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Modulating Charge Separation Efficiency of Water Oxidation Photoanodes with Polyelectrolyte‐Assembled Interfacial Dipole Layers
摘要： The charge separation efficiency of water oxidation photoanodes is modulated by depositing polyelectrolyte multilayers on their surface using layer-by-layer (LbL) assembly. The deposition of the polyelectrolyte multilayers of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonate) induces the formation of interfacial dipole layers on the surface of Fe2O3 and TiO2 photoanodes. The charge separation efficiency is modulated by tuning their magnitude and direction, which in turn can be achieved by controlling the number of bilayers and type of terminal polyelectrolytes, respectively. Specifically, the multilayers terminated with anionic poly(styrene sulfonate) exhibit a higher charge separation efficiency than those with cationic counterparts. Furthermore, the deposition of water oxidation molecular catalysts on top of interfacial dipole layers enables more efficient photoelectrochemical water oxidation. The approach exploiting the polyelectrolyte multilayers for improving the charge separation efficiency is effective regardless of pH and types of photoelectrodes. Considering the versatility of the LbL assembly, it is anticipated that this study will provide insights for the design and fabrication of efficient photoelectrodes.
关键词： interfacial dipole,polyelectrolyte multilayers,charge separation,photoelectrodes
更新于2025-09-16 10:30:52
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P3HT-based visible-light organic photodetectors using PEI/PAA multilayers as a p-type buffer layer
摘要： A low leakage current is critical for achieving organic photodetectors (OPDs) with high detectivity. The insertion of buffer layers is an effective approach for reducing the reverse-biased leakage current. In this study, polyelectrolyte multilayers comprising polyethyleneimine (PEI) and polyacrylic acid (PAA) were introduced by a spin-assisted layer-by-layer technique into an OPD as a p-type buffer layer. Although PEI/PAA multilayers are insulators, when used as a buffer layer in our device, they suppressed the leakage current and also provided a high photocurrent due to the light-assisted tunneling effect. The prepared device configuration was ITO/(PEI/PAA)2/P3HT:PC60BM/Yb/Al. The performances of the OPDs were investigated by measuring the current–voltage characteristics, external quantum efficiency, and transient photocurrent. In addition, the operating mechanism of the OPDs was confirmed by impedance analysis. The device comprising (PEI/PAA)2 showed a specific detectivity of 3.11 × 1012 Jones and a bandwidth of 103.2 kHz at ?1 V and 525 nm. This performance is a numerical value that can be used in devices such as a line scan camera. In addition, because this device is fabricated by a low-temperature solution process, flexible and large-area substrates can be used.
关键词： light-assisted tunneling effect,organic photodetectors,PEI/PAA multilayers,p-type buffer layer,low-temperature solution process
更新于2025-09-16 10:30:52
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Plasmonics of Diffused Silver Nanoparticles in Silver/Nitride Optical Thin Films
摘要： Metal-dielectric multilayers are versatile optical devices that can be designed to combine the visible transmittance of dielectrics with the electronic properties of metals for plasmonic and meta-material applications. However, their performances are limited by an interfacial optical absorption often attributed entirely to the metal surface roughness. Here, we show that during deposition of AlN/Ag/AlN and SiNx/Ag/SiNx multilayers, significant diffusion of Ag into the top dielectric layer form Ag nanoparticles which excite localized surface plasmon resonances that are primarily responsible for the interfacial optical absorption. Based on experimental depth profiles, we model the multilayer’s silver concentration profile as two complementary error functions: one for the diffused Ag nanoparticles and one for the interface roughness. We apply the Maxwell-Garnett and Bruggeman effective medium theories to determine that diffusion characteristics dominate the experimental absorption spectra. The newfound metal nanoparticle diffusion phenomenon effectively creates a hybrid structure characteristic of both metal-dielectric multilayer and metal-dielectric composite.
