Surface phonon polaritons (SPhPs) are important building blocks of nanophotonics, as they enable strong light–matter interaction on the nanoscale, are well-suited for applications in the mid- to far-infrared regime, and can show low losses. SrTiO3 is an interesting material for SPhPs, because it allows for reversible, nonvolatile doping with free charge carriers via oxygen vacancies and for local switching with conductive AFM tips. As a result, SrTiO3 could enable programmable nanophotonics with tunable SPhPs and direct writing of metasurfaces. Surface polariton properties can be determined by mapping their real-space propagation using scattering-type scanning near-field optical microscopy (s-SNOM), which is sensitive to the high local electric fields with nanoscale lateral resolution. Low-confinement (LC) SPhPs with wavevectors close to that of free-space radiation, such as in SrTiO3 and the model polar dielectric SiC, can be difficult to investigate in s-SNOM due to interference effects with the incident illumination and fringe spacings exceeding the scan range or the size of the focus spot. Here, we present s-SNOM measurements of LC-SPhPs on SiC and SrTiO3 launched at gold stripes, retrieve physical quantities such as launching amplitude and phase, and show that they are influenced strongly by gold stripe geometry as well as illumination angle. Using two complementary measurements, we show a convenient way to determine the out-of-plane angle of the s-SNOM setup. Finally, we predict how control over the free charge carrier concentration in SrTiO3 could enable tunable LC-SPhPs, showing the potential of SrTiO3 for programmable nanophotonics.

Using c-AFM and s-SNOM, we show the influence of local inhomogeneities on the LAO/STO 2DEG formation by mapping its distribution. The nanoscopic arrangement of insulating regions alters the conductive behavior down to low temperatures.

This paper deals with the results of numerical and experimental investigations of tangential endwall contoured (TEWC) blades. The contouring is restricted to the blade passage and is implemented on the root and the shrouds for all blade rows. The investigated results of the new blade design have been compared to a reference blade design, which differs only in terms of the contouring. For this reason, the differences of the flow conditions can solely be attributed to the endwall contouring. All investigations have been carried out at different blade loadings in order to determine the potential improvement of the blading with respect to the efficiency. The analysis has emphasized an efficiency improvement for the design point and an efficiency decrease for high blade loading. The under- and overturning are considered by means of the angle distributions behind the stages and serve as an indicator for the losses caused by the passage vortex. An attenuation of the passage vortex in the casing area resulting from the load relief in the casing-sided area can be observed. The contouring in the hub-area however leads to a higher development of the horseshoe vortex at high blade loading.

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