Two-stage growth for highly ordered epitaxial C₆₀ films on Au(111)

As an organic semiconductor and a prototypical acceptor molecule in organic photovoltaics, C₆₀ has broad relevance to the world of organic thin film electronics. Although highly uniform C₆₀ thin films are necessary to conduct spectroscopic analysis of the electronic structure of these C₆₀-based materials, reported C₆₀ films show a relatively low degree of order beyond a monolayer. Here, we develop a generalizable two-stage growth technique that consistently produces single-domain C₆₀ films of controllable thicknesses, using Au(111) as an epitaxially well-matched substrate. We characterize the films using low-energy electron diffraction, low-energy electron microscopy, scanning tunneling microscopy, and angle-resolved photoemission spectroscopy (ARPES). We report highly oriented epitaxial film growth of C₆₀/Au(111) from 1 monolayer (ML) up to 20 ML films. The high-quality of the C₆₀ thin films enables the direct observation of the electronic dispersion of the HOMO and HOMO-1 bands via ARPES without need for small spot sizes. Our results indicate a path for the growth of organic films on metallic substrates with long-range ordering.