Direct Synthesis of B−C−N Single-Walled Nanotubes by Bias-Assisted Hot Filament Chemical Vapor Deposition

Abstract

Soon after the discovery of carbon nanotubes, the ternary system of BCN nanotubes began to attract increasing research interest. [1][2][3] A prime advantage of the BCN nanotubes over their carbon counterparts is the relative simplicity in controlling the tube electronic properties. 2,3 A pristine carbon single-walled nanotube (C-SWNT) may behave either as metal or as semiconductor with varying band gaps, depending sensitively on the tube diameter and chirality whose control remains a formidable challenge for all known synthetic methods. By contrast, the electronic structure of BCN nanotubes is predicted to be controlled largely by their chemistry rather than their geometry, such that the band gap could be tailored over a wide range merely by varying the tube's chemical composition. 2,3 Direct synthesis of the B-and N-doped multi-walled carbon nanotubes (BCN-MWNTs) was first attempted by Stéphan et al. in 1994. 2a Since then, considerable progress has been made in the synthesis of the ternary BCN-MWNTs and/or nanofibers by different means of arc-discharge, laser ablation, and chemical vapor deposition (CVD). 2,4,5 At the same time, theoretical understanding of the structural and electronic properties concerning the BCN nanotubes has also been largely advanced. 3,6 The majority of the theoretical work, however, has been dealing with the SWNT structures rather than MWNTs (or nanofibers). 3,6 There are clearly many fundamental differences between those two systems. 7 Importantly, it is only the SWNTs' structure that would make the study of their intrinsic structural and physical properties easier and more valuable. 3,[6][7][8] In this regard, exploring synthetic methods for producing high-quality ternary BCN-SWNTs is highly desirable, though it seems to be an even more difficult task. Up to now, the only existing example of the ternary BCN-SWNTs synthesis was achieved via an alternative post-growth treatment route, that is, by substitution reaction of the presynthesized pristine C-SWNTs with B 3 O 2 and N 2 at high temperature. 9 As far as the direct synthesis route is concerned, although a few studies showed the possibility of direct doping of C-SWNTs solely with B or N, 10,11 evidences for the presence of the ternary SWNTs simultaneously composed of the B, C, and N elements have not been identified yet.Herein, we report on the direct, large-scale synthesis of ternary BCN-SWNTs via a bias-assisted hot filament CVD (HF-CVD) process. The same HF-CVD system has previously been used in our group to grow turbostratic BCN films and oriented BCN MWNTs. 12 This work is a continuation of our ongoing efforts toward the rational growth of BCN nanostructures. In the present contribution, the BCN-SWNTs' growth by HF-CVD was achieved over the powdery MgO-supported Fe-Mo bimetallic catalyst (denoted as Fe-Mo/MgO), by using CH 4 , B 2 H 6 , and ethylenediamine vapor as the reactant gases. Details of the catalyst preparation and the HF-CVD growth process are presented in the Supporting Information.In Figure 1a, we display the...

Synthesis, Structure, and Properties of Single‐Walled Carbon Nanotubes

“…[105][106][107][108] Nevertheless, as far as we are aware, substitutional doping of SWCNTs has proved to be much more difficult, and it is not until very recently that some reports concerning the synthesis of B-and/or N-doped SWCNTs are emerging. [119][120][121] Although very challenging, substitutional doping of CNTs at the single-shell structural level is no doubt accompanied with high expectations. As a knowledge of the pure C system shows, there are many differences between SWCNTs and MWCNTs, and the SWCNT structure should be more fundamental.…”

Converting Metallic Single‐Walled Carbon Nanotubes into Semiconductors by Boron/Nitrogen Co‐Doping

“…[15] Very recently, we have realized the direct synthesis of BCN-SWNTs by chemical vapor deposition. [16] Herein, we report the fabrication of field-effect transistor (FET) devices using the as-prepared BCN-SWNTs. Electronic transport measurements elucidate that the BCN-SWNTs are purely semiconducting.…”

Synthesis of Inorganic Nanotubes

“…[212] In this method, a FeÀMo catalyst supported on MgO powder is used for the decomposition of a mixture of CH 4 , B 2 H 6 , and ethylenediamine. The as-grown SWNTs have clean and smooth surfaces with diameters in the range of 0.8-2.5 nm and lengths up to micrometers.…”