G. Y. Liu

Structural transition and atomic ordering in the non-stoichiometric double perovskite Sr2FexMo2-xO6

The structural transition and atomic ordering of a new series of ordered double perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied by X-ray powder diffraction (XRD). Rietveld refinement of the powder diffraction profiles indicates that the crystal structure of the compounds Sr2FexMo2-xO6 changes from a tetragonal I4/mmm lattice to a cubic Fm(3)over-bar-m lattice around x = 1.2 and the lattice parameters decrease slightly as Fe content increases. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95

EFFECT OF NANOCRYSTALLINE AND TWIN BOUNDARIES ON CORROSION BEHAVIOR OF 316L STAINLESS STEEL USING SMAT

By means of surface mechanical attrition treatment (SMAT), the grain size with a diameter of about 60nm formed at about 20μm depth and numerous mechanical twins at about 50μm depth from the treated surface were synthesized in 316L stainless steel because of the different distributions of strain and strain rate along depth orientation. For instance the maximum strain rate reached 103–104s−1 on the top surface. The relationship between the microstructure and the corrosion property was studied in 0.05M H2SO4+ 0.25M Na2SO4 aqueous solution, and the results show an extreme improvement of corrosion resistance owing to the appearance of twin boundaries and the obvious reduction in corrosion resistance attributed to the presence of nanocrystaline boundaries.

O3-sourced atomic layer deposition of high quality Al2O3 gate dielectric for normally-off GaN metal-insulator-semiconductor high-electron-mobility transistors

High quality Al2O3 film grown by atomic layer deposition (ALD), with ozone (O3) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al–O–H and Al–Al bonds in ALD-Al2O3 has been realized by substituting conventional H2O source with O3. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O3-Al2O3 and 2-nm H2O-Al2O3 interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 × 1012 cm−2, contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance RON,sp of 0.49 mΩ cm2.

Structure and magnetoresistance of the double perovskite Sr2FeMoO6 doped at the Fe site

The structural, magnetic and transport properties of the compounds Sr2(Fe1−xMnx)MoO6 (0 ≤ x ≤ 0.45) have been studied. The saturated magnetization, Curie temperature and low-field magnetoresistance of the compounds decrease with x, while the resistivity increases by several orders of magnitude when x exceeds a critical value. A positive magnetoresistance has been observed for x = 0.45. A possible percolation mechanism is proposed to elucidate the observations; it also suggests a coexistence of (Mn3+, Mo5+) and (Mn2+, Mo6+) valence pairs and a saturated substitution of Mn3+ for Fe3+.

High-

This letter reports a 0.2- μm gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an AlN/SiN_x (4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The AlN/SiN_x-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage (BV_DS) of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range (V_DS=3-24 V). Owing to the additional positive polarization charge in the AlN passivation layer, the access resistance R_s in the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitance C_gd, contributing to a high power-gain cutoff frequency f_MAX of 182 GHz and a high Johnsons figure of merit of BV_DS × f T of 6.43 × 10¹² V/s simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters.

f_{{\rm MAX}}

Phase relationships at ambient temperature in the pseudobinary system Pr5Si4-Pr5Ge4 were studied by X-ray powder diffraction (XRD). Three structurally distinct phase regions exist in this system. The Pr5Si4-based solid solution where Ge statistically substitutes for Si crystallizes in the Zr5Si4-type tetragonal structure with space group P4(1)2(1)2. The Pr5Ge4-based solid solution where Si statistically substitutes for Ge crystallizes in Sm5Ge4-type orthorhombic structure with space group Pnma. The crystal structure of a ternary intermediate phase, which exists between 1.65 less than or equal to x less than or equal to 2.6, is determined for the first time, and shown to be the Gd5Si2Ge2-type monoclinic structure with space group P112(1)/a. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structure. The lattice parameters, atomic occupations, interatomic distances of the Pr5Si4, Pr5Ge4 and Pr5Si2Ge2 compounds were derived

High Johnson's Figure-of-Merit 0.2-

In this letter, we report high-performance enhancement-mode (E-mode) Al2O3/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) fabricated with high-temperature low-damage gate recess technique. The high-temperature gate recess is implemented by increasing the substrate temperature to 180 °C to enhance the desorption of chlorine-based etching residues during the dry etching of AlGaN barrier. High-crystal-quality Al2O3 gate dielectric was grown by atomic-layer deposition using O3 as the oxygen source to suppress hydrogen-induced weak bonds. The fabricated E-mode MIS-HEMTs exhibit a threshold voltage of 1.6 V, a pulsed drive current of 1.13 A/mm, and very low OFF-state standby power of

\mu{\rm m}

6.8 \times 10-8 W/mm at VGS = 0 V and VDS = 30 V. At 4 GHz and in pulse-mode operation, the output power density and power-added efficiency were measured to be 5.76 W/mm and 57%, both of which are the highest for GaN-based E-mode MIS-HEMTs reported to date.

Gate AlGaN/GaN HEMTs on Silicon Substrate With

The crystal structure and magnetic properties of a new series of ordered double-perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied. The crystal structure changes from a tetragonal I4/mmm lattice to a cubic Fm (3) over barm lattice around x = 1.2. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95. The saturated magnetization increases from x = 0.8 to 0.95 and then decreases from x = 0.95 to 1.5. The Curie temperature exhibits an abrupt drop around x = 1.2, where the structural transition takes place. These complex behaviours are strongly correlated to antisite defect concentration in the compounds.

{\rm AlN}/{\rm SiN}_{{\rm x}}

0The crystal structures of La5Si4 and Nd5Si4 were studied by X-ray powder diffraction (XRD). Both of these compounds crystallize in the tetragonal Zr5Si4 type structure with space group P4(1)2(1)2. The Rietveld powder diffraction profile fitting technique was used for the refinement of the crystal structure. The lattice parameters are a=8.0467(0) Angstrom, c=15.4476(1) Angstrom for La5Si4 and a=7.8694(0) Angstrom, c=14.8077(1) Angstrom for Nd5S4. Atomic occupations, interatomic distances and coordination polyhedra in La5Si4 and Nd5Si4 were derived