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Downloaded from https://academic.oup.com/nsr/article/5/3/310/4077041 by DeepDyve user on 19 July 2022 310 Natl Sci Rev, 2018, Vol. 5, No. 3 PERSPECTIVES MATERIALS SCIENCE The road to chirality-speciﬁc growth of single-walled carbon nanotubes Shuchen Zhang, Lianming Tong and Jin Zhang Moore’s law has been declared to be Single-walled carbon nanotubes chirality are mainly explored through eventually nearing its end after nearly (SWNTs) are regarded as one of catalyst design in the CVD process. five decades, with silicon being the main the most promising candidates as build- Although the CVD method has been building block for all computing chips ing blocks in next-generation electronics extensively studied, how to improve the . The main roadblock in the devel- . The most advanced opportunities selectivity of SWNTs is still a great chal- opment of transistors is the occurrence demand the ability to form perfectly lenge. The key factors include the exact of the tunneling effect when the de- aligned, horizontal arrays of SWNTs symmetry matching between catalysts vices become small enough. A possi- with controlled structure using the and SWNTs in thermodynamics, and ble solution is finding alternative ma- chemical vapor deposition (CVD) the optimization of the growth condition terials to fabricate a ‘millivolt switch’, method. according to the growth kinetics of which is at least as fast as silicon coun- At present, the growth efficiency different SWNTs. The cooperation terparts and generates much less heat. and selectivity of SWNTs with specific of the two factors will open up new Downloaded from https://academic.oup.com/nsr/article/5/3/310/4077041 by DeepDyve user on 19 July 2022 PERSPECTIVES Zhang et al. 311 Metal Bimetal Carbide these solid catalysts, nucleation in ther- catalysts catalysts catalysts modynamics of SWNTs on solid cata- Liquid Solid lysts should be studied. We put forward Co,Fe … Co/Mo, Fe/Ru, W/Co … WC, Mo C the theory of symmetry matching be- VS Target: 99.9999% tween the edge of SWNTs and the face of (14,4) solid catalysts. This not only can predict Thermodynamics+ Kinetics (12,6) the chirality-specified growth of SWNTs (12,6) through the symmetry of the catalysts, (8,4) but also can provide guidance to design (16,0) new catalysts to enrich the SWNTs with (6,5) (12, 6) (9,8) pre-defined chirality. Nevertheless, the (6,5) (6,5) symmetry matching is a simple model of (9,9) Thermodynamics (9,8) bonding between catalysts and SWNTs, (6,5) (7,5) (6,5) (7,5) and needs much deeper investigation in (8,4) (6,5) (7,5) both theory and experiments. (6,5) (6,5) (7,5) (9,8) The growth of SWNTs, as a typical (15,8) (7,5) (8,3) 20 chemical reaction, is also affected by ki- (7,6) (6,6) netics. In 2009, Feng Ding et al. sug- (15,11) (8,4) gested a screw-dislocation theory to ex- (10,9) 0 VLS plain the kinetics growth behavior of 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 SWNTs, in which the growth rate is pro- Year portional to the Burgres vector of the dislocation that is related to the chiral an- Figure 1. The development of selective SWNTs growth using different catalysts based on different gle . They successfully explained the growth modes. VLS and VS are the main mechanisms to explain the growth of SWNTs on different enrichment of near-armchair carbon nan- catalyst surfaces. Almost all the near-armchair tubes were enriched with a low selectivity in the otubes (see Fig. 1). However, this the- power sample. The solid catalysts with extremely high melting points are marked in blue. The solid ory only considered liquid catalysts. The catalysts are beneficial for the chirality-specified growth of SWNTs based on the VS mechanism on kinetic growth behavior should be fur- the substrate surface. The vertical axis represents the reported abundance of SWNTs with specific ther simulated on solid catalysts. This was chirality, and the target of the abundance before 2020 is marked by the red dashed line. done by Yakobson et al. in 2014 . A slab model of solid catalyst was in- opportunities for the chirality-specific will lead to many possibilities during the troduced to modify the