Liu Zu-Li

Electric and magnetic properties of multiferroic (BiFeO3)1−x–(PbTiO3)x films prepared by the sol–gel process

(BiFeO3)1−x–(PbTiO3)x solution films have been prepared on LaNiO3/SiO2/Si substrates by the sol–gel process at an annealing temperature of 500 °C. X-ray diffraction patterns indicate that a cubic phase transition occurs in the film with x = 0.1. Cross section scanning shows the thickness of the films is about 470 nm. Coexistent ferroelectricity and magnetism at room temperature are observed by measuring ferroelectricity and magnetism. The study of ferroelectricity indicates that the remnant polarization and applicable drive field are increased by the ratio x of PbTiO3. The film with x = 0.05 has the maximum saturation magnetization. In addition, dielectric property as a function of frequency is studied.

Monte Carlo simulation of thin-film growth on a surface with a triangular lattice

The thin-film growth process on a triangular lattice surface is studied by a Monte Carlo simulation (MCS). Four kinetic processes are considered: atom deposition, adatom diffusion, adatom nucleation and adatom reevaporation. We pay close attention to the substrate temperature and the interaction between the adatom and neighboring particles. The interaction energy between the adatom and the neighboring atoms around it is calculated by the Morse potential. The results show that the higher the temperature, the more compact the island. As the temperature is low, the film growth becomes fractal growth. At higher temperature, the island becomes more regular in shape that resembles the surface morphology.

Magnetic Properties of a Mixed Spin-2 and Spin-5/2 Heisenberg Ferrimagnetic System on a Two-Dimensional Honeycomb Lattice: Green's Function Approach

The multisublattice Greens function technique is applied to study the magnetic properties of a mixed spin-2 and spin-5/2 Heisenberg ferrimagnetic system on a two-dimensional honeycomb lattice. The role of the different interactions in the Hamiltonian is explored. When only the nearest-neighbor interaction and the single-ion anisotropy are included, our results indicate that there are compensation points at finite temperatures. When the next-nearest-neighbor interaction exceeds a minimum value that depends on the other parameters in the Hamiltonian, the compensation point disappears. The next-nearest-neighbor interaction has the effect of changing the compensation temperature.

Effect of N2-Gas Partial Pressure on the Structure and Properties of Copper Nitride Films by DC Reactive Magnetron Sputtering

Copper nitride thin films were deposited on glass substrates by reactive direct current (DC) magnetron sputtering at various N2-gas partial pressures and room temperature. X-ray diffraction measurements showed that the films were composed of Cu3N crystallites and exhibited a preferential orientation of the [111] direction at a low nitrogen gas (N2) partial pressure. The film growth preferred the [111] and the [100] direction at a high N2 partial pressure. Such preferential film growth is interpreted as being due to the variation in the Copper (Cu) nitrification rate with the N2 pressure. The N2 partial pressure affects not only the crystal structure of the film but also the deposition rate and the resistivity of the Cu3N film. In our experiment, the deposition rate of Cu3N films was 18 nm/min to 30 nm/min and increased with the N2 partial pressure. The resistivity of the Cu3N films increased sharply with the increasing N2 partial pressure. At a low N2 partial pressure, the Cu3N films showed a metallic conduction mechanism through the Cu path, and at a high N2 partial pressure, the conductivity of the Cu3N films showed a semiconductor conduction mechanism.

Fabrication and photoluminescence characteristics of In2O3 nanohillocks

Uniformly distributed polycrystalline indium nanohillocks are synthesized on silicon substrates with Au catalyst by using the radio frequency magnetic sputtering technique. The results show that the Au catalyst plays a key role in the formation of indium nanohillocks. After thermally oxidizing the indium nanohillocks at 500 °C in air for 5 h, the indium nanohillocks totally transform into In2O3 nanohillocks. The energy-dispersive X-ray spectroscopy result indicates that many oxygen vacancies and oxygen—indium vacancy pairs exist in the In2O3 nanohillocks. Photoluminescence spectra under an Ne laser excitation at 280 nm show broad emissions at 420 nm and 470 nm with a shoulder at 450 nm related to oxygen vacancies and oxygen—indium vacancies at room temperature.

Properties of Al-doped copper nitride films prepared by reactive magnetron sputtering

Cu3N and AlxCu3N films were prepared with reactive magnetron sputtering method. The two films were deposited on glass substrates at 0.8 Pa N2 partial pressure and 100 °C substrate temperature by using a pure Cu and Al target, respectively. X-ray diffraction (XRD) measurements show that the un-doped film was composed of Cu3N crystallites with anti-ReO3 structure and adopted [111] preferred orientation. XRD shows that the growth of Al-doped copper nitride films (AlxCu3N) was affected strongly by doping Al, the intensity of [111] peak decreases with increasing the concentration of Al and the high concentration of Al could prevent the Cu3N from crystallization. AFM shows that the surface of AlxCu3N film is smoother than that of Cu3N film. Compared with the Cu3N films, the resistivities of the Al-doped copper nitride films (AlxCu3N) have been reduced, and the microhardness has been enhanced.

Gold Nanobelt Reorientation by Molecular Dynamics Simulation

The embedded atom method is used to study the structure stability of gold nanobelt. The Au nanobelts have a rectangular cross-section with 100 orientation along the x-, y- and z-axes. Free surfaces are used along the x- and y-directions, and periodic boundary condition is used along z-direction. The simulation is performed at different temperatures and cross-section sizes. Our results show that the structure stability of the Au nanobelts depends on the nanobelt size, initial orientation, boundary conditions and temperature. A critical temperature exists for Au nanobelts to transform from initial 100 nanobelt to final 110 nanobelt. The mechanism of the reorientation is the slip and spread of dislocation through the nanobelt under compressive stress caused by tensile surface-stress components.

Electrical Characteristics and Microstructures of Sm2O3-Doped Bi4Ti3O12Ceramics

We investigate the electrical properties of Sm-doped Bi4−xSmxTi3O12 (BST) ceramics prepared by a conventional electroceramic technique. The x-ray diffraction analysis reveals the Bi-layered perovskite structure in all samples. The SEM micrographs show randomly oriented and plate-like morphology. For the samples with x = 0.4 and 1.0, the current–voltage characteristics exhibit negative differential resistance behaviour and the P–V hysteresis loops are characterized by large leakage current, whereas for the samples with x = 0.6 and 0.8, the current–voltage characteristics show simple ohmic behaviour and the P–V hysteresis loops are of the saturated and undistorted hysteresis. The remanent polarization and coercive field of the BST ceramic with x = 0.8 are above 32 μC/cm2 and 70 kV/cm, respectively.

Monte-Carlo simulation for electron-neutral collision processes in normal and abnormal discharge cathode sheath region

Electron-neutral collision processes in helium DC normal and abnormal discharges have been studied using Monte-Carlo simulation (MCS). Four types of collisions (elastic, metastable excitation, excitation and ionization collision) are considered. Comparing normal discharge with abnormal discharge, we find that the number of collisions decreases and the collision rates increase through the cathode region in abnormal discharge. The collision rates calculated from electron instantaneous energy is different than that calculated from electron mean energy. The results also show that the elastic collision is the greatest proportion and plays an important role in electron-neutral collision processes in the cathode fall region. The effects of collision on the electron mean energy is also studied.

First-principle studies on the electronic structure of Fe3O4(110) surface

The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with FeA vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-FeA vac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.