|
“Epitaxial stress-free growth of high crystallinity ferroelectric PbZr0.52Ti0.48O3 on GaN/AlGaN/Si(111) substrate”. Li L, Liao Z, Gauquelin N, Minh Duc Nguyen, Hueting RJE, Gravesteijn DJ, Lobato I, Houwman EP, Lazar S, Verbeeck J, Koster G, Rijnders G, Advanced Materials Interfaces 5, 1700921 (2018). http://doi.org/10.1002/ADMI.201700921
Abstract: <script type='text/javascript'>document.write(unpmarked('Due to its physical properties gallium-nitride (GaN) is gaining a lot of attention as an emerging semiconductor material in the field of high-power and high-frequency electronics applications. Therefore, the improvement in the performance and/or perhaps even extension in functionality of GaN based devices would be highly desirable. The integration of ferroelectric materials such as lead-zirconate-titanate (PbZrxTi1-xO3) with GaN has a strong potential to offer such an improvement. However, the large lattice mismatch between PZT and GaN makes the epitaxial growth of Pb(Zr1-xTix)O-3 on GaN a formidable challenge. This work discusses a novel strain relaxation mechanism observed when MgO is used as a buffer layer, with thicknesses down to a single unit cell, inducing epitaxial growth of high crystallinity Pb(Zr0.52Ti0.48)O-3 (PZT) thin films. The epitaxial PZT films exhibit good ferroelectric properties, showing great promise for future GaN device applications.'));
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.279
Times cited: 15
DOI: 10.1002/ADMI.201700921
|
|
|
“Etching induced formation of interfacial FeMn in IrMn/CoFe bilayers”. O'Donnell D, Hassan S, Du Y, Gauquelin N, Krishnan D, Verbeeck J, Fan R, Steadman P, Bencok P, Dobrynin AN, Journal of physics: D: applied physics 52, 165002 (2019). http://doi.org/10.1088/1361-6463/AB03BD
Abstract: The effect of ion etching on exchange bias in IrMn3/Co70Fe30 bilayers is investigated. In spite of the reduction of saturation magnetization caused by the embedding of Tr from the capping layer into the Co70Fe30 layer during the etching process, the exchange bias in samples with the same thickness of the Co70Fe30 layer is reducing in proportion to the etching power. X-ray magnetic circular dichroism measurements revealed the emergence of an uncompensated Mn magnetization after etching, which is antiferromagnetically coupled to the ferromagnetic layer. This suggests etching induced formation of small interfacial FeMn regions which leads to the decrease of effective exchange coupling between ferromagnetic and antiferromagnetic layers.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.588
DOI: 10.1088/1361-6463/AB03BD
|
|
|
“Evidence for exchange bias coupling at the perovskite/brownmillerite interface in spontaneously stabilized SrCoO3-\delta/SrCoO2.5 bilayers”. Behera BC, Jana S, Bhat SG, Gauquelin N, Tripathy G, Kumar PSA, Samal D, Physical review B 99, 024425 (2019). http://doi.org/10.1103/PHYSREVB.99.024425
Abstract: Interface effect in complex oxide thin-film heterostructures lies at the vanguard of current research to design technologically relevant functionality and explore emergent physical phenomena. While most of the previous works focus on the perovskite/perovskite heterostructures, the study of perovskite/brownmillerite interfaces remains in its infancy. Here, we investigate spontaneously stabilized perovskite-ferromagnet (SrCoO3-delta)/brownmillerite-antiferromagnet (SrCoO2.5) bilayer with T-N > T-C and discover an unconventional interfacial magnetic exchange bias effect. From magnetometry investigations, it is rationalized that the observed effect stems from the interfacial ferromagnet/antiferromagnet coupling. The possibility for coupled ferromagnet/spin-glass interface engendering such effect is ruled out. Strikingly, a finite coercive field persists in the paramagnetic state of SrCoO3-delta,whereas the exchange bias field vanishes at T-C . We conjecture the observed effect to be due to the effective external quenched staggered field provided by the antiferromagnetic layer for the ferromagnetic spins at the interface. Our results not only unveil a paradigm to tailor the interfacial magnetic properties in oxide heterostructures without altering the cations at the interface, but also provide a purview to delve into the fundamental aspects of exchange bias in such unusual systems, paving a big step forward in thin-film magnetism.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 2
DOI: 10.1103/PHYSREVB.99.024425
|
|
|
“Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces by charge-transfer-induced modulation doping”. Chen YZ, Trier F, Wijnands T, Green RJ, Gauquelin N, Egoavil R, Christensen DV, Koster G, Huijben M, Bovet N, Macke S, He F, Sutarto R, Andersen NH, Sulpizio JA, Honig M, Prawiroatmodjo GEDK, Jespersen TS, Linderoth S, Ilani S, Verbeeck J, Van Tendeloo G, Rijnders G, Sawatzky GA, Pryds N, Nature materials 14, 801 (2015). http://doi.org/10.1038/nmat4303
Abstract: Two-dimensional electron gases (2DEGs) formed at the interface of insulating complex oxides promise the development of all-oxide electronic devices. These 2DEGs involve many-body interactions that give rise to a variety of physical phenomena such as superconductivity, magnetism, tunable metalinsulator transitions and phase separation. Increasing the mobility of the 2DEG, however, remains a major challenge. Here, we show that the electron mobility is enhanced by more than two orders of magnitude by inserting a single-unit-cell insulating layer of polar La1−xSrxMnO3 (x = 0, 1/8, and 1/3) at the interface between disordered LaAlO3 and crystalline SrTiO3 produced at room temperature. Resonant X-ray spectroscopy and transmission electron microscopy show that the manganite layer undergoes unambiguous electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits Shubnikovde Haas oscillations and fingerprints of the quantum Hall effect, demonstrating unprecedented high mobility and low electron density.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 39.737
