“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
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“Towards Reproducible and Transparent Science of (Big) Electron Microscopy Data Using Version Control”. Nord M, Verbeeck J, Microscopy and microanalysis
T2 –, Microscopy &, Microanalysis 2019, 4-8 August, 2019, Portland, Oregon 25, 232 (2019). http://doi.org/10.1017/S1431927619001892
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
DOI: 10.1017/S1431927619001892
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Nord M, Verbeeck J (2019) Open Source Development Tools for Robust and Reproducible Electron Microscopy Data Analysis. 138–139
Keywords: P3; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 1.891
DOI: 10.1017/S1431927619001429
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“Fast electron low dose tomography for beam sensitive materials”. Esteban DA, Vanrompay H, Skorikov A, Béché, A, Verbeeck J, Freitag B, Bals S, Microscopy And Microanalysis 27, 2116 (2021). http://doi.org/10.1017/S1431927621007649
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
DOI: 10.1017/S1431927621007649
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“Resistance minimum in LaAlO3/Eu1-xLaxTiO3/SrTiO3 heterostructures”. Lebedev N, Huang Y, Rana A, Jannis D, Gauquelin N, Verbeeck J, Aarts J, Physical review materials 6, 075003 (2022). http://doi.org/10.1103/PHYSREVMATERIALS.6.075003
Abstract: In this paper we study LaAlO3/Eu1-xLaxTiO3/SrTiO3 structures with nominally x = 0, 0.1 and different thicknesses of the Eu1-xLaxTiO3 layer. We observe that both systems have many properties similar to previously studied LaAlO3/EuTiO3/SrTiO3 and other oxide interfaces, such as the formation of a two-dimensional electron liquid for two unit cells of Eu1-xLaxTiO3; a metal-insulator transition driven by the increase in thickness of the Eu1-xLaxTiO3 layer; the presence of an anomalous Hall effect when driving the systems above the Lifshitz point with a back-gate voltage; and a minimum in the temperature dependence of the sheet resistance below the Lifshitz point in the one-band regime, which becomes more pronounced with increasing negative gate voltage. However, and notwithstanding the likely presence of magnetism in the system, we do not attribute that minimum to the Kondo effect, but rather to the properties of the SrTiO3 crystal and the inevitable effects of charge trapping when using back gates.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.4
DOI: 10.1103/PHYSREVMATERIALS.6.075003
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“The effect of microstructure and film composition on the mechanical properties of linear antenna CVD diamond thin films”. Mary Joy R, Pobedinskas P, Baule N, Bai S, Jannis D, Gauquelin N, Pinault-Thaury M-A, Jomard F, Sankaran KJ, Rouzbahani R, Lloret F, Desta D, D’Haen J, Verbeeck J, Becker MF, Haenen K, Acta materialia 264, 119548 (2024). http://doi.org/10.1016/j.actamat.2023.119548
Abstract: This study reports the impact of film microstructure and composition on the Young’s modulus and residual stress in nanocrystalline diamond (NCD) thin films ( thick) grown on silicon substrates using a linear antenna microwave plasma-enhanced chemical vapor deposition (CVD) system. Combining laser acoustic wave spectroscopy to determine the elastic properties with simple wafer curvature measurements, a straightforward method to determine the intrinsic stress in NCD films is presented. Two deposition parameters are varied: (1) the substrate temperature from 400 °C to 900 °C, and (2) the [P]/[C] ratio from 0 ppm to 8090 ppm in the H2/CH4/CO2/PH3 diamond CVD plasma. The introduction of PH3 induces a transition in the morphology of the diamond film, shifting from NCD with larger grains to ultra-NCD with a smaller grain size, concurrently resulting in a decrease in Young’s modulus. Results show that the highest Young’s modulus of (113050) GPa for the undoped NCD deposited at 800 °C is comparable to single crystal diamond, indicating that NCD with excellent mechanical properties is achievable with our process for thin diamond films. Based on the film stress results, we propose the origins of tensile intrinsic stress in the diamond films. In NCD, the tensile intrinsic stress is attributed to larger grain size, while in ultra-NCD films the tensile intrinsic stress is due to grain boundaries and impurities.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/j.actamat.2023.119548
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“Epitaxial growth of the candidate ferroelectric Rashba material SrBiO3by pulsed laser deposition”. Verdierre G, Gauquelin N, Jannis D, Birkhölzer YA, Mallik S, Verbeeck J, Bibes M, Koster G, APL materials 11, 031109 (2023). http://doi.org/10.1063/5.0138222
