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The role of double TiO 2 layers at the interface of FeSe/SrTiO 3 superconductors
We determine the surface reconstruction of SrTiO 3 used to achieve superconducting FeSe films in experiments, which is different from the 1×1 TiO 2 -terminated SrTiO 3 assumed by most previous theoretical studies. In particular, we identify the existence of a double TiO 2 layer at the FeSe/SrTiO 3 interface that plays two important roles. First, it facilitates the epitaxial growth of FeSe. Second, ab initio calculations reveal a strong tendency for electrons to transfer from an oxygen deficient SrTiO 3 surface to FeSe when the double TiO 2 layer is present. The double layer helps to remove the hole pocket in the FeSe at the Γ point of the Brillouin zone and leads to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards the resolution of many open questions about this superconductor.
Two-dimensional ferroelectric topological insulators in functionalized atomically thin bismuth layers
We introduce a class of two-dimensional (2D) materials that possess coexisting ferroelectric and topologically insulating orders. Such ferroelectric topological insulators (FETIs) occur in noncentrosymmetric atomic layer structures with strong spin-orbit coupling (SOC). Here, we showcase a prototype 2D FETI in an atomically thin bismuth layer functionalized by CH 2 OH, which exhibits a large ferroelectric polarization that is switchable by a ligand molecule rotation mechanism and a strong SOC that drives a band inversion leading to the topologically insulating state. An external electric field that switches the ferroelectric polarization also tunes the spin texture in the underlying atomic lattice. Moreover, the functionalized bismuth layer exhibits an additional quantum order driven by the valley splitting at the K and K' points in the Brillouin zone stemming from the symmetry breaking and strong SOC in the system, resulting in a remarkable state of matter with the simultaneous presence of the quantum spin Hall and quantum valley Hall effect. These phenomena are predicted to exist in other similarly constructed 2D FETIs, thereby offering a unique quantum material platform for discovering novel physics and exploring innovative applications.
Hybridization of Bogoliubov Quasiparticles between Adjacent CuO 2 Layers in the Triple-Layer Cuprate Bi 2 Sr 2 Ca 2 Cu 3 O 10 + δ Studied by Angle-Resolved Photoemission Spectroscopy
Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO 2 layers in the triple-layer cuprate high-temperature superconductor Bi 2 Sr 2 Cu 2 Cu 3 O 10+δ is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anticrossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the d-wave superconducting gap of both BQP bands smoothly develops with momentum without an abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off nodal to the antinodal region, which is explained by the momentum dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs as well as the combination of phonon modes of the triple CuO 2 layers and spin fluctuations represented by a four-well model are discussed.
Giant negative electrostriction and dielectric tunability in a van derWaals layered ferroelectric
Abstract not provided
Long-range magnetic order in hydroxide-layer-doped (Li[subscript 1;#8722;x;#8722;y]FexMn[subscript y]OD)FeSe
Abstract not provided
Layer-by-Layer Nanoarchitectonics of Electrochemically Active Thin Films Comprised of Radical-Containing Polymers
Electroactive coatings based on non-conjugated redox-active polymers have increased in popularity with the development of thin film organic batteries. Here, control over coating deposition, redox-activity, and ion transport are key to improving their energy storage performance. In this work, the synthesis, solution state electrochemical characterization, and layer-by-layer (LbL) assembly of a nitroxide-based polycation and polyanion are presented. Solution state electrochemical characterization indicates that the rate of electron transfer for the nitroxide polyanion is much higher as compared to the nitroxide polycation. LbL thin films of the nitroxide polyanion and nitroxide polycation are assembled, demonstrating linear growth and tunable thickness (28 nm/layer pair). This work confirms that the ion transport mechanism of the LbL films during the redox reaction is influenced depending on the charge of the terminating layer, where the nitroxide polyanion can participate in self-doping, which leads to a contribution from cation transport. The nitroxide polyanion-terminated film also exhibits a higher capacity and a slightly reduced charge transfer resistance. However, it was also observed that a more pronounced capacity fade occurred for the polyanion-terminated film than the polycation-terminated film. Taken together, this highlights how oppositely charged radical-containing polyelectrolytes can form electroactive coatings for possible applications in energy storage or sensing.
Broadband perfect absorber based on one ultrathin layer of refractory metal
Not Available
Diagnostic Comparison between Lithium-rich Layered Oxides and Classical Layered Oxides
Established combined characterization techniques to study oxygen activities. Confirmed oxygen anion redox reversibly contributing to the overall capacity of Li-rich layered oxides. Identified the structure irreversible transformation and large amount of strain formation induced by oxygen vacancies formation. Applied GSIR modification method to precisely control oxygen activity in Li-rich layered oxides. Identified several possible contributing factors to irreversible capacity loss routinely seen on the first cycle of classical layered oxides: phase transformation in bulk classical diffusion limitations irreversible surface side reactions generation of dislocations or other extended defects loss of electrical connectivity among cathode particles
Replacing Metal-Based Lightning Strike Protection Layer of CFRPS by 3D Printed Electronically Conductive Polymer Layer
Electrically conductive adhesive layers were deposited on top of aerospace grade carbon fiber reinforced plastic (CFRP) panels using a small-scale 3D printer. Polylactic acid (PLA) filaments with copper filler (CU-PLA) and graphene filler (GO-PLA) were used to print around 0.7 mm thick electrically conductive layer on top of CFRP panels. 3D printed polymeric layers were tested for their effectiveness as a lightning strike protection (LSP) material by subjected to a simulated lightning strike. A painted, electrically non-conductive unprotected panel was also tested for comparison. In the case of the CU-PLA protected sample, a high electrical conductivity proved to be useful in fast dissipation of the lightning current. Fast current dissipation helped to reduce the resistive heating after a lightning strike. Thermography and high-speed camera analysis were employed to study the heat generation and current dissipation during the lightning strike. These results established that a useful Faraday Cage was applied via additive manufacturing successfully. This work shows the successful application of 3D printing for producing LSP technologies, with future work aimed at investigating optimal printable electrically conductive thermoset material candidates.
