Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y₃Fe₅O₁₂ (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y₃Fe₅O₁₂/Ba_0.6Sr_0.4TiO₃ (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.     

Enhanced figure of merit of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) and SWCNT thermoelectric composites by doping with FeCl3

Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT) generally has a large Seebeck coefficient, and single-walled carbon nanotubes (SWCNTs) have high electrical conductivity. In this work, we prepared F8BT/SWCNT composites to combine the good Seebeck coefficient of the polymer and the excellent electrical conductivity of SWCNTs to achieve enhanced thermoelectric properties. For the composite materials, the maximum power factor of 1 μW mK⁻² was achieved when the SWCNT content was 60%, with the maximum ZT value of 4.6 × 10⁻⁴. After ferric chloride was employed as the oxidative dopant for the composites, the electrical conductivity of the composites improved significantly. The maximum value of power factor (1.7 μW mK⁻²) was achieved when the SWCNT content was 60%, and the ZT value of 7.1 × 10⁻⁴ was about 1.5 times as high as that of the composites with undoped F8BT. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47011.     

Effects of SnO2 layer coated on carbon nanofiber for the methanol oxidation reaction

Carbon nanofibers (CNFs) are used as active materials for electrodes in various energy devices, such as lithium ion secondary batteries, supercapacitors, and fuel cells. Recent studies have shown that nanoscale coatings on carbon nanotubes increase the output and lifespan of these devices owing to the improvement of their mechanical and chemical properties. Among various coating methods, atomic layer deposition (ALD) can adjust the thickness of the coating layer conformally without any directional growth. Therefore, ALD can coat particles with high aspect ratios, such as CNFs, even at nanometer levels of thickness.In this work, we grew two different morphologies of a SnO₂ layer on CNF. We used two types of ALD equipment: flow-type ALD (static ALD), and fluidized bed reactor-type ALD (dynamic ALD). Static ALD could form a discontinuous SnO₂, while a uniform SnO₂ layer was formed by pre-inserting a layer of Al₂O₃. On the other hand, dynamic ALD formed a uniform SnO₂ layer without pre-insertion of an Al₂O₃ layer. X-ray photoelectron spectroscopy analysis revealed that both Sn⁴⁺ and Sn²⁺ were present in SnO₂ on the CNF deposited by static ALD, probably due to the formation of an interfacial layer between the SnO₂ and CNF. When the dynamic ALD method was used, only Sn⁴⁺ was present in the SnO₂ on CNF. Cyclic voltammetry analysis was performed to characterize the electrochemical properties of the SnO₂-coated CNF as an electrode on a direct methanol fuel cell. It was revealed that the discontinuous SnO₂ on CNF deposited by static ALD showed the highest current efficiency as well as enhanced electrocatalytic stability.     

光电化学刻蚀方法去除SiC衬底外延石墨烯缓冲层及其表征

高温条件下裂解碳化硅（SiC）单晶,在直径5 cm的4H-SiC（0001）面制备出单层石墨烯。利用光电化学刻蚀方法,使KOH刻蚀液与SiC发生反应,降低石墨烯与衬底之间的相互作用力,去掉原位生长过程中SiC衬底与石墨烯之间存在的缓冲层,获得准自由的双层石墨烯。首先通过对比不同的电流密度和光照强度,总结出电流密度为6 mA·cm^-2、紫外灯与样品间距为3 cm时,石墨烯缓冲层的去除效率以及石墨烯质量皆为最佳。采用此优化后工艺处理的样品,拉曼光谱表明原位生长的缓冲层与衬底脱离,表现出准自由石墨烯的特性。X射线光电子能谱（XPS）C1s谱图中代表上层石墨烯与衬底Si悬键结合的S1、S2特征峰消失,即石墨烯缓冲层消失。通过分析刻蚀过程中的电化学曲线,提出了刻蚀过程的化学反应过程中的动态特性。     

Temperature-mediated control of the growth of an entangled carbon nanofiber layer on stainless steel micro-structured reactors

A well-adhered layer of carbon nanofibers (CNFs) was grown on stainless steel microreactors by decomposition of a hydrocarbon over microreactors previously coated with Ni dispersed on alumina. In a previous work, we reported that the growth temperature and hydrocarbon (methane or ethane) modulated the morphology and size of the grown carbon species. Using ethane, the carbon yield increased dramatically for temperatures exceeding 898 K. At these temperatures some carbon protrusions arise, which plug microreactor channels and render the microreactor unsuitable for use. For methane at all the tested temperatures or for ethane at the lowest temperatures (853 and 873 K), the microreactor channels were covered completely by a uniform mat of entangled CNFs ready for catalytic use. Here, we show that the growth temperature and hydrocarbon can also control the primary structure of CNFs, either rolled graphitic planes parallel to the axis (multi-wall carbon nanotubes) or graphitic planes forming an angle with respect to the axis (fishbone type).     

Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth

The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalyst particles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are “replaced” by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering the mechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.     

