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“Long-range orientation and atomic attachment of nanocrystals in 2D honeycomb superlattices”. Boneschanscher MP, Evers WH, Geuchies JJ, Altantzis T, Goris B, Rabouw FT, van Rossum SAP, van der Zant HSJ, Siebbeles LDA, Van Tendeloo G, Swart I, Hilhorst J, Petukhov AV, Bals S, Vanmaekelbergh D;, Science 344, 1377 (2014). http://doi.org/10.1126/science.1252642
Abstract: Oriented attachment of synthetic semiconductor nanocrystals is emerging as a route for obtaining new semiconductors that can have Dirac-type electronic bands like graphene, but also strong spin-orbit coupling. The two-dimensional assembly geometry will require both atomic coherence and long-range periodicity of the superlattices. We show how the interfacial self-assembly and oriented attachment of nanocrystals results in two-dimensional (2D) metal chalcogenide semiconductors with a honeycomb superlattice. We present an extensive atomic and nanoscale characterization of these systems using direct imaging and wave scattering methods. The honeycomb superlattices are atomically coherent, and have an octahedral symmetry that is buckled; the nanocrystals occupy two parallel planes. Considerable necking and large-scale atomic motion occurred during the attachment process.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 37.205
Times cited: 304
DOI: 10.1126/science.1252642
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“Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth”. Yalcin AO, Fan Z, Goris B, Li WF, Koster RS, Fang CM, van Blaaderen A, Casavola M, Tichelaar FD, Bals S, Van Tendeloo G, Vlugt TJH, Vanmaekelbergh D, Zandbergen HW, van Huis MA;, Nano letters 14, 3661 (2014). http://doi.org/10.1021/nl501441w
Abstract: Here, we show a novel solidsolidvapor (SSV) growth mechanism whereby epitaxial growth of heterogeneous semiconductor nanowires takes place by evaporation-induced cation exchange. During heating of PbSe-CdSe nanodumbbells inside a transmission electron microscope (TEM), we observed that PbSe nanocrystals grew epitaxially at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis of atomic-resolution TEM observations and detailed atomistic simulations reveals that the growth process is mediated by vacancies.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 42
DOI: 10.1021/nl501441w
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“Monitoring galvanic replacement through three-dimensional morphological and chemical mapping”. Goris B, Polavarapu L, Bals S, Van Tendeloo G, Liz-Marzán LM, Nano letters 14, 3220 (2014). http://doi.org/10.1021/nl500593j
Abstract: Galvanic replacement reactions on metal nanoparticles are often used for the preparation of hollow nanostructures with tunable porosity and chemical composition, leading to tailored optical and catalytic properties. However, the precise interplay between the three-dimensional (3D) morphology and chemical composition of nanostructures during galvanic replacement is not always well understood as the 3D chemical imaging of nanoscale materials is still challenging. It is especially far from straightforward to obtain detailed information from the inside of hollow nanostructures using electron microscopy techniques such as SEM or TEM. We demonstrate here that a combination of state-of-the-art EDX mapping with electron tomography results in the unambiguous determination of both morphology transformation and elemental composition of nanostructures in 3D, during galvanic replacement of Ag nanocubes. This work provides direct and unambiguous experimental evidence toward understanding the galvanic replacement reaction. In addition, the powerful approach presented here can be applied to a wide range of nanoscale transformation processes, which will undoubtedly guide the development of novel nanostructures.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 120
DOI: 10.1021/nl500593j
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“Seeing and measuring in 3D with electrons”. Bals S, Goris B, Altantzis T, Heidari H, Van Aert S, Van Tendeloo G, Comptes rendus : physique 15, 140 (2014). http://doi.org/10.1016/j.crhy.2013.09.015
Abstract: Modern TEM enables the investigation of nanostructures at the atomic scale. However, TEM images are only two-dimensional (2D) projections of a three-dimensional (3D) object. Electron tomography can overcome this limitation. The technique is increasingly focused towards quantitative measurements and reaching atomic resolution in 3D has been the ultimate goal for many years. Therefore, one needs to optimize the acquisition of the data, the 3D reconstruction techniques as well as the quantification methods. Here, we will review a broad range of methodologies and examples. Finally, we will provide an outlook and will describe future challenges in the field of electron tomography.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.048
Times cited: 15
DOI: 10.1016/j.crhy.2013.09.015
