Transmission Electron Micro Research Articles

Loops at carbon edges: Boron-assisted passivation and tunable surface properties of carbon nanofibers

During thermal treatment of carbon materials, unstable edge sites can easily convert to structurally stable loop structures. Hence, in the present work, carbon edges are physically passivated via high-temperature treatment in the presence of boron atoms to accelerate loop formation. The highly accelerated loop formation, along with stacking multi-layers at the carbon edges, is systematically investigated via high resolution transmission electron micro microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and thermal gravimetric analysis (TGA). The boron-added carbon nanofibers (CNFs) at high temperature exhibit a greatly enhanced electrical conductivity due to the high mobility of boron atoms within the carbon structure. In particular, engineering of the loop structures on the carbon edges can alter the overall electrocatalytic activities of the carbon-based materials, as demonstrated in the reductive conversion of 4-nitrophenol (4-NP) and in the hydrogen evolution reaction (HER). This work not only suggests suitable methods for carbon edge passivation, but also opens up a route towards the advanced design of high-stability carbon materials in various fields.

A new morphology of retained austenite obtained by intercritical tempering of 13Cr-4Ni martensitic stainless steel

This research investigates the effect of various intercritical tempering in a 13Cr-4Ni stainless steel on the morphology, size, and γ-stabilizer elements enrichment of the retained austenite, i.e. the austenite retained at room temperature after intercritical heat treatments. A comparative microstructural and chemical composition study was conducted on AISI415 steel using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro hardness measurements for three tempering conditions giving the same retained austenite volume fraction (10%). These tempering conditions were: 620 °C 1 h, 600 °C 4 h, and 580 °C 10 h. The intercritical tempering at low temperature does not provide greater γ-stabilizer elements enrichment of the austenite. In this condition, the morphology of the formed retained austenite can be described as thin hollow particles with short lamellae shapes, which is significantly different than the morphology obtained at higher temperatures; the latter being characterised by thick and long lamellae. The retained austenite produced by tempering at low temperature is surrounded from both internal and external sides by martensite phases. Furthermore, it increases the austenite-martensite interfacial area that contributes to increase the barrier energy to martensitic transformation induced plasticity (TRIP).

Application of extracellular vesicles from mesenchymal stem cells promotes hair growth by regulating human dermal cells and follicles.

BACKGROUNDDermal papillae (DP) and outer root sheath (ORS) cells play important roles in hair growth and regeneration by regulating the activity of hair follicle (HF) cells.AIMTo investigate the effects of human mesenchymal stem cell-derived extracellular vesicles (hMSC-EVs) on DP and ORS cells as well as HFs. EVs are known to regulate various cellular functions. However, the effects of hMSC-EVs on hair growth, particularly on human-derived HF cells (DP and ORS cells), and the possible mechanisms underlying these effects are unknown. METHODShMSC-EVs were isolated and characterized using transmission electron micro scopy, nanoparticle tracking analysis, western blotting, and flow cytometry. The activation of DP and ORS cells was analyzed using cellular proliferation, migration, western blotting, and real-time polymerase chain reaction. HF growth was evaluated ex vivo using human HFs.RESULTSWnt3a is present in a class of hMSC-EVs and associated with the EV membrane. hMSC-EVs promote the proliferation of DP and ORS cells. Moreover, they translocate β-catenin into the nucleus of DP cells by increasing the expression of β-catenin target transcription factors (Axin2, EP2 and LEF1) in DP cells. Treatment with hMSC-EVs also promoted the migration of ORS cells and enhanced the expression of keratin (K) differentiation markers (K6, K16, K17, and K75) in ORS cells. Furthermore, treatment with hMSC-EVs increases hair shaft elongation in cultured human HFs.CONCLUSIONThese findings suggest that hMSC-EVs are potential candidates for further preclinical and clinical studies on hair loss treatment.

