MXENE COMPOSITIONS FEATURING FIVE ATOMIC LAYERS
20220363916 · 2022-11-17
Inventors
- Yury Gogotsi (Warminster, PA)
- Christopher Eugene SHUCK (Philadelphia, PA, US)
- Babak ANASORI (Fishers, IN, US)
- Grayson Brouse DEYSHER (San Diego, CA, US)
Cpc classification
C04B2235/3418
CHEMISTRY; METALLURGY
C04B2235/76
CHEMISTRY; METALLURGY
C04B2235/3239
CHEMISTRY; METALLURGY
C09D1/00
CHEMISTRY; METALLURGY
C04B2235/40
CHEMISTRY; METALLURGY
International classification
Abstract
Provided are 5-layered MXene materials having the formulas M.sub.5X.sub.4T.sub.x; (M′aM″b)X.sub.4T.sub.x (where a+b=5); and (M′.sub.aM″.sub.b).sub.5X.sub.4T.sub.x (where a+b=1). Also provided are related methods, compositions, and applications.
Claims
1. A composition, comprising: (a) at least one layer having first and second surfaces, each layer described by a formula M.sub.5X.sub.4T.sub.x and comprising a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of M.sub.5X.sub.4, such that each X is positioned within an array of M, wherein M is at least one Group IIIB, IVB, VB, or VIB metal or a lanthanide, wherein X is C and/or N, and wherein T.sub.x represents optionally present surface termination groups; or (b) at least one layer having first and second surfaces, each layer described by a formula (M′.sub.aM″.sub.b)X.sub.4T.sub.x and comprising a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of (M′.sub.aM″.sub.b)X.sub.4, such that each X is positioned within an array of M′ and M″, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein X is C and/or N, wherein a+b=5, and wherein T.sub.x represents optionally present surface termination groups, or (c) at least one layer having first and second surfaces, each layer described by a formula (M′.sub.aM″.sub.b).sub.5X.sub.4T.sub.x and comprising a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of (M′.sub.aM″.sub.b).sub.5X.sub.4, such that each X is positioned within an array of M′ and M″, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein X is C and/or N, wherein a+b=1, and wherein T.sub.x represents optionally present surface termination groups.
2. The composition according to claim 1, wherein at least one of the first surface and the second surface comprises surface terminations T.sub.x, the surface terminations independently comprising alkoxide, alkyl, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfonate, thiol, or any combination thereof.
3. The composition of claim 1, wherein the composition is characterized as a stacked structure comprising a plurality of the layers.
4. The composition of claim 1, wherein the composition is characterized as being a solid solution.
5. The composition of claim 1, wherein the layer is characterized as comprising 5 atomic layers of M.
6. The composition of claim 5, wherein the layer is characterized as comprising a twinned structure.
7. The composition of claim 1, wherein the composition is characterized as being in flake form.
8. The composition of claim 7, wherein the flake defines a cross-sectional dimension of greater than 1 micrometer.
9. The composition of claim 8, wherein the flake defines a cross-sectional dimension of from about 1 to about 10 micrometers.
10. The composition of claim 1, wherein a layer defines a thickness of at least about 1 nm.
11. The composition of claim 10, wherein a layer defines a thickness of from about 1 to about 2 nm.
12. A component, the component comprising a composition according to claim 1.
13. The component of claim 12, wherein the component is characterized as an optical component, an optomechanical component, a plasmonic component, a signal receiver, a signal transmitter, a fiber, a textile, a radiation shield, or any combination thereof.
14. A component, the component comprising disposed thereon a coating, the coating comprising a composition according to claim 1.
15. A composition, the composition comprising a suspension of a composition according to claim 1.
16. A method, the method comprising synthesizing a composition according to claim 1.
17. A method, comprising removing the A-group element from a MAX phase material so as to form a product composition having the empirical formula of M.sub.5X.sub.4 or M.sub.5X.sub.4(T.sub.s).
18. The method of claim 17, further comprising delaminating layers of the product composition from one another.
19. The method of claim 18, further comprising forming a suspension of delaminated layers of the product composition.
20. The method of claim 19, further comprising forming a free-standing structure of the product composition.
21. A composition, (a) the composition being characterized as having an empirical formula M.sub.5AX.sub.4, wherein M is a Group IIIB, IVB, VB, or VIB metal, and wherein X is C and/or N; or (b) the composition being characterized as having an empirical formula (M′.sub.aM″.sub.b)AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=5, and wherein X is C and/or N; or (c) the composition being characterized as having an empirical formula (M′.sub.aM″.sub.b).sub.5AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=1, and wherein X is C and/or N.
22. The composition of claim 21, wherein A is Al, As, Cd, Ga, Ge, P, Pb, In, S, Sn, or Tl.
23. The composition of claim 21, wherein M, M′, and M″ is independently Cr, Ti, Mo, Nb, V, or Ta, or a combination thereof.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The file of this patent or application contains at least one drawing/photograph executed in color. Copies of this patent or patent application publication with color drawing(s)/photograph(s) will be provided by the Office upon request and payment of the necessary fee.
[0032] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. In the drawings:
[0033]
[0034]
[0035]
[0036]
[0037]
[0038]
[0039]
[0040]
[0041]
[0042]
[0043]
[0044]
[0045]
[0046]
[0047]
[0048]
[0049]
[0050]
[0051]
[0052]
[0053]
[0054]
[0055]
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0056] The present disclosure may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention.
[0057] Also, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. The term “plurality”, as used herein, means more than one. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable, and it should be understood that steps may be performed in any order.
[0058] It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. All documents cited herein are incorporated herein in their entireties for any and all purposes.
[0059] Further, reference to values stated in ranges include each and every value within that range. In addition, the term “comprising” should be understood as having its standard, open-ended meaning, but also as encompassing “consisting” as well. For example, a device that comprises Part A and Part B may include parts in addition to Part A and Part B, but may also be formed only from Part A and Part B.
Terms
[0060] A MXene composition is, generally, any of the compositions described in at least one of U.S. patent application Ser. No. 14/094,966 (filed Dec. 3, 2013), 62/055,155 (filed Sep. 25, 2014), 62/214,380 (filed Sep. 4, 2015), 62/149,890 (filed Apr. 20, 2015), 62/127,907 (filed Mar. 4, 2015) or International Applications PCT/US2012/043273 (filed Jun. 20, 2012), PCT/US2013/072733 (filed Dec. 3, 2013), PCT/US2015/051588 (filed Sep. 23, 2015), PCT/US2016/020216 (filed Mar. 1, 2016), or PCT/US2016/028,354 (filed Apr. 20, 2016), preferably where the MXene composition comprises titanium and carbon (e.g., Ti.sub.3C.sub.2, Ti.sub.2C, Mo.sub.2TiC.sub.2, etc.).
[0061] While MXene compositions include any and all of the compositions described in the patent applications and issued patents mentioned elsewhere herein, in some embodiments, MXenes are materials comprising or consisting essentially of a M.sub.n+1X.sub.n(T.sub.s) composition having at least one layer, each layer having a first and second surface, each layer comprising
[0062] a substantially two-dimensional array of crystal cells.
[0063] each crystal cell having an empirical formula of M.sub.n+1X.sub.n, such that each X is positioned within an octahedral array of M,
[0064] wherein M is at least one Group 3, 4, 5, 6, or 7,
[0065] wherein each X is C and/or N, and
[0066] n=4;
[0067] wherein at least one of said surfaces of the layers has surface terminations, T.sub.s, independently comprising alkoxide, alkyl, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, or a combination thereof;
[0068] As described elsewhere within this disclosure, the M.sub.n+1X.sub.n(T.sub.s) materials produced in these methods and compositions have at least one layer, and sometimes a plurality of layers, each layer having a first and second surface, each layer comprising a substantially two-dimensional array of crystal cells; each crystal cell having an empirical formula of M.sub.n+1X.sub.n, such that each X is positioned within an array of M, wherein M is at least one Group 3, 4, 5, 6, or 7 metal (corresponding to Group IIIB, IVB, VB, VIB or VIIB metal), wherein X is C and/or N and n=4; wherein at least one of said surfaces of the layers has surface terminations, T.sub.s, comprising alkoxide, alkyl, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, or a combination thereof.