Abstract: Among oxides, bismuthates have been gaining much interest due to their unique features. In addition to their superconducting properties, they show potential for applications as topological insulators and as possible spin-to-charge converters. After being first investigated in their bulk form in the 1980s, bismuthates have been successfully grown as thin films. However, most efforts have focused on BaBiO<sub>3</sub>, with SrBiO<sub>3</sub>receiving only little attention. Here, we report the growth of epitaxial films of SrBiO<sub>3</sub>on both TiO<sub>2</sub>-terminated SrTiO<sub>3</sub>and NdO-terminated NdScO<sub>3</sub>substrates by pulsed laser deposition. SrBiO<sub>3</sub>has a pseudocubic lattice constant of ∼4.25 Å and grows relaxed on NdScO<sub>3</sub>. Counter-intuitively, it grows with a slight tensile strain on SrTiO<sub>3</sub>despite a large lattice mismatch, which should induce compressive strain. High-resolution transmission electron microscopy reveals that this occurs as a consequence of structural domain matching, with blocks of 10 SrBiO<sub>3</sub>unit planes matching blocks of 11 SrTiO<sub>3</sub>unit planes. This work provides a framework for the synthesis of high quality perovskite bismuthates films and for the understanding of their interface interactions with homostructural substrates.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.1
DOI: 10.1063/5.0138222
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“Unusual structural rearrangement and superconductivity in infinite layer cuprate superlattices”. Samal D, Gauquelin N, Takamura Y, Lobato I, Arenholz E, Van Aert S, Huijben M, Zhong Z, Verbeeck J, Van Tendeloo G, Koster G, Physical review materials 7, 054803 (2023). http://doi.org/10.1103/PhysRevMaterials.7.054803
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.4
DOI: 10.1103/PhysRevMaterials.7.054803
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“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
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“Characterization of a Timepix detector for use in SEM acceleration voltage range”. Denisov N, Jannis D, Orekhov A, Müller-Caspary K, Verbeeck J, Ultramicroscopy 253, 113777 (2023). http://doi.org/10.1016/j.ultramic.2023.113777
Abstract: Hybrid pixel direct electron detectors are gaining popularity in electron microscopy due to their excellent properties. Some commercial cameras based on this technology are relatively affordable which makes them attractive tools for experimentation especially in combination with an SEM setup. To support this, a detector characterization (Modulation Transfer Function, Detective Quantum Efficiency) of an Advacam Minipix and Advacam Advapix detector in the 15–30 keV range was made. In the current work we present images of Point Spread Function, plots of MTF/DQE curves and values of DQE(0) for these detectors. At low beam currents, the silicon detector layer behaviour should be dominant, which could make these findings transferable to any other available detector based on either Medipix2, Timepix or Timepix3 provided the same detector layer is used.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2023.113777
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“Deep learning for automated materials characterisation in core-loss electron energy loss spectroscopy”. Annys A, Jannis D, Verbeeck J, Annys A, Jannis D, Verbeeck J, Scientific reports 13, 13724 (2023). http://doi.org/10.1038/S41598-023-40943-7
Abstract: Electron energy loss spectroscopy (EELS) is a well established technique in electron microscopy that yields information on the elemental content of a sample in a very direct manner. One of the persisting limitations of EELS is the requirement for manual identification of core-loss edges and their corresponding elements. This can be especially bothersome in spectrum imaging, where a large amount of spectra are recorded when spatially scanning over a sample area. This paper introduces a synthetic dataset with 736,000 labeled EELS spectra, computed from available generalized oscillator strength tables, that represents 107 K, L, M or N core-loss edges and 80 chemical elements. Generic lifetime broadened peaks are used to mimic the fine structure due to band structure effects present in experimental core-loss edges. The proposed dataset is used to train and evaluate a series of neural network architectures, being a multilayer perceptron, a convolutional neural network, a U-Net, a residual neural network, a vision transformer and a compact convolutional transformer. An ensemble of neural networks is used to further increase performance. The ensemble network is used to demonstrate fully automated elemental mapping in a spectrum image, both by directly mapping the predicted elemental content and by using the predicted content as input for a physical model-based mapping.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.6
DOI: 10.1038/S41598-023-40943-7
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“Convexity constraints on linear background models for electron energy-loss spectra”. Van den Broek W, Jannis D, Verbeeck J, Ultramicroscopy 254, 113830 (2023). http://doi.org/10.1016/j.ultramic.2023.113830
