31 research outputs found
Giant spin-orbit splitting of point defect states in monolayer WS
The spin-orbit coupling (SOC) effect has been known to be profound in
monolayer pristine transition metal dichalcogenides (TMDs). Here we show that
point defects, which are omnipresent in the TMD membranes, exhibit even
stronger SOC effects and change the physics of the host materials drastically.
In this Article we chose the representative monolayer WS\sub{2} slabs from the
TMD family together with seven typical types of point defects including
monovacancies, interstitials, and antisites. We calculated the formation
energies of these defects, and studied the effect of spin-orbit coupling (SOC)
on the corresponding defect states. We found that the S monovacancy (V\sub{S} )
and S interstitial (adatom) have the lowest formation energies. In the case of
V\sub{S} and both of the W\sub{S and W\sub{S2} antisites, the defect states
exhibit giant splitting up to 296 meV when SOC is considered. Depending on the
relative position of the defect state with respect to the conduction band
minimum (CBM), the hybrid functional HSE will either increase the splitting by
up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close
to CBM). Furthermore, we found that both the W\sub{S} and W\sub{S2} antisites
possess a magnetic moment of 2 localized at the antisite W atom and
the neighboring W atoms. All these findings provide new insights in the defect
behavior under SOC point to new possibilities for spintronics applications for
TMDs.Comment: 8 pages, 6 figure
The role of point defects in PbS, PbSe and PbTe: a first principles study
Intrinsic defects are of central importance to many physical and chemical processes taking place in compound nanomaterials, such as photoluminescence, accommodation of off-stoichiometry and cation exchange. Here, the role of intrinsic defects in the above mentioned processes inside rock salt (RS) lead chalcogenide systems PbS, PbSe and PbTe (PbX) was studied systematically using first principles density functional theory. Vacancy, interstitial, Schottky and Frenkel defects were considered. Rock salt PbO was included for comparison. The studied physical properties include defect formation energy, local geometry relaxation, Bader charge analysis, and electronic structure. The defect formation energies show that monovacancy defects and Schottky defects are favoured over interstitial and Frenkel defects. Schottky dimers, where the cation vacancy and anion vacancy are adjacent to each other, have the lowest defect formation energies at 1.27 eV, 1.29 eV and 1.21 eV for PbS, PbSe and PbTe, respectively. Our results predict that a Pb monovacancy gives rise to a shallow acceptor state, while an X vacancy generates a deep donor state, and Schottky defects create donor-acceptor pairs inside the band gap. The surprisingly low formation energy of Schottky dimers suggests that they may play an important role in cation exchange processes, in contrast to the current notion that only single point defects migrate during cation exchange
The accurate calculation of the band gap of liquid water by means of GW corrections applied to plane-wave density functional theory molecular dynamics simulations
Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For simulations of phase transformations and chemical reactions in water or aqueous solutions whereby an accurate description of the electronic structure is required, we suggest to use these advanced GW corrections in combination with the statistical analysis of quantum mechanical MD simulations
The accurate calculation of the band gap of liquid water by means of GW corrections applied to plane-wave density functional theory molecular dynamics simulations
MvH acknowledges a VIDI grant from the Dutch Science Foundation NWO. JK was supported by the Austrian Science Fund (FWF) within the SFB ViCoM (Grant F 41)
Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth
Here,
we show a novel solid–solid–vapor (SSV) growth
mechanism whereby epitaxial growth of heterogeneous semiconductor
nanowires takes place by evaporation-induced cation exchange. During
heating of PbSe-CdSe nanodumbbells inside a transmission electron
microscope (TEM), we observed that PbSe nanocrystals grew epitaxially
at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis
of atomic-resolution TEM observations and detailed atomistic simulations
reveals that the growth process is mediated by vacancies
Kansalliskirjaston sanomalehtiaineistot: käyttäjät ja tutkijat kesällä 2018
Here,
we show a novel solid–solid–vapor (SSV) growth
mechanism whereby epitaxial growth of heterogeneous semiconductor
nanowires takes place by evaporation-induced cation exchange. During
heating of PbSe-CdSe nanodumbbells inside a transmission electron
microscope (TEM), we observed that PbSe nanocrystals grew epitaxially
at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis
of atomic-resolution TEM observations and detailed atomistic simulations
reveals that the growth process is mediated by vacancies