Dielectric Properties of Ultrathin CaF2 Ionic Crystals

Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF₂) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF₂ shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO₂, TiO₂, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF₂ is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.     

Formation of a Network Structure in the Gaseous Reduction of Magnetite Doped with Alumina

Reduction of un-doped magnetite is developed topochemically with the formation of a dense iron shell. However, the reduction of alumina-doped magnetite to wüstite proceeds with the formation of a network-like structure which consists of criss-crossed horizontal and vertical plates of wüstite. Reduction of magnetite includes the conversion of Fe³⁺ to Fe²⁺ and the movement of iron cations from the tetrahedral sites on the {400} and {220} planes of magnetite to the octahedral sites on the {200} planes of wüstite. Alumina has a negligibly small solubility in wüstite. In the reduction of magnetite doped with Al₂O₃, rejected Al³⁺ cations from wüstite diffuse to the magnetite–hercynite solid solution. Enrichment of the Fe₃O₄–FeAl₂O₄ solution with alumina in the vicinity of the reduction interface restricts the growth of {220} planes of wüstite and nucleation of {220} planes adjusted to the existing planes, preventing the merging of wüstite plates during the reduction process. Reduction of magnetite from the magnetite–hercynite solid solution practically stops when the Al³⁺ content at the interface approaches the solubility limit. Wüstite in the separated plates is reduced further to iron.     

Additive-Free Aqueous MXene Inks for Thermal Inkjet Printing on Textiles

Direct printing of functional inks onto flexible substrates allows for scalable fabrication of wearable electronics. However, existing ink formulations for inkjet printing require toxic solvents and additives, which make device fabrication more complex, limit substrate compatibility, and hinder device performance. Even water-based carbon or metal nanoparticle inks require supplemental surfactants, binders, and cosolvents to produce jettable colloidal suspensions. Here, a general approach is demonstrated for formulating conductive inkjet printable, additive-free aqueous Ti₃C₂T_x MXene inks for direct printing on various substrates. The rheological properties of the MXene inks are tuned by controlling the Ti₃C₂T_x flake size and concentration. Ti₃C₂T_x-based electrical conduits and microsupercapacitors (MSCs) are printed on textile and paper substrates by optimizing the nozzle geometry for high-resolution inkjet printing. The chemical stability and electrical properties of the printed devices are also studied after storing the devices for six months under ambient conditions. Current collector-free, textile-based MSCs show areal capacitance values up to 294 mF cm⁻² (2 mV s⁻¹) in poly(vinyl alcohol)/sulfuric acid gel electrolyte, surpassing reported printed MXene-based MSCs and inkjet-printed MSCs using other 2D nanomaterials. This work is an important step toward increasing the functional capacity of conductive inks and simplifying the fabrication of wearable textile-based electronics.     

Transport and recombination in solar cells: New perspectives

The functioning of the solar cells relies on the photo-generation of carriers in p–n junctions and their subsequent recombination in the quasi-neutral regions. A number of basic issues concerning the physics of the operation of solar cells still remain obscure. This paper reports on some unsolved basic problems, namely: a model of the recombination processes that does not contradict Maxwell's equations; the role played by space charges in the transport phenomena, and the formation of quasi-neutral regions under the presence of non-equilibrium photo-generated carriers. In this work, a new formulation of the theory that explains the underlying physical phenomena involved in the generation of a photo-e.m.f. is presented.     

