Tuning Electronic Structure and Magnetic Properties of Flat Stanene by Hydrogenation and Al/P Doping: A First Principle DFT Study

A Stanene, is a two-dimensional material composed of tin atoms arranged in a single hexagonal layer, in a manner similar to graphene. First principle studies based on density functional theory were performed to investigate the effects of hydrogenation and Al/P doping on electronic structure and magnetic properties of stanene. Hydrogenation opens the bandgap of stanene and changes it from nonmagnetic to the ferromagnetic material through H 1s states and Sn 5p states hybridization. Al/P atom at hollow site prevent electrons of adjacent Sn atoms to connect so that inducing unpaired electrons. The combination of hydrogenation and Al/P doping increases its magnetization. The sequence based on its magnetic moment from small to large is as follows: pure stanene, Al-doped stanene, P-doped stanene, hydrogenated stanene, Al-doped hydrogenated stanene, and P-doped hydrogenated stanene. The controllable transformation from nonmagnetic metallic to a magnetic semiconductor is a key requirement for materials to be used as spintronic materials. Thus, these results may shed light on designing the stanene-based electronic and spintronics materials.

Investigation on Mg3Sb2/Mg2Si Heterogeneous Nucleation Interface Using Density Functional Theory

In this study, the cohesive energy, interfacial energy, electronic structure, and bonding of Mg2Si (111)/Mg3Sb2 (0001) were investigated by using the first-principles method based on density functional theory. Meanwhile, the mechanism of the Mg3Sb2 heterogeneous nucleation potency on Mg2Si grains was revealed. The results indicated that the Mg3Sb2 (0001) slab and the Mg2Si (111) slab achieved bulk-like characteristics when the atomic layers N ≥ 11, and the work of adhesion of the hollow-site (HCP) stacking structure (the interfacial Sb atom located on top of the Si atom in the second layer of Mg2Si) was larger than that of the other stacking structures. For the four HCP stacking structures, the Sb-terminated Mg3Sb2/Si-terminated Mg2Si interface with a hollow site showed the largest work of adhesion and the smallest interfacial energy, which implied the strongest stability among 12 different interface models. In addition, the difference in the charge density and the partial density of states indicated that the electronic structure of the Si-HCP-Sb interface presented a strong covalent, and the bonding of the Si-HCP-Mg interface and the Mg-HCP-Sb interface was a mixture of a covalent bond and a metallic bond, while the Mg-HCP-Mg interfacial bonding corresponded to metallicity. As a result, the Mg2Si was conducive to form a nucleus on the Sb-terminated-hollow-site Mg3Sb2 (0001) surface, and the Mg3Sb2 particles promoted the Mg2Si heterogeneous nucleation, which was consistent with the experimental expectations.

MOLECULAR ADSORPTION OF NO ON WmMon (m + n≤6) CLUSTERS

Geometric and electronic properties of nitric oxide adsorption on WmMon ([Formula: see text] 6) clusters have been systematically calculated by density functional theory (DFT) at the generalized gradient approximation (GGA) level for ground-state structures. NO molecule prefers top site with nitrogen-end bridging a tungsten atom for W[Formula: see text]Mo[Formula: see text] and W3Mo2 clusters. While NO tends to locate on the hollow site for WMo5, W2Mo4 and W3Mo3 clusters, and dissociation of NO molecule happens on W3Mo, N–O bond lengths expand in accordance with the variation of adsorption energy with the increasing number of tungsten atoms, originating from metal [Formula: see text] back-donation. Electron transfer occurs among 4d state of Mo, 5d state of W, 2p state of N and 2p state of O.

Adsorption mechanism of CO molecule on Al(111) surface: periodic DFT investigation

The adsorption mechanism of the CO molecule on Al(111) surface has been investigated systematically at the atom-molecule level by the method of periodic density functional theory. The adsorption energies, adsorption structures, charge transfer, and density of states have been calculated in a wide range of coverage. It is found that the hcp-hollow site is the energetically favorable site. A significant positive correlation has been found between the adsorption energy (Eads) and coverage. The adsorbed CO molecules are almost perpendicular on the surface with the C atom facing the surface. There is an obvious charge transfer from Al atoms to the C atom; the Al atoms that have interaction with the C atom offer the most charge. The 4σ, 1π, and 5σ molecular orbitals of CO are found to contribute to bonding with the Al. The charges filling in the 2π molecular orbital contribute to C–O bond activation. In conclusion, the passivation of aluminum surface and the activation of CO molecule occur simultaneously in the adsorption of CO on Al surface.

