Binary nanostructure array, in which the sub-component arrays are made of two (or more) different materials or structures in one unit, has been demonstrated to be an innovative principle for designing and constructing functional devices and systems [1–5]. In particular, when the binary sub-components are at the interplay distance, intimate coupling between the two components becomes dominant and endows the macroscopic materials with novel properties and superior functionalities that cannot be achieved by either of the building blocks. In order to qualitatively disentangle the interplay between the building blocks, different strategies, such as ‘bottom-up’ chemical processes and ‘top-down’ physical approaches, have recently been explored. However, these strategies have limited compositional and morphological options, and the resultant binary nanocrystal superlattices and nanodots have poor uniformity and distribution. To address this point, a team led by Yong Lei at the Ilmenau University of Technology, Germany, recently reported a new concept for binary nanostructuring , which employed a unique binary-pore anodized aluminium oxide (AAO) template for realizing large-scale binary structures (Fig. 1). A key process of their technique was using a selective etching process to generate such unique templates. Briefly, using an imprinting/anodization process, an AAO template with an array of square pores (denoted ‘A-pores’) is prepared; by applying selective etching to the bottom side of the template in an NaOH solution, a different set of round pores (denoted ‘B-pores’) appears. The binary-pore template has two sets of differently shaped pores (A- and B-pores) with two barriers located on the opposite side of the template, enabling the modulation of the pore size and shape of each set with a high degree of freedom, and the deposition of different materials in each set of pores individually. Figure 1. View largeDownload slide (A) Binary-pore templates with independently controllable A-pore (square-shaped) and B-pore (round-shaped) sizes: (A1) and (A2) The B-pore sizes are about 158 and 225 nm while the A-pore size is fixed; (A3) and (A4) the A-pore sizes are about 119 and 130 nm while the B-pore size is fixed. (B) SEM image of a typically large-scale ternary-pore template (50 × 20 μm). (C) SEM images (tilted views) of different binary nanostructure arrays: nanowire/nanowire (C1), nanowire/nanotube (C2), nanotube/nanotube (C3), nanodot/nanodot (C4). All scale bars: 400 nm. Figure 1. View largeDownload slide (A) Binary-pore templates with independently controllable A-pore (square-shaped) and B-pore (round-shaped) sizes: (A1) and (A2) The B-pore sizes are about 158 and 225 nm while the A-pore size is fixed; (A3) and (A4) the A-pore sizes are about 119 and 130 nm while the B-pore size is fixed. (B) SEM image of a typically large-scale ternary-pore template (50 × 20 μm). (C) SEM images (tilted views) of different binary nanostructure arrays: nanowire/nanowire (C1), nanowire/nanotube (C2), nanotube/nanotube (C3), nanodot/nanodot (C4). All scale bars: 400 nm. It is concluded that, based on in situ SEM investigation and electric field simulation, the growth of the unique binary-pore structures originates from a combination of electric-field-assisted dissolution and plastic oxide flow. Based on this pore growth mechanism, the authors have also successfully developed ternary- (C-pores) (Fig. 1(B)) and quadruple-pore templates (C and D pores) with the same selective etching process. The morphology of the new etched third set of C-pores in the ternary-pore template can be adjusted not only by the selective etching time but also by the size difference between the A- and B-pores. Therefore, decreasing the size difference between the A- and B-pores causes the shape of the C-pores to gradually change from oval to round. The binary-pore templates are realizable over a wide range of interpore distances from 142 ± 13 to 573 ± 27 nm, indicating the high capabilities for adjusting the structural parameters of the resultant binary nanostructures. Using different well-established deposition processes such as electrochemical deposition and atomic layer deposition, the researcher proved that 0- and 1D binary materials (arrays of nanodots, nanowires and nanotubes) with different shapes, sizes and compositions were synthesized (Fig. 1(C)). Because the binary materials are highly dependent on the binary-pore template, countless binary materials are expected to be fabricated by use of suitable fabrication strategies. To demonstrate the potential of the binary nanostructuring concept in puzzling model systems of significant current interest, wireless photosynthesis cells, plasmonic devices and vertical nanowire transistors were demonstrated. These ‘smoking gun’ experiments exhibit superior properties compared to their corresponding single-component counterparts. Briefly, the significant achievement of this work originates from the unique binary-pore template and flexible choice of synthesis strategies, which allows precise control over the size, shape, composition and dimension of each sub-component (Fig. 2). Inspired by this work, it can be expected that a new generation of multi-functional and innovative devices/systems based on these emerging different binary materials may appear in electronic, optoelectronic and other fields in the future. Figure 2. View largeDownload slide Schematic of the binary nanostructuring concept: from the fabrication of binary materials with precise control of size, shape, composition, dimension and intercomponent spacing to new materials and functions. Figure 2. View largeDownload slide Schematic of the binary nanostructuring concept: from the fabrication of binary materials with precise control of size, shape, composition, dimension and intercomponent spacing to new materials and functions. REFERENCES 1. Shevchenko EV , Talapin DV , Kotov NA et al. Nature 2006 ; 439 : 55 – 9 . CrossRef Search ADS PubMed 2. Dong AG , Chen J , Vora PM et al. Nature 2010 ; 466 : 474 – 7 . CrossRef Search ADS PubMed 3. Ye XC , Zhu CH , Ercius P et al. Nat Commun 2015 ; 6 : 10052 . CrossRef Search ADS PubMed 4. Shegai T , Chen S , Miljkovic VD et al. Nat Commun 2011 ; 2 : 481 . CrossRef Search ADS PubMed 5. Liu N , Tang ML , Hentschel M et al. Nat Mater 2011 ; 10 : 631 – 6 . CrossRef Search ADS PubMed 6. Wen L , Xu R , Mi Y et al. Nat Nanotech 2017 ; 12 : 244 – 50 . CrossRef Search ADS © The Author(s) 2017. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd. All rights reserved. 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National Science Review – Oxford University Press
Published: Jun 30, 2017
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