Speaker
Description
Organic semiconductors are highly relevant materials concerning future electronic devices due to their advantageous properties like high charge injection ability. Thin layers of acenes on metals like copper or silver are discussed to induce complex electronic characteristics, depending on factors like substrate metal workfunction and molecule adsorbate electron affinity. In this study the growth and energy level alignment of the rod-like, long chain acene heptacene on a Cu(110) surface is evaluated. The impact on the charge transfer to this electron-acceptor molecule on the metal substrate is crucial. Our results show that the orientation of the 7A molecules can be controlled by the preparation conditions. This has also strong influence on the electronic properties. Photoemission tomography is used to investigate molecular geometries and assign specific emissions to molecule orbitals [1]. The findings are supported by other surface science techniques such as STM and LEED. Thermal cycloreversion of diheptacene isomers during evaporation produces highly oriented and epitaxial monolayers of heptacene on the metal surface. The molecules are oriented either along or perpendicular to the close-packed metal rows of Cu(110). Our combined experimental and computational results show that for heptacene oriented along the Cu rows, the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 are occupied. The LUMO+1 receives no charge for molecules aligned perpendicular to the Cu rows. The possibility to tune the energy level alignment and charge transfer at organic-metal interfaces by means of adjustable molecular alignment is fully corroborated by our experiments and density functional calculations.
Acknowledgment
Financial support through FWF (FWF project number I 4145)
References
1. Hurdax, Philipp, et al. “Controlling the Electronic and Physical Coupling on Dielectric Thin Films.” Beilstein Journal of Nanotechnology, vol. 11, no. 1, 2020, pp. 1492–1503.
| Speaker Country | Austria |
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