Self-affine surface morphology of plastically deformed metals

We analyze the surface morphology of metals after plastic deformation over a range of scales from 10 nm to 2 mm, using a combination of atomic force microscopy and scanning white-light interferometry. We demonstrate that an initially smooth surface during deformation develops self-affine roughness over almost four orders of magnitude in scale. The Hurst exponent $H$ of one-dimensional surface profiles is initially found to decrease with increasing strain and then stabilizes at $H \approx 0.75$. By analyzing their statistical properties we show that the one-dimensional surface profiles can be mathematically modelled as graphs of a fractional Brownian motion. Our findings can be understood in terms of a fractal distribution of plastic strain within the deformed samples

Polymer micro-molding of femtosecond laser micromachined substrates

Micro-molding can be used for the cost-effective fabrication of elements such as active or passive components in MEMS devices, hydrophobic surfaces, cell-growth scaffolds or optical components such micro-lens arrays and gratings. This method is also particularly interesting for examining high-aspect ratio laser-machined structures fabricated in glass material. Thanks to this technique, surfaces not accessible with common imaging techniques can be observed on their molded negative structure with very high fidelity. As an illustration, we issue the use of the PDMS molding technique to analyze the quality of high aspect ratio holes and channels structures. Furthermore, we show preliminary results on the molding of a novel type of complex structures formed in glass using temporal and spatial beam shaping

Scale-free statistics of plasticity-induced surface steps on KCl single crystals

Experimental investigations of plastic flow have demonstrated temporal intermittency as deformation proceeds in a series of intermittent bursts with scale-free size distribution. In the present investigation, a corresponding spatial intermittency is demonstrated for plastic flow of KCl single crystals. Deformation bursts lead to large surface steps with a height distribution that is consistent with the distribution of strain increments in deformation of micron-size samples and the energy distribution of acoustic emission bursts observed in deformation of macroscopic single-crystal samples of a wide class of materials. © 2007 IOP Publishing Ltd and SISSA