Role of 1D Metallic Nanowires in Polydomain Graphene for Highly Transparent Conducting Films

Choi, Hyung Ouk; Kim, Dae Woo; Kim, Seon Joon; Yang, Seung Bo; Jung, Hee Tae

doi:10.1002/adma.201306234

Cited by 44 publications

(31 citation statements)

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“…Among these methods, surface anchoring is of particular interest because surface‐induced alignment of soft materials over large areas is highly feasible. Typically, it has been accomplished via rubbing of polymer films, photoalignment, ion‐beam irradiation, self‐assembly of monolayers, preparation of 2D material surfaces, and patterned of grooved surfaces via lithography …”

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“…This limited adoption of anchoring surfaces may be attributed to the very weak anchoring energy of the surfaces studied and the very strong interaction between molecules, which necessitate ultrastrong anchoring energy to overcome the self‐interaction of molecules on the surface. In efforts to prepare highly effective surfaces distinct from conventional polymer surfaces obtained by rubbing, photoalignment, and ion‐beam irradiation, crystalline surfaces of 2D materials such as graphene and molybdenum dioxide (MoS 2 ) have been used to anchor soft materials . However, the hexagonal symmetry of 2D materials can induce multidirectional alignment of soft materials even in a single‐crystal 2D surface, and the range of aligned molecules may be limited to those possessing strong π–π interactions with 2D materials .…”

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“…In efforts to prepare highly effective surfaces distinct from conventional polymer surfaces obtained by rubbing, photoalignment, and ion‐beam irradiation, crystalline surfaces of 2D materials such as graphene and molybdenum dioxide (MoS 2 ) have been used to anchor soft materials . However, the hexagonal symmetry of 2D materials can induce multidirectional alignment of soft materials even in a single‐crystal 2D surface, and the range of aligned molecules may be limited to those possessing strong π–π interactions with 2D materials . In this regard, grooved surfaces can provide a powerful approach, because the anchoring energy and anchoring direction of their patterned surface can be artificially designed by controlling the direction, amplitude, and period of the patterned substrate according to Berreman's theory .…”

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“…Interestingly, a singular anchoring direction of n CBs on the BP surface was well maintained during repeated phase transition from the isotropic to smectic to nematic phase (Figure S4, Supporting Information). Nematic‐phase n CB molecules can selectively align along three crystalline directions ((100), (010), and (−1−10)) of graphene and MoS 2 single domains because of their hexagonal symmetry during repeated transition from the nematic to the isotropic phase . This alignment indicates the strong pinning effects of the BP surface on the aligning direction of n CBs.…”

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Ultrastrong Anchoring on the Periodic Atomic Grooves of Black Phosphorus

Kim

Jeong

Kwon

et al. 2016

Adv Materials Inter

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the range of aligned molecules may be limited to those possessing strong π-π interactions with 2D materials. [19][20][21] In this regard, grooved surfaces can provide a powerful approach, because the anchoring energy and anchoring direction of their patterned surface can be artificially designed by controlling the direction, amplitude, and period of the patterned substrate according to Berreman's theory. [22][23][24] Despite the success achieved with aligning lyotropic chromonic liquid crystals (LC) by introducing patterned surfaces with high aspect ratio, [22] the anchoring energy of the grooved surfaces used in these attempts is still low for anchoring of various soft materials such as polymeric materials and dendrimers. This limitation is due to the restriction of the surface anchoring energy of the patterned surface to above 20 nm by the resolution of current lithographic techniques. [22][23][24] Here, we demonstrate for the first time that black phosphorus (BP) with atomic-scale grooves and a puckered honeycomb structure of adjacent phosphorus atoms enables alignment of a wide range of soft materials, including thermotropic LCs such as 4-cyano-4′-alkylbiphenyl (nCB) and 4-cyano-4′-alkyloxybiphenyl (nOCB), the lyotropic LC sunset yellow (SSY), and fluorinated dendrimers. Especially, SSY and dendrimer molecules are difficult to align through known surfaceanchoring techniques. We found that the planar direction of the aligned soft materials is fixed in a single direction, following the direction of the atomic grooves of BP. This result is attributed to the regular and atomic-scale grooves of BP with height of 2 Å and period of 4.33 Å. [26] These induce an ultrastrong azimuthal anchoring energy of soft materials, ≈0.235 N m −1 (for 5CB), which is two orders of magnitude higher than that of previously reported anchoring methods. Thus, our surface-anchoring technology represents a new approach for aligning a wide range of soft materials using well-designed atomic-scale grooves of BP. Such an approach can be used in various methods for realizing high-performance optoelectronic devices and biotechnological applications.The overall procedure for aligning various soft materials on the BP surface is illustrated in Figure 1. Briefly, BP flakes were exfoliated through a mechanical method using commercial 3M tape and then transferred onto SiO 2 /Si substrates for polarized optical microscopy (POM) observations and onto a Si nitride (SiN) grid for transmission electron microscopy (TEM) observations (Figure 1a). [27] The BP substrate was coated with various soft materials, namely, nCB, nOCB, SSY, and fluorinated dendrimer, by either spin-coating or a sandwiched-cell or solution-casting method, depending on the materials and observation tools (for specific experimental conditions, see the Experimental Section; Figure 1b). Thermotropic nCBs, nOCBs, and lyotropic SSY were used because the anchoring behavior of Controlling the molecular orientation of soft materials is one of the most important issues in physical and materials ...

