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Buried ${\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ superlattices on Au-GaAs Schottky diodes have been used as an energy filter to study the energetic current distribution in ballistic electron-emission microscopy (BEEM) at room temperature and $T=100\mathrm{K}.$ Due to the large difference in electron masses in Au and GaAs we find that parallel momentum conservation leads to considerable electron refraction at the Au-GaAs interface. As a consequence, the energetic distribution of the ballistic electron current is inverted beyond the Au-GaAs interface and an almost linear behavior of the BEEM spectrum is observed in the energetic regime of the superlattice miniband.

The recent development from micro- to nanotechnology enables new ideas and new physical effects to be implemented in both conventional and novel devices. Examples of fast developing fields in this context are electronic, photonic and magnetic components for sensor, memory, and logic applications. Optical lithography, the traditional path of patterning, is supplemented with sophisticated methods to access the nanoworld.

In this work we introduce a molecular beam epitaxy (MBE)-grown InAs layer as base in ballistic electron emission spectroscopy/microscopy (BEES/BEEM). Compared to the commonly used thin metal film as base, the transmission coefficient and the attenuation length can be enhanced by more than one order of magnitude. At low temperatures (T = 100 K), a passivated InAs layer yields an attenuation length of the order of 70-90 nm, instead of the 5 nm obtained on Au films. This feature makes InAs a promising new base material for BEEM. To clarify the mechanism of this behaviour, temperature-dependent BEEM studies on InAs-GaAs heterostructures were performed. Unlike samples with metal base layers, it is found that the transmission coefficient of the InAs base decreases with decreasing temperature. In addition, a strongly increasing conduction band offset at the InAs/GaAs interface with decreasing temperature is observed.

Inkjet printing is a versatile method to apply surface modification procedures in a spatially controlled, cost-effective and mass-fabrication compatible manner. Utilizing this technology, we investigate two different approaches for functionalizing label-free optical waveguide based biosensors: a) surface modification with amine-based functional polymers (biotin-modified polyethylenimine (PEI-B)) employing active ester chemistry and b) modification with dextran based hydrogel thin films employing photoactive benzophenone crosslinker moieties. Whereas the modification with PEI-B ensures high receptor density at the surface, the hydrogel films can serve both as a voluminous matrix binding matrix and as a semipermeable separation layer between the sensor surface and the sample. We use the two surface modification strategies both individually and in combination for binding studies towards the detection of the protein inflammation biomarker, C-reactive protein (CRP). For the specific detection of CRP, we compare two kinds of capture molecules, namely biotinylated antibodies and biotinylated CRP-specific DNA based aptamers. Both kinds of capture molecules were immobilized on the PEI-B by means of streptavidin-biotin affinity binding. As transducer, we use an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) photonic sensing platform operating at a wavelength of 850nm (TM-mode).