Niobium Atoms Research Articles

Atomic Nb-doping of WS2 for high-performance synaptic transistors in neuromorphic computing

Owing to the controllable growth and large-area synthesis for high-density integration, interest in employing atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for synaptic transistors is increasing. In particular, substitutional doping of 2D materials allows flexible modulation of material physical properties, facilitating precise control in defect engineering for eventual synaptic plasticity. In this study, to increase the switch ratio of synaptic transistors, we selectively performed experiments on WS2 and introduced niobium (Nb) atoms to serve as the channel material. The Nb atoms were substitutionally doped at the W sites, forming a uniform distribution across the entire flakes. The synaptic transistor devices exhibited an improved switch ratio of 103, 100 times larger than that of devices prepared with undoped WS2. The Nb atoms in WS2 play crucial roles in trapping and detrapping electrons. The modulation of channel conductivity achieved through the gate effectively simulates synaptic potentiation, inhibition, and repetitive learning processes. The Nb-WS2 synaptic transistor achieves 92.30% recognition accuracy on the Modified National Institute of Standards and Technology (MNIST) handwritten digit dataset after 125 training iterations. This study’s contribution extends to a pragmatic and accessible atomic doping methodology, elucidating the strategies underlying doping techniques for channel materials in synaptic transistors.

New Piezoceramic SrBi2Nb2-2xWxSnxO9: Crystal Structure, Microstructure and Dielectric Properties.

By using the method of high-temperature solid-phase reaction, the new piezoceramic SrBi2Nb2-2xWxSnxO9 was obtained, where partial substitution of niobium (Nb) atoms with Sn4+ and W6+ atoms in the compound SrBi2Nb2O9 occurred in the octahedra of the perovskite layer (B-position). X-ray diffraction investigations showed that these compounds are single-phase SrBi2Nb2-2xWxSnxO9 (x = 0.1, 0.2) and two-phase SrBi2Nb2-2xWxSnxO9 (x = 0.3, 0.4), but all of them had the structure of Aurivillius-Smolensky phases (ASPs) with close parameters of orthorhombic unit cells. It corresponded to the space group A21am. The temperature dependences of the relative permittivity ε/ε0 and the tangent of the dielectric loss angle tan d were defined at various frequencies. It was found that doping SrBi2Nb2-2xWxSnxO9 (x = 0.1) improved the electrophysical properties of the compound: losses decreased, and the relative permittivity increased. This result was obtained for the first time. Moreover, a new result was obtained that indicated an improvement in the electrophysical properties of SrBi2Nb2O9 using the chemical element Sn (tin). This refutes the previously existing opinion about the impossibility to use Sn as a doping element.

First-Principle Study on Tailoring the Martensitic Transformation of B2 Nb50−xTixRu50 Shape-Memory Alloy for Structural Applications

NbRu has a potential as a high-temperature shape-memory alloy (HTSMA) because it has a martensitic transformation temperature above 1000 °C. However, its shape-memory properties could be improved for consideration in the aerospace and automotive industry. The unsatisfactory shape-memory properties could be associated with the presence of a brittle tetragonal L10 martensitic phase. Therefore, in an attempt to modify the transformation path from B2→L10 in preference of either B2→orthorhombic or B2→monoclinic (MCL), an addition of B2 phase stabiliser, titanium (Ti), has been considered in this study to partially substitute niobium (Nb) atoms. The ab initio calculations have been conducted to investigate the effect of Ti addition on the thermodynamic, elastic, and electronic properties of the Nb50−xTixRu50 in B2 and L10 phases. The results showed that the B2 and L10 phases had comparable stability with increasing Ti content. The simulated data presented here was sufficient for the selection of suitable compositions that would allow the L10 phase to be engineered out. The said composition was identified within 15–30 at.% Ti. These compositions have a potential to be considered when designing alloys for structural application at high temperatures above 200 °C.

Exploring the Structural and Electronic Properties of Niobium Carbide Clusters: A Density Functional Theory Study.

