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Boron nitride (BN) is a promising 2D material as well as a potential wide-bandgap semiconductor. Chemical vapor deposition (CVD) is commonly used to deposit single layers or thin films of BN, but the deposition process is insufficiently understood at an atomic scale. the CVD of BN is studied using two boron precursors, the organoboranes, triethylborane, and trimethylborane. Using high resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy, this study shows that hexagonal-BN (h-BN) nucleates and grows epitaxially for approximate to 4 nm before it either polytype transforms to rhombohedral-BN (r-BN), turns to less ordered turbostratic-BN or is terminated by a layer of amorphous carbon. this study proposes that the carbon in the organoboranes deposits on the epitaxially growing h-BN surface and this either leads to the polytype transition to r-BN, the transition to less ordered BN growth, or complete surface poisoning with carbon terminating BN growth. These results question the use of organoboranes in CVD of epitaxial BN films, and the polytype stability of h-BN growing on graphene. The influence of carbon toward epitaxial h-BN growth is examined using high-resolution microscopy. For most of the film, carbon induced a polytype transition from h-BN to local r-BN to turbostatic-BN ending epitaxial growth. In some localized BN structures, carbon is absent, here the epitaxial film growth is sustained to higher thickness with a uniform polytype transition from h-BN to r-BN. image, Funding Agencies|Swedish Research Council [2017-04164]; Swedish Foundation for Strategic Research; Swedish National Infrastructure in Advanced Electron Microscopy [2021-00171, RIF21-0026]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoeping University [2009-00971]

Near-stoichiometric chromium diboride films were subject to in situ annealing inside a scanning transmission electron microscope to access the thermal behavior of the film and embedded structural planar defects. Independent of films' stoichiometry, the planar defects were unaffected by the applied heat treatments. On the contrary, the interfaces between the boron-rich tissue phase and the CrB2 phase were reshaped in the overstoichometric CrB2 film. At high temperatures, diffusion of contact metal species (platinum) from the focused ion beam sample preparation was triggered, with subsequent migration onto the sample. This resulted in the formation of metal-rich regions as directly observed and characterized at the atomic level. We determined that platinum did not react with the diboride structure but is accommodated by various defects present in the film., Funding Agencies|Knut och Alice Wallenbergs Stiftelse10.13039/501100004063; Knut and Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Research Council (VR); Swedish Foundation for Strategic Research (SSF) [EML16-0004]; Swedish National Infrastructure in Advanced Electron Microscopy [2021-00171, RIF21-0026]; VR [2021-03652]; Carl Tryggers Stiftelse [CTS:21 1272]

Synthesis of high-entropy sublattice nitride (HESN) coatings by magnetron sputtering is typically done using custom-made alloyed targets with specific elemental compositions. This approach is expensive, requires long delivery times, and offers very limited flexibility to adjust the film composition. Here, we demonstrate a new method to grow HESN films, which relies on elemental targets arranged in the multicathode configuration with substrates rotating during deposition. TiVNbMoWN films are grown at a temperature of similar to 520(degrees)C using Ti, V, Nb, and Mo targets operating in the direct current magnetron sputtering mode, while the W target, operated by high power impulse magnetron sputtering (HiPIMS), provides a source of heavy ions. The energy of the metal ions EW+ is controlled in the range from 80 to 620 eV by varying the amplitude of the substrate bias pulses V-s, synchronized with the metal-ion-rich phase of HiPIMS pulses. We demonstrate that W(+ )irradiation provides dynamic recoil mixing of the film-forming components in the near-surface atomic layers. For EW+ >= 320 eV the multilayer formation phenomena, inherent for this deposition geometry, are suppressed and, hence, compositionally uniform HESN films are obtained, as confirmed by the microstructural and elemental analysis.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/)

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., Funding Agencies|Knut and Alice Wallenberg (KAW) Foundation for Fellowship/Scholar Grants; Goran Gustafsson foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Research Council [RIF21-0026]; Swedish National Infrastructure in Advanced Electron Microscopy [2018-05973, 2021-00171]; Swedish National Infrastructure for Computing (SNIC); Swedish Research Council [2018-05973] Funding Source: Swedish Research Council