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“Three-dimensional elemental mapping at the atomic scale in bimetallic nanocrystals”. Goris B, de Backer A, Van Aert S, Gómez-Graña S, Liz-Marzán LM, Van Tendeloo G, Bals S, Nano letters 13, 4236 (2013). http://doi.org/10.1021/nl401945b
Abstract: A thorough understanding of the three-dimensional (3D) atomic structure and composition of coreshell nanostructures is indispensable to obtain a deeper insight on their physical behavior. Such 3D information can be reconstructed from two-dimensional (2D) projection images using electron tomography. Recently, different electron tomography techniques have enabled the 3D characterization of a variety of nanostructures down to the atomic level. However, these methods have all focused on the investigation of nanomaterials containing only one type of chemical element. Here, we combine statistical parameter estimation theory with compressive sensing based tomography to determine the positions and atom type of each atom in heteronanostructures. The approach is applied here to investigate the interface in coreshell Au@Ag nanorods but it is of great interest in the investigation of a broad range of nanostructures.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 90
DOI: 10.1021/nl401945b
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“Au@Ag nanoparticles : halides stabilize {100} facets”. Gómez-Graña S, Goris B, Altantzis T, Fernández-López C, Carbó-Argibay E, Guerrero-Martínez A, Almora-Barrios N, López N, Pastoriza-Santos I, Pérez-Juste J, Bals S, Van Tendeloo G, Liz-Marzán LM;, The journal of physical chemistry letters 4, 2209 (2013). http://doi.org/10.1021/jz401269w
Abstract: Seed-mediated growth is the most efficient methodology to control the size and shape of colloidal metal nanoparticles. In this process, the final nanocrystal shape is defined by the crystalline structure of the initial seed as well as by the presence of ligands and other additives that help to stabilize certain crystallographic facets. We analyze here the growth mechanism in aqueous solution of silver shells on presynthesized gold nanoparticles displaying various well-defined crystalline structures and morphologies. A thorough three-dimensional electron microscopy characterization of the morphology and internal structure of the resulting core-shell nanocrystals indicates that {100} facets are preferred for the outer silver shell, regardless of the morphology and crystallinity of the gold cores. These results are in agreement with theoretical analysis based on the relative surface energies of the exposed facets in the presence of halide ions.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.353
Times cited: 131
DOI: 10.1021/jz401269w
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“Band structure quantization in nanometer sized ZnO clusters”. Schouteden K, Zeng Y-J, Lauwaet K, Romero CP, Goris B, Bals S, Van Tendeloo G, Lievens P, Van Haesendonck C, Nanoscale 5, 3757 (2013). http://doi.org/10.1039/c3nr33989k
Abstract: Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 13
DOI: 10.1039/c3nr33989k
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“Procedure to count atoms with trustworthy single-atom sensitivity”. Van Aert S, de Backer A, Martinez GT, Goris B, Bals S, Van Tendeloo G, Rosenauer A, Physical review : B : condensed matter and materials physics 87, 064107 (2013). http://doi.org/10.1103/PhysRevB.87.064107
Abstract: We report a method to reliably count the number of atoms from high-angle annular dark field scanning transmission electron microscopy images. A model-based analysis of the experimental images is used to measure scattering cross sections at the atomic level. The high sensitivity of these measurements in combination with a thorough statistical analysis enables us to count atoms with single-atom sensitivity. The validity of the results is confirmed by means of detailed image simulations. We will show that the method can be applied to nanocrystals of arbitrary shape, size, and atom type without the need for a priori knowledge about the atomic structure.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 106
DOI: 10.1103/PhysRevB.87.064107
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“Hydrophobic interactions modulate self-assembly of nanoparticles”. Sánchez-Iglesias A, Grzelczak M, Altantzis T, Goris B, Pérez-Juste J, Bals S, Van Tendeloo G, Donaldson SH, Chmelka BF, Israelachvili JN, Liz-Marzán LM;, ACS nano 6, 11059 (2012). http://doi.org/10.1021/nn3047605
Abstract: Hydrophobic interactions constitute one of the most important types of nonspecific interactions in biological systems, which emerge when water molecules rearrange as two hydrophobic species come close to each other. The prediction of hydrophobic interactions at the level of nanoparticles (Brownian objects) remains challenging because of uncontrolled diffusive motion of the particles. We describe here a general methodology for solvent-induced, reversible self-assembly of gold nanoparticles into 3D clusters with well-controlled sizes. A theoretical description of the process confirmed that hydrophobic interactions are the main driving force behind nanoparticle aggregation.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 311
