A complex study of the electron-phonon interaction in thin NbC films with electron mean free path lϭ2 -13 nm gives strong evidence that electron scattering is significantly modified due to the interference between electron-phonon and elastic electron scattering from impurities. The interference T 2 term, which is proportional to the residual resistivity, dominates over the Bloch-Grüneisen contribution to resistivity at low temperatures up to 60 K. The electron energy relaxation rate is directly measured via the relaxation of hot electrons heated by modulated electromagnetic radiation. In the temperature range 1.5-10 K the relaxation rate shows a weak dependence on the electron mean free path and strong temperature dependence ϳT n , with the exponent nϭ2.5-3. This behavior is explained well by the theory of the electron-phonon-impurity interference taking into account the electron coupling with transverse phonons determined from the resistivity data.

The crossover between the electron–phonon relaxation and the diffusion transport of hot electrons in an NbC microbolometer has been studied. At least an 80 ps relaxation time can be achieved in 0.2 μm long bridges of the material with a diffusivity of 8 cm2/s. The high diffusivity is accompanied by a large sheet resistance (≊10 Ω) that simplifies the match of the mixer device made of NbC to planar antenna at terahertz frequencies. The intrinsic noise mechanisms imply a very low mixer noise temperature of the order of a few tens of Kelvin, independent on the radiation frequency.

No abstract

Pulsed-laser deposition of smooth high-Tc superconducting films almost free from droplets and precipitates with the use of velocity filtration of plasma particles is reported. We have removed droplets from laser-induced plasma by using a shutter technique; a reduction of the droplet density by a factor of 105 has been achieved. We have applied the technique to the preparation of high quality YBa2Cu3O7−δ films on (100)-oriented SrTiO3, MgO, Y2O3-stabilized ZrO2 (YSZ) substrates and, furthermore, on (11̄02)-oriented sapphire covered with (100) sublayers of Si and (100) YSZ buffer layers.

A study of epitaxial growth of YBa2Cu3O7−δ films on oxidized Si with yttria- and zirconia-based buffer layers is reported. Using substrates with either SiO2 free or naturally oxidized (100) surfaces of Si it was found that a thin SiO2 layer on top of the Si favors high-quality superconducting film formation. Compared to yttria-stabilized ZrO2 (YSZ) single layers, YSZ\Y2O3 double and YSZ/Y2O3\YSZ triple layers allows the deposition of thin YBa2Cu3O7−δ films with improved properties including reduced aging effects. In epitaxial YBa2Cu3O7−δ films grown on the double buffer layers a critical temperature Tc(R=0)=89.5 K and critical current densities of 3.5×106 A/cm2 at 77 K and 1×107 A/cm2 at 66 K were reached.