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The single electron transport driven by surface acoustic waves (SAWs) is analyzed in the low power regime. The close-to-equilibrium regime might help in opening up a new route towards precisely controlled single electron transport and a quantum standard of current with low uncertainty at gigahertz frequencies.

The potential of the combined magneto-optic indicator film (MOIF) and magnetic force microscopy (MFM) is demonstrated for lithographically patterned Co Pt film with out-of plane anisotropy. MOIF magnetization data reveal magnetization reversals in micron-sized structures, while the corresponding MFM images related the results to the magnetic configuration of the elements.

In order to determine magnetic stray field and magnetization distributions of thin magnetic patterns and arrays, we developed a new quantitative imaging technique based on magneto-optical indicator films (MOIF) combined with inverse magnetostatic methods. The method is applied to hard magnetic FePt and PrCo5 films which exhibit out-of-plane and in-plane easy magnetization axes, respectively. The films are patterned with standard electron beam lithography into square shaped elements with sizes between 10 μm and 500 nm. The magnetization values obtained from the MOIF method are compared to those of integral magnetometer measurements and show a good agreement, if the sensor properties are taken into account, properly. As an outlook, a concept for combining MOIF imaging with magnetic force microscopy is demonstrated which allows for quantitative magnetization imaging with a resolution down to 10 nm. [ABSTRACT FROM AUTHOR]

We experimentally and theoretically investigate the distortion that an external electro-optic sampling tip imprints on a measured voltage pulse that propagates along a coplanar stripline. By using the electro-optic effect of the GaAs substrate on which the stripline is fabricated we obtain the undisturbed voltage pulse, which serves as a reference pulse. This allows us to quantitatively compare the voltage pulse measured with the external electro-optic sampling tip to the undisturbed voltage pulse. The sensitivity of the sampling measurement and the distortion of the voltage pulse are determined for different heights of the tip which is lifted off the stripline. The experimental data agree very well with numerical finite difference calculations. We find that small changes of the tip height already influence the measurements strongly. From the experiments we infer an optimum working height of the sampling tip of only 0.5 μm. Our investigations help to improve the accuracy of electro-optic sampling measurements. [ABSTRACT FROM AUTHOR]

We have generated shift and injection currents in unstrained, undoped (110)-grown GaAs/Al0.3Ga0.7As quantum wells with a single optical pulse and detected them via free-space terahertz experiments. By properly choosing the polarization state of the excitation pulse, it is possible to generate both currents alone along certain crystal directions or to simultaneously generate them along the same crystal direction. A comparison of injection and shift currents allows us to estimate the strength of the injection current. At an excitation energy of 1.53 eV the injection current tensor element is ≈i2×107 A/(V2 s). This corresponds to an injection of electrons with an average velocity of ≈10 km/s. Moreover, a comparison of the intensity dependence of shift and injection currents under identical experimental conditions demonstrates a stronger saturation of the shift current. [ABSTRACT FROM AUTHOR]

If a spatially nonuniform carrier distribution is optically excited in an electrically biased semiconductor, complicated carrier motion can be expected due to temporal and spatial variations of the screened electric field. We present an experimental method that allows one to quantify the drift velocity of carrier ensembles versus time in time-dependent electric fields. The method is based on the analysis of spatially resolved photoluminescence images at different times, recorded with a streak camera. With this technique, we have studied the details of carrier sweep out in photoconductive switches. [ABSTRACT FROM AUTHOR]

The distortion of voltage pulses measured with external electro-optic sampling (EOS) is investigated by using the electro-optic effect of the GaAs substrate. The optimum working height can be used to improve the accuracy of the characterization of ultrafast electrical device using external EOS probes.

Shift and injection currents in unstrained, undoped (110)-grown GaAs/Al0.3Ga0.7As quantum wells are generated with a single optical pulse and detected through free-space terahertz experiments. It is possible to generate both currents alone along certain crystal directions or to simultaneously generate them along the same crystal direction by properly choosing the polarization state of the excitation pulse.

Atomic and magnetic force microscopy measurements on magnetic iron particles produced by a self-assembly method is presented. Magnetic force microscopy suggests that the particles can be permanently magnetized with external fields of different orientations.

An experimental technique is presented for the detection of pump-induced transmission and phase changes with high sensitivity and ultrafast temporal resolution over an arbitrarily wide time window.