Transformation of amorphous carbon clusters to fullerenes

Transformation of amorphous carbon clusters into fullerenes under high temperature is studied using molecular dynamics simulations at microsecond times. Based on the analysis of both structure and energy of the system, it is found that fullerene formation occurs in two stages. Firstly, fast transformation of the initial amorphous structure into a hollow sp$^2$ shell with a few chains attached occurs with a considerable decrease of the potential energy and the number of atoms belonging to chains and to the amorphous domain. Then, insertion of remaining carbon chains into the sp$^2$ network takes place at the same time with the fullerene shell formation. Two types of defects remaining after the formation of the fullerene shell are revealed: 7-membered rings and single one-coordinated atoms. One of the fullerene structures obtained contains no defects at all, which demonstrates that defect-free carbon cages can be occasionally formed from amorphous precursors directly without defect healing. No structural changes are observed after the fullerene formation, suggesting that defect healing is a slow process in comparison with the fullerene shell formation. The schemes of the revealed reactions of chain atoms insertion into the fullerene shell just before its completion are presented. The results of the performed simulations are summarized within the paradigm of fullerene formation due to selforganization of the carbon system.Comment: 35 pages, 9 figure

Formation of nickel-carbon heterofullerenes under electron irradiation

arXiv.-- et al.A way to produce new metal-carbon nanoobjects by transformation of a graphene flake with an attached transition metal cluster under electron irradiation is proposed. The transformation process is investigated by molecular dynamics simulations by the example of a graphene flake with a nickel cluster. The parameters of the nickel-carbon potential (I. V. Lebedeva et al., J. Phys. Chem. C, 2012, 116, 6572) are modified to improve the description of the balance between the fullerene elastic energy and graphene edge energies in this process. The metal-carbon nanoobjects formed are found to range from heterofullerenes with a metal patch to particles consisting of closed fullerene and metal clusters linked by chemical bonds. The atomic-scale transformation mechanism is revealed by the local structure analysis. The average time of formation of nanoobjects and their lifetime under electron irradiation are estimated for the experimental conditions of high-resolution transmission electron microscopy (HRTEM). The sequence of images of nanostructure evolution with time during its observation by HRTEM is also modelled. Furthermore, the possibility of batch production of studied metal-carbon nanoobjects and solids based on these nanoobjects is discussed.AS, IL, AK and AP acknowledges Russian Foundation of Basic Research (14-02-00739-a). AP acknowledges Samsung Global Research Outreach Program. IL acknowledges support from the Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme (Grant Agreement PIIF-GA-2012-326435 RespSpatDisp), Grupos Consolidados del Gobierno Vasco (IT-578-13) and the computational time on the Supercomputing Center of Lomonosov Moscow State University and the Multipurpose Computing Complex NRC “Kurchatov Institute.” EB acknowledges EPSRC Career Acceleration Fellowship, New Directions for EPSRC Research Leaders Award (EP/G005060), and ERC Starting Grant for financial support.Peer Reviewe

LED-based Fourier transform spectroscopy of H216O in the range 15500-16000 cm-1

The vibrational-rotational absorption spectrum of water vapor within the range 15500–16000 cm−1 is measured and analyzed. The spectrum is recoded with an IFS-125M Fourier transform spectrometer with a resolution of 0.03 cm−1, at pressure of 25 mbar, at a temperature of 24°C, and at an optical path length of 34.8 m. The measurements are performed using a multipass White cell with a base length of 60 cm. A light-emitting diode is used as a radiation source. The signal-to-noise ratio is about 104, which makes it possible to measure the parameters of lines with intensities on the order of 10−27 cm/molecule. The centers, intensities, and half-widths of lines are determined by fitting the Voigt profile parameters to measured data set by the least squares method. A list of more than 430 lines is formed based on the analysis of the spectrum. The obtained results are compared with calculated and experimental data of other authors

