Gap Edge Research Articles

(Digital Presentation) Synthesis and Characterization of Au-Doped TiO2

We used a three-step anodization procedure to produce titanium oxide (TiO2) nanotubes in order to investigate the effects of varied electrolyte concentrations and anodization voltages on optical characteristics. Different electrolyte solution concentrations and anodization voltages altered wall thicknesses and tube diameters, according to our observations from the XRD pattern, TEM pictures, and optical examinations. While the band gap and band edge values of TiO2 nanotubes altered with different anodization voltages, the band gap, and band edge values remained constant. Furthermore, we discovered that at various electrolyte solution concentrations, the optimum solution concentration for growing compact TiO2 nanotubes is 70 percent porosity. Various morphologies of TiO2 nanostructures, such as sheet, rod, and tube, were obtained in the next section of the study by modifying the experimental settings (e.g., growth methods, differently used gases, and process temperatures). Titanium dioxide (TiO2) nanosheets, nanorods, and nanotubes were created utilizing anodizing methods and chemical vapor deposition (CVD). TiO2 nanorods were synthesized on treated Ti foil with HCl by CVD after TiO2 nanosheets coated with Au catalyst were grown in CVD. TiO2 nanotubes are then manufactured using a three-step anodization method. We found that produced nanostructures can be used for a variety of applications due to compatibility changes in morphological, structural, and optical properties.

Interface modes in planar one-dimensional magnonic crystals

We present the concept of Zak phase for spin waves in planar magnonic crystals and discuss the existence condition of interface modes localized on the boundary between two magnonic crystals with centrosymmetric unit cells. Using the symmetry criterion and analyzing the logarithmic derivative of the Bloch function, we study the interface modes and demonstrate the bulk-to-edge correspondence. Our theoretical results are verified numerically and extended to the case in which one of the magnonic crystals has a non-centrosymmetric unit cells. We show that by shifting the unit cell, the interface modes can traverse between the band gap edges. Our work also investigate the role of the dipolar interaction, by comparison the systems both with exchange interaction only and combined dipolar-exchange interactions.

Tree growth at gap edges. Insights from long term research plots in mixed mountain forests

The structure and dynamics of Central Europe’s forests are increasingly characterized by canopy gaps which either result from disturbances or from planned silvicultural actions. It remains, however, unclear, whether the neighborhood to a gap has effects on tree growth which cannot be sufficiently covered by existing standard models so far. In order to test for such effects, we used data from a series of long term experiments in Southern German mixed mountain forests. In parallel, we developed a method for an automatized detection of canopy gaps and gap edge trees given such data. We found that the basal area growth of such trees amounted to about 15–30% more compared to what could be covered by a classic spatial competition index, with a plausible ranking of the main species. Our results suggest, in addition, that an exposition to a gap has a longer lasting effect on tree growth, even after the gap has closed again. With regard to such long-term effects, we found that tree size at the first exposition matters, with strong species-specific differentiation. We concluded that gap exposition effects on tree growth, given their order of magnitude, require being included in tree growth models which are used for planning purposes.

Effect of Static Magnetic Field on <i>Anchusa-Italica</i>-Doped Pentacene

This work is devoted to the influence of magnetized water on dye extracted from Anchusa Italica plant and doped pentacene thin films. The findings resulted in optoelectronic behavior, showing that using magnetized water in the extraction process gives rise to distinct and superior characteristics as compared to using regular water. The Fourier-transform infrared method was used to analyze the structural properties of an Anchusa Italica-doped pentacene thin film. A comparative study on two samples was carried out: the first sample was affected by a static magnetic field and the other one was not. Optical properties including the absorption spectra absorption coefficient, optical energy gap, conventional and refractive factors were investigated by applying ultraviolet-visible spectroscopy ranging from 300 to 900 nm. The estimated band gap edge of the dye/doped pentacene affected with magnetization was reduced from 2.61 to 1.76 eV and converted into the recommended direct band gap to contribute to optical systems. The absorption spectra of the sample with magnetization effect appears to be more efficient than the one extracted using regular water. The power transmission coefficients (indirect to direct) were also affected because of the magnetic extraction procedure. The complex refractive index was used to study the magnetization effect on the resonance mode and transparent indicator. The absorption index was enhanced to 570 nm in the spectrum, whereas there was also a low attenuation coefficient. This is the first time that magnetized sol has been used in dye extraction processes.

Porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel for efficient visible-light photocatalytic degradation over oxytetracycline

The polyimide is a promising semiconductor photocatalyst. However, its photocatalytic activity is poor because of its small specific surface area, low visible light absorption and easy recombination of photoexcited electron and hole. Herein, porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel with excellent photocatalytic performance is prepared via supercritical fluid drying technology. The material aerogel has large surface area and the structure is porous network. The carbon quantum dots increase the visible light absorption of the polyimide aerogel. The ZnS quantum dots change the VB edge, CB edge and band gap of the polyimide aerogel. Both carbon quantum dots and ZnS quantum dots could improve the charge transfer and facilitate the separation of photoexcited electron and hole. The visible-light photocatalytic performance over oxytetracycline of porous polyimide/carbon quantum dots/ZnS quantum dots material aerogel is increased largely compared to pure polyimide aerogel. The photocatalytic degradation mechanism of the polyimide material aerogel is proposed. ·O2− and h+ play the key role in the photocatalytic degradation. This work supplies an effective method to prepare visible-light photocatalytic materials.

Band-Edge Effect-Induced Electrochemiluminescence Signal Amplification Based on Inverse Opal Photonic Crystals for Ultrasensitive Detection of Carcinoembryonic Antigen.

Photonic crystals (PCs) have emerged as a promising electrochemiluminescence (ECL) matrix in the domain of immunoassay. Making maximum use of light manipulation properties of PCs is highly desired for improving the sensitivity. In this work, we proposed a band-edge effect-induced ECL enhancement strategy based on silica inverse opal PCs (SIOPCs). By fine-tuning the lattice constant and carefully calibrating the stopband position, we found that the band edge of the stopband exerted significant influences on the ECL intensity and spectral distribution. The high density of states at the blue edge of the photonic band gap increased the radiative transition probability of ECL emitters and enhanced the photon extraction during propagation, giving rise to ∼20-fold ECL signal amplification accompanied by a redistributed ECL spectrum for the Ru(bpy)32+-TPrA system. In combination with the intrinsic structural superiority, like large specific surface area and interconnected macropores, the developed SIOPC electrode was successfully applied in constructing a sandwich-type immunosensor. The fabricated immunosensor displayed a very low detection limit of 0.032 pg/mL and a wide linear range of 0.1 pg/mL-150 ng/mL for a carcinoembryonic antigen assay, showing its potential application in disease diagnosis.

Prediction of half-metallic gap formation and Fermi level position in Co-based Heusler alloy epitaxial thin films through anisotropic magnetoresistance effect

We have investigated the temperature $(T)$ dependence of the anisotropic magnetoresistance (AMR) effect of ${\mathrm{Co}}_{2}{\mathrm{FeGa}}_{0.5}{\mathrm{Ge}}_{0.5}$ (CFGG) epitaxial thin films having different compositions and atomic orders to examine the relation between AMR and the half-metallic electronic structure based on a developed theoretical model. The $T$ dependence of the resistance change (\ensuremath{\Delta}\ensuremath{\rho}) of the AMR normalized at 10 K is minimal in the CFGG films having a standard composition and high atomic order. In contrast, the films having a large atomic disorder due to the Co-rich composition exhibit a large reduction of \ensuremath{\Delta}\ensuremath{\rho} with $T$. Our theoretical model of AMR well explains this behavior; namely, the half-metallic ferromagnets having the Fermi level $({E}_{\mathrm{F}})$ around the center of the half-metallic gap are predicted to show a small $T$ dependence of \ensuremath{\Delta}\ensuremath{\rho} because of no/few localized $d\ensuremath{\downarrow}$ states at ${E}_{\mathrm{F}}$. On the contrary, a large change of \ensuremath{\Delta}\ensuremath{\rho} with $T$ is expected for the half-metallic materials having ${E}_{\mathrm{F}}$ close to gap edges or large in-gap states because of the contribution of thermally excited s-d scattering involving the $d\ensuremath{\downarrow}$ states. Moreover, we have also investigated the variation of \ensuremath{\Delta}\ensuremath{\rho} with $T$ for the thin films of various half-metallic Co-based Heusler alloys and found the behavior that agrees with our theoretical prediction. The present study proves that the formation of a half-metallic gap and the position of ${E}_{\mathrm{F}}$ in a half-metallic material are readily predictable from the $T$ dependence of \ensuremath{\Delta}\ensuremath{\rho} of the AMR effect, which can be a facile way for efficient screening of half-metallic materials.

