Ultrafast VLS growth of epitaxial beta- Ga(2)O(3) nanowires.

Well-defined monoclinic nanostructures of beta- Ga(2)O(3) were grown in a chemical vapor deposition apparatus using metallic gallium and oxygen as sources. Stable growth conditions were deduced for nanorods, nanoribbons, nanowires and cones. The types of nanostructures are determined by the growth temperature. We suppose that the vapor-solid growth mechanism rules the growth of nanoribbons and rods. For the nanowires we observed catalytic gold droplets atop, characteristic for the VLS growth mechanism with an extremely high growth rate of up to 10 microm min(-1). Nanowires grown on Al(2)O(3) substrates showed an excellent tendency to grow epitaxially, mapping the hexagonal symmetry of Al(2)O(3)(0001).

An intercepted feedback mode for light sensitive spectroscopic measurements in atomic force microscopy.

In most atomic force microscopes (AFMs), the motion of the tip is detected by the deflection of a laser beam shining onto the cantilever. AFM applications such as scanning capacitance spectroscopy or photocurrent spectroscopy, however, are severely disturbed by the intense stray light of the AFM laser. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. The versatility of this feedback method is demonstrated by measuring tip-force dependent Schottky barrier heights on GaAs samples.

Two color, low intensity photocurrent feedback for local photocurrent spectroscopy.

In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAsInAs heterostructures.

Bridging the gap--biocompatibility of microelectronic materials.

There is an increasing interest in cell-based microelectronic biosensors for high-throughput screening of new products from the biotech pipeline. This requires fundamental knowledge of the biocompatibility of the materials used as the growing support for the cells. Using monolayer-forming Caco-2 cells of human origin, the biocompatibility of silicon wafers coated with various metals, dielectrics and semiconductors was assessed. Besides microscopic inspection, proliferation of cells indicating viability as well as brush border enzyme activity indicating differentiation of adherent growing cells were chosen as parameters to estimate biocompatibility. The type of wafer used for deposition of the coating initially influences the biocompatibility of the final product. Whereas p-doped silicon was fully biocompatible, n-doped silicon reduced the proliferation of cells. Among the different coatings, Al and Ti even increased the cell growth as compared to glass. Culturing the cells for 6 days on coated wafers demonstrated that the differentiation of adhering cells on Ti- and ZrO2-coated wafers was comparable to glass, whereas coatings with Si3N4, Au, Al, and ITO reduced differentiation to 15-35%. In the cases of Au and Si3N4 this effect equilibrated with prolonged culturing. These results demonstrate the importance of a careful selection of the materials used for the production of cell-based biosensors.