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Novel 2D interfaces with silicon, graphene, MoTe2 and Ca2N

ʷ: Two-dimensional (2D) interfaces with diverse three-dimensional materials' contact have long been an issue familiar to scientists and engineers. These days, together with 2D materials and emerging 1D edge contact, the 2D interfaces are attracting renewed interests for various applications such as next-generation devices. In particular, polymorph engineering in group 6 TMDs, such as MX2 with M=(Mo, W) and X=(S, Se, Te), has allowed an intriguing theme in the interface science, a formation of homojunction in a single material.
 In this talk, I will briefly review interesting features of 2D interface including graphene [1]. Then, homojunctions between metallic (1T') and semiconducting (2H) MoTe2, generated by two methods (laser irradiation and contacting to low work function material), will be discussed [2]. The synthesis of high quality MoTe2 has been a key for these studies [3, 4]. We demonstrate that our high quality single-crystalline and semimetallic 1T'-MoTe2 exhibits a maximum carrier mobility of 4,000 cm2V-1s-1 and a giant magnetoresistance of 16,000% in a magnetic field of 14 Tesla at 1.8 Kelvin in the bulk form, and the few-layered 1T-MoTe2 reveals a bandgap of up to 60 meV in its monoclinic form. The small energy difference between 2H and 1T'-MoTe2, resulting in the presence of the two polymorphs, is also used for a novel way of structural phase transition, contact-driven phase change. Extremely low work function of Ca2N, ~2.3 eV, realizes a large charge transfer that can switch the material's symmetry in a long range of ~100 nm. These interface studies suggest novel contact-based 2D materials design and applications.
[1] Heejun Yang et al., Science 336, 1140 (2012).
[2] S. Cho et al., Science 349, 625 (2015).
[3] D. H. Keum et al., Nature Physics 11, 482 (2015).
[4] Heejun Yang et al., Nature Physics 13, 931 (2017)