This paper systematically investigates the structure, stability, and electronic properties of niobium carbide clusters, NbmCn (m = 5, 6; n = 1-7), using density functional theory. Nb5C2 and Nb5C6 possess higher dissociation energies and second-order difference energies, indicating that they have higher thermodynamic stability. Moreover, ab initio molecular dynamics (AIMD) simulations are used to demonstrate the thermal stability of these structures. The analysis of the density of states indicates that the molecular orbitals of NbmCn (m = 5, 6; n = 1-7) are primarily contributed by niobium atoms, with carbon atoms having a smaller contribution. The composition of the frontier molecular orbitals reveals that niobium atoms contribute approximately 73.1% to 99.8% to NbmCn clusters, while carbon atoms contribute about 0.2% to 26.9%.

Doped SnO2 thin films fabricated at low temperature by atomic layer deposition with a precise incorporation of niobium atoms

Nb-doped SnO2 (NTO) thin films were synthesized by atomic layer deposition technique at low temperature (100 °C). For an efficient incorporation of the Nb atoms, i.e. fine control of their amount and distribution, various supercycle ratios and precursor pulse sequences were explored. The thin film growth process studied by in-situ QCM revealed that the Nb incorporation is highly impacted by the surface nature as well as the amount of species available at the surface. This was confirmed by the actual concentration of the Nb atom incorporated inside the thin film as determined by XPS. Highly transparent thin films which transmit more than 95% of the AM1.5 global solar irradiance over a wide spectral range (300–1000 nm) were obtained. In addition, the Nb atoms influenced the optical band gap, conduction band, and valence band levels. While SnO2 thin film were too resistive, films tuned to conductive nature upon Nb incorporation with controlled concentration. Optimal incorporation level was found to be ⩽1 at.% of Nb, and carrier concentration reached up 2.5 × 1018 cm−3 for the as-deposited thin films. As a result, the high optical transparency accompanied with tuned electrical property of NTO thin films fabricated by ALD at low temperature paves the way for their integration into temperature-sensitive, nanostructured optoelectrical devices.

Niobium doping of CVD-WS2 monolayers using solid precursors with and without salt-KBr as a catalyst: A comparative study

The in situ doping of tungsten disulfide (WS2) monolayers with Niobium (Nb) atoms was obtained through the atmospheric pressure chemical vapor deposition (APCVD) method by controlling the Nb2O5 and WO3 precursors mass ratios. Samples were prepared employing the same growth parameters with and without the use of KBr salt as a catalyst. In both cases, the Nb incorporation quenches the luminescence intensity of the doped samples, and it depends on the Nb2O5:WO3 mass ratio. X-ray photoelectron spectroscopy (XPS) measurements were performed, and the observed redshift at the Fermi level indicated p-type doping. Nb-doped WS2 monolayers synthesized without the use of the catalyst have lower defect density, as revealed by a careful Raman analysis, and are free of agglomerates on their monolayers’ basal plane. The use of KBr as the catalyst increases the average crystal size but also increases the disorder effects compared with samples prepared without the use of salt. The presence of agglomerates of impurities at the surface of doped samples was observed in samples prepared with the use of salt as a catalyst. The controlled synthesis of p-type WS2 with low defect density is essential for developing electronic and photonic devices based on WS2 material.

Improvement of the Cantor alloy’s mechanical properties by alloying with niobium and zirconium

Created in 2004, the high-entropy (HEA) five-component Cantor alloy CoCrFeNiMn is still in the focus of attention of researchers in the field of physical materials science due to a good combination of strength and plastic properties, which open up prospects for its use in various high-tech industries. We performed a brief review of recent publications by domestic and foreign researchers on improving the mechanical properties of the Cantor alloy by alloying with niobium and zirconium, which proved themselves well in alloying traditional alloys. Zirconium alloying leads to a lower melting point due to the formation of eutectic with all elements of the Cantor alloy. Alloying with niobium atoms in the range of 0 – 16 at. % ensures the formation of a volume fraction of the Laves phases and σ–phase up to 42 %, which, in turn, is responsible for a fivefold increase in the yield strength from 202 to 1010 MPa. The work on the joint alloying of the Cantor alloy with Zr + Ti + Y2O3 , Nb + C, Nb + V systems was analyzed. With complex alloying, the mechanical properties are significantly improved. The paper reveals and discusses the physical mechanisms of hardening. Microalloying of 0.2 % Nb alloy with 1.3 % C provides an excellent combination of yield strength (~1096 MPa) and elongation (~12 %) after annealing at 700 °C.

