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Publications (10 of 16) Show all publications
Haldar, S., Amorim, R. G., Sanyal, B., Scheicher, R. . & Rocha, A. R. (2016). Energetic stability, STM fingerprints and electronic transport properties of defects in graphene and silicene. RSC Advances, 6(8), 6702-6708
Open this publication in new window or tab >>Energetic stability, STM fingerprints and electronic transport properties of defects in graphene and silicene
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2016 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 8, p. 6702-6708Article in journal (Refereed) Published
Abstract [en]

Novel two-dimensional materials such as graphene and silicene have been heralded as possibly revolutionary in future nanoelectronics. High mobilities, and in the case of silicene, its seemingly natural integration with current electronics could make them the materials of next-generation devices. Defects in these systems, however, are unavoidable particularly in large-scale fabrication. Here we combine density functional theory and the non-equilibrium Green’s function method to simulate the structural, electronic and transport properties of different defects in graphene and silicene. We show that defects are much more easily formed in silicene, compared to graphene. We also show that, although qualitatively similar, the effects of different defects occur closer to the Dirac point in silicene, and identifying them using scanning tunneling microscopy is more difficult particularly due to buckling. This could be overcome by performing direct source/drain measurements. Finally we show that the presence of defects leads to an increase in local current from which it follows that they not only contribute to scattering, but are also a source of heating.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-271340 (URN)10.1039/C5RA23052G (DOI)000368858000083 ()
Funder
Carl Tryggers foundation Swedish Research Council, 621-2009-3628Knut and Alice Wallenberg Foundation
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2017-12-01Bibliographically approved
Brumboiu, I. E., Haldar, S., Luder, J., Eriksson, O., Herper, H. C., Brena, B. & Sanyal, B. (2016). Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines. Journal of Chemical Theory and Computation, 12(4), 1772-1785
Open this publication in new window or tab >>Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines
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2016 (English)In: Journal of Chemical Theory and Computation, Vol. 12, no 4, p. 1772-1785Article in journal (Refereed) Published
Abstract [en]

There exists an extensive literature on the electronic structure of transition-metal phthalocyanines (TMPcs), either as single molecules or adsorbed on surfaces, where explicit intra-atomic Coulomb interactions of the strongly correlated orbitals are included in the form of a Hubbard U term. The choice of U is, to a large extent, based solely on previous values reported in the literature for similar systems. Here, we provide a systematic analysis of the influence of electron correlation on the electronic structure and magnetism of several TMPcs (MnPc, FePc, CoPc, NiPc, and CuPc). By comparing calculated results to valence-band photoelectron spectroscopy measurements, and by determining the Hubbard term from linear response, we show that the choice of U is not as straightforward and can be different for each different TMPc. This, in turn, highlights the importance of individually estimating the value of U for each system before performing any further analysis and shows how this value can influence the final results.

National Category
Physical Sciences Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-281097 (URN)10.1021/acs.jctc.6b00091 (DOI)000374196400034 ()26925803 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-03-17 Created: 2016-03-17 Last updated: 2017-01-25Bibliographically approved
Li, H., Daukiya, L., Haldar, S., Lindblad, A., Sanyal, B., Eriksson, O., . . . Leifer, K. (2016). Site-selective local fluorination of graphene induced by focused ion beam irradiation. Scientific Reports, 6, Article ID 19719.
Open this publication in new window or tab >>Site-selective local fluorination of graphene induced by focused ion beam irradiation
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 19719Article in journal (Refereed) Published
Abstract [en]

The functionalization of graphene remains an important challenge for numerous applications expected by this fascinating material. To keep advantageous properties of graphene after modification or functionalization of its structure, local approaches are a promising road. A novel technique is reported here that allows precise site-selective fluorination of graphene. The basic idea of this approach consists in the local radicalization of graphene by focused ion beam (FIB) irradiation and simultaneous introduction of XeF2 gas. A systematic series of experiments were carried out to outline the relation between inserted defect creation and the fluorination process. Based on a subsequent X-ray photoelectron spectroscopy (XPS) analysis, a 6-fold increase of the fluorine concentration on graphene under simultaneous irradiation was observed when compared to fluorination under normal conditions. The fluorine atoms are predominately localized at the defects as indicated from scanning tunneling microscopy (STM). The experimental findings are confirmed by density functional theory which predicts a strong increase of the binding energy of fluorine atoms when bound to the defect sites. The developed technique allows for local fluorination of graphene without using resists and has potential to be a general enabler of site-selective functionalization of graphene using a wide range of gases.

