Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous

Subscriber access provided by Fudan University

Article

Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous Pattern Films with High Transparency and Conductivity Ying He, Yuan Chen, Qingchi Xu, Jun Xu, and Jian Weng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b15016 • Publication Date (Web): 02 Feb 2017 Downloaded from http://pubs.acs.org on February 12, 2017

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 25

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

Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous Pattern Films with High Transparency and Conductivity Ying He†, Yuan Chen†, Qingchi Xu‡, Jun Xu‡,* and Jian Weng†,* †

Department of Biomaterials, College of Materials, Xiamen University, Xiamen 361005, China.

‡

Department of Physics, Research Institute for Biomimetics and Soft Matter, Fujian Provincial

Key Laboratory for Soft Functional Materials, Xiamen University, Xiamen, 361005, China.

KEYWORDS: honeycomb macroporous pattern, ultrathin gold nanowires, breath figure array, self-assembly, transparent and conductive film

1 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 25

ABSTRACT

Due to its promising properties, honeycomb macroporous pattern (HMP) film has attracted increasing attention. It has been realized in many artificial nanomaterials, but the formation of these HMPs was attributed to templates or polymer/supermolecule/surfactant assistant assembly. Pure metal HMP film has been difficult to produce using a convenient colloidal template-free method. In this report, a unique template-free approach for preparation of Au HMP film with high transparency and conductivity is presented. Ultrathin Au nanowires, considered a linear polymer analogue, are directly assembled into HMP film on various substrates using a traditional static breath figure method. Subsequent chemical crosslinking and oxygen plasma treatment greatly enhance the stability and conductivity of the HMP film. The resulting HMP film exhibits great potential as an ideal candidate for transparent flexible conductive nanodevices.


Page 3 of 25

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


INTRODUCTION A significant feature of nature is its ability to construct hierarchical structures to meet its demands at different scales. Once a remarkable structure is discovered, material scientists spare no effort to study the formation, character and functionalities of the structure. The ultimate aim is to mimic such structures with artificial materials to realize desired functions. The honeycomb structure is one of the best examples of this.1-4 Natural honeycomb has a hexagonal pattern and displays superior properties due to its large surface area, excellent structural stability and high porosity. Such properties inspire scientists to prepare honeycomb macroporous pattern (HMP) with artificial nanomaterials. The HMP films produced have attracted intense interest in diversified

applications

such

as

templates,5

surface-enhanced

Raman

scattering,6

superhydrophobic coating,7 optoelectronic devices,8 cell culture,9 and sensors.10 In particular, numerous studies revealed that HMP films could significantly improve conductivity without sacrificing transparency compared with other patterned thin films, indicating great potential as an ideal candidate for transparent conductive films.11-14 Over the past few years, various top-down and bottom-up approaches have been successfully developed for HMP film construction. Top-down approaches, typically lithography, have been widely used to create large-area HMP films.15 However, they usually require specific instruments and can only be applied to limited materials such as silicon and polymers.15, 16 Alternatively, the bottom-up colloidal template method is also popular for large-area HMP film fabrication.17 Yet the necessary templating process, including template preparation and removal, makes this approach sophisticated, time-consuming and uneconomical. The breath figure (BF) method is another commonly used approach for HMP film preparation.18-24 The typical BF method usually involves casting a drop of a nonpolar, low



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 25

boiling point solution on a substrate and subsequent evaporation in a humid environment. During evaporation, the water in the air is condensed into droplets on the substrate and serves as a soft template to induce the formation of honeycomb patterns. Thus, in comparison with other methods, the BF method is attractive because of its template-free process, low cost, time savings and easy operation. However, nonconductive organic molecules such as polymers,25 supermolecules,26 and amphiphilic surfactants27 are often necessary for applying BF method. Therefore fabrication of conductive HMP films, especially single-component metal HMP films, is seldom reported. On the other hand, metal nanomaterials-based HMP films are good candidates for optoelectronic-related applications owing to their improved conductivity. Although several examples of metal nanomesh HMP films have been reported using other methods,28-31 producing HMP with single-metal component using a simple approach such as the BF method is desired. Ultrathin Au nanowires (NWs), known for their excellent chemical stability, conductivity and mechanical properties, have wide applications in optoelectronic devices.32,

33

In particular,

ultrathin Au NWs could be assembled into densely packed 2D membranes with improved transparency and conductivity.34-36 Very recently, using hexagonal polydimethylsiloxane (PDMS) stamps as a template, Au NWs could self-assemble into HMP film (on polyethylene terephthalate PET) with tunable conductivity and transparency.37 Ultrathin Au NWs could also assemble into nanomesh films at the air/water interface and showed excellent performance as flexible transparent electrodes.38 Although conductive and transparent films from ultrathin Au NWs and even HMP films have been reported, the production of these HMP films normally relies on templates or interfacial assembly, and challenges remain in designing an easy templatefree fabrication method.


Page 5 of 25

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


Here, we report an easy strategy to fabricate HMP films from ultrathin Au NWs with the BF method without other polymers or surfactants (Scheme 1). With the inspiration that ultrathin NWs have a shared fundamental 1D morphology with linear polymer and display superior polymer-like flexibility39, 40 and could be treated as polymer-analogue or semi-polymer to selfassemble in a colloidal system,41, 42 we successfully integrate the ultrathin Au NWs into HMP film using the BF method, and produce highly transparent and conductive metal films. The ultrathin Au NWs-based HMP was initially created on silicon substrate using the traditional static BF method. Then, the prepared HMP film was subsequently “crosslinked” via inter-NW coalescence to fix Au meshes, which provides the HMP film with high stability for further oxygen plasma treatment to remove surface oleylamine (OA) and improve the electronic conductivity of the film. In addition to the Si substrate, we also prepared highly transparent and flexible conductive HMP films on transparent glass and flexible Teflon slice substrates.

