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“Charging of vitreous samples in cryogenic electron microscopy mitigated by graphene”. Zhang Y, van Schayck JP, Pedrazo-Tardajos A, Claes N, Noteborn WEM, Lu P-H, Duimel H, Dunin-Borkowski RE, Bals S, Peters PJ, Ravelli RBG, ACS nano 17, 15836 (2023). http://doi.org/10.1021/ACSNANO.3C03722
Abstract: Cryogenic electronmicroscopy can provide high-resolution reconstructionsof macromolecules embedded in a thin layer of ice from which atomicmodels can be built de novo. However, the interactionbetween the ionizing electron beam and the sample results in beam-inducedmotion and image distortion, which limit the attainable resolutions.Sample charging is one contributing factor of beam-induced motionsand image distortions, which is normally alleviated by including partof the supporting conducting film within the beam-exposed region.However, routine data collection schemes avoid strategies wherebythe beam is not in contact with the supporting film, whose rationaleis not fully understood. Here we characterize electrostatic chargingof vitreous samples, both in imaging and in diffraction mode. We mitigatesample charging by depositing a single layer of conductive grapheneon top of regular EM grids. We obtained high-resolution single-particleanalysis (SPA) reconstructions at 2 & ANGS; when the electron beamonly irradiates the middle of the hole on graphene-coated grids, usingdata collection schemes that previously failed to produce sub 3 & ANGS;reconstructions without the graphene layer. We also observe that theSPA data obtained with the graphene-coated grids exhibit a higher b factor and reduced particle movement compared to dataobtained without the graphene layer. This mitigation of charging couldhave broad implications for various EM techniques, including SPA andcryotomography, and for the study of radiation damage and the developmentof future sample carriers. Furthermore, it may facilitate the explorationof more dose-efficient, scanning transmission EM based SPA techniques.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 17.1
DOI: 10.1021/ACSNANO.3C03722
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“Two-dimensional particle-in cell/Monte Carlo simulations of a packed-bed dielectric barrier discharge in air at atmospheric pressure”. Zhang Y, Wang H-yu, Jiang W, Bogaerts A, New journal of physics 17, 083056 (2015). http://doi.org/10.1088/1367-2630/17/8/083056
Abstract: The plasma behavior in a parallel-plate dielectric barrier discharge (DBD) is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model, comparing for the first time an unpacked (empty) DBD with a packed bed DBD, i.e., a DBD filled with dielectric spheres in the gas gap. The calculations are performed in air, at atmospheric pressure. The discharge is powered by a pulse with a voltage amplitude of −20 kV. When comparing the packed and unpacked DBD reactors with the same dielectric barriers, it is clear that the presence of the dielectric packing leads to a transition in discharge behavior from a combination of negative streamers and unlimited surface streamers on the bottom dielectric surface to a combination of predominant positive streamers and limited surface discharges on the dielectric surfaces of the beads and plates. Furthermore, in the packed bed DBD, the electric field is locally enhanced inside the dielectric material, near the contact points between the beads and the plates, and therefore also in the plasma between the packing beads and between a bead and the dielectric wall, leading to values of $4\times {10}
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.786
Times cited: 22
DOI: 10.1088/1367-2630/17/8/083056
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“Formation of microdischarges inside a mesoporous catalyst in dielectric barrier discharge plasmas”. Zhang Y, Wang H-yu, Zhang Y-ru, Bogaerts A, Plasma sources science and technology 26, 054002 (2017). http://doi.org/10.1088/1361-6595/aa66be
Abstract: The formation process of a microdischarge (MD) in both μm- and nm-sized catalyst pores is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model. A parallel-plate dielectric barrier discharge configuration in filamentary mode is considered in ambient air. The discharge is powered by a high voltage pulse. Our calculations reveal that a streamer can penetrate into the surface features of a porous catalyst and MDs can be formed inside both μm- and nm-sized pores, yielding ionization inside the pore. For the μm-sized pores, the ionization mainly occurs inside the pore, while for the nm-sized pores the ionization is strongest near and inside the pore. Thus, enhanced discharges near and inside the mesoporous catalyst are observed. Indeed, the maximum values of the electric field, ionization rate and electron density occur near and inside the pore. The maximum electric field and electron density inside the pore first increase when the pore size rises from 4 nm to 10 nm, and then they decrease for the 100 nm pore, due to
a more pronounced surface discharge for the smaller pores. However, the ionization rate is highest for the 100 nm pore due to the largest effective ionization region.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 15
DOI: 10.1088/1361-6595/aa66be
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“Advanced imaging and simulations of precipitate interfaces in aluminium alloys and their role in phase transformations”. Zhang Z, Bourgeois L, Zhang Y, Rosalie JM, Medhekar N, MATEC web of conferences
T2 –, 17th International Conference on Aluminium Alloys (ICAA), October 26-29, 2020 , 09003 (2020). http://doi.org/10.1051/MATECCONF/202032609003
Abstract: Precipitation is accompanied by the formation and migration of heterophase interfaces. Using the combined approach of advanced imaging and atomistic simulations, we studied the precipitate-matrix interfaces in various aluminium alloy systems, aiming to resolve their detailed atomic structures and illuminate their role in phase transformations.
Keywords: P1 Proceeding; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
DOI: 10.1051/MATECCONF/202032609003
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“Bulk plasma fragmentation in a C4F8 inductively coupled plasma : a hybrid modelling study”. Zhao S-X, Zhang Y-R, Gao F, Wang Y-N, Bogaerts A, Journal of applied physics 117, 243303 (2015). http://doi.org/10.1063/1.4923230
Abstract: A hybrid model is used to investigate the fragmentation of C4F8 inductive discharges. Indeed, the resulting reactive species are crucial for the optimization of the Si-based etching process, since they determine the mechanisms of fluorination, polymerization, and sputtering. In this paper, we present the dissociation degree, the density ratio of F vs. CxFy (i.e., fluorocarbon (fc) neutrals), the neutral vs. positive ion density ratio, details on the neutral and ion components, and fractions of various fc neutrals (or ions) in the total fc neutral (or ion) density in a C4F8 inductively coupled plasma source, as well as the effect of pressure and power on these results. To analyze the fragmentation behavior, the electron density and temperature and electron energy probability function (EEPF) are investigated. Moreover, the main electron-impact generation sources for all considered neutrals and ions are determined from the complicated C4F8 reaction set used in the model. The C4F8 plasma fragmentation is explained, taking into account many factors, such as the EEPF characteristics, the dominance of primary and secondary processes, and the thresholds of dissociation and ionization. The simulation results are compared with experiments from literature, and reasonable agreement is obtained. Some discrepancies are observed, which can probably be attributed to the simplified polymer surface kinetics assumed in the model.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.068
Times cited: 11
DOI: 10.1063/1.4923230
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