Adjusting the chemical composition at surfaces or interfaces of alloys has been shown to be an effective approach to achieve desired properties of nanostructured materials. In recent years, metallic glasses with nanometer-sized structures, called nano glasses, have attracted attention. In fact, nano glasses exhibit remarkable interface-related properties such as the improved mechanical, biological, magnetic and catalytic properties in comparison to the corresponding melt-quenched glasses of identical overall composition. Even though considerable research has been performed in order to study the the properties of nanoglasses, the knowledge of the atomic and the chemical structure of the interfaces between the glassy regions of nanoglasses is still rather limited.
As an approach to directly investigate the local structure of nano glasses, we have developed radial distribution function (RDF) mapping (see 4D STEM analysis). Using this approach (Fig. 1), we could show that e.g. the Fe25Sc75 nanoglass (NG) contains 3 main component phases. They are distributed heterogeneously at the nano scale (5-10 nm). By comparing the RDFs of the component phases with the RDFs of bulk metalic glasses (BMGs), the 3 component phases are found to be (i) a Sc-rich phase with a simillar atomic packing to the Fe25Sc75 BMG, (ii) a Fe-rich phase with an atomic packing in a good agreement with the Fe90Sc10 BMG, and (iii) an oxide phase due to the unavoidable oxidation of the 20 nm thin FIB lamella.
Figure 1: Left: RDFs of the 3 different phases in an Fe25Sc75 nanoglass. They are a Sc rich FeSc phase (top, solid black line) similar to the Fe25Sc75 bulk metallic glass (BMG) (top, green dashed line), Fe-rich phase (middle, red solid line) similar to the Fe90Sc10 BMG (middle, dashed pink line), and an oxidazes phase (bottom, solid blue line). Right: the RDF maps of the nanoglass shows the distribution of the 3 phases: Sc-rich (top), Fe-rich (middle) and the oxide phase (bottom).