中国沙棘乙醇提取物的体外及对HepG2细胞的抗氧化活性

本文从生化角度全面分析了中国沙棘乙醇提取物的体外抗氧化活性,并在评价细胞毒性的基础上,以Hep G2细胞为模型,利用流式细胞仪评估了提取物的细胞抗氧化能力。结果表明,中国沙棘乙醇提取物对ABTS自由基具有良好的清除效果,当浓度为5 mg/m L时,其清除能力与阳性对照BHT相当;中国沙棘乙醇提取物对NO自由基也有良好的清除效果,但其整体清除能力不及BHT;当浓度为5 mg/m L时,中国沙棘乙醇提取物对亚油酸脂质过氧化表现抑制,但其抑制效果低于BHT;中国沙棘乙醇提取物的总抗氧化能力随浓度的增大而增强,当浓度为5 mg/m L时,其总抗氧化能力与同浓度下的BHT接近。在浓度为0.05~5 mg/m L范围内,中国沙棘乙醇提取物对Hep G2细胞不显示毒性;当处理浓度为0.5、1、5 mg/m L时,中国沙棘乙醇提取物的阳性细胞率与阳性对照相比分别降低了75.22%、72.36%和78.2%。中国沙棘乙醇提取物不仅在体外条件下具有良好的抗氧化活性,而且在Hep G2细胞内表现出良好的抗氧化能力。      

Succinyl Chitosan-Colistin Conjugates as Promising Drug Delivery Systems

The growth of microbial multidrug resistance is a problem in modern clinical medicine. Chemical modification of active pharmaceutical ingredients is an attractive strategy to improve their biopharmaceutical properties by increasing bioavailability and reducing drug toxicity. Conjugation of antimicrobial drugs with natural polysaccharides provides high efficiency of these systems due to targeted delivery, controlled drug release and reduced toxicity. This paper reports a two-step synthesis of colistin conjugates (CT) with succinyl chitosan (SucCS); first, we modified chitosan with succinyl anhydride to introduce a carboxyl function into the polymer molecule, which was then used for chemical grafting with amino groups of the peptide antibiotic CT using carbodiimide chemistry. The resulting polymeric delivery systems had a degree of substitution (DS) by CT of 3–8%, with conjugation efficiencies ranging from 54 to 100% and CT contents ranging from 130–318 μg/mg. The size of the obtained particles was 100–200 nm, and the ζ-potential varied from −22 to −28 mV. In vitro release studies at pH 7.4 demonstrated ultra-slow hydrolysis of amide bonds, with a CT release of 0.1–0.5% after 12 h; at pH 5.2, the hydrolysis rate slightly increased; however, it remained extremely low (1.5% of CT was released after 12 h). The antimicrobial activity of the conjugates depended on the DS. At DS 8%, the minimum inhibitory concentration (MIC) of the conjugate was equal to the MIC of native CT (1 µg/mL); at DS of 3 and 5%, the MIC increased 8-fold. In addition, the developed systems reduced CT nephrotoxicity by 20–60%; they also demonstrated the ability to reduce bacterial lipopolysaccharide-induced inflammation in vitro. Thus, these promising CT-SucCS conjugates are prospective for developing safe and effective nanoantibiotics.     

Electrically controlled light scattering in FLC cells

Abstract— Three types of light‐scattering effects distinguished by physical mechanisms were studied in detail in monomeric ferroelectric liquid‐crystal (FLC) compositions at different boundary conditions and electrical pulse regimes. The total time of the scattering switching on and switching off is less than 150, 250, and 500 μsec at ±50 V for different scattering types in helix and non‐helix FLCs. They are quite fast, and FLC cells are quite transparent and were used in a stack of 30–100 light‐scattering shutters for a volumetric screen of a 3‐D display.     

Optical Diagnostics of Heterogeneous Gas-Flame Flows

The results of optical measurements of the parameters of particles and gas in a heterogeneous gas-flame flow are presented. A visualization of the flow of a plasma and a gas, along with interferometric and pyrometric measurements, enables one to investigate the structure and parameters of the carrier flux and of particles and their interference.     

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO₂/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y_In varied from 0.0011 to 0.045 in these deposited Pb_1−yIn_yTe films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In₂Te₃ pseudobinary system also. The results of XRD show that the lattice parameter a_PbTe of PbTeIn/Si and PbTeIn/SiO₂/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011y_In0.045.