Insulating Buffer Layer Research Articles

Mitigating interfacial carrier crowding by an ultrathin LiF interlayer towards efficient and stable perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskite-based light-emitting diodes (PeLEDs) have attracted intensive attention due to their high quantum yields, tunable emission wavelengths, and solution-processing capability, showing great potential in next-generation display and lighting applications. However, further performance enhancement in PeLEDs is severely limited by the uncontrolled transfer of charge carriers under bias, leading to crowding of interfacial carriers and severe efficiency roll-off. Herein, we insert an ultra-thin dielectric buffer layer of lithium fluoride (LiF) into the electron transport layer (ETL) to regulate the transfer dynamics of electrons and passivate the interfacial defects simultaneously. The dielectric LiF interlayer can effectively reduce the efficiency roll-off in PeLEDs by improving the charge balance through preventing the overwhelming injection of electrons. Moreover, the fluoride anions from LiF can passivate the surface defects of the perovskite film, enhancing the radiative recombination. As a result, the LiF interlayer-assisted quasi-2D PeLED presents an outstanding external quantum efficiency (EQE) of 24.03% and a maximum brightness of 30 845 cd m−2. The operational stability of the device is also extended, with a half-lifetime (T50) of 71.28 min (at an initial luminance of 1 000 cd m−2), which is 7.4-fold longer than that for the control device.Graphical

The Optimal Operating Point for Linearizing an Integrated Optical Lithium Niobate Directional Coupler Modulator

The influence of an operating point on the linearity of an integrated optical lithium niobate directional coupler modulator was studied. It was found that the optimal setting for the position of an operating point for suppressing the third-order intermodulation distortion depended on the power of the high-frequency modulation signal. Thus, despite the simple design of the device, the directional coupler modulator requires a complex algorithm for setting an operating point to achieve a high linearity of operation. An active system for setting an operating point based on the low-frequency pilot signal and zeroing its third harmonic was used to demonstrate the possibility of linearization when the amplitude of the modulation signal changes. The use of an operating point control system became possible after limiting the drift of the operating point by etching the dielectric buffer layer in the interelectrode gap. The results obtained look promising for high-performance analog optical links.

Improved Breakdown Strength and Restrained Leakage Current of Sandwich Structure Ferroelectric Polymers Utilizing Ultra-Thin Al2O3 Nanosheets.

Flexible capacity applications demand a large energy storage density and high breakdown electric field strength of flexible films. Here, P(VDF-HFP) with ultra-thin Al2O3 nanosheet composite films were designed and fabricated through an electrospinning process followed by hot-pressing into a sandwich structure. The results show that the insulating ultra-thin Al2O3 nanosheets and the sandwich structure can enhance the composites' breakdown strength (by 24.8%) and energy density (by 30.6%) compared to the P(VDF-HFP) polymer matrix. An energy storage density of 23.5 J/cm3 at the ultrahigh breakdown strength of 740 kV/mm can be therefore realized. The insulating test and phase-field simulation results reveal that ultra-thin nanosheets insulating buffer layers can reduce the leakage current in composites; thus, it affects the electric field spatial distribution to enhance breakdown strength. Our research provides a feasible method to increase the breakdown strength of ferroelectric polymers, which is comparable to those of non-ferroelectric polymers.

Improved Soft Magnetic Properties in FeNi@MgO Composites by Sol-Gel-Based Surface Coating and High-Temperature Heat Treatment

In this study, we utilized MgO as an insulating buffer layer to enhance the thermal stability and soft magnetic properties of Fe-Ni soft magnetic composites (SMCs) and investigated the effect of high-temperature heat treatment on those soft magnetic properties. By employing the sol-gel process, a uniform MgO insulating layer with a thickness of 600 nm was coated onto Fe-Ni magnetic powder. Subsequently, high-density SMCs were fabricated through high-pressure compaction molding. The MgO layer remained intact up to 800 °C, leading to the FeNi@MgO@MK SMCs exhibiting enhanced permeability and reduced hysteresis loss due to grain enlargement and elimination of defects, such as dislocation stacking. Notably, the dynamic loss increase after high-temperature heat treatment was significantly regulated compared to the case of the uncoated counterpart. The results underscore the potential to improve the thermal stability and soft magnetic properties of MgO-coated Fe-Ni SMCs, rendering them suitable for various electromagnetic applications.

