Nanoelectronics: From carbon nanostructures to 1D and 2D semiconductors beyond graphene

If graphene had a band gap, it would probably be the optimum 2D system for electronics applications. Layered transition metal dichalcogenides (TMDs) with a robust intrinsic band gap appear as the next-best alternative. Only after a long search, however, optimum strategies have been devised to make low-resistance, ohmic contacts to TMDs [1]. In the meantime, a new class of 2D semiconductors has been rapidly gaining attention, namely layered black phosphorus and related phosphorene monolayers [2]. These 2D systems display a tunable, direct fundamental band gap and thus are ideal candidates for optoelectronics applications. Recent Quantum Monte Carlo (QMC) calculations show that the inter-layer bonding, while weak, is not well described by dispersive van der Waals (vdW) interactions [3]. QMC results differ qualitatively from vdW-enhanced DFT functionals and the common designation of similar systems as “van der Waals solids” is strictly incorrect. Also other group V systems including monolayers of AsxP1-x [4], IV-VI compounds such as SiS [5] with the same average valence, and related 2D phosphorus carbide [6] share the same nonplanarity of their structure with phosphorene. Same as in phosphorene, the fundamental band gap in these systems depends sensitively on the number of layers and in-layer strain. Surprisingly, the story of group V semiconductors does not end with layered 2D systems. A previously unknown 1D structure of coiled phosphorus, shown in Fig. 1, represents the most stable P allotrope to date. The predicted structure [7] has recently been synthesized and contained inside carbon nanotubes [8]. In all cases, predictive ab initio calculations provide a useful guidance to experimental studies.* Partly supported by the NSF/AFOSR EFRI 2-DARE grant number #EFMA-1433459. References: [1] Jie Guan, Hsun-Jen Chuang, Zhixian Zhou, and David Tománek, ACS Nano 11, 3904 (2017).[2] H. Liu et al. ACS Nano 8, 4033 (2014).[3] L. Shulenburger, A.D. Baczewski, Z. Zhu, J. Guan, and D. Tománek, Nano Lett. 15, 8170 (2015).[4] Zhen Zhu, Jie Guan, and David Tománek, Nano Lett. 15, 6042 (2015).[5] Zhen Zhu, Jie Guan, Dan Liu, and David Tománek, ACS Nano 9, 8284 (2015).[6] Jie Guan, Dan Liu, Zhen Zhu, and David Tománek, Nano Lett. 16, 3247 (2016).[7] Dan Liu, Jie Guan, Jingwei Jiang, and David Tománek, Nano Lett. 16, 7865 (2016).[8] Jinying Zhang et al. Angew. Chem. Int. Ed. 56, 1850-1854 (2017).