Times cited: 170
DOI: 10.1038/nmat4303
|
|
|
“Facile dry coating method of high-nickel cathode material by nanostructured fumed alumina (Al2O3) improving the performance of lithium-ion batteries”. Herzog MJ, Gauquelin N, Esken D, Verbeeck J, Janek J, Energy technology 9, 2100028 (2021). http://doi.org/10.1002/ENTE.202100028
Abstract: Surface coating is a crucial method to mitigate the aging problem of high-Ni cathode active materials (CAMs). By avoiding the direct contact of the CAM and the electrolyte, side reactions are hindered. Commonly used techniques like wet or ALD coating are time consuming and costly. Therefore, a more cost-effective coating technique is desirable. Herein, a facile and fast dry powder coating process for CAMs with nanostructured fumed metal oxides are reported. As the model case, the coating of high-Ni NMC (LiNi0.7Mn0.15Co0.15O2) by nanostructured fumed Al2O3 is investigated. A high coverage of the CAM surface with an almost continuous coating layer is achieved, still showing some porosity. Electrochemical evaluation shows a significant increase in capacity retention, cycle life and rate performance of the coated NMC material. The coating layer protects the surface of the CAM successfully and prevents side reactions, resulting in reduced solid electrolyte interface (SEI) formation and charge transfer impedance during cycling. A mechanism on how the coating layer enhances the cycling performance is hypothesized. The stable coating layer effectively prevents crack formation and particle disintegration of the NMC. In depth analysis indicates partial formation of LixAl2O3/LiAlO2 in the coating layer during cycling, enhancing lithium ion diffusivity and thus, also the rate performance.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Times cited: 25
DOI: 10.1002/ENTE.202100028
|
|
|
“Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth”. van der Torren AJH, Liao Z, Xu C, Gauquelin N, Yin C, Aarts J, van der Molen SJ, Physical Review Materials 1, 075001 (2017). http://doi.org/10.1103/PhysRevMaterials.1.075001
Abstract: The two-dimensional electron gas occurring between the band insulators SrTiO 3 and LaAlO 3 continues to attract considerable interest, due to the possibility of dynamic control over the carrier density, and the ensuing phenomena such as magnetism and superconductivity. The formation of this conducting interface is sensitive to the growth conditions, but despite numerous investigations, there are still questions about the details of the physics involved. In particular, not much is known about the electronic structure of the growing LaAlO 3 layer at the growth temperature (around 800 ◦ C) in oxygen (pressure around 5 × 10 −5 mbar), since analysis techniques at these conditions are not readily available. We developed a pulsed laser deposition system inside a low-energy electron microscope in order to study this issue. The setup allows for layer-by-layer growth control and in-situ measurements of the angle-dependent electron reflection intensity, which can be used as a fingerprint of the electronic structure of the surface layers during growth. By using different substrate terminations and growth conditions we observe two families of reflectivity maps, which we can connect either to samples with an AlO 2 -rich surface and a conducting interface; or to samples with a LaO-rich surface and an insulating interface. Our observations emphasize that substrate termination and stoichiometry determine the electronic structure of the growing layer, and thereby the conductance of the interface.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Times cited: 2
DOI: 10.1103/PhysRevMaterials.1.075001
|
|
|
“Functionalization of graphitic carbon nitride systems by cobalt and cobalt-iron oxides boosts solar water oxidation performances”. Benedet M, Andrea Rizzi G, Gasparotto A, Gauquelin N, Orekhov A, Verbeeck J, Maccato C, Barreca D, Applied surface science 618, 156652 (2023). http://doi.org/10.1016/j.apsusc.2023.156652
Abstract: The ever-increasing energy demand from the world population has made the intensive use of fossil fuels an overarching threat to global environment and human health. An appealing alternative is offered by sunlight-assisted photoelectrochemical water splitting to yield carbon-free hydrogen fuel, but kinetic limitations associated to the oxygen evolution reaction (OER) render the development of cost-effective, eco-friendly and stable electrocatalysts an imperative issue. In the present work, OER catalysts based on graphitic carbon nitride (g-C3N4) were deposited on conducting glass substrates by a simple decantation procedure, followed by functionalization with low amounts of nanostructured CoO and CoFe2O4 by radio frequency (RF)-sputtering, and final annealing under inert atmosphere. A combination of advanced characterization tools was used to investigate the interplay between material features and electrochemical performances. The obtained results highlighted the formation of a p-n junction for the g-C3N4-CoO system, whereas a Z-scheme junction accounted for the remarkable performance enhancement yielded by g-C3N4-CoFe2O4. The intimate contact between the system components also afforded an improved electrocatalyst stability in comparison to various bare and functionalized g-C3N4-based systems. These findings emphasize the importance of tailoring g-C3N4 chemico-physical properties through the dispersion of complementary catalysts to fully exploit its applicative potential.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.7
Times cited: 11
DOI: 10.1016/j.apsusc.2023.156652
|
|
|
