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“Monolayer alkali and transition-metal monoxides : MgO, CaO, MnO, and NiO”. Shayeganfar F, Vasu KS, Nair RR, Peeters FM, Neek-Amal M, Physical review B 95, 144109 (2017). http://doi.org/10.1103/PHYSREVB.95.144109
Abstract: Two-dimensional crystals with strong interactions between layers has attracted increasing attention in recent years in a variety of fields. In particular, the growth of a single layer of oxide materials (e.g., MgO, CaO, NiO, and MnO) over metallic substrates were found to display different physical properties than their bulk. In this study, we report on the physical properties of a single layer of metallic oxide materials and compare their properties with their bulk and other two-dimensional (2D) crystals. We found that the planar structure of metallic monoxides are unstable whereas the buckled structures are thermodynamically stable. Also, the 2D-MnO and NiO exhibit different magnetic (ferromagnetic) and optical properties than their bulk, whereas band-gap energy and linear stiffness are found to be decreasing from NiO to MgO. Our findings provide insight into oxide thin-film technology applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 21
DOI: 10.1103/PHYSREVB.95.144109
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“Slippage dynamics of confined water in graphene oxide capillaries”. Kalashami HG, Neek-Amal M, Peeters FM, Physical review materials 2, 074004 (2018). http://doi.org/10.1103/PHYSREVMATERIALS.2.074004
Abstract: The permeation of water between neighboring graphene oxide (GO) flakes, i.e., 2D nanochannels, are investigated using a simple model for the GO membrane. We simulate the hydrophilic behavior of nanocapillaries and study the effect of surface charge on the dynamical properties of water flow and the influence of Na+ and Cl- ions on water permeation. Our approach is based on extensive equilibrium molecular dynamics simulations to obtain a better understanding of water permeation through charged nanochannels in the presence of ions. We found significant change in the slippage dynamics of confined water such as a profound increase in viscosity/slip length with increasing charges over the surface. The slip length decreases one order of magnitude (i.e., 1/30) with increasing density of surface charge, while it increases by a factor of 2 with ion concentration. We found that commensurability induced by nanoconfinement plays an important role on the intrinsic dynamical properties of water.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1103/PHYSREVMATERIALS.2.074004
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“Out-of-plane permittivity of confined water”. Jalali H, Ghorbanfekr H, Hamid I, Neek-Amal M, Rashidi R, Peeters FM, Physical Review E 102, 022803 (2020). http://doi.org/10.1103/PHYSREVE.102.022803
Abstract: The dielectric properties of confined water is of fundamental interest and is still controversial. For water confined in channels with height smaller than h = 8 angstrom, we found a commensurability effect and an extraordinary decrease in the out-of-plane dielectric constant down to the limit of the dielectric constant of optical water. Spatial resolved polarization density data obtained from molecular dynamics simulations are found to be antisymmetric across the channel and are used as input in a mean-field model for the dielectric constant as a function of the height of the channel for h > 15 angstrom. Our results are in excellent agreement with a recent experiment [L. Fumagalli et al., Science 360, 1339 (2018)].
