Molecular Ordering in PCBM–Au(111) Interface Formation

Abstract

Structure evolution in monolayer films of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) deposited on Au(111) was determined via ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Molecular organization was monitored from a glassy phase, produced via a pulsed microaersol molecular beam deposition source, through ordered arrangements, following thermal annealing. At lower PCBM densities, two double-row structures arise, involving distinct PCBM hydrogen-bonding motifs, reminiscent of patterns produced by solvent-free deposition. At higher PCBM monolayer densities, hexagonal close-packed islands of PCBM form, with a 0.98 nm nearest-neighbor spacing in good agreement with structure predictions [Napoles-DuartePhys. Rev. B 2008, 78, 035425]. Under UHV conditions, solvent molecules are retained in the organic layer to temperatures up to 200 °C, inhibiting PCBM ordering. Following complete solvent removal, nanosized hexagonal close-packed PCBM islands show arrested development, indicating a kinetic barr...