Publications by authors named "Per O Å Persson"

35 Publications

Boridene: Two-dimensional MoB with ordered metal vacancies obtained by chemical exfoliation.

Science 2021 08;373(6556):801-805

Materials Design, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

Extensive research has been invested in two-dimensional (2D) materials, typically synthesized by exfoliation of van der Waals solids. One exception is MXenes, derived from the etching of constituent layers in transition metal carbides and nitrides. We report the experimental realization of boridene in the form of single-layer 2D molybdenum boride sheets with ordered metal vacancies, MoBT (where T is fluorine, oxygen, or hydroxide surface terminations), produced by selective etching of aluminum and yttrium or scandium atoms from 3D in-plane chemically ordered (MoY)AlB and (MoSc)AlB in aqueous hydrofluoric acid. The discovery of a 2D transition metal boride suggests a wealth of future 2D materials that can be obtained through the chemical exfoliation of laminated compounds.
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http://dx.doi.org/10.1126/science.abf6239DOI Listing
August 2021

Out-Of-Plane Ordered Laminate Borides and Their 2D Ti-Based Derivative from Chemical Exfoliation.

Adv Mater 2021 Sep 5;33(38):e2008361. Epub 2021 Aug 5.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, SE-581 83, Sweden.

Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M SiB (T2) phases, the finding of a family of laminated quaternary metal borides, M' M″SiB , with out-of-plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti MoSiB , establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti MoSiB and select removal of Si and MoB sub-layers is validated by derivation of a 2D material, TiO Cl , of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of ≈4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.
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http://dx.doi.org/10.1002/adma.202008361DOI Listing
September 2021

Electrochemical Lithium Storage Performance of Molten Salt Derived VSnC MAX Phase.

Nanomicro Lett 2021 Jul 22;13(1):158. Epub 2021 Jul 22.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Industrial Technology, Chinese Academy of Sciences, Ningbo, 315201, Zhejiang, People's Republic of China.

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of VSnC MAX phase by the molten salt method. VSnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g and volumetric capacity of 570 mAh cm as well as superior rate performance of 95 mAh g (110 mAh cm) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn-Li (de)alloying reaction that occurs at the edge sites of VSnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at VC layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.
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http://dx.doi.org/10.1007/s40820-021-00684-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8298715PMC
July 2021

Synthesis and Characterisation of Nanocomposite Mo-Fe-B Thin Films Deposited by Magnetron Sputtering.

Materials (Basel) 2021 Apr 1;14(7). Epub 2021 Apr 1.

Department of Chemistry-Ångström, Uppsala University, SE-751 21 Uppsala, Sweden.

Several ternary phases are known in the Mo-Fe-B system. Previous ab initio calculations have predicted that they should exhibit a tempting mix of mechanical and magnetic properties. In this study, we have deposited Mo-Fe-B films with a Fe-content varying from 0-37 at.% using non-reactive DC (direct current) magnetron sputtering. The phase composition, microstructure, and mechanical properties were investigated using X-ray diffraction, scanning transmission electron microscopy, and nanoindentation measurements. Films deposited at 300 °C and with >7 at.% Fe are nanocomposites consisting of two amorphous phases: a metal-rich phase and a metal-deficient phase. Hardness and elastic modulus were reduced with increasing Fe-content from ~29 to ~19 GPa and ~526 to ~353 GPa, respectively. These values result in H/E ratios of 0.089-0.052 GPa, thereby indicating brittle behaviour of the films. Also, no indication of crystalline ternary phases was observed at temperatures up to 600 °C, suggesting that higher temperatures are required for such films to form.
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http://dx.doi.org/10.3390/ma14071739DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8037313PMC
April 2021

Ultrafast, One-Step, Salt-Solution-Based Acoustic Synthesis of TiC MXene.

ACS Nano 2021 Mar 26;15(3):4287-4293. Epub 2021 Feb 26.

Department of Physics, Chemistry, and Biology (IFM) Linköping University, SE-581 83 Linköping, Sweden.

