大型放射光施設 SPring-8

Speaker: Dr. Jun Fujii

Language: English

Affiliation: Consiglio Nazionale delle Ricerche (CNR), Istituto Officina dei Materiali (IOM)

Title: APE-NFFA Laboratory : Nanoscience Laboratory in Synchrotron Facility

Abstract:
　APE (Advanced Photoelectric Effect experiments) – NFFA (Nanoscience Foundries & Fine Analysis) laboratory was designed as a state-of-the art facility for sample growth, sample characterization and advanced on-line spectroscopy at Elettra ^[1]. The sample growth part is composed of Pulsed Laser Deposition (PLD) and Molecular Beam Epitaxy (MBE) systems as well as a sample preparation chamber with classical physical vapor deposition type evaporators. The characterization part offers variety techniques (LEED-Auger, Scanning Electron Microscope (SEM), Tunneling Electron Microscope (TEM), Scanning Tunneling Microscope (STM)/ Scanning Tunneling Spectroscopy (STS), Magnetic-Optic Kerr Effect (MOKE), X-ray Diffraction (XRD)) to analyze and optimize nanoscience samples. The laboratory is integrated with synchrotron radiation beamlines for Angular Resolved PhotoElectron Spectroscopy (ARPES) and spin-ARPES, X-ray Absoprtion Spectrscopy (XAS), X-ray Magnetic Circular Dichroism (XMCD), X-ray Magnetic Linear Dichroism (XMLD) and X-ray PhotoElectron Spectroscopy (XPS). Elettra is the third generation ring (2 and 2.4GeV) that has been operated since October 1993 and since 2010 operates in the top up mode for both 2 and 2.4 GeV operational energy. Elettra is composed of 12 double bend achromats and 11 6m straight sections for insertion devices (ID’s) (4.6m usable for ID’s) forming a ring roughly 260 m in circumference. Currently 28 beamlines utilize the radiation generated from the Elettra sources. It is currently planning a major upgrade of the ring and of the beamlines in the framework of project Elettra 2.0, which will be presented in the talk.

　I will present two examples of the investigations carried out at the laboratory: The surface electronic states of anatase TiO₂ films grown with PLD and the electronic and magnetic properties of La₁-xCaxMnO₃ (LCMO) films grown with MBE. Stoichiometric anatase TiO₂ is an insulator with 3.2eV band gap. However after annealing or under photoirradiation, the surface of anatase shows metallic character, which is attributed to the doping of electrons by the creation of oxygen vacancies ^[2]. The role of oxygen vacancies has been strongly debated in the last decade, involved in the local and non-local character of the doped electrons, and the 2D or 3D character of the non-local electrons ^[3,4,5]. Here we combine X-ray based electron spectroscopies and model calculation providing clarification on the role, the formation and the control of defects states. The electronic structure of transition metal oxides (TMOs) displays dramatic responses to small external perturbations. In strained La₁-xCaxMnO₃ (LCMO) films with room-temperature insulating phase, we observe a novel metallic phase appearing when cooling down to 60 K, after an adequate post-growth annealing treatment in oxygen atmosphere. On the contrary, as-grown samples are metallic already at 250 K, and their metallicity is accompanied by in-plane long range magnetic order. We have investigated the mechanism of the competition between insulating and metallic phases and the analysis of the ferro or antiferromagnetic character of the metallic phase by means of both chemically and magnetically sensitive spectroscopic analysis, combined with careful characterization and growth of samples.

1.trieste.nffa.eu/
2.S. Moser et al.. Phys. Rev. Lett. 110, 196403 (2013).
3.B. Gobaut et al., ACS Appl. Mater. Interfaces 9, 23099 (2017).
4.Y. Aiura et al., J. Phys. Chem. C 122, 19661 (2018).
5.R. Yukawa et al., Phys. Rev. Lett. 97, 165428 (2018).