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“CO₂, conversion to CO via plasma and electrolysis : a techno-economic and energy cost analysis”. Osorio-Tejada J, Escriba-Gelonch M, Vertongen R, Bogaerts A, Hessel V, Energy &, environmental science (2024). http://doi.org/10.1039/D4EE00164H
Abstract: Electrification and carbon capture technologies are essential for achieving net-zero emissions in the chemical sector. A crucial strategy involves converting captured CO2 into CO, a valuable chemical feedstock. This study evaluates the feasibility of two innovative methods: plasma activation and electrolysis, using clean electricity and captured CO2. Specifically, it compares a gliding arc plasma reactor with an embedded novel carbon bed system to a modern zero-gap type low-temperature electrolyser. The plasma method stood out with an energy cost of 19.5 GJ per tonne CO, marking a 43% reduction compared to electrolysis and conventional methods. CO production costs for plasma- and electrolysis-based plants were $671 and $962 per tonne, respectively. However, due to high uncertainty regarding electrolyser costs, the CO production costs in electrolysis-based plants may actually range from $570 to $1392 per tonne. The carbon bed system in the plasma method was a key factor in facilitating additional CO generation from O-2 and enhancing CO2 conversion, contributing to its cost-effectiveness. Challenges for electrolysis included high costs of equipment and low current densities. Addressing these limitations could significantly decrease production costs, but challenges arise from the mutual relationship between intrinsic parameters, such as CO2 conversion, CO2 input flow, or energy cost. In a future scenario with affordable feedstocks and equipment, costs could drop below $500 per tonne for both methods. While this may be more challenging for electrolysis due to complexity and expensive catalysts, plasma-based CO production appears more viable and competitive.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 32.5
DOI: 10.1039/D4EE00164H
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“3D-cavity-confined CsPbBr₃, quantum dots for visible-light-driven photocatalytic C(sp³)-H bond activation”. Gao Y-J, Jin H, Esteban DA, Weng B, Saha RA, Yang M-Q, Bals S, Steele JA, Huang H, Roeffaers MBJ, Carbon Energy , e559 (2024). http://doi.org/10.1002/CEY2.559
Abstract: Metal halide perovskite (MHP) quantum dots (QDs) offer immense potential for several areas of photonics research due to their easy and low-cost fabrication and excellent optoelectronic properties. However, practical applications of MHP QDs are limited by their poor stability and, in particular, their tendency to aggregate. Here, we develop a two-step double-solvent strategy to grow and confine CsPbBr3 QDs within the three-dimensional (3D) cavities of a mesoporous SBA-16 silica scaffold (CsPbBr3@SBA-16). Strong confinement and separation of the MHP QDs lead to a relatively uniform size distribution, narrow luminescence, and good ambient stability over 2 months. In addition, the CsPbBr3@SBA-16 presents a high activity and stability for visible-light-driven photocatalytic toluene C(sp(3))-H bond activation to produce benzaldehyde with similar to 730 mu mol g(-1) h(-1) yield rate and near-unity selectivity. Similarly, the structural stability of CsPbBr3@SBA-16 QDs is superior to that of both pure CsPbBr3 QDs and those confined in MCM-41 with 1D channels.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
DOI: 10.1002/CEY2.559
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“Importance of design and operating parameters in a sonication system for viscous solutions : effects of input power, horn tip diameter and reactor capacity”. Bampouli A, Goris Q, Hussain MN, Louisnard O, Stefanidis GD, Van Gerven T, Chemical engineering and processing 198, 109715 (2024). http://doi.org/10.1016/J.CEP.2024.109715
Abstract: This study investigates the distribution of ultrasound (US) energy in a batch system for solutions with viscosity ranging from 1 to approximately 3000 mPas. Sonication was performed using horn type configurations operating at 20-30 kHz and rated power capacity of 50 or 200 W. Two different tip diameters (3 or 7 mm) and two insertion depths (35 or 25 mm) within vessels of different sizes ( approximate to 60 or 130 ml) were utilized. Additionally, a special conical tip design was employed. For each experimental setup, the calorimetric efficiency was estimated, the cavitationally active regions were visualized using the sonochemiluminescence (SCL) method and bubble cluster formation inside the vessel was macroscopically observed using a high speed camera (HSC). In the viscosity range tested, the calorimetry results showed that the efficiency and continuous operation of the device depend on both the rated power and the horn tip diameter. The ratio between electrical and calorimetric power input remained consistently around 40 to 50% across the different configurations for water, but for the 123.2 mPas solution exhibited significant variation ranging from 40 to 85%. Moreover, the power density in the smaller reactor was found to be nearly double compared to the larger one. The SCL analysis showed multiple cavitationally active zones in all setups, and the zones intensity decreased considerably with increase of the solutions viscosity. The results for the cone tip were not conclusive, but can be used as the basis for further investigation. The current research highlights the importance of thoroughly understanding the impact of each design parameter, and of establishing characterization methodologies to assist in the future development of scaled-up, commercial applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.3
DOI: 10.1016/J.CEP.2024.109715
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“Shifts in mycorrhizal types of fungi and plants in response to fertilisation, warming and herbivory in a tundra grassland”. Le Noir de Carlan C, Kaarlejarvi E, De Tender C, Heinecke T, Eskelinen A, Verbruggen E, New phytologist (2024). http://doi.org/10.1111/NPH.19816
Abstract: Climate warming is severely affecting high-latitude regions. In the Arctic tundra, it may lead to enhanced soil nutrient availability and interact with simultaneous changes in grazing pressure. It is presently unknown how these concurrently occurring global change drivers affect the root-associated fungal communities, particularly mycorrhizal fungi, and whether changes coincide with shifts in plant mycorrhizal types. We investigated changes in root-associated fungal communities and mycorrhizal types of the plant community in a 10-yr factorial experiment with warming, fertilisation and grazing exclusion in a Finnish tundra grassland. The strongest determinant of the root-associated fungal community was fertilisation, which consistently increased potential plant pathogen abundance and had contrasting effects on the different mycorrhizal fungal types, contingent on other treatments. Plant mycorrhizal types went through pronounced shifts, with warming favouring ecto- and ericoid mycorrhiza but not under fertilisation and grazing exclusion. Combination of all treatments resulted in dominance by arbuscular mycorrhizal plants. However, shifts in plant mycorrhizal types vs fungi were mostly but not always aligned in their magnitude and direction. Our results show that our ability to predict shifts in symbiotic and antagonistic fungal communities depend on simultaneous consideration of multiple global change factors that jointly alter plant and fungal communities.
