MoN Layers Research Articles

Sputtered MoN nanolayer as a multifunctional polysulfide catalyst for high-performance lithium–sulfur batteries

Two major obstacles for the practical application of lithium–sulfur batteries are sluggish redox kinetics and the shuttle effect of lithium polysulfides (LiPSs). Herein, MoN nanolayer-decorated multilayer graphene is fabricated via magnetron sputtering then serves as a multifunctional interlayer in Li–S batteries to suppress the shuttle effect and enhance redox kinetics. It is revealed that after the initial discharge process, the MoN layers break up into independent microreaction units consisting of MoN bodies and MoS2 edges, forming a heterogeneous composite catalyst in situ. The MoN bodies not only have high sulfur affinity to trap LiPSs but also enhance their redox kinetics. At the same time, the MoS2 edge weakens the mobility of LiPSs via the anchoring effect. As a result, Li–S cells using the interlayer present superior cycling stability under a high sulfur loading of 4.8 ​mg ​cm−2. This work may open a new avenue for developing high-performance Li–S batteries.

Modulation effect on mechanical properties of nanolayered MoN/MoSiN coatings

The combination of molybdenum nitride, MoN, and molybdenum silicon nitride, MoSiN, to be a naolayered MoN/MoSiN film was developed by the reactive radio frequency, r.f., magnetron sputtering system. The MoN and MoSiN building layers were designed and fabricated with a crystalline and an amorphous/nanocrystalline feature, respectively. The effect of thickness modulation of the c-MoN and a-MoSiN layers on microstructure and mechanical properties of the MoN/MoSiN coatings were investigated. With a fixed 50.0 nm crystallines MoN building layer, the amorphous/nanocrystalline MoSiN building layer with a designed thickness of 25.0 nm would suppress the continuous growth of crystalline phases. For mechanical characterization, the change in modulation did not lead to significant influence on hardness and Young's modulus. When a large thickness ratio of c-MoN/a-MoSiN was applied, phenomenal increase in scratch and wear resistance was observed due to higher volumetric ratio of hard crystalline MoN layer and discontinuity of crystalline phase growth through building layers in the nanolayered MoN/MoSiN coatings.

Input power effect on microstructure and mechanical properties of Mo[sbnd]Si[sbnd]N multilayer coatings

The MoSiN single layer and multilayer films were fabricated by a reactive radio frequency, r.f., magnetron sputtering system with pure Mo and Si targets. The Ar/N2 flow ratio was fixed at 12/8, while r.f. input powers for Mo and Si were 135 W and 0 to 150 W, respectively. The corresponding Si contents in the coating ranged from 0 to approximately 20 at.%. The microstructure of the MoSiN single layers evolved from Mo2N (111) crystalline to amorphous feature with input powers and related Si doping amounts. The MoSiN multilayer coatings were fabricated with crystalline MoN, crystalline and amorphous MoSiN layers with sequential stacking of any two building layers. The multilayer film made of MoN and crystalline MoSiN layers showed an obvious crystalline microstructure, while the amorphous MoSiN layer incorporated multilayer MoSiN systems effectively suppressed the continuity of the columnar growth. The correlation between mechanical properties, including hardness, Young's modulus, indentation cracking, and scratch behavior, were investigated and discussed in terms of film microstructure evolution.

Point-defect engineering of MoN/TaN superlattice films: A first-principles and experimental study

Superlattice architecture represents an effective strategy to improve performance of hard protective coatings. Our model system, MoN/TaN, combines materials well-known for their high ductility as well as a strong driving force for vacancies. In this work, we reveal and interpret peculiar structure-stability-elasticity relations for MoN/TaN combining modelling and experimental approaches. Chemistry of the most stable structural variants depending on various deposition conditions is predicted by Density Functional Theory calculations using the concept of chemical potential. Importantly, no stability region exists for the defect-free superlattice. The X-ray Diffraction and Energy-dispersive X-ray Spectroscopy experiments show that MoN/TaN superlattices consist of distorted fcc building blocks and contain non-metallic vacancies in MoN layers, which perfectly agrees with our theoretical model for these particular deposition conditions. The vibrational spectra analysis together with the close overlap between the experimental indentation modulus and the calculated Young's modulus points towards MoN0.5/TaN as the most likely chemistry of our coatings.

