Abstract
The surface crystallography and chemistry of a LaAlO3 single 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 10−10 Torr, 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 10−6 Torr 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 AlO2 layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3 is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.
Highlights
Pramana SS, Cavallaro A, Qi J, Nicklin CL, Ryan MP, Skinner SJ
The surface crystallography and chemistry of a LaAlO3 single crystal, a material mainly used as a substrate to deposit technologically important thin films, was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy
The termination of the LaAlO3 (001) surface has been reported to vary with temperature and oxygen partial pressure and there are inconclusive results reported in the literature[9,10,11]
Summary
Pramana SS, Cavallaro A, Qi J, Nicklin CL, Ryan MP, Skinner SJ. Understanding surface structure and chemistry of single crystal lanthanum aluminate. The surface crystallography and chemistry of a LaAlO3 single 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. One example is with SrTiO3 resulting in superconducting[1], strong spin-orbit coupling[2] and magnetic phenomena[3] This substrate is used to deposit low frequency dielectric SrTiO34 and high critical current density YBa2Cu3O7−x superconducting films[5]. Whilst the bulk structure of LaAlO3 has been documented at different temperatures and pressures, the surface crystallography and chemistry are less well understood due to the lack of characterisation techniques with appropriate sensitivity. Jacobs et al.[12] suggested that a termination of LaO (1.37 J m−2) was energetically favoured over AlO2 (1.79 J m−2)
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