Burgres vector growth of SWNTs. growth of SWNTs. Nevertheless, efforts of the dislocation, and they showed that During the CVD growth of SWNTs, have been made to control the chiral- (2 m, m) tubes have the highest kinetic catalysts facilitate the decomposition of ity of SWNTs by using solid-state cat- growth rate for the most dislocations . the carbon-feeding gases and serve as alysts through vapor-solid (VS) mech- Recently, our group proved it experimen- the nucleation centers of SWNTs . anisms instead of VLS mechanisms. In tally through controlling the concentra- The size and state of the catalyst af- the periodic table of elements, tungsten tion of carbon feeding to selectively poi- fect the chirality of SWNTs from a ther- and molybdenum are the metals with the son catalyst nanoparticles, on which the modynamics point of view. Therefore, highest melting points, but their catalytic tubes grow slowly. As a result, the tubes many researchers have tried to establish activities are poor. Hence, rational de- with smooth edges, such as the zigzag and sign of new solid-state catalysts based on the exact relationship between SWNTs armchair ones, are most difficult to en- and catalysts from both theoretical cal- tungsten or molybdenum is required to rich on solid catalysts, although (16, 0) culations and experimental observations. improve catalytic activity. In 2014, Yan and (6, 6) tubes have been reported to However, the traditional metal catalysts, Li et al. first introduced Co to form the be prepared successfully. It can be noted shown in Fig. 1 [4-7], showed relatively solid intermetallic W Co catalyst with 6 7 that (2 m, m) tubes could be enriched lower melting points, very different from unique structure and high stability and easily in addition to near-armchair tubes. the bulk melting point, and are termed obtained (12, 6) tubes with high selec- A fact is that the enrichment of near- as ‘liquid catalysts’. A generally accepted tivity, although the density was relatively armchair tubes has been realized in the vapor-liquid-solid (VLS) mechanism was low . We designed carbides of tung- powder sample, but with low selectivity put forward to explain the growth of sten and molybdenum as catalysts, which and, on the surface of substrate, (2 m, SWNTs on these catalysts. However, it have higher melting points and improved m) tubes could be enriched with high se- seems to be an extravagant hope that catalytic activity, and grew (8, 4) and lectivity (see Fig. 1). This may be due to the chirality selectivity will be satisfac- (12, 6) SWNT arrays with high density the difference of catalysts in contact with tory, because the instability of catalysts . To further understand the role of (n,m) Abundance (%) Growth Mode Downloaded from https://academic.oup.com/nsr/article/5/3/310/4077041 by DeepDyve user on 19 July 2022 312 Natl Sci Rev, 2018, Vol. 5, No. 3 PERSPECTIVES atmosphere when SWNTs are grown: for always satisfactory—for example, Raman Corresponding author. the latter, the catalyst was exposed to a is always resonant and transmission elec- E-mail: email@example.com homogeneous atmosphere and, for the tron microscope (TEM) is usually very former, a heterogeneous atmosphere was local—further efforts should be made REFERENCES formed by diffusion in the holes of sup- and more exact characterization methods ports. Obviously, in a homogeneous at- should be developed to yield enough 1. Waldrop MM. Nature 2016; 530: 144–7. mosphere, kinetic controlling of SWNTs discoveries in the controlled growth of 2. Franklin AD. Science 2015; 349: 6249. growth could be operated easily. SWNTs using the catalyst-mediated 3. 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Center for Nanochemistry, Beijing Science and National Science Review In summary, due to the well-known Engineering Center for Nanocarbons, College of 5: 310–312, 2018 limits in various characterization meth- Chemistry and Molecular Engineering, Peking doi: 10.1093/nsr/nwx080 ods, which make the current static not University, China Advance access publication 8 August 2017
National Science Review – Oxford University Press
Published: May 1, 2018
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