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Synthesis of two-dimensional molybdenum carbide, Mo2C, from the gallium based atomic laminate Mo2Ga2C
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Department of Materials Science & Engineering, Drexel University, Philadelphia, USA.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
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2015 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 108, p. 147-150Article 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. Vol. 108, p. 147-150
Keyword [en]
2D materials, Layered structures, MXene, Transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS)
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-121255DOI: 10.1016/j.scriptamat.2015.07.003ISI: 000360250700035OAI: oai:DiVA.org:liu-121255DiVA, id: diva2:852829
Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2018-05-24Bibliographically approved
In thesis
1. Synthesis and characterization of Mo-based nanolaminates
Open this publication in new window or tab >>Synthesis and characterization of Mo-based nanolaminates
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. p. 37
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1729
National Category
Physical Sciences Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-121262 (URN)978-91-7685-948-3 (ISBN)
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
2. Synthesis and characterization of Mo- and W-based atomic laminates
Open this publication in new window or tab >>Synthesis and characterization of Mo- and W-based atomic laminates
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mn+1AXn (MAX) phases are inherently nanolaminated compounds based on transition metals (M), A group elements (A), and carbon or/and nitrogen (X), which exhibit a unique combination of ceramic and metallic properties. My thesis work has focused on exploring novel MAX phase chemistries, including elemental combinations beyond those traditionally used for MAX phases, and their graphene-analogous 2D counterpart, MXenes.  

The first part of the thesis investigates Mo-based MAX phases, which are among the least studied, despite indication of superconducting properties and potential for derivation of Mo-based MXenes. Initially, I performed theoretical calculations focused on evaluation of phase stability of the Mon+1GaCn MAX phases, and synthesized the predicted stable Mo2GaC in thin film form using DC magnetron sputtering. Close to phase pure epitaxial films were grown at ~590 °C, and electrical resistivity measurements using a four-point probe technique suggest a superconducting behavior with a critical temperature of ~7 K. The follow-up of this work, was synthesis of a new MAX related material, Mo2Ga2C, also by means of DC magnetron sputtering. The theoretical predictions as well as the materials characterization by X-ray diffraction and neutron powder diffraction, suggested a Ga bilayer interleaved between a set of Mo2C blocks, arranged in a simple hexagonal structure.   

It is known that selectively etching of the A-layer in a MAX phase, shown for A=Al, can lead to realization of a MXene. Hence, the next step in my research was to explore the possibility of etching of A=Ga in Mo2GaC as well as in Mo2Ga2C, targeting a Mo2C MXene, as motivated by theoretically proposed superior thermoelectric properties of this 2D material. While Mo2GaC did not allow removal of the A-layer, I showed that Mo2C MXene could be realized from etching Mo2Ga2C thin films, removing the Ga bilayer, in 50% hydrofluoric acid at a temperature of ~50 °C for a duration of ~3 h. Hence, the results did not only produce the first Mo-based MXene, it also showed that MXenes can be obtained for etching A-elements other than Al. This, in turn, increase the pathways for expanding the family of MXenes.    

I thereafter set out to explore the magnetic properties resulting from Mn-alloying of the non-magnetic Mo2GaC MAX 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 °C, 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 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.  

The second part of my research has been dedicated to realizing new MAX phase related, chemically ordered compounds and their MXene derivatives, and to initiate exploration of their properties. Materials synthesis was performed by pressureless bulk sintering, and inspired by theoretical calculations we showed evidence for a new so called o-MAX phase, Mo2ScAlC2, with an out-of-plane chemically ordered structure. It is the first experimentally verified Sc-containing MAX phase, which makes its corresponding MXene, Mo2ScC2, also presented in this work, the first MXene including Sc. Moreover, I discovered two so called i-MAX phases including W, (W2/3Sc1/3)2AlC and (W2/3Y1/3)2AlC, which display in-plane chemical ordering in the M-layer. Furthermore, both was shown to allow synthesis of their corresponding 2D counterpart; W1.33C MXene, with ordered vacancies.  Initial test on these novel MXenes showed a high potential for hydrogen evolution reaction.  

Altogether, I have in my thesis work realized 6 novel MAX phases and related materials, and have shown evidence for 4 new MXenes. These materials inspire a wide range of future studies, with respect to fundamental properties as well as potential for future applications.   

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 59
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1933
National Category
Condensed Matter Physics Nano Technology
Identifiers
urn:nbn:se:liu:diva-148012 (URN)10.3384/diss.diva-148012 (DOI)9789176853122 (ISBN)
Public defence
2018-06-11, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-24 Created: 2018-05-24 Last updated: 2018-05-24Bibliographically approved

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Meshkian, RaheleNäslund, Lars-ÅkeLu, JunBarsoum, Michel W.Rosén, Johanna

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