摘要:

A multilayer highTcsuperconducting field‐effect transistor‐like structure was made from ultrathin YBa2Cu3O7−xfilms. An epitaxially grown dielectric SrTiO3insulation layer, which had a forward bias breakdown voltage of about 20 V, allowed an electric field induced change in the channel layer of 1.25×1013carrier/cm2per volt of the gate voltage. A significant modulation of the normal state and superconducting properties was observed in samples with YBa2Cu3O7−xchannel layers of a few unit cells thick. By applying gate voltage of different polarities,Tcwas both suppressed and enhanced by ∼1 K. The resistance was modulated by as much as 20% in the normal state and by over 1500% near the zero resistance temperature.

ISSN:0003-6951    

DOI:10.1063/1.105656

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have fabricated and tested superconducting first‐order gradiometers made from YBa2Cu3O7−&dgr;(YBCO) thin‐film flux transformers coupled to YBCO dc SQUIDs. The flux transformers consisted of 10‐turn input coils with 5‐&mgr;m linewidth and two pick‐up loops with 600‐&mgr;m linewidth, each of which surrounded an area of 2.1 by 2.8 mm. All levels were patterned by wet etching. A magnetic field gradient of 1 nT/m resulted in a flux of 5.8×10−4&Fgr; in the SQUID which corresponds to a responsivity of 1.21×10−9m3. The 1/fnoise level at 77 K and 10 Hz was 0.6 nT/m&sqrt;Hz and was dominated by SQUID noise.

ISSN:0003-6951    

DOI:10.1063/1.105657

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on the study of the submillimeter absorptivity of high‐Tcsuperconductors by a new method, the photothermal interference spectroscopy. Absorption in a sample leads to a temperature change of the sample and, by heat transfer, also of a gas volume adjacent to the sample and to a change of refractive index in the gas volume that we detect by an interferometric method. We demonstrate the feasibility of the method by determination of the absorptivity of high‐Tcsuperconducting YBa2Cu3O7−&dgr;samples for submillimeter radiation at a frequency near 1 THz. The absorptivity shows a peak atTc, that is most likely due to fluctuation effects, a strong drop belowTcand a finite value at low temperatures, with a peak near 15 K.

ISSN:0003-6951    

DOI:10.1063/1.105658

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this work we provide the report on the preparation of a bulkn‐type NdCeCuO superconductor using a high‐pressure high‐temperature sintering procedure. The superconductor was obtained by sintering as‐prepared material at 4.0 GPa at 530 °C for 20 min and required no additional reducing treating. The sample shows a higher onset temperatureTcon(32 K), a higher zero resistance temperatureTc0(22 K), and a much lower resistivity than a standard bulk sample. Indeed the room‐temperature resistivity and the quasimetallic resistivity in the normal state for our polycrystalline sample are similar to those of single crystals. This high‐pressure sintering procedure reduces weak link effects and opens the possibility of preparing high‐quality bulkn‐type superconductors.

ISSN:0003-6951    

DOI:10.1063/1.105659

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have studied the magnetic interference of the critical currents of synthetic planar thin‐film grain‐boundary Josephson junctions. We find that the effective area of these junctions scales as the square of the widthwin contrast to the usualw(2&lgr;+d) dependence of sandwich‐type Josephson junctions. This behavior is a simple consequence of the magnetic response of thin‐film superconductors to perpendicular applied fields. A model based on the London theory yields the observed behavior. In addition, we find the correction to the interference pattern due to the effect of the corners.

ISSN:0003-6951    

DOI:10.1063/1.105660

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Granular films of nominal composition (Fe,Co,Ni)50(SiO2)50were prepared by rf sputter deposition and characterized by transmission electron microscopy. In each case the films were found to consist of small metal particles, several nanometers in size, embedded in an amorphous silica matrix. The chemical composition of the metal particles was studied, for the first time, by x‐ray photoelectron spectroscopy. These measurements detected the presence of the metal oxides Fe3O4, FeO, Fe2O3, CoO, NiO, and Ni2O3associated with the Fe, Co, and Ni particles, respectively.

ISSN:0003-6951    

DOI:10.1063/1.105661

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Current dopant diffusion theory is based on dopant‐point‐defect interaction, and assumes that the number of dopant‐defect pairs is much smaller than the unpaired dopant concentration. In cases where a large number of excess defects are created from implantation damage, this may no longer be a valid assumption. A new derivation of the dopant and defect equations is presented which is valid for any concentration of dopant‐defect pairs.

ISSN:0003-6951    

DOI:10.1063/1.105662

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We describe a series of experiments using local heating to deposit copper from solution onto a palladium pattern. We show that palladium, the more noble metal, does not dissolve during thermally induced exchange plating when sacrificial copper is appropriately placed with respect to the palladium. Rather, the palladium becomes cathodic locally without dissolution, consistent with its position in the electronegativity series. However, without sacrificial copper, no deposition occurs. These results help to explain the mechanisms for a recently described electrochemical ‘‘open’’ microcircuit repair method.

ISSN:0003-6951    

DOI:10.1063/1.105663

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new perovskite Pb(In1/2Ta1/2)O3compound was successfully prepared through the wolframite phase oxide, utilizing fast firing for the enhancement of formation of the perovskite phase and densification. Dielectric properties of Pb(In1/2Ta1/2)O3are found to be typical of a ferroelectric relaxor exhibiting a broad maximum of the permittivity at 5 °C at 1 kHz, strong dielectric dispersion around room temperature, and rounded polarization‐electric field hysteresis loops.

ISSN:0003-6951    

DOI:10.1063/1.105664

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.106375

出版商:AIP    

年代:1991

数据来源: AIP