Convolutive Deconvolutive Voltammetry of Charge Transfer Complexes of 4,4’-Bipyridine With Benzoquinone Derivatives

Convolutive, deconvolutive cyclic voltammetric, digital simulation, chrono- amperometric, scanning electron microscopy (SEM) and transmission electron micro- scopy (TEM) were used for clarifying the characterization of charge transfer complex (CT) of 4,4’-bipyridine with benzoquinone derivatives. These studies were achieved at a gold electrode in TBAPL/CH2Cl2. The kind of the electrode reaction and the kinetic parameters of the CT complex under study were calculated and explained via the above methods, then confirmed via digital simulation. SEM and TEM were performed for characterization of the structural morphology of the presented complex as well as showing the nanostructured of the complex.

Unraveling dislocation mediated plasticity and strengthening in crack-resistant ZnAlMg coatings

Mg-alloyed zinc coatings suffer from early cracking during deformation due to the combined influences of detrimental constituents (e.g., Zn/MgZn2 binary eutectic), unfavorable crystal orientations and incompatible local plastic deformation. This study addresses the crack resistance and deformation mechanisms of a ZnAlMg coating, in the absence of binary eutectic, by using correlative in-situ scanning electron microscopy tensile tests, electron backscatter diffraction, scanning transmission electron microscopy and micro digital image correlation methods. The plasticity and strengthening mechanisms of the binary eutectic-free ZnAlMg coating are thoroughly unravelled via theoretical and experimental approaches including dislocation slip trace analysis, Taylor factor calculations, quantitative dislocation density determination and slip/strain transfer across the grain boundaries. It has been found that the microstructure of the coating, comprising of primary zinc and ternary eutectic, effectively accommodates the applied strain without cracking till fracture of steel substrate. The absence of binary eutectic and the activation of abundant deformation mechanisms in the coating microstructure, promote local compatible plastic deformation and inhibit early damage. Effective slip transfer is unveiled by activation of pyramidal <c+a> slip in addition to primary dislocation slip systems. The present findings deliver significant insights and solution for improvement in the formability of Mg-alloyed zinc coatings on steel sheets by tailoring the microstructure.

Graphene decorated aluminum nano composite with improved micro hardness and electrical conductivity

Composites of Al-graphene (0.2–0.6 wt%) were successfully prepared by solid state technique. Powder composites were prepared by ball milling technique. Ball milling was carried out under argon atmosphere. 4 hrs of milling was carried out for developing uniform powder composite. For developing lattice diffusion between Al and graphene, sintering at 570 °C for 7 hrs was done under argon atmosphere. Composites were evaluated by X-ray diffraction (XRD), transmission electron microscope (TEM), micro Raman, electrical conductivity and micro hardness. The typical Al + graphene (0.6 wt%) composite was found to show significant higher hardness and electrical conductivity in comparisons to pure Aluminium.

Synthesis and antimicrobical activity of composite oxides nanoparticles based on ZnO

It should be noted that zinc oxide nanoparticles have increased antibacterial activity. ZnO/Me composite nanoparticles have a more pronounced antimicrobial effect in comparison with monometallic nanoparticles obtained by similar conditions. In present work ZnO/Ag and ZnO/CuO composite nanoparticles were obtained by the electrical explosion of Zn and Cu or Zn and Ag wires in oxygen containing atmosphere. Composite nanoparticles were characterized by transmission electron microscopy, XRD analysis and micro electrophoresis. Antibacterial activity of composite nanoparticles against Gram-positive E.coli and Gram-negative MRSA was studied. The as-synthesized nanoparticles demonstrated excellent bactericidal effect due to their unique properties including not only components additive effect but also synergetic one.

Mechanical properties of ultra-hard nanocrystalline cubic boron nitride

Nanostructure and mechanical properties of bulk nanocristalline cubic boron nitride have been studied by transmission electron microscopy and micro- and nanoindentation. The obtained data on hardness, elastic properties, and fracture toughness clearly indicate that nano-cubic (F4¯3m) boron nitride belongs to a family of advanced ultrahard materials.

