First-principle study of nitrogen incorporation in amorphous carbon

Stress reduction of Cu-doped diamond-like carbon films from ab initio calculations

“…First, for pure-DLC films, the 1 st C-C nearest neighbor peak with increasing the density is displaced from 1.46 Å at 2.03 g/cm 3 to 1.50 Å at 2.87 g/cm 3 , which is dependent on the hybridization ratio. In addition, the RDF of pure-DLC films from this calculations is in agreement with the previous experimental 21, 22 and theoretical results, 14,16,[23][24][25][26] suggesting that the simulated results reflect the nature of real system. The 1 st peak is known to be related to the atomic bond lengths, and the 2 nd peak has correlation with both the bond angles and bond lengths.…”

“…13 The initial configuration contained 64 atoms in a simple cubic supercell with constant volume and under periodic boundary conditions throughout the simulation, which has been proved that such system was suitable and accurate to reveal the characteristics of amorphous carbon systems. [14][15][16] To obtain Cu-DLC systems, a two-step process composed of melt-quenching by ab initio molecular dynamics (AIMD) simulation and geometric optimization by static calculations was used, which has been demonstrated to provide a good description of DLC materials and to reveal the intrinsic relation between the structure and properties. 14,17,18 During the AIMD simulation, the system was first equilibrated at 8000K for 1ps to become completely liquid and to eliminate its correlation to the initial configuration using a canonical ensemble with a Nose thermostat for temperature-control and a time step of 1 fs, which was confirmed by calculating RDF of the samples; then, the samples were quenched from 8000 to 1 K at cooling rate of 1.6×10 16 K/s.…”

“…[14][15][16] To obtain Cu-DLC systems, a two-step process composed of melt-quenching by ab initio molecular dynamics (AIMD) simulation and geometric optimization by static calculations was used, which has been demonstrated to provide a good description of DLC materials and to reveal the intrinsic relation between the structure and properties. 14,17,18 During the AIMD simulation, the system was first equilibrated at 8000K for 1ps to become completely liquid and to eliminate its correlation to the initial configuration using a canonical ensemble with a Nose thermostat for temperature-control and a time step of 1 fs, which was confirmed by calculating RDF of the samples; then, the samples were quenched from 8000 to 1 K at cooling rate of 1.6×10 16 K/s. For the subsequent geometric optimization of amorphous structure, a full relaxation of the atomic positions based on conjugated gradient method 19 was repeated until the Hellmann-Feynman force on each atom was below 0.01 eV/Å, and the self-consistent loop was created using an energy convergence criterion of 10 −5 eV.…”

“…To provide more representative models of the actual Cu-DLC systems than the direct substitution of carbon by metal atoms in the pre-generated pure-DLC networks, Cu atoms were introduced by substituting carbon atoms in the liquid carbon sample at densities of 2.87 or 2.03 g/cm 3 . 14,18 Pure-DLC films were also involved for comparison with Cu-doped ones. Then, the RDF, sp …”

Raman spectra of nitrogen-doped tetrahedral amorphous carbon from first principles

“…Using a cutoff distance of 1.85 Å in the determination of the nearest neighbor atoms, we found that the percentage of sp 3 carbon atoms was 87.1% in ta-C:N, showing a small variation compared with the sp 3 fraction in the pure ta-C network, which was 88.8% at the same density in our previous calculation [17] . It indicates that the low content of nitrogen incorporation does not affect the fraction of sp 3 hybridized carbon atoms, which is in agreement with the previous calculation [22] and experimental results [3] . The topology of all sp 2 sites in ta-C:N is also displayed in Figure 1, which plays an important role in vibrational properties because of their larger scattering cross section.…”