Guojian Li

Composition, concentration and configuration dependence of the icosahedral transformations in Cu-based bimetallic clusters

The dependence of icosahedral transformations on the composition, concentration and configuration in Cu-based bimetallic clusters was studied by using molecular dynamics with the embedded atom method. The results show that the transformation is strongly related to the release of excess energy and can be controlled by tuning the composition, concentration and configuration. The transformation can be easily induced by the addition of Co while it is difficult in the case of Ni. The transformation temperature Ttrans decreases with the increase in Co concentration and increases with the increase in Ni concentration. The transformation can be controlled by fabricating different configurations and distributions of the composition.

EFFECTS OF HIGH MAGNETIC FIELD ON THE STRUCTURAL EVOLUTION AND MAGNETIC PROPERTIES OF NANOCRYSTALLINE Ni FILMS

This paper studies the effects of a high magnetic field on the structural evolution and magnetic properties of nanocrystalline Ni films prepared on quartz substrates by a molecular beam vapor deposition (MBVD) method. Atomic force microscope, X-ray diffractometer, transmission electron microscope and vibrating sample magnetometer were used to study the microstructures and magnetic properties of the Ni films. The results indicate that high magnetic field has no obvious influence on crystal structures except changing the lattice constant of the Ni films. However, the high magnetic field can refine particle size. The film deposited under magnetic field tends to grow through columnar mode because of the magnetized particles aligning along the direction of magnetic field. Furthermore, the ordered and dense arrangement of Ni atoms results in more spins contained in per unit volume and improves the saturation magnetization (Ms). Ms of the 6 T Ni film increases by 70% (578 emu/cm3) than that of the film without magnetic field (341 emu/cm3), and the coercivity is also slightly increased for the 6 T film.

High magnetic field-induced synthesis of one-dimensional FePt nanomaterials

6 Tesla high magnetic field has been employed to synthesize FePt nanomaterials. The results show that the applied high magnetic field can facilitate one-dimensional anisotropic growth of FePt nanomaterials. The mechanism of high magnetic field-induced anisotropic growth has been discussed. With the effect of high magnetic field, FePt nanomaterials would be magnetized and their easy magnetization axis would be parallel to the field direction. The magnetized nanoparticles with same orientation easily attach to form a one-dimensional nanostructure by magnetic dipolar interactions. Moreover, the magnetized nanomaterials preferred anisotropic growth with higher aspect ratio to lower the demagnetization energy.

Size-dependent structure and magnetic properties of co-evaporated Fe-SiO2 nanoparticle composite film under high magnetic field

Composite film of Fe nanoparticles embedded in a SiO2 matrix has been prepared by the co-evaporation of Fe and SiO2. Both source temperature and in-situ high magnetic field (HMF) have been used to adjust the Fe particle size and the growth of Fe-SiO2film. The size of Fe particle decreased with increasing the source temperature without HMF. When HMF was presented during the growth of the film, the size of Fe particle was enlarged and reduced for source temperatures of 1300 °C and 1400 °C, respectively. Meanwhile, the preferred orientation of the filmgrown at 1400 °C became uniform with the application of HMF. In addition, it is also found that the film was formed in two layers. One layer is formed by the Fe particle, while the other is free of Fe particles due to the existence of more SiO2. The structural variation has a significant effect on the magnetic properties. The coercivity (90 Oe) of the 1300 °C film is much higher than that (6 Oe) of the 1400 °C film with a small particle size and uniform orientation. The saturation magnetization can be increased by increasing the Fe particle volume fraction. This study develops a new method to tune the soft magnetic properties by the co-evaporation of Fe and SiO2.

