Nb Heterostructure Research Articles

Skyrmion-(Anti)Vortex Coupling in a Chiral Magnet-Superconductor Heterostructure

We report experimental coupling of chiral magnetism and superconductivity in [IrFeCoPt]/Nb heterostructures. The stray field of skyrmions with radius ≈50 nm is sufficient to nucleate antivortices in a 25nm Nb film, with unique signatures in the magnetization, critical current, and flux dynamics, corroborated via simulations. We also detect a thermally tunable Rashba-Edelstein exchange coupling in the isolated skyrmion phase. This realization of a strongly interacting skyrmion-(anti)vortex system opens a path toward controllable topological hybrid materials, unattainable to date.

Au nanorods decorated TiO2 nanobelts with enhanced full solar spectrum photocatalytic antibacterial activity and the sterilization file cabinet application

TiO2 photocatalysts have been widely studied and applied for removing bacteria, but its antibacterial efficiency is limited to the ultraviolet (UV) range of the solar spectrum. In this work, we use the gold (Au) nanorods to enhance the visible and near-infrared (NIR) light absorption of TiO2 NBs, a typical UV light photocatalyst, thus the enhancement of its full solar spectrum (UV, visible and NIR) photocatalytic antibacterial properties is achieved. Preliminary surface plasmon resonance (SPR) enhancement photocatalytic antibacterial mechanism is suggested. On one hand, transverse and longitudinal SPR of Au NRs is beneficial for visible and NIR light utilization. On the other hand, Au NRs combined with TiO2 NBs to form the heterostructure, which can improve the photogenerated carrier separation and direct electron transfer increases the hot electron concentration while Au NRs as the electron channel can well restrain charge recombination, finally produces the high yield of radical oxygen species and exhibits a superior antibacterial efficiency. Furthermore, we design a sterilization file cabinet with Au NR/TiO2 NB heterostructures as the photocatalytic coating plates. Our study reveals that Au NR/TiO2 NB heterostructure is a potential candidate for sterilization of bacteria and archives protection.

Photocatalytic activity of Nb heterostructure (NaNbO3/Na2Nb4O11) and Nb/clay materials in the degradation of organic compounds

In this article, Nb heterostructure-based (NaNbO3/Na2Nb4O11) and Nb/Clay-based materials were prepared, characterized and evaluated for the Rhodamine B (C28H31ClN2O3) photodegradation under UV radiation (253.7 nm). As far as this research understands, this is the first time that the photocatalytic activity of the Nb heterostructure (NaNbO3/Na2Nb4O11) is reported. Nb heterostructure is composed of sodium niobate and disodium tetraniobium hendecaoxide (NaNbO3/Na2Nb4O11). The material was synthesized by a simple and economic method via basic precipitation of ammoniacal niobium oxalate (NH4 [NbO (C2O4)2·H2O] XH2O) followed by thermal treatment at 500 °C. Nb/Clay-based materials were synthesized from the natural clay suspension (Montmorillonite) precursor. The addition of Nb to the natural clay by the methodology employed in this work modified the band-gap energy and increased the specific surface area of the resultant materials (to almost twice the value of the original specific surface area). Furthermore, this addition also decreased the luminescence and trap centres and potentiated the photocatalytic activity of the Nb/Clay materials. The Nb heterostructure showed higher photocatalytic activity in Rhodamine B photodegradation (recorded up to 95% removal at natural conditions). Similar values were reported to Nb/Clay materials. Despite the natural clay having more luminescence and trap centres than Nb/Clay materials, it recorded very low photocatalytic activity. Nb addition to natural clay increased the photocatalytic activity of the material, which would give other use to clay along with being used as an adsorbent.

Growth and Characterization of Vanadium Dioxide/Niobium Doped Titanium Dioxide Heterostructures for Ultraviolet Detection

AbstractThe properties of VO2/TiO2:Nb heterostructures are engineered for their potential use in ultraviolet (UV) detection and observed external quantum efficiency (EQE) exceeding 100% in both near UV (405 nm) and UV‐C (254 nm) spectral regions. The proposed UV detection scheme is based on vanadium dioxide (VO2) thin films epitaxially grown on niobium doped titanium dioxide (TiO2:Nb). Such VO2/TiO2:Nb heterostructure exhibits enhanced photocurrent due to cation doping engineering in a space‐charge region thus yielding favorable conditions for hole tunneling from TiO2:Nb into VO2. The heterostructure is engineered and photocurrent is optimized by varying the VO2 film thickness, reaching up to 5000% EQE for 405 nm and up to 17 000% EQE for 254 nm light, indicating that the VO2/TiO2:Nb system can be fine‐tuned for efficient UV photodetection.

