Search query: Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers†

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abstract: In this study, a transition from metallic to semiconducting like behavior has been demonstrated in two dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M3C2 and M4C3 MXenes. The MXene structure consists of n 1 layers of near close packed M layers with C or N occupying the octahedral site between them in an [MX]nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M'2M''C2 and M'2M''2C3 where M' and M' are two different early transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M' atoms only occupy the outer layers and the M' atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M' C layers. Using X ray atomic pair distribution function (PDF) analysis on Mo2TiC2 and Mo2Ti2C3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC]nM structures. The electronic properties of these Mo containing MXenes are compared with their Ti3C2 counterparts, and are found to be no longer metallic like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo2TiC2Tx exhibits semiconductor like transport behavior, while Ti3C2Tx is a metal. This finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.
author_names: Babak Anasori

Chenyang Shi

Eun Ju Moon

Yu Xie

Cooper A Voigt

Paul R C Kent

Steven J May

Simon J L Billinge

Michel W Barsoum

Yury Gogotsi
title: Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers.
venue: Nanoscale horizons
year: 2016

abstract: Abstract In 2011, a new family of two dimensional (2D) carbides, carbonitrides and nitrides labeled MXenes was discovered. Since then the number of papers on these materials has increased exponentially for several reasons amongst them: their hydrophilic nature, excellent electronic conductivities and ease of synthesizing large quantities in water. This unique combination of properties and ease of processing has positioned them as enabling materials for a large, and quite varied, host of applications from energy storage to electromagnetic shielding, transparent conductive electrodes, electrocatalysis, to name a few. Since the initial synthesis of Ti3C2 in hydrofluoric acid, many more compositions were discovered, and different synthesis pathways were explored. Most of the work done so far has been conducted on top down synthesis where a layered parent compound is etched and then exfoliated. Three bottom up synthesis methods, chemical vapor deposition, a template method and plasma enhanced pulsed laser deposition have been reported. The latter methods enable the synthesis of not only high quality ultrathin 2D transition metal carbide and nitride films, but also those that could not be synthesized by selective etching. This article reviews and summarizes the most important breakthroughs in the synthesis of MXenes and high quality ultrathin 2D transition metal carbide and nitride films.
author_names: Louisiane Verger

Chuan Xu

Varun Natu

Hui-Ming Cheng

Wencai Ren

Michel W Barsoum
title: Overview of the synthesis of MXenes and other ultrathin 2D transition metal carbides and nitrides
venue: Current Opinion in Solid State and Materials Science
year: 2019

abstract: MXenes are 2D transition metal carbides with high potential for overcoming limitations of conventional two dimensional electronics. In this context, various MXenes have shown magnetic properties suitable for applications in spintronics, yet the number of MXenes reported so far is far smaller than their parental MAX phases. Therefore, we have studied the structural, electronic and magnetic properties of bimetallic and vacancy ordered MXenes derived from a new (V2/3Zr1/3)2AlC MAX phase to assess whether MXene exfoliation would return stable magnetic materials. In particular, we have investigated the properties of pristine and surface functionalized (V2/3Zr1/3)2CX2 bimetallic and (V2/3#1/3)2CX2 (where denotes the vacancies) vacancy ordered MXenes (X O, F and OH) Our density functional theory (DFT) calculations showed that modifying the MXene stoichiometry and/or MXene surface functionalization changes MXene properties. After testing all possible combinations of metallic motifs and functionalization, we identified (V2/3Zr1/3)2CX2, (V2/3#1/3)2CF2 and (V2/3#1/3)2C(OH)2 as stable structures. Among them, (V2/3Zr1/3)2CO2 MXene is predicted to be an FM intrinsic half semiconductor with a remarkably high Curie temperature (TC) of 270 K. The (V2/3Zr1/3)2C(OH)2 MXene exhibits a rather low work function (WF) (1.37 eV) and is thus a promising candidate for ultra low work function electron emitters. Conversely, the (V2/3#1/3)2CF2 MXene has a rather high WF and hence can be used as a hole injector for Schottky barrier free contact applications. Overall, our proof of concept study shows that theoretical predictions of MXene exfoliation and properties support further experimental research towards developing spintronics devices.
author_names: Shuo Li

