This investigation reports the influence of Ti-C and Ti-W cathode composition on an industrial-scale dc vacuum arc plasma source. Further, we analyze the influence of plasma generation and plasma properties on the resulting cathode surface after the operation and on basic film properties. The results are compared with previous work focused on Ti-Al and Ti-Si compound cathodes. For all Ti-X compound cathodes (X = W, C, Al, and Si), a direct correlation between plasma ion energy/charge and the cohesive energy of the cathode was demonstrated, with a small number of exceptions to a limited set of specific cathode compositions. Hence, the "velocity rule" and effects from different electron temperatures were suggested to be important for gaining a more detailed understanding of plasma properties. A discrepancy was found between the cathode and plasma ion composition, though the difference was reduced in a corresponding comparison between the cathode and the deposited film composition. A significant contribution of a flux of neutrals and/or macroparticles to the final film composition was, therefore, suggested. The effect of the melting point of the cathode phase composition on the intensity of macroparticle generation and the smoothness of the cathode surface operation was also investigated. The presented results contribute to the fundamental understanding of vacuum arc plasma generation and transport and are of importance for further development and applicability of Ti-based coatings from arc deposition.

Aqueous ammonium-ion batteries (AAIBs) are appealing due to their relatively low cost and good rate performance. In general, AAIBs are environmentally friendlier than their non-aqueous counterparts. However, it is still a challenge to achieve highly reversible AAIBs with decent voltages and energy/power densities. Herein, we report on a full-cell configuration using alpha-MoO3/Ti3C2Tz films as anodes, and (NH4)(x)MnO2/CNTs films as cathodes in a 1 M ammonium acetate (NH4Ac) electrolyte. At 2 V, the operating cell voltage, OCV, is one of the highest reported for AAIBs. A maximum energy density of similar to 32 Wh kg(-1) (similar to 54 Wh L-1) at 0.2 A g(-1) and a maximum power density of similar to 10 kW kg(-1) (similar to 17 kW L-1) at 10 A g(-1) are attained. When the full cells are cycled 2,000 times at 1 A g(-1) they retain similar to 73 % of their initial capacity. When cycling at 10 A g(-1), similar to 96 % of capacity is retained after 43,500 cycles. After 10 h, self-discharge reduces the OCV to similar to 72 % of its original value. This work provides a roadmap for developing high performance AAIBs with high voltages and high energy/power densities. Before this is possible it is imperative that the self-discharge rate be substantially reduced.

Functional 2D materials are interesting for a wide range of applications. The rapid growth of the MXene family is due to its compositional diversity, which, in turn, allows significant tuning of the properties, and hence their applicability. The properties are to a large extent dictated by surface terminations. In the present work, we demonstrate the influence of termination species (O, NH, N, S, F, Cl, Br, I) on the changes in electronic structure, work function, dynamical stability, and atomic charges and distances of MXenes (Ti2C, Nb2C, V2C, Mo2C, Ti3C2, and Nb4C3). Among these systems, the work function values were not previously reported for & SIM;60% of the systems, and most of the previously reported MXenes with semiconducting nature are here proven to be dynamically unstable. The results show that the work function generally decreases with a reduced electronegativity of the terminating species, which in turn is correlated to a reduced charge of both the metal and terminating species and an increased metal-termination distance. An exception to this trend is NH terminations, which display a significantly reduced work function due to an intrinsic dipole moment within the termination. Furthermore, the results suggest that halogen terminations improve the electrical conductivity of the materials.

Out-of-plane chemically ordered transitionmetal boride(o-MAB) phases, Ta4M & DPRIME;SiB2 (M & DPRIME; = V, Cr), and a structurally equivalent disordered solidsolution MAB phase, Ta4MoSiB2, are synthesized.DFT calculations are used to examine the dynamic stability, elasticproperties, and electronic density states of the MAB phases. We report on the synthesis of computationally predictedout-of-planechemically ordered transition metal borides labeled o-MAB phases, Ta4M & DPRIME;SiB2 (M & DPRIME; =V, Cr), and a structurally equivalent disordered solid solution MABphase Ta4MoSiB2. The boride phases were preparedusing solid-state reaction sintering of the constituting elements.High-resolution scanning transmission electron microscopy along withRietveld refinement of the powder-X-ray diffraction patterns revealedthat the synthesized o-MAB phases Ta4CrSiB2 (98 wt % purity) and Ta4VSiB2 (81 wt% purity) possess chemical ordering with Ta preferentially residingin the 16l position and Cr and V in the 4c position, whereas Ta4MoSiB2 (46wt % purity) was concluded to form a disordered solid solution. Densityfunctional theory (DFT) calculations were used to investigate thedynamic stability, elastic properties, and electronic density statesfor the MAB phases, confirming the stability and suggesting the boridesbased on Cr and Mo to be stiffer than those based on V and Nb.

We report the synthesis of three out-of-plane chemically ordered quaternary transition metal borides (o-MAB phases) of the chemical formula M4CrSiB2 (M = Mo, W, Nb). The addition of these phases to the recently discovered o-MAB phase Ti4MoSiB2 shows that this is indeed a new family of chemically ordered atomic laminates. Furthermore, our results expand the attainable chemistry of the traditional M5SiB2 MAB phases to also include Cr. The crystal structure and chemical ordering of the produced materials were investigated using high-resolution scanning transmission electron microscopy and X-ray diffraction by applying Rietveld refinement. Additionally, calculations based on density functional theory were performed to investigate the Cr preference for occupying the minority 4c Wyckoff site, thereby inducing chemical order.

A desired prerequisite when performing a quantum mechanical calculation is to have an initial idea of the atomic positions within an approximate crystal structure. The atomic positions combined should result in a system located in, or close to, an energy minimum. However, designing low-energy structures may be a challenging task when prior knowledge is scarce, specifically for large multi-component systems where the degrees of freedom are close to infinite. In this paper, we propose a method for identification of low-energy crystal structures within multi-component systems by combining cluster expansion and crystal structure predictions with density-functional theory calculations. Crystal structure prediction searches are applied to the Mo2AlB2 and Sc2AlB2 ternary systems to identify candidate structures, which are subsequently used to explore the quaternary (pseudo-binary) (MoxSc1-x)(2)AlB2 system through the cluster expansion formalism utilizing the ground-state search approach. Furthermore, we show that utilizing low-energy structures found within the cluster expansion ground-state search as seed structures within crystal structure predictions of (MoxSc1-x)(2)AlB2 can significantly reduce the computational demands. With this combined approach, we not only correctly identified the recently discovered Mo(4/3)Sc(2/3)AlB(2)i-MAB phase, comprised of in-plane chemical ordering of Mo and Sc and with Al in a Kagome lattice, but also predict additional low-energy structures at various concentrations. This result demonstrates that combining crystal structure prediction with cluster expansion provides a path for identifying low-energy crystal structures in multi-component systems by employing the strengths from both frameworks.