Keywords: A1 Journal article; Plant and Ecosystems (PLECO) – Ecology in a time of change
Impact Factor: 9.4
DOI: 10.1111/NPH.19816
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“Giant tunability of Rashba splitting at cation-exchanged polar oxide interfaces by selective orbital hybridization”. Xu H, Li H, Gauquelin N, Chen X, Wu W-F, Zhao Y, Si L, Tian D, Li L, Gan Y, Qi S, Li M, Hu F, Sun J, Jannis D, Yu P, Chen G, Zhong Z, Radovic M, Verbeeck J, Chen Y, Shen B, Advanced materials (2024). http://doi.org/10.1002/ADMA.202313297
Abstract: The 2D electron gas (2DEG) at oxide interfaces exhibits extraordinary properties, such as 2D superconductivity and ferromagnetism, coupled to strongly correlated electrons in narrow d-bands. In particular, 2DEGs in KTaO3 (KTO) with 5d t2g orbitals exhibit larger atomic spin-orbit coupling and crystal-facet-dependent superconductivity absent for 3d 2DEGs in SrTiO3 (STO). Herein, by tracing the interfacial chemistry, weak anti-localization magneto-transport behavior, and electronic structures of (001), (110), and (111) KTO 2DEGs, unambiguously cation exchange across KTO interfaces is discovered. Therefore, the origin of the 2DEGs at KTO-based interfaces is dramatically different from the electronic reconstruction observed at STO interfaces. More importantly, as the interface polarization grows with the higher order planes in the KTO case, the Rashba spin splitting becomes maximal for the superconducting (111) interfaces approximately twice that of the (001) interface. The larger Rashba spin splitting couples strongly to the asymmetric chiral texture of the orbital angular moment, and results mainly from the enhanced inter-orbital hopping of the t2g bands and more localized wave functions. This finding has profound implications for the search for topological superconductors, as well as the realization of efficient spin-charge interconversion for low-power spin-orbitronics based on (110) and (111) KTO interfaces. An unambiguous cation exchange is discovered across the interfaces of (001), (110), and (111) KTaO3 2D electron gases fabricated at room temperature. Remarkably, the (111) interfaces with the highest superconducting transition temperature also turn out to show the strongest electron-phonon interaction and the largest Rashba spin splitting. image
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
DOI: 10.1002/ADMA.202313297
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Lembrechts J, Clavel J, Lenoir J, Haider S, McDougall K, Nunez M, Alexander J, Barros A, Milbau A, Seipel T, Verbruggen E, Nijs I (2024) Dataset: Roadside disturbance promotes plant communities with arbuscular mycorrhizal associations in mountain regions worldwide
Abstract: Aim: We aimed to assess the impact of road disturbances on the dominant mycorrhizal types in ecosystems at the global level and how this mechanism can potentially lead to lasting plant community changes. Location: Globally distributed mountain regions Time Period: 2007-2018 Taxa studied: Plants (linked to their associated mycorrhizal fungi) Methods: We used a database of coordinated plant community surveys following mountain roads from 894 plots in 11 mountain regions across the globe in combination with an existing database of mycorrhizal-plant associations in order to approximate the relative abundance of mycorrhizal types in natural and disturbed environments. Results: Our findings show that roadside disturbance promotes the cover of plants associated with arbuscular mycorrhizal (AM) fungi. This effect is especially strong in colder mountain environments and in mountain regions where plant communities are dominated by ectomycorrhizal (EcM) or ericoid-mycorrhizal (ErM) associations. Furthermore, non-native plant species, which we confirmed to be mostly AM plants, are more successful in environments dominated by AM associations. Main Conclusions: These biogeographical patterns suggest that changes in mycorrhizal types could be a crucial factor in the worldwide impact of anthropogenic disturbances on mountain ecosystems. Indeed, roadsides foster AM-dominated systems, where AM-fungi might aid AM-associated plant species while potentially reducing the biotic resistance against invasive non-native species, often also associated with AM networks. Restoration efforts in mountain ecosystems will have to contend with changes in the fundamental make-up of EcM- and ErM plant communities induced by roadside disturbance.
Keywords: Dataset; Plant and Ecosystems (PLECO) – Ecology in a time of change
DOI: 10.5061/dryad.0p2ngf27s
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Lu Q (2024) Precipitation behavior and heat resistance properties of Al-Cu-Mg-Ag-(Si) alloy. VIII, 212 p
Abstract: With the rapid increase in the speed of new-generation aerospace vehicles, conventional heat-resistant aluminum alloys cannot meet the long-term service of the equipment. Therefore, the development of new high-strength heat-resistant aluminum alloys is of great strategic for the sustainable and high-quality development of industries. Al-Cu-Mg-Ag alloy is an age-hardenable heat-resistant aluminum alloy and has high strength and heat resistance. The addition of alloying elements such as Si and Sc to Al-Cu-Mg-Ag alloy introduces a competitive relationship among the σ-Al5Cu6Mg2, θ′-Al2Cu, and Ω phases. Therefore, a systematic investigation of precipitation behavior and heat resistance of Al-Cu-Mg-Ag-(Si) is essential for guiding the design of high-strength heat-resistant aluminum alloys. Combined characterization testing methods such as scanning electron microscopy, transmission electron microscopy, atom probe tomography, microhardness testing, and tensile testing with simulation calculation methods such as calculation of phase diagram, first-principles calculations, and Ab initio molecular dynamics, the effects of heat treatment processes and element content on the precipitation behavior, mechanical properties, and heat resistance of Al-Cu-Mg-Ag-(Si) alloys were systematically investigated. Furthermore, a multiple interface segregation structure was constructed at the θ′/Al interface, and a new Al-Cu-Mg-Ag-Si-Sc alloy with synergistically improved strength and heat resistance was developed. The main conclusions are as follows: (1) Based on the Kampmann-Wagner-Numerical theory, the relationship between the coarsening rate of the Ω phase and the aging process was analyzed, revealing for the first time that the critical size of Ω phase ( ) under thermal exposure temperature was the key factor determining the coarsening rate of Ω phase during long time thermal exposure heat treatment. After artificial ageing, when the size of Ω phase was smaller than the critical size , the dissolution of smaller Ω phase leaded to a rapid decrease in the number density of Ω phases, thereby reducing the heat resistance of the alloy. When the size of Ω phase was greater than or equal to the critical size , the coarsening rate of Ω phase was consistent, but a larger initial size would result in a larger final size after long-term thermal exposure. Therefore, the closer the size of Ω phase in the alloy is to the critical size under heat exposure temperature, the better the heat resistance of the alloy. (2) A concept of constructing a multiple interface segregation structure at the precipitate/matrix interface was proposed, and based on this concept, a multiple interface segregation structure containing the C/L-AlMgSiCu interfacial phase, newly discovered χ-AgMg interfacial phase, and Sc segregation layer was successfully constructed at the θ′/Al interface. The existence of the multiple interface segregation structure ensured that the designed Al-Cu-Mg-Ag-Si-Sc alloy maintains a yield strength of 400 MPa after thermal exposure at 200 C for 100 h, with a strength retention rate of 97%, creating a new record for the synergistic improvement of strength and heat resistance in aluminum alloys. In addition, combining transmission electron microscopy ex-situ/in-situ characterization with first-principles calculations, it is shown that the χ-AgMg interface phase will be destroyed due to the diffusion of the outer Ag layer during thermal exposure, and gradually dissolve into the matrix, but it can still delay the coarsening behavior of θ′-Al2Cu phase. (3) The criteria for determining whether Ω phase can precipitate are updated in Al-Cu-Mg-Ag-Si alloys with low Mg/Si ratio based on phase diagram thermodynamic calculations and multi-scale structural characterization. When W(Mg)/W(Si) > 1.4 and X(Ag)/X(Mgexcess) > 1, Ω phase can precipitate in Al-Cu-Mg-Ag-Si alloys, where X(Mgexcess) represents the atomic percentage of residual Mg elements after the formation of the AlMgSiCu quaternary precipitate phase C/L phase in the supersaturated solid solution, and the W(Mg) is the mass fraction of Mg in the supersaturated solid solution before artificial ageing. (4) The effects of alloy element content on precipitation behavior and heat resistance of Al-Cu-Mg-Ag-Si alloys were systematically analyzed. Critical conditions for the precipitation of σ-Al5Cu6Mg2 and Ω phase in Al-Cu-Mg-Ag-Si alloys are revealed. Based on calculation of phase diagram results, the conditions for precipitating σ-Al5Cu6Mg2 phase in the alloy are: ① W(Mg)/W(Si) > 1.8; ② W(Cu) > 2.7W(Mg) – 5W(Si). When W(Mg)/W(Si) < 1.8, the alloy is mainly precipitated with C/L/Q′-AlMgSiCu. When W(Cu) < 2.7W(Mg) – 5W(Si), the alloy will generate GPB zone. In addition, W(Ag)/W(Si) > 4 is the critical condition which the Ω phase can the main precipitates in Al-Cu-Mg-Ag-Si alloys. Furthermore, the correlation between precipitate types and heat resistance was summarized, showing that Al-Cu-Mg-Ag-(Si) alloys with Ω phase as the main strengthening phase are more suitable for the preparation of structures with short service time but high temperature, while Al-Cu-Mg-Ag-(Si) alloys with low Mg content and multiple segregation structures are more suitable for structures requiring long-term service at medium to high temperatures. This study, for the first time, combines calculation of phase diagram with multi-scale microstructure characterization, systematically unraveling the effects of element content on precipitation behavior, strength, and heat resistance of Al-Cu-Mg-Ag-(Si) alloys. In addition, a concept of constructing a multiple interface segregation structure at the precipitate/matrix interface was proposed to synergistically improve alloy strength and heat resistance. This work provides theoretical guidance for optimizing the composition and processing of Al-Cu-Mg-Ag-(Si) alloy and regulating the microstructure. Furthermore, it also offers new ideas and theoretical guidance for the development of novel high-strength heat-resistant alloys in other systems.
