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142 results on '"Grammatikopoulos, Panagiotis"'

3. Ferromagnetic–Antiferromagnetic Coupling in Gas‐Phase Synthesized M(Fe, Co, and Ni)–Cr Nanoparticles for Next‐Generation Magnetic Applications.

Author

Bohra, Murtaza, Giaremis, Stefanos, KS, Abisegapriyan, Mathioudaki, Stella, Kioseoglou, Joseph, and Grammatikopoulos, Panagiotis

Subjects
MAGNETIC cooling, PHYSICAL laws, EXCHANGE bias, MAGNETICS, MAGNETOCALORIC effects
Abstract

Combining ferromagnetic–antiferromagnetic materials in nanoalloys (i.e., nanoparticles, NPs, containing more than one element) can create a diverse landscape of potential electronic structures. As a result, a number of their magnetic properties can be manipulated, such as the exchange bias between NP core and shell, the Curie temperature of nanoparticulated samples, or their magnetocaloric effect. In this work, such a family of materials (namely M–Cr NPs where M is Fe, Co, Ni, or some combination of them) is reviewed with respect to the tunability of their magnetic properties via optimized doping with Cr up to its solubility limit. To this end, gas‐phase synthesis has proven a most effective method, allowing excellent control over the physical structure, composition, and chemical ordering of fabricated NPs by appropriately selecting various deposition parameters. Recent advances in this field (both experimental and computational) are distilled to provide a better understanding of the underlying physical laws and point toward new directions for cutting‐edge technological applications. For each property, a relevant potential application is associated, such as memory cells and recording heads, induced hyperthermia treatment, and magnetic cooling, respectively, aspiring to help connect the output of fundamental and applied research with current real‐world challenges. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Computer simulation of dislocation interaction with radiation-induced obstacles in iron

Author

Grammatikopoulos, Panagiotis, Bacon, David, and Bullough, Tim

Subjects
620, TK Electrical engineering. Electronics Nuclear engineering, QA76 Computer software
Abstract

Assessment of candidate materials for fusion power plants provide one of the major structural materials challenges of the next decades. Computer simulation provides a useful alternative to experiments on real-life irradiated materials. Within the framework of a multi-scale modelling approach, atomic scale studies by molecular dynamics (MD) and statics (MS) are of importance, since they enable understanding of atomic interaction mechanisms invisible at coarser scales. Nano-scale defect clusters, such as voids, solute-atom precipitates and dislocation loops can form in metals irradiated by high-energy atomic particles. Since they are obstacles to dislocation glide, they can affect plasticity, substantially changing the yield and flow stresses and ductility. In this study, a model for α-Fe developed by Osetsky and Bacon [26] has been used, that enables dislocation motion under applied shear strain at various temperatures and strain rates. Three main results were obtained. First, the two interatomic potentials used (A97 [79] and A04 [31]) were assessed with respect to reproducing dislocation properties. Both were in good agreement but for one fact: an unexpected and not previously reported displacement of core atoms along the direction of the dislocation line of a 1/2[111](1-10) edge dislocation was observed for the A97 potential. A connection of this phenomenon with differences in Peierls stress values for the two potentials was proposed. Second, the interaction of a 1/2[111](1-10) edge dislocation with a number of different configurations of spherical voids and Cu-precipitates 2 and 4 nm in diameter was investigated. The defects were centred on, above and below the dislocation glide plane. The mechanisms governing the interactions were analysed. For the first time it was observed that by interacting with a void, the dislocation can undergo both positive and negative climb, depending on the void position. A bcc to fcc phase transition was observed for the larger precipitates, in agreement with literature findings. Third, the obstacle strength of 1/2‹111› and ‹100› loops was obtained under various conditions and geometries for both potentials. Interactions are sometimes complex, but could be described in terms of conventional dislocation reactions in which Burgers vector is conserved. The critical resolved shear stress for dislocation breakaway and the fraction of interstitials left behind are wide-ranging. Finally, a mapping of all obstacle strengths was created for the purpose of comparison. ‹100› loops with Burgers vector parallel to the dislocation glide plane and 1/2‹111› loops proved to be strong obstacles. Small size voids are stronger than Cu-precipitates of the same size. The complexity of some reactions and the variety of obstacle strengths poses a challenge for the development of continuum models of dislocation behaviour in irradiated iron.

