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Experiments showed that multiwalled carbon nanotubes (MWCNT) can be used as masks against irradiation to create metallic nanowires in a substrate. In order to understand the limitations of this application, it is interesting to know the energy and number of carbon atoms emerging from the MWCNT after the irradiation and how the structure of the MWCNT is modified. Using a molecular dynamics code that we have previously developed, we have simulated the continuous irradiation of MWCNT with carbon and argon projectiles. We have obtained that the use of carbon instead of argon to irradiate the MWCNT increases de effectiveness of the MWCNTs as masks, due to the ability of the carbon projectiles to be part of the MWCNT structure and partially mend the damage produced during irradiation. We have analyzed the number, energy, and spatial distribution of the recoils generated during irradiation and the change of the MWCNT structure as a function of the incident energy (100 and 500 eV), fluence (up to 4.5 · 10 15 ions / cm 2 ), and number of shells (up to 5-shells) of the MWCNT. These results determine the effectiveness of MWCNT as a mask, being useful to understand whether the atoms emerging from the MWCNT produce damage in the substrate or not. We find that for carbon projectiles the efficiency of MWCNT as masks does not depend much on the fluence, but on the number of nanotube shells and projectile incident energy. On the other hand, for a given nanotube and fluence, we observe a threshold incident energy below which the nanotube acts as a perfect mask. [ABSTRACT FROM AUTHOR]

The idea of using carbon nanotubes (CNTs) as masks against irradiation has recently emerged, because of the region of a given material covered by a CNT can be protected from the effects of irradiation, creating nanowires. In this case, it is interesting to know in detail the number of generated recoils and their energy. In order to obtain these data, we simulate the irradiation of CNTs with carbon ions using a molecular dynamics code. To describe the interaction between carbon ions we use the Brenner potential joined smoothly to the Universal ZBL potential at short distances. We have analyzed the energy distributions of the carbon atoms emerging from the CNT for single projectile irradiation with incident energies from 30 eV to 5 keV. Our results show that the number and the energy of the recoil carbon atoms emerging from the CNT increases with the projectile incident energy. In average, each projectile with incident energy of 1 keV produces ∼3.6 recoils, which have a mean energy of 150 eV, while projectiles with 5 keV produce ∼7 recoils with a mean energy of 400 eV. [ABSTRACT FROM AUTHOR]

Abstract: We simulate the irradiation of carbon nanotubes (CNT) with carbon ions using a molecular dynamics code. In order to describe the interaction between carbon ions we use the Tersoff or Brenner potential, both joined smoothly to the Universal ZBL potential at short distances. We have analyzed the defects produced after irradiation, the subsequent modification of the CNT structure, and their dependence on the used interatomic potential, the projectile energy (from 10 eV to 5keV) and the dose. For single projectile irradiation, we have obtained that the coordination defect number increases with the projectile energy, although a saturation value is achieved at high projectile energies (∼3keV). For continuous projectile irradiation, we have observed that for low energies (∼10eV) the accumulation of adatoms produces a bump in the irradiated region. However, at intermediate energies (∼100eV) the irradiation produces vacancies which are healed through non-hexagonal rings. This gives rise to a shrinking of the CNT diameter in the irradiated region. Finally, if the projectile energy is high enough (∼1keV) the continuous irradiation produces the breaking of the CNT. [Copyright &y& Elsevier]

Abstract: The electronic energy loss of swift H and He ions in solid Ag is studied theoretically within the dielectric formalism, considering the different equilibrium charge states of the projectile inside the target. Excitation of the weakly-bound (outer) electrons is described by a superposition of Mermin-type energy-loss functions, whereas the contribution to the projectile energy loss due to the ionization of the K, L and M shells of the Ag atoms is included through hydrogenic or numerical generalized oscillator strengths. This method is used to evaluate the stopping power and the energy-loss straggling parameter of H and He ions in Ag as a function of the projectile energy, showing a good agreement with available experimental data. The contribution of the target inner-shells to the energy loss begins to be appreciable at projectile energies larger than a few hundred keV/u, being more important for the energy-loss straggling parameter than for the stopping cross section. [Copyright &y& Elsevier]

Abstract: We calculate the electronic energy loss of swift H+ and He+ ion beams in several solids with applications in material science and microelectronics, namely Ti, Fe, Ge, Pd, LiF and Si3N4. Our calculations are based on the dielectric formalism, where the charge density of the projectile is described by the Brandt–Kitagawa model, with the addition of projectile polarization. We take into account the different charge states of the projectile inside the target and the energy loss due to electron capture and loss processes. Using a realistic description of the target energy loss function, we obtain results that show a good agreement with available experimental data in a wide range of projectile energies. [Copyright &y& Elsevier]

Abstract: We have theoretically studied the electronic stopping cross section and the energy loss straggling of swift light ions (H+ and He+) moving through several compound semiconductors (GaAs, ZnSe, InP and SiC) as a function of the incident projectile energy. The calculations have been done using the dielectric formalism, in which the electronic structure of the projectile is described by the modified Brandt–Kitagawa model and the energy loss function (ELF) of the semiconductors is obtained using a linear combination of Mermin-type ELF to describe the outer electron excitations and generalized oscillator strengths to take into account the excitations of the inner-shell electrons. The different charge states that the projectile can acquire during its travel through the solid, as a result of electronic capture and loss processes, has been also considered. The contributions to the projectile energy loss from both the outer- and the inner-shell electron excitations are analyzed. The comparison of our calculated stopping cross sections with available experimental data shows a good agreement in a wide range of incident projectile energies. [Copyright &y& Elsevier]

The irradiation of carbon based nanostructures with ions and electrons has been shown to be an appropriate tool to tailor their properties. The defects induced in the nanostructures during irradiation are able to modify their mechanical and electronic properties. Here we simulate the irradiation of carbon nanotubes with carbon ions using a molecular dynamics code. We use the Tersoff potential joined smoothly to the Universal Ziegler-Biersack-Littmark potential at short distances. We study the number of defects produced after irradiation with a single carbon ion finding a saturation with its energy at ∼ 3 keV. We observe, after continuum irradiation with low energy ions, the formation of bumps in the irradiated region. For larger energy ions we find that the diameter of the nanotube shrinks as shown in previous works. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]