| AVS 61st International Symposium & Exhibition | |
| Surface Science | Friday Sessions |
| Session SS+EM-FrM |
| Session: | Semiconductor Surfaces and Interfaces 2 |
| Presenter: | Sujitra Pookpanratana, National Institute of Standards and Technology (NIST) |
| Authors: | S.J. Pookpanratana, National Institute of Standards and Technology (NIST) H.-J. Jang, National Institute of Standards and Technology (NIST) A.N. Brigeman, National Institute of Standards and Technology (NIST) J.I. Basham, National Institute of Standards and Technology (NIST) O.A. Kirillov, National Institute of Standards and Technology (NIST) D.J. Gundlach, National Institute of Standards and Technology (NIST) O.D. Jurchescu, Wake Forest University C.A. Richter, NIST C.A. Hacker, NIST |
| Correspondent: | Click to Email |
Organic-based electronics are attractive because they have potential manufacturing advantages such as mechanical flexibility and simpler processing (solution-based, low temperature, and atmosphere conditions). Molecular-based semiconductors offer a nearly limitless range of possibilities in tailoring the chemical composition and structure for a desired electronic, optical, or film-processing property. Probing and understanding molecular surfaces and interfaces is essential for the further development of organic-based photovoltaics, light emitting diodes, and field-effect transistors. Organic-organic interfaces are key in some of those devices, and understanding the impact of a self-assembled monolayer (SAM) has when an organic semiconductor is on top of it, is a complex issue.1 This strategy is commonly implemented as a way to modify the hole injection barrier between an organic material and an inorganic substrate.
Here, we have investigated the interaction between a pi-conjugated organic semiconductor (tris-(8-hydroxyquinoline) aluminum, Alq3) on SAM’s of different tail and backbone composition. We have used ultraviolet and X-ray photoelectron spectroscopies to monitor the energy level alignment and chemical structure at the interface. The SAM’s strongly interact with the Au substrate, where an interface dipole can down shift or up shift the surface work function. After Alq3 is deposited onto the SAM-coated substrates, we find that the highest occupied molecular orbital of Alq3 is relatively constant (with respect to the substrate Fermi level) on all surfaces, suggesting Fermi level pinning.2 However, the composition of the SAM’s did strongly influence the growth and chemical structure of the Alq3 at the interface. The photoemission signal arising from the Au substrate is least attenuated when the SAM/Au surface is hydrophobic when compared to a hydrophilic SAM/Au or bare Au surface. The difference in substrate attenuation suggests that that the early growth of the Alq3 layer strongly depends on this surface property. This finding is corroborated with microscopy of the same samples. In addition, Alq3 chemically reacts with a fluorinated SAM at the organic-organic interface as indicated by the shifting and asymmetric broadening of Al and N core levels. These results will be discussed in context of painting a comprehensive picture of the organic-organic interface formation that influences the chemical composition, electronic structure and physical structure at the interface.
[1] F. Rissner et al, ACS Nano 3, (2009) 3513.
[2] L. Lindell et al., Appl. Phys. Lett. 102, (2013) 223301.