Zhenkui Zhang

Magnetic properties of phthalocyanine-based organometallic nanowire

Using first principles calculations, we investigate the electronic and magnetic properties of transition metal phthalocyanine (M-Pc, M = Cr, Mn, Co, Ni, Cu, and Zn) nanowire (M-PcNW). Our calculations show that Ni-PcNW and Zn-PcNW are nonmagnetic, while Cr-PcNW and Cu-PcNW are antiferromagnetic with small energy difference and Co-PcNW show paramagnetic due to their long spin coherence length. Most importantly, we predicate that Mn-PcNW frameworks display long-ranged ferromagnetic spin ordering, offering strong spin polarization around Fermi level. Moreover, Mn-PcNW frameworks are half-metals, which make Mn-PcNW frameworks ideal candidates for spintronic devices. These results may shed light on further experimental studies on molecular spintronics.

Quantum confinement effect on the vacancy-induced spin polarization in carbon, silicon, and germanium nanoparticles: Density functional analysis

Density functional calculations were carried out to examine the vacancy-induced spin polarization in diamond, silicon, and germanium nanoparticles and the magnetic coupling between the vacancy-induced defect states in those nanoparticles. Our calculations show that the vacancy-induced defect states are spin-polarized in diamond nanoparticles regardless of their size but this happens in silicon and germanium nanoparticles only when their size is small, which is in reasonable agreement with the experimentally observed magnetic behaviors. The vacancy-induced defect states on adjacent vacancies prefer to couple ferromagnetically in C nanoparticles but antiferromagnetically in Si and Ge nanoparticles.

Ferromagnetism and manipulation of topological surface states in Bi2Se3 family by 2p light elements

The manipulation effects by doping of 2p light elements X (X = B, C, and N) on topological surface states in V2VI3 (V = Bi and Sb, VI = Se and Te) are systemically explored. Our results unveil that X doping at anion sites can induce magnetic moments and gap opening at the Dirac point. To have a stable magnetic ground state, the dopant 2p states must be sufficiently localized, which closely depends on the X-V bond lengths. The incorporation of 2p dopants paves a promising way of tuning the properties of topological insulators and may find applications in spintronics.

The surface termination effect on the quantum confinement and electron affinities of 3C-SiC quantum dots: a first-principles study

In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems.

Native defects and impurities in Zn3 N2: first-principle studies using gradient-correction approximation

First-principle density-functional calculations were performed to investigate the electronic structures, atomic structures and formation energies for native defects, oxygen impurities and related complexes in Zn3N2. The formation energy calculated shows that the configurations of substitutional O for N and O plus a N vacancy complex (ON(1)–VN(2)) are energetically favorable in both N-rich and Zn-rich growth conditions. The electronic structures demonstrate that N vacancy, substitutional O, and ON(1)–VN(2) complex defective Zn3 N2 are of n-type conduction character.