[0069] Supplementing the descriptions above, M.sub.n+1X.sub.n(T.sub.s), compositions may be viewed as comprising free standing and stacked assemblies of two dimensional crystalline solids. Collectively, such compositions are referred to herein as “M.sub.n+1X.sub.n(T.sub.s),” “MXene,” “MXene compositions,” or “MXene materials.” Additionally, these terms “M.sub.n+1X.sub.n(T.sub.s),” “MXene,” “MXene compositions,” or “MXene materials” also refer to those compositions derived by the chemical exfoliation of MAX phase materials, whether these compositions are present as free-standing 2-dimensional or stacked assemblies (as described further below). Reference to the carbide equivalent to these terms reflects the fact that X is carbon, C, in the lattice. Such compositions comprise at least one layer having first and second surfaces, each layer comprising: a substantially two-dimensional array of crystal cells; each crystal cell having an empirical formula of M.sub.n+1X.sub.n, where M, X, and n are defined above. These compositions may be comprised of individual or a plurality of such layers. In some embodiments, the M.sub.n+1X.sub.n(T.sub.s) MXenes comprising stacked assemblies may be capable of, or have atoms, ions, or molecules, that are intercalated between at least some of the layers. In other embodiments, these atoms or ions are lithium. In still other embodiments, these structures are part of an energy-storing device, such as a battery or supercapacitor. In still other embodiments these structures are added to polymers to make polymer composites.
[0070] The term “crystalline compositions comprising at least one layer having first and second surfaces, each layer comprising a substantially two-dimensional array of crystal cells” refers to the unique character of these materials. For purposes of visualization, the two-dimensional array of crystal cells may be viewed as an array of cells extending in an x-y plane, with the z-axis defining the thickness of the composition, without any restrictions as to the absolute orientation of that plane or axes. It is preferred that the at least one layer having first and second surfaces contain but a single two-dimensional array of crystal cells (that is, the z-dimension is defined by the dimension of approximately one crystal cell), such that the planar surfaces of said cell array defines the surface of the layer; it should be appreciated that real compositions may contain portions having more than single crystal cell thicknesses.
[0071] That is, as used herein, “a substantially two-dimensional array of crystal cells” refers to an array which preferably includes a lateral (in x-y dimension) array of crystals having a thickness of a single cell, such that the top and bottom surfaces of the array are available for chemical modification.
[0072] Metals of Group 3, 4, 5, 6, or 7 (corresponding to Group IIIB, IVB, VB, VIB, or VIIB), either alone or in combination, said members including, e.g., Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W. For the purposes of this disclosure, the terms “M”, or “M′”, or “M″”, or “M atoms,” “M elements,” or “M metals” may also include Mn. Also, for purposes of this disclosure, compositions where M comprises Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or mixtures thereof constitute independent embodiments. Similarly, the oxides of M may comprise any one or more of these materials as separate embodiments. For example, M may comprise any one or combination of Hf, Cr, Mn, Mo, Nb, Sc, Ta, Ti, V, W, or Zr. In other preferred embodiments, the transition metal is one or more of Ti, Zr, V, Cr, Mo, Nb, Ta, or a combination thereof. In even more preferred embodiments, the transition metal is Ti, Ta, Mo, Nb, V, Cr, or a combination thereof.
[0073] The range of compositions available can be seen as extending even further when one considers that each M-atom position within the overall M.sub.n+1X.sub.n matrix can be represented by more than one element. That is, one or more type of M-atom can occupy each M-position within the respective matrices. In certain exemplary non-limiting examples, these can be (M′.sub.aM″.sub.b)X.sub.4, where M′ and M″ are different metals (e.g., members of the same group), and a+b=5; or (M′.sub.aM″.sub.b).sub.5X.sub.4T.sub.x, where M′ and M″ are different metals (e.g., members of the same group), and a+b=1. As some non-limiting examples, such a composition can be (V.sub.1/2Nb.sub.1/2).sub.5C.sub.4 or (V.sub.1/3Nb.sub.2/3).sub.5N.sub.4.
[0074] In the same way, one or more type of X-atom can occupy each X-position within the matrices, for example solid solutions of the formulae M.sub.5(C.sub.jN.sub.k).sub.4 (where j+k=1); (M′.sub.aM″.sub.b)(C.sub.jN.sub.k).sub.4 (where a+b=5 and j+k=1); and (M′.sub.aM″.sub.b).sub.5(C.sub.jN.sub.k).sub.4 (where a+b=1 and j+k=1).
[0075] MXene materials can be prepared by selectively removing an A group element from a precursor MAX-phase material. Depending on the specific MAX being considered, these A group elements may be independently defined as including Al, As, Cd, Ga, Ge, P, Pb, In, S, Sn, or Tl. These same materials are contemplated as independent embodiments for the A element used in the present invention. Some of these A-group elements may be removed in aqueous media, for example, by a process comprising a treatment with a fluorine-containing acid. For example, Al, As, Ga, Ge, In, P, Pb, S, or Sn may be removed in this way, although Al is especially amenable to such extractions. Aqueous hydrofluoric acid is particularly suitable for this purpose, whether used as provided, or generated in situ by other conventional methods. Such methods include the use of any one or more of the following:
[0076] (a) aqueous ammonium hydrogen fluoride (NH.sub.4F.HF);
[0077] (b) an alkali metal bifluoride salt (i.e., QHF.sub.2, where Q is Li, Na, or K), or a combination thereof; or
[0078] (c) at least one fluoride salt, such as an alkali metal, alkaline earth metal, or ammonium fluoride salt (e.g., LiF, NaF, KF, CsF, CaF.sub.2, tetraalkyl ammonium fluoride (e.g., tetrabutyl ammonium fluoride)) in the presence of at least one mineral acid that is stronger than HF (i.e., has a higher Ka value) and can react with fluorides to form HF in situ (such as HCl, HBr, HI, H.sub.3PO.sub.4, HNO.sub.3, oxalic acid, or H.sub.2SO.sub.4); or
[0079] (d) a combination of two or more of (a)-(c). in some cases, the use of molten fluoride salts in inert atmosphere (Ar, N.sub.2) may be used to remove the group 13 or 14 element (e.g., at 500-600° C., e.g., above the melting temperature of LiF, NaF, KFCsF, CaF.sub.2 salts).
[0080] In specific embodiments, the fluorine-containing acid is derived from lithium fluoride and a strong aqueous mineral acid, such as HCl, HNO.sub.3, or H.sub.2SO.sub.4, preferably HCl.
[0081] It also appears that the use of aqueous HF in the presence of one or more alkali halides, such as LiCl, provides advantages over using HF alone, or by reacting LiF with aqueous HCl. The use of LiF with aqueous HCl avoids the handling issues associated with the use of aqueous HF and provides higher yields of single-layer flakes, in some cases it may be difficult to remove LiF impurities and the removal of the A-element (e.g., Al) is slower. The use of LiCl with aqueous HF provides more crystalline MXene phases, with better control of the basal spacing (c parameter) and it is easier to vary the procedures especially for those involving ion intercalation. The foregoing is exemplary only, however, and does not limit the scope of the present disclosure or the appended claims.
[0082] Two-dimensional (2D) materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have gained significant attention due to their unique electronic, photonic, electrochemical, and optical properties. The 2D nature of these materials allows for novel applications compared to their bulk counterparts such as transitors.sup.1, solar cells, touch screens, biosensors, and lasers. In 2011, MXenes were introduced as a new family of 2D materials.
[0083] MXenes are 2D transition metal carbides and nitrides that have the formula unit M.sub.n+1X.sub.nT.sub.x where M stands for an early transition metal (Ti, Nb, V, Cr, Mo, Ta, etc.), X stands for carbon and/or nitrogen, T.sub.x represents surface termination groups such as —OH, ═O and —F, and n is an integer from 1 to 3. Here, the common notation M.sub.n+1X.sub.n will be used and we do not show the T.sub.x for brevity. Within the three types of M.sub.2X, M.sub.3X.sub.2, and M.sub.4X.sub.3 MXene structures, there are several available compositional possibilities including the mono-metal MXenes, ordered double metal MXenes with in-plane and out-of-plane ordering ((M′M″).sub.n+1X.sub.n), divacancy MXenes with the formula unit M.sub.1.33X.sub.n, and solid solution MXenes containing a mixture of multiple metals in the M sites.
[0084] MXenes have become increasingly researched due to exceptional properties such as high volumetric capacitance, antibacterial properties, electrochromic behavior, high electronic conductivity, and optical transparency. These properties have demonstrated to be beneficial for numerous applications including energy storage, catalysis, antennas and RFID tags, electromagnetic interference (EMI) shielding, sensors, and as plasmonic metamaterials. Furthermore, it has been shown that the MXene composition and structure play a vital role in the observed properties. A list of experimentally synthesized MXenes reported to date, including the one reported here, is shown in
[0085] MXenes can be produced by the selective chemical etching of specific atomic planes from layered carbide/nitride precursors. Most commonly, M.sub.n+1AX.sub.n(MAX) phases are the precursor materials and MXenes are produced by selectively etching the A layers, where A represents Al or Si. The resulting MXene structure is dependent on that of its MAX phase precursor, which has limited the MXene family to materials with 2, 3, or 4 atomic layers of transition metal. Provided here is a new, unexpected MXene with 5 atomic layers of transition metal (e.g., M.sub.5X.sub.4). The new MXene can be made from by synthesizing its precursor MAX phase with 5 atomic layers of transition metal.
