| 1. |
- Bolton, Kim, et al.
(författare)
-
Carbon Nanotube Growth Mechanisms
- 2007
-
Ingår i: Proceedings of Diamond 2007, the 18th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide.
-
Konferensbidrag (refereegranskat)abstract
- We have used a variety of computational methods to study key aspects of single-walled carbon nanotube (SWNT) growth. Molecular dynamics (MD) studies based on an empirical force field showed; for example; why SWNT growth occurs in a temperature window and why; for 1-2 nm catalyst particles; the SWNT diameter varies linearly with the size of the particle. In addition; the liquid or solid phase of the catalyst particle is strongly dependent on particle size; and smaller particles (< 1.5 nm) are liquid at typical chemical vapor deposition temperatures whereas larger particles (> 5 nm) are solid. The phase of particles of intermediate sizes depends on the exact temperature and on their carbon content. The effect of substrates on metal-carbide properties and SWNT growth has been studied by combing density functional (DFT) and MD methods. A major effect of flat; inert substrates is to flatten the catalyst particles thereby increasing their melting points. DFT has also been used to study the catalyst-SWNT interaction which is critical for the growth of long SWNTs; and is also being used to study the importance of the SWNT cap structure on its chirality. This knowledge is important; for example; when using SWNTs as seeds for the growth of longer nanotubes.
|
|
| 2. |
|
|
| 3. |
- Duan, Haiming, et al.
(författare)
-
Initial growth of single-walled carbon nanotubes on supported iron clusters: a molecular dynamics study
- 2007
-
Ingår i: EUROPEAN PHYSICAL JOURNAL D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 43:1-3, s. 185-188
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations were used to study the initial growth of single-walled carbon nanotubes (SWNTs) on a supported iron cluster (Fe-50). Statistical analysis shows that the growth direction of SWNTs becomes more perpendicular to the substrate over time due to the weak interaction between carbon nanotube and the substrate. The diameter of the nanotube also increases with the simulation time and approaches the size of the supported iron cluster.
|
|
| 4. |
- Duan, Haiming, et al.
(författare)
-
Size dependent melting mechanisms of iron nanoclusters
- 2007
-
Ingår i: CHEMICAL PHYSICS. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 333:1, s. 57-62
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations were used to study the change in the mechanism of iron cluster melting with increasing cluster size. Melting of smaller clusters (e.g., Fe-55 and Fe-100) occurs over a large temperature interval where the phase of the cluster repeatedly oscillates between liquid and solid. In contrast, larger clusters (e.g., Fe-300) have sharper melting points with surface melting preceding bulk melting. The importance of the simulation time, the force field and the definition of cluster melting is also discussed.
|
|
| 5. |
|
|
| 6. |
- Harutyunyan, Avetik, et al.
(författare)
-
Hidden features of the catalyst nanoparticles favorable for single-walled carbon nanotube growth
- 2007
-
Ingår i: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:16
-
Tidskriftsartikel (refereegranskat)abstract
- Combining in situ studies of the catalyst activity during single-walled carbon nanotube (SWCNT) growth by mass spectrometry with differential scanning calorimetry and Raman spectroscopy results, the authors expose the favorable features of small catalyst for SWCNT growth and their relationship with synthesis parameters. The sequential introduction of C-12 and C-13 labeled hydrocarbon reveals the influence of catalyst composition on its lifetime and the growth termination path. Ab initio and molecular dynamics simulations corroborate "V"-shape liquidus line of metal-carbon nanoparticle binary phase diagram, which explains observed carbon-induced solid-liquid-solid phase transitions during nanotube growth.
|
|
| 7. |
- Jiang, A., et al.
(författare)
-
Theoretical study of the thermal behaviour of free and alumina-supported Fe-C nanoparticles
- 2007
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 75:20
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular-dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large Fe1-xCx nanoparticles (x=0-0.16, N=80-1000, nonmagic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles (N=50-80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range, the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical-vapor deposition.
|
|
