Bulk Effects Research Articles

Managing the Double-Edged Sword of Ni3+ in Sputter-Deposited NiOx by Interfacial Redox Reactions for Efficient Perovskite Solar Cells

Nickel oxide (NiOx) is widely used as a promising hole transport material for perovskite solar cells (PSCs). A high concentration of Ni3+ in the NiOx film is generally beneficial for charge transport of the PSCs; however, chemical redox reactions between surface Ni3+ and perovskite materials result in decomposition of perovskite materials, which causes carrier recombination and impedes charge transport at the perovskite–NiOx interface. Herein, we employ magnetron sputtering to fabricate NiOx thin films with adjustable Ni3+ concentrations to optimize the hole-transporting properties. A thin layer of phenylethylamine iodide (PEAI) is further introduced to reduce the detrimental Ni3+ at the surface of NiOx, which eliminates the formation of undesirable defects and chemical species when in contact with the perovskite layer, leading to a dramatic increase in the power conversion efficiency (PCE) from 16.37 to 20.01%, which is one of the best performance using sputtered charge transport layers. The unencapsulated devices retain 88% of their initial PCE after storage in a nitrogen atmosphere for 1000 h under light. We further perform solar cell capacitance simulator (SCAPS) simulation to understand the effects of bulk and interfacial charge transport on the performance of PSCs, which agree with our experimental results. This work not only highlights the double-edged sword effect of the Ni3+ content on the performance and stability of PSCs but also demonstrates a simple yet effective strategy to avoid the undesirable reaction between Ni3+ and perovskite materials in the fabrication of PSCs with sputter-deposited NiOx.

The synergistic effect of bulk-surface modification onto the wear resistance of the ultrahigh molecular weight polyethylene

The paper investigates the effect of bulk and surface modification on the adhesive and tribological properties of ultra-high molecular weight polyethylene (UHMWPE) and shows that bulk modification with nano- and micro-sized modifiers (montmorillonite, shungite, exfoliated graphite) mainly reduces the friction coefficient but leads to a decrease in the wear resistance of the corresponding composites. It is found that gas-phase surface fluorination provides an increase in the wear resistance of experimental samples in all cases due to a combination of nanotexturing and chemomorphological transformations of the surface layers of the modified polymers. The significant dependence of the nanotexture on the technique and mode of modification is demonstrated using the original approaches to the quantitative characterization of the experimental samples’ surfaces’ scanning electron microscopy-images (formed with the scanning electron microscope). It is shown that the surface fluorination not only makes possible to significantly compensate for the increase of the friction coefficient of bulk-modified UHMWPE in comparison with the original one but also provides a nonlinear multiplicative increase in the wear resistance.

Quantum Hall Effect in Bulk (Multilayered) Organic Crystal

The multilayer quantum Hall effect is discovered in an organic massless Dirac electron system, α-(BETS)2I3 under pressure at low temperatures and a magnetic field of approximately 1 T.

Magnetic characteristics of sengon wood-impregnated magnetite nanoparticles synthesized by the co-precipitation method

<abstract> <p>This study was conducted to synthesize magnetic wood through the ex situ impregnation method of magnetite nanoparticles and analyze its physical properties and characterization. The process was initiated with the synthesis of magnetite nanoparticles by the co-precipitation method and the nano-magnetite was successfully synthesized with a particle distribution of 17–233 nm at an average size of 75 nm. Furthermore, the impregnation solution consisted of three different levels of magnetite nanoparticles dispersed in furfuryl alcohol, untreated and furfurylated wood for comparison. Sengon wood (<italic>Falcataria moluccana</italic> Miq.) was also used due to its low physical properties. The impregnation process was conducted by immersing the samples in the solution at a vacuum of −0.5 bar for 30 min, followed by a pressure of 1 bar for 2 h. There was also an improvement in the physical properties, such as weight percent gain, bulking effect, anti-swelling efficiency and density, while the water uptake continued to decrease. Additionally, magnetite nanoparticles appeared in wood microstructure image, supported by the result of ferrum content in chemical element analysis. The results showed that chemical change analysis proved the presence of Fe–O functional group cross-linked with wood polymer. The diffractogram also reported the appearance of magnetite nanoparticles peak and a decrease in crystallinity due to an increase in the concentration. Based on the analysis, sengon wood was classified as a superparamagnetic material with soft magnetic characteristics and the optimum treatment was furfurylated-magnetite 12.5% wood.</p> </abstract>

Metal-insulator transition and resistive switching in Y-doped CeO2 ceramics.

