Seminar given by Dr. Hannu-PekkaKomsa from the Department of Applied Physics of Aalto University, Finland
Time: 10:00-11:00 am on November 9th (Wednesday), 2016
Place: Room 318, No. 11 Teaching Blding
Coordinator: Dr. Chuanhong Jin
TITLE: Defects in 2D materials: their production under irradiation, evolution, and properties from first principles
ABSTRACT:
Two-dimensional (2D) materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides (TMDs) have recently received lots of attention due to their unique properties and numerous potential applications. All these materials have defects, which naturally affect their characteristics. Moreover, defects and impurities can deliberately be introduced by irradiation or chemical treatment to tailor the properties of these systems.
In my talk, I will present the results of our first-principles theoretical studies of defects in 2D systems, compare them to the experimental transmission electron microscopy data, and discuss how defect and impurities can be used to engineer the electronic structure of 2D materials. Specifically, we showed that vacancies in TMDs produced by the electron beam agglomerate and form line structures, which can be used for engineering material properties [2,8]. In some chalcogen-deficient TMDs, rotational defects appear under electron beam [4], which eventually give rise to formations of new grains inside the material. We further demonstrated that TMDs can be doped by filling the vacancies with impurity atoms or introducing impurities during the growth stage [1,3].
We also studied the atomic scale morphology of non-stoichiometric TMD MoSe(2−x) and showed that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains [5]. Using density functional theory calculations, we further demonstrated that MTBs are thermodynamically stable structures in Se-deficient sheets. These line defects host localized states close to the valence band minimum thus giving rise to enhanced conductance along straight MTBs.
On the other hand, in 2D materials with anisotropic atomic structure, defect stability and dynamics can present distinct features. For instance, in ReS2 the vacancies are seen to be preferentially produced at certain chalcogen sites [6]. These sites, located between the Re diamond chains, also exhibit lowest formation energy. Finally, we computationally predicted the irradiation stability of pristine phosphorene, traced the first steps in damage evolution, and studied the defect dynamics [7].
[1] H-P. Komsa, J. Kotakoski, S. Kurasch, O. Lehtinen, U. Kaiser, and A. V. Krasheninnikov, Phys. Rev. Lett. 109, 035503 (2012).
[2] H.-P. Komsa, S. Kurasch, O. Lehtinen, U. Kaiser, and A. V. Krasheninnikov, Phys. Rev. B 88, 035301 (2013).
[3] Y.-C. Lin, D.O. Dumcenco, H.-P. Komsa, Y. Niimi, A.V. Krasheninnikov, Y.-S. Huang, and K. Suenaga, Advanced Materials 26, 2857 (2014).
[4] Y.-C. Lin, T. Björkman, H.-P. Komsa, F.-S. Huang, C.-H. Yeh, K.-H. Lin, J. Jadczak, Y.-S. Huang, P.-W. Chiu, A. V. Krasheninnikov, K. Suenaga, Three-fold rotational defects in two-dimensional transition metal dichalcogenides, Nature Commun. 6, 6737 (2015).
[5] O. Lehtinen, H.-P. Komsa, A. Pulkin, M.B. Whitwick, M.-W. Chen, O.V. Yazyev, A. Kis, U. Kaiser, and A.V. Krasheninnikov, ACS Nano 9, 3274 (2015).
[6] Y.-C. Lin, H.-P. Komsa, C.-H. Yeh, T. Björkman, Z.-Y. Liang, C.-H. Ho, Y.-S. Huang, P.-W. Chiu, A. V. Krasheninnikov, K. Suenaga, Single-Layer ReS 2 : Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy, ACS Nano 9, 11249 (2015).
[7] V. Vierimaa, A. V. Krasheninnikov, H.-P. Komsa, Phosphorene under electron beam: from monolayer to one-dimensional chains, Nanoscale 8, 7949 (2016)
In my talk, I will present the results of our first-principles theoretical studies of defects in 2D systems, compare them to the experimental transmission electron microscopy data, and discuss how defect and impurities can be used to engineer the electronic structure of 2D materials. Specifically, we showed that vacancies in TMDs produced by the electron beam agglomerate and form line structures, which can be used for engineering material properties [2,8]. In some chalcogen-deficient TMDs, rotational defects appear under electron beam [4], which eventually give rise to formations of new grains inside the material. We further demonstrated that TMDs can be doped by filling the vacancies with impurity atoms or introducing impurities during the growth stage [1,3].
We also studied the atomic scale morphology of non-stoichiometric TMD MoSe(2−x) and showed that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains [5]. Using density functional theory calculations, we further demonstrated that MTBs are thermodynamically stable structures in Se-deficient sheets. These line defects host localized states close to the valence band minimum thus giving rise to enhanced conductance along straight MTBs.
On the other hand, in 2D materials with anisotropic atomic structure, defect stability and dynamics can present distinct features. For instance, in ReS2 the vacancies are seen to be preferentially produced at certain chalcogen sites [6]. These sites, located between the Re diamond chains, also exhibit lowest formation energy. Finally, we computationally predicted the irradiation stability of pristine phosphorene, traced the first steps in damage evolution, and studied the defect dynamics [7].
[1] H-P. Komsa, J. Kotakoski, S. Kurasch, O. Lehtinen, U. Kaiser, and A. V. Krasheninnikov, Phys. Rev. Lett. 109, 035503 (2012).
[2] H.-P. Komsa, S. Kurasch, O. Lehtinen, U. Kaiser, and A. V. Krasheninnikov, Phys. Rev. B 88, 035301 (2013).
[3] Y.-C. Lin, D.O. Dumcenco, H.-P. Komsa, Y. Niimi, A.V. Krasheninnikov, Y.-S. Huang, and K. Suenaga, Advanced Materials 26, 2857 (2014).
[4] Y.-C. Lin, T. Björkman, H.-P. Komsa, F.-S. Huang, C.-H. Yeh, K.-H. Lin, J. Jadczak, Y.-S. Huang, P.-W. Chiu, A. V. Krasheninnikov, K. Suenaga, Three-fold rotational defects in two-dimensional transition metal dichalcogenides, Nature Commun. 6, 6737 (2015).
[5] O. Lehtinen, H.-P. Komsa, A. Pulkin, M.B. Whitwick, M.-W. Chen, O.V. Yazyev, A. Kis, U. Kaiser, and A.V. Krasheninnikov, ACS Nano 9, 3274 (2015).
[6] Y.-C. Lin, H.-P. Komsa, C.-H. Yeh, T. Björkman, Z.-Y. Liang, C.-H. Ho, Y.-S. Huang, P.-W. Chiu, A. V. Krasheninnikov, K. Suenaga, Single-Layer ReS 2 : Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy, ACS Nano 9, 11249 (2015).
[7] V. Vierimaa, A. V. Krasheninnikov, H.-P. Komsa, Phosphorene under electron beam: from monolayer to one-dimensional chains, Nanoscale 8, 7949 (2016)
[8] E. Sutter, Y. Huang, H.-P. Komsa, M. Ghorbani-Asl, A. V. Krasheninnikov, P. Sutter, Electron-Beam Induced Transformations of Layered Tin Dichalcogenides, Nano Lett. 16, 4410 (2016)