Keywords: Doctoral thesis; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
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Kummamuru NB (2024) Methane and hydrogen storage in clathrate hydrates. XXV, 260 p
Abstract: In a world increasingly reliant on alternative energy sources, the quest for efficient and secure storage solutions is paramount. This doctoral thesis explores the exciting potential of a familiar material – water – to act as a vault for next-generation energy sources like hydrogen (H2) and methane (CH4). Nature offers a solution in the form of clathrate hydrates, fascinating cage-like structures formed from water molecules that can trap these gas molecules within their framework. This research investigates on improving the formation kinetics and gas storage capabilities of clathrate hydrates utilizing porous materials and the interstitial space between non-porous materials to augment the contact between gas and water thereby catalysing the growth of hydrates and unlocking their full potential as efficient and secure energy storage reservoirs. A key outcome of this research is the formulation of an empirical correlation, offering predictive insights into CH4 hydrate phase equilibrium conditions. Innovative approaches utilizing thermally conductive beads have yielded substantial enhancements in CH4 uptake. Furthermore, the identification of optimal water content within porous materials showcases a pathway to maximize CH4 storage capacity and hydrate growth kinetics. In the domain of hydrogen storage, attention is also directed towards unstirred systems, where the integration of functionalized porous materials has demonstrated a significant improvement in the rate of hydrate formation and the overall H2 storage capacity. A noteworthy achievement of this research lies in the successful storage of H2 within confined CH4 hydrates through a gas exchange process and the preliminary results show the potential for safer and more sustainable method for H2 storage at mild thermodynamic conditions, offering promising prospects for future energy systems.
Keywords: Doctoral thesis; Engineering sciences. Technology; Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS); Laboratory for the electrification of chemical processes and hydrogen (ElectrifHy)
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“Grain boundary-mediated plasticity in aluminum films unraveled by a statistical approach combining nano-DIC and ACOM-TEM”. Baral P, Kashiwar A, Coulombier M, Delannay L, Hoummada K, Raskin JP, Idrissi H, Pardoen T, Acta materialia 276, 120081 (2024). http://doi.org/10.1016/J.ACTAMAT.2024.120081
Abstract: Nanomechanical on-chip testing is combined with nanoscale in situ digital image correlation and automated crystal orientation mapping in TEM to deliver novel statistically representative quantitative data about the deformation mechanisms in nanocrystalline aluminum films. The films are very ductile, with a rare stable multiple necking process with local strains reaching up to 0.45 and macroscopic elongation up to 0.17. The strain fields with resolution below 100 nm are related to the underlying microstructure and crystallographic orientation maps. This reveals nanoscopic shear bands forming preferentially along GB with high misorientations, tilted at +/− 45° with respect to loading direction. The analysis of these data prove that the strong strain delocalization process is promoted by GB migration and grain rotation, leading to large strain rate sensitivity. The distribution of misorientation angles between grains evolve during deformation. The GBs with misorientation between 20° and 40°, which are the GBs with highest energy, involve the largest strains.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2024.120081
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“Toward the rational design of Cu electrocatalysts for improved performance of the NO3RR”. Hoekx S, Daems N, Arenas Esteban D, Bals S, Breugelmans T, ACS applied energy materials 7, 3761 (2024). http://doi.org/10.1021/ACSAEM.3C03207
Abstract: Cu is one of the most promising materials as an electrocatalyst for the nitrate reduction reaction (NO3RR) to ammonia, a reaction that can simultaneously remove nitrates from wastewater and produce ammonia, a high-value commodity chemical. However, a rational approach to catalyst design is lacking, limiting efficient catalyst optimization. In this work, we propose a way to synthesize monodisperse, polycrystalline Cu NPs with small variances in size by changing the carbon chain length of the phosphonic acid-based ligand. Cu NPs with 8.3, 10.0, and 11.9 nm diameters are successfully synthesized, and high-resolution electron microscopy and tomography are used to characterize these NPs in depth. By isolating Cu NP size as a parameter, we can unequivocally establish its effect on electrochemical performance for the NO3RR to ammonia under optimal operating conditions for the catalyst (0.1 M KOH electrolyte at -1.25 V vs RHE, as established in the first phase). The smallest Cu NPs (8.3 nm with a TDPA ligand) perform best, achieving Faradaic efficiencies (FEs) of 85.4% and absolute current densities of similar to 250 mA cm(-2), with increasing current densities and constant FEs as the particle size decreases. To allow for a rational approach to Cu-based catalyst design from a stability perspective, this work completed a first study of the main degradation pathway that the Cu NPs undergo during NO3RR. High-resolution electron microscopy and tomography are used to characterize the particles at various stages of the reaction. The NPs undergo agglomeration, pulverization, and particle detachment due to the reaction, starting at a particle size of 8.3 nm and progressively getting smaller, but leveling off, until a NP size of 2.6 nm is reached after 2 h of electrolysis. This decrease in NP size goes paired with a decrease in FE from 83% after the first 15 min to 74% after 2 h at -0.75 V vs RHE, despite the increase in active surface area. These insights into the most prominent degradation mechanisms allow for rational adjustments to future catalysts to combat these changes; for example, by embedding NPs in a tailored support, morphological degradation could be impeded. Therefore, these insights allow for a rational approach to the improvement of the stability of Cu-based catalysts for the NO3RR, a very important but often an overlooked aspect of catalyst design.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 6.4
DOI: 10.1021/ACSAEM.3C03207
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“The synergistic influence of metal cations on the drying and viscosity of linseed oil assessed by means of model samples containing synthesised metal carboxylates”. Kirkpatrick S, Sanyova J, Janssens K, van der Snickt G, Heritage science 12, 209 (2024). http://doi.org/10.1186/S40494-024-01309-Y
Abstract: The recent multi-analytical study carried out on the Van Eyck's Ghent Altarpiece showed the simultaneous presence of several kinds of metal carboxylates in oil-rich glaze layers. This outcome raised the question whether these carboxylates had already formed during the preparation of the oil binder by the artists. In the case of early-stage formation, they may have had an impact on the drying rate of the resulting oil, as well as on its handling properties. This hypothesis was investigated using a model system of in-house-prepared linseed oil containing incremental concentrations (2-5-10 wt.%) of relevant metal carboxylates (i.e. Ca-, Zn-, Cu-, and Pb oleates and stearates). This paper describes the influence of these type of molecules on the drying rate of linseed oil and, to an extent, on its viscosity. The drying time of the linseed oil, to which one or more metal carboxylates were added, was measured with a drying recorder while the viscosity was assessed with a rheometer. When introduced together, some of these metal carboxylates act in synergy to shorten the drying time with respect to the situation when the same metal carboxylates were added separately to linseed oil. Mixtures of Ca- and Zn-oleates proved to have a larger effect than other binary combinations. Addition of two metal oleates (combination of Ca/Zn/Cu/Pb) reduced the drying time even more. On the other hand, specific combinations of three metal stearates and/or oleates also demonstrated a significant synergistic effect towards increasing the viscosity of the binder. Especially combinations of Ca/Zn/Cu and Ca/Zn/Pb stearates and oleates gave rise to the highest level of linseed oil viscosity increase, when compared to the situation in which the same metal carboxylates were added separately.