Numerical simulation of atomic layer deposition for thin deposit formation in a mesoporous substrate

ZnO deposition in porous γ-Al₂O₃ via atomic layer deposition (ALD) is the critical first step for the fabrication of zeolitic imidazolate framework membranes using the ligand-induced perm-selectivation process (Science, 361 (2018), 1008–1011). A detailed computational fluid dynamics (CFD) model of the ALD reactor is developed using a finite-volume-based code and validated. It accounts for the transport processes within the feeding system and reaction chamber. The simulated precursor spatiotemporal profiles assuming no ALD reaction were used as boundary conditions in modeling diethylzinc reaction/diffusion in porous γ-Al₂O₃, the predictions of which agreed with experimental electron microscopy measurements. Further simulations confirmed that the present deposition flux is much less than the upper limit of flux, below which the decoupling of reactor/substrate is an accurate assumption. The modeling approach demonstrated here allows for the design of ALD processes for thin-film membrane formation including the synthesis of metal–organic framework membranes.     

Microstructure analysis with TEM for zeolite layer formed in pore of porous alumina substrate

A zeolite membrane for CO₂ gas separation was synthesized on a porous Al₂O₃ substrate by hydrothermal synthesis. Observations using transmission electron microscopy (TEM) showed that zeolite had formed in the pores of the substrate (in the “composite layer”). High-resolution TEM observations showed that the zeolite in the pores was MFI and that the crystal grains of the zeolite were connected directly without any grain boundary phases. This suggests that the composite layer can be pinhole free, so the zeolite membrane could function as an effective gas filter. EDS analysis showed that Al/Si ratio of a zeolite framework was larger in the composite layer. This will be a primary factor in densification of zeolite grains at the composite layer.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Surface engineering of the flexible metallic substrate by SDP-Gd-Zr-O layer for IBAD-MgO templates

Tuning substrate properties is an effective methodology to modulate the texture development of MgO films deposited by ion beam-assisted deposition (IBAD) process for epitaxial oxide films. Herein, a solution deposition planarization (SDP) technique is employed to deposit Gd-Zr-O layer for engineering surface properties of the flexible metal substrate. The correlation between the Gd-Zr-O thin film microstructure and the IBAD-MgO texture is investigated. The coordinated study on atomic force microscopy (AFM) and reflection high-energy electron diffraction (RHEED) reveal that the grain coarsening during high-temperature sintering negatively influences the texture formation of IBAD-MgO. Moreover, the chemical environment of the atoms on the surface of Gd-Zr-O seed layer also plays a critical role, which is normally overlooked. The X-ray photoelectron spectroscopy (XPS) analysis indicates that the carbon residue and intermediate phase result in the poor texture of the IBAD-MgO. This phenomenon is related to the partial decomposition and synthesis reactions due to the lower sintering temperature or reduced surface to volume ratio. We demonstrate the high-quality texture of IBAD-MgO layer, deposited on mono-coated thick Gd-Zr-O film, by using optimal heat-treatment conditions. The cross-sectional TEM images present the dense Gd-Zr-O film with Gd₂Zr₂O₇ nanograins. The multifunctionalities, such as planarization, a barrier layer, and seed layer, of Gd-Zr-O layers are realized in full-stacked CeO₂/LaMnO₃/IBAD-MgO/SDP-Gd-Zr-O/C276 samples. This work demonstrates a route for simplifying the architecture of 2G-HTS using Gd-Zr-O layer and explores the effect of the surface properties on texture formation in IBAD-MgO layer.     

Investigation of the specific attenuation cross-section of aerosols deposited on fiber filters with a polar photometer to determine black carbon

A polar photometer was used to investigate phase functions of glass fiber filters with varying aerosol particle loadings. Angle-resolved analysis revealed that the shape of the normalized phase function S_n(θ) in the transmitted hemisphere is independent of aerosol composition and determined exclusively by the fibrous filter matrix, while S_n(θ) in the reflected hemisphere depends on the scattering properties of the aerosol sample. Cross sensitivities of the specific attenuation cross section with respect to scattering components were examined with well-defined laboratory generated aerosol samples. The specific attenuation cross section at θ=165° (reflected hemisphere) was found considerably less dependent of the aerosol composition than any angular position in the transmitted hemisphere, and is therefore best suited for the determination of black carbon (BC). The angular position θ=165° was calibrated with an almost pure BC test aerosol. BC mass loadings of ambient aerosol samples (0.15–20 μg cm^-2) determined with this calibration function were in good agreement with values analyzed by coulometry.     

The use of a carbon nanotube layer on a polyurethane multifilament substrate for monitoring strains as large as 400%

A noninvasive approach is used to fabricate electronically conductive and flexible polymer fibers by fixing carbon nanotube (CNT) networks as a thin layer on thermoplastic polyurethane (TPU) multifilaments. The anchoring of the CNT layer is achieved by partially embedding or penetrating CNTs from the dispersion into the swollen multifilament surface. Thus a stable and high conductivity (up to 10² S/m at 10 wt.% CNT loading) of the resulting CNTs–TPU fibers is realized while the mechanical properties of the TPU multifilament, especially the strain to failure of >1500%, are not affected by increasing the thickness of the CNT layer. Real time analysis of the resistance of the CNTs–TPU fibers during incremental tensile loading tests reveal that the increase of resistance as a function of the strain is attributed to stretching-induced deformation, alignment, and, at high strains, destruction of the conducting network. Moreover, the changes in resistance are highly reversible under cyclic stretching up to a strain deformation of 400%.     

