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Nanostructured materials for gas sensing applications
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis I have investigated the use of nanostructured films as sensing and contact layers for field effect gas sensors in order to achieve high sensitivity, selectivity, and long term stability of the devices in corrosive environments at elevated temperatures. Electrochemically synthesized Pd and Au nanoparticles deposited as sensing layers on capacitive field effect devices were found to give a significant response to NOx with small, or no responses to H2, NH3, and C3H6. Pt nanoparticles incorporated in a TiC matrix are catalytically active, but the agglomeration and migration of the Pt particles towards the substrate surface reduces the activity of the sensing layer. Magnetron sputtered epitaxial films from the Ti-Si-C and the Ti-Ge-C systems were grown on 4H-SiC substrates in order to explore their potential as high temperature stable ohmic contact materials to SiC based field effect gas sensors. Ti3SiC2 thin films deposited on 4H-SiC substrates were found to yield ohmic contacts to n-type SiC after a high temperature rapid thermal anneal at 950 ºC. Investigations on the growth mode of Ti3SiC2 thin films with varying Si content on 4H-SiC substrates showed the growth to be lateral step-flow with the propagation of steps with a height as small as half a unit cell. The amount of Si present during deposition leads to differences in surface faceting of the films and Si-supersaturation conditions gives growth of Ti3SiC2 films with the presence of TiSi2 crystallites. Current-voltage measurements of the as-deposited Ti3GeC2 films indicate that this material is also a promising candidate for achieving long term stable contact layers to 4H-SiC for operation at elevated temperatures in corrosive environments. Further investigations into the Ti-Ge-C system showed that the previously unreported solid solutions of (Ti,V)2GeC, (Ti,V)3GeC2 and (Ti,V)4GeC3 can be synthesized, and it was found that the growth of these films is affected by the nature of the substrate.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. , 61 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1377
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-69641ISBN: 9789173931403 (print)OAI: oai:DiVA.org:liu-69641DiVA: diva2:430396
Public defence
2011-09-09, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-07-08 Created: 2011-07-08 Last updated: 2017-12-14Bibliographically approved
List of papers
1. Au Nanoparticles as Gate Material for NOx Field Effect Capacitive Sensors
Open this publication in new window or tab >>Au Nanoparticles as Gate Material for NOx Field Effect Capacitive Sensors
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2008 (English)In: Sensor letters, ISSN 1546-198X (print) 1546-1971 (online), Vol. 6, no 4, 577-584 p.Article in journal (Refereed) Published
Abstract [en]

Gold nanoparticles (Au-NPs) are electrochemically synthesized in the presence of tetra-alkylammonium stabilizers and used as active element in Field Effect capacitive gas sensors. Before use, the sensing area is treated by a relatively mild annealing procedure aimed to partially remove the organic stabilizer without loosing the nano-structured character of the particles. Both pristine and annealed materials have been subjected to a spectroscopic and morphological characterization (by means of UV-Vis, XPS, TEM, SEM techniques). Preliminary results on the application of AuNPs as gate material for NO, sensing are reported. The sensor is able to detect NO, with appreciable selectivity and low response towards the other tested gases (C3H6, CO, H-2, NH3).

Keyword
Gold Nanoparticle, FET, XPS, Gas Sensor
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16140 (URN)10.1166/sl.2008.433 (DOI)
Available from: 2009-01-08 Created: 2009-01-07 Last updated: 2014-01-09
2. Electrochemically Synthesised Pd- and Au-nanoparticles as sensing layers in NOx-sensitive field effect devices
Open this publication in new window or tab >>Electrochemically Synthesised Pd- and Au-nanoparticles as sensing layers in NOx-sensitive field effect devices
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2008 (Swedish)In: Smart Sensors and Sensing Technology / [ed] Subhas Chandra Mukhopadhyay and Gourab Sen Gupta, Berlin, Heidelberg: Springer , 2008, 63-75 p.Conference paper, Published paper (Other academic)
Abstract [en]

An environmental pollutant of great concern is NOx (nitrogen monoxide and nitrogen dioxide). Here we report the utilisation of electrochemically synthesised gold and palladium nanoparticles as catalytically active gate material on gas sensitive field effect sensor devices. The synthesised nanoparticles have been characterised by TEM and XPS, and the morphology of the thermally treated nanostructured sensing layers has been investigated using SEM and XPS. Measurements on the gas response of the palladium as well as the gold nanoparticle sensors towards a number of analytes found in automotive gas exhausts were performed and their response patterns were compared. The initial gas response measurements show interesting sensing properties for both the gold and the palladium nanoparticle sensors towards NOx detection.

