Srdjan Milenkovic

Nanomechanics of single crystalline tungsten nanowires

Single crystalline tungsten nanowires were prepared from directionally solidified NiAl-W alloys by a chemical release from the resulting binary phase material. Electron back scatter diffraction (EBSD) proves that they are single crystals having identical crystallographic orientation. Mechanical investigations such as bending tests, lateral force measurements, and mechanical resonance measurements were performed on 100-300 nm diameter wires. The wires could be either directly employed using micro tweezers, as a singly clamped nanowire or in a doubly clamped nanobridge. The mechanical tests exhibit a surprisingly high flexibility for such a brittle material resulting from the small dimensions. Force displacement measurements on singly clamped W nanowires by an AFM measurement allowed the determination of a Youngs modulus of 332 GPa very close to the bulk value of 355 GPa. Doubly clamped W nanowires were employed as resonant oscillating nanowires in a magnetomotively driven resonator running at 117 kHz. The Youngs modulus determined from this setup was found to be higher 450 GPa which is likely to be an artefact resulting from the shift of the resonance frequency by an additional mass loading.

Arrays of iso-oriented gold nanobelts.

For the first time single crystalline gold nanobelt arrays with identical crystallographic orientation were obtained. A combined method consisting of directional solid-state transformation of a Fe-Au eutectoid and a well controlled electrochemical treatment enables production of arrays of nanobelts with a desired length. They have an average thickness of 25 nm and width of 200-250 nm, respectively. The obtained gold nanobelt arrays were characterized by electron backscattered diffraction (EBSD), X-ray diffraction, and XPS. The underlying mechanisms and the potential of this method for the production of nanosensors are discussed.

Gold Nanostructures by Directional Solid-state Decomposition

This study addresses a novel approach of obtaining gold nanostructures, via directional eutectoid decomposition and selective etching of Fe-Au alloys. The eutectoid transformation occurs at 2.3%Au, which agrees perfectly with existing DTA and calculated data. The results are thus experimentally supporting the calculated part of the binary Fe-Au phase diagram. Gold nanofibres were rectangular in shape, constrained with two perpendicular crystallographic directions, showing the faceted nature of the Au phase. In addition, it was shown that a range of gold nanostructures, including gold nanoparticles, short nanorods, and nanofibres might be achieved depending on the processing route. The uniformity and regularity of the obtained nanostructures are limited, due to a non-cooperative mechanism of the eutectoid transformation. These homomorph gold nanostructures have the same high potential as other gold nanostructures but also the advantage of being inherently organized in a single crystalline matrix.

Reactivity of gold nanobelts with unique {110} facets.

Gold nanobelts were synthesized by directional solidification of the Fe-Au eutectoid followed by selective phase dissolution. Cleaning from organic molecules was performed in alkaline solution by PbO(2) deposition/dissolution to avoid surface reconstruction. The electrochemical behaviour of the Au nanobelts was determined by structure-sensitive electrochemical reactions, and the findings confirm the results obtained by selected area electron diffraction (SAED). The underpotential deposition (UPD) of lead under alkaline conditions and cyclic voltammograms (CVs) in sulphuric acid revealed an unusual large amount of (110) domains (>65%). Finally, after cleaning the Au nanobelts showed a higher and stable electrocatalytic behaviour toward methanol oxidation in alkaline media. The possible mechanism and the potential applications of the Au nanobelts are discussed.

Strengthening mechanisms for Fe–Al-based alloys with increased creep resistance at high temperatures

Lack of strength, in particular creep resistance, has been considered as the principal shortcoming of Fe-Al-based alloys for long which prevented their use for structural applications at high temperatures. Only recently it has been realized that various strengthening mechanisms are available by which Fe-Al-based alloys can be sufficiently strengthened for applications at high temperatures. From the recent studies at the Max-Planck-Institut fur Eisenforschung GmbH (MPIE) examples of applying different strengthening mechanisms are presented by which Fe-Al-based alloys with considerable creep resistance have been obtained.