“Gate-tuned anomalous Hall effect driven by Rashba splitting in intermixed LaAlO3/GdTiO3/SrTiO3”. Lebedev N, Stehno M, Rana A, Reith P, Gauquelin N, Verbeeck J, Hilgenkamp H, Brinkman A, Aarts J, Scientific Reports 11, 10726 (2021). http://doi.org/10.1038/s41598-021-89767-3
Abstract: The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behaviour of the two-dimensional electron system forming at the interface of SrTiO<sub>3</sub>-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the influence of magnetic ions by measuring intermixed LaAlO<sub>3</sub>/GdTiO<sub>3</sub>/SrTiO<sub>3</sub>at temperatures below 10 K. We find that, as function of gate voltage, the system undergoes a Lifshitz transition while at the same time an onset of AHE is observed. However, we do not observe clear signs of ferromagnetism. We argue the AHE to be due to the change in Rashba spin-orbit coupling at the Lifshitz transition and conclude that also paramagnetic moments which are easily polarizable at low temperatures and high magnetic fields lead to the presence of AHE, which needs to be taken into account when extracting carrier densities and mobilities.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.259
Times cited: 5
DOI: 10.1038/s41598-021-89767-3
|
|
|
“Germanium vacancy centre formation in CVD nanocrystalline diamond using a solid dopant source”. Mary Joy R, Pobedinskas P, Bourgeois E, Chakraborty T, Görlitz J, Herrmann D, Noël C, Heupel J, Jannis D, Gauquelin N, D'Haen J, Verbeeck J, Popov C, Houssiau L, Becher C, Nesládek M, Haenen K, Science talks 5, 100157 (2023). http://doi.org/10.1016/j.sctalk.2023.100157
Keywords: A3 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1016/j.sctalk.2023.100157
|
|
|
“Getting rid of anti-solvents: gas quenching for high performance perovskite solar cells”. Conings B, Babayigit A, Klug M, Bai S, Gauquelin N, Sakai N, Wang JT-W, Verbeeck J, Boyen H-G, Snaith H, 2018 Ieee 7th World Conference On Photovoltaic Energy Conversion (wcpec)(a Joint Conference Of 45th Ieee Pvsc, 28th Pvsec &, 34th Eu Pvsec) (2018). http://doi.org/10.1109/PVSC.2018.8547987
Abstract: As the field of perovskite optoelectronics developed, a plethora of strategies has arisen to control their electronic and morphological characteristics for the purpose of producing high efficiency devices. Unfortunately, despite this wealth of deposition approaches, the community experiences a great deal of irreproducibility between different laboratories, batches and preparation methods. Aiming to address this issue, we developed a simple deposition method based on gas quenching that yields smooth films for a wide range of perovskite compositions, in single, double, triple and quadruple cation varieties, and produces planar heterojunction devices with competitive efficiencies, so far up to 20%.
Keywords: P1 Proceeding; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
DOI: 10.1109/PVSC.2018.8547987
|
|
|
“Giant tunability of Rashba splitting at cation-exchanged polar oxide interfaces by selective orbital hybridization”. Xu H, Li H, Gauquelin N, Chen X, Wu W-F, Zhao Y, Si L, Tian D, Li L, Gan Y, Qi S, Li M, Hu F, Sun J, Jannis D, Yu P, Chen G, Zhong Z, Radovic M, Verbeeck J, Chen Y, Shen B, Advanced materials (2024). http://doi.org/10.1002/ADMA.202313297
Abstract: The 2D electron gas (2DEG) at oxide interfaces exhibits extraordinary properties, such as 2D superconductivity and ferromagnetism, coupled to strongly correlated electrons in narrow d-bands. In particular, 2DEGs in KTaO3 (KTO) with 5d t2g orbitals exhibit larger atomic spin-orbit coupling and crystal-facet-dependent superconductivity absent for 3d 2DEGs in SrTiO3 (STO). Herein, by tracing the interfacial chemistry, weak anti-localization magneto-transport behavior, and electronic structures of (001), (110), and (111) KTO 2DEGs, unambiguously cation exchange across KTO interfaces is discovered. Therefore, the origin of the 2DEGs at KTO-based interfaces is dramatically different from the electronic reconstruction observed at STO interfaces. More importantly, as the interface polarization grows with the higher order planes in the KTO case, the Rashba spin splitting becomes maximal for the superconducting (111) interfaces approximately twice that of the (001) interface. The larger Rashba spin splitting couples strongly to the asymmetric chiral texture of the orbital angular moment, and results mainly from the enhanced inter-orbital hopping of the t2g bands and more localized wave functions. This finding has profound implications for the search for topological superconductors, as well as the realization of efficient spin-charge interconversion for low-power spin-orbitronics based on (110) and (111) KTO interfaces. An unambiguous cation exchange is discovered across the interfaces of (001), (110), and (111) KTaO3 2D electron gases fabricated at room temperature. Remarkably, the (111) interfaces with the highest superconducting transition temperature also turn out to show the strongest electron-phonon interaction and the largest Rashba spin splitting. image
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
DOI: 10.1002/ADMA.202313297
|
|
|
“High-strain-induced local modification of the electronic properties of VO₂, thin films”. Birkholzer YA, Sotthewes K, Gauquelin N, Riekehr L, Jannis D, van der Minne E, Bu Y, Verbeeck J, Zandvliet HJW, Koster G, Rijnders G, ACS applied electronic materials 4, 6020 (2022). http://doi.org/10.1021/ACSAELM.2C01176
