Electronic and thermal signatures of phosphorene grain boundaries under uniaxial strain

in Physical Review Materials (2022), 6(114003),

Two-dimensional materials have great potential for applications as high-performance electronic devices and efficient thermal rectificators. Among them, pristine phosphorene, a single layer of black ... [more ▼]

Two-dimensional materials have great potential for applications as high-performance electronic devices and efficient thermal rectificators. Among them, pristine phosphorene, a single layer of black phosphorus, has shown promising properties such as ultrahigh charge mobility, a tunable band gap, and mechanical flexibility. However, the introduction of extended structural defects such as grain boundaries (GBs) has, in general, a detrimental influence on the electronic and thermal transport properties by causing additional scattering events. In this computational study, based on a combination of a density-functional parametrized tight-binding approach with the Landauer theory of quantum transport, we show that applying a strain can help to partially counteract this effect. We exemplify this by addressing the electronic and phononic transmission of two specific grain boundaries containing 5|7 (GB1) and 4|8 (GB2) defects, respectively. Under uniaxial strain, the electronic band gaps can be reduced for both types of GB, while the respective thermal conductance is only weakly affected despite rather strong changes in the frequency-resolved phonon transmission. The combination of both effects mainly produces an increase of about a factor of 2 in the thermoelectric figure of merit ZT for a GB2 system. Hence, our results provide insights into the manipulation of transport properties as well as the generation of potential thermoelectric materials based on phosphorene. [less ▲]

Native defects in monolayer GaS and GaSe: Electrical properties and thermodynamic stability

in Physical Review Materials (2022), 6(11), 114002

Structural, electronic, and thermodynamic properties of native defects in GaS and GaSe monolayers are investigated by means of accurate ab initio calculations. Based on their charge transition levels we ... [more ▼]

Structural, electronic, and thermodynamic properties of native defects in GaS and GaSe monolayers are investigated by means of accurate ab initio calculations. Based on their charge transition levels we assess the influence of the studied defects on the electrical properties of the monolayers. Specifically, we show that native defects do not behave as shallow dopants and their presence cannot account for the experimentally observed intrinsic doping. In addition, we predict that native defects are efficient compensation and recombination centers. Besides pointing out their detrimental nature, we also calculate the corresponding finite-temperature formation energies and provide a window of growth conditions able to reduce the concentration of all relevant native defects. [less ▲]

Role of higher-order effects in spin-misalignment small-angle neutron scattering of high-pressure torsion nickel

in Physical Review Materials (2021), 5

Revealing defect-induced spin disorder in nanocrystalline Ni

in Physical Review Materials (2021), 5(4), 044409

Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation

in Physical Review Materials (2021), 5(2), 024404

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium ... [more ▼]

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscope allows for local implantation and patterning down to the nanometer resolution, which is of interest for device applications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally by helium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM) study shows that the implantation causes an elongation of the BiFeO3 unit cell and ultimately a transition towards the so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset of amorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phase transition from the R-like to T-like BiFeO3 appears as first-order in character, with regions of phase coexistence and abrupt changes in lattice parameters. [less ▲]

Anisometric mesoscale nuclear and magnetic texture in sintered Nd-Fe-B magnets

in Physical Review Materials (2020), 4

Effect of grain-boundary diffusion process on the geometry of the grain microstructure of Nd−Fe−B nanocrystalline magnets

in Physical Review Materials (2019), 3(084410),

First-principles screening of ABO(3) oxides with two magnetic sublattices

in PHYSICAL REVIEW MATERIALS (2019), 3(6),

Theoretical investigation of lattice thermal conductivity and electrophononic effects in SrTiO3

in PHYSICAL REVIEW MATERIALS (2019), 3(4),

Theoretical study of scattering in graphene ribbons in the presence of structural and atomistic edge roughness

in Physical Review Materials (2019), 3(2), 024001

We investigate the diffusive electron-transport properties of charge-doped graphene ribbons and nanoribbons with imperfect edges. We consider different regimes of edge scattering, ranging from wide ... [more ▼]

We investigate the diffusive electron-transport properties of charge-doped graphene ribbons and nanoribbons with imperfect edges. We consider different regimes of edge scattering, ranging from wide graphene ribbons with (partially) diffusive edge scattering to ribbons with large width variations and nanoribbons with atomistic edge roughness. For the latter, we introduce an approach based on pseudopotentials, allowing for an atomistic treatment of the band structure and the scattering potential, on the self-consistent solution of the Boltzmann transport equation within the relaxation-time approximation and taking into account the edge-roughness properties and statistics. The resulting resistivity depends strongly on the ribbon orientation, with zigzag (armchair) ribbons showing the smallest (largest) resistivity and intermediate ribbon orientations exhibiting intermediate resistivity values. The results also show clear resistivity peaks, corresponding to peaks in the density of states due to the confinement-induced subband quantization, except for armchair-edge ribbons that show a very strong width dependence because of their claromatic behavior. Furthermore, we identify a strong interplay between the relative position of the two valleys of graphene along the transport direction, the correlation profile of the atomistic edge roughness, and the chiral valley modes, leading to a peculiar strongly suppressed resistivity regime, most pronounced for the zigzag orientation. [less ▲]