|
“Experimental weathering studies of igneous rocks (alkali-granite, granodiorite, gabbro and granite) and sedimentary gneiss under hydrothermal conditions”. Van 't dack L, Beusen J-M, Claesson T, Vandelannoote R, van Grieken R, Gijbels R, , 363 (1985)
Keywords: P3 Proceeding; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
|
|
“Sources and elemental composition of ambient PM2.5 in three European cities”. Vallius M, Janssen NAH, Heinrich J, Hoek G, Ruuskanen J, Cyrys J, Van Grieken R, de Hartog JJ, Kreyling WG, Pekkanen J, The science of the total environment 337, 147 (2005). http://doi.org/10.1016/J.SCITOTENV.2004.06.018
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.SCITOTENV.2004.06.018
|
|
“Phosphorus scarcity contributes to nitrogen limitation in lowland tropical rainforests”. Vallicrosa H, Lugli LF, Fuchslueger L, Sardans J, Ramirez-Rojas I, Verbruggen E, Grau O, Brechet L, Peguero G, Van Langenhove L, Verryckt LT, Terrer C, Llusia J, Ogaya R, Marquez L, Roc-Fernandez P, Janssens I, Penuelas J, Ecology 104, e4049 (2023). http://doi.org/10.1002/ECY.4049
Abstract: There is increasing evidence to suggest that soil nutrient availability can limit the carbon sink capacity of forests, a particularly relevant issue considering today's changing climate. This question is especially important in the tropics, where most part of the Earth's plant biomass is stored. To assess whether tropical forest growth is limited by soil nutrients and to explore N and P limitations, we analyzed stem growth and foliar elemental composition of the five stem widest trees per plot at two sites in French Guiana after 3 years of nitrogen (N), phosphorus (P), and N + P addition. We also compared the results between potential N-fixer and non-N-fixer species. We found a positive effect of N fertilization on stem growth and foliar N, as well as a positive effect of P fertilization on stem growth, foliar N, and foliar P. Potential N-fixing species had greater stem growth, greater foliar N, and greater foliar P concentrations than non-N-fixers. In terms of growth, there was a negative interaction between N-fixer status, N + P, and P fertilization, but no interaction with N fertilization. Because N-fixing plants do not show to be completely N saturated, we do not anticipate N providing from N-fixing plants would supply non-N-fixers. Although the soil-age hypothesis only anticipates P limitation in highly weathered systems, our results for stem growth and foliar elemental composition indicate the existence of considerable N and P co-limitation, which is alleviated in N-fixing plants. The evidence suggests that certain mechanisms invest in N to obtain the scarce P through soil phosphatases, which potentially contributes to the N limitation detected by this study.
Keywords: A1 Journal article; Plant and Ecosystems (PLECO) – Ecology in a time of change
Impact Factor: 4.8
DOI: 10.1002/ECY.4049
|
|
“Hall magnetocapitance in two-dimensional electron systems”. Valkering AMC, Sommerfeld PKH, van de Ven RAM, van der Heijden RW, Blom FAP, Lea MJ, Peeters FM, Physical review letters 81, 5398 (1998). http://doi.org/10.1103/PhysRevLett.81.5398
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 8.462
Times cited: 4
DOI: 10.1103/PhysRevLett.81.5398
|
|
“Climate variable choice in Ricardian studies of European Agriculture”. Vaitkeviciute J, Chakir R, Van Passel S, Revue économique 70, 375 (2019). http://doi.org/10.3917/RECO.703.0375
Abstract: The Ricardian model has been employed frequently to study the impact of climate change on European agriculture. This paper contributes to this literature by using a panel data of FADN EU regions and the period 2004-2012 and by taking into account both individual heterogeneity as well as spatial autocorrelation among EU regions. We tested three hypotheses related to the degree days model. Our results show that climate outside the defined growing season matters for European agriculture, and excluding it could underestimate climate change impacts. Our results should support public policy decisions about efficient and effective mitigation and adaptation policy measures in EU agriculture.