Abstract: Vanadium dioxide (VO2) is a popular candidate for electronic and optical switching applications due to its well-known semiconductor-metal transition. Its study is notoriously challenging due to the interplay of long- and short-range elastic distortions, as well as the symmetry change and the electronic structure changes. The inherent coupling of lattice and electronic degrees of freedom opens the avenue toward mechanical actuation of single domains. In this work, we show that we can manipulate and monitor the reversible semiconductor-to-metal transition of VO2 while applying a controlled amount of mechanical pressure by a nanosized metallic probe using an atomic force microscope. At a critical pressure, we can reversibly actuate the phase transition with a large modulation of the conductivity. Direct tunneling through the VO2-metal contact is observed as the main charge carrier injection mechanism before and after the phase transition of VO2. The tunneling barrier is formed by a very thin but persistently insulating surface layer of the VO2. The necessary pressure to induce the transition decreases with temperature. In addition, we measured the phase coexistence line in a hitherto unexplored regime. Our study provides valuable information on pressure-induced electronic modifications of the VO2 properties, as well as on nanoscale metal-oxide contacts, which can help in the future design of oxide electronics.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 2
DOI: 10.1021/ACSAELM.2C01176
|
|
|
“High-TCInterfacial Ferromagnetism in SrMnO3/LaMnO3Superlattices”. Keunecke M, Lyzwa F, Schwarzbach D, Roddatis V, Gauquelin N, Müller-Caspary K, Verbeeck J, Callori SJ, Klose F, Jungbauer M, Moshnyaga V, Advanced functional materials , 1808270 (2019). http://doi.org/10.1002/adfm.201808270
Abstract: Heterostructures of strongly correlated oxides demonstrate various intriguing and potentially useful interfacial phenomena. LaMnO3/SrMnO3 superlattices are presented showcasing a new high‐temperature ferromagnetic phase with Curie temperature, TC ≈360 K, caused by electron transfer from the surface of the LaMnO3 donor layer into the neighboring SrMnO3 acceptor layer. As a result, the SrMnO3 (top)/LaMnO3 (bottom) interface shows an enhancement of the magnetization as depth‐profiled by polarized neutron reflectometry. The length scale of charge transfer, λTF ≈2 unit cells, is obtained from in situ growth monitoring by optical ellipsometry, supported by optical simulations, and further confirmed by high resolution electron microscopy and spectroscopy. A model of the inhomogeneous distribution of electron density in LaMnO3/SrMnO3 layers along the growth direction is concluded to account for a complex interplay between ferromagnetic and antiferromagnetic layers in superlattices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 15.621
Times cited: 26
DOI: 10.1002/adfm.201808270
|
|
|
“Increased Performance Improvement of Lithium-Ion Batteries by Dry Powder Coating of High-Nickel NMC with Nanostructured Fumed Ternary Lithium Metal Oxides”. Herzog MJ, Gauquelin N, Esken D, Verbeeck J, Janek J, ACS applied energy materials 4, 8832 (2021). http://doi.org/10.1021/acsaem.1c00939
Abstract: Dry powder coating is an effective approach to protect the surfaces of layered cathode active materials (CAMs) in lithium-ion batteries. Previous investigations indicate an incorporation of lithium ions in fumed Al2O3, ZrO2, and TiO2 coatings on LiNi0.7Mn0.15Co0.15O2 during cycling, improving the cycling performance. Here, this coating approach is transferred for the first time to fumed ternary LiAlO2, Li4Zr3O8, and Li4Ti5O12 and directly compared with their lithium-free equivalents. All materials could be processed equally and their nanostructured small aggregates accumulate on the CAM surfaces to quite homogeneous coating layers with a certain porosity. The LiNixMnyCozO2 (NMC) coated with lithium-containing materials shows an enhanced improvement in overall capacity, capacity retention, rate performance, and polarization behavior during cycling, compared to their lithium-free analogues. The highest rate performance was achieved with the fumed ZrO2 coating, while the best long-term cycling stability with the highest absolute capacity was obtained for the fumed LiAlO2-coated NMC. The optimal coating agent for NMC to achieve a balanced system is fumed Li4Ti5O12, providing a good compromise between high rate capability and good capacity retention. The coating agents prevent CAM particle cracking and degradation in the order LiAlO2 ≈ Al2O3 > Li4Ti5O12 > Li4Zr3O8 > ZrO2 > TiO2. A schematic model for the protection and electrochemical performance enhancement of high-nickel NMC with fumed metal oxide coatings is sketched. It becomes apparent that physical and chemical characteristics of the coating significantly influence the performance of NMC. A high degree of coating-layer porosity is favorable for the rate capability, while a high coverage of the surface, especially in vulnerable grain boundaries, enhances the long-term cycling stability and improves the cracking behavior of NMCs. While zirconium-containing coatings possess the best chemical properties for high rate performances, aluminum-containing coatings feature a superior chemical nature to protect high-nickel NMCs.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Times cited: 15
DOI: 10.1021/acsaem.1c00939
|
|
|
“Induced giant piezoelectricity in centrosymmetric oxides”. Park D-s, Hadad M, Riemer LM, Ignatans R, Spirito D, Esposito V, Tileli V, Gauquelin N, Chezganov D, Jannis D, Verbeeck J, Gorfman S, Pryds N, Muralt P, Damjanovic D, Science 375, 653 (2022). http://doi.org/10.1126/science.abm7497
Abstract: Giant piezoelectricity can be induced in centrosymmetric oxides by controlling the long-range motion of oxygen vacancies.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 56.9
Times cited: 51
DOI: 10.1126/science.abm7497
|
|
|
“Influence of the structure on the properties of NaxEuy(MoO4)z red phosphors”. Morozov VA, Lazoryak BI, Shmurak SZ, Kiselev AP, Lebedev OI, Gauquelin N, Verbeeck J, Hadermann J, Van Tendeloo G, Chemistry of materials 26, 3238 (2014). http://doi.org/10.1021/cm500966g
