P. Zhao

A first-principles study of the spin transport properties of a 4H-TAHDI-based multifunctional spintronic device with graphene nanoribbon electrodes

By using the nonequilibrium Greens function formalism in combination with the density functional theory, we have investigated the spin transport properties of a 4H-TAHDI-based multifunctional spintronic device constructed by contacting a 4H-TAHDI molecule with two ferromagnetic zigzag-edge graphene nanoribbon electrodes. The results show that perfect giant magnetoresistance, spin-filtering, bipolar spin-rectifying, and negative differential resistance effects can be realized simultaneously. The mechanisms were proposed for these interesting phenomena. Our results demonstrate that this system holds promise in the design of a high-performance multifunctional single-molecule spintronic device.

Spin transport of dibenzotetraaza[14]annulene complexes with first row transition metals

Based on spin-polarized first-principles density functional theory in conjunction with the nonequilibrium Greens function method, the spin transport properties of transition metal (TM)–dibenzotetraaza[14]annulene (DBTAA) complexes (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) sandwiched between two Au electrodes are investigated. The results show that Fe– and Co–DBTAA can display perfect spin filtering behavior in a wide bias voltage region. Moreover, it is found that the connected position of anchoring groups on the complexes affect significantly the spin filtering efficiency. The observed spin filtering behavior is explained by the spin-resolved transmission spectrum and molecular projected self-consistent Hamiltonian state analyses.

Electronic properties of silicene superlattices: roles of degenerate perturbation and inversion symmetry breaking

Using both the first-principles method and the tight-binding method, we have carried out detailed studies on the electronic properties of silicene superlattices. According to the band-folding picture, in the hexagonal silicene superlattice (M,N) when both M and N are integer multiples of 3, the simultaneous folding of K and K′ points to the Γ point results in the fourfold degeneracy. In the orthogonal one [P,Q], the fourfold degeneracy occurs if Q = 3q (q is an integer) is satisfied. By introducing degenerate perturbation to remove the fourfold degeneracy, the bandgap could be opened no matter whether the inversion symmetry remains or not. For the other cases, the bandgaps could be kept closed by the inversion symmetry preservation. Besides, the studied transport properties confirm the bandgap tuning by applying degenerate perturbation to the silicene superlattice. The new bandgap opening mechanism with degenerate perturbation could benefit further experimental studies of the silicene-based nanostructures for applications in nanoelectronics.

Effect of early-strength-enhancing agents on setting time and early mechanical strength of belite–barium calcium sulfoaluminate cement

Belite–barium calcium sulfoaluminate (C2.75B1.25A3

Freezing resistance of high iron phoasphoaluminate cement

) cement is a new type of belite-rich cement with great long-term mechanical performance and good durability. Its early-age mechanical property was found to be comparable to that of Grade 32.5 ordinary Portland cement. In order to further improve its early hydration activity, the effect of two known early-strength agents on the performance of the belite–barium calcium sulfoaluminate cement was investigated by means of XRD, pore structure and TGA. It was found that Na2SO4 and Ca(HCOO)2 can be used as an early-strength-enhancing agents for this type of cement with the best dosage of 0.5 and 2.0% by weight, respectively. Ca(HCOO)2 was preferable to this type of cement from the durability point of view.

Crystal structure and magnetic properties of the novel mixed-valence copper coordination polymer constructed from two kinds of inorganic units

The influence of freeze-thaw cycle on the mechanical properties of high iron phoasphoaluminate cement was investigated in the present study. The visual examination was conducted to evaluate the surface damage. The deterioration considering the weight loss, modulus loss of relative dynamic elastic and strength loss of mortar were also investigated. The morphology of hydration products were analysed by SEM. Compared with ordinary Portland cement and sulphoaluminate cement, the frost resistance of high iron phosphoraluminate cement is better. Hydration products of high iron phoasphoaluminate cement contain sheet crystals, and a lot of gel form a dense three-dimensional network structure, which results in a lower porosity. Different from ordinary Portland cement, the hydration product of high iron phoasphoaluminate cement does not contain Ca(OH)2, and low alkalinity reduces its osmotic pressure. The lower porosity and osmotic pressure are the two main reasons which causes in the higher frost resistance of high iron phoasphoaluminate cement.

Negative differential resistance in a carbon nanotube-based molecular junction

A novel mixed-valence CuI/CuII coordination polymer [CuI(μ2-Cl)CuII(μ3-S)(Phen)]n (I) (Phen = 1,10-phenanthroline) has been hydrothermally synthesized and structurally characterized by elemental analyses and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis reveals that a unique one-dimensional infinite chain-like structure is constructed by two unusual zigzag chains of [CuCl]n and [CuS]n. Both of the zigzag chains are used as the second building units (SBU) to produce a 2D helix-like layer at the aid of the C-H...Cl hydrogen bonding interactions between Phen groups and [CuCl]n chains. An interesting three-dimensional network is formed with the supramolecular van der Waals contacting among the 2D layers. Finally, the magnetic properties of the title compound have been investigated in the temperature range 2–300 K.