[0086] In some instances, the presence of different MAX phases (M.sub.2AC, and M.sub.4AC.sub.3) as impurities can result in a MXene that contains other MXenes (for example, M.sub.2C and M.sub.4C.sub.3 in a M.sub.5C.sub.4 MXene). A M.sub.5AX.sub.4 MAX phase with no other MAX phase impurities can be used to synthesize the first phase pure M.sub.5X.sub.4 MXene, though this is not at all times a requirement.
[0087] Here we present an example Mo.sub.4VAlC.sub.4 MAX phase with no other MAX phase impurities, allowing for the synthesis of Mo.sub.4VC.sub.4 MXene. We provide structural characterization via high-resolution transmission electron microscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy. In addition, chemical characterization via energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy is presented with the optical, electrical, and thermal properties of Mo.sub.4VC.sub.4 determined via UV-vis-NIR spectrophotometry, temperature-dependent resistivity, and thermogravimetric analysis. Density functional theory calculations were used to show the theoretical stabilities of other M.sub.5AX.sub.4 phases. Due to the increased number of atomic layers in their structure, MXenes with 5 atomic transition metal layers have attractive mechanical properties allowing for stronger metal matrix composites, better EMI shielding capabilities, and higher electrical conductivity for electronic applications.
[0088] It should be understood that although Mo.sub.4VAlC.sub.4 is used herein as an example MAX-phase material for the further formation of a 5-layer MXene (Mo.sub.4VC.sub.4), it should be understood that both Mo.sub.4VAlC.sub.4 MAX-phase material and Mo.sub.4VC.sub.4 MXene are illustrative only and do not limit the scope of the present disclosure or the appended claims.
[0089] Experimental Procedure
[0090] Synthesis of Mo.sub.4VAlC.sub.4 MAX
[0091] Molybdenum (99.9% Alfa Aesar, −250 mesh), vanadium (99.5% Alfa Aesar, −325 mesh), vanadium (III) oxide (98% Sigma Aldrich), aluminum (99.5% Alfa Aesar, −325 mesh), and graphite (99% Alfa Aesar, −325 mesh) powders were hand-mixed with a mortar and pestle for 5 min in a molar ratio of 4:0.9:0.05:1.2:3.5 (Mo:V:V.sub.2O.sub.3:Al:C). To determine the proper Mo:V mixing ratio, we mixed a series different ratios from 0-100% Mo (
[0092] Synthesis of Mo.sub.4VC.sub.4 MXene
[0093] A schematic for the synthesis of Mo.sub.4VC.sub.4 MXene is shown in
[0094] Exfoliation of the ML MXene was achieved by dispersing 0.25 g of ML Mo.sub.4VC.sub.4 powder in a 10 mL solution of 10 wt. % tetramethylammonium hydroxide (TMAOH, 25 wt. %—diluted to 10 wt. %, Sigma Aldrich) and stirred at 400 rpm at 25° C. for 24 h. Another series of washing cycles was used to remove the TMAOH. In brief, the mixture was centrifuged at 8,000 rpm (8230 rcf) for 30 min to settle the material and, after decanting the alkaline supernatant, the sediment was re-dispersed with DI water and this was repeated 5 times. High-speed centrifugation was needed due to the stability of the Mo.sub.4VC.sub.4 flakes in the alkaline solution. Once the decanted supernatant had a pH<8, the remaining sediment was re-dispersed in 30 mL of DI water and bath sonicated (100 W, 40 kHz) for 1 h with argon bubbling through it. After sonication, the solution was centrifuged at 3500 rpm (2550 rcf) for 1 h. The resulting supernatant was carefully removed with a pipette to avoid re-dispersal of, and contamination with, the ML MXene/MAX phase sediment and transferred into a separate bottle.
[0095] Mo.sub.4VC.sub.4 Film Preparation
[0096] To obtain a free-standing film of Mo.sub.4VC.sub.4, the colloid containing delaminated MXene flakes was filtered via vacuum-assisted filtration through a Celgard membrane (Celgard 3501-64 nm porous polypropylene). The resulting MXene films were dried in a vacuum desiccator for 18 h at 25° C.
[0097] Structural Characterization
[0098] Crystal structures were characterized with X-ray diffraction (XRD). Rigaku SmartLab and MiniFlex X-ray diffractometers were used and Ni-filtered Cu-Ku radiation was used at 40 kV/30 mA and 40 kV/15 mA respectively. The step size of the scan was 0.01° with a step duration of 4 s for the as-produced Mo.sub.4VAlC.sub.4 and 2 s and ML Mo.sub.4VC.sub.4 and Mo.sub.4VC.sub.4 films. The appended table provides the position of XRD peaks, d spacings, and corresponding intensities for the as-prepared Mo.sub.4VAlC.sub.4 sample powder from 3-120°.
[0099] Microscopy
[0100] Scanning electron microscopy (SEM) micrographs were obtained with a Zeiss Supra 50VP scanning electron microscope and an FEI Strata DB235 Dual Beam Focused Ion Beam SEM. Transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and selected area electron diffraction (SAED) were performed on a JEOL JEM F200 and JEOL NEOARM at an operating voltage of 200 kV. The colloids containing delaminated Mo.sub.4VC.sub.4 flakes and particles of Mo.sub.4VAlC.sub.4 and ML Mo.sub.4VC.sub.4 were drop-cast onto TEM grids. Atomic force microscopy (AFM) was performed with a Bruker Multimode 8 with a Si tip (Budget Sensors Tap300Al-G; f.sub.0=300 kHz, k=40 N/m) via a standard tapping mode in air. The colloid containing delaminated Mo.sub.4VC.sub.4 flakes was drop-cast onto oxygen plasma-cleaned SiO.sub.2/Si wafers.
[0101] Compositional Characterization
[0102] Chemical compositions were determined by energy dispersive X-ray spectroscopy (EDS) measurements. EDS spectra of the MAX phase and ML MXene particles were recorded by a FEI Strata DB235 Dual Beam Focused Ion Beam SEM with EDS with a 25 kV beam and an average of 360,000 counts per spectrum. Atomic-resolution EDS spectra of the MAX and MXene atomic layers were recorded.
[0103] Chemical compositions were also determined via X-ray photoelectron spectroscopy (XPS). XPS spectra were collected by a spectrometer (Physical Electronics, Versa Probe 5000, MN) using a monochromatic Al Ku X-ray source with 200 μm spot size. Charge neutralization was performed using a dual-beam charge neutralizer. The sample was sputtered with high energy Ar (2 kV, 2 pA) for 2 min inside the analysis chamber. High-resolution spectra were collected at a pass energy of 23.5 eV with a step size of 0.05 eV, whereas the survey spectra were collected at a pass energy of 117 eV with a step size of 0.5 eV. The quantification and peak fitting of the core-level spectra was performed using Casa XPS software package with Shirley-type background.
[0104] Raman spectra were obtained with an inverted reflection mode Renishaw (2008, Glouceshire, UK) instrument, equipped with 63× (NA=0.7) objectives and a diffraction-based room-temperature spectrometer. The laser line used was 514 nm (Ar laser with 488 and 514 nm emissions) with an 1800 line/mm grating. The power of the laser was kept in the ˜0.5-1 mW range. Mapping was performed by raster scanning in the streamline mode at a 0.5μ x-axis step, the final spectra were an average of all collected data. Fitting was performed in Renishaw WiRE 3.4 software. The Mo.sub.4VAlC.sub.4 MAX phase and Mo.sub.4VC.sub.4 ML MXene powder were pressed in a 13 mm diameter die to form pellets that were analyzed with the spectrometer.
[0105] Optical Properties
[0106] UV-visible spectrophotometry spectra were obtained by spray coating thin films of Mo.sub.4VC.sub.4 onto oxygen plasma-cleaned glass slides. Films of various thickness were measured via UV-vis spectrophotometry from 300-1000 nm (Thermo Scientific Evolution 201) and from 1100 to 2500 nm (Nicolet iS50R FT-IR) operating in transmission mode. Glass slides were used as a blank. Transmission was measured on three locations on each film and the average spectra are reported.
[0107] Electrical Properties
[0108] Electrical resistivity was measured using a Jandel cylindrical four-point probe with a ResTest Test Unit. The thickness of Mo.sub.4VC.sub.4 MXene films was measured with a micrometer. The thickness of each film and the resistivity was measured on 10 places on each film and the average values are reported.