Abstract: Scheelite related compounds (A',A '')(n)[(B',B '')O-4](m) with B', B '' = W and/or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emitting-diode) and solid-state lasers. Cation substitution in CaMoO4 of Ca2+ by the combination of Na+ and Eu3+, with the creation of A cation vacancies, has been investigated as a factor for controlling the scheelite-type structure and the luminescent properties. Na5Eu(MoO4)(4) and NaxEu(2-x)/33+square(2-x)/3MoO4 (0.138 <= x <= 0.5) phases with a scheelite-type structure were synthesized by the solid state method; their structural characteristics were investigated using transmission electron microscopy. Contrary to powder synchrotron X-ray diffraction before, the study by electron diffraction and high resolution transmission electron microscopy in this paper revealed that Na0.286Eu0.571MoO4 has a (3 + 2)D incommensurately modulated structure and that (3 + 2)D incommensurately modulated domains are present in Na0.200Eu0.600MoO4. It also confirmed the (3 + 1)D incommensurately modulated character of Na(0.138)Eu(0.621)Mo04. The luminescent properties of all phases under near-ultraviolet (n-UV) light have been investigated. The excitation spectra of these phosphors show the strongest absorption at about 395 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. The emission spectra indicate an intense red emission due to the D-5(0) -> F-7(2) transition of Eu3+, with local minima in the intensity at Na0.286Eu0.571MoO4 and Na0.200Eu0.600MoO4 for similar to 613 nm and similar to 616 nm bands. The phosphor Na5Eu(MoO4)(4) shows the brightest red light emission among the phosphors in the Na2MoO4-Eu2/3MoO4 system and the maximum luminescence intensity of Na5Eu(MoO4)(4) (lambda(ex) = 395 nm) in the D-5(0) -> F-7(2) transition region is close to that of the commercially used red phosphor YVO4:Eu3+ (lambda(ex) = 326 nm). Electron energy loss spectroscopy measurements revealed the influence of the structure and Na/Eu cation distribution on the number and positions of bands in the UV-optical-infrared regions of the EELS spectrum.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 53
DOI: 10.1021/cm500966g
|
|
|
“Inhomogeneous superconductivity and quasilinear magnetoresistance at amorphous LaTiO₃/SrTiO₃, interfaces”. Lebedev N, Stehno M, Rana A, Gauquelin N, Verbeeck J, Brinkman A, Aarts J, Journal Of Physics-Condensed Matter 33, 055001 (2020). http://doi.org/10.1088/1361-648X/ABC102
Abstract: We have studied the transport properties of LaTiO3/SrTiO3 (LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, transmission electron microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conductivity arises mainly on the STO side of the interface, and shows all the signs of the two-dimensional electron gas usually observed at interfaces between STO and LTO or LaAlO3, including the presence of two electron bands and tunability with a gate voltage. Analysis of magnetoresistance (MR) and superconductivity indicates the presence of spatial fluctuations of the electronic properties in our samples. That can explain the observed quasilinear out-of-plane MR, as well as various features of the in-plane MR and the observed superconductivity.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.7
Times cited: 1
DOI: 10.1088/1361-648X/ABC102
|
|
|
“Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams”. Benedoue S, Benedet M, Gasparotto A, Gauquelin N, Orekhov A, Verbeeck J, Seraglia R, Pagot G, Rizzi GA, Balzano V, Gavioli L, Noto VD, Barreca D, Maccato C, Nanomaterials 13, 1035 (2023). http://doi.org/10.3390/nano13061035
Abstract: Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe2O4, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.3
Times cited: 3
DOI: 10.3390/nano13061035
|
|
|
“Interface degradation and field screening mechanism behind bipolar-cycling fatigue in ferroelectric capacitors”. Do MT, Gauquelin N, Nguyen MD, Blom F, Verbeeck J, Koster G, Houwman EP, Rijnders G, Apl Materials 9, 021113 (2021). http://doi.org/10.1063/5.0038719
Abstract: Polarization fatigue, i.e., the loss of polarization of ferroelectric capacitors upon field cycling, has been widely discussed as an interface related effect. However, mechanism(s) behind the development of fatigue have not been fully identified. Here, we study the fatigue mechanisms in Pt/PbZr0.52Ti0.48O3/SrRuO3 (Pt/PZT/SRO) capacitors in which all layers are fabricated by pulsed laser deposition without breaking the vacuum. With scanning transmission electron microscopy, we observed that in the fatigued capacitor, the Pt/PZT interface becomes structurally degraded, forming a 5 nm-10 nm thick non-ferroelectric layer of crystalline ZrO2 and diffused Pt grains. We then found that the fatigued capacitors can regain the full initial polarization switching if the externally applied field is increased to at least 10 times the switching field of the pristine capacitor. These findings suggest that polarization fatigue is driven by a two-step mechanism. First, the transient depolarization field that repeatedly appears during the domain switching under field cycling causes decomposition of the metal/ferroelectric interface, resulting in a non-ferroelectric degraded layer. Second, this interfacial non-ferroelectric layer screens the external applied field causing an increase in the coercive field beyond the usually applied maximum field and consequently suppresses the polarization switching in the cycled capacitor. Our work clearly confirms the key role of the electrode/ferroelectric interface in the endurance of ferroelectric-based devices.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.335
Times cited: 5
DOI: 10.1063/5.0038719
|
|
|
“Interfacial dielectric layer as an origin of polarization fatigue in ferroelectric capacitors”. Do MT, Gauquelin N, Nguyen MD, Wang J, Verbeeck J, Blom F, Koster G, Houwman EP, Rijnders G, Scientific Reports 10, 7310 (2020). http://doi.org/10.1038/s41598-020-64451-0
