邀请报告: MBE growth, defect engineering, and properties of functional oxides
报告人： Sr. Research Scientist Yingge Du
Pacific Northwest National Laboratory
报告时间：2016年07月19日(星期二) 上午10:00
报告地点：唐仲英楼A313
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, Sr
CrO3-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.