Y-doped ceria, Y0.16Ce0.84O1.92, is an oxide ion conductor that shows n-type conductivity under a small applied voltage. With increasing voltage, resistive switching by 2-3 orders of magnitude occurs that is reversible with some hysteresis and is enhanced in atmospheres of reduced pO2. The switching is a bulk effect, is not associated with Schottky barriers or with a crystallographic transition, occurs rapidly after a premonitory onset period depending on conditions and shows characteristics of a Mott transition. This is the third known example of low field-induced resistive switching in a bulk ceramic and represents an emergent phenomenon in materials that are taken outside their zone of thermodynamic stability.

Characteristics of Magnetic Sengon Wood Impregnated with Nano Fe3O4 and Furfuryl Alcohol

Sengon (Falcataria moluccana Miq.) tree offers a wood of low quality and durability owing to its low density and thin cell walls. This study aimed to improve the properties of sengon wood by making the wood magnetic, producing new functions, and characterizing magnetic sengon wood. Each wood sample was treated using one of the following impregnation solutions: Untreated, 7.5% nano magnetite-furfuryl alcohol (Fe3O4-FA), 10% nano Fe3O4-FA, and 12.5% nano Fe3O4-FA. The impregnation process began with vacuum treatment at 0.5 bar for 2 h, followed by applying a pressure of 1 bar for 2 h. The samples were then tested for dimensional stability and density and characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM–EDX), Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD) analysis, and vibrating sample magnetometry (VSM) analysis. The results showed that the Fe3O4-FA impregnation treatment considerable affected the dimensional stability, measured in terms of weight percent gain, anti-swelling efficiency, water uptake, and bulking effect, as well as the density of sengon wood. Changes in wood morphology were detected by the presence of Fe deposits in the cell walls and cell cavities of the wood using SEM–EDX analysis. XRD and FTIR analyses showed the appearance of magnetite peaks in the diffractogram and Fe-O functional groups. Based on the VSM analysis, treated sengon wood is classified as a superparamagnetic material with soft magnetic properties. Overall, 10% Fe3O4-FA treatment led to the highest increase in dimensional stability and density of sengon wood.

The effect of π-linker bulk on the photophysical properties of 2-phenylfuro[2,3-b]quinoxaline-based FQ–π–FQ-type compounds

Employing a 2-phenylfuro[2,3-b]quinoxaline scaffold as a fluorophore, and phenyl, biphenyl, anthracene and benzothiadiazole as π-linkers, Ph-dFQ, bPh-dFQ, ADN-dFQ and Bth-dFQ were constructed, along with BIZ-FQ with a benzimidazole unit, to screen suitable blue emitters.

Synthesis and reactivity of alkali metal aluminates bearing bis(organoamido)phosphane ligand.

In this study, we report a group of alkali metal aluminates bearing bis(organoamido)phosphane ligand. The starting complex {[PhP(NtBu)2]AlMe2}Li·OEt2 (1) was prepared by stepwise deprotonation of the parent PhP(NHtBu)2 by nBuLi and AlMe3. Further derivatization of aluminate 1 was performed by the virtual substitution of lithium -{[PhP(NtBu)2]AlMe2}K (2), methyl substituents - {[PhP(NtBu)2]AlH2}Li·THF (3), modification of steric bulk and induction effects on the phosphorus atom - {[tBuP(N-2,6-iPr2C6H3)2]AlMe2}Li·(OEt2)2 (4), and phosphorus atom oxidation state {[Ph(Y)P(NtBu)2]AlMe2}Li (Y = O (5), S (6), Se (7), Te (8)). The structure causing non-covalent interactions in 1-4 were evaluated with the help of theoretical calculations and topological analysis ranging from π-electron system-metal to agostic interactions of various types. The further reactions of 1 with various nucleophiles were found to be a versatile tool for the preparation of iminophosphonamides via the formation of P-E bond (E = Si, Ge, Sn, Pb, P, and C) and followed by P(III) → P(V) tautomeric shift.

