron fiber less researched. In addition, the length of obtained suspended polymer fibers is generally less than 2mm by a direct drawing process. The free-standing silver precursor nanofiber arrays obtained by continues dry spinning can bridge a longer distance (10 cm), furthermore, continues dry spinning can arrange fibers into uniform arrays with a pitch of down to 5 microns in our present experimental conditions, while the ability of direct drawing is limited by the positioning of the pulling rod, generally at the level of hundreds of microns. The continuous dry spinning can produce consecutive submicron fibers with maximum speed of 8 m/s. Patterned silver fiber meshes have been obtained to form woven mats, which serve as transparent electrode with high performance (7 Ω/sq at 96 %), high flexibility and high stretchability (mechanical stable with strain of ~130 %). The fabrication of the silver submicron fiber arrays is based on the continuous dry spinning method, which is illustrated in Figure 1a, which can produce continuous submicron fibers with high speed, and does not need to use the high voltage or other auxiliary measures, only balance of rotational speed of substrate and solution flow, enable continuously spinning of submicron fibers uninterruptly. The extra-long silver ultrathin fibers were obtained by sintering AgNO3/PVP precursor fibers in the muffle furnace. The spinnability of the precursor solution has close relationship with molecular weight of polymer, and the long chain molecule is more likely to be entangled than the short chain molecule. For one-dimensional materials, a stream of liquid flow shows Rayleigh instability, which has a closed relationship about the surface tension of the liquid, a higher surface tension tends to break the continuity of the fiber, to tune the surface tension of the precursor solution, surface active agent was applied to the preparation of the precursor solution, sodium dodecyl sulfate was added in the deionized water to facilitate easy-drawing of the solution by reducing the surface tension.

The

digital photo of preparation process of extra-long

AgNO3/polymer submicron fibers is shown in Figure S1. Continuous dry spinning has many excellent advantages over electrospinning, including elimination of


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high-voltage or conductive collector substrate and rapid production of orderly matrix of fibers on user-defined substrate. Furthermore, extra-long single fiber with maximum speed of 8 m/s in ambient condition can be rapidly manufactured, as shown in Video S1. The other advantage about continuous dry spinning is that the free-standing individual nanofiber can be obtained by hand drawing (Video S2). Figure 1b shows the actual preparation process and excellent transmittance of the silver nanofiber arrays which are twisted on the hollowed-out stainless steel sheet, the details that the fibers wrapped the edge of the rotatory substrate are shown in Figure S2. The digital photo of the double needles and four needles spun simultaneously is shown in Figure S3, we believe that it will be possible to spinning of fibers with hundreds of thousands of needle at the same time, which will greatly improve production efficiency. The SEM image of the fibers shows that the fiber did not undergo further stretching after deposition. The overall diameter along the fiber axis is uniform (Figure S4), and the surface of fibers is smooth. Since there is no signs of tension, so we speculate that the tensile process of fibers occur before they are deposited on the substrate, which means that after solution came out from the injection needle, and before attached to the substrate, in the short period of time, it has experienced rapid solvent evaporation and fiber curing process, this requires that the selected solvent properties can be rapidly evaporate at room temperature, or need auxiliary heating measures to accelerate the process of solvent evaporation, achieve the goal of curing fibers, this is also related to the humidity of the experimental environment, temperature conditions, as well as the distance from the injector to the collection substrate. Our current system of humidity is controlled in less than or equal to 60% humidity will be more easily to spinning of continues fibers , because of the solvent is acetonitrile, which will fastly evaporate at room temperature, so there is no heating measures, the distance of syringe to substrate depend on the size of substrate. The free-standing silver precursor submicron fiber arrays can bridge a long distance (10 cm) and possess high transmittance (97 %). Different spacing of the submicron fibers is easily controlled by adjusting the forward speed of the substrate and rotatory speed of the substrate. A minimum spacing of ~5 µm is achieved. In theory, the fibers


