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Functional Nanostructures for Gas Sensors
Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-113763ISBN: 978-91-7519-133-1 (print)OAI: oai:DiVA.org:liu-113763DiVA: diva2:784586
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
List of papers
1. Single-step synthesis process of Ti3SiC2 ohmic contacts on 4H-SiC by sputter-deposition of Ti
Open this publication in new window or tab >>Single-step synthesis process of Ti3SiC2 ohmic contacts on 4H-SiC by sputter-deposition of Ti
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2015 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 99, 53-56 p.Article in journal (Refereed) Published
Abstract [en]

We report a single-step procedure for growth of ohmic Ti3SiC2 on 4H-SiC by sputter-deposition of Ti at 960 °C, based on the Ti–SiC solid-state reaction during deposition. X-ray diffraction and electron microscopy show the growth of interfacial Ti3SiC2. The as-deposited contacts are ohmic, in contrast to multistep processes with deposition followed by rapid thermal annealing. This procedure also offers the possibility of direct synthesis of oxygen-barrier capping layers before exposure to air, potentially improving contact stability in high-temperature and high-power devices.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Silicon carbide, MAX phase, Physical vapor deposition, High temperature
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113760 (URN)10.1016/j.scriptamat.2014.11.025 (DOI)000348881100014 ()
Note

We acknowledge the support from the VINN Excellence Center in research and innovation on Functional Nanoscale Materials (FunMat) by the Swedish Governmental Agency for Innovation Systems. P.E and J.L. also acknowledge support from the Swedish Foundation for Strategic Research through the Future Research Leaders 5 program and the Synergy Grant FUNCASE, Functional Carbides and Advanced Surface Engineering. In addition, we thank Dr. Hans Hogberg, Dr. Arni Sigurdur Ingason and Dr. Fredrik Eriksson for discussions and help with experiments.

Available from: 2015-01-30 Created: 2015-01-30 Last updated: 2017-12-05Bibliographically approved
2. Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Open this publication in new window or tab >>Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
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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.

Keyword
Cone-point, MAX phase, MXene, Dirac fermion, Spin-orbit coupling
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113761 (URN)10.1103/PhysRevB.92.155142 (DOI)000363512700002 ()
Available from: 2015-05-01 Created: 2015-01-30 Last updated: 2017-12-05Bibliographically approved
3. Monolayer iron oxide grown on porous platinum sensing layers of carbon monoxide sensors
Open this publication in new window or tab >>Monolayer iron oxide grown on porous platinum sensing layers of carbon monoxide sensors
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Mono-layer iron oxide has been deposited through e-beam evaporation on a silica supported poly-crystalline platinum (Pt) model catalyst and its CO oxidation characteristics obtained from mass spectrometry measurements under various CO and O2 concentrations (ranging from 100 to 900 ppm and 3 to 7 %, respectively) as well as at different temperatures (ranging from 130 to 220 °C) and compared to the CO oxidation on corresponding non-coated Pt samples. Fabricating the model system as a Metal Oxide Semiconductor (MOS) structure from 4H-SiC with a top layer of SiO2 (as the support material) and a thin, discontinuous polycrystalline Pt film as the metal (the active catalyst material) also provided the possibility to investigate whether changes in catalyst surface conditions could be electronically monitored through the changes in capacitance they induce across the MOS structure.

A low-temperature shift in the activity to CO oxidation for the iron oxide modified compared to bare Pt catalysts similar to what has previously been reported on single-crystalline Pt was found also for the near-realistic MOS model catalyst. This low-temperature shift was furthermore reflected in the electrical measurements, strongly indicating a correlation between the MOS capacitance and the CO oxidation characteristics, both in the case of iron oxide coated and non-coated Pt samples. By monitoring the MOS capacitance during more than 200 hours of continuous operation and analyzing the iron oxide coated samples by photo electron spectroscopy it could also be concluded that the iron oxide coated model catalyst seemingly retains its CO oxidation characteristics and chemical/compositional integrity over time. These findings might not only point to the applicability of iron oxide modified Pt in practical applications but may also open up new possibilities regarding the utilization of MOS model systems in studying and understanding as well as tailor CO oxidation (and other) catalysts and/or gas sensors for specific applications.

Keyword
Silicon carbide, MAX phase, Physical vapor deposition, High temperature
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113762 (URN)
Available from: 2015-01-30 Created: 2015-01-30 Last updated: 2015-01-30Bibliographically approved

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