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.366
Times cited: 38
DOI: 10.1103/PHYSREVE.102.022803
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“Electronic properties of oxidized graphene : effects of strain and an electric field on flat bands and the energy gap”. Alihosseini M, Ghasemi S, Ahmadkhani S, Alidoosti M, Esfahani DN, Peeters FM, Neek-Amal M, The journal of physical chemistry letters (2021). http://doi.org/10.1021/ACS.JPCLETT.1C03286
Abstract: A multiscale modeling and simulation approach, including first-principles calculations, ab initio molecular dynamics simulations, and a tight binding approach, is employed to study band flattening of the electronic band structure of oxidized monolayer graphene. The width offlat bands can be tuned by strain, the external electric field, and the density of functional groups and their distribution. A transition to a conducting state is found for monolayer graphene with impurities when it is subjected to an electric field of similar to 1.0 V/angstrom. Several parallel impurity-induced flat bands appear in the low-energy spectrum of monolayer graphene when the number of epoxy groups is changed. The width of the flat band decreases with an increase in tensile strain but is independent of the electric field strength. Here an alternative and easy route for obtaining band flattening in thermodynamically stable functionalized monolayer graphene is introduced. Our work discloses a new avenue for research on band flattening in monolayer graphene.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 9.353
Times cited: 7
DOI: 10.1021/ACS.JPCLETT.1C03286
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“Large CO2 uptake on a monolayer of CaO”. Berdiyorov GR, Neek-Amal M, Hussein IA, Madjet ME, Peeters FM, Journal of materials chemistry A : materials for energy and sustainability 5, 2110 (2017). http://doi.org/10.1039/C6TA08810D
Abstract: Density functional theory calculations are used to study gas adsorption properties of a recently synthesized CaO monolayer, which is found to be thermodynamically stable in its buckled form. Due to its topology and strong interaction with the CO2 molecules, this material possesses a remarkably high CO2 uptake capacity (similar to 0.4 g CO2 per g adsorbent). The CaO + CO2 system shows excellent thermal stability (up to 1000 K). Moreover, the material is highly selective towards CO2 against other major greenhouse gases such as CH4 and N2O. These advantages make this material a very promising candidate for CO2 capture and storage applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 8.867
Times cited: 2
DOI: 10.1039/C6TA08810D
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“Interlink between Abnormal Water Imbibition in Hydrophilic and Rapid Flow in Hydrophobic Nanochannels”. Zhou R, Neek-Amal M, Peeters FM, Bai B, Sun C, Physical Review Letters 132, 184001 (2024). http://doi.org/10.1103/PhysRevLett.132.184001
Abstract: Nanoscale extension and refinement of the Lucas-Washburn model is presented with a detailed analysis of recent experimental data and extensive molecular dynamics simulations to investigate rapid water flow and water imbibition within nanocapillaries. Through a comparative analysis of capillary rise in hydrophilic nanochannels, an unexpected reversal of the anticipated trend, with an abnormal peak, of imbibition length below the size of 3 nm was discovered in hydrophilic nanochannels, surprisingly sharing the same physical origin as the well-known peak observed in flow rate within hydrophobic nanochannels. The extended imbibition model is applicable across diverse spatiotemporal scales and validated against simulation results and existing experimental data for both hydrophilic and hydrophobic
Keywords: A1 Journal Article; CMT
Impact Factor: 8.6
Times cited: 1
DOI: 10.1103/PhysRevLett.132.184001
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“Anomalous dynamical behavior of freestanding graphene membranes”. Ackerman ML, Kumar P, Neek-Amal M, Thibado PM, Peeters FM, Singh S, Physical review letters 117, 126801 (2016). http://doi.org/10.1103/PHYSREVLETT.117.126801
Abstract: We report subnanometer, high-bandwidth measurements of the out-of-plane (vertical) motion of atoms in freestanding graphene using scanning tunneling microscopy. By tracking the vertical position over a long time period, a 1000-fold increase in the ability to measure space-time dynamics of atomically thin membranes is achieved over the current state-of-the-art imaging technologies. We observe that the vertical motion of a graphene membrane exhibits rare long-scale excursions characterized by both anomalous mean-squared displacements and Cauchy-Lorentz power law jump distributions.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 8.462
Times cited: 46
DOI: 10.1103/PHYSREVLETT.117.126801
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“Hydration effects and negative dielectric constant of nano-confined water between cation intercalated MXenes”. Jalali H, Khoeini F, Peeters FM, Neek-Amal M, Nanoscale 13, 922 (2021). http://doi.org/10.1039/D0NR03953E