Black phosphorus mediated long-range SPR imaging sensor with ultrahigh imaging sensitivity, penetration depth and figure of merit

In this paper, we proposed a black phosphorus (BP) mediated long-range surface plasmon resonance (LRSPR) imaging sensor (Structure: 2S2G prism/Teflon/Ag/BP/Sensing medium) for refractive index (RI) sensing. MATLAB and COMSOL simulation software is used for analytical analysis of the proposed design at 633 nm characteristic wavelength. Use of Teflon dielectric buffer layer (DBL) and thin Ag film generates long-range surface plasmon polaritons (LRSPPs) at both interface of Ag film. BP layer is used as biorecognition element (BRE) layer for attachment of analytes due to its unique electrical, optical and electronic properties useful for sensing applications. The proposed sensor demonstrates maximum imaging sensitivity (29,971 RIU−1), detection accuracy (111 Deg.−1), angular figure of merit, FoMang. (2568 RIU−1), imaging figure of merit, FoMimg (810,027 RIU−1) and penetration depth, PD (1957 nm). Ultrahigh imaging sensitivity, FoMimg and micron size PD of the proposed sensor can be efficiently utilized for the deep analytes sensing even in smaller concentrations. Thus, BP mediated proposed RI sensor could provide potential application for micron size biomolecule sensing.

Thin‐Film Lithium Niobate Optical Modulators with an Extrapolated Bandwidth of 170 GHz

High‐speed modulators with low driving voltage, low loss, and compact size are essential for future optical communication systems. Thin‐film lithium niobate modulators have met each of these criteria separately, but simultaneous achievement of all of them has been challenging on this platform. Low driving voltage electro‐optic modulators necessitate either a narrow gap between the electrodes or an elongated Mach–Zehnder arms, both of which adversely affect the microwave loss, hence the bandwidth. Herein, this trade‐off is alleviated by placing the optical waveguides nonsymmetrically with respect to the electrodes and by including a dielectric buffer layer beneath the electrodes. Exploiting this novel design yields a modulator with a measured roll‐off of only 2 dB from low frequencies up to 100 GHz, and with an extrapolated 3 dB bandwidth of 170 GHz. The measured voltage–length product of this subterahertz device is 3.3 V cm. Another device, optimized for a lower voltage–length product of 2.2 V cm, exhibits a 3 dB electro‐optic bandwidth of 84 GHz. The devices are also tested for eight‐level pulse‐amplitude modulation (PAM‐8) and demonstrate data rates of up to 240 Gb s−1at 80 Gbaud, validating that the modulators are a propitious candidate for next‐generation optical communication systems.

Nano-optical designs for high-efficiency monolithic perovskite–silicon tandem solar cells

Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.

An Emerging Mineral‐Based Dielectric Material: Intrinsic Dielectric Properties and Modulated

AbstractHigh energy density polymer nanocomposites reinforced with high dielectric constant ferroelectric nanoparticles exhibit great potential for energy storage applications in modern electronic and electrical systems. However, further improvements in the Ue of polymer nanocomposites with a higher breakdown strength (Eb) is of utmost importance. Tuning the permittivity from the filler center to the surrounding matrix in composites can alleviate local charge concentrations. Here, a gradient dielectric constant buffer layer is constructed via induced selectively titanium dioxide is inserted into the multilayer aluminosilicate. This gradient‐structured buffer layer remarkably weakened the charge density around the ferroelectric particles, which gave rise to high breakdown strength and increased the energy density of the polymer nanocomposites. Furthermore, the density functional theory (DFT) calculation reveals an active charge transfer between buffer layer and poly(vinylidene fluoride‐co‐hexafluoropropylene). The space charge density distribution is simulated via finite element methods to verify the experimental dielectric breakdown results in the nanocomposite films. Therefore, this work provides a new strategy to balance the coupling relationship between energy density and breakdown strength.

β -Ga2O3 MESFETs with insulating Mg-doped buffer grown by plasma-assisted molecular beam epitaxy

In this work, we develop in situ Mg doping techniques in plasma-assisted molecular beam epitaxy (PAMBE) of β-Ga2O3 to compensate Si dopants at the substrate epilayer growth interface and eliminate parasitic leakage paths. Both abrupt and uniform Mg doping profiles over a wide range of concentrations were achieved in β-Ga2O3 epilayers grown by PAMBE. Capacitance–voltage characteristics of Si and Mg co-doped samples confirmed the compensating effect of the Mg dopants. Mg delta-doping was then integrated into a β-Ga2O3 metal-semiconductor field effect transistor structure and shown to be effective in eliminating source leakage. The results presented here show that Mg doping is a promising way to engineer insulating buffer layers for β-Ga2O3 lateral devices grown by PAMBE.

