Self-Assembly of Complex Multimetal Nanostructures from Perforated

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

Self-Assembly of Complex Multi-Metal Nanostructures from Perforated Lamellar Block Copolymer Thin Films Seung Keun Cha, Gil Yong Lee, Jeong Ho Mun, Hyeong Min Jin, Chang Yun Moon, Jun Soo Kim, Kwang Ho Kim, Seong-Jun Jeong, and Sang Ouk Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b03319 • Publication Date (Web): 12 Apr 2017 Downloaded from http://pubs.acs.org on April 13, 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 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

ACS Applied Materials & Interfaces

Self-Assembly of Complex Multi-Metal Nanostructures from Perforated Lamellar Block Copolymer Thin Films Seung Keun Cha,† Gil Yong Lee,† Jeong Ho Mun,† Hyeong Min Jin,† Chang Yun Moon,† Jun Soo Kim, † Kwang Ho Kim,* ‡ Seong-Jun Jeong,*§ and Sang Ouk Kim*† †

National Creative Research Initiative (CRI) Center for Multi-Dimensional Directed

Nanoscale Assembly, Department of Material Science and Engineering, KAIST, Daejeon 34141, Republic of Korea ‡

Department of Materials Science and Engineering, Pusan National University, Pusan 46241,

Republic of Korea §

Device Lab., Device & System Research Center, Samsung Advanced Institute of

Technology, Suwon 16678, Republic of Korea

KEYWORDS: block copolymer, self-assembly, metal nanostructure, catalyst, hydrogen evolution

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

ABSTRACT: We introduce a facile and effective fabrication of complex multi-metallic nanostructures by means of block copolymer self-assembly. Two- and three-dimensional complex nanostructures, such as ‘nanomesh’, and ‘double layered nanomeshes’, and ‘surface parallel cylinders on nanomesh’, can be achieved by employing the self-assembly of perforated lamellar morphology in block copolymer thin films. Simultaneous integration of various metallic elements, including Pt, Au, and Co, into the self-assembled morphologies generates multi-metal complex nanostructures with highly interconnected morphology and large surface. The resultant metal nanostructures with large surface area, robust electrical connectivity and well-defined alloy composition demonstrate a high performance electrochemical catalysis for hydrogen evolution reaction (current density: 6.27 mA/cm2 @ 0.1 V & Tafel slope: 43 mV/dec).

2 ACS Paragon Plus Environment

Page 2 of 23

Page 3 of 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


1. INTRODUCTION Nanoscale

self-assembly offers enormous potential for highly

efficient scalable

nanofabrication.1-6 Functional nanopattern structures prepared from self-assembly principle can be useful for a broad spectrum of application fields, including electronics, photonics, sensors and energy storage/conversion.7-11 Block copolymer (BCP) self-assembly is a wellestablished representative self-assembly principle, which has been widely exploited for nanopatterning applications particularly aiming at semiconductor device fabrication.12-21 It provides dense periodic arrays of self-assembled nanodomains with a typical characteristic dimension in 3-50 nm.13, 22-27 In contrast to the sphere, cylinder or lamellar self-assembled morphology commonly used for line or dot array patterning, perforated lamellar (PL) phase, known to be metastable in bulk phase but can be stabilized in thin films.28-31 A. Knoll et al. reported that cylinder-forming BCP thin films generated PL structures in specific conditions due to an interplay between surface field and confinement effects.30 K. Lyakhova et al. demonstrated that various structures including PL phase were found in BCP thin films resulting from the different surface fields of the two interfaces.31 Such PL morphology may provide densely ordered nanoporous structures, which can be utilized as a template for complex nanoporous structure formation, such as membranes.32 In this work, we demonstrate a simple and effective self-assembly of multi-metal complex nanoporous structures with interconnected morphology using perforated lamellar BCP selfassembly. Various nanoporous structures including two-dimensional (2D) nanomesh to threedimensional (3D) nanocomplex structures can be stabilized in BCP thin films by judicious control of film thickness and interfacial energy. Subsequently, highly specific incorporation of metallic precursors into the self-assembled hydrophilic nanodomains generates multi-metal complex nanostructures. Among various resultant metal nanostructures, Pt nanomesh 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

utilized as a model catalyst for electrochemical hydrogen evolution reaction (HER). Owing to the highly interconnected reliable electrical pathway and enough surface area, Pt nanomesh catalysts exhibit an improved HER performance than flat Pt catalysts and similar level with the Tafel slope of commercial Pt/C catalysts.