Regulating charge carrier recombination in Cu2ZnSn(S,Se)4 solar cells via cesium treatment: bulk and interface effects

Cs treatment in a CZTSSe system could enhance device performance by affecting defect characteristics and carrier–transport properties.

Maximizing spin Hall magnetoresistance in heavy metal/crystalline metallic ferromagnet multilayers with opposite spin Hall angles.

Interconversion between charge and spin through spin-orbit coupling at a heavy metal (HM)/ferromagnet (FM) interface plays a key role in determining the amplitude of spin Hall magnetoresistance (SMR), which might maximally facilitate its applications in novel electronics. In this study, annealed NiFe films grown on MgO (100) substrates capped with Pt and Ta are reported to exhibit a maximum SMR. When the measuring temperature is reduced, the SMR rises and is significantly larger in crystalline NiFe than in amorphous NiFe. Another physical process for the negative SMR in Ta(dTa)/Pt(3 nm)/annealed NiFe samples is attributed to the interfacial spin-orbit coupling (ISOC) driven spin current (Js) generation and its reciprocal effects. Moreover, spin accumulation is enhanced at Pt(3 nm)/annealed NiFe interfaces after capping with a Ta layer, which functions as a spin sink in a certain thinner thickness range. With the cooperative interaction of choosing the proper Ta's thickness and annealing NiFe layers, the maximum SMR is obtained. Our results pave the way for rational interface engineering to enhance SMR for developing high-efficiency spintronic devices.

Electron and spin transport in an ultrathin Al film

The effects of surface and bulk scattering on electronic and spin transport in aluminum-based ultrathin films are predicted using the Landauer-B\"uttiker formalism and a recursive Green's function technique. The effects of surface roughness, grain boundaries, vacancies, and surface reconstruction on resistivity, spin diffusion length, and Elliott-Yafet constant $\ensuremath{\beta}$ are investigated for a 3.6-nm-thickness Al film. It is demonstrated that for a thin sputtered film, point vacancies are the dominant contribution to the momentum relaxation, and spin relaxation is dominated by the combined effect of surface reconstruction and point vacancies, which yields a reasonable spin diffusion length and the Elliot-Yafet constant. Calculations reveal that the presence of surface corrugations results in a clear departure from Matthiessen's rule and the Elliott-Yafet prediction of $\ensuremath{\beta}$, as shown by introducing random surface corrugations. It is also found that spin diffusion length induced by surface roughness is proportional to the inverse square root of the ratio between root mean square height $\ensuremath{\delta}h$ and lateral correlation length $\ensuremath{\xi}$ of a given rough surface, i.e., ${(\ensuremath{\delta}\ensuremath{\xi})}^{\ensuremath{-}1/2}$ as opposed to ${(\ensuremath{\delta}\ensuremath{\xi})}^{\ensuremath{-}1}$ as is the mean free path; this can be attributed to the interference of extended surface features.

Performance transition in droplet-based electricity generator with optimized top electrode arrangements

Harvesting electrical energy from water droplet is a sustainable and promising way to meet challenges in energy scarcity. The water kinetic energy has been successfully harvested into electricity energy by droplet-based electricity generator (DEG). By virtue of its novel transistor-like design with a top electrode, the DEG achieves a high instantaneous power density basing on bulk effect instead of interfacial effect. Despite this, how top electrode arrangement influences the electricity generation as a basic question is still obscure. Here, we study the impact of top electrode arrangement on the output performance of DEG. A transition between open system and closed system is found in the generator when the top electrode arrangement changes at vertical and horizontal direction. Such transition is further analyzed from the working mechanism, droplet dynamic behavior and output performance. Finally, an optimal top electrode arrangement is acquired, which will provide guidance in DEG design. We envision that such optimal top electrode arrangement of DEG will open new pathway for efficiently harvesting water droplet kinetic energy.