Keywords: A1 Journal article; Art; Antwerp Cultural Heritage Sciences (ARCHES); Antwerp X-ray Imaging and Spectroscopy (AXIS)
Impact Factor: 2.5
DOI: 10.1186/S40494-024-01309-Y
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Brasili S, Gielis J (2024) Legacy and innovation across symmetry's dimensions. 005–006
Keywords: L1 Letter to the editor; Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS)
DOI: 10.26830/SYMMETRY_2024_1_005
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“The potential of electrochemical sensors to unveil counterfeits : Xanax as a case study”. Mazurkow JM, Montiel FN, Van Echelpoel R, Kusior A, De Wael K, Electrochimica acta 494, 144458 (2024). http://doi.org/10.1016/J.ELECTACTA.2024.144458
Abstract: The illicit drug market has been constantly evolving in the last decades, with a significant rise in counterfeit medicines posing serious public health risks. Benzodiazepines (BZDs) such as alprazolam (generally sold under the brand name Xanax), have particularly become the target of counterfeiting efforts due to their addictive nature and upsurge of unregulated designer BZDs. These counterfeit versions frequently resemble legitimate products but contain harmful adulterants or other potent illicit substances. Few methods have been developed to tackle counterfeit pills, usually limited to accurate and sophisticated laboratory equipment. This study explores the feasibility of combining electrochemical fingerprinting with data analysis to overcome the limitations of traditional methods. First, the electrochemical behavior of selected BZDs is studied, and analytical parameters such as pH are optimized. Then, the electroanalysis of common adulterants and illicit drugs is addressed and integrated into a user-friendly app, including a flowchart system. The proposed electrochemical strategy enables the detection of counterfeit Xanax by identifying the presence or absence of alprazolam. It also allows determination of the alprazolam content within a pill while meeting the fundamental requirements of the end users. This study represents an on-site methodology to address the growing challenges posed by BZDs, easily transferable to counterfeit medicines from other drug groups.
Keywords: A1 Journal article; Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab); Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS)
Impact Factor: 6.6
DOI: 10.1016/J.ELECTACTA.2024.144458
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“Imaging the suppression of ferromagnetism in LaMnO₃, by metallic overlayers”. Folkers B, Jansen T, Roskamp TJ, Reith P, Timmermans A, Jannis D, Gauquelin N, Verbeeck J, Hilgenkamp H, Rosario CMM, Physical review materials 8, 054408 (2024). http://doi.org/10.1103/PHYSREVMATERIALS.8.054408
Abstract: LaMnO 3 (LMO) thin films epitaxially grown on SrTiO 3 (STO) usually exhibit ferromagnetism above a critical layer thickness. We report the use of scanning SQUID microscopy (SSM) to study the suppression of the ferromagnetism in STO / LMO / metal structures. By partially covering the LMO surface with a metallic layer, both covered and uncovered LMO regions can be studied simultaneously. While Au does not significantly influence the ferromagnetic order of the underlying LMO film, a thin Ti layer induces a strong suppression of the ferromagnetism, over tens of nanometers, which increases with time on a timescale of days. Detailed electron energy loss spectroscopy analysis of the Ti-LaMnO 3 interface reveals the presence of Mn 2 + and an evolution of the Ti valence state from Ti 0 to Ti 4 + over approximately 5 nm. Furthermore, we demonstrate that by patterning Ti / Au overlayers, we can locally suppress the ferromagnetism and define ferromagnetic structures down to sub -micrometer scales.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.4
DOI: 10.1103/PHYSREVMATERIALS.8.054408
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“Interlayer affected diamond electrochemistry”. Chen X, Dong X, Zhang C, Zhu M, Ahmed E, Krishnamurthy G, Rouzbahani R, Pobedinskas P, Gauquelin N, Jannis D, Kaur K, Hafez AME, Thiel F, Bornemann R, Engelhard C, Schoenherr H, Verbeeck J, Haenen K, Jiang X, Yang N, Small methods , 2301774 (2024). http://doi.org/10.1002/SMTD.202301774
Abstract: Diamond electrochemistry is primarily influenced by quantities of sp3-carbon, surface terminations, and crystalline structure. In this work, a new dimension is introduced by investigating the effect of using substrate-interlayers for diamond growth. Boron and nitrogen co-doped nanocrystalline diamond (BNDD) films are grown on Si substrate without and with Ti and Ta as interlayers, named BNDD/Si, BNDD/Ti/Si, and BNDD/Ta/Ti/Si, respectively. After detailed characterization using microscopies, spectroscopies, electrochemical techniques, and density functional theory simulations, the relationship of composition, interfacial structure, charge transport, and electrochemical properties of the interface between diamond and metal is investigated. The BNDD/Ta/Ti/Si electrodes exhibit faster electron transfer processes than the other two diamond electrodes. The interlayer thus determines the intrinsic activity and reaction kinetics. The reduction in their barrier widths can be attributed to the formation of TaC, which facilitates carrier tunneling, and simultaneously increases the concentration of electrically active defects. As a case study, the BNDD/Ta/Ti/Si electrode is further employed to assemble a redox-electrolyte-based supercapacitor device with enhanced performance. In summary, the study not only sheds light on the intricate relationship between interlayer composition, charge transfer, and electrochemical performance but also demonstrates the potential of tailored interlayer design to unlock new capabilities in diamond-based electrochemical devices. Diamond electrochemistry is revealed to be affected by the interlayers between boron/nitrogen co-doped nanocrystalline diamond (BNDD) film and a Si substrate. A BNDD/Ta/Ti/Si electrode exhibits faster electron transfer processes and smaller electron transfer resistance of redox probes for [Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+ than the other electrodes, because the interlayer thus determines the intrinsic activity and reaction kinetics of diamond films. image
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.4
DOI: 10.1002/SMTD.202301774
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“Evaluation of corrosion impeding concretion layers formed on shipwreck steel in the Belgian North Sea”. Laureys A, Richardson P, Verhasselt K, Chaves IA, Melchers RE, Van Den Bergh K, Depover T, Verbeken K, Potters G, De Baere K, Corrosion 80, 539 (2024). http://doi.org/10.5006/4341
Abstract: Steel shipwrecks buried along the Belgian and French North Sea coast have proven to show very low corrosion rates due to concretion. This work aims to provide an in-depth analysis of the formed concretion layers and gain a more complete understanding of the gradual deposition processes in the North Sea. Detailed microstructural characterization by scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction of two different specimens demonstrates that the concretion includes a complex structure of multiple layers. Closest to the metal surface, a layer of 100% akaganeite is found. It forms from corrosion products exhibiting high Cl- ions concentrations at the metal surface. Next, other iron oxides, such as goethite, lepidocrocite, and magnetite, are observed. Then, layers that both contain corrosion products and compounds from the environment are present. These layers contain calcium carbonates (calcite and aragonite), calcium sulfate (gypsum), and quartz (sand). Moreover, due to a displacement of calcium by iron, an additional phase is formed consisting out of hard, dense siderite mixed into calcite. Finally, the surface of the concretion is covered by a biofilm.
