Epitaxial Growth of Ultrathin δ-Like ΜοΝ Films on Ru(0001)

Khaniya, Asim; Kaden, William E.

doi:10.1007/s11244-019-01198-7

Cited by 2 publications

(1 citation statement)

References 59 publications

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“…Several groups have successfully demonstrated different approaches allowing for the controllable synthesis of various phase-pure molybdenum nitride structures. − Of particular interest to this paper is the recent work of Khaniya and Kaden, which reports the epitaxial growth of MoN films on Ru(0001) via an ion-assisted and physical vapor deposition approach. The films produced in that work appear ripe for direct comparisons between surface-science experiments and density functional theory (DFT) predictions due to their single-crystalline and atomically planar terminations, which exhibit a long-range order and elemental stoichiometry compatible with δ-MoN(0001).…”

Section: Introductionmentioning

confidence: 99%

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

2022

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In this work, we employed density functional theory to elucidate the energetics associated with elementary steps along a Langmuir–Hinshelwood mechanism for the Haber–Bosch synthesis of ammonia from N2 and H2 on a hexagonal, Mo-terminated molybdenum nitride surface. Using nudged elastic band calculations, we determined the energy barriers involved in the reaction processes. An active site consisting of four nearest-neighbor Mo atoms, previously identified as an active site on similar surfaces, was chosen to investigate the reaction processes. Using this approach, we calculate a barrier of ∼0.5 eV for the dissociation of N2. The superior activity of the dissociation of the strong N2 bonds is rationalized based on the unique geometric and electronic configurations present at these active sites. Despite the favorable energetics for nitrogen dissociation, the energy cost for hydrogenation of NH x (0 ≤ x ≤ 2) species is shown to be energetically limiting for the formation of ammonia through the Langmuir–Hinshelwood mechanism at these sites, with elementary step activation barriers calculated to be as large as ∼2 eV. A comparison to Haber–Bosch results derived from a similar γ-Mo2N model system suggests the relative independence of surface chemistry and bulk stoichiometry for rhombic Mo4 active sites present on molybdenum nitrides.

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Section: Introductionmentioning

confidence: 99%

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

2022

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Wafer-scale development, characterization, and high temperature stabilization of epitaxial Cr2O3 films grown on Ru(0001)

Cumston,

Patrick,

Hegazy

et al. 2024

The Journal of Chemical Physics

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This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5–20 nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4 mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru–Cr2O3–Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions.

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Epitaxial Growth of Ultrathin δ-Like ΜοΝ Films on Ru(0001)

Cited by 2 publications

References 59 publications

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

Wafer-scale development, characterization, and high temperature stabilization of epitaxial Cr2O3 films grown on Ru(0001)

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