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Ultrastrong Anchoring on the Periodic Atomic Grooves of Black Phosphorus

Kim

Jeong

Kwon

et al. 2016

Adv Materials Inter

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“…Preparation of the Graphene Substrate : A natural graphite flake was exfoliated through the conventional scotch tape method and then transferred to the SiO 2 /Si substrate. Single‐layer graphene was synthesized through the CVD method . In the first step, Cu foil was inserted into a quartz tube, which was then heated to 1040 °C under H 2 flowing at a rate of 8 sccm and having a pressure of 90 mTorr.…”

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Epitaxial Crystallization Behaviors of Various Metals on a Graphene Surface

Kim

Choi

et al. 2016

Adv Materials Inter

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and Ni, significantly influence graphene crystallization during the CVD process, [23][24][25][26] while there are several reports for the preferred growth of Au nanoparticles to [111] direction on the graphene surface and for the relaxation of residual stress of metal film by applying graphene. [27,28] Here, we investigate the epitaxial crystallization behaviors of various metals on the surface of graphene. The target metals (Ni, Cu, Pt, Au, and Fe) were deposited on the graphene surface by e-beam evaporation, and then further thermal annealing was conducted to induce crystallization of the deposited metal films. Experimental results of electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the atomic layer of graphene can dramatically change the crystallization behaviors of metals. Face-centered cubic (FCC) metals like Ni, Au, Cu, and Pt displayed a preferred orientation along the [111] direction on the graphene layer, whereas Fe, which has a body-centered cubic (BCC) structure, displayed a preferred orientation along the [100] direction. This orientation can be due to metal crystallization along a direction that reduces the stress resulting from lattice misfit between graphene and metals. In particular, the lattice parameter (0.249 nm) of Ni (111) was close to that of graphene (0.246 nm), and the size of the graphene domains influenced the domain structure of Ni. Although the orientation of a crystallized metal film was determined by graphene, many tilted small domains were observed in the other crystallized metal films, particularly in Cu, Pt, and Fe. Furthermore, epitaxial crystallization of metals on the 3D structure was demonstrated using a Ni mesh with a graphene coating as a supporting substrate. Our study indicates the effectiveness of graphene as a 3D epitaxy substrate. We believe that our findings may not only aid in understanding the interaction of metals and graphene at their interface, but also provide insight into the use of graphene as a substrate for controlling the crystalline directions of metals in their potential applications such as electronic devices, electro catalysis, and photo catalysis based on graphene and metal hybrid materials.In order to observe the crystallization behaviors of various metals on a graphene surface, the nanocrystalline metals Ni, Au, Cu, Pt, and Fe were deposited by e-beam evaporation on the surfaces of graphene exfoliated by the scotch tape method or CVD-grown graphene (Figure 1A-C). It is worth noting that the epitaxial crystallization behaviors of metals on both CVDgrown graphene and graphene exfoliated by the scotch tape method were similar in terms of crystal orientation. To obtain single-crystal graphene sheets, a single-crystal natural graphite flake (Asbury Carbon) was exfoliated using the scotch tape method and then transferred to a SiO 2 /Si substrate. To prepare large-area graphene, a conventional CVD method using Cu and Ni foil was performed, as previously reported. [16,17]

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2D Hybrid Nanostructured Dirac Materials for Broadband Transparent Electrodes

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Broadband transparent electrodes based on 2D hybrid nanostructured Dirac materials between Bi2 Se3 and graphene are synthesized using a chemical vapor deposition (CVD) method. Bi2 Se3 nanoplates are preferentially grown along graphene grain boundaries as "smart" conductive patches to bridge the graphene boundary. These hybrid films increase by one- to threefold in conductivity while remaining highly transparent over broadband wavelength. They also display outstanding chemical stability and mechanical flexibility.

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Role of 1D Metallic Nanowires in Polydomain Graphene for Highly Transparent Conducting Films

Cited by 44 publications

References 50 publications

Ultrastrong Anchoring on the Periodic Atomic Grooves of Black Phosphorus

Ultrastrong Anchoring on the Periodic Atomic Grooves of Black Phosphorus

Epitaxial Crystallization Behaviors of Various Metals on a Graphene Surface

2D Hybrid Nanostructured Dirac Materials for Broadband Transparent Electrodes

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