Published
2009
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10. Gas-phase synthesis of nanoparticles : current application challenges and instrumentation development responses

Author

Grammatikopoulos, Panagiotis, Bouloumis, Theodoros, Steinhauer, Stephan, Grammatikopoulos, Panagiotis, Bouloumis, Theodoros, and Steinhauer, Stephan

Abstract

Nanoparticles constitute fundamental building blocks required in several fields of application with current global importance. To fully exploit nanoparticle properties specifically determined by the size, shape, chemical composition and interfacial configuration, rigorous nanoparticle growth and deposition control is needed. Gas-phase synthesis, in particular magnetron-sputtering inert-gas condensation, provides unique opportunities to realise engineered nanoparticles optimised for the desired use case. Here, we provide an overview of recent nanoparticle growth experiments via this technique, how the latter can meet application-specific requirements, and what challenges might impede the wide-spread adoption for scalable industrial synthesis. More specifically, we discuss the timely topics of energy, catalysis, and sensing applications enabled by gas-phase synthesised nanoparticles, as well as recently emerging advances in neuromorphic devices for unconventional computing. Having identified the most relevant challenges and limiting factors, we outline how advances in nanoparticle source instrumentation and/or in situ diagnostics can address current shortcomings. Eventually we identify common trends and directions, giving our perspective on the most promising and impactful applications of gas-phase synthesised nanoparticles in the future., QC 20230911

Published
2023
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17. Nano-vault architecture mitigates stress in silicon-based anodes for lithium-ion batteries

Author

Okinawa Institute of Science and Technology, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Haro Remón, Marta, Kumar, Pawan, Zhao, Junlei, Koutsogiannis, Panagiotis, Porkovich, Alexander James, Ziadi, Zakaria, Bouloumis, Theodoros, Singh, Vidyadhar, Juárez-Pérez, Emilio J., Toulkeridou, Evropi, Nordlund, Kai, Djurabekova, Flyura, Sowwan, Mukhles, Grammatikopoulos, Panagiotis, Okinawa Institute of Science and Technology, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Haro Remón, Marta, Kumar, Pawan, Zhao, Junlei, Koutsogiannis, Panagiotis, Porkovich, Alexander James, Ziadi, Zakaria, Bouloumis, Theodoros, Singh, Vidyadhar, Juárez-Pérez, Emilio J., Toulkeridou, Evropi, Nordlund, Kai, Djurabekova, Flyura, Sowwan, Mukhles, and Grammatikopoulos, Panagiotis

Published
2021

30. Gas-Phase Synthesis of Trimetallic Nanoparticles

Author

Mattei, Jean-Gabriel, primary, Grammatikopoulos, Panagiotis, additional, Zhao, Junlei, additional, Singh, Vidyadhar, additional, Vernieres, Jerome, additional, Steinhauer, Stephan, additional, Porkovich, Alexander, additional, Danielson, Eric, additional, Nordlund, Kai, additional, Djurabekova, Flyura, additional, and Sowwan, Mukhles, additional

Published
2019
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31. Single Nanoparticle Activities in Ensemble : A Study on Pd Cluster Nanoportals for Electrochemical Oxygen Evolution Reaction

Author

Datta, Abheek, Porkovich, Alexander J., Kumar, Pawan, Nikoulis, Giorgos, Kioseoglou, Joseph, Sasaki, Toshio, Steinhauer, Stephan, Grammatikopoulos, Panagiotis, Sowwan, Mukhles, Datta, Abheek, Porkovich, Alexander J., Kumar, Pawan, Nikoulis, Giorgos, Kioseoglou, Joseph, Sasaki, Toshio, Steinhauer, Stephan, Grammatikopoulos, Panagiotis, and Sowwan, Mukhles

Abstract

Comprehensive understanding of the electrochemical activity of single nanoparticles (NPs) is in critical need for opening new avenues in the broad field of electrochemistry. Published reports on single-NP electrocatalysts typically include complicated and difficult methods of synthesis and characterization; moreover, these methods usually fail to provide a reliable way to measure the activities of individual NPs within larger ensembles of particles, i.e., in real-life nanocatalyst systems. In the present work, we synthesized from the gas phase Pd NPs that act as nanoportals for electron transfer within surface-oxidized Mg thin films. The physical synthesis method provided excellent control over the deposition density and, hence, enabled the design of a system where each individual open nanoportal forms an independent active single-NP electrode (SNPE). Being uncoupled from one another, these SNPEs contribute separately toward the total electrocatalytic activity while simultaneously providing a measure of their average, individual activities. We were thus able to fabricate a stable, steady-state electrode for the electrochemical oxygen evolution reaction (OER) and to study the activity and stability of the SNPEs over a period of 20 days; the former depended on the size of the NPs, while the latter depended on the SNPEs' resistance to aerial oxidation. The remarkable stability of the ensemble catalysts under OER conditions proves that this concept can be used for further studies on the activities of different single NPs in numerous real-life systems., QC 20191126

Published
2019
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33. NanoMaterialsCAD: Flexible Software for the Design of Nanostructures.