Keywords: A1 Journal article; Engineering sciences. Technology; Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS)
Impact Factor: 1.6
DOI: 10.5006/4341
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“Magneto-optical conductivity of monolayer transition metal dichalcogenides in the presence of proximity-induced exchange interaction and external electrical field”. Li Y, Xiao YM, Xu W, Ding L, Milošević, MV, Peeters FM, Physical review B 109, 165441 (2024). http://doi.org/10.1103/PHYSREVB.109.165441
Abstract: We theoretically investigate the magneto-optical (MO) properties of monolayer (ML) transition metal dichalcogenides (TMDs) in the presence of external electrical and quantizing magnetic fields and of the proximity-induced exchange interaction. The corresponding Landau Level (LL) structure is studied by solving the Schr & ouml;dinger equation and the spin polarization in ML-TMDs under the action of the magnetic field is evaluated. The impact of trigonal warping on LLs and MO absorption is examined. Furthermore, the longitudinal MO conductivity is calculated through the dynamical dielectric function under the standard random-phase approximation (RPA) with the Kubo formula. We take ML-MoS 2 as an example to examine the effects of proximity-induced exchange interaction, external electrical and magnetic fields on the MO conductivity induced via intra- and interband electronic transitions among the LLs. For intraband electronic transitions within the conduction or valence bands, we can observe two absorption peaks in terahertz (THz) frequency range. While the interband electronic transitions between conduction and valence LLs show a series of absorption peaks in the visible range. We find that the proximity-induced exchange interaction, the carrier density, the strengths of the external electrical and magnetic fields can effectively modulate the positions of the absorption peaks and the shapes of the MO absorption spectra. The results obtained from this study can benefit to an in-depth understanding of the MO properties of ML-TMDs which can be potentially applied for magneto-optic, spintronic, and valleytronic devices working in visible to THz frequency bandwidths.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
DOI: 10.1103/PHYSREVB.109.165441
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“Electron-phonon coupling and thermal conductivity of MAB compounds”. Kocabas T, Samanta B, Barboza E da S, Sevik C, Milošević, MV, Çakir D, Physical review materials 8, 055002 (2024). http://doi.org/10.1103/PHYSREVMATERIALS.8.055002
Abstract: We investigated the electron-phonon ( e -ph ) coupling and vibrational thermal conductivity in the representative MAB compounds, namely MoAlB, WAlB, Tc 2 AlB 2 , and Cr 2 AlB 2 . The spectral distribution functions of e -ph interaction, obtained through ab initio linear-response calculations, reveal that the electron-phonon coupling values range from low (0.15) to moderate (0.58). With such e -ph coupling, out of the considered compounds, only Tc 2 AlB 2 exhibits a superconducting transition, at 4 K. We further evaluated the thermal conductivity and associated properties like scattering rates, obtained using ab initio and other methodologies. The latter included the iterative solution of the Peierls-Boltzmann transport equation, using HIPHIVE package for advanced optimization and machine learning techniques, and employing maximum likelihood estimation to approximate scattering rates from a limited set of scattering processes. We found that these methods yield nearly identical predictions for thermal conductivity values, with a significant decrease in the computational cost compared to the first-principles methods. We examined interactions arising from both three-phonon (3 ph ) and four -phonon (4 ph ) scattering processes. The 4 ph interactions demonstrated a smaller yet significant impact on the overall vibrational thermal conductivity, most notably in Tc 2 AlB 2 . Our findings indicate that Cr 2 AlB 2 has the highest thermal conductivity across all considered crystal directions, with the thermal conductivity being spatially anisotropic, most pronouncedly in Tc 2 AlB 2 . Finally, we show that empirical expressions based on Slack models are well suited for screening the thermal conductivity properties of MAB phases, and can be employed to establish upper and lower limits of their thermal conductivity.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.4
DOI: 10.1103/PHYSREVMATERIALS.8.055002
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“Enhanced piezoelectricity by polarization rotation through thermal strain manipulation in PbZr0.6Ti0.4O3 thin films”. Huang S, Houwman E, Gauquelin N, Orekhov A, Chezganov D, Verbeeck J, Hu S, Zhong G, Koster G, Rijnders G, Advanced Materials Interfaces 11, 2400048 (2024). http://doi.org/10.1002/ADMI.202400048
Abstract: Lead based bulk piezoelectric materials, e.g., PbZrxTi1-xO3 (PZT), are widely used in electromechanical applications, sensors, and transducers, for which optimally performing thin films are needed. The results of a multi-domain Landau-Ginzberg-Devonshire model applicable to clamped ferroelectric thin films are used to predict the lattice symmetry and properties of clamped PZT thin films on different substrates. Guided by the thermal strain phase diagrams that are produced by this model, experimentally structural transitions are observed. These can be related to changes of the piezoelectric properties in PZT(x = 0.6) thin films that are grown on CaF2, SrTiO3 (STO) and 70% PbMg1/3Nb2/3O3-30% PbTiO3 (PMN-PT) substrates by pulsed laser deposition. Through temperature en field dependent in situ X-ray reciprocal space mapping (RSMs) and piezoelectric force microscopy (PFM), the low symmetry monoclinic phase and polarization rotation are observed in the film on STO and can be linked to the measured enhanced properties. The study identifies a monoclinic -rhombohedral M-C-M-A-R crystal symmetry path as the polarization rotation mechanism. The films on CaF2 and PMN-PT remain in the same symmetry phase up to the ferroelectric-paraelectric phase transition, as predicted. These results support the validity of the multi-domain model which provides the possibility to predict the behavior of clamped, piezoelectric PZT thin films, and design films with enhanced properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.4
DOI: 10.1002/ADMI.202400048
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“Longitudinal and transverse mobilities of n-type monolayer transition metal dichalcogenides in the presence of proximity-induced interactions at low temperature”. Liu J, Xu W, Xiao YM, Ding L, Li HW, Van Duppen B, Milošević, MV, Peeters FM, Physical review B 109, 195418 (2024). http://doi.org/10.1103/PHYSREVB.109.195418
Abstract: We present a detailed theoretical investigation on the electronic transport properties of n-type monolayer (ML) transition metal dichalcogenides (TMDs) at low temperature in the presence of proximity-induced interactions such as Rashba spin-orbit coupling (RSOC) and the exchange interaction. The electronic band structure is calculated by solving the Schr & ouml;dinger equation with a k <middle dot> p Hamiltonian, and the electric screening induced by electron-electron interaction is evaluated under a standard random phase approximation approach. In particular, the longitudinal and transverse or Hall mobilities are calculated by using a momentum-balance equation derived from a semiclassical Boltzmann equation, where the electron-impurity interaction is considered as the principal scattering center at low temperature. The obtained results show that the RSOC can induce the in-plane spin components for spin-split subbands in different valleys, while the exchange interaction can lift the energy degeneracy for electrons in different valleys. The opposite signs of Berry curvatures in the two valleys would introduce opposite directions of Lorentz force on valley electrons. As a result, the transverse currents from nondegenerate valleys can no longer be canceled out so that the transverse current or Hall mobility can be observed. Interestingly, we find that at a fixed effective Zeeman field, the lowest spin-split conduction subband in ML-TMDs can be tuned from one in the K'-valley to one in the K-valley by varying the Rashba parameter. The occupation of electrons in different valleys also varies with changing carrier density. Therefore, we can change the magnitude and direction of the Hall current by varying the Rashba parameter, effective Zeeman field, and carrier density by, e.g., the presence of a ferromagnetic substrate and/or applying a gate voltage. By taking the ML-MoS2 as an example, these effects are demonstrated and examined. The important and interesting theoretical findings can be beneficial to experimental observation of the valleytronic effect and to gaining an in-depth understanding of the ML-TMD systems in the presence of proximity-induced interactions.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