[0109] Temperature-dependence of resistivity and Hall measurements were performed in physical property measurement system (PPMS, Evercool II, Quantum Design). Free-standing MXene films were wired to the PPMS sample holder using silver wire and silver paint in 4-point and van de Pauw configurations. The resistance of the film was recorded from 10 to 300 K with a heating/cooling rate of 4 K/min. Magnetoresistance (MR) and Hall resistance were measured at 10 K with a magnetic field up to 5 Tesla applied perpendicular to the sample surface.
[0110] Thermal Analysis
[0111] The thermal stability of a Mo.sub.4VC.sub.4 film was studied by thermogravimetric analysis (SDT 650, TA Instruments) connected to a mass spectrometer (Discovery, TA Instruments). Free-standing MXene films with masses around 5 mg were packed in a 90 μL alumina pan and heated to 1500° C. at a constant heating rate of 10° C./min under Ar atmosphere (100 mL/min). The furnace was purged with Ar gas (100 mL/min) for 1 h before the analysis to remove air residue.
[0112] Density Functional Theory Calculations
[0113] The Vienna Ab-Initio Simulation Package (VASP) was used for all DFT calculations. Structural relaxations were performed with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and projector augmented wave (PAW) pseudopotentials, with a 520 eV plane-wave basis cutoff, a 8×8×1 Γ centered k-point mesh for structural relaxations, and forces on each atom converged to below 10.sup.−2 eV/A. Electronic property calculations and total energies were converged to 10.sup.−8 eV and a dense 18×18×1 Γ centered k-point mesh was used. 2×2×1 supercells (with 32 Mo atoms and 8 V atoms) were constructed to approximate disordered Mo.sub.4VC.sub.4 solid solutions. The Mo:V composition of 4:1 was kept fixed in all solid solution calculations and 18 configurations were generated by randomly positioning the Mo and V atoms in the structure. Meshes were adjusted appropriately for 2×2×1 supercell solid solution calculations. The calculations for the stabilities of other M′.sub.4M′AlC.sub.4 MAX phases were limited to ordered phases where M″ was sandwiched between two atomic layers of M′ on both sides. Calculations of formation energies relative to the most stable unary phases provide trends in stability. However, the materials with negative formation energies could decompose into competing binary carbide, intermetallic, or other MAX phases that are more stable. Likewise, there may be materials with more stable solid solution phases that have not been considered here. The work presented here is meant to serve as a benchmark and to provide trends in stability as a function of M element composition.
[0114] Results and Discussion
[0115] Synthesis and Structural Characterization
[0116] To identify the proper chemistry for M.sub.5AlC.sub.4 synthesis, we mixed six sets of starting powder mixtures with Mo.sub.x:V.sub.5-x ratios where x=5, 4, 3, 2, 1, and 0. We used XRD after the MAX synthesis process at 1650° C. and determined that only the sample with a Mo:V ratio of 4:1 produced a M.sub.5AlC.sub.4 phase, as shown in
[0117] We also used XRD to examine the crystal structure of both the Mo.sub.4VAlC.sub.4 MAX phase and Mo.sub.4VC.sub.4 MXene (
[0118] Similar to other Al-containing MAX phases, we attempted to etch the Al layers with HF. During the first centrifugation wash cycle after the HF selective etching, the supernatant had a slight green tint (
[0119] Although the foregoing example describes chemical exfoliation, it should be understood that exfoliation can also be accomplished by other approaches, e.g., electrochemically. In various embodiments, MAX phase materials are selectively exfoliated to form the corresponding MXene by the application of potentiostatic or galvanostatic polarization. Still further, in addition to those embodiments described for the compositions provided above, other embodiments provide for compositions provided by the methods of preparation described herein. For example, those composition obtained from subjecting a MAX phase material to a chemical exfoliation process, said exfoliation process comprising treatment with aqueous HF and sonication, wherein a substantial portion of the A atoms are removed should also be considered within the scope of the present invention.
[0120] Microscopy
[0121] SEM of Mo.sub.4VAlC.sub.4 (
[0122] Upon further examination at higher-resolution it was discovered that the center Mo/V plane of atoms is a twin plane forming a herring bone-type structure (
[0123] After delamination, Mo.sub.4VC.sub.4 colloid was drop-cast onto porous alumina and SEM shows the individual 2D flakes (
[0124] Compositional Characterization
[0125] After determining the atomic structure, we turned our attention to the composition. As a qualitative tool, we used EDS to explore the compositions of the Mo.sub.4VAlC.sub.4 MAX phase particles after HCl washing, ML Mo.sub.4VC.sub.4 MXene particles, and the free-standing film of delaminated MXene (Table 1). Since the MAX powder likely contained binary carbide impurities that remained after HCl washing, EDS was done on particles with a visible layered structure, similar to
TABLE-US-00001 TABLE 1 EDS measurements of Mo:V:Al:C:F:O atomic ratios for the MAX phase (3 particles measured), ML MXene (6 particles measured), and free-standing film of delaminated MXene (5 spots measured). The values shown are atomic percentage normalized so that (MoV) = 5. Error is defined as one standard deviation Sample Mo V Al c F O Mo.sub.4VAlC.sub.4 3.89 ± 1.11 ± 0.29 ± 0.41 ± — 0.15 ± 0.02 0.02 0.13 0.08 0.02 Mo.sub.4VC.sub.4 (ML) 4.06 ± 0.94 ± — 5.72 ± 0.54 ± 1.83 ± 0.07 0.07 0.46 0.03 0.07 Mo.sub.4VC.sub.4 (DL) 4.04 ± 0.96 ± — 1.80 ± 0.01 ± 0.47 ± 0.04 0.04 0.29 0.01 0.12
[0126] While the Mo:V ratio used for synthesizing the Mo.sub.4VAlC.sub.4 MAX phase was 4:1, the resulting material had a ratio of Mo.sub.3.89:V.sub.1.11 (Table 1). After the HF treatment, the resulting Mo.sub.4VC.sub.4 MXene had a ratio of Mo.sub.4.06:V.sub.0.94. After delamination with TMAOH, the ratio remained about the same—Mo.sub.4.04:V.sub.0.96. The fluctuations in the Mo:V ratio are likely within reasonable error of the EDS detector, which means the selective etching was done for Al layers. The slight change in the Mo/V ratio might also be due to dissolution of some V atoms from the surface layer of the carbide, which agrees with the green color of the solution during the first wash. The amount of fluorine present decreases after delamination. It has been shown previously that TMAOH decreases F content, specifically for the Mo-containing MXenes.sup.60-61. Nonetheless, the fluorine content before delamination is still significantly lower compared to titanium-based MXenes, which is in agreement with previously reported work indicating that Mo on the surface preferentially bonds with —OH or ═O terminations rather than —F.sup.63.
