MAX Phases Barsoum, Michel W
2013, 2013-11-13
eBook
In this comprehensive yet compact monograph, Michel W. Barsoum, one of the pioneers in the field and the leading figure in MAX phase research, summarizes and explains, from both an experimental and a ...theoretical viewpoint, all the features that are necessary to understand and apply these new materials. The book covers elastic, electrical, thermal, chemical and mechanical properties in different temperature regimes. By bringing together, in a unifi ed, self-contained manner, all the information on MAX phases hitherto only found scattered in the journal literature, this one-stop resource offers researchers and developers alike an insight into these fascinating materials.
Since their discovery in 2011, the number of 2D transition metal carbides and nitrides (MXenes) has steadily increased. Currently more than 40 MXene compositions exist. The ultimate number is far ...greater and in time they may develop into the largest family of 2D materials known. MXenes’ unique properties, such as their metal‐like electrical conductivity reaching ≈20 000 S cm−1, render them quite useful in a large number of applications, including energy storage, optoelectronic, biomedical, communications, and environmental. The number of MXene papers and patents published has been growing quickly. The first MXene generation is synthesized using selective etching of metal layers from the MAX phases, layered transition metal carbides and carbonitrides using hydrofluoric acid. Since then, multiple synthesis approaches have been developed, including selective etching in a mixture of fluoride salts and various acids, non‐aqueous etchants, halogens, and molten salts, allowing for the synthesis of new MXenes with better control over their surface chemistries. Herein, a brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided. The fact that their production is readily scalable in aqueous environments, with high yields bodes well for their commercialization.
The transition metal carbides and nitrides (MXenes) are among the largest 2D material families. MXenes’ unique properties, such as their metal‐like electrical conductivity, render them quite useful in a large number of applications including energy storage, optoelectronic, biomedical, communications, and environmental. A brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided.
Recently a new, large family of two‐dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from ...the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2AlC, Ti3AlC2, and Ta4AlC3. MXenes combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. This article reviews progress—both experimental and theoretical—on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.
MXenes are a new family of two‐dimensional early transition metal carbides and carbonitrides produced by etching a metal layer from ternary layered carbides called MAX phases. This review describes the progress—both theoretical and experimental—in the synthesis, understanding of structure, measuring of properties, and development of applications of MXenes. In addition, future research directions and challenging open questions are discussed.
2D transition metal carbides, known as MXenes, are transparent when the samples are thin enough. They are also excellent electrical conductors with metal‐like carrier concentrations. Herein, these ...characteristics are exploited to replace gold (Au) in GaAs photodetectors. By simply spin‐coating transparent Ti3C2‐based MXene electrodes from aqueous suspensions onto GaAs patterned with a photoresist and lifted off with acetone, photodetectors that outperform more standard Au electrodes are fabricated. Both the Au‐ and MXene‐based devices show rectifying contacts with comparable Schottky barrier heights and internal electric fields. The latter, however, exhibit significantly higher responsivities and quantum efficiencies, with similar dark currents, hence showing better dynamic range and detectivity, and similar sub‐nanosecond response speeds compared to the Au‐based devices. The simple fabrication process is readily integratable into microelectronic, photonic‐integrated circuits and silicon photonics processes, with a wide range of applications from optical sensing to light detection and ranging and telecommunications.
Ti3C2‐based MXene contacts—spin‐coated from an aqueous colloidal suspension onto a GaAs substrate—are compared with vacuum‐deposited titanium/gold electrodes for the photodetection of light. Such an MXene‐based device has better detectivity, quantum efficiency, and a higher dynamic range as compared to the conventional Au‐based metal–semiconductor–metal devices.
•Surface chemistry of MXenes characterized by XPS.•Studied the surface chemistry of the MXenes Ti3C2Tx, Ti2CTx, Ti3CNTx, Nb2CTx and Nb4C3Tx.•Freshly prepared and aged surfaces were compared.•Four ...surface moieties were confirmed, including O, OH and F, H2Oads.
In this work, a detailed high resolution X-ray photoelectron spectroscopy (XPS) analysis is presented for select MXenes—a recently discovered family of two-dimensional (2D) carbides and carbonitrides. Given their 2D nature, understanding their surface chemistry is paramount. Herein we identify and quantify the surface groups present before, and after, sputter-cleaning as well as freshly prepared vs. aged multi-layered cold pressed discs. The nominal compositions of the MXenes studied here are Ti3C2Tx, Ti2CTx, Ti3CNTx, Nb2CTx and Nb4C3Tx, where T represents surface groups that this work attempts to quantify. In all the cases, the presence of three surface terminations, O, OH and F, in addition to OH-terminations relatively strongly bonded to H2O molecules, was confirmed. From XPS peak fits, it was possible to establish the average sum of the negative charges of the terminations for the aforementioned MXenes. Based on this work, it is now possible to quantify the nature of the surface terminations. This information can, in turn, be used to better design and tailor these novel 2D materials for various applications.
Abstract
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, (Mo
2/3
Sc
1/3
)
2
AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D Mo
1.33
C sheets with ordered metal divacancies and high electrical conductivities. At ∼1,100 F cm
−3
, this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, Mo
2
C, 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.
•MXenes constitute a family of 2D materials of about 30 different compositions.•Bottom-up synthesis enables the production high-quality thin 2D transition metal carbide and nitride films.•Different ...synthesis pathways have been reported that avoid the use of hazardous HF.•Solid solutions and chemical order in MAX phases have expanded the chemistry of MXenes.
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.
Heterocyclic pyrrole molecules are in situ aligned and polymerized in the absence of an oxidant between layers of the 2D Ti3C2Tx (MXene), resulting in high volumetric and gravimetric capacitances ...with capacitance retention of 92% after 25 000 cycles at a 100 mV s−1 scan rate.
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