Avian whiffling-inspired gaps provide an alternative method for roll control

Some bird species exhibit a flight behavior known as whiffling, in which the bird flies upside-down during landing, predator evasion, or courtship displays. Flying inverted causes the flight feathers to twist, creating gaps in the wing’s trailing edge. It has been suggested that these gaps decrease lift at a potentially lower energy cost, enabling the bird to maneuver and rapidly descend. Thus, avian whiffling has parallels to an uncrewed aerial vehicle (UAV) using spoilers for rapid descent and ailerons for roll control. However, while whiffling has been previously described in the biological literature, it has yet to directly inspire aerodynamic design. In the current research, we investigated if gaps in a wing’s trailing edge, similar to those caused by feather rotation during whiffling, could provide an effective mechanism for UAV control, particularly rapid descent and banking. To address this question, we performed a wind tunnel test of 3D printed wings with a varying amount of trailing edge gaps and compared the lift and rolling moment coefficients generated by the gapped wings to a traditional spoiler and aileron. Next, we used an analytical analysis to estimate the force and work required to actuate gaps, spoiler, and aileron. Our results showed that gapped wings did not reduce lift as much as a spoiler and required more work. However, we found that at high angles of attack, the gapped wings produced rolling moment coefficients equivalent to upwards aileron deflections of up to 32.7° while requiring substantially less actuation force and work. Thus, while the gapped wings did not provide a noticeable benefit over spoilers for rapid descent, a whiffling-inspired control surface could provide an effective alternative to ailerons for roll control. These findings suggest a novel control mechanism that may be advantageous for small fixed-wing UAVs, particularly energy-constrained aircraft.

Tailoring the optical characteristics and band-gap of BG doped PMMA/FTO nanocomposite films for laser power attenuation: New approach

Herein a good adherent film of PMMA doped with the various ratio of BG-dye deposited on optically flat FTO-substrates by using a well-controlled spin coating process. The average crystallite size and microstrain were determined by X-ray diffraction pattern analysis and were found to be 21.7219 nm and 0.0016, respectively, with a significant change with the amount of BG-dye doping in the matrix of PMMA film. Both linear and nonlinear optical characteristics, as well as their related parameters, were measured using a UV–Vis–NIR spectrophotometer. As a result of doping BG-dye molecules into the host PMMA matrix system, optical absorption studies revealed significant changes in optical characteristics. BG-dye doped PMMA film revealed impressive absorption bands in the range of 350–750 nm, depending on the degree of doping of BG-dye into the PMMA film. Another distinguished property is the attenuation of the complete absorption in the range of 552–688 nm and observed as a cut-off-absorbance. The point of the art of this contribution is the various applications for optical limitation systems like Cut-off filters and other related optical devices due to the remarkable optical features. The BG-dye doping influenced all optical metrics, including the absorption band, absorption edge, and direct and/or indirect energy band gap. The direct energy gap's first region is in the range of 1.77–1.97 eV, whereas the second is in the range of 2.68–2.82 eV, and the third is in the range of 3.67–4.09 eV. The indirectly allowed transitions are divided into two regions, the first of which is in the 1.74–1.82 eV range and the second of which is in the 3.69–3.98 eV range. The appearance of extra energy levels is confirmed by fluctuations in the optical band gap, which are aided by the influence of dopant concentration of BG-dye dopant wt.%. The ratio of BG-dye into the PMMA film is promising for the optical respective of the green light for the cut-off filter as well as optoelectronic device applications.

