Photoelectron spectroscopy of transition metal oxide interfaces

Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot OX11 0DE, UK

^a e-mail: jorg.zegenhagen@diamond.ac.uk

Received: 5 February 2015
Revised: 23 March 2015
Accepted: 14 April 2015
Published online: 21 May 2015

Abstract

In the present paper we review applications of the photoelectron spectroscopy (PES) technique to the investigation of transition metal oxide (TMO) interfaces. We summarize very briefly some of the principle, specific characteristics of TMOs. Because of the buried nature of the interfaces, the photoelectrons must penetrate certain thicknesses of material, which is easier with higher kinetic energies in the keV range. Thus, we also briefly summarize some of the hallmarks of hard X-ray photoelectron spectroscopy (HAXPES), before presenting four explicit samples of the analysis of TMO interfaces: The LaAlO₃/SrTiO₃ (0 0 1) interface, which had attracted attention because of the discovery of a sheet of high mobility electrons below the thin layer of LaAlO₃; superlattices of the two insulators CaCuO₂ and SrTiO₃, which can be prepared to become superconducting at about 40 K; epitaxial films of the 90 K superconductor GdBa₂Cu₃O_7−δ on NdGaO₃; and finally the analysis of the nucleation of the 90 K superconductor YBa₂Cu₃O_7−δ on SrTiO₃ (0 0 1). The latter two cases of the investigation of the superconducting films are examples of photoelectron spectroscopy by X-ray standing wave (XSW) excitation. Because of this, the bare essential features of the XSW technique are also briefly reviewed.