Keywords: A1 Journal article; Economics; Engineering Management (ENM)
DOI: 10.3917/RECO.703.0375
|
|
“Extended Ginzburg-Landau formalism : systematic expansion in small deviation from the critical temperature”. Vagov AV, Shanenko AA, Milošević, MV, Axt VM, Peeters FM, Physical review : B : condensed matter and materials physics 85, 014502 (2012). http://doi.org/10.1103/PhysRevB.85.014502
Abstract: Based on the Gor'kov formalism for a clean s-wave superconductor, we develop an extended version of the single-band Ginzburg-Landau (GL) theory by means of a systematic expansion in the deviation from the critical temperature T(c), i.e., tau = 1 – T/T(c). We calculate different contributions to the order parameter and the magnetic field: the leading contributions (proportional to tau(1/2) in the order parameter and. t in the magnetic field) are controlled by the standard GL theory, while the next-to-leading terms (proportional to tau(3/2) in the gap and proportional to tau(2) in the magnetic field) constitute the extended GL (EGL) approach. We derive the free-energy functional for the extended formalism and the corresponding expression for the current density. To illustrate the usefulness of our formalism, we calculate, in a semianalytical form, the temperature-dependent correction to the GL parameter at which the surface energy becomes zero, and analytically, the temperature dependence of the thermodynamic critical field. We demonstrate that the EGL formalism is not just a mathematical extension to the theory: variations of both the gap and the thermodynamic critical field with temperature calculated within the EGL theory are found in very good agreement with the full BCS results down to low temperatures, which dramatically improves the applicability of the formalism compared to its standard predecessor.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 36
DOI: 10.1103/PhysRevB.85.014502
|
|
“Superconductivity between standard types: Multiband versus single-band materials”. Vagov A, Shanenko AA, Milošević, MV, Axt VM, Vinokur VM, Aguiar JA, Peeters FM, Physical review B 93, 174503 (2016). http://doi.org/10.1103/PhysRevB.93.174503
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 37
DOI: 10.1103/PhysRevB.93.174503
|
|
“Two-band superconductors : extended Ginzburg-Landau formalism by a systematic expansion in small deviation from the critical temperature”. Vagov A, Shanenko AA, Milošević, MV, Axt VM, Peeters FM, Physical review : B : condensed matter and materials physics 86, 144514 (2012). http://doi.org/10.1103/PhysRevB.86.144514
Abstract: We derive the extended Ginzburg-Landau (GL) formalism for a clean s-wave two-band superconductor by employing a systematic expansion of the free-energy functional and the corresponding matrix gap equation in powers of the small deviation from the critical temperature tau = 1 – T/T-c. The two lowest orders of this expansion produce the equation for T-c and the standard GL theory. It is shown that in agreement with previous studies, this two-band GL theory maps onto the single-band GL model and thus fails to describe the difference in the spatial profiles of the two-band condensates. We prove that this difference appears already in the leading correction to the standard GL theory, which constitutes the extended GL formalism. We derive linear differential equations that determine the leading corrections to the band order parameters and magnetic field, discuss the validity of these equations, and consider examples of an important interplay between the band condensates. Finally, we present numerical results for the thermodynamic critical magnetic field and temperature-dependent band gaps for recent materials of interest, which are in very good agreement with those obtained from the full BCS approach in a wide temperature range. To this end, we emphasize the advantages of our extended GL theory in comparison with the often used two-component GL-like model based on an unreconstructed two-band generalization of the Gor'kov derivation.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 44
DOI: 10.1103/PhysRevB.86.144514
|
|
“Generalized Galitskii approach for the vertex function of a Fermi gas with resonant interaction”. Vagov A, Schomerus H, Shanenko A, Physical review : B : condensed matter and materials physics 76, 214513 (2007). http://doi.org/10.1103/PhysRevB.76.214513