Abstract: In this paper convexity constraints are derived for a background model of electron energy loss spectra (EELS) that is linear in the fitting parameters. The model outperforms a power-law both on experimental and simulated backgrounds, especially for wide energy ranges, and thus improves elemental quantification results. Owing to the model’s linearity, the constraints can be imposed through fitting by quadratic programming. This has important advantages over conventional nonlinear power-law fitting such as high speed and a guaranteed unique solution without need for initial parameters. As such, the need for user input is significantly reduced, which is essential for unsupervised treatment of large datasets. This is demonstrated on a demanding spectrum image of a semiconductor device sample with a high number of elements over a wide energy range.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2023.113830
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“In Situ Plasma Studies Using a Direct Current Microplasma in a Scanning Electron Microscope”. Grünewald L, Chezganov D, De Meyer R, Orekhov A, Van Aert S, Bogaerts A, Bals S, Verbeeck J, Advanced Materials Technologies (2024). http://doi.org/10.1002/admt.202301632
Abstract: Microplasmas can be used for a wide range of technological applications and to improve the understanding of fundamental physics. Scanning electron microscopy, on the other hand, provides insights into the sample morphology and chemistry of materials from the mm‐ down to the nm‐scale. Combining both would provide direct insight into plasma‐sample interactions in real‐time and at high spatial resolution. Up till now, very few attempts in this direction have been made, and significant challenges remain. This work presents a stable direct current glow discharge microplasma setup built inside a scanning electron microscope. The experimental setup is capable of real‐time in situ imaging of the sample evolution during plasma operation and it demonstrates localized sputtering and sample oxidation. Further, the experimental parameters such as varying gas mixtures, electrode polarity, and field strength are explored and experimental<italic>V</italic>–<italic>I</italic>curves under various conditions are provided. These results demonstrate the capabilities of this setup in potential investigations of plasma physics, plasma‐surface interactions, and materials science and its practical applications. The presented setup shows the potential to have several technological applications, for example, to locally modify the sample surface (e.g., local oxidation and ion implantation for nanotechnology applications) on the µm‐scale.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 6.8
DOI: 10.1002/admt.202301632
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“A combined experimental and computational approach to understanding CdS pigment oxidation in a renowned early 20th century painting”. Mayda S, Monico L, Krishnan D, De Meyer S, Cotte M, Garrevoet J, Falkenberg G, Sandu ICA, Partoens B, Lamoen D, Romani A, Miliani C, Verbeeck J, Janssens K, Chemistry of materials 35, 10403 (2023). http://doi.org/10.1021/ACS.CHEMMATER.3C01470
Abstract: Cadmium sulfide (CdS)-based yellow pigments have been used in a number of early 20th century artworks, including The Scream series painted by Edvard Munch. Some of these unique paintings are threatened by the discoloration of these CdS-based yellow oil paints because of the oxidation of the original sulfides to sulfates. The experimental data obtained here prove that moisture and cadmium chloride compounds play a key role in promoting such oxidation. To clarify how these two factors effectively prompt the process, we studied the band alignment between CdS, CdCl2, and Cd-(OH)Cl as well as the radicals center dot OH and H3O center dot by density functional theory (DFT) methods. Our results show that a stack of several layers of Cd-(OH)Cl creates a pocket of positive holes at the Cl-terminated surface and a pocket of electrons at the OH-terminated surface by leading in a difference in ionization energy at both surfaces. The resulting band alignment indicates that Cd-(OH)Cl can indeed play the role of an oxidative catalyst for CdS in a moist environment, thus providing an explanation for the experimental evidence.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT); Antwerp X-ray Imaging and Spectroscopy (AXIS)
Impact Factor: 8.6
DOI: 10.1021/ACS.CHEMMATER.3C01470
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“Low-dose 4D-STEM tomography for beam-sensitive nanocomposites”. Hugenschmidt M, Jannis D, Kadu AA, Grünewald L, De Marchi S, Perez-Juste J, Verbeeck J, Van Aert S, Bals S, ACS materials letters 6, 165 (2023). http://doi.org/10.1021/ACSMATERIALSLETT.3C01042