Transformation of amorphous carbon clusters to fullerenes

Transformation of amorphous carbon clusters into fullerenes under high temperature is studied using molecular dynamics simulations at microsecond times. On the basis of the analysis of both the structure and energy of the system, it is found that fullerene formation occurs in two stages. First, fast transformation of the initial amorphous structure into a hollow sp shell with a few chains attached occurs with a considerable decrease of the potential energy and the number of atoms belonging to chains and to the amorphous domain. Then insertion of the remaining carbon chains into the sp network takes place at the same time as the fullerene shell formation. Two types of defects remaining after the formation of the fullerene shell are revealed: seven-membered rings and single one-coordinated atoms. One of the fullerene structures obtained contains no defects at all, which demonstrates that defect-free carbon cages can be occasionally formed from amorphous precursors directly without defect healing. No structural changes are observed after the fullerene formation, suggesting that defect healing is a slow process in comparison with the fullerene shell formation. The schemes of the revealed reactions of chain atom insertion into the fullerene shell just before its completion are presented. The results of the performed simulations are summarized within the paradigm of fullerene formation due to self-organization of the carbon system.This research was supported by the Russian Foundation of Basic Research (Grant 14-02-00739-a). I.V.L. acknowledges Grupos Consolidados del Gobierno Vasco (Grant IT-578-13) and EU-H2020 Project “MOSTOPHOS” (No. 646259).Peer Reviewe

Long triple carbon chains formation by heat treatment of graphene nanoribbon: Molecular dynamics study with revised Brenner potential

The method for production of atomic chains by heating of graphene nanoribbons (GNRs) is proposed and studied by molecular dynamics simulations. The Brenner potential is revised to adequately describe formation of atomic chains, edges and vacancy migration in graphene. A fundamentally different behaviour is observed for zigzag-edge GNRs with 3 and 4 atomic rows (3 and 4-ZGNRs) at 2500 K: formation of triple, double and single carbon chains with the length of hundreds of atoms in 3-ZGNRs and edge reconstruction with only short chains and GNR width reduction in 4-ZGNRs. The chain formation mechanism in 3-ZGNRs is revealed by analysis of bond reorganization reactions and is based on the interplay of two processes. The first one is breaking of bonds between 3 zigzag atomic rows leading to triple chain formation. The second one is bond breaking within the same zigzag atomic row, which occurs predominantly through generation of pentagons with subsequent bond breaking in pentagons and results in single or double chain formation. The DFT calculations of the barriers for relevant reactions are consistent with the mechanism proposed. The possibility of chain-based nanoelectronic devices with a controllable number of chains is discussed.ASS, AMP and AAK acknowledge the Russian Foundation for Basic Research, Russia (Grant 18-02-00985). IVL acknowledges Grupos Consolidados del Gobierno Vasco, Spain (IT-578-13) and EU-H2020 project "MOSTOPHOS" (n. 646259).Peer reviewe

LED-based Fourier transform spectroscopy of H216O in the range 15500-16000 cm-1

The vibrational-rotational absorption spectrum of water vapor within the range 15500–16000 cm−1 is measured and analyzed. The spectrum is recoded with an IFS-125M Fourier transform spectrometer with a resolution of 0.03 cm−1, at pressure of 25 mbar, at a temperature of 24°C, and at an optical path length of 34.8 m. The measurements are performed using a multipass White cell with a base length of 60 cm. A light-emitting diode is used as a radiation source. The signal-to-noise ratio is about 104, which makes it possible to measure the parameters of lines with intensities on the order of 10−27 cm/molecule. The centers, intensities, and half-widths of lines are determined by fitting the Voigt profile parameters to measured data set by the least squares method. A list of more than 430 lines is formed based on the analysis of the spectrum. The obtained results are compared with calculated and experimental data of other authors

Formation of nickel clusters wrapped in carbon cages: Toward new endohedral metallofullerene synthesis

