Defects in Oxygen-Depleted Titanate Nanostructures

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• 作者：Andrea Vittadini ; Michael Schirmer ; Marie-Madeleine Walz ; Florian Vollnhals ; Thomas Lukasczyk ; Hans-Peter Steinr眉ck ; Hubertus Marbach ; Alexander Riss ; Michael J. Elser ; Benedikt Sch眉rer ; Oliver Diwald
• 刊名：Langmuir
• 出版年：2012
• 出版时间：May 22, 2012
• 年：2012
• 卷：28
• 期：20
• 页码：7851-7858
• 全文大小：496K
• 年卷期：v.28,no.20(May 22, 2012)
• ISSN：1520-5827

文摘

The identification of defects and their controlled generation in titanate nanostructures is a key to their successful application in photoelectronic devices. We comprehensively explored the effect of vacuum annealing on morphology and composition of Na₂Ti₃O₇ nanowires and protonated H₂Ti₃O₇ nanoscrolls using a combination of scanning electron microscopy, Auger and Fourier-transform infrared (FT-IR) spectroscopy, as well as ab initio density functional theory (DFT) calculations. The observation that H₂Ti₃O₇ nanoscrolls are more susceptible to electronic reduction and annealing-induced n-type doping than Na₂Ti₃O₇ nanowires is attributed to the position of the conduction band minimum. It is close to the vacuum level and, thus, favors the Fermi level-induced compensation of donor states by cation vacancies. In agreement with theoretical predictions that suggest similar formation energies for oxygen and sodium vacancies, we experimentally observed the annealing induced depletion of sodium from the surface of the nanowires.