Filamentary growth of metals: Microstructure and properties of (nano-) whiskers
October 1-6, 2017
One dimensional nanostructures have the prospect to change the properties of materials used in contemporary devices. Physical properties change with dimension and size. Ceramics, semiconductor and carbon materials are easily synthesized as one dimensional structures with typical diameters of several nanometers and length-diameter ratios of 1000:1. However, only the metals as one of the oldest are difficult to fabricate in similar geometries. In contrast, micrometer diameter, millimeter length macroscopic metallic nanowires were grown and reported decades ago via the reduction of metal halides, based on a process described already in 1574. Recently we developed a process to grow perfect defect and flaw free nanostructures with diameters of several ten nanometers, attached on substrates. The initiator mediated filamentary crystal growth process is based on the physical vapour deposition technique. Metals with face centered (Cu, Ag, Au, Pd, Ni, Co) crystal structure were synthesized successfully with the new technique. Typical diameters of the nanowhiskers are 100 nm and lengths of up to 200 μm are observed, giving aspect ratios of up to 2000:1. Traditional theories attribute the growth of whiskers with the presence of a screw-dislocation. However, studies by transmission electron microscopy did disprove this growth mechanism. An alternative growth mechanism will be discussed. The formation of the nanowhiskers is controlled by diffusion processes of adatoms on the substrate surface and in the emerging interface under the growing nanostructures. By changing substrate material or sequencing different materials during growth allow for the formation of alloy nanowhiskers. This will be described exemplarily by Metal-Si and binary metal alloys (Au-Ni and Ag-Ni).
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Gunther Richter, "Filamentary growth of metals: Microstructure and properties of (nano-) whiskers" in "Nanomechanical Testing in Materials Research and Development VI", Karsten Durst, Technical University of Darmstadt, Germany Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/nanomechtest_vi/106