arXiv subjects

Antoine Dewandre

Publications and source records attributed to Antoine Dewandre.

5 recordsLinked to original sources

arXiv2020

Spontaneous interlayer compression in commensurately stacked van der Waals heterostructures

Interest in layered two dimensional materials, particularly stacked heterostructures of transition metal dichalcogenides, has led to the need for a better understanding of the structural and electronic changes induced by stacking. Here, we investigate the effects of idealized heterostructuring, with periodic commensurate stacking, on the structural, electronic, and vibrational properties, when compared to the counterpart bulk transition metal dichalcogenide. We find that in heterostructures with dissimilar chalcogen species there is a strong compression of the inter-layer spacing, compared to the bulk compounds. This compression of the heterostructure is caused by an increase in the strength of the induced polarization interaction between the layers, but not a full charge transfer. We argue that this effect is real, not due to the imposed commensurability, and should be observable in heterostructures combining different chalcogens. Interestingly, we find that incommensurate stacking of Ti-based dichalcogenides leads to the stabilization of the charge density wave phonon mode, which is unstable in the 1T phase at low temperature. Mixed Ti- and Zr-heterostructures are still unstable, but with a charge density wave or a ferroelectric instability.

cond-mat.mtrl-sci↗

arXiv2019

Spectroscopic properties of few-layer tin chalcogenides

Stable structures of layered SnS and SnSe and their associated electronic and vibrational spectra are predicted using first-principles DFT calculations. The calculations show that both materials undergo a phase transformation upon thinning whereby the in-plane lattice parameters converge to a pseudo-cubic phase, similar to the high-temperature behaviour observed for their bulk counterparts. The electronic properties of layered SnS and SnSe evolve to an almost symmetric dispersion whilst the gap changes from indirect to direct. Characteristic signatures in the phonon dispersion curves and surface phonon states where only atoms belonging to surface layers vibrate can also be observed for these materials.

cond-mat.mtrl-sci↗

arXiv2019

Vibrational and dielectric properties of monolayer transition metal dichalcogenides

First-principles studies of two-dimensional transition metal dichalcogenides have contributed considerably to the understanding of their dielectric, optical, elastic, and vibrational properties. The majority of works to date focus on a single material or physical property. Here we use a single first-principles methodology on the whole family of systems, to investigate in depth the relationships between different physical properties, the underlying symmetry and the composition of these materials, and observe trends. We compare to bulk counterparts to show strong interlayer effects in triclinic compounds. Previously unobserved relationships between these monolayer compounds become apparent. These trends can then be exploited by the materials science, nanoscience, and chemistry communities to better design devices and heterostructures for specific functionalities.

cond-mat.mtrl-sci↗

arXiv2018

Vibrational and dielectric properties of the bulk transition metal dichalcogenides

Interest in the bulk transition metal dichalcogenides for their electronic, photovoltaic, and optical properties has grown and led to their use in many technological applications. We present a systematic investigation of their interlinked vibrational and dielectric properties, using density functional theory and density functional perturbation theory, studying the effects of the spin-orbit interaction and of the long-range e$^-$- e$^-$ correlation as part of our investigation. This study confirms that the spin-orbit interaction plays a small role in these physical properties, while the direct contribution of dispersion corrections is of crucial importance in the description of the interatomic force constants. Here, our analysis of the structural and vibrational properties, including the Raman spectra, compare well to experimental measurement. Three materials with different point groups are showcased and data trends on the full set of fifteen existing hexagonal, trigonal, and triclinic materials are demonstrated. This overall picture will enable the modeling of devices composed of these materials for novel applications.

cond-mat.mtrl-sci↗

arXiv2017

Origin of the Counterintuitive Dynamic Charge in the Transition-Metal Dichalcogenides

We investigate the chemical bonding characteristics of the transition metal dichalcogenides based on their static and dynamical atomic charges within Density Functional Theory. The dynamical charges of the trigonal transition metal dichalcogenides are anomalously large, while in their hexagonal counterparts, their sign is even counterintuitive i.e. the transition metal takes the negative charge. This phenomenon cannot be understood simply in terms of a change in the static atomic charge as it results from a local change of polarization. We present our theoretical understanding of these phenomena based on the perturbative response of the system to a static electric field and by investigating the hybridization of the molecular orbitals near the Fermi level. Furthermore, we establish a link between the sign of the Born effective charge and the $π$-backbonding in organic chemistry and propose an experimental procedure to verify the calculated sign of the dynamical charge in the transition metal dichalcogenides.

cond-mat.mtrl-sci↗