[0127] An atomic-resolution EDS spectrum was also obtained to determine whether the Mo/V layers were ordered or disordered solid solutions (
[0128] XPS was used to quantify the transition metal ratio, and the C content in Mo.sub.4VC.sub.4 MXene and its precursor. XPS of Mo.sub.4VAlC.sub.4 MAX phase is discussed herein. The Mo 3d region (
[0129] The Raman spectra of Mo.sub.4VAlC.sub.4, ML Mo.sub.4VC.sub.4 and a free-standing film of delaminated Mo.sub.4VC.sub.4 MXene (
[0130] Thermal Analysis
[0131] The thermal behavior of a Mo.sub.4VC.sub.4 film was determined by thermogravimetric analysis (TGA) coupled with mass spectrometry (MS) under Ar flow. The thermogram (
[0132] For a sample treated at 500° C. under Ar flow, there is another shift in the (002) peak indicating a decrease in c-LP of 3.8 Å from the sample treated at 150° C. and a total of 7.8 Å decrease in c-LP from the as prepared sample (
[0133] Overall, our TGA-MS results show that H.sub.2O and TMA.sup.+ ions occupy similar amounts of space between the MXene flakes. The temperatures for the removal of residual H.sub.2O and TMAOH are in agreement with previously reported results for another Mo-containing MXene; Mo.sub.2C..sup.24 Our results indicate that Mo-containing MXenes have similar thermal behaviors due to similar bonding strengths between Mo and molecules on the surface, but these behaviors have been shown to be different than MXenes with other M elements. The next weight loss began at ˜505° C. and was indicated by C leaving the structure as CO. This is similar to the behavior exhibited by Mo.sub.2C. After the heat treatment at 900° C. under Ar flow, after the next two peaks (638° C. and 742° C.) that occur immediately after each other (
[0134] Electrical and Optical Properties
[0135] The electrical resistivity of an as-prepared Mo.sub.4VC.sub.4 free-standing film was measured with a 4-point probe. Each film's thickness and resistivity values were quite uniform (standard deviation=0.82 μm and 0.10 mΩ cm respectively). The resistivity was measured to be 4.18 mΩ cm (conductivity 240 S/cm). To remove the effects of water and TMAOH intercalants, the as-prepared sample was heated at 500° C. in an Ar atmosphere for 5 h. We chose 500° C. annealing temperature based on our TGA results (
[0136] The electrical resistivity of Mo.sub.4VC.sub.4 films as a function of temperature was measured after drying at 150° C. in a vacuum oven and annealing at 500° C. under an Ar atmosphere. The results (
[0137] The magnetoresistance was measured at 10 K with a magnetic field up to 5 Tesla applied perpendicular to the sample surface. Mo.sub.4VC.sub.4 exhibits a positive MR as shown in
[0138] Delaminated Mo.sub.4VC.sub.4 solutions were deposited onto glass substrates using a spray coating method to screen the optical properties. As determined via UV-vis-NIR spectroscopy, with multiple spray coatings, there is a decrease in transparency observed across all measured wavelengths (
[0139] Density Functional Theory
[0140] DFT calculations were performed to determine the preferred termination groups that can exist on the surface of Mo.sub.4VC.sub.4 MXene. The results of these calculations indicate that —OH is the most preferred termination group with −9.10 eV formation energy. ═O and —F terminations are not as stable (−5.39 eV and −6.56 eV respectively) which agrees with the experimental results presented here (
[0141] DFT calculations were also performed to determine the thermodynamic stability of other M.sub.5AlC.sub.4 MAX phases. Specifically, the formation energies of ordered M′.sub.4M′AlC.sub.4 compositions were calculated where M′ and M″ were Hf, Zr, Ti, Ta, Nb, V, Sc, Mo, and W. A summary of the predicted stability of these phases is shown in
[0142] Interestingly, other phases studied, such as ordered phases containing Hf, Zr, and Ta, are predicted to be more stable than the synthesized Mo.sub.4VAlC.sub.4. The effect that the M′ element has on the stability was determined to be much greater than that of M″. W- and Mo-containing compositions are the least stable and are the only two M′ elements that produce some unstable compositions. For both Mo— and W-based MAX phases specifically, it is known that Mo and W avoid stacking with C in a face center cubic structure (FCC), so adding another M element can allow for Mo— and W-based MAX/MXene to be synthesized as the additional M element will occupy some of the FCC sites thus relieving stress within the crystal structure. However, here we considered only ordered phases in
[0143] These calculations show that there is potential for expansion to other M.sub.5AlC.sub.4 MAX phases, allowing for more M.sub.5X.sub.4 MXenes to be produced. It is important to note that while many of these ordered M′.sub.4M′AlC.sub.4 phases were determined to be stable compared to their respective unary phases, there may be binary carbides, intermetallics, or other competing MAX phases that are more stable for these compositions. Full evaluation of the possibilities for new M′.sub.4M″X.sub.4 MXene synthesis requires solid solution calculations, precise determination of this 5-layered crystal structure, dynamical and phase stability analysis.sup.72, and calculating exfoliation energies.sup.46. However, the results presented here give insight into the stability trends of M′.sub.4M′AlC.sub.4 MAX phases and indicate the huge space of new promising structures to explore via computation and machine leaming.sup.73 to accelerate the expansion of the MXene family.
[0144] Additional Disclosure
[0145] Mo.sub.4VAlC.sub.4 MAX Phase Synthesis and Washing
[0146] To explore the entire (MoV).sub.5AlC.sub.4 system, we mixed samples covering the whole range from 0-100% Mo (
[0147] While the MAX phase sample powder contained only one type of MAX phase, there were additional impurities present. To remove some of these, namely Al.sub.4C.sub.3, the powder was washed with 12 M HCl. XRD confirms the removal of Al.sub.4C.sub.3 after washing (
[0148] Interestingly, V.sub.2O.sub.3 is required in the initial mixing powder to form the Mo.sub.4VAlC.sub.4 phase. As for the V source, we used V:V.sub.2O.sub.3 0.9:0.05 instead of pure V in the starting powder mixture for the MAX synthesis. Without the addition of V.sub.2O.sub.3 the resulting material contains Mo.sub.2C and VC (
[0149] The mixture of elemental and oxide powders (molybdenum (99.9% Alfa Aesar, −250 mesh), vanadium (99.5% Alfa Aesar, −325 mesh), vanadium (III) oxide (98% Sigma Aldrich), aluminum (99.5% Alfa Aesar, −325 mesh), and graphite (99% Alfa Aesar, −325 mesh)) was divided into 7 g quantities that were each poured into 10 mL alumina crucibles. To compact the powder in the crucibles, they were each tapped gently on the counter 80 times, rotating the crucible 90 degrees after every 20 taps to ensure a level top for even heating.
[0150] To wash the MAX after the HCl treatment, 50 mL of HCl/MAX phase mixture was poured into a 50-mL centrifuge tube and centrifuged at 3500 rpm (2550 rcf) for 2 min. Afterwards, the MAX phase particles had settled to the bottom of the centrifuge tube as sediment and the supernatant was transparent. There were also many particles of PTFE floating in the solution. This is due to the high hardness of the MAX phase sample powder which wears away the PTFE stir bars. These particles should be skimmed off to avoid contamination of the sample. This supernatant was decanted off into an appropriate HCl waste bottle. Fresh DI water was added to the tube and, after securing the cap, the tube was hand-shaken to re-disperse the MAX phase sediment. The same centrifugation and decantation procedure was repeated 4 additional times to neutralize the MAX phase.
[0151] Mo.sub.4VC.sub.4 Multilayer MXene Washing
[0152] The 40 mL of HF/MXene solution was poured into a 250 mL centrifuge tube. Additional DI water was added to fill the tube. The tube was centrifuged at 3500 rpm (2550 rcf) for 3 min. Afterwards all the ML MXene had settled to the bottom of the tube and the supernatant was transparent with a slight tint of green due to dissolved vanadium oxide (
[0153] Mo.sub.4VC.sub.4 MXene Delamination Washing
[0154] A more aggressive centrifugation cycle was needed to wash the delaminated SF MXene. Washing can still be done at 3500 rpm (2550 rcf) however it takes much longer to settle the MXene flakes. Typically, at 3500 rpm (2550 rcf), each washing cycle is >1 h. Since the solution heats up during this long centrifugation, in between washes, the solution should be cooled back down in a refrigerator for 10 min before the next centrifugation to avoid oxidation and degradation of the flakes. Ideally, centrifugation can be done at 8000 rpm (8230 rcf) for 30 min cycles. For delaminating 0.25 g of ML MXene, 5 washes are needed to achieve a neutral pH.
[0155] Mo.sub.4VC.sub.4 MXene Delamination Optimization
[0156] As a part of optimizing the delamination procedure, various concentrations of TMAOH were used to delaminate samples. TMAOH can lead to degradation of the MXene flakes so ideally, the lowest TMAOH concentration possible that still produces a reasonable yield (>1 mg/mL) should be used. After washing each sample to neutral pH, the sediment was bath sonicated for 1 h with Argon bubbling. Each sample, containing 30 mL of solution, was centrifuged at 3500 rpm (2550 rcf) for 1 h to obtain a dark supernatant. After centrifugation, the supernatants were carefully removed with a 3 mL pipette and transferred into a vacuum-assisted filtration setup. The resulting films were dried in a vacuum desiccator overnight and then weighed with a Mettler Toledo UMX2 Ultra-microbalance to determine the mass yield of each TMAOH concentration. After testing 6 different concentrations ranging from 1-25 wt. %, all samples had roughly the same yield (
[0157] In addition to the yield of the delamination method, the quality of the resulting flakes is also important. Some of the colloid of each of these samples was drop-cast onto porous alumina substrates and SEM was used to determine the apparent quality of the flakes. These samples are shown in
[0158] Microscopy
[0159]
[0160]
[0161] Mo.sub.4VAlC.sub.4 X-ray Diffraction Data
TABLE-US-00002 TABLE 2 Peak positions and normalized intensities from the XRD pattern of the Mo.sub.4VAlC.sub.4 MAX phase sample powder. The d spacings of each peak are also provided d Spacing Normalized 2θ (°) (Å) Intensity 6.26 14.108 0.299 12.58 7.031 0.215 18.92 4.687 0.275 20.97 4.233 0.113 22.97 3.869 0.091 25.37 3.508 0.109 27.02 3.297 0.108 31.85 2.807 0.190 34.65 2.587 0.126 35.15 2.551 0.427 35.88 2.501 0.105 35.89 2.500 0.101 36.76 2.443 0.704 37.16 2.418 0.371 38.46 2.339 0.765 39.42 2.284 0.613 39.76 2.265 1.000 42.88 2.107 0.513 43.40 2.083 0.420 46.97 1.933 0.131 47.73 1.904 0.135 52.77 1.733 0.089 55.05 1.667 0.080 56.88 1.617 0.098 58.18 1.584 0.219 61.99 1.496 0.345 62.50 1.485 0.148 64.11 1.451 0.119 68.67 1.366 0.136 70.54 1.334 0.204 71.49 1.319 0.069 72.66 1.300 0.062 73.44 1.288 0.084 74.30 1.276 0.152 74.54 1.272 0.348 74.75 1.269 0.207 75.42 1.259 0.218 75.94 1.252 0.130 76.22 1.248 0.142 77.34 1.233 0.117 78.29 1.220 0.127 78.52 1.217 0.097 82.53 1.168 0.094 90.31 1.086 0.070 93.98 1.053 0.080 94.27 1.051 0.059 95.47 1.041 0.056 97.99 1.021 0.056 99.58 1.009 0.075 101.42 0.995 0.114 101.78 0.993 0.093 103.95 0.978 0.079 104.37 0.975 0.074 104.61 0.973 0.069 105.03 0.971 0.114 105.35 0.969 0.120 106.67 0.960 0.127 107.07 0.958 0.124 108.19 0.951 0.082 109.1 0.946 0.097 109.63 0.942 0.096 110.16 0.939 0.121 113.73 0.920 0.125 114.12 0.918 0.090 116.9 0.904 0.068
[0162] DFT Calculations
[0163] Examples of the solid solution structures used for the Mo.sub.4VAlC.sub.4 calculations are provided in
[0164] Here we report Mo.sub.4VC.sub.4, the first MXene with 9 atomic layers (5 transition metal and 4 carbon/nitrogen). We also present its precursor Mo.sub.4VAlC.sub.4 MAX phase which is the first known MAX phase to exhibit twinning on the center M layers of atoms which makes Mo.sub.4VC.sub.4 MXene unique from all other known MXenes for two reasons. This new MXene is disordered on the M site as indicated by atomic-resolution EDS. Besides the optimized synthesis method, we present structural, chemical, thermal, optical, and electronic characterization of Mo.sub.4VAlC.sub.4 and Mo.sub.4VC.sub.4. In addition, DFT results show the great potential for additional M.sub.5AX.sub.4 phases. Due to their higher thickness, M.sub.5X.sub.4 MXenes have the potential to be useful in many applications including, but not limited to, structural materials, optoelectronic devices with high figure of merit, and electronics. Mo.sub.4VAlC.sub.4 MAX phase and Mo.sub.4VC.sub.4 MXene are the first step into a new territory for the MXene family of 2D nanomaterials.
