Structural and elemental analysis of iron and indium doped zinc oxide by spectroscopic imaging in Cs-corrected STEM

Abstract

ZnO with additions of Fe 2O 3 or In 2O 3 shows characteristic inversion domain structures. ZnO domains are separated by two types of inversion domain boundaries (IDBs): basal b-IDBs parallel to (0 0 0 1) planes, and complementary pairs of three possible variants of pyramidal p-IDBs parallel to { 2 1 ¯ 1 ¯ 5 } lattice planes. The structure and composition of IDBs were investigated in a sophisticated aberration-corrected scanning transmission electron microscope (probe-corrected TEM/STEM). It is shown that Fe and In additions are essentially located in monolayers within the IDBs, and EELS electron spectroscopic imaging (ESI) as well as EDS spectroscopic imaging by X-rays (SIX) are capable of rapidly mapping the element distribution. With solid solubility of trivalent dopant species well below 1 at.% within ZnO domains, the lateral spacings of b-IDBs are inversely proportional to the dopant concentration. Quantification of data acquired by ESI and SIX from well defined sample regions in STEM both confirm the assumption of one full monolayer of dopants per IDB. Atom columns of cations are well resolved in HAADF STEM imaging; experimental contrast intensities are approximately proportional to Z 1.6. Furthermore, annular bright-field (ABF)-STEM imaging is capable of resolving oxygen columns even in thick sample regions, thus providing highly localized information on atom positions and lattice distortions, and enables the construction of more reliable structure models of IDBs in doped ZnO.