Sabine Schwarz

Impact of sputter deposition parameters on molybdenum nitride thin film properties

Molybdenum and molybdenum nitride thin films are presented, which are deposited by reactive dc magnetron sputtering. The influence of deposition parameters, especially the amount of nitrogen during film synthesization, to mechanical and electrical properties is investigated. The crystallographic phase and lattice constants are determined by x-ray diffraction analyses. Further information on the microstructure as well as on the biaxial film stress are gained from techniques such as transmission electron microscopy, scanning electron microscopy and the wafer bow. Furthermore, the film resistivity and the temperature coefficient of resistance are measured by the van der Pauw technique starting from room temperature up to 300 °C. Independent of the investigated physical quantity, a dominant dependence on the sputtering gas nitrogen content is observed compared to other deposition parameters such as the plasma power or the sputtering gas pressure in the deposition chamber.

Colloidally prepared Pt nanowires versus impregnated Pt nanoparticles: comparison of adsorption and reaction properties.

Ligand-capped Pt nanowires, prepared by colloidal synthesis and deposited on a high surface area γ-Al(2)O(3) support, were subjected to surface characterization by electron microscopy and FTIR spectroscopy using CO as a probe molecule. The structural, adsorption, and catalytic reaction properties of the colloidal Pt nanowires were compared to those of conventional, impregnated Pt nanoparticles on the same Al(2)O(3) support. In situ FTIR spectroscopy indicated ligand effects on the CO resonance frequency, irreversible CO-induced surface roughening upon CO adsorption, and a higher resistance of colloidal catalysts toward oxidation (both in oxygen and during CO oxidation), suggesting that the organic ligands might protect the Pt surface. Elevated temperature induced a transformation of Pt nanowires to faceted Pt nanoparticles. The colloidal catalyst was active for hydrodechlorination of trichloroethylene (TCE), but no ligand effect on selectivity was obtained.

Highly conductive and pure gold nanostructures grown by electron beam induced deposition

This work introduces an additive direct-write nanofabrication technique for producing extremely conductive gold nanostructures from a commercial metalorganic precursor. Gold content of 91 atomic % (at. %) was achieved by using water as an oxidative enhancer during direct-write deposition. A model was developed based on the deposition rate and the chemical composition, and it explains the surface processes that lead to the increases in gold purity and deposition yield. Co-injection of an oxidative enhancer enabled Focused Electron Beam Induced Deposition (FEBID)—a maskless, resistless deposition method for three dimensional (3D) nanostructures—to directly yield pure gold in a single process step, without post-deposition purification. Gold nanowires displayed resistivity down to 8.8 μΩ cm. This is the highest conductivity achieved so far from FEBID and it opens the possibility of applications in nanoelectronics, such as direct-write contacts to nanomaterials. The increased gold deposition yield and the ultralow carbon level will facilitate future applications such as the fabrication of 3D nanostructures in nanoplasmonics and biomolecule immobilization.

Microstructural Investigation of Interfacial Features in Al Wire Bonds

In the present study the microstructure of ultrasonically bonded Al wires on AlSiCu and AlSi metallization was investigated by means of scanning electron microscopy, electron back-scattered diffraction, and high-resolution transmission electron microscopy techniques. Detailed microstructural investigations were conducted on samples in the as-bonded condition, subsequent to power cycling tests, and after long-time thermal exposure to reveal the temperature-dependent evolution of the interfaces and the metallization layer. Typical interfacial features were found to be ultrafine and nanoscaled grains of Al and Al2O3, amorphous Al oxide particles, voids, and pores, with regions of high density of dislocations and dislocation loops within the larger grains of the wire and metallization. The observed interface features confirm the suggested mechanism of formation of bonding interface by emergence of submicron grains at the thin interfacial boundary between the metallic pair as a result of dynamic recrystallization and interdiffusion. While isothermal and/or thermomechanical cycling lead to strong grain growth in the metallization layer and the Al wire, the nanostructured interfacial regions mainly remain, indicating a high thermal stability and strength of the interface. Furthermore, evaluation of a large number of wire bonds prepared using standard bonding conditions showed the presence of a certain percentage of nonbonded areas and microstructural variations between the interconnects processed under nominally identical conditions. However, it was found that, if a sufficient effective bonding interface is provided, the long-time reliability of Al wire bonds is maintained due to the stability and strength of the nanostructured interface.

Boosting Hydrogen Production from Methanol and Water by in situ Activation of Bimetallic Cu−Zr Species

A bimetallic Cu/Cu51Zr14 precatalyst, activated in situ, for hydrogen generation from methanol and water provides very high CO2 selectivity (>99.9 %) and high H2 yields. Referenced to the geometric surface area of our model surface, higher activity of at least one order of magnitude was observed in comparison to supported Cu/ZrO2 and Cu/ZnO/ZrO2 catalysts. Evolution of structural activation monitored by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and electron microscopy indicates transformation of the bimetallic Cu/Cu51Zr14 precatalyst into an active, selective, and self‐stabilizing state with coexistence of dispersed Cu and partially hydroxylated tetragonal ZrO2. The outstanding performance is assigned to the presence of a high interface‐site concentration following in situ decomposition of the intermetallic compound. These active sites result from the cooperation of Cu, responsible for methanol activation, and tetragonal ZrO2, which activates the water by surface hydroxylation.

Nanostructured clathrates and clathrate-based nanocomposites

Intermetallic clathrates are candidate materials for thermoelectric applications above room temperature. Here, we explore whether their intrinsically low lattice thermal conductivities can be further reduced by nanostructuring and whether this can further enhance their thermoelectric performance. As bulk nanostructuring routes we studied melt spinning and ball milling. To optimize the compaction process and/or stabilize the nanostructure we varied the process parameters, used additives, and studied clathrate-based composites. Initial results on clathate nanowires as simpler model nanostructures are also presented.

Low voltage TEM for semiconductor analysis

Valence electron energy loss spectrometry (VEELS) is more and more employed for the quantification of dielectric properties in semiconductor research. The improvement of the energy resolution of the thermo-ionic emitter (lanthanum-hexaboride) is obtained by decreasing the acceleration-to-Wehnelt voltage ratio and by inserting a smaller Wehnelt diaphragm. These modifications lead to an improved energy resolution of 0.25 eV full width at half maximum and 3.03 eV full width at thousandth maximum at 20 keV beam energy, which is pretty close to the one of a monochromated field emission gun. Beside the improved energy resolution we demonstrate the accuracy of low voltage VEELS in terms of band gap determination of AlxGa1−xAs, with x varying from zero to 0.58. The experimental results are compared with a well established semi-empirical model commonly used for the calculation of the properties of III-V semiconductors.

EELS and EFTEM-investigations of aluminum alloy 6016 concerning the elements Al, Si and Mg

Aluminum alloys are one of the most promising materials concerning high hardness and low weight (important for the use in automotive engineering) and consequently low cost in operation (low fuel consumption), and comparatively low costs in fabrication. For the investigations done in this work, the aluminum alloy 6016 containing Mg and Si as major elemental additions, have been taken into account. The precipitation sequence in Al-Mg-Si alloys consists of: Al (SSS) — clusters of Si atoms, clusters of Mg atoms — dissolution of Mg clusters — formation of Mg/Si co-clusters — small precipitates of unknown structure - Beta″ precipitates — B′ and Beta″ precipitates - Beta(Mg2Si) precipitates [1].