Nano Science Seminar: Atomic scale growth and investigation of novel 2D materials
e-mail: hasegawa@issp.u-tokyo.ac.jp
Modifying bulk surfaces by metal deposition is well established method to create low dimensional materials for fundamental studies of quantum properties. However, the confinement to materials surfaces, makes it challenging to integrate these materials into devices. In contrast to bulk surfaces, van der Waals materials are stable as free-standing 2D sheets in various environments and can be readily manipulated and integrated with other materials. Here we explore if such 2D transition metal dichalcogenides can be modified by metal deposition (similar to bulk surfaces) to create nanostructures with new properties.
2D materials are lacking dangling bonds and thus unlike bulk surfaces, are considered to interact weakly with metal atoms and thus are assumed to favor the agglomeration of atoms into clusters on their surface. Here we show that for some transition metal dichalcogenides (TMDs) this notion of a weak interaction of vapor deposited metals on TMDs is not always true and their 2D-crystal structure can be modified by reaction with vapor deposited metals. We discuss this on the example of two different TMDs, semiconducting Mo-dichalcogenides and semi-metallic PtTe2. For the former we show that Mo-deposition results in the formation of metallic 1D line-defect networks and we discuss the underlying materials physics of their formation [1]. Moreover, the 1D electronic nature of these defects, embedded in the semiconducting host material, is confirmed by angle resolved photoemission spectroscopy that shows signatures of a Tomonaga Luttinger liquid [2]. The modification of MoSe2 can also be expanded to hetero-atoms and these may induce magnetism in the material, forming a diluted ferromagnetic 2D-semiconductor [3]. Finally, for PtTe2 we show that Pt-deposition converts the 2D-PtTe2 (ditelluride) into metastable 2D-PtTe (monotelluride) [4]. In the monolayer, this enables the construction of a metal/semiconductor junction in 2D materials, whose interface properties can be studied by scanning tunneling spectroscopy.
[1] P.M. Coelho, H.-P. Komsa, H.C. Diaz, Y. Ma, A.V. Krasheninnikov, M. Batzill. Post-Synthesis Modifications of Two-Dimensional MoSe2 or MoTe2 by Incorporation of Excess Metal Atoms into the Crystal Structure. ACS Nano 12, 3975-3984 (2018)[2] Y. Ma, H.C. Diaz, J. Avila, C. Chen, V. Kalappattil, R. Das, M.-H. Phan, T. Čadež, J.M.P. Carmelo, M. C Asensio, M. Batzill. Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe2 grain boundary. Nat. Commun. 8, 14231 (2017)
[3] P.M. Coelho, H.‐P. Komsa, K. Lasek, V. Kalappattil, J. Karthikeyan, M.‐H. Phan, A.V. Krasheninnikov, M. Batzill. Room‐Temperature Ferromagnetism in MoTe2 by Post‐Growth Incorporation of Vanadium Impurities. Adv. Electr. Mater. 5, 1900044 (2019).
[4] K. Lasek, M. Ghorbani-Asl, V. Pathirage, A.V. Krasheninnikov, M. Batzill. Controlling Stoichiometry in Ultrathin van der Waals Films: PtTe2, Pt2Te3, Pt3Te4, and Pt2Te2. ACS Nano doi.: 10.1021/acsnano.2c04303 (2022).