Large-Scale Fabrication of Boron Nitride Nanotubes via a Facile Chemical Vapor Reaction Route and Their Cathodoluminescence Properties
Bo Zhong
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2
Xiaoxiao Huang
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2
Guangwu Wen
0
1
2
Hongming Yu
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2
Xiaodong Zhang
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2
Tao Zhang
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2
Hongwei Bai
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2
0
School of Materials Science and Engineering, Harbin Institute of Technology
, 150001, Harbin,
People's Republic of China
1
School of Materials Science and Engineering, Harbin Institute of Technology (Weihai)
, 264209, Weihai,
People's Republic of China
2
School of Materials Science and Engineering, Harbin Institute of Technology
, 150001, Harbin,
People's Republic of China
Cylinder- and bamboo-shaped boron nitride nanotubes (BNNTs) have been synthesized in large scale via a facile chemical vapor reaction route using ammonia borane as a precursor. The structure and chemical composition of the as-synthesized BNNTs are extensively characterized by X-ray diffraction, scanning electron microscopy, highresolution transmission electron microscopy, and selected-area electron diffraction. The cylinder-shaped BNNTs have an average diameter of about 100 nm and length of hundreds of microns, while the bamboo-shaped BNNTs are 100-500 nm in diameter with length up to tens of microns. The formation mechanism of the BNNTs has been explored on the basis of our experimental observations and a growth model has been proposed accordingly. Ultraviolet-visible and cathodoluminescence spectroscopic analyses are performed on the BNNTs. Strong ultraviolet emissions are detected on both morphologies of BNNTs. The band gap of the BNNTs are around 5.82 eV and nearly unaffected by tube morphology. There exist two intermediate bands in the band gap of BNNTs, which could be distinguishably assigned to structural defects and chemical impurities.
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Introduction
As structural analogs of carbon nanotubes (CNTs),
boron nitride nanotubes (BNNTs) have attracted
continuous attention owing to their extraordinary structural
and physical properties [1,2]. Similar to CNTs, BNNTs
possess a superior Youngs modulus and a high thermal
conductivity [3-6]. BNNTs are electrical insulator and
transparent to visible light due to a wide band gap
(around 5.25.8 eV) that is almost independent of tube
chirality [7,8]. Furthermore, BNNTs exhibit excellent
chemical stability and inoxidizability [2,9]. The unique
structure-induced properties of BNNTs bring a series of
opportunities for their potential applications as
hydrogen storage media, biological probes, piezoelectric
materials, composite reinforcements and harsh-environment
semiconductor devices [10-17]. These promises have
motivated intense research efforts seeking to develop
synthetic strategies for preparing BNNTs.
Despite the structural similarity between BNNTs
and conventional CNTs, great challenges have been
encountered in fabricating BNNTs compared with the
relative ease of synthesizing CNTs. Many techniques,
such as arc-discharge [1], ball milling and annealing
[18-21], laser ablation [22-24], chemical vapor
deposition [25,26], oven heating proper B and N containing
precursors [27,28], template confining [29,30], and so
forth, have been attempted to fabricate the BNNTs in
recent years. Although some success has been achieved
in producing pure and well-crystallized BNNTs, these
techniques generally require special equipments or
complex synthesis procedures and the yields of BNNTs are
commonly disappointingly low.
Here, we describe a facile growth technique that can
easily and reliably produce macroscopic amounts
(~200 mg per experimental run) of BNNTs with
cylinder and bamboo-shaped morphologies. Ammonia
borane (AB, H3BNH3), which contains only B, N and H
elements, is demonstrated to be an effective starting
material for the fabrication of BNNTs. The structures
and luminescence performance of the as-synthesized
BNNTs have been extensively characterized. A two-step
growth model has been established based on the analysis of
the structures of BNNTs and the reaction process. The
present work provides a facile synthetic approach and a deeper
insight into the luminescence performance of BNNTs,
which facilitates large-scale production of BNNTs and their
application as compact ultraviolet (UV) laser devices.
Experimental
In this study, we present a simple approach for the
fabrication of BNNTs in a gas pressure furnace. Ammonia
borane (AB) synthesized according to Ramachandran
[31] was used as a starting material, and ferrocene
was used as a catalyst. In a typical procedure, AB powder
(4.0 g) and ferrocene (1.5 g) were mixed and charged into
an graphite crucible of about 2 l capacity using a piece of
graphite paper as inner lining, then the crucible was
loaded into the furnace chamber. The chamber was
sealed and pumped down to a base pressure of 0.1 Pa.
Subsequently, 0.8 MPa high pure nitrogen was pressed
into the furnace chamber. The furnace was heated to
1,450C at a rate of 10C min-1 and held for 60 min
before it was finally cooled to room temperature. The
BNNTs were found on the graphite paper. The samples
obtained were extensively characterized by scanning
electron microscopy (SEM, MX2 (...truncated)