In-situ investigation of surface band-bending in the ZnO(0001)-OH/electrolyte interface via the excitonic response
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DPG-Tagung der Sektion Kondensierte Materie (SKM)
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In recent years, the effects of adsorbates on the surface band-bending in ZnO have been studied in UHV and characterized by Valence-Band XPS ,; showing an alteration of the space-charge region due to the electron transfer that occurs in the absorption processes. In this work we aim to understand the surface optical properties of a hydroxide stabilized ZnO(0001)-OH surface, previously obtained by chemical etching by Valtiner et al. , in contact with 0.1M NaClO4 as an electrolyte at a certain applied potential. By changing the cell applied potential, we can, in principle, produce any form of band bending at the semiconductor surface  including the flat-band condition. We use in-situ spectroscopic ellipsometry while varying the cell applied potential in order to study the response of the discrete excitons due to the inner electrical fields created by the band bending. We can identify the flat-band potential (Vfb) as the one where the imaginary part of the pseudo-dielectric function shows no change at the energy corresponding to the discrete exciton transition. By modulating the potential barrier at the interface we are able to investigate the response of the excitons at any given applied potential. Furthermore, given the significant sensibility of the band-bending to a surface dipole change, it is possible to use this technique to look into the effects of a modification of the surface such as adsorbates.