title: Understanding surface structure and chemistry of single crystal lanthanum aluminate.
abstract: The surface crystallography and chemistry of a LaAlO3single crystal, a material mainly used as a substrate to deposit technologically important thin films (e.g. for superconducting and magnetic devices), was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy. The surface was determined to be terminated by Al-O species, and was significantly different from the idealised bulk structure. Termination reversal was not observed at higher temperature (600 °C) and chamber pressure of 10-10Torr, but rather an increased Al-O occupancy occurred, which was accompanied by a larger outwards relaxation of Al from the bulk positions. Changing the oxygen pressure to 10-6Torr enriched the Al site occupancy fraction at the outermost surface from 0.245(10) to 0.325(9). In contrast the LaO, which is located at the next sub-surface atomic layer, showed no chemical enrichment and the structural relaxation was lower than for the top AlO2layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
authors.forename: Stevin S
authors.initials: SS
authors.lastname: Pramana
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavallaro
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
authors.forename: Jiahui
authors.initials: J
authors.lastname: Qi
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom.
authors.forename: Chris L
authors.initials: CL
authors.lastname: Nicklin
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
authors.forename: Mary P
authors.initials: MP
authors.lastname: Ryan
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Skinner