We investigate chemical functionalization of graphene by carboxyl (COOH) groups using first principles computational methods. The binding energies and equilibrium geometries of COOH groups covalently attached to graphene clusters with no surface defects, Stone-Wales defects, and vacancies are examined in the framework of density functional theory combined with the generalized gradient approximation. We find that the attachment of COOH groups induces substantial structural changes in graphene. Our calculations show that the binding of the COOH group to graphene is significantly stronger in the presence of surface defects. This result suggest an important role of point surface defects in the carboxylation of graphene.

The structural, magnetic and electron-transport properties of cubic Mn3Ga have been investigated. The alloys prepared by arc melting and melt-spinning show an antiferromagnetic spin order at room temperature but undergo coupled structural and magnetic phase transitions at 600 and 800 K. First-principles calculations show that the observed magnetic properties are consistent with that of a cubic Mn3Ga crystallizing in the disordered Cu3Au-type structure. The samples exhibit metallic electron transport with a resistance minimum near 30 K, followed by a logarithmic upturn below the minimum. The observed anomaly in the low-temperature resistivity has been discussed as a consequence of electron scattering at the low-lying excitations of the structurally disordered Mn3Ga lattice.

We study the mechanism of covalent functionalization of boron (B)- and nitrogen (N)-doped graphene and carbon nanotubes by carboxyl (COOH) groups. Our calculations are carried out using an ab initio density functional pseudopotential computational method combined with the generalized gradient approximation for the exchange-correlation functional. The binding energies and equilibrium structures of carboxylated B/N-doped graphene sheets and carbon nanotubes are examined in cases of graphene and nanotubes containing no surface defects, containing Stone–Wales defects, and containing vacancies. We find that B doping increases and N doping decreases the binding energy of COOH groups to defect-free and defective graphene and carbon nanotubes. This result suggests that substitutional doping may significantly alter the surface reactivity of carbon nanomaterials.

We present a first-principles computational study of the interactions between the boron (B) and nitrogen (N) dopant atoms in graphene. Our calculations are carried out using density functional theory combined with the generalized gradient approximation for the exchange-correlation functional. The total energies, equilibrium geometries, electronic charge distributions, and densities of states of doped graphene sheets are examined in cases of BÀB, NÀN, and BÀN co-doped graphene. We find the BÀB and NÀN interactions to be repulsive and the BÀN interaction to be attractive. In all cases studied, dopant-dopant interactions appear to have a relatively short range. The interaction energy between the two dopant atoms is found to be inversely proportional to the square of the separation distance. We interpret these results in terms of donor-acceptor interactions and structural relaxation. The strong bonding between the B and N atoms indicates the possibility of the formation of isolated patches of hexagonal boron nitride in BÀN co-doped graphene. V

Ferromagnetic Cr2Te3 nanorods were synthesized by a one-pot high-temperature organic-solution-phase method. The crystalline phases and magnetic properties can be systematically tuned by varying the molar ratio of the Cr and Te precursors. A magnetically hard phase, identified as chemically ordered Cr2Te3, is the dominating one at the precursor ratio between Cr : Te = 1 : 1.2 and 1 : 1.8. A magnetically soft phase, attributed to chemical disorder due to composition inhomogeneity and stacking faults, is present under either Cr-rich or Te-rich synthesis conditions. A large coercivity of 9.6 kOe is obtained for a Cr : Te precursor ratio of 1 : 1.8, which is attributed to the large magnetocrystalline anisotropy of ordered Cr2Te3 nanorods, and verified by density-functional theory calculations. The hard and soft phases sharing coherent interfaces co-exist in a seemingly single-crystalline nanorod, showing an unusual transition from exchange-coupled behavior at higher temperatures to two-phase behavior as the temperature is lowered.