Speaker
Description
Even trace amounts of impurity atoms can greatly influence the structural and functional properties of Materials. Applications of this effect range from doping of semiconductors to strengthening of alloys. One important research topic for these applications is the temperature dependent bulk diffusion of impurity atoms in their host lattice. While this has been studied in great detail using computational approaches and experiments on larger scales, atomic-scale observations of the diffusion of impurity atoms are surprisingly lacking.
In this work, we show the diffusion dynamics of individual tungsten atoms in an aluminium matrix using in situ High Resolution Scanning Transmission Electron Microscopy (HRSTEM). The temperature dependence of diffusion is elucidated using a MEMS-based in situ heating holder. We deposit the material using a unique combination of magnetron sputtering (for Al) in conjunction with a nanoparticle gun (for W). With this technique, we are able to get finely dispersed tungsten atoms in a crystalline aluminium thin film, ideally suited for TEM investigations.
We observe that diffusion is largely facilitated by vacancies, which cause random walk patterns of substitutional impurities. In some instances, substitutional impurities may also diffuse to an octahedral interstitial site, which is then followed by diffusion from one interstitial site to another. Looking at different grain orientations, we see preferential diffusion along certain crystallographic planes. Finally, we investigate the effect of defects such as grain boundaries and twins on diffusion. While the movement of the impurity atoms is greatly enhanced by arbitrary grain boundaries, we see very little influence of twin boundaries on the overall speed of diffusion. With this work, we expect to deepen the general understanding of diffusion mechanisms at the atomic scale, benefiting future material developments.
| Speaker Country | Switzerland |
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