2. EXPERIMENTAL SECTION 2.1. Fabrication of monolayer metal nanomesh patterns Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP, Mn = 18 kg/mol for PS and 9 kg/mol for P2VP) was purchased from Polymer Source, Inc. PS-b-P2VP was dissolved in toluene (Sigma-Aldrich) to prepare different concentrations of BCP solutions (from 0.8 to 2 wt%). Thin BCP films (~35 nm) were spin-cast on a cleaned Si wafers by adjusting the solution concentration and the spinning speed. Thermal annealing of the BCP films in a vacuum oven at 250 °C induces well-ordered monolayer PL nanostructures. The samples were immersed in weakly acidic aqueous platinum precursor (K2PtCl4, Strem Chemicals) solution to load metal anions selectively into the protonated vinyl groups.17 After rinsing and drying the samples, O2 plasma treatment (50 sccm, 50 W, controlled time) removed polymer layers and left metal nanomesh patterns. For bimetallic nanomesh, platinum and another metal precursors (HAuCl4, K3Co(CN)6, or Na2PdCl4, Strem Chemicals) were simultaneously dissolved in weakly acidic aqueous solution. 2.2. Multi-step process for 3D complex nanostructures After metal loading into the annealed BCP samples, UV crosslinking was performed to fix the BCP morphology. A new layer of BCP film was spin-cast on the crosslinked films with suitable thickness. The same procedures including thermal annealing, metal loading, and 4 ACS Paragon Plus Environment

Page 4 of 23

Page 5 of 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


plasma treatment were performed again. Upon the metal loading process into the first and second BCP layers, a variety of multi-metallic 3D nanostructures could be synthesized with a combination of metal precursors. 2.3. Single-step approach for 3D complex nanostructures Thick BCP films (55-90 nm) were spin-cast on the Si substrates and thermally annealed in the same way above. According to the film thickness, various 3D nanoporous structures were self-assembled. After metal ion loading and O2 plasma etching, 3D metallic nanoporous structures were generated. Judicious optimization of plasma etching condition (1 min for double layered nanomesh, and 2 min for nanomesh/lines) was required for the successful 3D nanostructure formation without collapse. 2.4. Hydrogen evolution reaction (HER) measurements For the conductive substrate formation for HER measurement, thin films of Cr (~10 nm) and Au (~80 nm) were deposited on the Si substrate by e-beam evaporation. Pt nanomesh was fabricated on the Cr/Au deposited Si substrate with the same process mentioned above. Pt/C and flat Pt film samples were used as references. Electrochemical reactions were performed by employing a three-electrode system (Bio-Logic SP-200) with 5 mV/s scan rate in 0.5 M H2SO4 solution. Ag/AgCl and graphite electrode were used as reference and counter electrodes. 2.5. Characterization Morphology of BCP thin films and metal nanostructures were imaged by a Hitachi S-4800 FE-SEM. The elemental analysis of multi-metallic nanomesh structures were performed with X-ray photoelectron spectroscopy (XPS) (K-alpha, Thermo VG Scientific).



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. RESULTS AND DISCUSSION 2D metal nanomesh structures were produced as follows (Figure 1(a)). Compositionally asymmetric PS-b-P2VP BCP thin film of ~35 nm-thick was spin-coated on a Si wafer and annealed at 250 °C for self-assembly. The BCP thin film spontaneously self-assembled into a hexagonally perforated lamellar (PL) morphology. We note that the PL phase was known to be stabilized in thin films of the specific thickness (35 nm) as a result of surface reconstruction.29-31, 33 After self-assembly, the thermal-annealed samples were then immersed in diluted HCl (aq) solution including various metallic anion precursors. Protonated P2VP blocks protruded from PS surface layer in the acidic condition, which facilitated a metal precursor loading process (Figure 1(a) cross section).20 Finally, oxygen (O2) plasma etching process removed all the organic components and produced metal nanomesh structures on the Si substrates. Figures 1(b) and (c) exhibit the plane-view scanning electron microscopy (SEM) images of the Pt loaded PL BCP thin films before and after O2 plasma treatment (see Figures S1(a) & (b) for low magnification large-area SEM images). Note that during immersion in the acidic aqueous solution of platinum precursor (K2PtCl4), negatively charged PtCl42precursor was complexed with the protonated nitrogens in the P2VP domains by electrostatic interaction. The bright matrix and the dark dots represent Pt loaded P2VP and PS nanodomains, respectively (Figure 1(b)). After O2 plasma etching (for 1 min), the obtained Pt nanomesh showed hexagonal nanoscale holes of 30 nm-period (Figure 1(c)). Note that in this work, O2 plasma etching condition was carefully controlled for optimized nanomesh patterns. As shown in Figures S1(c) & (d), O2 plasma etching for 30 sec, generates smaller hole diameter (~21 nm) and thicker metal interconnected frames (~11 nm), because of the polymer residue. By contrast, O2 plasma etching for 3 min results in the hole diameter and