Spin and charge transport in ferromagnet-superconductor-ferromagnet heterostructures: Stoner versus spin mass mismatch mechanism

We study transport phenomena through a ballistic ferromagnet-superconductor-ferromagnet (F/S/F) junction, comparing the case in which the ferromagnetic order in the two F layers is of the standard Stoner type with the case where it is driven by a spin mass mismatch (SMM). It is shown that the two mechanisms lead to a different behavior in the charge and the spin conductances, especially when compared to the corresponding non-superconducting ferromagnet-normal-ferromagnet (F/N/F) junctions. In particular, when the injected current is perpendicular to the barrier, for high barrier transparency and large magnetization of the F layers, the large mass mismatch gives rise to an enhancement of both low-bias charge and spin conductances of the F/S/F junction, which is not observed in the equal-mass case. When all the allowed injection directions are considered, the low bias enhancement of the charge conductance for SMM leads still holds for high barrier transparency and large magnetization of the F layers. However, in the case of non-transparent interfaces, spin transport with SMM ferromagnets exhibits an opposite sign response with respect to the Stoner case at high biases for all magnetization values, also manifesting a significant amplification induced by superconductivity at the gap edge. The above mentioned differences can be exploited to probe the nature of the electronic mechanism underlying the establishment of the ferromagnetic order in a given material.

Subgap states spectroscopy in a quantum dot coupled to gapped hosts: Unified picture for superconductor and semiconductor bands

We present a unified theory of quantum phase transitions for half-filled quantum dots (QDs) coupled to gapped host bands. We augment the bands by an additional weakly coupled metallic lead, which allows us to analyze the system by using standard numerical renormalization-group techniques. The ground-state properties of the systems without the additional metallic lead are then extrapolated in a controlled way from the broadened subgap spectral functions. We show that a broad class of narrow-gap-semiconductor tunneling densities of states (TDOSs) support the existence of two distinct phases known from their superconducting counterpart: the 0 phase, which is marked by the singlet ground state, and the $\ensuremath{\pi}$ phase regime with the doublet ground state. To keep a close analogy with the superconducting case, we focus on the influence of particle-hole asymmetry of the TDOS on the subgap spectral features. Nevertheless, we also discuss the possibility of inducing singlet-doublet quantum phase transitions in experimental setups by varying the filling of the QD. In addition, for gapped TDOS functions with smoothed gap edges, we demonstrate that all subgap peaks may leak out of the gap into the continuous part of the spectrum, an effect that has no counterpart in the superconducting Anderson model.

Experimental and Simulation Analysis of Warm Shearing Process Parameters for Rolled AZ31B Magnesium Alloy Plate

The study was carried out on a KRUMAN-CLS1016-NC shearing machine at a shear temperature of 20 °C to 250 °C and a shear edge clearance of 8% to 10% for a rolled AZ31B magnesium alloy plate with a thickness of 8.35 mm. The height and area share of the bright zone in the shear section were analyzed by macroscopic measurements and super depth-of-field experiments, and combined with DEFORM-3D finite element simulations, the optimal shear program was determined using the orthogonal experimental method. It was found that, with the increase of shear temperature and shear edge clearance, the height and area of the burnish band first increased and then decreased. In addition, from the simulated orthogonal test, it can be obtained that the effect of shear temperature on the height of the burnish band is superior to that of the shear edge gap, so the selection of shear temperature is preferred. In this paper, the shear temperature of 150 °C and the shear edge clearance of 12% were finally determined as the best shear process parameters for the rolled AZ31B magnesium alloy sheet.