Abstract: Electron tomography is essential for investigating the three-dimensional (3D) structure of nanomaterials. However, many of these materials, such as metal-organic frameworks (MOFs), are extremely sensitive to electron radiation, making it difficult to acquire a series of projection images for electron tomography without inducing electron-beam damage. Another significant challenge is the high contrast in high-angle annular dark field scanning transmission electron microscopy that can be expected for nanocomposites composed of a metal nanoparticle and an MOF. This strong contrast leads to so-called metal artifacts in the 3D reconstruction. To overcome these limitations, we here present low-dose electron tomography based on four-dimensional scanning transmission electron microscopy (4D-STEM) data sets, collected using an ultrafast and highly sensitive direct electron detector. As a proof of concept, we demonstrate the applicability of the method for an Au nanostar embedded in a ZIF-8 MOF, which is of great interest for applications in various fields, including drug delivery.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1021/ACSMATERIALSLETT.3C01042
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“Phase coexistence induced surface roughness in V2O3/Ni magnetic heterostructures”. Ignatova K, Vlasov E, Seddon SD, Gauquelin N, Verbeeck J, Wermeille D, Bals S, Hase TPA, Arnalds UB, APL Materials 12 (2024). http://doi.org/10.1063/5.0195961
Abstract: We present an investigation of the microstructure changes in V2O3 as it goes through its inherent structural phase transition. Using V2O3 films with a well-defined crystal structure deposited by reactive magnetron sputtering on r-plane Al2O3 substrates, we study the phase coexistence region and its impact on the surface roughness of the films and the magnetic properties of overlying Ni magnetic layers in V2O3/Ni hybrid magnetic heterostructures. The simultaneous presence of two phases in V2O3 during its structural phase transition was identified with high resolution x-ray diffraction and led to an increase in surface roughness observed using x-ray reflectivity. The roughness reaches its maximum at the midpoint of the transition. In V2O3/Ni hybrid heterostructures, we find a concomitant increase in the coercivity of the magnetic layer correlated with the increased roughness of the V2O3 surface. The chemical homogeneity of the V2O3 is confirmed through transmission electron microscopy analysis. High-angle annular dark field imaging and electron energy loss spectroscopy reveal an atomically flat interface between Al2O3 and V2O3, as well as a sharp interface between V2O3 and Ni.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 6.1
DOI: 10.1063/5.0195961
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“High-Throughput Morphological Chirality Quantification of Twisted and Wrinkled Gold Nanorods”. Vlasov E, Heyvaert W, Ni B, Van Gordon K, Girod R, Verbeeck J, Liz-Marzán LM, Bals S, ACS Nano (2024). http://doi.org/10.1021/acsnano.4c02757
Abstract: Chirality in gold nanostructures offers an exciting opportunity to tune their differential optical response to left- and right-handed circularly polarized light, as well as their interactions with biomolecules and living matter. However, tuning and understanding such interactions demands quantification of the structural features that are responsible for the chiral behavior. Electron tomography (ET) enables structural characterization at the single-particle level and has been used to quantify the helicity of complex chiral nanorods. However, the technique is time-consuming and consequently lacks statistical value. To address this issue, we introduce herein a high-throughput methodology that combines images acquired by secondary electron-based electron beam-induced current (SEEBIC) with quantitative image analysis. As a result, the geometric chirality of hundreds of nanoparticles can be quantified in less than 1 h. When combining the drastic gain in data collection efficiency of SEEBIC with a limited number of ET data sets, a better understanding of how the chiral structure of individual chiral nanoparticles translates into the ensemble chiroptical response can be reached.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 17.1
DOI: 10.1021/acsnano.4c02757
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“Stabilizing perovskite Pb(Mg0.33Nb0.67)O3-PbTiO3 thin films by fast deposition and tensile mismatched growth template”. Ni S, Houwman E, Gauquelin N, Chezganov D, Van Aert S, Verbeeck J, Rijnders G, Koster G, ACS applied materials and interfaces 16, 12744 (2024). http://doi.org/10.1021/ACSAMI.3C16241