Author

Nikoulis, Giorgos, Grammatikopoulos, Panagiotis, Steinhauer, Stephan, and Kioseoglou, Joseph

Abstract

NanoMaterialsCAD is a new open source tool dedicated to the creation, manipulation, and 3D visualization of crystalline structures at the nanoscale. It is designed for preprocessing atomistic configurations to be used as input for atomistic (e.g., molecular dynamics or Monte Carlo) or ab initio (e.g., density functional theory) computer simulations. It offers several tools for designing complex nanostructures (including nanoparticles, nanowires, nanotubes, nanoscrolls, etc., and combinations/permutations of them) which are either lacking or cumbersome in other existing packages. Through its intuitive graphical user interface (GUI) it enables facile ways to design and modify the size/shape and relative positions of nanoobjects while observing the changes in real time. NanoMaterialsCAD is written in C++, and exploits Open Graphics Library (OpenGL) (for the GUI), Win32API (for interaction with Windows), and Assembly (for fast data management). The source code and executable file are available for download from GitHub (https://github.com/cossphy/NanoMaterialsCAD). It is aspired that NanoMaterialsCAD will be adopted by the nanomaterials modeling community as a valuable resource; to this end it will be kept improving, incorporating more nanostructures, and adding extra functionalities to its toolbox. [ABSTRACT FROM AUTHOR]

Published
2021
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40. Coating

Author

Grammatikopoulos, Panagiotis, primary and Sowwan, Mukhles, additional

Published
2017
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42. Gas Phase Synthesis of Multifunctional Fe-Based Nanocubes

Author

Vernieres, Jerome, primary, Steinhauer, Stephan, additional, Zhao, Junlei, additional, Chapelle, Audrey, additional, Menini, Philippe, additional, Dufour, Nicolas, additional, Diaz, Rosa E., additional, Nordlund, Kai, additional, Djurabekova, Flyura, additional, Grammatikopoulos, Panagiotis, additional, and Sowwan, Mukhles, additional

Published
2017
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45. Hydrogen Flux through Size Selected Pd Nanoparticles into Underlying Mg Nanofilms.

Author

Kumar, Sushant, Pavloudis, Theodore, Singh, Vidyadhar, Nguyen, Hoa, Steinhauer, Stephan, Pursell, Christopher, Clemens, Bruce, Kioseoglou, Joseph, Grammatikopoulos, Panagiotis, and Sowwan, Mukhles

Subjects
HYDROGEN storage, HYDROGEN absorption & adsorption, HYDROGENATION, MAGNESIUM films, PALLADIUM, METAL nanoparticles, NANOFILMS
Abstract

Abstract: The application of Mg for hydrogen storage is hindered due to the slow absorption of hydrogen in Mg films. Herein, the hydrogenation process is explored theoretically using density functional theory calculations, and energy barriers are compared for hydrogen diffusion through Pd nanoparticle/Mg film interfaces and their variations, i.e., Pd(H)/Mg(O). Decomposing the mechanism into basic steps, it is shown that Pd undergoes a strain‐induced crystallographic phase transformation near the interface, and indicated that hydrogen saturation of Pd nanoparticles enhances their efficiency as nanoportals. Using energetic arguments, it is explained why hydrogen diffusion is practically prohibited through native Mg oxide and seriously suppressed through existing hydride domains. Hydrogen flux is experimentally investigated through the nanoportals in Pd‐nanoparticle decorated Mg films by pressure‐composition isotherm measurements. An r ≈ t1/3 relationship is theoretically calculated for the radial growth of hemispherical hydride domains, and this relationship is confirmed by atomic force microscopy. The diffusion constant of hydrogen in Mg films is estimated as DHfilm ≈ 8 × 10−18 m2 s−1, based on transmission electron microscopy characterization. The unique nanoportal configuration allows direct measurement of hydride domain sizes, thus forming a model system for the experimental investigation of hydrogenation in any material. [ABSTRACT FROM AUTHOR]

