Single-layer vanadium nitride (VN) and bilayer Pd0.96Fe0.04/VN and VN/Pd0.92Fe0.08 thin-film heterostructures for possible spintronics applications were synthesized on (001)-oriented single-crystalline magnesium oxide (MgO) substrates utilizing a four-chamber ultrahigh vacuum deposition and analysis system. The VN layers were reactively magnetron sputtered from a metallic vanadium target in Ar/N2 plasma, while the Pd1− x Fe x layers were deposited by co-evaporation of metallic Pd and Fe pellets from calibrated effusion cells in a molecular beam epitaxy chamber. The VN stoichiometry and Pd1− x Fe x composition were controlled by X-ray photoelectron spectroscopy. In situ low-energy electron diffraction and ex situ X-ray diffraction show that the 30 nm thick single-layer VN as well as the double-layer VN(30 nm)/Pd0.92Fe0.08(12 nm) and Pd0.96Fe0.04(20 nm)/VN(30 nm) structures have grown cube-on-cube epitaxially. Electric resistance measurements demonstrate a metallic-type temperature dependence for the VN film with a small residual resistivity of 9 μΩ·cm at 10 K, indicating high purity and structural quality of the film. The transition to the superconducting state was observed at 7.7 K for the VN film, at 7.2 K for the Pd0.96Fe0.04/VN structure and at 6.1 K for the VN/Pd0.92Fe0.08 structure with the critical temperature decreasing due to the proximity effect. Contrary to expectations, all transitions were very sharp with the width ranging from 25 mK for the VN film to 50 mK for the VN/Pd0.92Fe0.08 structure. We propose epitaxial single-crystalline thin films of VN and heteroepitaxial Pd1− x Fe x /VN and VN/Pd1− x Fe x (x ≤ 0.08) structures grown on MgO(001) as the materials of a choice for the improvement of superconducting magnetic random access memory characteristics.

A thin-film superconductor(S)/ferromagnet(F) F1/S/F2-type Pd0.96Fe0.04(20 nm)/VN(30 nm)/Pd0.92Fe0.08(12 nm) heteroepitaxial structure was synthesized on (001)-oriented single-crystal MgO substrate utilizing a combination of the reactive magnetron sputtering and the molecular-beam epitaxy techniques in ultrahigh vacuum conditions. The reference VN film, Pd0.96Fe0.04/VN, and VN/Pd0.92Fe0.08 bilayers were grown in one run with the target sample. In-situ low-energy electron diffraction and ex-situ X-ray diffraction investigations approved that all the Pd1−xFex and VN layers in the series grew epitaxial in a cube-on-cube mode. Electric resistance measurements demonstrated sharp transitions to the superconducting state with the critical temperature reducing gradually from 7.7 to 5.4 K in the sequence of the VN film, Pd0.96Fe0.04/VN, VN/Pd0.92Fe0.08, and Pd0.96Fe0.04/VN/Pd0.92Fe0.08 heterostructures due to the superconductor/ferromagnet proximity effect. Transition width increased in the same sequence from 21 to 40 mK. Magnetoresistance studies of the trilayer Pd0.96Fe0.04/VN/Pd0.92Fe0.08 sample revealed a superconducting spin-valve effect upon switching between the parallel and antiparallel magnetic configurations, and anomalies associated with the magnetic moment reversals of the ferromagnetic Pd0.92Fe0.08 and Pd0.96Fe0.04 alloy layers. The moderate critical temperature suppression and manifestations of superconducting spin-valve properties make this kind of material promising for superconducting spintronics applications.

In the present work, an attempt to improve DAFC by replacing platinum with cheaper materials. Ni acetate-Ag nitrate supported by carbon nanofibers with three different samples (S1 95-5, S2 90-10, and S3 80-20%) for Ni and Ag, respectively, were synthesized by using the electrospinning method and then calcined under an Argon atmosphere at 900 C. Numerous analysis methods were employed to examine the chemical structure, the morphology, and the electrochemical (EC) features. The scanning electron microscope (SEM) confirms that all samples with different Ag concentrations exhibit good nanofiber morphology and a clear appearance of the nanoparticles. According to energy dispersive X-ray (EDX) mapping, the results prove that the carbonized polyvinyl alcohol nanofibers (PVANFs) have a consistent and even distribution of nickel and silver with an accurate percentage as previously prepared by molar ratio. Transmission electron microscope (TEM) shows that the interior structure has an amorphous carbon nanofiber structure with embedded crystalline spheres of silver and nickel. From X-ray diffraction (XRD) analysis, no hydroxide or oxide phases can be identified in the XRD pattern, which prove the existence of Ni-Ag nanoparticles in the metallic phase. For the electrooxidation of ethanol and methanol, the samples' electrocatalytic characteristics were examined. The effects of the electrolyte concentration, scan rate on the catalytic performance and electrode stability were studied using cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance measurements (EIS). CV, chronoamperometry, and EIS reveal that the S2 sample has the best, superior electro-oxidation activity for both methanol and ethanol with the highest current density. Hence, This research provided a promising approach to fabricating a promising bimetallic Ni-Ag/CNFs catalyst to replace platinum in direct DAFCs.