Моделирование процессов формирования и исследование свойств нанопленок Co-Fe-Nb

The article presents the study of the formation and the analysis of the structure and properties of nanomaterials, which are cobalt-iron-niobium thin-film systems. A mathematical model is presented that allows to describe the combined behavior of atomic spins and coordinates. The generalized version of the model can use any type of the force interaction potential and take into account various contributions to the magnetic Hamiltonian depending on the specific problem being solved. When conducting computational experiments, the force potential of the modified embedded atom method (MEAM) was considered; to take into account magnetic interactions, a simplified magnetic Hamiltonian that includes the exchange interaction and the Zeeman interaction was used. The implementation of the mathematical model is presented in the LAMMPS software package, which was used to carry out numerical calculations. During the computational experiments, two separate problems were considered. In the first problem, the processes of deposition, interaction and ordering of a multilayer atomistic cobalt-iron-niobium system were analyzed. It has been shown that when niobium atoms are deposited onto a substrate, a relief nanofilm with irregularities up to a nanometer in height is formed. The contact between iron and niobium nanofilms is more blurred compared to the similar area of the contact between cobalt and iron nanofilms. In the second problem, the self-organization and reorientation of atomic spins in an iron nanofilm with a crystalline structure were analyzed. Calculations were carried out with and without an existing external magnetic field. The appearance of skyrmions (vortex flows) during the spin interaction of iron atoms was recorded. The simulation has shown that under the influence of an external magnetic field, an induced magnetic moment appears in the iron nanofilm, opposite to the induction vector of the external field.

Effect of Introducing Defects and Doping on Different Properties of Monolayer MoS2

Herein, the comprehensive study of different properties of undoped MoS2, MoS2 lattice with sulfur (S) and, molybdenum (Mo) vacancy, and MoS2 with substitutional doping of niobium (Nb), vanadium (V), and zinc (Zn) atoms is done. The density functional theory (DFT) is used and the electronic properties like density of states, band structure, electron density, and optical properties like dielectric function, optical conductivity, and refractive index are studied. It is observed that undoped MoS2 monolayer shows direct bandgap semiconductor characteristics with a bandgap of around 1.79 eV. P‐type characteristics are observed for Nb‐, V‐, and Zn‐doped MoS2 lattices. The real part and imaginary parts of all optical parameters along x and z directions for different MoS2 supercells are found to be anisotropic in nature up to a photon energy of almost 11 eV and thereafter they show nearly isotropic nature. Finally, it is found that the obtained properties of MoS2 monolayer as per literature are suitable for next‐generation MOSFET application.

Unraveling the atomic and electronic structure of nanocrystals on superconducting Nb(110): Impact of the oxygen monolayer

The niobium surface is almost always covered by a native oxide layer which greatly influences the performance of superconducting devices. Here we investigate the highly stable niobium oxide overlayer of Nb(110), which is characterized by its distinctive nanocrystal structure as observed by scanning tunneling microscopy (STM). Our ab initio density functional theory (DFT) calculations show that a subtle reconstruction in the surface niobium atoms gives rise to rows of fourfold coordinated oxygen separated by regions of threefold coordinated oxygen. The fourfold oxygen rows are determined to be the source of the nanocrystal pattern observed in STM and the two chemical states of oxygen observed in core-level x-ray photoelectron spectroscopy (XPS) are ascribed to the threefold and fourfold oxygens. Furthermore, we find excellent agreement between the DFT calculated electronic structure with scanning tunneling spectroscopy and valence XPS measurements.

Structural Engineering Enabled Bimetallic (Ti1- y Nby )2 AlC Solid Solution Structure for Efficient Electromagnetic Wave Absorption in Gigahertz.