Page 6 of 23

Page 7 of 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


interconnected line width of ~25 and ~5 nm, respectively. Carbon element decreases with etching time, but it is hard to completely remove the BCP layer (see Figures S2(a) & (b)), presumably due to the blocking effect for the upper metal nanomesh. In addition, the resultant metal nanomesh becomes considerably oxidized during the O2 plasma treatment (Figure S2(c)).

For the formation of 3D metal complex nanostructures, such as “double layered metal nanomeshes” or “nanolines on nanomesh”, a multi-step process was utilized (see illustration in Figure 1(a)). Firstly, Pt loaded monolayer PL forming PS-b-P2VP BCP samples were prepared as described above and crosslinked by UV light to preserve the nanoscale structure during the following overlay process. Subsequently, second PS-b-P2VP BCP layer was prepared in the same way over the crosslinked first layer. Phase morphology of the second layer was delicately dependent on the film thickness. Typically, the second BCP thin films with the thicknesses of 35 nm and 30 nm were deposited, where PL and surface parallel cylinder phases were formed, respectively. After the second Pt loading process, the polymer template was completely removed by O2 plasma etching. The resultant 3D Pt nanocomplex structures with Pt nanomesh bottom layer are shown in Figures 1(d) and (e). Plane-view SEM images reveal that the underlying Pt nanomesh layers are well-maintained and intact. The hole diameter and interconnected line width of the double layered Pt nanomesh structure were ~25 and ~5 nm (Figure 1(d)), respectively, and Pt line width in Pt nanolines/nanomesh complex was 5 nm (Figure 1(e)). This multi-step approach can be further repeated for thicker 3D nanoporous structures.



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

3D metal complex nanostructures could also be established by single step deposition of BCP films with precisely controlled thickness (see illustration in Figure 2(a)). Compositionally asymmetric BCP thin film enables various nanostructures, including wetting layer (dis), spherical microdomains, a perforated lamellar (PL), and cylinders (C┴ or C//), as results of surface reconstruction modulated by interference and confinement effects.30, 33 Interestingly, PS-b-P2VP BCP thin films (Mn = 18 kg/mol for PS and 9 kg/mol for P2VP) with the thicknesses of ~35 and ~60 nm demonstrated single and double layered PL phases, respectively (Figure 2(b)). When the film thickness was ~83 nm, “double layered surface parallel cylinders/PL complex phase” was observed, which may be strongly influenced by thickness commensurability and surface/interfacial energies. As shown in Figure 2(c), the self-assembled BCP nanostructure consisted of cylinder bottom layer and PL top layer, where the Si substrate was preferentially wetted by P2VP blocks. We should note that the morphologies shown in Figures 2(b) & (c) are 3D Pt complex nanostructures after Pt ion loading and O2 plasma etching. The O2 plasma etching time was also carefully controlled (for “double layered Pt nanomeshes” and “nanolines/nanomesh”, O2 plasma etching time were 1 min and 2 min, respectively). Brief etching less than 1 minute was not enough to reveal the bottom nanostructures and long etching over 3 minutes destroyed the 3D complex nanostructures (Figure S3).