Abstract: We present a generalized Galitskii approach for the Bethe-Salpeter equation for the two-particle vertex function of a Fermi system with the resonant interaction by accounting for the resonant state in the scattering potential and utilizing the universal form of the resonant scattering amplitude. The procedure can be carried out both for the normal as well as for the condensate state. In both cases, the vertex function in the vicinity of the resonance is shown to formally coincide with that obtained for a weakly attractive Fermi gas. Thus we justify the popular calculational framework in which results for the weakly attractive Fermi gas are formally extrapolated into the domain of strong coupling, and further to the repulsive side of the resonance, where molecular states are formed.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 8
DOI: 10.1103/PhysRevB.76.214513
|
|
“Competition between pure dephasing and photon losses in the dynamics of a dot-cavity system”. Vagov A, Glaessl M, Croitoru MD, Axt VM, Kuhn T, Physical review : B : condensed matter and materials physics 90, 075309 (2014). http://doi.org/10.1103/PhysRevB.90.075309
Abstract: We demonstrate that in quantum-dot cavity systems, the interplay between acoustic phonons and photon losses introduces novel features and characteristic dependencies in the system dynamics. In particular, the combined action of both dephasing mechanisms strongly affects the transition from the weak-to the strong-coupling regime as well as the shape of the spectral triplet that represents the quantum-dot occupation in Fourier space. The width of the central peak in the triplet is expected to decrease with rising temperature, while the widths and heights of the side peaks depend nonmonotonically on the dot-cavity coupling.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PhysRevB.90.075309
|
|
“High pulse area undamping of Rabi oscillations in quantum dots coupled to phonons”. Vagov A, Croitoru MD, Axt VM, Kuhn T, Peeters FM, Physica status solidi B –, Basic solid state physics 243, 2233 (2006). http://doi.org/10.1002/pssb.200668029
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 1.674
Times cited: 16
DOI: 10.1002/pssb.200668029
|
|
“Nonmonotonic field dependence of damping and reappearance of Rabi oscillations in quantum dots”. Vagov A, Croitoru MD, Axt VM, Kuhn T, Peeters FM, Physical review letters 98, 1 (2007). http://doi.org/10.1103/PhysRevLett.98.227403
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Electron microscopy for materials research (EMAT)
Impact Factor: 8.462
Times cited: 91
DOI: 10.1103/PhysRevLett.98.227403
|
|
“Real time path integrals in studies of quantum dots dynamics: non-monotonous decay rate and reappearance of rabi rotations”. Vagov A, Croitoru MD, Axt VM, Kuhn T, Peeters F, Path Integrals : New Trends and Perspectives, Proceedings , 57 (2008). http://doi.org/10.1142/9789812837271_0007
Abstract: The dynamics of strongly confined laser driven semiconductor quantum dots coupled to phonons is studied theoretically by calculating the time evolution of the reduced density matrix using the path integral method. We explore the cases of long pulses, strong dot-phonon and dot-laser coupling and high temperatures, which up to now have been inaccessible. We find that the decay rate of the Rabi oscillations is a non-monotonic function of the laser field leading to the decay and reappearance of the Rabi oscillations in the field dependence of the dot exciton population.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
DOI: 10.1142/9789812837271_0007
|
|
“Direct reagentless detection of the affinity binding of recombinant His-tagged firefly luciferase with a nickel-modified gold electrode”. Vagin MY, Trashin SA, Beloglazkina EK, Majouga AG, Mendeleev communications 25, 290 (2015). http://doi.org/10.1016/J.MENCOM.2015.07.021
Abstract: The direct reagentless electrochemical detection of recombinant firefly luciferase binding with a gold electrode modified with nickel complex of 1,16-di[4-(2,6-dihydroxycarbonyl)pyridyl]-1,16-dioxa-8,9-dithiahexadecane has been carried out.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.MENCOM.2015.07.021
|
|
