摘要:

The evidence is reported for enhancement of critical current densityJcin YBa2Cu3O7−&dgr;thick films with the addition of Ag, which is correlated with improvements in structural properties. An improvement of 50% inJc(up to ∼500 A/cm2atT=4.2 K) was obtained in films made from YBCO+60wt % Ag powder, fabricated by the spin‐on technique on (100) SrTiO3, which is correlated with improvements in structure. The resulting films are 10 &mgr;m thick, uniform, partially textured, and show good adherence. The critical temperatureTcis improved by the addition of Ag, and a reduction in the density of microcracks and in the amount of secondary phases in the sintered films was observed. Normal‐state resistivity is reduced by almost three orders of magnitude, making these films potentially useful for electronic applications in interconnects and novel hybrid circuits.

ISSN:0021-8979    

DOI:10.1063/1.348371

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of transverse stress on the critical current of two substantially different Nb3Sn superconductors, a bronze‐process conductor and an internal‐tin conductor, has been measured. Photomicrographs of the two conductors reveal a basic difference in their microstructure. The bronze‐process conductor exhibits columnar grains that are radially oriented within the Nb3Sn filaments, while the grains of the internal‐tin conductor are more equiaxed and randomly oriented. The radial orientation of the bronze‐process grains defines an anisotropy between the axial and transverse directions that might account for the greater sensitivity of the critical current to transverse stress reported previously. The effect of transverse stress measured on the internal‐tin conductor, however, is comparable to that of the bronze‐process conductor. Thus, these data indicate that the transverse stress effect is not highly dependent on either grain morphology or fabrication process. From an engineering standpoint the similarity of the transverse stress effect for these two types of Nb3Sn superconductors represents an important simplification for setting first‐order quantitative limits on the mechanical design of large superconducting magnets.

ISSN:0021-8979    

DOI:10.1063/1.348372

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Metal‐insulator‐semiconductor field effect transistors have been fabricated using laser ablation to deposit YBaCuO thin films onto SrTiO3, MgO, LaAlO3, and LaGaO3substrates. The substrates were used as gate insulators. The conductivity of two films on SrTiO3could be modulated, while for other samples the conductivity was independent of the gate voltage. The field‐effect mobility was extracted and found to be of magnitude comparable to the mobility of metallic YBa2Cu3O7.

ISSN:0021-8979    

DOI:10.1063/1.348373

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Samples of YBa2Cu3O7−xwithxranging from ∼0 to 0.65 have been analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in the midinfrared region (400–6000 cm−1). Spectral line shapes vary gradually as a function of oxygen stoichiometry, and the reflectance at 400 and 1000 cm−1decreases linearly with decreasing oxygen content. Spectra of samples that were incompletely synthesized or exposed to a 4% CO2atmosphere at 650 °C clearly indicated the presence of carbonate. DRIFTS is therefore a quick, nondestructive method for determining oxygen content in YBa2Cu3O7−xpowders, and for detecting carbonate species due to synthesis error or reaction with CO2‐bearing atmosphere.

ISSN:0021-8979    

DOI:10.1063/1.348374

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Soluble poly (3‐alkylthiophene) can be transformed into a conducting polymer gel by using a radical initiator. The volume of the sample in chloroform shrinks drastically upon introduction of ethanol, and also by doping. The shrinkage ratio depends on the preparation conditions of the sample. The spectrum of the gel also changes reversibly as the volume varies.

ISSN:0021-8979    

DOI:10.1063/1.348375

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A method for reducing the interface‐state density in polysilicon gate metal‐nitride‐oxide‐semiconductor (MNOS) capacitors is reported. The method involves deposition of a sacrificial blanket aluminum layer on top of a chemical‐vapor‐deposition (CVD) oxide over MNOS capacitors. The entire stack was then annealed at 450 °C in nitrogen and then the metal and CVD oxide were stripped away. The interface state density was reduced from 1011to 1010cm−2eV−1after this anneal. It is believed that Al reacts with trace water in the CVD oxide and generates active hydrogen. The hydrogen diffuses to the Si/SiO2interface and passivates the interface states.

ISSN:0021-8979    

DOI:10.1063/1.348376

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A nanocrystalline Ni‐P alloy prepared by the crystallization method has been studied by using positron lifetime spectroscopy. The lifetime results and the corresponding interfacial defects in the sample are discussed in comparison with those of the nanocrystalline iron materials prepared by compacting ultrafine powders.

ISSN:0021-8979    

DOI:10.1063/1.348377

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Narrow InAs‐base GaSb/InAs hot‐electron transistors have been grown by low‐pressure metalorganic chemical vapor deposition. The InAs bases are 30, 50, and 100 A˚ thick. The ground‐state electron subband energyE0is determined from values of collector current. For thinner wells, values ofE0are well explained by a simple effective mass calculation. Here, a mixing of InAs conduction‐band states with GaSb valence‐band states is neglected because of symmetry mismatch. The effect of nonparabolicity of the InAs conduction band is taken into account.

ISSN:0021-8979    

DOI:10.1063/1.348378

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.348980

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In the reaction of Co modification of &ggr;‐Fe2O3, we found a very interesting phenomenon. When cations of Ca2+, Sr2+, or Ba2+belonging to IIA metals are adsorbed on the surface of &ggr;‐Fe2O3prior to Co2+ion adsorption, the coercivity of Co modified &ggr;‐Fe2O3is signifcantly increased compared to &ggr;‐Fe2O3modified only with Co2+. In contrast, when the Mg2+ion is adsorbed prior to Co2+ion adsorption, the coercivity is rarely increased. In this paper, we made the following hypotheses in order to interpret these phenomena: (1) Co2+ions are adsorbed both on the tetrahedral (A) site and the octahedral (B) site in the spinel structure of &ggr;‐Fe2O3. When Co2+ion occupies the B site and forms cobalt ferrite, the coercivity increases as a result of the surface magnetic anisotropy. (2) Because cations of alkaline earth metals (Ca,Sr,Ba) are easily adsorbed on the A site, adding alkaline earth metal before cobalt addition results in an increase in adsorption selectivity of Co2+ion on the B site. (3) On the other hand, Mg2+ion which is easily adsorbed on the B site prevents Co2+ion occupancy of the B site and as a result the coercivity does not increase.

ISSN:0021-8979    

DOI:10.1063/1.348381

出版商:AIP    

年代:1991

数据来源: AIP