The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+delta) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700-900 degrees C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 degrees C exhibited intense diffraction peaks along the growth direction corresponding to (000l) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+delta film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+delta can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 degrees C) and has the potential to be used as a template for III-nitride growth on Si substrates.

Heterojunction photocatalysts have recently emerged for use in degradation of organic pollutants, typically being suspended in effluent solution to degrade it. Post degradation, the catalyst must be removed from the treated solution, which consumes both energy and time. Moreover, the separation of nano catalysts from the treated solution is challenging. In the present work, we explore fabrication of immobilized TiO2-PEDOT:PSS hybrid heterojunction catalysts with the support of a PVA (polyvinyl alcohol) matrix. These photocatalytic films do not require any steps to separate the powdered catalyst from the treated water. While the PVA-based films are unstable in water, their stability could be significantly enhanced by heat treatment, enabling efficient removal of organic effluents like methylene blue (MB) and bisphenol-A (BPA) from the aqueous solution under simulated sunlight irradiation. Over 20 cycles, the heterojunction photocatalyst maintained high photocatalytic activity and showed excellent stability. Hence, an immobilization of the TiO2-PEDOT:PSS hybrid heterojunction is suggested to be beneficial from the viewpoint of reproducible and recyclable materials for simple and efficient wastewater treatment.

The sluggish kinetics associated with the oxygen evolution reaction (OER) limits the sustainability of fuel production and chemical synthesis. Developing catalysts based on Earth abundant elements with a reasonable strategy could solve the challenge. Here, we present a heterostructure built from CrOx and CuS whose interface gives rise to the advent of new functionalities in catalytic activity. Using X-ray photoelectron and absorption spectroscopies, we identified the multiple oxidation states and low coordination number of Cr metal in CrOx-CuS heterostructure. Benefitting from these features, CrOx-CuS generates oxygen gas through water splitting with a low over potential of 190 mV vs RHE at a current density of 10 mA cm-2. The catalyst shows no evident deactivation after a 36-hours operation in alkaline medium. The high catalytic activity, inspired by first principles calculations, and long-time durability make it one of the most effective OER electrocatalysts.

MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4T x . Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M(5)AX(4) mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4T x and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M(5)AX(4) MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.

Zero-field NMR investigations on the 69Ga, 71Ga, and 55Mn nuclei have been performed at 4.2 K on a 100 nm thick epitaxial Mn2GaC(0001) MAX phase film grown on a MgO(111) substrate. This nano-laminated structure consists of ferromagnetic Mn-C-Mn stacks interleaved with monolayers of gallium. A resolved quadrupolar structure of the observed gallium resonances is a fingerprint of a well-defined crystal field confirming high crystal quality. The nuclei of non-magnetic gallium atoms are shown to experience the transferred hyperfine magnetic field of 15.75 T (& PLUSMN;0.05 T), which is due to polarization of their 4s electron shell by the magnetic moments of manganese neighbors, evidencing the presence of an uncompensated ferromagnetic moment within the manganese sublattice. The average magnetic moment of manganese was found to be around 2 & mu;B, strongly contrasting with the reported remnant magnetization of only 0.3 & mu;B. Moreover, the 55Mn NMR spectrum in-dicates the presence of magnetically non-equivalent manganese sites within this structure. The observed features of the 69,71Ga and 55Mn NMR spectra cannot be reconciled with any of the hitherto proposed collinear ar-rangements of manganese moments and suggest their non-collinear arrangement across a gallium layer. Nevertheless a more advanced study is required to elucidate the detailed nature of magnetic structure in this material.

Belonging to the enyne family, enetriynes comprise a distinct electron-rich all-carbon bonding scheme. However, the lack of convenient synthesis protocols limits the associated application potential within, e.g., biochemistry and materials science. Herein we introduce a pathway for highly selective enetriyne formation via tetramerization of terminal alkynes on a Ag(100) surface. Taking advantage of a directing hydroxyl group, we steer molecular assembly and reaction processes on square lattices. Induced by O-2 exposure the terminal alkyne moieties deprotonate and organometallic bis-acetylide dimer arrays evolve. Upon subsequent thermal annealing tetrameric enetriyne-bridged compounds are generated in high yield, readily self-assembling into regular networks. We combine high-resolution scanning probe microscopy, X-ray photoelectron spectroscopy and density functional theory calculations to examine the structural features, bonding characteristics and the underlying reaction mechanism. Our study introduces an integrated strategy for the precise fabrication of functional enetriyne species, thus providing access to a distinct class of highly conjugated pi-system compounds. Enetriynes, which belong to the enyne family, are characterized by a distinct electron-rich carbon-bonding scheme. Here, the authors report the formation of enetriynes with high selectivity by tetramerization of terminal alkynes on Ag(100).

The factors controlling the top-down synthesis of MXenes, by selectively removing the A elements from parent MAX phases, is still under debate. In particular, understanding why some MAX phases can be used for creating MXenes, while others cannot, is of immense interest and would greatly support computational screening and identification of new two-dimensional materials that could also be created by chemical exfoliation. Here we computationally study the etching of MAX phases in hydrofluoric acid, considering the complete exfoliation process and competing processes during the initial steps of the synthesis. The results are compared to experiments and MAX phases successfully converted to MXenes, as well as so far unsuccessful attempts, including previously unpublished experimental data, rationalizing why some MAX phases are exfoliable while others are not. Our results provide an improved understanding of the synthesis of MXenes under acid conditions, anticipated to be vital for our ability to discover novel two-dimensional materials.

