Han Sheng-Hao

Giant Magnetoresistance in La0.67Ca0.33MnO3/Alq3/Co Sandwiched-Structure Organic Spin Valves

La0.67Ca0.33MnO3/Alq3/Co sandwiched-structure organic spin valves are fabricated by vacuum thermal evaporation method. A giant magnetoresistance (GMR) of 14% is observed at low temperature 100 K. At 30 K, the magnetoresistance can increase to 50%. The large GMR of the device is attributed to the high spin polarization and low conductivity of the La0.67Ca0.33MnO3 contact. The magnetoresistance ΔR/R and the coercive field of the Co electrode depend strongly on temperature. The large high-field magnetoresistance reported on La0.67Sr0.33MnO3/Alq3/Co organic spin valves [Nature 427 (2004) 821] is not observed in our La0.67Ca0.33MnO3/Alq3/Co organic spin valves.

Effect of RF power on the properties of transparent conducting zirconium-doped zinc oxide films prepared by RF magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films with high transparency and relatively low resistivity have been successfully prepared by radio frequency (RF) magnetron sputtering at room temperature. The RF power is varied from 75 to 150 W. At first the crystallinity and conductivity of the film are improved and then both of them show deterioration with the increase of the RF power. The lowest resistivity achieved is 2.07×10−3Ω cm at an RF power of 100 W with a Hall mobility of 16 cm2V−1s−1 and a carrier concentration of 1.95×1020 cm−3. The films obtained are polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. All the films have a high transmittance of approximately 92% in the visible range. The optical band gap is about 3.33 eV for the films deposited at different RF powers.

Vibrational analysis of L-serine using the density functional theory

In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory (DFT) within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10–200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.

Magnetic microstructures of PryFe90-yB10 (y=8-11.76) nanocrystalline ribbons using magnetic force microscopy

Magnetic microstructure of melt-spun PryFe90−yB10 (y = 8, 8.5, 9, 9.5, 10 and 11.76) nanocrystalline ribbons in an as-grown state has been studied using a magnetic force microscope. The magnetic domains are characterized by dark areas adjacent to bright areas in a sub-micron scale and in random distribution. By comparing with the size of the micro-crystals measured from the TEM image, the exchange coupling effect was confirmed to exist in all the ribbons. Using the roughness analysis, the variation of the root mean-square values of the phase shifts obtained from the magnetic force images versus the content y of Pr were measured, which is very consistent with the curve of the residual induction Br versus the content y.

New observations on hydrogen bonding in ice by density functional theory simulations

In this paper, we report on a series of computational simulations on hydrogen bonding in two ice phases (Ih and Ic) using CASTEP with PW91 and RPBE exchange‐correlation based on ab initio density functional theory. The strength of the H-bond is correlated with intramolecular O‐H stretching, and the energy splitting exists for both the H-bond and covalent O‐H stretching. By analyzing the dispersion relationship of w(q), we observe the separation of the longitudinal optic (LO) mode from transverse optic (TO) mode at the gamma point, seemingly interpreting the controversial two H-bond peaks in the vibrational spectrum of ice recorded by inelastic incoherent neutron scattering experiments. The test of ambient environment on phonon density of sates (PDOS) shows that the relaxed tetrahedral structure is the most stable structural configuration for water clusters.

Reverse polarization in conjugated heterocycle polythiophene

Reverse polarization in polythiophene under an applied electric field has been studied in the framework of the tight-binding model. It is found that the applied electronic field has a great influence on the excited states of polythiophene. The effect of the heteroatoms on the polarization has been calculated and analysed carefully. It is indicated that a reverse polarization of biexcitons in polythiophene will be observed more easily. The heteroatoms increase this reversed polarization strength apparently.

Magnetic and Crystalline Microstructures of the Sr–La–Co M-type Ferrites by Magnetic Force Microscopy

With proper erosion of sample surface and making a grid of crystal boundaries, the magnetic and crystalline microstructures of Sr–La–Co M-type ferrites of nominal composition of La0.2Sr08Fe11.8Co0.2O19 (at.%) have been investigated by using magnetic force microscopy. By calculating average diameter and thickness, and average alignment degree of the grains of the ferrites, recognizing their domain patterns and calculating the proportion of grains with single domain or multi-domains, the Sr–La–Co M-type ferrites with high magnetic performance have been characterized at microcrystalline and micromagnetic level. In addition, we has interpreted why the grains always present plate-like domains.

Electronic confinement in quasi-one-dimensional triblock copolymers

A tight-binding calculation to describe the triblock copolymer xPA(polyacetylene)/nPPP (poly(p-phenylene))/yPA or xPPP/nPA/yPPP is presented. The interfacial coupling between homopolymer segments is attributed to the hopping of π-electrons and the coupling of σ-bonds. The dependence of the band gap of triblock copolymers on the interfacial couplings or on the composite segment lengths is studied. The influence of composite segment lengths on the electron density is also studied. For nPPP/xPA/nPPP structures, the band gap varies with PA segment length over a wide range of 1.32-2.74eV. For nPA/xPPP/nPA structures, the band gap is invariant with PPP segment length. It is found that a spontaneous tunnelling phenomenon could take place in nPA/xPPP/nPA structures. Furthermore, the polaron caused by doping an electron into nPA/xPPP/nPA will tend to be confined in one of the well (PA) parts. This kind of confinement may increase the electron-hole recombination probability.

Electronic States in Quasi-one-Dimensional Copolymeric Sandwich Structures

The electronic properties of xPA/nPPP/yPA sandwiched copolymers with a well-barrier-well structure have been studied by using a tight-binding calculation. It was found that the electronic properties of the neutral states of these sandwiched copolymers are sensitive to the constitutions of PPP and PA monomers and the interface coupling between PA and PPP. It is verified that the quantum tunnelling effect will occur at the lowest conductive state of xPA/nPPP/xPA copolymers.

Domain structures of Nd13Fe80B7 magnets during HDDR process

The domain structures of Nd13Fe80B7 alloy at different stages of the HDDR process have been revealed using a magnetic force microscope. In the as-cast samples, the columnar crystals with easy axis perpendicular to one another are clearly characterized by their different domain structures. For the insufficient and sufficient HD treatment, an obvious change of domain structure occurs, which is related to the variation of composition and crystalline microstructure during the HD process. And for the samples after sufficient DR processing, it is confirmed that the configuration of the columnar crystals is retained by the detected domain structures.