M. Salvato

Interface transparency and proximity effect in Nb/Cu triple layers realized by sputtering and molecular beam epitaxy

We have investigated, in the framework of the proximity effect theory, the ninterface transparency T between Nb and Cu in the case of high quality nNb/Cu trilayers fabricated by molecular beam epitaxy (MBE) and sputtering ndeposition techniques. The obtained T values do not seem to be strongly ninfluenced by the fabrication methods but more by the intrinsic properties of nthe two metals; a slightly higher value for T has even been deduced for the nMBE prepared samples. The proximity effect in these samples has also been nstudied in the presence of an external magnetic field. In the parallel nconfiguration a significant shift towards lower values of the 2D–3D ncrossover temperature has been observed for MBE samples, in good nagreement with very recent theoretical predictions. In the perpendicular case na positive curvature of the temperature dependence of the upper critical field nhas been detected, which was less pronounced for sputtered samples. Both nthe effects have been observed only for trilayers with low Nb nthickness (<600 A) which confirms the crucial influence of the interface ntransparency on the values of the upper critical field in such samples.

Temperature scaling of the flux pinning force in Bi2Sr2Ca1Cu2O8+x thin films

The electrical transport properties of Bi2Sr2Ca1Cu2O8+x thin films have been measured in the temperature range from 20 to 50 K and in external magnetic fields up to 4 T. The dependence of the normalized pinning force f=Fp/Fp,max on the reduced magnetic field h=H/H* (H* is the irreversibility field) exhibits a scaling law behavior, indicating that a single pinning mechanism is present in the investigated temperature range. The Fp(H) curves were analyzed within the framework of the classical Anderson–Kim theory of flux creep, taking into consideration the nonlinear current dependence of the pinning energy U and its dependence on the temperature T, the magnetic field H, and the current density J. Under these assumptions a generalized formula for Fp was obtained which, assuming a suitable U(J) dependence, was able to explain the f(h) curve in the observed temperature range.

Superconducting properties of Nb-CuMn multilayers

In the last years, superconducting multilayers have attracted a large amount of studies due to their interesting properties. Infact, these systems can be used, for example, to investigate the coupling between superconducting layers in different situations (superconducting/insulator, superconducting/metallic, superconducting/magnetic), to analyze the properties of superconductivity in the presence of reduced dimensionality, or to better check effects also observed in high critical temperature layered oxides [1–3]. In particular, the study of interlaver superconducting coupling via magnetic separating slabs has lately gained an increased interest because the coexistence between superconductivity and magnetism seems to play an important role in many properties of high temperature compounds [4].

Single walled carbon nanotube/Si heterojunctions for high responsivity photodetectors

Single walled carbon nanotube/n-Si (SWCNT/n-Si) hetero-junctions have been obtained by depositing SWCNT ultra-thin films on the surface of an n-Si substrate by dry transfer method. The as obtained junctions are photo sensitive in the measured wavelength range (300-1000 nm) and show zero bias responsivity and detectivity values of the order of 1 A W-1 and 1014 Jones respectively, which are higher than those previously observed in carbon based devices. Moreover, under on-off light excitation, the junctions show response speed as fast as 1 μs or better and noise equivalent powers comparable to commercial Si photomultipliers. Current-voltage measurements in dark and under illumination suggest that the devices consist of Schottky and semiconductor/semiconductor junctions both contributing to the fast and high responses observed.

Low temperature conductivity of carbon nanotube aggregates

We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results.

Carbon Nanotubes Guides for Nickel Electrical Interconnects

We present an innovative approach for interconnections based on aligning nanosized nickel particles along single-walled carbon nanotubes bundles. The nanotubes are first deposited to connect normal gold contacts or niobium nitride superconducting pads and a successive step in fabrication, based on an electrochemical method, enables us to “coat” the nanotubes with nickel particles. This technique, as shown by field-emission SEM analysis, generates chains of nickel particles aligned along the nanotubes connecting the contact electrodes. The temperature dependence of the resistance of the chains of Ni nanoparticles evidences the metallic nature of the obtained interconnection and shows values of the resistances up to three orders of magnitudes lower than those of the bare nanotubes bundles. The ease of the fabrication process and its reliability candidate our technique as a possible solution for interconnects applications.

Integrating superconductive and optical circuits

We have integrated on oxidized silicon wafers superconductive films and Josephson junctions along with sol-gel optical channel waveguides. The fabrication process is carried out in two steps that result to be solid and noninvasive. It is demonstrated that 660nm light, coupled from an optical fiber into the channel sol-gel waveguide, can be directed toward superconducting tunnel junctions whose current-voltage characteristics are affected by the presence of the radiation. The response of the junction biased at various currents as a function of the optical pumping is presented and discussed according to a nonequilibrium superconductivity model.

Hybrid superconducting neutron detectors

A new neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction 10B+n

Superconductive niobium films coating carbon nanotube fibers

rightarrow