MAX/MAB phases are a series of non-van der Waals ternary layered ceramic materials with a hexagonal structure, rich in elemental composition and crystal structure, and embody physical properties of both ceramics and metals. They exhibit great potential for applications in extreme environments such as high temperature, strong corrosion, and irradiation. In recent years, two-dimensional (2D) materials derived from the MAX/MAB phase (MXene and MBene) have attracted enormous interest in the fields of materials physics and materials chemistry and become a new 2D van der Waals material after graphene and transition metal dichalcogenides. Therefore, structural modulation of MAX/MAB phase materials is essential for understanding the intrinsic properties of this broad class of layered ceramics and for investigating the functional properties of their derived structures. In this paper, we summarize new developments in MAX/MAB phases in recent years in terms of structural modulation, theoretical calculation, and fundamental application research and provide an outlook on the key challenges and prospects for the future development of these layered materials.

On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybrid-ization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocou-pling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C-C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

MXenes hold immense potential given their superior electrical properties. The practical adoption of these promising materials is, however, severely constrained by their oxidative susceptibility, leading to significant performance deterioration and lifespan limitations. Attempts to preserve MXenes have been limited, and it has not been possible thus far to reverse the materials performance. In this work, we show that subjecting oxidized micron or nanometer thickness dry MXene films-even those constructed from nanometer-order solution-dispersed oxidized flakes-to just one minute of 10 MHz nanoscale electromechanical vibration leads to considerable removal of its surface oxide layer, whilst preserving its structure and characteristics. Importantly, electrochemical performance is recovered close to that of their original state: the pseudocapacitance, which decreased by almost 50% due to its oxidation, reverses to approximately 98% of its original value, with good capacitance retention ( approximate to 93%) following 10,000 charge-discharge cycles at 10 A g(-1). These promising results allude to the exciting possibility for rejuvenating the material for reuse, therefore offering a more economical and sustainable route that improves its potential for practical translation. Despite their vast potential, the practical deployment of MXenes has been hampered by their tendency to be oxidized. Here, the authors show that simply vibrating MXene films in just a minute can remove the oxide layer formed and restore their electrochemical performance close to its original state.

This work was inspired by new experimental findings where we discovered a two-dimensional (2D) material comprised of titanium-oxide-based one-dimensional (1D) sub-nanometer filaments. Preliminary results suggest that the 2D material contains considerable amounts of carbon, C, in addition to titanium, Ti, and oxygen, O. The aim of this study is to investigate the low-energy, stable atomic forms of 2D titanium carbo-oxides as a function of C content. Via a combination of first-principles calculations and an effective structure sampling scheme, the stable configurations of C-substitutions are comprehensively searched by templating different 2D TiO2 polymorphs and considering a two O to one C replacement scheme. Among the searched stable configurations, a structure where the (101) planes of anatase bound the top and bottom surfaces with a chemical formula of TiC1/4O3/2 was of particularly low energy. Furthermore, the variations in the electronic band structure and chemical bonding environments caused by the high-content C substitution are investigated via additional calculations using a hybrid exchange-correlation functional.

The recent discovery of chemical ordering in quaternary borides offers new ways of exploring properties and functionalities of these laminated phases. Here, we have synthesized and investigated chemical ordering of the laminated Mo4MnSiB2 (T2) phase, thereby introducing a magnetic element into the family of materials coined o-MAB phases. By X-ray diffraction and scanning transmission electron microscopy, we provide evidence for out-of-plane chemical ordering of Mo and Mn, with Mo occupying the 16l site and Mn preferentially residing in the 4c site. Mn and B constitute quasi-two-dimensional layers in the laminated material. We have therefore also studied the magnetic properties by magnetometry, and no sign of long-range magnetic order is observed. An initial assessment of the magnetic ordering has been further studied by density functional theory (DFT) calculations, and while we find an antiferromagnetic configuration to be the most stable one, ferromagnetic ordering is very close in energy.

Supercapacitors based on two-dimensional MXene (Ti3C2Tz) have shown extraordinary performance in ultrathin electrodes with low mass loading, but usually there is a significant reduction in high-rate performance as the thickness increases, caused by increasing ion diffusion limitation. Further limitations include restacking of the nanosheets, which makes it challenging to realize the full potential of these electrode materials. Herein, we demonstrate the design of a vertically aligned MXene hydrogel composite, achieved by thermal-assisted self-assembled gelation, for high-rate energy storage. The highly interconnected MXene network in the hydrogel architecture provides very good electron transport properties, and its vertical ion channel structure facilitates rapid ion transport. The resulting hydrogel electrode show excellent performance in both aqueous and organic electrolytes with respect to high capacitance, stability, and high-rate capability for up to 300 mu m thick electrodes, which represents a significant step toward practical applications.

We have computationally studied the formation mechanism of the biphenylene network via the intermolecular HF zipping, as well as identified key intermediates experimentally, on the Au(111) surface. We elucidate that the zipping process consists of a series of defluorinations, dehydrogenations, and C–C coupling reactions. The Au substrate not only serves as the active site for defluorination and dehydrogenation, but also forms C–Au bonds that stabilize the defluorinated and dehydrogenated phenylene radicals, leading to "standing" benzyne groups. Despite that the C–C coupling between the "standing" benzyne groups is identified as the rate-limiting step, the limiting barrier can be reduced by the adjacent chemisorbed benzyne groups. The theoretically proposed mechanism is further supported by scanning tunneling microscopy experiments, in which the key intermediate state containing chemisorbed benzyne groups can be observed. This study provides a comprehensive understanding towards the on-surface intermolecular HF zipping, anticipated to be instructive for its future applications.

Carbon-based hybrid nanostructures have shown to be promising candidates as cost-efficient and effective fillers for electromagnetic interference shielding and RF absorption. In this work, hybrids of graphene-augmented inorganic (alumina) nanofibers (GAIN) have been incorporated in epoxy resin to fabricate a multilayer struc-ture with tunable absorption. Highly aligned graphene augmented alumina nanofibers of 10 +/- 2 nm in diameter were produced with the help of a hot wall one-step catalyst-free chemical vapor deposition method at 1000 degrees C. Effective medium approximation has been used to calculate the intrinsic dielectric properties of GAIN nanofibers. The highest loss tangent of 0.4 has been achieved in a 5 mm thick composite containing 1 vol% of randomly oriented nanofibers. Furthermore, aligned graphene augmented nanofibers were embedded in an epoxy resin matrix to examine the effect of fiber alignment on the dielectric properties of the composite. Based on the ob-tained dielectric data, a superposed three-layer structure has been fabricated, offering an absorption of >90% in the entire X-band and an absorption peak of-25 dB at similar to 11 GHz. Several multilayer designs based on finite element method coupled with Monte Carlo simulations have been proposed to tune the absorption character-istics. This work demonstrates the potential of the hybrid nanofibers with a dual loss function for versatile design options in the area of RF absorption.