Abstract: Using electrochemical methods a profound enhancement of the capacitance of electric double layer capacitor electrodes was reported when water molecules are strongly confined into the two-dimensional slits of titanium carbide MXene nanosheets [A. Sugahara et al., Nat. Commun., 2019, 10, 850]. We study the effects of hydration on the dielectric properties of nanoconfined water and supercapacitance properties of the cation intercalated MXene. A model for the electric double layer capacitor is constructed where water molecules are strongly confined in two-dimensional slits of MXene. We report an abnormal dielectric constant and polarization of nano-confined water between MXene layers. We found that by decreasing the ionic radius of the intercalated cations and in a critical hydration shell radius the capacitance of the system increases significantly (similar or equal to 200 F g(-1)) which can be interpreted as a negative permittivity. This study builds a bridge between the fundamental understanding of the dielectric properties of nanoconfined water and the capability of using MXene films for supercapacitor technology, and in doing so provides a solid theoretical support for recent experiments.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 7.367
Times cited: 7
DOI: 10.1039/D0NR03953E
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“Thermal activated rotation of graphene flake on graphene”. Peymanirad F, Singh SK, Ghorbanfekr-Kalashami H, Novoselov KS, Peeters FM, Neek-Amal M, 2D materials 4, 025015 (2017). http://doi.org/10.1088/2053-1583/AA58A4
Abstract: The self rotation of a graphene flake over graphite is controlled by the size, initial misalignment and temperature. Using both ab initio calculations and molecular dynamics simulations, we investigate annealing effects on the self rotation of a graphene flake on a graphene substrate. The energy barriers for rotation and drift of a graphene flake over graphene is found to be smaller than 25 meV/atom which is comparable to thermal energy. We found that small flakes (of about similar to 4 nm) are more sensitive to temperature and initial misorientation angles than larger one (beyond 10 nm). The initial stacking configuration of the flake is found to be important for its dynamics and time evolution of misalignment. Large flakes, which are initially in the AA-or AB-stacking state with small misorientation angle, rotate and end up in the AB-stacking configuration. However small flakes can they stay in an incommensurate state specially when the initial misorientation angle is larger than 2 degrees. Our results are in agreement with recent experiments.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 16
DOI: 10.1088/2053-1583/AA58A4
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“Indentation of graphene nano-bubbles”. Faraji F, Neek-Amal M, Neyts EC, Peeters FM, Nanoscale 14, 5876 (2022). http://doi.org/10.1039/D2NR01207C
Abstract: Molecular dynamics simulations are used to investigate the effect of an AFM tip when indenting graphene nano bubbles filled by a noble gas (i.e. He, Ne and Ar) up to the breaking point. The failure points resemble those of viral shells as described by the Foppl-von Karman (FvK) dimensionless number defined in the context of elasticity theory of thin shells. At room temperature, He gas inside the bubbles is found to be in the liquid state while Ne and Ar atoms are in the solid state although the pressure inside the nano bubble is below the melting pressure of the bulk. The trapped gases are under higher hydrostatic pressure at low temperatures than at room temperature.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.7
Times cited: 2
DOI: 10.1039/D2NR01207C
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“Multilayer graphene, Moire patterns, grain boundaries and defects identified by scanning tunneling microscopy on the m-plane, non-polar surface of SiC”. Xu P, Qi D, Schoelz JK, Thompson J, Thibado PM, Wheeler VD, Nyakiti LO, Myers-Ward RL, Eddy CR, Gaskill DK, Neek-Amal M, Peeters FM;, Carbon 80, 75 (2014). http://doi.org/10.1016/j.carbon.2014.08.028
Abstract: Epitaxial graphene is grown on a non-polar n(+) 6H-SiC m-plane substrate and studied using atomic scale scanning tunneling microscopy. Multilayer graphene is found throughout the surface and exhibits rotational disorder. Moire patterns of different spatial periodicities are found, and we found that as the wavelength increases, so does the amplitude of the modulations. This relationship reveals information about the interplay between the energy required to bend graphene and the interaction energy, i.e. van der Waals energy, with the graphene layer below. Our experiments are supported by theoretical calculations which predict that the membrane topographical amplitude scales with the Moire pattern wavelength, L as L-1 + alpha L-2. (C) 2014 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.337
Times cited: 14
DOI: 10.1016/j.carbon.2014.08.028
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“Tunable natural terahertz and mid-infrared hyperbolic plasmons in carbon phosphide”. Dehdast M, Valiollahi Z, Neek-Amal M, Van Duppen B, Peeters FM, Pourfath M, Carbon 178, 625 (2021). http://doi.org/10.1016/J.CARBON.2021.03.040
