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Ab initio molecular dynamics simulations are performed to study the liquid and undercooled liquid of zirconium. Local structure orders in the liquid at temperatures from 2500 K down to 1830 K are analyzed by using the recently developed cluster alignment method. Our study clearly shows the presence of body-centered-cube (BCC) short-range order in the undercooled liquid in addition to icosahedral order. A strong fluctuation and competition between the short-range icosahedra and BCC orders in the undercooled liquid at 1830 K are also demonstrated from the cluster alignment scheme. [ABSTRACT FROM AUTHOR]

Characteristics of In(Ga)As quantum ring infrared photodetectors (QRIPs) were investigated under normal incidence configuration. Compared with quantum dot infrared photodetectors (QDIPs), QRIPs showed wider photocurrent spectra, more stable responsivity with temperature change, and lower dark current activation energy. The wide detection band comes from the transitions from the quantum ring (QR) ground states to different excited states. The shallow confinement states generate higher dark current and enhance the carrier flow between the QRs within the same QR layer. This carrier flow averages out the repulsive potential and makes QRIPs behave similarly to the quantum well infrared photodetectors instead of QDIPs. With an Al0.27Ga0.73As current blocking layer, the performance of QRIPs was greatly enhanced. [ABSTRACT FROM AUTHOR]

Self-assembled In0.22Ga0.78As quantum dots (QDs) grown on Si substrate with Ge/SiGe as buffer layer grown by metal organic vapor phase epitaxy were investigated. Transmission electron microscopy and atomic force microscopy images were used to observe the size and space distribution of the In0.22Ga0.78As QDs grown on the GaAs/Ge/GeSi/Si layer structure. The influence of the growth temperature on the QDs size and density distribution was investigated. For QDs grown at 450 °C, the density of the In0.22Ga0.78As dots was estimated to be 1×1011 cm-2 and the In0.22Ga0.78As QDs thickness was 5 ML (monolayer) thick. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO3 (BST) thin films are among the best-known ferroelectric and dielectric materials. Ce-doped BST films have been fabricated by pulsed laser deposition in order to enhance their dielectric properties. X-ray diffraction, atomic force microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Ce-doped BST films, respectively. A strong influence of Ce doping on the properties of the BST films has been observed. First, a small amount of Ce dopant makes easy epitaxial growth of a BST film with a smooth surface on a MgO substrate. Second, residual stress in a BST film on a MgO substrate can be reduced by Ce doping, as demonstrated by the blueshift of phonon peaks in Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Si–Ba0.5Sr0.5TiO3 composite thin films were deposited by pulsed laser deposition technique on (100) Nb:SrTiO3 substrates. The crystal structure and surface morphology of the thin films have been characterized by x-ray diffraction and atomic force microscopy, respectively. Experimental results suggested that the Si composition has played a positive role in improving the dielectric properties of the thin films. With the increased Si concentration, the dielectric loss was significantly reduced, accompanied with a tolerable reduction of tunability. In particular, the 14% Si composite film exhibited a dielectric loss of 0.005, which is much lower than that of the undoped Ba0.5Sr0.5TiO3 (BST) film. Moreover, a proper concentration of Si in the film improved the figure of merit from 9 of the undoped BST to 23 of 1.4% Si composite films. [ABSTRACT FROM AUTHOR]

Magnetization response to in-plane applied fields has been studied, using Stoner-Wohlfarth model, on the bilayer systems of synthetic antiferromagnet having an anisotropy configuration in which the induced intrinsic uniaxial anisotropy is set either parallel or orthogonal to the shape anisotropy. It has been found that the toggle-mode magnetoresistance random access memory operation is possible even when the shape anisotropy exceeds the intrinsic anisotropy to some extent due to the anisotropic effect of the magnetostatic coupling and that the minimum operating field and maximum relative operating field margin are attained when the two anisotropy compensate each other. The optimal operating fields increase with the increase of the absolute value of the total anisotropy constant. However, the tolerance of total anisotropy constant in the positive direction is greater than in the negative direction if zero total anisotropy is chosen to be optimal. [ABSTRACT FROM AUTHOR]

The magnetization behavior of generalized synthetic antiferromagnet (SAF) is investigated by analytic/numeric method, applying Stoner-Wohlfarth model to each layer. Critical conditions for toggle-mode switching are given using the critical-field curves obtained from the field trajectories giving a constant value to the average angle of the magnetizations of the two layers or to the angle between the two, leaving the other variable. The critical fields for the toggle operation are found to be expressed by analytical formulas including only controllable element parameters, facilitating the parameter optimization for the memory element. The results obtained for the generalized SAF are useful in determining the tolerance for the parameter imbalance. Half-select disturb effect is still one of the important issues to be taken into account in designing the memory element. [ABSTRACT FROM AUTHOR]

