VN Layers Research Articles

Ultrathin and Air‐Stable Lithium Metal Anodes with Superlong Cycling Life in Ether/Ester‐Based Electrolytes

Ultrathin and air‐stable Li metal anodes hold great promise toward high‐energy and high‐safety Li metal batteries (LMBs). However, the application of LMBs is technically impeded by existing Li metal anodes with large thickness, high reactivity, and poor performance. Here, we developed a novel and scalable approach for the construction of a 10‐μm‐thick flexible and air‐stable Li metal anode by conformally encapsulating Li within a multifunctional VN film. Specifically, the highly lithiophilic VN layer guides a uniform deposition of Li, while abundant and multilevel pores arising from assembly of ultrathin nanosheets enable a spatially confined immersion of metallic Li, thus ensuring an ultrathin and sandwiched Li anode. More impressively, the strong hydrophobicity of VN surface can effectively improve the stability of anode to humid air, whereas the highly conductive framework greatly boosts charge transfer dynamics and enhances Li utilization and high‐rate capability. Benefiting from such fascinating features, the constructed Li‐VN anode exhibits ultrastable cycling stability in both ether (2500 h) and carbonate (900 h) electrolytes, respectively. Moreover, even exposed to ambient air for 12 h, the anode still can retain ~78% capacity, demonstrating excellent air‐defendable capability. This work affords a promising strategy for fabricating high‐performance, high‐safety, and low‐cost LMBs.

Thermostability, oxidation, and high-temperature tribological properties of nano-multilayered AlCrSiN/VN coatings

In this study, monolithic AlCrSiN, VN, and nano-multilayered AlCrSiN/VN coatings were deposited using a hybrid deposition system combining arc ion plating and pulsed direct current magnetron sputtering. The microstructure, thermostability, mechanical, oxidation and tribological properties of the coatings were comparably investigated. The multilayered AlCrSiN/VN coating exhibited a face-centered cubic (fcc) structure with (200) preferred orientation and showed the highest hardness (30.7 ± 0.5 GPa) among these three coatings due to the multilayer interface enhancement mechanism and higher compressive stress. The AlCrSiN sublayers effectively prevented the V element from rapid outward diffusion to the surface of AlCrSiN/VN coating at elevated temperatures, which improved the oxidation resistance of the coating. Decomposition of V (Cr)–N bonds occurred at annealing temperatures from 800 °C to 1000 °C and V2N phase appeared at 1100 °C. The AlCrSiN/VN coating showed excellent tribological performance at high temperatures by combining the merits of VN layers for low friction coefficient and AlCrSiN layers for superior oxidation resistance. Compared to VN and AlCrSiN coatings, AlCrSiN/VN coating showed the lowest wear rate of 2.6×10-15 m3/N·m at 600 °C and lowest friction coefficient of 0.26 at 800 °C with a relativity low wear rate of 39.4×10-15 m3/N·m.

Spin valve effect in VN/GaN/VN van der Waals heterostructures

Nitride-based van der Waals magnetic heterostructures can simultaneously utilize both charge and spin degrees of electrons, which are important materials for low-dimensional spintronic devices. In this work, we study the stabilities and the electronic and magnetic properties of GaN/VN and VN/GaN/VN van der Waals heterostructures via first-principles calculations. The GaN/VN van der Waals heterostructure is a half-metal with 100% spin polarization, which can be applied in a spin filter and spin injection. Although monolayer GaN is a nonmagnetic semiconductor, it can introduce half-metallic characters via the magnetic proximity effect in both GaN/VN and VN/GaN/VN van der Waals heterostructures. The easy magnetization axis of hexagonal VN transits from the out-of-plane to the in-plane direction after combining with hexagonal GaN due to the different orbital occupations. Moreover, the electronic properties of the VN/GaN/VN van der Waals heterostructure depend largely on the magnetic configurations of the VN layers. By applying parallel or antiparallel magnetic configurations, the VN/GaN/VN van der Waals heterostructure presents half-metallic and semiconducting characters. The transformation indicates that the VN/GaN/VN van der Waals heterostructure is a promising candidate for room-temperature van der Waals spin valve devices.

