摘要:

The electrical properties of the mismatched interface between InAs and GaP have been investigated. High-resolution transmission electron microscopy images show the presence of strain relieving, 90° misfit dislocations at this interface. Hall measurements and electrochemical capacitance–voltage profiling indicate the presence of a high-density sheet of carriers (electrons and holes) at the interface. A linkage is drawn between interfacial carriers and misfit dislocations. A model based on Fermi-level pinning in InAs at the interface by misfit dislocations is proposed to account for the observed electrical behavior. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121348

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In Si &dgr;-modulation-dopedGaAs/In0.2Ga0.8As/AlxGa1−xAsquantum well structures (QWs), the electrons from the ionized Si donors are initially confined in the V-shaped potential well (V-PW) formed at the position of a Si &dgr;-doped layer. The efficiency of electrons transferring from the V-PW to the QW was investigated as a function of Si &dgr;-doping concentration in the symmetricGaAs/In0.2Ga0.8As/GaAsQW at 1.7 K. The electron density in the QW increases linearly with an increase of Si &dgr;-doping concentration, while the electron transfer efficiency remains unchanged either in the dark or under the illumination. The asymmetricGaAs/In0.2Ga0.8As/Al0.2Ga0.8AsQW has a relatively higher electron transfer efficiency. The effect of grading the Al mole fraction over theAlxGa1−xAsspacer layer on the electron transfer efficiency was also reported. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121349

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have studied the isothermal, magnetic field(H‖c)dependent rf powerP(H)dissipation(Hrf‖a)in the superconducting state ofBi2Sr2CaCu2O8single crystals prior to and after irradiation with 250 MeV107Ag17+ions. In the pristine state,P(H)shows an initial decrease with increase in field, reaches a minimum atHM(T)and increases monotonically forH>HM(T).This behavior arises when the electromagnetic coupling between the pancake vortices in adjacent CuO layers becomes dominant on increasing the field and minimizes the distortions of the flux lines by confining the 2D vortices. In the post irradiated state, such an initial decrease and the minimum inP(H)is not observed but only a much reduced rf dissipation that monotonically increases with field fromH=0onwards is seen. We attribute this difference to the strong enhancement of the tilt modulusC44of the flux lines on irradiation when the pancake vortices in adjacent CuO bilayers are pinned along the track forming a well-stacked flux line in the field direction(‖c).We have also observed that the rf dissipation disappears at a certain temperatureTsf,at which the normal core of the flux line becomes commensurate with the columnar track diameter. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121350

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The application of high temperature superconductor (HTS) Josephson junctions in digital rapid single flux quantum circuits requires a careful study of the influence of thermal noise on the bit error rate (BER). We have determined experimentally, for the first time, the BER of a HTS rapid single flux quantum circuit. A comparator, formed by two Josephson junctions, was integrated in a Josephson transmission line ring oscillator, allowing us to perform high speed testing of the comparator at GHz frequencies. For fabrication, focused-electron-beam-irradiated junctions have been used because of their small parameter spread and excellent alignment possibilities. A BER of less than10−11was obtained at 39 K. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121351

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Magnetic CoNi/Pt interfaces are studied as a function of their preparation conditions by magnetization-induced second-harmonic generation (MSHG) measurements. A detailed method has been developed to decompose the total MSHG response into magnetic and crystallographic contributions for each interface. Although the bulk magnetism of the CoNi film (3 nm thick) shows only a subtle dependence on the sputtering Ar pressure, the interfaces appear to be dramatically affected. It can be shown that the crystallographic part probes the increase in the interface roughness while the magnetic one clearly reveals a maximum in the in-plane magnetization of the interface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121352

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Different mechanisms of spin-dependent tunneling are analyzed with respect to their role in tunnel magnetoresistance (TMR). Microscopic calculation within a realistic model shows that direct tunneling in iron group systems leads to about a 30&percent; change in resistance, which is close but lower than experimentally observed values. The larger observed values of the TMR might be a result of tunneling involving surface polarized states. It is found that tunneling via resonant defect states in the barrier radically decreases the TMR by order of magnitude. One-magnon emission is shown to reduce the TMR, whereas phonons increase the effect. The inclusion of both magnons and phonons reasonably explains an unusual bias dependence of the TMR. The model presented here is applied qualitatively to half metallics with 100&percent; spin polarization, where one-magnon processes are suppressed and the change in resistance in the absence of spin mixing on impurities may be arbitrarily large. Even in the case of imperfect magnetic configurations, the resistance change can be a few 1000&percent;. Examples of half-metallic systems areCrO2/TiO2andCrO2/RuO2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121342

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The first-order nature of the magnetic phase transformation at 360 °C and the presence of a Bi-rich eutectic at 265 °C have inhibited the application of MnBi thin films for high density magneto-optical data storage. It is suggested that partial substitution of Cr for Mn should both lower the Curie temperature,Tc,and decouple the lattice and magnetic transitions so as to allow reversible Curie point writing. It is found experimentally that 10&percent; substitution of Cr for Mn reduces the apparentTcto∼250 °Cwhile retaining a Kerr rotation angle greater than 1° at 633 nm, as measured through the silica glass substrate. Observations of increasingHcwith temperature in bothMnBiand(Mn,Cr)Bithin films suggest that the low-temperature phase is ferrimagnetic. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121355

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An expandable system has been developed to operate multiple probes for the atomic force microscope in parallel at high speeds. The combined improvements from parallelism and enhanced tip speed in this system represent an increase in throughput by over two orders of magnitude. A modular cantilever design has been replicated to produce an array of 50 cantilevers with a 200 &mgr;m pitch. This design contains a dedicated integrated sensor and integrated actuator where the cells can be repeated indefinitely. Electrical shielding within the array virtually eliminates coupling between the actuators and sensors. The reduced coupling simplifies the control electronics, facilitating the design of a computer system to automate the parallel high-speed arrays. This automated system has been applied to four cantilevers within the array of 50 cantilevers, with a 20 kHz bandwidth and a noise level of less than 50 Å. For typical samples, this bandwidth allows us to scan the probes at 4 mm/s. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121353

出版商:AIP    

年代:1998

数据来源: AIP