Abstract: Hyperbolic polaritons in ultra thin materials such as few layers of van derWaals heterostructures provide a unique control over light-matter interaction at the nanoscale and with various applications in flat optics. Natural hyperbolic surface plasmons have been observed on thin films of WTe2 in the light wavelength range of 16-23 mu m (similar or equal to 13-18 THz) [Nat. Commun. 11, 1158 (2020)]. Using time-dependent density functional theory, it is found that carbon doped monolayer phosphorene (beta-allotrope of carbon phosphide monolayer) exhibits natural hyperbolic plasmons at frequencies above similar or equal to 5 THz which is not observed in its parent materials, i.e. monolayer of black phosphorous and graphene. Furthermore, we found that by electrostatic doping the plasmonic frequency range can be extended to the mid-infrared. (C) 2021 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.337
Times cited: 11
DOI: 10.1016/J.CARBON.2021.03.040
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“Clogging and unclogging of hydrocarbon-contaminated nanochannels”. Javdani Z, Hassani N, Faraji F, Zhou R, Sun C, Radha B, Neyts E, Peeters FM, Neek-Amal M, The journal of physical chemistry letters 13, 11454 (2022). http://doi.org/10.1021/ACS.JPCLETT.2C03016
Abstract: The recent advantages of the fabrication of artificial nanochannels enabled new research on the molecular transport, permeance, and selectivity of various gases and molecules. However, the physisorption/chemisorption of the unwanted molecules (usually hydrocarbons) inside nanochannels results in the alteration of the functionality of the nanochannels. We investigated contamination due to hydrocarbon molecules, nanochannels made of graphene, hexagonal boron nitride, BC2N, and molybdenum disulfide using molecular dynamics simulations. We found that for a certain size of nanochannel (i.e., h = 0.7 nm), as a result of the anomalous hydrophilic nature of nanochannels made of graphene, the hydrocarbons are fully adsorbed in the nanochannel, giving rise to full uptake. An increasing temperature plays an important role in unclogging, while pressure does not have a significant role. The results of our pioneering work contribute to a better understanding and highlight the important factors in alleviating the contamination and unclogging of nanochannels, which are in good agreement with the results of recent experiments.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 5.7
DOI: 10.1021/ACS.JPCLETT.2C03016
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“Electrically controlled water permeation through graphene oxide membranes”. Zhou K-G, Vasu KS, Cherian CT, Neek-Amal M, Zhang JC, Ghorbanfekr-Kalashami H, Huang K, Marshall OP, Kravets VG, Abraham J, Su Y, Grigorenko AN, Pratt A, Geim AK, Peeters FM, Novoselov KS, Nair RR, Nature 559, 236 (2018). http://doi.org/10.1038/S41586-018-0292-Y
Abstract: Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies(1-7). Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength(3,8). Electrical control over water transport is an attractive alternative; however, theory and simulations(9-14) have often yielded conflicting results, from freezing of water molecules to melting of ice(14-16) under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes(17-21). Such membranes have previously been shown to exhibit ultrafast permeation of water(17,22) and molecular sieving properties(18,21), with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 40.137
Times cited: 216
DOI: 10.1038/S41586-018-0292-Y
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“Melting of partially fluorinated graphene : from detachment of fluorine atoms to large defects and random coils”. Singh SK, Costamagna S, Neek-Amal M, Peeters FM, The journal of physical chemistry: C : nanomaterials and interfaces 118, 4460 (2014). http://doi.org/10.1021/JP4109333
Abstract: The melting of fluorographene is very unusual and depends strongly on the degree of fluorination. For temperatures below 1000 K, fully fluorinated graphene (FFG) is thermomechanically more stable than graphene but at T-m approximate to 2800 K FFG transits to random coils which is almost 2 times lower than the melting temperature of graphene, i.e., 5300 K. For fluorinated graphene up to 30% ripples causes detachment of individual F-atoms around 2000 K, while for 40%-60% fluorination large defects are formed beyond 1500 K and beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The results agree with recent experiments on the dependence of the reversibility of the fluorination process on the percentage of fluorination.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.536
Times cited: 16
DOI: 10.1021/JP4109333
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“Boron nitride mono layer : a strain-tunable nanosensor”. Neek-Amal M, Beheshtian J, Sadeghi A, Michel KH, Peeters FM, The journal of physical chemistry: C : nanomaterials and interfaces 117, 13261 (2013). http://doi.org/10.1021/jp402122c
