Visualising emergent phenomena at oxide interfaces

Knowledge of atomic-level details of structure, chemistry, and electronic states is paramount for a comprehensive understanding of emergent properties at oxide interfaces. We utilise a novel methodology based on atomic-scale electron energy loss spectroscopy (EELS) to spatially map the electronic states tied to the formation of a two-dimensional electron gas (2DEG) at the prototypical non-polar/polar $TiO_2$/$LaAlO_3$ interface. Combined with differential phase contrast analysis we directly visualise the microscopic locations of ions and charge and find that 2DEG states and $Ti^{3+}$ defect states exhibit different spatial distributions. Supported by density functional theory (DFT) and inelastic scattering simulations we examine the role of oxygen vacancies in 2DEG formation. Our work presents a general pathway to directly image emergent phenomena at interfaces using this unique combination of arising microscopy techniques with machine learning assisted data analysis procedures.Comment: 17 pages, 10 figure

Direct-ARPES and STM investigation of FeSe thin film growth by Nd:YAG laser

Funding: D.M. acknowledges the receipt of a fellowship from the ICTP Programme for Training and Research in Italian Laboratories, Trieste, Italy. R.A. and A.B. acknowledges the support by the Austrian Science Fund (FWF) through Projects No. P26830, No. P31423 and H2020 NFFA-Europe 654360.Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials.Publisher PDFPeer reviewe

Effet de la contrainte liée à l’épitaxie sur l’anisotropie magnétique dans les couches minces de LSMO en vue d’applications spintroniques

We report a quantitative analysis of thickness dependent epitaxial strain-induced effects in La1-xSrxMnO3 (LSMO) (001) (x = 0.33) thin films of thicknesses (50, 25 and 12 nm) grown on various single crystal substrates such as SrTiO3 (STO) (001), STO buffered MgO (001), NdGaO3 (NGO) (110) and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001) by Pulsed Laser Deposition (PLD) technique. We also report the composition dependent magnetic properties of LSMO thin films with x = 0.33 and 0.38 in particular grown onto LSAT (001) substrate by Molecular Beam Epitaxy (MBE). The study mainly includes measurements such as X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), temperature dependent four-probe resistivity, magnetization properties by Superconducting Quantum Interference Device (SQUID), magnetic anisotropy by Magneto-Optical Kerr Magnetometry (MOKE). Our results highlight the detailed study of angular evolution and thickness dependent magnetic anisotropy, remanence, coercivity and switching field in epitaxial LSMO thin films. Temperature-dependent studies are also performed on few selected films. We will also discuss the cause of magnetic anisotropy in LSMO films i.e., magneto-crystalline and magnetostriction anisotropy and the effects of steps or substrate mis-cut induced anisotropy.Nous présentons une étude des effets de contrainte induits par l’épitaxie dans des couches minces La1-xSrxMnO3 (LSMO) (001) (x = 0.33) pour 3 épaisseurs de films (50, 25 et 12 nm) déposés par Ablation Laser Pulsée (PLD) sur différents substrats tels que SrTiO3 (STO) (001), STO buffered MgO (001), NdGaO3 (NGO) (110) et (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001). L’étude est complétée par l’effet de la composition sur les propriétés magnétiques de couches minces de La1-xSrxMnO3 avec x=0,33 et 0,38 déposées par Epitaxie à Jets Moléculaires (MBE). Des caractérisations par diffraction de rayons X (XRD), et microscopie à force atomique (AFM), des mesures de résistivité électrique en quatre points en fonction de la température, d’aimantation par magnetometrie à SQUID (Superconducting Quantum Interference Device) et d’anisotropie magnétique par magnétométrie magnéto-optique Kerr vectorielle (MOKE) sont présentées. Les évolutions angulaires de l’anisotropie magnétique, de l’aimantation à rémanence, du champ coercitif et du champ de renversement d’aimantation ont ainsi pu être analysées pour des films épitaxiés LSMO de différentes épaisseurs. Des études en fonction de la température complètent les données. L’origine de l’anisotropie (magnétique, magnétocristalline, magnétostrictive ou liée aux effets de marches et d’angle de désorientation du substrat) est finalement discutée

Substrate strain induced effects in La0.7Sr0.3MnO3 thin films

International audienc

Substrate induced strain effects in La0.7Sr0.3MnO3 thin films

PosterInternational audienc

In-plane magnetic anisotropy studies of bi-axially strained La0.7Sr0.3MnO3 thin films by Magneto-Optical Kerr Magnetometry

International audienc

Pulsed laser deposited LaInO3 thin films and their photoluminescence characteristics

Photoluminescence studies of pulsed laser deposition grown LaInO3 thin films on TiO2 terminated SrTiO3 substrate showed a broad-band blue emission peaking at 412 nm, which is primarily attributed to the charge transfer transitions between oxygen and indium, inter (d-f) and intra (f-f) band transitions. The results are analysed based on the mechanism of absorption and emission within the d(10) levels of In3+ ions. Broadening of the photoluminescence emission is observed with reduction in size of the crystallite owing to quantum confinement effects

Supporting Information - Ion-induced lateral damage in the focused ion beam patterning of topological insulator Bi2Se3 thin films

Figure S1: Evolution of structural damage with increasing ion dose, Figure S2: Evolution of the I–V characteristics with increasing ion dose, Figure S3: Additional Transmission Electron Microscopy images for the 12.5 nm- thick sample, Figure S4: Additional Transmission Electron Microscopy images for the 40 nm- thick sample, Figure S5: Transmission Electron Microscopy images for the 52 nm- thick sample, Figure S6: Additional Transmission Electron Microscopy images for the 55 nm- thick sample, Figure S7: Transmission Electron Microscopy image with Fast Fourier Transforms of damaged regions. Reference [30] is cited in the Supplementary File.Peer reviewe

Ion-induced lateral damage in the focused ion beam patterning of topological insulator Bi2Se3 thin films

This article belongs to the Topic Advances in Functional Thin Films.Focused Ion Beam patterning has become a widely applied technique in the last few decades in the micro- and nanofabrication of quantum materials, representing an important advantage in terms of resolution and versatility. However, ion irradiation can trigger undesired effects on the target material, most of them related to the damage created by the impinging ions that can severely affect the crystallinity of the sample, compromising the application of Focused Ion Beam to the fabrication of micro- and nanosized systems. We focus here on the case of Bi2Se3, a topological material whose unique properties rely on its crystallinity. In order to study the effects of ion irradiation on the structure of Bi2Se3, we irradiated with Ga+ ions the full width of Hall-bar devices made from thin films of this material, with the purpose of inducing changes in the electrical resistance and characterizing the damage created during the process. The results indicate that a relatively high ion dose is necessary to introduce significant changes in the conduction. This ion dose creates medium-range lateral damage in the structure, manifested through the formation of an amorphous region that can extend laterally up to few hundreds of nanometers beyond the irradiated area. This amorphous material is no longer expected to behave as intrinsic Bi2Se3, indicating a spatial limitation for the devices fabricated through this technique.The financial support of the Gobierno de Aragón is acknowledged through a doctoral fellowship (R.G.A) and through the grant E13-20R, with European Social Funds (Construyendo Europa desde Aragón). The authors acknowledge support from networks COST FIT4NANO and CSIC Research Platform PTI-001, and from MCIN/AEI/10.13039/501100011033 through the grant PID2020-112914RB-I00.Peer reviewe