Seminars Archive

Band Bending at Ferroelectric Surfaces and Interfaces Investigated by X-ray Photoelectron Spectroscopy

Abstract
X-ray photoelectron spectroscopy (XPS) is a widely utilized technique for characterization of surfaces and interfaces, owing to its chemical and surface sensitivity [1]. Ferroelectrics are also intensely used and investigated materials nowadays, but only quite recently models were proposed for charge compensation of the depolarization field [2]. Amongst a wide variety of techniques derived from basic XPS, recently it was shown that high resolution XPS combined with great care in compensating charge effects may lead to a new functionality of this technique, in quantifying band bending at surfaces and interfaces [3-8]. More specifically, the core level shifts are sensitive to the conduction and valence band bending at interfaces, which is of particular interest for ferroelectrics and for metal/ferroelectric interfaces. In this work I will review most recent results obtained by using XPS to quantify band bendings at metal-semiconductor (Schottky) interfaces [4], at free ferroelectric surfaces [3,5], and at metal-ferroelectric surfaces [6], evidencing new phenomena such as competing Schottky barrier and reduction of the surface potential through over-compensation by charge provided by the metal [7], or preferential adsorption of molecules onto areas of given out-of-plane polarization [8], which opens new functionalities of ferroelectrics in surface chemistry and catalysis. References: [1] S. Hüfner, Photoelectron Spectroscopy: Principles and Applications, 3rd Ed, Springer, Berlin, 2003. [2] L. Pintilie and M. Alexe, J. Appl. Phys. 98, 124103 (2005). [3] F. Chen and A. Klein, Phys. Rev. B 86, 094105 (2012). [4] N.G. Apostol, L.E. Stoflea, G.A. Lungu, C. Chirila, L. Trupina, R.F. Negrea, C. Ghica, L. Pintilie, C.M. Teodorescu, Appl. Surf. Sci. 273, 415-425 (2013). [5] N.G. Apostol, L.E. Stoflea, G.A. Lungu, C.A. Tache, L. Pintilie, C.M. Teodorescu, Mater. Sci. Eng. B 178, 1317-1322 (2013). [6] N.G. Apostol, L.E. Stoflea, G.A. Lungu, L.C. Tanase, C. Chirila, L. Frunza, L. Pintilie, C.M. Teodorescu, Thin Solid Films 545, 13-21 (2013). [7] N.G. Apostol, L.E. Stoflea, C. Chirila, L. Trupina, R. Negrea, L. Pintilie, C.M. Teodorescu, ACS Appl. Mater. Interf., submitted (revised) (2013). [8] L.E. Stoflea, N.G. Apostol, N. Răduţoiu, C.M. Teodorescu, Phys. Stat. Solidi - RRL, submitted (2013).