Photoinduced Desorption of Hyperthermal Oxygen and Metal Atoms from Oxide Nanostructures

Predictive and controlled modification of electronic and atomic structures of surfaces using light requires understanding of individual photoinduced processes in relation to specific surface structures as well as knowledge of the mechanisms of energy accumulation and release in these processes (see Figure). [1,2] Recently, we have demonstrated experimentally that hyperthermal oxygen and Mg and Ca atoms can be emitted from nanostructured MgO and CaO under irradiation by low-fluence laser light with photons of sub-band-gap energies (4.7 eV). [3] At the same time, only thermal oxygen atoms are desorbed under 7.9 eV irradiation of these materials. [4] In this contribution we apply an ab initio embedded cluster calculations to understand the difference between the processes induced by the low-energy and high-energy photons and to develop mechanisms of electron and hole trapping and exciton localisation induced by electronic excitation of these systems. A combination of several photo-induced processes provides an efficient two-step mechanism for emission of hyperthermal low-coordinated Mg(Ca) and O atoms induce