“Application of combined micro-proton-induced X-ray emission and micro-synchrotron radiation X-ray fluorescence techniques for the characterization of impact materials around Barringer Meteor Crater”. Uzonyi I, Szöör G, Vekemans B, Vincze L, Rozsa P, Szabo G, Somogyi A, Adams F, Kiss ÁZ, Spectrochimica acta: part B : atomic spectroscopy 59, 1717 (2004). http://doi.org/10.1016/J.SAB.2004.05.030
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.SAB.2004.05.030
|
|
“Characterization of impact materials around Barringer meteor crater by micro-PIXE nd micro-SRXRF techniques”. Uzonyi I, Szöör G, Rozsa P, Vekemans B, Vincze L, Adams F, Drakopoulos M, Somogyi A, Kiss ÁZ, Nuclear instruments and methods in physics research: B: beam interactions with materials and atoms 219/220, 555 (2004). http://doi.org/10.1016/J.NIMB.2004.01.119
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.NIMB.2004.01.119
|
|
“A packed-bed DBD micro plasma reactor for CO 2 dissociation: Does size matter?”.Uytdenhouwen Y, Van Alphen S, Michielsen I, Meynen V, Cool P, Bogaerts A, Chemical engineering journal 348, 557 (2018). http://doi.org/10.1016/j.cej.2018.04.210
Abstract: DBD plasma reactors are of great interest for environmental and energy applications, such as CO2 conversion, but they suffer from limited conversion and especially energy efficiency. The introduction of packing materials has been a popular subject of investigation in order to increase the reactor performance. Reducing the discharge gap of the reactor below one millimetre can enhance the plasma performance as well. In this work, we combine both effects and use a packed-bed DBD micro plasma reactor to investigate the influence of gap size reduction, in combination with a packing material, on the conversion and efficiency of CO2 dissociation. Packing materials used in this work were SiO2, ZrO2, and Al2O3 spheres as well as glass wool. The results are compared to a regular size reactor as a benchmark. Reducing the discharge gap can greatly increase the CO2 conversion, although at a lower energy efficiency. Adding a packing material further increases the conversion when keeping a constant residence time, but is greatly dependent on the material composition, gap and sphere size used. Maximum conversions of 50–55% are obtained for very long residence times (30 s and higher) in an empty reactor or with certain packing material combinations, suggesting a balance in CO2 dissociation and recombination reactions. The maximum energy efficiency achieved is 4.3%, but this is for the regular sized reactor at a short residence time (7.5 s). Electrical characterization is performed to reveal some trends in the electrical behaviour of the plasma upon reduction of the discharge gap and addition of a packing material.
Keywords: A1 Journal article; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.216
Times cited: 22
DOI: 10.1016/j.cej.2018.04.210
|
|
“The Potential Use of Core-Shell Structured Spheres in a Packed-Bed DBD Plasma Reactor for CO2 Conversion”. Uytdenhouwen Y, Meynen V, Cool P, Bogaerts A, Catalysts 10, 530 (2020). http://doi.org/10.3390/catal10050530
Abstract: This work proposes to use core-shell structured spheres to evaluate whether it allows to individually optimize bulk and surface effects of a packing material, in order to optimize conversion and energy efficiency. Different core-shell materials have been prepared by spray coating, using dense spheres (as core) and powders (as shell) of SiO2, Al2O3, and BaTiO3. The materials are investigated for their performance in CO2 dissociation and compared against a benchmark consisting of a packed-bed reactor with the pure dense spheres, as well as an empty reactor. The results in terms of CO2 conversion and energy efficiency show various interactions between the core and shell material, depending on their combination. Al2O3 was found as the best core material under the applied conditions here, followed by BaTiO3 and SiO2, in agreement with their behaviour for the pure spheres. Applying a thin shell layer on the cores showed equal performance between the different shell materials. Increasing the layer thickness shifts this behaviour, and strong combination effects were observed depending on the specific material. Therefore, this method of core-shell spheres has the potential to allow tuning of the packing properties more closely to the application by designing an optimal combination of core and shell.
