Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 51: Oxides and insulators: Epitaxy and growth

O 51.9: Talk

Wednesday, March 28, 2012, 18:45–19:00, HE 101

Morphology and optical properties of Cr-doped MgO films — •Fernando Stavale, Niklas Nilius, and Hans-Joachim Freund — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany

MgO thin films doped with varying amounts of Cr have been analyzed from a structural, morphological and optical point of view, using cathodo- and photo-luminescence spectroscopy performed in an STM setup. Whereas at low Cr concentration, the MgO rocksalt structure is maintained, transition to a spinel-like magnesium chromate occurs at higher doping level. Depending on the Cr concentration, several zero-phonon and phonon-mediated emission lines are detected at around 700 nm in the optical spectra, originating from transition within the d-state manifold of the Cr ions. Their wavelength position and intensity provides insight into the local environment of the Cr centers. The development of the phonon sidebands, on the other hand, is governed by the excitation scheme, and the bands become particularly strong for an electronic stimulation of the system. The role of the Stark effect on the band positions is quantified by comparing photo- and cathodo-luminescence spectra performed at different tip-electric fields.