Effect of bulk and surface composition of Ni + Ga intermetallic compound catalysts in propane steam/wet reforming: Origins of nearly ideal experimental product selectivity

In our prior studies, Ni + Ga IMCs were isolated as promising wet reforming catalysts that achieved nearly ideal product distributions of H2 and either CO or CO2 and exhibited excellent stability (reduced coke formation). A systematic understanding of IMC surface chemistry as a function of constituent element selection directed our studies to the Ni + Ga IMC compositional space. However, Ni + Ga IMC surface chemistry towards oxygen and in oxidation reaction steps remained to be understood. This study focuses upon exploring the origin of the performance of Ni + Ga IMCs in the wet reforming of propane with a specific focus on controlling the fate of atomic H and understanding the control of oxidation steps to dictate CO vs CO2 production. Additionally, a simple kinetic coupling parameter was developed to predict coke formation and catalyst stability with excellent agreement between predictions and experimentally observed stability.

Surface Degradation of Oil-Immersed Nomex Paper Caused by Partial Discharge of High-Frequency Voltage

The oil-paper insulation of high-frequency (HF) transformers frequently withstands high-frequency over-voltages at frequencies of several kHz and above. This leads to the occurrence of partial discharge (PD), which causes premature insulation failure in HF transformers. In order to investigate the effect of PD under high-frequency stresses on oil-impregnated Nomex paper, this paper analyzes the surface morphology, bond-broken types of the molecular chain, and product types formed for oil paper after PD degradation. Then, the damage mechanism of oil-immersed Nomex paper between high-frequency and AC stress is explored. The experimental results show that the branches of creepage do not exist in the oil-paper insulation during the entire discharge process under high-frequency stresses, and that their damage degree is higher than that of AC stress. This is mainly because the benzene ring of oil-impregnated Nomex paper is destroyed and opened caused by high-energy particles, the heating effect in HF discharge, and the bulk effect. These results help to improve the design theory of insulation structures and to develop PD-resistant insulation materials in HF transformers.

The effect of particle anisotropy on the modulation of turbulent flows

We investigate the modulation of turbulence caused by the presence of finite-size dispersed particles. Bluff (isotropic) spheres versus slender (anisotropic) fibres are considered to understand the influence of the shape of the objects on altering the carrier flow. While at a fixed mass fraction – but different Stokes number – both objects provide a similar bulk effect characterized by a large-scale energy depletion, a scale-by-scale analysis of the energy transfer reveals that the alteration of the whole spectrum is intrinsically different. For bluff objects, the classical energy cascade shrinks in its extension but is unaltered in the energy content and its typical features, while for slender ones we find an alternative energy flux which is essentially mediated by the fluid–solid coupling.

Physical Properties of Fast-Growing Wood-Polymer Nano Composite Synthesized through TiO2 Nanoparticle Impregnation.

Mangium (Acacia mangium Willd.) is a fast-growing wood that is widely grown in Indonesia. The impregnation method is needed to improve the qualities of the wood. In this study, TiO2 nanoparticle (79.17 nm) was produced using the hydrothermal method. The purpose of this study was to analyze the effect of TiO2 nanoparticle impregnation on the density and dimensional stability of mangium and the effectiveness of the presence of TiO2 nanoparticle in wood in degrading pollutants. The mangium samples (2 cm × 2 cm × 2 cm) were placed inside impregnation tube. The impregnation solutions included water (untreated), 1% TiO2 nanoparticle, and 5% TiO2 nanoparticles. The samples were analyzed for density, weight percent gain (WPG) dan bulking effect (BE). Samples were also analyzed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). TiO2 nanoparticle resulted in an increase in density, WPG, and BE-treated mangium. Based on XRD and FTIR results, TiO2 nanoparticle was successfully impregnated into mangium wood. Scanning electron microscopy–energy-dispersive X-ray spectroscopy analysis indicated that TiO2 nanoparticle covered the surface of the wood cells. The TiO2-impregnated mangium wood has a higher photocatalyst activity than untreated, indicating better protection from UV radiation and pollutants.