Dual functions of alternating current electroluminescent device for light emission and humidity detection

Alternating current electroluminescent (AC-EL) device can be considered as a potential candidate for next generation of multifunctional light-emitting sources. In this work, we present a new design of AC-EL device with inclusion of a silver oxide humidity-sensing layer instead of an insulating buffer layer for humidity detection. The ZnS:Cu, Cl and ZnS:Ag+(Zn,Cd)S:Ag phosphors were used as an emissive layer prepared by screen printing method. The silver oxide (AgO/Ag2O) nanoparticles synthesized via a green method were employed as a humidity sensing layer. The developed AC-EL devices exhibited high response, good productivity, high stability, high repeatability and linear relationship with humidity in range of 10%–90% RH as well as no significant effects with several VOCs/gases such as NH3, CO2, acetone, methanol, toluene and propan at room temperature. The effects of parameters such as excitation frequency, applied voltage, and waveforms on the luminance intensity are discussed. The development of the present AC-EL device offers a simplified architecture to enable sensing functions of the AC-EL device via monitoring of light emission changing.

Antimonene mediated long-range SPR imaging sensor with ultrahigh imaging sensitivity and figure of merit

We proposed a long-range surface plasmon (LR-SPR) resonance imaging sensor based on antimonene and magnesium fluoride (MgF2) polymer with ultra-high imaging sensitivity (Simg) and figure of merit (FOM). The effect of dielectric buffer layers (DBL) (such as Cytop, Teflon, MgF2, and LiF) and plasmonic metals (Au, Ag, and Al) on the stimulating long-range surface plasmon polaritons (LR-SPPs) is explored in this work. We numerically demonstrated that the proposed LR-SPR imaging sensor configuration (antimonene-aluminum-MgF2 on 2S2G chalcogenide glass prism) could achieve much higher imaging sensitivity (7028.1 RIU−1) and FOM (335 RIU−1) than the reported papers by taking advantage of antimonene's sensing ability and aluminum's steeper reflectance curve. As a result, the proposed LR-SPR imaging sensor in the field of biosensing is a promising tool for detecting biomolecules. Finally, a fair comparison between the most recently published research publications on prism coupled LR-SPR sensor and the proposed work is made.

Ultra-narrowband and highly-directional THz thermal emitters based on the bound state in the continuum

AbstractThe development of novel and cost-effective THz emitters, with properties superior to current THz sources, is an active and important field of research. In this work, we propose and numerically demonstrate a simple yet effective approach of realizing terahertz sources working in continuous-wave form, by incorporating the new physics of bound state in the continuum (BIC) into thermal emitters. By deliberately designing the structure of slotted disk array made of high-resistivity silicon on top of a low index dielectric buffer layer supported by a conducting substrate, a quasi-BIC mode with ultra-high quality factor (∼104) can be supported. Our results reveal that the structure can operate as an efficient terahertz thermal emitter with near-unity emissivity and ultranarrow bandwidth. For example, an emitter working at 1.3914 THz with an ultranarrow linewidth less than 130 MHz, which is roughly 4 orders of magnitude smaller than that obtained from a metallic metamaterial-based thermal emitter, is shown. In addition to its high monochromaticity, this novel emitter has additional important advantages including high directionality and linear polarization, which makes it a promising candidate as the new generation of THz sources. It holds a great potential for practical applications where high spectral resolving capability is required.

Investigation of the superconducting properties of NbN films deposited by DC magnetron sputtering on a high-k dielectric HfO2 buffer layer

The influence of the buffer layer of hafnia dielectric (HfO2) on the superconducting properties of niobium nitride films (NbN), produced by the technique of reactive magnetron depositing has been investigated for the first time. This study presents a comprehensive analysis of morphological, microstructural, and electrophysical parameters of thin NbN films. The dependence of transition critical temperature on the thickness of the HfO2 buffer layer has been obtained. For the first time, it has been demonstrated that the superconducting properties of niobium nitride films at the HfO2 buffer layer have high superconductive parameters, namely, T c ∼ 13 K (with a the film thickness of approximately 30 nm) and high critical current density of approximately 107 A cm−2. The relation between the thickness of the HfO2 buffer layer with the critical current density of niobium nitride films has been determined. It appeared that the values of critical current density increase significantly up to 13 MA cm− 2 when the thickness of the hafnia buffer layer is more than 2 nm.

Silicon-integrated lead-free BaTiO3-based film capacitors with excellent energy storage performance and highly stable irradiation resistance

The energy storage density and thermal stability of silicon-based lead-free BZTS film capacitors are greatly improved by inserting a high resistance dielectric HfO2 buffer layer between the BZTS thin film and the Si substrate.