关键词： Plasmonics,Metal-dielectric multilayers,Optical thin films,Silver nanoparticles,Localized surface plasmon resonances
更新于2025-09-16 10:30:52
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Precession damping in [Co <sub/>60</sub> Fe <sub/>40</sub> /Pt] <sub/>5</sub> multilayers with varying magnetic homogeneity investigated with femtosecond laser pulses
摘要： We report on the ultrafast magnetization dynamics of [Co60Fe40/Pt]5 multilayers studied with femtosecond laser pulses. The samples were grown at room temperature by DC magnetron sputtering with Ta capping and Pt buffer layers and present the same thickness and perpendicular magnetic anisotropy as determined by vibrating sample magnetometry. Controlled growth rate of the Pt buffer layer modified the anisotropy fields and magnetic domain sizes as measured by magnetic force microscopy (MFM). An estimation of the average magnetic domain sizes was obtained from the profile of the self-correlation transform of the MFM images. For multilayers having an average magnetic domain size of 490 nm, we report a damped precession of the magnetization which decays with a time constant of ～100 ps and which has a frequency which varies from 8.4 GHz to 17.0 GHz as the external field increases from 192 mT to 398 mT. Fitting the precession dynamics with the Landau-Lifshitz-Gilbert equation we evaluated the damping α, which decreases from 0.18 to 0.05 with increasing magnetic domain sizes (127 nm to 490 nm). These α values are higher than for single layers suggesting an enhanced scattering and spin pumping effects from the Pt adjacent layers. In addition, the precession frequency increases from 2.04 GHz to 11.50 GHz as the anisotropy field of the multilayers increases from 6.5 kOe to 13.0 kOe. Finally, a comparative analysis between micromagnetic simulations and MFM images allowed us to determine the exchange stiffness (Aex) in the [Co60Fe40/Pt]5 multilayers.
关键词： exchange stiffness,femtosecond laser pulses,Landau-Lifshitz-Gilbert equation,[Co60Fe40/Pt]5 multilayers,damping,magnetic force microscopy,ultrafast magnetization dynamics,perpendicular magnetic anisotropy
更新于2025-09-12 10:27:22
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Graphene Multilayers for Quantum Microwave Signal Up-Conversion to the Optical Domain
摘要： We propose a new scheme for tunable quantum microwave signal upconversion to the optical frequency domain using graphene multilayers. The graphene layers are electrically connected, biased by a quantum level microwave signal, and subjected to intensive optical pump. The principle of operation is based on modifying the graphene conductivity by the biasing microwave signal. It then follows that an upper optical sideband is generated, while the lower sideband is resonantly attenuated by the destruction of the layered medium . Our calculations show large number of upconverted photons for microvolt driving microwave signal.
关键词： quantum microwave signal,graphene multilayers,optical frequency domain,upconversion
更新于2025-09-11 14:15:04
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Correlation between defect absorption and nano-second laser-induced damage of HfO2/SiO2 based high reflective coatings at 1064?nm
摘要： The distribution of defect weak absorption and nanosecond pulse laser induced damage characteristics of HfO2/SiO2 multilayers were investigated. A combination of in-situ measurements of defect weak absorption distribution and laser induced damage threshold (LIDT) map was proposed, whereby the evolution of defect weak absorption and the laser induced damage morphology under laser irradiation was studied. During the laser irradiation, some nodular and scalded defects can be removed or passivated by the low flux laser, and the absorption of these defect types was reduced accordingly. Besides, catastrophic destruction defects with enhanced absorption after laser irradiation would develop into catastrophic damage. Further, two-dimensional scanning of the sample surface was used to study the relationship between defects weak absorption and the LIDT. The results indicated that the correlation of defects weak absorption intensity distribution and LIDT map depended on defect evaluation properties during the laser irradiation.
关键词： Nanosecond pulse laser,HfO2/SiO2 multilayers,High reflective coatings,Laser-induced damage,Defect absorption
更新于2025-09-11 14:15:04
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The enhanced magnetoelectric effect and piezoelectric properties in the lead-free Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 nano-multilayers composite thin films
摘要： The lead-free multiferroic nano-multilayers composite thin films were fabricated on basis of ferroelectric (FE) Bi3.15Nd0.85Ti3O12 (BNT) and ferromagnetic (FM) La0.7Ca0.3MnO3 (LCMO) parents with 8 nm/6 nm periodicity, respectively. The crystal structure, switching of polarization, magnetization and temperature dependence of magnetoelectric coupling (ME) effect for the multiferroic BNT/LCMO composite thin films were investigated in detail, respectively. Ferroelectric behavior along with an enhanced remnant polarization (2Pr) of 42 mC/cm2, saturated magnetization around 151 emu/cm3, the enhanced piezoelectric coefficient d33 of 263 pm/V and the enhanced magnetoelectric effect voltage coefficient of 72.1 mV/cm*Oe were obtained. The results show that the lead-free multiferroic films exhibit both good ferroelectric, dielectric and magnetic properties, as well as the enhanced ME effects, indicating that the coupling effects of electric and magnetic field exist in the fabricated Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 (BNT/LCMO) nano-multilayer thin films, and the strong ME effect originating from the magnetic-mechanical-electric interaction and interface coupling were demonstrated. These results can be particularly important for developing nano-composite multiferroic devices.
