Tuning the electron injection barrier between Co and C60 using Alq3 buffer layer

Abstract

We demonstrate that the electron injection barrier (Δe) between Co and C60 can be tuned by inserting a thin Alq3 interlayer. Using ultraviolet photoemission spectroscopy, Δe of C60 on Alq3 -predecorated Co (Δe =0.3 eV) was found to be reduced by 0.3 eV compared with that of C60 deposited directly on the bare Co metal surface (Δe =0.6 eV). Due to Fermi level pining at the Alq3 /Co interface, this tuning effect is independent of the thickness of Alq3 interlayer from multilayer to monolayer. Based on the experimental results, band level alignment diagrams are proposed for C60 /Co and C60 / Alq 3 /Co interfaces with two different Alq3 thicknesses. Our findings could have potential applications for the reduction in the carrier injection barrier in organic spin valves. © 2010 American Institute of Physics.