Abstract: Origins of polarization fatigue in ferroelectric capacitors under electric field cycling still remain unclear. Here, we experimentally identify origins of polarization fatigue in ferroelectric PbZr0.52Ti0.48O3 (PZT) thin-film capacitors by investigating their fatigue behaviours and interface structures. The PZT layers are epitaxially grown on SrRuO3-buffered SrTiO3 substrates by a pulsed laser deposition (PLD), and the capacitor top-electrodes are various, including SrRuO3 (SRO) made by in-situ PLD, Pt by in-situ PLD (Pt-inPLD) and ex-situ sputtering (Pt-sputtered). We found that fatigue behaviour of the capacitor is directly related to the top-electrode/PZT interface structure. The Pt-sputtered/PZT/SRO capacitor has a thin defective layer at the top interface and shows early fatigue while the Pt-inPLD/PZT/SRO and SRO/PZT/SRO capacitor have clean top-interfaces and show much more fatigue resistance. The defective dielectric layer at the Pt-sputtered/PZT interface mainly contains carbon contaminants, which form during the capacitor ex-situ fabrication. Removal of this dielectric layer significantly delays the fatigue onset. Our results clearly indicate that dielectric layer at ferroelectric capacitor interfaces is the main origin of polarization fatigue, as previously proposed in the charge injection model.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.6
Times cited: 18
DOI: 10.1038/s41598-020-64451-0
|
|
|
“Interplay of strain and indium incorporation in InGaN/GaN dot-in-a-wire nanostructures by scanning transmission electron microscopy”. Woo SY, Gauquelin N, Nguyen HPT, Mi Z, Botton GA, Nanotechnology 26, 344002 (2015). http://doi.org/10.1088/0957-4484/26/34/344002
Abstract: The interplay between strain and composition is at the basis of heterostructure design to engineer new properties. The influence of the strain distribution on the incorporation of indium during the formation of multiple InGaN/GaN quantum dots (QDs) in nanowire (NW) heterostructures has been investigated, using the combined techniques of geometric phase analysis of atomic-resolution images and quantitative elemental mapping from core-loss electron energy-loss spectroscopy within scanning transmission electron microscopy. The variation in In-content between successive QDs within individual NWs shows a dependence on the magnitude of compressive strain along the growth direction within the underlying GaN barrier layer, which affects the incorporation of In-atoms to minimize the local effective strain energy. Observations suggest that the interfacial misfit between InGaN/GaN within the embedded QDs is mitigated by strain partitioning into both materials, and results in normal stresses inflicted by the presence of the surrounding GaN shell. These experimental measurements are linked to the local piezoelectric polarization fields for individual QDs, and are discussed in terms of the photoluminescence from an ensemble of NWs.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.44
Times cited: 19
DOI: 10.1088/0957-4484/26/34/344002
|
|
|
“Intrinsic thermal instability of methylammonium lead trihalide perovskite”. Conings B, Drijkoningen J, Gauquelin N, Babayigit A, D'Haen J, D'Olieslaeger L, Ethirajan A, Verbeeck J, Manca J, Mosconi E, Angelis FD, Boyen HG;, Laser physics review 5, 1500477 (2015). http://doi.org/10.1002/aenm.201500477
Abstract: Organolead halide perovskites currently are the new front-runners as light absorbers in hybrid solar cells, as they combine efficiencies passing already 20% with deposition temperatures below 100 °C and cheap solution-based fabrication routes. Long-term stability remains a major obstacle for application on an industrial scale. Here, it is demonstrated that significant decomposition effects already occur during annealing of a methylammonium lead triiode perovskite at 85 °C even in inert atmosphere thus violating international standards. The observed behavior supports the view of currently used perovskite materials as soft matter systems with low formation energies, thus representing a major bottleneck for their application, especially in countries with high average temperatures. This result can trigger a broader search for new perovskite families with improved thermal stability.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.721
Times cited: 1691
DOI: 10.1002/aenm.201500477
|
|
|
“KEu(MoO4)2 : polymorphism, structures, and luminescent properties”. Morozov VA, Arakcheeva AV, Pattison P, Meert KW, Smet PF, Poelman D, Gauquelin N, Verbeeck J, Abakumov AM, Hadermann J, Chemistry of materials 27, 5519 (2015). http://doi.org/10.1021/acs.chemmater.5b01622
Abstract: In this paper, with the example of two different polymorphs of KEu(MoO4)2, the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A′,A″)n[(B′,B″)O4]m is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 9231203 K and ambient pressure: a low temperature anorthic α-phase and a monoclinic high temperature β-phase with an incommensurately modulated structure. The structures of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic β-KEu(MoO4)2 has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(αβ0)00, a = 5.52645(4) Å, b = 5.28277(4) Å, c = 11.73797(8) Å, γ = 91.2189(4)o, q = 0.56821(2)a*0.12388(3)b*), whereas the anorthic α-phase is (3+1)-dimensional commensurately modulated (superspace group I1̅(αβγ)0, a = 5.58727(22) Å, b = 5.29188(18)Å, c = 11.7120(4) Å, α = 90.485(3)o, β = 88.074(3)o, γ = 91.0270(23)o, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the α-phase, while a 3-dimensional Eu3+-framework is observed for the β-phase structure. The luminescent properties of KEu(MoO4)2 samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 26
DOI: 10.1021/acs.chemmater.5b01622