The current quest for two-dimensional transition metal carbides and nitrides (MXenes) has been to circumvent the slow, hazardous, and laborious multistep synthesis procedures associated with conventional chemical MAX phase exfoliation. Here, we demonstrate a one-step synthesis method with local TiAlC MAX to TiCT MXene conversion on the order of milliseconds, facilitated by proton production through solution dissociation under megahertz frequency acoustic excitation. These protons combined with fluorine ions from LiF to selectively etch the MAX phase into MXene, whose delamination is aided by the acoustic forcing. These results have important implications for the future applicability of MXenes, which crucially depend on the development of more efficient synthesis procedures. For proof-of-concept, we show that flexible electrodes fabricated by this method exhibit comparable electrochemical performance to that previously reported.
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http://dx.doi.org/10.1021/acsnano.0c07242DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8034768PMC
March 2021

Flexible Free-Standing MoO/TiCT MXene Composite Films with High Gravimetric and Volumetric Capacities.

Adv Sci (Weinh) 2021 Feb 31;8(3):2003656. Epub 2020 Dec 31.

Department of Physics, Chemistry and Biology (IFM) Linköping University Linköping 581 83 Sweden.

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, TiCT MXene is mixed with MoO nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive TiCT flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO nanobelts, in turn, prevent the restacking of the TiCT nanosheets. Benefitting from these advantages, a MoO/TiCT film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g and 1836 C cm at 1 A g for an ≈ 10 µm thick film; and 767 C g and 1664 C cm at 1 A g for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO/TiCT films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg and 39.2 Wh L, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.
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http://dx.doi.org/10.1002/advs.202003656DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7856882PMC
February 2021

Halogenated TiC MXenes with Electrochemically Active Terminals for High-Performance Zinc Ion Batteries.

ACS Nano 2021 Jan 8;15(1):1077-1085. Epub 2021 Jan 8.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, China.

The class of two-dimensional metal carbides and nitrides known as MXenes offer a distinct manner of property tailoring for a wide range of applications. The ability to tune the surface chemistry for expanding the property space of MXenes is thus an important topic, although experimental exploration of surface terminals remains a challenge. Here, we synthesized TiC MXene with unitary, binary, and ternary halogen terminals, .., -Cl, -Br, -I, -BrI, and -ClBrI, to investigate the effect of surface chemistry on the properties of MXenes. The electrochemical activity of Br and I elements results in the extraordinary electrochemical performance of the MXenes as cathodes for aqueous zinc ion batteries. The -Br- and -I-containing MXenes, ., TiCBr and TiCI, exhibit distinct discharge platforms with considerable capacities of 97.6 and 135 mAh·g. TiC(BrI) and TiC(ClBrI) exhibit dual discharge platforms with capacities of 117.2 and 106.7 mAh·g. In contrast, the previously discovered MXenes TiCCl and TiC(OF) exhibit no discharge platforms and only ∼50% of capacities and energy densities of TiCBr. These results emphasize the effectiveness of the Lewis-acidic-melt etching route for tuning the surface chemistry of MXenes and also show promise for expanding the MXene family toward various applications.
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http://dx.doi.org/10.1021/acsnano.0c07972DOI Listing
January 2021

Tailored synthesis approach of (MoY)AlC i-MAX and its two-dimensional derivative MoCT MXene: enhancing the yield, quality, and performance in supercapacitor applications.

Nanoscale 2021 Jan 18;13(1):311-319. Epub 2020 Dec 18.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden.

A vacancy-ordered MXene, MoCT, obtained from the selective etching of Al and Sc from the parent i-MAX phase (MoSc)AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (MoY)AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY alloy instead of elemental Al and Y for the synthesis of (MoY)AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, MoAlC. Furthermore, through a modified etching procedure, we obtain a MoCT MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm) and gravimetric (436 F g) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the MoCT MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.
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http://dx.doi.org/10.1039/d0nr07045aDOI Listing
January 2021

Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering.

J Am Chem Soc 2020 Oct 13;142(43):18583-18591. Epub 2020 Oct 13.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal TiInB. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of MAlB (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of MoYAlB and MoScAlB of space group 3̅ (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagomé ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential two-dimensional derivatives.
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http://dx.doi.org/10.1021/jacs.0c08113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7596753PMC
October 2020

A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte.