Junjie He

Petr Nachtigall

Luk'avs Grajciar

Federico Brivio
title: Control of spintronic and electronic properties of bimetallic and vacancy ordered vanadium carbide MXenes via surface functionalization.
venue: Physical chemistry chemical physics PCCP
year: 2019

abstract: With the development of electronic devices such as integrated circuits toward the continual increase in power density and consumption, the efficient heat dissipation and low thermal expansion of materials become one of the most important issue. However, conventional polymers have the problem of poor thermal dissipation performance, which hinder application for electronic devices. In this work, the two dimensional material, MXene (Ti3C2) is used as the reinforcement additive to optimize the thermal properties of polymers. We reported the preparation of multilayer Ti3C2 MXene by HF etching method and obtained few layer Ti3C2 MXene by simple ultrasonication. Meanwhile, Ti3C2/epoxy composites were prepared by a solution blending method. The results show that the thermal properties of the composites are improved in comparison with the neat epoxy. Thermal conductivity value (0.587 W/mK) of epoxy composite with only 1.0 wt% Ti3C2 MXene fillers, is increased by 141.3% compared with that of neat epoxy. In addition, the composite presents an increased glass transition temperature, high thermal stability and lower coefficient of thermal expansion. This work is of great significance for the research of high performance composite materials.
author_names: Ruiyang Kang

Zhenyu J Zhang

Liangchao Guo

Junfeng Cui

Yapeng Chen

Xiao Hou

Bo Wang

Cheng-Te Lin

Nan Jiang

Jinhong Yu
title: Enhanced Thermal Conductivity of Epoxy Composites Filled with 2D Transition Metal Carbides (MXenes) with Ultralow Loading
venue: Scientific Reports
year: 2019

abstract: Strain engineering appears as an effective way to modulate physical and chemical properties of two dimensional (2D) materials. In contrast to their three dimensional counterparts, 2D materials can withstand high strain before rapture, which promises unique opportunities to control and tune their electronic, optical, and magnetic properties. Recently predicted Hf 2 MnC 2 O 2 and Hf 2 VC 2 O 2 double transition metal ferromagnetic semiconductor MXenes show robust ferromagnetic ground state with high Curie temperature. In this study, we investigated the structural, electronic, and magnetic properties of those 2D materials under the biaxial strain using density functional theory. Both strain free monolayers are indirect bandgap semiconductors. Strain engineering can be exploited to turn semiconductor monolayers into metallic or semi metallic ones depending on the size and type of the applied strain. For instance, a semiconductor to metal transition occurs at 3 compression and 8% tension in Hf 2 MnC 2 O 2 and also at 2 compression and 9% tension in Hf 2 VC 2 O 2. Electron and hole effective masses are able to be tuned significantly. The ferromagnetic phase becomes stronger (weaker) as compared to the anti ferromagnetic phase of both types of monolayers by applying the biaxial tensile (compressive) strain. Our calculations indicated that the Curie temperature T C) is highly sensitive to the size and type of strain. T C increases (decreases) with the tensile (compressive) strain. While T C is 444 K at a compressive strain of 4% it becomes 1577 K at a tensile strain of 8% for Hf 2 MnC 2 O 2.Strain engineering appears as an effective way to modulate physical and chemical properties of two dimensional (2D) materials. In contrast to their three dimensional counterparts, 2D materials can withstand high strain before rapture, which promises unique opportunities to control and tune their electronic, optical, and magnetic properties. Recently predicted Hf 2 MnC 2 O 2 and Hf 2 VC 2 O 2 double transition metal ferromagnetic semiconductor MXenes show robust ferromagnetic ground state with high Curie temperature. In this study, we investigated the structural, electronic, and magnetic properties of those 2D materials under the biaxial strain using density functional theory. Both strain free monolayers are indirect bandgap semiconductors. Strain engineering can be exploited to turn semiconductor monolayers into metallic or semi metallic ones depending on the size and type of the applied strain. For instance, a semiconductor to metal transition occurs at 3 compression and 8% tension
author_names: Edirisuriya M D Siriwardane

Deniz Cakir
title: Strain engineering of electronic and magnetic properties of double transition metal ferromagnetic semiconductor MXenes
venue: Journal of Applied Physics
year: 2019

abstract: MXenes have demonstrated high performance as negative electrodes in supercapacitors with aqueous electrolytes due to their high redox capacitance. However, oxidation limits their use under positive potential, requiring asymmetric devices with positive electrodes made of other materials which are usually less capacitive compared to MXenes and therefore limit the device performances. Here, we report the synthesis of two dimensional molybdenum vanadium carbides (MoxV4 xC3) previously unexplored double transition metal MXenes, by selective etching of aluminum from MoxV4 xAlC3 MAX phase precursors. Unlike the ordered double transition metal MXenes reported previously, MoxV4 xC3 exhibits a Mo V solid solution in the transition metal layers. We have synthesized and characterized four different compositions of MoxV4 xC3 with x 1, 1.5, 2, and 2.7. We showed that by changing the Mo V ratio, the surface terminations (O F ratio) and electrical and electrochemical properties of the resulting MXenes can be tuned. The Mo2.7V1.3C3 composition showed a remarkable volumetric capacitance (up to 860 F cm 3) and high electrical conductivity (830 S cm 1) at room temperature. Moreover, these solid solution MXenes have demonstrated the ability to operate in a wider range of positive potentials compared to other MXenes. Following this discovery, we coupled a Mo2.7V1.3C3 positive electrode with a well studied Ti3C2 MXene negative electrode to create an all MXene supercapacitor, as a proof of concept.
author_names: David Pinto