|
|
|
“Long-Range Domain Structure and Symmetry Engineering by Interfacial Oxygen Octahedral Coupling at Heterostructure Interface”. Liao Z, Green RJ, Gauquelin N, Macke S, Li L, Gonnissen J, Sutarto R, Houwman EP, Zhong Z, Van Aert S, Verbeeck J, Sawatzky GA, Huijben M, Koster G, Rijnders G, Advanced functional materials 26, 6627 (2016). http://doi.org/10.1002/adfm.201602155
Abstract: In epitaxial thin film systems, the crystal structure and its symmetry deviate from the bulk counterpart due to various mechanisms such as epitaxial strain and interfacial structural coupling, which is accompanyed by a change in their properties. In perovskite materials, the crystal symmetry can be described by rotations of sixfold coordinated transition metal oxygen octahedra, which are found to be altered at interfaces. Here, it is unraveled how the local oxygen octahedral coupling at perovskite heterostructural interfaces strongly influences the domain structure and symmetry of the epitaxial films resulting in design rules to induce various structures in thin films using carefully selected combinations of substrate/buffer/film. Very interestingly it is discovered that these combinations lead to structure changes throughout the full thickness of the film. The results provide a deep insight into understanding the origin of induced structures in a perovskite heterostructure and an intelligent route to achieve unique functional properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 23
DOI: 10.1002/adfm.201602155
|
|
|
“Low-field switching of noncollinear spin texture at La0.7Sr0.3MnO3-SrRuO3interfaces”. Das S, Rata AD, Maznichenko I V, Agrestini IS, Pippel E, Gauquelin N, Verbeeck J, Chen K, Valvidares SM, Vasili HB, Herrero-Martin J, Pellegrin E, Nenkov K, Herklotz A, Ernst A, Mertig I, Hu Z, Doerr K, Physical review B 99, 024416 (2019). http://doi.org/10.1103/PHYSREVB.99.024416
Abstract: Interfaces of ferroic oxides can show complex magnetic textures which have strong impact on spintronics devices. This has been demonstrated recently for interfaces with insulating antiferromagnets such as BiFeO3. Here, noncollinear spin textures which can be switched in very low magnetic field are reported for conducting ferromagnetic bilayers of La0.7Sr0.3MnO3-SrRuO3 (LSMO-SRO). The magnetic order and switching are fundamentally different for bilayers coherently grown in reversed stacking sequence. The SRO top layer forms a persistent exchange spring which is antiferromagnetically coupled to LSMO and drives switching in low fields of a few milliteslas. Density functional theory reveals the crucial impact of the interface termination on the strength of Mn-Ru exchange coupling across the interface. The observation of an exchange spring agrees with ultrastrong coupling for the MnO2/SrO termination. Our results demonstrate low-field switching of noncollinear spin textures at an interface between conducting oxides, opening a pathway for manipulating and utilizing electron transport phenomena in controlled spin textures at oxide interfaces.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PHYSREVB.99.024416
|
|
|
“Metal-insulator transition of SrVO 3 ultrathin films embedded in SrVO 3 / SrTiO 3 superlattices”. Wang J, Gauquelin N, Huijben M, Verbeeck J, Rijnders G, Koster G, Applied Physics Letters 117, 133105 (2020). http://doi.org/10.1063/5.0020615
Abstract: The metal-insulator transition (MIT) in strongly correlated oxides is a topic of great interest for its potential applications, such as Mott field effect transistors and sensors. We report that the MIT in high quality epitaxial SrVO3 (SVO) thin films is present as the film thickness is reduced, lowering the dimensionality of the system, and electron-electron correlations start to become the dominant interactions. The critical thickness of 3 u.c is achieved by avoiding effects due to off-stoichiometry using optimal growth conditions and excluding any surface effects by a STO capping layer. Compared to the single SVO thin films, conductivity enhancement in SVO/STO superlattices is observed. This can be explained by the interlayer coupling effect between SVO sublayers in the superlattices. Magnetoresistance and Hall measurements indicate that the dominant driving force of MIT is the electron–electron interaction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4
Times cited: 8
DOI: 10.1063/5.0020615
|
|
|
“Metal–insulator-transition engineering by modulation tilt-control in perovskite nickelates for room temperature optical switching”. Liao Z, Gauquelin N, Green RJ, Müller-Caspary K, Lobato I, Li L, Van Aert S, Verbeeck J, Huijben M, Grisolia MN, Rouco V, El Hage R, Villegas JE, Mercy A, Bibes M, Ghosez P, Sawatzky GA, Rijnders G, Koster G, America 115, 9515 (2018). http://doi.org/10.1073/pnas.1807457115
Abstract: In transition metal perovskites ABO3 the physical properties are largely driven by the rotations of the BO6 octahedra, which can be tuned in thin films through strain and dimensionality control. However, both approaches have fundamental and practical limitations due to discrete and indirect variations in bond angles, bond lengths and film symmetry by using commercially available substrates. Here, we introduce modulation tilt control as a new approach to tune the ground state of perovskite oxide thin films by acting explicitly on the oxygen octahedra rotation modes, i.e. directly on the bond angles. By intercalating the prototype SmNiO3 target material with a tilt-control layer, we cause the system to change the natural amplitude of a given rotation mode without affecting the interactions. In contrast to strain and dimensionality engineering, our method enables a continuous fine-tuning of the materials properties. This is achieved through two independent adjustable parameters: the nature of the tilt-control material (through its symmetry, elastic constants and oxygen rotation angles) and the relative thicknesses of the target and tilt-control materials. As a result, a magnetic and electronic phase diagram can be obtained, normally only accessible by A-site element substitution, within the single SmNiO3 compound. With this unique approach, we successfully adjusted the metal-insulator transition (MIT) to room temperature to fulfill the desired conditions for optical switching applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.661