DOI: 10.1103/PHYSREVB.109.195418
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“8-pmmn borophene : edge states in competition with Landau levels and local vacancy states”. Nazar ND, Peeters FM, Costa Filho RN, Vazifehshenas T, Physical chemistry, chemical physics 26, 16153 (2024). http://doi.org/10.1039/D3CP05638D
Abstract: The tight-binding method is used to investigate the electronic and magnetic properties of borophene nano-ribbons (BNRs) in the presence of a perpendicular magnetic field. Most BNRs exhibit metallic characteristics due to edge bands. Additionally, the appearance of Landau levels (LLs) is strongly influenced by the edge states, contrasting with the sheet platform which produces distinct LLs. We also investigated single atomic vacancy disorders in BNRs and observed localized vacancy states (LVSs) resulting from atomic disorder. Both LVSs and LLs are influenced by the edge states, underscoring that the electronic and magnetic properties of BNRs are strongly edge-dependent. This aspect is crucial for consideration in experimental, theoretical, and computational studies.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.3
DOI: 10.1039/D3CP05638D
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“Hydrogenation-controlled band engineering of dumbbell graphene”. Song Y, Chen M, Xie X, Liu X, Li J, Peeters FM, Li L, Nano energy 127, 109763 (2024). http://doi.org/10.1016/J.NANOEN.2024.109763
Abstract: The stability of the dumbbell structure has been confirmed by previous theory and experiment. Based on firstprinciples calculations, we proposed hexagonal dumbbell graphene (HDB C10) and rectangular dumbbell graphene (RDB C10) monolayers containing periodically raised C (CR) atoms. They turn out to have high mobility semiconductor properties. By adsorbing H atoms on these CR atoms, their band structures can be widely tuned from semiconductor to semimetal. When considering adsorption of two/four H atoms on the unit cell of the dumbbell structure, the bandgap can be increased, and isolated flat band structures can be obtained by further adding or removing H atoms. Remarkably, two different Dirac band structures can be found in the HDB/RDB C10H2-I monolayers. The HDB C10H2-I shows a Dirac cone with isotropic Fermi velocities, while the RDB C10H2-I monolayer exhibits a quasi-one-dimensional Dirac nodal line with varying Fermi velocities along the XS path. Tight-binding (TB) models are constructed including nearest neighbor (NN) and next NN hopping in order to understand our DFT results. These TB models are related to the Su-Schrieffer-Heeger model, and are able to explain the tunable topological properties of the RDB C10H2-I monolayer. They not only are able to explain the different kinds of Fermi velocity, but also can predict the emergence of topological edge states, providing a good platform for research on Dirac fermions. The HDB/RDB C10 monolayer exhibits more freedom of tunable band structures and more stable hydrogen storage capacity, making it superior to graphene. Finally, possible experimental synthesis paths of these DB monolayers are provided.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 17.6
DOI: 10.1016/J.NANOEN.2024.109763
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“Strain and stacking registry effects on the hyperbolicity of exciton polaritons in few-layer black phosphorus”. Thomen DMN, Sevik C, Milošević, MV, Teles LK, Chaves A, Physical review B 109, 245413 (2024). http://doi.org/10.1103/PHYSREVB.109.245413
Abstract: We analyze, from first -principles calculations, the excitonic properties of monolayer black phosphorus (BP) under strain, as well as of bilayer BP with different stacking registries, as a base platform for the observation and use of hyperbolic polaritons. In the unstrained case, our results confirm the in -plane hyperbolic behavior of polaritons coupled to the ground -state excitons in both mono- and bilayer systems, as observed in recent experiments. With strain, we reveal that the exciton-polariton hyperbolicity in monolayer BP is enhanced (reduced) by compressive (tensile) strain in the zig-zag direction of the crystal. In the bilayer case, different stacking registries are shown to exhibit hyperbolic exciton polaritons with different dispersion, while also peaking at different frequencies. This renders both mechanical stress and stacking registry control as practical tools for tuning physical properties of hyperbolic exciton polaritons in black phosphorus, which facilitates detection and further optoelectronic use of these quasiparticles.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
DOI: 10.1103/PHYSREVB.109.245413
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“Strong spin-lattice coupling and high-temperature magnetic ordering in monolayer chromium dichalcogenides”. Gonzalez-Garcia A, Bacaksiz C, Frauenheim T, Milošević, MV, Physical review materials 8, 064001 (2024). http://doi.org/10.1103/PHYSREVMATERIALS.8.064001
Abstract: We detail the magnetic properties of monolayer CrX2 and its Janus counterparts CrXY (X, Y = S, Se, Te, with X not equal Y) using ab initio methods and Landau-Lifshitz-Gilbert magnetization dynamics, and uncover the pronouncedly strong interplay between their structure symmetry and the magnetic order. The relaxation of nonmagnetic chalcogen atoms, that carry large spin-orbit coupling, changes the energetically preferential magnetic order between in-plane antiferromagnetic and tilted ferromagnetic one. The considered Janus monolayers exhibit sizable Dzyaloshinskii-Moriya interaction, in some cases above 20% of the isotropic exchange, and critical temperature of the long-range magnetic order in the vicinity or even significantly above the room temperature.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.4
DOI: 10.1103/PHYSREVMATERIALS.8.064001
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“Collective excitations in three-dimensional Dirac systems”. Li QN, Vasilopoulos P, Peeters FM, Xu W, Xiao YM, Milošević, MV, Physical review B 109, 115123 (2024). http://doi.org/10.1103/PHYSREVB.109.115123
Abstract: We provide the plasmon spectrum and related properties of the three-dimensional (3D) Dirac semimetals Na 3 Bi and Cd 3 As 2 based on the random -phase approximation. The necessary one -electron eigenvalues and eigenfunctions are obtained from an effective k <middle dot> p Hamiltonian. Below the energy at which the velocity v z along the k z axis vanishes, the density of states differs drastically from that of a 3D electron gas (3DEG) or graphene. The dispersion relation is anisotropic for wave vectors parallel ( q ) and perpendicular ( q z ) to the ( x , y ) plane and is markedly different than that of graphene or a 3DEG. The same holds for the energy -loss function. Both depend sensitively on the position of the Fermi energy E F relative to the region of the Berry curvature of the bands. For E F below the energy at which v z vanishes, the range of the relevant wave vectors q and q z shrinks, for q z by about one order of magnitude.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