Perforated P2VP lamellar phase is an attractive nanotemplate for highly interconnected multimetal nanostructures. Figure 3 shows plane-view SEM images of bimetallic nanomeshes produced by the simultaneous incorporation of two different metal precursors (of Pt-Au, PtPd, or Pt-Co). Interestingly, when single precursor of Au, Pd or Co was loaded without Pt precursor, the resultant morphologies readily collapsed (Figures 3(b), (e), and (h)). By


Page 8 of 23

Page 9 of 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


contrast, pure Pt nanomesh showed an excellent morphological stability (Figures 1 & 2). This can be attributed to a high loading density of Pt precursor into BCP templates with a strong agglomeration behavior. As shown in Figure S4, Pt nanodots showed densely agglomerated morphologies with small diameters (13~15 nm). In contrast, Pd (15~18 nm) and Au dots (16~20 nm) showed coarsely packed nanocluster morphologies with larger diameters, which indicates that loaded metal patterns does not exactly follow the BCP nanotemplate. Co anions were not loaded into the BCP template enough, so the resultant Co dot pattern was unclear with many defects. These results demonstrate that Pt is a good metal element to maintain the entire nanopatterns of BCP films, enabling the stable nanomesh morphology during the metal loading and plasma etching process. As a result, when the Pt composition was above 50 mol% in the multi-metallic nanostructure formation, the morphological stability was significantly improved (Figures 3(d), (g), and (j)). The exact chemical compositions of the bimetallic nanomeshes were confirmed by XPS analysis (Figure S5 and Table 1). The fabricated bimetallic nanomeshes were composed of Pt (38 at%) – Au (62 at%), Pt (56 at%) – Pd (44 at%), and Pt (79 at%) – Co (21 at%), respectively.

Multi-metal complex 3D nanostructures could be accomplished by multi-step repetition of BCP self-assembly and metallization cycles (see Figure 4(a)). Firstly, Pt and another metal precursors were loaded into the fist self-assembled PL BCP layers. Subsequently, the samples were illuminated by UV light for the morphology fixing by chemical crosslinking. The second BCP layer was overlaid upon the crosslinked BCP layer by spin-coating and thermally annealed for self-assembly. Subsequent metal loading process with Pt and 3rd metal precursors and O2 plasma treatment achieved 3D multi-metal complex nanostructures. Figures 4(b) & (c) show the plane-view SEM images of “double layered nanomeshes” with



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

Pt-Co top layer and Pt-Pd bottom layer, and Pt-Au top layer and Pt-Co bottom layer, respectively. The chemical composition of the multi-metal complex nanostructures was also confirmed by the XPS analysis (Figure 4(d) and S6). The fabricated trimetallic complex nanostructure were composed of Pt (52.8 at%) - Pd (33.8 at%) - Co (13.4 at%) and Pt (53.7 at%) – Co (26.9 at%) –Au (19.4 at%), respectively (Table S1). To confirm the contamination possibility of the preceding lower layer during the subsequent metal process, we prepared a Pt precursor loaded PS-b-P2VP BCP film. After its crosslinking and immersion into a Co precursor solution, its metal nanomesh was carefully analyzed by XPS. Note that its polymer part was sufficiently removed by O2 plasma before XPS analysis. As shown in Figure S7, we have not found the second metal element (Co) other than the first metal element (Pt) in the metal nanomesh within the detection limit. The result clearly demonstrates that the metal loading processes, we utilized, enable the multi-complex metal nanomesh structures without any contaminations between each layer. It may be due to the weak interaction between metal anions and crosslinked P2VP blocks. These results elucidate that our scalable approach successfully achieved 3D multi-metal complex nanostructures, while maintaining the underlying different bimetallic nanomeshes. Note that we could also fabricate the multi-metal complex nanostructures based on “nanolines on nanomesh” with Pt-Co-Pd alloy (see Figure S8).

Finally, we performed the electrochemical hydrogen evolution reaction (HER) measurements using three electrode setup in an acidic solution condition to characterize the HER catalyst performance of the fabricated metallic nanomesh structures. Hydrogen is attracting enormous research attention as a promising alternative energy carrier. To date, various catalyst materials have been exploited to maximize the energy conversion efficiency. In this work, the


Page 10 of 23

Page 11 of 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


highly interconnected and large surface area Pt nanomesh was applied to HER catalyst. As a reference for HER performance, commercial Pt/C catalyst and flat Pt film were also characterized. Figure 5 shows typical polarization curves (I−V plot) and Tafel plots of three samples. While commercial Pt/C catalyst showed the highest HER performance, the improved HER performance of Pt nanomesh was also demonstrated (current density of Pt/C = 17.5 mA/cm2 @ 0.1 V, Ptnanomesh = 6.27 mA/cm2 @ 0.1 V, and Ptflat = 1.04 mA/cm2 @ 0.1 V, respectively). The Tafel slope of Pt nanomesh was similar level with that of Pt/C catalyst (Tafel slope (T) of three samples: T(Pt/C) = 36 mV/dec, T(Pt nanomesh) = 43 mV/dec, and T(flat Pt film) = 85 mV/dec). These superior HER performance of Pt nanomesh could be attributed to the highly connected robust electrical pathway and large active catalytic surface area of the nanomesh structure.