Abstract: The influence of triaxial in-plane strain on the electronic properties of a hexagonal boron-nitride sheet is investigated using density functional theory. Different from graphene, the triaxial strain localizes the molecular orbitals of the boron-nitride flake in its center depending on the direction of the applied strain. The proposed technique for localizing the molecular orbitals that are close to the Fermi level in the center of boron nitride flakes can be used to actualize engineered nanosensors, for instance, to selectively detect gas molecules. We show that the central part of the strained flake adsorbs polar molecules more strongly as compared with an unstrained sheet.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.536
Times cited: 38
DOI: 10.1021/jp402122c
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“Unconventional two-dimensional vibrations of a decorated carbon nanotube under electric field : linking actuation to advanced sensing ability”. de Aquino BRH, Neek-Amal M, Milošević, MV, Scientific reports 7, 13481 (2017). http://doi.org/10.1038/S41598-017-12647-2
Abstract: We show that a carbon nanotube decorated with different types of charged metallic nanoparticles exhibits unusual two-dimensional vibrations when actuated by applied electric field. Such vibrations and diverse possible trajectories are not only fundamentally important but also have minimum two characteristic frequencies that can be directly linked back to the properties of the constituents in the considered nanoresonator. Namely, those frequencies and the maximal deflection during vibrations are very distinctively dependent on the geometry of the nanotube, the shape, element, mass and charge of the nanoparticle, and are vastly tunable by the applied electric field, revealing the unique sensing ability of devices made of molecular filaments and metallic nanoparticles.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.259
Times cited: 1
DOI: 10.1038/S41598-017-12647-2
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“Ionized water confined in graphene nanochannels”. de Aquino BRH, Ghorbanfekr-Kalashami H, Neek-Amal M, Peeters FM, Physical chemistry, chemical physics 21, 9285 (2019). http://doi.org/10.1039/C9CP00075E
Abstract: When confined between graphene layers, water behaves differently from the bulk and exhibits unusual properties such as fast water flow and ordering into a crystal. The hydrogen-bonded network is affected by the limited space and by the characteristics of the confining walls. The presence of an extraordinary number of hydronium and hydroxide ions in narrow channels has the following effects: (i) they affect water permeation through the channel, (ii) they may interact with functional groups on the graphene oxide surface and on the edges, and (iii) they change the thermochemistry of water, which are fundamentally important to understand, especially when confined water is subjected to an external electric field. Here we study the physical properties of water when confined between two graphene sheets and containing hydronium and hydroxide. We found that: (i) there is a disruption in the solvation structure of the ions, which is also affected by the layered structure of confined water, (ii) hydronium and hydroxide occupy specific regions inside the nanochannel, with a prevalence of hydronium (hydroxide) ions at the edges (interior), and (iii) ions recombine more slowly in confined systems than in bulk water, with the recombination process depending on the channel height and commensurability between the size of the molecules and the nanochannel height – a decay of 20% (40%) in the number of ions in 8 ps is observed for a channel height of h = 7 angstrom (bulk water). Our work reveals distinctive properties of water confined in a nanocapillary in the presence of additional hydronium and hydroxide ions.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 10
DOI: 10.1039/C9CP00075E
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“Transport of hydrogen isotopes through interlayer spacing in van der Waals crystals”. Hu S, Gopinadhan K, Rakowski A, Neek-Amal M, Heine T, Grigorieva IV, Haigh SJ, Peeters FM, Geim AK, Lozada-Hidalgo M, Nature nanotechnology 13, 468 (2018). http://doi.org/10.1038/S41565-018-0088-0
Abstract: Atoms start behaving as waves rather than classical particles if confined in spaces commensurate with their de Broglie wavelength. At room temperature this length is only about one angstrom even for the lightest atom, hydrogen. This restricts quantum-confinement phenomena for atomic species to the realm of very low temperatures(1-5). Here, we show that van der Waals gaps between atomic planes of layered crystals provide angstrom-size channels that make quantum confinement of protons apparent even at room temperature. Our transport measurements show that thermal protons experience a notably higher barrier than deuterons when entering van der Waals gaps in hexagonal boron nitride and molybdenum disulfide. This is attributed to the difference in the de Broglie wavelengths of the isotopes. Once inside the crystals, transport of both isotopes can be described by classical diffusion, albeit with unexpectedly fast rates comparable to that of protons in water. The demonstrated angstrom-size channels can be exploited for further studies of atomistic quantum confinement and, if the technology can be scaled up, for sieving hydrogen isotopes.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 38.986
