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

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Using spectroscopic ellipsometry and Drude-Lorentz oscillator fitting, we determined the dielectric function and optical conductivity versus photon energy from 0.76 to 6.6 eV of 10 nm thick Ni1 − xPtx alloy (0<x<0.25) films deposited on thick thermal oxides. We find absorption peaks near 1.6 and 5.0 eV due to interband optical transitions. There is a significant broadening of the UV peak with increasing Pt content, since the bandwidth of the 3d electrons in Ni is smaller than that of the 5d bands in Pt. Our experimental observation is consistent with ab initio calculations of the density of states for Ni, Pt, and the Ni3Pt compound. Annealing the metals at 500°C for 30 s increases the optical conductivity.