Post by williamplayer on Apr 24, 2014 13:03:42 GMT
George Washington University's Micro-propulsion and Nanotechnology Laboratory
The MpNL is actively investigating the production and properties of both Carbon Nanotubes (CNT) and Graphene by arc plasma synthesis. The approach has demonstrated several advantages over other processes. The video clip provides an overview of recent experiments.
Simultaneous Production of Nanotubes and Graphene.
Carbon nanotubes (CNT) are tubular carbon-based fullerene structures that are produced from graphitic carbon. Since the discovery of CNT synthesized by arc discharge, interest in CNTs has been stimulated by their unique mechanical, thermal and electrical properties and various potential applications. The primary objective of our research is understanding of SWNT synthesis mechanism in arc discharge and developing methods and approaches to control parameters of discharge which, in turn, will allow controlling SWNT synthesis.
Current Research Objectives
Single Wall Carbon Nanotubes
The tuning of the distribution of single-wall carbon nanotubes (SWCNTs) produced by the anodic arc production method via the application of non-uniform magnetic fields to the gap region during synthesis was demonstrated. Raman, ultraviolet-visible near-infrared absorbance and near-infrared fluorescence spectroscopies were used to characterize samples together with scanning electron microscopy. Application of the non-uniform magnetic field (0.2 to 2) kG results in a broadening of the diameter range of SWCNTs produced towards decreased diameters, with substantial fractions of produced SWCNTs being of small diameter, less than 1.3 nm, at the highest field. The ability to tune production of the arc production method may allow for improvement in achievable SWCNT properties.
Figure 1. Tuning of SWCNT distribution using applied magnetic field
Figure 2. Thermal stability of SWNT sample experimental setup
Figure 3. Thermal stability of SWNT synthesized sample
Figure 4. UV-vis-NIR data for length separated SWNT sample
The unique properties of graphene and carbon nanotubes made them the most promising nanomaterials attracting enormous attention, due to the prospects for applications in various nanodevices, from nanoelectronics to sensors and energy conversion devices. Here we report on a novel deterministic, single-step approach to simultaneous production and magnetic separation of graphene flakes and carbon nanotubes in an arc discharge by splitting the high-temperature growth and low temperature separation zones using a non-uniform magnetic field and tailor-designed catalyst alloy, and depositing nanotubes and graphene in different areas. Our results are very relevant to the development of commercially-viable, single-step production of bulk amounts of high-quality graphene.
Figure 5. Microanalysis of the samples shown. (a, b) 3D reconstruction and profile of the specimens collected at the top side of the magnet. The presence of flake-like structures with the surface size of around 1 mm2 and a height variation of 1–2 nm, as well as the occurrence of ''bumps/wrinkles'' with the height variation about ~0.5 nm are clearly revealed. (c) Raman spectra of the samples collected from the side surfaces of the magnet, cathode, and chamber walls. (d) Fragment of TEM photo of the folded graphene layers. (e) SAED pattern generated by the specimen collected from the top surface of the magnet.
We are also studying the effect of magnetic field on formation of carbon nanotubes by placing a permanent magnet (marked with PM in the figure) in the vicinity of the arc jet. Effect of magnetic fieldWe are also studying the effect of magnetic field on formation of carbon nanotubes by placing a permanent magnet (marked with PM in the figure) in the vicinity of the arc jet.
Figure 7. (a) Distribution of magnetic field, (b, d) photographs of arc plasmas jet and (c) schematic diagram of electrodes position and direction magnetic field in the gap for the case when the interelectrode gap is positioned about 75 mm above the bottom of permanent magnet. (e-h) The same images for the interelectrode gap 95 mm above the bottom of permanent magnet. (i) SEM image of graphene flakes produced in arc plasma jets. (j) TEM image of the few-layer graphene. Inset: Electron diffraction pattern.
Carbon Nanotubes and Graphene
The MpNL is actively investigating the production and properties of both Carbon Nanotubes (CNT) and Graphene by arc plasma synthesis. The approach has demonstrated several advantages over other processes. The video clip provides an overview of recent experiments.