High Thermoelectric Performance in Mg2(Si0.3Sn0.7) by Enhanced Phonon Scattering

Owing to the high thermoelectric (TE) conversion efficiency, low cost, and environmental friendliness Mg2Si0.3Sn0.7 solid solution has emerged as the material of choice for the n-leg of a TE generator for mid-temperature (room temperature to 800 K) applications. Dimensionless TE figure-of-merit (ZT) values of 1.3 (at 700 K) have been reported in this compound when optimally doped. High ZT values in this compound are due to a combination of improved electrical properties (band convergence effect) and reduced lattice thermal conductivity (alloy scattering of phonons). Here we demonstrate that the TE performance in this solid solution can be improved further (ZTmax = 1.7 at T = 673 K, which is a record in silicide-based TE materials) by enhancing phonon scattering with embedded nanoprecipitates. The high ZT values are obtained when Mg2Si0.3Sn0.7 is codoped with Bi and Cr. While Bi helps in optimizing the electrical transport properties, Cr results in formation of nanoprecipitates. Transmission electron micro...

Effects of three drying methods of post space dentin bonding used in a direct resin composite core build-up method

PurposeThe purpose of this study was to evaluate drying methods for post space dentin bonding in a direct resin composite core build-up method. MethodsExperiment 1: Four root canal plastic models, having diameters of 1.0 or 1.8mm and parallel or tapered shapes, were prepared. After drying each post space using three drying methods (air drying, paper-point drying, or ethanol drying, which involves filling the space with 99.5 vol% ethanol followed by air drying), the residual liquid in the models was weighed. Experiment 2: Thirty endodontically treated single-root teeth were dried using the above-described drying methods and filled with dual-cure resin composite. The bonded specimens were sectioned into square beams of approximately 1mm2 for microtensile bond strength (μTBS) testing. Nine teeth were observed through transmission electron microscopy (TEM) and micro computed tomography (μCT). The weight of residual liquid and μTBS were analyzed using Scheffé multiple comparison. ResultsExperiment 1: The results of air drying were significantly different from those of paper-point drying (p<0.001) and ethanol drying (p<0.001), and no significant difference was observed between paper-point drying and ethanol drying. Experiment 2: The μTBS significantly decreased in the order of ethanol drying, paper-point drying, and air drying (air drying/ethanol drying: p<0.001, air drying/paper-point drying: p=0.048, ethanol drying/paper-point drying: p=0.032). TEM and μCT observation revealed a sufficient dentin/adhesive interface in the ethanol drying group. ConclusionsEthanol drying was found to be more effective for post space dentin bonding, as compared with air drying and paper-point drying.

Magnetic Field-Induced Polymerization of Molecularly Imprinted Polymers

In this work, we developed a novel approach for the preparation of molecularly imprinted polymer (MIP) coatings directly onto magnetic multicore nanoparticles (MMCs) using alternating magnetic fields to trigger the polymerization reaction. MIPs were synthesized with rhodamine 123 (R123) as model template molecule, methacrylic acid as functional monomer, and trimethylolpropane trimethacrylate as cross-linker. The amount of iron oxide nanoparticles and the composition of the polymerization mixture were optimized to enable the thermal polymerization of a thin MIP shell on each MMC using electromagnetic heating without altering the properties of the recognition layer. The thickness of the polymerized MIP layer grafted onto the MMCs was fine-tuned by adjusting the dose of electromagnetic field (101.4 kHz, total power dissipation = 105 W). The resulting magnetic multicore MIP nanoparticles (MMC-MIPs) were characterized by Fourier transform infrared and X-ray diffraction spectroscopy, transmission electron micro...

