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Sandwich-type MgB2/MgO/MgB2 Josephson junctions with Au or MgB2 interconnection were fabricated using hybrid physical-chemical vapor deposited MgB2 thin films and RF-magnetron-sputtered MgO barrier. The junctions show properties similar to those in high-Jc Nb junctions with Jc up to 275 kA/cm2 at 4 K, which remains nonzero up to 40 K. Critical current modulations by applied magnetic field and constant voltage steps under microwave radiation were observed. Combined with the larger energy gaps in MgB2 than in Nb, the junctions presented here allow simple MgB2 digital circuits to work over 20 K or with a clock speed above 1 THz. [ABSTRACT FROM AUTHOR]

Carbon-doped MgB2 thin films deposited by hybrid physical-chemical vapor deposition (HPCVD) can have Hc2(0 K)∼70 T, anomalously high compared to bulk samples which have Hc2 about half this value. Using transmission electron microscopy, the authors show that the carbon content in HPCVD-grown Mg(B1-xCx)2 grains is x≤5%, and that most carbon forms an amorphous intergranular phase. The authors also find extensive structural disorder, including rotations about the c axis and small tilts of the c axis, with a domain size of 5–20 nm. The authors propose that strong electron scattering from the nanoscale disorder is responsible for the very high Hc2 in such films [ABSTRACT FROM AUTHOR]

Measurement of critical current density Jc, normal state resistivity ρn, and upper critical field Hc2 on pure and 10% SiC-doped MgB2 bulks show systematic enhancement of Hc2 by SiC addition and by lowering reaction temperature. Hc2(10 K) exceeds 33 T, while the extrapolated zero temperature value exceeds 40 T. The Rowell [Supercond. Sci. Technol. 16, R17 (2003)] analysis suggests that only 8%–17% of the MgB2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades Hc2 and flux pinning, making the measured Jc a complex balance between connectivity, Hc2, and flux pinning induced by grain boundaries and precipitates. [ABSTRACT FROM AUTHOR]

Fluctuation electron microscopy (FEM) measurements and simulations have identified nanoscale aluminum-like medium-range order in rapidly quenched amorphous Al92Sm8 which devitrifies by primary Al crystallization. Al92Sm8 amorphized by plastic deformation shows neither Al nanoscale order, nor primary crystallization. Annealing the rapidly quenched material below the primary crystallization temperature reduces the degree of nanoscale Al order measured by FEM. The FEM measurements suggest that 10–20 Å diameter regions with Al crystal-like order are associated with primary crystallization in amorphous Al92Sm8, which is consistent with the quenched-in cluster model of primary crystallization. [ABSTRACT FROM AUTHOR]

Simulations from a family of atomistic structural models for unhydrogenated amorphous silicon suggest that fluctuation electron microscopy experiments have observed orientational order of paracrystalline grains in amorphous silicon. This order may consist of correlations in the orientation of nearby paracrystalline grains or anisotropy in the grain shape. This observation makes a natural connection to the known growth modes of microcrystalline silicon and may be useful for other materials systems. [ABSTRACT FROM AUTHOR]

Measurement of critical current density Jc, normal state resistivity ρn, and upper critical field Hc2 on pure and 10% SiC-doped MgB2 bulks show systematic enhancement of Hc2 by SiC addition and by lowering reaction temperature. Hc2(10 K) exceeds 33 T, while the extrapolated zero temperature value exceeds 40 T. The Rowell [Supercond. Sci. Technol. 16, R17 (2003)] analysis suggests that only 8%–17% of the MgB2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades Hc2 and flux pinning, making the measured Jc a complex balance between connectivity, Hc2, and flux pinning induced by grain boundaries and precipitates. [ABSTRACT FROM AUTHOR]