N, S co-doped graphene quantum dots promote charge separation of Bi4O5BrxI2−x solid solution and enhance visible light photocatalytic performance

Design and synthesis of photocatalysts with high charge separation and transfer efficiency are of considerable significance in environmental remediation. Herein, N, S co-doped graphene quantum dots (N, S-GQDs) decorated Bi4O5BrxI2−x solid solution was synthesized by temperature controlled in-situ coprecipitation method. The light absorption and absorption edge gap were improved significantly because of the formation of solid solution Bi4O5BrxI2−x, as well as N, S-GQDs was uniformly dispersed in the Bi4O5BrxI2−x nanosheets with diameter of about 10 nm, which enriched surface structure of Bi4O5BrxI2−x. Due to the enrichment electron effect of N,S-GQDs, the electron transferred from N,S-GQDs to Bi4O5Br0.8I1.2 and enriched on the N,S-GQDs surface, resulting in efficient interface charge transfer and separation and the formation of superoxide radicals. These prominent advantages bring improved photocatalytic activity of the N, S-GQDs/ Bi4O5Br0.8I1.2 for efficient removal of phenol. It displayed the optimal photocatalytic phenol degradation rate of 97.04% under visible light irradiation, which was 3.81 times higher than that of Bi4O5Br0.8I1.2 solid solution. This work could provide new insight into enhancing the photocatalytic performance of Bi4O5Br0.8I1.2 solid solution by graphene quantum dots modification and provide a strategy for photocatalytic phenol degradation.

A low accretion efficiency of planetesimals formed at planetary gap edges

Observations and models of giant planets indicate that such objects are enriched in heavy elements compared to solar abundances. The prevailing view is that giant planets accreted multiple Earth masses of heavy elements after the end of core formation. Such late solid enrichment is commonly explained by the accretion of planetesimals. Planetesimals are expected to form at the edges of planetary gaps, and here we address the question of whether these planetesimals can be accreted in large enough amounts to explain the inferred high heavy element contents of giant planets. We performed a series of N-body simulations of the dynamics of planetesimals and planets during the planetary growth phase, taking gas drag into account as well as the enhanced collision cross section caused by the extended envelopes. We considered the growth of Jupiter and Saturn via gas accretion after reaching the pebble isolation mass and we included their migration in an evolving disk. We find that the accretion efficiency of planetesimals formed at planetary gap edges is very low: less than 10% of the formed planetesimals are accreted even in the most favorable cases, which in our model corresponds to a few Earth masses. When planetesimals are assumed to form beyond the feeding zone of the planets, extending to a few Hill radii from a planet, accretion becomes negligible. Furthermore, we find that the accretion efficiency increases when the planetary migration distance is increased and that the efficiency does not increase when the planetesimal radii are decreased. Based on these results, we conclude that it is difficult to explain the large heavy element content of giant planets with planetesimal accretion during the gas accretion phase. Alternative processes most likely are required, such as accretion of vapor deposited by drifting pebbles.

The Appearance of Vortices in Protoplanetary Disks in Near-infrared Scattered Light

Azimuthally asymmetric structures have been discovered in millimeter continuum emission from many protoplanetary disks. One hypothesis is that they are vortices produced by the Rossby wave instability, for example at the edges of planet-opened gaps or dead zones. Confirming the vortex nature of these structures will have profound implications to planet formation. One way to test the hypothesis is to compare the observed morphology of vortex candidates in near-infrared scattered light with theoretical expectations. To this end, we synthesize the appearance of vortices in H-band polarized light by combining hydrodynamic and radiative transfer simulations of the Rossby wave instability at a dead-zone edge. In a disk at 140 pc, at the peak in its evolution a vortex at 65 au may appear as a radially narrow arc 50%–70% brighter compared with an axisymmetric disk model. The contrast depends on the inclination of the disk and the position angle of the vortex only weakly. Such contrast levels are well detectable in imaging observations of bright disks using instruments such as the Very Large Telescope/SPHERE, Subaru/SCExAO, and Gemini/GPI. A vortex also casts a shadow in the outer disk, which may aid its identification. Finally, at modest-to-high inclinations (e.g., 60°) a vortex may mimic a one-armed spiral. In the HD 34282 disk, such a one-armed spiral with a shadowed region on the outside has been found in scattered light. This feature roughly coincides with an azimuthal asymmetry in millimeter continuum emission, signifying the presence of a vortex.

Dynamical landscape of transitional pipe flow.