Synthesis of monolayer MoNx and nanomultilayer CrN/Mo2N coatings using arc ion plating

Monolayer MoNx and nano-multilayer CrN/Mo2N coatings were prepared by arc ion plating and characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), friction tester and hardness tester. The results from TEM and XRD analysis showed that the crystal structure of MoNx and CrN/Mo2N coatings has a cubic lattice structure. The microhardness of MoNx coatings deposited at lower N2 pressure is about 2100 HV which is higher than 1950 HV of the coatings deposited at higher N2 pressure. The variation of friction coefficient of MoNx coatings influenced by N2 pressure is obvious at higher N2 pressure. The modulation period of CrN/Mo2N coatings is from 58.5 nm to 11.17 nm with increasing substrate rotation speed (Srs) in the range of 1–5 rpm. The maximum hardness of CrN/Mo2N nanomultilayer coatings, when the Srs is 7 rpm, is approximately 2950 HV. The value is 1.5 times higher than those of the MoNx monolayer coating (2000 HV). These enhancement effects in superlattice films could be attributed to the resistance to dislocation glide across interface between the MoN and CrN layers. The value of average friction coefficient of CrN/Mo2N nanomultilayer coatings is about 0.33 which is higher than 0.3 of MoNx coatings and lower than 0.6 of CrN. The wear rate of CrN/Mo2N nanomultilayer coatings is about 7 × 10−7 mm3/N·m which is obviously lower than 3.3 × 10−6 mm3/N·m of CrN coatings and higher than 1.2 × 10−7 mm3/N·m of MoNx coatings.

Microstructure evolution and indentation cracking behavior of MoN multilayer films

Molybdenum nitride, MoN, multilayer films tailored by MoN single layers with versatile structure features are produced through radio frequency magnetron sputtering technique. The MoN layers were manipulated to exhibit crystalline (C), preferred orientation (P) and amorphous (A) phases with gas inlet and input power control. The MoN multilayer films were successfully prepared using alternatively stacking of single layers to form C/P, C/A, and P/A assemblies, i.e. MCP, MCA, and MPA films respectively. The multilayer coatings were controlled at a total thickness of 1 μm with each building layer of 50 nm. Through microstructure analyses, the columnar crystalline structure in single layer films was suppressed by tailored layers. Intact heterostructural interfaces with building layers at early deposition stages could be observed for crystalline incorporated multilayers, like MCP and MCA assemblies. On the other hand, the continuous columnar crystalline structure could be found in multilayers containing amorphous layers, which tended to be pliant to the crystalline phases and preferred orientation during deposition. The columnar grains grew through several layer interfaces in late deposition stages for multilayers, especially for MPA film. Through Rockwell C indentation test, adhesion and cracking behaviour of the single and multilayer MoN films were evaluated. The structure tailored MoN multilayers showed better adhesion as compared to the single layer films. Adhesive cracking due to preferred orientation was suppressed by the tailoring structure with crystalline layers.

Influence of the bilayer thickness of nanostructured multilayer MoN/CrN coating on its microstructure, hardness, and elemental composition

Multilayer nanostructured coatings consisting of alternating MoN and CrN layers were obtained by vacuum cathode evaporation under various conditions of deposition. The transition from micron sizes of bilayers to the nanometer scale in the coatings under investigation leads to an increase in hardness from 15 to 35.5 GPa (with a layer thickness of about 35 nm). At the same time, when the number of bilayers in the coating decreases, the average Vickers hardness increases from 1267 HV0.05 to 3307 HV0.05. An increase in the value of the potential supplied to the substrate from–20 to–150 V leads to the formation of growth textures in coating layers with the [100] axis, and to an increase in the intensity of reflections with increasing bilayer thickness. Elemental analysis carried out with the help of Rutherford backscattering, secondary ion mass spectrometry and energy dispersion spectra showed a good separation of the MoN and CrN layers near the surface of the coatings.