Keywords: A1 Journal article; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.9
DOI: 10.3390/catal10050530
|
|
“How gas flow design can influence the performance of a DBD plasma reactor for dry reforming of methane”. Uytdenhouwen Y, Hereijgers J, Breugelmans T, Cool P, Bogaerts A, Chemical Engineering Journal 405, 126618 (2021). http://doi.org/10.1016/j.cej.2020.126618
Abstract: DBD plasma reactors are commonly used in a static ‘one inlet – one outlet’ design that goes against reactor design principles for multi-component reactions, such as dry reforming of methane (DRM). Therefore, in this paper we have developed a novel reactor design, and investigated how the shape and size of the reaction zone, as well as gradual gas addition, and the method of mixing CO2 and CH4 can influence the conversion and product com position of DRM. Even in the standard ‘one inlet – one outlet’ design, the direction of the gas flow (i.e. short or long path through the reactor, which defines the gas velocity at fixed residence time), as well as the dimensions of the reaction zone and the power delivery to the reactor, largely affect the performance. Using gradual gas addition and separate plasma activation zones for the individual gases give increased conversions within the same operational parameters, by optimising mixing ratios and kinetics. The choice of the main (pre-activated) gas and the direction of gas flow largely affect the conversion and energy cost, while the gas inlet position during separate addition only influences the product distribution.
Keywords: A1 Journal article; Engineering sciences. Technology; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 6.216
DOI: 10.1016/j.cej.2020.126618
|
|
“On the kinetics and equilibria of plasma-based dry reforming of methane”. Uytdenhouwen Y, Bal Km, Neyts Ec, Meynen V, Cool P, Bogaerts A, Chemical Engineering Journal 405, 126630 (2021). http://doi.org/10.1016/j.cej.2020.126630
Abstract: Plasma reactors are interesting for gas-based chemical conversion but the fundamental relation between the plasma chemistry and selected conditions remains poorly understood. Apparent kinetic parameters for the loss and formation processes of individual components of gas conversion processes, can however be extracted by performing experiments in an extended residence time range (2–75 s) and fitting the gas composition to a firstorder kinetic model of the evolution towards partial chemical equilibrium (PCE). We specifically investigated the differences in kinetic characteristics and PCE state of the CO2 dissociation and CH4 reforming reactions in a dielectric barrier discharge reactor (DBD), how these are mutually affected when combining both gases in the dry reforming of methane (DRM) reaction, and how they change when a packing material (non-porous SiO2) is added to the reactor. We find that CO2 dissociation is characterized by a comparatively high reaction rate of 0.120 s−1 compared to CH4 reforming at 0.041 s−1; whereas CH4 reforming reaches higher equilibrium conversions, 82% compared to 53.6% for CO2 dissociation. Combining both feed gases makes the DRM reaction to proceed at a relatively high rate (0.088 s−1), and high conversion (75.4%) compared to CO2 dissociation, through accessing new chemical pathways between the products of CO2 and CH4. The addition of the packing material can also distinctly influence the conversion rate and position of the equilibrium, but its precise effect depends strongly on the gas composition. Comparing different CO2:CH4 ratios reveals the delicate balance of the combined chemistry. CO2 drives the loss reactions in DRM, whereas CH4 in the mixture suppresses back reactions. As a result, our methodology provides some of the insight necessary to systematically tune the conversion process.