关键词： Temperature dependence of ME effect,Lead-free BNT/LCMO nano-multilayers,Ferroelectric properties,Magnetization
更新于2025-09-10 09:29:36
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UV distributed Bragg reflectors build from porous silicon multilayers
摘要： UV Distributed Bragg reflectors were fabricated by a two-step thermal oxidation process over porous silicon multilayers (PS-ML), which were prepared by room-temperature electrochemical anodization of silicon wafers. The optical behavior of the PS-ML before and after oxidation was studied by reflectance measurements. It was observed an UV shift from 430 to 300 nm in the peak of the reflectance spectrum after oxidation of the PS-ML. This was attributed to the presence of silicon oxide over the surface of the silicon filaments. Such oxide also reduced the refractive index of each porous silicon monolayer. The bandgap of the PS-ML was calculated by the Kubelka-Munk approximation, which showed an increase in the bandgap from 3.11 to 4.36 eV after the thermal oxidation process. It was suggested that the observed optical response could opens the possibility of fabrication of UV optoelectronic devices based entirely in the silicon technology.
关键词： Porous silicon,thermal oxidation,multilayers,ultraviolet (UV)
更新于2025-09-09 09:28:46
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Lifetime Stability and Microstructure Properties of Cr/B <sub/>4</sub> C X-ray Reflective Multilayer Coatings
摘要： This paper demonstrates that highly re?ective Cr/B4C multilayer interference coatings with nanometric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable re?ective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B4C multilayers is also examined, with emphasis on the B4C-on-Cr interface where a signi?cant diffusion layer is formed and on the oxide in the top B4C layer. Multiple characterization techniques (X-ray re?ectivity at different photon energies, X-ray photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B4C layer structure.
关键词： Multilayers,Chrominum,Soft X-rays,Boron Carbide
更新于2025-09-04 15:30:14
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Spin coated multilayered CuO/ZnO films with high output power under irradiation
摘要： Thin films of pure CuO, pure ZnO and CuO/ZnO multilayers were synthesized using the spin coating technique. CuO and ZnO layers were spin coated for 30 s at speeds of 2000 and 1500 rpm, respectively. All the samples were subsequently annealed at 500 0C for one hour in air. Structural properties of films investigated using XRD patterns indicated the crystallization of single phase of CuO and ZnO. Optical band gaps of samples determined by UV-Visible spectrums were in the range of the band gaps of CuO and ZnO. The main objective of the preparation of multilayered CuO/ZnO was enhancing the output power by combining wide band gap and narrow band gap materials. CuO with higher photocurrent and ZnO with higher photovoltage were employed to achieve this task. Photocurrent, photovoltage and impedance were measured in order to investigate the electrical properties of these samples. A liquid junction photocell with electrolyte potassium iodide (KI) was employed to measure photovoltaic properties. A multilayer with ZnO as the top layer provides a higher output power of 3.6 μW/cm2 compared to the output power of a multilayer with CuO as the top layer (1.1 μW/cm2). This is the highest output power reported for a multilayer of CuO/ZnO without any dye coating in KI electrolyte. The highest output power of our multilayered samples is more than twice the previously reported highest output powers of pure CuO and pure ZnO thin film samples without dye coating. Chemical properties of samples were confirmed by FTIR. Crystallite sizes were in the range from 23 to 28 nm. Impedance curves of the samples were measured under dark and light conditions. Two semicircles could be observed at Nyquist plots of both multilayer samples.
关键词： photovoltaic properties,spin coating,XRD,Cupric Oxide,multilayers,Zinc Oxide
更新于2025-09-04 15:30:14