11 research outputs found
Imaging Oxygen Defects and their Motion at a Manganite Surface
Manganites are technologically important materials, used widely as solid
oxide fuel cell cathodes: they have also been shown to exhibit
electroresistance. Oxygen bulk diffusion and surface exchange processes are
critical for catalytic action, and numerous studies of manganites have linked
electroresistance to electrochemical oxygen migration. Direct imaging of
individual oxygen defects is needed to underpin understanding of these
important processes. It is not currently possible to collect the required
images in the bulk, but scanning tunnelling microscopy could provide such data
for surfaces. Here we show the first atomic resolution images of oxygen defects
at a manganite surface. Our experiments also reveal defect dynamics, including
oxygen adatom migration, vacancy-adatom recombination and adatom bistability.
Beyond providing an experimental basis for testing models describing the
microscopics of oxygen migration at transition metal oxide interfaces, our work
resolves the long-standing puzzle of why scanning tunnelling microscopy is more
challenging for layered manganites than for cuprates.Comment: 7 figure
The surface layer of cleaved bilayer manganites
Recently, several informative reports have been published on spectroscopy experiments performed on cleaved surfaces of the bilayered colossal magnetoresistive manganite La2-2xSr1+2xMn2O7 (Konoto et al 2004 Phys. Rev. Lett. 93 107201, Freeland et al 2005 Nat. Mater. 4 62, Mannella et al 2005 Nature 438 474, Ronnow et al 2006 Nature 440 1025). For the detailed interpretation of these results, it is of importance to know exactly which layer within the crystal structure is exposed to the surface upon cleavage. Here we combine crystal structure arguments, scanning tunnelling microscopy and x-ray photoelectron spectroscopy measurements to demonstrate that the crystals cleave between the rare-earth rock-salt oxide layers, leaving one outermost rare-earth oxide layer before the first electronically active MnO bilayer
The surface layer of cleaved bilayer manganites
Recently, several informative reports have been published on spectroscopy experiments performed on cleaved surfaces of the bilayered colossal magnetoresistive manganite La2−2x Sr1+2x Mn2O7 (Konoto et al 2004
Phys. Rev. Lett. 93 107201, Freeland et al 2005 Nat. Mater. 4 62, Mannella et al 2005 Nature 438 474, Rønnow et al 2006 Nature 440 1025). For the detailed interpretation of these results, it is of importance to know exactly which layer within the crystal structure is exposed to the surface upon cleavage. Here we combine crystal structure arguments, scanning tunnelling microscopy and x-ray photoelectron spectroscopy measurements to demonstrate that the crystals cleave between the rare-earth rock-salt oxide layers, leaving one outermost rare-earth oxide layer before the first electronically active MnO bilayer
Analysis of the electronic configuration of the pulsed laser deposited La 0.7 Ca 0.3 MnO 3 thin films
Abstract The electronic properties of La 0.7 Ca 0.3 MnO 3Àd thin films grown by the pulsed reactive crossed beam laser ablation method are investigated. The effects of post-deposition annealing of epitaxial La 0.7 Ca 0.3 MnO 3Àd thin films have been investigated using X-ray photoelectron spectroscopy (surface sensitive) and hard X-ray absorption spectroscopy (bulk sensitive). The films deposited in the high vacuum are oxygen deficient and contain mostly Mn 3+ . High temperature annealing in a flowing oxygen atmosphere partially changes the Mn oxidation state from +3 towards +3.4. These changes should favor a metal-like conduction and a ferromagnetic double exchange transport mechanism in the annealed thin films.