Investigation of CVD graphene as-grown on Cu foil using simultaneous scanning tunneling/atomic force microscopy

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of graphene reveal either a triangular or honeycomb pattern at the atomic scale depending on the imaging parameters. The triangular patterns at the atomic scale are particularly difficult to interpret, as the maxima in the images could be every other carbon atom in the six-fold hexagonal array or even a hollow site. Carbon sites exhibit an inequivalent electronic structure in HOPG or multilayer graphene due to the presence of a carbon atom or a hollow site underneath. In this work, we report small-amplitude, simultaneous STM/AFM imaging using a metallic (tungsten) tip, of the graphene surface as-grown by chemical vapor deposition (CVD) on Cu foils. Truly simultaneous operation is possible only with the use of small oscillation amplitudes. Under a typical STM imaging regime the force interaction is found to be repulsive. Force–distance spectroscopy revealed a maximum attractive force of about 7 nN between the tip and carbon/hollow sites. We obtained different contrast between force and STM topography images for atomic features. A honeycomb pattern showing all six carbon atoms is revealed in AFM images. In one contrast type, simultaneously acquired STM topography revealed hollow sites to be brighter. In another, a triangular array with maxima located in between the two carbon atoms was acquired in STM topography.

Strong Adsorption of Al-Doped Bilayer Graphene Toward Anticancer Cisplatin

The adsorption of cisplatin on pristine monolayer graphene (MLG), pristine bilayer graphene (BLG) and Al-doped BLG (Al-BLG) was investigated using density functional theory. The obtained results showed that pristine MLG and pristine BLG were not sensitive to cisplatin. Adsorption energy can be primarily influenced by the atomic species rather than the adsorption position. Moreover, it is strong chemisorption of hollow-site Al-BLG (H-Al-BLG) toward cisplatin. The most stable configurations are the Pt or Cl atom interaction with the Al atom of H-Al-BLG. In conclusion, H-Al-BLG is a kind of potential high quality delivery carrier for anticancer cisplatin.

Identifying the structure of 4-chlorophenyl isocyanide adsorbed on Au(111) and Pt(111) surfaces by first-principles simulations of Raman spectra

A high-precision Raman simulation method is developed. Using this method, we reveal that 4-chlorophenyl isocyanide prefers to adsorb on the top site of Au(111) with a vertical configuration, but with a bent configuration on the hollow site of Pt(111).

A computational approach towards understanding hydrogen gas adsorption in Co–MIL-88A

The hydrogen adsorption is most favorable at the hollow site of Co–MIL-88A.

Adsorption Behaviors of Cobalt on the Graphite and SiC Surface: A First-Principles Study

Graphite and silicon carbide (SiC) are important materials of fuel elements in High Temperature Reactor-Pebble-bed Modules (HTR-PM) and it is essential to analyze the source term about the radioactive products adsorbed on graphite and SiC surface in HTR-PM. In this article, the adsorption behaviors of activation product Cobalt (Co) on graphite and SiC surface have been studied with the first-principle calculation, including the adsorption energy, charge density difference, density of states, and adsorption ratios. It shows that the adsorption behaviors of Co on graphite and SiC both belong to chemisorption, with an adsorption energy 2.971 eV located at the Hollow site and 6.677 eV located at the hcp-Hollow site, respectively. Combining the charge density difference and density of states, it indicates that the interaction of Co-SiC system is stronger than Co-graphite system. Furthermore, the variation of adsorption ratios of Co on different substrate is obtained by a model of grand canonical ensemble, and it is found that when the temperature is close to 650 K and 1700 K for graphite surface and SiC surface, respectively, the Co adatom on the substrate will desorb dramatically. These results show that SiC layer in fuel element could obstruct the diffusion of Co effectively in normal and accidental operation conditions, but the graphite may become a carrier of Co radioactivity nuclide in the primary circuit of HTR-PM.