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spacing can be infinitely close, but the uniform spacing is 5 µm due to the device error in our lab. Typically, fibers deposited on the edge of the substrate bear a larger shear stress and can be more easily affected by touching with the substrate. Under a low rotation speed, the fibers receive a low shear stress, fibers deposited on the edge of the substrate still maintain the intact of the morphology. However, speeding up the rotation speed of the substrate, will find that the fibers have not completely dry before deposited onto the substrate, make the surface of fiber has certain degree of viscosity, leading to partly bonding together between adjacent fibers, as shown in Figure S5. According to the experience of experiment, for our silver precursor, we observed the rotation speed of substrate below 1000 r/m can avoid the problem of adhesion between adjacent fibers, also including fibers and substrate, the uniform fibers arrays on the edge of the substrate as shown in Figure S6. Meanwhile, along with the rotational speed of the substrate increased, the diameter of the fiber significantly reduced, as shown in Figure 1c, the constant transformation of liquid cone on the nozzle into a fiber is shown in Video S3. Figure 1d demonstrates the precise spacing distribution based rotational speed of the substrate (0.1, 1.0, and 3.0 m/s). Under the same rotational speed (500 RPM) of the substrate, we explored the relationship between solution viscosity and fiber diameter, as shown in Figure 1e, the fiber diameter increased following increase of the solution viscosity. Maintaining the same viscosity (500 cP) of the solution while increasing the rotational speed of substrate, causing the shear stress acting on the fiber to be negatively compared with the fiber diameter (Figure 1f). To find the optimal sintering temperature of AgNO3/polymer fibers, we analyzed the DTA-TG curves of AgNO3/polymer fibers and found that two steep peaks were involved in the mass loss (Figure S7). The first steep peak occurred in nearly 200 °C, which indicates that there is a mass loss of approximately 65%. Meanwhile, the second steep peak occurred in nearly 400 °C, which indicates a mass loss of only approximately 25%. The microstructural evolution of the silver submicron fibers on the basis of sintering temperature shows that as the temperature increases from 250 °C to 350 °C, the average size of silver particle in the surface of fibers gradually


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increases (Figure S8), The X-ray diffraction (XRD) patterns of the crystal phase of AgNO3/PVP precursor composite fibers are shown in Figure S9. The XRD patterns of before and after sintering samples are totally different. The peak of the fiber patterns corresponds well to the fcc phase of metal silver after calcination. Raman test shows that before sintering, the AgNO3/PVP precursor composite fibers only have Raman active mode at 1039 cm−1 (NO3− ion), whereas there are two Raman active modes at 1343 cm−1 and 1572 cm−1, which corresponds to amorphous carbon after sintering. After the silver submicron fibers were calcinated at 250°C for 2 h, the intensity of amorphous carbon peak becomes inappreciable, as shown in Figure S10. The position of the chemical bonding state of silver nanofiber mesh calcinated at 250 °C was tested using X-ray photoelectron spectroscopy (XPS). As shown in Figure S11, the two peaks at 368.12 eV and 374.12 eV in the Ag 3d XPS spectrum of silver fibers correspond to that of Ag 3d5/2 and Ag 3d3/2 respectively. The presence of the residual C and O elements in the silver nanofiber are minute enough to a negligible extent in comparison with Ag0 (368.25 eV and 374.25 eV). Figure S12 shows the TEM image of a single silver fiber, which further confirmed that the silver nanofiber composed of small silver grains integrated tightly. The HRTEM image indicates that the silver grain reveals clear lattice fringes, which corresponds to the interplanar spacing at d=0.235 nm. The surface of the silver fiber reveals the existence of the amorphous carbon film, with thickness lesser than 10 nm, which greatly improved the surface smoothness and toughness of silver fiber. To demonstrate the direct-spinning technique, Figure 2a shows a typical sample of a silver submicron fibers mesh with excellent photoelectric conductivity and regular mesh structure. The SEM image of silver submicron fibers mesh at a scale bar of 100 µm shows that the distribution of fiber spacing is uniform, the spacing deviation of fiber is 2um, the diameter deviation of fiber is 100nm, The deviation of the fibers diameter and fiber spacing mainly depend on the fluid volume uneven during to internal pressure of the syringe needle and the air disturbance during the spinning progress, as well as the device error. Embedded SEM image indicates that the silver crystalline grains firmly combined with each other. The junctions of silver fibers are