Scheme 1. Preparation of highly transparent and conductive HMP film from ultrathin Au NWs.

RESULTS AND DISCUSSION Our HMP film started from ultrathin Au NWs that were synthesized as previously reported.4345

The as-synthesized Au NWs were purified with ethanol and re-dispersed in chloroform. Figure

1a shows a typical transmission electron microscopy (TEM) image of the s ultrathin Au NWs. 5 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 6 of 25

The average diameter and length of the ultrathin Au NWs were around 2 nm and about 554 nm (the diameter and length distribution were shown in Figure S1e, S2e), respectively. The distance between each NW is approximately 3 nm, which was in agreement with the closely packed OA bilayer.44, 46 The uniformly distributed OA on the surface of Au NWs prevents contact of the Au surface of different wires and thus stabilize the ultrathin NWs.

Figure 1. (a) TEM image of ultrathin Au NWs; (b) SEM and (c) High-resolution SEM image of the HMP film prepared from ultrathin Au NW on Si substrate; (d) Typical optical microscopy image of the HMP film; (e) AFM image of HMP film and (f) AFM cross-sectional height plot corresponding to the line in (e).


Page 7 of 25

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


The HMP film was then created using the static BF method with the purified Au NWs. Briefly, Au NWs chloroform solution (0.5 mg/mL, see details in experimental section) was directly casted onto a Si substrate, which was then placed in a closed container in humid conditions. As the solvent evaporated, small water droplets condensed on the substrate and formed pore arrays. These arrays served as soft templates for the assembly of the ultrathin Au NWs. Upon complete evaporation of the solvent and water droplets, the pore arrays disappeared, and an Au NWs HMP formed. Figure 1b shows a scanning electron microscope (SEM) image of the HMP film with a nearly hexagonal pattern on Si substrate. Close inspection of the pattern revealed that each pore has an average diameter of 4.75 ± 0.79 µm (Figure 1c, Table S1). Furthermore, Figure 1c clearly shows that the Au meshes resulted from parallel alignment of the closely packed Au NWs, with a wall thickness of approximately 0.25 ± 0.06 µm and a height between 200-300 nm, determined by atomic force microscopy (AFM) (Figure 1e, f). Notably, HMP films can be produced over a large area (up to 0.25 cm2) without significant defects (Figure 1d, and Figure S3). Usually, polymers or surfactants are necessary to prepare HMP film using the BF method.47-49 However, in our system, the honeycomb pattern was obtained without adding any polymer or surfactant except for the residual OA on the surface of the Au NWs resulted from the synthesis. We further demonstrates that OA is not necessary for the assembly by washing the Au NWs with ethanol to remove OA. As shown in Figure S4, Fourier transform infrared (FT-IR) analysis suggested that trace amount of OA was present in the centrifugation supernatant before wash, while after wash there was no OA in the solution. Furthermore, X-ray photoelectron spectroscopy (XPS) spectra showed that surface OA of Au NWs also decreased after EtOH wash, suggesting the successful removal of OA in solution (Figure S5, Table S2). However, the honeycomb pattern could be still obtained from the bare Au NWs after washing using the static



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 8 of 25

BF method (Figure S6). This result also suggests that it is the linear structure and high flexibility of ultrathin Au NWs, which is similar to its corresponding polymeric properties that makes them compatible with the classic static BF method to form the HMPs. Similar to the polymeric HMP film, the morphology of the HMP film obtained from Au NWs was readily affected by the concentration and length (analogue to the MW of linear polymers) of the Au NWs. As shown in Figure S7, when the concentration of Au NWs was lowered to 0.25 mg/mL (1/2 of the optimized concentration), the pattern obtained had non-ordered pores with discontinuous walls. Obviously, there were not enough Au NWs in solution to separate the water droplets so they tended to fuse into large ones. Conversely, when the concentration of Au NWs was increased to 2.0 mg/mL (4 times of the optimized concentration), excess Au NWs tangled with each other in solution and restricted the motion of the Au NWs, resulting in a disordered pattern with relatively thick walls (Figure S7).50 The molecular weight of linear polymers significantly affects the pattern of BF obtained.51 Similarly, the length of ultrathin NW may affect the BF pattern. Ultrathin Au NWs (diameter around 2 nm) with three lengths, 448 nm, 554 nm, and > 1 µm, were synthesized by controlling the amount of water in the synthesis of the NWs (Figure S1, and Figure S2). Then, these different length Au NWs were used in the BF method. HMP pattern was obtained from NWs with an average length of 554 nm (Figure 1b, c), while a multi-layered pattern with irregular pores were obtained from NWs with an average length > 1 µm, as the long NWs tangled easily (Figure S8a). An irregular pattern was obtained from NWs with an average length of 448 nm because the short NWs were difficult to assemble into pores (Figure S8c). Moreover, length of the NWs is closely related to viscosity of the solution (Figure S9).52 Longer NW solution has higher viscosity and thus the motion of individual NWs is limited. Conversely, solution of


