“Self-limiting growth of two-dimensional palladium between graphene oxide layers”. Su Y, Prestat E, Hu C, Puthiyapura VK, Neek-Amal M, Xiao H, Huang K, Kravets VG, Haigh SJ, Hardacre C, Peeters FM, Nair RR, Nano letters 19, 4678 (2019). http://doi.org/10.1021/ACS.NANOLETT.9B01733
Abstract: The ability of different materials to display self-limiting growth has recently attracted an enormous amount of attention because of the importance of nanoscale materials in applications for catalysis, energy conversion, (opto)-electronics, and so forth. Here, we show that the electrochemical deposition of palladium (Pd) between graphene oxide (GO) sheets result in the self-limiting growth of 5-nm-thick Pd nanosheets. The self-limiting growth is found to be a consequence of the strong interaction of Pd with the confining GO sheets, which results in the bulk growth of Pd being energetically unfavorable for larger thicknesses. Furthermore, we have successfully carried out liquid exfoliation of the resulting Pd-GO laminates to isolate Pd nanosheets and have demonstrated their high efficiency in continuous flow catalysis and electrocatalysis.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 12.712
Times cited: 17
DOI: 10.1021/ACS.NANOLETT.9B01733
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“Effect of grain boundary on the buckling of graphene nanoribbons”. Neek-Amal M, Peeters FM, Applied physics letters 100, 101905 (2012). http://doi.org/10.1063/1.3692573
Abstract: The buckling of graphene nano-ribbons containing a grain boundary is studied using atomistic simulations where free and supported boundary conditions are invoked. We consider the buckling transition of two kinds of grain boundaries with special symmetry. When graphene contains a large angle grain boundary with theta = 21.8 degrees, the buckling strains are larger than those of perfect graphene when the ribbons with free (supported) boundary condition are subjected to compressive tension parallel (perpendicular) to the grain boundary. This is opposite for the results of theta = 32.2 degrees. The shape of the deformations of the buckled graphene nanoribbons depends on the boundary conditions, the presence of the particular used grain boundaries, and the direction of applied in-plane compressive tension. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692573]
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.411
Times cited: 18
DOI: 10.1063/1.3692573
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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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“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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“Reversible structural transition in nanoconfined ice”. Satarifard V, Mousaei M, Hadadi F, Dix J, Sobrino Fernández M, Carbone P, Beheshtian J, Peeters FM, Neek-Amal M, Physical review B 95, 064105 (2017). http://doi.org/10.1103/PHYSREVB.95.064105
Abstract: The report on square ice sandwiched between two graphene layers by Algara-Siller et al. [Nature (London) 519, 443 (2015)] has generated a large interest in this system. By applying high lateral pressure on nanoconfined water, we found that monolayer ice is transformed to bilayer ice when the two graphene layers are separated by H = 6,7 angstrom. It was also found that three layers of a denser phase of ice with smaller lattice constant are formed if we start from bilayer ice and apply a lateral pressure of about 0.7 GPa with H = 8,9 angstrom. The lattice constant (2.5-2.6 angstrom) in both transitions is found to be smaller than those typical for the known phases of ice and water, i.e., 2.8 angstrom. We validate these results using ab initio calculations and find good agreement between ab initio O-O distance and those obtained from classical molecular dynamics simulations. The reversibility of the mentioned transitions is confirmed by decompressing the systems.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 23
DOI: 10.1103/PHYSREVB.95.064105
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“Tuning the electronic properties of graphene-graphitic carbon nitride heterostructures and heterojunctions by using an electric field”. Bafekry A, Neek-Amal M, Physical Review B 101, 085417 (2020). http://doi.org/10.1103/PHYSREVB.101.085417
Abstract: Integration of graphene-based two-dimensional materials is essential for nanoelectronics applications. Using density-functional theory, we systematically investigate the electronic properties of vertically stacked graphene-graphitic carbon nitrides (GE/GCN). We also studied the covalently lateral stitched graphene-graphitic carbon nitrides (GE-GCN heterojunctions). The effects of perpendicular electric field on the electronic properties of six different heterostructures, i.e., (i) one layer of GE on top of a layer of CnNm with (n, m) = (3,1), (3,4), and (4,3) and (ii) three heterostructures CnNm/Cn'Nm', where (n, m) not equal (n', m') are elucidated. The most important calculated features are (i) the systems GE/C3N4, C3N/C3N4, GE-C3N, GE-C4N3, and C3N-C3N4 exhibit semiconducting characteristics having small band gaps of Delta(0)=20, 250, 100, 100, 80 meV, respectively while (ii) the systems GE/C4N3, C3N/C4N3, and C3N-C4N3 show ferromagnetic-metallic properties. In particular, we found that, in semiconducting heterostructures, the band gap increases nontrivially with increasing the absolute value of the applied perpendicular electric field. This work is useful for designing heterojunctions and heterostructures made of graphene and other two-dimensional materials such as those proposed in recent experiments [X. Liu and M. C. Hersam Sci. Adv. 5, 6444 (2019)].