DOI: 10.1103/PHYSREVB.109.115123
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Chinnabathini VC (2024) Gas phase bimetallic nanoclusters-modified TiO2 supports as efficient photo(electro)catalysts for self-cleaning surfaces and water splitting. xviii, 149 p
Abstract: In the context of global challenges such as climate change and environmental pollution, photocatalysis evolved as one of the promising strategies for sustainable energy conversion and pollutant degradation. In this thesis, photocatalysis using gas phase deposited bimetallic nanoclusters (BNCs) on TiO2 supports is studied in the context of self-cleaning surfaces and photoelectrochemical (PEC) water splitting applications. Thanks to their plasmonic properties, BNCs made of coinage metals can serve as efficient cocatalysts for the degradation of organic pollutants and surface contaminants under light irradiation. They also hold great promise for PEC water splitting, a promising pathway for renewable hydrogen production, which can be used in hydrogen fuel cells or for the environmentally friendly production of fuels in, for example, CO2 hydrogenation processes. The small size and high surface-to-volume ratio of plasmonic BNCs play pivotal roles in influencing the efficiency and selectivity of photocatalytic processes. BNCs have unique optical, physical, chemical, and structural properties distinctly different from their bulk and monometallic counterparts. These properties can be fine-tuned at the single particle level by their size, composition, and atomic arrangement, but also by interaction with other particles through the coverage and through interaction with the support. To design better photocatalysts it is crucial to carefully understand the BNCs’ characteristic properties, especially at the atomic level where synergies between different elements are sought. To achieve this objective, BNCs with well-defined sizes and compositions are deposited on TiO2 supports and we studied their structural properties and their influence on the photocatalytic activity. The general procedure followed in this thesis is the production and deposition of BNCs on TiO2 by the cluster beam deposition (CBD) technique, followed by structural and optical characterization to understand their tailored properties, and photocatalytic testing either for photodecomposition of organic molecules or PEC water splitting. In a first study, AuxAg1-x (x = 1, 0.9, 0.7, 0.5, 0.3, and 0) alloy BNCs with different compositions are synthesized in the gas phase and deposited from a molecular beam on TiO2 P25 supports. The photocatalytic self-cleaning activity of as-prepared samples is tested under UV and visible light towards stearic acid (SA) degradation. SA is a widely accepted model contaminant, which represents the group of organic fouling compounds that typically contaminates glass surfaces. A composition-dependent activity is observed with the Au0.3Ag0.7 nanocluster modified TiO2 exhibiting the highest photoactivity. Scanning transmission electron microscopy (STEM) measurements reveal that, for a mass loading corresponding to an equivalent of 4 atomic monolayers (MLs), the BNCs are uniformly distributed over the surface. The clusters have an average size of 3.5 ± 0.5 nm and are crystalline in nature. The atomic structure is characterized by X-ray absorption fine structure (XAFS) spectroscopy and their electronic structure by X-ray photoelectron spectroscopy (XPS). These measurements demonstrate a charge redistribution between the Ag and Au atoms when alloyed at the nanoscale. The effect of this charge redistribution is likely the stabilization of Ag against oxidation and directly affects the catalytic properties of the clusters. It is suggested that the highest photoactivity of 4 ML loaded Au0.3Ag0.7 under solar light results from a combination of four main possible contributing factors: (i) injection in TiO2 of excited carriers that are generated by the localized surface plasmon resonance (LSPR) effect of the BNCs in the visible light wavelength range which overlaps with the sun’s irradiance spectrum. (ii) a strong near-field enhancement that increases the photoabsorption by the TiO2 for photons that have enough energy to overcome the high bandgap, (iii) the optimized total metal loading of 4 ML leaves enough of the TiO2 surface accessible for light absorption, and finally (iv) an effective charge distribution between Au and Ag. This study demonstrates that CBD is an efficient approach for fabricating well-defined, tunable AuAg plasmon-based photocatalysts for self-cleaning applications, outperforming their monometallic counterparts as well as bimetallic alternatives obtained through colloidal methods. In a second study, titania nanotubes (TNTs) are modified with a series of AuxCu1-x (x = 1, 0.75, 0.5, 0.25, and 0) BNCs using the CBD technique. Based on the results of the first study, we opted again for a loading of 4 ML. TNTs are known for their high surface area, fast charge transfer, and corrosion resistance, while keeping the inherent strengths of traditional TiO2 materials. They prove to be promising photoanodes, enhancing photocurrent in PEC applications for water oxidation. In this work the TNTs are grown via anodic oxidation of a titanium metal foil. The crystalline anatase phase of the grown TNTs is confirmed by the X-ray diffraction technique (XRD), while transmission electron microscopy (TEM) provides information about the size and composition of the deposited BNCs. XAFS provides further structural information, while XPS measurements reveal charge redistribution between Au and Cu, which can aid in the enhancement of the PEC activity. Oxidation of as-prepared electrodes over the time results in structural changes with CuxO at the outer shell functioning as a protective layer, while the majority of the core is an alloy. The optical properties, studied through UV-Vis spectroscopy confirm the extended absorption range of the cluster-modified TNTs towards the visible region. The charge carrier recombination rate is derived from photoluminescence (PL) measurements. The as-prepared electrodes are tested photoelectrochemically for the generation of an anodic photocurrent using simulated sunlight. It is found that the AuxCu1-x (x = 1, 0.75, 0.5, 0.25 and 0) BNC modified TNTs show a remarkable enhancement in the anodic photocurrent relative to pristine TNTs, with Au0.25Cu0.75 exhibiting the highest photocurrent. This is due to the combination of many possible factors. Firstly, the charge redistribution between Au and Cu and increase stability of the Au0.25Cu0.75 electrode as observed in XAFS, indicates that the electronic effect in the cluster is also one of the governing factors for PEC activity. Secondly, formation of a surface CuOx layer, protects against further corrosion of the metallic AuCu BNCs cores. Third, reduced recombination of charge carriers is indicated by lower photoluminescent (PL) intensity compared to pristine TNTs and all other electrodes except pure gold, as observed in PL spectra. This implies that the generated charge carriers are efficiently separated by Au0.25Cu0.75 NCs acting as electron sinks and easily available for redox reactions. Fourth, the highest interfacial charge transfer efficiency is evidenced by the electrochemical impedance spectroscopy (EIS), leading to more efficacious charge migration and separation, facilitating the water oxidation surface reaction. A final beneficial factor is the uniform deposition of well-defined, size- and composition-controlled, ligand-free BNCs. Such BNCs provide more effective surface sites to the reaction medium, in contrast to electrodes synthesized by e.g. sol-gel methods, where (in)organic residues on metal surfaces may decrease the efficiency.