Synthesis, Characterization, and Magnetoresistive Properties of the Epitaxial Pd0.96Fe0.04/VN/Pd0.92Fe0.08 Superconducting Spin-Valve Heterostructure.

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.

Application of magnetron sputtering to deposit a multicomponent separator with polysulfide chemisorption and electrode stabilization for high-performance lithium‑sulfur batteries

Lithium‑sulfur battery has attracted immense attention because of its extraordinary high energy density and theoretical capacity. However, its practical application has been seriously hindered by the rapid capacity degradation associated with the “shuttle effect” and unstable electrodes. Such negative issues during charge-discharge process could be alleviated by modification of the separator, which is demonstrated in this paper. Here, we report a sandwich-type vanadium nitride/polyvinylidene fluoride-polymethylmethacrylate/hexagonal boron nitride separator (VN/PVDF-PMMA/hBN) by electrospinning of PVDF-PMMA nanofiber membrane, followed by magnetron sputtering of VN and hBN layer at the opposite size of the membrane. Compared to conventional coating method, magnetron sputtering led to an ultrathin coating layer of 200 nm. The sputtered VN/PVDF-PMMA/hBN separator showed higher porosity (68.7%) than commercial polypropylene (PP) separator (44.5%), and significantly high electrolyte uptake (335.8% s. 175.9%), which can lead to rapid transportation of lithium ions. In the meantime, the membrane showed clear benefit in inhibiting polysulfide diffusion and lithium metal electrode stabilization due to the presence of polar CO groups that interact with the polysulfides. As a result, the LiS battery with VN/PVDF-PMMA/hBN separator showed a high initial discharge capacity of 1077.4 mAh g−1 at 0.2C, which only slightly decreased to 905.1 mAh g−1 after 200 cycles. Significantly higher than the battery with commercial PP separator.

Strain rate and temperature effects on the mechanical properties of TiN/VN composite: Molecular dynamics study

The second nearest-neighbor modified embedded-atom method (2NN MEAM) potential of Ti–V–N ternary system is developed based on the newly optimized interaction potentials of binary systems. The obtained potentials can excellently reproduce the structural, elastic and surface properties of the relevant systems. Then the effects of the strain rate and temperature on the mechanical properties of TiN/VN composite are studied by using the present potentials. It is found that strain rates have almost no influence on the Young's modulus of TiN/VN composite, but have a great influence on the inelastic properties. Whereas both the Young's modulus and the inelastic properties are sensitive to temperature. It is also found that the fracture of TiN/VN composite is a brittle fracture taking place in the VN layers.

Effects of modulation periods on mechanical properties of V/VN nano-multilayers

Metal/ceramic nano-multilayers, which possess the advantages of both metal and ceramics, have attracted intensive attention. In this work, the mechanical properties of V/VN nano-multilayers with different modulation periods (λs) were investigated using molecular dynamics simulations. The relationships between the microstructures and stress-strain (σ - ε) curves during in-plane tension and out-of-plane compression were explored, and the effects of λ were discussed. It shows that: (i) three kinds of V/VN nano-multilayers with different interfacial structures have different stabilities during deformation; (ii) dislocations nucleate firstly from the interfaces, propagate on {111} planes in VN layers, and deposit on the adjacent interface, and finally shift to V layers with the increase of applied strain; (iii) the nano-multilayer with larger λ has larger elastic modulus, elastic limit and lattice integrity, and strain hardening and cracks would appear in the nano-multilayers with λ > 42.90 Å.

Influence of nitride buffer layers on superconducting properties of niobium nitride

Niobium nitride thin films were deposited using reactive magnetron sputtering simultaneously on sapphire substrates with TiN, VN, and AlN buffer layers. Deposition temperature was varied from 400 to 840 °C. It was found that the crystal structure, surface roughness, and transition temperatures of the resulting NbN films depend strongly on both the growth temperature and the type of the buffer layer. The use of VN and TiN buffer layers for growing NbN at 400 °C improved transition temperatures compared to NbN grown at 840 °C on sapphire. While increasing the temperature improved the superconducting performance of films grown directly on sapphire, it caused hexagonal δ′-NbN and ε-NbN phases to emerge on the buffered films. A highly oriented hexagonal ε-NbN film was achieved by using a TiN buffer and an 840 °C deposition temperature. The ability to deposit high performance NbN at a lower temperature will improve and simplify the fabrication of advanced superconducting devices such as superconducting single photon detectors.