Abstract: Because of its low hysteresis, high dielectric constant, and strong piezoelectric response, Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT) thin films have attracted considerable attention for the application in PiezoMEMS, field-effect transistors, and energy harvesting and storage devices. However, it remains a great challenge to fabricate phase-pure, pyrochlore-free PMN-PT thin films. In this study, we demonstrate that a high deposition rate, combined with a tensile mismatched template layer can stabilize the perovskite phase of PMN-PT films and prevent the nucleation of passive pyrochlore phases. We observed that an accelerated deposition rate promoted mixing of the B-site cation and facilitated relaxation of the compressively strained PMN-PT on the SrTiO3 (STO) substrate in the initial growth layer, which apparently suppressed the initial formation of pyrochlore phases. By employing La-doped-BaSnO3 (LBSO) as the tensile mismatched buffer layer, 750 nm thick phase-pure perovskite PMN-PT films were synthesized. The resulting PMN-PT films exhibited excellent crystalline quality close to that of the STO substrate.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.5
DOI: 10.1021/ACSAMI.3C16241
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“Atomic resolution mapping using quantitative high-angle annular dark field scanning transmission electron microscopy”. Van Aert S, Verbeeck J, Bals S, Erni R, van Dyck D, Van Tendeloo G, Microscopy and microanalysis 15, 464 (2009). http://doi.org/10.1017/S1431927609093957
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 1.891
Times cited: 1
DOI: 10.1017/S1431927609093957
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“Quantitative electron microscopy of (Bi,Pb)2Sr2Ca2Cu3O10+\delta/Ag multifilament tapes during initial stages of annealing”. Bals S, Verbeeck J, Van Tendeloo G, Liu Y-L, Grivel J-C, Journal of the American Ceramic Society 88, 431 (2005). http://doi.org/10.1111/j.1551-2916.2005.00094.x
Abstract: The microstructural and compositional evolution during initial annealing of a superconducting (Bi,Pb)(2)Sr2Ca2Cu3O10+delta/Ag tape is studied using quantitative transmission electron microscopy. Special attention is devoted to the occurrence of Pb-rich liquids, which are crucial for the Bi2Sr2CaCu2O8+delta to (Bi,Pb)(2)Sr2Ca2Cu3O10+delta transformation. Ca and/or Pb-rich (Bi,Pb)(2)Sr2CaCu2O8+delta grains dissolve into a liquid, which reacts with Ca-rich phases to increase the liquid's Ca-content. This leads to (Bi,Pb)(2)Sr2Ca2Cu3O10+delta formation. Apparently, a Ca/Sr ratio of around I is sufficient to keep (Bi,Pb)(2)Sr2Ca2Cu3O10+delta nucleation going. It is confirmed that Ag particles are transported from the Ag-sheath into the oxide core by the liquid and not by mechanical treatment of the tape.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.841
Times cited: 1
DOI: 10.1111/j.1551-2916.2005.00094.x
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“Tomographic spectroscopic imaging, an experimental proof of concept”. van den Broek W, Verbeeck J, Schryvers D, de Backer S, Scheunders P, Ultramicroscopy 109, 296 (2009). http://doi.org/10.1016/j.ultramic.2008.11.022
Abstract: Recording the electron energy loss spectroscopy data cube with a series of energy filtered images is a dose inefficient process because the energy slit blocks most of the electrons. When recording the data cube by scanning an electron probe over the sample, perfect dose efficiency is attained; but due to the low current in nanoprobes, this often is slower, with a smaller field of view. In W. Van den Broek et al. [Ultramicroscopy, 106 (2006) 269], we proposed a new method to record the data cube, which is more dose efficient than an energy filtered series. It produces a set of projections of the data cube and then tomographically reconstructs it. In this article, we demonstrate these projections in practice, we present a simple geometrical model that allows for quantification of the projection angles and we present the first successful experimental reconstruction, all on a standard post-column instrument.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 1
DOI: 10.1016/j.ultramic.2008.11.022
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“Fabrication, microstructure, and enhanced thermionic electron emission properties of vertically aligned nitrogen-doped nanocrystalline diamond nanorods”. Sankaran KJ, Deshmukh S, Korneychuk S, Yeh C-J, Thomas JP, Drijkoningen S, Pobedinskas P, Van Bael MK, Verbeeck J, Leou K-C, Leung K-T, Roy SS, Lin I-N, Haenen K, MRS communications 8, 1311 (2018). http://doi.org/10.1557/MRC.2018.158
Abstract: Vertically aligned nitrogen-doped nanocrystalline diamond nanorods are fabricated from nitrogen-doped nanocrystalline diamond films using reactive ion etching in oxygen plasma. These nanorods show enhanced thermionic electron emission (TEE) characteristics, viz.. a high current density of 12.0 mA/cm(2) and a work function value of 4.5 eV with an applied voltage of 3 Vat 923 K. The enhanced TEE characteristics of these nanorods are ascribed to the induction of nanographitic phases at the grain boundaries and the field penetration effect through the local field enhancement from nanorods owing to a high aspect ratio and an excellent field enhancement factor.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.01
Times cited: 1
DOI: 10.1557/MRC.2018.158