Keywords: Doctoral thesis; Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS)
DOI: 10.63028/10067/2067580151162165141
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Ninakanti R (2024) Synthesis and electron microscopy characterization of novel core-shell and self-assembled nanostructures for plasmon-enhanced photocatalysis. 163 p
Abstract: The global challenge posed by increasing levels of greenhouse gases and the associated detrimental impacts of global warming necessitate a strategic shift from traditional fossil fuel-based energy systems to more sustainable, renewable, and circular energy and material solutions. Consequently, the potential of photoactive nanoparticles, particularly those that harness light-driven processes, has captured extensive scientific interest as a viable approach to mitigating energy and environmental challenges on a global scale. Although, the adoption of solar light based solutions in the chemical industry has been very less due to sluggish reaction rates and its cascading effects on its economics. The primary focus of this dissertation is the study of plasmonic metal nanoparticles and metal oxide nanoparticles, emphasizing their applications in light-driven energy conversion. The distinctive properties of plasmonic materials, especially surface plasmon resonance (SPR), are pivotal in these applications. SPR involves the oscillation of electron clouds at the surface of nanoparticles when resonating with incident electromagnetic radiation, significantly enhancing solar radiation absorption. This feature is crucial for addressing the limitations of semiconductor photocatalysts like TiO2, which typically exhibit restricted absorption of solar irradiation. The objective of this dissertation is to further optimize the plasmonic enhancement mechanisms by strategically tuning the interactions between plasmonic nanoparticles and TiO2. This is achieved through the development of core-shell nanostructures and the self-assembly of supraparticles, designed to enhance plasmonic photocatalytic systems. The dissertation begins by elucidating the basic concepts and ideations behind the construction of these nanostructures and their roles in enhancing plasmonic photocatalysis, focusing on mechanisms such as near-electric field enhancement, electron transfer, and enhanced photon absorption. To achieve these objectives, modified synthesis techniques were developed to fabricate novel Au@TiO2 core-shell structures with precisely controlled TiO2 shell thickness and self-assembled Au-TiO2 supraparticles with variable sizes. The thesis further delves into the structural characterization of these synthesized nanoparticles, introducing both basic and advanced electron microscopy techniques. For the specific applications of these structures, it was found that Au@TiO2 core-shell nanoparticles with an optimal 4nm TiO2 shell thickness show significant enhancement in the hydrogen evolution reaction. Additionally, the largest Au-TiO2 supraparticles demonstrate superior efficacy in hydrogen peroxide generation. This work not only deepens the scientific understanding of plasmonic materials but also contributes to the development of renewable energy materials.
Keywords: Doctoral thesis; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Antwerp engineering, PhotoElectroChemistry & Sensing (A-PECS)
DOI: 10.63028/2067680151162165141
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Gao C (2024) Exploring electron ptychography for low dose imaging. xii, 146 p
Abstract: Transmission electron microscopy is an important technique in the exploration of materials’ structures. This is especially true since the development of electron optical aberration correctors greatly facilitated atomic resolution imaging. We are currently experiencing an ongoing revolution in electron microscopy with the widespread adoption of direct electron detectors. Scientists have reported a lot of key scientific findings facilitated by direct electron detectors. One particular research domain is electron ptychography, which holds promise for unraveling the intricate structures of highly beam-sensitive materials like bio samples and achieving super-resolution without the limitation of aperture in the condenser lens system. Nevertheless, challenges persist both in experimental setups and algorithmic processes. Issues such as the comparatively sluggish scanning speed of cameras and contrast reversals of the reconstructed phase for relatively thick specimens, disrupting phase or weak phase approximations, remain noteworthy limitations. This thesis addresses these challenges by the event-driven Timepix3 detector, presenting a viable solution to the speed bottleneck. Moreover, innovative approaches for applying electron ptychography to relatively thick samples, employing a middle focusing strategy, are proposed. This research aims to push the boundaries of electron microscopy, offering solutions to existing limitations and advancing the field towards more efficient and accurate imaging techniques.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
DOI: 10.63028/10067/2067770151162165141
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“First-principles exploration of superconductivity in intercalated bilayer borophene phases”. Šoškić, BN, Bekaert J, Sevik C, Šljivančanin Ž, Milošević, MV, Physical review materials 8, 064803 (2024). http://doi.org/10.1103/PHYSREVMATERIALS.8.064803
Abstract: We explore the emergence of phonon-mediated superconductivity in bilayer borophenes by controlled intercalation with elements from the groups of alkali, alkaline-earth, and transition metals, using systematic first-principles and Eliashberg calculations. We show that the superconducting properties are primarily governed by the interplay between the out-of-plane (????????) boron states and the partially occupied in-plane (????+????????,????) bonding states at the Fermi level. Our Eliashberg calculations indicate that intercalation with alkaline-earth-metal elements leads to the highest superconducting critical temperatures (????????). Specifically, Be in ????4, Mg in ????3, and Ca in the kagome bilayer borophene demonstrate superior performance with ???????? reaching up to 58 K. Our study therefore reveals that intercalated bilayer borophene phases are not only more resilient to chemical deterioration, but also harbor enhanced ???????? values compared to their monolayer counterparts, underscoring their substantial potential for the development of boron-based two-dimensional superconductors.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.4
DOI: 10.1103/PHYSREVMATERIALS.8.064803
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“High-Tc Berezinskii-Kosterlitz-Thouless transition in two-dimensional superconducting systems with coupled deep and quasiflat electronic bands with Van Hove singularities”. Paramasivam SK, Gangadharan SP, Milošević, MV, Perali A, Physical review B 110, 024507 (2024). http://doi.org/10.1103/PHYSREVB.110.024507
Abstract: In the pursuit of higher critical temperature of superconductivity, quasiflat electronic bands and Van Hove singularities in two dimensions (2D) have emerged as a potential approach to enhance Cooper pairing on the basis of mean-field expectations. However, these special electronic features suppress the superfluid stiffness and, hence, the Berezinskii-Kosterlitz-Thouless (BKT) transition in 2D superconducting systems, leading to the emergence of a significant pseudogap regime due to superconducting fluctuations. In the strong-coupling regime, one finds that superfluid stiffness is inversely proportional to the superconducting gap, which is the predominant factor contributing to the strong suppression of superfluid stiffness. Here we reveal that the aforementioned limitation is avoided in a 2D superconducting electronic system with a quasiflat electronic band with a strong pairing strength coupled to a deep band with weak electronic pairing strength. Owing to the multiband effects, we demonstrate a screening-like mechanism that circumvents the suppression of the superfluid stiffness. We report the optimal conditions for achieving a large enhancement of the BKT transition temperature and a substantial shrinking of the pseudogap regime by tuning the intraband couplings and the pair-exchange coupling between the two band-condensates.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
DOI: 10.1103/PHYSREVB.110.024507
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