Times cited: 32
DOI: 10.1038/S41565-018-0088-0
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“Graphene ripples as a realization of a two-dimensional Ising model : a scanning tunneling microscope study”. Schoelz JK, Xu P, Meunier V, Kumar P, Neek-Amal M, Thibado PM, Peeters FM, Physical review: B: condensed matter and materials physics 91, 045413 (2015). http://doi.org/10.1103/PhysRevB.91.045413
Abstract: Ripples in pristine freestanding graphene naturally orient themselves in an array that is alternately curved-up and curved-down; maintaining an average height of zero. Using scanning tunneling microscopy (STM) to apply a local force, the graphene sheet will reversibly rise and fall in height until the height reaches 60%-70% of its maximum at which point a sudden, permanent jump occurs. We successfully model the ripples as a spin-half Ising magnetic system, where the height of the graphene plays the role of the spin. The permanent jump in height, controlled by the tunneling current, is found to be equivalent to an antiferromagnetic-to-ferromagnetic phase transition. The thermal load underneath the STM tip alters the local tension and is identified as the responsible mechanism for the phase transition. Four universal critical exponents are measured from our STM data, and the model provides insight into the statistical role of graphene's unusual negative thermal expansion coefficient.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 21
DOI: 10.1103/PhysRevB.91.045413
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“Rippling, buckling, and melting of single- and multilayer MoS2”. Singh SK, Neek-Amal M, Costamagna S, Peeters FM, Physical Review B 91, 014101 (2015). http://doi.org/10.1103/PhysRevB.91.014101
Abstract: Large-scale atomistic simulations using the reactive empirical bond order force field approach is implemented to investigate thermal and mechanical properties of single-layer (SL) and multilayer (ML) molybdenum disulfide (MoS2). The amplitude of the intrinsic ripples of SL MoS2 are found to be smaller than those exhibited by graphene (GE). Furthermore, because of the van der Waals interaction between layers, the out-of-plane thermal fluctuations of ML MoS2 decreases rapidly with increasing number of layers. This trend is confirmed by the buckling transition due to uniaxial stress which occurs for a significantly larger applied tension as compared to graphene. For SL MoS2, the melting temperature is estimated to be 3700 K which occurs through dimerization followed by the formation of small molecules consisting of two to five atoms. When different types of vacancies are inserted in the SL MoS2 it results in a decrease of both the melting temperature as well as the stiffness.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 40
DOI: 10.1103/PhysRevB.91.014101
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“AA-stacked bilayer square ice between graphene layers”. Sobrino Fernandez MM, Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 92, 245428 (2015). http://doi.org/10.1103/PhysRevB.92.245428
Abstract: Water confined between two graphene layers with a separation of a few A forms a layered two-dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that flat monolayer ice with a rhombic-square structure nucleates between the graphene layers which is nonpolar and nonferroelectric. We provide different energetic considerations and H-bonding results that explain the interlayer and intralayer properties of two-dimensional ice. The controversial AA stacking found experimentally [Algara-Siller et al., Nature (London) 519, 443 (2015)] is consistent with our minimum-energy crystal structure of bilayer ice. Furthermore, we predict that an odd number of layers of ice has the same lattice structure as monolayer ice, while an even number of ice layers exhibits the square ice AA stacking of bilayer ice.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 40
DOI: 10.1103/PhysRevB.92.245428
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“Diffusion of fluorine on and between graphene layers”. Sadeghi A, Neek-Amal M, Berdiyorov GR, Peeters FM, Physical review : B : condensed matter and materials physics 91, 014304 (2015). http://doi.org/10.1103/PhysRevB.91.014304
Abstract: Using first-principles calculations and reactive force field molecular dynamics simulations, we study the structural properties and dynamics of a fluorine (F) atom, either adsorbed on the surface of single layer graphene (F/GE) or between the layers of AB stacked bilayer graphene (F@ bilayer graphene). It is found that the diffusion of the F atom is very different in those cases, and that the mobility of the F atom increases by about an order of magnitude when inserted between two graphene layers. The obtained diffusion constant for F/GE is twice larger than that experimentally found for gold adatom and theoretically found for C-60 molecule on graphene. Our study provides important physical insights into the dynamics of fluorine atoms between and on graphene layers and explains the mechanism behind the separation of graphite layers due to intercalation of F atoms.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 15
