2D Transition-Metal Dichalcogenides: Doping, Alloying and Electronic Structure Engineering

Séminaire du département de physique concernant les propriétés de matériaux bi-dimensionnels qui pourraient concurrencer le graphène dans un certain nombre de domaines d'application.

Following isolation of a single sheet of graphene, many other 2D systems were manufactured. Among them, single transition metal dichalcogenides (TMD) sheets have received a particular attention, as these materials exhibit intriguing electronic, optical and mechanical properties which can controlled be by varying material composition.  Moreover, the properties can further be tuned by introduction of defects and impurities.

In this talk, I will present the results of our first-principles theoretical studies of the response of 2D TMDs to electron irradiation obtained in collaboration with several experimental groups [1-3].  We showed that vacancies produced by the electron beam agglomerate and form line structures, which can be used for engineering material properties [2]. We also assessed the radiation hardness of 2D TMD systems [1]. We further showed that TMDs can be doped by filling the vacancies with impurity atoms or introducing impurities during the growth stage [3]. We also studied the stability and electronic properties of single layers of mixed TMDs, such as MoS2x Se2(1−x), which can be referred to as 2D random alloys [4]. We demonstrated that 2D mixed ternary MoS2/MoSe2/MoTe2 compounds are thermodynamically stable at room temperature, so that such materials can be manufactured by CVD or exfoliation techniques as confirmed now by several experimental groups. By applying the effective band theory approach we showed that the direct gap in these material can continuously be tuned. Using GW first-principles calculations for few-layer and bulk MoS2, we investigated [5] the effects of quantum confinement on the electronic and optical structure of this layered material and effects of the environment [6]. By solving the Bethe-Salpeter equation, we evaluated the exciton energy in these systems which dramatically increases from 0.1 eV in the bulk MoS2 to about 1 eV in the monolayer.  The fundamental band gap increases as well, so that the optical transition energies remain nearly constant.

I will finally touch upon defects in bilayer 2D silica [7] and show that defects are strikingly similar to those in graphene with their morphology governed by the hexagonal symmetry of the lattice [8-9].
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1. H.-P. Komsa, J. Kotakoski, S. Kurasch, O. Lehtinen, U. Kaiser, and  A.V. Krasheninnikov, Phys. Rev. Lett. 109 (2012)  035503.
2. H.-P. Komsa, S. Kurasch, O. Lehtinen, U. Kaiser, and A.V. Krasheninnikov, Phys. Rev. B 88 (2013) 035301.
3. Y.-C. Lin, D.O. Dumcenco, H.-P. Komsa, Y. Niimi, A.V. Krasheninnikov, Y.-S. Huang, and K. Suenaga, Advanced Materials (2014) in press.
4. H.-P. Komsa and A.V. Krasheninnikov, J. Phys. Chem. Lett. 3 (2012) 3652.
5. H.-P. Komsa and A.V. Krasheninnikov, Phys. Rev. B (Rapid Comm.) 86 (2012) 241201.
6. H.-P. Komsa and A.V. Krasheninnikov, Phys. Rev. B 88 (2013) 085318.
7. P. Y. Huang, et al., Nano Letters 12 (2012) 1081.
8. T. Björkman, S. Kurasch, O. Lehtinen, J. Kotakoski, O.Yazyev, A. Srivastava, V. Skakalova, J. Smet, U. Kaiser, and A.V. Krasheninnikov, Scientific Reports 3 (2013) 3482.
9. F. Ben Romdhane, T. Bjorkman, J.A. Rodrıguez-Manzo, O. Cretu, A.V. Krasheninnikov, and F. Banhart, ACS Nano 7 (2013) 5175.

Contact : Ph. Lambin - philippe.lambin@unamur.be
Télecharger : vCal