Keywords
graphene, site-selective, fluorination, focused ion beam
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-268033 (URN)10.1038/srep19719 (DOI)000368926300001 ()26822900 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2017-12-01Bibliographically approved
Li, H., Daukiya, L., Haldar, S., Lindblad, A., Sanyal, B., Eriksson, O., . . . Leifer, K. (2015). Nanoscale structural and electronic modifications of graphene. In: : . Paper presented at Functional Materials for Today and Tomorrow, Kolkata, India.
Open this publication in new window or tab >>Nanoscale structural and electronic modifications of graphene
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2015 (English)Conference paper, Oral presentation with published abstract (Other academic)
National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-285514 (URN)
Conference
Functional Materials for Today and Tomorrow, Kolkata, India
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2017-01-25Bibliographically approved
Haldar, S., Vovusha, H., Yadav, M. K., Eriksson, O. & Sanyal, B. (2015). Systematic study of structural, electronic, and optical properties of atomic-scale defects in the two-dimensional transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te). Physical Review B. Condensed Matter and Materials Physics, 92(23), Article ID 235408.
Open this publication in new window or tab >>Systematic study of structural, electronic, and optical properties of atomic-scale defects in the two-dimensional transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te)
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 23, article id 235408Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-269013 (URN)10.1103/PhysRevB.92.235408 (DOI)000366086300009 ()
Funder
Knut and Alice Wallenberg FoundationCarl Tryggers foundation Swedish Research Council
Available from: 2015-12-12 Created: 2015-12-12 Last updated: 2017-12-01
Chowdhury, S., Baidya, S., Nafday, D., Haldar, S., Kabir, M., Sanyal, B., . . . Mookerjee, A. (2014). A real-space study of random extended defects in solids: Application to disordered Stone–Wales defects in graphene. Physica. E, Low-Dimensional systems and nanostructures, 61(0), 191-197
Open this publication in new window or tab >>A real-space study of random extended defects in solids: Application to disordered Stone–Wales defects in graphene
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2014 (English)In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 61, no 0, p. 191-197Article in journal (Refereed) Published
Abstract [en]

Abstract We propose here a first-principles, parameter free, real space method for the study of disordered extended defects in solids. We shall illustrate the power of the technique with an application to graphene sheets with randomly placed Stone–Wales defects and shall examine the signature of such random defects on the density of states as a function of their concentration. The technique is general enough to be applied to a whole class of systems with lattice translational symmetry broken not only locally but by extended defects and defect clusters. The real space approach will allow us to distinguish signatures of specific defects and defect clusters.

Keywords
Extended disordered defect, Real space recursion method
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-225553 (URN)10.1016/j.physe.2014.04.002 (DOI)000340626600029 ()
Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2017-12-05Bibliographically approved
Haldar, S., Pujari, B. S., Bhandary, S., Cossu, F., Eriksson, O., Kanhere, D. G. & Sanyal, B. (2014). Fen (n=1–6) clusters chemisorbed on vacancy defects in graphene: Stability, spin-dipole moment, and magnetic anisotropy. Physical Review B. Condensed Matter and Materials Physics, 89, 205411
Open this publication in new window or tab >>Fen (n=1–6) clusters chemisorbed on vacancy defects in graphene: Stability, spin-dipole moment, and magnetic anisotropy
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, p. 205411-Article in journal (Refereed) Published
Abstract [en]

