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Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-1785-0864
Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2817-3574
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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 15Article in journal (Refereed) Published
Abstract [en]

We investigated the structural and electrical properties of 2D MXene sheets by means of firstprinciples density functional theory (DFT) calculations. To describe the Kohn-Sham states, plane wave basis set and projector augmented wave method (PAW) were used as implemented in the Vienna ab initio Simulation Package (VASP). We applied PBE parameterization of the generalized gradient approximation of the exchange and correlation energy functional to account for many-body effects of the interacting electron system. Convergent sampling of the Brillouin-zone was achieved by a Γ-centered 15×15×1 grid. In order to model a single sheet of MXene we ensured at least 30 Å vacuum between the periodically repeated sheets. For the structural optimization 1×10−3 eV/Å force criteria was used. The relativistic spin-orbit coupling effects were also included in our simulations regarding band structure and density of states.

Place, publisher, year, edition, pages
2015. Vol. 92, no 15
Keyword [en]
Cone-point, MAX phase, MXene, Dirac fermion, Spin-orbit coupling
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-113761DOI: 10.1103/PhysRevB.92.155142ISI: 000363512700002OAI: oai:DiVA.org:liu-113761DiVA: diva2:784567
Available from: 2015-05-01 Created: 2015-01-30 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Functional Nanostructures for Gas Sensors
Open this publication in new window or tab >>Functional Nanostructures for Gas Sensors
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This research focuses on three main topics within the aims of FUNMAT, which are:

  1. Ohmic contacts to high-temperature chemical gas sensors.
  2. Studies of catalytic monolayers on active gate metal in SiC-based gas sensors.
  3. Investigating potential sensing properties of the nanoscale material MXene.

Within the first research topic, we study the growth of Ohmic contacts to 4H-SiC for high temperature and corrosive environment applications, being a need in chemical gas sensors e.g. for automotive industry. For this purpose, common commercially-synthesized contacts are not suitable, due to either the presence of low-melting point elements or rapid oxidation. Improving the previously reported growth methods, designing durable oxygen-barrier capping layers, and synthesizing new contact-materials are our main focuses.

For the second research topic, we investigate the improvement of the sensing performance of platinum-based sensing layers in silicon carbide field-effect gas sensors, which have many industrial applications. This project started with modification of field-effect-based metal oxide semiconductor CO sensors by the synthesis of one monolayer iron oxide on the platinum sensing layers of the sensors. Monolayer metal oxides have been reported to enhance the catalytic properties of platinum which is a promising result to be used in improving the performance of gas sensors.

And finally, the third research topic covers studies of newly synthesized materials to be explored for any potential sensing property. Our focus is on metal carbide nano-sheets known as MXene phases and to study their  gas adsorption properties. Due to several uninvestigated features of newly synthesized materials, ab.initio. theoretical studies are of importance.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 52 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1705
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113763 (URN)978-91-7519-133-1 (ISBN)
Presentation
2015-02-20, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-01-30 Created: 2015-01-30 Last updated: 2015-01-30Bibliographically approved
2. Novel Layered and 2D Materials for Functionality Enhancement of Contacts and Gas Sensors
Open this publication in new window or tab >>Novel Layered and 2D Materials for Functionality Enhancement of Contacts and Gas Sensors
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chemical gas sensors are widely-used electronic devices for detecting or measuring the density levels of desired gas species. In this study, materials with established or potential applications for gas sensors are treated. For the case of high-temperature applications (≈ 600 °C), semiconductor-based gas sensors suffer from rapid oxidation of the metallic ohmic contacts, the same cause-of-failure as for the general case of high-temperature semiconductor electronics. 4H-SiC is an ideal semiconductor for high-temperature applications. Ti3SiC2 is a known ohmic contact to 4H-SiC with the known two-step synthesis process of post-annealing of pre-deposited Ti/Al multilayers or sputter-deposition of Ti3SiC2 films at > 900 °C. Here, sputter-deposition of Ti on 4H-SiC at > 900 °C is presented as a novel single-step method for the synthesis of Ti3SiC2 ohmic contacts, based on a concurrent reaction between sputter-deposited Ti and 4HSiC. Ti3SiC2, similar to any other known ohmic contact, degrade rapidly in high-temperature oxidizing ambient. To try to overcome this obstacle, noble metal diffusion into Ti3SiC2 has been s studied with the goal to retain ohmic properties of Ti3SiC2 and harnessing oxidation resistivity of noble metals. A novel exchange intercalation between Ti3SiC2 and Au is discovered which results in the almost complete exchange of Si with Au giving rise to novel Ti3AuC2 and Ti3Au2C2. Ti3IrC2 is also synthesized through exchange intercalation of Ir into Ti3Au2C2. All the aforementioned phases showed ohmic properties to 4H-SiC. This technique is also studied based on Ti2AlC and Ti3AlC2 resulting in the synthesis of novel Ti2Au2C and Ti3Au2C2, respectively. Using Ti3AuC2 and an Au/IrOx capping layer, an ohmic contact was manufactured, which maintained ohmic properties and showed no structural defects after 1000 h of aging at 600 °C air.

