Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 81: Oxide and Insulator Surfaces III

O 81.3: Talk

Thursday, April 3, 2014, 16:30–16:45, PHY C 213

Importance of Space-Charge effects for the Concentration of Defects at Metal-Oxide Surfaces — Norina A. Richter¹, Sabrina Sicolo², •Sergey V. Levchenko¹, Joachim Sauer², and Matthias Scheffler¹ — ¹Fritz-Haber-Institut der Max-Planck-Gesellschaft — ²Humboldt Universität zu Berlin

We consider the charge-carrier conductivity induced by doping as a thermodynamic factor in the context of defect formation. As a technologically relevant example, we study surface oxygen vacancies (F centers) in MgO. Defect formation energies are determined using ab initio atomistic thermodynamics in combination with hybrid density-functional theory (DFT), with parameters of the exchange-correlation functional optimized according to a condition on DFT ionization energies. Formation energies for neutral defects are validated by coupled-cluster CCSD(T) calculations for embedded clusters. The virtual-crystal approximation [1] is used for a realistic modeling of doping. We find that at catalytically relevant conditions charge transfer between surface defects and dopants in deeper layers leads to formation of a macroscopically extended space-charge region. The concentration of F_s²⁺ centers at the (100) terrace of p-type MgO can be as high as 1%, while F_s⁺ and F_s⁰ concentrations are negligible in both p-type and n-type MgO [2].—[1] L. Vegard, Z. Phys. 5, 17 (1921); M. Scheffler, Physica B+C, 146, 176 (1987); [2] N.A. Richter, et al., Phys. Rev. Lett. 111, 045502 (2013).