4. CONCLUSIONS We have successfully fabricated hexagonally perforated metallic nanoscale mesh structures via PL-forming BCP self-assembly. Such a 2D nanomesh structure formation principle could be further developed for 3D complex nanoporous structures by reliable repetition of multistep process. The peculiar characteristic of P2VP self-assembled nanodomains to specifically attract various anionic metal precursors facilitates diverse multi-metallic complex nanostructures with different alloy compositions at each different mesh layer. It was found that highly specific Pt precursor is crucial for the structural stability of metal nanostructures. Nonetheless, synergistic integration of other metallic elements to form versatile multimetallic complex 3D nanoscale morphologies can be potentially useful for advanced technologies, including electronics, photonics, and catalysis.



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 1. (a) Schematic illustration of the self-assembly process for integrating 2D metal nanomesh and 3D metal complex nanostructures. Plane-view SEM images of (b) Pt precursor loaded hexagonally perforated lamellar forming PS-b-P2VP BCP thin film, (c) 2D Pt nanomesh after O2 plasma etching for 1 min, and (d) double layered Pt nanomesh and (e) Pt nanolines on nanomesh complex structures.


Page 12 of 23

Page 13 of 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


Figure 2. (a) Schematic illustration of the single step process for 3D metal nanostructures, based on the precise control of BCP film thickness for surface reconstruction. Plane-view SEM images of (b) double layered Pt nanomesh structures after O2 plasma etching for 1 min, and (c) Pt nanomesh on Pt lines after O2 plasma etching for 2 min.



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. (a) Schematic procedure for bimetallic nanomeshes by means of simultaneous loading of two different metallic precursors. Plane-view SEM images of metal nanomeshes, according to the relative compositions of different metals (Pt-Au, Pt-Pd, or Pt-Co); (b), (e) & (h) at 0 mol% Pt, (c), (f) & (i) at 25 mol% Pt, and (d), (g) & (j) at 50 mol% Pt, respectively.


Page 14 of 23

Page 15 of 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


Figure 4. (a) Schematic procedure of 3D multi-metal complex nanomesh by multi-step process. SEM images of 3D multi-metallic nanomeshes with the elements of (b) Pt-Pd-Co (bottom Pt-Pd, top Pt-Co), and (c) Pt-Co-Au (bottom Pt-Co, top Pt-Au). (d) XPS spectra of the Pt-Pd-Co multi-metallic nanomesh double layer (b).



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 5. (a) Polarization curves of flat Pt film, Pt/C and Pt nanomesh, and (b) corresponding Tafel plots.


Page 16 of 23

Page 17 of 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


Element Pt-Au Pt-Pd Pt-Co

Composition of Pt (at%) 38 56 79

Composition of second metal (at%) 62 44 21

Table 1. Composition of bimetallic nanomeshes of Pt-Au, Pt-Pd, and Pt-Co analyzed by XPS. The molar ratio between two precursors is 1/1.



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

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: Additional SEM images of flat Pt nanomeshes and unoptimized complex nanostructures, SEM images and corresponding diameters of diverse metal nanodots, XPS analysis of Pt nanomesh and multi-metallic nanomeshes, SEM images of multi-metallic complex nanomesh/cylinder structures (PDF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] *E-mail: [email protected] *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT


Page 18 of 23

Page 19 of 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


This research was supported by Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2013M3A6B1078874).

