Structural characterisation of tribologically influenced silicon carbide ceramic surfaces

Tribologically influenced ceramic surfaces are usually only looked at in terms of the wear effects: surface topography, friction coefficient, loss rates. Current efforts go towards a deeper understanding of mechanisms and kinetics. To gain this, the effects of the wear of ceramics on the phases and microstructures have to be analysed in detail. As an example for this, we studied tribologically influenced silicon carbide ceramics worn under water lubrication. Because structural changes occur within the uppermost μm and tribochemical reaction layers are often restricted to the nm-range, appropriate analytical tools have to be used and those come only now available. We will show how the currently developed techniques of X-ray microdiffraction combined with Raman spectroscopy can resolve many issues. Another recent improvement, transmission electron microscopy (TEM) on cross-sections prepared via the focused ion beam technology (FIB), helps to verify the findings of the former techniques.     

Ledge-flow-controlled catalyst interface dynamics during Si nanowire growth

Self-assembled nanowires offer the prospect of accurate and scalable device engineering at an atomistic scale for applications in electronics, photonics and biology. However, deterministic nanowire growth and the control of dopant profiles and heterostructures are limited by an incomplete understanding of the role of commonly used catalysts and specifically of their interface dynamics. Although catalytic chemical vapour deposition of nanowires below the eutectic temperature has been demonstrated in many semiconductor-catalyst systems, growth from solid catalysts is still disputed and the overall mechanism is largely unresolved. Here, we present a video-rate environmental transmission electron microscopy study of Si nanowire formation from Pd silicide crystals under disilane exposure. A Si crystal nucleus forms by phase separation, as observed for the liquid Au-Si system, which we use as a comparative benchmark. The dominant coherent Pd silicide/Si growth interface subsequently advances by lateral propagation of ledges, driven by catalytic dissociation of disilane and coupled Pd and Si diffusion. Our results establish an atomistic framework for nanowire assembly from solid catalysts, relevant also to their contact formation.