Facile "needle-scratching" method for fast catalyst patterns used for large-scale growth of densely aligned single-walled carbon-nanotube arrays

Floating Bimetallic Catalysts for Growing 30 cm-Long Carbon Nanotube Arrays with High Yields and Uniformity

Ultralong carbon nanotubes (CNTs) are considered as promising candidates for many cutting-edge applications. However, restricted by the extremely low yields of ultralong CNTs, their practical applications can hardly be realized. Therefore, new methodologies shall be developed to boost the growth efficiency of ultralong CNTs and alleviate their areal density decay at the macroscale level. Herein, a facile, universal, and controllable method for the in situ synthesis of floating bimetallic catalysts (FBCs) is proposed to grow ultralong CNT arrays with high yields and uniformity. Ferrocene and metal acetylacetonates serve as catalyst precursors, affording the successful synthesis of a series of FBCs with controllable compositions. Among these FBCs, the optimized FeCu catalyst increases the areal density of ultralong CNT arrays to a record-breaking value of ≈8100 CNTs mm-1 and exhibits a lifetime 3.40 times longer than that of Fe, thus achieving both high yields and uniformity. A 30-centimeters-long and high-density ultralong CNT array is also successfully grown with the assistance of FeCu catalysts. As evidenced by this kinetic model and molecular dynamics simulations, the introduction of Cu into Fe can simultaneously improve the catalyst fluidity and decrease carbon solubility, and an optimal catalytic performance will be achieved by balancing this tradeoff.

Synthesis of Ultralong Carbon Nanotubes with Ultrahigh Yields

Ultralong carbon nanotubes (CNTs) are in huge demand in many cutting-edge fields due to their macroscale lengths, perfect structures, and extraordinary properties, while their practical application is limited by the difficulties in their mass production. Herein, we report the synthesis of ultralong CNTs with a dramatically increased yield by a simple but efficient substrate interception and direction strategy (SIDS), which couples the advantages of floating-catalyst chemical vapor deposition with the flying-kite-like growth mechanism of ultralong CNTs. The SIDS-assisted approach prominently improves the catalyst utilization and significantly increases the yield. The areal density of the ultralong CNT arrays with length of over 1 cm reached a record-breaking value of ∼6700 CNTs mm^-1, which is 2-3 orders of magnitude higher than the previously reported values obtained by traditional methods. The SIDS provides a solution for synthesizing high-quality ultralong CNTs with high yields, laying the foundation for their mass production.

Aligned carbon nanotubes: from controlled synthesis to electronic applications

Single-wall carbon nanotubes (SWNTs) possess superior geometrical, electronic, chemical, thermal, and mechanical properties and are very attractive for applications in electronic devices and circuits. To make this a reality, the nanotube orientation, density, diameter, electronic property, and even chirality should be well controlled. This Feature article focuses on recent achievements researchers have made on the controlled growth of horizontally aligned SWNTs and SWNT arrays on substrates and their electronic applications. Principles and strategies to control the morphology, structure, and properties of SWNTs are reviewed in detail. Furthermore, electrical properties of field-effect transistors fabricated on both individual SWNTs and aligned SWNT arrays are discussed. State-of-the-art electronic devices and circuits based on aligned SWNTs and SWNT arrays are also highlighted.

Sorting out semiconducting single-walled carbon nanotube arrays by washing off metallic tubes using SDS aqueous solution

Semiconducting single-walled carbon nanotube (s-SWNT) arrays are produced via a procedure analogous to a surfactant-assisted decontamination process. Aligned individual SWNT arrays grow on a quartz surface as a mixture of metallic SWNTs (m-SWNTs) and s-SWNTs. They are immersed in a sodium dodecyl sulfate (SDS) solution, and the SDS molecules selectively adsorb onto m-SWNTs. This SDS coating minimizes the interaction between m-SWNTs and the substrate, thus the m-SWNTs are easily washed off during ultrasonication while the s-SWNT arrays remain on the substrate. The percentage of s-SWNTs in the arrays can be higher than 90%.

CVD-grown horizontally aligned single-walled carbon nanotubes: synthesis routes and growth mechanisms

Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided.

Chemically functionalized surface patterning

Patterning substrates with versatile chemical functionalities from micro- to nanometer scale is a long-standing and interesting topic. This review provides an overview of a range of techniques commonly used for surface patterning. The first section briefly introduces conventional micropatterning tools, such as photolithography and microcontact printing. The second section focuses on the currently used nanolithographic techniques, for example, scanning probe lithography (SPL), and their applications in surface patterning. Their advantages and disadvantages are also demonstrated. In the last section, dip-pen nanolithography (DPN) is emphatically illustrated, with a particular stress on the patterning and applications of biomolecules.

Generation of dual patterns of metal oxide nanomaterials based on seed-mediated selective growth

A facile route for the generation of the dual patterns of metal oxide nanomaterials, for example, ZnO and CuO, has been developed by printing the oxide seeds through a combination of microcontact printing (microCP) and microfluidic (microF) techniques, followed by the simultaneous growth of the two metal oxide nanomaterials in a one-step solution reaction based on hydrothermal, seed-mediated selective growth. The obtained dual patterns of ZnO nanorods and CuO nanoneedles show a sharp boundary between them, indicating well-defined dual-pattern generation. Also, the simultaneous growth of metal oxide nanomaterials is highly material-selective for the specific seeds prepatterned on substrates, resulting in the selective growth of ZnO nanorods and CuO nanoneedles on the ZnO and CuO seeds, respectively. Moreover, the generation of high-quality dual patterns has been similarly realized on a flexible poly(ethylene terephthalate) (PET) wafer. This study demonstrates the well-controlled hydrothermal growth of different metal oxide nanomaterials in the same reaction solution on the preprinted oxide seeds on the target substrates. It opens up an avenue to develop multifunctional devices of different metal oxides with the combination of microCP and microF techniques.