Herein we report on the synthesis of a metastable (Cr,Y)(2)AlC MAX phase solid solution by co-sputtering from a composite Cr-Al-C and elemental Y target, at room temperature, followed by annealing. However, direct high-temperature synthesis resulted in multiphase films, as evidenced by X-ray diffraction analyses, room-temperature depositions, followed by annealing to 760 degrees C led to the formation of phase pure (Cr,Y)(2)AlC by diffusion. Higher annealing temperatures caused a decomposition of the metastable phase into Cr2AlC, Y5Al3, and Cr-carbides. In contrast to pure Cr2AlC, the Y-containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y-content dependent and was increased by similar to 200 degrees C for 5 at.% Y compared to Cr2AlC. Calculations predicting the metastable phase formation of (Cr,Y)(2)AlC and its decomposition are in excellent agreement with the experimental findings.

Significant efforts have been dedicated to developing Ti3C2Tz-based MXene aqueous supercapacitors (SCs) with improved energy and power densities. Notably less research has been devoted to an equally important characteristic of aqueous SCs, viz. self-discharge (SD). The SD rates are rarely reported despite their crucial importance from a practical point of view. Herein, the SD rates in four different aqueous electrolytes: H2SO4, KOH, LiCl, and LiBr in Ti3C2Tz-based aqueous SCs are compared. For the latter two, the SD rates vary as a function of salt concentration in the electrolytes with higher LiCl or LiBr concentrations having the lowest SD rates, viz. 78.3% and 81.5% in 14m LiCl and LiBr, respectively, after 10h. Further, the influence of dissolved oxygen and the purities of the starting powders are examined, and it is concluded that parasitic reactions, including oxygen, are responsible for the SD.

Two-dimensional (2D) materials offer advantages that their 3D counterparts do not. The conventional method for the bulk synthesis of 2D materials has predominantly been through etching layered solids. Herein, we convert - through a bottom-up approach - 10 binary and ternary titanium carbides, nitrides, borides, phosphides, and silicides into 2D flakes by immersing them in a tetramethylammonium hydroxide solution at temperatures in the 25-85 degrees C range. Based on X-ray diffraction, density functional theory, X-ray photoelectron, electron energy loss, Raman, X-ray absorption near edge structure spectroscopies, transmission and scanning electron microscope images and selected area diffraction, we conclude that the resulting flakes are carbon containing anatase-based layers that are, in turn, comprised of approximate to 6 x 10 angstrom(2) nanofilaments in cross-section some of which are few microns long. Electrodes made from some of these films performed well in lithium-ion and lithium-sulphur systems. These materials also reduce the viability of cancer cells thus showing potential in biomedical applications. Synthesizing 2D materials, at near ambient conditions, with non-layered, inexpensive, green precursors (e.g., TiC) is paradigm shifting and will undoubtedly open new and exciting avenues of research and applications.

Inspired by the recent discovery of Ti4MoSiB2, a quaternary phase with out-of-plane chemical order that we denote as o-MAB, we perform an extensive first-principles study to explore the attained chemical order and disorder (solid-solution) upon metal alloying of M(5)AB(2) (T2 phases), with M from Groups 3 to 9 and A = Al, Si, P, Ga, and Ge. We show that the attainable chemistries of T2 can be significantly expanded and predict 35 chemically ordered o-MAB phases and 121 solid solutions of an MM-4 AB(2) stoichiometry. The possibility of realizing o-MAB or solid solution MAB phases combined with multiple elemental combinations previously not observed in these borides suggests an increased property tuning potential. Furthermore, five ternary T2 phases, yet to be synthesized, are also predicted to be stable.

Electrochromic (EC) materials that change color with voltage have been widely studied for use in dynamic windows. However, colorless-to-colorful switching with high contrast ratio is generically unattainable, especially for colorless-to-black electrochromic materials with an ultrahigh contrast ratio over the entire visible region. In this work, we developed Nb1.33C MXene-based dynamic windows with colorless-to-black switching of up to 75% reversible change in transmittance from 300 to 1,500 nm. By exploring the electrochromic effects of different electrolytes through in situ optical changes and electrochemical quartz crystal microbalance (EQCM), it is found that electrochromic behavior is greatly influenced by the extent of reversible Li+ insertion/deinsertion between the two-dimensional Nb1.33C MXene nanosheets. In addition, a colorless-to-black EC device based on Nb1.33C with an overall integrated contrast ratio over 80% was successfully constructed by a solution-processable spin coating method. This work enables a simple route to fabricate MXene-based high-performance electrochromic smart windows, which is important for further expanding the application of MXenes to optoelectronic and photonic applications.

We perform a theoretical study of the electronic structure and magnetic properties of the prototypical magnetic MAX-phase Mn2GaC with the main focus given to the origin of magnetic interactions in this system. Using the density functional theory+dynamical mean-field theory (DFT+DMFT) method, we explore the effects of electron-electron interactions and magnetic correlations on the electronic properties, magnetic state, and spectral weight coherence of paramagnetic and magnetically ordered phases of Mn2GaC. We also benchmark the DFT-based disordered local moment approach for this system by comparing the obtained electronic and magnetic properties with that of the DFT+DMFT method. Our results reveal a complex magnetic behavior characterized by a near degeneracy of the ferro-and antiferromagnetic configurations of Mn2GaC, implying a high sensitivity of its magnetic state to fine details of the crystal structure and unit-cell volume, consistent with experimental observations. We observe robust local-moment behavior and orbital-selective incoherence of the spectral properties of Mn2GaC, implying the importance of orbital-dependent localization of the Mn 3d states. We find that Mn2GaC can be described in terms of local magnetic moments, which may be modeled by DFT with disordered local moments. However, the magnetic properties are dictated by the proximity to the regime of formation of local magnetic moments, in which the localization is in fact driven by Hunds exchange interaction, and not the Coulomb interaction.