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naturally interconnected after calcination, which provides the path for electron transportation within different well-connected individual silver fibers, as shown in Figure 2b. To verify whether the fiber diameter is controllable, Figure 2c shows the SEM image of transverse and longitudinal fiber arrays with different diameters (transverse fiber is 2 µm; longitudinal fiber is 500 nm). AFM image shows that the silver submicron fibers mesh has almost negligible altitude intercept, proving that the surface of fiber mesh has high degree of smoothness (Figure 2d). To demonstrate the distribution of silver elements in the silver submicron fibers mesh is uniform, we characterized the silver mapping of the nanofiber mesh, the silver element is uniformly distributed and completely connected into the wire (Figure 2e). Transparent conductors have been indispensable in various devices, such as touch panels, display screens, and solar cells38,39. Indium tin oxide (ITO) has been the most widely used material for transparent electrodes. However, ITO is difficult to further develop in flexible electronics because of high cost of raw material and the innate brittleness of ceramics39,40. Compared with ceramics, metals are ductile, and silver is the most conductive among all metals. The transparent electrode-based silver nanowires (AgNWs) exhibited superior properties than ITO41. Transparent electrode-based AgNWs can be used as an alternative to conventional ITO based on their low sheet resistance (10 < Rs < 50 Ω/sq) and high transmittance (T > 80 %)41-51. However, AgNW-based electrodes still present several of drawbacks, such as low uniformity, undesirable surface roughness, and the inevitable optical haze based on light scattering. In addition, the production volume is limited by the high cost of AgNWs. Transparent electrodes based highly oriented silver submicron fibers arrays have better conductivity because there are less junction resistances. In addition, extra-long silver fibers have superior mechanical compliance according to percolation theory, Moreover, optical haze of the transparent electrodes will also be greatly reduced owing to the special array structure. To investigate the photoelectric property of silver submicron fibers mesh, we manufactured samples of different transmittance and tested their sheet resistance. As shown in Figure 3a, the sheet resistance as a function of transmittance at a wavelength


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of 550 nm is superior to state-of-the-art device-level ITO52, and is also more excellent compared with other transparent conductive electrodes, such as graphene-based electrodes53, silver nanotrough54, solution-processed AgNWs55, and CNT films56. The excellent performance of silver nanofiber mesh electrodes is attributed to the perfect connection of junctions between individual silver fibers. Moreover, based on percolation theory, silver submicron fibers mesh has prominent flexibility because of the ultra-high aspect ratio. It is noteworthy that the sheet resistance decreased when sintering temperature was augmented (Figure 3b). However, the flexibility of silver fiber reduced sharply, and the toughness also markedly decreased. Based on experiments, the sample with heat treatment for 2 h have a good balance between the flexibility and electrical conductivity. The silver submicron fibers mesh was transferred onto a PET substrate to characterize their stability to the flexibility and stretchability of silver fiber mesh. The minimum bending diameter is near to 1 mm (Figure 3c). After the PET substrate is repeatedly bended to 2 mm for 10000 times (Figure 3d), no obvious degradation of conductivity was noted. However, the metal film of the spattered platinum with thickness of 300nm, as a reference, had severely degraded electrical conductivity. The stretchability of the silver nanofiber mesh was examined by transferring the silver submicron fibers mesh onto a substrate of polydimethylsiloxane (PDMS) film without further treatment. Sheet resistance only increased by 12% after 30% uniaxial stretching, as shown in Figure 3e. The sheet resistance is measured through four-probe method, and the adopted value of sheet resistance is the average value of five measurements. Figure 4a shows that the silver submicron fibers mesh can be successfully attached in the surfaces of different materials, including PI film, PET film, and nylon mesh. Figure S13 further shows that the silver submicron fibers mesh can be firmly attached in cambered quartz plate, green leaves, and gloves. Figure 4b shows the freestanding silver mesh, which can be easily spread out after wrinkled (the size of fibers mesh = 8 cm×8 cm). Silver mapping proved that the silver fibers did not break after the fiber meshes were rolled. The silver fibers mesh was spread to further demonstrate the