Despite the high potential of endohedral metallofullerenes (EMFs) for application in biology, medicine and molecular electronics, and recent efforts in EMF synthesis, the variety of EMFs accessible by conventional synthetic methods remains limited and does not include, for example, EMFs of late transition metals. We propose a method in which EMF formation is initiated by electron irradiation in aberration-corrected high-resolution transmission electron spectroscopy (AC-HRTEM) of a metal cluster surrounded by amorphous carbon inside a carbon nanotube serving as a nanoreactor and apply this method for synthesis of nickel EMFs. The use of AC-HRTEM makes it possible not only to synthesize new, previously unattainable nanoobjects but also to study in situ the mechanism of structural transformations. Molecular dynamics simulations using the state-of-the-art approach for modeling the effect of electron irradiation are performed to rationalize the experimental observations and to link the observed processes with conditions of bulk EMF synthesis.A.S.S., I.V.L., A.A.K., and A.M.P. acknowledge the Russian Foundation of Basic Research (14-02-00739-a). I.V.L. acknowledges the financial support from Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13) and EU-H2020 project “MOSTOPHOS” (no. 646259). A.N.K., T.W.C., and R.L.M. acknowledge the ERC and EPSRC for financial support, and the Nanoscale & Microscale Research Centre (nmRC). T.Z., J.B., and U.K. gratefully acknowledge the funding by the DFG (German Research Foundation) and the Ministry of Science, Research and the Arts (MWK) of Baden Wuerttemberg in the framework of the SALVE (Sub Angstrom Low-Voltage Electron Microscopy) project.Peer Reviewe

Transformation of a graphene nanoribbon into a hybrid 1D nanoobject with alternating double chains and polycyclic regions

Molecular dynamics simulations show that a graphene nanoribbon with alternating regions which are one and three hexagons wide can transform into a hybrid 1D nanoobject with alternating double chains and polycyclic regions under electron irradiation in HRTEM. A scheme of synthesis of such a nanoribbon using Ullmann coupling and dehydrogenation reactions is proposed. The reactive REBO-1990EVC potential is adapted for simulations of carbon–hydrogen systems and is used in combination with the CompuTEM algorithm for modeling of electron irradiation effects. The atomistic mechanism of formation of the new hybrid 1D nanoobject is found to be the following. Firstly hydrogen is removed by electron impacts. Then spontaneous breaking of bonds between carbon atoms leads to the decomposition of narrow regions of the graphene nanoribbon into double chains. Simultaneously, thermally activated growth of polycyclic regions occurs. Density functional theory calculations give barriers along the growth path of polycyclic regions consistent with this mechanism. The electronic properties of the new 1D nanoobject are shown to be strongly affected by the edge magnetism and make this nanostructure promising for nanoelectronic and spintronic applications. The synthesis of the 1D nanoobject proposed here can be considered as an example of the general three-stage strategy of production of nanoobjects and macromolecules: (1) precursors are synthesized using a traditional chemical method, (2) precursors are placed in HRTEM with the electron energy that is sufficient only to remove hydrogen atoms, and (3) as a result of hydrogen removal, the precursors become unstable or metastable and transform into new nanoobjects or macromolecules.A. S. S., A. M. P. and A. A. K. acknowledge the Russian Foundation of Basic Research (Grants 18-02-00985 and 20-52-00035). S. V. R. and N. A. P. acknowledge the Belarusian Republican Foundation for Fundamental Research (Grant No. F20R-301) and Belarusian National Research Program ‘‘Convergence-2020’’. This work has been carried out using the computing resources of the federal collective usage center Complex for Simulation and Data Processing for Mega-science Facilities at NRC ‘‘Kurchatov Institute’’, http://ckp.nrcki.ru/ and was supported by the Research Center ‘‘Kurchatov Institute (order No. 1569 of July 16, 2019). D. G. O. has received funding from the Spanish Agencia Estatal de Investigacion (Grant No. PID2019-107338RB-C63).Peer reviewe