Zirconium diboride (ZrB2) films have been deposited by direct current magnetron sputtering (DCMS) from a ZrB2 compound target on Al2O3 (0001) substrates held at 600, 700, 800, and 900 degrees C, and with two different axial magnetic field strengths, 34 and 104 G, generated using a coil surrounding the substrate. Plasma probe measurements show an increase of the ion fluxes on floating-potential substrates of the two different configurations by a factor of 2.8 for 104 G compared to 34 G, while the ion energy remained relatively constant at approximate to 12 eV. Time-of-flight elastic recoil detection analysis (ToF-ERDA) show that films deposited with a magnetic field of 34 G are highly overstoichiometric with B/Zr ratios approximate to 2.4, while films deposited with 104 G exhibit a B/Zr ratios approximate to 2.1. The levels of oxygen and carbon in the films are below 1 at. % irrespective of growth conditions. X-ray diffraction (XRD) 0/20 scans, complemented by pole figure measurements, reveal that all deposited films are 0001-oriented. XRD 0/20 scans of the 000t peak intensities and co (rocking-curve) widths show increased ZrB2 crystal quality with increasing temperature for both magnetic field strengths. Minimum electrical resistivity of approximate to 100 p omega cm is achieved for an axial magnetic field of 104 G, independent of temperature.

i-MXenes, a new family of 2D transition metal carbides with in-plane ordered vacancies, have shown great potential in aqueous supercapacitor (SC) applications due to their high volumetric capacitances and energy densities. However, how vacancies affect their electrochemical performance, in general, and their self-discharge (SD) behavior in particular, remains unexplored. Herein, we compare the electrochemical performance of vacancy rich, ordered Mo_1.33CT_z i-MXene to that of Mo₂CT_z (with much less vacancies) in a 1 M sulfuric acid (H₂SO₄) or 15 M of lithium bromide (LiBr) electrolyte. The Mo_1.33CT_z exhibits higher volumetric capacitances and energy densities, but at the cost of a higher SD rate. Specifically, the Mo_1.33CT_z symmetric SCs deliver an energy density as high as 25.4 mWh cm(-3) at 152.4 mW cm^-3, with 65.4% voltage retention after 10 h in 15 M LiBr. In comparison, the Mo₂CT_z symmetric SCs have a maximum energy density of 20.8 mWh cm^-3 at 124.9 mW cm^-3, with 73.1% voltage retention after 10 h in the same electrolyte. The SD rates in the H₂SO₄ electrolyte are quite rapid.

Carbon-based substrates are widely used as current collectors for high-performance energy storage materials in supercapacitors. However, these substrates exhibit negligible charge storage due to inferior electrochemical activity and small surface area. Herein, electrochemical activation is utilized to enhance the electrochemical activity of - inherently inactive - commercial graphite sheets for supercapacitive applications. The results reveal that the electrochemically activated graphite sheets render a 30-fold increase in areal capacitance, i.e., from 22 to 447 mF cm(-2), which can be ascribed to the activation of graphite oxide functional groups on the surface. Also, the influence of electrochemical activation time on electrochemical performance is explored in detail, followed by the fabrication and characterization of symmetric supercapacitors based on the optimum process parameters in single-cell and tandem configurations, demonstrating the potential of electrochemically activated graphite sheets in practical applications.

Epitaxial growth of ZrB2 films on Si(100) substrates at 900 degrees C is demonstrated using direct-current magnetron sputter deposition from sintered ZrB2 targets. This case of epitaxial growth is structurally more challenging than on Si(111), 4 H-SiC(001), and Al2O3(001). From pole figure measurements, two epitaxial relationships are determined: A) in-plane: ZrB 2 [ 001 ] parallel to Si [ 110 ] and ZrB 2 [ 110 ] parallel to Si [ 110 ] , out-of-plane: ZrB 2 ( 100 ) parallel to Si ( 100 ) , and B) in-plane: ZrB 2 [ 1 2 over bar 1 ] parallel to Si [ 110 ] and the same multiply rotated 90 degrees around the 102 axis, out of plane: ZrB 2 ( 102 ) parallel to Si ( 100 ) . From full width at half maximum (FWHM) values from rocking curve measurements (omega-scans) of the 100 and 102 peaks, a measure of epitaxial quality for these two preferred orientations is obtained. Both omega-scans and theta/2 theta diffractograms show higher quality for the A-type with a FWHM value of 2.00 degrees compared with 4.97 degrees for the B-type. The film composition is found to be ZrB2.3 from time-of-flight elastic recoil detection analysis. The B-type crystallographic relationship ZrB 2 ( 102 ) parallel to Si ( 100 ) and ZrB 2 [ 1 2 over bar 0 ] parallel to Si [ 110 ] has not been previously reported.

Structural characterization in on-surface synthesis is primarily carried out by Scanning Probe Microscopy (SPM) which provides high lateral resolution. Yet, important fresh perspectives on surface interactions and molecular conformations are gained from adsorption heights that remain largely inaccessible to SPM, but can be precisely measured with both elemental and chemical sensitivity by Normal-Incidence X-ray Standing Wave (NIXSW) analysis. Here, we study the evolution of adsorption heights in the on-surface synthesis and post-synthetic decoupling of porous covalent triazine-phenylene networks obtained from 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (TBPT) precursors on Ag(111). Room temperature deposition of TBPT and mild annealing to ~150 C result in full debromination and formation of organometallic intermediates, where the monomers are linked into reticulated networks by C-Ag-C bonds. Topologically identical covalent networks comprised of triazine vertices that are interconnected by biphenyl units are obtained by a thermally activated chemical transformation of the organometallic intermediates. Exposure to iodine vapor facilitates decoupling by intercalation of an iodine monolayer between the covalent networks and the Ag(111) surface. Accordingly, Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) and NIXSW experiments are carried out for three successive sample stages: organometallic intermediates, covalent networks directly on Ag(111) and after decoupling. NIXSW analysis facilitates the determination of adsorption heights of chemically distinct carbon species, i.e. in the phenyl and triazine rings, and also for the organometallic carbon atoms. Thereby, molecular conformations are assessed for each sample stage. The interpretation of experimental results is informed by Density Functional Theory (DFT) calculations, providing a consistent picture of adsorption heights and molecular deformations in the networks that result from the interplay between steric hindrance and surface interactions. Quantitative adsorption heights, i.e. vertical distances between adsorbates and surface, provide detailed insight into surface interactions, but are underexplored in on-surface synthesis. In particular, the direct comparison with an in situ prepared decoupled state unveils the surface influence on the network structure, and shows that iodine intercalation is a powerful decoupling strategy.