Keywords: A1 Journal article; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.216
DOI: 10.1016/j.cej.2020.126630
|
|
“How process parameters and packing materials tune chemical equilibrium and kinetics in plasma-based CO2 conversion”. Uytdenhouwen Y, Bal Km, Michielsen I, Neyts Ec, Meynen V, Cool P, Bogaerts A, Chemical engineering journal 372, 1253 (2019). http://doi.org/10.1016/j.cej.2019.05.008
Abstract: Plasma (catalysis) reactors are increasingly being used for gas-based chemical conversions, providing an alternative method of energy delivery to the molecules. In this work we explore whether classical concepts such as
equilibrium constants, (overall) rate coefficients, and catalysis exist under plasma conditions. We specifically
investigate the existence of a so-called partial chemical equilibrium (PCE), and how process parameters and
packing properties influence this equilibrium, as well as the overall apparent rate coefficient, for CO2 splitting in
a DBD plasma reactor. The results show that a PCE can be reached, and that the position of the equilibrium, in
combination with the rate coefficient, greatly depends on the reactor parameters and operating conditions (i.e.,
power, pressure, and gap size). A higher power, higher pressure, or smaller gap size enhance both the equilibrium constant and the rate coefficient, although they cannot be independently tuned. Inserting a packing
material (non-porous SiO2 and ZrO2 spheres) in the reactor reveals interesting gap/material effects, where the
type of material dictates the position of the equilibrium and the rate (inhibition) independently. As a result, no
apparent synergistic effect or plasma-catalytic behaviour was observed for the non-porous packing materials
studied in this reaction. Within the investigated parameters, equilibrium conversions were obtained between 23
and 71%, while the rate coefficient varied between 0.027 s−1 and 0.17 s−1. This method of analysis can provide
a more fundamental insight in the overall reaction kinetics of (catalytic) plasma-based gas conversion, in order
to be able to distinguish plasma effects from true catalytic enhancement.
Keywords: A1 Journal article; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.216
Times cited: 3
DOI: 10.1016/j.cej.2019.05.008
|
|
Uytdenhouwen Y (2020) Tuning the performance of a DBD plasma reactor for CO2 reforming. 303 p
Keywords: Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
|
|
“New insights into the early stages of nanoparticle electrodeposition”. Ustarroz J, Ke X, Hubin A, Bals S, Terryn H, The journal of physical chemistry: C : nanomaterials and interfaces 116, 2322 (2012). http://doi.org/10.1021/jp210276z
Abstract: Electrodeposition is an increasingly important method to synthesize supported nanoparticles, yet the early stages of electrochemical nanoparticle formation are not perfectly understood. In this paper, the early stages of silver nanoparticle electrodeposition on carbon substrates have been studied by aberration-corrected TEM, using carbon-coated TEM grids as electrochemical electrodes. In this manner we have access to as-deposited nanoparticle size distribution and structural characterization at the atomic scale combined with electrochemical measurements, which represents a breakthrough in a full understanding of the nanoparticle electrodeposition mechanisms. Whereas classical models, based upon characterization at the nanoscale, assume that electrochemical growth is only driven by direct attachment, the results reported hereafter indicate that early nanoparticle growth is mostly driven by nanocluster surface movement and aggregation. Hence, we conclude that electrochemical nulceation and growth models should be revised and that an electrochemical aggregative growth mechanism should be considered in the early stages of nanoparticle electrodeposition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 104
DOI: 10.1021/jp210276z
|
|
“A generalized electrochemical aggregative growth mechanism”. Ustarroz J, Hammons JA, Altantzis T, Hubin A, Bals S, Terryn H, Journal of the American Chemical Society 135, 11550 (2013). http://doi.org/10.1021/ja402598k
Abstract: The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the VolmerWeber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 124
DOI: 10.1021/ja402598k
|
|
“Electrodeposition of Ag nanoparticles onto carbon coated TEM grids : a direct approach to study early stages of nucleation”. Ustarroz J, Gupta U, Hubin A, Bals S, Terryn H, Electrochemistry communications 12, 1706 (2010). http://doi.org/10.1016/j.elecom.2010.10.002