In this work, we have studied the chemical and magnetic interactions of Fen (n = 1–6) clusters with vacancy defects (monovacancy to correlated vacancies with six missing C atoms) in a graphene sheet by ab initio density functional calculations combined with Hubbard U corrections for correlated Fe-d electrons. It is found that the vacancy formation energies are lowered in the presence of Fe, indicating an easier destruction of the graphene sheet. Due to strong chemical interactions between Fe clusters and vacancies, a complex distribution of magnetic moments appear on the distorted Fe clusters which results in reduced averaged magnetic moments compared to the free clusters. In addition to that, we have calculated spin-dipole moments and magnetic anisotropy energies. The calculated spin-dipole moments arising from anisotropic spin density distributions vary between positive and negative values, yielding increased or decreased effective moments. Depending on the cluster geometry, the easy axis of magnetization of the Fe clusters shows in-plane or out-of-plane behavior.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-224610 (URN)10.1103/PhysRevB.89.205411 (DOI)000341351300003 ()
Funder
Carl Tryggers foundation EU, European Research Council
Available from: 2014-05-14 Created: 2014-05-14 Last updated: 2017-12-05Bibliographically approved
Schmitz, D., Schmitz-Antoniak, C., Warland, A., Darbandi, M., Haldar, S., Bhandary, S., . . . Wende, H. (2014). The dipole moment of the spin density as a local indicator for phase transitions. Scientific Reports, 4, 5760
Open this publication in new window or tab >>The dipole moment of the spin density as a local indicator for phase transitions
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2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 5760-Article in journal (Refereed) Published
Abstract [en]

The intra-atomic magnetic dipole moment - frequently called < T-z > term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe2+ and Fe3+ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-229027 (URN)10.1038/srep05760 (DOI)000339157000003 ()
Available from: 2014-07-26 Created: 2014-07-26 Last updated: 2017-12-05Bibliographically approved
Haldar, S., Srivastava, P., Eriksson, O., Sen, P. & Sanyal, B. (2013). Designing Fe Nanostructures at Graphene/h-BN Interfaces. The Journal of Physical Chemistry C, 117(42), 21763-21771
Open this publication in new window or tab >>Designing Fe Nanostructures at Graphene/h-BN Interfaces
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 42, p. 21763-21771Article in journal (Refereed) Published
Abstract [en]

Tailor-made magnetic nanostructures offer a variety of functionalities useful for technological applications. In this work, we explore the possibilities of realizing Fe nanostructuresat the interfaces of 2D graphene and h-BN by ab initio density functional calculations. With the aid of ab initio Born-Oppenheimer molecular dynamics simulations and diffusion barriers calculated by the nudged elastic band method, we find that (i) diffusion barriers of Fe on BN are much smaller than those on graphene, (ii) the Fe adatoms form clusters within a short time interval (similar to 2.1 ps), and (iii) Fe clusters diffuse easily across the C-N interface but become immobile at the C-B interface. The calculated magnetic exchange coupling between Fe clustersat C-B interfaces varies nonmonotonically as a function of the width of BN separating thegraphene parts. One may envisage design of magnetic nanostnictures at the C-B interface of 2Dgraphene/h-BN hybrids to realize interesting applications related to spintronics.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-208999 (URN)10.1021/jp405346r (DOI)000326260000016 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2013-10-14 Created: 2013-10-14 Last updated: 2017-12-06Bibliographically approved
Haldar, S., Bhandary, S., Chandrachud, P., Pujari, B. S., Katsnelson, M. I., Eriksson, O., . . . Sanyal, B. (2012). Ab Initio Studies on the Hydrogenation at the Edgesand Bulk of Graphene. In: Ottaviano, Luca; Morandi, Vittorio (Ed.), GraphITA 2011 (pp. 203-208). Springer
Open this publication in new window or tab >>Ab Initio Studies on the Hydrogenation at the Edgesand Bulk of Graphene
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2012 (English)In: GraphITA 2011 / [ed] Ottaviano, Luca; Morandi, Vittorio, Springer, 2012, p. 203-208Chapter in book (Refereed)
Place, publisher, year, edition, pages
Springer, 2012
Series
Carbon Nanostructures, ISSN 2191-3013
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-171941 (URN)10.1007/978-3-642-20644-3 (DOI)978-3-642-20643-6 (ISBN)978-3-642-20644-3 (ISBN)
Available from: 2012-03-29 Created: 2012-03-29 Last updated: 2017-01-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3161-4326

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