Page 9 of 25

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


shorter NW has lower viscosity, and thus shorter NWs could not separate the water droplets. The effect of the concentration and the length of Au NWs on the morphologies of the HMP film was fairly consistent with that of reported polymer-based HMP films. The solvent used to dissolve polymers also has an important effect on the morphology of the pattern produced by BF. Based on reported results, solvents with low boiling point and low water immiscibility are suitable for the BF process.53 Such trend was also inherited in our NWs system. Four solvents (Table S3) were used to disperse the Au NWs (Figure S10) and porous patterns could be observed with carbon disulfide and chloroform solvents (Figure S10a, c). The pore size of the films prepared from chloroform was larger and more homogeneous than that of the films prepared from carbon disulfide. This result can be attributed to the high boiling point of chloroform. As the boiling point increases, the volatility of the solvent decreases, and water droplets have more time and opportunities to coalesce on the surface of the solution, leading to larger pores. In contrast, discontinued HMPs were obtained when benzene was used as the solvent (Figure S10b). The low volatility of benzene lead to slow evaporation, which could not allow water vapor to condense on the surface of the solution to form the soft honeycomb template. Meanwhile, no HMP was obtained with tetrahydrofuran as the solvent due to its miscibility with water (Figure S10d). Humidity is another key factor that affect the morphology of produced pattern by BF. The relative humidity of the atmosphere influences the water condensation at the air/liquid interface and, consequently, influence the size of water droplets.54 As the water droplets act as a sacrificed template for microporous thin films, they determine the pore sizes of the micropores and the morphology of the array. To investigate the influence of the humidity on the formation of HMP film, we fabricated films in environments with different humidity. Humidity lower than 50 %



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 10 of 25

cannot facilitate the condensation of water, leading to thin film without porous (Figure S11a and S11b). As the humidity increased to 70%, films with non-homogeneous pores could be formed (Figure S11c). The pore size increased as the humidity increased (90%, Figure S11d). Generally speaking, the higher the humidity, the larger the water droplets formed. Atmosphere temperature affects the evaporation of the solvent, the condensation of the water droplets, as well as the viscosity of the solution. Figure S12 shows the effects of atmosphere temperature on the morphology of HMP films. The porous films could be produced at 15 °C and 25 °C (Figure S12a and 12b), while the patterns formed at 35 °C and 45 °C are significantly irregular (Figure S12c and 12d). Furthermore, the pore size of the HMP film increased as the temperature increased. It is well known that the evaporation rate of solvent increases with the temperature, and thus the increase of temperature difference. Water vapor in the atmosphere condensed onto the surface of the solution quickly, leading to the coalescence of droplets.55 For polymeric HMP film produced by the BF method, the morphology is affected by several factors such as weight of materials, concentration of solution, solvent, humidity of atmosphere, and the temperature of atmosphere etc. We have systematically investigated the effects of these factor on the morphology of HMP film prepared from ultrathin Au NWs, which are fairly in agreement with those in typical polymeric BF film.56 As the assembly process does not involve specific interaction between solvent and solute, the method for preparation of HMP film is expected to be extended to other polymer-like ultrathin nanomaterials. Compared with polymer, an obvious advantage of ultrathin Au NWs is their high conductivity. However, the closely packed OA on the surface of Au NWs blocked the inter-NW contact, which seriously weakens the conductivity of the obtained HMP films. Subsequently, oxygen plasma treatment was employed to remove surface OA for improving the conductivity of the


Page 11 of 25

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


prepared film.35, 57 Direct exposing the Au NWs HMP film to oxygen plasma for 3 min lead to the decrease of the sheet resistance to 156 Ω/sq. The Au NWs after plasma treatment were significantly sintered, and the HMP film was broken (Figure S13). To overcome this limitation, we attempted to strengthen the as-prepared HMP film by “crosslinking” the ultrathin Au NW network. Using a slightly modified H2O2 treatment,44 the inter-NW coalescence of the Au NWs was promoted in synthesized HMP film. After heating the synthesized HMP film in H2O2 solution for 5 min, the overall shape of the HMP film was not obviously changed (Figure S14), while the frame of HMP was strengthened by inter-NW coalescence of the parallel closely packed ultrathin NWs. This strengthened HMP film show no obvious change after 3 min of plasma irradiation (Figure 2a, b). Even when the plasma treatment was extended to 10 min, no obvious fragmentation was observed (Figure S15). Grazing incidence small-angle X-ray scattering (GISAXS) measurement was used to characterize the inter-NW coalescence. Figure 2d presents a typical single Au NWs pattern before H2O2 treatment. The peak at qy= 1.4 nm-1 was approximately in agreement with the 4 nm (see supporting information for details) center-to-center NW distance (Figure 2c, black line). Upon H2O2 treatment, the single NW pattern could be identified (Figure 2e) but the center-tocenter NW distance was slightly decreased (Figure 2c, green line), demonstrating the happening of inter-NW coalescence. GISAXS measurement of the “crosslinked” HMP film after oxygen plasma treatment showed a similar pattern, in which the “crosslinked” pattern remained (Figure 2f and Figure 2c blue line). However, GISAXS measurement of the “un-crosslinked” HMP film after oxygen plasma treatment did not show the single NWs pattern (Figure 2g and Figure 2c, red line), suggesting complete destruction of the NW.



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 12 of 25

The inter-NW coalescence most likely belongs to the cold welding phenomenon, which is an ambient condition approach for making coalescence between nanostructures.58,