REFERENCES (1) Akcora, P.; Liu, H.; Kumar, S. K.; Moll, J.; Li, Y.; Benicewicz, B. C.; Schadler, L. S.; Acehan, D.; Panagiotopoulos, A. Z.; Pryamitsyn, V.; Ganesan, V.; Ilavsky, J.; Thiyagarajan, P.; Colby, R. H.; Douglas, J. F. Anisotropic Self-Assembly of Spherical Polymer-Grafted Nanoparticles. Nat. Mater. 2009, 8, 354-359. (2) Grzelczak, M.; Vermant, J.; Furst, E. M.; Liz-Marzán, L. M. Directed Self-Assembly of Nanoparticles. ACS Nano 2010, 4, 3591-3605. (3) Lopes, W. A.; Jaeger, H. M. Hierarchical Self-Assembly of Metal Nanostructures on Diblock Copolymer Scaffolds. Nature 2001, 414, 735-738. (4) Spatz, J. P.; Mössmer, S.; Hartmann, C.; Möller, M.; Herzog, T.; Krieger, M.; Boyen, H.G.; Ziemann, P.; Kabius, B. Ordered Deposition of Inorganic Clusters from Micellar Block Copolymer Films. Langmuir 2000, 16, 407-415. (5) Zeng, H.; Li, J.; Liu, J. P.; Wang, Z. L.; Sun, S. Exchange-Coupled Nanocomposite Magnets by Nanoparticle Self-Assembly. Nature 2002, 420, 395-398. (6) Zhang, Y.; Lu, F.; Yager, K. G.; van der Lelie, D.; Gang, O. A General Strategy for the DNA-Mediated Self-Assembly of Functional Nanoparticles into Heterogeneous Systems. Nat. Nanotechnol. 2013, 8, 865-872. (7) Atwater, H. A.; Polman, A. Plasmonics for Improved Photovoltaic Devices. Nat. Mater. 2010, 9, 205-213. 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

(8) Corma, A.; Atienzar, P.; Garcia, H.; Chane-Ching, J.-Y. Hierarchically Mesostructured Doped Ceo2 with Potential for Solar-Cell Use. Nat. Mater. 2004, 3, 394-397. (9) Leite, E.; Weber, I.; Longo, E.; Varela, J. A. A New Method to Control Particle Size and Particle Size Distribution of Sno2 Nanoparticles for Gas Sensor Applications. Adv. Mater. 2000, 12, 965-968. (10) Maier, S. A.; Brongersma, M. L.; Kik, P. G.; Meltzer, S.; Requicha, A. A.; Atwater, H. A. Plasmonics—a Route to Nanoscale Optical Devices. Adv. Mater. 2001, 13, 1501-1505. (11) Tseng, R. J.; Huang, J.; Ouyang, J.; Kaner, R. B.; Yang, Y. Polyaniline Nanofiber/Gold Nanoparticle Nonvolatile Memory. Nano Lett. 2005, 5, 1077-1080. (12) Chang, J.-B.; Son, J. G.; Hannon, A. F.; Alexander-Katz, A.; Ross, C. A.; Berggren, K. K. Aligned Sub-10-Nm Block Copolymer Patterns Templated by Post Arrays. ACS Nano 2012, 6, 2071-2077. (13) Jeong, S. J.; Xia, G.; Kim, B. H.; Shin, D. O.; Kwon, S. H.; Kang, S. W.; Kim, S. O. Universal Block Copolymer Lithography for Metals, Semiconductors, Ceramics, and Polymers. Adv. Mater. 2008, 20, 1898-1904. (14) KG, A. T.; Gotrik, K.; Hannon, A.; Alexander-Katz, A.; Ross, C.; Berggren, K. Templating Three-Dimensional Self-Assembled Structures in Bilayer Block Copolymer Films. Science 2012, 336, 1294-1298. (15) Kim, S. H.; Misner, M. J.; Xu, T.; Kimura, M.; Russell, T. P. Highly Oriented and Ordered Arrays from Block Copolymers Via Solvent Evaporation. Adv. Mater. 2004, 16, 226231. (16) Kim, S. O.; Solak, H. H.; Stoykovich, M. P.; Ferrier, N. J.; de Pablo, J. J.; Nealey, P. F. Epitaxial Self-Assembly of Block Copolymers on Lithographically Defined Nanopatterned Substrates. Nature 2003, 424, 411-414. (17) Mun, J. H.; Chang, Y. H.; Shin, D. O.; Yoon, J. M.; Choi, D. S.; Lee, K. M.; Kim, J. Y.;