Microstructures play a critical role to influence the polarization behavior of dielectric materials, which determines the electromagnetic response ability in gigahertz. However, the relationship between them, especially in the solid-solution structures is still absent. Herein, a series of (Ti1- y Nby )2 AlC MAX phase solid solutions with nano-laminated structures have been employed to illuminate the aforementioned problem. The relationship has been investigated by the lattice distortion constructed via tuning the composition from Ti to Nb in the M-site atomic layer. Experimental characterizations indicated that the dielectric response behaviors between declined conduction loss and boosted polarization loss can be well balanced by niobium atom manipulative solid-solution engineering, which is conducive to impedance matching and electromagnetic absorption performance. Theoretical calculation further proved that the origin of electric dipoles is ascribed to the charge density differences resulting from the altered microscopic atomic distribution. As a result, the Ti1.2 Nb0.8 AlC exhibits the mostly optimized microwave absorption property, in which a minimum reflection loss of -42dB and an effective absorption bandwidth of 4.3GHz under an ultra-thin thickness of 1.4mm can be obtained. This work provides insight into the structural engineering in modifying electromagnetic response performance at gigahertz and which can be expanded to other solid-solution materials.

Structure Determination and Analysis of the Ceramic Material La0.987Ti1.627Nb3.307O13 by Synchrotron and Neutron Powder Diffraction and DFT Calculations

In this paper, the ternary system La2O3-TiO2-Nb2O5 is studied to find new ternary phases with useful electrical properties. The solid solution La3−xTi5−3xNb10−2xO39.5−12.5x was recently identified, and this study focuses on the structural characterization of this solid solution with x = 0.04. The crystal structure, representing a new structural type, was determined from synchrotron and neutron powder diffraction data. The unit cell parameters are a = 7.332 Å, b = 7.421 Å, c = 10.673 Å, α = 84.15°, ß = 80.16°, γ = 60.37°, and space group P1¯. The titanium and niobium atoms are disordered in five different crystallographic sites coordinated octahedrally by oxygen atoms. The eight-coordinated La atoms are embedded in the octahedral framework. Ti and Nb preferentially occupy different sites, and this feature was studied using periodic density functional theory methods. Energies of possible Ti/Nb distributions were calculated and the results agree well with the site occupancies obtained by combined Rietveld refinement of synchrotron and neutron powder diffraction patterns. The geometries optimized by DFT also agree well with the structural parameters determined by diffraction. The general agreement between the theoretical calculations and the experimental data justifies the quantum chemical methods as reliable complementary tools for the structural investigation of ceramic materials.

DFT and ab-initio molecular dynamics of pyrochlore surface dissolution in aqueous media – Effect of cleavage plane and surface atomic vacancies

Pyrochlore, as a complex oxide mineral containing the critical niobium element, offers a rich diversity of surface chemical compositions in different cleavage directions. Hence, very little is known about the structure and stability of pyrochlore’s low-index surfaces. Accordingly, this study aims to investigate the hydration behavior of the defect-free and surface-depleted (110) and (111) Ca2Nb2O6F pyrochlore, terminated with F and Ca ions, under implicit and explicit consideration of water molecules using DFT and ab-initio molecular dynamics (AIMD) simulations. Our results revealed that the F&Ca-terminated (110) surface possesses strong hydrophilic characteristics compared to the (111) cleavage plane. The (110) surface becomes hydroxylated on the undercoordinated oxygen and niobium atoms by the dissociative reactions of water at the interface. Our simulations further captured a major intra-surface reconstruction in the (110) direction upon surface ion depletion. On the defect-free (111) surface, water-surface interactions were limited to a single hydrogen bond between each fluoride on the outermost layer and the water’s hydrogen. The ions removal from the (111) surface led to the exposure of Nb atoms and activated water-surface interaction by making the lower position oxygens accessible by the water molecules. The AIMD simulation results suggested that fluorides are prone to diffuse from the surface after solvation, while oxygen loss could also be an active mechanism for surface stability. Later, the insights could serve as the foundation for future studies to tailor advanced pyrochlore flotation procedures.

