charge storage, [7,8] electromagnetic interference shielding, [9] filtering, [10] and a range of additional applications. [7] MXenes constitute a large and growing family of 2D materials [11,12] that are obtained from the laminated M n+1 AX n (MAX) phases (M is a transition metal, A is a group A element-mostly groups 13 and 14-and X is C and/or N) [13] by chemical etching of the atomically thin A element layers that separate sheets of M n+1 X n . As the A element is removed, the MXene surfaces are immediately functionalized by surface terminating species, T x . [6,14] Hence, the proper MXene formula is M n+1 X n T x . Accordingly, the MXene properties can be tuned through structure, intrinsic composition, and surface terminations. The structure is inherited from the parent MAX phase (hexagonal, space group P6 3 /mmc), but compositional tuning displays an extraordinary toolbox for property tuning through MXenes based on single M and X elements, as well as alloys on both M and X. [12,15] In addition, there are reports on MXenes forming out-of-plane [16] and in-plane [17] double-M elemental ordering, as well as vacancy-ordered structures. [18,19] Manipulation of the surface terminations constitutes the final and most powerful variable for property tuning. [20] Despite several theoretical investigations, [21][22][23] noninherent terminations have remained experimentally unexplored. Currently, the MXene preparation dictates that T x is inherent to the etchant and predominantly a combination of O and F, where OH has also been considered as a minor [24] or even negligible contribution. [25] In the area of carbon capture (CC), MXenes are predicted to be highly efficient for capturing CO 2 , enabling capture of 2-8 mol CO 2 kg −1 . [20,21] However, the MXene surfaces were assumed to be termination free, an experimentally unrealistic starting point, given the current wet-chemical preparation routes for MXenes. To unlock the MXene potential for noninherent terminations or adsorption of other molecules, such as CO 2 , we have subjected the archetype Ti 3 C 2 T x MXene to a novel approach. Using in situ environmental transmission electron microscopy (ETEM), single Ti 3 C 2 T x sheets were subjected to an initial high-temperature treatment to desorb F, [25] and a subsequent H 2 exposure to remove the persistent O from the surfaces. The thereafter termination-depleted MXene was subsequently exposed to CO 2 gas, resulting in the first MXene to be terminated by a noninherent molecule. Additionally, termination-depleted MXene surfaces were exposed to N 2 gas after which no N adsorption was observed, Global warming caused by burning of fossil fuels is indisputably one of mankind's greatest challenges in the 21st century. To reduce the everincreasing CO 2 emissions released into the atmosphere, dry solid adsorbents with large surface-to-volume ratio such as carbonaceous materials, zeolites, and metal-organic frameworks have emerged as promising material candidates for capturing CO 2 . However, challenges remain because of limited CO...

MXenes are a rapidly growing family of 2D materials that exhibit a highly versatile structure and composition, allowing for significant tuning of the material properties. These properties are, however, ultimately limited by the surface terminations, which are typically a mixture of species, including F and O that are inherent to the MXene processing. Other and robust terminations are lacking. Here, we apply high-resolution scanning transmission electron microscopy (STEM), corresponding image simulations and first-principles calculations to investigate the surface terminations on MXenes synthesized from MAX phases through Lewis acidic melts. The results show that atomic Cl terminates the synthesized MXenes, with mere residual presence of other termination species. Furthermore, in situ STEM-electron energy loss spectroscopy (EELS) heating experiments show that the Cl terminations are stable up to 750 °C. Thus, we present an attractive new termination that widely expands the MXenes' functionalization space and enable new applications.

We propose a design route for the next generation of nitride alloys via a concept of multicomponent alloying based on self-organization on the nanoscale via a formation of metastable intermediate products during the spinodal decomposition. We predict theoretically and demonstrate experimentally that quasi-ternary (TiCrAl)N alloys decompose spinodally into (TiCr)N and (CrAl)N-rich nanometer sized regions. The spinodal decomposition results in age hardening, while the presence of Cr within the AlN phase delays the formation of a detrimental wurtzite phase leading to a substantial improvement of thermal stability compared to the quasi-binary (TiAl)N or (CrAl)N alloys.