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
Times cited: 24
DOI: 10.1103/PHYSREVB.101.085417
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“Breakdown of universal scaling for nanometer-sized bubbles in graphene”. Villarreal R, Lin P-C, Faraji F, Hassani N, Bana H, Zarkua Z, Nair MN, Tsai H-C, Auge M, Junge F, Hofsaess HC, De Gendt S, De Feyter S, Brems S, Ahlgren EH, Neyts EC, Covaci L, Peeters FM, Neek-Amal M, Pereira LMC, Nano Letters 21, 8103 (2021). http://doi.org/10.1021/ACS.NANOLETT.1C02470
Abstract: We report the formation of nanobubbles on graphene with a radius of the order of 1 nm, using ultralow energy implantation of noble gas ions (He, Ne, Ar) into graphene grown on a Pt(111) surface. We show that the universal scaling of the aspect ratio, which has previously been established for larger bubbles, breaks down when the bubble radius approaches 1 nm, resulting in much larger aspect ratios. Moreover, we observe that the bubble stability and aspect ratio depend on the substrate onto which the graphene is grown (bubbles are stable for Pt but not for Cu) and trapped element. We interpret these dependencies in terms of the atomic compressibility of the noble gas as well as of the adhesion energies between graphene, the substrate, and trapped atoms.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 12.712
Times cited: 24
DOI: 10.1021/ACS.NANOLETT.1C02470
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“Buckled circular monolayer graphene : a graphene nano-bowl”. Neek-Amal M, Peeters FM, Journal of physics : condensed matter 23, 045002 (2011). http://doi.org/10.1088/0953-8984/23/4/045002
Abstract: We investigate the stability of circular monolayer graphene subjected to a radial load using non-equilibrium molecular dynamics simulations. When monolayer graphene is radially stressed, after some small circular strain (~0.4%) it buckles and bends into a new bowl-like shape. Young's modulus is calculated from the linear relation between stress and strain before the buckling threshold, which is in agreement with experimental results. The prediction of elasticity theory for the buckling threshold of a radially stressed plate is presented and its results are compared to the one of our atomistic simulation. The Jarzynski equality is used to estimate the difference between the free energy of the non-compressed states and the buckled states. From a calculation of the free energy we obtain the optimum radius for which the system feels the minimum boundary stress.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.649
Times cited: 27
DOI: 10.1088/0953-8984/23/4/045002
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“Two-dimensional graphitic carbon nitrides: strain-tunable ferromagnetic ordering”. Bafekry A, Neek-Amal M, Peeters FM, Physical Review B 101, 165407 (2020). http://doi.org/10.1103/PHYSREVB.101.165407
Abstract: Using first-principle calculations, we systematically study strain tuning of the electronic properties of two- dimensional graphitic carbon nitride nanosheets with empirical formula CnNm. We found the following: (i) the ferromagnetic ordered state in the metal-free systems (n, m) = (4,3), (10,9), and (14,12) remains stable in the presence of strain of about 6%. However, the system (9,7) loses its ferromagnetic ordering when increasing strain. This is due to the presence of topological defects in the (9,7) system, which eliminates the asymmetry between spin up and spin down of the p(z) orbitals when strain is applied. (ii) By applying uniaxial strain, a band gap opens in systems which are initially gapless. (iii) In semiconducting systems which have an initial gap of about 1 eV, the band gap is closed with applying uniaxial strain.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.7
Times cited: 27
DOI: 10.1103/PHYSREVB.101.165407
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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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“Thermomechanical properties of graphene : valence force field model approach”. Lajevardipour A, Neek-Amal M, Peeters FM, Journal of physics : condensed matter 24, 175303 (2012). http://doi.org/10.1088/0953-8984/24/17/175303
Abstract: Using the valence force field model of Perebeinos and Tersoff (2009 Phys. Rev. B 79 241409(R)), different energy modes of suspended graphene subjected to tensile or compressive strain are studied. By carrying out Monte Carlo simulations it is found that: (i) only for small strains (vertical bar epsilon vertical bar (sic) 0.02) is the total energy symmetrical in the strain, while it behaves completely differently beyond this threshold; (ii) the important energy contributions in stretching experiments are stretching, angle bending, an out-of-plane term, and a term that provides repulsion against pi-pi misalignment; (iii) in compressing experiments the two latter terms increase rapidly, and beyond the buckling transition stretching and bending energies are found to be constant; (iv) from stretching-compressing simulations we calculated the Young's modulus at room temperature 350 +/- 3.15 N m(-1), which is in good agreement with experimental results (340 +/- 50 N m(-1)) and with ab initio results (322-353) N m(-1); (v) molar heat capacity is estimated to be 24.64 J mol(-1) K-1 which is comparable with the Dulong-Petit value, i. e. 24.94 J mol(-1) K-1, and is almost independent of the strain; (vi) nonlinear scaling properties are obtained from height-height correlations at finite temperature; (vii) the used valence force field model results in a temperature independent bending modulus for graphene, and (viii) the Gruneisen parameter is estimated to be 0.64.