A facile chemical reduction method for synthesis of platinum–iron catalysts on carbon fiber papers for methanol oxidation

Abstract To enhance catalytic activity and durability for methanol oxidation reaction (MOR), we have fabricated bimetallic Pt–Fe catalysts on carbon fiber papers (denoted as Pt–Fe@CFP) by a facile chemical reduction method using iron as the precursor, ascorbic acid and sodium hypophosphite as the reductants, respectively. When ascorbic acid is using as the reductant, the Pt–Fe@CFP catalysts are composed of platinum and disordered Pt–Fe phases. The atomic ratio between Pt and Fe can be adjusted by altering deposition conditions. The Pt–Fe@CFP catalysts with Pt/Fe ratio of 1.1, which deposited with surfactant CTAB in bath at room temperature, exhibit excellent catalytic activity and stability in MOR. However, when sodium hypophosphite is employed as the reductant, the co-deposition of phosphorus would lead to a decreased catalytic performance in MOR.

Reactive Diffusion at the Liquid Al/Solid Cu Interface in a High Magnetic Field

The kinetics of the reactive diffusion at the liquid Al/solid Cu interface was investigated at T = 973 K, 1023 K, and 1073 K in a high magnetic field of 11.5 T. During the annealing process, three stable compounds (δ, ξ2, and η2) layers were formed at the interface of the couples, and a power function relationship between the mean thickness of the diffusion layers and the annealing time kept stable. Without magnetic field, the exponent of the power function for each compound layer was higher than 0.5, but it was close to or even smaller than 0.5 with a magnetic field. Compared with the field-free environment, the migration of the liquid/solid interface due to interdiffusion decreased in the presence of a magnetic field. A considerable decrease in the effective diffusion coefficient under a magnetic field provided a likely explanation for the experimental results.

Phase alignment based on crystal orientation in Mn-Sb and Al-Ni alloys induced by high magnetic fields

Those materials with an one dimensional phase-aligned structure have a large amount of potentiality as engineering materials because of their exceptional optical, electrical and anisotropically mechanical properties. Many researchers are now working determinedly to explore the methods for fabricating this kind of material. Recently, high magnetic fields have been used to fabricate non-magnetic materials with textured structure where anisotropic magnetic energy should be strong enough to induce preferred crystal orientation. Based on this mechanism, we developed an in situ process for fabricating phase-aligned composites using high magnetic fields. In this work, hypoeutectic Mn-Sb and hypereutectic Al-Ni alloys were solidified in various magnetic fields. The primary MnSb dendrites in the solidified Mn-Sb alloys were found to be macrostructurally aligned along the field direction, while the primary Al3Ni phases in the Al-Ni alloys were found to be macrostructurally aligned perpendicular to the field direction. The X-ray diffraction (XRD) measurement results suggested that these two phases were also oriented by the magnetic field. It was believed that the above-mentioned alignment is based on the crystal orientation and relevant to the heat flux direction, the preferred growth direction and the concentration field around crystallized crystals.

Lone-Pair Electrons Do Not Necessarily Lead to Low Lattice Thermal Conductivity: An Exception of Two-Dimensional Penta-CN2

It has long been documented in the literature that lone-pair electrons (LPE) are generally thought to lead to low lattice thermal conductivity (κL) of bulk materials by inducing strong phonon anharmonicity. Herein, we show an exceptional case of two-dimensional (2D) penta-CN2 that possesses LPE but exhibits more than doubled κL (660.71 W m-1 K-1) than the LPE free counterpart of penta-graphene (252.95 W m-1 K-1), which is unexpected and contradictory to the traditional theory of LPE leading to low κL. Based on the comparative study of four 2D systems possessing LPE and their respective LPE free counterparts (planar C3N vs graphene and penta-CN2 vs penta-graphene), the underlying mechanism is found lying in the bonds homogenization in penta-CN2 due to the wide spatial extension of the nonsymmetrically distributed LPE, which compensates the lattice anharmonicity due to LPE and is responsible for the opposite tendency of LPE-affected κL in the four 2D systems.