59

The cold

welding between ultrathin Au NWs has been investigated in recent literatures,60 whose key feature is the similar lattice orientation before and after the coalescence. In our system, interNW coalescence occurs at ambient condition, and the similar lattice orientation (fcc) could be observed in both original Au NWs and the coalesced Au NW bundle (see details in Figure S16). Thus, it is conceivable that inter-NW coalescence here is ascribed to cold welding process. Although the fundamental mechanism is still under exploration, it is proposed that such process involves transportation of surface Au atoms via rapidly atomic diffusion, surface relaxation which minimizes the overall surface free energy, and the lattice matching via orientedattachment. Furthermore, H2O2 plays an important role during coalescence, as no obvious coalesced sites can be found in the absence of H2O2 (Figure S17). H2O2 probably serves as a reductant, which reduces Au ions (on surface of Au NW) to Au atom, so as to promote the surface ligand (OA) dissociation and surface Au atoms diffusion. The reduction of surface Au ions to Au atoms is confirmed by XPS analysis (Figure S18, and Table S4). Other reductants, such as ascorbic acid, also can be used to replace H2O2 and promote the inter-NW coalescence (Figure S19), demonstrating the importance of reductant in the coalescence process. The sheet resistance of the crosslinked HMP film was reduced to 125 Ω/sq after 3 min plasma treatment and did not suffer significant changes when the plasma treatment time was extended to 10 min (131 Ω/sq). The great improvement in conductivity could be attributed to successful removal of surface OA which creates tunnel barriers and inhibits electron transport from NW to NW. Furthermore, the inter-NW coalescence took place over the whole HMP film, creating large number of connected junctions (Figure S16b). These connected junctions gave increasing of


Page 13 of 25

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


cross-section area of NW at these junction points, and improved the conductivity of HMP film. Thus, apart from improving the stability of the HMP film during the plasma treatment, the crosslinking process also helps improve the conductivity of the HMP film by adding junctions with the inter-NW coalescence (Figure 2b) to increase electron flow.

Figure 2. (a) SEM image of HMP film after H2O2 treatment and oxygen plasma treatment; (b) High-magnification SEM image of (a); GISAXS patterns of (d) as-prepared HMP film from ultrathin Au NWs; (e) HMP film after H2O2 treatment; (f) HMP film after H2O2 treatment and subsequent oxygen plasma treatment; and (g) directly oxygen plasma-treated HMP film. The intensity distribution of the corresponding lines in (d)-(g) is shown in (c).

To further extend the scope of HMP as transparent conductive electrodes, the Au NW HMP film was prepared on different transparent substrates, such as glass and flexible Teflon slices (Figure 3). Similar to the films formed on Si substrate, these HMP films have pore diameters of 4-6 µm, wall thicknesses of 0.3-1 µm and heights of ~2.5 µm (Figure 3a, a1, S20, Table S1).



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 14 of 25

These results demonstrate the generality of this method for preparing HMP films from Au NWs using BF on different substrates.

Figure 3. SEM images of the ultrathin Au NW HMP film (a), (a1) before and (b), (b1) after H2O2 treatment for 5 min and subsequent oxygen plasma treatment for 3 min; (c), (c1) optical transmittance spectra of HMP film after H2O2 treatment and oxygen plasma treating, with the corresponding optical photographs. (a-c) The glass slice and (a1-c1) the flexible Teflon slice.

The HMP on glass and flexible Teflon substrate could also undergo H2O2 and oxygen plasma treatment (Figure 3b, b1). After treatment, both films became more structured in comparison to the original ones, which was probably attributed to the shrinkage of Au NWs bundles, as well as the reorganization of surface Au atom during inter-NW coalescence. It is worth to mention that, these treated HMP films on glass and flexible Teflon substrates exhibited outstanding optical


Page 15 of 25

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


transmittance (Figure 3c, c1). The films on glass and flexible Teflon substrates were visually nearly transparent. Optical extinction of the films using a UV-vis spectrophotometer showed high optical transmittance (86.4 % for the film on the glass slice and 91.8 % for the film on the Teflon slice in the visible light region from 400 to 800 nm (Figure 3c, c1). A simple geometric model could be employed estimate the transmittance of the film at 550 nm: the transmittance of the mesh is regarded as the fraction of clear apertures uncovered by Au NWs. The Au NWs coverage is calculated as 87.7 % and 93.2 % for the HMP films on glass and Teflon slices, respectively (Table S1, see Supporting Information for details), which are well consistent with the experimental results. It should also be noted that the disordered Au film (prepared by direct dropping solution without the BF method on flexible Teflon slice) had a transmittance of 63.9 % at 550 nm after H2O2 and plasma treatment (Figure S21a), much lower than that of the HMP film obtained using the BF method. The HMP films on Teflon slice exhibited a comparable transmittance and sheet resistance to ITO films and other common used metal films (see details in Figure S22), but had a better flexibility. Therefore, such HMP film possess great potential for transparent conductive. More importantly, the HMP film not only promises high transparency and excellent conductivity, but greatly saves cost. With the thickness of 0.25 µm, a non-porous Au film will cost 38.6 g of Au per m2, while film with HMP costs 2.62 g of Au per m2. Thus, 93.2 % of Au would be theoretically saved (see Supporting Information for details).



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 25

Figure 4. (a) Current-voltage curves for the ultrathin Au NW HMP film on different substrates; (b) Flexibility test: the ultrathin Au NW film on Teflon slice were bent under tension around a 2 mm radius plastic rod and the conductivity was subsequently measured in the flat state; photographs of a closed circuit connected to an LED light with the bent (c) and stretched (d) ultrathin Au NW HMP film.

The sheet resistances of the HMP after treatment with oxygen plasma were 210 and 159 Ω/sq for film prepared on glass and flexible Teflon slices, respectively (Figure 4a). Both sheet resistances were higher than the theoretical values (see Supporting Information for details), which might due to partial disruption of the Au frames as well as defects in the grid.61 The disordered Au NW film (produced by directly dropping solution without the BF method on a flexible Teflon slice) had similar sheet resistance, 135 Ω/sq, which showed that the HMP film obtained using the BF method did not reduce the conductivity of the ultrathin Au NW film (Figure S21b).


