Synchrotron Photoluminescence Spectroscopy of Boron Nitride Nanotubes with Different Metal Impurities
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Synchrotron Photoluminescence Spectroscopy of Boron Nitride Nanotubes with Different Metal Impurities Jun Yu1, Ying Chen2, Luhua Li1,2, Bing-Ming Cheng3, Dehong Yu4 Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia 2 Institute for Technology Research and Innovation, Deakin University, Waurn Ponds, VIC 3217, Australia 3 National Synchrotron Radiation Research Center, Hsinchu, Taiwan 4 Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Height, NSW2234, Australia 1
ABSTRACT The influence of impurities in boron nitride nanotubes (BNNTs) on their photoluminescence (PL) behaviors has been investigated. Similar PL spectra were obtained from the bulk disk samples of cold-pressed BNNTs and dispersed individual BNNTs deposited on a CaF2 substrate. Metal impurities such as catalyst Fe and coated Au particles do not affect PL emissions from BNNTs if they do not change nanotube electronic structures. INTRODUCTION Boron nitride nanotubes (BNNTs) can be simply seen as rolled-up hexagonal boron nitride sheet(s). Since hexagonal boron nitride (h-BN) has a wide band gap of almost 6 eV [1], BNNTs are also expected to inherit the same property. Recently, many interesting optical properties including strong excitonic transitions and various light emissions are found in BNNTs [2-5]. However, determination of the electronic structures and optical properties of materials with the bandgaps as wide as 6 eV is difficult as conventional laser-sourced photoluminescence (PL) spectroscopy cannot cover the PL range up to such a high energy, corresponding to a wavelength of around 200 nm [6,7]. PL spectroscopy with synchrotron vacuum ultraviolet (VUV) source has to be used as the synchrotron radiation can cover a full energy range up to 6.2 eV allowing the light emission to be measured in the range from 200 to 800 nm. Previous PL investigation of carbon nanotubes (CNTs) has suggested that nanotube purity, size and environment (individual tube or tube assemble) can affect the PL spectra [8,9], and most BNNT samples often contain a small amount of metal particles as they are needed as catalysts to help the nanotube growth [10,11]. These catalyst particles may exist inside the nanotubes or stay outside of nanotubes as inclusion depending on different nanotubes [12]. Therefore, it is important to investigate the influence of metal impurities on the PL spectra. This work focuses on PL studies of the BNNTs in different forms and containing different metal impurities. EXPERIMENTAL DETAILS BNNTs were synthesized using the ball milling and annealing method [10]. Boron powder (Sigma-Aldrich) with purity of 95-97% was used as the starting material and anhydrous
NH3 as the reaction gas for milling and annealing processes. Ball milling treatment was conducted at room temperature using a rotating steel ball mill with four hardened steel balls and a stainless steel cell [13]. Several grams of the boron p
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