W. Liu

ZnO-based film bulk acoustic resonator for high sensitivity biosensor applications

Zinc oxide (ZnO)-based film bulk acoustic resonator consisting of a piezoelectric element (Au∕ZnO∕Pt) and a Bragg reflector (ZnO∕Pt multilayer structure) has been fabricated by magnetron sputtering. The transmission electron microscopy and x-ray diffraction measurements revealed that all thin film layers in the device were well crystallized and highly textured. By electrical measurements, it was found that the device had a high resonant frequency (3.94GHz) and mass sensitivity (8970Hzcm2∕ng). The use of the device as a biosensor was demonstrated by comparing the resonant properties of the device with/without coatings of biospecies.

Structural and electrical characteristics of Ge nanoclusters embedded in Al2O3 gate dielectric

Structural and electrical characteristics of the metal–insulator–semiconductor (MIS) structures of Al/Al2O3/Si containing Ge nanoclusters are experimentally demonstrated. Secondary ion mass spectroscopy results indicate the out-diffusion of Ge after annealing at 800u200a°C in N2 ambient for 30 min. An increment of leakage current is observed due to the out-diffusion of Ge. Capacitance–voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by the hysteresis in the C–V curves in the annealed sample.

Magnetostriction and anisotropy compensation in TbxDy1-xPr0.3(Fe0.9B0.1)(1.93) alloys

Structure and magnetostriction of Dy0.7-xTbxPr0.3(Fe0.9B0.1)(1.93) (0less than or equal toxless than or equal to0.70) alloys have been studied. The easy magnetization direction of the Laves phase in the Dy0.7-xTbxPr0.3(Fe0.9B0.1)(1.93) alloys with 0less than or equal tox axis, while that of the Laves phase in those alloys with 0.25less than or equal toxless than or equal to0.70 lies along axis, as determined by means of x-ray crystallography study. When x is increased from 0.15 to 0.25, the change of the easy magnetization direction from to axis is detected also by Mossbauer spectra, in good agreement with the results of x-ray crystallography. The Laves phase Tb0.25Dy0.45Pr0.3(Fe0.9B0.1)(1.93) has a large spontaneous magnetostriction (lambda(111)approximate to1850 ppm) and a low anisotropy at room temperature, which could make it a good candidate material for magnetostriction applications

Al2O3 coated α-Fe solid solution nanocapsules prepared by arc discharge

Al2O3 coated alpha-Fe solid solution nanocapsules are prepared by arc-discharging a bulk AlNiCo permanent magnet. The size of the nanocapsule is in range of 3-300 nm and the thickness of the shell is 1-6 nm. Al atoms in the AlNiCo magnet form the shell of amorphous Al2O3 to prevent the nanocapsules from further oxidation. The magnetic properties of saturation magnetization J(s) = 85 A m(2)/kg and coercive force H-j(c) = 27.5 kA/m are achieved for the nanocapsules

Linear and third-order nonlinear optical absorption of amorphous Ge nanoclusters embedded in Al2O3 matrix synthesized by electron-beam coevaporation

Amorphous germanium (α-Ge) nanoclusters embedded in Al2O3 matrix are synthesized on fused-quartz glass substrate at room temperature by vacuum electron-beam coevaporation. Linear optical transmittance measurements reveal an indirect optical absorption edge with a blueshift as large as 1.6 eV due to the quantum confinement effects. The Z-scan method is used to study the third-order nonlinear absorption process of the synthesized samples, which clearly show a two-photon nonlinear process. Results also suggest that Ge nanocluster density or size is of great influence to the value of nonlinear absorption coefficient β.

Influence of the AlN interlayer crystal quality on the strain evolution of GaN layer grown on Si (111)

The strain evolution in metal organic chemical vapor deposition growth of GaN on Si (111) substrate with an AlN interlayer is studied. During the growth of GaN film on AlN interlayer, the growth stress changes from compression to tension. The study shows that the density of V trenches in the AlN interlayer surface and the threading dislocations generated in the AlN interlayer have a significant influence on this strain evolution process. The dislocations generated in AlN interlayer may thread across the interface and play a key role in the strain evolution process of the GaN layer grown on AlN interlayer.

Anisotropic behavior of exchange coupling in textured Nd2Fe14B/α-Fe multilayer films

Exchange coupling has been realized in textured Nd2Fe14B/α-Fe multilayer films. A Mo spacer layer has proved to be effective for preventing interdiffusion at the interface region between the hard-magnetic Nd16Fe71B13 and the soft-magnetic α-Fe layer in these multilayer films. Anisotropic behavior of the exchange coupling in the films is observed by means of magnetic measurements. Furthermore, the effective critical correlation length is found to exhibit anisotropic behavior, which is smaller in the parallel than in the perpendicular direction at the same temperature. This anisotropic behavior of the multilayer films can be well explained by taking into account the shape anisotropy of the textured grains.

High Pr-content (Tb0.2Pr0.8)(Fe0.4Co0.6)1.93−xBx magnetostrictive alloys

High Pr-content (Tb0.2Pr0.8)(Fe0.4Co0.6)(1.93-x)B-x magnetostrictive alloys (0.05 <= x <= 0.15) with a single cubic Laves phase were synthesized by arc-melting and subsequent annealing. The Curie temperature, T-c, and the lattice parameter, a, of the Laves phase in the alloys increase with increasing the boron content up to x=0.10, which is ascribed to the preferential occupation of boronin the interstitial sites of the Laves phase. The addition of a small amount of boron to the(Tb0.2Pr0.8)(Fe0.4Co0.6)(1.93) alloy reduces the magnetocrystalline anisotropy constant K-1 and improves the magnetostriction lambda(a)=lambda(parallel to)-lambda(perpendicular to) at relatively low magnetic fields at room temperature. The composition dependence of the ratio lambda(a)/K-1 for (Tb0.2Pr0.8)(Fe0.4Co0.6)(1.93-x)B-x alloys reaches a maximum value at x=0.10, suggesting that the (Tb0.2Pr0.8)(Fe0.4Co0.6)(1.83)B-0.1 alloy should be a good candidate material for magnetostriction applications. (c) 2005 American Institute of Physics.

Exchange bias in antiferromagnetic coupled Fe3O4+Cr2O3 nanocomposites

Exchange bias (EB) and magnetic properties of ferrimagnetic (FI) Fe3O4 and antiferromagnetic (AFM) Cr2O3 nanocomposites prepared by mechanical alloying have been investigated. A large EB field of 2.2 kOe at 10 K is observed in one of the nanocomposites, which may be related to the uncompensated and pinned AFM spins at the interface between FI and AFM phases of the nanocomposites. The EB field varies with the strength of cooling field and the content of the Cr2O3 phase, the phenomena observed are explained in terms of interfacial exchange interaction between the two phases.

Performance improvement of phase-change memory cell with cup-shaped bottom electrode contact

Cup-shaped tungsten (W) bottom electrode contact (BEC) was proposed for phase-change memory (PCM) cell and compared with the same size solid BEC. The reset voltage of 2.5V and the shortest reset time of 10ns were obtained for cup-shaped W-BEC based PCM cell, which is much better than those of the solid BEC based PCM cell. The improved performance of the cup-shaped W-BEC based PCM cell is attributed to the mushroom heating region with high heating efficiency, the inner edge contact of W-BEC and Ge2Sb2Te5, and the reduced thermal diffusion from the bottom electrode, which is further verified by theoretical simulation.