Reduction of graphene oxide at the interface between a Ni layer and a SiO2 substrate

Reduction of graphene oxide (GO) was carried out on SiO₂ using a thin Ni overlayer as a catalyst. A Ni/GO/SiO₂ structure was heated at 800 °C in high vacuum for 6 min. After removing the Ni overlayer, formation of graphene was confirmed by Raman spectroscopy. For the Ni overlayer thinner than 40 nm, GO was reduced to graphene on-site. For the thicker Ni overlayer, however, GO was completely decomposed and graphene was formed in a segregation and/or precipitation process. The use of GO with a thin Ni overlayer enabled on-site and transfer-free fabrication of graphene without use of such flammable gases as methane and hydrogen.     

Determination of conditions for depositing crystalline calcium chloride hydrate on the heat and moisture exchanging layer of breathing filters

The moisture content and hygroscopicity of viscose fiber and filter material of the heat-exchanging layer of a breathing filter were determined as a function of the mass fraction of calcium chloride, drying temperature, and the calcium chloride soaking method in order to define these parameters.     

Dynamics and criteria for bubble instabilities in a single layer film blowing extrusion

In this paper, the performance of a new in‐line scanning camera system for the study of various bubble instabilities in film blowing extrusion is critically evaluated. Three commercial film‐grade polyethylenes, LmPE, LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating various bubble instabilities such as draw resonance, helicoidal instability, and frost line height instability are proposed by using the new device. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of the take‐up ratio (TUR), blow‐up ratio (BUR) and frost line height (FLH). In addition, effects of melt temperature and mass flow rates on dynamics of the bubble instabilities are discussed. It was found that the new system could capture the main characteristics of all bubble instabilities quantitatively. It was also found that magnitude and periodicity of radius variation during draw resonance of LmPE decreased as TUR increased at constant FLH and BUR. This implies that the origin of draw resonance in film blowing seems to be different from that observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the die center, decreased as TUR increased. However, the bubble could not be stabilized as expected. A graphical quantification approach to determine the stable zone in the bubble stability map is also discussed.     

Simulation and experimental determination of the macro-scale layer thickness distribution of electrodeposited Cu-line patterns on a wafer substrate

The impact of adjacent patterned zones with different active area densities on the current density and electrodeposited layer thickness distribution over a wafer substrate is examined, both by experiment and numerical simulation. The experiments consist in running an acid copper plating process on the patterned wafer, and layer thickness measurements by means of X-ray fluorescence (XRF) and atomic force microscopy (AFM). The simulations are based on a potential model approach taking into account electrolyte ohmic drop and electrode polarization effects, combined to a boundary element method (BEM) approach to compute the current density distribution over the electrodes. Experimental and computed layer thickness distributions are in very good agreement.     

新型固定床颗粒层除尘器的研究

介绍了新型固定床颗粒层除尘器的结构、组合式流化床清灰机构的工作原理以及除尘器的特点。实验表明,新型固定床颗粒层除尘器操作简单,组合流化床清灰装置能满足颗粒层清灰要求。     

Investigation of mass transfer on single droplets for the reactive extraction of zinc with D2EHPA

Investigations of mass transfer behavior with the standard test system of the European Federation of Chemical Engineering (EFCE) for the reactive extraction zinc + D2EHPA (di(2‐ethylhexyl) phosphoric acid) were carried out. Experiments were performed with single droplets in a mass transfer cell on lab‐scale. In the experiments, contact time for the mass transfer between droplets and continuous phase, concentrations of zinc, D2EHPA and sulfuric acid, diameter of droplets and hole‐diameter of sieve trays were varied. These experimental results show a systematic investigation of single droplet mass transfer behavior for the standard test system of the EFCE for the reactive extraction of zinc with D2EHPA. In the mass transfer model reported here, all transient effects are considered with an instability parameter, which was determined through experiments in a mass transfer cell. The simulation results with obtained instability parameters are in a good agreement with the experimental results. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Activated carbon nanofiber produced from electrospun PAN nanofiber as a solid phase extraction sorbent for the preconcentration of organophosphorus pesticides

Activated carbon nanofibers (CNFs) were derived from electrospun nanofibers with subsequent heat treatment. They were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The applicability of activated CNFs for preconcentration and determination of organophosphorus pesticides (OPPs) was investigated by high-performance liquid chromatography with diode array detector (HPLC-DAD). Some important parameters influencing the extraction efficiency, such as amount of sorbent, pH, flow rate and amount of salt, were investigated by response surface method (RSM). The obtained results showed that this analytical method will be useful for the analysis of OPPs in tap water with high precision and accuracy.