An in situ correlative STEM-EDS and HRTEM based nanoscale chemical characterization of solid-liquid interfaces in an aluminium alloy.

The chemistry and the structure of solid-liquid interface in an Al-Si based alloy during high temperature phase transformation were characterized at nanoscale using scanning Transmission Electron Microscopy-EDS and HRTEM. Such studies were until recently limited by large sample drift associated with conventional heating holders. This study was made possible thanks to the modern low-drift MEMS-chip based localized heating technology. The results reveal that (i) the structural interface between solid (111) oriented Si phase and the liquid phase (i.e. decay of crystalline order) coexisting at 600°C is 3.2 nm wide (ii) the STEM-EDS chemical maps show inhomogeneous distribution of the elements with the solid phase being rich in Si and the liquid phase rich in Al (iii) the HRTEM and the HAADF images display respectively dark and bright intensity bands along the interface which could be due to apparent enrichment of Cu at the interface region resulting in enhanced amplitude-contrast (darker band in HRTEM) and Z-contrast (bright band in HAADF) and (iv) intriguingly, the concentration profiles within (i.e. compositional width) and across the solid-liquid interface display element-specific complex and asymmetric variation in the chemical widths.

Electron energy-loss near-edge structures of 3d transition metal oxides recorded at high-energy resolution.

Near-edge fine structures of the metal L(2,3) and O K-edges in transition metal-oxides have been studied with a transmission electron microscope equipped with a monochromator and a high-resolution imaging filter. This system enables the recording of EELS spectra with an energy resolution of 0.1eV thus providing new near-edge fine structure details which could not be observed previously by EELS in conventional TEM instruments. EELS-spectra from well-defined oxides like titanium oxide (TiO(2)), vanadium oxide (V(2)O(5)), chromium oxide (Cr(2)O(3)), iron oxide (Fe(2)O(3)), cobalt oxide (CoO) and nickel oxide (NiO) have been measured with the new system. These spectra are compared with EELS data obtained from a conventional microscope and the main spectral features are interpreted. Additionally, the use of monochromised TEMs is discussed in view of the natural line widths of K and L(2,3) edges.