title: Donor characteristics of transition-metal-doped oxides: Cr-doped MgO versus Mo-doped CaO.
abstract: The ability of Mo (Cr) impurities in a CaO (MgO) matrix to act as charge donors to adsorbed gold has been investigated by means of scanning tunneling microscopy and density functional theory. Whereas CaO(Mo) features a robust donor characteristic, as deduced from a charge-transfer-driven crossover in the Au particles' geometry in the presence of dopants, MgO(Cr) is electrically inactive. The superior performance of the CaO(Mo) system is explained by the ability of the Mo ions to evolve from a +2 oxidation state in ideal CaO to a +5 state by transferring up to three electrons to the Au adislands. Cr ions in MgO, on the other hand, are stable only in the +2 and +3 charge states and can provide a single electron at best. Since this electron is likely to be captured by cationic vacancies or morphological defects in the real oxide, no charge transfer to Au particles takes place in this case. On the basis of our findings, we have developed general rules on how to optimize the electron donor characteristics of doped oxide materials.
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany.
authors: Fernando
authors: F
authors: Stavale
authors: Xiang
authors: X
authors: Shao
authors: Niklas
authors: N
authors: Nilius
authors: Hans-Joachim
authors: HJ
authors: Freund
authors: Stefano
authors: S
authors: Prada
authors: Livia
authors: L
authors: Giordano
authors: Gianfranco
authors: G
authors: Pacchioni