Abstract: An innovative experimental approach to study the electrodeposition of small nanoparticles and the early stages of electrochemical nucleation and growth is presented. Carbon coated gold TEM grids are used as substrates for the electrodeposition of silver nanoparticles so that electrochemical data, FESEM, HAADFSTEM and HRTEM data can be acquired from the same sample without the need to remove the particles from the substrate. It is shown that the real distribution of nanoparticles cannot be resolved by FESEM whereas HAADFSTEM analysis confirms that a distribution of small nanoparticles (d ≈ 12 nm) coexist with large nanoparticles corresponding to a bimodal size distribution. Besides, particles grown under the same conditions have been found to present different structures such as monocrystals, polycrystals or aggregates of smaller particles.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.396
Times cited: 52
DOI: 10.1016/j.elecom.2010.10.002
|
|
“Electrodeposition of Highly Porous Pt Nanoparticles Studied by Quantitative 3D Electron Tomography: Influence of Growth Mechanisms and Potential Cycling on the Active Surface Area”. Ustarroz J, Geboes B, Vanrompay H, Sentosun K, Bals S, Breugelmans T, Hubin A, ACS applied materials and interfaces 9, 16168 (2017). http://doi.org/10.1021/acsami.7b01619
Abstract: Nanoporous Pt nanoparticles (NPs) are promising fuel cell catalysts due to their large surface area and increased electrocatalytic activity towards the oxygen reduction reaction (ORR). Herein, we report on the infuence of the growth mechanisms on the surface properties of electrodeposited Pt dendritic NPs with large surface areas. The electrochemically active surface was studied by hydrogen underpotential deposition (HUPD) and compared for the rst time to high angle annular dark eld scanning transmission electron microscopy (HAADF-STEM) quantitative 3D electron tomography of individual nanoparticles. Large nucleation overpotential leads to a large surface coverage of Pt roughened spheroids, which provide large roughness factor (Rf ) but low mass-specic electrochemically active surface area (EASA). Lowering the nucleation overpotential leads to highly porous Pt NPs with pores protruding to the center of the structure. At the expense of smaller Rf , the obtained EASA values of these structures are in the range of these of large surface area supported fuel cell catalysts. The active surface area of the Pt dendritic NPs was measured by electron tomography and it was found that the potential cycling in the H adsorption/desorption and Pt oxidation/reduction region, which is generally performed to determine the EASA, leads to a signicant reduction of that surface area due to a partial collapse of their dendritic and porous morphology. Interestingly, the extrapolation of the microscopic tomography results to macroscopic electrochemical parameters indicated that the surface properties measured by H UPD are comparable to the values measured on individual NPs by electron tomography after the degradation caused by the H UPD measurement. These results highlight that the combination of electrochemical and quantitative 3D surface analysis techniques is essential to provide insights into the surface properties, the electrochemical stability and, hence, the applicability of these materials. Moreover, it indicates that care must be taken with widely used electrochemical methods of surface area determination, especially in the case of large surface area and possibly unstable nanostructures, since the measured surface can be strongly aected by the measurement itself.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 7.504
Times cited: 24
DOI: 10.1021/acsami.7b01619
|
|
“The role of nanocluster aggregation, coalescence, and recrystallization in the electrochemical deposition of platinum nanostructures”. Ustarroz J, Altantzis T, Hammons JA, Hubin A, Bals S, Terryn H, Chemistry of materials 26, 2396 (2014). http://doi.org/10.1021/cm403178b
Abstract: By using an optimized characterization approach that combines aberration-corrected transmission electron microscopy, electron tomography, and in situ ultrasmall angle X-ray scattering (USAXS), we show that the early stages of Pt electrochemical growth on carbon substrates may be affected by the aggregation, self-alignment, and partial coalescence of nanoclusters of d ≈ 2 nm. The morphology of the resulting nanostructures depends on the degree of coalescence and recrystallization of nanocluster aggregates, which in turn depends on the electrodeposition potential. At low overpotentials, a self-limiting growth mechanism may block the epitaxial growth of primary nanoclusters and results in loose dendritic aggregates. At more negative potentials, the extent of nanocluster coalescence and recrystallization is larger and further growth by atomic incorporation may be allowed. On one hand, this suggests a revision of the VolmerWeber island growth mechanism. Whereas this theory has traditionally assumed direct attachment as the only growth mechanism, it is suggested that nanocluster self-limiting growth, aggregation, and coalescence should also be taken into account during the early stages of nanoscale electrodeposition. On the other hand, depending on the deposition potential, ultrahigh porosities can be achieved, turning electrodeposition in an ideal process for highly active electrocatalyst production without the need of using high surface area carbon supports.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 55