An infrared photodetector that contains a superlattice structure and a blocking barrier was investigated. The photodetector shows advantages including a low operating voltage (<0.7 V), wide detection bandwidth, flexible miniband engineering, and in particular, voltage-tunable spectral responsivity. The blocking barrier not only prohibits the dark current but also acts as a high-pass energy filter to tune the spectral responsivity. The zero background peak detectivity of our detector is 3.7×10[sup 9] cm Hz[sup 0.5]/W (9.7 μm) at -0.5 V and 2.2×10[sup 10] cm Hz[sup 0.5]/W (6.7 μm) at -0.1 V. Since the spectral responsivity at different biases is independent, temperature sensing is feasible by taking the ratio of the measured photocurrent at different biases. A demonstration of temperature sensing by using our superlattice infrared photodetector with a blocking barrier is also shown in this article. Those results show the superlattice is a simple and efficient structure for the design of a multicolor infrared photodetector. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on electrochemical capacitance-voltage profiling of zinc selenide. Findings of carrier concentration measurement; Demand for a rapid method of measurement of the carrier concentration distribution; Behavior of the semiconductor/electrolyte interface if the electrolyte is concentrated.

Reports on the use of 13C and 12C diamond chips as sensors in Raman spectroscopy. Measurement of pressure at any temperature and hydrostatic pressure; Interference between the Raman spectrum from the diamond anvils and the pressure sensors; Pressure dependence of the Raman line of the 12C diamond; Temperature dependence of the diamond Raman line.

Provides information on experimental observation and theoretical results of self-defocusing and ring structure effects using cadmium tellurium crystals at room temperature. Probable cause of the induced nonlinear change in the index of refraction; Detection of the temporal profile of the incident and transmitted pulses; Use of silicon photodetectors.

Our previous study revealed that setting the induced intrinsic anisotropy orthogonal to the shape anisotropy to the toggle-MRAM (toggle mode magnetoresistive random access memory) element, thus giving zero total anisotropy, can reduce the operating field substantially with a greater margin. It has been confirmed that further reduction of the operating field is possible by applying a bias field keeping a substantial operating field margin, and that by choosing a proper bias field and the coupling field between the two magnetic layers composing a synthetic antiferromagnet memory element, the “orthogonal anisotropy” toggle-MRAM can be endowed with a greater margin than the conventional Stoner-Wohlfarth-type MRAM for the same strength of operating field, memory life, and half-select disturb robustness. [ABSTRACT FROM AUTHOR]

Crystal structure and magnetic properties of the NdCo[sub 9.5-x]Fe[sub x]V[sub 2.5] compounds with x=0–3.5 have been investigated. The lattice parameters increase linearly with the Fe content and the Curie temperature increases substantially at small amount of Fe content and then gradually with the further increase of x. A domain-wall pinning phenomenon was observed in all of the compounds and becomes less obvious as x increases. At a higher field, the compounds exhibit a field-induced metamagnetic transition. The critical field for the metamagnetic transition increases first then decreases with the Fe content, whereas the difference of the magnetization between 14 and 5 T increases with x. The observation can be understood by considering an interplay of the volume expansion, enhanced exchange coupling parameter J[sub RT] and the T sublattice moment μ[sub T] due to the Fe substitution for Co. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

For sputtered Co[sub 57]Mn[sub 43]/Si film samples with different ferromagnetic thickness, the spectra of the complex magneto-optical polar Kerr rotation and optical constants were ex-situ measured. For 5 nm-thick Co[sub 57]Mn[sub 43] film, the Kerr rotation around 4.3 eV was enhanced by a factor of about 10 times with lower loss of the signal intensity as compared to the thick film. Numerical calculations show that the enhancement effect is attributed to an interplay between optical properties of Co[sub 57]Mn[sub 43] and substrate Si that has a strong interband transition (E[sub 2]) near 4.3 eV. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the standing waves in gallium arsenide coplanar waveguides. Advantages of the coplanar waveguide in monolithic millimeter-wave integrated circuits; Information on the electron-optic sampling technique; Measurements of the standing waves.

Studies the optical and structural properties of epitaxially lifted off GaAs films. Experimental procedure used; Definition of the structural properties.

Presents a study which reported a systematic modification of thin YBa[sub2]Cu[sub3]O[suby] films with a scanning microscope. Function of the scanning tunneling microscope (STM); Benefits from the results on the surface structure of thin films; Techniques useful for the fabrication of nanoscale devices; Role of a STM system.

The effects of cobalt doping on the electrical conductivity of La0.1Bi0.9Fe1-xCoxO3 (LBFCO, x = 0, 0.01, 0.03) ceramics were investigated. It is found that the leakage current increases with cobalt dopant concentration in LBFCO. On the application of bias voltage LBFCO ceramics with cobalt doping exhibits resistive switching effects at room temperature and threshold switching effects at elevated temperatures (50 °C and 80 °C). X-ray photoelectron spectroscopy of LBFCO ceramics show that cobalt dopant is bivalent as an acceptor, which induces an enhancement of oxygen vacancy concentration in LBFCO ceramics. Possible mechanisms for both resistive switching and threshold switching effects are discussed on the basis of the interplay of bound ferroelectric charges and mobile charged defects. [ABSTRACT FROM AUTHOR]