Synthesis of Nitrogen Doped Protein Based Carbon as Pt Catalysts Supports for Oxygen Reduction Reaction

Nitrogen (N)-doped protein-based carbon as platinum (Pt) catalyst supports from tofu for oxygen reduction reactions are synthesized using a carbonization and reduction method. We successfully prepare 5 wt% Pt@N-doped protein-based carbon, 10 wt% Pt@N-doped protein-based carbon, and 20 wt% Pt@N-doped protein-based carbon. The morphology and structure of the samples are characterized by field emission scanning electron microscopy and transmission electron micro scopy, and crystllinities and chemical bonding are identified using X-ray diffraction and X-ray photoelectron spectroscopy. The oxygen reduction reaction are measured using a linear sweep voltammogram and cyclic voltammetry. Among the samples, 10 wt% Pt@N-doped protein-based carbon exhibits exellent electrochemical performance with a high onset potential of 0.62 V, a high E1/2 of 0.55 V, and a low ΔE1/2= 0.32 mV. Specifically, as compared to the commercial Pt/C, the 10 wt% Pt@N-doped proteinbased carbon had a similar oxygen reduction reaction perfomance and improved electrochemical stability.

Design, Self-Assembly, and Switchable Wettability in Hydrophobic, Hydrophilic, and Janus Dendritic Ligand–Gold Nanoparticle Hybrid Materials

Controlling nanoparticles’ (NPs) surface polarity, colloidal stability, and self-assembly into well-defined complex architectures is of paramount importance for emergent nano- and biotechnologies, and each depends strongly on the ligand shell composition and chemical nature. In this study, a series of dendritic ligands with hydrophobic, hydrophilic, and Janus surface groups was synthesized, grafted onto Au NPs, and their effects on the self-assembly behavior and surface polarity of the corresponding hybrid materials were investigated. A generalized, flexible strategy was utilized for ligand synthesis that independently introduces dendritic end groups, responsible for the surface polarity and colloidal properties, and specific surface NPs binding groups, reducing the number of synthetic steps. The dendritic ligands obtained were grafted onto NP surfaces through solution phase ligand-exchange, and the resulting NP–dendron hybrids were studied using a variety of techniques such as transmission electron micro...

Microstructure evolution characteristics of Inconel 625 alloy from selective laser melting to heat treatment

Superalloy Inconel 625 has been widely used in selective laser melting (SLM). Since SLM-induced microstructure with columnar grains, strong texture, porosity, and undesired properties, heat treatment is often used to tune the microstructure and mechanical properties. However, the microstructure evolution of IN 625 from SLM to heat treatment is poorly understood. In this study, IN 625 samples were SLMed and then heat treated at elevated temperatures. Microstructure evolution characteristics of the processed IN 625 alloy have been characterized using optical metallography, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction, and micro indentation. Fine dendrite microstructures with strong texture parallel to layer build-up direction was observed in the as-SLM samples due to rapid cooling and epitaxial growth. High dislocation density and high microhardness were found in the γ matrix which also contains high Z-contrast precipitates. After annealing at high temperatures, random grain growth accompanied by dislocation annihilation and twinning occurs. The decrease in lattice parameter and the prevalence of large grain boundary misorientation in the γ matrix suggests that SLM-induced residual stress be significantly reduced. In addition, the uncertainty of mechanical properties due to the process variations was quantified.

Case study: Formation of white etching layers in a failed rolling element bearing race

The aim of this investigation was to study the formation of white etching layer (WEL) induced by rolling contact fatigue (RCF) in a bearing steel. Through sectioning a failed bearing, the microstructure of the WEL was investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and micro indentation test. The result showed that the WEL is harder than the matrix. It consists of refined grains of martensite, austenite and carbides. In contrast to the thermally-induced WELs, where the austenite is the result of phase transformation due to austenitization, the austenite in the WELs of the current study comes from the original retained austenite. No phase transformation occurred, indicating that the WEL was formed under deformation induced the mechanism. WELs and white etching areas (WEAs) were compared in detail. The result suggested that WELs and WEAs are actually the similar responses to large shear deformation in RCF of martensitic bearing steels.

The Effect and Mechanism of Transdermal Penetration Enhancement of Fu's Cupping Therapy: New Physical Penetration Technology for Transdermal Administration with Traditional Chinese Medicine (TCM) Characteristics.

