36 research outputs found
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 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 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
Preserving p-conjugation in covalently functionalized carbon nanotubes for optoelectronic applications
Covalent functionalization tailors carbon nanotubes for a wide range of applications in varying environments. Its strength and stability of attachment come at the price of degrading the carbon nanotubes sp 2 network and destroying the tubes electronic and optoelectronic features. Here we present a non-destructive, covalent, gram-scale functionalization of single-walled carbon nanotubes by a new 2+1] cycloaddition. The reaction rebuilds the extended p-network, thereby retaining the outstanding quantum optoelectronic properties of carbon nanotubes, including bright light emission at high degree of functionalization (1 group per 25 carbon atoms). The conjugation method described here opens the way for advanced tailoring nanotubes as demonstrated for light-triggered reversible doping through photochromic molecular switches and nanoplasmonic gold-nanotube hybrids with enhanced infrared light emission
Effects of extrinsic point defects in phosphorene: B, C, N, O and F Adatoms
Phosphorene is emerging as a promising 2D semiconducting material with a
direct band gap and high carrier mobility. In this paper, we examine the role
of the extrinsic point defects including surface adatoms in modifying the
electronic properties of phosphorene using density functional theory. The
surface adatoms considered are B, C, N, O and F with a [He] core electronic
configuration. Our calculations show that B and C, with electronegativity close
to P, prefer to break the sp3 bonds of phosphorene, and reside at the
interstitial sites in the 2D lattice by forming sp2 bonds with the native
atoms. On the other hand, N, O and F, which are more electronegative than P,
prefer the surface sites by attracting the lone pairs of phosphorene. B, N and
F adsorption will also introduce local magnetic moment to the lattice.
Moreover, B, C, N and F adatoms will modify the band gap of phosphorene
yielding metallic transverse tunneling characters. Oxygen does not modify the
band gap of phosphorene, and a diode like tunneling behavior is observed. Our
results therefore offer a possible route to tailor the electronic and magnetic
properties of phosphorene by the adatom functionalization, and provide the
physical insights of the environmental sensitivity of phosphorene, which will
be helpful to experimentalists in evaluating the performance and aging effects
of phosphorene-based electronic devices
Quantum Network Models and Classical Localization Problems
A review is given of quantum network models in class C which, on a suitable
2d lattice, describe the spin quantum Hall plateau transition. On a general
class of graphs, however, many observables of such models can be mapped to
those of a classical walk in a random environment, thus relating questions of
quantum and classical localization. In many cases it is possible to make
rigorous statements about the latter through the relation to associated
percolation problems, in both two and three dimensions.Comment: 23 pages. To appear in '50 years of Anderson Localization', E
Abrahams, ed. (World Scientific)
Plasma-Assisted Synthesis of Carbon Nanotubes
The application of plasma-enhanced chemical vapour deposition (PECVD) in the production and modification of carbon nanotubes (CNTs) will be reviewed. The challenges of PECVD methods to grow CNTs include low temperature synthesis, ion bombardment effects and directional growth of CNT within the plasma sheath. New strategies have been developed for low temperature synthesis of single-walled CNTs based the understanding of plasma chemistry and modelling. The modification of CNT surface properties and synthesis of CNT hybrid materials are possible with the utilization of plasma
Modeling the properties of carbon nanotubes for sensor-based devices
We acknowledge funding from the European Community through NoE Nanoquanta (NMP4-CT-2004-500198), SANES (NMP4-T-2006-017310), DNA-NANODEVICES (IST-2006-029192) and NANO-ERA Chemistry projects, UPV/EHU (SGIker Arina) and the Basque Governement.Peer reviewe