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.649
Times cited: 29
DOI: 10.1088/0953-8984/24/17/175303
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“Electronic properties of graphene nano-flakes : energy gap, permanent dipole, termination effect, and Raman spectroscopy”. Singh SK, Neek-Amal M, Peeters FM, The journal of chemical physics 140, 074304 (2014). http://doi.org/10.1063/1.4865414
Abstract: The electronic properties of graphene nano-flakes (GNFs) with different edge passivation are investigated by using density functional theory. Passivation with F and H atoms is considered: C-Nc X-Nx (X = F or H). We studied GNFs with 10 < N-c < 56 and limit ourselves to the lowest energy configurations. We found that: (i) the energy difference Delta between the highest occupied molecular orbital and the lowest unoccupied molecular orbital decreases with N-c, (ii) topological defects (pentagon and heptagon) break the symmetry of the GNFs and enhance the electric polarization, (iii) the mutual interaction of bilayer GNFs can be understood by dipole-dipole interaction which were found sensitive to the relative orientation of the GNFs, (iv) the permanent dipoles depend on the edge terminated atom, while the energy gap is independent of it, and (v) the presence of heptagon and pentagon defects in the GNFs results in the largest difference between the energy of the spin-up and spin-down electrons which is larger for the H-passivated GNFs as compared to F-passivated GNFs. Our study shows clearly the effect of geometry, size, termination, and bilayer on the electronic properties of small GNFs. This study reveals important features of graphene nano-flakes which can be detected using Raman spectroscopy. (C) 2014 AIP Publishing LLC.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.965
Times cited: 30
DOI: 10.1063/1.4865414
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“Strain-engineered graphene through a nanostructured substrate : 2 : pseudomagnetic fields”. Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 85, 195446 (2012). http://doi.org/10.1103/PhysRevB.85.195446
Abstract: The strain-induced pseudomagnetic field in supported graphene deposited on top of a nanostructured substrate is investigated by using atomistic simulations. A step, an elongated trench, a one-dimensional barrier, a spherical bubble, a Gaussian bump, and a Gaussian depression are considered as support structures for graphene. From the obtained optimum configurations we found very strong induced pseudomagnetic fields which can reach up to similar to 1000 T due to the strain-induced deformations in the supported graphene. Different magnetic confinements with controllable geometries are found by tuning the pattern of the substrate. The resulting induced magnetic fields for graphene on top of a step, barrier, and trench are calculated. In contrast to the step and trench the middle part of graphene on top of a barrier has zero pseudomagnetic field. This study provides a theoretical background for designing magnetic structures in graphene by nanostructuring substrates. We found that altering the radial symmetry of the deformation changes the sixfold symmetry of the induced pseudomagnetic field.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 31
DOI: 10.1103/PhysRevB.85.195446
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“Electric-field-induced structural changes in water confined between two graphene layers”. Fernandez MS, Peeters FM, Neek-Amal M, Physical review B 94, 045436 (2016). http://doi.org/10.1103/PHYSREVB.94.045436
Abstract: An external electric field changes the physical properties of polar liquids due to the reorientation of their permanent dipoles. Using molecular dynamics simulations, we predict that an in-plane electric field applied parallel to the channel polarizes water molecules which are confined between two graphene layers, resulting in distinct ferroelectricity and electrical hysteresis. We found that electric fields alter the in-plane order of the hydrogen bonds: Reversing the electric field does not restore the system to the nonpolar initial state, instead a residual dipole moment remains in the system. The square-rhombic structure of 2D ice is transformed into two rhombic-rhombic structures. Our study provides insights into the ferroelectric state of water when confined in nanochannels and shows how this can be tuned by an electric field.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 31