MXenes have been introduced as a high energy and power density electrochemical supercapacitor material owing to their high specific capacitance and electrochemical stability. The operating potential window and, in turn, energy density of MXene based symmetric and asymmetric supercapacitors can be effectively enhanced by the proper choice of aqueous electrolyte. Herein, we investigate the electrochemical behavior of vacancy-containing 𝑖-MXene (Mo_1.33CT_z) in sulfate based aqueous electrolytes with univalent (Li⁺, Na⁺, or K⁺) or divalent (Mg²⁺, Mn²⁺, or Zn²⁺) cations. The results show that the Mo_1.33CT_z MXene electrodes can be operated in a potential window higher than 1 V without degradation in these sulfate electrolytes. The Mo_1.33CT_z MXene electrodes deliver a high volumetric capacitance up to ~677 F cm^-3 as measured in 1.0 M MnSO₄ solution. Furthermore, symmetric (Mo_1.33CT_z//Mo_1.33CT_z) and asymmetric (Mo_1.33CT_z//nitrogen-doped activated carbon (NAC)) devices in 0.5 M K₂SO₄ solution can be operated with a cell voltage of about 1.1 V and 1.8 V, respectively. The asymmetric devices retain about 97% of their initial capacitance after 5000 charge/discharge cycles. Overall, the results reveal that the choice of the intercalating cations is a viable route to boost the performance of Mo_1.33CT_z MXene and to construct energy storage devices.

Recent experiments [Barbero et al. Phys. Rev. B 95, 094505 (2017)] have established that bulk superconductivity (T_c ∼ 8.3-8.7 K) can be induced in AlB₂-type ZrB₂ and HfB₂, highly covalent refractory ceramics, by vanadium (V) doping. These AlB₂-structured phases provide an alternative to earlier diamon-like or diamond-based superconducting and superhard materials. However, the underlying mechanism for doping-induced superconductivity in these materials is yet to be addressed. In this paper, we have used first-principles calculations to probe electronic structure, lattice dynamics, and electron-phonon coupling (EPC) in V-doped ZrB₂ and consequently examine the origin of the superconductivity. We find that, while doping-induced stress weakens the EPC, the concurrently induced charges strengthen it. The calculated critical transition temperature (T_c) in electron (and V)-doped ZrB₂ is at least one order of magnitude lower than experiments, despite considering the weakest possible Coulomb repulsion between electrons in the Cooper pair, hinting a complex origin of superconductivity in it.

High-entropy (HE) ceramics, by analogy with HE metallic alloys, are an emerging family of multielemental solid solutions. These materials offer a large compositional space, with a corresponding large range of properties. Here, we report the experimental realization of a 3D HE MAX phase, Ti1,0V0.7Cr0.05Nb1.0Ta1.0AlC3, and a corresponding 2D HE MXene in the form of freestanding flakes of average composition Ti1.1V0.7CrxNb1.0Ta0.6C3Tz (T-z = -F, -O, -OH), as produced by selective removal of AI from the HE MAX phase in aqueous hydrofluoric acid (HF). Initial tests on HE MXene "paper" electrodes show their high potential as electrode materials in supercapacitors through volumetric and gravimetric capacitances of 1688 F/cm(3) and 490 F/g, respectively, originating from a combination of diffusion- and surface-controlled charge storage processes. The introduction of the HE concept into the field of 2D materials suggests a wealth of future 2D materials and applications.

In this study, we have used density functional theory (DFT) calculations to characterize if and how defects influence the stability and electronic/mechanical properties of MB2 (AlB2-type) for different transition metal M. From a point defect analysis including vacancies, interstitials, and anti-sites, we identify vacancies to be most favored, or least unfavored. To provide insight into possible vacancy ordering, we focus on vacancies on M- and B-sublattices for nine metals (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W), modelled both as disordered and ordered. We demonstrate and explain why vacancies have a significant impact for M from Group 4 (Ti, Zr, Hf), Group 5 (Nb, Ta) and 6 (Mo, W) with improved thermodynamical and dynamical stability as well as mechanical properties. This by diverging from the ideal composition through controlled off-stoichiometry in terms of vacancies in M- or B-deficient structures. Line compounds TiB2, ZrB2 and HfB2 account for B-poor or M-rich conditions by forming planar defects comprised of vacant B. This in contrast to the ordered M- and B vacancies identified for MoB2 and WB2, with an optimal result at 33.33% M- and 25% B-vacancies, respectively, which significantly improves the stability and concurrent properties through elimination of antibonding states and minimization of non-bonding states. Similar behavior with enhanced stability and properties is demonstrated for NbB2 and TaB2 with an optimum around 10% M- and 17% B-vacancies, respectively.

On-surface synthesis is a powerful methodology for the fabrication of low-dimensional functional materials. The precursor molecules usually anchor on different metal surfaces via similar configurations. The activation energies are therefore solely determined by the chemical activity of the respective metal surfaces. Here, we studied the influence of the detailed adsorption configuration on the activation energy on different metal surfaces. We systematically studied the desulfonylation homocoupling for a molecular precursor on Au(111) and Ag(111) and found that the activation energy is lower on inert Au(111) than on Ag(111). Combining scanning tunneling microscopy observations, synchrotron radiation photoemission spectroscopy measurements, and density functional theory calculations, we elucidate that the phenomenon arises from different molecule-substrate interactions. The molecular precursors anchor on Au(111) via Au-S interactions, which lead to weakening of the phenyl-S bonds. On the other hand, the molecular precursors anchor on Ag(111) via Ag-O interactions, resulting in the lifting of the S atoms. As a consequence, the activation barrier of the desulfonylation reactions is higher on Ag(111), although silver is generally more chemically active than gold. Our study not only reports a new type of on-surface chemical reaction but also clarifies the influence of detailed adsorption configurations on specific on-surface chemical reactions.