Interface-induced electronic structure toughening of nitride superlattices

We report on first-principles study of uniaxial strength for brittle cleavage of AlN/VN, AlN/TiN and VN/TiN systems. In agreement with previous studies we predict that the VN/TiN exhibits interface induced toughening of VN as compared to bulk values, and a similar effect is predicted also to occur in the VN/AlN system. However, a more detailed insight reveals, that the theoretical critical stress for brittle cleavage largely oscillates (even below the critical stress for bulk) with the distance from the interface inside the VN layer, a phenomenon not present (or hugely reduced) in TiN and AlN layers. The oscillating values for critical stress well correlate with the same behavior of interplanar distances and charge density. The origin of these unexpected properties was pinpointed to structural instabilities of cubic VN.

Investigating the influence of epitaxial modulation on the evolution of superhardness of the VN/TiB2 multilayers

A series of the VN/TiB2 nanomultilayers with different modulation ratios (tVN:tTiB2) and different modulation periods were synthesized via a magnetron sputtering system. The cross-sectional transmission electron microscopy (TEM) and x-ray diffraction (XRD) examinations indicated that in the alternately deposited monolayers of the VN and TiB2, due to the influence of the crystal (111)VN texture, TiB2 layer presented epitaxial growth on the surface of the VN layer when its tVN:tTiB2 was 5:1. Moreover, the formation of the TiB2 crystal promoted the growth of (200)VN and significantly improved the preferential growth of nanomultilayers. With decreasing tVN:tTiB2 to 1:7, the thin VN layer was crystallized under the introduction of crystalline TiB2 layers. A type of double epitaxial growth was observed to be a main reason for the coherent growth of the VN/TiB2 nanomultilayers within a certain thickness. Consequently, the multilayers appeared to have a corresponding superhard effect, which presented a corresponding anomalous enhancement of hardness and elastic modulus. The highest hardness and elastic modulus reached 41.8 and 492.4GPa, respectively, at a 1:7 ratio of tVN:tTiB2. Residual stresses were also released due to the coherent growth in the interfaces. Meanwhile, the coherent growth model of the multilayer was used to explain the growth mechanism of the VN/TiB2 nanomultilayers in this study.

Heterostructures design for Hf-Nitride/V-Nitride system

The multilayered films were grown via reactive r.f. magnetron sputtering technique by systematically varying the bilayer period (Λ) and the bilayer number (n), while maintaining constant the total coating thickness (~2.4μm) on silicon(100) substrates. The multilayers were characterized through high-angle X-ray diffraction (HA-XRD), low-angle X-ray diffraction (LA-XRD), HfN and VN layers were analyzed via X-ray Photoelectron Spectroscopy (XPS) and electron and transmission microscopy (TEM). The HA-XRD results showed preferential growth in the face-centered cubic (111) crystal structure for HfN/VN multilayer systems with the (111)[100]HfN//(200)[100]VN epitaxial relation. The maximum coherent assembly was observed with presence of satellite peaks.

Determination of superlattice effect on metal–ceramic nano-structures

Binary nitrides multilayer systems were grown on silicon (100) substrates with the aim to study the coherent assembly in HfN/VN material. Multilayers films were grown via reactive r.f. magnetron sputtering technique by systematically varying the bilayer period (Λ) and the bilayer number (n) while maintaining constant the total coating thickness (∼2.4μm). The layers were characterized by high angle X-ray diffraction (HA-XRD), low angle X-ray diffraction (LA-XRD). HfN and VN layers were analyzed by X-ray photoelectron spectroscopy (XPS) and electron and transmission microscopy (TEM). HA-XRD results showed preferential growth in the face-centered cubic (111) crystal structure for HfN/VN multilayer systems with the epitaxial relation (111) [100]HfN//(200) [100]VN. The maximum coherent assembly was observed with presence of satellite peaks. With this idea, ternary and binary nitrides films have been designed and deposited on Si (100) substrates with bilayer periods (Λ) in a broad range, from nanometers to micrometers. The films were fabricated to study the structural evolution, coherent assembly progress and optical properties such as the critical angle, dispersion coefficient, index of refraction for HfN/VN multilayers with decreasing bilayer thickness.

