Article Abstracts
- A. P. Burden and S. R. P. Silva, "Fullerenes and Nanotube Formation in Terestrial Cool 'Dusty Plasmas'", Appl. Phys. Lett. 73 (1998) 3082-3084.
The simultaneous generation of dust during the deposition of semiconducting thin films by radio frequency plasma enhanced chemical vapor deposition has so far been regarded as a troublesome by-product. However, we present results from recent microstructural investigations of carbonaceous dust particles from a methane precursor that demonstrate that the technique may be suited to generating fullerene molecules, nanotubes, and nanoparticles. Chemical analysis reveals that these particles contain few contaminant species, and we deduce that they nucleated in the plasma, with the carbon ions possibly self-arranging through the action of coulombic forces. ©1998 American Institute of Physics
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- A. P. Burden and S. R. P. Silva, "Fullerene-like carbon nanoparticles generated by radio-frequency plasma enhanced chemical vapour deposition", Phil. Mag. Lett., 78 (1998) 15-19.
We report a preliminary microstructural analysis of carbonaceous dust generated by radio-frequency plasma-enhanced chemical vapour deposition using methane as a precursor. The extracted dust has been analysed by high resolution transmission electron microscopy and a significant population of fullerene-like aggregates of carbon nanoparticles and nanotubes revealed. This is believed to be the first report of material containing curved graphene layers generated by this technique, and we conclude that the method could be adapted to produce bulk quantities for industrial applications.
Request article - B.O. Boskovic, V. Stolojan, R.U.A. Khan, S. Haq, S.R.P. Silva, "Large Area Synsthesis of Carbon Nanofibres at Room temperature", Nature Materials, 1 (2002) 165-168.
Carbon nanotubes, first identified by Iijima, require for their production a source of elemental carbon and a transfer of energy that is specific to the type of source and the growth environment. Methods developed so far involve arc discharge, and vaporization using laser, , pyrolysis, and chemical vapour deposition of hydrocarbons. Here, we show growth of carbon nanofibres from radio-frequency plasma-enhanced chemical vapour deposition at room temperature, which was made possible by substituting the thermal energy requirements for the growth with plasma decomposition of methane on the Ni catalyst. Electron microscopy analysis provides evidence for a 'tip' growth model, with the Ni catalyst particle attached to the tip of the nanofibre. Energy-filtered imaging shows the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni-C droplet as a nucleation site for the carbon nanofibres, so that the carbon diffuses across the surface. The reduced distortion of the catalyst particles at low temperatures leads to a more uniform growth of the carbon nanofibres over large areas. The lower growth temperature allows for the removal of the silicon dioxide barrier layer associated with catalytic growth, and should allow in situ growth of nanofibres on relatively large areas of temperature-sensitive substrates, such as plastics, organics and even paper.
Request article - B.O. Boskovic, V. Stolojan, D.A. Zeze, R.D. Forrest, S.R.P. Silva, "Structural analysis of carbon nanofibres synthesised at room temperature", Proc. Of 7th Applied Diamond Conference / 3rd Frontier Carbon Technology (ADC/FCT) Editors: M. Murakawa, M. Miyoshi, Y. Koga, L. Shafer and Y. Tzeng, pg. 59-63 (2003).
Request article - R.C. Smith, C.H.P. Poa, D.C. Cox, J.D. Carey and S.R.P. Silva, "Electron field emission from room temperature grown carbon nanofibres", J. Appl. Phys. 95 (2004) 3153-3157.
The observation of field induced electron emission from room temperature grown carbon nanofibers at low (5 V/µm) macroscopic electric fields is reported. The nanofibers were deposited using methane as a source gas in a conventional rf plasma enhanced chemical vapor deposition reactor using a Ni metal catalyst previously subjected to an Ar plasma treatment. Analysis of the scanning electron microscopy images of the nanofibers show them to possess an average diameter of 300 nm and that the nanofibers are observed to be radially dispersed over an area of 50 µm in diameter. No evidence of hysteresis in the current-voltage characteristic or conditioning of the emitters is observed. The mechanism for emission at low fields is attributed to field enhancement at the tips rather than from the surrounding amorphous carbon film which is shown to have a higher threshold field (20 V/µm) for emission. ©2004 American Institute of Physics.
Request article - B.O. Boskovic, V. Stolojan, D.A. Zeze, R. D. Forrest, S. Haq, S.R.P. Silva, "Branched Carbon Nanofibre Network Synthesis at Room Temperature Using Radio Frequency Supported Microwave Plasmas", J. Appl. Phys. 96 (2004) 3443-3446.
Carbon nanofibers have been grown at room temperature using a combination of radio frequency and microwave assisted plasma-enhanced chemical vapor deposition. The nanofibers were grown, using Ni powder catalyst, onto substrates kept at room temperature by using a purposely designed water-cooled sample holder. Branched carbon nanofiber growth was obtained without using a template resulting in interconnected carbon nanofiber network formation on substrates held at room temperature. This method would allow room-temperature direct synthesized nanofiber networks over relatively large areas, for a range of temperature sensitive substrates, such as organic materials, plastics, and other polymers of interest for nanoelectronic two-dimensional networks, nanoelectromechanical devices, nanoactuators, and composite materials. ©2004 American Institute of Physics
Request article - M.H. Rummeli, E. Borowiak-Palen, T. Gemming, T. Pichler, M. Knupfer, M. Kalbac, L. Dunsch, O. Jost, S.R.P. Silva, W. Pompe and B. Buchner, "Novel Catalysts, Room Temperature, and the Importance of Oxygen for the Synthesis of Single-Walled Carbon Nanotubes", Nanoletters Vol. 5(7) (2005) 1209-1215.