We review results of recent combined theoretical and experimental studies of Ti1−xAlxN, an archetypical alloy system material for hard-coating applications. Theoretical simulations of lattice parameters, mixing enthalpies, and elastic properties are presented. Calculated phase diagrams at ambient pressure, as well as at pressure of 10 GPa, show a wide miscibility gap and broad region of compositions and temperatures where the spinodal decomposition takes place. The strong dependence of the elastic properties and sound wave anisotropy on the Al-content offers detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloy films and multilayers. TiAlN/TiN multilayers can further improve the hardness and thermal stability compared to TiAlN since they offer means to influence the kinetics of the favorable spinodal decomposition and suppress the detrimental transformation to w-AlN. Here, we show that a 100 degree improvement in terms of w-AlN suppression can be achieved, which is of importance when the coating is used as a protective coating on metal cutting inserts.

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Prediction of rock salt structure of (InN)32 nanoparticles from first principles calculations J. Chem. Phys. 138, 114310 (2013) Coexistence of incommensurate and commensurate spiral orders and pressure effect on polycrystalline CoCr2O4 J. Appl. Phys. 113, 17E129 (2013) Vibrational, elastic, and structural properties of cubic silicon carbide under pressure up to 75GPa: Implication for a primary pressure scale J. Appl. Phys. 113, 113503 (2013) Pressure and temperature effects on intermolecular vibrational dynamics of ionic liquids J. Chem. Phys. 138, 104503 (2013) Additional information on J. Appl. Phys. In the present work, the decomposition of unstable arc evaporated Ti 0.6 Al 0.4 N at elevated temperatures and quasihydrostatic pressures has been studied both experimentally and by firstprinciples calculations. High pressure and high temperature (HPHT) treatment of the samples was realized using the multi anvil press and diamond anvil cell techniques. The products of the HPHT treatment of Ti 0.6 Al 0.4 N were investigated using x-ray diffractometry and transmission electron microscopy. Complimentary calculations show that both hydrostatic pressure and high temperature stabilize the cubic phase of AlN, which is one of the decomposition products of Ti 0.6 Al 0.4 N. This is in agreement with the experimental results which in addition suggest that the presence of Ti in the system serves to increase the stability region of the cubic c-AlN phase. The results are industrially important as they show that Ti 0.6 Al 0.4 N coatings on cutting inserts do not deteriorate faster under pressure due to the cubic AlN to hexagonal AlN transformation. V C 2013 American Institute of Physics.[http://dx

Synthesis of delaminated 2D W1.33C (MXene) has been performed by selectively etching Al as well as Sc/Y from the recently discovered nanolaminated i-MAX phases (W2/3Sc1/3)2AlC and (W2/3Y1/3)2AlC. Both quaternary phases produce MXenes with similar flake morphology, and with a skeletal structure due to formation of ordered vacancies. The measured O, OH, and F terminations, however, differ in amount as well as in relative ratios, depending on parent material, evident from X-ray photoelectron spectroscopy. These findings are correlated to theoretical simulations based on first principles, investigating the W1.33C and the effect of termination configurations on structure, formation energy, stability, and electronic structure. The theoretical results indicate a favored F-rich surface composition, though with a system going from insulating/semiconducting to metallic for different termination configurations, suggesting a high tuning potential of these materials. Additionally, free-standing W1.33C films of 2-4 µm thickness and with up to 10 wt% polymer (PEDOT:PSS) was tested as electrodes in supercapacitors, showing capacitances up to 600 F cm -3 in 1M H2SO4 and high capacitance retention for at least 10 000 cycles at 10 A g -1 . This is highly promising results compared to other W-based materials to date.

The true origin of the 0.25 and 0.85 conductance features which have been observed in biased split-gate quantum wires and quantum point contacts in semiconductor heterostructures is debated in the literature; one suggestion is that they are caused by spontaneous spin polarization due to the electron-electron interactions. The present work confirms that spontaneous spin splitting may occur within the system and is responsible for both the 0.25 and 0.85 plateaux. We have also shown that the 0.25 plateau consists of two regions, one that is spin polarized, and one that is degenerate with a conductance that remains essentially the same at both sides of the transition. This finding could be of interest for semiconductor spintronics because it opens the possibility for spin manipulation by electric means only.