Nanoengineering carbon nanotubes: The effects of electron irradiation on nanotube structure
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Nanoengineering carbon nanotubes: The effects of electron irradiation on nanotube structure Katherine McDonell1, Gwénaëlle Proust1, 2 and Luming Shen1 1 The University of Sydney, School of Civil Engineering, Sydney, N.S.W, Australia 2 The University of Sydney, Australian Centre for Microscopy & Microanalysis, Sydney, N.S.W, Australia ABSTRACT A combined experimental and simulation approach into the impacts of electron irradiation on carbon nanotube morphology was conducted. Single-walled nanotubes (SWCNTs) were irradiated using a JEOL Transmission Electron Microscope (TEM) using a range of accelerating voltages varying from 90keV to 200keV and temperatures between 300K and 800K with different exposure periods (order of minutes). The effects of irradiation were observed and characterised using electron microscopy and Raman spectroscopy. Specimens were observed prior to, during and following irradiation to discern any changes that occurred in SWCNTs as a result of irradiation. Raman spectroscopy was used to characterise the different allotropes of carbon present in irradiated and non-irradiated samples of SWCNTs. Experimental conditions were mimicked using molecular dynamics simulation. SWCNTs were irradiated under conditions equivalent to experimental electron beam intensity and specimen temperature using AIREBO [1,2] and Primary Knock-on (PKA) approximation [3]. The preliminary results indicate that electron beam intensity and temperature affect the type and frequency of modification to CNT structure. INTRODUCTION The properties of carbon nanotubes (CNT) have been extensively researched following their discovery in 1991[4]. Nanotube mechanical properties associated with Van der Waals interactions such as bending modulus are significantly lower than that of isolated nanotubes [5]. Irradiation is a powerful tool for the manipulation of carbon nanotube structure and therefore properties [6], as CNTs are extremely sensitive to irradiation [5]. Irradiation has been shown to induce modifications ranging from phase change such as amorphisation to cross linking [5,7]. Irradiation has also been shown to improve bending modulus [8]. However, the connection between irradiation induced morphological changes and the resulting impact on properties has not yet been clearly established [9]. Experimental techniques have been successfully used to detect irradiation induced modification. On the other hand, there are difficulties with determining atomic scale modifications experimentally [3]. Molecular Dynamics (MD) simulations been shown to mimic the evolution of atomic structure during irradiation across time scales and at magnifications which are not possible in experimentation [3]. In this paper, a combined experimental and simulation approach to electron irradiation induced morphological changes to CNT structure has been outlined. At low accelerating voltages little modification occurs whereas at higher accelerating voltages amorphisation occurs [10]. At elevated temperatures, CNTs are able to mend themselves although defects crea
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