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they were stored in room-air after the annealing procedure and prior to the SEM/EDX study. 100The Si content of the A layers in the novel structure is negligible, based on EDX results, and and what is present in similar systems, see S3 and S6. These calculations showed that 115

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Implications regarding requirements of performing a successive electrospinning and producing nanoporous polyetherimide (PEI) fibers are discussed through electrospinning PEI solutions of three nonvolatile solvents, that is, dimethylforamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), under atmospheres of constant temperature and varying levels of relative humidity (RH). The results demonstrate depending on nature of miscibility area in ternary phase diagram, a minimum RH is necessary to stabilize fiber formation. Furthermore, RH of operating environment affects diameter and both surface and interior morphologies of PEI electrospun fibers through involving the rate of phase demixing and viscoelasticity of solution. Considering fibers produced from NMP solutions because of delayed demixing, solvent drying precedes phase demixing or takes place in a comparable rate in high RH which leads to solid cross-section and texture-less surface with slight porosity. By choosing DMF or DMAc as electrospinning solvent, thicker fibers with rough surface and porous cross-section are expected.

Two-dimensional (2D) materials, especially their most prominent member, graphene, have greatly influenced many scientific areas. Moreover, they have become a base for investigating the relativistic properties of condensed matter within the emerging field of "Dirac physics." This has ignited an intense search for new materials where charge carriers behave as massless or massive Dirac fermions. Here, by the use of density functional theory and symmetry analysis, we theoretically show the existence of Dirac electrons in a series of 2D transition-metal carbides, known as MXenes. They possess eight conical crossings in the first Brillouin zone with giant spin-orbit splitting. Our findings indicate that the 2D band structure of MXenes is protected against external perturbations and preserved even in multilayer phases. These results, together with the broad possibilities to engineer the properties of these phases, make them a potential candidate for studying novel Dirac-physics-based applications.

Incorporation of layers of noble metals in non-van der Waals layered materials may be used to form novel layered compounds.Recently, we demonstrated a high-temperature-induced exchange process of Au with Si in the layered phase Ti 3 SiC 2 , resulting in the formation of Ti 3 AuC 2 and Ti 3 Au 2 C 2 . Here, we generalize this technique showing that Au/Ti 2 AlC and Au/Ti 3 AlC 2 undergo an exchange reaction at 650 8C to form Ti 2 Au 2 C and Ti 3 Au 2 C 2 and determine their structures by electron microscopy, X-ray diffraction, and ab initio calculations. These results imply that noble-metal-containing layered phases should be possible to synthesize in many systems.The metal to be introduced should be inert to the transition-metal carbide layers, and exhibit negative heat of mixing with the initial A element in a liquid phase or two-phase liquid/solid region at the annealing temperature.Phases with nanolaminated or atomically layered structures are an extensive research topic for the synthesis of novel materials and two-dimensional structures. Layered ceramics constitute a large class of materials including both van der Waals (vdW) materials, such as graphite or transition-metal dichalcogenides, and non-vdW solids. vdW materials are commonly applied for the formation of new two-dimensional materials, and allow for intercalation of foreign species, both ionic such as in Li-ion batteries 1,2 and neutral as in the case of intercalation of zerovalent noble metals in vdW solids. [3][4][5] In contrast, incorporation of noble-metal layers in non-vdW layered materials to form novel compounds is an outstanding challenge. Recently, we demonstrated a high-temperature-induced exchange process of Au with Si in the layered phase Ti 3 SiC 2 , resulting in the formation of the novel Ti 3 AuC 2 and Ti 3 Au 2 C 2 phases by an ordered replacement of the A-layer crystal planes; from Si-planes to Au or Au 2 planes.6 Furthermore, Ir-exchange with Au in Ti 3 AuC 2 yielded the new phase Ti 3 IrC 2 . 6 The starting phase Ti 3 SiC 2 is an archetype member of the M n+1 AX n phases, a large family of layered transition-metal carbides and nitrides [7][8][9][10]

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Electrospinning of polymer solutions under a high humidity environment is studied. It is shown that the porous morphology formed after phase separation can be preserved or collapsed depending on three factors: phase demixing time, physical gelation, and viscoelastic properties of the polymer-rich phase. Fibers with rough surfaces and nonporous cross sections are produced when poly(ether imide)/dimethylformamide is electrospun. This is due to accelerated vitrification-related gelation of the water/dimethylformamide/poly(ether imide) system on the fiber surface. Similar phase behavior can be expected for a ternary system based on polystyrene. However, the new system results in fibers with smooth surfaces and porous cross sections. This discrepancy can be resolved by considering delayed gelation as well as lower elastic and loss moduli of the polymer-rich phase in the latter system. Further evidence is also provided by poly(ether sulfone) and polysulfone. Crystallization-induced gelation observed for poly(vinylidene fluoride) fibers can well account for the obtained morphology. However, crystallizationinduced gelation cannot lock in the fiber morphology similar to the vitrification-related gelation.