TABLE-US-00003 TABLE 3 Calculated formation energy (eV/formula unit) and lattice parameters (Å) of ordered M′.sub.4M″AlC.sub.4 MAX phase compositions M′ M″ a.sub.ordered c.sub.ordered E.sub.formation Sc Sc 3.311 31.567 −4.738 Sc Ti 3.250 31.241 −7.106 Sc V 3.215 30.965 −6.200 Sc Zr 3.314 31.631 −8.043 Sc Nb 3.263 31.404 −8.144 Sc Mo 3.222 31.287 −6.563 Sc Hf 3.301 31.574 −8.567 Sc Ta 3.256 31.417 −9.134 Sc W 3.216 31.322 −6.944 Ti Ti 3.087 28.518 −13.552 Ti Sc 3.127 29.169 −11.436 Ti V 3.062 28.166 −12.025 Ti Zr 3.147 28.900 −13.391 Ti Nb 3.115 28.596 −12.622 Ti Mo 3.075 28.674 −10.600 Ti Hf 3.138 28.862 −14.031 Ti Ta 3.109 28.604 −13.499 Ti W 3.076 28.644 −10.784 V V 2.929 27.508 −7.735 V Sc 2.993 27.923 −8.163 V Ti 2.953 27.674 −9.748 V Zr 3.023 27.923 −8.865 V Nb 3.007 27.714 −7.410 V Mo 2.947 28.008 −5.681 V Hf 3.017 27.855 −9.590 V Ta 3.010 27.601 −8.170 V W 2.955 27.985 −5.425 Zr Zr 3.343 30.689 −15.681 Zr Sc 3.343 30.817 −13.311 Zr Ti 3.299 30.203 −14.499 Zr V 3.286 29.770 −12.143 Zr Nb 3.312 30.319 −14.100 Zr Mo 3.295 30.080 −11.214 Zr Hf 3.331 30.641 −16.119 Zr Ta 3.301 30.366 −14.664 Zr W 3.278 30.268 −11.604 Nb Nb 3.158 29.627 −8.919 Nb Sc 3.170 29.763 −10.467 Nb Ti 3.141 29.376 −10.773 Nb V 3.116 29.209 −8.069 Nb Zr 3.202 29.654 −11.390 Nb Mo 3.139 29.475 −6.668 Nb Hf 3.190 29.572 −11.928 Nb Ta 3.160 29.575 −9.651 Nb W 3.140 29.483 −6.373 Mo Mo 3.081 28.628 0.419 Mo Sc 3.134 28.763 −3.987 Mo Ti 3.049 28.872 −3.473 Mo V 3.000 29.038 −1.328 Mo Zr 3.203 28.178 −3.648 Mo Nb 3.093 28.797 −1.376 Mo Hf 3.192 28.182 −4.117 Mo Ta 3.085 28.802 −1.933 Mo W 3.074 28.680 1.063 Hf Hf 3.298 30.258 −17.452 Hf Sc 3.307 30.484 −14.732 Hf Ti 3.260 29.919 −15.961 Hf V 3.245 29.495 −13.845 Hf Zr 3.307 30.358 −16.970 Hf Nb 3.273 30.023 −15.363 Hf Mo 3.255 29.801 −12.780 Hf Ta 3.263 30.071 −16.141 Hf W 3.246 29.900 −12.899 Ta Ta 3.134 29.490 −11.489 Ta Sc 3.149 29.664 −12.692 Ta Ti 3.115 29.359 −12.623 Ta V 3.090 29.201 −10.203 Ta Zr 3.179 29.524 −13.038 Ta Nb 3.133 29.593 −10.841 Ta Mo 3.120 29.369 −8.577 Ta Hf 3.173 29.448 −13.609 Ta W 3.121 29.348 −8.218 W W 3.078 28.704 3.601 W Sc 3.125 28.848 −2.124 W Ti 3.058 28.817 −1.420 W V 3.042 28.571 0.853 W Zr 3.118 29.077 −1.452 W Nb 3.095 28.880 0.855 W Mo 3.081 28.699 2.845 W Hf 3.113 28.955 −1.820 W Ta 3.084 28.891 0.413
EMBODIMENTS
[0165] The following embodiments are exemplary only and do not serve to limit the scope of the present disclosure or of the appended claims
[0166] Embodiment 1. A composition, comprising:
[0167] A composition, comprising:
[0168] (a) at least one layer having first and second surfaces, each layer described by a formula M.sub.5X.sub.4T.sub.x and comprising
[0169] a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of M.sub.5X.sub.4, such that each X is positioned within an array of M,
[0170] wherein M is at least one Group IIIB, IVB, VB, or VIB metal or a lanthanide,
[0171] wherein X is C and/or N, and
[0172] wherein T.sub.x represents optionally present surface termination groups; or
[0173] (b) at least one layer having first and second surfaces, each layer described by a formula (M′.sub.aM″.sub.b)X.sub.4T.sub.x and comprising
[0174] a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of (M′.sub.aM″.sub.b)X.sub.4, such that each X is positioned within an array of M′ and M″,
[0175] wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals,
[0176] wherein X is C and/or N,
[0177] wherein a+b=5, and
[0178] wherein T.sub.x represents optionally present surface termination groups, or
[0179] (c) at least one layer having first and second surfaces, each layer described by a formula (M′.sub.aM″.sub.b).sub.5X.sub.4T.sub.x and comprising
[0180] a substantially two-dimensional array of crystal cells, each crystal cell having an empirical formula of (M′.sub.aM″.sub.b).sub.5X.sub.4, such that each X is positioned within an array of M′ and M″,
[0181] wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals,
[0182] wherein X is C and/or N,
[0183] wherein a+b=1, and
[0184] wherein T.sub.x represents optionally present surface termination groups.
[0185] A is described as an A-group (mostly IIIA and IVA, or groups 13 and 14) element. See, e.g., M. W. Barsoum, et al., “Synthesis and Characterization of a Remarkable Ceramic: Ti.sub.3SiC.sub.2,” J. Amer. Ceramics. Soc., 79, 1953-1956 (1996); M. W. Barsoum, “The M.sub.N+1AX.sub.N Phases: A New Class of Solids: Thermodynamically Stable Nanolaminates,” Progress in Solid State Chemistry, 28, 201-281 (2000), both of which are incorporated by reference herein. A can be, e.g., Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb.