Page 20 of 23

Page 21 of 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


Cha, S. K.; Lee, J. Y.; Jeong, J. R.; Kim, Y. H.; Kim, S. O. Monodisperse Pattern Nanoalloying for Synergistic Intermetallic Catalysis. Nano Lett. 2013, 13, 5720-5726. (18) Park, S.; Lee, D. H.; Xu, J.; Kim, B.; Hong, S. W.; Jeong, U.; Xu, T.; Russell, T. P. Macroscopic 10-Terabit–Per–Square-Inch Arrays from Block Copolymers with Lateral Order. Science 2009, 323, 1030-1033. (19) Stoykovich, M. P.; Müller, M.; Kim, S. O.; Solak, H. H.; Edwards, E. W.; De Pablo, J. J.; Nealey, P. F. Directed Assembly of Block Copolymer Blends into Nonregular DeviceOriented Structures. Science 2005, 308, 1442-1446. (20) Chai, J.; Wang, D.; Fan, X.; Buriak, J. M. Assembly of Aligned Linear Metallic Patterns on Silicon. Nat. Nanotechnol. 2007, 2, 500-506. (21) Park, M.; Harrison, C.; Chaikin, P. M.; Register, R. A.; Adamson, D. H. Block Copolymer Lithography: Periodic Arrays of~ 1011 Holes in 1 Square Centimeter. Science 1997, 276, 1401-1404. (22) Jeong, J. W.; Park, W. I.; Kim, M.-J.; Ross, C.; Jung, Y. S. Highly Tunable SelfAssembled Nanostructures from a Poly (2-Vinylpyridine-B-Dimethylsiloxane) Block Copolymer. Nano Lett. 2011, 11, 4095-4101. (23) Matsen, M. W.; Bates, F. S. Origins of Complex Self-Assembly in Block Copolymers. Macromolecules 1996, 29, 7641-7644. (24) Park, S.; Wang, J.-Y.; Kim, B.; Chen, W.; Russell, T. P. Solvent-Induced Transition from Micelles in Solution to Cylindrical Microdomains in Diblock Copolymer Thin Films. Macromolecules 2007, 40, 9059-9063. (25) Shin, D. O.; Mun, J. H.; Hwang, G. T.; Yoon, J. M.; Kim, J. Y.; Yun, J. M.; Yang, Y. B.; Oh, Y.; Lee, J. Y.; Shin, J.; Lee, K. J.; Park, S.; Kim, J. U.; Kim, S. O. Multicomponent Nanopatterns by Directed Block Copolymer Self-Assembly. ACS Nano 2013, 7, 8899-8907. (26) Ramanathan, M.; Tseng, Y.-C.; Ariga, K.; Darling, S. B. Emerging Trends in Metal-



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

Containing Block Copolymers: Synthesis, Self-Assembly,

Page 22 of 23

and Nanomanufacturing

Applications. J. Mater. Chem. C 2013, 1, 2080-2091. (27) Peng, Q.; Tseng, Y.-C.; Darling, S. B.; Elam, J. W. Nanoscopic Patterned Materials with Tunable Dimensions Via Atomic Layer Deposition on Block Copolymers. Adv. Mater. 2010, 22, 5129-5133. (28) Knoll, A.; Lyakhova, K.; Horvat, A.; Krausch, G.; Sevink, G.; Zvelindovsky, A.; Magerle, R. Direct Imaging and Mesoscale Modelling of Phase Transitions in a Nanostructured Fluid. Nat. Mater. 2004, 3, 886-891. (29) Fasolka, M. J.; Banerjee, P.; Mayes, A. M.; Pickett, G.; Balazs, A. C. Morphology of Ultrathin Supported Diblock Copolymer Films: Theory and Experiment. Macromolecules 2000, 33, 5702-5712. (30) Knoll, A.; Horvat, A.; Lyakhova, K. S.; Krausch, G.; Sevink, G. J. A.; Zvelindovsky, A. V.; Magerle, R. Phase Behavior in Thin Films of Cylinder-Forming Block Copolymers. Phys. Rev. Lett. 2002, 89, 035501. (31) Lyakhova, K.; Sevink, G.; Zvelindovsky, A.; Horvat, A.; Magerle, R. Role of Dissimilar Interfaces in Thin Films of Cylinder-Forming Block Copolymers. J. Chem. Phys. 2004, 120, 1127-1137. (32) Lee, A.; Elam, J. W.; Darling, S. B. Membrane Materials for Water Purification: Design, Development, and Application. Environ. Sci.: Water Res. Tenchol. 2016, 2, 17-42. (33) Tsarkova, L.; Sevink, G. A.; Krausch, G. Nanopattern Evolution in Block Copolymer Films: Experiment, Simulations and Challenges. In Complex Macromolecular Systems I; Müller A. E., Schmidt H.; Springer: Berlin Heidelberg, 2010; pp 33-73.


Page 23 of 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


Table of Contents


Self-Assembly of Complex Multimetal Nanostructures from Perforated

Recommend Documents