Background: In this paper, a new type of physical penetration technology for transdermal administration with traditional Chinese medicine (TCM) characteristics is presented. Fu’s cupping therapy (FCT), was established and studied using in vitro and in vivo experiments and the penetration effect and mechanism of FCT physical penetration technology was preliminarily discussed. Methods: With 1-(4-chlorobenzoyl)-5-methoxy-2-methylindole-3-ylacetic acid (indomethacin, IM) as a model drug, the establishment of high, medium, and low references was completed for the chemical permeation system via in vitro transdermal tests. Furthermore, using chemical penetration enhancers (CPEs) and iontophoresis as references, the percutaneous penetration effect of FCT for IM patches was evaluated using seven species of in vitro diffusion kinetics models and in vitro drug distribution; the IM quantitative analysis method in vivo was established using ultra-performance liquid chromatography-tandem mass spectrometry technology (UPLC-MS/MS), and pharmacokinetic parameters: area under the zero and first moment curves from 0 to last time t (AUC0–t, AUMC0–t), area under the zero and first moment curves from 0 to infinity (AUC0–∞, AUMC0–∞), maximum plasma concentration (Cmax) and mean residence time (MRT), were used as indicators to evaluate the percutaneous penetration effect of FCT in vivo. Additionally, we used the 3K factorial design to study the joint synergistic penetration effect on FCT and chemical penetration enhancers. Through scanning electron microscopy (SEM) and transmission electron microscope (TEM) imaging, micro- and ultrastructural changes on the surface of the stratum corneum (SC) were observed to explore the FCT penetration mechanism. Results: In vitro and in vivo skin permeation experiments revealed that both the total cumulative percutaneous amount and in vivo percutaneous absorption amount of IM using FCT were greater than the amount using CPEs and iontophoresis. Firstly, compared with the control group, the indomethacin skin percutaneous rate of the FCT low-intensity group (FCTL) was 35.52%, and the enhancement ratio (ER) at 9 h was 1.76X, roughly equivalent to the penetration enhancing effect of the CPEs and iontophoresis. Secondly, the indomethacin percutaneous ratio of the FCT middle-intensity group (FCTM) and FCT high-intensity group (FCTH) were 47.36% and 54.58%, respectively, while the ERs at 9 h were 3.58X and 8.39X, respectively. Thirdly, pharmacokinetic data showed that in vivo indomethacin percutaneous absorption of the FCT was much higher than that of the control, that of the FCTM was slightly higher than that of the CPE, and that of the FCTM group was significantly higher than all others. Meanwhile, variance analysis indicated that the combination of the FCT penetration enhancement method and the CPE method had beneficial effects in enhancing skin penetration: the significance level of the CPE method was 0.0004, which was lower than 0.001, meaning the difference was markedly significant; the significance level of the FCT was also below 0.0001 and its difference markedly significant. The significance level of factor interaction A × B was lower than 0.0001, indicating that the difference in synergism was markedly significant. Moreover, SEM and TEM images showed that the SC surfaces of Sprague-Dawley rats treated with FCT were damaged, and it was difficult to observe the complete surface structure, with SC pores growing larger and its special “brick structure” becoming looser. This indicated that the barrier function of the skin was broken, thus revealing a potentially major route of skin penetration. Conclusion: FCT, as a new form of transdermal penetration technology, has significant penetration effects with TCM characteristics and is of high clinical value. It is worth promoting its development.

N-(3-hydroxymethyl-β-carboline-1-yl-ethyl- 2-yl)-l-Phe: development toward a nanoscaled antitumor drug capable of treating complicated thrombosis and inflammation.

