Two-Dimensional Transition Metal Dichalcogenides under Electron Irradiation: Defect Production and Doping

Hannu-Pekka Komsa, Jani Kotakoski, Simon Kurasch, Ossi Lehtinen, Ute Kaiser, and Arkady V. Krasheninnikov

Phys. Rev. Lett. 109, 035503 – Published 17 July 2012

Abstract

Using first-principles atomistic simulations, we study the response of atomically thin layers of transition metal dichalcogenides (TMDs)—a new class of two-dimensional inorganic materials with unique electronic properties—to electron irradiation. We calculate displacement threshold energies for atoms in 21 different compounds and estimate the corresponding electron energies required to produce defects. For a representative structure of ${MoS}_{2}$ , we carry out high-resolution transmission electron microscopy experiments and validate our theoretical predictions via observations of vacancy formation under exposure to an 80 keV electron beam. We further show that TMDs can be doped by filling the vacancies created by the electron beam with impurity atoms. Thereby, our results not only shed light on the radiation response of a system with reduced dimensionality, but also suggest new ways for engineering the electronic structure of TMDs.

Received 7 May 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.035503

Authors & Affiliations

Hannu-Pekka Komsa¹, Jani Kotakoski^1,2, Simon Kurasch³, Ossi Lehtinen¹, Ute Kaiser³, and Arkady V. Krasheninnikov^1,4

¹Department of Physics, University of Helsinki, P.O. Box 43, 00014 Helsinki, Finland
²Department of Physics, University of Vienna, Boltzmanngasse 5, 1190 Wien, Austria
³Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, University of Ulm, 89081 Ulm, Germany
⁴Department of Applied Physics, Aalto University, P.O. Box 11100, 00076 Aalto, Finland

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 109, Iss. 3 — 20 July 2012

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) The setup used in the dynamical DFT simulations of atom sputtering from TMDs under electron irradiation. Initial energy acquired due to the impact of an energetic electron was assigned to the recoil atom, then DFT molecular dynamics was used to model the evolution of the system. (b) ${MoS}_{2}$ sheet with a S vacancy. The charge densities of the occupied and unoccupied defect states are visualized by transparent (blue) and solid (red) isosurfaces, respectively.Reuse & Permissions
Figure 2
Displacement threshold energies $T_{d}$ obtained from DFT molecular dynamics calculations (crosses) and formation energies of chalcogen vacancies with nonrelaxed (dashed lines) and relaxed (solid lines) geometries in transition metal dichalcogenides ${MeX}_{2}$ , $X = S$ , Se, Te.Reuse & Permissions
Figure 3
Cross section for sputtering a sulfur atom from ${MoS}_{2}$ , ${WS}_{2}$ , and ${TiS}_{2}$ sheets as calculated through the McKinley-Feshbach formalism and the dynamical values of the displacement thresholds. Dotted lines are the data for the static lattice, and solids lines are the results of calculations where lattice vibrations are taken into account, assuming a Maxwell-Boltzmann velocity distribution. The cross denotes the experimentally determined cross section for ${MoS}_{2}$ . The inset shows the same data for a larger range of electron energies.Reuse & Permissions
Figure 4
AC HR-TEM images of single-layer ${MoS}_{2}$ . Atoms are dark and white spots correspond to the holes in the hexagonal structure. During continuous 80 keV electron irradiation, a crack formed in the membrane (a). The edges are terminated with Mo atoms, as can be determined from the contrast in the inset. Also an increasing number of S vacancies is observed. Most of them are single vacancies but also double vacancies, where the top and bottom S atoms are removed, can be found. Structure models and corresponding HR-TEM image simulations for both vacancy types are shown in (b),(d) for the single and (c),(e) for the double vacancy. Experimental examples are shown in (f). To enhance the visibility of the defect, a Gaussian filter ( $0.7 Å$ FWHM) was applied to (d), (e), and (f). Scale bars are 5 nm (a) and $5 Å$ (f).Reuse & Permissions
Figure 5
(a) Substitution energies of the impurity atoms in ${MoS}_{2}$ layer calculated for three different chemical potentials: isolated atoms (plus, blue), diatomic molecules (dot, red), and molecules with hydrogen (cross, green). The solid phase reference is also given for carbon and silicon (black). (b) Respective local density of states of the impurity atoms, the spin-up and spin-down components. The gray areas denote the band edges of the ${MoS}_{2}$ layer. (c)–(e) Series of AC HR-TEM images demonstrating vacancy filling. The left arrow (red) highlights an initial S vacancy that picks up an atom between (d) and (e), and the right arrow (green) indicates a S atom that is sputtered away between (c) and (d), forming a single vacancy.Reuse & Permissions

Physical Review Letters