Place, publisher, year, edition, pages
Berlin, Heidelberg: Springer, 2008
Series
Lecture notes in Electrical Engineering, ISSN 1876-1100 ; 20
Keyword
NOx- sensor · gold · palladium · nanoparticle · field effect sensor
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44313 (URN)10.1007/978-3-540-79590-2_5 (DOI)76301 (Local ID)978-3-540-79589-6 (ISBN)978-3-540-79590-2 (ISBN)76301 (Archive number)76301 (OAI)
Conference
The 2nd International Conference on Sensing Technology, ICST 2007, November 26-28, Massey, New Zealand
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2016-06-13Bibliographically approved
3. Carbide and nanocomposite thin films in the Ti-Pt-C system
Open this publication in new window or tab >>Carbide and nanocomposite thin films in the Ti-Pt-C system
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2010 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 18, 5104-5109 p.Article in journal (Refereed) Published
Abstract [en]

Thin films in the Ti-Pt-C system were deposited by non-reactive, DC-magnetron sputtering. Samples were characterised using X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. A previously not reported metastable solid solution carbide, (Ti1-xPtx)C-y with a Pt/Ti ratio of up to 0.43 was observed. This solid solution phase was present both as single phase in polycrystalline samples, and together with amorphous carbon (a-C) in nanocomposite samples. Annealing of nanocomposite samples leads to the decomposition of the solid solution phase and the formation of a nc-TiCx/a-C/nc-Pt nanocomposite. Test sensors for automotive gas exhausts manufactured from such a three-phase material suffer from complete oxidation of the coating at 400 degrees C with no observed sensor activity.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
Solid solution carbide; Nanocomposite; Sputtering; Gas sensor; Annealing; Transmission electron microscopy; X-ray photoelectron spectroscopy; X-ray diffraction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58177 (URN)10.1016/j.tsf.2010.03.017 (DOI)000279659900013 ()
Note
Original Publication: Erik Lewin, Kristina Buchholt, Jun Lu, Lars Hultman, Anita Lloyd Spetz and Ulf Jansson, Carbide and nanocomposite thin films in the Ti-Pt-C system, 2010, Thin Solid Films, (518), 18, 5104-5109. http://dx.doi.org/10.1016/j.tsf.2010.03.017 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-08-11 Created: 2010-08-09 Last updated: 2017-12-12
4. Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide
Open this publication in new window or tab >>Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide
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2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 4, 042108- p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial Ti3SiC2 (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 degrees C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10(-4) Omega cm(2). Transmission electron microscopy shows that the interface between Ti3SiC2 and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing.

Place, publisher, year, edition, pages
American Institute of Physics, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67170 (URN)10.1063/1.3549198 (DOI)000286676600025 ()
Note

Original Publication: Kristina Buchholt, R Ghandi, M Domeij, C-M Zetterling, Jun Lu, Per Eklund, Lars Hultman and Anita Lloyd Spetz, Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide, 2011, APPLIED PHYSICS LETTERS, (98), 4, 042108. http://dx.doi.org/10.1063/1.3549198 Copyright: American Institute of Physics http://www.aip.org/

Available from: 2011-04-01 Created: 2011-04-01 Last updated: 2017-12-11Bibliographically approved
5. Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)
Open this publication in new window or tab >>Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)
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2012 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 343, no 1, 133-137 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial Ti3GeC2 thin films were deposited on 4 degrees off-cut 4H-SiC(0001) using magnetron sputtering from high purity Ti, C, and Ge targets. Scanning electron microscopy and helium ion microscopy show that the Ti3GeC2 films grow by lateral step-flow with {11 (2) over bar0} faceting on the SiC surface. Using elastic recoil detection analysis, atomic force microscopy, and X-Ray diffraction the films were found to be substoichiometric in Ge with the presence of small Ge particles at the surface of the film.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Surface structure, Atomic force microscopy, Helium ion microscopy, Physical vapor deposition processes, Titanium compound
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77103 (URN)10.1016/j.jcrysgro.2012.01.020 (DOI)000302422300023 ()
Note

Funding Agencies|VINN Excellence Center in Research and Innovation on Functional Nanoscale Materials (FunMat) by Swedish Governmental Agency for Innovation Systems (VINNOVA)||

The status of this article was previously Manuscript.

