A mechanism of photo-induced desorption of oxygen atoms from MgO nano-crystals

Using embedded cluster quantum mechanical calculations we developed a model of photo-induced processes and desorption of MgO surface corners. Our calculations suggest that hyper-thermal desorption of both oxygen and magnesium atoms may take place from corner sites at the MgO surface as a result of sequential absorption of two photons and formation of a bi-exciton. Preliminary desorption experiments utilizing MgO thin films irradiated by 4.66 eV nano-second laser pulses support these conclusions. These films are known for their columnar structure with many low-coordinated surface sites. The photon energy was specifically chosen to match the excitation energy of surface corners, which is known from previous experimental studies and theoretical calculations. Our experiments for the first time demonstrated desorption of oxygen atoms with hyper-thermal velocities.