C.Z. Jiang

Greatly reduced leakage current in BiFeO3 thin film by oxygen ion implantation

Oxygen ions are implanted into BiFeO3 films on LaNiO3/SrTiO3(1 0 0) substrates. The evolution of films is characterized by x-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy. The leakage current density of the implanted films is lowered by two orders of magnitude in comparison with unimplanted BFO films. The mechanisms for reduced leakage current in BiFeO3 thin films are discussed.

Large reversible electric-voltage manipulation of magnetism in NiFe/BaTiO3 heterostructures at room temperature

NiFe/BaTiO3 heterostructures were grown on (0 0 1)-SrTiO3 single crystal substrates with SrRuO3 as a buffer layer via pulsed laser deposition and off-axis magnetron sputtering. The magneto-optical Kerr effect measurement on the heterostructures demonstrated that the magnetism of the NiFe thin film can be reversibly manipulated by switching the electric voltage applied on the BaTiO3 layer, with a large change in the magnetic coercive field and saturation magnetization of the NiFe thin films. An analogous on–off switch of magnetism in the NiFe thin films was demonstrated and a novel way for Curie point writing based on the heterostructure was also proposed. Our results may provide a useful way for manipulating magnetism of bits in high-density information storage with better thermal performance and reduced power consumption.

Formation of Zn?ZnO core?shell nanoclusters by Zn/F sequential ion implantation

Zn nanoclusters were formed in highly-pure amorphous silica slices by 160 keV Zn ions implantation with a dose of 2 × 1017 ions cm−2. The Zn implanted sample was then implanted with F ions at 40 keV with 2 × 1017 ions cm−2. TEM and HRTEM studies indicate some core–shell nanoclusters have been formed in the Zn/F sequentially implanted sample. An extended x-ray absorption fine structure spectrum of the Zn/F sequentially implanted sample shows the existence of both Zn and ZnO. The oxygen atoms in the substrate are replaced by implanted F ions, producing O2 molecules, which partially oxidize the already formed Zn nanoclusters and form ZnO nanoshells. A bond length contraction of ZnO and Zn nanoclusters with different sizes was observed, which can be explained by the surface tension of nanoclusters and the compression stress from surrounding substrate effects. The latter was confirmed by the Fourier transform infrared attenuated total reflection spectra.

The use of electron backscatter diffraction to measure the elastic strain fields in a misfit dislocation-free InGaAsP/InP heterostructure

Elastic strain fields at the interface of the epilayer and buffer layer of the InGaAsP/InP heterostructure were characterized by electron backscatter diffraction (EBSD) technology based on scanning electron microscopy. The InGaAsP/InP heterostructure which contained lattice misfit was under a dislocation-free condition. Image quality (IQ) was used as the strain sensitive parameter. From the image quality map and image quality curve, we observed directly the distribution of the elastic strain fields at the interface along the direction perpendicular to the interface as well as the interface structure between the epilayer and buffer layer by transmission electron microscopy and high resolution transmission microscopy.

Growth Spindle-Like ZnO Nanocrystalline Thin Films on Nickel Layers by Dc Magnetron Sputtering and its Thermal Annealing Properties

A novel spindle-like zinc oxide (ZnO) nanocrystalline thin film was successfully fabricated on Ni thin film layer by ultrahigh-vacuum dc magnetron sputtering. Then the as-grown films were annealed in air at various temperatures from 673 to 1073 K, the corresponding structural features and surface morphology were studied by X-ray diffraction (XRD) and field emission scanning electronic microscopy (FE-SEM). The results reveal that the dominant direction of grains movement changed from perpendicular to parallel to the film interfaces. A correlation of the band gap and photoluminescence (PL) properties of nanocrystalline ZnO films with particle size morphologies and strain was discussed. Especially, PL emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.