Recently, a 2D metal boride - boridene - has been experimentally realized in the form of single-layer molybdenum boride sheets with ordered metal vacancies, through selective etching of the nanolaminated 3D parent borides (Mo_2/3Y_1/3)₂AlB₂ and (Mo_2/3Sc_1/3)₂AlB₂. The chemical formula of the boridene was suggested to be Mo_4/3B_2-xT_z, where T_z denotes surface terminations. Here, the termination composition and material properties of Mo_4/3B_2-xT_z from both theoretical and experimental perspectives are investigated. Termination sites are considered theoretically for termination species T = O, OH, and F, and the energetically favored termination configuration is identified at z = 2 for both single species terminations and binary termination mixes of different stoichiometries in ordered and disordered configurations. Mo_4/3B_2-xT_z is shown to be dynamically stable for multiple termination stoichiometries, displaying semiconducting, semimetallic, or metallic behavior depending on how different terminations are combined. The approximate chemical formula of a freestanding film of boridene is attained as Mo_1.33B_1.9O_0.3(OH)_1.5F_0.7 from X-ray photoelectron spectroscopy (XPS) analysis which, within error margins, is consistent with the theoretical results. Finally, metallic and additive-free Mo_4/3B_2-xT_z shows high catalytic performance for the hydrogen evolution reaction, with an onset potential of 0.15 V versus the reversible hydrogen electrode.

The laminated ternary boride Mo5SiB2 of T2 structure have two symmetrically inequivalent metallic sites, 16l and 4c, being occupied in a 4:1 ratio. The phase was recently shown to be stable for 80% substitution of Mo for Ti, at the majority site, forming an out-of-plane chemically ordered quaternary boride: Ti4MoSiB2. Considering that the hypothetical Ti5SiB2 is theoretically predicted as not stable, a key difference in bonding characteristics is indicated for full substitution of Mo for Ti at the metallic sites. To explore the origin of formation of Ti4MoSiB2, we here investigate the electronic properties and bonding characteristics of Mo5SiB2, Ti4MoSiB2 and Ti5SiB2 through their density of states, projected crystal orbital Hamilton population (pCOHP), Bader charge partitioning and second order force constants. The bond between the two different metallic sites is found to be key to the stability of the compounds, evident from the pCOHP of this bond showing a peak of bonding states close to the Fermi level, which is completely filled in Mo5SiB2 and Ti4MoSiB2, while only partially filled in Ti5SiB2. Furthermore, the lower electronegativity of Ti compared to Mo results in charge accumulation at the Si and B sites, which coincides with a reduced bond strength in Ti5SiB2 compared to Mo5SiB2 and Ti4MoSiB2. Bandstructure calculations show that all three structures are metallic. The calculated mechanical and elastic properties show reduced bulk (B) and elastic (E) moduli when introducing Ti in Mo5SiB2, from 279 and 365 GPa to 176 and 258 GPa, respectively. The Pugh criteria indicates also a slight reduction in ductility, with a G/B ratio increasing from 0.51 to 0.59.

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo2/3RE1/3)(2)AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo2/3Dy1/3)(2)AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions.

Fiber type devices are promising for applications in wearable and portable electronics. However, scalable fabrication of fiber electrodes with multifunctional performance for use in distinct fields remains challenging. Herein, high performance smart fibers based on Mo1.33C i-MXene nanosheets and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hybrid paste are fabricated with an easily scalable spinning approach. The hybrid fibers produced by this method can be applied in both high-performance supercapacitors and electrochemical transistors (ECTs). When assembled into a fiber type asymmetric supercapacitor with reduced graphene oxide (rGO) fiber, a capacitance of 105 F g(-1) and an energy density of 37 mW h g(-1) were reached for a potential window of 1.6 V. The hybrid fiber based ECT shows high transconductance and fast response time. This work demonstrates the potential of i-MXene-based fiber electrodes for multifunctional applications, to aid in the development of the next-generation, high-performance wearable electronic devices.

Energy storage devices such as rechargeable batteries and supercapacitors are of great importance for establishing clean energy sources. Accordingly, the production of these devices needs to rely on sustainable and environmentally friendly materials. This report provides an insight on the use of two-dimensional transition metal carbides (MXene) based electrodes, here shown for Mo(1.33)CTz-Ti3C2Tz mixed MXene, in Zn-ion hybrid supercapacitors (ZHSC) using aqueous and nonaqueous (acetonitrile-based) electrolytes. The effect of anion carriers on the accessible capacity, rate capability, and life span of the MXene//Zn hybrid supercapacitor is explored in-depth. Halide carriers such as chloride (Cl-) and iodide (I-) feature a superior performance, however, a fast passivation is observed in Cl- based electrolytes and a narrow potential window is achieved in I based electrolytes. Importantly, a few micron layer of Ti3C2Tz MXene coated on the surface of the Zn anode is found to inhibit the side reactions and passivation observed in ZnCl2 solutions, which enables the use of such low-cost Zn salt in MXene//Ti3C2Tz -coated-Zn cells. The cells can be reversibly cycled over 10,000 cycles, delivering a capacity up to 200 mAh g(-1 )at low rate (0.5 mV s(-1)) and a capacity retention of about 36% at high rate (100 mV s(-1)). Furthermore, the Ti3C2Tz surface coating layer enhanced the coulombic efficiency in Zn (CF3SO3)(2) electrolyte without affecting the accessible capacity or the rate capability. This work sheds light on the use of MXenes in sustainable low-cost ZHSC with high energy density and power density as a positive electrode material as well as a surface coating material for the Zn negative electrode.

Aqueous asymmetric supercapacitors (AASCs) can have high voltages and high energy densities. However, the rational design of AASCs with proper negative and positive electrodes remains a challenge. Herein, we report on an AASC using Mo1.33CTz MXene films as the negative electrode, and tetramethylammonium cation intercalated birnessite (TMA(+)-MnO2) films as the positive electrode in a 21 mol kg(-1) lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) electrolyte. Benefiting from a high, stable voltage of 2.5 V, an energy density of 86.5 Wh L-1 at 2 mV s(-1) and a power density of 10.3 kW L-1 at 1 Vs(-1) were achieved. The cells also exhibit excellent cycling stability (>98% after 1,0000 cycles at 100 mV s(-1)) and a 51.1 % voltage retention after 10 h. This good performance is attributed to the high stable potential window and high volumetric capacitances of both Mo1.33CTz and TMA(+)-MnO2 electrodes in highly concentrated electrolytes. This work provides a roadmap for developing high performance AASCs with high voltages and high energy/power densities, with relatively slow self-discharge rates.