Published
2018
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46. In SituObservation of Metal to Metal Oxide Progression: A Study of Charge Transfer Phenomenon at Ru–CuO Interfaces

Author

Porkovich, Alexander, Ziadi, Zakaria, Kumar, Pawan, Kioseoglou, Joseph, Jian, Nan, Weng, Lin, Steinhauer, Stephan, Vernieres, Jerome, Grammatikopoulos, Panagiotis, and Sowwan, Mukhles

Abstract

Surface charge and charge transfer between nanoclusters and oxide supports are of paramount importance to catalysis, surface plasmonics, and optical energy harvesting areas. At present, high-energy X-rays and theoretical investigation are always required to determine the chemical state changes in the nanoclusters and the oxide supports, as well as the underlying transfer charge between them. This work presents the idea of using chrono-conductometric measurements to determine the chemical states of the Ru nanoclusters on CuO supports. Both icosahedral and single-crystal hexagonal close-packed Ru nanoclusters were deposited through gas-phase synthesis. To study the charge transfer phenomenon at the interface, a bias was applied to cupric oxide nanowires with metallic nanocluster decoration. In situconductometric measurements were performed to observe the evolution of Ru into RuOxunder heating conditions. Structural elucidation techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, and Kelvin probe force microscopy were employed to study the corresponding progression of structure, chemical ordering, and surface potential, respectively, as Ru(0) was oxidized to RuOxon the supporting oxide surface. Experimental and theoretical investigation of charge transfer between the nanocluster and oxide support highlighted the importance of metallic character and structure of the nanoclusters on the interfacial charge transfer, thus allowing the investigation of surface charge behavior on oxide-supported catalysts, in situ, during catalytic operation viaconductometric measurements.

Published
2019
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47. Computer simulation of dislocation interaction with radiation-induced obstacles in iron

Author

Grammatikopoulos, Panagiotis, Bacon, David, and Bullough, Tim

Subjects
TK, QA76
Abstract

Assessment of candidate materials for fusion power plants provide one of the major structural materials challenges of the next decades. Computer simulation provides a useful alternative to experiments on real-life irradiated materials. Within the framework of a multi-scale modelling approach, atomic scale studies by molecular dynamics (MD) and statics (MS) are of importance, since they enable understanding of atomic interaction mechanisms invisible at coarser scales. Nano-scale defect clusters, such as voids, solute-atom precipitates and dislocation loops can form in metals irradiated by high-energy atomic particles. Since they are obstacles to dislocation glide, they can affect plasticity, substantially changing the yield and flow stresses and ductility. In this study, a model for α-Fe developed by Osetsky and Bacon [26] has been used, that enables dislocation motion under applied shear strain at various temperatures and strain rates. Three main results were obtained. First, the two interatomic potentials used (A97 [79] and A04 [31]) were assessed with respect to reproducing dislocation properties. Both were in good agreement but for one fact: an unexpected and not previously reported displacement of core atoms along the direction of the dislocation line of a 1/2[111](1-10) edge dislocation was observed for the A97 potential. A connection of this phenomenon with differences in Peierls stress values for the two potentials was proposed. Second, the interaction of a 1/2[111](1-10) edge dislocation with a number of different configurations of spherical voids and Cu-precipitates 2 and 4 nm in diameter was investigated. The defects were centred on, above and below the dislocation glide plane. The mechanisms governing the interactions were analysed. For the first time it was observed that by interacting with a void, the dislocation can undergo both positive and negative climb, depending on the void position. A bcc to fcc phase transition was observed for the larger precipitates, in agreement with literature findings. Third, the obstacle strength of 1/2‹111› and ‹100› loops was obtained under various conditions and geometries for both potentials. Interactions are sometimes complex, but could be described in terms of conventional dislocation reactions in which Burgers vector is conserved. The critical resolved shear stress for dislocation breakaway and the fraction of interstitials left behind are wide-ranging. Finally, a mapping of all obstacle strengths was created for the purpose of comparison. ‹100› loops with Burgers vector parallel to the dislocation glide plane and 1/2‹111› loops proved to be strong obstacles. Small size voids are stronger than Cu-precipitates of the same size. The complexity of some reactions and the variety of obstacle strengths poses a challenge for the development of continuum models of dislocation behaviour in irradiated iron.

Published
2011
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