报告题目：MBE growth, defect engineering, and properties of functional oxides
时间：7月19日（周二） 10:00-11:00
地点：南京大学鼓楼校区唐仲英楼A313
Abstract：This talk will highlight the most recent research activities in our oxide epitaxy group where we aim to modify and control the structure and properties (e.g., electronic, optical, magnetic, and ion transport) of complex oxides.Perovskite oxides exhibit a broad range of structural, compositional, and functional properties, which can be further tuned or even drastically transformed by means of judicious elemental doping and defect engineering. We show that Sr substitution of La in LaCrO3, a wide gap Mott insulator, can lead to hole doping into the top of valence band with the formation of Cr4+(3d2) and make SrxLa1-xCrO3 (x<0.25) a high performance p-type transparent conductive oxide (p-TCO). Using oxygen-assisted molecular beam epitaxy (MBE), all-perovskite pn junctions consisting of SrxLa1-xCrO3 (x = 0.125) films and Nb doped SrTiO3(001) (NbSTO) substrates were fabricated and characterized. At x > 0.65, hole-induced insulator-to-metal transition is observed, but only on the films with in-plane compressive strain. In particular, the end member, SrCrO3-d, under different strain states (compressive vs. tensile) displays drastically different phase stability and O2- ion transport properties, which is of considerable interest in solid oxide fuel cells where fast oxygen ion transport at lower operating temperature is highly desired. In another example, I will present how we tune the structure and electronic properties of WO3 epitaxial thin films, and use them as model cathode materials for in situ TEM studies. The atomic scale ion (Li+, Na+, and Ca2+) intercalation and conversion reactions are revealed by STEM, EELS, NBD, and theory.