The development of abundant, cheap, and highly active catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important for hydrogen production. Nanolaminate ternary transition metal carbides (MAX phases) and their derived two-dimensional transition metal carbides (MXenes) have attracted considerable interest for electrocatalyst applications. Herein, four new MAX@MXene core-shell structures (Ta2CoC@ Ta2CTx, Ta2NiC@Ta2CTx, Nb2CoC@Nb2CTx, and Nb2NiC@Nb2CTx), in which the core region is Co/Ni-MAX phases while the edge region is MXenes, have been prepared. Under alkaline electrolyte conditions, the Ta2CoC@Ta2CTx core-shell structure showed an overpotential of 239 mV and excellent stability during the HER with MXenes as the active sites. For the OER, the Ta2CoC@Ta2CTx core- shell structure showed an overpotential of 373 mV and a small Tafel plot (56 mV dec-1), which maintained a bulk crystalline structure and generated Co-based oxyhydroxides that formed by surface reconstruction as active sites. Considering rich chemical compositions and structures of MAX phases, this work provides a new strategy for designing multifunctional electrocatalysts and also paves the way for further development of MAX phase-based materials for clean energy applications., Funding Agencies|Pioneer

Intercalated layered materials offer distinctive properties and serve as precursors for important two-dimensional (2D) materials. However, intercalation of non-van der Waals structures, which can expand the family of 2D materials, is difficult. We report a structural editing protocol for layered carbides (MAX phases) and their 2D derivatives (MXenes). Gap-opening and species-intercalating stages were respectively mediated by chemical scissors and intercalants, which created a large family of MAX phases with unconventional elements and structures, as well as MXenes with versatile terminals. The removal of terminals in MXenes with metal scissors and then the stitching of 2D carbide nanosheets with atom intercalation leads to the reconstruction of MAX phases and a family of metal-intercalated 2D carbides, both of which may drive advances in fields ranging from energy to printed electronics., Funding Agencies|Key R&D Projects of Zhejiang Province; Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang; International Partnership Program of Chinese Academy of Sciences [2022C01236]; Advanced Energy Science and Technology Guangdong Laboratory [2019R01003]; Ningbo Top-talent Team Program [174433KYSB20190019]; Ningbo "3315 plan" [HND20TDTHGC00]; National Natural Science Foundation of China; China Postdoctoral Science Foundation [2018A-03-A]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows Program [21671195, 52172254, 52250005, 52202325, U2004212]; Wallenberg Scholar Program [2020M680082]; Swedish National Infrastructure in Advanced Electron Microscopy [KAW 2020.0196]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University SFO-Mat-LiU [KAW 2019.0290]; US National Science Foundation [2021-00171, RIF21-0026]; [2009 00971]; [DMR-2041050]

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., Funding Agencies|Knut and Alice Wallenberg (KAW) Foundation for a Fellowship/Scholar Grant; Swedish Foundation for Strategic Research (SSF) [EM16-0004]; Swedish Research Council [2018-05973]; Knut and Alice Wallenberg (KAW) Foundation; Swedish Foundation for Strategic Research (SSF) [EM16-0004]; Swedish Research Council [RIF21-0026]; Goran Gustafsson foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2018-05973]; Swedish National Infrastructure in Advanced Electron Microscopy [200900971, 2021-00171]

Traditional age hardening mechanisms in refractory ceramics consist of precipitation of fine particles. These processes are vital for widespread wear-resistant coating applications. Here, we report novel Guinier-Preston zone hardening, previously only known to operate in soft light-metal alloys, taking place in refractory ceramics like multicomponent nitrides. The added superhardening, discovered in thin films of Ti-Al-W-N upon high temperature annealing, comes from the formation of atomic-plane-thick W disks populating {111} planes of the cubic matrix, as observed by atomically resolved high resolution scanning transmission electron microscopy and corroborated by ab initio calculations and molecular dynamics simulations. Guinier-Preston zone hardening concurrent with spinodal decomposition is projected to exist in a range of other ceramic solid solutions and thus provides a new approach for the development of advanced materials with outstanding mechanical properties and higher operational temperature range for the future demanding applications., Funding: Swedish Research Council VR [2018-03957, 2021-03652, 2021-04426]; Swedish Energy Agency [51201-1]; Knut and Alice Wallenberg Foundation [KAW2019.0290, CTS 20:150]; Carl Tryggers Stiftelse [21:1272, 2017-00646_9]; Swedish Research Council VR-RFI [VR-2018-0597]; Swedish Foundation for Strategic Research [2021-00171]; Swedish Research Council [RIF21-0026]; Swedish National Infrastructure in Advanced Electron Microscopy [22-4, 2022-03071]; Aforsk Foundation; Competence Center Functional Nanoscale Materials (FunMat-II) VINNOVA; [KAW2016.0358]; [RIF14-0053]

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., Funding Agencies|Knut and Alice Wallenberg (KAW) Foundation [KAW 2020.0033]; Swedish Research Council [2019-04233, 2021-00471, 2018-05973]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Deutsche Forschungsgemeinschaft (DFG) [CRC/TRR 270, 405553726]