DOI: 10.1103/PHYSREVB.94.045436
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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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“Thermal mirror buckling in freestanding graphene locally controlled by scanning tunnelling microscopy”. Neek-Amal M, Xu P, Schoelz JK, Ackerman ML, Barber SD, Thibado PM, Sadeghi A, Peeters FM, Nature communications 5, 4962 (2014). http://doi.org/10.1038/ncomms5962
Abstract: Knowledge of and control over the curvature of ripples in freestanding graphene are desirable for fabricating and designing flexible electronic devices, and recent progress in these pursuits has been achieved using several advanced techniques such as scanning tunnelling microscopy. The electrostatic forces induced through a bias voltage (or gate voltage) were used to manipulate the interaction of freestanding graphene with a tip (substrate). Such forces can cause large movements and sudden changes in curvature through mirror buckling. Here we explore an alternative mechanism, thermal load, to control the curvature of graphene. We demonstrate thermal mirror buckling of graphene by scanning tunnelling microscopy and large-scale molecular dynamic simulations. The negative thermal expansion coefficient of graphene is an essential ingredient in explaining the observed effects. This new control mechanism represents a fundamental advance in understanding the influence of temperature gradients on the dynamics of freestanding graphene and future applications with electro-thermal-mechanical nanodevices.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 12.124
Times cited: 36
DOI: 10.1038/ncomms5962
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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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“Self-organized platinum nanoparticles on freestanding graphene”. Xu P, Dong L, Neek-Amal M, Ackerman ML, Yu J, Barber SD, Schoelz JK, Qi D, Xu F, Thibado PM, Peeters FM;, ACS nano 8, 2697 (2014). http://doi.org/10.1021/nn406394f
Abstract: Freestanding graphene membranes were successfully functionalized with platinum nanoparticles (Pt NPs). High-resolution transmission electron microscopy revealed a homogeneous distribution of single-crystal Pt NPs that tend to exhibit a preferred orientation. Unexpectedly, the NPs were also found to be partially exposed to the vacuum with the top Pt surface raised above the graphene substrate, as deduced from atomic-scale scanning tunneling microscopy images and detailed molecular dynamics simulations. Local strain accumulation during the growth process is thought to be the origin of the NP self-organization. These findings are expected to shape future approaches in developing Pt NP catalysts for fuel cells as well as NP-functionalized graphene-based high-performance electronics.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 13.942
Times cited: 38
DOI: 10.1021/nn406394f
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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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“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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“Induced polarization and electronic properties of carbon-doped boron nitride nanoribbons”. Beheshtian J, Sadeghi A, Neek-Amal M, Michel KH, Peeters FM, Physical review : B : condensed matter and materials physics 86, 195433 (2012). http://doi.org/10.1103/PhysRevB.86.195433
Abstract: The electronic properties of boron nitride nanoribbons (BNNRs) doped with a line of carbon atoms are investigated using density functional calculations. By replacing a line of alternating B and N atoms with carbons, three different configurations are possible depending on the type of the atoms which bond to the carbons. We found very different electronic properties for these configurations: (i) the NCB arrangement is strongly polarized with a large dipole moment having an unexpected direction, (ii) the BCB and NCN arrangements are nonpolar with zero dipole moment, (iii) the doping by a carbon line reduces the band gap regardless of the local arrangement of the borons and the nitrogens around the carbon line, and (iv) the polarization and energy gap of the carbon-doped BNNRs can be tuned by an electric field applied parallel to the carbon line. Similar effects were found when either an armchair or zigzag line of carbon was introduced.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 41
DOI: 10.1103/PhysRevB.86.195433
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“Lattice thermal properties of graphane : thermal contraction, roughness, and heat capacity”. Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 83, 235437 (2011). http://doi.org/10.1103/PhysRevB.83.235437
