Doctoral thesis (Dissertations and theses)
Advanced Raman Spectroscopy of Ultrathin RNiO3 films
Schober, Alexander
2018
 

Files


Full Text
Manuscipt_Alexander_Schober.pdf
Publisher postprint (29.58 MB)
Download

All documents in ORBilu are protected by a user license.

Send to



Details



Keywords :
Raman spectroscopy; nickelates; ultrathin film
Abstract :
[en] The present work aims at investigating the structural properties of ultrathin rare-earth nickelate films by Raman Spectroscopy. Two remarkable cases are studied: LaNiO3 deposited epitaxially on LaAlO3, which shows a metal-to-insulator (MIT) transition but only in the ultrathin film regime, and NdNiO3 deposited epitaxially on NdGaO3 showing an upward shift of its MIT temperature by 130 K but only when deposited along the [111]pc direction of the substrate. The extremely small size of the films and overlap of the film and substrate signatures represent an experimental challenge and require the development of ingenious measurement and analysis strategies. To overcome these limitations, we propose the creation of a multidimensional dataset through depth profile acquisitions, in combination with multivariate analysis tools that were employed to extract the signature of the films. Different analysis strategies were used in both cases to adapt to the specificities of the respective samples. For the LNO films deposited along the [001]pc orientation of LAO, Raman depth profile measurements in combination with a Principal Component Analysis (PCA) allowed us to dissociate the signals from the film and the substrate. The evolution of the LNO peaks does not suggest any phase transition, thus, suggesting that a mechanism unrelated to the MIT of other nickelates is triggering the insulating state. This was further validated by ab initio calculations and TEM imaging. All acquired data point towards the following: as LNO becomes very thin, the surface layer (≈ 2pc u.c.), which is the most rigid part of the structure, imposes its structural and insulating characteristic. In the ultrathin regime this continues to a point where the surface of the film alters the interfacial unit cells of the substrate. For the NNO films deposited along the [111]pc orientation of NGO, depth profile measurements in combination with a Non-negative Matrix Factorisation (NMF) allowed us to dissociate the signals from the film and the substrate. The dissociation was performed at room temperature and the acquired knowledge was then utilised to fit an entire temperature series from 5 to 390 K. Comparing the tendency of the Raman signatures with other rare-earth nickelate allowed to support the proposed position of the film in the phase diagram of nickelates by a structural measurement. More generally, the methodology developed in this work is applicable to other systems and opens new perspectives for application of Raman spectroscopy on ultra-thin films.
Research center :
LIST - Luxembourg Institute of Science & Technology
Disciplines :
Physics
Author, co-author :
Schober, Alexander ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit ; Luxembourg Institute of Science and Technology, Belvaux, Luxembourg > Materials Research and Technology Department
Language :
English
Title :
Advanced Raman Spectroscopy of Ultrathin RNiO3 films
Defense date :
31 May 2018
Number of pages :
165
Institution :
Unilu - University of Luxembourg, Luxembourg
Degree :
Docteur en Physique
Promotor :
Kreisel, Jens
Guennou, Mael
President :
Jury member :
Noheda, Beatriz
Ghosez, Philippe
Focus Area :
Physics and Materials Science
Name of the research project :
Advanced Raman spectroscopy on perovksite oxide nanostructures
Funders :
Luxembourg Institute for Science and Technology (LIST)
FNR - Fonds National de la Recherche [LU]
Available on ORBilu :
since 28 June 2018

Statistics


Number of views
303 (15 by Unilu)
Number of downloads
248 (3 by Unilu)

Bibliography


Similar publications



Contact ORBilu