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flexibility and transparency of silver fiber mesh, and the silver fiber mesh still had 89% transparency after it was folded twice (Figure 4c). Video S4 shows the high transparency and flexibility of silver fibers mesh. The SEM image of folded fiber mesh, which shows that there is no evidence of fracture in the folded part of silver fiber mesh, is shown in Figure 4d. Figure 5a shows that the 5 cm-long, 400 nm-diameter single silver fiber functioned in a LED lamp. The fiber is too thin to be seen by the naked eye. Through close-up of the digital photos, the single fiber still can hardly be seen. The resistivity of single silver fiber is 42.19 nΩ·m (calculated through R=ρL/S). The resistivity of bulk silver under the condition of 20 °C is 15.87nΩ·m, so the resistivity of silver fiber is about three times compared the resistivity of bulk silver (Figure S14). Lower electrical conductivity compared the bulk silver possibly due to the effect of residual carbon and electron scattering. The Figure 5b shows the single fiber winding process and the optical image of single fiber arrays. The single 500 m-long invisible fiber is enwound on the glass rod, as shown in Figure 5c. Although the length of the glass rod is only 20 cm, according to the processing parameters, we calculated the theoretical length of the single fiber to be 528 m. To investigate whether the single fiber is broken after it is enwound, we made a 28 m-long single precursor fiber enwound on the ceramic rod (the length of fiber calculated on the basis of the preparation parameters), which acted as a conductor wire after heat treatment and connecting a LED lamp. After applying a voltage of 5 V to the whole circuit, LED lamp is successfully worked, as shown in Figure 5d, which indicates the extra-long silver nanofiber enwound on the ceramic rod no cracks or break. The spacing in fiber arrays is approximately 5 µm by SEM observation, as shown in Figure 5e. To explore more application value of extra-long silver nanofiber, a fast-heating device is manufactured by entwisting the extra-long silver precursor fibers on the glass substrate with subsequent heat treatment at 250 °C for 2 hour. The sheet resistance of silver fiber arrays is 20 Ω/sq, we verified that the silver submicron fiber arrays possess fast thermal response at low input voltage, as shown in Figure S15. The direct current voltage was supplied to the silver submicron fibers arrays by painting


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silver paste on the edge of silver fiber arrays. The infrared thermal imaging camera records the thermal image of silver nanofiber arrays powered by an applied voltage of 0.5 V, 1.0 V, and 2.0 V. The temperature of silver nanofiber arrays rapidly increased to 136 °C, 141 °C, and 144 °C within 3 s, utilizing the advantage of rapid heating-up of silver fiber arrays, make it possible as a window defrosters. In conclusion, finitely long and highly conductive silver submicron fibers with minimum diameter of ~200 nm and length of more than kilometers through continuous dry spinning has been demonstrated. We prepared a large-sized silver submicron fibers mesh (8 cm×8 cm), which exhibits excellent optical and electrical properties and also has remarkable flexibility and tensile properties, made with extra-long AgNO3/polymer fibers after heat treatment. Such silver nanofiber mesh can be used in flexible solar cells, touch screen and touch sensors, and flat panel displays. The extra-long highly conductive Ag submicron fibers can directly serve as highly conducting and flexible current and heat transport channels. The continuous dry spinning used to prepare extra-long metal submicron fibers has great potential for numerous applications, ranging from flexible electronics to energy conversion.


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ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. Details of sample preparation, data acquisition, and the data analysis. (PDF) The production of continuous single submicron fibers with high speed (8m/s) collected on the rotatory roller. (AVI) Single, continuous and free-standing individual fiber obtained easily by hand drawing. (AVI) The constant transformation of liquid cone on the nozzle tip. (AVI) Highly transparent and flexible silver submicron fibers mesh. (AVI) AUTHOR INFORMATION Corresponding author * Email: [email protected] Author Contributions H.W. and Y.C. designed the research; X.B and S.L. synthesized and characterized the specimens; X.B. and Y.H. performed mechanical testing. All authors analyzed data, discussed the results and commented on the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This study was supported by the National Basic Research of China (Grant Nos. 2015CB932500 and 2013CB632702), National Natural Science Foundations of China (Grant Nos. 51302141).


