Search Results - (Author, Cooperation:J. Schubert)

2018-03-06

Rockefeller University Press

0022-1007

1540-9538

Medicine

2011-07-08

Nature Publishing Group (NPG)

0028-0836

1476-4687

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Chemistry and Pharmacology

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Natural Sciences in General

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2018-10-24

National Academy of Sciences

0027-8424

1091-6490

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2018-09-11

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

1089-7550

AIP Digital Archive

Physics

The long-term stability of epitaxial thin film structures of superconducting Y1Ba2Cu3O7−x on silicon wafers (100), using a yttria-stabilized ZrO2(YSZ) buffer, is presented and compared to identical structures on SrTiO3 (100) and yttria-stabilized ZrO2 (100) single crystals. For Y1Ba2Cu3O7−y/YSZ/Si heterostructures, the maximum Y1Ba2Cu3O7−y film thickness is limited to 50 nm; otherwise thermal strain induces microcracks. Thinner films are more stable, but nevertheless show aging over several weeks, which affects critical current density and room-temperature resistivity, but not the critical temperature Tc.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Thin films of high-temperature superconducting YBaCuO deposited by dc-sputtering on SrTiO3 substrates are structured by electron beam lithography on a submicron scale. Details of the technology processes involved are presented. The sudden transition of structures below 1 μm into the semiconducting state is discussed.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Thin epitaxial films of monoclinic pure and cubic yttria-stabilized (YSZ) ZrO2 were deposited onto Si(100) by electron-beam evaporation. The degree of crystalline perfection was controlled by the growth temperature. Epitaxial YBa2Cu3O7−x films were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperature Tc0 of 86–89 K, a critical current density jc of 106 A/cm2 at 77 K, and a channeling minimum yield of 12% was obtained on YSZ buffers showing a minimum yield of 7%. Even a 14-nm-thick YSZ buffer enabled the growth of an YBa2Cu3O7−x film with Tc0 of 86 K and a minimum yield of 12%. With decreasing quality of the YSZ buffer layers the crystalline quality of the superconductor also decreased. The disorder in the YBa2Cu3O7−x films, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa2Cu3O7−x exhibited a pronounced texture with a minimum yield of 72%. The comparatively rough surface of the monoclinic pure ZrO2 severely hampered the c-axis alignment of the YBa2Cu3O7−x, resulting in superconductor films of inferior quality.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. The best magnetic field noise values of 22 and 11.5 fT/Hz1/2 in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about 200 fT/Hz1/2 at 10 Hz) was present. Computer simulation showed that the loss in this trilayer system was dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The rf coupling coefficient krf between the resonator and the flip-chip-coupled SQUID was also estimated. The values krf2(approximate)14×10−3 obtained for the layout with two input coils, and krf2(approximate)45×10−3 for the layout with the labyrinth resonator were considerably higher than the typical value of krf2(approximate)7×10−3 for the single-layer coplanar resonator. These high coupling coefficients have compensated the somewhat degraded unloaded quality factor of the resonator, thus securing the optimum operation of the rf SQUID. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We communicate a detailed study of the epitaxial growth of CeO2 on MgO. The key feature of the growth is the dependence of the in-plane orientation of the CeO2 epitaxial layer on the MgO surface morphology. Atomic force microscopic (AFM) measurements, x-ray analyses, as well as high-resolution transmission electron microscopy (HRTEM) investigations reveal that on rough substrates a cube-on-cube growth of CeO2 on MgO occurs while on smooth substrates the CeO2 unit cell is rotated around the surface normal by 45° with respect to the MgO unit cell when the deposition rate is low (∼0.3 A(ring)/s) during the first stages of growth. This growth mechanism can be used for a defined fabrication of 45° grain boundaries in the CeO2 layer by controlling the surface roughness of the MgO substrate. This report demonstrates that these 45° grain boundaries may be used to fabricate YBa2Cu3O7−x Josephson junctions. © 1995 American Institute of Physics.

