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Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.

Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.

MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.

New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.

In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 41 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1679
National Category
Materials Chemistry Inorganic Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-111128DOI: 10.3384/lic.diva-111128ISBN: 978-91-7519-225-3 (print)OAI: oai:DiVA.org:liu-111128DiVA: diva2:753538
Presentation
2014-10-24, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note

The series name Linköping Studies in Science and Technology Licentiate Thesis in this publication is incorrect. Correct name is Linköping Studies in Science and Technology. Thesis.

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases
Open this publication in new window or tab >>Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases
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2014 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 126, no 19, 4977-4980 p.Article in journal (Refereed) Published
Abstract [en]

Porous carbons are widely used in energy storage and gas separation applications, but their synthesis always involves high temperatures. Herein we electrochemically selectively extract, at ambient temperature, the metal atoms from the ternary layered carbides, Ti3AlC2, Ti2AlC and Ti3SiC2 (MAX phases). The result is a predominantly amorphous carbide-derived carbon, with a narrow distribution of micropores. The latter is produced by placing the carbides in HF, HCl or NaCl solutions and applying anodic potentials. The pores that form when Ti3AlC2 is etched in dilute HF are around 0.5 nm in diameter. This approach forgoes energy-intensive thermal treatments and presents a novel method for developing carbons with finely tuned pores for a variety of applications, such as supercapacitor, battery electrodes or CO2 capture.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
Carbide; Cyclovoltammetrie; Elektrochemie; Kohlenstoff; Oxidationen
National Category
Chemical Sciences Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-111125 (URN)10.1002/ange.201402513 (DOI)
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
2. New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-Ion Batteries
Open this publication in new window or tab >>New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-Ion Batteries
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2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 43, 15966-15969 p.Article in journal (Refereed) Published
Abstract [en]

New two-dimensional niobium and vanadium carbides have been synthesized by selective etching, at room temperature, of Al from Nb2AlC and V2AlC, respectively. These new matrials are promising electrode materials for Li-ion batteries, demonstrating good capability to handle high charge-discharge rates. Reversible capacities of 170 and 260 mA.h.g(-1) at 1 C, and 110 and 125 mA.h.g(-1) at 10 C were obtained for Nb2C and V2C-based electrodes, respectively.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102084 (URN)10.1021/ja405735d (DOI)000326487800001 ()
Note

Funding Agencies|Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies (BATT) Program|DE-AC02-05CH112316951370|Knut and Alice Wallenberg Foundation||

Available from: 2013-12-02 Created: 2013-11-29 Last updated: 2017-12-06
3. Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
Open this publication in new window or tab >>Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
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2014 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 7, 2374-2381 p.Article in journal (Refereed) Published
Abstract [en]

Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of similar to 1 x 1 cm(2) Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit similar to 90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to similar to 100 K. Below 100 K, the films resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.

Place, publisher, year, edition, pages
American Chemical Society, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106852 (URN)10.1021/cm500641a (DOI)000334572300023 ()
Available from: 2014-05-28 Created: 2014-05-23 Last updated: 2017-12-05Bibliographically approved
4. X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
Open this publication in new window or tab >>X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.

National Category
Physical Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111127 (URN)
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2016-08-31Bibliographically approved

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