Centre d’Élaboration de Matériaux et d’Etudes Structurales (UPR 8011)

Accueil > Recherche > SINanO : Surfaces, Interfaces et Nano-Objets > Thématiques de Recherche

Interfaces : formation mechanisms and impact on the mechanical, magnetic, electronic and optical properties

SINanO Highlights - The names of the team members are in blue

Noble Metal Nanocluster Formation in Epitaxial Perovskite Thin Films

M. Lee, R. Arras, R. Takahashi, B. Warot-Fonrose, H. Daimon, M.J. Casanove, M. Lippmaa

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We studied the synthesis of nanocomposite materials consisting of noble metal clusters embedded in an oxide semiconductor matrix. The embedded nanostructures form in a simple self-organized single-step growth process. The primary interest is in developing materials for photo-electrochemical energy conversion where spatially inhomogeneous band structures can enhance photogenerated charge separation and carrier extraction from a semiconductor. We show that spontaneous segregation of metallic Ir occurs during the initial growth of an Ir:SrTiO3 thin film. Cross-sectional transmission electron microscopy suggests that the nanoscale Ir clusters are epitaxial with the host lattice, and their presence is not detectable by surface morphology measurements. Published in ACS Omega 3 ,2169-2173 (2018).

Strain induced atomic structure at Ir-doped LaAlO3/SrTiO3 interface

M. Lee, R. Arras, B. Warot-Fonrose, T. Hungria, M. Lippmaa, H. Daimon, M.J. Casanove

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The structure of Ir-doped LaAlO3/SrTiO3(001) interfaces was investigated at the atomic scale using probe-corrected transmission electron microscopy in high-angle annular dark-field scanning mode (HAADF-STEM) and electron energy loss spectroscopy (EELS), combined with first principles calculations. We report the evolution of the strain state experimentally measured in a 5 unit-cell thick LaAlO3 film as a function of the Ir concentration in the topmost SrTiO3 layer. It is shown that the LaAlO3 layers remain fully elastically strained up to 3% of Ir doping, whereas a higher doping level seems to promote strain relaxation through enhanced cationic interdiffusion. The observed differences between the energy loss near edge structure (ELNES) of Ti-L2 ;3 and O-K edges at non-doped and Ir-doped interfaces are consistent with the location of the Ir dopants at the interface, up to 3% of Ir doping. These findings, supported by the results of density functional theory (DFT) calculations, provide strong evidence that the effect of dopant concentration on the properties of this kind of interface should not be analyzed without essential information coming from fine structural and chemical analysis of the grown structures.


Inhomogeneous spatial distribution of the magnetic transition in an iron-rhodium thin films

C. Gatel, B. Warot-Fontrose, N. Biziere, L. A. Rodriguez, D. Reyes, R. Cours, M. Castiella, and M.J. Casanove

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Monitoring a magnetic state using thermal or electrical activation is mandatory for the development of new magnetic devices, for instance in heat or electrically assisted magnetic recording or room-temperature memory resistor. Compounds such as FeRh, which undergoes a magnetic transition from an antiferromagnetic state to a ferromagnetic state around 100 °C, are thus highly desirable. However, the mechanisms involved in the transition are still under debate. Here we use in situ heating and cooling electron holography to quantitatively map at the nanometre scale the magnetization of a cross-sectional FeRh thin film through the antiferromagnetic–ferromagnetic transition. Our results provide a direct observation of an inhomogeneous spatial distribution of the transition temperature along the growth direction. Most interestingly, a regular spacing of the ferromagnetic domains nucleated upon monitoring of the transition is also observed. Beyond these findings on the fundamental transition mechanisms, our work also brings insights for in operando analysis of magnetic devices.

This work has been published in Nature Communications.

Elastic properties of AlAs-like and InSb-like strained interfaces in [InAs/AlSb] heterostructures

Y. Claveau, M. Vallet, H. Tang, N. Combe and A. Ponchet

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[AlSb/InAs] multilayer (period 3 nm) built with two perfect Al-As type interfaces : Interplanar distances d in the growth direction are calculated by DFT (blue dots) and linear elasticity (green squares)
[AlSb/InAs] multilayer (period 3 nm) built with two perfect Al-As type interfaces : Interplanar distances d in the growth direction are calculated by DFT (blue dots) and linear elasticity (green squares)

