Commensurate Assembly of C-60 on Black Phosphorus for Mixed-Dimensional van der Waals Transistors

2D crystals can serve as templates for the realization of new van der Waals (vdW) heterostructures via controlled assembly of low-dimensional functional components. Among available 2D crystals, black phosphorus (BP) is unique due to its puckered atomic surface topography, which may lead to strong epitaxial phenomena through guided vdW assembly. Here, it is demonstrated that a BP template can induce highly oriented assembly of C-60 molecular crystals. Transmission electron microscopy and theoretical analysis of the C-60/BP vdW heterostructure clearly confirm that the BP template results in oriented C-60 assembly with higher-order commensurism. Lateral and vertical devices with C-60/BP junctions are fabricated via a lithography-free clean process, which allows one to investigate the ideal electrical properties of pristine C-60/BP junctions. Effective tuning of the C-60/BP junction barrier from 0.2 to 0.5 eV and maximum on-current density higher than 10(4) mA cm(-2) are achieved with graphite/C-60/BP vertical vdW transistors. Due to the formation of high-quality C-60 film and the semitransparent graphite top-electrode, the vertical transistors show high photoresponsivities up to approximate to 100 A W-1 as well as a fast response time under visible light illumination.