Abstract | Future technologies will require new paradigms in design, functionality, scalability and a reduction in power consumption to meet our global energy challenges, reduce our environmental footprint and sustain or evolve the information age. Hybrid inorganic-organic systems (HIOS) offer a promising route because they may combine the best features of two distinct material classes or even achieve entirely new synergies. My group is developing and using quantum mechanical techniques (e.g. density-functional theory and Green's function methods) and computer programs to describe such hybrid systems on the most fundamental level. The atomistic insight we gain helps us to reach a quantum mechanical understanding of hybrid systems and to improve their properties for future devices. In this presentation, I will address molecular layers of strong acceptors that are used to change the work function of inorganic semiconductors. Focussing on the level alignment of ZnO-based HIOS interfaces, I will show that the build-up of space charge layers and the associated band-bending, that are common text book knowledge for inorganic semiconductors, can have profound and unexpected effects at the interface [1]. Then, I will address charge carrier dynamics. For ZnO we have recently identified hole polarons by combining infrared reflection-absorption spectroscopy with our quantum mechanical calculations [2]. The formation of these pseudoparticles might affect charge transport across HIOS interfaces. Last, I will address the question whether charge at organic-inorganic transfers to a molecule as a whole unit (integer charge transfer (ICT)) or resides on several molecules simultaneously (partial charge transfer (PCT)). For tetracyanoethene (TCNE) molecules adsorbed on an NaCl-passivated Cu(100)-surface we observe signatures of the charge-transfer mechanism in several observables, such as valence and core spectra and the bond length distribution of the individual molecules [3]. With our DFT formalism we can now discriminate between ICT and PCT. References: [1] Y. Xu, O. T. Hofmann, R. Schlesinger, S. Winkler, J. Frisch, J. Niederhausen, A. Vollmer, S. Blumstengel, F. Henneberger, N. Koch, P. Rinke, and M. Scheffer, Phys. Rev. Lett. 111, 226802 (2013) [2] H. Sezen, H. Shang, F. Bebensee, C. Yang, M. Buchholz, A. Nefedov, S. Heissler, C. Carbogno, M. Scheffer, P. Rinke, and C. Woll, Nat. Commun. 6, 6901 (2015) [3] O. T. Hofmann, P. Rinke, M. Scheffer and G. Heimel, ACS Nano 9, 5391 (2015) |