Структура и свойства биоинертного покрытия Mo – Nb, сформированного на медицинском сплаве Titanium Grade 5 электровзрывным методом

In this article, an attempt was made to solve the problem of creating a coating for an implant that has better biological compatibility than the medical titanium alloy Titanium Grade 5. A Mo – Nb coating of the composition Mo – Nb is formed on the titanium grade 5 medical alloy by the electroexplosive method. The coating is formed as a result of the simultaneous electric explosion of molybdenum and niobium foils. A set of studies has been carried out to establish the structure, phase composition, and properties of the formed coatings. The coatings were studied by scanning and transmission electron microscopy. It is shown that the hardness of the surface layer of the coating by 60 % and Young’s modulus by 43 % exceed the corresponding characteristics of the Titanium Grade 5 alloy. The thickness of the layer with high (relative to the substrate) values of hardness and Young’s modulus reaches 80 µm. It was found that the wear parameter of the coating is 1.8 times, and the friction coefficient of the coating is 1.6 times higher than the wear parameter and the friction coefficient of the substrate. It has been established that in the surface layer, along with the coating atoms, there are Al, Ti, V atoms, which indicates that the coating is doped with substrate atoms, as well as oxygen and carbon atoms. The layering of the coating by elemental composition was revealed, namely, the top of the coating is enriched with niobium atoms, the lower part of the coating is enriched with molybdenum atoms. It is shown that the coating has a polycrystalline structure formed by a solid solution based on molybdenum. In the bulk and along the grain boundaries, there are inclusions of the second phase of the composition a-Ti, Nb, Mo9Ti4, and NbTi4 of various shapes and sizes. The studies of the phase composition did not reveal compounds based on vanadium and aluminum, which reduce the biocompatibility of the coatings. The identified phases contain only molybdenum, niobium and titanium, which are bioinert. This fact suggests that, as in studies of the phase composition of the surface of the coatings and its change in thickness, the biocompatibility of the obtained coatings will be higher compared to the Titanium Grade 5 titanium alloy. The conducted complex of studies makes it possible to recommend the resulting coatings for further clinical trials. These coatings are expected to be used in the future for better survival of titanium implants in the human body.

Computational investigation of tuning the electronic ability and featured for heterofullerene based dye sensitized solar cells

The structural characteristics of the heteroatom substituted fullerene to improve its physical and chemical properties are discussed in this work, highlighting possible applications in aromaticity, photocatalysis, solar cells, and superconducting materials. The energy gap of doped fullerene lowers significantly, making C31Nb a more reactive material and transforming it into an efficient superconductor. The molecular structure, energy and relative stabilities of the heterofullerene were examined and evaluated to determine the material's identification. According to the results analysis, the extra niobium atom and substituted carbon atom improve the electronic stability of heterofullerene. Using 13C NMR nuclear independent chemical shift, the stability of each fullerene and aromatic found in nature is discovered. Furthermore, the simulated infrared spectra of fullerene are reviewed, and the major distinctive peaks are given to different functional groups. NBO study which shows the intermolecular charge transfer from the donor to the acceptor in doped fullerene, demonstrates that the strong intermolecular contact between carbon and niobium atoms makes this material a notable material for NLO property.

Spectroscopic evidence of flat bands in breathing kagome semiconductor Nb3I8

Kagome materials have become solid grounds to study the interplay among geometry, topology, correlation, and magnetism. Recently, niobium halide semiconductors Nb3X8 (X = Cl, Br, I) have been predicted to be two-dimensional magnets and these materials are also interesting for their breathing kagome geometry. However, experimental electronic structure studies of these promising materials are still lacking. Here, we report the spectroscopic evidence of flat and weakly dispersing bands in breathing-kagome semiconductor Nb3I8 around 500 meV binding energy, which is well supported by our first-principles calculations. These bands originate from the breathing kagome lattice of niobium atoms and have niobium d-orbital character. They are found to be sensitive to the polarization of the incident photon beam. Our study provides insight into the electronic structure and flat band topology in an exfoliable kagome semiconductor, thereby providing an important platform to understand the interaction of geometry and electron correlations in two-dimensional materials.