Elastic properties of [InAs/AlSb] heterostructures coherently grown on a (001) InAs substrate are investigated by the density functional theory and compared to the prediction of the linear elasticity theory. The stress-strain curves of the four involved binaries (InAs, AlAs, AlSb, and InSb) are first studied : a significant deviation to the linear elasticity theory is observed for strain above 2.5% (in absolute value). Nevertheless, the relationship between the out-of-plane and in-plane strains is in a good agreement with the prediction of the linear elasticity theory. In the heterostructures, highly strained perfect AlAs-like and InSb-like interfaces are examined. The interfacial strains calculated using the density functional theory are in a surprisingly good agreement with the prediction of the linear elasticity theory. The reduction of the layer thickness to the thinnest possible InAs or AlSb layers while keeping perfect interfaces does not change theseconclusions. Appl. Phys. Lett. 109, 041903 (2016).


Highly strained AlAs-type interfaces in InAs/AlSb heterostructures

M. Vallet, Y. Claveau, B. Warot-Fonrose, C. Gatel, J. Nicolai, N. Combe, C. Magen, R. Teissier, A. N. Baranov and A. Ponchet

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Out-of-plane strain maps and profiles for small (a, d), medium (b, e) and large (c, f) masks.
Out-of-plane strain maps and profiles for small (a, d), medium (b, e) and large (c, f) masks.

Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated by atomic resolution scanning transmission electron microscopy. Experimental strain profiles were compared to those coming from a model structure. High negative out-of-plane strains with the same order of magnitude as perfect Al-As interfaces were observed. The effects of the geometrical phase analysis used for strain determination were evidenced and discussed in the case of abrupt and huge variations of both atomic composition and bond length as observed in these interfaces. Intensity profiles performed on the same images confirmed that changes of chemical composition are the source of high strain fields at interfaces. The results show that spontaneously assembled interfaces are not perfect but extend over 2 or 3 monolayers. Appl. Phys. Lett. 108, 211908 (2016).

Formation of strained interfaces in AlSb/InAs multilayers grown by MBE for quantum cascade lasers

J. Nicolaï, B. Warot-Fonrose, C. Gatel, R.Teissier, A. N. Baranov, C. Magen and A. Ponchet

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Interfacial strains can be observed from strain map (a) and profile (b). Interfacial layers are also evidenced in STEM-HAADF images (c) and associated profile of intensity (d).
Interfacial strains can be observed from strain map (a) and profile (b). Interfacial layers are also evidenced in STEM-HAADF images (c) and associated profile of intensity (d).

Structural and chemical properties of InAs/AlSb interfaces have been studied by transmission electron microscopy. InAs/AlSb multilayers were grown by molecular beam epitaxy with different growth sequences at interfaces. The out-of-plane strain, determined using high resolution microscopy and geometrical phase analysis, has been related to the chemical composition of the interfaces analyzed by high angle annular dark field imaging. Considering the local strain and chemistry, we estimated the interface composition and discussed the mechanisms of interface formation for the different growth sequences. In particular, we found that the formation of the tensile AlAs-type interface is spontaneously favored due to its high thermal stability compared to the InSb-type interface. We also showed that the interface composition could be tuned using an appropriate growth sequence. Journal of Applied Physics, 118, 035305 (2015).

Sb surfactant mediated growth of InAs/AlAs0.56Sb0.44 strained quantum well for intersubband absorption at 1.55 µm

Y. Zhao, J. Nicolaï, N. Bertru, H. Folliot, M. Perrin, C. Gatel, B. Warot-Fonrose and A. Ponchet

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Surfactant mediated growth of strained InAs/AlAs0.56Sb0.44 quantum wells on InP (001) substrate is investigated. X ray diffraction and transmission electron microscopy analysis reveal that the supply of antimony on InAs surface delays the 2D to 3D growth transition and allows the growth of thick InAs/AlAsSb quantum wells. Quantum well as thick as 7 ML, without defect was achieved by Sb surfactant mediated growth. Further high resolution transmission electron microscopy measurement and geometric phase analysis show that InAs/AlAsSb interfaces are not abrupt. At InAs on AlAsSb interface, the formation of a layer presenting lattice parameter lower than InP leads to a tensile stress. From energetic consideration, the formation of As rich AlAsSb layer at interface is deduced. At AlAsSb on InAs interface, a compressive layer is formed. The impact on optical properties and the chemical composition of this layer are discussed from microscopic analysis and photoluminescence experiments.