Structure engineering in vacuum-arc-deposited coatings of the MoN–CrN system

The possibilities of structure engineering in multilayer coatings of the MoN–CrN system with relatively low heats of formation of component transition metal nitrides are demonstrated by varying pressure P N of reactive gas (nitrogen) and negative bias voltage–U s applied to a metal substrate. It is established that, by changing P N from 7 × 10–4 to 3 × 10–3 Torr, it is possible to obtain coatings in two significantly different structural-phase states. A multilayer nonisostructural composite with hexagonal crystalline lattice in CrN layers and cubic type lattice in MoN layers is formed at low pressure, whereas an isostructural state with cubic lattice in both nitride layers is formed at high pressure. The existence of two types of structural states allows multilayer coatings with controlled hardness to be obtained, which reaches 38 GPa in the isostructural state.

Effect of bilayer period on structural and mechanical properties of nanocomposite TiAlN/MoN multilayer films synthesized by cathodic arc ion-plating

TiAlN/MoN multilayers were deposited on Si (100) and cemented carbide substrates using TiAl and Mo targets in a cathodic arc ion plating system with 1-fold rotation. The bilayer thickness (Λ) of all the layers was controlled via rotational speed of substrate holder within a rage of 21 to 124nm. The TiAlN/MoN has a multilayered structure in which nano-crystalline TiAlN layers alternate with the nano-crystalline MoN layers. The Ti:Al ratios measured by EDS over all samples were closed to the designed ratio and corresponded to Ti0.70Al0.30N composition. TiAlN/MoN nanoscale multilayer thin films exhibited a TiAlN (200), TiAlN (220), MoN (202) and MoN (200) crystalline orientation. The highest hardness and Young's modulus were obtained with a bilayer period of 25nm, while wear rate decreased with decreasing bilayer period. On average, nanoindentation measurements combined with atomic force microscopy (AFM) and cross-sectional scanning electron microscopy (SEM) revealed improved mechanical properties of TiAlN/MoN films with decreasing bilayer period were attributed to their densified microstructure with development of fine grains and reduced surface roughness.

Probing the influence from residual Ti interstitials on water adsorption on TiO2(110)

Reduced, stoichiometric and oxidized TiO${}_{2}$(110) surfaces have been compared using valence photoelectron spectroscopy. The results show that the intensity from the band-gap state carries contributions from both oxygen surface vacancies and residual Ti interstitials, present after the sample cleaning procedure. The density of Ti interstitials was found to be 0.05 \ifmmode\pm\else\textpm\fi{} 0.02 monlayers (ML), while the density of oxygen vacancies was estimated to 0.09 \ifmmode\pm\else\textpm\fi{} 0.01 ML. Both these values are in good agreement with previous STM studies. O 1$s$ core-level photoelectron spectra show that oxidation of the interstitials had negligible effect on the OH-H${}_{2}$O balance within the first water layer. The characteristic OH-H${}_{2}$O balance found on a surface free from oxygen vacancies previously reported [Walle et al., Phys. Rev. B 80, 235436 (2009)] is therefore an inherent property of the TiO${}_{2}$(110) surface; that is, the primary mechanism leading to partial dissociation is not related to the presence of residual Ti interstitials.