Hydrogen storage capacity of the niobium atom adsorbed on carbon and boron nitride planar nanoflakes

In the present work, we investigate the capacity of the niobium atom adsorbed on the carbon and boron nitride planar flakes to store hydrogen molecules. Specifically, the Nb adsorbed on the circumcoronene (Nb@C), hexagonal boron nitride (Nb@h − BN), and the h − BN with the central ring substituted by carbons (Nb@C6/h − BN). The Nb@C and Nb@C6/h − BN systems present a hybridization among the carbon and niobium orbitals, which implies higher binding energy between the Nb atom and the corresponding flake, contrasting with the observed for the Nb@h − BN cluster. All the Nb@flakes possess multiplicity different from one, reinforcing the importance of considering the various accessible spin-state. Despite the high number of adsorbed hydrogen molecules supported by the Nb@flakes, the stability of the whole system is affected as the number of molecular hydrogen increases. The Nb@C6/h − BN is the system that satisfies the conditions of stability and H2 storage capacity. We highlight that the storage capacity of a given system must be measured considering not only the number of hydrogen molecules supported by the structure but also taking into account how the presence of nH2 affects the stability of the whole material.

Local atomic structure of the high refractive index La2O3–Nb2O5–B2O3 glasses

High refractive glasses in the La2O3–Nb2O5–B2O3 (LNB) system were synthesized by the melt-quenching technique and correlations between their compositions and structural features were clarified. It was found that the refraction index of the LNB glasses is tunable from 1.71 to 1.98 by the variation of the Nb2O5 fraction from 5 to 30 mol%. The infrared spectroscopy analysis implies on the presence of three and four coordinated borate units, as well as six coordinated niobium atoms. The X-ray absorption (La L3-edge and Nb K-edge XANES and EXAFS) spectroscopy and total X-ray scattering results show that niobium atoms maintain octahedral oxygen coordination despite the wide variation of the Nb2O5 content, while average lanthanum coordination number is versatile and changes from ~8 to ~10. The interatomic distance values testify that the niobium octahedra in the glass network are connected only “by corners”. The stability of niobium local atomic structure implies that the main source of the changes in the optical properties of studied glasses is the variation of the Nb2O5 content. The deeper understanding of the local atomic structure of the high refractive index LNB glasses paves ways for the development of new glass wafers for cutting-edge augmented reality devices.

Developing a Chemical and Structural Understanding of the Surface Oxide in a Niobium Superconducting Qubit

Superconducting thin films of niobium have been extensively employed in transmon qubit architectures. Although these architectures have demonstrated improvements in recent years, further improvements in performance through materials engineering will aid in large-scale deployment. Here, we use information retrieved from secondary ion mass spectrometry and electron microscopy to conduct a detailed assessment of the surface oxide that forms in ambient conditions for transmon test qubit devices patterned from a niobium film. We observe that this oxide exhibits a varying stoichiometry with NbO and NbO2 found closer to the niobium film/oxide interface and Nb2O5 found closer to the surface. In terms of structural analysis, we find that the Nb2O5 region is semicrystalline in nature and exhibits randomly oriented grains on the order of 1-3 nm corresponding to monoclinic N-Nb2O5 that are dispersed throughout an amorphous matrix. Using fluctuation electron microscopy, we are able to map the relative crystallinity in the Nb2O5 region with nanometer spatial resolution. Through this correlative method, we observe that the highly disordered regions are more likely to contain oxygen vacancies and exhibit weaker bonds between the niobium and oxygen atoms. Based on these findings, we expect that oxygen vacancies likely serve as a decoherence mechanism in quantum systems.

DFT calculations of solute-vacancy binding in Zirconium-based Zr–Nb–Sn alloy

The energetic properties of ternary Zr–Nb–Sn Zirconium-based alloy with concentration of dissolved alloying elements ∼ 1 . 5 % are studied by using density functional theory. The possibility of alloying additions separated by different distances to dissolve/segregate in a host matrix is analyzed with the help of mixing energy and solute–solute binding energy. The ability of solutes to trap single vacancy is discussed by studying formation energy of a vacancy, located on a different distances from both solute atoms and the corresponding solute–solute–vacancy binding. This study provides an insight into the details of vacancy energetics in Zirconium-based alloys exploited in nuclear-power plants. • In ternary Zirconium-based alloys solutes Sn and Nb are the second-nearest neighbors. • Non-equilibrium vacancies will segregate nearby Tin atoms and far from Niobium atoms.