Weidong Fei

Aging behaviors of alumina borate whisker reinforced AC8A-AI composite

The aging behavior of alumina borate whisker (Al18B4O33w/AC8A-Al) composite was examined by hardness and differential scanning calorimetry heat flow measurement. Microstructures were investigated by transmission electronic microscope. The results indicated that the interfacial reaction played an important role in the aging precipitation behavior of the composite. As the interfacial reaction between the whiskers and AC8A-Al alloy consumed the Mg atom of the matrix in the composite, the time to the peak aging of the composite was almost same as that of the AC8A-Al alloy. The free precipitation zone can be found nearby some whisker in the composite, duo to Mg content decreased in the matrix.

Effects of total thickness on (001) texture, surface morphology, and magnetic properties of [Fe/Pt]n multilayer films by monatomic layer deposition

Atomic-scale [Fe/Pt]n multilayer films with different total thickness were prepared on thermally oxidized Si (100) substrates at room temperature by monatomic layer deposition using dc-magnetron and rf-magnetron sputtering. Effects of the total thickness on (001) texture, surface morphology, and magnetic properties of the postannealed films have been investigated. It is found that the particlelike structure films with perfect (001) texture and perpendicular magnetic anisotropy are obtained with a thickness of less than or equal to 6.5 nm. After 500 °C annealing, the films with thickness of 6.5 and 11.9 nm show very smooth surface. In addition, with increasing total thickness of the films, (001) texture and perpendicular magnetic anisotropy of the annealed films deteriorate, and the films become continuous in structure. The total thickness of the films also affects the exchange-coupling interaction among FePt magnetic grains and the magnetization reversal process.

Structure and magnetic properties of magnetron-sputtered FePt/Au superlattice films

Using dc magnetron sputtering, FePt/Au multilayer films were prepared, and the effects of Au thickness and annealing temperature on structure and magnetic properties of the FePt/Au films were investigated. The as-deposited FePt/Au multilayer films with a thicker Au layer show a superlattice structure. The interatomic layer spacing d(2 2 0) in face centered cubic (fcc) FePt lattice increases with increase in Au thickness. Accordingly, the strain energy stored in the fcc FePt lattice increases. After annealing at 300 °C, ordered FePt films were obtained, and the in-plane and out-of-plane coercivities of the films were found to increase with the increase in the Au layer thickness. When the Au layer thickness is 3.5 nm, the in-plane and out-of-plane coercivities of the films can reach 2.08 kOe and 1.56 kOe, respectively. The strain energy stored in fcc FePt lattice is responsible for the lower temperature ordering of FePt phase. For the films annealed at high temperature, the thicker Au layer in the films restrained the ordering of the FePt phase, which leads to the decrease in the coercivities of the films with increasing Au thickness.

Parametric study of sputtered Sr-deficient SrBi2Ta2O9 thin films

Sr-deficient SrBi2Ta2O9 (SBT) thin films for nonvolatile ferroelectric random access memory applications were deposited by radio-frequency magnetron sputtering on Pt∕Ta∕SiO2∕Si substrates. The effect of deposition parameters on microstructures and chemical composition were studied using x-ray diffraction (XRD), field emission scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The composition of the films was dependent on the sputtering conditions. The undesirable pyrochlore phase could be eliminated by adjusting process pressure, target power density, and target-to-substrate distance. The evolution of microstructures at various deposition conditions was attributed to changes in the Bi∕Ta and Sr∕Ta ratios. When Sr became deficient and Bi excessive (Sr0.74Bi2.2Ta2O9+x as determined by XPS), no pyrochlore phase was detected with XRD. Under an electric field of 240kV∕cm, the Sr-deficient SBT film demonstrated a remnant polarization (2Pr) of 11.6μC∕cm2 and a coercive field (2Ec) of 96kV∕cm.

90° switching of polarization in La3+-doped SrBi2Ta2O9 thin films

The crystal structure and polarization switching behavior of SrBi1.4La0.6Ta2O9 (SBLT) thin films have been studied by x-ray diffraction and piezoresponse force microscopy (PFM), respectively. Compared with SrBi2Ta2O9 (SBT), SBLT thin films show a reduced orthorhombic distortion. The polarization rotation of SBLT thin film, which is driven by negative and positive direct current (dc) biases, has been investigated by a combination of vertical and lateral PFM (VPFM and LPFM, respectively). After dc bias applications, the VPFM image is hardly changed, whereas the LPFM image experiences an obvious variation. It is believed that such difference is caused by 90° polarization switching. However, this kind of switching can be only realized by the exchange of a axis and b axis. By virtue of the reduced orthorhombic distortion, the a-b exchange in SBLT is easier than that in SBT. Unfortunately, stress is created due to the 90° polarization switching in SBLT thin films. The internal stress is found to increase with t...

Two-dimensional electron gas in the KNbO3:Y ultrathin film

First-principles calculations are used to study KNbO3:Y ultrathin film. The conducting two-dimensional electron gas (2DEG) is found in KNbO3:Y film, whereas SrTiO3:Y superlattice is insulating [Science 331, 886 (2011)]. The carrier density of 2DEG of KNbO3:Y film is twice that of LaTiO3/SrTiO3 superlattice, which is in agreement with the theoretical results of KNbO3:La superlattice. It is found that the charge densities of different monolayers are modulated by the polarization effect of KNbO3. We predict that 2DEG may be in other rare-earth atoms-doped KNbO3 film.