Disrupted Attosecond Charge Carrier Delocalization at a Hybrid Organic/Inorganic Semiconductor Interface

Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is known regarding the fate of charge carriers at metal oxide interfaces, particularly on ultrafast time scales. Using core–hole clock spectroscopy, we investigate the ultrafast charge carrier dynamics of conductive ZnO films at a hybrid interface with an organic semiconductor. The adsorption of C₆₀ on the ZnO surface strongly suppresses the ultrafast carrier delocalization and increases the charge carrier residence time from 400 attoseconds to nearly 30 fs. Here, we show that a new hybridized interfacial density of states with substantial molecular character is formed, fundamentally altering the observed carrier dynamics. The remarkable change in the dynamics sheds light on the fate of carriers at hybrid organic/inorganic semiconductor interfaces relevant to organic optoelectronics and provides for the first time an atomistic picture of the electronically perturbed near-interface region of a metal oxide

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

We investigate the prototypical hybrid interface formed between PTCDA and conductive <i>n</i>-doped ZnO films by means of complementary optical and electronic spectroscopic techniques. We demonstrate that shallow donors in the vicinity of the ZnO surface cause an <i>integer</i> charge transfer to PTCDA, which is clearly restricted to the first monolayer. By means of DFT calculations, we show that the experimental signatures of the anionic PTCDA species can be understood in terms of strong hybridization with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron-transport level but requires rather an atomistic understanding of the interfacial interactions. The study reveals that defect sites and dopants can have a significant influence on the specifics of interfacial coupling and thus on carrier injection or extraction

Controlling the Spin Texture of Topological Insulators by Rational Design of Organic Molecules

We present a rational design approach to customize the spin texture of surface states of a topological insulator. This approach relies on the extreme multifunctionality of organic molecules that are used to functionalize the surface of the prototypical topological insulator (TI) Bi₂Se₃. For the rational design we use theoretical calculations to guide the choice and chemical synthesis of appropriate molecules that customize the spin texture of Bi₂Se₃. The theoretical predictions are then verified in angular-resolved photoemission experiments. We show that, by tuning the strength of molecule–TI interaction, the surface of the TI can be passivated, the Dirac point can energetically be shifted at will, and Rashba-split quantum-well interface states can be created. These tailored interface propertiespassivation, spin-texture tuning, and creation of hybrid interface stateslay a solid foundation for interface-assisted molecular spintronics in spin-textured materials