Planar defect structures appearing in transition metal diboride (TMB2) thin films, grown by different magnetron sputtering-deposition approaches over a wide compositional and elemental range, were systematically investi-gated. Atomically resolved scanning transmission electron microscopy (STEM) imaging, electron energy loss spec-troscopy (EELS) elemental mapping, and first principles calculations have been applied to elucidate the atomic structures of the observed defects. Two distinct types of antiphase boundary (APB) defects reside on the {1(1) over bar 00} planes. These defects are without (named APB-1) or with (APB-2) local deviation from stoichiometry. APB-2 de-fects, in turn, appear in different variants. It is found that APB-2 defects are governed by the films composition, while APB-1 defects are endemic. The characteristic structures, interconnections, and circumstances leading to the formation of these APB-defects, together with their formation energies, are presented.

The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: Ti3C2Tx. Herein, freestanding Ti3C2Tx MXene films, composed only of Ti3C2Tx MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of Ti3C2Tx- based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the Tx-Ti-C titanium species situated on the surfaces of the MXene flakes, whereas the Ti-C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine Ti3C2Tx MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the Tx-Ti-C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the Ti3C2Tx electrodes. As the capacities of Ti3C2Tx MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the Tx-Ti-C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.

Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti(1-x)Al(x)B(2-y )diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y & ISIN; (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x & ISIN; (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 +/- 1.1 GPa and an elastic modulus of 523 & PLUSMN; 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 +/- 1 GPa and 36 +/- 1 GPa, and an elastic modulus of 569 +/- 7 GPa and 493 +/- 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.

Self-assembly of three-dimensional molecules is scarcely studied on surfaces. Their modes of adsorption can exhibit far greater variability compared to (nearly) planar molecules that adsorb mostly flat on surfaces. This additional degree of freedom can have decisive consequences for the expression of intermolecular binding motifs, hence the formation of supramolecular structures. The determining molecule-surface interactions can be widely tuned, thereby providing a new powerful lever for crystal engineering in two dimensions. Here, we study the self-assembly of triptycene derivatives with anthracene blades on Au(111) by Scanning Tunneling Microscopy, Near Edge X-ray Absorption Fine Structure and Density Functional Theory. The impact of molecule-surface interactions was experimentally tested by comparing pristine with iodine-passivated Au(111) surfaces. Thereby, we observed a fundamental change of the adsorption mode that triggered self-assembly of an entirely different structure.

On-surface synthesis has recently emerged as a powerful strategy to design conjugated polymers previously precluded in conventional solution chemistry. Here, an N-containing pentacene-based precursor (tetraazapentacene) is ex-professo synthesized endowed with terminal dibromomethylene (:CBr2) groups to steer homocoupling via dehalogenation on metallic supports. Combined scanning probe microscopy investigations complemented by theoretical calculations reveal how the substrate selection drives different reaction mechanisms. On Ag(111) the dissociation of bromine atoms at room temperature triggers the homocoupling of tetraazapentacene units together with the binding of silver adatoms to the nitrogen atoms of the monomers giving rise to a N-containing conjugated coordination polymer (P1). Subsequently, P1 undergoes ladderization at 200 degrees C, affording a pyrrolopyrrole-bridged conjugated polymer (P2). On Au(111) the formation of the intermediate polymer P1 is not observed and, instead, after annealing at 100 degrees C, the conjugated ladder polymer P2 is obtained, revealing the crucial role of metal adatoms on Ag(111) as compared to Au(111). Finally, on Ag(100) the loss of :CBr2 groups affords the formation of tetraazapentacene monomers, which coexist with polymer P1. Our results contribute to introduce protocols for the synthesis of N-containing conjugated polymers, illustrating the selective role of the metallic support in the underlying reaction mechanisms.

Titanium boride, TiBx, thin films were grown by direct current magnetron co-sputtering from a compound TiB2 target and a Ti target at an Ar pressure of 2.2 mTorr (0.3 Pa) and substrate temperature of 450 ?degrees C. While keeping the power of the TiB2 target constant at 250 W, and by varying the power on the Ti target, P-Ti, between 0 and 100 W, the B/Ti ratio in the film could be continuously and controllably varied from 1.2 to 2.8, with close-tostoichiometric diboride films achieved for P-Ti = 50 W. This was done without altering the deposition pressure, which is otherwise the main modulator for the composition of magnetron sputtered TiBx diboride thin films. The film structure and properties of the as-deposited films were compared to those after vacuum-annealing for 2 h at 1100 ?degrees C. As-deposited films consisted of small (?50 nm) randomly oriented TiB2 crystallites, interspersed in an amorphous, sometimes porous tissue phase. Upon annealing, some of the tissue phase crystallized, but the diboride average grain size did not change noticeably. The near-stoichiometric film had the lowest resistivity, 122 mu omega cm, after annealing. Although this film had growth-induced porosity, an interconnected network of elongated crystallites provides a path for conduction. All films exhibited high hardness, in the 25-30 GPa range, where the highest value of similar to 32 GPa was obtained for the most Ti-rich film after annealing. This film had the highest density and was nano-crystalline, where dislocation propagation is interrupted by the off-stoichiometric grain boundaries.

Recently, we presented a family of in-plane chemically ordered transition metal borides of the general formula (M-2/3M-1/3")(2)AlB2. Here, we investigate incorporation of magnetic rare earth (RE) elements into this structure by synthesis and analysis of Mo4/3RE2/3AlB2, where RE = Ho, Tb, and Er. The crystal structure is verified by X-ray diffraction and scanning transmission electron microscopy, while the composition is derived from energy dispersive X-ray analysis. Through magnetization measurements, we also show that Mo4/3Ho2/3AlB2 orders antiferromagnetically below 9 K. We suggest that (M-2/3M-1/3")(2)AlB2 could potentially be a versatile platform for new magnetic materials, in 3D as well as 2D. [GARPHICS] IMPACT STATEMENT This paper introduces magnetic elements to i-MAB phases family with a formula of Mo4/3RE2/3AlB2 (RE = Ho, Er, and Tb), which opens a venue for further exploration of chemically ordered magnetic materials.