Ivan P. Nevirkovets

Enhancement of the electrochemical capacitance of TiO2 nanotube arrays through controlled phase transformation of anatase to rutile

Here, we report the fabrication of self-organized titania (TiO(2)) nanotube array supercapacitor electrodes through controlled phase transformation of TiO(2), with aerial capacitances as high as 2.6 mF cm(-2), which far exceeds the values so far reported in the literature. The role of phase transformation in the electrochemical charge-discharge behaviour of nanocrystalline TiO(2) nanotubes is investigated and discussed in detail. The ease of synthesis and the exceptional electrochemical properties make these nanotube arrays an alternative candidate for use in energy storage devices.

Globular reduced graphene oxide-metal oxide structures for energy storage applications

In this work, we employed an in situspray pyrolysis approach to fabricate metal oxide-graphene composites with highly porous morphologies. The materials exhibited unique globular structures comprising metal oxide nanoparticles embedded between graphene sheets with high capacitance.

ANOMALOUS CRITICAL CURRENT IN DOUBLE-BARRIER NB/AL-ALOX-AL-ALOX-NB DEVICES

Double-barrier Nb/Al–AlOx–Al–AlOx–Nb devices with a “dirty” middle Al layer were fabricated and investigated. An anomalously large Josephson critical current at low temperatures and a nonmonotonic dependence of the device resistance on the thickness of the middle Al layer were found.

Advanced microwave-assisted production of hybrid electrodes for energy applications

Carbon nanotubes are one of the most prominent materials in research for creating electrodes for portable electronics. When coupled with metallic nanoparticles the performance of carbon nanotube electrodes can be dramatically improved. Microwave reduction is an extremely rapid method for producing carbon nanotube-metallic nanoparticle composites, however, this technique has so far been limited to carbon nanotube soot. An understanding of the microwave process and the interactions of metallic nanoparticles with carbon nanotubes have allowed us to extend this promising functionalisation route to pre-formed CNT electrode architectures. Nanoparticle reduction onto pre-formed architectures reduces metallic nanoparticle waste as particles are not formed where there is insufficient porosity for electrochemical processes. A two-fold increase in capacitive response, stable over 500 cycles, was observed for these composites, with a maximum capacitance of 300 F g−1 observed for a carbon Nanoweb electrode.

Microwave absorption measurements using a broad-band meanderline approach

We describe a technique that permits broad-band, field-dependent ferromagnetic and electron paramagnetic resonance absorption measurements that is applicable to thin films and patterned micro-/nanostructured arrays and is based on a wire-wound meanderline approach. Techniques to prepare meanderlines and perform microwave measurements are described along with some demonstrations involving an electron paramagnetic resonance calibration/test material, 2,2-diphenyl-1-picryl-hydrazyl, and a ferromagnetic cobalt thin film.

Possible manifestation of Andreev bound states in double-barrier Nb/Al/AlOx/Al/AlOx/Nb tunnel junctions

Abstract We have experimentally investigated electron transport in double-barrier Nb/Al/AlO x /Al/AlO x /Nb devices. At low temperatures, the devices reveal a novel magnetic-field-sensitive subgap structure in the current-voltage characteristics, which is interpreted as a manifestation of Andreev bound states. A correlation between phase-coherent and nonequilibrium properties is suggested.

Superconducting-Ferromagnetic Transistor

We report experimental results on the dc and ac characterization of multiterminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively), which display transistor-like properties. We investigated two types of such superconducting-ferromagnetic transistors (SFTs): ordinary devices with a single acceptor (SIS) junction, and devices with a double acceptor. The devices with the single SIS acceptor were investigated and demonstrated a modulation of the maximum Josephson current as a function of the SFIFS current injection level. For devices of the second type, by applying an ac signal (in the kilohertz range) with a constant dc bias current to the injector (SFIFS) junction, we observed a voltage gain of about 25 on the double acceptor with the operating point chosen in the subgap region of the acceptor current-voltage characteristic. We also observed an excellent input-output isolation in our SFIFSIS devices. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.

Hybrid superconductor?ferromagnet transistor-like device

We demonstrate theoretically and experimentally that a ferromagnetic layer as thin as a few nanometres, which is almost transparent for non-superconducting charge transport, can be used as a cut-off filter to block transport of charge-carrier superconducting correlations. This property may be exploited in some applications, as is exemplified by the case of double-barrier S1IS2FIS3 multi-terminal devices (with S, I, and F denoting a superconductor, an insulator, and a ferromagnetic metal, respectively), whose principle of operation is based on a nonequilibrium superconducting state driven by tunnel injection of quasiparticles. Using the F layer makes the device asymmetric and considerably improves input–output isolation in comparison with the formerly investigated symmetric S1IS2IS3 devices.

A superconducting transistorlike device having good input-output isolation.

A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.

A qubit device based on manipulations of Andreev bound states in double-barrier josephson junctions

Abstract A qubit system exploiting manipulations of the Andreev bound state (ABS) levels in the SINIS junction by applying appropriate bias voltages and transport currents is suggested. The parameters of the SINIS setup may be chosen in such a way that only two ABS levels are present; this is in agreement with our experimental data obtained using Nb/Al double-barrier junctions. In the qubit Hamiltonian, H , the two ABS levels are presented as the ‘↑’ and ‘↓’ spin states, while the controlling physical parameters (voltage across one of the barriers and the transport current) are mapped to the ‘magnetic fields’ B x n and B z n . The phase decoherence time is estimated.