[0186] Each of M, M′, and M″ can independently be at least one Group IIIB (e.g., Sc, Y, La, Ac), Group IVB (Ti, Zr, Hf, Rf), Group Group VB (V, Nb, Ta, Db), or Group VIB (Cr, Mo, W, Sg) metal. For example, M, M′, and M″ can independently be Cr, Mo, Nb, Ta, Ti, or V, or a combination thereof. Cr, Mo, Nb, Ta, Ti, and V are considered particularly suitable.
[0187] Without limitation, example M.sub.5X.sub.4 compositions include, e.g., Cr.sub.5C.sub.4, Cr.sub.5N.sub.4, Ti.sub.5C.sub.4, Ti.sub.5N.sub.4, Mo.sub.5C.sub.4, Mo.sub.5N.sub.4, Nb.sub.5C.sub.4, Nb.sub.5N.sub.4, V.sub.5C.sub.4, V.sub.5N.sub.4, Ta.sub.5C.sub.4, and Ta.sub.5N.sub.4.
[0188] Other example (M′.sub.aM″.sub.b)X.sub.4 (where a+b=5), compositions according to the present disclosure can be, without limitation, Cr.sub.aMo.sub.bC.sub.4, Cr.sub.aMo.sub.bN.sub.4, Cr.sub.aNb.sub.bC.sub.4, Cr.sub.aNb.sub.bN.sub.4, Cr.sub.aTa.sub.bC.sub.4, Cr.sub.aTa.sub.bN.sub.4, Cr.sub.aTi.sub.bC.sub.4, Cr.sub.aTi.sub.bN.sub.4, Cr.sub.aV.sub.bC.sub.4, Cr.sub.aV.sub.bN.sub.4, Mo.sub.aNb.sub.bC.sub.4, Mo.sub.aNb.sub.bN.sub.4, Mo.sub.aTa.sub.bC.sub.4, Mo.sub.aTa.sub.bN.sub.4, Mo.sub.aTi.sub.bC.sub.4, Mo.sub.aTi.sub.bN.sub.4, Mo.sub.aV.sub.bC.sub.4, Mo.sub.aV.sub.bN.sub.4, Nb.sub.aTa.sub.bC.sub.4, Nb.sub.aTa.sub.bN.sub.4, Nb.sub.aTi.sub.bC.sub.4, Nb.sub.aTi.sub.bN.sub.4, Nb.sub.aV.sub.bC.sub.4, Nb.sub.aV.sub.bN.sub.4, Ta.sub.aTi.sub.bC.sub.4, Ta.sub.aTi.sub.bN.sub.4, Ta.sub.aV.sub.bC.sub.4, Ta.sub.aV.sub.bN.sub.4, Hf.sub.aSc.sub.bN.sub.4, Hf.sub.aSc.sub.bC.sub.4, Zr.sub.aTi.sub.bC.sub.4, Zr.sub.aTi.sub.bN.sub.4, Zr.sub.aTa.sub.bN.sub.4, Zr.sub.aTa.sub.bC.sub.4, W.sub.aTa.sub.bN.sub.4, W.sub.aTa.sub.bC.sub.4, W.sub.aTi.sub.bN.sub.4, W.sub.aTi.sub.bC.sub.4, Y.sub.aTa.sub.bN.sub.4, Y.sub.aTa.sub.bC.sub.4, Y.sub.aTi.sub.bN.sub.4, Y.sub.aTi.sub.bC.sub.4, W.sub.aNb.sub.bN.sub.4, W.sub.aNb.sub.bC.sub.4, W.sub.aV.sub.bN.sub.4, W.sub.aV.sub.bC.sub.4, Y.sub.aNb.sub.bN.sub.4, Y.sub.aNb.sub.bC.sub.4, Y.sub.aV.sub.bN.sub.4, Y.sub.aV.sub.bC.sub.4 wherein a+b=5.
[0189] Other example (M′.sub.aM″.sub.b).sub.5X.sub.4 (where a+b=1), compositions according to the present disclosure can be, without limitation, (Cr.sub.aMo.sub.b).sub.5C.sub.4, (Cr.sub.aMo.sub.b).sub.5N.sub.4, (Cr.sub.aNb.sub.b).sub.5C.sub.4, (Cr.sub.aNb.sub.b).sub.5N.sub.4, (Cr.sub.aTa.sub.b).sub.5C.sub.4, (Cr.sub.aTa.sub.b).sub.5N.sub.4, (Cr.sub.aTi.sub.b).sub.5C.sub.4, (Cr.sub.aTi.sub.b).sub.5N.sub.4, (Cr.sub.aV.sub.b).sub.5C.sub.4, (Cr.sub.aV.sub.b).sub.5N.sub.4, (Mo.sub.aNb.sub.b).sub.5C.sub.4, (Mo.sub.aNb.sub.b).sub.5N.sub.4, (Mo.sub.aTa.sub.b).sub.5C.sub.4, (Mo.sub.aTa.sub.b).sub.5N.sub.4, (Mo.sub.aTi.sub.b).sub.5C.sub.4, (Mo.sub.aTi.sub.b).sub.5N.sub.4, (Mo.sub.aV.sub.b).sub.5C.sub.4, (Mo.sub.aV.sub.b).sub.5N.sub.4, (Nb.sub.aTa.sub.b).sub.5C.sub.4, (Nb.sub.aTa.sub.b).sub.5N.sub.4, (Nb.sub.aTi.sub.b).sub.5C.sub.4, (Nb.sub.aTi.sub.b).sub.5N.sub.4, (Nb.sub.aV.sub.b).sub.5C.sub.4, (Nb.sub.aV.sub.b).sub.5N.sub.4, (Ta.sub.aTi.sub.b).sub.5C.sub.4, (Ta.sub.aTi.sub.b).sub.5N.sub.4, (Ta.sub.aV.sub.b).sub.5C.sub.4, (Ta.sub.aV.sub.b).sub.5N.sub.4, (Hf.sub.aSc.sub.b).sub.5N.sub.4, (Hf.sub.aSc.sub.b).sub.5C.sub.4, (Zr.sub.aTi.sub.b).sub.5C.sub.4, (Zr.sub.aTi.sub.b).sub.5N.sub.4, (Zr.sub.aTa.sub.b).sub.5N.sub.4, (Zr.sub.aTa.sub.b).sub.5C.sub.4, (W.sub.aTa.sub.b).sub.5N.sub.4, (W.sub.aTa.sub.b).sub.5C.sub.4, (W.sub.aTi.sub.b).sub.5N.sub.4, (W.sub.aTi.sub.b).sub.5C.sub.4, (Y.sub.aTa.sub.b).sub.5N.sub.4, (Y.sub.aTa.sub.b).sub.5C.sub.4, (Y.sub.aTi.sub.b).sub.5N.sub.4, (Y.sub.aTi.sub.b).sub.5C.sub.4, (W.sub.aNb.sub.b).sub.5N.sub.4, (W.sub.aNb.sub.b).sub.5C.sub.4, (W.sub.aV.sub.b).sub.5N.sub.4, (W.sub.aV.sub.b).sub.5C.sub.4, (Y.sub.aNb.sub.b).sub.5N.sub.4, (Y.sub.aNb.sub.b).sub.5C.sub.4, (Y.sub.aV.sub.b).sub.5N.sub.4, (Y.sub.aV.sub.b).sub.5C.sub.4, wherein a+b=1.
[0190] As described elsewhere herein, a and b can each independently be integers, e.g., 1, 2, 3, or 4, such that a+b=5. But this is not a requirement, as the range of compositions available can be seen as extending even further when one considers that each M-atom position within the overall M.sub.n+1X.sub.n matrix can be represented by more than one element. That is, one or more type of M-atom can occupy each M-position within the respective matrices. In certain exemplary non-limiting examples, these can be characterized as (M′.sub.jM″.sub.k).sub.5X.sub.4, wherein M′ and M″ are different metals (which can be of the same group), and j+k=1. As a non-limiting example, such a composition can be (V.sub.1/2Nb.sub.1/2).sub.5C.sub.4 or (V.sub.1/3Nb.sub.2/3).sub.5N.sub.4. Other examples include, e.g., (Cr.sub.1/4Mo.sub.3/4).sub.5C.sub.4, (Cr.sub.1/4Mo.sub.3/4).sub.5N.sub.4, (Cr.sub.1/5Nb.sub.4/5).sub.5C.sub.4, (Cr.sub.1/5Nb.sub.4/5).sub.5N.sub.4, (Nb.sub.2/5Ta.sub.3/5).sub.5C.sub.4, (Nb.sub.2/5Ta.sub.3/5).sub.5N.sub.4, (Nb.sub.1/6Ti.sub.5/6).sub.5C.sub.4, (Nb.sub.1/6Ti.sub.5/6).sub.5N.sub.4, and (Nb.sub.1/10V.sub.9/10).sub.5C.sub.4.