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“Simultaneous heteroepitaxial growth of SrO (001) and SrO (111) during strontium-assisted deoxidation of the Si (001) surface”. Jovanović, Z, Gauquelin N, Koster G, Rubio-Zuazo J, Ghosez P, Verbeeck J, Suvorov D, Spreitzer M, Rsc Advances 10, 31261 (2020). http://doi.org/10.1039/D0RA06548J
Abstract: Epitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surface<italic>i.e.</italic>formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.9
Times cited: 1
DOI: 10.1039/D0RA06548J
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“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
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“Single femtosecond laser pulse excitation of individual cobalt nanoparticles”. Savchenko TM, Buzzi M, Howald L, Ruta S, Vijayakumar J, Timm M, Bracher D, Saha S, Derlet PM, Béché, A, Verbeeck J, Chantrell RW, Vaz CAF, Nolting F, Kleibert A, Physical Review B 102, 205418 (2020). http://doi.org/10.1103/PhysRevB.102.205418
Abstract: Laser-induced manipulation of magnetism at the nanoscale is a rapidly growing research topic with potential for applications in spintronics. In this work, we address the role of the scattering cross section, thermal effects, and laser fluence on the magnetic, structural, and chemical stability of individual magnetic nanoparticles excited by single femtosecond laser pulses. We find that the energy transfer from the fs laser pulse to the nanoparticles is limited by the Rayleigh scattering cross section, which in combination with the light absorption of the supporting substrate and protective layers determines the increase in the nanoparticle temperature. We investigate individual Co nanoparticles (8 to 20 nm in size) as a prototypical model system, using x-ray photoemission electron microscopy and scanning electron microscopy upon excitation with single femtosecond laser pulses of varying intensity and polarization. In agreement with calculations, we find no deterministic or stochastic reversal of the magnetization in the nanoparticles up to intensities where ultrafast demagnetization or all-optical switching is typically reported in thin films. Instead, at higher fluences, the laser pulse excitation leads to photo-chemical reactions of the nanoparticles with the protective layer, which results in an irreversible change in the magnetic properties. Based on our findings, we discuss the conditions required for achieving laser-induced switching in isolated nanomagnets.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.7
Times cited: 1
DOI: 10.1103/PhysRevB.102.205418
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“Asymmetric Interfacial Intermixing Associated Magnetic Coupling in LaMnO3/LaFeO3 Heterostructures”. Chen B, Gauquelin N, Green RJ, Verbeeck J, Rijnders G, Koster G, Frontiers in physics 9 (2021). http://doi.org/10.3389/fphy.2021.698154
Abstract: The structural and magnetic properties of LaMnO<sub>3</sub>/LaFeO<sub>3</sub>(LMO/LFO) heterostructures are characterized using a combination of scanning transmission electron microscopy, electron energy-loss spectroscopy, bulk magnetometry, and resonant x-ray reflectivity. Unlike the relatively abrupt interface when LMO is deposited on top of LFO, the interface with reversed growth order shows significant cation intermixing of Mn<sup>3+</sup>and Fe<sup>3+</sup>, spreading ∼8 unit cells across the interface. The asymmetric interfacial chemical profiles result in distinct magnetic properties. The bilayer with abrupt interface shows a single magnetic hysteresis loop with strongly enhanced coercivity, as compared to the LMO plain film. However, the bilayer with intermixed interface shows a step-like hysteresis loop, associated with the separate switching of the “clean” and intermixed LMO sublayers. Our study illustrates the key role of interfacial chemical profile in determining the functional properties of oxide heterostructures.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.3389/fphy.2021.698154
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“Low-cost electron detector for scanning electron microscope”. Vlasov E, Denisov N, Verbeeck J, HardwareX 14, e00413 (2023). http://doi.org/10.1016/j.ohx.2023.e00413
Abstract: Electron microscopy is an indispensable tool for the characterization of (nano) materials. Electron microscopes are typically very expensive and their internal operation is often shielded from the user. This situation can provide fast and high quality results for researchers focusing on e.g. materials science if they have access to the relevant instruments. For researchers focusing on technique development, wishing to test novel setups, however, the high entry price can lead to risk aversion and deter researchers from innovating electron microscopy technology further. The closed attitude of commercial entities about how exactly the different parts of electron microscopes work, makes it even harder for newcomers in this field. Here we propose an affordable, easy-to-build electron detector for use in a scanning electron microscope (SEM). The aim of this project is to shed light on the functioning of such detectors as well as show that even a very modest design can lead to acceptable performance while providing high flexibility for experimentation and customization.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.1016/j.ohx.2023.e00413