Page 17 of 25

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


In addition to transmittance and conductivity, the flexibility and stability of HMP film electrodes were also evaluated for their application in flexible electronics. A circuit composed of HMP film on a flexible Teflon slice, a LED light and a battery was set up to test the conductivity of the HMP film under mechanical deformation (Figure 4c, d). The LED light maintained continuous lighting regardless of what happened to the film in flat or deformed states (including bent or stretched). The results indicated that the film maintained good conductivity even in a harsh folded status. To test stability, the sheet resistance of the HMP film on a flexible Teflon slice was measured over repeated bending cycles with a bending radius of 2 mm. As shown in Figure 4b, the sheet resistance of the HMP film on flexible Teflon slice changed little after 1000 cycles. These results suggested that the conductivity of the flexible HMP film was highly stable under mechanical deformation. Notably, the figure of merit of the flexible HMP film was estimated of 2.67,62 close to the commercialized indium tin oxide (ITO) (see Supporting Information for details).Thus, compared with fragile ITO, the flexible film would tremendously enhance the lifetime of the electronic device and allow for more potential applications. CONCLUSIONS In conclusion, we successfully prepared HMP film from ultrathin Au NWs using a templatefree BF method. Further crosslinking of the obtained film via inter-NW coalescence and subsequent removal of surface OA by oxygen plasma treatment led to enhanced stability and conductivity of the HMP film. Particularly, the HMP film could be prepared on transparent glass substrate and flexible Teflon slice. The prepared flexible HMP film exhibits high transparency and conductivity and could potentially be applied in flexible electronics. Furthermore, the method is based on non-specific interfacial assembly and thus may be extended to prepare HMP films using various inorganic ultrathin nanomaterials.



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 18 of 25

EXPERIMENTAL SECTION Materials. All chemicals were obtained from the sources denoted and used without further purification. Gold (III) chloride trihydrate was purchased from Sigma Aldrich. Oleylamine (OA) was purchased from J&K Scientific Co., Ltd. (Beijing, China). Triisopropylsilane (TIPS) was purchased from Alfa Aesar. Other chemicals were purchased from Xilong Chemical Co., Ltd. (Shantou, China). Teflon slice (Teflon Fluorinated ethylene propylene) was purchase from DuPont. Synthesis of ultrathin Au NWs. Ultrathin Au nanowires (Au NWs) were prepared following a previously reported method. 100 µL OA was mixed with 3 mg HAuCl4·3H2O in 2.5 ml tetrahydrofuran, followed by the addition of 150 µL TIPS and 100 µL deionized water to form a yellow solution. Then, the reaction proceeded at room temperature without stirring for 4-5 hours until the color gradually changed to dark red. The synthesized Au NWs (200 µL in tetrahydrofuran) were centrifuged, washed with ethanol and the precipitate was readily dispersed in 400 µL chloroform for future use. Preparation of the HMP Film. The static BF process was conducted in a 25 mL wide-mouth glass vial with a rubber plug. A piece of substrate (e.g., 5 mm*5 mm silicon wafer) was placed onto the top of a plastic stand in the glass vial. A saturated relative humidity in the vial was created by adding 2 mL distilled water into the bottle beforehand. The substrate was 1 cm higher than the liquid level. The HMP film was prepared by casting 10 µL of Au NWs dissolved in chloroform onto the substrate with a pipette. As the organic solvent evaporated, the transparent solution became turbid. The film was removed after 5 minutes with complete solvent evaporation. All experiments were carried out at room temperature unless stated otherwise.


Page 19 of 25

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


Crosslinking of the HMP film. The crosslinking of HMP film was conducted in H2O2/OA solution, which was prepared as follows. 50 µL H2O2 (30 %, v/v) was diluted to 5 mL, where 50 µL ethanol solution of OA (1 %, v/v) was added. Then HMP film was immersed in 5 mL above mixture in a 20 mL vial, and heated at 60 oC for 5 min. Finally the film was taken out and dried with nitrogen for next step. Subsequent plasma treatment of the crosslinked HMP film. After the cross-liking progress, the slice with the HMP film on it was exposed to oxygen plasma in a plasma apparatus (ZEPTO, Diener) for 3 minutes to remove OA on the surface of the Au NWs. Characterization. Single Au NWs were characterized by transmission electron microscopy (JEM 2100, Hitachi). The morphology of the Au NW layers was characterized by scanning electron microscopy (SU70, Hitachi). The optical microscopy image was obtained using a Transmission-reflecting polarizing microscope (ECLIPSE/Ci-S, Nikon). The transmittance spectra were generated using a UV-vis Spectrometer in transmission mode (UV-2550, Shimadzu). For transmittance data, they were all obtained by subtracting the transmittance of substrate. AFM images were recorded using an atomic force microscope (DI Multimode V/DI Multimode V, Veeco) in tapping mode. The current−voltage curves were generated using a quartz crystal microbalance (CHI440C). The FTIR spectra were generated using a Fourier Transform Infrared Spectrometer (NICOLET iS10). GISAXS measurements were carried out using a Xeuss 2.0 system (Xenocs SA, Grenoble, France). X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI Quantum 2000 (USA). ASSOCIATED CONTENT Supporting Information. Calculation of optical transmittance, sheet resistance, figure of merit; Characterization of as-synthesized Au NWs with different length; Table of comparison of 19 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 20 of 25

HPM film on different substrate; Table of comparison of solvents used to produce Au NWs HMP film; IR spectra of purification supernatant; XPS spectra of Au NWs; HRTEM images of Au NWs; SEM images of HMP film obtained under different conditions; SEM images of HMP film obtained with plasma treatment for different duration; SEM images of HMP film crosslinked with other reductant; Optical transmittance and conductivity of non-porous Au film. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] * E-mail: [email protected] Notes The authors declare no competing financial interests. ACKNOWLEDGMENTS This study is financially supported by the National Nature Science Foundation of China (21401153, 31371005), the Fundamental Research Funds for the Central Universities (20720150016, 20720150017), and National Key Scientific Research Projects (2014CB932004). REFERENCES 1. Zhang, Q. C.; Yang, X. H.; Li, P.; Huang, G. Y.; Feng, S. S.; Shen, C.; Han, B.; Zhang, X. H.; Jin, F.; Xu, F.; Lu, T. J., Bioinspired Engineering of Honeycomb Structure - Using Nature to Inspire Human Innovation. Prog. Mater. Sci. 2015, 74, 332-400. 2. Ma, H. M.; Hao, J. C., Ordered Patterns and Structures via Interfacial Self-Assembly: Superlattices, Honeycomb Structures and Coffee Rings. Chem. Soc. Rev. 2011, 40, 5457-5471.