[0191] Embodiment 2. The composition of Embodiment 1, wherein at least one of the first surface and the second surface comprises surface terminations T.sub.x, the surface terminations independently comprising alkoxide, alkyl, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfonate, thiol, or any combination thereof.
[0192] Embodiment 3. The composition of any one of Embodiments 1-2, wherein the composition is characterized as a stacked structure comprising a plurality of the layers.
[0193] Embodiment 4. The composition of any one of Embodiments 1-2, wherein the composition is characterized as being a solid solution.
[0194] Embodiment 5. The composition of any one of Embodiments 1-4, wherein the layer is characterized as comprising 5 atomic layers of M. The layer can have a twinned structure, in some embodiments. In some embodiments, the layer can have a non-twinned structure.
[0195] Embodiment 6. The composition of Embodiment 5, wherein the layer is characterized as comprising a twinned structure.
[0196] Embodiment 7. The composition of any one of Embodiments 1-6, wherein the composition is characterized as being in flake form. It should be understood that the term “flake” does not require that the composition have irregular borders or define two parallel surfaces; the term also encompasses chips, peels, rods, fragments, and the like.
[0197] Embodiment 8. The composition of Embodiment 7, wherein the flake defines a cross-sectional dimension of greater than 1 micrometer (μm). It should be understood, however, that a flake can define a cross-sectional dimension of less than about 1 micrometer (μm).
[0198] Embodiment 9. The composition of Embodiment 8, wherein the flake defines a cross-sectional dimension of from about 1 to about 10 micrometers.
[0199] Embodiment 10. The composition of any one of Embodiments 1-9, wherein a layer defines a thickness of at least about 1 nm.
[0200] Embodiment 11. The composition of Embodiment 10, wherein a layer defines a thickness of from about 1 to about 2 nm.
[0201] Embodiment 12. A component, the component comprising a composition according to any one of Embodiments 1-11.
[0202] Embodiment 13. The component of Embodiment 12, wherein the component is characterized as an optical component, an optomechanical component, a plasmonic component, a signal receiver, a signal transmitter, a fiber, a textile, a radiation shield, or any combination thereof.
[0203] Embodiment 14. A component, the component having disposed thereon a coating, the coating comprising a composition according to any one of Embodiments 1-11.
[0204] Embodiment 15. A composition, the composition comprising a suspension of a composition according to any one of Embodiments 1-11.
[0205] Embodiment 16. A method, the method comprising synthesizing a composition according to any one of Embodiments 1-11.
[0206] Embodiment 17. A method, comprising removing the A-group element from a MAX phase material so as to form a product composition having the empirical formula of M.sub.5X.sub.4(T.sub.x) (wherein M is a Group IIIB, IVB, VB, or VIB metal and wherein X is C and/or N); (M′.sub.aM″.sub.b)AX.sub.4(T.sub.x), wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=5, and wherein X is C and/or N; or (M′.sub.aM″.sub.b).sub.5AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=1, and wherein X is C and/or N. Exemplary product compositions are at least those in Embodiments 1-11.
[0207] MAX phase materials are themselves known to exist as laminated structures with anisotropic properties. These materials are layered hexagonal (space group P6.sub.3/mmc), with two formula units per unit cell. Near close-packed M-layers are interleaved with pure A-group element layers, with the X-atoms filling the octahedral sites between the former.
[0208] Within the MAX phase structure, the M.sub.n+1X.sub.1 layers are chemically quite stable, possibly owing to the strength of the M-X bond. By comparison, the A-group atoms are the most reactive species, reflective of their relatively weak binding. For example, heating Ti.sub.3SiC.sub.2 in a C-rich atmosphere or heating in molten cryolite or molten aluminum is known to result in the loss of Si and the formation of TiC.sub.x. In the case of cryolite, the vacancies that form lead to the formation of a partially ordered cubic TiC.sub.0.67 phase. In both cases, the high temperatures lead to a structural transformation from a hexagonal to a cubic lattice and a partial loss of layering. In some cases, such as Ti.sub.2InC, simply heating in vacuum at ˜800° C., results in loss of the A-group element and TiC.sub.x formation. Removing of both the M and A elements from MAX structure by high temperature chlorination results in a porous carbon known as carbide derived carbon with useful and unique properties.
[0209] Embodiment 18. The method of Embodiment 17, further comprising delaminating layers of the product composition from one another. Delamination can be accomplished by, e.g., sonication, mechanical means, chemical means, and other techniques known to those of ordinary skill in the art.
[0210] Embodiment 19. The method of Embodiment 18, further comprising forming a suspension of delaminated layers of the product composition.
[0211] Embodiment 20. The method of Embodiment 19, further comprising forming a free-standing structure of the product composition.
[0212] Embodiment 21. A composition,
[0213] (a) the composition characterized as having an empirical formula M.sub.5AX.sub.4, wherein M is a Group IIIB, IVB, VB, or VIB metal, and wherein X is C and/or N; or
[0214] (b) the composition characterized as having an empirical formula (M′.sub.aM″.sub.b)AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=5, and wherein X is C and/or N; or
[0215] (c) the composition characterized as having an empirical formula (M′.sub.aM″.sub.b).sub.5AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=1, and wherein X is C and/or N.
[0216] Examples of M.sub.5AX.sub.4 include, without limitation, Ti.sub.5AlC.sub.4, Nb.sub.5AlC.sub.4, Mo.sub.5AlN.sub.4, V.sub.5SiC.sub.4, V.sub.5GeN.sub.4, Ti.sub.5PbC.sub.4, Ti.sub.5PbN.sub.4, Sc.sub.5AlC.sub.4, and Y.sub.5TlC.sub.4,
[0217] Examples of (M′.sub.aM″.sub.b)AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=5, and wherein X is C and/or N, include, without limitation, Cr.sub.1Mo.sub.4AlC.sub.4, Cr.sub.1Mo.sub.4AlN.sub.4, Cr.sub.2Nb.sub.3TlC.sub.4, Cr.sub.2Nb.sub.3TlN.sub.4, Cr.sub.1Ta.sub.4GeC.sub.4, Cr.sub.1Ta.sub.4GeN.sub.4, Cr.sub.2Ti.sub.3SiC.sub.4, Cr.sub.2Ti.sub.3SiN.sub.4, Cr.sub.2V.sub.3PbC.sub.4, Cr.sub.2V.sub.3PbN.sub.4, Mo.sub.1Nb.sub.4AlC.sub.4, Mo.sub.1Nb.sub.4AlN.sub.4, Mo.sub.2Ta.sub.3AlC.sub.4, Mo.sub.2Ta.sub.3AlN.sub.4, Mo.sub.1Ti.sub.4AlC.sub.4, and Mo.sub.1Ti.sub.4AlN.sub.4.
[0218] Examples of (M′.sub.aM″.sub.b).sub.5AX.sub.4, wherein M′ and M″ are different Group IIIB, IVB, VB, or VIB metals, wherein a+b=1, and wherein X is C and/or N include, without limitation, (Cr.sub.1/2Mo.sub.1/2).sub.5AlC.sub.4, (Cr.sub.3/5Mo.sub.2/5).sub.5AlN.sub.4, (Cr.sub.5/6Nb.sub.1/6).sub.5TlC.sub.4, (Cr.sub.1/2Nb.sub.1/2).sub.5TlN.sub.4, (Cr.sub.3/5Ta.sub.2/5).sub.5GeC.sub.4, (Cr.sub.3/5Ta.sub.2/5).sub.5GeN.sub.4, (Cr.sub.1/3Ti.sub.2/3).sub.5SiC.sub.4, (Cr.sub.1/2Ti.sub.1/2).sub.5SiN.sub.4, (Cr.sub.2/3V.sub.1/3).sub.5PbC.sub.4, (Cr.sub.1/2V.sub.1/2).sub.5PbN.sub.4, (Mo.sub.1/5Nb.sub.4/5).sub.5AlC.sub.4, (Mo.sub.1/5Nb.sub.4/5).sub.5AlN.sub.4, (Mo.sub.1/3Ta.sub.2/3).sub.5AlC.sub.4, (Mo.sub.1/3Ta.sub.2/3).sub.5AlN.sub.4, (Mo.sub.1/5Ti.sub.4/5).sub.5AlC.sub.4, and (Mo.sub.1/5Ti.sub.4/5)AlN.sub.4.
[0219] In some embodiments, M′ and M″ are from the same group, e.g., both metals are from Group IIB (such as Cr and Mo).
[0220] Embodiment 22. The composition of claim 21, wherein A is Al, As, Cd, Ga, Ge, P, Pb, In, S, Sn, or Ti.
[0221] Embodiment 23. The composition of any one of claims 21-22, wherein M, M′, and M″ is independently Cr, Ti, Mo, Nb, V, or Ta, or a combination thereof.