Weiwei Ju

First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.

Adsorption sensitivity of graphane decorated with B, N, S, and Al towards HCN: a first-principles study

The geometric structure, adsorption energy, electronic structure, and magnetic properties of hydrogenated graphene (graphane) with the adsorption of a HCN molecule were investigated by first-principles calculations. Compared with graphane, the adsorption of HCN on H-vacancy defected graphane (VHG) exhibited higher stability, which implied that the H-vacancy improved the sensitivity of graphane. However, the small adsorption energies and large bond distance indicated that the weak adsorption of a HCN molecule on the graphane and VHG substrates was due to physisorption. By introducing dopants (B, N, S, and Al), the activity of graphane was significantly improved. The adsorption of HCN changed to chemisorption on the graphane with dopants. Meanwhile, the opening of band gaps by HCN adsorption can be used as an electronic signal to detect HCN gas. Interestingly, the spin polarized density of states (PDOS) results suggested that the adsorption of HCN on VHG and S-doped VHG exhibited magnetic character and half-metallicity behavior. These results could provide useful information to design gas sensors for HCN or spintronic devices based on graphane.

Adsorption of H2S on graphane decorated with Fe, Co and Cu: a DFT study

Herein, density functional theory (DFT) calculations were performed to investigate the adsorption of a H2S molecule on the surface of hydrogenated graphene (graphane). In our results, we found that the appearance of an H-vacancy significantly improved the reactivity of graphane due to the unpaired electrons of the vacancy site. However, small adsorption energy and low charge transfer indicated that the interaction between the H2S molecule and the pure H-vacancy-defected graphane occurred via physisorption. By introducing transition-metal dopants (Fe, Co, and Cu), the adsorption process of the H2S molecule changed to chemisorption. Furthermore, the adsorption of H2S induced a decrease in the band gaps, which could be seen as signal for the detection of H2S gas.

Exotic d0 magnetism in partial hydrogenated silicene

The intriguing d0 magnetic properties of partially hydrogenated silicene are investigated via first-principles calculations. H atoms are assembled along the diagonal line of 4 × 4 supercell. The magnetism can be engineered through transforming the adsorption sites of H atoms. With odd number of H atoms, the systems demonstrate stable magnetism, and the total magnetic moment of each system is 1 μB. No magnetism is found in those systems with equal number of H atoms for sublattice A and sublattice B. Molecular dynamics simulations show the configurations and magnetism of the systems are stable at room temperature. Our work motivates promising applications for silicene in spintronics device.

Adsorption sensitivity of defected graphene towards NO molecule: a DFT study

Based on density functional theory, we studied the adsorption of a nitrogen monoxide (NO) molecule on the surface of perfect graphene (PG) and vacancy-defected graphene (VG), with the aim of searching the potential of graphene as an NO gas sensor. Different possible configurations have been considered for adsorption on vacancy-defected graphene split. The results indicated that the adsorption of the NO molecule on VG exhibited larger adsorption energy, higher charge transfer, smaller band length than that of perfect graphene. Meanwhile, the VG structure transformed a semiconductor into a conductor by the adsorption of the NO molecule. Furthermore, the partial electronic density of states (PDOS) results showed that hybridizations between the NO molecule and VG were mainly contributed by N-2p, O-2p, and C-2p orbitals. These results could provide useful information for the design of gas sensors based on graphene.

Strong enhancement of spin–orbit splitting induced by σ–π coupling in Pb-decorated silicene

Electronic properties and spin–orbit (SO) splitting of silicene adsorbed with Cu, Ag, Au and Pb atoms at different coverages are investigated by means of first-principles calculations. All four kinds of adatoms we studied tend to adsorb at hollow sites. The adsorption of Pb atoms enhances the hybridization of σ electrons and π electrons around the Fermi level in silicene, resulting in considerable SO splitting (∼100 meV). Only a small degree of SO splitting is achieved in NM–silicene (NM stands for noble metal atoms, i.e. Cu, Ag, and Au) systems. Our results suggest that the σ–π coupling is a very important factor for the enhancement of SO coupling in silicene. The concentration and the intrinsic SO coupling of adatoms will also affect SO splitting in these systems. All structures we studied are stable at room temperature. Our work provides an imperative understanding of the physical mechanism of enhancing SO coupling in two dimensional materials.