Page 21 of 25

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


3. Polini, M.; Guinea, F.; Lewenstein, M.; Manoharan, H. C.; Pellegrini, V., Artificial Honeycomb Lattices for Electrons, Atoms and Photons. Nat. Nanotechnol. 2013, 8, 625-633. 4. Xu, X.; Heng, L. P.; Zhao, X. J.; Ma, J.; Lin, L.; Jiang, L., Multiscale Bio-Inspired Honeycomb Structure Material with High Mechanical Strength and Low Density. J. Mater. Chem. 2012, 22, 10883-10888. 5. Caruso, R. A.; Antonietti, M., Silica Films with Bimodal Pore Structure Prepared by Using Membranes as Templates and Amphiphiles as Porogens. Adv. Funct. Mater. 2002, 12, 307-312. 6. Kong, L.; Dong, R.; Ma, H.; Hao, J., Au NP Honeycomb-Patterned Films with Controllable Pore Size and Their Surface-Enhanced Raman Scattering. Langmuir 2013, 29, 4235-4241. 7. Ma, H. M.; Gao, P. C.; Fan, D. W.; Du, B.; Hao, J. C.; Wei, Q., Assembly of Graphene Nanocomposites into Honeycomb-Structured Macroporous Films with Enhanced Hydrophobicity. New J. Chem. 2013, 37, 1307-1311. 8. Ma, Y.; Fang, C. L.; Ding, B.; Ji, G.; Lee, J. Y., Fe-Doped MnxOy with Hierarchical Porosity as a High-Performance Lithium-ion Battery Anode. Adv. Mater. 2013, 25, 4646-4652. 9. Wu, X.; Wang, S., Regulating MC3T3-E1 Cells on Deformable Poly(ε-caprolactone) Honeycomb Films Prepared Using a Surfactant-Free Breath Figure Method in a Water-Miscible Solvent. ACS Appl. Mater. Inter. 2012, 4, 4966-4975. 10. Chen, P.C.; Wan, L.-S.; Ke, B.-B.; Xu, Z.-K., Honeycomb-Patterned Film Segregated with Phenylboronic Acid for Glucose Sensing. Langmuir 2011, 27, 12597-12605. 11. Yin, S. Y.; Men, X. J.; Sun, H.; She, P.; Zhang, W.; Wu, C. F.; Qin, W. P.; Chen, X. D., Enhanced Photocurrent Generation of Bio-Inspired Graphene/ZnO Composite Films. J. Mater. Chem. A 2015, 3, 12016-12022. 12. Lee, S. H.; Kim, H. W.; Hwang, J. O.; Lee, W. J.; Kwon, J.; Bielawski, C. W.; Ruoff, R. S.; Kim, S. O., Three-Dimensional Self-Assembly of Graphene Oxide Platelets into Mechanically Flexible Macroporous Carbon Films. Angew. Chem. Int. Ed. 2010, 49, 1008410088. 13. Huang, Y.; Bai, X. P.; Zhou, M.; Liao, S. Y.; Yu, Z. F.; Wang, Y. P.; Wu, H., LargeScale Spinning of Silver Nanofibers as Flexible and Reliable Conductors. Nano Lett. 2016, 16, 5846-5851. 14. Huang, Y.; Liao, S. Y.; Ren, J.; Khalid, B.; Peng, H. L.; Wu, H., A Transparent, Conducting Tape for Flexible Electronics. Nano Res. 2016, 9, 917-924. 15. Hedrick, J. L.; Brown, K. A.; Kluender, E. J.; Cabezas, M. D.; Chen, P. C.; Mirkin, C. A., Hard Transparent Arrays for Polymer Pen Lithography. ACS Nano 2016, 10, 3144-3148. 16. Fuhrmann, B.; Leipner, H. S.; Hoeche, H.-R.; Schubert, L.; Werner, P.; Gösele, U., Ordered Arrays of Silicon Nanowires Produced by Nanosphere Lithography and Molecular Beam Epitaxy. Nano Lett. 2005, 5, 2524-2527. 17. Yu, Q.; Huang, H. W.; Chen, R.; Yang, H. S.; Peng, X. S.; Ye, Z. Z., FiltrationAssembling Colloidal Crystal Templates for Ordered Macroporous Nanoparticle Films. J. Mater. Chem. 2011, 21, 18089-18094. 18. Bunz, U. H. F., Breath Figures as a Dynamic Templating Method for Polymers and Nanomaterials. Adv. Mater. 2006, 18, 973-989. 19. Hoa, M. L. K.; Lu, M. H.; Zhang, Y., Preparation of Porous Materials with Ordered Hole Structure. Adv. Colloid Interfac. 2006, 121, 9-23.



