摘要:

H, C, and O impurity concentrations in metalorganic chemical vapor deposition grown InGaN were found to be dependent on the hydrogen andNH3flow rates. By increasing the hydrogen flow rate from 0 to 100 sccm, a decrease of greater than two orders of magnitude in the C and O impurity levels and one order of magnitude in the H impurity level was observed. Increasing theNH3flow rate from 1 to 5 slm results in a decrease in the C concentration and an increase in the H and O concentrations indicating that high purityNH3(99.999&percent;) can be a significant source of O contamination. Additional studies show that when the InN percent in the InGaN films increases, the impurity concentrations increase regardless of changes in the growth conditions. The InGaN films were grown from 710 to 780 °C and the impurity concentrations were characterized by secondary ion mass spectrometry. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119775

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have explored the low temperature capability of a scanning-tip microwave near-field microscope to study superconductors. The shift in the quality factor of the microscope resonator can be used to obtain the temperature dependence of the surface resistance of a local region under the tip. PatternedYBa2Cu3O7−xfilms were scanned at various temperatures and surface resistance mapping was performed with high spatial resolution at 1.2 GHz. Superconducting transitions at different positions on a film can be detected. Edge-region defects in wet-etched patterns were observed and were shown to be nonsuperconducting at microwave frequencies at 80 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119776

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

YBa2Cu3O7−&dgr;films grown on rolling-assisted biaxially textured substrates carry critical current densities105–106A/cm2at 77 K and low applied magnetic fields. In the low-field and low-current regime, ac transport current studies show hysteresis energy loss (per cycle and per unit length) roughly the value expected for a superconductor of elliptic cross section. The critical currentIcwas deduced from observed dc and dynamic current-voltage relations. The power loss rises sharply asI0(the maximum current in each cycle) is raised aboveIc.In the present configuration, ferromagnetic hysteresis of the Ni substrate contributes little or no loss. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119777

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In situmagnetoresistance measurements on lithographically defined spin-valve elements were performed by means of Lorentz transmission electron microscopy. The observation of a magnetic domain structure and the simultaneous magnetoresistance measurement by applying controlled field and controlled current have led to a clear correlation between giant magnetoresistance and changes in the magnetic domain structure. A study of the spin-valve behavior with the increase of the applied current value is also shown. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119778

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By monitoring the electric current image during conducting atomic force microscopy nano-patterning, a phenomenon that we term “resonant conducting” was found. This was characterized by a sharp peak atV=2.45±0.05 Vin the averaged current-voltage plot. The electrical current is irreversible and decays very rapidly after repeat scanning, which implies that the resonant current is associated with the transient process from a hydrogen de-passivation to an oxygen passivation under the specific electrical field. On the practical side, “resonant conducting” provides a very sensitive method for visualization of H passivation of silicon on a nano-meter scale. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119779

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed an aluminum single-electron transistor device which was modified to incorporate an additional floating node in between the gate and the electrometer. At high gate voltages, Fowler–Nordheim type emission occurred between the gate and the floating node where the charges were stored. The emission events were evidenced by the oscillatory electrometer current which allowed estimation of the number of storage electrons. We demonstrated experimentally the nonvolatile memory function of this device and the results were justified by numeric simulations. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119780

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the effect of a depolarizing field on the properties of a ferroelectric capacitor. By systematically adjusting the amount of charge available to compensate the polarization, we can control the strength of the field inside the ferroelectric. We find that even a few percent of uncompensated polarization charge results in a significant suppression of measured ferroelectric properties, and a complete lack of compensating charge leaves a greatly reduced, although nonzero, polarization. The effect of a depolarizing field is briefly discussed in terms of proposed ferroelectric device applications. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119781

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Weak field piezoelectric coefficient and strain were investigated in ferroelectricSrBi2Ta2O9(SBT) thin films by means of optical interferometry. Though the maximum polarization and dielectric constant were small enough (7&mgr;C/cm2and 150, respectively), the piezoelectric coefficient attained 17 pm/V under the dc electric field. This value is comparable with the piezoelectric coefficients reported previously on poled SBT ceramics. Electrically induced strain of5⋅10−4was observed using bipolar driving field of 300 kV/cm. No piezoelectric fatigue was found until109switching pulses, in agreement with polarization data. The piezoelectric properties and strains were successfully described by using a simple electrostriction equation with the effective electrostriction coefficient of 0.1m4/C2.The electromechanical behavior of SBT films suggested no or weak contribution of non-180° domain walls to the strain response. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119782

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ferroelectric thin films ofBaxSr1−xTiO3with compositional gradients normal to the growth surface have been formed by the successive deposition and annealing of films having step-variable Ba to Sr ratios. By suitably tailoring the magnitude and sense of the gradient in Ba to Sr ratio, directional potentials can be built into the structures yielding a new, but controllable, hysteresis phenomenon. Slater’s empirical model for ferroelectric materials has been extended to also describe thin films with polarization gradients normal to the growth surface, i.e., graded ferroelectric devices. This model accounts for several aspects of these structures, including: the broadness of the permittivity plots with temperature, the formation of a spontaneous potential upon oscillatory field excitation, offsets in the hysteresis graphs along the displacement axis with directions which are gradient dependent, and the electric field dependence of that offset. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119783

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.120563

出版商:AIP    

年代:1997

数据来源: AIP