Superfluid Density and Vortex Dynamics in S/F/S Heterostructures

We present electrical transport measurements in the microwave range in Superconductor/Ferromagnet/ Superconductor Nb/Pd 0.84Ni 0.16/Nb heterostructures, with different thickness of the ferromagnetic layer. We employ a wideband (1–20 GHz) Corbino disk technique to obtain the real part of the microwave resistivity in the vortex state. We focus on the fundamental properties that can be derived from measurements of the pinning property of the vortices. In particular, we estimate the superfluid density at the same reduced temperature. We describe the method to derive from the measurements the pinning constant kp, and to estimate the the superfluid density. We find a strong reduction of the superfluid density with the ferromagnetic layer thickness. Finally, we compare our results to zero-temperature superfluid density estimated in bilayers.

Modulation of charge carrier dynamics of NaxH2−xTi3O7-Au-Cu2O Z-scheme nanoheterostructures through size effect

For the first time we presented the interfacial charge carrier dynamics for three-component semiconductor-metal-semiconductor Z-scheme nanoheterostructure system. The samples were prepared by selectively depositing a thin layer of Cu2O on the Au surface of Au nanoparticle-decorated NaxH2−xTi3O7 nanobelts (denoted as ST-Au NBs) using the photodeposition method. For ST-Au-Cu2O NB heterostructures, the embedded Au may act as carrier-transfer mediator to promote the electron transfer from the conduction band of ST to the valence band of Cu2O. This vectorial charge transfer would give rise to electron accumulation at Cu2O and hole concentration at ST, which achieved superior charge carrier separation over the two-component counterparts of ST-Au and ST-Cu2O. The quantum size effect was significant in the deposited Cu2O, which was exploited to tune the band structure of Cu2O, modulate the charge carrier dynamics of ST-Au-Cu2O NBs, and thereby enhance the resultant photocatalytic performance. Time-resolved photoluminescence spectra were measured to quantitatively analyze the electron transfer event between ST and Au for ST-Au-Cu2O NBs, which was found dependent on the Cu2O shell thickness. As the Cu2O thickness decreased, ST-Au-Cu2O NBs showed an increased electron-scavenging rate constant due to the increased driving force of electron transfer. The carrier dynamics results were fundamentally consistent with those of the performance evaluation in photocatalysis, in which ST-Au-Cu2O NBs exhibited enhanced photocatalytic efficiency as the Cu2O thickness decreased. Systematic understanding of the interfacial charge dynamics of Z-scheme mechanism shall pave the way for the realization of artificial photosynthesis by using heterogeneous photocatalysts, where the effectiveness of charge separation and the merit of high redox powers are determinant.

Analysis of the Temperature Stability of Overdamped ${\hbox{Nb}}/{\hbox{Al-}}{\hbox{AlO}}_{x}/{\hbox{Nb}}$ Josephson Junctions

The temperature stability is one of the most important factors determining the successful application of the Josephson effect to the ac voltage standard or to analog and digital electronics. Whereas SIS hysteretic junctions with an Ambegaokar-Baratoff (A&B) I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> (T) behavior exhibit a reduced drift around the working temperature of the liquid helium, metallic-barrier SNS junctions follow a Kulik-Omelianchuck (K&O) behavior with a sharp temperature dependence of Ic in this region. The objective of our research is to study this aspect for overdamped Nb/Al-AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb heterostructures with current densities of 10-75 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and characteristic voltages from 100 to more than 500 muV, that have been fabricated at INRiM. The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> (T) characteristics, measured for Josephson heterostructures with different thickness, s, and exposure, E, essentially deviate from A&B and K&O curves, because of proximity effect caused by the comparatively high value of s (up to 100 nm). We study theoretically two extreme limits: the clean and the dirty limit for the interlayer between the superconducting electrodes and discuss the temperature stability of the junctions characterizing it with the temperature derivative dI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> /dT. The combined experimental and theoretical analysis of the problem provides a way for understanding, controlling and improving the design of the Nb/Al-AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb junctions in order to enhance their reliability.

Spin-polarized quasiparticles injection in La0.7Sr0.3MnO3∕SrTiO3∕Nb heterostructure devices

We report the effect of spin-polarized quasiparticle injection from a ferromagnetic manganite into a conventional Nb superconductor in a La0.7Sr0.3MnO3∕SrTiO3∕Nb heterostructure. A 8-terminal stacked trilayer geometry was used, where the injected current Iinj enters a superconducting microbridge and leaves it symmetrically by tunneling through a SrTiO3 barrier. A high dynamic gain G=−dIc∕dIinj was observed from 1.7 up to 8.5K, where Ic is the microbridge critical current. For a dc injection current, G was measured to be 290 at 1.7K. A SrTiO3 barrier of thickness in the range 3.5–8.5nm was found to provide a suitable spin injection length of the order of the bridge length and a low Joule heating level. In this confined stacked device geometry it was found that Joule dissipation in the manganite and barrier does not contribute significantly to the suppression of Ic, in contrast with previous studies.

