Electron, phonon, and interfacial transport in 2D materials and heterostructures*

This talk will present recent highlights from our research on two-dimensional (2D) materials. Results span from fundamental measurements and simulations, to applications taking advantage of unusual 2D material properties. We measured record velocity saturation in graphene [1], and the thermal properties of graphene nanoribbons [2]. We have also grown monolayer 2D semiconductors by CVD over large areas, including MoS₂ [3], WSe₂, MoSe₂ [4], and multilayer MoTe₂ and WTe₂ [5]. ZrSe₂ and HfSe₂ have native high-K dielectrics ZrO₂ and HfO₂, which are of key technological relevance [6]. Improving electrical contacts [7], we demonstrated 10 nm transistors using monolayer MoS₂, with the highest current reported to date (>400 µA/µm), near ballistic limits [8]. Current density in such 2D devices is ultimately limited by self-heating and phonon scattering [9], in part due to the weak van der Waals bonds between 2D materials and their environment, which lead to a large thermal resistance of this interface [10]. On the other hand, we exploited this weak interface to improve energy efficiency in phase-change memory [11], and we tuned it by Li intercalation, demonstrating MoS₂-based thermal transistors [12]. These studies reveal fundamental limits and some applications of 2D materials, taking advantage of their unique properties.

[1] M. Yamoah, et al., ACS Nano 11, 9914 (2017). [2] M.-H. Bae et al., Nature Comm. 4, 1734 (2013). [3] K. Smithe et al., ACS Nano 11, 8456 (2017). [4] K. Smithe et al., ACS AMI 1, 572 (2018). [5] M. Mleczko et al., ACS Nano 10, 7507 (2016). [6] M. Mleczko et al., Science Adv. 3, e1700481 (2017). [7] C. English et al., Nano Lett. 16, 3824 (2016). [8] C. English et al., IEEE Intl. Electron Devices Meeting (IEDM), Dec 2016. [9] K. Smithe et al., Nano Lett. 18, 4516 (2018). [10] E. Yalon et al., Nano Lett. 17, 3429 (2017). [11] C. Ahn et al., Nano Lett. 15, 6809 (2015). [12] A. Sood et al. Nature Comm. 9, 4510 (2018).