Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 55: Oxide and insulator surfaces: Structure, epitaxy and growth II

O 55.7: Talk

Wednesday, March 11, 2026, 12:15–12:30, HSZ/0204

Titanium intermixing into cuprous oxide thin films: An STM and XPS study — •Bo-Yi Zhong and Niklas Nilius — Carl-von-Ossietzky University, Institute of Physics, D-26111 Oldenburg, Germany

According to DFT calculations, gap size and p-type conductivity of binary Cu2O can be tuned over wide ranges by doping the material with transition metal ions. To test this assumption, we have prepared Cu/Ti mixtures and exposed them to different oxidation conditions. Mixing is only revealed at low temperature and gives rise to amorphous oxide films without diffraction pattern. Annealing in oxygen triggers a gradual phase separation, with TiOx moving to the surface and CuOx remaining at the interface to the Pt(111) support. The phase separation produces a distinct intensity behavior of the Ti 2p and Cu 2p XPS peaks as a function of temperature. Morphologically, the Ti ions get embedded into the surface reconstruction of Cu2O(111) at low Ti content, as observed in atomically resolved STM images. With rising Ti level, the surface Ti-O forms large crystallites exposing distinct stripe-patterns on their surface, suggesting a TiO2(110)-type morphology. Moreover, STM spectroscopy finds a gap state at 1.5 eV in Ti-poor preparations, compatible with the empty-state resonance of the Ti impurities. At higher Ti content, the gap state broadens and evolves to the TiO2 conduction band. The electronic response of the phase-separated system, with Cu2O at the interface and TiO2 at the surface, resembles the one of a pn-junction.

Keywords: Oxide mixing; Cu; Ti; Phase separation; pn junction