Abstract: Using atomistic simulations, we determine the roughness and the thermal properties of a suspended graphane sheet. As compared to graphene, we found that (i) hydrogenated graphene has a larger thermal contraction, (ii) the roughness exponent at room temperature is smaller, i.e., ≃ 1.0 versus ≃ 1.2 for graphene, (iii) the wavelengths of the induced ripples in graphane cover a wide range corresponding to length scales in the range 30125 Å at room temperature, and (iv) the heat capacity of graphane is estimated to be 29.32±0.23 J/mol K, which is 14.8% larger than that for graphene, i.e., 24.98±0.14 J/mol K. Above 1500 K, we found that graphane buckles when its edges are supported in the x-y plane.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 42
DOI: 10.1103/PhysRevB.83.235437
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“Defected graphene nanoribbons under axial compression”. Neek-Amal M, Peeters FM, Applied physics letters 97, 153118 (2010). http://doi.org/10.1063/1.3496467
Abstract: The buckling of defected rectangular graphene nanoribbons when subjected to axial stress with supported boundary conditions is investigated using atomistic simulations. The buckling strain and mechanical stiffness of monolayer graphene decrease with the percentage of randomly distributed vacancies. The elasticity to plasticity transition in the stress-strain curve, at low percentage of vacancies, are found to be almost equal to the buckling strain thresholds and they decrease with increasing percentage of vacancies.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.411
Times cited: 43
DOI: 10.1063/1.3496467
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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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“Linear reduction of stiffness and vibration frequencies in defected circular monolayer graphene”. Neek-Amal M, Peeters FM, Physical review : B : condensed matter and materials physics 81, 11 (2010). http://doi.org/10.1103/PhysRevB.81.235437
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 44
DOI: 10.1103/PhysRevB.81.235437
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“Dependence of the shape of graphene nanobubbles on trapped substance”. Ghorbanfekr-Kalashami H, Vasu KS, Nair RR, Peeters FM, Neek-Amal M, Nature communications 8, 15844 (2017). http://doi.org/10.1038/ncomms15844
Abstract: Van der Waals (vdW) interaction between two-dimensional crystals (2D) can trap substances in high pressurized (of order 1 GPa) on nanobubbles. Increasing the adhesion between the 2D crystals further enhances the pressure and can lead to a phase transition of the trapped material. We found that the shape of the nanobubble can depend critically on the properties of the trapped substance. In the absence of any residual strain in the top 2D crystal, flat nanobubbles can be formed by trapped long hydrocarbons (that is, hexadecane). For large nanobubbles with radius 130 nm, our atomic force microscopy measurements show nanobubbles filled with hydrocarbons (water) have a cylindrical symmetry (asymmetric) shape which is in good agreement with our molecular dynamics simulations. This study provides insights into the effects of the specific material and the vdW pressure on the microscopic details of graphene bubbles.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 12.124
Times cited: 44
DOI: 10.1038/ncomms15844
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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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“Thermal rippling behavior of graphane”. Costamagna S, Neek-Amal M, Los JH, Peeters FM, Physical review : B : condensed matter and materials physics 86, 041408 (2012). http://doi.org/10.1103/PhysRevB.86.041408
Abstract: Thermal fluctuations of single layer hydrogenated graphene (graphane) are investigated using large scale atomistic simulations. By analyzing the mean square value of the height fluctuations < h(2)> and the height-height correlation function H(q) for different system sizes and temperatures, we show that hydrogenated graphene is an unrippled system in contrast to graphene. The height fluctuations are bounded, which is confirmed by a H(q) tending to a constant in the long wavelength limit instead of showing the characteristic scaling law q(4-eta)(eta similar or equal to 0.85) predicted by membrane theory. This unexpected behavior persists up to temperatures of at least 900 K and is a consequence of the fact that in graphane the thermal energy can be accommodated by in-plane bending modes, i.e., modes involving C-C-C bond angles in the buckled carbon layer, instead of leading to significant out-of-plane fluctuations that occur in graphene.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 46
DOI: 10.1103/PhysRevB.86.041408
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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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