Nat Mater 2020 Aug 13;19(8):894-899. Epub 2020 Apr 13.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, China.

Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of materials that have attracted attention as energy storage materials. MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution; most other MAX phases have not been explored. Here a redox-controlled A-site etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX-phase precursors with A elements Si, Zn and Ga. A negative electrode of TiC MXene material obtained through this molten salt synthesis method delivers a Li storage capacity of up to 738 C g (205 mAh g) with high charge-discharge rate and a pseudocapacitive-like electrochemical signature in 1 M LiPF carbonate-based electrolyte. MXenes prepared via this molten salt synthesis route may prove suitable for use as high-rate negative-electrode materials for electrochemical energy storage applications.
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http://dx.doi.org/10.1038/s41563-020-0657-0DOI Listing
August 2020

Tactile sensory coding and learning with bio-inspired optoelectronic spiking afferent nerves.

Nat Commun 2020 03 13;11(1):1369. Epub 2020 Mar 13.

NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076, Aalto, Finland.

The integration and cooperation of mechanoreceptors, neurons and synapses in somatosensory systems enable humans to efficiently sense and process tactile information. Inspired by biological somatosensory systems, we report an optoelectronic spiking afferent nerve with neural coding, perceptual learning and memorizing capabilities to mimic tactile sensing and processing. Our system senses pressure by MXene-based sensors, converts pressure information to light pulses by coupling light-emitting diodes to analog-to-digital circuits, then integrates light pulses using a synaptic photomemristor. With neural coding, our spiking nerve is capable of not only detecting simultaneous pressure inputs, but also recognizing Morse code, braille, and object movement. Furthermore, with dimensionality-reduced feature extraction and learning, our system can recognize and memorize handwritten alphabets and words, providing a promising approach towards e-skin, neurorobotics and human-machine interaction technologies.
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http://dx.doi.org/10.1038/s41467-020-15105-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7070032PMC
March 2020

Multielemental single-atom-thick layers in nanolaminated V(Sn, ) C ( = Fe, Co, Ni, Mn) for tailoring magnetic properties.

Proc Natl Acad Sci U S A 2020 Jan 26;117(2):820-825. Epub 2019 Dec 26.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, 315201 Ningbo, Zhejiang, China;

Tailoring of individual single-atom-thick layers in nanolaminated materials offers atomic-level control over material properties. Nonetheless, multielement alloying in individual atomic layers in nanolaminates is largely unexplored. Here, we report 15 inherently nanolaminated V( Sn)C ( = Fe, Co, Ni, Mn, and combinations thereof, with x ∼ 1/3) MAX phases synthesized by an alloy-guided reaction. The simultaneous occupancy of the 4 magnetic elements and Sn in the individual single-atom-thick A layers constitutes high-entropy MAX phase in which multielemental alloying exclusively occurs in the 2-dimensional (2D) A layers. V( Sn)C exhibit distinct ferromagnetic behavior that can be compositionally tailored from the multielement A-layer alloying. Density functional theory and phase diagram calculations are performed to understand the structure stability of these MAX phases. This 2D multielemental alloying approach provides a structural design route to discover nanolaminated materials and expand their chemical and physical properties. In fact, the magnetic behavior of these multielemental MAX phases shows strong dependency on the combination of various elements.
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http://dx.doi.org/10.1073/pnas.1916256117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6969549PMC
January 2020

Slot-Die-Printed Two-Dimensional ZrS Charge Transport Layer for Perovskite Light-Emitting Diodes.

ACS Appl Mater Interfaces 2019 Dec 13;11(51):48021-48028. Epub 2019 Dec 13.

CHOSE-Centre of Hybrid and Organic Solar Energy, Department of Electronics Engineering , University of Rome Tor Vergata , Rome 00133 , Italy.

