arXiv subjects

Paul H. Mayrhofer

Publications and source records attributed to Paul H. Mayrhofer.

22 records · Page 2Linked to original sources

arXiv2012

Surface energies of AlN allotropes from first principles

In this Letter we present first principle calculation of surface energies of rock-salt (B1), zinc-blende (B3), and wurtzite (B4) AlN allotropes. Out of several low-index facets, the highest energies are obtained for mono-atomic surfaces (i.e. only by either Al or N atoms): $γ_{\{111\}}^{\rm B1}=410\uu{meV/Å}^2$, $γ_{\{100\}}^{\rm B3}=346\uu{meV/Å}^2$, $γ_{\{111\}}^{\rm B3}=360\uu{meV/Å}^2$, and $γ_{\{0001\}}^{\rm B4}=365\uu{meV/Å}^2$. The difference between Al- and N-terminated surfaces in these cases is less then $20\uu{meV/Å}^2$. The stoichiometric facets have energies lower by $100\uu{meV/Å}^2$ or more. The obtained trends could be rationalised by a simple nearest-neighbour broken-bond model.

cond-mat.mtrl-sci↗

arXiv2012

First principles study of water-based self-assembled nanobearing effect in CrN/TiN multilayer coatings

Recently, we have reported on low friction CrN/TiN coatings deposited using a hybrid sputtering technique. These multilayers exhibit friction coefficients $μ$ below 0.1 when tested in atmosphere with a relative humidity $\approx25%$, but $μ$ ranges between 0.6-0.8 upon decreasing the humidity below 5%. Here we use first principle calculations to study O and H adatom energetics on TiN and CrN (001) surfaces. The diffusional barrier of H on TiN(001) is about half of the value on CrN(001) surface, while both elements are stronger bonded on CrN. Based on these results we propose a mechanism for a water-based self-assembled nanobearing.

cond-mat.mtrl-sci↗

arXiv2012

Towards predictive modelling of near-edge structures in electron energy loss spectra of AlN based ternary alloys

Although electron energy loss near edge structure analysis provides a tool for experimentally probing unoccupied density of states, a detailed comparison with simulations is necessary in order to understand the origin of individual peaks. This paper presents a density functional theory based technique for predicting the N K-edge for ternary (quasi-binary) nitrogen alloys by adopting a core hole approach, a methodology that has been successful for binary nitride compounds. It is demonstrated that using the spectra of binary compounds for optimising the core hole charge ($0.35\,\mathrm{e}$ for cubic Ti$_{1-x}$Al$_x$N and $0.45\,\mathrm{e}$ for wurtzite Al$_x$Ga$_{1-x}$N), the predicted spectra evolutions of the ternary alloys agree well with the experiments. The spectral features are subsequently discussed in terms of the electronic structure and bonding of the alloys.

cond-mat.mtrl-sci↗

arXiv2011

Trends in the elastic response of binary early transition metal nitrides

Motivated by an increasing demand for coherent data that can be used for selecting materials with properties tailored for specific application requirements, we studied elastic response of nine binary early transition metal nitrides (ScN, TiN, VN, YN, ZrN, NbN, LaN, HfN, and TaN) and AlN. In particular, single crystal elastic constants, Young's modulus in different crystallographic directions, polycrystalline values of shear and Young's moduli, and the elastic anisotropy factor were calculated. Additionally, we provide estimates of the third order elastic constants for the ten binary nitrides.

cond-mat.mtrl-sci↗