DOI: 10.1021/cm403178b
|
|
“Ti surface doping of LiNi0.5Mn1.5O4−δpositive electrodes for lithium ion batteries”. Ulu Okudur F, D'Haen J, Vranken T, De Sloovere D, Verheijen M, Karakulina OM, Abakumov AM, Hadermann J, Van Bael MK, Hardy A, RSC advances 8, 7287 (2018). http://doi.org/10.1039/C7RA12932G
Abstract: The particle surface of LiNi0.5Mn1.5O4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiOx’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi(0.5−w)Mn(1.5+w)−tTitO4 phase and Ti-rich LiNi0.5Mn1.5−yTiyO4 segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li+. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 9
DOI: 10.1039/C7RA12932G
|
|
“Solution-gel-based surface modification of LiNi0.5Mn1.5O4-δ with amorphous Li-Ti-O coating”. Ulu Okudur F, Batuk M, Hadermann J, Safari M, De Sloovere D, Kumar Mylavarapu S, Joos B, D'Haen J, Van Bael MK, Hardy A, RSC advances 13, 33146 (2023). http://doi.org/10.1039/D3RA05599J
Abstract: LNMO (LiNi0.5Mn1.5O4-delta) is a high-energy density positive electrode material for lithium ion batteries. Unfortunately, it suffers from capacity loss and impedance rise during cycling due to electrolyte oxidation and electrode/electrolyte interface instabilities at high operating voltages. Here, a solution-gel synthesis route was used to coat 0.5-2.5 mu m LNMO particles with amorphous Li-Ti-O (LTO) for improved Li conduction, surface structural stability and cyclability. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis coupled with energy dispersive X-ray (EDX) showed Ti-rich amorphous coatings/islands or Ti-rich spinel layers on many of the LTO-modified LNMO facets, with a thickness varying from about 1 to 10 nm. The surface modification in the form of amorphous islands was mostly possible on high-energy crystal facets. Physicochemical observations were used to propose a molecular mechanism for the surface modification, combining insights from metalorganic chemistry with the crystallographic properties of LNMO. The improvements in functional properties were investigated in half cells. The cell impedance increased faster for the bare LNMO compared to amorphous LTO modified LNMO, resulting in R-ct values as high as 1247 Omega (after 1000 cycles) for bare LNMO, against 216 Omega for the modified material. At 10C, the modified material boosted a 15% increase in average discharge capacity. The improvements in electrochemical performance were attributed to the increase in electrochemically active surface area, as well as to improved HF-scavenging, resulting in the formation of protective byproducts, generating a more stable interface during prolonged cycling.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.9
DOI: 10.1039/D3RA05599J
|
|
“Band-gap tuning of graphene by Be doping and Be, B co-doping : a DFT study”. Ullah S, Hussain A, Syed WA, Saqlain MA, Ahmad I, Leenaerts O, Karim A, RSC advances 5, 55762 (2015). http://doi.org/10.1039/c5ra08061d
Abstract: First-principles density functional theory (DFT) calculations were carried out to investigate the structural and electronic properties of beryllium (Be) doped and Be and boron (B) co-doped graphene systems. We observed that not only the concentration of impurity atoms is important to tune the band-gap to some desired level, but also the specific substitution sites play a key role. In our system, which consists of 32 atoms, a maximum of 4Be and, in the co-doped state, 2Be and 3B atom substitutions are investigated. Both dopants are electron deficient relative to C atoms and cause the Fermi level to shift downward (p-type doping). A maximum band gap of 1.44 eV can be achieved on incorporation of 4Be atoms. The introduction of Be is more sensitive in terms of geometry and stability than B. However, in opening the energy gap, Be is more effective than B and N (nitrogen). Our results offer the possibility to modify the band-gap of graphene sufficiently for utilization in diverse electronic device applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.108
Times cited: 33
DOI: 10.1039/c5ra08061d
|