X. S. Wu

Effect of Nd dopant on magnetic and electric properties of BiFeO3 thin films prepared by metal organic deposition method

Polycrystalline Bi1−xNdxFeO3 (x=0–0.15) thin films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic deposition method. The effect of Nd dopant on the structural, electric, and magnetic properties was studied. It was found that the ferroelectric polarization and saturation magnetization of the films were enhanced by appropriate Nd doping due to the structural distortion and the suppressed cycloidal spin structure. Meanwhile, Nd-doped BiFeO3 thin films exhibited magnetic anisotropy because of the magnetocrystalline anisotropy.

Investigation on the magnetic and electrical properties of crystalline Mn0.05Si0.95 films

The magnetic and electrical properties of crystalline Mn0.05Si0.95 films prepared by post-thermal treatment of the as-deposited amorphous Si-Mn (95at.%−5at.%) have been investigated. Both the temperature dependence and field dependence of magnetization were measured using superconducting quantum interference devices, and it has been indicated that the film materials are ferromagnetic with Curie temperature over 400K. X-ray diffraction analysis revealed full crystallization of the films and the incorporation of Mn into the host crystalline Si lattice. Behavior of thermally activated conduction processes of the films has been evinced by electrical property measurement for the films.

Multiferroic properties and dielectric relaxation of BiFeO3∕Bi3.25La0.75Ti3O12 double-layered thin films

BiFeO3 (BFO)∕Bi3.25La0.75Ti3O12 (BLT) films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic decomposition method. The multiferroic and dielectric properties of the films were studied. It was found that the ferroelectric polarization and dielectric constant of the films were enhanced by introducing BLT as a barrier layer between BFO and Pt bottom electrode, while the ferromagnetism of BFO was not influenced. More interestingly, the films showed dielectric relaxor behavior, and the possible causes of which were discussed.

Domain reversal and relaxation in LiNbO3 single crystals studied by piezoresponse force microscope

The LiNbO3 crystal was polarized and characterized by the piezoresponse force mode of scanning probe microscope. By using the Kolmogorov-Avrami-Ishibashi [Izv. Akad. Nauk, USSR: Ser. Math. 3, 355 (1937); J. Chem. Phys. 8, 212 (1940); J. Phys. Soc. Jpn. 63, 1031 (1994); 63, 1601 (1994)] theory to analyze the relaxation process after domain switching, it was found that (1) the percent of final switched domains after poling increased with the enhancing poling voltage, (2) the nucleation time was a constant to a certain sample, (3) the dimension of domain growth decreased with the enhancing poling voltage, and (4) the relaxation time had a maximum at a medial voltage. The corresponding mechanism for domain switching was discussed, which is hopefully useful for domain engineering.

Dislocation density and strain distribution in SrTiO3 film grown on (110) DyScO3 substrate

High quality SrTiO3 thin film on (1 1 0) DyScO3 substrate is grown by laser molecular beam epitaxy. The lattice strain resulting from the lattice mismatch between the substrate and the film relaxes gradually with depth. A critical thickness of about 30 nm for sharp strain relaxation is observed. The dislocation density, which forms to relax the lattice strain, is estimated to be about 108 cm−2 according to the high resolution x-ray diffraction. The edge dislocation density is slightly larger than that of the screw ones.

Strain distribution in epitaxial SrTiO3 thin films

The lattice strain distributions of epitaxial SrTiO3 films deposited on LaAlO3 were investigated by in situ x-ray diffraction at the temperature range of 25–300K, grazing incident x-ray diffraction, and high resolution x-ray diffraction. The nearly linear temperature dependence of the out-of-plane lattice constant of SrTiO3 was observed in the measured temperature range. The depth distribution of the lattice strain at room temperature for SrTiO3 films includes the surface layer, strained layer, and interface layer.

Stress effects on ferroelectric and fatigue properties of Nd- and La-doped Bi4Ti3O12 thin films

The ferroelectric properties of Bi3.15Nd0.85Ti3O12 and Bi3.25La0.75Ti3O12 thin films under applied uniaxial stress were investigated. It was observed in both films that the remnant polarization (Pr) increased with tensile stress, while it decreased with compressive stress. On the contrary, the coercive field (Ec) decreased with the stress changing from maximum compression to maximum tension. Fatigue behavior of the films was improved under either compressive or tensile stress compared with zero stress (free state). These results can be well explained in the scenario of domain reorientation under stress; however, the polarization-strain coupling mechanism could not be simply ruled out.

Temperature-dependent strain relaxation of the AlGaN barrier in AlGaN∕GaN heterostructures with and without Si3N4 surface passivation

The temperature dependence of strain relaxation in Al0.22Ga0.78N layers, with and without a Si3N4 surface passivation layer, was investigated at temperatures from room temperature to 813K using high-resolution x-ray diffraction. A small strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers at high temperature. After passivating, an additional in-plane tensile strain and an initial increase of the residual tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the residual tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced strain relaxation occurs in the 50-nm-thick one. The degree of strain relaxation of the passivated 50-nm-thick Al0.22Ga0.78N layer increases by about 33%, which results in the two-dimensional electron gas concentration reduction of about 16% at the whole temperature range in our measurements.

Stress impact on dielectric properties of Bi3.15Nd0.85Ti3O12 films

Dielectric properties of Bi3.15Nd0.85Ti3O12 films under applied uniaxial stress were investigated. The results showed that the dielectric constant and loss increased with the stress changing from maximum compression (−70 MPa) to maximum tension (+70 MPa). Further studies discovered that the variation of the dielectric constant under stress was more distinct at higher testing ac field and ambient temperature. These observations were explained based on the domain wall movability related with the stress-induced domain reorientation.

IMPROVED ELECTRIC PROPERTIES OF Nd-DOPED BiFeO3 THIN FILMS PREPARED BY METAL ORGANIC DECOMPOSITION METHOD

ABSTRACT Polycrystalline BiFeO3 (BFO) and Bi0.9 Nd0.1 FeO3 thin films were prepared by a simple MOD method on (111) Pt/Ti/SiO2/Si substrates. The effect of Nd dopant on the electric properties of BFO was studied. It was found that Nd doping in BFO film reduced the leakage current due to the decreased oxygen vacancies and Fe2 + fraction, and thus enhanced the ferroelectric and dielectric characteristics. Meanwhile, the conduction mechanisms of our films were space-charge limited in lower electric field and Ohmic in higher electric field.