The stoichiometric (100) surface of alkaline earth oxide surfaces such as MgO(100) are considered rather inert with respect to chemical interactions. With respect to charge transfer reactions it was shown that both transition metal doping as well as the use of ultrathin films of only a few monolayer thickness can induce charge transfer to adsorbates with a high electron affinity such as oxygen molecules.1-3 To address the question of charge transfer on a molecular level thin and ultrathin single crystalline alkaline earth oxide films grown on Mo(100) were investigated using electron paramagnetic resonance (EPR) spectroscopy. On the one hand we will discuss the properties of ultrathin MgO films between 4 and 10 ML thickness focusing on the adsorption properties of molecular oxygen. While molecular oxygen is thought to be weakly physisorbed on bulk stoichiometric MgO(100) surfaces, the stoichiometric surfaces of the thin films bind oxygen much stronger, showing a desorption only above 300 K. In addition, electron spin resonance spectroscopy done under ultrahigh vacuum conditions show that these oxygen molecules are in fact O2- radical species on the surface, being created by a charge transfer from the metal substrate onto the oxygen molecule. Spectroscopic evidence for structural modifications of the MgO surface namely polaronic distortions will be discussed. The situation on the ultrathin film will be compared to transition metal doped alkaline earth oxide films, which are thick enough (typically around 20 ML) to ensure that charge transfer from the metal substrate does not occur. We will discuss the geometric and electronic properties of the transition metal dopants focusing on Mo ions and discuss their impact on the redox chemistry of these surfaces. [1] Hellman, A.; Klacar, S.; Grönbeck, H. J. Am. Chem. Soc. 2009, 131, 16636 [2] Frondelius, P.; Häkkinen, H.; Honkala, K. Phys. Chem. Chem. Phys. 2010, 12, 1483. [3] Stavale, F.; Shao, X.; Nilius, N.; Freund, H. J.; Prada, S.; Giordano, L.; Pacchioni, G. J. Am. Chem. Soc. 2012, 134, 11380.

Electron transfer reactions at single crystal oxide surfaces as monitored by electron paramagnetic resonance spectroscopy: Alkaline earth oxide surfaces as exploratory examples

249th National Meeting (2015)

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