Tensile and fracture process of the TiN/VN interface from first principles

We have conducted a comprehensive first-principles investigation of tensile and fracture process of the TiN/VN interface by focusing on the strain–stress relationships, the ideal tensile strength and bonding breaking process. The deformation analysis reveals that all bonds are extended at the initial stage until the critical point of fracture is reached. The fracture occurs between the second and third layers on the VN side in both (111) and (001) interfaces and the interaction of potential bonds of facture weakens gradually with the increment of strain during the tensile process. By using several analytical techniques, we identify a charge transfer in both the TiN and VN layers near to interface at the points of fracture during the tensile process, which plays a crucial role in affecting the fracture process. We further demonstrate that the fracture of the TiN/VN interface occurs within the VN and that adhesion energy cannot be simply used to represent tensile strength.

Elastic constants, Poisson ratios, and the elastic anisotropy of VN(001), (011), and (111) epitaxial layers grown by reactive magnetron sputter deposition

Elastic constants are determined for single-crystal stoichiometric NaCl-structure VN(001), VN(011), and VN(111) epitaxial layers grown by magnetically unbalanced reactive magnetron sputter deposition on 001-, 011-, and 111-oriented MgO substrates at 430 °C. The relaxed lattice parameter ao = 0.4134 ± 0.0004 nm, obtained from high-resolution reciprocal space maps, and the mass density ρ = 6.1 g/cm3, determined from the combination of Rutherford backscattering spectroscopy and film thickness measurements, of the VN layers are both in good agreement with reported values for bulk crystals. Sub-picosecond ultrasonic optical pump/probe techniques are used to generate and detect VN longitudinal sound waves with measured velocities v001 = 9.8 ± 0.3, v011 = 9.1 ± 0.3, and v111 = 9.1 ± 0.3 km/s. The VN c11 elastic constant is determined from the sound wave velocity measurements as 585 ± 30 GPa; the c44 elastic constant, 126 ± 3 GPa, is obtained from surface acoustic wave measurements. From the combination of c11, c44, vhkl, and ρ we obtain the VN c12 elastic constant 178 ± 33 GPa, the VN elastic anisotropy A = 0.62, the isotropic Poisson ratio ν = 0.29, and the anisotropic Poisson ratios ν001 = 0.23, ν011 = 0.30, and ν111 = 0.29.

Influence of VN 2-D Inserted Layers Thickness on Microstructure and Mechanical Property of TiSiN Nanocomposite Film

Using V and TiSi targets, a series of TiSiN nanocomposite films being inserted by VN nano-layers with different thickness were prepared by RF magnetron sputtering method. Using X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM) and nano-indentation techniques, the influences of VN inserted layer thickness on microstructure and mechanical property of TiSiN nanocomposite film were investigated. The results show that, when the VN inserted layer thickness is small, the TiSiN film transforms from nanocomposite structure into nanomultilayered structure, leading to the decrease of hardness. As the VN inserted layers thicken, the hardness of film renewedly increases. When the VN inserted thickness is 0.5 nm, the film presents columnar crystals which continuously crosses through the nanomultilayers. TiSiN and VN layers exhibit coherent epitaxial growth structure, and the hardness accordingly reaches 37.2 GPa. With further increase of the VN inserted layer thickness, the coherent epitaxial growth structure is broken and the hardness of film decreases.