In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.
Request article - G.Y. Chen, V. Stolojan, S.R.P. Silva, H. Herman and S. Haq, "Carbon spheres generated in 'dusty plasmas'", Carbon 43 (2005) 704-708.
The formation of spherical hydrogenated amorphous carbon (a-C:H) particulates generated in a radio frequency plasma enhanced chemical vapour deposition (rf-PECVD) system is reported. These particulates appear as a white powder-no other contaminants appear to be present. electron energy loss spectroscopy (EELS) shows characteristics typical of a-C:H with a reduced plasmon energy due to hydrogen incorporation. Raman spectroscopy however revealed a 1456 cm-1 line which was previously not reported on a-C:H films deposited using similar processes. Infrared (IR) spectroscopy shows that these spheres are mainly partially oxidised, methyl-rich, aliphatic hydrocarbons.
Request article - E. Mendoza, S.J. Henley, C.H.P. Poa, G.Y. Chen, C.E. Giusca, A.A.D.T. Adikaari, J.D. Carey and S.R.P. Silva, "Large area growth of carbon nanotube arrays for sensing platforms", Sensors and Actuators B 109 (2005) 750-80.
This paper reviews the process of growing large area arrays of carbon nanotubes (CNT) to be used as sensing platforms. First the work explores different methods to prepare Ni catalyst particles. More precisely, the work shows how the nanostructured arrays of catalyst are obtained by thermal annealing of Ni thin films, laser nanostructuring of Ni thin films and formation by organic dendrimers in aqueous solution. The growth process by chemical vapour deposition (CVD) is detailed and the influence of the catalyst particles on the final morphology of the tubes is discussed. A discussion of the advantages and disadvantages of each Ni nanoparticle technique to grow CNT arrays as a sensing platform is presented
Request article - C.H. Poa, S.J. Henley, G.Y. Chen, A.A.D.T. Adikaari, C.E. Guisca, V. Stolojan and S.R.P. Silva, "Growth and field emission properties of vertically aligned carbon nanofibers", J. Appl. Phys. 97 (2005) 114308.
Vertically aligned carbon nanofibers (VACNFs) were synthesized on Ni-coated Si substrates using a dc plasma-enhanced chemical-vapor deposition system. The size of the Ni islands used as catalyst to grow the VACNFs was formed by both thermal annealing and laser processing on thin metal layers. It was observed that the diameter of the carbon nanofibers is strongly dependent on the initial Ni island dimension. By varying the laser power from 228 to 279 mJ/cm2, the size of these Ni islands can be controlled independent of the initial Ni film thickness. Electron field-emission results show that the emission threshold field is dependent on both the height and radius of these VACNFs and also field shielding effects. Threshold fields as low as 2 V/µm was obtained from the sample with the largest height over radius ratio. ©2005 American Institute of Physics
Request article - E. Mendoza, S.J. Henley, C.H.P. Poa, V. Stolojan, G.Y. Chen, C.E. Giusca, J.D. Carey and S.R.P. Silva, "Dendrimer assisted catalytic growth of mats of multiwall carbon nanofibers", Carbon 43 (2005) 2229-2231.
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Request article - G.Y. Chen, C.H.P. Poa, S.J. Henley, V. Stolojan, S.R.P. Silva and S. Haq, "Deployment of titanium thermal barrier for low-termperature carbon nanotube growth", Appl. Phys. Lett. 87, 253115 (2005).
Chemical vapor-synthesized carbon nanotubes are typically grown at temperatures around 600 °C. We report on the deployment of a titanium layer to help elevate the constraints on the substrate temperature during plasma-assisted growth. The growth is possible through the lowering of the hydrocarbon content used in the deposition, with the only source of heat provided by the plasma. The nanotubes synthesized have a small diameter distribution, which deviates from the usual trend that the diameter is determined by the thickness of the catalyst film. Simple thermodynamic simulations also show that the quantity of heat, that can be distributed, is determined by the thickness of the titanium layer. Despite the lower synthesis temperature, it is shown that this technique allows for high growth rates as well as better quality nanotubes. ©2005 American Institute of Physics
Request article - V. Stolojan, Y. Tison, G.Y. Chen and S.R.P. Silva, "Controlled Growth Reversal of catalytic carbon nanotube growth under electron beam irradiation", Nanoletters 2006, 6 (9), pp 1837-1841
The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.
Request article - PCP Watts, SM Lyth, E Mendoza and SRP Silva, "Polymer supported carbon nanotube arrays for field emission and sensor devices", Appl Phys Lett 89 (10), 103113 (2006).
The authors report a simple method for providing a polymer support structure for carbon nanotube (CNT) arrays for device applications. This method has a twofold effect: firstly it secures the nanotubes to the substrate and secondly it significantly decreases the threshold field for field emission from 26.2 to 9.7 V/µm. This method ensures that the main body and tips of the CNTs are polymer-free and therefore can also be applied to CNT sensor array device fabrication. ©2006 American Institute of Physics
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