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Synthesis and characterization of Mo-based nanolaminates
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Mn+1AXn (MAX) phases are nanolaminated compounds based on a transition metal (M), a group A element (A), and carbon or/and nitrogen (X), which exhibit a unique combination of ceramic and metallic properties. Mo-based MAX phases are among the least studied, despite indication of superconducting properties and high potential for fabrication of the grapheneanalogous 2D counterpart, Mo2C MXene. Furthermore, incorporation of Mn atoms in these MAX phases may induce a magnetic response.

In this work, I have performed theoretical calculations focused on evaluation of phase stability of the Mon+1GaCn MAX phases, and have synthesized the predicted stable Mo2GaC in thin film form using magnetron sputtering. Close to phase pure epitaxial films were grown at ~590 ºC, and electrical resistivity measurements using a four point probe technique suggest a superconducting behavior with a critical temperature of ~7 K.

The A-layer in the MAX phase can be selectively etched using different types of acids, leading to exfoliation of the MX-layers and realization of MXenes. After synthesis of the MAX phase related material Mo2Ga2C, the previously non-explored Mo2C MXene could be fabricated from etching Mo2Ga2C thin films in 50% hydrofluoric acid at a temperature of ~50 ºC for a duration of ~3 h.

Motivated by the realization of laminated Mo-based materials in 3D as well as 2D, I set out to explore the magnetic properties resulting from Mn-alloying of the non-magnetic Mo2GaC phase. For that purpose, (Mo,Mn)2GaC was synthesized using a DC magnetron sputtering system with Ga and C as elemental targets and a 1:1 atomic ratio Mo:Mn compound target. Heteroepitaxial films on MgO(111) substrates were grown at ~530 ºC, as confirmed by X-ray diffraction. Compositional analysis using energy dispersive X-ray spectroscopy showed a 2:1 ratio of the M and A elements and a 1:1 ratio for the Mo and Mn atoms in the film. Vibrating sample magnetometry was utilized in order to measure the magnetic behavior of the films, showing a magnetic response up to at least 300 K, and with a coercive field of 0.06 T, which is the highest reported for any MAX phase to date.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 37 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1729
National Category
Physical Sciences Physical Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-121262ISBN: 978-91-7685-948-3 (print)OAI: oai:DiVA.org:liu-121262DiVA: diva2:852912
Presentation
2015-10-09, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note

The series name Linköping Studies in Science and Technology Licentiate Thesis is incorrect. The correct series name is Linköping Studies in Science and Technology Thesis.

Available from: 2015-09-11 Created: 2015-09-10 Last updated: 2015-09-11Bibliographically approved
List of papers
1. Theoretical stability, thin film synthesis and transport properties of the Mon+1GaCn MAX phase
Open this publication in new window or tab >>Theoretical stability, thin film synthesis and transport properties of the Mon+1GaCn MAX phase
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2015 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 9, no 3, 197-201 p.Article in journal (Refereed) Published
Abstract [en]

The phase stability of Mon +1GaCn has been investigated using ab-initio calculations. The results indicate stability for the Mo2GaC phase only, with a formation enthalpy of 0.4 meV per atom. Subsequent thin film synthesis of Mo2GaC was performed through magnetron sputtering from elemental targets onto Al2O3 [0001], 6H-SiC [0001] and MgO [111] substrates within the temperature range of 500 degrees C and 750 degrees C. High structural quality films were obtained for synthesis on MgO [111] substrates at 590 degrees C. Evaluation of transport properties showed a superconducting behavior with a critical temperature of approximately 7 K, reducing upon the application of an external magnetic field. The results point towards the first superconducting MAX phase in thin film form.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2015
Keyword
superconducting MAX phases; Mo2GaC; ab-initio calculations; magnetron sputtering; thin films
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117388 (URN)10.1002/pssr.201409543 (DOI)000351674600009 ()
Note

Funding Agencies|European Research Council under European Community/ERC [258509]; Swedish Research Council (VR) [642-2013-8020, 621-2012-4425]; KAW Fellowship program; SSF synergy grant FUNCASE; Icelandic Research Fund

Available from: 2015-04-24 Created: 2015-04-24 Last updated: 2017-12-04
2. Synthesis of two-dimensional molybdenum carbide, Mo2C, from the gallium based atomic laminate Mo2Ga2C
Open this publication in new window or tab >>Synthesis of two-dimensional molybdenum carbide, Mo2C, from the gallium based atomic laminate Mo2Ga2C
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2015 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 108, 147-150 p.Article in journal (Refereed) Published
Abstract [en]

We report on the synthesis of a two-dimensional transition metal carbide, Mo2C, (MXene) obtained by immersing Mo2Ga2C thin films in hydrofluoric acid. Experimental evidences for neither synthesis of a Mo-based MXene nor selective etching of Ga from an atomic nanolaminate have previously been presented. MXene formation is verified through X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. This discovery unlocks new potential applications for Mo-based MXenes in a host of applications, from thermoelectrics to catalysis and energy storage.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
2D materials, Layered structures, MXene, Transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS)
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121255 (URN)10.1016/j.scriptamat.2015.07.003 (DOI)000360250700035 ()
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2017-12-04Bibliographically approved
3. A magnetic atomic laminate from thin film synthesis: (Mo0.5Mn0.5)2GaC
Open this publication in new window or tab >>A magnetic atomic laminate from thin film synthesis: (Mo0.5Mn0.5)2GaC
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2015 (English)In: APL MATERIALS, ISSN 2166-532X, Vol. 3, no 7, 076102Article in journal (Refereed) Published
Abstract [en]

We present synthesis and characterization of a new magnetic atomic laminate: (Mo0.5Mn0.5)(2)GaC. High quality crystalline films were synthesized on MgO(111) substrates at a temperature of similar to 530 degrees C. The films display a magnetic response, evaluated by vibrating sample magnetometry, in a temperature range 3-300 K and in a field up to 5 T. The response ranges from ferromagnetic to paramagnetic with change in temperature, with an acquired 5T-moment and remanent moment at 3 K of 0.66 and 0.35 mu(B) per metal atom (Mo and Mn), respectively. The remanent moment and the coercive field (0.06 T) exceed all values reported to date for the family of magnetic laminates based on so called MAX phases.

Place, publisher, year, edition, pages
American Institute of Physics (AIP): Open Access Journals / AIP Publishing LLC, 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-120878 (URN)10.1063/1.4926611 (DOI)000358923500003 ()
Note

Funding Agencies|European Research Council under the European Community Seventh Framework Program [258509]; Swedish Research Council (VR) [642-2013-8020, 621-2012-4425]; KAW Fellowship program; SSF synergy grant FUNCASE; Icelandic Research Fund [141518-051]

Available from: 2015-08-28 Created: 2015-08-28 Last updated: 2015-09-17

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