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“Secondary electron induced current in scanning transmission electron microscopy: an alternative way to visualize the morphology of nanoparticles”. Vlasov E, Skorikov A, Sánchez-Iglesias A, Liz-Marzán LM, Verbeeck J, Bals S, ACS materials letters , 1916 (2023). http://doi.org/10.1021/acsmaterialslett.3c00323
Abstract: Electron tomography (ET) is a powerful tool to determine the three-dimensional (3D) structure of nanomaterials in a transmission electron microscope. However, the acquisition of a conventional tilt series for ET is a time-consuming process and can therefore not provide 3D structural information in a time-efficient manner. Here, we propose surface-sensitive secondary electron (SE) imaging as an alternative to ET for the investigation of the morphology of nanomaterials. We use the SE electron beam induced current (SEEBIC) technique that maps the electrical current arising from holes generated by the emission of SEs from the sample. SEEBIC imaging can provide valuable information on the sample morphology with high spatial resolution and significantly shorter throughput times compared with ET. In addition, we discuss the contrast formation mechanisms that aid in the interpretation of SEEBIC data.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.1021/acsmaterialslett.3c00323
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“Absence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles”. Vijayakumar J, Savchenko TM, Bracher DM, Lumbeeck G, Béché, A, Verbeeck J, Vajda Š, Nolting F, Vaz Caf, Kleibert A, Nature communications 14, 174 (2023). http://doi.org/10.1038/s41467-023-35846-0
Abstract: Understanding chemical reactivity and magnetism of 3<italic>d</italic>transition metal nanoparticles is of fundamental interest for applications in fields ranging from spintronics to catalysis. Here, we present an atomistic picture of the early stage of the oxidation mechanism and its impact on the magnetism of Co nanoparticles. Our experiments reveal a two-step process characterized by (i) the initial formation of small CoO crystallites across the nanoparticle surface, until their coalescence leads to structural completion of the oxide shell passivating the metallic core; (ii) progressive conversion of the CoO shell to Co<sub>3</sub>O<sub>4</sub>and void formation due to the nanoscale Kirkendall effect. The Co nanoparticles remain highly reactive toward oxygen during phase (i), demonstrating the absence of a pressure gap whereby a low reactivity at low pressures is postulated. Our results provide an important benchmark for the development of theoretical models for the chemical reactivity in catalysis and magnetism during metal oxidation at the nanoscale.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 1
DOI: 10.1038/s41467-023-35846-0
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“Phase object reconstruction for 4D-STEM using deep learning”. Friedrich T, Yu C-P, Verbeeck J, Van Aert S, Microscopy and microanalysis 29, 395 (2023). http://doi.org/10.1093/MICMIC/OZAC002
Abstract: In this study, we explore the possibility to use deep learning for the reconstruction of phase images from 4D scanning transmission electron microscopy (4D-STEM) data. The process can be divided into two main steps. First, the complex electron wave function is recovered for a convergent beam electron diffraction pattern (CBED) using a convolutional neural network (CNN). Subsequently, a corresponding patch of the phase object is recovered using the phase object approximation. Repeating this for each scan position in a 4D-STEM dataset and combining the patches by complex summation yields the full-phase object. Each patch is recovered from a kernel of 3x3 adjacent CBEDs only, which eliminates common, large memory requirements and enables live processing during an experiment. The machine learning pipeline, data generation, and the reconstruction algorithm are presented. We demonstrate that the CNN can retrieve phase information beyond the aperture angle, enabling super-resolution imaging. The image contrast formation is evaluated showing a dependence on the thickness and atomic column type. Columns containing light and heavy elements can be imaged simultaneously and are distinguishable. The combination of super-resolution, good noise robustness, and intuitive image contrast characteristics makes the approach unique among live imaging methods in 4D-STEM.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.8
Times cited: 1
DOI: 10.1093/MICMIC/OZAC002
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