摘要:

Annealing at higher temperature (700 °C) of structures with two‐dimensional and three‐dimensional arrays in InAs–GaAs quantum dots (QDs) results in an increase in the size and in a corresponding decrease in the indium composition of the QDs. The change in the In composition is monitored by the contrast pattern in theplan‐viewtransmission electron microscopy (TEM) images viewed under thestrongbeamimaging conditions. Increase in the size of the QDs is manifested by the plan‐view TEM images taken under [001] zone axis illumination as well as by the cross‐section TEM images. We show that the dots maintain their geometrical shape upon annealing. Luminescence spectra demonstrate a shift of the QD luminescence peak toward higher energies with an increase in the annealing time (10–60 min) in agreement with the decrease in indium composition revealed in TEM studies. The corresponding decrease in the QD localization energy results in an effective evaporation of carriers from QDs at room temperature, and the intensity of the QD luminescence decreases, and the intensity of the wetting layer and the GaAs matrix luminescence increase with the increase in the annealing time. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116843

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Hall coefficients and resistivities of a series of Bi2+xSr2−xCuOysingle crystals were measured to investigate the relation between the carrier concentration and the disorder of the system in the superconductor‐insulator transition. Excimer‐laser cutting technique was applied to fabricate the Hall‐bar shaped samples in order to determine precisely the transport properties of the single crystals. The Hall coefficients were found to be independent of the temperature, which suggests Coulomb interaction was negligible in the localized regime of Bi2+xSr2−xCuOy. We found the Ioffe–Legel conditionkFl∼1 laid aroundn0∼8×1020cm−3in this system, and the carriers in the localized regime were essentially ‘‘metallic.’’ ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116844

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have obtained parametric gain at 19 GHz from a distributed Josephson junction parametric amplifier whose active gain medium consists of a series array of 1000 Josephson junctions embedded in a coplanar waveguide. When cooled to 1.7 K the amplifier provides 16 dB gain in a mode where the internally generated double sideband noise referred to input is 0.5±0.1 K. This noise is consistent with Nyquist noise generated from the losses. An instantaneous bandwidth of 125 MHz has been observed with a peak gain of 12 dB. The 3 dB compression point with a peak gain of 14.6 dB is ‐90.5 dB and the dynamic range is 38 dB. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116845

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ion scattering techniques in the 5–50 keV range have the potential to yield quantitative information on the composition of high‐temperature superconductor (HTc) films. To demonstrate this we have designed and built an ion scattering spectrometer, compact enough forinsituuse, as an analytical tool for vacuum deposition processes. Data collected from La2−xSrxCuO4films demonstrate the excellent mass resolution available using heavy incident ions. Modeling of the data has been carried out using both a simple empirical method and a full Monte Carlo code. In addition to stoichiometric information, the contribution of light recoiled elements to the spectrum is determined. The estimated composition, based on these models is compared with the composition obtained using high energy Rutherford backscattering spectrometry (RBS) to verify the quantitative capabilities of the technique. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117311

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It is simply demonstrated that the giant magnetoimpedance (GMI) response of a plate or ribbon is rigorously equivalent to the response of the same sample in ferromagnetic resonance (FMR) experiment. Thus, all of the solutions for FMR response behavior of metals may be applied to the description of GMI. For situations which have not been studied before, the methods which have been developed over the past 40 years for theoretical description of FMR in metals may be applied to predict the GMI behavior. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117312

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The sputter deposited (Pt/Co/Pt/Ni) multilayer films were studied as possible alternative low Curie temperature multilayers for magneto‐optical recording. The Curie temperatures of these multilayers were found to be between 150 and 300 °C, which are much lower than those of Co/Pt multilayers or (Co,Ni)/Pt multilayers. The coercivities of these multilayers were between 450 and 800 Oe. The Kerr spectra of these multilayers exhibited enhancement of the Kerr rotation at lower wavelengths. These multilayers were found to show comparable magnetic and magneto‐optical properties to Co/Pt multilayers and have an added feature of low Curie temperature making them attractive for magneto‐optical storage applications. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117313

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011–1015ions/cm2) of 200 keV Ar+ions. The implanted samples were examined by ion channeling and x‐ray diffraction techniques. The channeling results clearly showed that the magnitude of the induced lattice disorder did not increase greatly for implantation doses up to 5×1013ions/cm2. In this low dose implantation regime, the magnetoresistance {MR=[R(0)−R(H)]/R(0)} increased by 50%, the peak resistivity went up by two orders of magnitude, and the magnetoresistivity peak temperature decreased by 130 K compared to the original, unimplanted sample. For doses ≥5×1013ions/cm2, the damage was significant and caused the sample to become semiconducting. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117314

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Exchange‐biased magnetic sandwiches are shown to exhibit ‘‘giant’’ magnetoresistive properties when deposited on free‐standing organic films. This allows for the possibility of preparing flexible magnetoresistance heads or head arrays for tape or floppy‐disk drive and hard‐disk drive applications. Similar structures deposited on thin organic layers spin coated onto silicon substrates also exhibit giant magnetoresistive behavior. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117315

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Three‐dimensional elemental mappings of Co–Cr–Ta thin film sputter‐deposited at 200 °C were obtained using a three‐dimensional atom probe. We have confirmed that Ta atoms are dissolved in the film homogeneously, and no segregation of Ta was found at the grain boundaries. On the other hand, Cr atoms are inhomogenously dissolved within grains, and it is strongly enriched at the grain boundaries forming a Cr‐enriched grain boundary phase with a thickness of approximately 4 nm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117316

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a technique to fabricate nanostructures with an atomic force microscope (AFM). By taking advantage of the AFM tip sharpness, we engrave a narrow furrow in a soft polyimide layer. The furrow is then transferred using dry etching to a thin germanium layer which forms a suspended mask. Metallic layers are then evaporated through this mask. Metallic lines with a 40 nm linewidth and single‐electron transistors have been fabricated. This lift‐off technique can be used on any substrate and allows easy alignment with previously fabricated structures. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117317

出版商:AIP    

年代:1996

数据来源: AIP