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 22 of 25

20. Hernandez-Guerrero, M.; Stenzel, M. H., Honeycomb Structured Polymer Films via Breath Figures. Polym. Chem. 2012, 3, 563-577. 21. Heng, L. P.; Wang, B.; Li, M. C.; Zhang, Y. Q.; Jiang, L., Advances in Fabrication Materials of Honeycomb Structure Films by the Breath-Figure Method. Materials 2013, 6, 460482. 22. Escale, P.; Rubatat, L.; Billon, L.; Save, M., Recent Advances in Honeycomb-Structured Porous Polymer Films Prepared via Breath Figures. Eur. Polym. J. 2012, 48, 1001-1025. 23. Wan, L. S.; Zhu, L. W.; Ou, Y.; Xu, Z. K., Multiple Interfaces in Self-Assembled Breath Figures. Chem. Commun. 2014, 50, 4024-4039. 24. Munoz-Bonilla, A.; Fernandez-Garcia, M.; Rodriguez-Hernandez, J., Towards Hierarchically Ordered Functional Porous Polymeric Surfaces Prepared by The Breath Figures Approach. Prog. Polym. Sci. 2014, 39, 510-554. 25. Nishikawa, T.; Nonomura, M.; Arai, K.; Hayashi, J.; Sawadaishi, T.; Nishiura, Y.; Hara, M.; Shimomura, M., Micropatterns Based on Deformation of a Viscoelastic Honeycomb Mesh. Langmuir 2003, 19, 6193-6201. 26. Lord, H. T.; Quinn, J. F.; Angus, S. D.; Whittaker, M. R.; Stenzel, M. H.; Davis, T. P., Microgel stars via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerisation - a Facile Route to Macroporous Membranes, Honeycomb Patterned Thin Films and Inverse Opal Substrates. J. Mater. Chem. 2003, 13, 2819-2824. 27. Fukuhira, Y.; Yabu, H.; Ijiro, K.; Shimomura, M., Interfacial Tension Governs The Formation of Self-organized Honeycomb-Patterned Polymer Films. Soft Matter. 2009, 5, 20372041. 28. Stannard, A., Dewetting-Mediated Pattern Formation in Nanoparticle Assemblies. J. Phys.-Condens. Mat. 2011, 23. 083001 29. Khanal, B. P.; Zubarev, E. R., Rings of Nanorods. Angew. Chem. Int. Ed. 2007, 46, 21952198. 30. Song, C. H.; Han, C. J.; Ju, B. K.; Kim, J. W., Photoenhanced Patterning of Metal Nanowire Networks for Fabrication of Ultraflexible Transparent Devices. ACS Appl. Mater. Inter. 2016, 8, 480-489. 31. Suh, Y. D.; Hong, S.; Lee, J.; Lee, H.; Jung, S.; Kwon, J.; Moon, H.; Won, P.; Shin, J.; Yeo, J.; Ko, S. H., Random Nanocrack, Assisted Metal Nanowire-Bundled Network Fabrication for a Highly Flexible and Transparent Conductor. RSC Adv. 2016, 6, S7434-S7440. 32. Chen, Y. L.; Lee, C. Y.; Chiu, H. T., Growth of Gold Nanowires on Flexible Substrate for Highly Sensitive Biosensing: Detection of Thrombin as an Example. J. Mater. Chem. B 2013, 1, 186-193. 33. Moon, C. H.; Zhang, M. L.; Myung, N. V.; Haberer, E. D., Highly Sensitive Hydrogen Sulfide (H2S) Gas Sensors from Viral-Templated Nanocrystalline Gold Nanowires. Nanotechnology 2014, 25, 135205. 34. Chen, Y.; Ouyang, Z.; Gu, M.; Cheng, W. L., Mechanically Strong, Optically Transparent, Giant Metal Superlattice Nanomembranes From Ultrathin Gold Nanowires. Adv. Mater. 2013, 25, 80-85. 35. Sanchez-Iglesias, A.; Rivas-Murias, B.; Grzelczak, M.; Perez-Juste, J.; Liz-Marzan, L. M.; Rivadulla, F.; Correa-Duarte, M. A., Highly Transparent and Conductive Films of Densely Aligned Ultrathin Au Nanowire Monolayers. Nano Lett. 2012, 12, 6066-6070. 36. Azulai, D.; Belenkova, T.; Gilon, H.; Barkay, Z.; Markovich, G., Transparent Metal Nanowire Thin Films Prepared in Mesostructured Templates. Nano Lett. 2009, 9, 4246-4249. 22 ACS Paragon Plus Environment