Liquid-phase exfoliation of zirconium trisulfide (ZrS) was used to produce stable and ready-to-use inks for solution-processed semiconductor thin-film deposition. Ribbon-like layered crystals of ZrS were produced by the chemical vapor transport method and were then exfoliated in three different solvents: dimethylformamide, ethanol, and isopropyl alcohol. The resulting ZrS dispersions were compared for stability and the ability to form continuous films on top of the perovskite layer in light-emitting diodes with the ITO/PEDOT:PSS/MAPbBr/2D-ZrS/LiF/Al structure. Film deposition was performed by using either spray or slot-die coating methods. The slot-die coating route proved to produce better and more uniform films with respect to spray coating. We found that the 2D ZrS electron injection layer (EIL) stabilized the interface between the perovskite and LiF/Al cathode, reducing the turn-on voltage to 2.8 V and showing a luminance that does not degrade during voltage sweep. On the other hand, EIL-free devices show electroluminescence on the first voltage sweep that reduces almost to zero in the subsequent sweeps. Combining physical device simulation and density functional theory calculation, we are able to explain these results in terms of lowering the electron injection barrier at the cathode.
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http://dx.doi.org/10.1021/acsami.9b16457DOI Listing
December 2019

Synthesis of (VSc)AlC i-MAX phase and VC MXene scrolls.

Nanoscale 2019 Aug;11(31):14720-14726

Thin Film Physics Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)2AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)2AlC, where x ≤ 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4× reduction in etching time for (V2-xScx)2AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.
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http://dx.doi.org/10.1039/c9nr02354bDOI Listing
August 2019

Single-Atom-Thick Active Layers Realized in Nanolaminated Ti(AlCu)C and Its Artificial Enzyme Behavior.

ACS Nano 2019 08 24;13(8):9198-9205. Epub 2019 Jul 24.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering , Chinese Academy of Sciences , Ningbo , Zhejiang 315201 , China.

A Ti(AlCu)C phase with Cu atoms with a degree of ordering in the A plane is synthesized through the A site replacement reaction in CuCl molten salt. The weakly bonded single-atom-thick Cu layers in a Ti(AlCu)C MAX phase provide actives sites for catalysis chemistry. As-synthesized Ti(AlCu)C presents unusual peroxidase-like catalytic activity similar to that of natural enzymes. A fabricated Ti(AlCu)C/chitosan/glassy carbon electrode biosensor prototype also exhibits a low detection limit in the electrochemical sensing of HO. These results have broad implications for property tailoring in a nanolaminated MAX phase by replacing the A site with late transition elements.
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http://dx.doi.org/10.1021/acsnano.9b03530DOI Listing
August 2019

Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes.

J Am Chem Soc 2019 Mar 7;141(11):4730-4737. Epub 2019 Mar 7.

Engineering Laboratory of Advanced Energy Materials , Ningbo Institute of Industrial Technology, Chinese Academy of Sciences , Ningbo , Zhejiang 315201 , China.

Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesizing a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition-metal halides. The approach is a top-down route that enables the late transitional element atom (Zn in the present case) to occupy the A site in the pre-existing MAX phase structure. Using this replacement reaction between the Zn element from molten ZnCl and the Al element in MAX phase precursors (TiAlC, TiAlC, TiAlN, and VAlC), novel MAX phases TiZnC, TiZnC, TiZnN, and VZnC were synthesized. When employing excess ZnCl, Cl-terminated MXenes (such as TiCCl and TiCCl) were derived by a subsequent exfoliation of TiZnC and TiZnC due to the strong Lewis acidity of molten ZnCl. These results indicate that A-site element replacement in traditional MAX phases by late transition-metal halides opens the door to explore MAX phases that are not thermodynamically stable at high temperature and would be difficult to synthesize through the commonly employed powder metallurgy approach. In addition, this is the first time that exclusively Cl-terminated MXenes were obtained, and the etching effect of Lewis acid in molten salts provides a green and viable route to preparing MXenes through an HF-free chemical approach.
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http://dx.doi.org/10.1021/jacs.9b00574DOI Listing
March 2019

Two-Dimensional Hydroxyl-Functionalized and Carbon-Deficient Scandium Carbide, ScC OH, a Direct Band Gap Semiconductor.

ACS Nano 2019 Feb 4;13(2):1195-1203. Epub 2019 Feb 4.

Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Engineering and Technology , Chinese Academy of Sciences , Ningbo , Zhejiang 315201 , China.

Two-dimensional (2D) materials have attracted intense attention in nanoscience and nanotechnology due to their outstanding properties. Among these materials, the emerging family of 2D transition metal carbides, carbonitrides, and nitrides (referred to as MXenes) stands out because of the vast available chemical space for tuning materials chemistry and surface termination, offering opportunities for property tailoring. Specifically, semiconducting properties are needed to enable utilization in optoelectronics, but direct band gaps are experimentally challenging to achieve in these 2D carbides. Here, we demonstrate the fabrication of 2D hydroxyl-functionalized and carbon-deficient scandium carbide, namely, ScC OH, by selective etching of a layered parent ScAlC compound. The 2D configuration is determined as a direct band gap semiconductor, with an experimentally measured band gap approximated at 2.5 eV. Furthermore, this ScC OH-based device exhibits excellent photoresponse in the ultraviolet-visible light region (responsivity of 0.125 A/W at 360 nm/10 V, and quantum efficiency of 43%). Thus, this 2D ScC OH direct band gap semiconductor may find applications in visible light detectors, photocatalytic chemistry, and optoelectronic devices.
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http://dx.doi.org/10.1021/acsnano.8b06279DOI Listing
February 2019

Electronic and optical characterization of 2D TiC and NbC (MXene) thin films.

J Phys Condens Matter 2019 Apr 22;31(16):165301. Epub 2019 Jan 22.

Department of Physics, Chemistry and Biology (IFM), Thin Film Physics Division, Linköping University, SE-58183 Linköping, Sweden.

Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are a new class of 2D materials, with extensive opportunities for property tailoring due to the numerous possibilities for varying chemistries and surface terminations. Here, TiAlC and NbAlC MAX phase epitaxial thin films were deposited on sapphire substrates by physical vapor deposition. The films were then etched in LiF/HCl solutions, yielding Li-intercalated, 2D TiCT and NbCT films, whose terminations, transport and optical properties were characterized. The former exhibits metallic conductivity, with weak localization below 50 K. In contrast, the Nb-based film exhibits an increase in resistivity with decreasing temperature from RT down to 40 K consistent with variable range hopping transport. The optical properties of both films were determined from spectroscopic ellipsometry in the 0.75 to 3.50 eV range. The results for TiCT films confirm the metallic behavior. In contrast, no evidence of metallic behavior is observed for the NbCT film. The present work therefore demonstrates that one fruitful approach to alter the electronic and optical properties of MXenes is to change the nature of the transition metal.
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http://dx.doi.org/10.1088/1361-648X/ab00a2DOI Listing
April 2019

2D Transition Metal Carbides (MXenes) for Carbon Capture.

Adv Mater 2019 Jan 4;31(2):e1805472. Epub 2018 Nov 4.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.

Global warming caused by burning of fossil fuels is indisputably one of mankind's greatest challenges in the 21st century. To reduce the ever-increasing CO emissions released into the atmosphere, dry solid adsorbents with large surface-to-volume ratio such as carbonaceous materials, zeolites, and metal-organic frameworks have emerged as promising material candidates for capturing CO . However, challenges remain because of limited CO /N selectivity and long-term stability. The effective adsorption of CO gas (≈12 mol kg ) on individual sheets of 2D transition metal carbides (referred to as MXenes) is reported here. It is shown that exposure to N gas results in no adsorption, consistent with first-principles calculations. The adsorption efficiency combined with the CO /N selectivity, together with a chemical and thermal stability, identifies the archetype Ti C MXene as a new material for carbon capture (CC) applications.
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http://dx.doi.org/10.1002/adma.201805472DOI Listing
January 2019

On the Structural Stability of MXene and the Role of Transition Metal Adatoms.

