Realizing nearly-free-electron like conduction band in a molecular film through mediating intermolecular van der Waals interactions

Xingxia Cui; Ding Han; Hongli Guo; Linwei Zhou; Jingsi Qiao; Qing Liu; Zhihao Cui; Yafei Li; Chungwei Lin; Limin Cao; Wei Ji; Hrvoje Petek; Min Feng

doi:10.1038/s41467-019-11300-y

Realizing nearly-free-electron like conduction band in a molecular film through mediating intermolecular van der Waals interactions

Nat Commun. 2019 Jul 29;10(1):3374. doi: 10.1038/s41467-019-11300-y.

Authors

Xingxia Cui¹, Ding Han¹, Hongli Guo¹, Linwei Zhou², Jingsi Qiao², Qing Liu¹, Zhihao Cui¹, Yafei Li¹, Chungwei Lin³, Limin Cao¹, Wei Ji⁴, Hrvoje Petek⁵, Min Feng^{6

7}

Affiliations

¹ School of Physics and Technology and Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Wuhan University, Wuhan, 430072, China.
² Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, 100872, China.
³ Mitsubishi Electric Research Laboratories, 201 Broadway, Cambridge, MA, 02139, USA.
⁴ Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, 100872, China. wji@ruc.edu.cn.
⁵ Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, PA, 15260, USA. petek@pitt.edu.
⁶ School of Physics and Technology and Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Wuhan University, Wuhan, 430072, China. fengmin@whu.edu.cn.
⁷ Institute for Advanced Studies, Wuhan University, Wuhan, 430072, China. fengmin@whu.edu.cn.

Abstract

Collective molecular physical properties can be enhanced from their intrinsic characteristics by templating at material interfaces. Here we report how a black phosphorous (BP) substrate concatenates a nearly-free-electron (NFE) like conduction band of a C₆₀ monolayer. Scanning tunneling microscopy reveals the C₆₀ lowest unoccupied molecular orbital (LUMO) band is strongly delocalized in two-dimensions, which is unprecedented for a molecular semiconductor. Experiment and theory show van der Waals forces between C₆₀ and BP reduce the inter-C₆₀ distance and cause mutual orientation, thereby optimizing the π-π wave function overlap and forming the NFE-like band. Electronic structure and carrier mobility calculations predict that the NFE band of C₆₀ acquires an effective mass of 0.53-0.70 m_e (m_e is the mass of free electrons), and has carrier mobility of ~200 to 440 cm²V^-1s^-1. The substrate-mediated intermolecular van der Waals interactions provide a route to enhance charge delocalization in fullerenes and other organic semiconductors.