DOI: 10.1103/PhysRevB.91.014304
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“Membrane amplitude and triaxial stress in twisted bilayer graphene deciphered using first-principles directed elasticity theory and scanning tunneling microscopy”. Neek-Amal M, Xu P, Qi D, Thibado PM, Nyakiti LO, Wheeler VD, Myers-Ward RL, Eddy CR, Gaskill DK, Peeters FM, Physical review : B : condensed matter and materials physics 90, 064101 (2014). http://doi.org/10.1103/PhysRevB.90.064101
Abstract: Twisted graphene layers produce a moire pattern (MP) structure with a predetermined wavelength for a given twist angle. However, predicting the membrane corrugation amplitude for any angle other than pure AB-stacked or AA-stacked graphene is impossible using first-principles density functional theory (DFT) due to the large supercell. Here, within elasticity theory, we define the MP structure as the minimum-energy configuration, thereby leaving the height amplitude as the only unknown parameter. The latter is determined from DFT calculations for AB-and AA-stacked bilayer graphene in order to eliminate all fitting parameters. Excellent agreement with scanning tunneling microscopy results across multiple substrates is reported as a function of twist angle.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 12
DOI: 10.1103/PhysRevB.90.064101
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“Stabilized silicene within bilayer graphene : a proposal based on molecular dynamics and density-functional tight-binding calculations”. Berdiyorov GR, Neek-Amal M, Peeters FM, van Duin ACT, Physical review : B : condensed matter and materials physics 89, 024107 (2014). http://doi.org/10.1103/PhysRevB.89.024107
Abstract: Freestanding silicene is predicted to display comparable electronic properties as graphene. However, the yet synthesized silicenelike structures have been only realized on different substrates which turned out to exhibit versatile crystallographic structures that are very different from the theoretically predicted buckled phase of freestanding silicene. This calls for a different approach where silicene is stabilized using very weakly interacting surfaces. We propose here a route by using graphene bilayer as a scaffold. The confinement between the flat graphene layers results in a planar clustering of Si atoms with small buckling, which is energetically unfavorable in vacuum. Buckled hexagonal arrangement of Si atoms similar to freestanding silicene is observed for large clusters, which, in contrast to Si atoms on metallic surfaces, is only very weakly van der Waals coupled to the graphene layers. These clusters are found to be stable well above room temperature. Our findings, which are supported by density-functional tight-binding calculations, show that intercalating bilayer graphene with Si is a favorable route to realize silicene.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 43
DOI: 10.1103/PhysRevB.89.024107
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“Electronic structure of a hexagonal graphene flake subjected to triaxial stress”. Neek-Amal M, Covaci L, Shakouri K, Peeters FM, Physical review : B : condensed matter and materials physics 88, 115428 (2013). http://doi.org/10.1103/PhysRevB.88.115428
Abstract: The electronic properties of a triaxially strained hexagonal graphene flake with either armchair or zigzag edges are investigated using molecular dynamics simulations and tight-binding calculations. We found that (i) the pseudomagnetic field in strained graphene flakes is not uniform neither in the center nor at the edge of zigzag terminated flakes, (ii) the pseudomagnetic field is almost zero in the center of armchair terminated flakes but increases dramatically near the edges, (iii) the pseudomagnetic field increases linearly with strain, for strains lower than 15% but increases nonlinearly beyond it, (iv) the local density of states in the center of the zigzag hexagon exhibits pseudo-Landau levels with broken sublattice symmetry in the zeroth pseudo-Landau level, and in addition there is a shift in the Dirac cone due to strain induced scalar potentials, and (v) there is size effect in pseudomagnetic field. This study provides a realistic model of the electronic properties of inhomogeneously strained graphene where the relaxation of the atomic positions is correctly included together with strain induced modifications of the hopping terms up to next-nearest neighbors.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 46
DOI: 10.1103/PhysRevB.88.115428
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“Melting of graphene clusters”. Singh SK, Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 87, 134103 (2013). http://doi.org/10.1103/PhysRevB.87.134103
