Dr. Arkady Krashenninikov,
Department of Applied Physics,
Aalto University, Finland
and Department of Physics, University of Helsinki, Finland

Abstract

Native and irradiation-induced defects in two-dimensional materials:
graphene, boron-nitride, transition metal dichacolgenides,
and silica

Isolation of a single sheet of graphene indicated that strictly two-dimensional (2D) materials can exist at finite temperatures. Indeed, inorganic 2D systems such as hexagonal BN sheets, transition metal dichalcogenides (TMD) with a common structural formula MeX₂, where Me stands for transition metals (Mo, W, Ti, etc.), X for chalcogens (S, Se, Te), and SiO₂ layers were later manufactured by various methods. All these materials have defects, which naturally affect their properties. Moreover, defects can deliberately be introduced by ion and electron irradiation to tailor the properties of the system [1].

In my talk, I will summarize our knowledge about defects [2] in graphene and other 2D materials. I will also touch upon defect production in 2D systems under impacts of energetic ions [3] and electrons [4,7] and present theoretical data obtained in collaboration with several experimental groups [3,6]. I will also dwell upon defect-mediated engineering of the electronic structure of 2D materials such as BN [5] or TMDs [7]. 

Besides, I will discuss mixed TMDs, such as MoS_2x Se_2(1?x), which can be referred to as 2D random alloys [8]. Our simulations indicate 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 that the direct gap in these material can continuously be tuned. I will further present advanced first-principles calculations of the electronic structure of TMDs [9].

1. A.V. Krasheninnikov and F. Banhart, Nature Materials, 6 (2007) 723.
2. F. Banhart, J. Kotakoski and A. V. Krasheninnikov, ACS Nano, 5 (2011) 26.
3. M. Kalbac, et al., Advanced Materials 25 (2013) 1004.
4. J.C. Meyer, et al., Phys. Rev. Lett. 108 (2012) 196102.
5. N. Berseneva, A. V. Krasheninnikov, and R.M. Nieminen, Phys. Rev. Lett. 107 (2011) 035501.
6. R. R. Nair, et al., Nature Physics 8 (2012) 199.
7. H.-P. Komsa, et al., Phys. Rev. Lett. 109 (2012) 035503.
8. H.-P. Komsa and A. V. Krasheninnikov,  J. Phys. Chem. Lett. 3 (2012) 3652. 
9. H.-P. Komsa and A. V. Krasheninnikov, Phys. Rev. B (Rapid Comm.) 86 (2012) 241201.