Improve on Corrosion Resistant Surface for AISI 4140 Steel Coated with VN and HfN Single Layer Films

Improve on Corrosion Resistant Surface for AISI 4140 Steel Coated with VN and HfN Single Layer Films

Microstructure evolution of the Si 3N 4/Si 3N 4 joints brazed using Au–Ni–V filler alloys with different V content

Au–Ni–V filler alloys with different vanadium contents were designed to braze Si 3N 4 ceramic at 1373 K for 30 min, and the microstructures of brazing seams were investigated by SEM and TEM. When the Au–Ni–V filler alloy contains 5 at.% V, round-like Ni[Si, V, Au] precipitates form in the Au[Ni] solid solution matrix and a VN reaction layer with 0.5 μm thickness appears on Si 3N 4 interface. When the V content increases to 10 at.%, a new polygonal Ni 2SiV 3 phase occurs in the seam, and the Ni[Si, V, Au] precipitate coarsens and VN layer thickens. With increase of V contents to 15 and 20 at.%, laminar Ni[Au] and polygonal Ni 3V precipitates form. With 25 at.% V content in the filler alloy, the Ni 2SiV 3 and Ni 3V precipitates distribute homogenously in the brazing seam. These microstructure evolutions were attributed to the reaction between Si 3N 4 and vanadium, which forms VN reaction layer and releases Si into the molten alloy.

Unveiling the atomic and electronic structure of the VN/MgO interface

We report a quantitative comparison of the interface structure of VN/MgO(001) using ab initio density-functional theory (DFT), aberration-corrected high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy (EELS). By HRTEM, we show an atomic resolution structure of epitaxially grown VN film on MgO with a clearly resolved oxygen and nitrogen sublattice across the interface. As revealed by DFT, the (002) interplanar spacing oscillates in the first several VN layers across the interface. Interfacial chemistry determined by EELS analysis shows the preponderance of O and V atom at the interface, resulting in a small detectable core-level shift.

Density functional theory applied toVN∕TiNmultilayers

By means of a density functional theory approach, materials properties of $\mathrm{V}\mathrm{N}[001](100)\ensuremath{\parallel}\mathrm{Ti}\mathrm{N}[001](100)$ multilayers are studied focusing on the elastic and mechanical properties of the interface. For the isolated bulk phases of TiN and VN, elastic constants and moduli are derived in order to analyze the matching conditions at the interface. Modeling of the mechanical properties was done in terms of brittle cleavage by calculating cleavage energies and critical stresses for the bulk phases as well as for the multilayer system. The interface energy of $\ensuremath{-}0.054\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ was derived for the lateral lattice parameter of MgO(100) according to the multilayer growth on this substrate. For this case, also atomic interlayer distances and critical stresses are determined and a Poisson ratio of the VN[001] and TiN[001] was evaluated. The values of $\ensuremath{\nu}=0.279$ and $\ensuremath{\nu}=0.235$, respectively, agree very well with the available experimental data. The strain energy and the interfacial cleavage properties of the multilayer are calculated as a function of the lateral lattice parameter illustrating growth conditions on different substrates. The cleavage energy at the interface considerably changes with respect to the lateral lattice parameter, but the critical stress of $\ensuremath{\approx}27\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ remains rather unchanged. The relaxation of atoms following an epitaxial strain of VN layers transforms VN into the structure with tetragonal-like stacking. This fact is an indication that stoichiometric VN is metastable against tetragonal distortion.

Microstructure and mechanical properties of VN/SiO 2 nanomultilayers synthesized by reactive sputtering

VN/SiO 2 nanomultilayers with various individual SiO 2 and VN layer thickness were prepared by reactive sputtering process. The crystallization condition of the SiO 2 layers and how they influence the characteristics of the multilayers were studied. The results reveal that under the template effect of the crystalline VN layer, as-deposited amorphous SiO 2 crystallizes at very low thickness (< ∼ 1 nm), and then grows epitaxially with VN layer in the VN/SiO 2 nanomultilayers. This leads to a remarkable increase in hardness. If the SiO 2 layers' thickness is further increased, they gradually transform into amorphous structure and block the epitaxial growth of the multilayers, resulting in a quick decline in hardness. On the other hand, the hardness of the multilayers is not sensitive to the VN layer thickness.