Stability of Carbon Nanotubes: How Small Can They Be? (original) (raw)
Related papers
Viability of sub-0.4-nm diameter carbon nanotubes
Physical Review B, 2002
Hartree-Fock ͑HF͒ and density functional theory calculations indicate that a ͑4,0͒ carbon nanotube ͑CNT͒ of sub-0.4-nm diameter is stable and its heat of formation is close to that of the stable C 36 (D 6h). Semiempirical molecular-orbital calculation shows that such narrow tubular structure is more stable than the corresponding opened fragment in the innermost zone of a large CNT. Simulated TEM images show that an extra-narrow CNT does not show the typical CNT image regardless of the microscopic resolution. In order to aid experimental identification, the Raman spectrum of the ͑4,0͒ CNT obtained from HF calculation shows A 1g breathing modes in 489-725 cm Ϫ1 .
Investigating the Diameter-Dependent Stability of Single-Walled Carbon Nanotubes
ACS Nano, 2009
We investigate the long-standing question of whether electrons accelerated at 80 kV are below the knock-on damage threshold for single-walled carbon nanotubes (SWNTs). Aberration-corrected high-resolution transmission electron microscopy is used to directly image the atomic structure of the SWNTs and provides in situ monitoring of the structural modification induced by electron beam irradiation at 80 kV. We find that SWNTs with small diameters of 1 nm are damaged by the electron beam, and defects are produced in the side walls that can lead to their destruction. SWNTs with diameters of 1.3 nm and larger are more stable against degradation, and stability increases with diameter. The effect of diameter, defects, and exterior contamination on the inherent stability of SWNTs under electron beam irradiation is investigated.
On the stability of single-walled carbon nanotubes and their binding strengths
Theoretical Chemistry Accounts, 2012
We have studied the relative stability of hydrogen-terminated single-walled carbon nanotubes (SWNTs) segments, and open-ended SWNT fragments of varying diameter and chirality that are present at the interface of the catalytic metal particles during growth. We have found that hydrogen-terminated SWNTs differ by \1 eV in stability among different chiralities, which presents a challenge for selective and property-controlled growth. In addition, both zigzag and armchair tubes can be the most stable chirality of hydrogen-terminated SWNTs, which is a fundamental obstacle for property-controlled growth utilizing thermodynamic stability. In contrast, the most armchair-like open-ended SWNTs segments are always the most stable ones, followed in sequence by chiral index up to the least stable zigzag segments. We explain the ordering by triple bond stabilization of the carbon dangling bonds at the open ends, which is a fragment stabilization effect that is only manifested when all bonds between two layers are broken. We show convincingly that the bond strength difference between zigzag and armchair tubes is not present when individual bonds are broken or formed.
Carbon, 2004
Various properties (geometry, band structure and the totally symmetric vibrational modes) of small diameter single-walled carbon nanotubes (SWCNTs) were investigated by first principles density functional theory (DFT) calculations. We studied 40 different SWCNTs, including 14 chiral ones down to diameters of 0.3 nm. The behavior of small diameter tubes is significantly different from that of the usual, larger diameter nanotubes. The diameter is larger than what is expected from simple folding. The bond lengths and bond angles are not uniform. The strong r-p rehybridization effect modifies the band structure with respect to the tight binding approximation. The frequency of the radial breathing mode (RBM) shows a softening with decreasing diameter as compared to the usual 1=d dependence and this softening depends strongly on chirality. RBM frequencies are further modified by the coupling with high frequency totally symmetric modes in a non-negligible way for small diameter tubes. These deviations cannot be described by a smooth monotonic function of the diameter.
Structural flexibility of carbon nanotubes
The Journal of Chemical Physics, 1996
We report high resolution electron microscope ͑HREM͒ observations and atomistic simulations of the bending of single and multi-walled carbon nanotubes under mechanical duress. Single and multiple kinks are observed at high bending angles. Their occurrence is quantitatively explained by the simulations, which use a realistic many-body potential for the carbon atoms. We show that the bending is fully reversible up to very large bending angles, despite the occurrence of kinks and highly strained tube regions. This is due to the remarkable flexibility of the hexagonal network, which resists bond breaking and bond switching up to very high strain values.
Length dependent stability of single-walled carbon nanotubes and how it affects their growth
Carbon
Using density-functional theory the stability of armchair and zigzag single-walled carbon nanotubes and graphene nanoribbons was investigated. We found that the stability of armchair and zigzag nanotubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each nanotube series. We explain these dependencies by competing edge and curvature effects. We have found that within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths. These results shed new insights into why (near) armchair nanotubes are the dominant product from catalytic chemical vapor deposition growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable nanotubes.
On the Stability and Abundance of Single Walled Carbon Nanotubes
Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product's relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.
Nanotechnology, 2007
Order(N ) tight-binding molecular dynamics (TBMD) simulations are performed to investigate the thermal stability of (10, 10) metallic single-walled carbon nanotubes (SWCNTs). Periodic boundary conditions (PBCs) are applied in the axial direction. The velocity Verlet algorithm along with the canonical ensemble molecular dynamics (NVT) is used to simulate the tubes at the targeted temperatures. The effects of slow and rapid temperature increases on the physical characteristics, structural stability and the energetics of the tube are investigated and compared. Simulations are carried out starting from room temperature and the temperature is raised in steps of 300 K. The stability of the simulated metallic SWCNT is examined at each step before it is heated to higher temperatures. The first indication of structural deformation is observed at 600 K. For higher heat treatments the deformations are more pronounced and the bond-breaking temperature is reached around 2500 K. Gradual (slow) heating and thermal equilibrium (fast heating) methods give the value of radial thermal expansion coefficient in the temperature range between 300 and 600 K as 0.31 × 10 −5 and 0.089 × 10 −5 K −1 , respectively. After 600 K, both methods give the same value of 0.089 × 10 −5 K −1 . The ratio of the total energy per atom with respect to temperature is found to be 3 × 10 −4 eV K −1 .