DOI: 10.1021/nn3047605
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“Atomic-scale determination of surface facets in gold nanorods”. Goris B, Bals S, van den Broek W, Carbó-Argibay E, Gómez-Graña S, Liz-Marzán LM, Van Tendeloo G, Nature materials 11, 930 (2012). http://doi.org/10.1038/NMAT3462
Abstract: It is widely accepted that the physical properties of nanostructures depend on the type of surface facets1, 2. For Au nanorods, the surface facets have a major influence on crucial effects such as reactivity and ligand adsorption and there has been controversy regarding facet indexing3, 4. Aberration-corrected electron microscopy is the ideal technique to study the atomic structure of nanomaterials5, 6. However, these images correspond to two-dimensional (2D) projections of 3D nano-objects, leading to an incomplete characterization. Recently, much progress was achieved in the field of atomic-resolution electron tomography, but it is still far from being a routinely used technique. Here we propose a methodology to measure the 3D atomic structure of free-standing nanoparticles, which we apply to characterize the surface facets of Au nanorods. This methodology is applicable to a broad range of nanocrystals, leading to unique insights concerning the connection between the structure and properties of nanostructures.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 39.737
Times cited: 261
DOI: 10.1038/NMAT3462
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“Low-dimensional semiconductor superlattices formed by geometric control over nanocrystal attachment”. Evers WH, Goris B, Bals S, Casavola M, de Graaf J, van Roij R, Dijkstra M, Vanmaekelbergh D, Nano letters 13, 2317 (2013). http://doi.org/10.1021/nl303322k
Abstract: Oriented attachment, the process in which nanometer-sized crystals fuse by atomic bonding of specific crystal facets, is expected to be more difficult to control than nanocrystal self-assembly that is driven by entropic factors or weak van der Waals attractions. Here, we present a study of oriented attachment of PbSe nanocrystals that counteract this tuition. The reaction was studied in a thin film of the suspension casted on an immiscible liquid at a given temperature. We report that attachment can be controlled such that it occurs with one type of facets exclusively. By control of the temperature and particle concentration we obtain one- or two-dimensional PbSe single crystals, the latter with a honeycomb or square superimposed periodicity in the nanometer range. We demonstrate the ability to convert these PbSe superstructures into other semiconductor compounds with the preservation of crystallinity and geometry.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 206
DOI: 10.1021/nl303322k
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“Quantitative structure determination of large three-dimensional nanoparticle assemblies”. Altantzis T, Goris B, Sánchez-Iglesias A, Grzelczak M, Liz-Marzán LM, Bals S, Particle and particle systems characterization 30, 84 (2013). http://doi.org/10.1002/ppsc.201200045
Abstract: Thumbnail image of graphical abstract To investigate nanoassemblies in three dimensions, electron tomography is an important tool. For large nanoassemblies, it is not straightforward to obtain quantitative results in three dimensions. An optimized acquisition technique, incoherent bright field scanning transmission electron microscopy, is combined with an advanced 3D reconstruction algorithm. The approach is applied to quantitatively analyze large nanoassemblies in three dimensions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.474
Times cited: 23
DOI: 10.1002/ppsc.201200045
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“Advanced reconstruction algorithms for electron tomography : from comparison to combination”. Goris B, Roelandts T, Batenburg KJ, Heidari Mezerji H, Bals S, Ultramicroscopy 127, 40 (2013). http://doi.org/10.1016/j.ultramic.2012.07.003
Abstract: In this work, the simultaneous iterative reconstruction technique (SIRT), the total variation minimization (TVM) reconstruction technique and the discrete algebraic reconstruction technique (DART) for electron tomography are compared and the advantages and disadvantages are discussed. Furthermore, we describe how the result of a three dimensional (3D) reconstruction based on TVM can provide objective information that is needed as the input for a DART reconstruction. This approach results in a tomographic reconstruction of which the segmentation is carried out in an objective manner.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 63
DOI: 10.1016/j.ultramic.2012.07.003
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Goris B (2014) Advanced electron tomography : 3 dimensional structural characterisation of nanomaterials down to the atomic scale. Antwerpen
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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