Differentiating and Understanding the Effects of Bulk and Surface Mo Doping on CO2 Hydrogenation over Pd/Anatase-TiO2

Differentiating and Understanding the Effects of Bulk and Surface Mo Doping on CO₂ Hydrogenation over Pd/Anatase-TiO₂

Toxicity of ceria nanoparticles to the regeneration of freshwater planarian Dugesia japonica: The role of biotransformation

Cerium oxide nanoparticles (n-CeO2) have wide applications ranging from industrial to consumer products, which would inevitably lead to their release into the environment. Despite the toxicity of n-CeO2 on aquatic organisms has been largely reported, research on developing organisms is still lacking. In this study, we investigate the toxic effects of n-CeO2 on the stem cells, tissue- and neuro-regeneration, using freshwater planarian Dugesia japonica as a model. Effects of bulk sized (μ-) CeO2 and ionic Ce (Ce3+) were compared with that of n-CeO2 to explore the origin of the toxic effects of n-CeO2. No overt toxicity was observed in μ-CeO2 treatment. n-CeO2 not only impaired the homeostasis of normal planarians, but also inhibited the regeneration processes of regenerated planarians, demonstrated by the inhibited blastema growth, disturbed antioxidant defense system at molecular levels, elevated DNA-damage and decreased stem cell proliferation. Regenerating organisms are more susceptible to n-CeO2 than the normal ones. Ce3+ exhibited significantly higher toxicity than n-CeO2, even though the total Ce uptake is 0.2 % less in Ce3+ than in n-CeO2 treated in planarian. X-ray absorption near edge spectroscopy (XANES) analysis revealed that 12.8 % of n-CeO2 (5.95 mg/kg Ce per planarian) was transformed to Ce3+ after interaction with planarian, suggesting that biotransformation at the nano-bio interface might play an important role in the observed toxicity. Since the biotransformation of n-CeO2 is a slow process, it may cause long-term chronic toxicity to planarians due to the slow while sustained release of toxic Ce3+ ions.

Molecular Simulation of Biobutanol Recovery Using LTA and CHA Zeolite Nanosheets with an External Surface

LTA and CHA zeolites with silica and silico-alumino-phosphate (SAPO) composition have been recently proposed by Van der Perre et al. (ChemSusChem2017,10, 2968) to recover butanol from a mixture of butanol, ethanol, acetone, and water. Such a mixture is obtained from biomass fermentation, which is a sustainable alternative for butanol production. Here, we establish a computational methodology to simulate the three-step process, consisting of selective adsorption of butanol, with some ethanol and water, from the initial mixture, using a silica LTA nanosheet; desorption of the adsorbed mixture by increasing the temperature; and adsorption of the desorbed products in a CHA (silica or SAPO) nanosheet. A combination of Monte Carlo simulations, allowing to reproduce or predict single- or multiple-component gas adsorption isotherms, and molecular dynamics, giving the time evolution of the selective adsorption and desorption processes, have been used to model the experimental setup. A recently parameterized force field of general use for zeolites, AlPOs, and SAPOs has been tuned up in order to describe all interactions arising from this model, allowing to capture the thermodynamics of the system, the flexibility of the frameworks, and the effects of surface and bulk in the permeability of the nanosheets.

A Review on Recent Advances in Mxenes for Energy Storage Application

MXenes can be used in batteries and supercapacitors for various purposes, including double-layered ion storage, redox-type ion storage, ion transfer regulation, steric hindrance, ion redistribution, electrocatalysts, electrodeposition substrates, etc. These materials perform a variety of functions in batteries and supercapacitors, including ion storage and redox-type ion storage, ion transfer regulation, steric hindrance, ion redistribution, electrocatalysts, electrodeposition substrates, and so on. This review discusses the effects of the MXene bulk and surface chemistries across various energy storage devices and clarify the correlations between their chemical properties and their use. Finally, we discuss the challenges and opportunities associated with MXene-based energy storage systems for future use.