Observation of the Same New Sheet Topology in Both the Layered Uranyl Oxide-Phosphate Cs 11 [(UO 2 ) 12 (PO 4 ) 3 O 13 ] and the Layered Uranyl Oxyfluoride-Phosphate Rb 11 [(UO 2 ) 12 (PO 4 ) 3 O 12 F 2 ] Prepared by Flux Crystal Growth
We report single crystals of four new layered uranyl phosphates, including three oxyfluoride-phosphates, were synthesized by molten flux methods using alkali chloride melts, and their structures were determined by single-crystal X-ray diffraction. Cs 11 [(UO 2 ) 12 (PO 4 ) 3 O 13 ] ( 1 ) and Rb 11 [UO 2 ) 12 (PO 4 ) 3 O 12 F 2 ] ( 2 ) contain uranyl phosphate layers exhibiting a new sheet topology that can be related to that of β-U 3 O 8 , while Cs 4.4 K 0.6 [(UO 2 ) 6 O 4 F(PO 4 ) 4 (UO 2 )] ( 3 ) and Rb 4.4 K 0.6 [(UO 2 ) 6 O 4 F(PO 4 ) 4 (UO 2 )] ( 4 ) contain layers of a known isomer of the prominent phosphuranylite topology. The location of the fluorine in structures 2 - 4 is discussed using bond valence sums. First principles calculations were used to explore why a pure oxide structure is obtained for the Cs containing phase ( 1 ) and in contrast an oxyfluoride phase for the Rb containing phase ( 2 ). Ion exchange experiments were performed on 1 and 2 and demonstrate the ability of these structures to exchange approximately half of the parent alkali cation with a target alkali cation in an aqueous concentrated salt solution. Optical measurements were performed on 1 and 2 and the UV-vis and fluorescence spectra show features characteristic of the UO 2 2 + uranyl group.
Photonic Curing of Nickel Oxide Transport Layer and Perovskite Active Layer for Flexible Perovskite Solar Cells: A Path Towards High-Throughput Manufacturing
High-throughput roll-to-roll (R2R) manufacturing of perovskite solar cells (PSCs) is currently limited by thermal processes that take tens of minutes each, translating to impractically long annealing tools at high web speeds. In addition, PSCs are usually made with metal oxide transport layer materials that require high temperatures for thermal annealing. Here, we demonstrate the fabrication of PSCs using photonic curing, instead of thermal annealing, to convert NiO x directly from sol-gel precursors for hole transport layers and to crystallize methylammonium lead iodide (MAPbI 3 ) active layers on flexible Willow ® Glass substrates. Photonic curing uses short, intense pulses of light to process materials at a high speed, hence it is compatible with R2R manufacturing. We achieved power conversion efficiencies (PCEs) of 11.7% in forward-scan and 10.9% in reverse-scan for PSCs made with photonic cured NiO x and MAPbI 3 films. Furthermore, both NiO x and MAPbI 3 films could be processed with a single photonic curing pulse, with a web speed of 5.7 m/min, and still produce PCEs comparable to thermally annealed control samples. Based on the single-pulse photonic curing condition for each film, we project a web speed of 26 m/min, laying a pathway to high-throughput production of perovskite solar modules.
Boundary layer loss sensitivity study using a modified ICRPG turbulent boundary layer computer program
Modifications of the turbulent boundary layer (TBL) computer program refer to a more accurate representation of boundary layer edge conditions, internal calculation of the Prandtl number, a changed friction coefficient relationship, and computation of the performance degradation. Important input parameters of the modified TBL program such as wall temperature distribution, Prandtl number, Stanton number, and velocity profile exponent were changed and the individual effects on significant boundary layer parameters, heat transfer, and performance degradation are described.
Calculation of three-dimensional compressible laminar and turbulent boundary layers. An implicit finite-difference procedure for solving the three-dimensional compressible laminar, transitional, and turbulent boundary-layer equations
An implicit finite-difference procedure is presented for solving the compressible three-dimensional boundary-layer equations. The method is second-order accurate, unconditionally stable (conditional stability for reverse cross flow), and efficient from the viewpoint of computer storage and processing time. The Reynolds stress terms are modeled by (1) a single-layer mixing length model and (2) a two-layer eddy viscosity model. These models, although simple in concept, accurately predicted the equilibrium turbulent flow for the conditions considered. Numerical results are compared with experimental wall and profile data for a cone at an angle of attack larger than the cone semiapex angle. These comparisons clearly indicate that the numerical procedure and turbulence models accurately predict the experimental data with as few as 21 nodal points in the plane normal to the wall boundary.
Prediction of outer layer mixing lengths in turbulent boundary layers
Predictions of mixing length by Pletcher's (1976) method (using a two-layer eddy viscosity model for a turbulent boundary layer at low Reynolds numbers) are compared to some values derived from turbulent boundary-layer profiles by other authors. The model is incorporated into a finite-difference scheme, to accurately predict low Reynolds number skin friction in supersonic flow.
Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow
The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.