Available from: 2012-05-04 Created: 2012-05-04 Last updated: 2017-12-07
6. Step-flow growth of nanolaminate Ti3SiC2 epitaxial layers on 4H-SiC(0 0 0 1)
Open this publication in new window or tab >>Step-flow growth of nanolaminate Ti3SiC2 epitaxial layers on 4H-SiC(0 0 0 1)
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2011 (English)In: SCRIPTA MATERIALIA, ISSN 1359-6462, Vol. 64, no 12, 1141-1144 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial Ti3SiC2(0 0 0 1) films were deposited on 4 degrees off-cut 4H-SiC(0 0 0 1) wafers using magnetron sputtering. A lateral step-flow growth mechanism of the Ti3SiC2 was discovered by X-ray diffraction, elastic recoil detection analysis, atomic force microscopy and electron microscopy. Helium ion microscopy revealed contrast variations on the Ti3SiC2 terraces, suggesting a mixed Si and Ti(C) termination. Si-rich growth conditions results in Ti3SiC2 layers with pronounced {1 1 (2) over bar 0) faceting and off-oriented TiSi2 crystallites, while stoichiometric growth yields truncated {1 (1) over bar 0 0) terrace edges.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
Sputtering, Atomic force microscopy (AFM), Helium ion microscopy (HIM), Transmission electron microscopy (TEM), Crystal structure
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68684 (URN)10.1016/j.scriptamat.2011.03.013 (DOI)000290422300019 ()
Note
Original Publication: Kristina Buchholt, Per Eklund, Jens Jensen, Jun Lu, Anita Lloyd Spetz and Lars Hultman, Step-flow growth of nanolaminate Ti3SiC2 epitaxial layers on 4H-SiC(0 0 0 1), 2011, SCRIPTA MATERIALIA, (64), 12, 1141-1144. http://dx.doi.org/10.1016/j.scriptamat.2011.03.013 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2016-08-31
7. Phase-stabilization and substrate effects on nucleation and growth of (Ti,V)(n+1)GeC(n) thin films
Open this publication in new window or tab >>Phase-stabilization and substrate effects on nucleation and growth of (Ti,V)(n+1)GeC(n) thin films
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2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 5, 053516Article in journal (Refereed) Published
Abstract [en]

Phase-pure epitaxial thin films of (Ti,V)(2)GeC have been grown onto Al(2)O(3)(0001) substrates via magnetron sputtering. The c lattice parameter is determined to be 12.59 A, corresponding to a 50/50 Ti/V solid solution according to Vegards law, and the overall (Ti,V): Ge: C composition is 2:1:1 as determined by elastic recoil detection analysis. The minimum temperature for the growth of (Ti,V)(2)GeC is 700 degrees C, which is the same as for Ti(2)GeC but higher than that required for V(2)GeC (450 degrees C). Reduced Ge content yields films containing (Ti,V)(3)GeC(2) and (Ti,V)(4)GeC(3). These results show that the previously unknown phases V(3)GeC(2) and V(4)GeC(3) can be stabilized through alloying with Ti. For films grown on 4H-SiC(0001), (Ti,V)(3)GeC(2) was observed as the dominant phase, showing that the nucleation and growth of (Ti,V)(n+1)GeC(n) is affected by the choice of substrate; the proposed underlying physical mechanism is that differences in the local substrate temperature enhance surface diffusion and facilitate the growth of the higher-order phase (Ti,V)(3)GeC(2) compared to (Ti,V)(2)GeC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-71221 (URN)10.1063/1.3631087 (DOI)000294968600055 ()
Note

The status of this article was previously Manuscript and the original title was (Ti, V)n+1GeCn thin films.

Available from: 2011-10-07 Created: 2011-10-07 Last updated: 2017-12-08

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