Philipp M. Leufke

Surface plasmon polariton absorption modulator.

A new compact electrically controlled surface plasmon polariton (SPP) absorption modulator operating at communication wavelengths is introduced. The modulator is controlled by changing the free carrier density and thereby the propagation loss of the SPP.

The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high-energy diffraction with the in situ synchrotron high-resolution X-ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target-substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X-ray reflectivity, in situ two-dimensional reciprocal space mapping of symmetric X-ray diffraction and acquisition of time-resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two-dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time-resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.

Ferroelectric vs. structural properties of large-distance sputtered epitaxial LSMO/PZT heterostructures

We report on large-distance rf-magnetron sputtering as a competitive alternative to pulsed laser deposition and off-axis sputtering for the growth of epitaxial PbZr0.52Ti0.48O3(PZT)thin films. To determine the characteristics of the PZT films, the studies were focused on the interplay between microstructural and ferroelectric properties. The films were deposited on insulating or conducting (Nb-doped) SrTiO3 and MgO substrates with La0.83Sr0.17MnO3 as bottom electrode. The uniformity and homogeneity of the samples was demonstrated by using large area (1.0 mm2) top electrodes. It is shown that epitaxial heterostructures of excellent crystalline and ferroelectric quality can be deposited from a stoichiometric PZT target without the need for excess PbO in the target or post-annealing of the samples.

Hybrid supercapacitors for reversible control of magnetism

Electric field tuning of magnetism is one of the most intensely pursued research topics of recent times aiming at the development of new-generation low-power spintronics and microelectronics. However, a reversible magnetoelectric effect with an on/off ratio suitable for easy and precise device operation is yet to be achieved. Here we propose a novel route to robustly tune magnetism via the charging/discharging processes of hybrid supercapacitors, which involve electrostatic (electric-double-layer capacitance) and electrochemical (pseudocapacitance) doping. We use both charging mechanisms—occurring at the La0.74Sr0.26MnO3/ionic liquid interface to control the balance between ferromagnetic and non-ferromagnetic phases of La1−xSrxMnO3 to an unprecedented extent. A magnetic modulation of up to ≈33% is reached above room temperature when applying an external potential of only about 2.0 V. Our case study intends to draw attention to new, reversible physico-chemical phenomena in the rather unexplored area of magnetoelectric supercapacitors.

High-speed Plasmonic Modulators

Plasmonic modulators integrated with silicon photonic circuits are discussed. First, a 29 μm long phase modulator operating at 40Gbit/s is demonstrated. Then, an absorption modulator is presented exploiting the plasma effect in metal oxide layers.