We have measured the magnetoresistance of narrow (600 -1000 A) and thin (150 -200 A) gold films, one dimensional with respect to weak localization and electron-electron interaction eAects. It is shown that electron-electron collisions with small energy transfer (Nyquist phase-breaking mechanism) govern the phase relaxation in such films over a wide temperature range. The Nyquist time~& was estimated from the magnetoresistance data on the basis of the theoretical dependence AR&"(H)that is applicable to the case when Nyquist phase relaxation dominates other phase-breaking proceses. The temperature dependence~&(T) cc T ' obtained in this way is in good agreement with the theoretical prediction for one-dimensional conductors.

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We have developed a process to fabricate nanostructures in oxide materials, especially YBa2Cu3O7−x (YBCO) thin films. The fabrication process is based on a multilayer mask with an amorphous carbon layer as a key component. Electron-beam lithography, reactive ion etching, and ion-beam etching have been the supporting techniques for the process. Nanobridges ranging in width from 50 to 170 nm have been fabricated and characterized. The initial YBCO film was 50 nm thick and had a Tc of 86 K. Tc of the fabricated bridges decreased about 3–5 K with respect to the initial film. The level of the critical current density was 4–9×105 A/cm2 at 77 K and 1.6–2×107 A/cm2 at 4.2 K. No increase of the critical current density was observed as the cross-section area became smaller. The process has also been applied to fabricate 30–50 nm wide trenches in a-axis-oriented YBCO on top of a similar-oriented PrBa2Cu3O7−x (PBCO) layer. No supercurrent was observed in such junctions. The current transport was governed by Mott variable range hopping.

The magnetic properties of two-dimensional arrays of Fe particles with well-defined geometry, prepared by electron lithography from epitaxial Fe (001) films of thickness of 50 nm, have been studied. Circular particles with diameters of 0.6 and 0.4 μm and rectangular particles 0.9 μm×0.3 μm and 0.7 μm×0.2 μm, were positioned in square and rectangular lattices, respectively, with lattice constants about twice the particle dimensions. Samples were prepared with the lattices oriented along the 〈100〉 and 〈110〉 directions. Hysteresis curves were obtained in the field range ±2 T at temperatures between 30 and 300 K. The hysteresis curves are characteristic for single particles with a multidomain zero-field state. The magnetization and demagnetization processes are mainly governed by the geometrical shape of the particles and their orientation with respect to the crystal directions and the applied field. This implies that the high quality in the epitaxial Fe films is preserved during the patterning process. Magnetic images, obtained by magnetic force microscopy, support the conclusions drawn from the magnetization measurements. The circular particles showed a fourfold symmetry in their magnetic image, which is compatible with the expected domain structure in a disk with cubic crystalline anisotropy.

We present in this report an InGaAs/InAlAs/InP high electron mobility transistor (InP HEMT) with record noise temperature at very low DC power dissipation. By minimizing parasitic contact and sheet resistances, and the gate current, a 130 nm gate length InP HEMT was optimized for cryogenic low noise operation. When integrated in a 4-8 GHz three-stage hybrid low noise amplifier operating at 10 K, a noise temperature of 1.2 K ± 1.3 K at 5.2 GHz was measured. The gain of the amplifier across the entire band was 44 dB, consuming only 4.2 mW of DC power. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz.