Electronic Properties of Structural Defects at the MgO (001) Surface

Abstract

We have calculated the ionization energies, electron affinities, optical excitation energies, and relaxed electron and hole states at corners, kinks, and steps of the MgO (001) surface. The calculations are performed using an embedded cluster model and density functional theory and take into account the long-range surface polarization. The extent of localization of electronic states associated with specific structural defects at the surface is studied by the participation function method. The positions of energy levels of the surface sites with respect to the top of the surface valence band and the vacuum level are determined. The results demonstrate the existence of deep and shallow electron traps at steps, corners, and kinks of the MgO (001) surface, and establish direct correlation between common surface features and their spectroscopic and other electronic properties.

Surface-specific visible light luminescence from composite metal oxide nanocrystals

“…Consequently, engineering protocols that aim at the reproducible adjustment of color and emission intensity can be developed. In previous work, we have shown how nanocrystalline MgO exhibits particle-size-dependent absorption and luminescence properties [9] which are connected to low-coordinated sites at the surface such as corners and edges [10][11][12]. We have also shown how doping with the higher group two metals Ca, Sr, and Ba leads to a red-shift in excitation and luminescence energies [13][14][15][16].…”

“…Excitation energies are also calculated by time-dependent density functional theory. This type of approach has proved extremely reliable for predicting the electronic, optical, and chemical properties of MgO nanopowders and a wide range of defects [11,12,24,30,31,[37][38][39]. In our implementation, Mg and O ions in the quantum cluster are described at the all electron level using a Gaussian 6-311G** basis set.…”

“…3 Transmission electron microscopy images of MgO powders doped with 2 (a), 4 (b), and 6 % (c) of Ba. The related particle size distributions are plotted in (d) previously been attributed to transitions between electronic states localized near corner features [9][10][11][12]. On introduction of Ba, the absorption onset is reduced by about 0.5 eV and the low-energy peak near 4.7 eV is no longer clearly discernable.…”

“…They are cheap, widely available, non-toxic, and highly stable. The luminescence in these materials has a surface origin, therefore as particle size is reduced quantum yield is improved, while multiple scattering is minimized [9][10][11][12]. AEO can be prepared as highly dispersed solids via gas-phase synthesis and, thus, in the absence of solvents or surface groups that may affect the surface electronic structure in a less controllable way.…”

Gundlach oscillations and Coulomb blockade of Co nanoislands on MgO/Mo(100) investigated by scanning tunneling spectroscopy at 300 K

“…The dI/dU curves show an additional peak at about −2.7 V only on the bright spots. Referring to theoretical calculations this occupied state can be attributed either to charged F + color centers or to MgO surface defects at 3-fold coordinated surface sites [33]. The defect state around −2.7 V has been previously observed at MgO-islands on Ag(001) [14,16], but in contrast to one of these works, we do not observe an empty state at ≈+1 V. This might be due to a shift of the empty state towards the conduction band of the MgO within the MgO/Mo(100) system.…”