Page 23 of 25

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


37. Maurer, J. H.; Gonzalez-Garcia, L.; Reiser, B.; Kanelidis, I.; Kraus, T., Templated SelfAssembly of Ultrathin Gold Nanowires by Nanoimprinting for Transparent Flexible Electronics. Nano Lett. 2016, 16, 2921-2925. 38. Gong, S.; Zhao, Y. M.; Yap, L. W.; Shi, Q. Q.; Wang, Y.; Bay, J. A. P. B.; Lai, D. T. H.; Uddin, H.; Cheng, W. L., Fabrication of Highly Transparent and Flexible NanoMesh Electrode via Self-assembly of Ultrathin Gold Nanowires. Adv. Electron. Mater. 2016, 2. 39. Shaw, S.; Cademartiri, L., Nanowires and Nanostructures that Grow like Polymer Molecules. Adv. Mater. 2013, 25, 4829-4844. 40. Ni, B.; Wang, X., Chemistry and Properties at a Sub-Nanometer Scale. Chem. Sci. 2016, 7, 3978-3991. 41. Hu, S.; Liu, H. L.; Wang, P. P.; Wang, X., Inorganic Nanostructures with Sizes down to 1 nm: A Macromolecule Analogue. J. Am. Chem. Soc. 2013, 135, 11115-11124. 42. Cademartiri, L.; Scotognella, F.; O'Brien, P. G.; Lotsch, B. V.; Thomson, J.; Petrov, S.; Kherani, N. P.; Ozin, G. A., Cross-Linking Bi2S3 Ultrathin Nanowires: A Platform for Nanostructure Formation and Biomolecule Detection. Nano Lett. 2009, 9, 1482-1486. 43. Feng, H. J.; Yang, Y. M.; You, Y. M.; Li, G. P.; Guo, J.; Yu, T.; Shen, Z. X.; Wu, T.; Xing, B. G., Simple and Rapid Synthesis of Ultrathin Gold Nanowires, Their Self-Assembly and Application in Surface-Enhanced Raman Scattering. Chem. Commun. 2009, 15, 1984-1986. 44. Xu, J.; Wang, Y. W.; Qi, X. Y.; Liu, C. C.; He, J. T.; Zhang, H.; Chen, H. Y., Preservation of Lattice Orientation in Coalescing Imperfectly Aligned Gold Nanowires by a Zipper Mechanism. Angew. Chem. Int. Ed. 2013, 52, 6019-6023. 45. Xu, J.; Wang, H.; Liu, C. C.; Yang, Y. M.; Chen, T.; Wang, Y. W.; Wang, F.; Liu, X. G.; Xing, B. G.; Chen, H. Y., Mechanical Nanosprings: Induced Coiling and Uncoiling of Ultrathin Au Nanowires. J. Am. Chem. Soc. 2010, 132, 11920-11922. 46. Pazos-Perez, N.; Baranov, D.; Irsen, S.; Hilgendorff, M.; Liz-Marzan, L. M.; Giersig, M., Synthesis of Flexible, Ultrathin Gold Nanowires in Organic Media. Langmuir 2008, 24, 98559860. 47. Deleuze, C.; Derail, C.; Delville, M. H.; Billon, L., Hierarchically Structured Hybrid Honeycomb Films via Micro to Nanosized Building Blocks. Soft Matter. 2012, 8, 8559-8562. 48. Zhu, L. W.; Wu, B. H.; Wan, L. S.; Xu, Z. K., Polystyrene with Hydrophobic End Groups: Synthesis, Kinetics, Interfacial Activity, and Self-Assemblies Templated by Breath Figures. Polym. Chem. 2014, 5, 4311-4320. 49. Shah, P. S.; Sigman, M. B.; Stowell, C. A.; Lim, K. T.; Johnston, K. P.; Korgel, B. A., Single-Step Self-Organization of Ordered Macroporous Nanocrystal Thin Films. Adv. Mater. 2003, 15, 971-974. 50. Xiong, X. P.; Lin, M. F.; Zou, W. W.; Liu, X. Y., Kinetic Control of Preparing Honeycomb Patterned Porous Film by the Method of Breath Figure. React. Funct. Polym. 2011, 71, 964-971. 51. Peng, J.; Han, Y. C.; Yang, Y. M.; Li, B. Y., The Influencing Factors on the Macroporous Formation in Polymer Films by Water Droplet Templating. Polymer 2004, 45, 447-452. 52. Chen, Y.; Wang Y. W.; Peng, J.; Xu, Q. C.; Weng, J.; Xu, J.; Assembly of Ultrathin Au Nanowires: From Polymer Analogue to Colloidal Block Manuscript submitted. 2017. 53. Ferrari, E.; Fabbri, P.; Pilati, F., Solvent and Substrate Contributions to the Formation of Breath Figure Patterns in Polystyrene Films. Langmuir 2011, 27, 1874-1881.



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 24 of 25

54. Wang, C. Y.; Mao, Y. D.; Wang, D. Y.; Qu, Q. S.; Yang, G. J.; Hu, X. Y., Fabrication of Highly Ordered Microporous Thin Films by PS-b-PAA Self-Assembly and Investigation of Their Tunable Surface Properties. J. Mater. Chem. 2008, 18, 683-690. 55. Zhao, B. H.; Zhang, J.; Wu, H. Y.; Wang, X. D.; Li, C. X., Fabrication of Honeycomb Ordered Polycarbonate Films Using Water Droplets as Template. Thin Solid Films 2007, 515, 3629-3634. 56. Zhang, A. J.; Bai, H.; Li, L., Breath Figure: A Nature-Inspired Preparation Method for Ordered Porous Films. Chem. Rev. 2015, 115, 9801-9868. 57. Maurer, J. H. M.; Gonzalez-Garcia, L.; Reiser, B.; Kanelidis, I.; Kraus, T., Sintering of Ultrathin Gold Nanowires for Transparent Electronics. ACS Appl. Mater. Inter. 2015, 7, 78387842. 58. Lu, Y.; Huang, J. Y.; Wang, C.; Sun, S. H.; Lou, J., Cold Welding of Ultrathin Gold Nanowires. Nat. Nanotechnol.2010, 5, 218-224. 59. Wagle, D. V.; Baker, G. A., Cold Welding: a Phenomenon for Spontaneous Self-Healing and Shape Genesis at the Nanoscale. Mater. Horiz. 2015, 2, 157-167. 60. Xu, J.; Wang, Y. W.; Qi, X. Y.; Liu, C. C.; He, J. T.; Zhang, H.; Chen, H. Y., Preservation of Lattice Orientation in Coalescing Imperfectly Aligned Gold Nanowires by a Zipper Mechanism. Angew. Chem. Int. Ed. 2013, 52, 6019-6023. 61. Van de Groep, J. V.; Spinelli, P.; Polman, A., Transparent Conducting Silver Nanowire Networks. Nano Lett. 2012, 12, 3138-3144. 62. Haacke, G., New Figure of Merit for Transparent Conductors. J.Applied Phy. 1976, 47, 4086-4089.


Page 25 of 25

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


TOC:


Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous

Recommend Documents