Photogenerated carrier injection to an n-type copper oxide superconductor

We have fabricated an isotype heterostructure made of an n-type superconductor (Sr 0.89Nd 0.11)CuO 2 film and an n-type SrTiO 3:Nb substrate by using the pulsed laser deposition technique and measured the current–voltage and photovoltaic properties under ultraviolet (UV) light irradiation. A large photovoltage of 0.8 V, which is positive to the film, is observed. This means that the photogenerated hole carriers in the SrTiO 3:Nb substrate are injected to the film. Under UV light irradiation, the superconducting transition of the film slightly shifts to lower temperature. The effect of the photocarrier injection on the superconducting transition temperature is discussed in terms of a proposed energy level diagram of the (Sr 0.89Nd 0.11)CuO 2/SrTiO 3:Nb heterostructure.

Photogenerated hole carrier injection to YBa2Cu3O7−x in an oxide heterostructure

We have fabricated a YBa2Cu3O7−x∕SrTiO3:Nb heterostructure and measured the current–voltage and photovoltaic properties under ultraviolet light irradiation at room temperature. A large photovoltage of 0.8V is observed and is positive to the film. The photovoltage appears under illumination of light with photon energy larger than 3.2eV. These results indicate that photogenerated hole carriers in the SrTiO3:Nb substrate are injected to the film. The maximum surface hole density is attained to be 3.5×1013cm−2 at a light power of 44mW∕cm2. The present photocarrier injection technique could apply to many transition metal oxides to control the hole carrier density externally.

Efficiency of Photocarrier Injection in a VO2/TiO2:Nb Heterostructure

The efficiency of photocarrier injection in a VO 2 /TiO 2 :Nb heterostructure is studied by measuring I – V characteristics at room temperature under ultraviolet light irradiation. It is revealed that photogenerated hole carriers in the TiO 2 :Nb substrate are injected and accumulated in the VO 2 film by the photovoltaic effect. The surface charge density is controlled successfully in a wide range of 10 9 –10 13 cm -2 as a function of light irradiance. The maximum hole density of 9×10 18 cm -3 is attained at a light irradiance of 133 mW/cm 2 , which is estimated by assuming the uniform distribution of holes in the film. It is suggested that high efficiency can be achieved by utilizing the large dielectric constant of titanium oxide substrates.

Ultraviolet light selective photodiode based on an organic–inorganic heterostructure

We show a perfect ultraviolet (UV) light selective and sensitive photovoltaic cell easily fabricated. The device consists of a water-soluble p-type semiconducting polymer PEDOT-PSS: poly(3,4-ethylenedioxythiophene) doped by poly(4-styrenesulfonate) film deposited on a Nb-doped titanium oxide (SrTiO3:Nb) substrate. For the PEDOT-PSS/SrTiO3:Nb heterostructure, the photosensitivity at zero bias for the UV light with L=1 mW/cm2 is estimated to be 0.05 A/W, corresponding to a quantum yield of 16% electron/photon. This device is only activated in the UV region (λ&amp;lt;390 nm), and then, it exhibits a large response to the UV–B light (290–320 nm).

Initial Growth Stages of Epitaxial BaTiO3 Films on Vicinal SrTiO3:Nb (001) Substrates

AbstractThe growth mechanism of epitaxial BaTiO3 films on vicinal Nb-doped SrTiO3 (SrTiO3:Nb) (001) substrate surfaces was studied in terms of surface morphology, crystalline orientation, microstructure, and film/substrate interface. Well-oriented BaTiO3 thin films were grown on SrTiO3 substrates with well-defined terraces by pulsed laser deposition. The regularly terraced TiO2-terminated surfaces of vicinal SrTiO3:Nb (001) substrates were prepared by a definite chemical and thermal treatment. Under our conditions, BaTiO3 seems to grow with a layer-then-island (Stranski-Krastanov) growth mechanism. In order to investigate the orientation and crystallinity of the BaTiO3 films, x-ray diffraction and high-resolution transmission electron microscopy were performed. Ferroelectricity of the BaTiO3 films was proved by electrical measurements performed on Pt/BaTiO3/SrTiO3:Nb heterostructures.