Band bending at copper and gold interfaces with ferroelectric Pb(Zr,Ti)O3 investigated by photoelectron spectroscopy

• Published in: Applied surface science 2015-11, Vol.354, p.459-468
• Main Authors: Apostol, Nicoleta G., Ştoflea, Laura E., Tănase, Liviu C., Bucur, Ioana Cristina, Chirilă, Cristina, Negrea, Raluca F., Teodorescu, Cristian M.
• Format: Article
• Language: English
• Subjects: Band bending; Band spectra; BEND PROPERTIES; Bending; Copper; Depolarization field; Ferroelectrics; Gold; INTERFACES; Lead zirco-titanate; Lead zirconate titanates; Photoelectron spectroscopy; PHOTOELECTRONS; Polarization; Pulsed laser deposition; SINGLE CRYSTALS; SPECTRA; Work functions; X-ray photoelectron spectroscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2015.02.167

•Synthesis of lead zirco-titanate (001) layers with nearly perfect stoichiometric transfer from substrates by pulsed laser deposition.•Copper forms continuous layers on Pb(Zr,Ti)O3, gold is deposited in form of nanoparticles.•Derivation of Schottky mechanism for band bending for gold deposited on lead zirco-titanate.•Cancellation of polarization-induced band bending for copper deposited on lead zirco-titanate.•Pb reduction observed only in the case of copper deposited on lead zirco-titanate. Interfaces formed by gold and copper on single crystal layers of (001) PbZr0.2Ti0.8O3 (PZT) produced by pulsed laser deposition and exhibiting outwards polarization are analyzed by X-ray photoelectron spectroscopy. The stoichiometry of the layers reproduces reasonably that of the PZT target. The band bending occurring at the interface between PZT and the metals is investigated by analyzing the core level shifts as function on the metal deposition. It is found that for Au/PZT(001) the gold layer is not continuous and the observed band bendings can be attributed to a Schottky mechanism, whereas for Cu/PZT(001) the copper layer is continuous; in this latter case, the observed band bendings towards higher energies (lower binding energies) can be attributed to a concomitant bending due to the Schottky effect together with the disappearance of the initial bending due to the outwards polarization of the samples. Metal Pb is observed to segregate only in the case of Cu/PZT(001), therefore the surface self-reduction might also be connected to the presence of a metal with lower work function, which for larger coverage forms a continuous metal layer, able to provide electrons to the surface. High resolution transmission electron spectroscopy yielded the disappearance of the tetragonal distortion in the case of Cu/PZT(001), in line with the assumption of disappearance of the polarization-induced band bending.