Babak Anasori

Hemesh Avireddy

Christopher Eugene Shuck

Kanit Hantanasirisakul

Grayson Deysher

Joan Ramon Morante

William Porzio

Husam N Alshareef

Yury Gogotsi
title: Synthesis and electrochemical properties of 2D molybdenum vanadium carbides solid solution MXenes
year: 2020

abstract: The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi transition metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas and biosensors, lubrication, and photo electro and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.
author_names: Babak Anasori

Maria R Lukatskaya

Yury Gogotsi
title: 2D metal carbides and nitrides (MXenes) for energy storage
year: 2017

abstract: Growing interest in the potential applications of two dimensional (2D) materials has fueled advancement in the identification of 2D systems with exotic properties. Increasingly, the bottleneck in this field is the synthesis of these materials. Although theoretical calculations have predicted a myriad of promising 2D materials, only a few dozen have been experimentally realized since the initial discovery of graphene. Here, we adapt the state of the art positive and unlabeled (PU) machine learning framework to predict which theoretically proposed 2D materials have the highest likelihood of being successfully synthesized. Using elemental information and data from high throughput density functional theory calculations, we apply the PU learning method to the MXene family of 2D transition metal carbides, carbonitrides, and nitrides, and their layered precursor MAX phases, and identify 18 MXene compounds that are highly promising candidates for synthesis. By considering both the MXenes and their precursors, we further propose 20 synthesizable MAX phases that can be chemically exfoliated to produce MXenes.
author_names: Nathan C Frey

Jin Wang

Gabriel Ivan Vega Bellido

Babak Anasori

Yury Gogotsi

Vivek B Shenoy
title: Prediction of Synthesis of 2D Metal Carbides and Nitrides (MXenes) and Their Precursors with Positive and Unlabeled Machine Learning.
venue: ACS nano
year: 2019

abstract: Summary In 2011, a new and growing family of two dimensional (2D) transition metal carbides, nitrides, and carbonitrides (MXenes) was discovered. Benefitting from intriguing electronic and structural properties, MXenes have received increasing attention and emerged as next generation nanomaterials for the exploration of environmentally friendly energy resources for catalysis in energy and environmental technologies. In this review, we systematically highlight the expeditious advances and achievements in design strategies, physico chemical properties, and catalytic applications of 2D layered MXenes and their nanocomposites in environmental science and renewable energy. In addition, we unravel the structural, optical, and electronic properties of MXenes to elucidate their key roles of ameliorating the niche areas of photo(electro)catalytic hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carabon dioxide reduction reaction, nitrogen reduction reaction, and pollutant degradation. This review concludes with invigorating perspectives, outlooks, and formidable challenges in the future development of MXene based materials for sustainable applications.
author_names: Jiahe Peng

Xingzhuo Chen

Wee-Jun Ong

Xiujian Zhao

Neng Li
title: Surface and Heterointerface Engineering of 2D MXenes and Their Nanocomposites: Insights into Electro and Photocatalysis
year: 2019

abstract: The ability in experiments to control the relative twist angle between successive layers in two dimensional (2D) materials offers an approach to manipulating their electronic properties; we refer to this approach as `twistronics. A major challenge to theory is that, for arbitrary twist angles, the resulting structure involves incommensurate (aperiodic) 2D lattices. Here, we present a general method for the calculation of the electronic density of states of aperiodic 2D layered materials, using parameter free Hamiltonians derived from ab initio density functional theory. We use graphene, a semimetal, and \mathrm{MoS}}_{2} a representative of the transition metal dichalcogenide family of 2D semiconductors, to illustrate the application of our method, which enables fast and efficient simulation of multilayered stacks in the presence of local disorder and external fields. We comment on the interesting features of their density of states as a function of twist angle and local configuration and on how these features can be experimentally observed.
author_names: Stephen Carr

Daniel Massatt

Shiang Fang

Paul Cazeaux

Mitchell Luskin

Efthimios Kaxiras
title: Twistronics: Manipulating the electronic properties of two dimensional layered structures through their twist angle
year: 2017