Times cited: 50
DOI: 10.1073/pnas.1807457115
|
|
|
“Nanoscale investigation by TEM and STEM-EELS of the laser induced yellowing”. Godet M, Vergès-Belmin V, Gauquelin N, Saheb M, Monnier J, Leroy E, Bourgon J, Verbeeck J, Andraud C, Micron 115, 25 (2018). http://doi.org/10.1016/j.micron.2018.08.006
Abstract: Nd-YAG QS laser cleaning of soiled stone at 1064 nm can sometimes result in a more yellow appearance compared to other cleaning techniques. Especially in France, this yellowing effect is still considered as a major aesthetic issue by the architects and conservators. One explanation states that the yellowing is linked to the formation of iron-rich nanophase(s) through the laser beam interaction with black crusts that would re-deposit on the cleaned substrate after irradiation. To characterize these nanophases, a model crust containing hematite was elaborated and laser irradiated using a Nd-YAG QS laser. The color of the sample shifted instantaneously from red to a bright yellow and numerous particles were ablated in a visible smoke. Transmission electron microscopy (TEM) was used to examine the morphology and the crystallinity of the neo-formed compounds, both on the surface of the samples and in the ablated materials. In addition, an investigation of the chemical and structural properties of the nanophases was conducted by X-ray dispersive energy (EDX) and electron energy loss (EELS) spectroscopies. It was found that both the surface of the sample and the ablated materials are covered by crystallized nano-spheres and nano-residues, all containing iron and oxygen, sometimes along with calcium and sulfur. In particular an interfacial area containing the four elements was evidenced between some nanostructures and the substrate. Magnetite Fe3O4 was also identified at the nanoscale. This study demonstrates that the laser yellowing of a model crust is linked to the presence of iron-rich nanophases including CaxFeySzOδ nanostructures and magnetite Fe3O4 at the surface after irradiation.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.98
Times cited: 9
DOI: 10.1016/j.micron.2018.08.006
|
|
|
“Nanoscale ordering in oxygen deficient quintuple perovskite Sm2-\epsilonBa3+\epsilonFe5O15-\delta : implication for magnetism and oxygen stoichiometry”. Volkova NE, Lebedev OI, Gavrilova LY, Turner S, Gauquelin N, Seikh MM, Caignaert V, Cherepanov VA, Raveau B, Van Tendeloo G, Chemistry of materials 26, 6303 (2014). http://doi.org/10.1021/cm503276p
Abstract: The investigation of the system SmBaFe-O in air has allowed an oxygen deficient perovskite Sm2-epsilon Ba3+epsilon Fe5O15-delta (delta = 0.75, epsilon = 0.125) to be synthesized. In contrast to the XRPD pattern which gives a cubic symmetry (a(p) = 3.934 angstrom), the combined HREM/EELS study shows that this phase is nanoscale ordered with a quintuple tetragonal cell, a(p) X a(p) X 5(ap). The nanodomains exhibit a unique stacking sequence of the A-site cationic layers along the crystallographic c-axis, namely SmBaBa/SmBa/SmBaSm, and are chemically twinned in the three crystallographic directions. The nanoscale ordering of this perovskite explains its peculiar magnetic properties on the basis of antiferromagnetic interactions with spin blockade at the boundary between the nanodomains. The variation of electrical conductivity and oxygen content of this oxide versus temperature suggest potential SOFC applications. They may be related to the particular distribution of oxygen vacancies in the lattice and to the 3d(5)(L) under bar configuration of iron.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 16
DOI: 10.1021/cm503276p
|
|
|
“Novel class of nanostructured metallic glass films with superior and tunable mechanical properties”. Ghidelli M, Orekhov A, Bassi AL, Terraneo G, Djemia P, Abadias G, Nord M, Béché, A, Gauquelin N, Verbeeck J, Raskin J-p, Schryvers D, Pardoen T, Idrissi H, Acta Materialia , 116955 (2021). http://doi.org/10.1016/j.actamat.2021.116955
Abstract: A novel class of nanostructured Zr50Cu50 (%at.) metallic glass films with superior and tunable mechanical
properties is produced by pulsed laser deposition. The process can be controlled to synthetize a wide
range of film microstructures including dense fully amorphous, amorphous embedded with nanocrystals
and amorphous nano-granular. A unique dense self-assembled nano-laminated atomic arrangement
characterized by alternating Cu-rich and Zr/O-rich nanolayers with different local chemical enrichment
and amorphous or amorphous-crystalline composite nanostructure has been discovered, while
significant in-plane clustering is reported for films synthetized at high deposition pressures. This unique
nanoarchitecture is at the basis of superior mechanical properties including large hardness and elastic
modulus up to 10 and 140 GPa, respectively and outstanding total elongation to failure (>9%), leading to
excellent strength/ductility balance, which can be tuned by playing with the film architecture. These
results pave the way to the synthesis of novel class of engineered nanostructured metallic glass films
with high structural performances attractive for a number of applications in microelectronics and
coating industry.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 27
DOI: 10.1016/j.actamat.2021.116955
|
|