Ti3SiC2 is a member of a large family of materials known as Mn+1AXn phases. While exchange reactions of Si (or Al) planes in Ti3SiC2 (Ti2AlC and Ti3AlC2) is presented here, a world-wide research already exists on chemical removal of the same atomic planes from different Mn+1AXn phases and the synthesis of Mn+1Xn sheets known as MXenes. I performed a theoretical study regarding simulation of electronic and structural properties of more than120 different possible MXene phases. The results show that some MXene phases, when terminated by particular gas species, turn into Dirac materials. That is, they possess massless Dirac fermions with different properties compared to graphene such as higher number of Dirac points at the Fermi level, giant spin orbit splitting, and preserved 2D-type electronic properties by extending the dimensionality. The general substantial change of the electronic properties of MXenes under different gas adsorption configurations stands out and can thus be harnessed for sensing applications.

Growth of monolayer iron oxide on porous Pt sensing layers is another novel approach used in this study for applying the unique properties of 2D materials for gas sensors. A low temperature shift in CO oxidation characteristics is presented. The approach is similar to that previously reported using bulk single crystal Pt substrate, the latter being an unrealistic model for sensors and catalysts. Monolayer-coated Pt sensing layers were fabricated as the metal component of a metal oxide semiconductor (MOS) capacitor device, whereby the electrical response of the MOS device could be used to map out the catalytic properties of the sensing layer. The monolayer-coated Pt surface showed to be stable with retained improved catalytic properties for > 200 h. The MOS device measurements are here utilized as a handy method for in-situ monitoring of the surface chemical properties of the monolayer-coated Pt and the approach is highly functional for use and characterization of monolayer coatings of widely used sensingor catalytic layers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 55 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1784
National Category
Physical Sciences Materials Chemistry Condensed Matter Physics Inorganic Chemistry Other Chemical Engineering Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-131474 (URN)10.3384/diss.diva-131474 (DOI)9789176856994 (ISBN)
Public defence
2016-10-21, Plank, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2016-09-22Bibliographically approved
3. Development of theoretical approaches for post-silicon information processing
Open this publication in new window or tab >>Development of theoretical approaches for post-silicon information processing
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Despite knowing the fundamental equations in most of the physics research areas, still there is an unceasing need for theoretical method development, thanks to the more and more challenging problems addressed by the research community. The investigation of post-silicon, non-classical information processing is one of the new and rapidly developing areas that requires tremendous amount of theoretical support, new understanding, and accurate theoretical predictions. My thesis focuses on theoretical method development for solid-state quantum information processing, mainly in the field of point defect quantum bits (qubits) in silicon carbide (SiC) and diamond. Due to recent experimental breakthroughs in this field, there are diverse theoretical problems, ranging from functional development for accurate first principles description of point defects, through complete theoretical characterization of qubits, to the modeling and simulation of actual quantum information protocols, that are needed to be addressed. The included articles of this thesis cover the development of (i) hybrid-DFT+Vw approach for the first principles description of mixed correlated and uncorrelated systems, (ii) zero-field-splitting tensor calculation for solid-state quantum bit characterization, (iii) a comprehensive model for dynamic nuclear spin polarization of solid-state qubits in semiconductors, and (iv) group theoretical description of qubits and novel twodimensional materials for topologically protected states.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 74 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1792
National Category
Condensed Matter Physics Other Physics Topics Other Engineering and Technologies not elsewhere specified Computer Science Other Computer and Information Science
Identifiers
urn:nbn:se:liu:diva-131853 (URN)10.3384/diss.diva-131853 (DOI)9789176856826 (ISBN)
Public defence
2016-11-11, Plank, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2016-10-21Bibliographically approved

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