Long-Range Surface Plasmon Resonance Configuration for Enhancing SERS with an Adjustable Refractive Index Sample Buffer to Maintain the Symmetry Condition

We propose a method to maintain the symmetry condition of the refractive index with respect to a dielectric buffer layer for a long-range surface plasmon resonance (LRSPR) configuration. The symmetry condition was maintained by changing the concentration of the ethylene glycol aqueous solution (sample buffer layer) to match the refractive index of the MgF2 film. Maintenance of the symmetry condition is necessary for exciting the LRSPR mode and increasing the electric field intensity near the film. We used a four-phase Kretschmann resonance setup composed of a K9 prism, MgF2 film, Ag film, and sample buffer layer. The incident angle-dependent surface-enhanced Raman scattering (SERS) spectra were measured in the evanescent field. At the SPR angle, the SERS signal of the symmetric configuration was 60 times higher than that of the conventional SPR configuration. Moreover, the electric field penetration depth of the symmetric long-range surface plasmon configuration (>1000 nm) was longer than that of their asymmetric counterparts. The enhancement factor of the symmetric configuration was 8.6 × 107, which corresponded to the lowest detectable concentration for 4-mercaptopyridine, reaching 1.0 × 10–10 M at the resonance angle. Thus, the symmetric LRSPR configuration has great potential for label-free sensing and detection of macromolecules and biomolecules.

Effect of buffer layer index on short range surface plasmon polariton based TE pass polarizer

We investigate theoretically the dependence of the extinction ratio, metal layer thickness and buffer thickness of a short length plasmonic polarizer on the buffer layer index. The polarizer section consists of a thin metal layer above the single mode dielectric waveguide separated by a low index dielectric buffer layer. Strong coupling between the surface plasmon polariton (SPP) mode and the guided mode takes place when their phase constants are matched. The SPP mode being of TM type, interacts with the guided TM mode and is completely absorbed by metal film due to resonant coupling between the two modes. The TE guided mode does not couple to the SPP mode and is passed un-attenuated through the polarizer. The buffer layer thickness can be optimized to maximize the TM mode attenuation and reduce the TE losses, which provides a large extinction ratio. Since the polarizer is based on the interference of the SPP mode and the waveguide mode, a periodic coupling of the field takes place between these two modes. It is shown that for properly optimized layer thicknesses, an extinction ratio exceeding 200 dB can be achieved for various buffer layer indices. Effect of buffer layer index on the polarizer length is also presented.

Structure and Morphology of Anthraquinone Triazene Films on Silicon Substrate

An optimal imposition method of anthraquinone triazenes on silicon lining was selected. This allowed to create a nanometer film that can be used as dielectric aromatic buffer layers. A morphological research of triazene films shows the existence of delocalized globular anthraquinone macromolecular microformation on the background of triazene uneven layers. The oxidized surface of the triazene substrate is applied better than those without the oxide. This is caused by distribution of electron density in triazene which creates an additional Si/SiO2 coupling system and by presence of voluminous aromatic substituents which impairs the uniformity of film deposition and reduces its thickness.

Current assisted memory effect in superconductor–ferromagnet bilayers: a potential candidate for memristors

AbstrsctSuperconductivity and ferromagnetism are two very useful phenomena, hoewever they rarely coexist in bulk materials. Bringing them together in an artificial hybrid bilayer produces some unusual results. We designed and studied a system of superconductor-ferromagnet bilayer with a thin insulating buffer layer between them. Such a superconductor-ferromagnet bilayer with magnetostatic coupling is proposed for use as a multibit superconductor memory device and a potential candidate as a memristor. Numerical simulations were performed by using Ginzburg–Landau and Landau–Lifshitz-Gilbert models for superconductor and ferromagnet materials, which highlighted some interesting resistive memory effects in the superconducting layer in the bilayer system. A vortex pattern in the superconductor was observed to be strongly coupled with the ferromagnet domain structure, while their dynamics were controlled by the current flowing through the superconductor. Carrier concentration, energy components and magnetization in the superconducting layer were studied as a function of applied current pulses in the superconductor layer, indicating the information storage of the current pulses. Multiple resistive states were observed, pointing towards the possibility that such a device could be used as a multibit data storage device.

III-nitride on silicon electrically injected microrings for nanophotonic circuits.

Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440mW/cm2 output power density at 20 mA from such microrings with diameters of 30 to 50 μm. The first steps towards achieving an integrated photonic circuit are demonstrated.

High critical current density YBa2Cu3O7 coating on conductive Nb-doped SrTiO3 and Ni double-buffered {100}〈001〉 textured pure Cu tape for low-cost coated conductors without generation of any insulative oxides at interfaces

For development of a low-cost superconducting wire operating at high-temperature, we propose a new approach using conductive rather than insulating buffer layers, combined with {100}〈001〉 textured pure Cu tape to form YBa2Cu3O7 (YBCO)/Nb-doped SrTiO3/Ni/Cu/stainless steel. The critical current density of the YBCO layer was 2.5 MA cm−2 at 77 K in a magnetic self-field. We also confirmed that some current flowed into the Cu tape through the conductive buffer layers when the current exceeded the critical current of the YBCO layer, suggesting that the textured Cu tape worked not only as a biaxial template but also as a stabilizer layer.