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Woo, E. Science. 2000, 290, (5499), 2123-2126. (23) Ellis, J.; Mavromatos, N. E.; Nanopoulos, D. V.; Sakharov, A. S. Nature. 2004, 428, (6981). (24) Tao, S. L.; Desai, T. A. Nano letters. 2007, 7, (6), 1463-1468. (25) Park, M.; Im, J.; Shin, M.; Min, Y.; Park, J.; Cho, H.; Park, S.; Shim, M. B.; Jeon, S.; Chung, D. Y.; Bae, J.; Park, J.; Jeong, U.; Kim, K. Nat Nanotechnol. 2012, 7, (12), 803-9. (26) Lin, C. W.; Zhao, Z.; Kim, J.; Huang, J. Sci Rep 2014, 4, 3812. (27) Kurra, N.; Kulkarni, G. U. Lab Chip 2013, 13, (15), 2866-73. (28) Han, J.-W.; Kim, B.; Li, J.; Meyyappan, M. The Journal of Physical Chemistry C 2012, 116, (41), 22094-22097. (29) Warren, H.; Gately, R. D.; Moffat, H. N.; in het Panhuis, M. RSC Advances 2013, 3, (44), 21936. (30) Kim, S. S.; Na, S. I.; Jo, J.; Tae, G.; Kim, D. Y. Advanced Materials. 2007, 19, (24), 4410-4415. (31) Russo, A.; Ahn, B. Y.; Adams, J. J.; Duoss, E. B.; Bernhard, J. T.; Lewis, J. A. Adv Mater 2011, 23, (30), 3426-30. (32) Qi, Z.; Zhang, F.; Di, C.-a.; Wang, J.; Zhu, D. Journal of Materials Chemistry C 2013, 1, (18), 3072. (33) Cho, D.-Y.; Eun, K.; Choa, S.-H.; Kim, H.-K. Carbon. 2014, 66, 530-538. (34) Takabayashi, Y.; Ganin, A. Y.; Jeglič, P.; Arčon, D.; Takano, T.; Iwasa, Y.; Ohishi, Y.; Takata, M.; Takeshita, N.; Prassides, K. Science. 2009, 323, (5921), 1585-1590. (35) Berry, S. M.; Harfenist, S. A.; Cohn, R. W.; Keynton, R. S. Journal of Micromechanics and Microengineering 2006, 16, (9), 1825-1832. (36) Horáček, I. Journal of applied polymer science 1994, 54, (11), 1759-1765. (37) Nain, A. S.; Wong, J. C.; Amon, C.; Sitti, M. Applied Physics Letters 2006, 89, (18), 183105. (38) Ye, S.; Rathmell, A. R.; Chen, Z.; Stewart, I. E.; Wiley, B. J. Adv Mater. 2014, 26, (39), 6670-87. (39) Kumar, A.; Zhou, C. ACS nano. 2010, 4, (1), 11-14. (40) Peng, H.; Dang, W.; Cao, J.; Chen, Y.; Wu, D.; Zheng, W.; Li, H.; Shen, Z. X.; Liu, Z. Nat Chem. 2012, 4, (4), 281-6. (41) Hong, B. H.; Bae, S. C.; Lee, C.-W.; Jeong, S.; Kim, K. S. Science. 2001, 294, (5541), 348-351. (42) Sun, Y.; Mayers, B.; Herricks, T.; Xia, Y. Nano letters. 2003, 3, (7), 955-960. (43) van de Groep, J.; Spinelli, P.; Polman, A. Nano Lett. 2012, 12, (6), 3138-44. (44) De, S.; Higgins, T. M.; Lyons, P. E.; Doherty, E. M.; Nirmalraj, P. N.; Blau, W. J.;


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Boland, J. J.; Coleman, J. N. ACS nano. 2009, 3, (7), 1767-1774. (45) Hu, L.; Kim, H. S.; Lee, J.-Y.; Peumans, P.; Cui, Y. ACS nano. 2010, 4, (5), 2955-2963. (46) Leem, D. S.; Edwards, A.; Faist, M.; Nelson, J.; Bradley, D. D.; de Mello, J. C. Adv Mater. 2011, 23, (38), 4371-5. (47) Gaynor, W.; Hofmann, S.; Christoforo, M. G.; Sachse, C.; Mehra, S.; Salleo, A.; McGehee, M. D.; Gather, M. C.; Lussem, B.; Muller-Meskamp, L.; Peumans, P.; Leo, K. Adv Mater. 2013, 25, (29), 4006-13. (48) Yu, Z.; Zhang, Q.; Li, L.; Chen, Q.; Niu, X.; Liu, J.; Pei, Q. Adv Mater. 2011, 23, (5), 664-8. (49) Wu, H.; Zhang, R.; Liu, X.; Lin, D.; Pan, W. Chemistry of materials. 2007, 19, (14), 3506-3511. (50) Krantz, J.; Richter, M.; Spallek, S.; Spiecker, E.; Brabec, C. J. Advanced Functional Materials. 2011, 21, (24), 4784-4787. (51) Hsu, P. C.; Liu, X.; Liu, C.; Xie, X.; Lee, H. R.; Welch, A. J.; Zhao, T.; Cui, Y. Nano Lett 2015, 15, (1), 365-71. (52) Minami, T. Thin Solid Films. 2008, 516, (17), 5822-5828. (53) Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Kim, H. R.; Song, Y. I.; Kim, Y. J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S. Nat Nanotechnol. 2010, 5, (8), 574-8. (54) Wu, H.; Kong, D.; Ruan, Z.; Hsu, P. C.; Wang, S.; Yu, Z.; Carney, T. J.; Hu, L.; Fan, S.; Cui, Y. Nat Nanotechnol. 2013, 8, (6), 421-5. (55) Guo, F.; Azimi, H.; Hou, Y.; Przybilla, T.; Hu, M.; Bronnbauer, C.; Langner, S.; Spiecker, E.; Forberich, K.; Brabec, C. J. Nanoscale. 2015, 7, (5), 1642-9. (56) Hecht, D. S.; Hu, L.; Irvin, G. Adv Mater. 2011, 23, (13), 1482-513.


