Band bending in Au/Pb(Zr,Ti)O₃ investigated by X-ray photoelectron spectroscopy: Dependence on the initial state of the film

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• 作者：Nicoleta G. Apostol ; Laura E. Stoflea ; George A. Lungu ; Liviu C. Tanase ; Cristina Chirila ; Ligia Frunza ; Lucian Pintilie ; Cristian M. Teodorescu
• 关键词：Ferroelectrics ; Schottky barrier ; X-ray photoelectron spectroscopy ; Band bending ; Surface charge
• 刊名：Thin Solid Films
• 出版年：2013
• 出版时间：31 October, 2013
• 年：2013
• 卷：545
• 期：Complete
• 页码：13-21
• 全文大小：3425 K

文摘

This work presents a systematic investigation by X-ray photoelectron spectroscopy of the mechanisms of interface formation and band bending for Au/Pb(Zr,Ti)O₃ (PZT) layers grown on SrTiO₃(001) with a SrRuO₃ buffer layer, as function on the initial state of the PZT surface. After isolating the chemical effects, such as the formation of metal Pb at some surfaces, the evolution of the core levels with Au deposition allows one to simultaneously investigate the Schottky barrier formation and the built-in potential effects (charging induced by the static ferroelectric polarization). Areas of the sample with outwards P⁽⁺⁾ and no polarization perpendicular to the surface P⁽⁰⁾ are identified for all samples. Only the freshly prepared sample exhibited inward polarization areas P^(?). The built-in potential is on the order of 0.9 eV, while the Schottky band bending ranges from 0.2 to 0.6 eV towards lower absolute energies, therefore indicating that the work function of PZT exceeds that of Au deposited. We report also a chemically differentiate value of the built-in potential, manifested by a preferential distribution of the charge accumulated at the surface on Ti and O atoms. The O 1s and Ti 2p core levels manifest quite strong variations with the Au thickness for freshly prepared samples, resulting in shifts on the order of 2 eV towards lower binding energies. Au deposited on areas with an outward polarization is positively charged by the same potential as atoms from the PZT film (0.8-0.9 eV), whereas Au deposited on areas with an inward polarization forms a continuous grounded layer, which progressively pumps the accumulated charge and removes the polarization of these areas.