Two-stage growth for highly ordered epitaxial C_60 films on Au(111)

As an organic semiconductor and a prototypical acceptor molecule in organic photovoltaics, C_60 has broad relevance to the world of organic thin film electronics. Although highly uniform C_60 thin films are necessary to conduct spectroscopic analysis of the electronic structure of these C_60-based materials, reported C_60 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 C_60 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 C_60/Au(111) from 1 monolayer (ML) up to 20 ML films. The high-quality of the C_60 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.