The transition to turbulence in pipes is characterized by a coexistence of laminar and turbulent states. At the lower end of the transition, localized turbulent pulses, called puffs, can be excited. Puffs can decay when rare fluctuations drive them close to an edge state lying at the phase-space boundary with laminar flow. At higher Reynolds numbers, homogeneous turbulence can be sustained, and dominates over laminar flow. Here we complete this landscape of localized states, placing it within a unified bifurcation picture. We demonstrate our claims within the Barkley model, and motivate them generally. Specifically, we suggest the existence of an antipuff and a gap-edge-states which mirror the puff and related edge state. Previously observed laminar gaps forming within homogeneous turbulence are then naturally identified as antipuffs nucleating and decaying through the gap edge. We also discuss alternatives to the suggested bifurcation diagram, which could be relevant for wall-bounded flows other than straight pipes.

Characterizing eclipsing white dwarf M dwarf binaries from multiband eclipse photometry

ABSTRACT With the prevalence of wide-field, time-domain photometric sky surveys, the number of eclipsing white dwarf (WD) systems being discovered is increasing dramatically. An efficient method to follow these up will be key to determining any population trends and finding any particularly interesting examples. We demonstrate that multiband eclipse photometry of binaries containing a WD and an M dwarf can be used to determine the masses and temperatures of the WDs to better than 5 per cent. For the M dwarfs, we measure their parameters to a precision of better than 6 per cent with the uncertainty dominated by the intrinsic scatter of the M dwarf mass–radius relationship. This precision is better than what can typically be achieved with low-resolution spectroscopy. The nature of this method means that it will be applicable to LSST data in the future, enabling direct characterization without follow-up spectroscopy. Additionally, we characterize three new post-common-envelope binaries from their eclipse photometry, finding two systems containing hot helium-core WDs with low-mass companions (one near the brown dwarf transition regime) and a possible detached cataclysmic variable at the lower edge of the period gap.

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Four-penta-graphenes: Novel two-dimensional fenestrane-based auxetic nanocarbon allotropes for nanoelectronics and optoelectronics

The great success of graphene has encouraged tremendous interest in searching for new two-dimensional (2D) carbon allotropes. Based on first-principles calculations, we proposed new 2D carbon allotropes obtained from the assembly of fenestrane molecule unit, named as four-penta-graphenes (fPG). The fPG monolayers are energetically more favorable than pentagraphene and show excellent dynamical, thermal, and mechanical stability. They exhibit exotic mechanical properties including anisotropic in-plane stiffness and auxetic behavior with sign-tunable Poisson's ratio. Their electronic properties are diverse, ranging from narrow band gap semiconductors to metal. The electronic band gap and band edge positions of the fPG semiconductors can be flexibly modulated by strain engineering. Indirect-to-direct band gap and semiconductor-to-metal transitions can be achieved by applying compressive and tensile strains, respectively. High mobility and anisotropic effective mass of carriers make these materials promising for nanoelectronics. Using many-body GW0+BSE approximations, we reveal that the fPG semiconductors exhibit strong excitonic effects with distinct optical absorption peaks in the visible range. These remarkable optical properties make them also promising devices for optoelectronics.

Flexural wave band gaps of steel bridge decks periodically stiffened with U-ribs: Mechanism and influencing factors

To effectively and efficiently control vibrations in steel bridge decks, the flexural wave band gap and vibration attenuation mechanism are studied. The band structures and displacement fields of the eigenmodes at the band gap edges of infinite periodic U-rib stiffened plates are calculated. The calculation method is combining the finite element method with Bloch periodic boundary conditions. A scaled specimen test of a finite periodic U-rib stiffened plate is used to validate the numerical results. A comparison of results confirms that introducing the U-rib allows the periodic U-rib stiffened plates to yield several flexural wave band gaps. In the band gaps, flexural wave propagation is stopped and clear flexural vibration suppression is achieved. Furthermore, the effects of geometric parameters and structural schemes on the flexural wave band gaps are analyzed in detail. Finally, by analyzing a specific case, it is demonstrated that the flexural wave band gaps and vibration attenuation properties can be controlled. This provides a new approach to vibration and noise control in steel bridges.