Configuration stability and electronic properties of diamane with boron and nitrogen dopants

The structural stability and electronic properties of N-doped and B-N-codoped cubic and hexagonal diamane (single-layer diamond) were investigated based on first-principles methods. The N atom tends to stay in the substitutional site rather than the interstitial site, and the most stable configuration is the structure where the N atom is located at the external substitutional site without H saturation. The B and N atoms codoped in diamane tend to gather to form a covalent bond, where N is saturated by H, since the stability of a lone pair of electrons in N is reduced by the B dopant. Moreover, B and N dopants can adjust the bandgap (0–3.52 eV) and reduce the formation energy (FE) of diamane to promote its synthesis. The formation energies of N-doped diamane are not sensitive to N distributions, and diamane containing a vertical B-N bond has the lowest FE due to the attraction between the N-dopant-induced electron and the B-dopant-induced hole.

Figure 1

The optimized configuration of diamane with one substituted N atom for (a) conf-1N, (b) conf-2N, and (c) conf-3N, corresponding to the concentration of 6.25 mol %. The upper and lower parts show the doped cubic diamane (CD) and hexagonal diamane (HD), respectively.

Figure 2

The electron localization function (ELF) of (a) conf-3N, (b) conf-1NN, (c) conf-BN (without H saturation), and (d) conf-1BN for cubic diamane (CD) along the $c$ direction. The red (blue) regions represent the localized (delocalized) electronic states.

Figure 3

(a) Energies of the $4\times 2$ supercells with two substituted N atoms (6.25 mol % N dopant) are shown as a function of N-N distance. Red circles and blue squares represent the energies of the ${\mathrm{C}}_{30}{\mathrm{N}}_2\mathrm{H}$ structure, while orange circles and green squares represent the energies of the ${\mathrm{C}}_{30}{\mathrm{N}}_2\mathrm{H}$ structure plus a hydrogen molecule. Side and top views of (b) conf-1NN, (c) conf-2NN, and (d) conf-3NN for cubic diamane (CD). The bond configurations around the N atom of conf-1NN and conf-2NN are shown in the insets. The dashed purple line shows the distance (2.48 or 2.39 Å) between two N atoms in conf-1NN or conf-2NN. conf-4NN (conf-5NN) is the configuration with the highest energy in ${\mathrm{C}}_{30}{\mathrm{N}}_2{\mathrm{H}}_{16}$ (${\mathrm{C}}_{30}{\mathrm{N}}_2{\mathrm{H}}_{14}$) for CD.

Figure 4

(a) Energies of the $4\times 2$ supercells with B-N codoped (6.25 mol % dopant, ${\mathrm{C}}_{30}{\mathrm{BNH}}_{16}$) as a function of B-N distance. Side view and top view of (b) conf-1BN, (c) conf-2BN, and (d) conf-3BN for cubic diamane (CD) with the data showing the bond length of B-N covalent bond. conf-4BN is the configuration with the highest energy in B-N-codoped CD.

Figure 5

The phonon dispersions of (a) conf-1N, (b) conf-2N, (c) conf-3N, (d) conf-1NN, (e) conf-2NN, (f) conf-3NN, (g) conf-4NN, (h) conf-5NN, (i) conf-1BN, (j) conf-2BN, (k) conf-3BN, and (l) conf-4BN for cubic diamane (CD), respectively.

Figure 6

The upper part shows the interlayer C-C bond length with molecular dynamics (MD) simulation time of (a) conf-3N and (b) conf-3BN for cubic diamane (CD). Side and top views of the final configuration after running 7-ps MD simulations by using a $2\times 2$ supercell for conf-3N and a $1\times 2$ supercell for conf-3BN are shown in the lower part.

Figure 7

The calculated bandgaps of cubic diamane (CD) and hexagonal diamane (HD) with 6.25 mol % N dopant and B-N codopant. Bars with simple color represent the direct bandgap, and bars with slanted lines on the surface represent the indirect bandgap. The dashed red and blue lines show the bandgap of pristine cubic and HD, respectively.

Figure 8

Partial density of states (PDOS) of (a) conf-1N, (b) conf-2N, and (c) conf-3N averaged to each atom, corresponding to the concentration of 6.25 mol %. The Fermi level is set to zero. The contribution of the $\mathrm{C}\text{−}{p}_x \left(\mathrm{N}\text{−}{p}_x\right)$ orbit is the same as that of the $\mathrm{C}\text{−}{p}_y \left(\mathrm{N}\text{−}{p}_y\right)$ orbit in (d) pristine diamane and (e) conf-3N.

Figure 9

The band structure and partial density of states (PDOS) of (a) conf-1NN and (b) conf-2NN corresponding to the concentration of 6.25 mol %. The Fermi level is set to zero. The contribution of the $\mathrm{C}\text{−}{p}_x$ orbit is the same as that of the $\mathrm{C}\text{−}{p}_y$ orbit in conf-1NN and conf-2NN.

Figure 10

Formation energies of diamane with different doping configurations at the concentration of 3.125, 6.25, and 12.5 mol %. The light green, light purple, and light blue regions indicate the configurations with B dopant, N dopant, and B-N codopant, respectively. The formation energy (FE) data of diamane with B doped is from Ref. [40]. The dashed red and blue lines show the FE of pristine cubic and hexagonal diamane, respectively.

Figure 11

Formation energies of diamane with different doping methods at the concentration of 6.25 mol %. The formation energy (FE) data of diamane with B doped is from Ref. [40].