Transparent ZnO:Al2O3 films with high breakdown voltage and resistivity

Transparent ZnO films with high breakdown voltage and resistivity were deposited by the radio frequency-assisted evaporation method. In this paper, we have investigated on the structural, optical, and electrical properties of ZnO:Al2O3. The preferred orientation of the columnar structured in situ-grown film was along (002). The resistivity of the films was five orders of magnitude larger than the currents highest resistivity. The breakdown voltage of the film (8571 V/mm) was five times higher than the highest reported breakdown voltage for a ZnO semiconductor. Furthermore, the ZnO:Al2O3 film was transparent in the visible and infrared regions even though the film had an Al content of about 7% and a thickness of 100 nm. The high-frequency dielectric constant of the ZnO:Al2O3 film was higher than that of Al2O3. The possible reasons for the transparent ZnO:Al2O3 film behavior were second-phase Al2O3, lower carrier concentration, and strong bound electrons. Less defects and strong bonding contribute 4 orders of magnitude improvement to the high resistivity of ZnO films. The obtained results suggest that ZnO:Al2O3 can be used as an insulator layer between the p-n junction in order to improve the efficiency of the solar cell device.Transparent ZnO films with high breakdown voltage and resistivity were deposited by the radio frequency-assisted evaporation method. In this paper, we have investigated on the structural, optical, and electrical properties of ZnO:Al2O3. The preferred orientation of the columnar structured in situ-grown film was along (002). The resistivity of the films was five orders of magnitude larger than the currents highest resistivity. The breakdown voltage of the film (8571 V/mm) was five times higher than the highest reported breakdown voltage for a ZnO semiconductor. Furthermore, the ZnO:Al2O3 film was transparent in the visible and infrared regions even though the film had an Al content of about 7% and a thickness of 100 nm. The high-frequency dielectric constant of the ZnO:Al2O3 film was higher than that of Al2O3. The possible reasons for the transparent ZnO:Al2O3 film behavior were second-phase Al2O3, lower carrier concentration, and strong bound electrons. Less defects and strong bonding contribute 4 orders...

Effect of high magnetic field on magnetic properties of oxidized ZnO:Co film prepared with different growth models

Growth models and high magnetic field (HMF) are employed to affect diluted magnetic performance of Co-doped ZnO (ZnO:Co) films which oxidize Co-Zn evaporated films at 300 °C for 120 min in open air. Nanograined boundaries and dense structure obtained in the co-deposition films are helpful to present a better diluted magnetic performance. Two phases of Zn and ZnO coexist in the films at a low oxidation temperature. Both the bilayer Co/Zn film and the application of HMF during the oxidation process offer an easy way to increase oxygen vacancies, which are inconducive to improve the ferromagnetism. The co-deposition 0 T film has the best diluted magnetic performance compared with the bilayer 0 T film. To be specific, saturation magnetization MS of the co-deposition 0 T film (100.1 emu/cm3) increases by 190%, squareness S increases from 0.31 to 0.75 and coercivity HC increases from 34.6 Oe to 183.5 Oe. With the application of HMF, the MS of the co-deposition films decreases by 44% to approximately 55.8 emu/cm3 and the HC increases to 118.4 Oe.Growth models and high magnetic field (HMF) are employed to affect diluted magnetic performance of Co-doped ZnO (ZnO:Co) films which oxidize Co-Zn evaporated films at 300 °C for 120 min in open air. Nanograined boundaries and dense structure obtained in the co-deposition films are helpful to present a better diluted magnetic performance. Two phases of Zn and ZnO coexist in the films at a low oxidation temperature. Both the bilayer Co/Zn film and the application of HMF during the oxidation process offer an easy way to increase oxygen vacancies, which are inconducive to improve the ferromagnetism. The co-deposition 0 T film has the best diluted magnetic performance compared with the bilayer 0 T film. To be specific, saturation magnetization MS of the co-deposition 0 T film (100.1 emu/cm3) increases by 190%, squareness S increases from 0.31 to 0.75 and coercivity HC increases from 34.6 Oe to 183.5 Oe. With the application of HMF, the MS of the co-deposition films decreases by 44% to approximately 55.8 emu/cm...