Nanoscale 2018 Jun;10(23):10850-10855

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

In the present communication, the atomic structure and coordination of surface adsorbed species on Nb2C MXene is investigated over time. In particular, the influence of the Nb adatoms on the structural stability and oxidation behavior of the MXene is addressed. This investigation is based on the plane-view geometry observations of single Nb2C MXene sheets by a combination of atomic-resolution scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and STEM image simulations.
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http://dx.doi.org/10.1039/c8nr01986jDOI Listing
June 2018

Self-Healing in Carbon Nitride Evidenced As Material Inflation and Superlubric Behavior.

ACS Appl Mater Interfaces 2018 May 3;10(19):16238-16243. Epub 2018 May 3.

Thin Film Physics Division, Department of Physics (IFM) , Linköping University , Linköping SE-581 83 , Sweden.

All known materials wear under extended mechanical contacting. Superlubricity may present solutions, but is an expressed mystery in C-based materials. We report negative wear of carbon nitride films; a wear-less condition with mechanically induced material inflation at the nanoscale and friction coefficient approaching ultralow values (0.06). Superlubricity in carbon nitride is expressed as C-N bond breaking for reduced coupling between graphitic-like sheets and eventual N desorption. The transforming surface layer acts as a solid lubricant, whereas the film bulk retains its high elasticity. The present findings offer new means for materials design at the atomic level, and for property optimization in wear-critical applications like magnetic reading devices or nanomachines.
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http://dx.doi.org/10.1021/acsami.8b03055DOI Listing
May 2018

W-Based Atomic Laminates and Their 2D Derivative W C MXene with Vacancy Ordering.

Adv Mater 2018 May 6;30(21):e1706409. Epub 2018 Apr 6.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.

Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W M ) AC, where M = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two-with a monoclinic C2/c structure-are predicted to be stable: (W Sc ) AlC and (W Y ) AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
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http://dx.doi.org/10.1002/adma.201706409DOI Listing
May 2018

Tailoring Structure, Composition, and Energy Storage Properties of MXenes from Selective Etching of In-Plane, Chemically Ordered MAX Phases.

Small 2018 Apr 3;14(17):e1703676. Epub 2018 Apr 3.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.

The exploration of 2D solids is one of our time's generators of materials discoveries. A recent addition to the 2D world is MXenes that possses a rich chemistry due to the large parent family of MAX phases. Recently, a new type of atomic laminated phases (coined i-MAX) is reported, in which two different transition metal atoms are ordered in the basal planes. Herein, these i-MAX phases are used in a new route for tailoriong the MXene structure and composition. By employing different etching protocols to the parent i-MAX phase (Mo Y ) AlC, the resulting MXene can be either: i) (Mo Y ) C with in-plane elemental order through selective removal of Al atoms or ii) Mo C with ordered vacancies through selective removal of both Al and Y atoms. When (Mo Y ) C (ideal stoichiometry) is used as an electrode in a supercapacitor-with KOH electrolyte-a volumetric capacitance exceeding 1500 F cm is obtained, which is 40% higher than that of its Mo C counterpart. With H SO , the trend is reversed, with the latter exhibiting the higher capacitance (≈1200 F cm ). This additional ability for structural tailoring will indubitably prove to be a powerful tool in property-tailoring of 2D materials, as exemplified here for supercapacitors.
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http://dx.doi.org/10.1002/smll.201703676DOI Listing
April 2018

Phase formation of nanolaminated MoAuC and Mo(AuGa)C by a substitutional reaction within Au-capped MoGaC and MoGaC thin films.

Nanoscale 2017 Nov;9(45):17681-17687

Thin Film Physics Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

Au-containing nanolaminated carbides MoAuC and Mo(AuGa)C were synthesized by a thermally induced substitutional reaction in MoGaC and MoGaC, respectively. The Au substitution of the Ga layers in the structures was observed using cross-sectional high-resolution scanning transmission electron microscopy. Expansion of c lattice parameters was also observed in the Au-containing phases compared to the original phases. Energy dispersive spectroscopy detected residual Ga in Au-substituted layers of both phases with a peculiar Ga in-plane ordering for Au : Ga = 9 : 1 ratio along the Au-Ga layers in Mo(AuGa)C. These results indicate a generalization of the Au substitution reaction for the A elements in MAX phases.
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http://dx.doi.org/10.1039/c7nr03663aDOI Listing
November 2017

Strategies to initiate and control the nucleation behavior of bimetallic nanoparticles.

