ZnCr2O4 Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS

The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (alpha-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size similar to 400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [21 over bar 1 over bar 3]/ZnCr2O4 [11 over bar 0] orientations, while ZnO [12 over bar 10]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 +/- 0.03 eV, in contrast to 3.22 +/- 0.01 eV for the ZnO matrix.