Abstract: Density-functional tight-binding and classical molecular dynamics simulations are used to investigate the structural deformations and melting of planar carbon nanoclusters C-N with N = 2-55. The minimum-energy configurations for different clusters are used as starting configurations for the study of the temperature effects on the bond breaking and rotation in carbon lines (N < 6), carbon rings (5 < N < 19), and graphene nanoflakes. The larger the rings (graphene nanoflakes) the higher the transition temperature (melting point) with ring-to-line (perfect-to-defective) transition structures. The melting point was obtained by using the bond energy, the Lindemann criteria, and the specific heat. We found that hydrogen-passivated graphene nanoflakes (CNHM) have a larger melting temperature with a much smaller dependence on size. The edges in the graphene nanoflakes exhibit several different metastable configurations (isomers) during heating before melting occurs. DOI: 10.1103/PhysRevB.87.134103
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 28
DOI: 10.1103/PhysRevB.87.134103
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“Spiral graphone and one-sided fluorographene nanoribbons”. Neek-Amal M, Beheshtian J, Shayeganfar F, Singh SK, Los JH, Peeters FM, Physical review : B : condensed matter and materials physics 87, 075448 (2013). http://doi.org/10.1103/PhysRevB.87.075448
Abstract: The instability of a free-standing one-sided hydrogenated/fluorinated graphene nanoribbon, i.e., graphone/fluorographene, is studied using ab initio, semiempirical, and large-scale molecular dynamics simulations. Free-standing semi-infinite armchairlike hydrogenated/fluorinated graphene (AC-GH/AC-GF) and boatlike hydrogenated/fluorinated graphene (B-GH/B-GF) (nanoribbons which are periodic along the zigzag direction) are unstable and spontaneously transform into spiral structures. We find that rolled, spiral B-GH and B-GF are energetically more favorable than spiral AC-GH and AC-GF which is opposite to the double-sided flat hydrogenated/fluorinated graphene, i.e., graphane/fluorographene. We found that the packed, spiral structures exhibit an unexpected localized highest occupied molecular orbital and lowest occupied molecular orbital at the edges with increasing energy gap during rolling. These rolled hydrocarbon structures are stable beyond room temperature up to at least T = 1000 K within our simulation time of 1 ns. DOI: 10.1103/PhysRevB.87.075448
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 14
DOI: 10.1103/PhysRevB.87.075448
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“Thermal properties of fluorinated graphene”. Singh SK, Srinivasan SG, Neek-Amal M, Costamagna S, van Duin ACT, Peeters FM, Physical review : B : condensed matter and materials physics 87, 104114 (2013). http://doi.org/10.1103/PhysRevB.87.104114
Abstract: Large-scale atomistic simulations using the reactive force field approach are implemented to investigate the thermomechanical properties of fluorinated graphene (FG). A set of parameters for the reactive force field potential optimized to reproduce key quantum mechanical properties of relevant carbon-fluorine cluster systems are presented. Molecular dynamics simulations are used to investigate the thermal rippling behavior of FG and its mechanical properties and compare them with graphene, graphane and a sheet of boron nitride. The mean square value of the height fluctuations < h(2)> and the height-height correlation function H(q) for different system sizes and temperatures show that FG is an unrippled system in contrast to the thermal rippling behavior of graphene. The effective Young's modulus of a flake of fluorinated graphene is obtained to be 273 N/m and 250 N/m for a flake of FG under uniaxial strain along armchair and zigzag directions, respectively. DOI: 10.1103/PhysRevB.87.104114
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 80
DOI: 10.1103/PhysRevB.87.104114
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“Thermomechanical properties of a single hexagonal boron nitride sheet”. Singh SK, Neek-Amal M, Costamagna S, Peeters FM, Physical review : B : condensed matter and materials physics 87, 184106 (2013). http://doi.org/10.1103/PhysRevB.87.184106
Abstract: Using atomistic simulations we investigate the thermodynamical properties of a single atomic layer of hexagonal boron nitride (h-BN). The thermal induced ripples, heat capacity, and thermal lattice expansion of large scale h-BN sheets are determined and compared to those found for graphene (GE) for temperatures up to 1000 K. By analyzing the mean-square height fluctuations < h(2)> and the height-height correlation function H(q) we found that the h-BN sheet is a less stiff material as compared to graphene. The bending rigidity of h-BN (i) is about 16% smaller than the one of GE at room temperature (300 K), and (ii) increases with temperature as in GE. The difference in stiffness between h-BN and GE results in unequal responses to external uniaxial and shear stress and different buckling transitions. In contrast to a GE sheet, the buckling transition of a h-BN sheet depends strongly on the direction of the applied compression. The molar heat capacity, thermal-expansion coefficient, and Gruneisen parameter are estimated to be 25.2 J mol(-1) K-1, 7.2 x 10(-6) K-1, and 0.89, respectively.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 80
DOI: 10.1103/PhysRevB.87.184106
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