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1089-7550

AIP Digital Archive

Physics

Epitaxial thin films of Y-doped SrZrO3 have been grown on MgO(001) by pulsed laser deposition. The deposition process has been performed at temperatures of 1000–1200 °C and at an oxygen pressure of 1.5×10−1 mbar. The samples are characterized by Rutherford backscattering spectrometry/channeling (RBS/C) and x-ray diffraction (XRD). We found an epitaxial relationship of SrZrO3 (0k0) [101](parallel)MgO (001) [100]. Good crystalline quality is confirmed by RBS/C minimum yield values of 9% and a FWHM of 0.35° of the XRD rocking curve. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Current-voltage characteristics, Josephson radiation spectra, and critical current versus magnetic-field dependences were measured in epitaxial, c-axis YBa2Cu3O7 step-edge Josephson junctions (SEJs) on SrTiO3 and LaAlO3 substrates with various step angles α. The results were correlated with microstructural data to determine the origin of the observed weak-link behavior. It was shown that on steps with α(approximately-greater-than)45° the SEJ is a series connection of two weak links unambiguously correlated with the occurrence of two 90° tilt grain boundaries. On steep steps, α≥70°, the boundary at the upper step edge has, on average, the (103) symmetry, while the lower one is predominantly of the basal-plane-faced (010)(001) type. Correspondingly, one link is weaker than the other, with the weaker link originating on the (010)(001) boundary. However, others have shown that analogous grain boundaries in planar (103) and biepitaxial a-axis/c-axis films do not exhibit a strong magnetic-field dependence of critical current, which is characteristic of a weak link. Hence, it is proposed that the weak-link behavior of boundaries on step edges originates from their defect structure. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Epitaxial waveguide structures of c-axis oriented BaTiO3 thin films on MgO(001) have been grown by pulsed laser deposition. The structural properties of the samples have been characterized by Rutherford backscattering spectrometry/ion channeling (RBS/C), x-ray diffraction, and atomic force microscopy. We found excellent crystalline quality even up to thicknesses of a few microns. This has been confirmed by RBS/C minimum yield values of 2%–3%, a full width at half maximum of 0.36° of the BaTiO3 (002) rocking curve, and a rms roughness of 1.1 nm for a 950 nm BaTiO3 film. The out-of-plane refractive index was measured to be close to the extraordinary bulk value with the birefringence being about one third of the bulk value. Waveguide losses of 2.9 dB/cm have been demonstrated. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the first spatially resolved measurement of the critical transport current density of c-axis oriented epitaxial Y1Ba2Cu3O7 films on 〈100〉 SrTiO3 using low-temperature scanning electron microscopy (LTSEM). The local critical current density, imaged with a spatial resolution of ∼1 μm, has been found to vary considerably in these films. Possible reasons for the observed spatial inhomogeneities are surface imperfections of the substrate and precipitates in the film. The spatial inhomogeneity of the critical current density in epitaxial films might be a reason for differences in the temperature dependences of the critical current density obtained by magnetic and transport measurements.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The evolution of microstructure in Al and Cu thin film lines during electromigration has been studied using a transmission electron microscopy. Grain boundary migration was found to be critically involved in the electromigration induced hillock formation that can be described as a three-dimensional growth of a single grain. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A system with two interacting plasma fluxes for the deposition of high-temperature superconductor films is presented. This system prevents the appearance of particles on a film surface, and permits one to obtain YBa2Cu3O7−x films with the surface defect concentration as low as 104 cm−2, a high critical temperature of 90 K, and a critical current density of 4×106 A/cm2 at 77 K. It is shown that high morphological quality films are obtained at a specific target-substrate distance.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High quality YBa2Cu3O7−x films on silicon-on-sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We present an improved reaction patterning technique to fabricate very stable thin film devices of YBaCuO on various substrates. Our approach includes in situ patterning and completely avoids the contact between YBaCuO superconductor and chemical or physical etchants. Very thin, high quality YBaCuO structures are grown on ridges or in trenches and in situ protected by passivating layers, demonstrating excellent long term stability.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A superconducting quantum interferometer device (SQUID) electronics with tank frequencies near 150 MHz was constructed to enhance the rf SQUID sensitivity. By these means we characterized our YBa2Cu3O7 thin-film rf SQUIDs with step-edge junctions immersed in liquid N2. We obtained transfer function values of over 40 μV/Φ0, at a 50 Ω input impedance, for both hysteretic and dispersive mode of rf SQUID operation. The rms white and 1/f flux noise levels were significantly lower than at the tank frequency of 20 MHz. The best magnetic field sensitivity at 77 K was 0.9 pT/Hz1/2, and the energy resolution 1.4×10−28 J/Hz, down to 0.3 Hz.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We fabricated and characterized microwave rf SQUIDs integrated into a planar, S-shaped λ/2 microstrip resonator. This 3 GHz resonator was fabricated from a pulsed-laser-deposited YBa2Cu3O7 epitaxial film. The SQUID structures incorporated double step-edge junctions and had a loop inductance of 120 pH. Such unoptimized SQUIDs operated between 4.2 and 85 K with dV/dΦ=18–20 μV/Φ0 at 77 K. At that temperature, the energy resolution of (8±2)×10−29 J/Hz above 0.1 Hz (in the best samples) was limited by the white noise, SΦ1/2=(7±1)×10−5 Φ0/Hz1/2. Optimization may increase dV/dΦ and improve the energy resolution by up to an order of magnitude.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We investigated one-dimensional arrays with up to 600 step-edge Josephson junctions (SEJ) fabricated by pulsed laser deposition of YBa2Cu3O7 (YBCO) films on steep steps in epitaxial LaAlO3 substrates. The steps were prepared by Ar-ion milling and the YBCO thin films were patterned either by Ar-ion milling or by an inhibit process. The current-voltage (I-V) characteristics and the Josephson emission of a single SEJ show that it consists of two resistively shunted-junction-type (RSJ) weak links in series which have different critical currents, IC1 and IC2. The I-V characteristics of our arrays were also close to the RSJ-model. The number of series-connected weak links deduced from the I-V curves was usually higher than the number of steps. Histograms of the individual weak link ICs showed two peaks at IC1 and IC2. The IC spread was about ±20% to ±40% of these two values. Radiation from arrays was detected and an evidence of phase locking in Josephson junction clusters obtained.

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