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Figure 1. Continuous dry spinning of extra-long silver submicron fibers. (a) The schematic of fabricating silver nanofiber arrays. (b) The photograph of actual preparation process and excellent transparency of silver nanofiber arrays enwound on the hollowed-out stainless steel sheet. (c) The constant transformation of liquid cone on the nozzle into a fiber with different rotational speed. (d) The SEM image of the silver nanofiber arrays with different spacing and diameters. (e) The relationship between viscosity of solution and diameter of fiber. (f) The shear stress and the diameter versus rotational speed of substrate.


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Figure 2. Ag fibers mesh made with extra-long silver submicron fibers. (a) The photograph of silver nanofiber mesh (including the show for the high conductivity of fiber mesh and the regular mesh structure). (b) The SEM image of the silver nanofiber mesh with scale bar is 20 µm. (c) The SEM image of the transverse and longitudinal fiber arrays with different diameters. (d) The silver submicron fibers mesh has almost negligible altitude intercept as seen through AFM image. (e) The SEM image and corresponding silver elemental mapping of the submicron fibers mesh.


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Figure 3. Ag fiber based transparent electrodes. (a) The transmittance vs. sheet resistance of Ag submicron fibers mesh. (b) Annealing temperature vs. sheet resistance. (c) The sheet resistance stability test of silver fiber mesh in different bending radius. (d) Sheet resistance as a function of the cycle number of bending to a radius of 2 mm. (e) Resistance change versus uniaxial strain for Ag submicron fibers mesh attached to PDMS substrate. Right column shows SEM image of the fiber grid after stretch.


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Figure 4. Flexibility, toughness, and transparency of silver submicron fibers mesh. (a) The silver submicron fibers mesh successfully attached on different surfaces. (b) The free-standing silver submicron fibers mesh can be easily spread out after wrinkling. (c) The photograph of the silver fiber mesh after it was folded twice. (d) The SEM image of folded silver fiber mesh.


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Figure 5. Extra-long single Ag nanofiber as conductor wire. (a) Photograph of the 400 nm-diameter single silver fiber functioning in a LED lamp. (b) The single fiber winding process and the optical images of single fiber arrays. (c) Photograph of the single half-kilometer long fiber enwound on the glass rod. (d) The photograph of one 28 m-long silver nanofiber as a conductor wire functioned in a LED lamp. (e) The SEM image and the spacing distribution of 28 m-long single silver nanofiber twined on the ceramic rod.


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Continuous dry spinning of extra-long silver submicron fibers. 170x188mm (300 x 300 DPI)


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Ag fibers mesh made with extra-long silver submicron fibers. 170x139mm (300 x 300 DPI)


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Ag fiber based transparent electrodes. 170x261mm (300 x 300 DPI)


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Flexibility, toughness, and transparency of silver submicron fibers mesh. 170x192mm (300 x 300 DPI)


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Extra-long single Ag nanofiber as conductor wire. 160x214mm (300 x 300 DPI)


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160x73mm (300 x 300 DPI)


Continuous Draw Spinning of Extra-Long Silver Submicron Fibers with

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