It is well documented that the surfaces of cancer cells, activated platelets and inflammatory cells are rich in P-selectin. N-(3-hydroxymethyl-β-carboline-1-yl-ethyl-2-yl)-l-Phe (HMCEF) is a P-selectin inhibitor capable of simultaneously inhibiting thrombosis and inflammation. Based on the knowledge that P-selectin is a common target for antithrombotic, anti-inflammatory and antitumor drugs, the aim of this study article was to estimate the possibility of HMCEF as a nanoscaled antitumor drug. Images of transmission electron micro scopy, scanning electron microscopy and atomic force microscopy proved that HMCEF forms nanoparticles with a diameter of <120 nm that promote delivery in blood circulation. In vitro HMCEF intercalates into calf thymus DNA, cuts off DNA pBR22 and inhibits the proliferation of cancer cells. In vivo HMCEF dose dependently (0.2, 2 and 200 nmol/kg per day) slows tumor growth in treated S180 mice, and has a minimal effective dose of 2 nmol/kg per day. At 200 nmol/kg per day, HMCEF does not affect the liver and the kidney of the treated S180 mice, and at 20,000 nmol/kg HMCEF does not affect the liver and the kidney of the treated healthy ICR mice. HMCEF is a promising antitumor drug, which is characterized by its high safety and efficacy in the prevention of the complications of thrombosis and inflammation in patients.

Synthesis of N and F co-doped TiO2 nanophotocatalysts for degradation of malathion in water

N and F codoped nanophotocatalysts were synthesized by sol–gel method and their photocatalytic activity were studied for the degradation of insecticide malathion. Photocatalysts were characterised by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope and micro Raman spectroscopy to determine the structural, morphological properties and phase composition. The particle size calculated by XRD are in agreement with the measured value by TEM. Band gap calculated by absorption spectra shows a shift in the absorption edge towards longer wavelength side. Photoluminescence spectra show emission behaviour of synthesized photocatalysts. In comparison with undoped TiO2, N, F codoped particles exhibits higher photocatalytic activity due to generation of more reactive oxidative species (ROS). Mechanism of ROS generation is graphically discussed.

Intercalation-assisted longitudinal unzipping of carbon nanotubes for green and scalable synthesis of graphene nanoribbons.

We have demonstrated an effective intercalation of multi-walled carbon nanotubes (MWCNTs) for the green and scalable synthesis of graphene nanoribbons (GNRs) using an intercalation-assisted longitudinal unzipping of MWCNTs. The key step is to introduce an intercalation treatment of raw MWCNTs with KNO3 and H2SO4, making it promising to decrease the strong van der Waals attractions in the MWCNTs bundles and between the coaxial graphene walls of CNTs. Systematic micro Raman, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) characterizations suggest that potassium, nitrate, and sulfate ions play an important role in the CNT intertube and intratube intercalations during the pretreatment. Detailed scanning electron microscopy (SEM), transmission electron microscopy, XRD, and micro Raman characterizations indicate that the developed methodology possesses the ability to synthesis GNRs effectively with an improved CNT concentration in H2SO4 of 10 mg/ml at 70 °C, which is amenable to industrial-scale production because of the decreased amount of strong acid. Our work provides a scientific understanding how to enhance the GNR formation by accelerating the CNT longitudinal unzipping via suitable molecular intercalation.

Optimizing the Charge Transfer Process by Synthesizing NiO Microspheres on Ni Foam through Microwave-assisted Method

The porous nickel oxide microsphere on Ni foam was adopted to optimize the charge transfer process to improve electrochemical performance by a microwave-assisted method. Microstructure and morphologies of the re- sulting materials were investigated by X-ray diffraction, scanning electron microscope, transmission electron micro- scope. Results showed that the as-prepared NiO microspheres with nickel sulfate had average diameter of ~2 µm. The ultrathin secondary nanoflakes composed of nanowire building blocks were interconnected with each other forming a highly open net-structure. Because of enhanced electron transfer capability, charge transfer resistances of the porous microsphere were reduced and the electrochemical performances were improved, the charge-discharge measurements tested at a discharge current of 0.5 A/g showed higher rate specific capacitance (455 F/g). The impedance characteriza- tion illustrated lower electronic and ionic resistance of porous NiO due to its superior surface properties for enhanced electrode electrolyte contact during the faradaic redox reactions.