Atomistic mechanisms underlying plasticity and crack growth in ceramics: a case study of AlN/TiN superlattices

We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1−xAlxN (0 ≤ x ≤ 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the model’s predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of ≈40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1−xAlxN (0 < x < 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.

Semi-Empirical Force-Field Model for the Ti1−xAlxN (0 ≤ x ≤ 1) System

Transition metal nitrides such as TiN and ZrN have a potential use as back electrodes in Cu(In,Ga)S or Cu(In,Ga)Se solar cells. Important properties of the back electrode are its conductivity, reflection at higher wavelengths, mechanical and chemical stability, and its barrier properties for impurity diffusion when metal foils are used as flexible substrate for the solar cells. Here, TiN thin films were deposited with reactive magnetron sputtering and were characterized with Rutherford backscattering spectroscopy, X-ray reflection, ellipsometry and UV-Vis-NIR optical spectroscopy. The resulting thin film density and optical reflection were characterized and compared to the particle fluxes towards the substrate. Therefore, the total momentum flux, total energy flux and momentum flux of target species towards the growing film were measured or simulated. A distinct relation between the density and optical reflection of the TiN films and the momentum flux of target species towards the substrate is shown. © 2011 Elsevier Ltd.

https://biblio.ugent.be/publication/1225519/file/1225527.pdf

Sputter deposited transition metal nitrides as back electrode for CIGS solar cells

We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom ($\mathrm{T}{\mathrm{i}}_{\mathrm{ad}}$) migration on, and descent from, square $\mathrm{TiN}\ensuremath{\langle}100\ensuremath{\rangle}$ epitaxial islands on TiN(001) at temperatures ($T$) ranging from 1200 to 2400 K. Adatom-descent energy barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for $\mathrm{T}{\mathrm{i}}_{\mathrm{ad}}$ descent via direct hopping vs push-out/exchange with a Ti island-edge atom for $T\ensuremath{\ge}1500\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We demonstrate that this effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push-out/exchange reaction pathway.

/pdf/effects-of-surface-vibrations-on-interlayer-mass-transport-3a1zgsyv8q.pdf

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results show that the CD method extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for $T$ close to the melting point ${T}_{m}$, up to 33 000 for $T\ensuremath{\approx}0.7\phantom{\rule{0.16em}{0ex}}{T}_{m}$.

/pdf/nonequilibrium-ab-initio-molecular-dynamics-determination-of-1yywd551qy.pdf

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN

Ti, Al and N adatom adsorption and diffusion on rocksalt cubic AlN (001) and (011) surfaces: Ab initio calculations

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Ti, Al and N adatom adsorption and diffusion on rocksalt cubic AlN (001) and (011) surfaces: Ab initio calculations