Nanoscale 2017 Jun;9(24):8149-8156

Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.

In this work we report strategies to nucleate bimetallic nanoparticles (NPs) made by gas phase synthesis of elements showing difficulty in homogeneous nucleation. It is shown that the nucleation assisted problem of bimetallic NP synthesis can be solved via the following pathways: (i) selecting an element which can itself nucleate and act as a nucleation center for the synthesis of bimetallic NPs; (ii) introducing H or CH as an impurity/trace gas to initiate nucleation during the synthesis of bimetallic NPs. The latter can solve the problem if none of the elements in a bimetallic NP can initiate nucleation. We illustrate the abovementioned strategies for the case of Mg based bimetallic NPs, which are interesting as hydrogen storage materials and exhibit both nucleation and oxidation issues even under ultra-high vacuum conditions. In particular, it is shown that adding H in small proportions favors the formation of a solid solution/alloy structure even in the case of immiscible Mg and Ti, where normally phase separation occurs during synthesis. In addition, we illustrate the possibility of improving the nucleation rate, and controlling the structure and size distribution of bimetallic NPs using H/CH as a reactive/nucleating gas. This is shown to be associated with the dimer bond energies of the various formed species and the vapor pressures of the metals, which are key factors for NP nucleation.
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http://dx.doi.org/10.1039/c7nr00916jDOI Listing
June 2017

Two-dimensional MoC MXene with divacancy ordering prepared from parent 3D laminate with in-plane chemical ordering.

Nat Commun 2017 04 25;8:14949. Epub 2017 Apr 25.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

The exploration of two-dimensional solids is an active area of materials discovery. Research in this area has given us structures spanning graphene to dichalcogenides, and more recently 2D transition metal carbides (MXenes). One of the challenges now is to master ordering within the atomic sheets. Herein, we present a top-down, high-yield, facile route for the controlled introduction of ordered divacancies in MXenes. By designing a parent 3D atomic laminate, (MoSc)AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D MoC sheets with ordered metal divacancies and high electrical conductivities. At ∼1,100 F cm, this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, MoC, with no vacancies, and one of the highest volumetric capacitance values ever reported, to the best of our knowledge. This structural design on the atomic scale may alter and expand the concept of property-tailoring of 2D materials.
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http://dx.doi.org/10.1038/ncomms14949DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5413966PMC
April 2017

Thermoelectric Properties of Solution-Processed n-Doped Ladder-Type Conducting Polymers.

Adv Mater 2016 Dec 27;28(48):10764-10771. Epub 2016 Oct 27.

Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, SE-60174, Norrköping, Sweden.

Ladder-type "torsion-free" conducting polymers (e.g., polybenzimidazobenzophenanthroline (BBL)) can outperform "structurally distorted" donor-acceptor polymers (e.g., P(NDI2OD-T2)), in terms of conductivity and thermoelectric power factor. The polaron delocalization length is larger in BBL than in P(NDI2OD-T2), resulting in a higher measured polaron mobility. Structure-function relationships are drawn, setting material-design guidelines for the next generation of conducting thermoelectric polymers.
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http://dx.doi.org/10.1002/adma.201603731DOI Listing
December 2016

Synthesis of MAX Phases in the Hf-Al-C System.

Inorg Chem 2016 Nov 11;55(21):10922-10927. Epub 2016 Oct 11.

Department of Materials Engineering, KU Leuven , Kasteelpark Arenberg 44, B-3001 Leuven, Belgium.

For the first time, MAX phases in the Hf-Al-C system were experimentally synthesized using reactive hot pressing. HfC was observed as the main competing phase. The lattice parameters of HfAlC and HfAlC were determined by Rietveld refinement based on the X-ray diffraction data. The atomic stacking sequence was revealed by high-resolution scanning transmission electron microscopy. Mixtures of 211 and 312 stacking were observed within the same grain, including 523 layers. This transition in atomic structure is discussed.
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http://dx.doi.org/10.1021/acs.inorgchem.6b01398DOI Listing
November 2016
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