Electronic and optical properties of rocksalt-phase tungsten nitride (B1-WN)

Abstract

The optical and electronic properties of rocksalt structure tungsten nitride (B1-WN) were investigated by x-ray photoelectron spectroscopy (XPS) and UV–visible-Fourier transform infrared optical reflectivity. Both 111-textured polycrystalline and epitaxial WN(111) films with [N]/[W] ratios of 1.12 and 0.87, respectively, were found to be electron conductors with partially filled W-5d conduction bands. However, their electronic behavior is dominated by high conduction electron losses, which are attributed to scattering at both anion and cation vacancies and are more pronounced for films with high nitrogen content, yielding high resistivity values of 1.4–2.8 mΩ cm. The dielectric function is well described with a Drude–Lorentz model over a large wavelength range from 0.2 to 100 μm, and exhibits an ε1 that becomes negative above a relatively high critical wavelength that increases with increasing nitrogen content from 22 to 100 μm. Compositional interpolation of XPS data provides a W4f7/2 electron binding energy for pure stoichiometric B1-WN of 31.9 eV, while increasing the N-content results in a reduction of the density of states from the W-5dt2g bands at and near the Fermi level. The overall results do not confirm the predicted promising plasmonic properties of B1-WN but instead reveal possible alternative applications for this compound as photothermal or epsilon-near-zero material.

Near-Zero Negative Real Permittivity in Far Ultraviolet: Extending Plasmonics and Photonics with B1-MoNx

“…MoN0.69 the fit renders the values Epu= 9.12 eV and D=1.48 eV, that provide a resistivity value of 133  cm, which is in fair agreement with the electrically measured 250  cm; this value is at least an order of magnitude smaller than the values for WNx20 , and comparable to the resistivity of other polycrystalline conductive nitrides5 , stoichiometric epitaxial NbN39 and TaN40 , under-stoichiometric (x<1) epitaxial TiNx41 and HfNx42 , epitaxial TiN with point defects43 , albeit higher by an order of magnitude than the resistivity of stoichiometric epitaxial TiN 41 , ZrN44 , HfN42 , and VN45 .…”

“…The two Lorentz oscillators are located at an energy position E 0 j = ℏω 0 j , with strength f j and damping (broadening) factor γ j . The Drude term in eq is characterized by the unscreened plasma energy E pu = ℏω pu , (which is associated with conduction electron density ,,,,, ) and the damping factor Γ D , which accounts for the various electron scattering mechanisms; − for the particular case of B1-MoN 0.69 , the fit renders the values E pu = 9.12 eV and Γ D = 1.48 eV, which provide a resistivity value of 133 μΩ cm, which is in fair agreement with the electrically measured 250 μΩ cm; this value is at least an order of magnitude smaller than the values for WN x and comparable to the resistivity of other polycrystalline conductive nitrides, stoichiometric epitaxial NbN and TaN, understoichiometric ( x < 1) epitaxial TiN x and HfN x , and epitaxial TiN with point defects, albeit higher by an order of magnitude than the resistivity of stoichiometric epitaxial TiN, ZrN, HfN, and VN …”

“…Among the various TMNs, the cubic B1-WN and B1-MoN were predicted to be the most efficient UV conductors, based on their experimental electron density values and the detailed calculations of the electron density of states of the valence band (VBEDOS) . However, this prediction was not confirmed for B1-WN, as epitaxial WN x has been recently found to exhibit excessive electron losses, due to the existence of both cation and anion vacancies, and consequent deviations from stoichiometry, which result in positive values of the real permittivity in the entire visible and UV ranges . On the other hand, B1-MoN was hardly stabilized in the cubic B1 structure so far and a variety of competitive MoN phases exist .…”

Synthesis, Crystal Structures, Mechanical Properties, and Formation Mechanisms of Cubic Tungsten Nitrides

“…Numerous calculations have recently predicted the same thermodynamically stable cubic tungsten mononitride of cP6-WN, which is structurally isotypic with NbO − and can be viewed as a defective cF8-WN with ordered vacant W and N sites (i.e., rocksalt-like phase) (Figure c). Note that rocksalt cF8-WN can readily be experimentally accessible, especially in thin-film forms, , although its stoichiometric sample with a large valence electron concentration (VEC) of 11 is electronically unfavorable due to the overfilling effect of its valence band with a maximum VEC of 10.5. ,− This indicates that the nitrogen deficiency should be intrinsic and occurs randomly in cF8-WN to reach a favorable valence-band filling for stabilizing its structure. , However, due to the challenging sample synthesis and difficulties in probing nitrogen and atomic vacancies, the crystal structures, compositions, and formation mechanisms of these two cubic tungsten nitrides have not yet been clearly elucidated, leading to many ambiguities of their mechanical and thermal properties.…”

Synergistic Effect of WN/Mo2C Embedded in Bioderived Carbon Nanofibers: A Rational Design of a Shuttle Inhibitor and an Electrocatalyst for Lithium–Sulfur Batteries

“…Figure 2i depicts the N 1s spectrum of WMCNFs, where the N−W bond at 396.9 eV further verifies the formation of the WN phase in the composite. 43 Besides, the distinguishable nitrogen species including pyridinic N, pyrrolic N, and graphitic N indicate that the amidogen of CFs can not only serve as the nitrogen source for WN but also be incorporated into the carbon framework to achieve the in situ N-modification.…”