Influence of the Flux Ratio N<sub>2</sub>/Ar on the Formation of Mo-N Modification Layers on Ti<sub>6</sub>Al<sub>4</sub>V by Plasma Reactive Sputtering

Ti6Al4V alloy is promising biology material with outstanding properties of low density, high specific strength, and exceptional corrosion resistance. However, one of its disadvantages is the poor tribological property. In this paper Mo-N hard surface modification layers were formed on Ti6Al4V at 900°C substrate temperature by plasma reactive sputtering. The flux ratio N2/Ar is an important parameter and its influence on the composition, structure and hardness of the Mo-N layers is studied. The Mo-N layers are duplex layers, composed of diffusing layer and surface coating. The component of Mo and N elements in the diffusing layer changes gradually which can enhance the load-bearing capacity to the coating and ensure the durability of the coating. With the increase of the flux ratio N2/Ar, the content of N element in the Mo-N layers increases. The Mo-N layers were polycrystalline γ- Mo2N with (200) plane oriented parallel to the substrate surface. The surface hardness of the formed layers is in the range HK1330-1430. The hardness of the Mo-N layers increases with the increase of the flux ratio N2/Ar and the reason is that the content of N element in the Mo-N layers increases.

Depth-resolved residual strain in MoN∕Mo nanocrystalline films

The authors have applied cross-sectional x-ray microdiffraction to measure depth-resolved in-plane residual strain in nanocrystalline MoN∕Mo bilayer films deposited on Si. Compressive strains with large gradients were found in the as-deposited films. After thermal annealing, the strain profiles and diffraction peak widths of the MoN and Mo layers were altered. These findings provide insights on the relationship between defects introduced during film processing and the effect of annealing on the structure and properties of magnetron-sputtered nanocrystalline films.

Microstructure and mechanical properties of multi-constituent superlattice coatings

Superlattice nitride coatings with four different layer constituents, i.e., ZrN, MoN, NbN and AlN, were synthesized using an unbalanced closed-field magnetron sputtering coater. At small superlattice modulation periods, both MoN and AlN layers adapted to the cubic B1 structure due to a template effect, and the coatings exhibited a strong (2 0 0) preferred orientation. Increasing the modulation period above a critical value led to the formation of hexagonal MoN and AlN layers with diminishing (2 0 0) preferred orientation. These microstructure changes were reflected in the coating mechanical properties. Relatively high hardness and Young's modulus values were obtained at small modulation periods, which decreased dramatically above the critical modulation period. The effects of substrate bias on the layer crystallographic structure, coating preferred orientation and mechanical properties were similar to those of the modulation period.

Sputter-deposited Mo and reactively sputter-deposited Mo-N films as barrier layers against Cu diffusion

This work studied the barrier capability of sputter-deposited Mo and reactively sputter-deposited Mo-N layers against Cu diffusion in a device structure of Cu/barrier/p +n junction diodes. With a 500 Å thick Mo film as barrier layer, the Cu/Mo/p +n junction diodes were capable of withstanding 30 min of thermal annealing at temperatures up to 500°C without causing degradation to the devices electrical characteristics. The incorporation of nitrogen in the Mo layer improved the barrier capability of the metal layer. In particular, the Mo-N films sputterdeposited in a gas mixture of Ar and N 2 with Ar/N 2 flow rates of 24/8 to 24/12 sccm were found to possess the best barrier capability. With a 500 Å thick Mo-N barrier layer, the thermal stability of Cu/Mo-N/p +n junction diodes were found to reach 600°C. At temperatures exceeding the thermal stability limit, we presumed that the failure of Cu/barrier/p +n junction diodes arose from two mechanisms: the grain boundary diffusion for the Mo film and the Mo-N films deposited with small N 2 flow rates, and the defects diffusion for the Mo-N barriers deposited with large N 2 flow rates. For the Mo-N films deposited in a gas mixture of medium nitrogen content (e.g. N 2 flow rate of 8 to 12 sccm), both of the failure mechanisms might exist simultaneously.

Mon-Tin Superconducting Artificial Superstructure Film

ABSTRACTWe succeeded in synthesizing MoN-TiN superconducting artificial superstructure film (SASF). The structure of MoN layers is estimated to be γ-Mo2 N. The behavior of Tc in SASFs is recognized by a proximity effect using adjustable parameters of bulk Tc. Calculated parameters are, however, different from Tc of single layered films.