Simultaneous Production of Nanotubes and Graphene.
Carbon nanotubes (CNT) are tubular carbon-based fullerene structures that are produced from graphitic carbon. Since the discovery of CNT synthesized by arc discharge, interest in CNTs has been stimulated by their unique mechanical, thermal and electrical properties and various potential applications. The primary objective of our research is understanding of SWNT synthesis mechanism in arc discharge and developing methods and approaches to control parameters of discharge which, in turn, will allow controlling SWNT synthesis.
Current Research Objectives
- Synthesis of single wall carbon nanotubes (CNT) and graphene
- Characterization of CNTs properties (thermal, structural, aspect ratio etc)
- Electric and Magnetic field effect on CNT synthesis
- Methods and analysis
- Plasma diagnostics
Single Wall Carbon Nanotubes
The tuning of the distribution of single-wall carbon nanotubes (SWCNTs) produced by the anodic arc production method via the application of non-uniform magnetic fields to the gap region during synthesis was demonstrated. Raman, ultraviolet-visible near-infrared absorbance and near-infrared fluorescence spectroscopies were used to characterize samples together with scanning electron microscopy. Application of the non-uniform magnetic field (0.2 to 2) kG results in a broadening of the diameter range of SWCNTs produced towards decreased diameters, with substantial fractions of produced SWCNTs being of small diameter, less than 1.3 nm, at the highest field. The ability to tune production of the arc production method may allow for improvement in achievable SWCNT properties.
Figure 1. Tuning of SWCNT distribution using applied magnetic field
Figure 2. Thermal stability of SWNT sample experimental setup
Figure 3. Thermal stability of SWNT synthesized sample
Figure 4. UV-vis-NIR data for length separated SWNT sample
Graphene
Properties
Properties
The unique properties of graphene and carbon nanotubes made them the most promising nanomaterials attracting enormous attention, due to the prospects for applications in various nanodevices, from nanoelectronics to sensors and energy conversion devices. Here we report on a novel deterministic, single-step approach to simultaneous production and magnetic separation of graphene flakes and carbon nanotubes in an arc discharge by splitting the high-temperature growth and low temperature separation zones using a non-uniform magnetic field and tailor-designed catalyst alloy, and depositing nanotubes and graphene in different areas. Our results are very relevant to the development of commercially-viable, single-step production of bulk amounts of high-quality graphene.
Figure 5. Microanalysis of the samples shown. (a, b) 3D reconstruction and profile of the specimens collected at the top side of the magnet. The presence of flake-like structures with the surface size of around 1 mm2 and a height variation of 1–2 nm, as well as the occurrence of ''bumps/wrinkles'' with the height variation about ~0.5 nm are clearly revealed. (c) Raman spectra of the samples collected from the side surfaces of the magnet, cathode, and chamber walls. (d) Fragment of TEM photo of the folded graphene layers. (e) SAED pattern generated by the specimen collected from the top surface of the magnet.
Effect of Magnetic Field
We are also studying the effect of magnetic field on formation of carbon nanotubes by placing a permanent magnet (marked with PM in the figure) in the vicinity of the arc jet. Effect of magnetic fieldWe are also studying the effect of magnetic field on formation of carbon nanotubes by placing a permanent magnet (marked with PM in the figure) in the vicinity of the arc jet.
Figure 7. (a) Distribution of magnetic field, (b, d) photographs of arc plasmas jet and (c) schematic diagram of electrodes position and direction magnetic field in the gap for the case when the interelectrode gap is positioned about 75 mm above the bottom of permanent magnet. (e-h) The same images for the interelectrode gap 95 mm above the bottom of permanent magnet. (i) SEM image of graphene flakes produced in arc plasma jets. (j) TEM image of the few-layer graphene. Inset: Electron diffraction pattern.
SOURCE: www.mpnl.seas.gwu.edu/index.php/research/nanotechnology/48-carbon-nanotubes