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Interpolation of Atomically Thin Hexagonal Boron Nitride and Graphene: Electronic Structure and Thermodynamic Stability in Terms of All-Carbon Conjugated Paths and Aromatic Hexagons
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 20, 10264-10271 p.Article in journal (Refereed) Published
Abstract [en]

Two-dimensional hexagonal composite materials (BN)(n)(C-2)(m) (n, m = 1, 2,...), which all are isoelectronic with graphene and hexagonal boron nitride (h-BN), have been studied by density functional theory (DFT) with a focus on the relative energies of different material isomers and their band gaps. The well-established chemical concepts of conjugation and aromaticity were exploited to deduce a rationale for identifying the thermodynamically most stable isomer of the specific composites studied. We find that (BN)(n)(C-2)(m) materials will not adopt structures in which the B, C, and N atoms are finely dispersed in the 2D sheet. Instead, the C atoms and C-C bonds, which provide for improved conjugation when compared to B-N bonds, gather and form all-carbon hexagons and paths; that is, the (BN)(n)(C-2)(m) materials prefer nanostructured distributions. Importantly, there are several isomers of similarly low relative energy for each (BN)(n)(C-2)(m) composite type, but the band gaps for these nearly isoenergetic isomers differ by up to 1.0 eV. This feature in the band gap variation of the most stable few isomers is found for each of the four composites studied and at two different DFT levels. Consequently, the formation of a distinct (BN)(n)(C-2)(m) material isomer with a precise (small) band gap will likely be nontrivial. Therefore, one likely has to invoke nonstandard preparation techniques that exploit nanopatterned h-BN or graphene with voids that can be filled with the complementary all-carbon or boron nitride segments.

Place, publisher, year, edition, pages
2011. Vol. 115, no 20, 10264-10271 p.
National Category
Physical Sciences Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-154600DOI: 10.1021/jp2016616ISI: 000290652200055OAI: oai:DiVA.org:uu-154600DiVA: diva2:421571
Available from: 2011-06-09 Created: 2011-06-08 Last updated: 2017-12-11Bibliographically approved
In thesis
1. First Principles Studies of Functional Materials Based on Graphene and Organometallics
Open this publication in new window or tab >>First Principles Studies of Functional Materials Based on Graphene and Organometallics
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Graphene is foreseen to be the basis of future electronics owing to its ultra thin structure, extremely high charge carrier mobility,  high thermal conductivity etc., which are expected to overcome the size limitation and heat dissipation problem in silicon based transistors. But these great prospects are hindered by the metallic nature of pristine graphene even at charge neutrality point, which allows to flow current even when a transistor is switched off. A part  of the thesis is dedicated to invoke electronic band gaps in graphene to overcome this problem. The concept of quantum confinement has been employed to tune the band gaps in graphene by  dimensional confinement along with the functionalization of the edges of these confined nanostructures. Thermodynamic stability of the functionalized zigzag edges with hydrogen, fluorine and reconstructed edges has been presented in the thesis. Keeping an eye towards the same goal of band gap opening,  a different route has been considered by admixing insulating hexagonal boron nitride (h-BN) with semimetal graphene. The idea has been implemented in two  dimensional h-BN-graphene composites and three dimensional stacked heterostructures. The study reveals the possibility of tuning band gaps by controlling the admixture. Occurrence of defects in graphene has significant effect on its electronic properties. By random insertion of defects, amorphous graphene is studied, revealing a semi-metal to a metal transition.

The field of molecular electronics and spintronics aims towards device realization at the molecular scale. In this thesis, different aspects of magnetic bistability in organometallic molecules have been explored in order to design  practical spintronics devices. Manipulation of spin states in organometallic molecules, specifically metal porphyrin molecules, is achieved by controlling surface–molecule interaction. It has been shown that by strain engineering in defected graphene, the magnetic state of adsorbed molecules can be changed. The spin crossover between different spin states can also be achieved by chemisorption on magnetic surfaces. A significant part of the thesis demonstrates that the surface-molecule interaction not only changes the spin state of the molecule, but allows to manipulate magnetic anisotropies and spin dipole moments via modified ligand fields. Finally, in collaboration with experimentalists, a practical realization of switching surface–molecule magnetic interactions by external magnetic fields is demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 90 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1120
Keyword
Graphene, Magnetism, Organometallics, Density functional theory, Electron correlation, Spin switching, Nanoribbons, Exchange interaction, Edge functionalization, Band gap
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-217175 (URN)978-91-554-8869-7 (ISBN)
Public defence
2014-03-14, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-02-21 Created: 2014-01-30 Last updated: 2014-04-29

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Bhandary, SumantaSanyal, BiplabOttosson, Henrik

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